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Bioactive lipids as modulators of immune check point inhibitors
Medical Hypotheses 135 (2020) 109473
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Bioactive lipids as modulators of immune check point inhibitors
T
a,b
Undurti N. Das a b
UND Life Sciences, 2221 NW 5th St, Battle Ground, WA 98604, USA BioScience Research Centre, GVP College of Engineering Campus and Department of Medicine, GVP Hospital and Medical College, Visakhapatnam 530048, India
A R T I C LE I N FO
A B S T R A C T
Keywords: Immune check point inhibitors Polyunsaturated fatty acids Arachidonic acid Prostaglandins NK cells Indoleamine 2 3-Dioxygenase Cancer
It is proposed that arachidonic acid (AA, 20:4 n-6) and other polyunsaturated fatty acids (PUFAs) in combination with immune check point inhibitors and tumor infiltrating lymphocytes (TILs) enhances the activity of T and NK cells and macrophages and thus, aids in the elimination of tumor cells and suppresses inflammatory side effects due to immune check point inhibitors.
Introduction Selective elimination of tumor cells with little or no action on normal cells is desired but is rarely achieved with the current methods of treatment of cancer. Recently check point inhibitors of PD-1 (programmed cell death 1 protein), PD-1 ligand (PD-L1), cytotoxic T-lymphocyte-associated protein 4 {CTLA-4 also called as CD152 (cluster of differentiation) 152} and adoptive cell transfer (ACT) have been developed that have been reported to be of significant benefit in the management of cancer when used alone or in combination with existing chemotherapeutic drugs [1–7]. But these check point inhibitors have significant on-target, off-tumor toxicity called as immune-related adverse events (IRAEs) that include dermatologic, gastrointestinal, hepatic, endocrine, and other less common inflammatory events. Of all the side effects described, cytokine release syndrome can sometimes be lethal [8–10]. Furthermore, these check point inhibitors have been reported to be effective in not more than ~30–40% of the patients who receive the therapy implying that more refinements of this approach are needed [11,12]. Immune check point inhibitors Immune checkpoint inhibitor (or simply called as check point inhibitors) therapy uses immune checkpoints which affect immune system functioning. Immune checkpoints can be stimulatory or inhibitory. Tumor cells use these checkpoints to protect themselves from immune system attacks. Checkpoint therapy blocks these inhibitory checkpoints, restoring immune system function [1]. One such immune
E-mail addresses: [email protected], [email protected]. https://doi.org/10.1016/j.mehy.2019.109473 Received 4 October 2019; Accepted 2 November 2019 0306-9877/ © 2019 Elsevier Ltd. All rights reserved.
check point receptor is the transmembrane programmed cell death 1 protein (PDCD1, PD-1; also known as CD279) and its ligand, PD-1 ligand 1 (PD-L1, CD274). PD-L1 on the cell surface binds to PD1 on an immune cell surface that results in inhibition of immune cell activity. PD-L1 functions as a key regulator of T cell activities [2,3]. Cancer cellmediated upregulation of PD-L1 on the cell surface inhibits T cell responses against tumor cells and thus, blocks T cell anti-tumor action. Antibodies that bind to either PD-1 or PD-L1 block this interaction and allows the T-cells to attack the tumor [4] (see Fig. 1). cTLA-4 CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), also known as CD152 (cluster of differentiation 152), is a protein receptor that downregulates immune responses [13-15]. CTLA4 is constitutively expressed in regulatory T cells and is upregulated in conventional T cells after activation. It acts as an “off” switch when bound to CD80 or CD86 on the surface of antigen-presenting cells including cancer cell. AntiCTLA-4 therapy in combination with other drugs is useful in suppressing the growth of cancer cells [16]. It is well documented that patients treated with check-point blockade (specifically CTLA-4 blocking antibodies), or a combination of check-point blocking antibodies, are at high risk of developing immune-related adverse events such as dermatologic, gastrointestinal, endocrine, or hepatic autoimmune reactions [17–19] (see Fig. 2).
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Fig. 1. Scheme showing interaction among APC (antigen presenting cell such macrophages/dendritic cells) and T cells and the tumor cell. (Modified from “Immunotherapy in the precision medicine era: Melanoma and beyond”. December 13, 2016, https://doi.org/10.1371/journal.pmed.1002196). (-) indicates inhibition of production of PGE2, an immunoinhibitory and pro-inflammatory molecule produced from arachidonic acid (AA). PGE2 may be produced by the macrophages (or other APCs) and/or tumor cells or both. It is likely that PGE2 and other immunosuppressors may be produced by the microenvironment surrounding (tumor milieu) the tumor cells. As a result of CTLA-4 binding to the costimulatory B7 ligands found on antigen-presenting cells (APCs) prevents signaling through CD28. Antibodies targeting CTLA-4 release this checkpoint to allow T cell activation (central immunoinhibition). Binding of the PD-L1 of the tumor cells to the PD-1 receptor on T cells results in peripheral immunoinhibition. Antibodies targeting either the ligand or its receptor releases this checkpoint. Activated APCs (macrophages, T cells and other immunocytes) may release AA and other PUFAs that are peroxidized by free radicals to form toxic lipid peroxides (LP) that act on tumor cells to induce their apoptosis.
Indoleamine-pyrrole 2,3-dioxygenase (IDO or INDO)
Tryptophan catabolism results in anergy and apoptosis of effector T cells. In addition, tryptophan metabolites kynurenine, kynurenic acid, 3-hydroxy-kynurenine, and 3-hydroxy-anthranilic acid are capable of suppressing T-cell function by inducing T-cell apoptosis [32]. Aryl hydrocarbon receptor (AHR) is a direct target of kynurenine [32–35]. Arachidonic acid (AA, 20:4n-6) metabolites, bilirubin, cAMP, tryptophan metabolites tryptamine, kynurenic acid, and 6-formylindolo [3,2b] carbazole (FICZ) are all ligands of the AHR. Tryptophan is utilized by gut microbiota to form indole derivatives: indole-3-acetic acid, indoxyl-3-sulfate, indole-3-propionic acid, and indole-3-aldehyde, which are ligands for the aryl hydrocarbon receptor (AHR). Activation of AHR of gut-resident T cells and innate lymphoid cells enhances the production of IL-22, which suppresses inflammation that may account for the two-way cross talk between microbes and the immune system [36]. Tryptophan is the precursor of neurotransmitter serotonin. Gut microbiota can enhance serotonin biosynthesis from colonic enterochromaffin cells (ECs), and thus, supply serotonin to the mucosa, lumen, and circulating platelets [36-38]. Short-chain fatty acids acetate and butyrate produced by the gut microbiota modulate the synthesis of serotonin by ECs. The expansion of the maternal population of pancreatic β cells during pregnancy is stimulated by serotonin. Inhibition of serotonin synthesis blocks β cell expansion [36,39,40]. AHR is enriched in interleukin 17 (IL-17)-producing CD4+ T cells
Indoleamine-pyrrole 2,3-dioxygenase (IDO or INDO) is the ratelimiting enzyme of tryptophan catabolism through the kynurenine pathway by inducing O2-dependent oxidation of L-tryptophan to Nformyl kynurenine. IDO limits T cell function and enhances immune tolerance to tumor antigens, suppresses T regulatory (Treg) and myeloid-derived suppressor cells and promotes tumor angiogenesis [20,21]. IDO is activated during tumor development. Depletion of tryptophan by the activated IDO halts the proliferation of T cells [22,23]. Thus, IDO is an immune checkpoint molecule and an immunomodulatory enzyme produced by activated macrophages and other immune cells [21]. Tryptophan is an essential amino acid for cell survival. The role of IDO is to control microbial growth by regulating tryptophan availability and accumulation of tryptophan catabolites that have immunosuppressive actions in the inflammatory environment [24,25]. IDO is expressed in normal tissues including endothelial cells in the placenta and lung, the epithelial cells in the female genital tract, the lymphoid tissues in mature dendritic cells (DCs), immune cells or syncytiotrophoblasts in the placenta and cancer cells [26,27]. IDO present in trophoblasts prevents T cell-driven rejection of allogeneic fetuses during pregnancy and thus, allow maternal tolerance to fetal allograft. Thus, IDO may have a role in the management of autoimmune diseases, induction of graft tolerance and immune escape of tumors [28–31]. 2
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Fig. 2. Mechanism of action of immune checkpoint inhibitors. Notes: T regs depend on the activity of CTLA-4, PD-1, and PD-L1 to induce immunosuppression. Ipilimumab and tremelimumab are monoclonal antibodies that inhibit CTLA-4, while nivolumab, pembrolizumab, atezolizumab, and durvalumab inhibit PD-1 and PD-L1. These drugs reduce immune checkpoint activity on a T reg-rich microenvironment, thus diminishing tumor evasion. T regs = regulatory T-cells; TCR = T-cell receptor; MHC = major histocompatibility complex.
Immune check point inhibitors in cancer
(TH17 cells) and controls the differentiation of naive CD4+ T cells [28,41]. Kynurenine regulates the generation of regulatory T cells (Treg). AHR restricts autoimmunity by favoring the generation of Treg [27,42,43]. Kynurenine brings about its immunosuppressive effects by acting on AHR and affecting CD8+ T cells [28,33]. It is noteworthy that a close interaction/cooperation exists between IL-22 and IL-17. For instance, Th17 cells also express IL-22. Both IL-17A and IL-22 expressions are initiated by transforming growth factor β signaling in the context of IL-6 and other proinflammatory cytokines. It is known that IL-22 is coexpressed in vitro and in vivo with both IL-17A and IL-17F that synergize their actions to regulate innate immunity [44] suggesting that IL-22 and IL-17 have anti-inflammatory actions [36,42–45] which can be influenced by tryptophan metabolites through AHR [36]. We observed that serotonin enhances the production of lipoxin A4 (LXA4), a potent anti-inflammatory metabolite of AA (unpublished data, 37). Based on this data, it is likely that cancer cells escape from immune surveillance system by upregulating enzyme, tryptophan dioxygenase to form kynurenine, an endogenous ligand for the aryl hydrocarbon receptor, which mediates invasive tumour growth. Tryptophan conversion to kynurenine by the indoleamine 2,3-dioxygenase enzymes IDO and IDO2, and also by tryptophan dioxygenase (TDO) and the elevated levels of AHR in tumor are an indication of poor prognosis in cancer. It is noteworthy that tryptophan activates biosynthesis of prostaglandins, that have immunosuppressive actions [46]. Thus, tryptophan metabolism is linked to AA-eicosanoid metabolism, yet another mechanism by which tryptophan can induce immunosuppression.
Immune check point inhibitors upregulate immune system and unleash their tumoricidal action. Drugs such as ipilimumab, an antiCTLA4 antibody, pembrolizumab and nivolumab, both monoclonal antibodies against PD-1, and combination BRAF and MEK inhibitors for patients whose tumors harbor BRAF mutation have produced considerable anti-tumor activity [47–50]. Despite these advances, still a significant percentage of patients remain unresponsive to immune check point inhibitors therapy [11,12]. Blocking IDO in combination with other immune check point inhibitors may produce encouraging results though a phase III clinical trial employing IDO inhibitor with other check point inhibitors gave a negative results [51]. Despite the relative success and enthusiasm about immune check point inhibitors in the treatment of cancer only a small proportion of patients are benefited [52]. A recent study revealed that only 35 (51%) patients showed a significant improvement in survival or quality of life over existing treatment options, placebo, or as add on treatment [11]. This suggests that survival gains due to the use of immune check point inhibitors over existing treatment options or placebo is only marginal [53–58]. In addition to their anti-cancer action, treatment with immune check point inhibitors produce significant side effects due to the release of pro-inflammatory cytokines IL-6 and TNF-α. Some of the common side effects associated with immune checkpoint inhibitors include decreased appetite (12%) and diarrhea (10%), inflammatory pneumonitis, and may target endocrine, mucocutaneous and renal (interstitial nephritis) sites and eye resulting in significant damage. Some side effects are life threatening such as inflammatory pneumonitis, cytokine storm 3
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TILs and/or CAR T cell therapy and PUFAs
requiring cessation of therapy and treatment with corticosteroids [5760]. In majority of the patients, cessation of the immune checkpoint inhibitor, initiation of steroids and supportive therapy is adequate to tide over the crisis. However, some patients developed long-term adverse events with deaths reported in a few cases due to uninhibited release of cytokines IL-6, TNF-α, IFN-γ, IL-1β, IL-2, IL-6, IL-8, and IL-10 described as cytokine release syndrome (CRS) or cytokine storm. It is noteworthy that occasionally hyperprogression of underlying cancer may occur with PD-1/PD-L1 inhibitors compared with chemotherapy and are likely to show high metastatic burden and poor prognosis [61] though the molecular mechanisms involved in hyperprogressive disease is not clear. It is evident from the preceding discussion that immune check point inhibitors are effective ~in 25% of the patients treated and is associated with significant side effects. This calls for newer therapeutic strategies that may be more fruitful especially, when used in combination with immune check point inhibitors for cancer.
It is likely that immune checkpoint inhibitors, TILs, NK cells, CAR T cell therapy, tumor infiltrating macrophages and dendritic cells induce apoptosis/ferroptosis of tumor cells and/or inhibit their growth by releasing cytotoxic lipids such as GLA, AA, EPA, DHA, LXA4, resolvins, protectins and/or maresins that, in turn, regulate formation of cytotoxic lipid peroxides. We and others have shown that various tumor cell growth inhibitory PUFAs enhance the formation of lipid peroxides in tumor cells that, in turn, inhibit the growth of tumor cells or induce tumor cells to undergo apoptosis/ferroptosis and/or necrosis [65–85,88–91,125]. Furthermore, expression of high levels of glutathione peroxidase and a lipid peroxide deficiency state renders tumor cells resistant to the cytotoxic action of various chemotherapeutic drugs and radiation [126,127]. This emphasizes the concept that enhancing free radical generation and consequent accumulation of toxic lipid peroxides in tumor cells is a common mechanisms by which radiation, various conventional chemotherapeutics, NK cells, TILs, TIMs and immune checkpoint inhibitors bring about their anti-cancer actions. The current anti-cancer therapeutic approaches activate phospholipase A2 (PLA2) resulting in the release of PUFAs from the cell membrane lipid pool that are peroxidized to form toxic lipid peroxides which ultimately induce apoptosis/ferroptosis/necrosis form of tumor cell death. This implies that tumor cells with low amounts of PUFAs are likely to be resistant to the anti-cancer therapeutic approaches including immune checkpoint inhibitors. It is possible that activated NK cells, TILs, TIMs and other immunocytes (including leukocytes) deliver PUFAs to tumor cells to enhance accumulation of toxic lipid peroxides to induce tumor cell death (see Fig. 3).
Bioactive lipids and cancer Several studies showed that polyunsaturated fatty acids (PUFAs), especially gamma-linolenic acid (GLA, 18:3 n-6), AA (arachidonic acid, 20:4 n-6), EPA (eicosapentaenoic acid, 20:5 n-3) and DHA (docosahexaenoic acid, 22:6n-3) have tumoricidal action both in vitro and in vivo [62–80]. These endogenous low molecular weight lipids (called as bioactive lipids) act specifically on tumor cells with little or no cytotoxic action on normal cells [62–80]. Of all the fatty acids tested, GLA seems to be a potent and selective tumoricidal molecule (GLA > AA > EPA ≥ DHA), especially against glioma cells [71–73,81–85]. Tumor cells have low Δ6 and Δ 5 desaturase activity [86–89] that are needed for the formation of GLA, AA and EPA and DHA from their respective precursors’ linoleic acid (LA, 18:2 n-6) and α-linolenic acid (ALA, 18:3 n-3). This renders tumor cells deficient in their long-chain metabolites GLA, AA, EPA and DHA. PUFAs deficiency is responsible for the low rates of lipid peroxidation seen in tumor cells. In contrast, tumor cells have relatively high content of antioxidant vitamin E. The uptake of GLA, AA, EPA and DHA is almost 1½ to 2 times lower in tumor compared to normal cells yet generation of free radicals and formation of toxic lipid peroxides are 3-7-fold higher in tumor cells compared to normal cells [80,90–92]. Antioxidants vitamin E, BHA and BHA inhibited the tumoricidal action of GLA and other long-chain fatty acids whereas pro-oxidants: coper and ferrous salts enhanced their toxicity. These in vitro results are supported by the observation that intra-tumoral injection/infusion of GLA can regress glioma in animal models without any side-effects [93–95]. GLA, AA, EPA and DHA can suppress Ras, myc, p53, Bax/BCL-2, gene expressions, decrease mRNA expression of E2F1, alter protein expression of VEGF, Flt1, ERK1, ERK2, MMP2, Cyclin D1, pRb, p53 and p27 and arrest mitosis [72,73,96,97]. In a limited, open-label clinical study performed in patients with stage IV glioma revealed that intra-tumoral injection/infusion of GLA regresses glioma without any side-effects [83,93,94]. Furthermore, GLA and other unsaturated fatty acids enhanced the sensitivity of tumor cells to chemotherapeutic drugs and radiation [84,98–107]. These interesting in vitro, in vivo and limited clinical studies are supported by the observation that lipids are a constitutive component of cytolytic granules of CTL and NK cells [108] and cytokine activated macrophages release linolenic acid (presumably GLA) and linolenic acid-activated macrophages have marked tumoricidal action [109–115]. GLA, AA, EPA and DHA and their metabolites PGE1, PGE2, lipoxins, resolvins, protectins and maresins suppress production of IL-1 IL-6 and TNF-α [116–124], which are involved in CRS. Based on these evidences, I propose that combining TILs and/or CAR T cell therapy (with or without conventional chemotherapy) with GLA/AA/EPA/DHA may enhance their selective tumoricidal action without the danger of CRS or much less CRS including those gliomas.
Conclusions and future perspectives Exploiting the specificity and ability of the immune system to eliminate tumor cells is an exciting opportunity but is associated with significant side effects. Immunocytes (NK cells, CTL cells, LAK, dendritic cells, leukocytes, etc.,) release cytotoxic molecules such as perforin and granzyme, cytokines IL-6, TNF-α and IFN-γ that augment ROS (reactive oxygen species) in the target (tumor) cells, deliver directly ROS to tumor cells and exosomes [128]. But little attention has been paid to the likelihood that PUFAs and their metabolites and toxic lipid peroxides may have a significant role in the anti-cancer action of immunocytes. NK cells and CTLs induce apoptosis of tumor cells even when perforin-granzyme pathway is inactivated and is dependent on the expression of soluble PLA2 (sPLA2) [129]. But it is known whether perforin and granzyme themselves can activate PLA2-this is an interesting possibility that needs to be evaluated. But it is well documented that PLD (phospholipase D) activation is needed in the CD16-triggered signaling cascade that leads to NK cytotoxic granule exocytosis that, in turn, is associated with AA release as well [130,131]. Formation of excess of toxic lipid peroxides and consequent tumor cell apoptosis/ferroptosis seems to be common pathway by which radiation, chemotherapeutic drugs and PUFAs kill tumor cells. Anti-inflammatory metabolites of PUFAs lipoxin A4 (from AA), resolvins (from EPA and DHA), protectins and maresins (from DHA) have tumor cell growth inhibitory actions with no action on normal cells [71,73]. It is likely that PUFAs (especially AA) are differentially metabolized by normal and tumor cells. Normal cells utilize PLA2-induced release of PUFAs, especially AA, to form LXA4 (and resolvins, protectins and maresins from EPA and DHA) whereas tumor cells utilize them to form mainly PGE2 and LTs. Thus, tumor cells have evolved several mechanisms to defer the formation of lipid peroxides and enhance the synthesis of PGE2 and LTs that enable them to avoid apoptosis/ferroptosis [65,71,73,91,125,132]. Prophylactic TNF blockade prevents dual CTLA-4 and PD-1 immunotherapy induced toxicity without impairing their efficacy [133]. PUFAs and their metabolites including PGE2, LXA4, resolvins, protectins, maresins inhibit TNF-α, IL-6 and 4
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Fig. 3. Scheme showing how cytokines and PUFAs induce apoptosis/ferroptosis/necrosis of tumor cells. Interferon-gamma (IFN-γ), IL-6, TNF-α and other cytotoxic molecules released from CD8+ T cells/macrophages/TILs/NK cells/immunocytes downregulate the expression of SLC3A2 and SLC7A11, two subunits of the glutamate–cystine antiporter system xc−, impair the uptake of cystine by tumor cells, and as a consequence, promotes accumulation of toxic lipid peroxide in tumor cell to induce their ferroptosis/apoptosis/necrosis. In addition, IFN-γ, TNF-α and IL-6 activate phospholipase A2 (PLA2) and induce the release of PUFAs (especially AA) from the cell membrane lipid pool to make them available for the formation of PGE2 (an immunosuppressor), LXA4 (an anti-inflammatory molecule that is cytoprotective of normal cells but inhibits tumor cell growth) and are substrates to lipid peroxides (that are cytotoxic to tumor cells). It is likely that there could occur a balance between PGE2 and LXA4 formation from AA-the balance being more tilted towards PGE2 in tumor cells and towards LXA4 in normal cells. PUFAs may also be released and made available to tumor cells by the surrounding milieu of normal/tumor cells. There could occur a competition for the uptake of PUFAs between immunocytes and tumor cells-the former to form LXA4 and lipid peroxides to be delivered to tumor cells and latter to form PGE2 to induce immunosuppression.
HMGB1 synthesis [134–139] and thus, it is anticipated that a combination of immune check point inhibitors with PUFAs (especially AA) would be highly effective against several types of tumors. The benefit of such effective anti-cancer therapy with few side effects need to be studied in future.
[9] Merryman RW, Kim HT, Zinzani PL, Carlo-Stella C, Ansell SM, Perales MA, et al. Safety and efficacy of allogenic hematopoietic stem cell transplant after PD-1 blockade in relapse/refractory lymphoma. Blood 2017;129:1380–8. [10] Berman D, Parker SM, Siegel J, Chasalow SD, Weber J, Galbraith S, et al. Blockade of cytotoxic T-lymphocyte antigen-4 by ipilimumab results in dysregulation of gastrointestinal immunity in patients with advanced melanoma. Cancer Immun 2010;10:11. [11] Davis C, Naci H, Gurpinar E, Poplavska E, Pinto A, Aggarwal A. Availability of evidence of benefits on overall survival and quality of life of cancer drugs approved by European Medicines Agency: retrospective cohort study of drug approvals 2009–13. Br Med J 2017;359:j4530. [12] Kim C, Prasad V. Cancer drugs approved on the basis of a surrogate end point and subsequent overall survival: An analysis of 5 5ears of US Food and Drug Administration approvals. JAMA Intern Med 2015;175:1992–4. [13] Waterhouse P, Penninger JM, Timms E, Wakeham A, Shahinian A, Lee KP, et al. Lymphoproliferative disorders with early lethality in mice deficient in Ctla-4. Science 1995;270:985–8. [14] Walunas TL, Bakker CY, Bluestone JA. CTLA-4 ligation blocks CD28-dependent T cell activation. J Exp Med 1996;183:2541–50. [15] Walunas TL, Lenschow DJ, Bakker CY, Linsley PS, Freeman GJ, Green JM, et al. CTLA-4 can function as a negative regulator of T cell activation. Immunity 1994;1:405–13. [16] Dranoff G. Immunotherapy at large: Balancing tumor immunity and inflammatory pathology. Nat Med 2013;19:1100–1. [17] Krummel MF, Allison JP. CD28 and CTLA-4 have opposing effects on the response of T cells to stimulation. J Exp Med 1995;182:459–65. [18] Liossis SN, Sfikakis PP, Tsokos GC. Immune cell signaling aberrations in human lupus. Immunol Res 1998;18:27–39. [19] Chang TT, Kuchroo VK, Sharpe AH. Role of the B7-CD28/CTLA-4 pathway in autoimmune disease. Curr Dir Autoimmun 2002;5:113–30. [20] Johnson TS, Munn DH. Host indoleamine 2,3-dioxygenase: contribution to systemic acquired tumor tolerance. Immunol Invest 2012;41:765–97. [21] Prendergast GC, Smith C, Thomas S, Mandik-Nayak L, Laury-Kleintop L, Metz R, et al. Indoleamine 2,3-dioxygenase pathways of pathogenic inflammation and immune escape in cancer. Cancer Immunol Immunother 2014;63:721–35. [22] Terness P, Bauer TM, Röse L, Dufter C, Watzlik A, Simon H, et al. Inhibition of allogeneic T cell proliferation by indoleamine 2,3-dioxygenase-expressing dendritic cells: mediation of suppression by tryptophan metabolites. J Exp Med 2002;196:447–57. [23] Munn DH, Shafizadeh E, Attwood JT, Bondarev I, Pashine A, Mellor AL. Inhibition of T cell proliferation by macrophage tryptophan catabolism. J Exp Med 1999;189:1363–72. [24] Yoshida R, Urade Y, Tokuda M, Hayaishi O. Induction of indoleamine 2,3-dioxygenase in mouse lung during virus infection. Proc Natl Acad Sci USA 1979;76:4084–6.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.mehy.2019.109473. References [1] Pardoll DM. The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer 2012;12:252–64. [2] Butte MJ, Keir ME, Phamduy TB, Sharpe AH, Freeman GJ. Programmed death-1 ligand 1 interacts specifically with the B7–1 costimulatory molecule to inhibit T cell responses. Immunity 2007;27:111–22. [3] Karwacz K, Bricogne C, MacDonald D, Arce F, Bennett CL, Collins M, et al. PD-L1 co-stimulation contributes to ligand-induced T cell receptor down-modulation on CD8+ T cells. EMBO Mol Med 2011;3:581–92. [4] Syn NL, Teng MWL, Mok TSK, Soo RA. De-novo and acquired resistance to immune checkpoint targeting. Lancet Oncol 2017;18:e731–41. [5] Noel PJ, Boise LH, Thompson CB. Regulation of T cell activation by CD28 and CTLA4. Adv Exp Med Biol 1996;406:209–17. [6] Dudley ME, Wunderlich JR, Robbins PF, Yang JC, Hwu P, Schwartzentruber DJ, et al. Cancer regression and autoimmunity in patients after clonal repopulation with antitumor lymphocytes. Science 2002;298:850–4. [7] Rosenberg SA, Restifo NP. Adoptive cell transfer as personalized immunotherapy for human cancer. Science 2015;348:62–8. [8] Naidoo J, Page DB, Li BT, Connell LC, Schindler K, Lacouture ME, et al. Toxicities of the anti-PD-1 and anti-PD-L1 immune checkpoint antibodies. Ann Oncol 2015;26:2375–91.
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U.N. Das
N Engl J Med 2016;375:1767–78. [57] Topalian SL, Hodi FS, Brahmer JR, et al. Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N Engl J Med 2012;366:2443–54. [58] Webb ES, Liu P, Baleeiro R, Lemoine NR, Yuan M, Wang Y. Immune checkpoint inhibitors in cancer therapy. J Biomed Res 2018;32:317–26. [59] Shimabukuro-Vornhagen A, Gödel P, Subklewe M, Stemmler HJ, Schlößer HA, Schlaak M, et al. Cytokine release syndrome. J ImmunoTherapy Cancer 2018;6:56. [60] Bajwa R, Cheema A, Khan T, Amirpour A, Paul A, Chaughtai S, et al. Adverse effects of immune checkpoint inhibitors (programmed death-1 inhibitors and cytotoxic T-lymphocyte-associated protein-4 inhibitors): results of a retrospective study. J Clin Med Res 2019;11:225–36. [61] Ferrara R, Mezquita L, Texier M, Lahmar J, Audigier-Valette C, Tessonnier L, et al. Hyperprogressive disease in patients with advanced non–small cell lung cancer treated with PD-1/PD-L1 inhibitors or with single-agent chemotherapy. JAMA Oncol 2018. https://doi.org/10.1001/jamaoncol.2018.3676. [62] Comba A, Maestri DM, Berra MA, Garcia CP, Das UN, Eynard AR, et al. Effect of ω3 and ω-9 fatty acid rich oils on lipoxygenases and cyclooxygenases enzymes and on the growth of a mammary adenocarcinoma model. Lipids Health Dis 2010;9:112-. [63] Bégin ME, Ells G, Das UN, Horrobin DF. Differential killing of human carcinoma cells supplemented with n-3 and n-6 polyunsaturated fatty acids. J Natl Cancer Inst 1986;77:1053–62. [64] Das UN. Effect of γ- Linolenic acid on the transcriptional activity of the HER-2neu (erbB-2) Oncogene. J Natl Cancer Inst 2006;98:718. [65] Das UN. Tumoricidal action of cis-unsaturated fatty acids and their relationship to free radicals and lipid peroxidation. Cancer Lett 1991;56:235–43. [66] Ge H, Kong X, Shi L, Hou L, Liu Z, Li P. Gamma-linolenic acid induces apoptosis and lipid peroxidation in human chronic myelogenous leukemia K562 cells. Cell Biol Int 2009;33:402–10. [67] Begin ME, Das UN, Ells G. Cytotoxic effects of essential fatty acids (EFA) in mixed cultures of normal and malignant human cells. Prog Lipid Res 1986;25:573–6. [68] Das UN, Madhavi N. Effect of polyunsaturated fatty acids on drug-sensitive and resistant tumor cells in vitro. Lipids Health Dis 2011;10:159. [69] Gillis RC, Daley BJ, Enderson BL, Karlstad MD. Eicosapentaenoic acid and γ-linolenic acid induce apoptosis in HL-60 cells. J Surg Res 2002;107:145–53. [70] Madhavi N, Das UN. Effect of n-6 and n-3 fatty acids on the survival of vincristine sensitive and resistant human cervical carcinoma cells in vitro. Cancer Lett 1994;84:31–41. [71] Sailaja P, Mani AM, Naveen KVG, Anasuya DH, Siresha B, Das UN. Effect of polyunsaturated fatty acids and their metabolites on bleomycin-induced cytotoxic action on human neuroblastoma cells in vitro. PLoS One 2014;9:e114766. [72] Sailaja P, Dwarakanath B, Das UN. Arachidonic acid activates extrinsic apoptotic pathway to enhance tumoricidal action of bleomycin against IMR-32 cells. Prostaglandins Leukot Essen Fatty Acids 2018;132:16–22. [73] Anasuya DH, Naidu VGM, Das UN. n-6 and n-3 Fatty acids and their metabolites augment inhibitory action of doxorubicin on the proliferation of human neuroblastoma (IMR-32) cells by enhancing lipid peroxidation and suppressing Ras, Myc, and Fos. BioFactors 2018;44:387–401. [74] D'Eliseo D, Di Renzo L, Santoni A, Velotti F. Docosahexaenoic acid (DHA) promotes immunogenic apoptosis in human multiple myeloma cells, induces autophagy and inhibits STAT3 in both tumor and dendritic cells. Genes Cancer 2017;8:426–37. [75] Molinari R, D'Eliseo D, Manzi L, Zolla L, Velotti F, Merendino N. The n-3 polyunsaturated fatty acid docosahexaenoic acid induces immunogenic cell death in human cancer cell lines via pre-apoptotic calreticulin exposure. Cancer Immunol Immunother 2011;60:1503–7. [76] Pizato N, Luzete BC, Kiffer LFMV, Corrêa LH, de Oliveira Santos I, Assumpção JAF, et al. Omega-3 docosahexaenoic acid induces pyroptosis cell death in triple-negative breast cancer cells. Sci Rep 2018;8:1952. [77] Das M, Das S. Identification of cytotoxic mediators and their putative role in the signaling pathways during docosahexaenoic acid (DHA)-induced apoptosis of cancer cells. Apoptosis 2016;21:1408–21. [78] Kang KS, Wang P, Yamabe N, Fukui M, Jay T, Zhu BT. Docosahexaenoic acid induces apoptosis in MCF-7 cells in vitro and in vivo via reactive oxygen species formation and caspase 8 activation. PLoS One 2010;5:e10296. [79] Gleissman H, Yang R, Martinod K, Lindskog M, Serhan CN, Johnsen JI, et al. Docosahexaenoic acid metabolome in neural tumors: identification of cytotoxic intermediates. FASEB J 2010;24:906–15. [80] Das UN. Essential fatty acids enhance free radical generation and lipid peroxidation to induce apoptosis of tumor cells. Clin Lipidol 2011;6:463–89. [81] Bell HS, Wharton SB, Leaver HA, Whittle IR. Effects of N-6 essential fatty acids on glioma invasion and growth: experimental studies with glioma spheroids in collagen gels. J Neurosurg 1999;91:989–96. [82] Antal O, Péter M, Hackler Jr L, Mán I, Szebeni G, Ayaydin F, et al. Lipidomic analysis reveals a radiosensitizing role of gamma-linolenic acid in glioma cells. Biochim Biophys Acta, Mol Cell Biol Lipids 2015;1851:1271–82. [83] Das UN. Gamma-linolenic acid therapy of human glioma-a review of in vitro, in vivo, and clinical studies. Med Sci Monit 2007;13:RA119–31. [84] Vartak S, McCaw R, Davis CS, Robbins ME, Spector AA. Gamma-linolenic acid (GLA) is cytotoxic to 36B10 malignant rat astrocytoma cells but not to 'normal' rat astrocytes. Br J Cancer 1998;77:1612–20. [85] Fujiwara F, Todo S, Imashuku S. Antitumor effect of gamma-linolenic acid on cultured human neuroblastoma cells. Prostaglandins Leukot Med 1986;23:311–20. [86] Nassar BA, Das UN, Huang YS, Ells G, Horrobin DF. The effect of chemical hepatocarcinogenesis on liver phospholipid composition in rats fed N-6 and N-3 fatty acid-supplemented diets. Proc Soc Exp Biol Med 1992;199:365–8.
[25] Pfefferkorn ER. Interferon gamma blocks the growth of Toxoplasma gondii in human fibroblasts by inducing the host cells to degrade tryptophan. Proc Natl Acad Sci USA 1984;81:908–12. [26] Theate I, van Baren N, Pilotte L, Moulin P, Larrieu P, Renauld JC, et al. Extensive profiling of the expression of the indoleamine 2,3-dioxygenase 1 protein in normal and tumoral human tissues. Cancer Immunol Res 2015;3:161–72. [27] Munn DH, Zhou M, Attwood JT, Bondarev I, Conway SJ, Marshall B, et al. Prevention of allogeneic fetal rejection by tryptophan catabolism. Science 1998;281:1191–3. [28] Platten M, Ho PP, Youssef S, Fontoura P, Garren H, Hur EM, et al. Treatment of autoimmune neuroinflammation with a synthetic tryptophan metabolite. Science 2005;310:850–5. [29] Cook CH, Bickerstaff AA, Wang JJ, Nadasdy T, Della Pelle P, Colvin RB, et al. Spontaneous renal allograft acceptance associated with “regulatory” dendritic cells and IDO. J Immunol 2008;180:3103–12. [30] Jasperson LK, Bucher C, Panoskaltsis-Mortari A, Taylor PA, Mellor AL, Munn DH, et al. Indoleamine 2,3-dioxygenase is a critical regulator of acute graft-versus-host disease lethality. Blood 2008;111:3257–65. [31] Moon YW, Hajjar J, Hwu P, Naing A. Targeting the indoleamine 2,3-dioxygenase pathway in cancer. J Immuno Therapy Cancer 2015;3:51. [32] Opitz CA, Wick W, Steinman L, Platten M. Tryptophan degradation in autoimmune diseases. Cell Mol Life Sci 2007;64:2542–63. [33] Opitz CA, Litzenburger UM, Sahm F, Ott M, Tritschler I, Trump S, et al. An endogenous tumour-promoting ligand of the human aryl hydrocarbon receptor. Nature 2011;478:197–203. [34] Mezrich JD, Fechner JH, Zhang X, Johnson BP, Burlingham WJ, Bradfield CA. An interaction between kynurenine and the aryl hydrocarbon receptor can generate regulatory T cells. J Immunol 2010;185:3190–8. [35] Nguyen NT, Kimura A, Nakahama T, Chinen I, Masuda K, Nohara K, et al. Aryl hydrocarbon receptor negatively regulates dendritic cell immunogenicity via a kynurenine-dependent mechanism. Proc Natl Acad Sci USA 2010;107:19961–6. [36] Das UN. Is there a role for bioactive lipids in the pathobiology of diabetes mellitus? Front Endocrinol 2017;8:182. [37] Yano JM, Yu K, Donaldson GP, Shastri GG, Ann P, Ma L, et al. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell 2015;161:264–76. [38] Reigstad CS, Salmonson CE, Rainey III JF, Szurszewski JH, Linden DR, Sonnenburg JL, et al. Gut microbes promote colonic serotonin production through an effect of short-chain fatty acids on enterochromaffin cells. FASEB J 2015;29:1395–403. [39] Kim H, Toyofuku Y, Lynn FC, Chak E, Uchida T, Mizukami H, et al. Serotonin regulates pancreatic beta cell mass during pregnancy. Nat Med 2010;16:804–9. [40] Georgia S, Bhushan A. Pregnancy hormones boost beta cells via serotonin. Nat Med 2010;16:756–7. [41] Stockinger B, Hirota K, Duarte J, Veldhoen M. External influences on the immune system via activation of the aryl hydrocarbon receptor. Semin Immunol 2011;23:99–105. [42] Veldhoen M, Hirota K, Westendorf AM, Buer J, Dumoutier L, Renauld JC, et al. The aryl hydrocarbon receptor links TH17-cell-mediated autoimmunity to environmental toxins. Nature 2008;453:106–9. [43] Quintana FJ, Basso AS, Iglesias AH, Korn T, Farez MF, Bettelli E, et al. Control of T(reg) and T(H)17 cell differentiation by the aryl hydrocarbon receptor. Nature 2008;453:65–71. [44] Liang SC, Tan XY, Luxenberg DP, Karim R, Dunussi-Joannopoulos K, Collins M, et al. Interleukin (IL)-22 and IL-17 are coexpressed by Th17 cells and cooperatively enhance expression of antimicrobial peptides. J Exp Med 2006;203:2271–9. [45] Ke Y, Liu K, Huang G-Q, Cui Y, Kaplan HJ, Shao H, et al. Anti-inflammatory role of IL-17 in experimental autoimmune uveitis. J Immunol 2009;182:3183–90. [46] Deby C, Damas J. Proceedings: Influence of tryptophan on the hypotensive effect of arachidonic acid. Arch Int Physiol Biochim 1974;82:742–4. [47] Robert C, Karaszewska B, Schachter J, Rutkowski P, Mackiewicz A, Stroiakovski D, et al. Improved overall survival in melanoma with combined dabrafenib and trametinib. N Engl J Med 2015;372:30–9. [48] Hodi FS, O'Day SJ, McDermott DF, Weber RW, Sosman JA, Haanen JB, et al. Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med 2010;363:711–23. [49] Robert C, Long GV, Brady B, Dutriaux C, Maio M, Mortier L, et al. Nivolumab in previously untreated melanoma without BRAF mutation. N Engl J Med 2015;372:320–30. [50] Eggermont AMM, Blank CU, Mandala M, Long GV, Atkinson V, Dalle S, et al. Adjuvant pembrolizumab versus placebo in resected stage III melanoma. N Engl J Med 2018;378:1789–801. [51] Garber K. A new cancer immunotherapy suffers a setback. Science 2018;360:588. [52] Wilkerson J, Fojo T. Progression-free survival is simply a measure of a drug’s effect while administered and is not a surrogate for overall survival. Cancer J 2009;15:379–85. [53] Zhou Y, Chen C, Zhang X, Fu S, Xue C, Ma Y, et al. Immune-checkpoint inhibitor plus chemotherapy versus conventional chemotherapy for first-line treatment in advanced non-small cell lung carcinoma: a systematic review and meta-analysis. J ImmunoTher Cancer 2018;6:155. [54] Zhuansun Y, Huang F, Du Y, Lin L, Chen R, Li J. Anti-PD-1/PD-L1 antibody versus conventional chemotherapy for previously-treated, advanced non-small-cell lung cancer: a meta-analysis of randomized controlled trials. J Thorac Dis 2017;9:655–65. [55] Saxena A, Ramana KV. Impact of immune checkpoint inhibitors in cancer immunotherapy. J Cancer Immunol Ther 2018;1:4–5. [56] Boussiotis VA. Molecular and biochemical aspects of the PD-1 checkpoint pathway.
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Medical Hypotheses 135 (2020) 109473
U.N. Das
immunological killing of tumor cells: II. Effector cell lipids. Lipids 1983;18:483–8. [114] Schlager SI, Ohanian SH. Role of membrane lipids in the immunological killing of tumor cells: I. Target cell lipids. Lipids 1983;18:475–82. [115] Schlager SI, Meltzer MS. Role of macrophage lipids in regulating tumoricidal activity. II. Internal genetic and external physiologic regulatory factors controlling macrophage tumor cytotoxicity also control characteristic lipid changes associated with tumoricidal cells. Cell Immunol 1983;80:10–9. [116] Kumar GS, Das UN. Effect of prostaglandins and their precursors on the proliferation of human lymphocytes and their secretion of tumor necrosis factor and various interleukins. Prostaglandins Leukot Essent Fatty Acids 1994;50:331–4. [117] Dooper MM, van Riel B, Graus YM, M'Rabet L. Dihomo-gamma-linolenic acid inhibits tumour necrosis factor-alpha production by human leucocytes independently of cyclooxygenase activity. Immunology 2003;110:348–57. [118] Rossetti RG, Brathwaite K, Zurier RB. Suppression of acute inflammation with liposome associated prostaglandin E1. Prostaglandins 1994;48:187–95. [119] Harizi H, Norbert G. Inhibition of IL-6, TNF-alpha, and cyclooxygenase-2 protein expression by prostaglandin E2-induced IL-10 in bone marrow-derived dendritic cells. Cell Immunol 2004;228:99–109. [120] Duffin R, O’Connor RA, Crittenden S, Forster T, Yu C, Zheng X, et al. Prostaglandin E2 constrains systemic inflammation through an innate lymphoid cell–IL-22 axis. Science 2016;351:1333–8. [121] FitzGerald GA. Bringing PGE2 in from the cold. Science 2015;348:1208–9. [122] Zhang Y, Desai A, Yang SY, Bae KB, Antczak MI, Fink SP, et al. Inhibition of the prostaglandin-degrading enzyme 15-PGDH potentiates tissue regeneration. Science 2015;348:aaa2340. https://doi.org/10.1126/science.aaa2340. [123] Liu C, Guan H, Cai C, Li F, Xiao J. Lipoxin A4 suppresses osteoclastogenesis in RAW264.7 cells and prevents ovariectomy-induced bone loss. Exp Cell Res 2017;352:293–303. [124] Poorani R, Bhatt AN, Dwarakanath BS, Das UN. COX-2, aspirin and metabolism of arachidonic, eicosapentaenoic and docosahexaenoic acids and their physiological and clinical significance. Eur J Pharmacol 2016;785:116–32. [125] Das UN. Saturated fatty acids, MUFAs and PUFAs regulate ferroptosis. Cell Chem Biol 2019;26:309–11. [126] Viswanathan V, Ryan MJ, Dhruv HD, Gill S, Eichhoff OM, Seashore-Ludlow B, et al. Dependency of a therapy-resistant state of cancer cells on a lipid peroxidase pathway. Nature 2017;547:453–7. [127] Hangauer MJ, Viswanathan V, Ryan MJ, Bole D, Eaton JK, Matov A, et al. Drugtolerant persister cancer cells are vulnerable to GPX4 inhibition. Nature 2017;551:247–50. [128] Paul S, Lal G. The Molecular mechanism of natural killer cells function and its importance in cancer immunotherapy. Front Immunol 2017;8:1124. [129] Costa-Junior HM, Hamaty FC, da Silva Farias R, Einicker-Lamas M, da Silva MH, Persechini PM. Apoptosis-inducing factor of a cytotoxic T cell line: involvement of a secretory phospholipase A2. Cell Tissue Res 2006;324:255–66. [130] Milella M, Gismondi A, Roncaioli P, Palmieri G, Morrone S, Piccoli M, et al. Beta 1 integrin cross-linking inhibits CD16-induced phospholipase D and secretory phospholipase A2 activity and granule exocytosis in human NK cells: role of phospholipase D in CD16-triggered degranulation. J Immunol 1999;162:2064–72. [131] Parmentier JH, Muthalif MM, Nishimoto AT, Malik KU. 20Hydroxyeicosatetraenoic acid mediates angiotensin ii-induced phospholipase d activation in vascular smooth muscle cells. Hypertension 2001;37(2 Pt 2):623–9. [132] Das UN, Begin ME, Ells G, Huang YS, Horrobin DF. Polyunsaturated fatty acids augment free radical generation in tumor-cells in vitro. Biochem Biophys Res Commun 1987;145:15–24. [133] Perez-Ruiz E, Minute L, Otano I, Alvarez M, Ochoa MC, Belsue V, et al. Prophylactic TNF blockade uncouples efficacy and toxicity in dual CTLA-4 and PD1 immunotherapy. Nature 2019;569:428–32. [134] Kumar SG, Das UN, Kumar KV, Madhavi Das NP, Tan BKH. Effect of n-6 and n-3 fatty acids on the proliferation and secretion of TNF and IL-2 by human lymphocytes in vitro. Nutrition Res 1992;12:815–23. [135] Das UN. Is lipoxins A4 a better alternative to anti-VEGF and anti-TNF-alpha antibody to prevent and treat age-related macular degeneration, diabetic macular edema and retinopathy? Med Sci Monit 2011;18:LE1–2. [136] Stuhlmeier KM, Kao JJ, Bach FH. Arachidonic acid influences proinflammatory gene induction by stabilizing the inhibitor-kappaBalpha/nuclear factor-kappaB (NF-kappaB) complex, thus suppressing the nuclear translocation of NF-kappaB. J Biol Chem 1997;272:24679–83. [137] Naveen KVG, Naidu VGM, Das UN. Arachidonic acid and lipoxin A4 attenuate alloxan-induced cytotoxicity to RIN5F cells in vitro and type 1 diabetes mellitus in vivo. BioFactors 2017;43:251–71. [138] Naveen KVG, Naidu VGM, Das UN. Arachidonic acid and lipoxin A4 attenuate streptozotocin-induced cytotoxicity to RIN5F cells in vitro and type 1 and type 2 diabetes mellitus in vivo. Nutrition 2017;35:61–80. [139] Naveen GV, Naidu G, Das UN. Amelioration of streptozotocin-induced type 2 diabetes mellitus in Wistar rats by arachidonic acid. Biochem Biophys Res Commun 2018;496:105–13.
[87] Dunbar LM, Bailey JM. Enzyme deletions and essential fatty acid metabolism in cultured cells. J Biol Chem 1975;250:1152–3. [88] Bendetti A. Loss of lipid peroxidation as a histochemical marker for preneoplastic hepatocellular foci of rats. Cancer Res 1984;44:5712–7. [89] Morton RE, Hartz JW, Reitz RC, Waite BM, Morris H. The acyl-CoA desaturases of microsomes from rat liver and the Morris 7777 hepatoma. Biochim Biophys Acta, Mol Cell Biol Lipids 1979;573:321–31. [90] Das UN, Begin ME, Ells G, Huang YS, Horrobin DF. Polyunsaturated fatty acids augment free radical generation in tumor cells in vitro. Biochem Biophys Res Commun 1987;145:15–24. [91] Das UN, Huang YS, Begin ME, Ells G, Horrobin DF. Uptake and distribution of cisunsaturated fatty acids and their effect on free radical generation in normal and tumor cells in vitro. Free Radical Biol Med 1987;3:9–14. [92] Das UN. Selective enhancement of free radicals in tumor cells as a strategy to kill tumor cells both in vitro and in vivo. In: Reddy CC, editor. Biological oxidation systems. New York: Academic Press; 1990. p. 607–24. [93] Naidu MR, Das UN, Kishan A. Intratumoral gamma-linoleic acid therapy of human gliomas. Prostaglandins Leukot Essent Fatty Acids 1992;45:181–4. [94] Das UN, Prasad VV, Reddy DR. Local application of gamma-linolenic acid in the treatment of human gliomas. Cancer Lett 1995;94:147–55. [95] Bakshi A, Mukherjee D, Bakshi A, Banerji AK, Das UN. Gamma-linolenic acid therapy of human gliomas. Nutrition 2003;19:305–9. [96] Miyake JA, Benadiba M, Colquhoun A. Gamma-linolenic acid inhibits both tumour cell cycle progression and angiogenesis in the orthotopic C6 glioma model through changes in VEGF, Flt1, ERK1/2, MMP2, cyclin D1, pRb, p53 and p27 protein expression. Lipids Health Dis 2009;8:8. [97] Benadiba M, Miyake JA, Colquhoun A. Gamma-linolenic acid alters Ku80, E2F1, and bax expression and induces micronucleus formation in C6 glioma cells in vitro. IUBMB Life 2009;61:244–51. [98] Sangeetha PS, Das UN. Gamma-linolenic acid and eicosapentaenoic acid potentiate the cytotoxicity of anti-cancer drugs on human cervical carcinoma (HeLa) cells in vitro. Med Sci Res 1993;21:457–9. [99] Madhavi N, Das UN. Reversal of KB-3-1 and KB-Ch-8-5 tumor cell drug-resistance by cis-unsaturated fatty acids in vitro. Med Sci Res 1994;22:689–92. [100] Das UN, Madhavi N, Padma M, Sagar PS. Can tumor cell drug-resistance be reversed by essential fatty acids and their metabolites? Prostaglandins Leukot Essen Fatty Acids 1998;58:39–54. [101] Germain E, Chajès V, Cognault S, Lhuillery C, Bougnoux P. Enhancement of doxorubicin cytotoxicity by polyunsaturated fatty acids in the human breast tumor cell line MDA-MB-231: relationship to lipid peroxidation. Int J Cancer 1998;75:578–83. [102] Mahéo K, Vibet S, Steghens JP, Dartigeas C, Lehman M, Bougnoux P, et al. Differential sensitization of cancer cells to doxorubicin by DHA: a role for lipoperoxidation. Free Radic Biol Med 2005;39:742–51. [103] Ilc K, Ferrero JM, Fischel JL, Formento P, Bryce R, Etienne MC, et al. Cytotoxic effects of two gamma linoleic salts (lithium gammalinolenate or meglumine gammalinolenate) alone or associated with a nitrosourea: an experimental study on human glioblastoma cell lines. Anticancer Drugs 1999;10:413–7. [104] Menendez JA, Ropero S, Lupu R, Colomer R. Omega-6 polyunsaturated fatty acid gamma-linolenic acid (18:3n–6) enhances docetaxel (Taxotere) cytotoxicity in human breast carcinoma cells: Relationship to lipid peroxidation and HER-2/neu expression. Oncol Rep 2004;11:1241–52. [105] Menéndez JA, Ropero S, del Barbacid MM, Montero S, Solanas M, Escrich E, et al. Synergistic interaction between vinorelbine and gamma-linolenic acid in breast cancer cells. Breast Cancer Res Treat 2002;72:203–19. [106] Menendez JA, Ropero S, Mehmi I, Atlas E, Colomer R, Lupu R. Overexpression and hyperactivity of breast cancer-associated fatty acid synthase (oncogenic antigen519) is insensitive to normal arachidonic fatty acid-induced suppression in lipogenic tissues but it is selectively inhibited by tumoricidal alpha-linolenic and gamma-linolenic fatty acids: a novel mechanism by which dietary fat can alter mammary tumorigenesis. Int J Oncol 2004;24:1369–83. [107] Kong X, Ge H, Chen L, Liu Z, Yin Z, Li P, et al. Gamma-linolenic acid modulates the response of multidrug-resistant K562 leukemic cells to anticancer drugs. Toxicol In Vitro 2009;23:634–9. [108] Baranov V, Nagaeva O, Hammarstrom S, Mincheva-Nilsson L. Lipids as a constitutive component of cytolytic granules. Histochem Cell Biol 2000;114:167–71. [109] Schlager SI, Ohanian SH. Correlation between lipid synthesis in tumor cells and their sensitivity to humoral immune attack. Science 1977;197:773–6. [110] Schlager SI, Ohanian SH, Borsos T. Correlation between the ability of tumor cells to incorporate specific fatty acids and their sensitivity to killing by a specific antibody plus guinea pig complement. J Natl Cancer Inst 1978;61:931–4. [111] Schlager SI, Ohanian SH. Modulation of tumor cell susceptibility to humoral immune killing through chemical and physical manipulation of cellular lipid and fatty acid composition. J Immunol 1980;125:1196–200. [112] Schlager SI, Madden LD, Meltzer MS, Bara S, Mamula MJ. Role of macrophage lipids in regulating tumoricidal activity. Cell Immunol 1983;77:52–68. [113] Schlager SI, Meltzer MS, Madden LD. Role of membrane lipids in the
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Medical Hypotheses journal homepage: www.elsevier.com/locate/mehy
Bioactive lipids as modulators of immune check point inhibitors
T
a,b
Undurti N. Das a b
UND Life Sciences, 2221 NW 5th St, Battle Ground, WA 98604, USA BioScience Research Centre, GVP College of Engineering Campus and Department of Medicine, GVP Hospital and Medical College, Visakhapatnam 530048, India
A R T I C LE I N FO
A B S T R A C T
Keywords: Immune check point inhibitors Polyunsaturated fatty acids Arachidonic acid Prostaglandins NK cells Indoleamine 2 3-Dioxygenase Cancer
It is proposed that arachidonic acid (AA, 20:4 n-6) and other polyunsaturated fatty acids (PUFAs) in combination with immune check point inhibitors and tumor infiltrating lymphocytes (TILs) enhances the activity of T and NK cells and macrophages and thus, aids in the elimination of tumor cells and suppresses inflammatory side effects due to immune check point inhibitors.
Introduction Selective elimination of tumor cells with little or no action on normal cells is desired but is rarely achieved with the current methods of treatment of cancer. Recently check point inhibitors of PD-1 (programmed cell death 1 protein), PD-1 ligand (PD-L1), cytotoxic T-lymphocyte-associated protein 4 {CTLA-4 also called as CD152 (cluster of differentiation) 152} and adoptive cell transfer (ACT) have been developed that have been reported to be of significant benefit in the management of cancer when used alone or in combination with existing chemotherapeutic drugs [1–7]. But these check point inhibitors have significant on-target, off-tumor toxicity called as immune-related adverse events (IRAEs) that include dermatologic, gastrointestinal, hepatic, endocrine, and other less common inflammatory events. Of all the side effects described, cytokine release syndrome can sometimes be lethal [8–10]. Furthermore, these check point inhibitors have been reported to be effective in not more than ~30–40% of the patients who receive the therapy implying that more refinements of this approach are needed [11,12]. Immune check point inhibitors Immune checkpoint inhibitor (or simply called as check point inhibitors) therapy uses immune checkpoints which affect immune system functioning. Immune checkpoints can be stimulatory or inhibitory. Tumor cells use these checkpoints to protect themselves from immune system attacks. Checkpoint therapy blocks these inhibitory checkpoints, restoring immune system function [1]. One such immune
E-mail addresses: [email protected], [email protected]. https://doi.org/10.1016/j.mehy.2019.109473 Received 4 October 2019; Accepted 2 November 2019 0306-9877/ © 2019 Elsevier Ltd. All rights reserved.
check point receptor is the transmembrane programmed cell death 1 protein (PDCD1, PD-1; also known as CD279) and its ligand, PD-1 ligand 1 (PD-L1, CD274). PD-L1 on the cell surface binds to PD1 on an immune cell surface that results in inhibition of immune cell activity. PD-L1 functions as a key regulator of T cell activities [2,3]. Cancer cellmediated upregulation of PD-L1 on the cell surface inhibits T cell responses against tumor cells and thus, blocks T cell anti-tumor action. Antibodies that bind to either PD-1 or PD-L1 block this interaction and allows the T-cells to attack the tumor [4] (see Fig. 1). cTLA-4 CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), also known as CD152 (cluster of differentiation 152), is a protein receptor that downregulates immune responses [13-15]. CTLA4 is constitutively expressed in regulatory T cells and is upregulated in conventional T cells after activation. It acts as an “off” switch when bound to CD80 or CD86 on the surface of antigen-presenting cells including cancer cell. AntiCTLA-4 therapy in combination with other drugs is useful in suppressing the growth of cancer cells [16]. It is well documented that patients treated with check-point blockade (specifically CTLA-4 blocking antibodies), or a combination of check-point blocking antibodies, are at high risk of developing immune-related adverse events such as dermatologic, gastrointestinal, endocrine, or hepatic autoimmune reactions [17–19] (see Fig. 2).
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Fig. 1. Scheme showing interaction among APC (antigen presenting cell such macrophages/dendritic cells) and T cells and the tumor cell. (Modified from “Immunotherapy in the precision medicine era: Melanoma and beyond”. December 13, 2016, https://doi.org/10.1371/journal.pmed.1002196). (-) indicates inhibition of production of PGE2, an immunoinhibitory and pro-inflammatory molecule produced from arachidonic acid (AA). PGE2 may be produced by the macrophages (or other APCs) and/or tumor cells or both. It is likely that PGE2 and other immunosuppressors may be produced by the microenvironment surrounding (tumor milieu) the tumor cells. As a result of CTLA-4 binding to the costimulatory B7 ligands found on antigen-presenting cells (APCs) prevents signaling through CD28. Antibodies targeting CTLA-4 release this checkpoint to allow T cell activation (central immunoinhibition). Binding of the PD-L1 of the tumor cells to the PD-1 receptor on T cells results in peripheral immunoinhibition. Antibodies targeting either the ligand or its receptor releases this checkpoint. Activated APCs (macrophages, T cells and other immunocytes) may release AA and other PUFAs that are peroxidized by free radicals to form toxic lipid peroxides (LP) that act on tumor cells to induce their apoptosis.
Indoleamine-pyrrole 2,3-dioxygenase (IDO or INDO)
Tryptophan catabolism results in anergy and apoptosis of effector T cells. In addition, tryptophan metabolites kynurenine, kynurenic acid, 3-hydroxy-kynurenine, and 3-hydroxy-anthranilic acid are capable of suppressing T-cell function by inducing T-cell apoptosis [32]. Aryl hydrocarbon receptor (AHR) is a direct target of kynurenine [32–35]. Arachidonic acid (AA, 20:4n-6) metabolites, bilirubin, cAMP, tryptophan metabolites tryptamine, kynurenic acid, and 6-formylindolo [3,2b] carbazole (FICZ) are all ligands of the AHR. Tryptophan is utilized by gut microbiota to form indole derivatives: indole-3-acetic acid, indoxyl-3-sulfate, indole-3-propionic acid, and indole-3-aldehyde, which are ligands for the aryl hydrocarbon receptor (AHR). Activation of AHR of gut-resident T cells and innate lymphoid cells enhances the production of IL-22, which suppresses inflammation that may account for the two-way cross talk between microbes and the immune system [36]. Tryptophan is the precursor of neurotransmitter serotonin. Gut microbiota can enhance serotonin biosynthesis from colonic enterochromaffin cells (ECs), and thus, supply serotonin to the mucosa, lumen, and circulating platelets [36-38]. Short-chain fatty acids acetate and butyrate produced by the gut microbiota modulate the synthesis of serotonin by ECs. The expansion of the maternal population of pancreatic β cells during pregnancy is stimulated by serotonin. Inhibition of serotonin synthesis blocks β cell expansion [36,39,40]. AHR is enriched in interleukin 17 (IL-17)-producing CD4+ T cells
Indoleamine-pyrrole 2,3-dioxygenase (IDO or INDO) is the ratelimiting enzyme of tryptophan catabolism through the kynurenine pathway by inducing O2-dependent oxidation of L-tryptophan to Nformyl kynurenine. IDO limits T cell function and enhances immune tolerance to tumor antigens, suppresses T regulatory (Treg) and myeloid-derived suppressor cells and promotes tumor angiogenesis [20,21]. IDO is activated during tumor development. Depletion of tryptophan by the activated IDO halts the proliferation of T cells [22,23]. Thus, IDO is an immune checkpoint molecule and an immunomodulatory enzyme produced by activated macrophages and other immune cells [21]. Tryptophan is an essential amino acid for cell survival. The role of IDO is to control microbial growth by regulating tryptophan availability and accumulation of tryptophan catabolites that have immunosuppressive actions in the inflammatory environment [24,25]. IDO is expressed in normal tissues including endothelial cells in the placenta and lung, the epithelial cells in the female genital tract, the lymphoid tissues in mature dendritic cells (DCs), immune cells or syncytiotrophoblasts in the placenta and cancer cells [26,27]. IDO present in trophoblasts prevents T cell-driven rejection of allogeneic fetuses during pregnancy and thus, allow maternal tolerance to fetal allograft. Thus, IDO may have a role in the management of autoimmune diseases, induction of graft tolerance and immune escape of tumors [28–31]. 2
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Fig. 2. Mechanism of action of immune checkpoint inhibitors. Notes: T regs depend on the activity of CTLA-4, PD-1, and PD-L1 to induce immunosuppression. Ipilimumab and tremelimumab are monoclonal antibodies that inhibit CTLA-4, while nivolumab, pembrolizumab, atezolizumab, and durvalumab inhibit PD-1 and PD-L1. These drugs reduce immune checkpoint activity on a T reg-rich microenvironment, thus diminishing tumor evasion. T regs = regulatory T-cells; TCR = T-cell receptor; MHC = major histocompatibility complex.
Immune check point inhibitors in cancer
(TH17 cells) and controls the differentiation of naive CD4+ T cells [28,41]. Kynurenine regulates the generation of regulatory T cells (Treg). AHR restricts autoimmunity by favoring the generation of Treg [27,42,43]. Kynurenine brings about its immunosuppressive effects by acting on AHR and affecting CD8+ T cells [28,33]. It is noteworthy that a close interaction/cooperation exists between IL-22 and IL-17. For instance, Th17 cells also express IL-22. Both IL-17A and IL-22 expressions are initiated by transforming growth factor β signaling in the context of IL-6 and other proinflammatory cytokines. It is known that IL-22 is coexpressed in vitro and in vivo with both IL-17A and IL-17F that synergize their actions to regulate innate immunity [44] suggesting that IL-22 and IL-17 have anti-inflammatory actions [36,42–45] which can be influenced by tryptophan metabolites through AHR [36]. We observed that serotonin enhances the production of lipoxin A4 (LXA4), a potent anti-inflammatory metabolite of AA (unpublished data, 37). Based on this data, it is likely that cancer cells escape from immune surveillance system by upregulating enzyme, tryptophan dioxygenase to form kynurenine, an endogenous ligand for the aryl hydrocarbon receptor, which mediates invasive tumour growth. Tryptophan conversion to kynurenine by the indoleamine 2,3-dioxygenase enzymes IDO and IDO2, and also by tryptophan dioxygenase (TDO) and the elevated levels of AHR in tumor are an indication of poor prognosis in cancer. It is noteworthy that tryptophan activates biosynthesis of prostaglandins, that have immunosuppressive actions [46]. Thus, tryptophan metabolism is linked to AA-eicosanoid metabolism, yet another mechanism by which tryptophan can induce immunosuppression.
Immune check point inhibitors upregulate immune system and unleash their tumoricidal action. Drugs such as ipilimumab, an antiCTLA4 antibody, pembrolizumab and nivolumab, both monoclonal antibodies against PD-1, and combination BRAF and MEK inhibitors for patients whose tumors harbor BRAF mutation have produced considerable anti-tumor activity [47–50]. Despite these advances, still a significant percentage of patients remain unresponsive to immune check point inhibitors therapy [11,12]. Blocking IDO in combination with other immune check point inhibitors may produce encouraging results though a phase III clinical trial employing IDO inhibitor with other check point inhibitors gave a negative results [51]. Despite the relative success and enthusiasm about immune check point inhibitors in the treatment of cancer only a small proportion of patients are benefited [52]. A recent study revealed that only 35 (51%) patients showed a significant improvement in survival or quality of life over existing treatment options, placebo, or as add on treatment [11]. This suggests that survival gains due to the use of immune check point inhibitors over existing treatment options or placebo is only marginal [53–58]. In addition to their anti-cancer action, treatment with immune check point inhibitors produce significant side effects due to the release of pro-inflammatory cytokines IL-6 and TNF-α. Some of the common side effects associated with immune checkpoint inhibitors include decreased appetite (12%) and diarrhea (10%), inflammatory pneumonitis, and may target endocrine, mucocutaneous and renal (interstitial nephritis) sites and eye resulting in significant damage. Some side effects are life threatening such as inflammatory pneumonitis, cytokine storm 3
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TILs and/or CAR T cell therapy and PUFAs
requiring cessation of therapy and treatment with corticosteroids [5760]. In majority of the patients, cessation of the immune checkpoint inhibitor, initiation of steroids and supportive therapy is adequate to tide over the crisis. However, some patients developed long-term adverse events with deaths reported in a few cases due to uninhibited release of cytokines IL-6, TNF-α, IFN-γ, IL-1β, IL-2, IL-6, IL-8, and IL-10 described as cytokine release syndrome (CRS) or cytokine storm. It is noteworthy that occasionally hyperprogression of underlying cancer may occur with PD-1/PD-L1 inhibitors compared with chemotherapy and are likely to show high metastatic burden and poor prognosis [61] though the molecular mechanisms involved in hyperprogressive disease is not clear. It is evident from the preceding discussion that immune check point inhibitors are effective ~in 25% of the patients treated and is associated with significant side effects. This calls for newer therapeutic strategies that may be more fruitful especially, when used in combination with immune check point inhibitors for cancer.
It is likely that immune checkpoint inhibitors, TILs, NK cells, CAR T cell therapy, tumor infiltrating macrophages and dendritic cells induce apoptosis/ferroptosis of tumor cells and/or inhibit their growth by releasing cytotoxic lipids such as GLA, AA, EPA, DHA, LXA4, resolvins, protectins and/or maresins that, in turn, regulate formation of cytotoxic lipid peroxides. We and others have shown that various tumor cell growth inhibitory PUFAs enhance the formation of lipid peroxides in tumor cells that, in turn, inhibit the growth of tumor cells or induce tumor cells to undergo apoptosis/ferroptosis and/or necrosis [65–85,88–91,125]. Furthermore, expression of high levels of glutathione peroxidase and a lipid peroxide deficiency state renders tumor cells resistant to the cytotoxic action of various chemotherapeutic drugs and radiation [126,127]. This emphasizes the concept that enhancing free radical generation and consequent accumulation of toxic lipid peroxides in tumor cells is a common mechanisms by which radiation, various conventional chemotherapeutics, NK cells, TILs, TIMs and immune checkpoint inhibitors bring about their anti-cancer actions. The current anti-cancer therapeutic approaches activate phospholipase A2 (PLA2) resulting in the release of PUFAs from the cell membrane lipid pool that are peroxidized to form toxic lipid peroxides which ultimately induce apoptosis/ferroptosis/necrosis form of tumor cell death. This implies that tumor cells with low amounts of PUFAs are likely to be resistant to the anti-cancer therapeutic approaches including immune checkpoint inhibitors. It is possible that activated NK cells, TILs, TIMs and other immunocytes (including leukocytes) deliver PUFAs to tumor cells to enhance accumulation of toxic lipid peroxides to induce tumor cell death (see Fig. 3).
Bioactive lipids and cancer Several studies showed that polyunsaturated fatty acids (PUFAs), especially gamma-linolenic acid (GLA, 18:3 n-6), AA (arachidonic acid, 20:4 n-6), EPA (eicosapentaenoic acid, 20:5 n-3) and DHA (docosahexaenoic acid, 22:6n-3) have tumoricidal action both in vitro and in vivo [62–80]. These endogenous low molecular weight lipids (called as bioactive lipids) act specifically on tumor cells with little or no cytotoxic action on normal cells [62–80]. Of all the fatty acids tested, GLA seems to be a potent and selective tumoricidal molecule (GLA > AA > EPA ≥ DHA), especially against glioma cells [71–73,81–85]. Tumor cells have low Δ6 and Δ 5 desaturase activity [86–89] that are needed for the formation of GLA, AA and EPA and DHA from their respective precursors’ linoleic acid (LA, 18:2 n-6) and α-linolenic acid (ALA, 18:3 n-3). This renders tumor cells deficient in their long-chain metabolites GLA, AA, EPA and DHA. PUFAs deficiency is responsible for the low rates of lipid peroxidation seen in tumor cells. In contrast, tumor cells have relatively high content of antioxidant vitamin E. The uptake of GLA, AA, EPA and DHA is almost 1½ to 2 times lower in tumor compared to normal cells yet generation of free radicals and formation of toxic lipid peroxides are 3-7-fold higher in tumor cells compared to normal cells [80,90–92]. Antioxidants vitamin E, BHA and BHA inhibited the tumoricidal action of GLA and other long-chain fatty acids whereas pro-oxidants: coper and ferrous salts enhanced their toxicity. These in vitro results are supported by the observation that intra-tumoral injection/infusion of GLA can regress glioma in animal models without any side-effects [93–95]. GLA, AA, EPA and DHA can suppress Ras, myc, p53, Bax/BCL-2, gene expressions, decrease mRNA expression of E2F1, alter protein expression of VEGF, Flt1, ERK1, ERK2, MMP2, Cyclin D1, pRb, p53 and p27 and arrest mitosis [72,73,96,97]. In a limited, open-label clinical study performed in patients with stage IV glioma revealed that intra-tumoral injection/infusion of GLA regresses glioma without any side-effects [83,93,94]. Furthermore, GLA and other unsaturated fatty acids enhanced the sensitivity of tumor cells to chemotherapeutic drugs and radiation [84,98–107]. These interesting in vitro, in vivo and limited clinical studies are supported by the observation that lipids are a constitutive component of cytolytic granules of CTL and NK cells [108] and cytokine activated macrophages release linolenic acid (presumably GLA) and linolenic acid-activated macrophages have marked tumoricidal action [109–115]. GLA, AA, EPA and DHA and their metabolites PGE1, PGE2, lipoxins, resolvins, protectins and maresins suppress production of IL-1 IL-6 and TNF-α [116–124], which are involved in CRS. Based on these evidences, I propose that combining TILs and/or CAR T cell therapy (with or without conventional chemotherapy) with GLA/AA/EPA/DHA may enhance their selective tumoricidal action without the danger of CRS or much less CRS including those gliomas.
Conclusions and future perspectives Exploiting the specificity and ability of the immune system to eliminate tumor cells is an exciting opportunity but is associated with significant side effects. Immunocytes (NK cells, CTL cells, LAK, dendritic cells, leukocytes, etc.,) release cytotoxic molecules such as perforin and granzyme, cytokines IL-6, TNF-α and IFN-γ that augment ROS (reactive oxygen species) in the target (tumor) cells, deliver directly ROS to tumor cells and exosomes [128]. But little attention has been paid to the likelihood that PUFAs and their metabolites and toxic lipid peroxides may have a significant role in the anti-cancer action of immunocytes. NK cells and CTLs induce apoptosis of tumor cells even when perforin-granzyme pathway is inactivated and is dependent on the expression of soluble PLA2 (sPLA2) [129]. But it is known whether perforin and granzyme themselves can activate PLA2-this is an interesting possibility that needs to be evaluated. But it is well documented that PLD (phospholipase D) activation is needed in the CD16-triggered signaling cascade that leads to NK cytotoxic granule exocytosis that, in turn, is associated with AA release as well [130,131]. Formation of excess of toxic lipid peroxides and consequent tumor cell apoptosis/ferroptosis seems to be common pathway by which radiation, chemotherapeutic drugs and PUFAs kill tumor cells. Anti-inflammatory metabolites of PUFAs lipoxin A4 (from AA), resolvins (from EPA and DHA), protectins and maresins (from DHA) have tumor cell growth inhibitory actions with no action on normal cells [71,73]. It is likely that PUFAs (especially AA) are differentially metabolized by normal and tumor cells. Normal cells utilize PLA2-induced release of PUFAs, especially AA, to form LXA4 (and resolvins, protectins and maresins from EPA and DHA) whereas tumor cells utilize them to form mainly PGE2 and LTs. Thus, tumor cells have evolved several mechanisms to defer the formation of lipid peroxides and enhance the synthesis of PGE2 and LTs that enable them to avoid apoptosis/ferroptosis [65,71,73,91,125,132]. Prophylactic TNF blockade prevents dual CTLA-4 and PD-1 immunotherapy induced toxicity without impairing their efficacy [133]. PUFAs and their metabolites including PGE2, LXA4, resolvins, protectins, maresins inhibit TNF-α, IL-6 and 4
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Fig. 3. Scheme showing how cytokines and PUFAs induce apoptosis/ferroptosis/necrosis of tumor cells. Interferon-gamma (IFN-γ), IL-6, TNF-α and other cytotoxic molecules released from CD8+ T cells/macrophages/TILs/NK cells/immunocytes downregulate the expression of SLC3A2 and SLC7A11, two subunits of the glutamate–cystine antiporter system xc−, impair the uptake of cystine by tumor cells, and as a consequence, promotes accumulation of toxic lipid peroxide in tumor cell to induce their ferroptosis/apoptosis/necrosis. In addition, IFN-γ, TNF-α and IL-6 activate phospholipase A2 (PLA2) and induce the release of PUFAs (especially AA) from the cell membrane lipid pool to make them available for the formation of PGE2 (an immunosuppressor), LXA4 (an anti-inflammatory molecule that is cytoprotective of normal cells but inhibits tumor cell growth) and are substrates to lipid peroxides (that are cytotoxic to tumor cells). It is likely that there could occur a balance between PGE2 and LXA4 formation from AA-the balance being more tilted towards PGE2 in tumor cells and towards LXA4 in normal cells. PUFAs may also be released and made available to tumor cells by the surrounding milieu of normal/tumor cells. There could occur a competition for the uptake of PUFAs between immunocytes and tumor cells-the former to form LXA4 and lipid peroxides to be delivered to tumor cells and latter to form PGE2 to induce immunosuppression.
HMGB1 synthesis [134–139] and thus, it is anticipated that a combination of immune check point inhibitors with PUFAs (especially AA) would be highly effective against several types of tumors. The benefit of such effective anti-cancer therapy with few side effects need to be studied in future.
[9] Merryman RW, Kim HT, Zinzani PL, Carlo-Stella C, Ansell SM, Perales MA, et al. Safety and efficacy of allogenic hematopoietic stem cell transplant after PD-1 blockade in relapse/refractory lymphoma. Blood 2017;129:1380–8. [10] Berman D, Parker SM, Siegel J, Chasalow SD, Weber J, Galbraith S, et al. Blockade of cytotoxic T-lymphocyte antigen-4 by ipilimumab results in dysregulation of gastrointestinal immunity in patients with advanced melanoma. Cancer Immun 2010;10:11. [11] Davis C, Naci H, Gurpinar E, Poplavska E, Pinto A, Aggarwal A. Availability of evidence of benefits on overall survival and quality of life of cancer drugs approved by European Medicines Agency: retrospective cohort study of drug approvals 2009–13. Br Med J 2017;359:j4530. [12] Kim C, Prasad V. Cancer drugs approved on the basis of a surrogate end point and subsequent overall survival: An analysis of 5 5ears of US Food and Drug Administration approvals. JAMA Intern Med 2015;175:1992–4. [13] Waterhouse P, Penninger JM, Timms E, Wakeham A, Shahinian A, Lee KP, et al. Lymphoproliferative disorders with early lethality in mice deficient in Ctla-4. Science 1995;270:985–8. [14] Walunas TL, Bakker CY, Bluestone JA. CTLA-4 ligation blocks CD28-dependent T cell activation. J Exp Med 1996;183:2541–50. [15] Walunas TL, Lenschow DJ, Bakker CY, Linsley PS, Freeman GJ, Green JM, et al. CTLA-4 can function as a negative regulator of T cell activation. Immunity 1994;1:405–13. [16] Dranoff G. Immunotherapy at large: Balancing tumor immunity and inflammatory pathology. Nat Med 2013;19:1100–1. [17] Krummel MF, Allison JP. CD28 and CTLA-4 have opposing effects on the response of T cells to stimulation. J Exp Med 1995;182:459–65. [18] Liossis SN, Sfikakis PP, Tsokos GC. Immune cell signaling aberrations in human lupus. Immunol Res 1998;18:27–39. [19] Chang TT, Kuchroo VK, Sharpe AH. Role of the B7-CD28/CTLA-4 pathway in autoimmune disease. Curr Dir Autoimmun 2002;5:113–30. [20] Johnson TS, Munn DH. Host indoleamine 2,3-dioxygenase: contribution to systemic acquired tumor tolerance. Immunol Invest 2012;41:765–97. [21] Prendergast GC, Smith C, Thomas S, Mandik-Nayak L, Laury-Kleintop L, Metz R, et al. Indoleamine 2,3-dioxygenase pathways of pathogenic inflammation and immune escape in cancer. Cancer Immunol Immunother 2014;63:721–35. [22] Terness P, Bauer TM, Röse L, Dufter C, Watzlik A, Simon H, et al. Inhibition of allogeneic T cell proliferation by indoleamine 2,3-dioxygenase-expressing dendritic cells: mediation of suppression by tryptophan metabolites. J Exp Med 2002;196:447–57. [23] Munn DH, Shafizadeh E, Attwood JT, Bondarev I, Pashine A, Mellor AL. Inhibition of T cell proliferation by macrophage tryptophan catabolism. J Exp Med 1999;189:1363–72. [24] Yoshida R, Urade Y, Tokuda M, Hayaishi O. Induction of indoleamine 2,3-dioxygenase in mouse lung during virus infection. Proc Natl Acad Sci USA 1979;76:4084–6.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.mehy.2019.109473. References [1] Pardoll DM. The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer 2012;12:252–64. [2] Butte MJ, Keir ME, Phamduy TB, Sharpe AH, Freeman GJ. Programmed death-1 ligand 1 interacts specifically with the B7–1 costimulatory molecule to inhibit T cell responses. Immunity 2007;27:111–22. [3] Karwacz K, Bricogne C, MacDonald D, Arce F, Bennett CL, Collins M, et al. PD-L1 co-stimulation contributes to ligand-induced T cell receptor down-modulation on CD8+ T cells. EMBO Mol Med 2011;3:581–92. [4] Syn NL, Teng MWL, Mok TSK, Soo RA. De-novo and acquired resistance to immune checkpoint targeting. Lancet Oncol 2017;18:e731–41. [5] Noel PJ, Boise LH, Thompson CB. Regulation of T cell activation by CD28 and CTLA4. Adv Exp Med Biol 1996;406:209–17. [6] Dudley ME, Wunderlich JR, Robbins PF, Yang JC, Hwu P, Schwartzentruber DJ, et al. Cancer regression and autoimmunity in patients after clonal repopulation with antitumor lymphocytes. Science 2002;298:850–4. [7] Rosenberg SA, Restifo NP. Adoptive cell transfer as personalized immunotherapy for human cancer. Science 2015;348:62–8. [8] Naidoo J, Page DB, Li BT, Connell LC, Schindler K, Lacouture ME, et al. Toxicities of the anti-PD-1 and anti-PD-L1 immune checkpoint antibodies. Ann Oncol 2015;26:2375–91.
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U.N. Das
N Engl J Med 2016;375:1767–78. [57] Topalian SL, Hodi FS, Brahmer JR, et al. Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N Engl J Med 2012;366:2443–54. [58] Webb ES, Liu P, Baleeiro R, Lemoine NR, Yuan M, Wang Y. Immune checkpoint inhibitors in cancer therapy. J Biomed Res 2018;32:317–26. [59] Shimabukuro-Vornhagen A, Gödel P, Subklewe M, Stemmler HJ, Schlößer HA, Schlaak M, et al. Cytokine release syndrome. J ImmunoTherapy Cancer 2018;6:56. [60] Bajwa R, Cheema A, Khan T, Amirpour A, Paul A, Chaughtai S, et al. Adverse effects of immune checkpoint inhibitors (programmed death-1 inhibitors and cytotoxic T-lymphocyte-associated protein-4 inhibitors): results of a retrospective study. J Clin Med Res 2019;11:225–36. [61] Ferrara R, Mezquita L, Texier M, Lahmar J, Audigier-Valette C, Tessonnier L, et al. Hyperprogressive disease in patients with advanced non–small cell lung cancer treated with PD-1/PD-L1 inhibitors or with single-agent chemotherapy. JAMA Oncol 2018. https://doi.org/10.1001/jamaoncol.2018.3676. [62] Comba A, Maestri DM, Berra MA, Garcia CP, Das UN, Eynard AR, et al. Effect of ω3 and ω-9 fatty acid rich oils on lipoxygenases and cyclooxygenases enzymes and on the growth of a mammary adenocarcinoma model. Lipids Health Dis 2010;9:112-. [63] Bégin ME, Ells G, Das UN, Horrobin DF. Differential killing of human carcinoma cells supplemented with n-3 and n-6 polyunsaturated fatty acids. J Natl Cancer Inst 1986;77:1053–62. [64] Das UN. Effect of γ- Linolenic acid on the transcriptional activity of the HER-2neu (erbB-2) Oncogene. J Natl Cancer Inst 2006;98:718. [65] Das UN. Tumoricidal action of cis-unsaturated fatty acids and their relationship to free radicals and lipid peroxidation. Cancer Lett 1991;56:235–43. [66] Ge H, Kong X, Shi L, Hou L, Liu Z, Li P. Gamma-linolenic acid induces apoptosis and lipid peroxidation in human chronic myelogenous leukemia K562 cells. Cell Biol Int 2009;33:402–10. [67] Begin ME, Das UN, Ells G. Cytotoxic effects of essential fatty acids (EFA) in mixed cultures of normal and malignant human cells. Prog Lipid Res 1986;25:573–6. [68] Das UN, Madhavi N. Effect of polyunsaturated fatty acids on drug-sensitive and resistant tumor cells in vitro. Lipids Health Dis 2011;10:159. [69] Gillis RC, Daley BJ, Enderson BL, Karlstad MD. Eicosapentaenoic acid and γ-linolenic acid induce apoptosis in HL-60 cells. J Surg Res 2002;107:145–53. [70] Madhavi N, Das UN. Effect of n-6 and n-3 fatty acids on the survival of vincristine sensitive and resistant human cervical carcinoma cells in vitro. Cancer Lett 1994;84:31–41. [71] Sailaja P, Mani AM, Naveen KVG, Anasuya DH, Siresha B, Das UN. Effect of polyunsaturated fatty acids and their metabolites on bleomycin-induced cytotoxic action on human neuroblastoma cells in vitro. PLoS One 2014;9:e114766. [72] Sailaja P, Dwarakanath B, Das UN. Arachidonic acid activates extrinsic apoptotic pathway to enhance tumoricidal action of bleomycin against IMR-32 cells. Prostaglandins Leukot Essen Fatty Acids 2018;132:16–22. [73] Anasuya DH, Naidu VGM, Das UN. n-6 and n-3 Fatty acids and their metabolites augment inhibitory action of doxorubicin on the proliferation of human neuroblastoma (IMR-32) cells by enhancing lipid peroxidation and suppressing Ras, Myc, and Fos. BioFactors 2018;44:387–401. [74] D'Eliseo D, Di Renzo L, Santoni A, Velotti F. Docosahexaenoic acid (DHA) promotes immunogenic apoptosis in human multiple myeloma cells, induces autophagy and inhibits STAT3 in both tumor and dendritic cells. Genes Cancer 2017;8:426–37. [75] Molinari R, D'Eliseo D, Manzi L, Zolla L, Velotti F, Merendino N. The n-3 polyunsaturated fatty acid docosahexaenoic acid induces immunogenic cell death in human cancer cell lines via pre-apoptotic calreticulin exposure. Cancer Immunol Immunother 2011;60:1503–7. [76] Pizato N, Luzete BC, Kiffer LFMV, Corrêa LH, de Oliveira Santos I, Assumpção JAF, et al. Omega-3 docosahexaenoic acid induces pyroptosis cell death in triple-negative breast cancer cells. Sci Rep 2018;8:1952. [77] Das M, Das S. Identification of cytotoxic mediators and their putative role in the signaling pathways during docosahexaenoic acid (DHA)-induced apoptosis of cancer cells. Apoptosis 2016;21:1408–21. [78] Kang KS, Wang P, Yamabe N, Fukui M, Jay T, Zhu BT. Docosahexaenoic acid induces apoptosis in MCF-7 cells in vitro and in vivo via reactive oxygen species formation and caspase 8 activation. PLoS One 2010;5:e10296. [79] Gleissman H, Yang R, Martinod K, Lindskog M, Serhan CN, Johnsen JI, et al. Docosahexaenoic acid metabolome in neural tumors: identification of cytotoxic intermediates. FASEB J 2010;24:906–15. [80] Das UN. Essential fatty acids enhance free radical generation and lipid peroxidation to induce apoptosis of tumor cells. Clin Lipidol 2011;6:463–89. [81] Bell HS, Wharton SB, Leaver HA, Whittle IR. Effects of N-6 essential fatty acids on glioma invasion and growth: experimental studies with glioma spheroids in collagen gels. J Neurosurg 1999;91:989–96. [82] Antal O, Péter M, Hackler Jr L, Mán I, Szebeni G, Ayaydin F, et al. Lipidomic analysis reveals a radiosensitizing role of gamma-linolenic acid in glioma cells. Biochim Biophys Acta, Mol Cell Biol Lipids 2015;1851:1271–82. [83] Das UN. Gamma-linolenic acid therapy of human glioma-a review of in vitro, in vivo, and clinical studies. Med Sci Monit 2007;13:RA119–31. [84] Vartak S, McCaw R, Davis CS, Robbins ME, Spector AA. Gamma-linolenic acid (GLA) is cytotoxic to 36B10 malignant rat astrocytoma cells but not to 'normal' rat astrocytes. Br J Cancer 1998;77:1612–20. [85] Fujiwara F, Todo S, Imashuku S. Antitumor effect of gamma-linolenic acid on cultured human neuroblastoma cells. Prostaglandins Leukot Med 1986;23:311–20. [86] Nassar BA, Das UN, Huang YS, Ells G, Horrobin DF. The effect of chemical hepatocarcinogenesis on liver phospholipid composition in rats fed N-6 and N-3 fatty acid-supplemented diets. Proc Soc Exp Biol Med 1992;199:365–8.
[25] Pfefferkorn ER. Interferon gamma blocks the growth of Toxoplasma gondii in human fibroblasts by inducing the host cells to degrade tryptophan. Proc Natl Acad Sci USA 1984;81:908–12. [26] Theate I, van Baren N, Pilotte L, Moulin P, Larrieu P, Renauld JC, et al. Extensive profiling of the expression of the indoleamine 2,3-dioxygenase 1 protein in normal and tumoral human tissues. Cancer Immunol Res 2015;3:161–72. [27] Munn DH, Zhou M, Attwood JT, Bondarev I, Conway SJ, Marshall B, et al. Prevention of allogeneic fetal rejection by tryptophan catabolism. Science 1998;281:1191–3. [28] Platten M, Ho PP, Youssef S, Fontoura P, Garren H, Hur EM, et al. Treatment of autoimmune neuroinflammation with a synthetic tryptophan metabolite. Science 2005;310:850–5. [29] Cook CH, Bickerstaff AA, Wang JJ, Nadasdy T, Della Pelle P, Colvin RB, et al. Spontaneous renal allograft acceptance associated with “regulatory” dendritic cells and IDO. J Immunol 2008;180:3103–12. [30] Jasperson LK, Bucher C, Panoskaltsis-Mortari A, Taylor PA, Mellor AL, Munn DH, et al. Indoleamine 2,3-dioxygenase is a critical regulator of acute graft-versus-host disease lethality. Blood 2008;111:3257–65. [31] Moon YW, Hajjar J, Hwu P, Naing A. Targeting the indoleamine 2,3-dioxygenase pathway in cancer. J Immuno Therapy Cancer 2015;3:51. [32] Opitz CA, Wick W, Steinman L, Platten M. Tryptophan degradation in autoimmune diseases. Cell Mol Life Sci 2007;64:2542–63. [33] Opitz CA, Litzenburger UM, Sahm F, Ott M, Tritschler I, Trump S, et al. An endogenous tumour-promoting ligand of the human aryl hydrocarbon receptor. Nature 2011;478:197–203. [34] Mezrich JD, Fechner JH, Zhang X, Johnson BP, Burlingham WJ, Bradfield CA. An interaction between kynurenine and the aryl hydrocarbon receptor can generate regulatory T cells. J Immunol 2010;185:3190–8. [35] Nguyen NT, Kimura A, Nakahama T, Chinen I, Masuda K, Nohara K, et al. Aryl hydrocarbon receptor negatively regulates dendritic cell immunogenicity via a kynurenine-dependent mechanism. Proc Natl Acad Sci USA 2010;107:19961–6. [36] Das UN. Is there a role for bioactive lipids in the pathobiology of diabetes mellitus? Front Endocrinol 2017;8:182. [37] Yano JM, Yu K, Donaldson GP, Shastri GG, Ann P, Ma L, et al. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell 2015;161:264–76. [38] Reigstad CS, Salmonson CE, Rainey III JF, Szurszewski JH, Linden DR, Sonnenburg JL, et al. Gut microbes promote colonic serotonin production through an effect of short-chain fatty acids on enterochromaffin cells. FASEB J 2015;29:1395–403. [39] Kim H, Toyofuku Y, Lynn FC, Chak E, Uchida T, Mizukami H, et al. Serotonin regulates pancreatic beta cell mass during pregnancy. Nat Med 2010;16:804–9. [40] Georgia S, Bhushan A. Pregnancy hormones boost beta cells via serotonin. Nat Med 2010;16:756–7. [41] Stockinger B, Hirota K, Duarte J, Veldhoen M. External influences on the immune system via activation of the aryl hydrocarbon receptor. Semin Immunol 2011;23:99–105. [42] Veldhoen M, Hirota K, Westendorf AM, Buer J, Dumoutier L, Renauld JC, et al. The aryl hydrocarbon receptor links TH17-cell-mediated autoimmunity to environmental toxins. Nature 2008;453:106–9. [43] Quintana FJ, Basso AS, Iglesias AH, Korn T, Farez MF, Bettelli E, et al. Control of T(reg) and T(H)17 cell differentiation by the aryl hydrocarbon receptor. Nature 2008;453:65–71. [44] Liang SC, Tan XY, Luxenberg DP, Karim R, Dunussi-Joannopoulos K, Collins M, et al. Interleukin (IL)-22 and IL-17 are coexpressed by Th17 cells and cooperatively enhance expression of antimicrobial peptides. J Exp Med 2006;203:2271–9. [45] Ke Y, Liu K, Huang G-Q, Cui Y, Kaplan HJ, Shao H, et al. Anti-inflammatory role of IL-17 in experimental autoimmune uveitis. J Immunol 2009;182:3183–90. [46] Deby C, Damas J. Proceedings: Influence of tryptophan on the hypotensive effect of arachidonic acid. Arch Int Physiol Biochim 1974;82:742–4. [47] Robert C, Karaszewska B, Schachter J, Rutkowski P, Mackiewicz A, Stroiakovski D, et al. Improved overall survival in melanoma with combined dabrafenib and trametinib. N Engl J Med 2015;372:30–9. [48] Hodi FS, O'Day SJ, McDermott DF, Weber RW, Sosman JA, Haanen JB, et al. Improved survival with ipilimumab in patients with metastatic melanoma. N Engl J Med 2010;363:711–23. [49] Robert C, Long GV, Brady B, Dutriaux C, Maio M, Mortier L, et al. Nivolumab in previously untreated melanoma without BRAF mutation. N Engl J Med 2015;372:320–30. [50] Eggermont AMM, Blank CU, Mandala M, Long GV, Atkinson V, Dalle S, et al. Adjuvant pembrolizumab versus placebo in resected stage III melanoma. N Engl J Med 2018;378:1789–801. [51] Garber K. A new cancer immunotherapy suffers a setback. Science 2018;360:588. [52] Wilkerson J, Fojo T. Progression-free survival is simply a measure of a drug’s effect while administered and is not a surrogate for overall survival. Cancer J 2009;15:379–85. [53] Zhou Y, Chen C, Zhang X, Fu S, Xue C, Ma Y, et al. Immune-checkpoint inhibitor plus chemotherapy versus conventional chemotherapy for first-line treatment in advanced non-small cell lung carcinoma: a systematic review and meta-analysis. J ImmunoTher Cancer 2018;6:155. [54] Zhuansun Y, Huang F, Du Y, Lin L, Chen R, Li J. Anti-PD-1/PD-L1 antibody versus conventional chemotherapy for previously-treated, advanced non-small-cell lung cancer: a meta-analysis of randomized controlled trials. J Thorac Dis 2017;9:655–65. [55] Saxena A, Ramana KV. Impact of immune checkpoint inhibitors in cancer immunotherapy. J Cancer Immunol Ther 2018;1:4–5. [56] Boussiotis VA. Molecular and biochemical aspects of the PD-1 checkpoint pathway.
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Medical Hypotheses 135 (2020) 109473
U.N. Das
immunological killing of tumor cells: II. Effector cell lipids. Lipids 1983;18:483–8. [114] Schlager SI, Ohanian SH. Role of membrane lipids in the immunological killing of tumor cells: I. Target cell lipids. Lipids 1983;18:475–82. [115] Schlager SI, Meltzer MS. Role of macrophage lipids in regulating tumoricidal activity. II. Internal genetic and external physiologic regulatory factors controlling macrophage tumor cytotoxicity also control characteristic lipid changes associated with tumoricidal cells. Cell Immunol 1983;80:10–9. [116] Kumar GS, Das UN. Effect of prostaglandins and their precursors on the proliferation of human lymphocytes and their secretion of tumor necrosis factor and various interleukins. Prostaglandins Leukot Essent Fatty Acids 1994;50:331–4. [117] Dooper MM, van Riel B, Graus YM, M'Rabet L. Dihomo-gamma-linolenic acid inhibits tumour necrosis factor-alpha production by human leucocytes independently of cyclooxygenase activity. Immunology 2003;110:348–57. [118] Rossetti RG, Brathwaite K, Zurier RB. Suppression of acute inflammation with liposome associated prostaglandin E1. Prostaglandins 1994;48:187–95. [119] Harizi H, Norbert G. Inhibition of IL-6, TNF-alpha, and cyclooxygenase-2 protein expression by prostaglandin E2-induced IL-10 in bone marrow-derived dendritic cells. Cell Immunol 2004;228:99–109. [120] Duffin R, O’Connor RA, Crittenden S, Forster T, Yu C, Zheng X, et al. Prostaglandin E2 constrains systemic inflammation through an innate lymphoid cell–IL-22 axis. Science 2016;351:1333–8. [121] FitzGerald GA. Bringing PGE2 in from the cold. Science 2015;348:1208–9. [122] Zhang Y, Desai A, Yang SY, Bae KB, Antczak MI, Fink SP, et al. Inhibition of the prostaglandin-degrading enzyme 15-PGDH potentiates tissue regeneration. Science 2015;348:aaa2340. https://doi.org/10.1126/science.aaa2340. [123] Liu C, Guan H, Cai C, Li F, Xiao J. Lipoxin A4 suppresses osteoclastogenesis in RAW264.7 cells and prevents ovariectomy-induced bone loss. Exp Cell Res 2017;352:293–303. [124] Poorani R, Bhatt AN, Dwarakanath BS, Das UN. COX-2, aspirin and metabolism of arachidonic, eicosapentaenoic and docosahexaenoic acids and their physiological and clinical significance. Eur J Pharmacol 2016;785:116–32. [125] Das UN. Saturated fatty acids, MUFAs and PUFAs regulate ferroptosis. Cell Chem Biol 2019;26:309–11. [126] Viswanathan V, Ryan MJ, Dhruv HD, Gill S, Eichhoff OM, Seashore-Ludlow B, et al. Dependency of a therapy-resistant state of cancer cells on a lipid peroxidase pathway. Nature 2017;547:453–7. [127] Hangauer MJ, Viswanathan V, Ryan MJ, Bole D, Eaton JK, Matov A, et al. Drugtolerant persister cancer cells are vulnerable to GPX4 inhibition. Nature 2017;551:247–50. [128] Paul S, Lal G. The Molecular mechanism of natural killer cells function and its importance in cancer immunotherapy. Front Immunol 2017;8:1124. [129] Costa-Junior HM, Hamaty FC, da Silva Farias R, Einicker-Lamas M, da Silva MH, Persechini PM. Apoptosis-inducing factor of a cytotoxic T cell line: involvement of a secretory phospholipase A2. Cell Tissue Res 2006;324:255–66. [130] Milella M, Gismondi A, Roncaioli P, Palmieri G, Morrone S, Piccoli M, et al. Beta 1 integrin cross-linking inhibits CD16-induced phospholipase D and secretory phospholipase A2 activity and granule exocytosis in human NK cells: role of phospholipase D in CD16-triggered degranulation. J Immunol 1999;162:2064–72. [131] Parmentier JH, Muthalif MM, Nishimoto AT, Malik KU. 20Hydroxyeicosatetraenoic acid mediates angiotensin ii-induced phospholipase d activation in vascular smooth muscle cells. Hypertension 2001;37(2 Pt 2):623–9. [132] Das UN, Begin ME, Ells G, Huang YS, Horrobin DF. Polyunsaturated fatty acids augment free radical generation in tumor-cells in vitro. Biochem Biophys Res Commun 1987;145:15–24. [133] Perez-Ruiz E, Minute L, Otano I, Alvarez M, Ochoa MC, Belsue V, et al. Prophylactic TNF blockade uncouples efficacy and toxicity in dual CTLA-4 and PD1 immunotherapy. Nature 2019;569:428–32. [134] Kumar SG, Das UN, Kumar KV, Madhavi Das NP, Tan BKH. Effect of n-6 and n-3 fatty acids on the proliferation and secretion of TNF and IL-2 by human lymphocytes in vitro. Nutrition Res 1992;12:815–23. [135] Das UN. Is lipoxins A4 a better alternative to anti-VEGF and anti-TNF-alpha antibody to prevent and treat age-related macular degeneration, diabetic macular edema and retinopathy? Med Sci Monit 2011;18:LE1–2. [136] Stuhlmeier KM, Kao JJ, Bach FH. Arachidonic acid influences proinflammatory gene induction by stabilizing the inhibitor-kappaBalpha/nuclear factor-kappaB (NF-kappaB) complex, thus suppressing the nuclear translocation of NF-kappaB. J Biol Chem 1997;272:24679–83. [137] Naveen KVG, Naidu VGM, Das UN. Arachidonic acid and lipoxin A4 attenuate alloxan-induced cytotoxicity to RIN5F cells in vitro and type 1 diabetes mellitus in vivo. BioFactors 2017;43:251–71. [138] Naveen KVG, Naidu VGM, Das UN. Arachidonic acid and lipoxin A4 attenuate streptozotocin-induced cytotoxicity to RIN5F cells in vitro and type 1 and type 2 diabetes mellitus in vivo. Nutrition 2017;35:61–80. [139] Naveen GV, Naidu G, Das UN. Amelioration of streptozotocin-induced type 2 diabetes mellitus in Wistar rats by arachidonic acid. Biochem Biophys Res Commun 2018;496:105–13.
[87] Dunbar LM, Bailey JM. Enzyme deletions and essential fatty acid metabolism in cultured cells. J Biol Chem 1975;250:1152–3. [88] Bendetti A. Loss of lipid peroxidation as a histochemical marker for preneoplastic hepatocellular foci of rats. Cancer Res 1984;44:5712–7. [89] Morton RE, Hartz JW, Reitz RC, Waite BM, Morris H. The acyl-CoA desaturases of microsomes from rat liver and the Morris 7777 hepatoma. Biochim Biophys Acta, Mol Cell Biol Lipids 1979;573:321–31. [90] Das UN, Begin ME, Ells G, Huang YS, Horrobin DF. Polyunsaturated fatty acids augment free radical generation in tumor cells in vitro. Biochem Biophys Res Commun 1987;145:15–24. [91] Das UN, Huang YS, Begin ME, Ells G, Horrobin DF. Uptake and distribution of cisunsaturated fatty acids and their effect on free radical generation in normal and tumor cells in vitro. Free Radical Biol Med 1987;3:9–14. [92] Das UN. Selective enhancement of free radicals in tumor cells as a strategy to kill tumor cells both in vitro and in vivo. In: Reddy CC, editor. Biological oxidation systems. New York: Academic Press; 1990. p. 607–24. [93] Naidu MR, Das UN, Kishan A. Intratumoral gamma-linoleic acid therapy of human gliomas. Prostaglandins Leukot Essent Fatty Acids 1992;45:181–4. [94] Das UN, Prasad VV, Reddy DR. Local application of gamma-linolenic acid in the treatment of human gliomas. Cancer Lett 1995;94:147–55. [95] Bakshi A, Mukherjee D, Bakshi A, Banerji AK, Das UN. Gamma-linolenic acid therapy of human gliomas. Nutrition 2003;19:305–9. [96] Miyake JA, Benadiba M, Colquhoun A. Gamma-linolenic acid inhibits both tumour cell cycle progression and angiogenesis in the orthotopic C6 glioma model through changes in VEGF, Flt1, ERK1/2, MMP2, cyclin D1, pRb, p53 and p27 protein expression. Lipids Health Dis 2009;8:8. [97] Benadiba M, Miyake JA, Colquhoun A. Gamma-linolenic acid alters Ku80, E2F1, and bax expression and induces micronucleus formation in C6 glioma cells in vitro. IUBMB Life 2009;61:244–51. [98] Sangeetha PS, Das UN. Gamma-linolenic acid and eicosapentaenoic acid potentiate the cytotoxicity of anti-cancer drugs on human cervical carcinoma (HeLa) cells in vitro. Med Sci Res 1993;21:457–9. [99] Madhavi N, Das UN. Reversal of KB-3-1 and KB-Ch-8-5 tumor cell drug-resistance by cis-unsaturated fatty acids in vitro. Med Sci Res 1994;22:689–92. [100] Das UN, Madhavi N, Padma M, Sagar PS. Can tumor cell drug-resistance be reversed by essential fatty acids and their metabolites? Prostaglandins Leukot Essen Fatty Acids 1998;58:39–54. [101] Germain E, Chajès V, Cognault S, Lhuillery C, Bougnoux P. Enhancement of doxorubicin cytotoxicity by polyunsaturated fatty acids in the human breast tumor cell line MDA-MB-231: relationship to lipid peroxidation. Int J Cancer 1998;75:578–83. [102] Mahéo K, Vibet S, Steghens JP, Dartigeas C, Lehman M, Bougnoux P, et al. Differential sensitization of cancer cells to doxorubicin by DHA: a role for lipoperoxidation. Free Radic Biol Med 2005;39:742–51. [103] Ilc K, Ferrero JM, Fischel JL, Formento P, Bryce R, Etienne MC, et al. Cytotoxic effects of two gamma linoleic salts (lithium gammalinolenate or meglumine gammalinolenate) alone or associated with a nitrosourea: an experimental study on human glioblastoma cell lines. Anticancer Drugs 1999;10:413–7. [104] Menendez JA, Ropero S, Lupu R, Colomer R. Omega-6 polyunsaturated fatty acid gamma-linolenic acid (18:3n–6) enhances docetaxel (Taxotere) cytotoxicity in human breast carcinoma cells: Relationship to lipid peroxidation and HER-2/neu expression. Oncol Rep 2004;11:1241–52. [105] Menéndez JA, Ropero S, del Barbacid MM, Montero S, Solanas M, Escrich E, et al. Synergistic interaction between vinorelbine and gamma-linolenic acid in breast cancer cells. Breast Cancer Res Treat 2002;72:203–19. [106] Menendez JA, Ropero S, Mehmi I, Atlas E, Colomer R, Lupu R. Overexpression and hyperactivity of breast cancer-associated fatty acid synthase (oncogenic antigen519) is insensitive to normal arachidonic fatty acid-induced suppression in lipogenic tissues but it is selectively inhibited by tumoricidal alpha-linolenic and gamma-linolenic fatty acids: a novel mechanism by which dietary fat can alter mammary tumorigenesis. Int J Oncol 2004;24:1369–83. [107] Kong X, Ge H, Chen L, Liu Z, Yin Z, Li P, et al. Gamma-linolenic acid modulates the response of multidrug-resistant K562 leukemic cells to anticancer drugs. Toxicol In Vitro 2009;23:634–9. [108] Baranov V, Nagaeva O, Hammarstrom S, Mincheva-Nilsson L. Lipids as a constitutive component of cytolytic granules. Histochem Cell Biol 2000;114:167–71. [109] Schlager SI, Ohanian SH. Correlation between lipid synthesis in tumor cells and their sensitivity to humoral immune attack. Science 1977;197:773–6. [110] Schlager SI, Ohanian SH, Borsos T. Correlation between the ability of tumor cells to incorporate specific fatty acids and their sensitivity to killing by a specific antibody plus guinea pig complement. J Natl Cancer Inst 1978;61:931–4. [111] Schlager SI, Ohanian SH. Modulation of tumor cell susceptibility to humoral immune killing through chemical and physical manipulation of cellular lipid and fatty acid composition. J Immunol 1980;125:1196–200. [112] Schlager SI, Madden LD, Meltzer MS, Bara S, Mamula MJ. Role of macrophage lipids in regulating tumoricidal activity. Cell Immunol 1983;77:52–68. [113] Schlager SI, Meltzer MS, Madden LD. Role of membrane lipids in the
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