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Cancer risks and perspectives: Molecular mechanisms
Mutation Research 768 (2014) 1–5
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Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis journal homepage: www.elsevier.com/locate/molmut Community address: www.elsevier.com/locate/mutres
Editorial
Cancer risks and perspectives: Molecular mechanisms
Strategies for the intervention and prevention of cancers, diabetes, cardiovascular diseases, HIV/AIDS and other diseases of overt inflammation including neurodegenerative diseases (Alzheimer’s and Parkinson’s disease) require an understanding of the basic molecular mechanism(s) by prophylactic agents (dietary antioxidant factors from food plants and medicinal plants in this context) that may potentially prevent or reverse the promotion or progression of the diseases [1,2]. Cancer is a group of diseases characterized by uncontrolled cell proliferation, evasion of cell death and the ability to invade and disrupt vital tissue function. Cancer cells can spread to other parts of the body through the blood and lymph systems. The main types cancer include: Carcinoma (which characterizes cancers that begin in the skin or in the tissues that line or cover internal organs with subtypes of carcinoma, including adenocarcinoma, basal cell carcinoma, squamous cell carcinoma, and transitional cell carcinoma), Sarcoma (which characterizes cancers that begin in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue), Leukemia (which characterizes cancers that start in blood-forming tissue such as the bone marrow and cause large numbers of abnormal blood cells to be produced which then enters the blood), Lymphoma and Myeloma (which characterizes cancers that begin in the cells of the immune system) and Central nervous system cancers (which characterizes the cancers that begin in the tissues of the brain and spinal cord). Cancer arises from a loss of normal growth control. In normal tissues, the rates of new cell growth and old cell death are kept in balance. In cancer, this balance is disrupted resulting from uncontrolled cell growth or loss of a cell’s ability to undergo apoptosis or cell suicide whereby old or damaged cells normally self-destruct. The classical model of carcinogenesis describes successive clonal expansion driven by the accumulation of mutations that eliminate restraints on proliferation and cell survival. Older cancer patients have variable physiologic ages necessitating the need to individualize their treatment for better outcome [3,4]. Given the increasing number of cancer survivors, there is a trend to shift patient care from a model that was focused on the immediate need to treat the tumor to a more holistic approach that aims to ensure both quantity and quality of life. The key tenets of quality of life are often associated with communication, trust, caring behavior, comfort, and social and spiritual support. Getting inadequate health information and lack of psychosocial care coupled with lack of and/or delay in coordinated care are among the barriers to quality care that a cancer patient may receive. From the healthcare provider’s perspective, workload or administrative burden, lack of coordinated care, bureaucracy of managed care and lack http://dx.doi.org/10.1016/j.mrfmmm.2014.09.001 0027-5107/© 2014 Published by Elsevier B.V.
of processes to support treatment guidelines tend to impact the quality of care received by the patient. These are often impacted by strategies being implemented by managed care to address cancer quality, which include decision support tools, pathways, guidelines, and cost reduction strategies (reviewed in [5]). In treating cancer, toxicity from systemic therapy with chemotherapeutic drugs and severe complications from radiation therapy are two most critical limiting factors associated with patient safety. This has led to seeking alternate chemopreventive approaches through dietary means and/or use of pharmacological and natural agents whose multiple intervention strategies, efficacy and acceptable toxicity are potentially anticipated to arrest or reverse the cellular and molecular processes of carcinogenesis. In this vein, progress in understanding the molecular changes that underlie cancer development offer the prospect of specifically targeting malfunctioning molecules and pathways to achieve more effective and rational cancer therapy. While the first-line therapy for advanced non-small cell lung cancer is platinum-based chemotherapy, patients with specific mutations may effectively be treated with targeted agents initially. In the treatment of patients suffering from advanced cancers with contemporary systemic therapies, the challenge is to attain therapeutic efficacy, while minimizing side effects. The side effects may range from nausea to tissue damage. In cancer survivors, the iatrogenic outcomes may include consequences of genomic mutations in patients themselves or their children. Thus the main challenge for the oncologists is not to cross the thin line between eradicating cancer cells in vivo, in the patients’ bodies, but not harm these patients’ healthy cells. This is a particularly tough challenge in advanced cancers, which metastasize to multiple and distant locations of the patients’ bodies. In this realm, there is a great promise in genetic engineering of stem cells (compatible with the patient’s immune system) guided to the specific tumour to deliver the therapeutic trans-genes into cancer cells to induce their death. The advanced stages are often beyond the therapeutic arsenal of local surgery, but require systemic therapies associated with severe side effects [3–7]. The seminal reviews, commentary and research papers contained in this Special Issue highlight developments to not only understand cancer but to treat the disease with a view to the minimization of side effects of such therapies. Commentaries deriving from the various articles therein are here presented as an introduction to the reader. The “regression” of cancer cells involves changes within metabolic machinery and survival strategies, which enables the cancer cells to behave as selfish “neo-endo-parasites” that exploit
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Editorial / Mutation Research 768 (2014) 1–5
the tumor stromal cells in order to extract nutrients from the surrounding microenvironment. Thus, anti-parasitic compounds might serve as promising anticancer drugs. Nitazoxanide (NTZ), a thiazolide compound, has shown antimicrobial properties against anaerobic bacteria, as well as against helminthes and protozoa. NTZ has also been successfully used to promote Hepatitis C virus elimination by improving interferon signaling and promoting autophagy. NTZ seems to be able to interfere with crucial metabolic and pro-death signaling such as drug detoxification, unfolded protein response, autophagy, anti-cytokine activities and c-Myc inhibition. Thus the ability of NTZ to interfere with integrated survival mechanisms of cancer cells ascribes it a unique chemotherapeutic strategy against cancer. Prostate cancer (PCA) is a leading cause of cancer-related deaths among men in the United States. Patients with localized PCA have a very high 5-year survival rate; however, in patients with clinically detectable metastatic disease, median survival is mostly reduced to 12–15 months. Thus preventing or inhibiting metastasis through nontoxic agents could be a rationalized approach for lowering high mortality among PCA patients. The natural flavonoid silibinin possesses strong anti-metastatic efficacy against PCA but its mechanism/s of its action still remain uncharacterized. One of the major events during metastasis is the replacement of cell–cell interaction with integrins-based cell–matrix interaction that controls motility, invasiveness and survival of cancer cells. Emerging data from studies on advanced human PCA PC3 cells’ interaction with extracellular matrix component fibronectin indicate that Silibinin treatment significantly decreased the fibronectin-induced motile morphology via targeting actin cytoskeleton organization in PC3 cells. Integrins recognize and bind specific ligands (such as fibronectin, vitornectin, collagen and laminin) resulting in clustering of integrins and recruitment and activation of signaling/adaptor molecules such as focal adhesion kinase (FAK), Src, integrin-linked kinase (ILK), PI3K/Akt, Ras/MAPK and Rho family of GTPases (Rac, Rho and Cdc42, etc.). These signaling cascades regulate a variety of cellular processes including cell adhesion, shape, EMT, migration, proliferation and apoptosis. Silibinin decreases the fibronectininduced cell proliferation and motility but significantly increased cell death in PC3 cells. Thus silibinin targets PCA cells’ interaction with fibronectin and inhibits their motility, invasiveness and survival, hence supporting silibinin use in PCA intervention including its metastatic progression. Oncologists and diabetologists quote scientific data from epidemiological and in vitro studies to show that high levels of insulin and glucose, in combination with oxidative stress and chronic inflammation, can heighten the risk of developing cancer amongst patients with diabetes. Although the cancers that have been consistently associated with type 2 diabetes include pancreatic, colorectal, breast and liver cancers, the preponderance of the disease risk factors such as obesity, inflammation, hyperglycemia, hyperinsulinaemia (as a result of insulin resistance and oxidative beta-cell damage) and the indirect influence of anti-diabetic medications are increasingly being defined. Experimental studies exploring the responsiveness of tumor growth to exogenous glucose are generally in agreement that hyperglycemic conditions indeed favor cell growth, anti-apoptosis, increased cell motility and boost invasiveness. The promotion of earlystage breast and prostate tumor growth under the influence of hyperinsulinemia is frequently related to the shared involvement of IGF-1 and IGFBP-3 receptors in phosphatidyl inositol 3-kinase (PI3K)/AKT and mitogen-activated protein kinase (MAPK) signaling pathways. Insulin resistance may also trigger cancer development via other mechanisms such as: over expression of estrogen, interleukin-6, leptin, TNF-alpha and plasminogen activator inhibitor-1. This theoretically suggests that normalization of glucose levels through insulin therapy could possibly constrain can-
cer progression. Fermented papaya preparation (FPP) has defined antioxidant and immune-modulating potentials. The ability of FPP influence signaling cascades associated with cell growth and survival presents a rational for chemopreventive adjunct that can be used in combination with traditional redox based therapies that target oxidative stress in the cancer micro environment. It is possible that cancer cells may develop some form of resistance during persistent reactive oxygen species (ROS) attack, rendering them more aggressive and resistant to chemical eradication. For example: continuous exposure of bladder cancer cells to arsenic trioxide (As2 O3 ) resulted in cancerous cells surmounting its genotoxic effects. It was found that the influence of As2 O3 enhanced the activation of cell’s intrinsic antioxidant system and promoted the expression of cell survival proteins (e.g. reduced glutathione) – a chain reaction involving transcription factors [8]. It is therefore interesting that the concept of ROS dependent mitogenic and anti-apoptosis signaling pathways represents a specific vulnerability that can be selectively targeted by antioxidants, representing a novel class of potential agents that could effectively eliminate cancer cells. Novel bioactive components including benzyl glucosinolate identified in aqueous extract of papaya exhibit anti-growth activity on several tumor cell lines. The demonstrated efficacy of FPP to control blood glucose, excessive inflammation and modulate free radical-induced oxidative damage which are triggers of liver, bladder, breast and prostate cancers in type 2 diabetes patients, may favorably mitigate the side effects of ensuing diabetes and cancer therapy. The following comments on proanthocyanidins, address the context of other neutraceuticals in this vein. The therapeutic benefits of grape seed proanthocyanidins (GSP) against oxidative stress and degenerative diseases including cardiovascular dysfunctions, acute and chronic stress, gastrointestinal distress, neurological disorders, pancreatitis, various stages of neoplastic processes and carcinogenesis (including detoxification of carcinogenic metabolites) is widely reported. It has been demonstrated that smokeless tobacco extract-induced oxidative stress and apoptosis in a primary culture of human oral keratinocytes have been significantly protected by GSP and exhibited superior protection as compared to a combination of vitamins C and E. GSP exhibited potent modulatory effects of pro-apoptotic and apoptotic regulatory bcl-XL, p53, c-myc, c-JUN, JNK-1 and CD36 genes. Longterm exposure to GSP may serve as a novel chemoprotectant against three stages of DMN-induced liver carcinogenesis and tumorigenesis including initiation, promotion and progression. GSP may selectively protect against oxidative stress, genomic integrity and cell death patterns in vivo. The pretreatment of the animals with GSP for 7 days followed by individual exposure to amiodarone, doxorubicin and dimethylnitrosoamine in order to assess the protective ability of GSP on the amiodarone-induced pulmonary toxicity, doxorubicin-induced cardiotoxicity and dimethylnitrosamineinduced spleen toxicity have shown that GSP exhibits excellent protection in terms of serum chemistry changes and restored genomic and histopathological integrity. Amiodarone, doxorubicin and dimethylnitrosamine cause massive damage to the pulmonary, heart, spleen and brain tissues, respectively, as compared to the control animals. GSP protects against structurally diverse drugand chemical-induced multi-organ toxicity, induces selective cytotoxicity toward human breast, lung, gastric and pancreatic cancer cells while maintaining growth and viability of normal cells. Thus a broad spectrum of studies have demonstrated that GSP prevents against DMN-induced hepatic carcinogenesis by selective preventive and cell death patterns, by modulating gene expression profiles and protecting genomic integrity. Apoptosis is a critical defense mechanism against the formation and progression of cancer and exhibits distinct morphological and biochemical traits. Targeting apoptotic pathways becomes an intriguing strategy for the development of chemotherapeutic
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agents particularly if the process is selective to cancer cells. This vein is directed at potential apoptosis inducing lead compounds isolated from marine organisms. Although this “silent world” has a much richer biodiversity than that of the terrestrial areas, efforts to exploit marine organisms for drug discovery is still at a relatively early stage. A large proportion of these natural products have been extracted from marine invertebrates (which not only produce a great number of marine natural products currently known but also show the largest diversity of natural products including alkaloids). The synthetic nucleoside analog cytarabine, is commonly used in the treatment of leukemia and lymphoma. Its development was initially inspired by a series of C-nucleoside-derived compounds isolated from the Caribbean sponge Cryptotheca crypta. The fluorinated derivative of cytarabine, gemcitabine, has shown significant activity in patients with solid tumors, such as pancreatic, breast, bladder, and non-small-cell lung cancer [9]. Interestingly, the marine-derived compounds that have entered phase I and II trials as antitumour agents (which includes didemnin B, aplidine, and ET-743) are derived from tunicates. Didemnin B is a cyclic depsipeptide isolated from the tunicate. Trididemnum solidum. Dildemnin B, has shown impressive antitumor activity in human tumor models in vitro as well as in tumors growing in athymic mice. Clinical trial involving didemnin B in patients with various solid tumors or non-Hodgkin lymphoma was discontinued due to severe neuromuscular and cardiotoxic effects. The ecteinascidins are derived from the Caribbean tunicate Ecteinascidia turbinate and also show significant antitumor activity in both murine and human tumor cell lines. The ET-743 is a tetrahydroisoquinoline alkaloid that acts by selective alkylation of guanine residues in the DNA minor groove. It therefore differs from the other DNA-alkylating agents so far introduced in the clinic and it also interacts with nuclear proteins. Further, Isomalabaricane-type triterpenoids are a rare group of triterpenoids with unique skeletons, often found in marine sponges (reviewed in [9,10]). Marine natural products may become a more significant part of the pipeline for developing new therapeutics in the future. However, as with all new emerging technologies, many challenges await the field of marine natural product biotechnology before it can reach its full potential of providing practical approaches to supplying complex marine organic molecules for clinical evaluation and development. Trianthema portulacastrum Linn. (Aizoaceae), a dietary and medicinal plant, has been found to exert antihepatotoxic and antihepatocarcinogenic properties in rodents. T. portulacastrum Linn. (Aizoaceae), an exotic weed and a native of tropical America, is a prostrate, glabrous and succulent annual that grows in South America, West Indies, South and tropical Africa and several tropical countries of Asia, including India, Bangladesh, Pakistan and Sri Lanka. This plant is used as a vegetable in Indian subcontinent and also considered as a valuable herb in the Indian traditional medicinal system, such as Ayurvedic medicine. Several parts of T. portulacastrum are traditionally used as alexiteric, alterative, analgesic, laxative and stomachic and also used for the treatment of alcohol poisoning, anemia, ascites, asthma, beri-beri, bronchitis, corneal ulcers, dropsy, edema, heart diseases, inflammation, liver disorders, migraine, night blindness, piles and rheumatism. A study was initiated to investigate mechanism-based chemopreventive potential of an ethanolic extract of T. portulacastrum (TPE) using the 7,12-dimethylbenz(a)anthracene (DMBA)-initiated rat mammary gland carcinogenesis model (an experimental tumor model that closely resembles human breast cancer). Following two weeks of TPE treatment, mammary tumorigenesis was initiated by oral administration of DMBA (50 mg/kg body weight). At the end of the study (16 weeks after DMBA exposure), TPE exhibited a striking reduction of DMBA-induced mammary tumor incidence, total tumor burden and average tumor weight and reversed intratumor histopathological alterations. TPE dose-dependently suppressed
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proliferating cell nuclear antigen and cyclin D1 expression, induced apoptosis, upregulated proapoptotic protein Bax, down regulated antiapoptotic protein Bcl-2 and diminished the expression of nuclear and cytosolic-catenin in mammary tumors. Thus TPE exerts chemopreventive effect in the classical DMBA model of breast cancer by suppressing abnormal cell proliferation and inducing apoptosis mediated through alteration of Bax/Bcl-2 ratio. The cellular machinery related to the apoptotic process is extremely conserved and mutations in genes that regulate apoptotic pathways, including the Bcl-2 family members, are very common in human malignancies. The genes belonging to the Bcl-2 family are cardinal regulators of the apoptotic process. The Bcl-2 protein overexpressed in a variety of human cancers, functions as a suppressor of apoptosis and this results in the survival of malignant cells. On the other hand, ectopic expression of other Bcl-2 family proteins, such as Bax, induces mitochondrial apoptosis and its expression is reduced in several types of cancers. Overexpression of Bcl-2 has been associated with downregulation of Bax. It is noteworthy that the increases in the Bax/Bcl-2 ratio is considered to be a reliable indicator of the overall propensity of a cell to undergo apoptosis. The seeds of Nigella sativa L., an annual Ranunculaceae herbaceous plant, have been used for traditionally medicine practice in the Middle East, Northern Africa and India for the treatment of asthma, cough, bronchitis, headache, rheumatism, fever, influenza, eczema, as a diuretic, anti-inflammatory lactagogue, and vermifuge. Among its contents of oils, proteins, alkaloids and saponins, thymoquinone (2-methyl-5-isopropyl-1,4benzoquinone; TQ) a monoterpene present in black cumin seeds has received wide attention for its potential prophylactic potentials exhibiting pharmacological activities that includes antioxidant, anti-inflammatory, antidiabetic and antitumor effects. TQ inhibits experimental carcinogenesis in a wide range of animal models and has been shown to arrest the growth of various cancer cells in culture as well as xenograft tumors in vivo. The mechanistic basis of anticancer effects of TQ includes the inhibition of carcinogen metabolizing enzyme activity and oxidative damage of cellular macromolecules, attenuation of inflammation, induction of cell cycle arrest and apoptosis in tumor cells, blockade of tumor angiogenesis, and suppression of migration, invasion and metastasis of cancer cells. TQ shows synergistic and/or potentiating anticancer effects when combined with clinically used chemotherapeutic agents. At the molecular level, TQ targets various components of intracellular signaling pathways, particularly a variety of upstream kinases and transcription factors, which are aberrantly activated during the course of tumorigenesis. The intraperitoneal administration of TQ significantly reduced the volume of human breast cancer (MDA-MB-231), gastric cancer, and colon cancer (HCT116) cells (xenograft model) in nude mice. TQ, when given by intratumoral injection, markedly diminished the growth of fibrosarcoma and squamous cell carcinomas cell xenograft tumors in mice. Likewise, subcutaneous injection of TQ inhibited human prostate cancer and lung cancer cell xenograft tumor growth in nude mice. The metabolically activated carcinogens can cause oxidative and/or covalent modification of DNA and the alteration of intracellular signaling network. Although cytochrome p450 (CYP) enzymes are primarily involved in detoxification process, activation of these enzymes, particularly CYP1 family members, may paradoxically cause biotransformation of polycyclic aromatic hydrocarbons into highly reactive carcinogenic intermediates. TQ diminishes the activities of certain CYP enzymes as the mechanism of its antitumor initiating effect and inhibits various hallmarks of cancer with mechanisms that include inhibition of carcinogen activation, inflammation and tumor cell proliferation, activation of antioxidant and/or detoxification enzymes, induction of cancer cell death, and suppression of tumor angiogenesis, invasion and metastasis. One of the hallmarks of cancer is that the tumor cells evade from cell death
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machinery. TQ induces apoptosis selectively in cancer cells without affecting normal cells. Although TQ functions as an antioxidant at a low concentration, studies have shown that the compound can induce cytotoxicity in cancer cells through generation of ROS at a relatively high concentration. The one electron reduction of TQ results in the formation of semiquinone, which can undergo redox cycling leading to the generation of ROS and can react with amino or thiol groups of amino acids. TQ induced cytotoxicity in human malignant T cells, prostate cancer, primary effusion lymphoma, laryngeal carcinoma (Hep2), HepG2, activated B-cell lymphoma, MCF-7, and colorectal cancer cells through the generation of ROS as evinced by the abrogation of cytotoxicity upon co-treatment of cells with N-acetyl cysteine (NAC). N-acetylcysteine is a powerful scavenger of hypochlorous acid (that can be produced in vivo in a reaction involving hydrogen peroxide and chloride anion that is catalyzed by the myeloperoxidase enzyme during impacting macrophage activity) and protects alpha 1-antiproteinase against inactivation by HOCl. NAC also reacts with hydroxyl radical with a rate constant of 1.36 × 10(10) M−1 s−1 , as determined by pulse radiolysis [11]. The generation of ROS by TQ led to the depletion of cellular glutathione level and activation of caspases, there by inducing cell death. Despite the advances in understanding the biochemistry behind the anticancer activity of TQ and the progress in formulating and/or synthesizing TQ-based analogs, detailed information about the pharmacokinetics of TQ or its derivatives is yet to be established. Genistein, a soy derived isoflavone, has substantial chemopreventive effects with numerous intracellular targets in exerting its cancer chemopreventive effects, which includes suppression of protein tyrosine kinases, inhibition of angiogenesis and metastasis, cell cycle arrest, attenuation of oxidative stress, and induction of apoptosis and differentiation of cancer cells. In the study reported in the Special Issue, the effects of genistein, on phorbol ester-induced expression of cyclooxygenase-2 (COX-2) that plays an important role in the pathophysiology of inflammation-associated carcinogenesis, was investigated. Here cultured human breast epithelial (MCF10A) cells were pretreated with genistein reduced COX2 expression induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Genistein failed to inhibit TPA-induced nuclear translocation and DNA binding of NF-B as well as degradation of IB. However, genistein abrogated the TPA-induced transcriptional activity of NF-B as determined by the luciferase reporter gene assay. Genistein inhibited phosphorylation of the p65 subunit of NF-B and its interaction with cAMP regulatory element-binding protein (CBP)/p300 and TATA-binding protein (TBP). TPA-induced NF-B phosphorylation was abolished by pharmacological inhibition of extracellular signal-regulated kinase (ERK). Likewise, pharmacologic inhibition or dominant negative mutation of ERK suppressed phosphorylation of p65. Thus genistein inhibits COX-2 expression through inhibition of the ERK-mediated phosphorylation of p65 and interference with subsequent interaction between NF-B and the co-activator protein CBP and recruitment of basal transcription factor, TATA-binding protein. Such inhibition of COX-2 expression and PGE2 secretion probably contributes to the anti-inflammatory and chemopreventive properties of genistein. Although in vitro studies have contributed significantly to identification of distinct molecular targets and signaling pathways affected by given phytochemicals, concentrations employed in mechanistic studies exceed those physiologically achievable in humans. The introductory remarks extends to the concept of polymer science and nanotechnology (embracing drug delivery), stem cell biology and the metabolic fate of prostaglandins in carcinogenesis. As is apparent from the foregoing discussions, various cancer cells over-express growth factors that lead to rapid formation of vessels. These vessels have leaky boundaries due to the absence of a smooth muscle layer and allow penetration of nanocarriers.
Nanocarriers are not only internalized into the cell through the endosome followed by release of the drug into the cytoplasm but accumulate in the tumor tissue that lacks effective lymphatic drainage via the EPR mediated passive targeting, and in other tissues with leaky endothelial walls such as the liver, spleen and bone marrow. Active targeting occurs through specific binding of ligands anchored on the surface of nanocarriers onto tumor cell receptors such as antibodies, folate or growth factors and cytokines. Indeed utilizing the active vascular targeting mechanisms will allow for the design of pharmaceutical formulations to deliver anticancer drugs to block pre-existing blood vessels of tumors and cause tumor cell death from ischemia and extensive hemorrhagic necrosis. Liposomes (lipid and lipoprotein vesicles) offer immense potential for targeting drugs to tumors. The Liposomal preparations daunorubicin (Doxil) and amphotericin B (Abelcet) have shown less cardiac and renal damage, respectively. The PEGylated liposomal doxorubicin, Doxil® was approved for ovarian cancer, AIDS-related Karposi’s Sarcoma and multiple myeloma suffers from a major side-effect which is palmar-plantar erythrodysesthesia (hand-foot syndrome), a major side effect. The development of nano-based systems has definitely proven to be more efficient in terms of decreased toxicity, bioavailability and sustained release of drugs and combatting MDR. Polymer design is key to the elaboration of effective drug carriers. Amphiphilic block copolymer micelles, PEGb-P(DX-co-MeDX) could be interesting carriers for the delivery of anti-cancer drugs because of the ability to control drug release through tuning of the hydrolytic degradability of the micellar core. The binding of the drugs to the hydrophobic polymer core and the tuning of the latter’s hydrolytic degradability through variation of the methyldioxanone units are factors that control release of the drugs. Micellar nanomedicine that can deliver multiple agents, i.e. combination therapy will be an important development in cancer therapeutics. Such nano-formulations would allow sequential release of drugs within the required therapeutic window and could also be engineered as to target several key cancerous pathways. Overproduction of prostaglandin E2 (PGE2) has been reported to be implicated in carcinogenesis. The intracellular level of PGE2 is maintained not only by its biosynthesis, but also by inactivation/degradation. 15-Hydroxyprostaglandin dehydrogenase (15-PGDH) is the key enzyme that catalyzes the conversion of oncogenic PGE2 to a biologically inactive keto metabolite. 15Deoxy-12,14 -prostaglandin J2 (15d-PGJ2) is one of the terminal products of cyclooxygenase-2and it upregulates the expression and the activity of 15-PGDH in human breast cancer MDA-MB231 cells. 15d-PGJ2 induces the expression of 15-PGDH through ROS-mediated activation of ERK1/2 and subsequently Elk-1 in the MDA-MB-231 cells, which may contribute to tumor suppressive activity of this cyclopentenone prostaglandin. It is noteworthy that in several types of human malignancies including breast cancer, constitutive overexpression of cyclooxygenase-2 and subsequent overproduction of prostaglandin E2 (PGE2) are frequently observed. High levels of PGE2 play a role in mammary carcinogenesis by conferring resistance to apoptosis and accelerating angiogenesis, invasion and tumor cell proliferation. The intracellular level of PGE2 can be regulated by its catabolism as well as synthesis. The 15-PGDH-mediated regulation of PGE2 catabolism in the tumor microenvironment represents a novel approach in the management of human breast cancer. The 15d-PGJ2 induces 15-PGDH expression via the ERK1/2-Elk-1 signaling pathway. 15PGDH functions as a tumor suppressor and can be considered as a novel molecular target for the prevention or treatment of human breast cancer and potentially other malignancies. Cancer cells produce regulatory signals that stimulate stromal cells to proliferate and migrate. In turn, stromal elements respond to these signals by releasing components necessary for tumor development that provide structural support, vasculature,
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and extracellular matrices. Mesenchymal stem cells (MSCs) have the ability to migrate and engraft into tumor sites and exert stimulatory or inhibitory effects on cancer cell growth, invasion, and metastasis through direct or indirect interactions with tumor cells. The MSCs are attractive candidate for delivery of anti-tumor agents, owing to their ability to home into tumor sites and to secrete cytokines. The potential role of MSCs in tumor progression as the constituents of the tumor niche and possible implications of MSCs in cancer therapy are increasingly being understood. Indeed the tumor microenvironment exhibits many molecular characteristics of a ‘never healing wound’ that continuously produces and releases various cytokines and other mediators that establish a state of inflammation in the tissue. These tumor-derived signals have a remarkable capacity for attracting various respondent cell types such as MSCs. While targeted migration and incorporation of MSCs toward the primary and metastatic tumor microenvironment have been observed with almost all tested types of cancers (including brain, breast, colon, lung, pancreatic, skin and ovarian), the underlying mechanisms responsible for the tumor-directed migratory potential of MSCs need to be fully elucidated before translation into clinical practice. Resistance to treatment with anticancer drugs results from a variety of factors including individual variations in patients and somatic cell genetic differences in tumors, even those from the same tissue of origin. Frequently resistance is intrinsic to the cancer, but as therapy becomes more and more effective, acquired resistance has also become common. The most common reason for acquisition of resistance to a broad range of anticancer drugs is expression of one or more energy-dependent transporters that detect and eject anticancer drugs from cells, but other mechanisms of resistance including insensitivity to drug-induced apoptosis and induction of drug-detoxifying mechanisms probably play an important role in acquired anticancer drug resistance. The invasion of tumor cells into lymph or blood vessels plays a crucial role in the metastatic process. Interestingly, lymphatic invasion is diagnosed when tumor cells are present in vessels with an unequivocal endothelial lining, yet lacking a thick (muscular) wall. Blood-vessel invasion refers to the involvement of veins, and is characterized histologically by the presence of tumor cells in vessels with a thick (muscular) wall or in vessels containing red blood cells. Intramural vessel invasion, which is limited to vessels in the submucosal and/or muscular layer, has to be differentiated from extramural vessel invasion, which includes vessels located beyond the muscularis propria (those within the pericolic or perirectal adipose tissue) [12]. What remains paramount is early cancer detection and early determination of propensity of the applicable treatment regime. The education of patients, proper lifestyle/dietary management and compliance with therapeutic regime directed at cancer encapsulate challenges of global magnitude. The Special Issue is commended to the reader.
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Acknowledgements The diligence of the authors in this special issue is greatly appreciated. This work would not have been possible without the professionalism of the Editorial and Management team of Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, a big thank you indeed. Okezie I. Aruoma is Professor of Pharmaceutical and Biomedical Sciences, Theeshan Bahorun is Professor of Applied Biochemistry and Arun K. Agnihotri is Professor of Forensic Pathology. References [1] O.I. Aruoma, T. Bahorun, Y. Clements, Inflammation, cellular and redox signaling mechanisms in cancer and degenerative diseases, Mutat. Res. 579 (2005) 1–5. [2] A.K. Agnihotri, T. Bahorun, O.I. Aruoma, Cancer: global health perspectives, Arch. Med. Biomed. Res. 1 (2014) 1–9. [3] L. Balducci, New paradigms for treating elderly patients with cancer: the comprehensive geriatric assessment and guidelines for supportive care, J. Support Oncol. 1 (2003) 30–37. [4] L. Sifer-Riere, V. Girre, M. Gisselbrecht, O. Saint-Jean, Physicians’ perception of cancer care for elderly patients: a qualitative sociological study based on a pilot geriatric oncology program, Crit. Rev. Oncol. Hematol. 75 (2010) 58–69. [5] L.M. Hess, G. Pohl, Perspectives of quality care in cancer treatment: a review of the literature, Am. Health Drug Benefits 6 (2013) 321–329. [6] R. Sidhu, A. Rong, S. Dahlberg, Evaluation of progression-free survival as a surrogate endpoint for survival in chemotherapy and targeted agent metastatic colorectal cancer trials, Clin. Cancer Res. 19 (2013) 969–976. [7] M.A. Phelps, T.E. Stinchcombe, J.S. Blachly, W. Zhao, L.J. Schaaf, S.L. Starrett, L. Wei, M. Poi, D. Wang, A. Papp, J. Aimiuwu, Y. Gao, J. Li, G.A. Otterson, W.J. Hicks, M.A. Socinski, M.A. Villalona-Calero, Erlotinib in African Americans with advanced non-small cell lung cancer: a prospective randomized study with genetic and pharmacokinetic analyses, Clin. Pharmacol. Ther. 96 (2014) 182–191. [8] D. Sumi, Y. Shinkai, Y. Kumagai, Signal transduction pathways and transcription factors triggered by arsenic trioxide in leukemia cells, Toxicol. Appl. Pharmacol. 244 (2010) 385–392. [9] G. Schwartsmann, A. Brondani da Rocha, R.G.S. Berlinck, J. Jimeno, Marine organisms as a source of new anticancer agents, Lancet Oncol. 2 (2001) 221–225. [10] L. Yong-Xin, S.W.A. Himaya, K. Se-Kwon, Triterpenoids of marine origin as anticancer agents, Molecules 18 (2013) 7886–7909. [11] O.I. Aruoma, B. Halliwell, B.M. Hoey, J. Butler, The antioxidant action of N-acetylcysteine: its reaction with hydrogen peroxide, hydroxyl radical, superoxide, and hypochlorous acid, Free Radic. Biol. Med. 6 (1989) 593–597. [12] N. Schneider, C. Langner, Prognostic stratification of colorectal cancer patients: current perspectives, Cancer Manag. Res. 6 (2014) 291–300.
Okezie I. Aruoma School of Pharmacy, American University of Health Sciences, Signal Hill, USA Theeshan Bahorun ANDI Center of Excellence for Biomedical and Biomaterials Research, University of Mauritius, Mauritius Arun K. Agnihotri SSR Medical College, Mauritius
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Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis journal homepage: www.elsevier.com/locate/molmut Community address: www.elsevier.com/locate/mutres
Editorial
Cancer risks and perspectives: Molecular mechanisms
Strategies for the intervention and prevention of cancers, diabetes, cardiovascular diseases, HIV/AIDS and other diseases of overt inflammation including neurodegenerative diseases (Alzheimer’s and Parkinson’s disease) require an understanding of the basic molecular mechanism(s) by prophylactic agents (dietary antioxidant factors from food plants and medicinal plants in this context) that may potentially prevent or reverse the promotion or progression of the diseases [1,2]. Cancer is a group of diseases characterized by uncontrolled cell proliferation, evasion of cell death and the ability to invade and disrupt vital tissue function. Cancer cells can spread to other parts of the body through the blood and lymph systems. The main types cancer include: Carcinoma (which characterizes cancers that begin in the skin or in the tissues that line or cover internal organs with subtypes of carcinoma, including adenocarcinoma, basal cell carcinoma, squamous cell carcinoma, and transitional cell carcinoma), Sarcoma (which characterizes cancers that begin in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue), Leukemia (which characterizes cancers that start in blood-forming tissue such as the bone marrow and cause large numbers of abnormal blood cells to be produced which then enters the blood), Lymphoma and Myeloma (which characterizes cancers that begin in the cells of the immune system) and Central nervous system cancers (which characterizes the cancers that begin in the tissues of the brain and spinal cord). Cancer arises from a loss of normal growth control. In normal tissues, the rates of new cell growth and old cell death are kept in balance. In cancer, this balance is disrupted resulting from uncontrolled cell growth or loss of a cell’s ability to undergo apoptosis or cell suicide whereby old or damaged cells normally self-destruct. The classical model of carcinogenesis describes successive clonal expansion driven by the accumulation of mutations that eliminate restraints on proliferation and cell survival. Older cancer patients have variable physiologic ages necessitating the need to individualize their treatment for better outcome [3,4]. Given the increasing number of cancer survivors, there is a trend to shift patient care from a model that was focused on the immediate need to treat the tumor to a more holistic approach that aims to ensure both quantity and quality of life. The key tenets of quality of life are often associated with communication, trust, caring behavior, comfort, and social and spiritual support. Getting inadequate health information and lack of psychosocial care coupled with lack of and/or delay in coordinated care are among the barriers to quality care that a cancer patient may receive. From the healthcare provider’s perspective, workload or administrative burden, lack of coordinated care, bureaucracy of managed care and lack http://dx.doi.org/10.1016/j.mrfmmm.2014.09.001 0027-5107/© 2014 Published by Elsevier B.V.
of processes to support treatment guidelines tend to impact the quality of care received by the patient. These are often impacted by strategies being implemented by managed care to address cancer quality, which include decision support tools, pathways, guidelines, and cost reduction strategies (reviewed in [5]). In treating cancer, toxicity from systemic therapy with chemotherapeutic drugs and severe complications from radiation therapy are two most critical limiting factors associated with patient safety. This has led to seeking alternate chemopreventive approaches through dietary means and/or use of pharmacological and natural agents whose multiple intervention strategies, efficacy and acceptable toxicity are potentially anticipated to arrest or reverse the cellular and molecular processes of carcinogenesis. In this vein, progress in understanding the molecular changes that underlie cancer development offer the prospect of specifically targeting malfunctioning molecules and pathways to achieve more effective and rational cancer therapy. While the first-line therapy for advanced non-small cell lung cancer is platinum-based chemotherapy, patients with specific mutations may effectively be treated with targeted agents initially. In the treatment of patients suffering from advanced cancers with contemporary systemic therapies, the challenge is to attain therapeutic efficacy, while minimizing side effects. The side effects may range from nausea to tissue damage. In cancer survivors, the iatrogenic outcomes may include consequences of genomic mutations in patients themselves or their children. Thus the main challenge for the oncologists is not to cross the thin line between eradicating cancer cells in vivo, in the patients’ bodies, but not harm these patients’ healthy cells. This is a particularly tough challenge in advanced cancers, which metastasize to multiple and distant locations of the patients’ bodies. In this realm, there is a great promise in genetic engineering of stem cells (compatible with the patient’s immune system) guided to the specific tumour to deliver the therapeutic trans-genes into cancer cells to induce their death. The advanced stages are often beyond the therapeutic arsenal of local surgery, but require systemic therapies associated with severe side effects [3–7]. The seminal reviews, commentary and research papers contained in this Special Issue highlight developments to not only understand cancer but to treat the disease with a view to the minimization of side effects of such therapies. Commentaries deriving from the various articles therein are here presented as an introduction to the reader. The “regression” of cancer cells involves changes within metabolic machinery and survival strategies, which enables the cancer cells to behave as selfish “neo-endo-parasites” that exploit
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the tumor stromal cells in order to extract nutrients from the surrounding microenvironment. Thus, anti-parasitic compounds might serve as promising anticancer drugs. Nitazoxanide (NTZ), a thiazolide compound, has shown antimicrobial properties against anaerobic bacteria, as well as against helminthes and protozoa. NTZ has also been successfully used to promote Hepatitis C virus elimination by improving interferon signaling and promoting autophagy. NTZ seems to be able to interfere with crucial metabolic and pro-death signaling such as drug detoxification, unfolded protein response, autophagy, anti-cytokine activities and c-Myc inhibition. Thus the ability of NTZ to interfere with integrated survival mechanisms of cancer cells ascribes it a unique chemotherapeutic strategy against cancer. Prostate cancer (PCA) is a leading cause of cancer-related deaths among men in the United States. Patients with localized PCA have a very high 5-year survival rate; however, in patients with clinically detectable metastatic disease, median survival is mostly reduced to 12–15 months. Thus preventing or inhibiting metastasis through nontoxic agents could be a rationalized approach for lowering high mortality among PCA patients. The natural flavonoid silibinin possesses strong anti-metastatic efficacy against PCA but its mechanism/s of its action still remain uncharacterized. One of the major events during metastasis is the replacement of cell–cell interaction with integrins-based cell–matrix interaction that controls motility, invasiveness and survival of cancer cells. Emerging data from studies on advanced human PCA PC3 cells’ interaction with extracellular matrix component fibronectin indicate that Silibinin treatment significantly decreased the fibronectin-induced motile morphology via targeting actin cytoskeleton organization in PC3 cells. Integrins recognize and bind specific ligands (such as fibronectin, vitornectin, collagen and laminin) resulting in clustering of integrins and recruitment and activation of signaling/adaptor molecules such as focal adhesion kinase (FAK), Src, integrin-linked kinase (ILK), PI3K/Akt, Ras/MAPK and Rho family of GTPases (Rac, Rho and Cdc42, etc.). These signaling cascades regulate a variety of cellular processes including cell adhesion, shape, EMT, migration, proliferation and apoptosis. Silibinin decreases the fibronectininduced cell proliferation and motility but significantly increased cell death in PC3 cells. Thus silibinin targets PCA cells’ interaction with fibronectin and inhibits their motility, invasiveness and survival, hence supporting silibinin use in PCA intervention including its metastatic progression. Oncologists and diabetologists quote scientific data from epidemiological and in vitro studies to show that high levels of insulin and glucose, in combination with oxidative stress and chronic inflammation, can heighten the risk of developing cancer amongst patients with diabetes. Although the cancers that have been consistently associated with type 2 diabetes include pancreatic, colorectal, breast and liver cancers, the preponderance of the disease risk factors such as obesity, inflammation, hyperglycemia, hyperinsulinaemia (as a result of insulin resistance and oxidative beta-cell damage) and the indirect influence of anti-diabetic medications are increasingly being defined. Experimental studies exploring the responsiveness of tumor growth to exogenous glucose are generally in agreement that hyperglycemic conditions indeed favor cell growth, anti-apoptosis, increased cell motility and boost invasiveness. The promotion of earlystage breast and prostate tumor growth under the influence of hyperinsulinemia is frequently related to the shared involvement of IGF-1 and IGFBP-3 receptors in phosphatidyl inositol 3-kinase (PI3K)/AKT and mitogen-activated protein kinase (MAPK) signaling pathways. Insulin resistance may also trigger cancer development via other mechanisms such as: over expression of estrogen, interleukin-6, leptin, TNF-alpha and plasminogen activator inhibitor-1. This theoretically suggests that normalization of glucose levels through insulin therapy could possibly constrain can-
cer progression. Fermented papaya preparation (FPP) has defined antioxidant and immune-modulating potentials. The ability of FPP influence signaling cascades associated with cell growth and survival presents a rational for chemopreventive adjunct that can be used in combination with traditional redox based therapies that target oxidative stress in the cancer micro environment. It is possible that cancer cells may develop some form of resistance during persistent reactive oxygen species (ROS) attack, rendering them more aggressive and resistant to chemical eradication. For example: continuous exposure of bladder cancer cells to arsenic trioxide (As2 O3 ) resulted in cancerous cells surmounting its genotoxic effects. It was found that the influence of As2 O3 enhanced the activation of cell’s intrinsic antioxidant system and promoted the expression of cell survival proteins (e.g. reduced glutathione) – a chain reaction involving transcription factors [8]. It is therefore interesting that the concept of ROS dependent mitogenic and anti-apoptosis signaling pathways represents a specific vulnerability that can be selectively targeted by antioxidants, representing a novel class of potential agents that could effectively eliminate cancer cells. Novel bioactive components including benzyl glucosinolate identified in aqueous extract of papaya exhibit anti-growth activity on several tumor cell lines. The demonstrated efficacy of FPP to control blood glucose, excessive inflammation and modulate free radical-induced oxidative damage which are triggers of liver, bladder, breast and prostate cancers in type 2 diabetes patients, may favorably mitigate the side effects of ensuing diabetes and cancer therapy. The following comments on proanthocyanidins, address the context of other neutraceuticals in this vein. The therapeutic benefits of grape seed proanthocyanidins (GSP) against oxidative stress and degenerative diseases including cardiovascular dysfunctions, acute and chronic stress, gastrointestinal distress, neurological disorders, pancreatitis, various stages of neoplastic processes and carcinogenesis (including detoxification of carcinogenic metabolites) is widely reported. It has been demonstrated that smokeless tobacco extract-induced oxidative stress and apoptosis in a primary culture of human oral keratinocytes have been significantly protected by GSP and exhibited superior protection as compared to a combination of vitamins C and E. GSP exhibited potent modulatory effects of pro-apoptotic and apoptotic regulatory bcl-XL, p53, c-myc, c-JUN, JNK-1 and CD36 genes. Longterm exposure to GSP may serve as a novel chemoprotectant against three stages of DMN-induced liver carcinogenesis and tumorigenesis including initiation, promotion and progression. GSP may selectively protect against oxidative stress, genomic integrity and cell death patterns in vivo. The pretreatment of the animals with GSP for 7 days followed by individual exposure to amiodarone, doxorubicin and dimethylnitrosoamine in order to assess the protective ability of GSP on the amiodarone-induced pulmonary toxicity, doxorubicin-induced cardiotoxicity and dimethylnitrosamineinduced spleen toxicity have shown that GSP exhibits excellent protection in terms of serum chemistry changes and restored genomic and histopathological integrity. Amiodarone, doxorubicin and dimethylnitrosamine cause massive damage to the pulmonary, heart, spleen and brain tissues, respectively, as compared to the control animals. GSP protects against structurally diverse drugand chemical-induced multi-organ toxicity, induces selective cytotoxicity toward human breast, lung, gastric and pancreatic cancer cells while maintaining growth and viability of normal cells. Thus a broad spectrum of studies have demonstrated that GSP prevents against DMN-induced hepatic carcinogenesis by selective preventive and cell death patterns, by modulating gene expression profiles and protecting genomic integrity. Apoptosis is a critical defense mechanism against the formation and progression of cancer and exhibits distinct morphological and biochemical traits. Targeting apoptotic pathways becomes an intriguing strategy for the development of chemotherapeutic
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agents particularly if the process is selective to cancer cells. This vein is directed at potential apoptosis inducing lead compounds isolated from marine organisms. Although this “silent world” has a much richer biodiversity than that of the terrestrial areas, efforts to exploit marine organisms for drug discovery is still at a relatively early stage. A large proportion of these natural products have been extracted from marine invertebrates (which not only produce a great number of marine natural products currently known but also show the largest diversity of natural products including alkaloids). The synthetic nucleoside analog cytarabine, is commonly used in the treatment of leukemia and lymphoma. Its development was initially inspired by a series of C-nucleoside-derived compounds isolated from the Caribbean sponge Cryptotheca crypta. The fluorinated derivative of cytarabine, gemcitabine, has shown significant activity in patients with solid tumors, such as pancreatic, breast, bladder, and non-small-cell lung cancer [9]. Interestingly, the marine-derived compounds that have entered phase I and II trials as antitumour agents (which includes didemnin B, aplidine, and ET-743) are derived from tunicates. Didemnin B is a cyclic depsipeptide isolated from the tunicate. Trididemnum solidum. Dildemnin B, has shown impressive antitumor activity in human tumor models in vitro as well as in tumors growing in athymic mice. Clinical trial involving didemnin B in patients with various solid tumors or non-Hodgkin lymphoma was discontinued due to severe neuromuscular and cardiotoxic effects. The ecteinascidins are derived from the Caribbean tunicate Ecteinascidia turbinate and also show significant antitumor activity in both murine and human tumor cell lines. The ET-743 is a tetrahydroisoquinoline alkaloid that acts by selective alkylation of guanine residues in the DNA minor groove. It therefore differs from the other DNA-alkylating agents so far introduced in the clinic and it also interacts with nuclear proteins. Further, Isomalabaricane-type triterpenoids are a rare group of triterpenoids with unique skeletons, often found in marine sponges (reviewed in [9,10]). Marine natural products may become a more significant part of the pipeline for developing new therapeutics in the future. However, as with all new emerging technologies, many challenges await the field of marine natural product biotechnology before it can reach its full potential of providing practical approaches to supplying complex marine organic molecules for clinical evaluation and development. Trianthema portulacastrum Linn. (Aizoaceae), a dietary and medicinal plant, has been found to exert antihepatotoxic and antihepatocarcinogenic properties in rodents. T. portulacastrum Linn. (Aizoaceae), an exotic weed and a native of tropical America, is a prostrate, glabrous and succulent annual that grows in South America, West Indies, South and tropical Africa and several tropical countries of Asia, including India, Bangladesh, Pakistan and Sri Lanka. This plant is used as a vegetable in Indian subcontinent and also considered as a valuable herb in the Indian traditional medicinal system, such as Ayurvedic medicine. Several parts of T. portulacastrum are traditionally used as alexiteric, alterative, analgesic, laxative and stomachic and also used for the treatment of alcohol poisoning, anemia, ascites, asthma, beri-beri, bronchitis, corneal ulcers, dropsy, edema, heart diseases, inflammation, liver disorders, migraine, night blindness, piles and rheumatism. A study was initiated to investigate mechanism-based chemopreventive potential of an ethanolic extract of T. portulacastrum (TPE) using the 7,12-dimethylbenz(a)anthracene (DMBA)-initiated rat mammary gland carcinogenesis model (an experimental tumor model that closely resembles human breast cancer). Following two weeks of TPE treatment, mammary tumorigenesis was initiated by oral administration of DMBA (50 mg/kg body weight). At the end of the study (16 weeks after DMBA exposure), TPE exhibited a striking reduction of DMBA-induced mammary tumor incidence, total tumor burden and average tumor weight and reversed intratumor histopathological alterations. TPE dose-dependently suppressed
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proliferating cell nuclear antigen and cyclin D1 expression, induced apoptosis, upregulated proapoptotic protein Bax, down regulated antiapoptotic protein Bcl-2 and diminished the expression of nuclear and cytosolic-catenin in mammary tumors. Thus TPE exerts chemopreventive effect in the classical DMBA model of breast cancer by suppressing abnormal cell proliferation and inducing apoptosis mediated through alteration of Bax/Bcl-2 ratio. The cellular machinery related to the apoptotic process is extremely conserved and mutations in genes that regulate apoptotic pathways, including the Bcl-2 family members, are very common in human malignancies. The genes belonging to the Bcl-2 family are cardinal regulators of the apoptotic process. The Bcl-2 protein overexpressed in a variety of human cancers, functions as a suppressor of apoptosis and this results in the survival of malignant cells. On the other hand, ectopic expression of other Bcl-2 family proteins, such as Bax, induces mitochondrial apoptosis and its expression is reduced in several types of cancers. Overexpression of Bcl-2 has been associated with downregulation of Bax. It is noteworthy that the increases in the Bax/Bcl-2 ratio is considered to be a reliable indicator of the overall propensity of a cell to undergo apoptosis. The seeds of Nigella sativa L., an annual Ranunculaceae herbaceous plant, have been used for traditionally medicine practice in the Middle East, Northern Africa and India for the treatment of asthma, cough, bronchitis, headache, rheumatism, fever, influenza, eczema, as a diuretic, anti-inflammatory lactagogue, and vermifuge. Among its contents of oils, proteins, alkaloids and saponins, thymoquinone (2-methyl-5-isopropyl-1,4benzoquinone; TQ) a monoterpene present in black cumin seeds has received wide attention for its potential prophylactic potentials exhibiting pharmacological activities that includes antioxidant, anti-inflammatory, antidiabetic and antitumor effects. TQ inhibits experimental carcinogenesis in a wide range of animal models and has been shown to arrest the growth of various cancer cells in culture as well as xenograft tumors in vivo. The mechanistic basis of anticancer effects of TQ includes the inhibition of carcinogen metabolizing enzyme activity and oxidative damage of cellular macromolecules, attenuation of inflammation, induction of cell cycle arrest and apoptosis in tumor cells, blockade of tumor angiogenesis, and suppression of migration, invasion and metastasis of cancer cells. TQ shows synergistic and/or potentiating anticancer effects when combined with clinically used chemotherapeutic agents. At the molecular level, TQ targets various components of intracellular signaling pathways, particularly a variety of upstream kinases and transcription factors, which are aberrantly activated during the course of tumorigenesis. The intraperitoneal administration of TQ significantly reduced the volume of human breast cancer (MDA-MB-231), gastric cancer, and colon cancer (HCT116) cells (xenograft model) in nude mice. TQ, when given by intratumoral injection, markedly diminished the growth of fibrosarcoma and squamous cell carcinomas cell xenograft tumors in mice. Likewise, subcutaneous injection of TQ inhibited human prostate cancer and lung cancer cell xenograft tumor growth in nude mice. The metabolically activated carcinogens can cause oxidative and/or covalent modification of DNA and the alteration of intracellular signaling network. Although cytochrome p450 (CYP) enzymes are primarily involved in detoxification process, activation of these enzymes, particularly CYP1 family members, may paradoxically cause biotransformation of polycyclic aromatic hydrocarbons into highly reactive carcinogenic intermediates. TQ diminishes the activities of certain CYP enzymes as the mechanism of its antitumor initiating effect and inhibits various hallmarks of cancer with mechanisms that include inhibition of carcinogen activation, inflammation and tumor cell proliferation, activation of antioxidant and/or detoxification enzymes, induction of cancer cell death, and suppression of tumor angiogenesis, invasion and metastasis. One of the hallmarks of cancer is that the tumor cells evade from cell death
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machinery. TQ induces apoptosis selectively in cancer cells without affecting normal cells. Although TQ functions as an antioxidant at a low concentration, studies have shown that the compound can induce cytotoxicity in cancer cells through generation of ROS at a relatively high concentration. The one electron reduction of TQ results in the formation of semiquinone, which can undergo redox cycling leading to the generation of ROS and can react with amino or thiol groups of amino acids. TQ induced cytotoxicity in human malignant T cells, prostate cancer, primary effusion lymphoma, laryngeal carcinoma (Hep2), HepG2, activated B-cell lymphoma, MCF-7, and colorectal cancer cells through the generation of ROS as evinced by the abrogation of cytotoxicity upon co-treatment of cells with N-acetyl cysteine (NAC). N-acetylcysteine is a powerful scavenger of hypochlorous acid (that can be produced in vivo in a reaction involving hydrogen peroxide and chloride anion that is catalyzed by the myeloperoxidase enzyme during impacting macrophage activity) and protects alpha 1-antiproteinase against inactivation by HOCl. NAC also reacts with hydroxyl radical with a rate constant of 1.36 × 10(10) M−1 s−1 , as determined by pulse radiolysis [11]. The generation of ROS by TQ led to the depletion of cellular glutathione level and activation of caspases, there by inducing cell death. Despite the advances in understanding the biochemistry behind the anticancer activity of TQ and the progress in formulating and/or synthesizing TQ-based analogs, detailed information about the pharmacokinetics of TQ or its derivatives is yet to be established. Genistein, a soy derived isoflavone, has substantial chemopreventive effects with numerous intracellular targets in exerting its cancer chemopreventive effects, which includes suppression of protein tyrosine kinases, inhibition of angiogenesis and metastasis, cell cycle arrest, attenuation of oxidative stress, and induction of apoptosis and differentiation of cancer cells. In the study reported in the Special Issue, the effects of genistein, on phorbol ester-induced expression of cyclooxygenase-2 (COX-2) that plays an important role in the pathophysiology of inflammation-associated carcinogenesis, was investigated. Here cultured human breast epithelial (MCF10A) cells were pretreated with genistein reduced COX2 expression induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Genistein failed to inhibit TPA-induced nuclear translocation and DNA binding of NF-B as well as degradation of IB. However, genistein abrogated the TPA-induced transcriptional activity of NF-B as determined by the luciferase reporter gene assay. Genistein inhibited phosphorylation of the p65 subunit of NF-B and its interaction with cAMP regulatory element-binding protein (CBP)/p300 and TATA-binding protein (TBP). TPA-induced NF-B phosphorylation was abolished by pharmacological inhibition of extracellular signal-regulated kinase (ERK). Likewise, pharmacologic inhibition or dominant negative mutation of ERK suppressed phosphorylation of p65. Thus genistein inhibits COX-2 expression through inhibition of the ERK-mediated phosphorylation of p65 and interference with subsequent interaction between NF-B and the co-activator protein CBP and recruitment of basal transcription factor, TATA-binding protein. Such inhibition of COX-2 expression and PGE2 secretion probably contributes to the anti-inflammatory and chemopreventive properties of genistein. Although in vitro studies have contributed significantly to identification of distinct molecular targets and signaling pathways affected by given phytochemicals, concentrations employed in mechanistic studies exceed those physiologically achievable in humans. The introductory remarks extends to the concept of polymer science and nanotechnology (embracing drug delivery), stem cell biology and the metabolic fate of prostaglandins in carcinogenesis. As is apparent from the foregoing discussions, various cancer cells over-express growth factors that lead to rapid formation of vessels. These vessels have leaky boundaries due to the absence of a smooth muscle layer and allow penetration of nanocarriers.
Nanocarriers are not only internalized into the cell through the endosome followed by release of the drug into the cytoplasm but accumulate in the tumor tissue that lacks effective lymphatic drainage via the EPR mediated passive targeting, and in other tissues with leaky endothelial walls such as the liver, spleen and bone marrow. Active targeting occurs through specific binding of ligands anchored on the surface of nanocarriers onto tumor cell receptors such as antibodies, folate or growth factors and cytokines. Indeed utilizing the active vascular targeting mechanisms will allow for the design of pharmaceutical formulations to deliver anticancer drugs to block pre-existing blood vessels of tumors and cause tumor cell death from ischemia and extensive hemorrhagic necrosis. Liposomes (lipid and lipoprotein vesicles) offer immense potential for targeting drugs to tumors. The Liposomal preparations daunorubicin (Doxil) and amphotericin B (Abelcet) have shown less cardiac and renal damage, respectively. The PEGylated liposomal doxorubicin, Doxil® was approved for ovarian cancer, AIDS-related Karposi’s Sarcoma and multiple myeloma suffers from a major side-effect which is palmar-plantar erythrodysesthesia (hand-foot syndrome), a major side effect. The development of nano-based systems has definitely proven to be more efficient in terms of decreased toxicity, bioavailability and sustained release of drugs and combatting MDR. Polymer design is key to the elaboration of effective drug carriers. Amphiphilic block copolymer micelles, PEGb-P(DX-co-MeDX) could be interesting carriers for the delivery of anti-cancer drugs because of the ability to control drug release through tuning of the hydrolytic degradability of the micellar core. The binding of the drugs to the hydrophobic polymer core and the tuning of the latter’s hydrolytic degradability through variation of the methyldioxanone units are factors that control release of the drugs. Micellar nanomedicine that can deliver multiple agents, i.e. combination therapy will be an important development in cancer therapeutics. Such nano-formulations would allow sequential release of drugs within the required therapeutic window and could also be engineered as to target several key cancerous pathways. Overproduction of prostaglandin E2 (PGE2) has been reported to be implicated in carcinogenesis. The intracellular level of PGE2 is maintained not only by its biosynthesis, but also by inactivation/degradation. 15-Hydroxyprostaglandin dehydrogenase (15-PGDH) is the key enzyme that catalyzes the conversion of oncogenic PGE2 to a biologically inactive keto metabolite. 15Deoxy-12,14 -prostaglandin J2 (15d-PGJ2) is one of the terminal products of cyclooxygenase-2and it upregulates the expression and the activity of 15-PGDH in human breast cancer MDA-MB231 cells. 15d-PGJ2 induces the expression of 15-PGDH through ROS-mediated activation of ERK1/2 and subsequently Elk-1 in the MDA-MB-231 cells, which may contribute to tumor suppressive activity of this cyclopentenone prostaglandin. It is noteworthy that in several types of human malignancies including breast cancer, constitutive overexpression of cyclooxygenase-2 and subsequent overproduction of prostaglandin E2 (PGE2) are frequently observed. High levels of PGE2 play a role in mammary carcinogenesis by conferring resistance to apoptosis and accelerating angiogenesis, invasion and tumor cell proliferation. The intracellular level of PGE2 can be regulated by its catabolism as well as synthesis. The 15-PGDH-mediated regulation of PGE2 catabolism in the tumor microenvironment represents a novel approach in the management of human breast cancer. The 15d-PGJ2 induces 15-PGDH expression via the ERK1/2-Elk-1 signaling pathway. 15PGDH functions as a tumor suppressor and can be considered as a novel molecular target for the prevention or treatment of human breast cancer and potentially other malignancies. Cancer cells produce regulatory signals that stimulate stromal cells to proliferate and migrate. In turn, stromal elements respond to these signals by releasing components necessary for tumor development that provide structural support, vasculature,
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and extracellular matrices. Mesenchymal stem cells (MSCs) have the ability to migrate and engraft into tumor sites and exert stimulatory or inhibitory effects on cancer cell growth, invasion, and metastasis through direct or indirect interactions with tumor cells. The MSCs are attractive candidate for delivery of anti-tumor agents, owing to their ability to home into tumor sites and to secrete cytokines. The potential role of MSCs in tumor progression as the constituents of the tumor niche and possible implications of MSCs in cancer therapy are increasingly being understood. Indeed the tumor microenvironment exhibits many molecular characteristics of a ‘never healing wound’ that continuously produces and releases various cytokines and other mediators that establish a state of inflammation in the tissue. These tumor-derived signals have a remarkable capacity for attracting various respondent cell types such as MSCs. While targeted migration and incorporation of MSCs toward the primary and metastatic tumor microenvironment have been observed with almost all tested types of cancers (including brain, breast, colon, lung, pancreatic, skin and ovarian), the underlying mechanisms responsible for the tumor-directed migratory potential of MSCs need to be fully elucidated before translation into clinical practice. Resistance to treatment with anticancer drugs results from a variety of factors including individual variations in patients and somatic cell genetic differences in tumors, even those from the same tissue of origin. Frequently resistance is intrinsic to the cancer, but as therapy becomes more and more effective, acquired resistance has also become common. The most common reason for acquisition of resistance to a broad range of anticancer drugs is expression of one or more energy-dependent transporters that detect and eject anticancer drugs from cells, but other mechanisms of resistance including insensitivity to drug-induced apoptosis and induction of drug-detoxifying mechanisms probably play an important role in acquired anticancer drug resistance. The invasion of tumor cells into lymph or blood vessels plays a crucial role in the metastatic process. Interestingly, lymphatic invasion is diagnosed when tumor cells are present in vessels with an unequivocal endothelial lining, yet lacking a thick (muscular) wall. Blood-vessel invasion refers to the involvement of veins, and is characterized histologically by the presence of tumor cells in vessels with a thick (muscular) wall or in vessels containing red blood cells. Intramural vessel invasion, which is limited to vessels in the submucosal and/or muscular layer, has to be differentiated from extramural vessel invasion, which includes vessels located beyond the muscularis propria (those within the pericolic or perirectal adipose tissue) [12]. What remains paramount is early cancer detection and early determination of propensity of the applicable treatment regime. The education of patients, proper lifestyle/dietary management and compliance with therapeutic regime directed at cancer encapsulate challenges of global magnitude. The Special Issue is commended to the reader.
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Acknowledgements The diligence of the authors in this special issue is greatly appreciated. This work would not have been possible without the professionalism of the Editorial and Management team of Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, a big thank you indeed. Okezie I. Aruoma is Professor of Pharmaceutical and Biomedical Sciences, Theeshan Bahorun is Professor of Applied Biochemistry and Arun K. Agnihotri is Professor of Forensic Pathology. References [1] O.I. Aruoma, T. Bahorun, Y. Clements, Inflammation, cellular and redox signaling mechanisms in cancer and degenerative diseases, Mutat. Res. 579 (2005) 1–5. [2] A.K. Agnihotri, T. Bahorun, O.I. Aruoma, Cancer: global health perspectives, Arch. Med. Biomed. Res. 1 (2014) 1–9. [3] L. Balducci, New paradigms for treating elderly patients with cancer: the comprehensive geriatric assessment and guidelines for supportive care, J. Support Oncol. 1 (2003) 30–37. [4] L. Sifer-Riere, V. Girre, M. Gisselbrecht, O. Saint-Jean, Physicians’ perception of cancer care for elderly patients: a qualitative sociological study based on a pilot geriatric oncology program, Crit. Rev. Oncol. Hematol. 75 (2010) 58–69. [5] L.M. Hess, G. Pohl, Perspectives of quality care in cancer treatment: a review of the literature, Am. Health Drug Benefits 6 (2013) 321–329. [6] R. Sidhu, A. Rong, S. Dahlberg, Evaluation of progression-free survival as a surrogate endpoint for survival in chemotherapy and targeted agent metastatic colorectal cancer trials, Clin. Cancer Res. 19 (2013) 969–976. [7] M.A. Phelps, T.E. Stinchcombe, J.S. Blachly, W. Zhao, L.J. Schaaf, S.L. Starrett, L. Wei, M. Poi, D. Wang, A. Papp, J. Aimiuwu, Y. Gao, J. Li, G.A. Otterson, W.J. Hicks, M.A. Socinski, M.A. Villalona-Calero, Erlotinib in African Americans with advanced non-small cell lung cancer: a prospective randomized study with genetic and pharmacokinetic analyses, Clin. Pharmacol. Ther. 96 (2014) 182–191. [8] D. Sumi, Y. Shinkai, Y. Kumagai, Signal transduction pathways and transcription factors triggered by arsenic trioxide in leukemia cells, Toxicol. Appl. Pharmacol. 244 (2010) 385–392. [9] G. Schwartsmann, A. Brondani da Rocha, R.G.S. Berlinck, J. Jimeno, Marine organisms as a source of new anticancer agents, Lancet Oncol. 2 (2001) 221–225. [10] L. Yong-Xin, S.W.A. Himaya, K. Se-Kwon, Triterpenoids of marine origin as anticancer agents, Molecules 18 (2013) 7886–7909. [11] O.I. Aruoma, B. Halliwell, B.M. Hoey, J. Butler, The antioxidant action of N-acetylcysteine: its reaction with hydrogen peroxide, hydroxyl radical, superoxide, and hypochlorous acid, Free Radic. Biol. Med. 6 (1989) 593–597. [12] N. Schneider, C. Langner, Prognostic stratification of colorectal cancer patients: current perspectives, Cancer Manag. Res. 6 (2014) 291–300.
Okezie I. Aruoma School of Pharmacy, American University of Health Sciences, Signal Hill, USA Theeshan Bahorun ANDI Center of Excellence for Biomedical and Biomaterials Research, University of Mauritius, Mauritius Arun K. Agnihotri SSR Medical College, Mauritius