Recent advances in clinical development of leukotriene B4 pathway drugs

Seminars in Immunology 33 (2017) 65–73

Contents lists available at ScienceDirect

Seminars in Immunology journal homepage: www.elsevier.com/locate/ysmim

Recent advances in clinical development of leukotriene B4 pathway drugs L. Bhatt, K. Roinestad, T. Van, E.B. Springman

MARK

⁎

Celtaxsys, Inc., 201 17th ST NW Suite 530, Atlanta, GA, 30363, United States

A R T I C L E I N F O

A B S T R A C T

Keywords: Leukotriene LTB4 BLT1 LTA4 hydrolase Drug development Clinical study

The LTB4 pathway is an attractive target for therapeutic drug development. Two broad classes of drugs have been pursued: antagonists of the primary LTB4 receptors (BLT1 and BLT2) and inhibitors of LTA4 Hydrolase (LTA4H), the rate limiting enzyme in the production of LTB4. An initial wave of effort culminated in the 1990s. Over the past 15 years, a second wave of more selective drug candidates, including at least 5 BLT antagonists and 6 LTA4H inhibitors, have reached Phase 2 clinical trials. Despite the extensive efforts to discover and develop LTB4 pathway targeting drugs, only one has reached the market to date. Recently discovered complexities in the pathway and challenges in matching pathway intervention with therapeutic effect could explain the limited clinical success of LTB4 pathway drugs, even though there is a large body of scientific evidence linking LTB4 to human diseases and demonstrating efficacy of these compounds in a wide array of preclinical models. Herein, we describe the clinical programs for the most prominent recent examples from each broad class and discuss the clinical outcomes and their implications for future development of LTB4 pathway drugs.

1. Introduction Because of its prominent role in initiating and propagating inflammatory immune response, particularly its ability to form a selfsustaining gradient that perpetuates neutrophil recruitment, much effort has been expended toward discovery and development of drugs targeting the Leukotriene B4 (LTB4) pathway. To date, these efforts have met with mixed success in the clinic, some of which can be attributed to subtle complexities in the pathway that have come to light only after many drugs were brought through clinical trials. Drugs targeting the LTB4 pathway fall into 2 broad classes that will be discussed in this review, antagonists of the known LTB4 receptors (BLT1 and BLT2) and inhibitors of the enzyme Leukotriene A4 Hydrolase (LTA4H), which is responsible for generation of LTB4. Among these broad classes, further subtypes of LTB4 targeting drugs are delineated by varying degrees of specificity for receptor subtypes or enzyme activities. Early antagonists of the LTB4 receptors did not discriminate between BLT1 and BLT2, because the BLT2 receptor was only discovered after many of these drugs were in development [1]. Adding to the complexity, the exact role of BLT2 in LTB4 signaling and inflammation remains unclear, with some studies even suggesting that LTB4 is not the primary ligand for BLT2 and that signaling through BLT2 has anti-inflammatory effects [2–4]. More recent examples of drugs targeting LTB4 receptors tend to focus on selectivity for BLT1. Among these, the most studied example is etalocib (LY293111), which is complicated by its additional off-target agonist activity toward peroxisome proliferator⁎

activator receptor gamma (PPARγ) [5,6]. The pathway is further complicated by the potential for anti-inflammatory effects by LTB4 activating PPARα [7,8]. Despite extensive efforts to develop BLT-targeting drugs, none have yet reached the market. Similar complexity exists for drugs targeting LTA4H, as this enzyme exhibits two different enzymatic activities. In addition to the well-described epoxide hydrolase activity responsible for stereo-specific conversion of LTA4 to LTB4, LTA4H also functions as an aminopeptidase with a preference for small peptide substrates (e.g. tripeptides) and an unusual affinity for unnatural amino acids [9–11]. Recent reports suggest that by hydrolyzing the tripeptide Pro-Gly-Pro (PGP), a proinflammatory product of collagen degradation, the aminopeptidase function of LTA4H may act as a counterbalance to the inflammatory effects of LTB4 production [12]. To date, however, the most advanced LTA4H inhibitor drugs have been those originating as broad spectrum aminopeptidase inhibitors, with ubenimex representing the only LTB4 pathway targeting drug to gain approval for treatment of a human disease. More recent efforts have been directed toward development of selective inhibitors of LTA4H, particularly those that exhibit selectivity for the epoxide hydrolase function of LTA4H versus its own aminopeptidase function [13]. The chemistry and nonclinical efficacy associated with both broad classes of LTB4 pathway drugs have been extensively reviewed in the past [14–16]. Therefore, this review is focused mainly on recent clinical developments of the current generation drug candidates, particularly highlighting the successes and failures of past programs alongside the

Corresponding author. E-mail address: [email protected] (E.B. Springman).

http://dx.doi.org/10.1016/j.smim.2017.08.007 Received 28 November 2016; Received in revised form 4 May 2017; Accepted 8 August 2017 1044-5323/ © 2017 Celtaxsys, Inc. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).

Seminars in Immunology 33 (2017) 65–73

L. Bhatt et al.

Table 1 Overview of Clinical Trials for BLT Antagonists. Nonproprietary Name

Alternate Name (s)

Companies

Reported Studies Phase 1

Phase 2

Program Status

Indications

Clinical Trials Registry Link

Additional References

Solid tumors, Non-small cell lung cancer, Pancreatic cancer COPD, Asthma, Rheumatoid arthritis, Cystic fibrosis

https://clinicaltrials.gov/ ct2/results?term= LY293111 https://clinicaltrials.gov/ ct2/results?term=BIIL +284 No US or EU listings

[5,6,17–23]

Etalocib

LY293111, VML295

Lilly

1

2

Inactive

Amelubant

BIIL 284

Boehringer Ingelheim

13

5

Inactive

Moxilubant

CGS-25019C, LTB-019

Novartis

1

1

Inactive

COPD

[24–45]

[46]

lasting for 21 days. Dose proportional PK was observed at steady state, although interpatient variability of Cmax and AUC was described as high (65% and 71%, respectively). At doses of 600 mg and higher, steady state plasma concentrations of etalocib exceeded the projected therapeutic levels. One patient with chondrosarcoma had stable disease for 336 days on treatment, and one patient with melanoma had stable disease for 168 days on treatment. A Phase 2 treatment study was conducted with etalocib added on top of gemcitabine therapy in patients with advanced or metastatic adenocarcinoma of the pancreas [22]. In this study, 130 patients were randomized to receive either 600 mg etalocib or placebo twice daily in addition to a regimen of gemcitabine and 6-month survival was monitored as the primary endpoint. There was no significant improvement in 6-month survival, progression-free survival, or response rate. It was concluded that treatment with etalocib did not demonstrate any added benefit in this patient population when added to gemcitabine treatment. A Phase 2 treatment study was conducted with etalocib added on top of gemcitabine-cisplatin as first-line therapy in patients with nonsmall cell lung carcinoma (NSCLC) [23]. In this study, 200 patients were randomized (195 were treated) to receive either 200 mg or 600 mg etalocib or placebo twice daily for 7 days, followed by concurrent treatment with cisplatin and gemcitabine in 21 day cycles. Progression free survival was monitored as the primary endpoint. There was no significant improvement in 6-month survival, progression-free survival, or response rate. It was concluded that treatment with etalocib did not demonstrate any added benefit in this patient population when added to gemcitabine-cisplatin treatment.

promise of ongoing and future programs. Non-proprietary names (e.g. USAN, INN) are used preferentially in cases where such names have been issued. 2. LTB4 receptor antagonists At least five BLT-targeting drugs of the current generation have entered Phase 2 clinical trials targeting treatment of disease conditions ranging from cystic fibrosis and rheumatoid arthritis to non-small cell lung cancer (Table 1). Chemical structures of these compounds are shown in Fig. 1. Other drug candidates have reached Phase 2 but remain unreported. As of yet, no BLT antagonist drugs have been approved for medical use. 2.1. Etalocib (LY293111; Lilly) Etalocib (LY293111) is the prototypical BLT antagonist of the current generation. It is a synthetic small molecule with approximately 18 nM potency for binding to BLT1 on isolated neutrophils. However, interpretation of the in vivo effects of etalocib is complicated by its offtarget agonist activity toward PPARγ. It is possible that treatment effects in nonclinical and clinical studies are as much related to its action on PPARγ as they are to its action on BLT1 [5,6,17]. Nonetheless, it is one of the most studied BLT1 antagonists and warrants discussion in the present context. A number of preclinical studies suggest that etalocib may have utility in treating lymphoma and pancreatic cancer [18–20]. Three clinical studies of etalocib have been reported, one Phase 1 study and two Phase 2 studies, all directed toward treatment of cancers. Additional clinical studies in healthy volunteers and patients with inflammatory diseases are mentioned in the literature but are not reported in detail. Etalocib was tested in a Phase 1 study in 38 patients with advanced solid tumors [21]. In this study, patients were given twice daily oral doses escalating from 200 to 800 mg over 5 dose level cycles, each

2.2. Amelubant (BIIL 284; Boehringer Ingelheim) Amelubant is a synthetic small molecule prodrug that is converted in vivo into two pharmacologically active forms, BIIL 260 and BIIL 315, a glucuronide adduct of BIIL 260 [24]. Both BIIL 260 and BIIL 315 are Fig. 1. Chemical structures of selected BLT Antagonists tested in phase 2 clinical trials.

66

Seminars in Immunology 33 (2017) 65–73

L. Bhatt et al.

treatment. The study had a primary endpoint of exercise endurance and included a large number of secondary endpoints [43]. While there was no change in exercise endurance, statistically significant differences were observed for Borg leg discomfort (P = 0.024) and oxygen saturation (P = 0.025). Spirometry measures showed no change in FEV1 or FEF25-75, and results for FVC were mixed. There were also no significant changes in sputum cell counts or sputum weight. Thus, it was concluded that amelubant treatment did not demonstrate meaningful therapeutic effect in COPD. A smaller phase 2a study was conducted in patients with mild to moderate asthma [44]. In this study, 38 asthma patients were treated for 14 days with either 150 mg amelubant or placebo, and endpoints were focused on assessing sputum biomarkers and lung function. While amelubant treatment inhibited BLT1 signaling, it did not reduce neutrophil or other cell counts in sputum and did not affect cytokine levels in sputum or pulmonary function tests. Finally, a fourth phase 2 study examined effects of amelubant doses of 75 mg and 150 mg in adult and pediatric (≥6 years of age) patients with CF over 24 weeks of treatment with co-primary endpoints of change in FEV1 and incidence of pulmonary exacerbations [27]. This study was terminated early due to increased pulmonary SAEs (36.1% vs 21.2%, P = 0.007) and increased protocol-defined pulmonary exacerbations (33.1% vs 18.2%, P = 0.005) in the amelubant treated adults. Although the rate of protocol-defined pulmonary exacerbations was actually lower in the pediatric patients treated with amelubant (19.8%) versus placebo (25.7%), the pediatric cohort was also terminated. The origin of the increase in pulmonary exacerbations in adult CF patients remains unclear, and sputum samples were not collected for analysis in this study. However, paradoxically, there were statistically significant increases in circulating neutrophil counts at week 4 in the pediatric cohort treated with amelubant and from week 4 to week 20 in the amelubant treated adults. A subsequent nonclinical study using a rodent model of pseudomonas infection suggested that amelubant treatment may have increased bacterial load in the lungs of the treated CF patients [45].

potent BLT1 antagonists in vitro (1.7 nM and 1.9 nM, respectively), whereas amelubant itself is a relatively weak BLT1 antagonist by comparison (230 nM). Amelubant entered at least 18 clinical trials, including 10 Phase 1 trials, 4 Phase 1b/2a trials, and 4 Phase 2 trials [25]. Synopses for 17 of these trials are publicly available from Boehringer Ingelheim as part of their clinical trials transparency policy [26]. All but one of these trials was carried to completion. A Phase 2 trial of amelubant in adults and children with cystic fibrosis (CF) was terminated early due to adverse events [27]. The Phase 1 program consisted of 9 studies in healthy volunteers and 1 study in patients with hepatic impairment [28–35]. In the first two studies, PK and PD were assessed after single doses ranging from 0.025 mg to 750 mg and multiple ascending doses ranging from 25 mg to 250 mg [28,31]. In the single dose PK/PD study, amelubant was administered as either an oral solution or an oral tablet. In the multiple dose PK/PD study, amelubant was administered only as a tablet. In both studies, BIIL 315 was the main active form in plasma, and doses of 25 mg or higher yielded complete inhibition of BLT1 signaling for up to 24 h after the dose. Four Phase 1 studies assessed various tablet forms and food effect in healthy volunteers, resulting in selection of a tablet form that yielded the highest relative bioavailability and smallest food effect [29,31,34,35]. A single dose study of 150 mg amelubant showed a significant increase in plasma exposure of BIIL 315 in hepatically impaired patients [33]. An ADME study using 14C-labeled amelubant in healthy volunteers confirmed BIIL 315 as the main active form in plasma [32]. There was almost no distribution of radiolabel into blood cells, and the primary route of elimination was via feces. Two additional Phase 1 studies in healthy volunteers were directed toward assessing drug–drug interactions between amelubant and specific drugs relevant to the disease conditions pursued in Phase 2 studies, theophylline and prednisone [36,37]. In these studies, healthy volunteers were treated orally with 150 mg/day amelubant or placebo once daily for 9 days. Test drug, 125 mg oral theophylline or 20 mg oral prednisone was administered on day 7 and PK was assessed. Amelubant treatment did not alter the PK of either theophylline or prednisone, and it was concluded that co-administration of these drugs with amelubant in subsequent clinical trials was acceptable. A Phase 1b/2a program consisting of 4 studies was conducted to study PK, PD and biomarkers in the targeted disease populations [38–41]. PK was studied in adult and pediatric CF patients in a single dose study and a 14-day multiple dose study, in adult chronic obstructive pulmonary disease (COPD) patients in a 14-day multiple dose study, and in adult rheumatoid arthritis (RA) patients in a 14-day multiple dose study. In all patient groups, the principal active form in plasma was BIIL 315, the glucuronide. In the COPD and RA studies, doses of 25 mg and higher yielded complete inhibition of BLT1 signaling from 2 h through 24 h after the final dose on day 14. In the COPD study, amelubant treatment significantly reduced macrophage counts in spontaneously expectorated or induced sputum. No changes in symptomology measures were observed in the RA study. Doses of 25 mg to 150 mg were considered appropriate for further study, with the 150 mg dose yielding a more rapid and durable inhibition of BLT1 signaling. The Phase 2 program, consisting of 4 trials, tested effects of amelubant in patients with RA, COPD, asthma and CF. One trial assessed the treatment effect of amelubant doses of 5 mg, 25 mg, or 75 mg versus placebo over 12 weeks of treatment in 342 adult patients with active RA [42]. A higher percentage of patients receiving 25 mg (28.9%) or 75 mg (28.7%) amelubant showed an ACR20 response at 12 weeks versus placebo (18.5%), but these differences were not statistically significant. No difference in plasma levels of the active form, BIIL 315, was observed between responders and non-responders. Amelubant treatment was safe and well tolerated at all three dose levels. The study concluded that BLT1 signaling is not a major contributor to RA related inflammation. Similarly, amelubant doses of 5 mg, 25 mg or 75 mg were studied versus placebo in 577 adult COPD patients over 12 weeks of

2.3. Moxilubant (CGS-25019C, LTB-019; Novartis) Moxilubant, also known as CGS-25019C and LTB-019, is a synthetic small molecule antagonist of BLT1 [46]. It inhibits LTB4 signaling with a potency of 2–4 nM. In a phase 1 study in 10 healthy volunteers, moxilubant was administered orally once or twice daily for 7 days at doses ranging from 100 to 500 mg. At dose levels of 150 mg and above, LTB4 pathway inhibition reached at least 75%. At doses of 300 mg and above, pathway inhibition reached 100%. A Phase 2 study was conducted in 24 patients with COPD treated with 240 mg/day moxilubant for 4 weeks [46]. In this study, there were no changes in sputum cell counts or biomarkers (myeloperoxidase, IL8, TNFα) or in spirometry measures (FEV1, FVC), even though plasma levels of moxilubant were sufficient to significantly reduce pathway signaling. It was concluded that treatment of COPD via BLT antagonism with moxilubant was not a useful approach. 2.4. Others At least two additional BLT receptor antagonists of the current generation appear to have reached phase 2 clinical trials: ONO-4057 (Ono) and Ro-25-4094 (Roche). However, primary sources for clinical trial designs and results were not found for these compounds. 3. LTA4 hydrolase inhibitors At least six LTA4 Hydrolase inhibitors of the current generation have entered clinical trials, with five of these reaching Phase 2. Of the LTA4H inhibitors, the compounds with broad aminopeptidase inhibitory activity have advanced farthest in the clinic (Table 2), with ubenimex representing the lone LTB4 pathway drug to reach the market. Chemical structures of these compounds are shown in Fig. 2. 67

Seminars in Immunology 33 (2017) 65–73

L. Bhatt et al.

[68]

[63–67]

[60–62]

[56–59]

Healthy volunteer Inactive

3.2. Tosedostat (CHR-2797; CTI Biopharma) Tosedostat is a synthetic small molecule peptidomimetic compound that contains a hydroxamic acid zinc-chelating function on one end of the molecule and an ester moiety on the other end [51,52]. The parent form (CHR-2797) inhibits several aminopeptidases, including aminopeptidase N (220 nM) and leucine aminopeptidase (100 nM) but not LTA4H (>1000 nM). However, after the ester function is removed by hydrolysis within cells to yield the carboxylic acid form (CHR-79888), it is a potent inhibitor of LTA4H (8 nM). Tosedostat has entered at least 11 clinical trials, including two phase 1 studies, one phase 1b study, four phase 1 and 2 studies combined and four phase 2 studies [53]. A phase 1 study in healthy male volunteers was conducted to evaluate the safety and tolerability and to assess the effect of high fat meal on the pharmacokinetics (PK) of once daily oral dose of 120 mg tosedostat. Estimated enrollment was 18 subjects with at least 12 subjects completing the study. Per study design, subjects were randomized to take two 60 mg capsules (120 mg dose) on days 1 and 8 with a highfat meal or in the fasted state for 10 days. Blood samples were collected through 48 h post dose for PK analysis. The current recruitment status of this study is unknown and study results have not been published. A phase 1 study was conducted to evaluate the safety and tolerability of tosedostat in patients with advanced solid tumors. Forty patients were treated for three years with daily oral administration of tosedostat in escalating doses from 10 mg to 320 mg. Primary endpoints of the study included safety, tolerability, dose-limiting toxicity (DLT) and maximum tolerated dose (MTD). Secondary endpoints included PK, pharmacodynamic (PD) effect in blood and tumor cells and preliminary assessment of anti-tumor activity of tosedostat. Dose-limiting toxicities

JNJ-40929837

BI 691751

–

–

Boehringer Ingelheim

5

–

Asthma Inactive

DG-051 –

Johnson & Johnson

–

1

Cardiovascular diseases (myocardial infarction) Inactive

CTX-4430 Acebilustat

deCode Genetics

–

1

Active 2 3

CHR-2797 Tosedostat

Celtaxsys

Active 8 3

Ubenimex (also known by the common name bestatin) is a naturally occurring dipeptide that inhibits a broad spectrum of aminopeptidases, including aminopeptidase N, leucine aminopeptidase, and LTA4H. Ubenimex has been approved in Japan since 1987 and marketed by Nippon-Kayaku with the trade name Bestatin™ for use as an adjunct to chemotherapy in acute non-lymphocytic leukemia. License to further develop ubenimex was recently acquired by Eiger Biopharmaceuticals, and it is currently being tested in Phase 2 clinical trials for treatment of pulmonary arterial hypertension (PAH) and lymphedema. In preclinical rodent studies, ubenimex was shown to reduce elevations in pulmonary artery pressure induced by the VEGF receptor kinase inhibitor sunitinib or the toxic alkaloid compound monocrotaline [47]. A phase 3 clinical trial of ubenimex was carried out in Japan from 1992 to 2000 in 400 patients with completely resected stage-I squamous cell lung carcinoma [48]. In this trial, placebo or 30 mg ubenimex was given orally once daily for 2 years as a post-operative treatment in the absence of other chemotherapy. Kaplan-Meyer analysis showed that 5-year survival was improved in the ubenimex treated group (71%) versus placebo (62%) and the difference was statistically significant by either log rank test (P = 0.017) or Wilcoxon test (P = 0.022). The ongoing phase 2 trials test 150 mg ubenimex given orally three times per day vs placebo over 24 weeks of treatment in patients with PAH or lymphedema. One trial, named LIBERTY, studies treatment effect in 45 adult PAH patients that fall into World Health Organization (WHO) group 1 and have disease severity consistent with WHO/New York Heart Association functional classification (NYHA-FC) II or III [49]. Clinical outcomes include a primary endpoint of pulmonary vascular resistance (PVR) as measured by right heart catheterization (RHC). An open-label extension trial is planned to assess safety over an additional 24 weeks of ubenimex treatment in PAH patients. The other trial, named ULTRA, tests treatment effect in 45 adult patients with secondary leg lymphedema with a primary endpoint of change in calf skin thickness, measured by caliper, in the most affected leg [50].

https://clinicaltrials.gov/ct2/results? term=ctx+4430 https://www.clinicaltrialsregister.eu/ctrsearch/trial/2007-004913-32/IS https://clinicaltrials.gov/ct2/results? term=JNJ-40929837 https://clinicaltrials.gov/ct2/results? term=BI+691751

[50–55]

https://clinicaltrials.gov/ct2/results? term=bestatin https://clinicaltrials.gov/ct2/results? term=Tosedostat PAH, Lymphedema Active 3 – Bestatin Ubenimex

Nippon-Kayaku, Eiger Biopharmaceuticals Chroma Therapeutics, CTI Biopharma

Phase 2 Phase 1

Acute myeloid leukemia, Myelodysplastic syndrome, Solid tumors, Advanced solid tumors, Pancreatic Cancer, Nonsmall cell lung cancer Cystic fibrosis, Acne vulgaris

Clinical Trials Registry Link Companies Alternate Name(s) Nonproprietary Name

Table 2 Overview of Clinical Trials for LTA4 Hydrolase Inhibitors.

Reported Studies

Program Status

Indications

[47–49]

Additional References

3.1. Ubenimex (Bestatin; Nippon-Kayaku, Eiger biopharmaceuticals)

68

Seminars in Immunology 33 (2017) 65–73

L. Bhatt et al.

Fig. 2. Chemical structures of selected LTA4 Hydrolase Inhibitors tested in phase 2 clinical trials.

DLT phase. In phase 1, three patients reported dose limiting toxicities: two patients from the 180 mg cohort with reversible thrombocytopenia and one patient from the 130 mg cohort with a Common Toxicity Criteria (CTC) grade 3 of ALT elevation. A dose of 130 mg was reported as the most acceptable dose (MAD) and 180 mg was reported as the MTD. The most common severe adverse event in the combined phase of the study was reduction in platelet count (CTC grades 3–5). There were 51 AML patients in this study out of which seven reached complete marrow response with <5% marrow blasts, and three achieving complete remission. Another seven reached a partial marrow response with marrow blasts between 5% and 15%. Based on the results, once daily dosing of up to 130 mg dose of tosedostat was well tolerated and had significant antileukemic activity [55]. A phase 1/2 study as a combination study of cytarabine or 5-azacitidine and tosedostat was conducted in patients with AML or high risk myelodysplastic syndrome (MDS). The Phase 1 part of the study was conducted to determine the highest tolerable dose of cytarabine that could be given with tosedostat and the highest tolerable dose of 5azacitidine that could be given with tosedostat to patients with AML or MDS. The Phase 2 part of the study was conducted to determine if tosedostat combined with cytarabine or 5-azacitidine could assist in controlling the disease. An estimated enrollment was 96 patients in this study. For both the phases of the study, tosedostat was administered as daily oral administration of 120 mg. After the first 4 weeks of therapy, a dose escalation to 180 mg was considered for patients not achieving a complete remission (CR) provided the patient had not experienced any grade >/ = 3 toxicity. In Phase 1, cytarabine was administered subcutaneously, twice daily starting at 7.5 mg and escalating to 10 mg for 10 days every 28-day cycle, whereas, 5-azacytidine was administered intravenously or subcutaneously at a starting dose of 50 mg/m2 and escalating to 75 mg/m2 for 7 days every 28-day cycle. This study is ongoing but currently not recruiting participants. A phase 1/2 study was conducted with co-administration of tosedostat and erlotinib in patients with histologically or pathologically confirmed Stage IIIB (with pleural effusion), Stage IV, or recurrent metastatic NSCLC. The primary endpoint for the Phase 1 part of the study was to evaluate the safety, tolerability and maximum tolerated dose. For the Phase 2 part of the study, the primary endpoint was to determine the objective tumor rate response of tosedostat when coadministered with erlotinib. Once daily oral doses of tosedostat for Phase 1 were 120 mg, 160 mg or 200 mg in combination with 150 mg erlotinib. Only two patients were enrolled in this study and it was therefore terminated due to poor recruitment. A Phase 1/2 study of tosedostat on top of capecitabine treatment in patients with metastatic pancreatic adenocarcinoma is currently

were thrombocytopenia, dizziness, and visual abnormalities in one patient, and anemia, blurred vision, and vomiting in a second patient at 320 mg, resulting in an inability to complete 28 days of study drug. The most commonly observed toxicities were fatigue, diarrhea, peripheral edema, nausea, dizziness, and constipation. One patient had a partial response (renal cell carcinoma) and four patients had stable disease for >6 months. Tosedostat and its active metabolite, CHR-79888, showed dose-proportional increases in plasma AUC and Cmax. The terminal half-life for tosedostat was∼1 to 3.5 h and between 6 and 11 h for CHR79888. Overall, tosedostat was well tolerated in this study and based on the results, 240 mg per day dose was recommended for a single agent therapy in solid tumors [52]. A phase 1b study was conducted to evaluate the safety and tolerability of tosedostat in combination with paclitaxel in patients with advanced or refractory tumors. An estimated 22 patients were treated for up to 18 weeks with paclitaxel (135–175 mg m−2) administered once every three weeks by infusion in combination with once daily oral administration of tosedostat (90 mg–240 mg). Blood samples were collected for PK assessment of paclitaxel, tosedostat and its metabolite, CHR-79888 on days 1, 21 and 22, with a 24 h sample taken the following day. Overall exposure of tosedostat and its metabolite increased in a dose proportional manner. Co-administration of tosedostat did not affect the PK of paclitaxel. Dose limiting toxicity (grade 3 dyspnoea) was observed in one patient taking 180 mg of tosedostat combined with 175 mg m−2 of paclitaxel. No formal MTDs were reached in this study even though a high number of paclitaxel infusion reactions were noted leading to interruption of tosedostat dosing for 5 days around subsequent paclitaxel infusion. Most frequently observed adverse events in this study were alopecia, fatigue, peripheral sensory neuropathy, paclitaxel hypersensitivity and rash. A serious adverse event (SAE) resulting in the death of one patient due to eosinophilic myocarditis, possibly related to study medication. Because of this SAE, the steering committee decided to terminate the study [54]. A combined phase 1/2 study was conducted in elderly and/or relapsing patients with acute myeloid leukemia (AML) or myelodysplastic syndrome to evaluate the safety, tolerability and anti-disease activity of tosedostat. The Phase 1 part of the study enrolled 16 patients and the primary endpoints were safety, tolerability, DLT and MTD. Daily oral doses of 60 mg, 90 mg, 130 mg or 180 mg tosedostat were administered to determine the dose for longer treatment. The Phase 2 part of the study enrolled 41 patients and the primary endpoint was to evaluate the antileukemic effect of tosedostat at a once daily dose of 130 mg as recommended from Phase 1. The total duration of both the phases of the study was 12 weeks which included the first 4 weeks as dose finding or 69

Seminars in Immunology 33 (2017) 65–73

L. Bhatt et al.

inhibit ex vivo stimulated production of LTB4. Furthermore, in a food effect sub-study, there was no change in drug exposure (AUC) when acebilustat was administered after consumption of a high fat meal compared to fasting. A Phase 1 drug–drug interaction study in 20 healthy volunteers tested CYP3A4 induction as determined by the effect of steady state acebilustat exposure on the pharmacokinetics of orally administered midazolam, a sensitive substrate for CYP3A4 [60]. This study showed no change in the plasma pharmacokinetics of either midazolam or its primary CYP3A4 metabolite, 1-OH-midazolam. Therefore, acebilustat is not an inducer of CYP3A4. This is important because a number of CF drugs, notably the recently approved drugs Kalydeco® and Orkambi® which modulate the CF transmembrane conductance receptor (CFTR), are substrates for CYP3A4. A Phase 1 study was conducted to assess the ability of acebilustat to reduce markers of inflammation in the blood and sputum of 17 adult CF patients [61]. Patients were treated with placebo or 50 or 100 mg acebilustat once daily for 15 days and the following biomarkers were evaluated: serum C-reactive protein (CRP), circulating neutrophils, sputum total white blood cells and neutrophils, sputum neutrophil elastase, sputum DNA, and sputum microbiology. Treatment with acebilustat resulted in favorable trends in all biomarkers of inflammation, including a 65% reduction in sputum neutrophils compared to baseline in the group treated with 100 mg acebilustat and a 58% reduction in sputum neutrophil elastase compared to placebo (P < 0.05, one-sided ttest) for the overall acebilustat treated group (50 and 100 mg acebilustat). Importantly, no change was observed in circulating neutrophil counts or in sputum bacterial load, suggesting a lack of immunosuppressive effect. Based on the results of the Phase 1 studies, the 50 mg and 100 mg once daily doses of acebilustat were selected for further study. A Phase 2 study (named EMPIRE-CF) is currently in progress to study the effect of 48 weeks acebilustat treatment (50 mg or 100 mg once daily) on lung function parameters in 195 adult CF patients [62]. The primary efficacy endpoint for this study is absolute change from baseline in percent predicted forced expiratory volume in 1 s (ppFEV1) versus placebo. Changes in rate of acute pulmonary exacerbation will also be studied as will changes in biomarkers of inflammation, including sputum neutrophil elastase, sputum DNA, sputum microbiology and serum CRP. A Phase 2 trial tested the effect of once daily oral acebilustat treatment on lesion counts in 124 patients with moderately severe facial acne vulgaris. [63]. In this study, acne patients were treated for 12 weeks 100 mg acebilustat or placebo in a 2:1 randomization. This trial has been completed but is not yet reported.

ongoing. Enrollment is projected to be 42 patients. The primary endpoint in the Phase 1 part of the study is to determine dose limiting toxicity and to recommend dose levels for Phase 2. The primary outcome of the Phase 2 part of the study is to determine progression-free survival rate (PFS). Tosedostat is administered as once daily oral dose for days 1–21 of each 21 day cycle and capecitabine is administered as twice daily oral dose on days 1–14 of each 21 day cycle. A Phase 2 study (named OPAL) was conducted in elderly patients with refractory or relapsed AML to evaluate the safety and efficacy of tosedostat. Estimated enrollment was 70 patients for part A of the study and 130 patients for part B. Thirty-eight patients were randomized and received daily oral administration of 120 mg tosedostat for 6 months. Another group of 38 patients were randomized and 35 received daily oral administration of 240 mg tosedostat for the first 2 months as an induction dose, followed by 120 mg dose for 4 months as a maintenance dose. The most common adverse events were febrile neutropenia, thrombocytopenia, fatigue, dyspnoea and pneumonia. Treatment related fatal adverse events were acute hepatitis, respiratory failure, pneumonia, atrial fibrillation, and left ventricular dysfunction. It was concluded that tosedostat had activity at both dose schedules in older patients with relapsed or refractory AML [56]. A Phase 2 study (named TOPAZ) was conducted to evaluate the long-term efficacy and safety profile of tosedostat in elderly patients suffering from refractory or relapsed AML [57]. This was an extension protocol to the OPAL study. The recruitment status for this study is unknown. A Phase 2 study of tosedostat in combination with either cytarabine or decitabine was conducted in patients with newly diagnosed AML or high-risk MDS [58]. Estimated enrollment was 34 patients in this study. Tosedostat was administered as a once daily oral dose for 35 days in combination with either cytarabine or decitabin administered intravenously (IV) for the first five days. The primary outcome of the study was determination of 4-month survival and complete remission (CR) rates of tosedostat in combination with either cytarabine or decitabine in untreated AMl or MDS. The study has been completed but the results have not been published. A Phase 2 study is currently ongoing to evaluate the safety and efficacy of tosedostat in adult patients with MDS who have failed prior hypomethylating agent-based therapy [59]. Estimated enrollment in this study is 80 patients. Arm A of the study is defined as patients with very low and intermediate risk MDS and arm B is defined as patients with high and very high risk MDS. A dose of 120 mg tosedostat is administered as once daily oral dose for each 28-day cycle. Patients will be assessed for disease response, on average, every two cycles as defined in the protocol. If the patients do not respond after two cycles, then tosedostat may be combined with azacitidine 75 mg/m2 SC or IV for 5 days. The primary endpoint for patients in arm A is transfusion independence and for arm B is overall survival. This study is actively recruiting participants.

3.4. DG-051 (deCode) DG-051 originated at deCode as the result of a fragment-based design program [64,65]. DeCode had previously identified LTA4H as a genetic risk factor for myocardial infarction (MI)[65]. DG-051 was found to be a potent inhibitor of LTA4H in vitro (45 nM) and in human whole blood (37 nM). It exhibited less potency against the aminopeptidase function of LTA4H (72 nM) and was otherwise highly selective for LTA4H versus other aminopeptidases. Information on the clinical trials for DG-051 is limited, as they do not appear in standard trial registries and the studies were not published. However, in company press releases, DG-051 is reported to have shown reductions in LTB4 of up to 70% after 7 days of once-daily treatment in healthy volunteers and dose-dependent reductions in blood LTB4 levels in patients with history of MI or coronary artery disease. Ultimately a Phase 2 trial was slated to test its ability to prevent MI in 400 patients but no further listings or reports for this study were found. DeCode was acquired by Amgen in 2012, and the status of DG-051 remains unknown.

3.3. Acebilustat (CTX-4430; Celtaxsys) To our knowledge, acebilustat is the only selective LTA4H inhibitor currently in clinical development. It is a synthetic small molecule that originated at Berlex and was subsequently acquired by Celtaxsys. Acebilustat is highly selective for LTA4H versus other metalloenzymes, shows 2-fold functional selectivity for LTA4H epoxide hydrolase (12 nM) versus LTA4H aminopeptidase (27 nM), and has good potency in human whole blood (64 nM). Three Phase 1 trials have been completed and a Phase 2 trial is currently ongoing in patients with CF. A Phase 1 single and multiple ascending dose trial was conducted in 96 healthy volunteers. This study demonstrated that blood pharmacokinetics were consistent with a once-daily dosing schedule, and doses of 50 mg and higher yielded plasma levels well-above the whole blood LTB4 IC50 [60]. An oral dose of 100 mg once daily produced a near maximal pharmacodynamic response as measured by its ability to 70

Seminars in Immunology 33 (2017) 65–73

L. Bhatt et al.

JNJ-40929837 is an LTA4H-selective synthetic small molecule with a potency for LTA4H inhibition of 1 nM [67]. In a Phase 1 study in healthy volunteers, it showed 95% inhibition of ex vivo stimulated LTB4 production in blood after administration of single or multiple oral doses of 100 mg or higher [68]. A Phase 2a study was conducted to assess the effects of JNJ40929837 at a dose level of 100 mg/day (either 100 mg QD or 50 mg BID) on airway hyperresponsiveness in 22 patients with mild atopic asthma following bronchial allergen challenge (BAC). While treatment of patients with JNJ-40929837 substantially reduced blood and sputum LTB4 levels following BAC, there was no change in either late or early airway hyperresponsiveness. Of particular note, the authors reported an increase in urinary LTE4 levels in the patients treated with JNJ40929837 prior to BAC, although the LTE4 level did not change further upon BAC. This increase in LTE4 was attributed to a potential shunting of excess LTA4 substrate to the LTC4 pathway due to blockade of its conversion to LTB4. In contrast, the related LTA4H inhibitor compound, JNJ-26993135, had previously shown favorable treatment effects in rodent models of allergic airway inflammation and hyperresponsiveness without evidence of shunting to the LTC4 pathway [69,70]. Whether this difference in outcomes arises from a difference in species or a difference in disease models remains unclear. Although JNJ-40929837 was unsuccessful in the human BAC model, the authors do not rule out potential utility in other neutrophil driven airway diseases such as COPD and CF. However, the program appears to have been halted or placed on hold, as no further clinical studies have been reported or listed in trial registries. It is possible that the observation of testicular toxicity in rats, reportedly due to a ratspecific metabolite, along with the negative result in the Phase 2a BAC study may have dampened enthusiasm for the program within the company [71].

male volunteers. This was a two-part study in which the first part assessed single rising oral solutions of the drug and the second part compared relative bioavailability of 10 mg oral tablets versus 10 mg oral solutions. Oral solutions of 0.5, 1.5, 5, 10, 15, 30, 60 and 90 mg were assessed in the first part to determine safety, tolerability PK and PD of single rising doses. An episode of tachycardia was observed in the highest dose studied (90 mg). Comparison of bioavailability for a subset of subjects considered extensive CYP2D6 metabolizers versus another subset of subjects also considered extensive metabolizers was conducted for 10 mg oral dosing solutions verses 10 mg tablets, as well as a cross-over where bioavailability for 10 mg tablets were compared between extensive and poor metabolizers. Equivalence was confirmed at the 90% confidence interval. An additional Phase 1 study with 18 male volunteers was initiated to study PK, PD, safety and tolerability of BI 69751 for 14 days to support further development as a clinical candidate. Emphasis was placed on detecting potential effect of the drug on heart rate. Criteria for exclusion included any finding in the medical examination, including BP (blood pressure), PR (pulse rate) or ECG (electro cardiogram), deviating from normal and judged as clinically relevant by the investigator and a pulse rate outside 45–80 bpm (beats per minutes) or repeated measurement of systolic blood pressure greater than 140 mmHg or diastolic blood pressure greater than 90 mm Hg. This study was randomized and double blinded with parallel assignment with a primary outcome of percent of subjects with drug related AEs and secondary outcomes including PK and PD. Only two dose levels were studied before premature termination, 0.5 mg per day for 14 days and 3 mg a day for 14 days. There were no cardiac AEs in the volunteers studied before termination. Recruitment issues were noted in the trial. The sponsor has since discontinued the development of BI 691751. It is speculated that the unusually long drug half-life in conjunction with a restrictive clinical cardiac profile for inclusion in clinical trials were factors in the decision to terminate further development.

3.6. BI 691751 (Boehringer Ingelheim)

4. Conclusion

BI 691751 is an oral LTA4H inhibitor of unknown structure. It was studied as a potential drug to inhibit growth and prevent rupture of atherosclerotic plaques, thereby reducing occurrence of major cardiovascular events in patients with diagnosed atherosclerotic disease. The clinical program for BI 691751 consisted of five phase 1 trials [72]. A Phase 1 study was conducted in 20 healthy male volunteers to assess the bioavailability of a single 10 mg oral dose of BI 691751 alone or with multiple doses of itraconazole (a potential inhibitor of CYP3A4). Safety and tolerability were also assessed. The study had an open-label, randomized, two period, two sequence, cross-over design with a washout period of at least seven weeks. Primary endpoints included AUC as well as Cmax for both arms in plasma and whole blood through 31 days post-dose. The geometric mean (geometric coefficient of variation) for AUC of itraconazole and BI 691751 combined to BI 691751 alone treatment (in whole blood) indicated noninferiority/ equivalence at the 90% confidence interval. A separate Phase 1 study to assess bioavailability with and without food in healthy male volunteers was withdrawn prior to enrollment. A Phase 1 study was conducted to assess safety, tolerability and PK for single rising oral doses of BI 691751 in 64 healthy Japanese and Chinese males. The study was randomized, double-blinded and placebo controlled. Doses studied were 5, 10, 30 and 60 mg. The primary outcome was drug related AE’s and the secondary outcomes included Cmax, Tmax, AUC and T1/2. No serious adverse events were reported for any of the participants and PK parameters were recorded. Interestingly, the half-life for the drug was unusually long. In the 60 mg cohort of 12 participants, plasma half-life averaged 81.3 h and in blood the half-life was determined on average as 377 h. An 81 patient Phase 1 study was conducted to investigate safety, tolerability, PK and PD of single rising doses of BI 691751 in healthy

Much effort has been expended toward development of safe and effective LTB4 pathway targeting drugs, both BLT antagonists and LTA4H inhibitors. Based on the lack of treatment effects in Phase 2 studies and apparent lack of active clinical development, the future of BLT receptor drug development is presently in question. A third wave of effort could be coming, as newer preclinical compounds more selective for BLT1 versus BLT2 are developed. LSN2792613 is one example of a third wave compound that demonstrates functional selectivity for BLT1 and shows promising reduction in infarct size in a preclinical ischemiareperfusion injury model [73]. The current focus of LTB4 pathway drug development has shifted to LTA4H inhibitors, with at least 3 programs active in clinical trials. Among the current generation of LTA4H inhibitors, interpretation of the clinical outcomes for ubenimex and tosedostat in the context of LTB4 pathway inhibition will be complicated by their off-target aminopeptidase inhibition. In the case of ubenimex, functional selectivity for inhibiting the aminopeptidase function of LTA4H vs its epoxide hydrolase (LTB4 producing) function is a further complication. The only selective LTA4H inhibitor currently in development is acebilustat, which has a 2-fold preference for inhibiting epoxide hydrolase function versus aminopeptidase function. Acebilustat has already shown promising signs of potential treatment effect via reductions in lung and systemic biomarkers in patients with cystic fibrosis [61]. Together, these drugs present the greatest hope for near-term success in demonstrating therapeutic effect for LTB4 pathway targeting drugs in human disease. Beyond the current wave of LTA4H inhibitors are an emerging wave of compounds targeting either greater functional specificity for inhibition of the epoxide hydrolase activity of LTA4H or augmentation of the aminopeptidase activity of LTA4H [13,74]. Matching treatment approach with disease indication is a significant

3.5. JNJ-40929837 (Janssen)

71

Seminars in Immunology 33 (2017) 65–73

L. Bhatt et al.

(2002) 963. [7] P. Devchand, et al., The PPAR-alpha-leukotriene B4 pathway to inflammation control, Nature 384 (1996) 39–43. [8] J. Fiedler, et al., Effect of peroxisome proliferator-activated receptor alpha activation on leukotriene B4 metabolism in isolated rat hepatocytes, J. Pharmacol. Exp. Ther. 299 (2001) 691–697. [9] L. Orning, et al., Leukotriene A4 hydrolase, J. Biol. Chem. 266 (1990) 1375–1378. [10] L. Orning, J.K. Gierse, F.A. Fitzpatrick, The bifunctional enzyme leukotriene-A4 hydrolase is an arginine aminopeptidase of high efficiency and specificity, J. Biol. Chem. 269 (1994) 11269–11273. [11] A. Byzia, et al., A remarkable activity of human leukotriene A4 hydrolase (LTA4H) toward unnatural amino acids, Amino Acids 46 (2014) 1313–1320. [12] R.J. Snelgrove, et al., A critical role for LTA4H in limiting chronic pulmonary neutrophil inflammation, Science 330 (2010) 90–94. [13] A. Stsiapanava, et al., Binding of pro-gly-pro at the active site of leukotriene A4 hydrolase/aminopeptidase and development of an epoxide hydrolase selective inhibitor, Proc. Nat. Acad. Sci. 111 (2014) 4227–4232. [14] A. Hicks, S.P. Monkarsh, A.F. Hoffman, R. Goodnow, Leukotriene B4 receptor antagonists as therapeutics for inflammatory disease: preclinical and clinical developments, Exp. Opin. Invest. Drugs 16 (2007) 1909–1920. [15] A. Fourie, Modulation of inflammatory disease by inhibitors of leukotriene A4 hydrolase, Curr. Opin. Invest. Drug 10 (2009) 1173–1182. [16] B. Caliskan, E. Banoglu, Overview of recent drug discovery approaches for new generation leukotriene A4 hydrolase inhibitors, Expert Opin. Drug Discov. 8 (2013) 49–63. [17] T. Adrian, et al., The role of PPARγ receptors and leukotriene B4 receptors in mediating the effects of LY293111 in pancreatic cancer, PPAR Res. 2008 (2008) 1–9. [18] W.-G. Tong, et al., Leukotriene B4 receptor antagonist LY293111 inhibits proliferation and induces apoptosis in human pancreatic cancer cells, Clin. Can. Res. 8 (2002) 3232–3242. [19] R. Hennig, et al., Effect of LY293111 in combination with gemcitabine in colonic cancer, Cancer Lett. 210 (2005) 41–46. [20] W. Zhang, T. McQueen, W. Schober, G. Rassidakis, M. Andreeff, M. Konopleva, Leukotriene B4 receptor inhibitor LY293111 induces cell cycle arrest and apoptosis in human anaplastic large-cell lymphoma cells via JNK phosphorylation, Leukemia 19 (2005) 1977–1984. [21] G.K. Schwartz, et al., Phase 1 and pharmacokinetic study of LY293111, an orally bioavailable LTB4 receptor antagonist, in patients with advanced solid tumors, J. Clin. Oncol. 23 (2005) 5365–5373. [22] M.W. Saif, et al., Randomized double-blind phase II trial comparing gemcitabine plus LY293111 versus gemcitabine plus placebo in advanced adenocarbinoma of the pancrease, Cancer J. 15 (2009) 339–343. [23] P.A. Janne, L. Paz-Ares, Y. Oh, C. Eschbach, V. Hirsh, N. Enas, L. Brail, J. von Pawel, Randomized double-blind, phase II trial comparing gemcitabine-cisplatin plus the LTB4 antagonist LY293111 versus gemcitabine-cisplatin plus placebo in first-line non-small-cell lung cancer, J. Thorac. Oncol. 9 (2014) 126–131. [24] F.W. Birke, et al., In vitro and in vivo pharmacological characterization of BIIL 284, a novel and potent leukotriene B4 receptor antagonist, J. Pharmacol. Exp. Ther. 297 (2001) 458–466. [25] ClinicalTrials. gov, Listings for Amebulant. U.S. National Institutes of Health, (2017) https://clinicaltrials.gov/ct2/results?term=amelubant&Search=Search. [26] Data sheet, Clinical Trial Result –Amelubant, Boehringer Ingelheim, 2017, http:// www.trials.boehringer-ingelheim.com/trial_results/clinical_trials_overview/ clinical_trial_result.c=n.i=9.html. [27] M.W. Konstan, et al., A random double blind, placebo controlled phase 2 trial of BIIL 284 BS (an LTB4 receptor antagonist) for the treatment of lung disease in children and adults with cystic fibrosis, J. Cyst. Fibros. 13 (2014) 148–155. [28] Trial Synopsis 543.1: A double-blind, randomised, placebo-controlled, parallelgroup study to investigate the safety, tolerability, biological effects and preliminary pharmacokinetics of increasing single oral doses of BIIL 284 BS (dose range: 0.025 mg–75 mg PSE solution, 25 mg, 75 mg, 250 mg and 750 mg WIF tablets) in healthy male volunteers as well as food effects at 75 mg (WIF tablet), Boehringer Ingelheim, 2017, http://www.trials.boehringer-ingelheim.com/public/trial_results_ documents/543/543.1_U99-1320.pdf. [29] Trial Synopsis 543.3: Randomised 3-way cross-over phase I study to investigate the relative bioavailability of BIIL 284 BS 75 mg tablet C and tablet D in comparison to WIF tablet in healthy volunteers, Boehringer Ingelheim, 2017, http://www.trials. boehringer-ingelheim.com/public/trial_results_documents/543/543.3_U01-1121. pdf. [30] Trial Synopsis 543.4: A double-blind, randomised, placebo-controlled, parallelgroup study to investigate the safety, tolerability, biological effects and preliminary pharmacokinetics of increasing repeated oral doses (9 days dosing) of BIIL 284 BS (doses: 25 mg, 150 mg, 250 mg as WIF tablets) in healthy male volunteers. Boehringer Ingelheim. https://trials.boehringer-ingelheim.com/public/trial_ results_documents/543/543.4_U00-1838.pdf. [31] Trial Synopsis 543.5: Randomised 3-way cross-over phase I study to investigate the effect of different food compositions (low fat and high fat meal) on bioavailability of BIIL 284 BS 75 mg tablet in healthy male volunteers. Boehringer Ingelheim. http://www.trials.boehringer-ingelheim.com/public/trial_results_documents/543/ 543.5_U01-1138.pdf. [32] Trial Synopsis 543.16: Investigation of Metabolism and Pharmacokinetics of [14C] BIIL 284 BS After Administration of a Single Oral Dose of 25 mg [14C] BIIL 284 BS in 6 Healthy Volunteers. Boehringer Ingelheim. http://www.trials.boehringeringelheim.com/public/trial_results_documents/543/543.16_U01-2020.pdf. [33] Trial Synopsis 543.26: The Pharmacokinetics, Safety and Tolerability of Single Dose

challenge for any targeted therapeutic, and especially so for inflammatory diseases where many signals and systems may interact to promote the disease process. In such cases, finding and targeting the pathway that has the highest impact on disease outcomes can be a trial and error process. The earliest drug development efforts toward LTB4 pathway targeting drugs were centered upon respiratory disease affecting broad populations, asthma and COPD, or disease with marked systemic inflammation, rheumatoid arthritis. More recent efforts have been directed toward diseases where the pathway can be better linked to human genetics (e.g. myocardial infarction) or disease process (e.g. PAH). While the question of therapeutic effect currently remains unanswered for these newer indications, the answers are coming soon. Furthermore, the body of evidence continues to mount for the potential relevance of LTB4 signaling to human cardiovascular and metabolic diseases [73–80]. As the lone active program targeting the LTB4 pathway in cancer indications, the progress of tosedostat will be important to monitor. Likewise, the outcomes of ongoing trials of ubenimex in pulmonary arterial hypertension and acebilustat in cystic fibrosis could provide significant new momentum in LTB4 pathway targeting. Irrespective of past failures, the LTB4 pathway seems destined to remain a pathway of high interest for therapeutic drug development, especially in new therapeutic indications supported by more definitive mechanistic biology. Emerging details on the LTB4 pathway, however, raise the following question: Is the LTB4 pathway truly a complex self-regulating system that promotes inflammation via LTB4 production and BLT signaling while at the same time dampening inflammation by PPARα activation and PGP elimination? If so, targeting this pathway is becoming only more difficult though, perhaps, better understood in ways that enable more finely targeted approaches in the future. What we do know is this: in cases of infection or inflammation, LTB4 is often the first responder and, at least initially, promotes its own production in a rapid amplification process [81]. In the context of its normal function, it is not surprising that the LTB4 pathway may self-regulate. After all, it is designed to respond and resolve rapidly, allowing other downstream systems such as cytokines and chemokines to do their work [82]. How this plays into disease states is unclear, but it is clear the LTB4 pathway is chronically overactive in numerous disease states when its signal should have long-since been extinguished. Perhaps disease conditions related to the LTB4 pathway arise from dysfunction of its self-regulation. Indeed, addition of resolving mediators has been shown to directly block (Resolvin E1) or indirectly counteract (Lipoxin A4) the LTB4BLT1 signaling pathway [83–85]. Engagement of such resolution mechanisms offers another potential approach to modulating the LTB4 pathway for future drug development. The final answers to role of the LTB4 pathway in human disease and to whether intervention in the LTB4 pathway can yield a significant therapeutic effect in human disease await the outcomes of ongoing clinical trials and future efforts to refine the next generation of even more specific pathway modulating chemical probes and match the therapeutic approach with the most relevant disease indication. References [1] T. Yokomizo, Leukotriene B4 receptors: novel roles in immunological regulations, Adv. Enzyme Reg. 51 (2001) 59–64. [2] T. Okuno, et al., 12(S)-hydroxyheptadeca-5Z, 8E, 10E-trienoic acid is a natural ligand for leukotriene B4 receptor 2, J. Exp. Med. 205 (2008) 759–766. [3] Y. Iizuku, et al., Protective role of the leukotriene B4 receptor BLT2 in murine inflammatory colitis, FASEB J. 24 (2010) 4678–4690. [4] Y. Matsunaga, et al., Leukotriene B4 receptor BLT2 negatively regulates allergic airway eosinophilia, FASEB J. 27 (2013) 3306–3314. [5] M.S. Marshall, B. Diaz, J. Brozinick, et al., LY293111 inhibits tumor cell growth cell growth in vitro through an apparent PPARgamma agonist activity, Proceedings 93rd Annual Meeting of American Association for Cancer Research (AACR ‘02) 43 (2002) 957. [6] M.S. Marshall, B. Diaz, J. Copp, et al., The LTB4 receptor antagonist, LY2931111 inhibits tumor cell growth in vitro independent of the LTB4 receptor, Proceedings 93rd Annual Meeting of American Association for Cancer Research (AACR ‘02) 43

72

Seminars in Immunology 33 (2017) 65–73

L. Bhatt et al.

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42] [43]

[44]

[45] [46]

[47] [48]

[49]

[50]

[51]

[52]

[53] [54]

BIIL 284 BS in Patients with Hepatic Impairment in Comparison to Healthy Volunteers (An Open Label, Matched Pair, One Center Study). Boehringer Ingelheim. http://www.trials.boehringer-ingelheim.com/public/trial_results_ documents/543/543.26_U02-3050.pdf. Trial Synopsis 543.28: Randomised 4-way cross-over phase I study to investigate the relative bioavailability of BIIL 284 BS 75 mg boli in comparison to tablet C in fasted condition and after ingestion of a standardised meal in healthy volunteers. Boehringer Ingelheim. https://trials.boehringer-ingelheim.com/public/trial_ results_documents/543/543.28_U01-1646.pdf. Trial Synopsis 543.31: Randomised, open-label, two-way crossover study in male healthy volunteers to investigate the relative bioavailability of BIIL 284 BS 5 mg Tablet FF in comparison to Tablet C after ingestion of a standardised meal. Boehringer Ingelheim. http://www.trials.boehringer-ingelheim.com/public/trial_ results_documents/543/543.31_U02-1540.pdf. Trial Synopsis 543.7: The Effects of Multiple Doses of BIIL 284 BS on the Pharmacokinetics of a Single Dose of Theophylline in Healthy Male Volunteers (A Randomized, Double-Blind, Placebo Controlled, Two-period, Two-way Crossover Study). Boehringer Ingelheim. http://www.trials.boehringer-ingelheim.com/ public/trial_results_documents/543/543.7_U02-1009.pdf. Trial Synopsis 543.24: The Effect of Multiple Doses of BIIL 284 BS on the Pharmacokinetics of a Single Dose of Prednisone in Healthy Male Subjects (A randomized, double-blind, placebo-controlled, two period, two-way cross-over study). Boehringer Ingelheim. http://www.trials.boehringer-ingelheim.com/ public/trial_results_documents/543/543.24_U01-3411.pdf. Trial Synopsis 543.36: A randomized, double-blind within dose, placebo-controlled study to investigate the safety, tolerability and pharmacokinetics of increasing single oral doses of BIIL 284 BS in adult and pediatric cystic fibrosis patients. Boehringer Ingelheim. https://trials.boehringer-ingelheim.com/public/trial_ results_documents/543/543.36_U03-3049.pdf. Trial Synopsis 543.37: A randomized, double-blind within dose, placebo-controlled study to investigate the safety, tolerability and pharmacokinetics of repeated oral doses (15-day dosing) of BIIL 284 BS in adult (150 mg) and pediatric (75 mg) cystic fibrosis patients. Boehringer Ingelheim. http://www.trials.boehringer-ingelheim. com/public/trial_results_documents/543/543.37_U03-3277.pdf. Trial Synopsis 543.10: Effect of 14-Day Treatment with BIIL 284 BS on Patients with COPD (Double-Blind, Placebo-Controlled, Randomised, Parallel Group Study). Boehringer Ingelheim. http://www.trials.boehringer-ingelheim.com/public/trial_ results_documents/543/543.10_U01-1368.pdf. Trial Synopsis 543.14: A double-blind, randomized, three parallel group placebocontrolled study to investigate pharmacokinetics, effect on expression of CD11b/ CD18 (Mac-1), as well as safety and efficacy of two oral doses of BIIL 284 BS (dosage: 25 mg daily, 150 mg daily) in patients with rheumatoid arthritis over two weeks. Boehringer Ingelheim. http://www.trials.boehringer-ingelheim.com/ public/trial_results_documents/543/543.14_U01-1167.pdf. F. Diaz-Gonzalez, et al., Clinical trial of a leukotriene B4 receptor antagonist, BIIL 284, in patients with rheumatoid arthritis, Ann. Rheum. Dis. 66 (2007) 628–632. Trial Synopsis 543.17: Effect of 12-week treatment of 5, 25 or 75 mg BIIL 284 BS on exercise endurance in patients with chronic obstructive pulmonary disease (doubleblind, double dummy, placebo-controlled, randomized, parallel group, dose ranging study). Boehringer Ingelheim. http://www.trials.boehringer-ingelheim.com/ public/trial_results_documents/543/543.17_U03-1179.pdf. Trial Synopsis 543.11: The effect BIIL 284 BS (14 day treatment) on inducedsputum variables in patients with bronchial asthma (a double-blind. randomized, placebo-controlled parallel study). Boehringer Ingelheim. http://www.trials. boehringer-ingelheim.com/public/trial_results_documents/543/543.11_U01-3012. pdf. G. Döring, et al., BIIL 284 reduces neutrophil numbers but increases P. aeruginosa bacteremia and inflammation in mouse lungs, J. Cyst. Fibros. 13 (2014) 156–163. L. Gronke, et al., Effect of oral leukotriene B4 receptor antagonist LTB019 on inflammatory sputum markers in patients with chronic obstructive pulmonary disease, Pulm. Pharmacol. Ther. 21 (2008) 409–417. W. Tian, et al., Blocking macrophage leukotriene B4 prevents endothelial injury and reverses pulmonary hypertension, Sci. Transl. Med. 5 (2013). Y. Ichinose, et al., Randomized double-blind placebo-controlled trial of bestatin in patients with resected stage 1 squamous-cell lung carcinoma, J. Nat. Can. Inst. 95 (2003) 605–610. A. Phase 2, Randomized, Double-BLInd, Placebo- Controlled Study of UBEnimex in Patients With Pulmonary ARTerial HYpertension (WHO Group 1) (LIBERTY). U.S. National Institutes of Health. https://clinicaltrials.gov/ct2/show/NCT02664558. Ubenimex in Adult Patients With Secondary Lymphedema of The Lower Limb: a Phase 2, RAndomized, Double-blind, Placebo-controlled Study of Efficacy, Safety, and Pharmacokinetics (ULTRA). U.S. National Institutes of Health. https:// clinicaltrials.gov/ct2/show/NCT02700529. D. Krige, et al., CHR-2797: an antiproliferative aminopeptidase inhibitor that leads to amino acid deprivation in human leukemic cells, Cancer Res. 68 (2008) 6669–6679. A.H.M. Reid, A. Protheroe, G. Attard, et al., A first-in-man phase 1 and pharmacokinetic study on CHR-2797 (Tosedostat), an inhibitor of M1 aminopeptidases, in patients with advanced solid tumors, Clin. Can. Res. 15 (2009) 4978–4985. ClinicalTrials.gov Search Results for Tosedostat. U.S. National Institutes of Health. https://clinicaltrials.gov/ct2/results?term=tosedostat&Search=Search. C. Herpen, et al., A phase 1b dose-escalation study to evaluate safety and tolerability of the addition of the aminopeptidase inhibitor tosedostat (CHR-2797) to

[55]

[56]

[57]

[58]

[59]

[60] [61] [62]

[63]

[64] [65]

[66]

[67] [68]

[69]

[70]

[71] [72] [73]

[74]

[75] [76]

[77] [78]

[79] [80] [81] [82] [83] [84] [85]

73

paclitaxel in patients with advanced solid tumors, Br. J. Cancer 103 (2010) 1362–1368. B. Lowenberg, et al., Phase I/II clinical study of tosedostat, an inhibitor of aminopeptidases, in patients with acute myeloid leukemia and myedodysplasia, J. Clin. Oncol. 28 (2010) 4333–4338. J. Cortes, et al., Two dosing regimens of tosedostat in elderly patients with relapsed or refractory acute myeloid leukaemia (OPAL): a randomized open-label phase 2 study, Lancet 14 (2013) 354–362. The TOPAZ Study, A Long-Term Extension Study in Elderly Subjects With Relapsed/ Refractory Acute Myeloid Leukemia to Allow Continued Therapy With Tosedostat, (2017) https://clinicaltrials.gov/ct2/show/NCT01180426. A Phase II Study of Tosedostat in Combination With Either Cytarabine or Decitabine in Newly Diagnosed AML or High-Risk MDS, (2017) https://clinicaltrials.gov/ct2/ show/NCT01567059. Phase II Clinical Study of the Clinical Efficacy and Safety of Tosedostat in Atients With Myelodysplastic Syndromes (MDS) After Failure of Hypomethylating Agent‐Based Therapy, (2017) https://clinicaltrials.gov/ct2/show/NCT02452346. J.S. Elborn, et al., Phase 1 studies of acebilustat: pharmacokinetic, pharmacodynamics, food effect, and CYP3A induction, Clin. Trans. Sci. Early View (2016) 1–8. J.S. Elborn, et al., Phase 1 studies of acebilustat: biomarker response and safety in patients with cystic fibrosis, Clin. Trans. Sci. Early View (2016) 1–7. A Phase 2, Multicenter, Randomized, Double-blind, Placebo-controlled, Parallelgroup Study to Evaluate the Efficacy, Safety, and Tolerability of CTX-4430 Administered Orally Once-Daily for 48 Weeks in Adult Patients With Cystic Fibrosis, (2017) https://clinicaltrials.gov/ct2/show/NCT02443688. A Multi-centre, Double-blind, Randomized, Parallel Group, Placebo Controlled Efficacy and Safety Study of Oral CTX-4430 for the Treatment of Moderate to Severe Facial Acne Vulgaris, (2017) https://clinicaltrials.gov/ct2/show/NCT02385760. D. Davies, et al., Discovery of leukotriene A4 hydrolase inhibitors using metabolomics biased fragment crystallography, J. Med. Chem. 52 (2009) 4694–4715. V. Sandanayaka, et al., Discovery of 4-[(2S)-2-{[4-(4-chlorophenoxy)phenoxy]methyl}-1-pyrrolidinyl]butanoic acid (DG-051) as a novel leukotriene A4 hydrolase inhibitor of leukotriene B4 biosynthesis, J. Med. Chem. 53 (2010) 575–585. A. Helgadottir, et al., A variant of the gene encoding leukotriene A4 hydrolase confers ethnicity-specific risk of myocardial infarction, Nat. Genet. 38 (2006) 68–74. V. Tanis, et al., Azabenzthiazole inhibitors of leukotriene A4 hydrolase, Bioorg. Med. Chem. Let. 22 (2012) 7504–7511. W. Barchuk, et al., Effects of JNJ-40929837, a leukotriene A4 hydrolase inhibitor, in a bronchial allergen challenge model of asthma, Pulm. Pharmacol. Ther. 29 (2014) 15–23. N.L. Rao, et al., Anti-inflammatory activity of a potent, selective leukotriene A4 hydrolase inhibitor in comparison with the 5-lipoxsygenase inhibitor zileuton, J. Pharmacol. Exp. Ther. 321 (2007) 1154–1160. N.L. Rao, et al., Leukotriene A4 hydrolase inhibition attenuates allergic airway inflammation and hyperreponsiveness, Am. J. Respir. Crit. Care Med. 181 (2010) 899–907. P. Ward, Testicular distribution and toxicity of a novel LTA4H inhibitor in rats, Toxicol. Appl. Pharmacol. 278 (2014) 26–30. ClinicalTrial. gov, Search Results for BI 69, U.S. National Institutes of Health, 1751, https://clinicaltrials.gov/ct2/results?term=BI+691751. V. de Hoog, et al., BLT1 antagonist LSN2792613 reduces infarct size in a mouse model of myocardial ischaemia-reperfusion injury, Cardiovasc. Res. 108 (2015) 367–376. E. De Oliveira, et al., Effect of the leukotriene A4 hydrolase aminopeptidase augmentor 4-meth-oxydiphenylmethane in a pre-clinical model of pulmonary emphysema, Bioorg. Med. Chem. Lett. 21 (2011) 6746–6750. R. Aiello, et al., Leukotriene B4 receptor antagonism reduces monocytic foam cells in mice, Arterioscler. Thromb. Vasc. Biol. 22 (2002) 443–449. E. Heller, et al., Inhibition of atherogenesis in BLT1-deficient mice reveals a role for LTB4 and BLT1 in smooth muscle cell recruitment, Circulation 112 (2005) 578–586. N. Ahluwalia, et al., Inhibited aortic aneurysm formation in BLT1-deficient mice, J. Immunol. 179 (2007) 691–697. M. Spite, et al., Deficiency of the leukotriene B4 receptor, BLT-1, protects against systemic insulin resistance in diet-induced obesity, J. Immunol. 187 (4) (2011) 1942–1949. P. Li, et al., LTB4 promotes insulin resistance in obese mice by acting on macrophages, hepatocytes and myocytes, Nat. Med. 21 (2015) 239–247. P. Li, et al., LTB4 causes macrophages-mediated inflammation and directly induces insulin resistance in obesity, Nat. Med. 21 (2015) 239–247. C.D. Sadik, A.D. Luster, Lipid-cytokine-chemokine cascades orchestrate leukocyte recruitment in inflammation, J. Leukoc. Biol. 91 (2012) 207–215. T. Lämmerman, et al., Neutrophil swarms require LTB4 and integrins at sites of cell death in vivo, Nature 498 (2013). Y. Sawada, et al., Resolvin E1 inhibits dendritic cell migration in the skin and attenuates contact hypersensitivity responses, J. Exp. Med. 212 (2015) 1921–1930. C.H. Lee, Resolvins as new fascinating drug candidates for inflammatory diseases, Arch. Pharm. Res. 35 (2012) 3–7. A. Papayianni, C.N. Serhan, H.R. Brady, Lipoxin A4 and B4 inhibit leukotrienestimulated interactions of human neutrophils and endothelial cells, J. Immunol. 156 (1996) 2264–2272.