The TRAIL to cancer therapy: Hindrances and potential solutions

Apoptosis is an ordered and orchestrated cellular process that occurs in physiological and pathological conditions. Resistance to apoptosis is a hallmark of virtually all malignancies. Despite being a cause of pathological conditions, apoptosis could be a promising target in cancer treatment. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of TNF cytokine superfamily. It is a potent anti-cancer agent owing to its specific targeting towards cancerous cells, while sparing normal cells, to induce apoptosis. However, resistance occurs either intrinsically or after multiple treatments which may explain why cancer therapy fails. This review summarizes the apoptotic mechanisms via extrinsic and intrinsic apoptotic pathways, as well as the apoptotic resistance mechanisms. It also reviews the current clinically tested recombinant human TRAIL (rhTRAIL) and TRAIL receptor agonists (TRAs) against TRAIL-Receptors, TRAIL-R1 and TRAIL-R2, in which the outcomes of the clinical trials have not been satisfactory. Finally, this review discusses the current strategies in overcoming resistance to TRAIL-induced apoptosis in pre-clinical and clinical settings.

Antibodies and Derivatives Targeting DR4 and DR5 for Cancer Therapy

Developing therapeutics that induce apoptosis in cancer cells has become an increasingly attractive approach for the past 30 years. The discovery of tumor necrosis factor (TNF) superfamily members and more specifically TNF-related apoptosis-inducing ligand (TRAIL), the only cytokine of the family capable of eradicating selectively cancer cells, led to the development of numerous TRAIL derivatives targeting death receptor 4 (DR4) and death receptor 5 (DR5) for cancer therapy. With a few exceptions, preliminary attempts to use recombinant TRAIL, agonistic antibodies, or derivatives to target TRAIL agonist receptors in the clinic have been fairly disappointing. Nonetheless, a tremendous effort, worldwide, is being put into the development of novel strategic options to target TRAIL receptors. Antibodies and derivatives allow for the design of novel and efficient agonists. We summarize and discuss here the advantages and drawbacks of the soar of TRAIL therapeutics, from the first developments to the next generation of agonistic products, with a particular insight on new concepts.

Tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL)

The concept to exploit death receptors for cancer therapy is very attractive, since these cell surface receptors have a direct connection to the intracellular cell death machinery. Among the death receptor superfamily, the tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL) receptor/ligand system is of special interest. TRAIL receptor agonists have recently entered the stage of clinical evaluation for the treatment of human cancers. Further insights into the regulatory mechanisms of TRAIL signaling will help to better understand the determinants of TRAIL sensitivity versus resistance of human cancers.

Death receptor agonist therapies for cancer, which is the right TRAIL?

The activation of cell-surface death receptors represents an attractive therapeutic strategy to promote apoptosis of tumor cells. Several investigational therapeutics that target this extrinsic pathway, including recombinant human Apo2L/TRAIL and monoclonal agonist antibodies directed against death receptors-4 (DR4) or -5 (DR5), have been evaluated in the clinic. Although Phase 1/1b studies provided encouraging preliminary results, findings from randomized Phase 2 studies failed to demonstrate significant clinical benefit. This has raised multiple questions as to why pre-clinical data were not predictive of clinical response. Results from clinical studies and insight into why current agents have failed to yield robust responses are discussed. In addition, new strategies for the development of next generation death receptor agonists are reviewed.

Manipulating the apoptotic pathway: potential therapeutics for cancer patients

This review summarizes the current state of scientific understanding of the apoptosis pathway, with a focus on the proteins involved in the pathway, their interactions and functions. This forms the rationale for detailing the preclinical and clinical pharmacology of drugs that modulate the pivotal proteins in this pathway, with emphasis on drugs that are furthest advanced in clinical development as anticancer agents. There is a focus on describing drugs that modulate three of the most promising targets in the apoptosis pathway, namely antibodies that bind and activate the death receptors, small molecules that inhibit the anti-apoptotic Bcl-2 family proteins, and small molecules and antisense oligonucleotides that inactivate the inhibitors of apoptosis, all of which drive the equilibrium of the apoptotic pathway towards apoptosis. These structurally different yet functionally related groups of drugs represent a promising novel approach to anticancer therapeutics whether used as monotherapy or in combination with either classical cytotoxic or other molecularly targeted anticancer agents.

Death receptors as targets in cancer

Anti-tumour therapies based on the use pro-apoptotic receptor agonists, including TNF-related apoptosis-inducing ligand (TRAIL) or monoclonal antibodies targeting TRAIL-R1 or TRAIL-R2, have been disappointing so far, despite clear evidence of clinical activity and lack of adverse events for the vast majority of these compounds, whether combined or not with conventional or targeted anti-cancer therapies. This brief review aims at discussing the possible reasons for the lack of apparent success of these therapeutic approaches and at providing hints in order to rationally design optimal protocols based on our current understanding of TRAIL signalling regulation or resistance for future clinical trials.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

A randomized phase 2 study of paclitaxel and carboplatin with or without conatumumab for first-line treatment of advanced non-small-cell lung cancer

INTRODUCTION

This study evaluated the efficacy, safety, and pharmacokinetics of conatumumab combined with paclitaxel-carboplatin (PC) as first-line treatment for advanced non-small-cell lung cancer (NSCLC).

METHODS

Patients (aged >18 years) with previously untreated advanced or recurrent NSCLC were randomized 1:1:1 (stratified by Eastern Cooperative Oncology Group performance status and disease stage) to receive up to six 3-week cycles of PC combined with conatumumab (arm 1, 3 mg/kg; arm 2, 15 mg/kg) or placebo (arm 3) every 3 weeks. The primary endpoint was progression-free survival (PFS). This study is registered with ClinicalTrials.gov (NCT00534027).

RESULTS

Between August 8, 2007 and April 9, 2009, 172 patients were randomized (arm 1, n = 57; arm 2, n = 56; arm 3, n = 59). Median PFS was 5.4 months (95% confidence interval [CI] 4.1-6.3) in arm 1 (hazard ratio [HR] 0.84 [95% CI 0.57-1.24]; p = 0.41), 4.8 months (95% CI 3.2-6.5) in arm 2 (HR 0.93 [0.64-1.35]; p = 0.57), and 5.5 months (95% CI 4.3-5.7) in arm 3. There was an interaction between tumor histology and the effect of conatumumab on PFS (squamous HR 0.47 [0.23-0.94]; nonsquamous HR 1.08 [0.74-1.57]; interaction p = 0.039).The most common grade of three or more adverse events were neutropenia, anemia, and thrombocytopenia. There was no evidence of pharmacokinetic interactions between conatumumab and PC. Of 158 patients assessable for FCGR3A polymorphisms, conatumumab treatment was associated with a trend toward longer overall survival (HR 0.72 [0.43-1.23]) among V-allele carriers (V/V or F/V; n = 54) but not among F-allele homozygotes (n = 34; HR 1.37 [0.66-2.86]).

CONCLUSION

Although well tolerated, the addition of conatumumab to PC did not improve outcomes in unselected patients with previously untreated advanced NSCLC.

On the TRAIL to successful cancer therapy? Predicting and counteracting resistance against TRAIL-based therapeutics

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and agonistic antibodies against TRAIL death receptors (DR) kill tumor cells while causing virtually no damage to normal cells. Several novel drugs targeting TRAIL receptors are currently in clinical trials. However, TRAIL resistance is a common obstacle in TRAIL-based therapy and limits the efficiency of these drugs. In this review article we discuss different mechanisms of TRAIL resistance, and how they can be predicted and therapeutically circumvented. In addition, we provide a brief overview of all TRAIL-based clinical trials conducted so far. It is apparent that although the effects of TRAIL therapy are disappointingly modest overall, a small subset of patients responds very well to TRAIL. We argue that the true potential of targeting TRAIL DRs in cancer can only be reached when we find efficient ways to select for those patients that are most likely to benefit from the treatment. To achieve this, it is crucial to identify biomarkers that can help us predict TRAIL sensitivity.

Randomized phase II study of dulanermin in combination with paclitaxel, carboplatin, and bevacizumab in advanced non-small-cell lung cancer

PURPOSE

To evaluate the efficacy and safety of dulanermin combined with paclitaxel and carboplatin (PC) and bevacizumab (PCB) as first-line treatment for advanced or recurrent non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Patients with squamous NSCLC and/or CNS metastases received PC every 3 weeks alone (arm 1) or with dulanermin 8 mg/kg for 5 days (arm 2). Patients with nonsquamous NSCLC received PCB alone (arm 3) or with dulanermin 8 mg/kg for 5 days (arm 4) or 20 mg/kg for 2 days (arm 5). The primary end point was the objective response rate (ORR).

RESULTS

Overall, 213 patients were randomly assigned (arm 1, n = 41; arm 2, n = 39; arm 3, n = 42; arm 4, n = 40; arm 5, n = 41). The ORR in arms 1 to 5 was 39% (95% CI, 24% to 56%), 38% (95% CI, 24% to 54%), 50% (95% CI, 35% to 65%), 40% (95% CI, 25% to 56%), and 40% (95% CI, 25% to 56%), respectively. The odds ratio for ORR was 1.04 (P = 1.000) for arm 1 versus arm 2, 1.53 (P = .391) for arm 3 and versus arm 4, and 1.53 (P = .391) for arm 3 versus arm 5. The most common grade ≥ 3 adverse events were neutropenia, asthenia, anemia, thrombocytopenia, and hemoptysis. Of 161 available serum samples, a trend toward increased caspase-cleaved cytokeratin-18 was observed after dulanermin treatment in cycles 1 and 2. Among 84 patients evaluated for GalNT14 expression, there was a trend toward favorable progression-free survival and overall survival with dulanermin treatment in those with high GalNT14 expression.

CONCLUSION

The addition of dulanermin to PC and PCB did not improve outcomes in unselected patients with previously untreated advanced or recurrent NSCLC.

Distinct TRAIL resistance mechanisms can be overcome by proteasome inhibition but not generally by synergizing agents

One impediment to the use of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor-targeted agents as antitumor drugs is the evolution of resistance, a common problem in cancer. On the contrary, many different kinds of drugs synergize with TRAIL in TRAIL-sensitive tumor cells, raising the question whether one can overcome resistance with the same drugs producing synergy. This is an important question, because recent clinical trials suggest that combination treatments with cytotoxic drugs and TRAIL receptor-targeted agents do not provide additional benefit compared with cytotoxic agents on their own. Such results might be expected if drug combinations that synergize in sensitive tumor cells but cannot overcome TRAIL resistance are used in patients whose tumors were not selected for retention of TRAIL sensitivity. We tested this idea by creating isogenic tumor cells with acquired TRAIL resistance or defined mechanisms of resistance that occur in human tumors and then comparing them to the TRAIL-sensitive parental cell line. Although diverse classes of anticancer drugs were all able to synergize with TRAIL in sensitive cells, most agents were unable to overcome resistance and there was no relationship between the amount of synergy seen with a particular agent and its ability to overcome acquired resistance. An important exception was proteasome inhibitors, which were, however, able to overcome diverse resistance mechanisms. Our findings suggest that one should select drugs for TRAIL receptor agonist combination therapy based not just on their ability to synergize, but rather on their ability to overcome resistance as well as synergize.

Summary of presentations from the 46th Annual Meeting of the American Society of Clinical Oncology: focus on non-small cell lung cancer (2010)

The promising results of crizotinib in molecularly selected patients with advanced non-small cell lung cancer (NSCLC) whose tumor cells had a novel fusion protein involving anaplastic lymphoma kinase presented at the 2010 American Society of Clinical Oncology reinforce once again the importance of understanding molecular heterogeneity of lung cancer and careful patient selection. Several other important issues were the subject of presentations related to lung cancer at the recently concluded American Society of Clinical Oncology annual meeting. The articles covered a wide variety of topics including optimal staging techniques to detect mediastinal nodal involvement, the role of platinum-based doublet chemotherapy in the management of elderly patients with advanced NSCLC, use of maintenance therapy with gemcitabine, and the impact of early introduction of organized palliative care in improving the quality of life of patients with advanced NSCLC. This report provides a brief overview of the presentations related to lung cancer that are relevant to clinical practice and future research.

Lung cancer therapeutics that target signaling pathways: an update

Claiming more than 150,000 lives each year, lung cancer is the deadliest cancer in the USA. First-line treatments in lung cancer include surgical resection and chemotherapy, the latter of which offers only modest survival benefits at the expense of often severe and debilitating side effects. Recent advances in elucidating the molecular biology of lung carcinogenesis have elucidated novel drug targets, and treatments are rapidly evolving into specialized agents that hone in on specific aspects of the disease. Of particular interest is blocking tumor growth by targeting the physiological processes surrounding angiogenesis, pro-tumorigenic growth factor activation, anti-apoptotic cascades and other cancer-promoting signal transduction events. This article looks at several areas of interest to lung cancer therapeutics and considers the current state of affairs surrounding the development of these therapies.