Targeting Upregulated cIAP2 in SOX10-Deficient Drug Tolerant Melanoma

Drug tolerance and minimal residual disease (MRD) are likely to prelude acquired resistance to targeted therapy. Mechanisms that allow persister cells to survive in the presence of targeted therapy are being characterized but selective vulnerabilities for these subpopulations remain uncertain. We identified cellular inhibitor of apoptosis protein 2 (cIAP2) as being highly expressed in SOX10-deficient drug tolerant persister (DTP) melanoma cells. Here, we show that cIAP2 is sufficient to induce tolerance to MEK inhibitors, likely by decreasing the levels of cell death. Mechanistically, cIAP2 is upregulated at the transcript level in SOX10-deficient cells and the AP-1 complex protein, JUND, is required for its expression. Using a patient-derived xenograft model, we demonstrate that treatment with the cIAP1/2 inhibitor, birinapant, during the MRD phase delays the onset of resistance to BRAF inhibitor and MEK inhibitor combination therapy. Together, our data suggest that cIAP2 upregulation in SOX10-deficient subpopulations of melanoma cells induces drug tolerance to MAPK targeting agents and provides a rationale to test a novel therapeutical approach to target MRD.

Efficacy of birinapant in combination with carboplatin in targeting platinum‑resistant epithelial ovarian cancers

Patients diagnosed with epithelial ovarian cancers (EOCs) often suffer from disease relapse associated with the emergence of resistance to standard platinum‑based chemotherapy. Treatment of patients with chemo‑resistant disease remains a clinical challenge. One mechanism of chemoresistance includes overexpression of pro‑survival proteins called inhibitors of apoptosis (IAP) which enable cancer cells to evade apoptosis. Due to their anti‑apoptotic activity, association with poor prognosis, and correlation with therapy resistance in multiple malignancies, IAP proteins have become an attractive target for development of anticancer therapeutics. Second mitochondrial activator of caspase (SMAC) mimetics are the most widely used IAP antagonists currently being tested in clinical trials as a monotherapy and in combination with different chemotherapeutic drugs to target different types of cancer. In the present study, the antitumor efficacy of combination therapy with birinapant, a bivalent SMAC mimetic compound, and carboplatin to target platinum‑resistant EOC cells was investigated. A 3D organoid bioassay was utilized to test the efficacy of the combination therapy in a panel of 7 EOC cell lines and 10 platinum‑resistant primary patient tumor samples. Findings from the in vitro studies demonstrated that the birinapant and carboplatin combination was effective in targeting a subset of ovarian cancer cell lines and platinum‑resistant primary patient tumor samples. This combination therapy was also effective in vitro and in vivo in targeting a platinum‑resistant patient‑derived xenograft (PDX) model established from one of the patient tumors tested. Overall, our study demonstrated that birinapant and carboplatin combination could target a subset of platinum‑resistant ovarian cancers and also highlights the potential of the 3D organoid bioassay as a preclinical tool to assess the response to chemotherapy or targeted therapies in ovarian cancer.

Targeting Apoptosis in Cancer

PURPOSE OF REVIEW

Apoptosis is a major mechanism of cancer cell death. Thus, evasion of apoptosis results in therapy resistance. Here, we review apoptosis modulators in cancer and their recent developments, including MDM2 inhibitors and kinase inhibitors that can induce effective apoptosis.

RECENT FINDINGS

Both extrinsic pathways (external stimuli through cell surface death receptor) and intrinsic pathways (mitochondrial-mediated regulation upon genotoxic stress) regulate the complex process of apoptosis through orchestration of various proteins such as members of the BCL-2 family. Dysregulation within these complex steps can result in evasion of apoptosis. However, via the combined evolution of medicinal chemistry and molecular biology, omics assays have led to innovative inducers of apoptosis and inhibitors of anti-apoptotic regulators. Many of these agents are now being tested in cancer patients in early-phase trials. We believe that despite a sluggish speed of development, apoptosis targeting holds promise as a relevant strategy in cancer therapeutics.

Expression of X-Linked Inhibitor of Apoptosis Protein (XIAP) in Breast Cancer Is Associated with Shorter Survival and Resistance to Chemotherapy

XIAP, the most potent inhibitor of cell death pathways, is linked to chemotherapy resistance and tumor aggressiveness. Currently, multiple XIAP-targeting agents are in clinical trials. However, the characterization of XIAP expression in relation to clinicopathological variables in large clinical series of breast cancer is lacking. We retrospectively analyzed non-metastatic, non-inflammatory, primary, invasive breast cancer samples for XIAP mRNA (n = 2341) and protein (n = 367) expression. XIAP expression was analyzed as a continuous value and correlated with clinicopathological variables. XIAP mRNA expression was heterogeneous across samples and significantly associated with younger patients' age (≤50 years), pathological ductal type, lower tumor grade, node-positive status, HR+/HER2- status, and PAM50 luminal B subtype. Higher XIAP expression was associated with shorter DFS in uni- and multivariate analyses in 909 informative patients. Very similar correlations were observed at the protein level. This prognostic impact was significant in the HR+/HER2- but not in the TN subtype. Finally, XIAP mRNA expression was associated with lower pCR rate to anthracycline-based neoadjuvant chemotherapy in both uni- and multivariate analyses in 1203 informative patients. Higher XIAP expression in invasive breast cancer is independently associated with poorer prognosis and resistance to chemotherapy, suggesting the potential therapeutic benefit of targeting XIAP.

Smac mimetics and TRAIL cooperate to induce MLKL-dependent necroptosis in Burkitt's lymphoma cell lines

Burkitt's lymphoma (BL) is a highly aggressive form of B-cell non-Hodgkin's lymphoma. The clinical outcome in children with BL has improved over the last years but the prognosis for adults is still poor, highlighting the need for novel treatment strategies. Here, we report that the combinational treatment with the Smac mimetic BV6 and TRAIL triggers necroptosis in BL when caspases are blocked by zVAD.fmk (TBZ treatment). The sensitivity of BL cells to TBZ correlates with MLKL expression. We demonstrate that necroptotic signaling critically depends on MLKL, since siRNA-induced knockdown and CRISPR/Cas9-mediated knockout of MLKL profoundly protect BL cells from TBZ-induced necroptosis. Conversely, MLKL overexpression in cell lines expressing low levels of MLKL leads to necroptosis induction, which can be rescued by pharmacological inhibitors, highlighting the important role of MLKL for necroptosis execution. Importantly, the methylation status analysis of the MLKL promoter reveals a correlation between methylation and MLKL expression. Thus, MLKL is epigenetically regulated in BL and might serve as a prognostic marker for treatment success of necroptosis-based therapies. These findings have crucial implications for the development of new treatment options for BL.

Matrix Drug Screen Identifies Synergistic Drug Combinations to Augment SMAC Mimetic Activity in Ovarian Cancer

Simple Summary

Recurrent ovarian cancer is difficult to treat due to the development of chemotherapy resistance. This resistance develops through multiple mechanisms to include the avoidance of cell death by cancer cells. Prior studies have shown birinapant, a second mitochondrial activator of caspases (SMAC) mimetic drug, to be promising in overcoming this acquired resistance. Despite good tolerability, however, therapy with single-agent birinapant exhibited minimal anti-cancer activity in women with recurrent ovarian cancer. By using a high-throughput drug screen we were able to identify potential therapeutic agents that augment birinapant activity, with docetaxel emerging favorably due to its marked synergy and known utility in the recurrent ovarian cancer setting. We showed that this synergy is the result of several complementary molecular pathways and hope to highlight the promising potential of this therapeutic drug combination for clinical testing where treatment options are often limited.

Abstract

Inhibitor of apoptosis (IAP) proteins are frequently upregulated in ovarian cancer, resulting in the evasion of apoptosis and enhanced cellular survival. Birinapant, a synthetic second mitochondrial activator of caspases (SMAC) mimetic, suppresses the functions of IAP proteins in order to enhance apoptotic pathways and facilitate tumor death. Despite on-target activity, however, pre-clinical trials of single-agent birinapant have exhibited minimal activity in the recurrent ovarian cancer setting. To augment the therapeutic potential of birinapant, we utilized a high-throughput screening matrix to identify synergistic drug combinations. Of those combinations identified, birinapant plus docetaxel was selected for further evaluation, given its remarkable synergy both in vitro and in vivo. We showed that this synergy results from multiple convergent pathways to include increased caspase activation, docetaxel-mediated TNF-α upregulation, alternative NF-kB signaling, and birinapant-induced microtubule stabilization. These findings provide a rationale for the integration of birinapant and docetaxel in a phase 2 clinical trial for recurrent ovarian cancer where treatment options are often limited and minimally effective.

Clinical MDR1 inhibitors enhance Smac-mimetic bioavailability to kill murine LSCs and improve survival in AML models

The specific targeting of inhibitor of apoptosis (IAP) proteins by Smac-mimetic (SM) drugs, such as birinapant, has been tested in clinical trials of acute myeloid leukemia (AML) and certain solid cancers. Despite their promising safety profile, SMs have had variable and limited success. Using a library of more than 5700 bioactive compounds, we screened for approaches that could sensitize AML cells to birinapant and identified multidrug resistance protein 1 inhibitors (MDR1i) as a class of clinically approved drugs that can enhance the efficacy of SM therapy. Genetic or pharmacological inhibition of MDR1 increased intracellular levels of birinapant and sensitized AML cells from leukemia murine models, human leukemia cell lines, and primary AML samples to killing by birinapant. The combination of clinical MDR1 and IAP inhibitors was well tolerated in vivo and more effective against leukemic cells, compared with normal hematopoietic progenitors. Importantly, birinapant combined with third-generation MDR1i effectively killed murine leukemic stem cells (LSCs) and prolonged survival of AML-burdened mice, suggesting a therapeutic opportunity for AML. This study identified a drug combination strategy that, by efficiently killing LSCs, may have the potential to improve outcomes in patients with AML.

Future Therapeutic Directions for Smac-Mimetics

It is well accepted that the ability of cancer cells to circumvent the cell death program that untransformed cells are subject to helps promote tumor growth. Strategies designed to reinstate the cell death program in cancer cells have therefore been investigated for decades. Overexpression of members of the Inhibitor of APoptosis (IAP) protein family is one possible mechanism hindering the death of cancer cells. To promote cell death, drugs that mimic natural IAP antagonists, such as second mitochondria-derived activator of caspases (Smac/DIABLO) were developed. Smac-Mimetics (SMs) have entered clinical trials for hematological and solid cancers, unfortunately with variable and limited results so far. This review explores the use of SMs for the treatment of cancer, their potential to synergize with up-coming treatments and, finally, discusses the challenges and optimism facing this strategy.

Physiologically-based pharmacokinetic and pharmacodynamic models for gemcitabine and birinapant in pancreatic cancer xenografts

The anticancer effects of combined gemcitabine and birinapant were demonstrated as synergistic in PANC-1 cells in vitro. In this study, pharmacokinetic information derived from experiments and the literature was utilized to develop full physiologically-based pharmacokinetic (PBPK) models that characterize individual drugs. The predicted intra-tumor drug concentrations were used as the driving force within a linked PBPK/PD model for treatment-mediated changes in tumor volume in a xenograft mouse model. The efficacy of the drug combination in vivo was evaluated mathematically as exhibiting additivity. The network model developed for drug effects in the in vitro cell cultures was applied successfully to link the in vivo tumor drug concentrations with tumor growth inhibition, incorporating more mechanistic features and accounting for disparate drug interaction outcomes in vitro and in vivo.

Inhibitors of apoptosis: clinical implications in cancer

Inhibitor of apoptosis (IAP) family comprises a group of endogenous proteins that function as main regulators of caspase activity and cell death. They are considered the main culprits in evasion of apoptosis, which is a fundamental hallmark of carcinogenesis. Overexpression of IAP proteins has been documented in various solid and hematological malignancies, rendering them resistant to standard chemotherapeutics and radiation therapy and conferring poor prognosis. This observation has urged their exploitation as therapeutic targets in cancer with promising pre-clinical outcomes. This review describes the structural and functional features of IAP proteins to elucidate the mechanism of their anti-apoptotic activity. We also provide an update on patterns of IAP expression in different tumors, their impact on treatment response and prognosis, as well as the emerging investigational drugs targeting them. This aims at shedding the light on the advances in IAP targeting achieved to date, and encourage further development of clinically applicable therapeutic approaches.

Birinapant sensitizes platinum-resistant carcinomas with high levels of cIAP to carboplatin therapy

Platinum drugs are the frontline therapy in many carcinomas, including high-grade serous ovarian cancers. Clinically, high-grade serous carcinomas have an apparent complete response to carboplatin, but tumors invariably recur and response to platinum drugs diminishes over time. Standard of care prohibits re-administration of platinum drugs to these patients who are labeled as having platinum-resistant disease. In this stage patients are treated with non-platinum agents and outcomes are often poor. In vivo and in vitro data presented here demonstrate that this clinical dogma should be challenged. Platinum drugs can be an effective therapy even for platinum-resistant carcinomas as long as they are combined with an agent that specifically targets mechanisms of platinum resistance exploited by the therapy-resistant tumor subpopulations. High levels of cellular inhibitor of apoptosis proteins cIAP1 and 2 (cIAP) were detected in up to 50% of high-grade serous and non-high-grade serous platinum-resistant carcinomas. cIAP proteins can induce platinum resistance and they are effectively degraded with the drug birinapant. In platinum-resistant tumors with ≥22.4 ng of cIAP per 20 μg of tumor lysate, the combination of birinapant with carboplatin was effective in eliminating the cancer. Our findings provide a new personalized therapeutic option for patients with platinum-resistant carcinomas. The efficacy of birinapant in combination with carboplatin should be tested in high-grade serous carcinoma patients in a clinical trial.

Promises and Challenges of Smac Mimetics as Cancer Therapeutics

Inhibitor of Apoptosis (IAP) proteins block programmed cell death and are expressed at high levels in various human cancers, thus making them attractive targets for cancer drug development. Second mitochondrial activator of caspases (Smac) mimetics are small-molecule inhibitors that mimic Smac, an endogenous antagonist of IAP proteins. Preclinical studies have shown that Smac mimetics can directly trigger cancer cell death or, even more importantly, sensitize tumor cells for various cytotoxic therapies, including conventional chemotherapy, radiotherapy, or novel agents. Currently, several Smac mimetics are under evaluation in early clinical trials as monotherapy or in rational combinations (i.e., GDC-0917/CUDC-427, LCL161, AT-406/Debio1143, HGS1029, and TL32711/birinapant). This review discusses the promise as well as some challenges at the translational interface of exploiting Smac mimetics as cancer therapeutics.

A dual role for Caspase8 and NF-κB interactions in regulating apoptosis and necroptosis of ovarian cancer, with correlation to patient survival

Ovarian cancer is a deadly disease characterized by primary and acquired resistance to chemotherapy. We previously associated NF-κB signaling with poor survival in ovarian cancer, and functionally demonstrated this pathway as mediating proliferation, invasion and metastasis. We aimed to identify cooperating pathways in NF-κB-dependent ovarian cancer cells, using genome-wide RNA interference as a loss-of-function screen for key regulators of cell survival with IKKβ inhibition. Functional genomic screen for interactions with NF-κB in ovarian cancer showed that cells depleted of Caspase8 died better with IKKβ inhibition. Overall, low Caspase8 was associated with shorter overall survival in three independent gene expression data sets of ovarian cancers. Conversely, Caspase8 expression was markedly highest in ovarian cancer subtypes characterized by strong T-cell infiltration and better overall prognosis, suggesting that Caspase8 expression increased chemotherapy-induced cell death. We investigated the effects of Caspase8 depletion on apoptosis and necroptosis of TNFα-stimulated ovarian cancer cell lines. Inhibition of NF-κB in ovarian cancer cells switched the effects of TNFα signaling from proliferation to death. Although Caspase8-high cancer cells died by apoptosis, Caspase8 depletion downregulated NF-κB signaling, stabilized RIPK1 and promoted necroptotic cell death. Blockage of NF-κB signaling and depletion of cIAP with SMAC-mimetic further rendered these cells susceptible to killing by necroptosis. These findings have implications for anticancer strategies to improve outcome for women with low Caspase8-expressing ovarian cancer.

Safety, pharmacokinetics, and pharmacodynamic properties of oral DEBIO1143 (AT-406) in patients with advanced cancer: results of a first-in-man study

Purpose

To assess safety/tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and antitumor activity of DEBIO1143, an antagonist of inhibitor apoptosis proteins.

Methods

This first-in-man study in patients with advanced cancer used an accelerated dose titration design. DEBIO1143 was given orally once daily on days 1–5 every 2 or 3 weeks until disease progressed or patients dropped out. The starting dose of 5 mg was escalated by 100 % in single patients until related grade 2 toxicity occurred. This triggered expansion to cohorts of three and subsequently six patients and reduction in dose increments to 50 %. Maximum tolerated dose (MTD) was exceeded when any two patients within the same cohort experienced dose-limiting toxicity (DLT). On days 1 and 5, PK and PD samples were taken.

Results

Thirty-one patients received doses from 5 to 900 mg. Only one DLT was reported at 180 mg. No MTD was found. Most common adverse drug reactions were fatigue (26 %), nausea (23 %), and vomiting (13 %). Average t_max and T_1/2 was about 1 and 6 h, respectively. Exposure increased proportionally with doses from 80 to 900 mg, without accumulation over 5 days. Plasma CCL2 increased at 3–6 h postdose and epithelial apoptosis marker M30 on day 5; cIAP-1 levels in PBMCs decreased at all doses >80 mg. Five patients (17 %) had stable disease as the best treatment response.

Conclusion

DEBIO1143 was well tolerated at doses up to 900 mg and elicited PD effects at doses greater 80 mg. Limited antitumor activity may suggest development rather as adjunct treatment.

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-015-2709-8) contains supplementary material, which is available to authorized users.

Small-molecule SMAC mimetics as new cancer therapeutics

Apoptosis is a tightly regulated cellular process and faulty regulation of apoptosis is a hallmark of human cancers. Targeting key apoptosis regulators with the goal to restore apoptosis in tumor cells has been pursued as a new cancer therapeutic strategy. XIAP, cIAP1, and cIAP2, members of inhibitor of apoptosis (IAP) proteins, are critical regulators of cell death and survival and are attractive targets for new cancer therapy. The SMAC/DIABLO protein is an endogenous antagonist of XIAP, cIAP1, and cIAP2. In the last decade, intense research efforts have resulted in the design and development of several small-molecule SMAC mimetics now in clinical trials for cancer treatment. In this review, we will discuss the roles of XIAP, cIAP1, and cIAP2 in regulation of cell death and survival, and the design and development of small-molecule SMAC mimetics as novel cancer treatments.

Phase I dose-escalation study of LCL161, an oral inhibitor of apoptosis proteins inhibitor, in patients with advanced solid tumors

PURPOSE

LCL161 antagonizes the function of inhibitor of apoptosis proteins (IAPs), thereby promoting cancer cell death. This first-in-human dose-escalation study assessed the maximum-tolerated dose (MTD), safety, pharmacokinetics, and pharmacodynamics of LCL161 in patients with advanced solid tumors. A second part of the study assessed the relative bioavailability of a tablet versus solution formulation.

PATIENTS AND METHODS

LCL161 was administered orally, once weekly, on a 21-day cycle to adult patients with advanced solid tumors by using an adaptive Bayesian logistic regression model with overdose control-guided dose escalation.

RESULTS

Fifty-three patients received at least one dose of LCL161 (dose range, 10 to 3,000 mg). LCL161 was well tolerated at doses up to 1,800 mg. Cytokine release syndrome (CRS) was the only dose-limiting toxicity (in three [6%] of 53 patients) and was the most common grades 3 to 4 event (in five [9%] of 53 patients). Vomiting, nausea, asthenia/fatigue, and anorexia were common but not severe. Although the MTD was not formally determined, an 1,800-mg dose was selected in compliance with the protocol for additional study, given the dose-limiting CRS at higher doses and pharmacodynamic activity at lower doses. LCL161 was rapidly absorbed, and exposure was generally increased with dose. The tablet formulation of LCL161 was better tolerated than the solution; tablet and solution formulations had similar exposures, and the solution was discontinued. No patient had an objective response. LCL161 induced degradation of cellular IAP1 protein in the blood, skin, and tumor and increased circulating cytokine levels.

CONCLUSION

The 1,800-mg dose of LCL161, administered as a single agent once weekly, in tablet formulation is the recommended dose for additional study. This combined dose and formulation was well tolerated and had significant pharmacodynamic activity, which warrants additional investigation.

Targeting apoptosis pathways for new cancer therapeutics

The past decade has witnessed tremendous advances in the discovery and development of novel small-molecule inhibitors targeting apoptosis pathways for cancer treatment, with some compounds now in clinical development. Early promising clinical data have been reported with these new classes of anticancer drugs. This review highlights the recent advancements in the development of small-molecule inhibitors targeting three major classes of antiapoptotic proteins: antiapoptotic B cell lymphoma 2 (BCL-2) proteins, inhibitor of apoptosis proteins (IAPs), and murine double-minute 2 (MDM2). Special emphasis is given to those that have been advanced into clinical trials. The challenges and future directions in the further preclinical and clinical development of these new anticancer drugs are also discussed.