Proapoptotic Receptor Agonists Research Articles

Anticancer efficacy of the hypoxia‐activated prodrug evofosfamide is enhanced in combination with proapoptotic receptor agonists against osteosarcoma

Tumor hypoxia is a major cause of treatment failure for a variety of malignancies. However, hypoxia also leads to treatment opportunities as demonstrated by the development of compounds that target regions of hypoxia within tumors. Evofosfamide is a hypoxia‐activated prodrug that is created by linking the hypoxia‐seeking 2‐nitroimidazole moiety to the cytotoxic bromo‐isophosphoramide mustard (Br‐IPM). When evofosfamide is delivered to hypoxic regions of tumors, the DNA cross‐linking toxin, Br‐IPM, is released leading to cell death. This study assessed the anticancer efficacy of evofosfamide in combination with the Proapoptotic Receptor Agonists (PARAs) dulanermin and drozitumab against human osteosarcoma in vitro and in an intratibial murine model of osteosarcoma. Under hypoxic conditions in vitro, evofosfamide cooperated with dulanermin and drozitumab, resulting in the potentiation of cytotoxicity to osteosarcoma cells. In contrast, under the same conditions, primary human osteoblasts were resistant to treatment. Animals transplanted with osteosarcoma cells directly into their tibiae developed mixed osteosclerotic/osteolytic bone lesions and consequently developed lung metastases 3 weeks post cancer cell transplantation. Tumor burden in the bone was reduced by evofosfamide treatment alone and in combination with drozitumab and prevented osteosarcoma‐induced bone destruction while also reducing the growth of pulmonary metastases. These results suggest that evofosfamide may be an attractive therapeutic agent, with strong anticancer activity alone or in combination with either drozitumab or dulanermin against osteosarcoma.

Metformin sensitizes triple-negative breast cancer to proapoptotic TRAIL receptor agonists by suppressing XIAP expression.

Despite robust antitumor activity in diverse preclinical models, TNF-related apoptosis-inducing ligand (TRAIL) receptor agonists have not demonstrated efficacy in clinical trials, underscoring the need to identify agents that enhance their activity. We postulated that the metabolic stress induced by the diabetes drug metformin would sensitize breast cancer cells to TRAIL receptor agonists. Human triple (estrogen receptor, progesterone receptor, and HER2)-negative breast cancer (TNBC) cell lines were treated with TRAIL receptor agonists (monoclonal antibodies or TRAIL peptide), metformin, or the combination. The effects on cell survival, caspase activation, and expression of TRAIL receptors and the antiapoptotic protein XIAP were determined. In addition, XIAP was silenced by RNAi in TNBC cells and the effects on sensitivity to TRAIL were determined. The antitumor effects of metformin, TRAIL, or the combination were evaluated in an orthotopic model of metastatic TNBC. Metformin sensitized diverse TNBC cells to TRAIL receptor agonists. Metformin selectively enhanced the sensitivity of transformed breast epithelial cells to TRAIL receptor agonist-induced caspase activation and apoptosis with little effect on untransformed breast epithelial cells. These effects of metformin were accompanied by robust reductions in the protein levels of XIAP, a negative regulator of TRAIL-induced apoptosis. Silencing XIAP in TNBC cells mimicked the TRAIL-sensitizing effects of metformin. Metformin also enhanced the antitumor effects of TRAIL in a metastatic murine TNBC model. Our findings indicate that metformin enhances the activity of TRAIL receptor agonists, thereby supporting the rationale for additional translational studies combining these agents.

Targeting the extrinsic apoptotic pathway in cancer: lessons learned and future directions.

Apoptosis is a metazoan process of controlled cell elimination that plays critical roles in embryonic development and adult tissue homeostasis. Apoptosis dysregulation contributes to several important diseases, including cancer. Two distinct yet interconnected signaling pathways control apoptosis by activating a core intracellular machinery of death proteases called caspases. The intrinsic apoptotic pathway engages caspases via members of the BCL-2 protein family and the mitochondria in reaction to severe cellular damage or stress. The extrinsic pathway activates caspases via cell-surface death receptors, which respond to cognate death ligands expressed on immune-effector cells. Tumor cells can acquire various apoptosis-evasion mechanisms; nevertheless, the transformed state of these cells makes them uniquely susceptible to apoptosis reactivation if resistance is circumvented. Molecular approaches to reengage the apoptotic pathways in cancer have been underway for over two decades. Gratifyingly, BCL-2 antagonists - which drive the intrinsic pathway - are beginning to bear clinical fruit. In contrast, clinical attempts to stimulate the extrinsic pathway with proapoptotic receptor agonists (PARAs) have been disappointing, despite compelling preclinical efficacy with this class of agents. Here, I discuss some of the possible reasons for this translational discrepancy and suggest strategies to overcome it with the next generation of PARAs.

Abstract LB-113: A novel role of Withaferin A as an effective pro-apoptotic receptor agonist (PARA) and insights into the underlying molecular mechanisms

Abstract Introduction: Despite significant progress towards screening efforts and targeted therapies, breast cancer is still a leading cause of cancer-related mortality among women. Novel therapeutic strategies are clearly needed for effective targeting of breast cancer. Natural products continue to generate interest for identification of potential chemopreventive and therapeutic agents. Withaferin A (WFA) is a bioactive small molecule that has been proposed as a new-generation molecule capable of eliciting growth inhibitory effect on cancer cells. The molecular mechanisms by which WFA mediates inhibition of breast cancer remain elusive. The present study was designed to systematically elucidate the underlying mechanisms by which WFA inhibits growth and metastatic potential of breast cancer cells. Results: Because many cellular signaling events involve induced-phosphorylation of key targets, in the present study we utilized phosphokinase arrays to gain insight into the intricacies of WFA-mediated signaling networks and discovered that WFA induces RSK phosphorylation in breast cancer cells. Further analysis revealed an integral role of ERK in WFA-mediated RSK activation and WFA-induced ERK/RSK signaling resulted in concomitant upregulation and activation of Elk1(ETS-like transcription factor-1) and CHOP (C-EBP homology protein) leading to transcriptional upregulation of Death Receptor protein-5 (DR5). It is interesting to note that in recent years, many phase 1 and 2 single agent and combination clinical trials have been conducted to examine the efficacy and safety of recombinant human TRAIL (dulanermin, (Amgen/Genentech)), and the agonistic monoclonal antibodies to DR5 (lexatumumab (Human Genome Sciences), conatumumab (Amgen), drozitumab (Genentech), tigatuzumab (Daiichi-Sankyo) and LBY135 (Novartis)). Studies with these pro-apoptotic receptor agonists (PARAs) have been encouraging but no full phase 3 studies have been performed suggesting the need for novel PARAs with improved properties. Here, we show that WFA is more effective than three other known DR5 activators, TRAIL, etoposide and celecoxib, in activation of DR5 in breast cancer cells hence, appears to be a good candidate for further development as an effective DR5 inducer. WFA treatment effectively inhibited breast tumorigenesis in vivo and analysis of WFA-treated xenografts and MMTV-neu mice tumors showed increased activation of ERK/RSK axis and DR5 along with elevated nuclear accumulation of Elk1 and CHOP. Conclusion: These data provided first in vitro and in vivo evidence of the integral role of a previously unrecognized crosstalk between WFA and ERK/RSK and CHOP/Elk1 axes in breast tumor growth inhibition. Also, our findings may potentially open new avenues of research on the role of withaferin A as a novel pro-apoptotic receptor agonist (PARA). Citation Format: Arumugam Nagalingam, Panjamurthy Kuppusamy, Neeraj Saxena, Dipali Sharma. A novel role of Withaferin A as an effective pro-apoptotic receptor agonist (PARA) and insights into the underlying molecular mechanisms. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-113. doi:10.1158/1538-7445.AM2014-LB-113

FOLFIRI plus dulanermin (rhApo2L/TRAIL) in a patient with BRAF-mutant metastatic colon cancer

Colorectal cancer patients with BRAF-mutant tumors have a more aggressive, rapidly progressing disease that is in critical need of novel therapeutic approaches. Indeed, whereas the median overall survival (OS) of colorectal cancer (CRC) patients receiving standard-of-care therapy is approximately two years or more if their tumors express wild-type BRAF and wild-type KRAS, median OS is less than twelve months with tumors expressing V600E-mutant BRAF and wild-type KRAS. Pro-apoptotic receptor agonists are a class of biologic agents under development to induce tumor-specific apoptosis and are being combined with classical chemotherapy or targeted agents in clinical trials. Herein, we present the case of a patient with bulky V600E-mutant BRAF hepatic flexure colon carcinoma, treated initially with FOLFOX plus bevacizumab neoadjuvant therapy and surgery. The patient had a rapid tumor relapse with metastatic disease to the liver and lung, and was enrolled in a phase 1b open-label clinical study, where he received the FOLFIRI regimen in combination with the pro-apoptotic receptor agonist dulanermin (rhApo2L/TRAIL). The patient maintained stable disease through 25 doses administered every two weeks before his disease progressed. After coming off study, the patient underwent surgical debulking and received intraperitoneal hyperthermic chemotherapy. He subsequently relapsed and was treated with FOLFIRI plus cetuximab. At the time of this report, the patient remains on active treatment. It is unclear what effect dulanermin may have had on the course of his disease, but it is noteworthy that the patient remained on FOLFIRI plus dulanermin therapy for a period that exceeded the median OS for patients with advanced, aggressive BRAF-mutant CRC. It is also noteworthy that at the time of this report the patient's overall survival since diagnosis has exceeded 30 months, which is beyond what is generally observed even for patients with CRC harboring wild-type BRAF and wild-type KRAS.

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. 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.

Phase Ib Study of Recombinant Circularly Permuted TRAIL (CPT) in Relapsed or Refractory multiple Myeloma Patients

AbstractAbstract 1857 Background:Circularly permuted TRAIL (CPT) is a recombinant mutant of human Apo2L/TRAIL developed by Beijing Sunbio Biotech Co. Ltd. as a targeted therapy for multiple myeloma and other hematologic malignancies. CPT is a dual pro-apoptotic receptor agonist that directly activates both pro-apoptotic receptors TRAIL-R1 (DR4) and TRAIL-R2 (DR5). CPT selectively induces apoptosis in a variety of cancer cells, while sparing most normal cells in the preclinical models. Objective:The safety, pharmacokinetics and preliminary efficacy of CPT in relapsed or refractory multiple myeloma patients (Ral/Ref MM) has been evaluated. Methods:This is a phase Ib, multiple-center, open-label, single/multiple dose-escalation study,18 patients were enrolled in the single dose-escalation study, and 29 patients were recruited in multiple dose-escalation study (including some patients from single dose-escalation study of CPT). Five escalation dosage levels include 5.0, 6.5, 8.0, 10.0 and 15.0 mg/kg/day. Patients received single dose of CPT, or once daily for 5 consecutive days (multiple dose) of each 21-days cycle. Patients receiving multiple doses were treated up to 4 cycles. The clinical response was evaluated at the end of each cycle by an independent review committee according to the criteria of the European Group for Blood and Marrow Transplantation (EBMT). Results:In single dose-escalation study, no dose limiting toxicity (DLT) and maximum tolerated dose (MTD) was observed. The most common treatment-related adverse events (≥10%) were elevated AST, fever, elevated LDH, leucopenia and shivers. In multiple dose-escalation study, the most common treatment-related adverse events(≥10%) were fever, leucopenia, elevated AST, fatigue and vomit. No significant difference of related adverse event was observed among the different dose groups. Two patients (33.3%) experienced laboratorial or clinical tumor lysis syndrome in 15.0 mg/kg multiple dose. The efficacy was evaluated in 27 patients, 1 patient achieved complete response (CR), 4 partial response (PR), 4 minor response (MR) and 12 no change (NC). No response better than MR was observed in 5.0mg/kg and 6.5mg/kg group. In 8.0mg/kg, 10.0mg/kg and 15.0mg/kg groups, the overall response rate (CR+PR %) was 33.33%, 16.67% and 33.33%, respectively. The disease control rate for five dose groups was 50.00%, 66.67%, 83.33%, 83.33% and 100% respectively, indicating that the optimal dose for CPT may be between 8.0 and 15.0mg/kg. PK results are linear at dose range from 5 mg/kg to 15 mg/kg with CL of 32.47±9.33 ml/h/kg, Vd of 51.89±9.20 ml/kg and t1/2 of 1.16±0.22h. No drug accumulation was observed in repeated administration. No anti-drug antibodies were detected after 1 to 4 cycle’s treatment. Conclusion:CPT was well tolerated up to 15mg/kg with promising efficacy in patients with Ral/Ref MM. The MTD has not been reached. A randomized phase 2 trial in patients with Ral/Ref MM is ongoing. Disclosures:Yang:Beijing Sunbio Biotech Co., Ltd.: Employment. Zhu:Beijing Sunbio Biotech Co., Ltd.: Employment.

Recombinant Circularly Permuted TRAIL (CPT) for the Treatment of Relapsed or Refractory Multiple Myeloma: An Open-Label, Multicenter Phase II Clinical Trial

AbstractAbstract 78 Background:Circularly permuted TRAIL (CPT) is a recombinant mutant of human Apo2L/TRAIL developed by Beijing Sunbio Biotech Co., Ltd. as a targeted therapy for multiple myeloma and other hematologic malignancies. CPT is a dual pro-apoptotic receptor agonist that directly activates both pro-apoptotic receptors TRAIL-R1 (DR4) and TRAIL-R2 (DR5). CPT selectively induces apoptosis in a variety of cancer cells, while sparing most normal cells in preclinical models. Objective:CPT has shown preliminary activities for patients with relapsed or refractory multiple myeloma (Rel/Ref MM) in phase I study. The aim of this phase II study is to investigate the effect and safety of CPT for Rel/Ref MM patients. Methods:In this multi-center, open-label, single arm phase II study, twenty-seven Rel/Ref MM patients were enrolled to receive CPT treatment alone at the dose of 2.5 mg/kg/day intravenously, once daily for 14 consecutive days of each 21-day cycle. Clinical responses to CPT after 2 cycle's treatment were assessed by an independent review committee according to the criteria of the European Group for Blood and Marrow Transplantation (EBMT). Results:Among the 27 patients, one patient (3.7%) achieved near complete response (nCR) and eight patients (29.63%) exhibited partial response (PR). The overall response rate (ORR) was 33.3%. The median PFS was not reached within 2 cycle’s treatment. The drug related adverse events (≥10%) included fever, AST/ALT elevation, leucopenia, neutropenia, rash, thrombocytopenia, and LDH elevation. The severe adverse events were occurred in 3 patients (11%), one of them was CPT-related liver injury. Anti-drug antibodies were detected in 6 patients without reduced efficacy or increased toxicities. Conclusions:The CPT is a very effective and well-tolerated new agent for Rel/Ref MM, and it is worthy to be further studied. Disclosures:Yang:Beijing Sunbio Biotech Co. Ltd.: Employment. Cui:Beijing Sunbio Biotech Co. Ltd.: Employment.

Circularly Permuted TRAIL (CPT) combined with Thalidomide for the Treatment of Relapsed or Refractory Multiple Myeloma: An Open-Label, Multicenter Phase II Clinical Trial.

AbstractAbstract 2958 Background:Circularly permuted TRAIL (CPT) is a recombinant mutant of human Apo2L/TRAIL developed by Beijing Sunbio Biotech Co. Ltd. as a targeted therapy for multiple myeloma and other hematologic malignancies. CPT is a dual pro-apoptotic receptor agonist that directly activates both pro-apoptotic receptors TRAIL-R1 (DR4) and TRAIL-R2 (DR5). CPT selectively induces apoptosis in a variety of cancer cells, while sparing most normal cells in preclinical models. Objective:CPT as a mono-therapy has shown definitive activities for patients with relapsed or refractory multiple myeloma (Rel/Ref MM) in phase I and phase II studies. The aim of this study is to observe the effect and safety of CPT in combination with thalidomide for Rel/Ref MM patients. Methods:In this multiple-center, open-label, single arm phase II study, 43 Rel/Ref MM patients who had received prior therapies and were resistant to thalidomide were recruited. These patients were divided into three groups, and received CPT 5.0mg/kg, 8.0mg/kg, and 10.0mg/kg on days1–5 of each 21-day cycle, respectively, until having finished six cycle‘s treatment or progression disease or intolerant adverse events. All the patients received thalidomide 100mg daily until to the disease progression or intolerant adverse events. Clinical responses of CPT were assessed by an independent review committee according to the criteria of the European Group for Blood and Marrow Transplantation (EBMT). Results:Among the 43 patients, 41 patients can be evaluated. There were 11, 15 and 15 patients in the three groups respectively. Among the 41 patients, two patients achieved complete response (CR), three showed near complete responses (nCR), four exhibited partial responses (PR), and five obtained minor responses (MR). The total response rates were 34% (including MR or better than MR), or 22% (including PR or better than PR). Among the three groups, the dose of 10mg/kg seemed to be optimal with 26.7% response rate (including PR or better than PR), superior to the other two groups. Duration of response of CPT was not evaluated accurately, because most patients who achieved PR, nCR, or CR were progression free at the end of the trial. The common treatment related adverse events (≥10%) were neutropenia, leucopoenia, fever, AST/ALT/LDH elevation, and thrombocytopenia. The grade 3 non-haematological toxicities were AST elevation (4.65%) and LDH elevation (2.33%). The elevation of AST and LDH seems to be related to tumor lysis, but not to liver injury. The grade 4 haematological toxicities were neutropenia and thrombocytopenia (2.33%, respectively) which might be related to thalidomide. Conclusions:The CPT combined with thalidomide was well-tolerated and an effective regimen for the treatment of Rel/Ref MM. The combination of CPT and thalidomide seems to be superior to CPT alone in CR/nCR response rate. Disclosures:Zheng:Beijing Sunbio Biotech Co., Ltd.: Employment. Zhu:Beijing Sunbio Biotech Co., Ltd.: Employment. Yang:Beijing Sunbio Biotech Co., Ltd.: Employment.

Proapoptotic Death Receptor Agonists Act as Vascular Disrupting Agents

Abstract Activation of DR5 on endothelial cells disrupts tumor vasculature and reduces tumor growth.

Intracellular-signaling tumor-regression modeling of the pro-apoptotic receptor agonists dulanermin and conatumumab.

Dulanermin (rhApo2L/TRAIL) and conatumumab bind to transmembrane death receptors and trigger the extrinsic cellular apoptotic pathway through a caspase-signaling cascade resulting in cell death. Tumor size time series data from rodent tumor xenograft (COLO205) studies following administration of either of these two pro-apoptotic receptor agonists (PARAs) were combined to develop a intracellular-signaling tumor-regression model that includes two levels of signaling: upstream signals unique to each compound (representing initiator caspases), and a common downstream apoptosis signal (representing executioner caspases) shared by the two agents. Pharmacokinetic (PK) models for each drug were developed based on plasma concentration data following intravenous and/or intraperitoneal administration of the compounds and were used in the subsequent intracellular-signaling tumor-regression modeling. A model relating the PK of the two PARAs to their respective and common downstream signals, and to the resulting tumor burden was developed using mouse xenograft tumor size measurements from 448 experiments that included a wide range of dose sizes and dosing schedules. Incorporation of a pro-survival signal--consistent with the hypothesis that PARAs may also result in the upregulation of pro-survival factors that can lead to a reduction in effectiveness of PARAs with treatment--resulted in improved predictions of tumor volume data, especially for data from the long-term dosing experiments.

XIAP Inhibition and Generation of Reactive Oxygen Species Enhances TRAIL Sensitivity in Inflammatory Breast Cancer Cells

We recently identified superoxide dismutase (SOD) overexpression and decreased induction of reactive oxygen species (ROS)-mediated apoptosis in models of inflammatory breast cancer (IBC) cells with acquired therapeutic resistance. This population of cells has high expression of X-linked inhibitor of apoptosis protein (XIAP), which inhibits both extrinsic and intrinsic apoptosis pathways. We therefore wanted to evaluate the effect of classical apoptosis-inducing agent TRAIL, a proapoptotic receptor agonist that selectively triggers death receptor (DR)-mediated apoptosis in cancer cells, in the IBC acquired resistance model. XIAP levels and subsequent inhibition of caspase activity inversely correlated with TRAIL sensitivity in our models of IBC. These include SUM149, a basal-type cell line isolated from primary IBC tumors and isogenic SUM149-derived lines rSUM149 and SUM149 wtXIAP, models of acquired therapeutic resistance with endogenous and exogenous XIAP overexpression, respectively. Inhibition of XIAP function using embelin, a plant-derived cell permeable small molecule, in combination with TRAIL caused a synergistic decrease in cell viability. Embelin treatment resulted in activation of extracellular signal-regulated kinase (ERK)1/2 and ROS accumulation, which correlated with downregulation of antioxidant protein SOD1 and consumption of redox modulator reduced glutathione in the XIAP-overexpressing cells. Simultaneous treatment with an SOD mimic, which protects against ROS accumulation, reversed the decrease in cell viability caused by embelin + TRAIL treatment. Embelin primes IBC cells for TRAIL-mediated apoptosis by its direct action on the anti-caspase activity of XIAP and by shifting the cellular redox balance toward oxidative stress-mediated apoptosis. Thus, ROS modulators represent a novel approach to enhance efficacy of TRAIL-based treatment protocols in IBC.

Proapoptotic Activation of Death Receptor 5 on Tumor Endothelial Cells Disrupts the Vasculature and Reduces Tumor Growth

The proapoptotic death receptor DR5 has been studied extensively in cancer cells, but its action in the tumor microenvironment is not well defined. Here, we uncover a role for DR5 signaling in tumor endothelial cells (ECs). We detected DR5 expression in ECs within tumors but not normal tissues. Treatment of tumor-bearing mice with an oligomeric form of the DR5 ligand Apo2L/TRAIL induced apoptosis in tumor ECs, collapsing blood vessels and reducing tumor growth: Vascular disruption and antitumor activity required DR5 expression on tumor ECs but not malignant cells. These results establish a therapeutic paradigm for proapoptotic receptor agonists as selective tumor vascular disruption agents, providing an alternative, perhaps complementary, strategy to their use as activators of apoptosis in malignant cells.

Complementary Proteomic Tools for the Dissection of Apoptotic Proteolysis Events

Proteolysis is a key regulatory event that controls intracellular and extracellular signaling through irreversible changes in a protein's structure that greatly alters its function. Here we describe a platform for profiling caspase substrates which encompasses two highly complementary proteomic techniques--the first is a differential gel based approach termed Global Analyzer of SILAC-derived Substrates of Proteolysis (GASSP) and the second involves affinity enrichment of peptides containing a C-terminal aspartic acid residue. In combination, these techniques have enabled the profiling of a large cellular pool of apoptotic-mediated proteolytic events across a wide dynamic range. By applying this integrated proteomic work flow to analyze proteolytic events resulting from the induction of intrinsic apoptosis in Jurkat cells via etoposide treatment, 3346 proteins were quantified, of which 360 proteins were identified as etoposide-induced proteolytic substrates, including 160 previously assigned caspase substrates. In addition to global profiling, a targeted approach using BAX HCT116 isogenic cell lines was utilized to dissect pre- and post-mitochondrial extrinsic apoptotic cleavage events. By employing apoptotic activation with a pro-apoptotic receptor agonist (PARA), a limited set of apoptotic substrates including known caspase substrates such as BH3 interacting-domain death agonist (BID) and Poly (ADP-ribose) polymerase (PARP)-1, and novel substrates such as Basic Transcription Factor 3, TRK-fused gene protein (TFG), and p62/Sequestosome were also identified.

Abstract P1-04-01: X-Linked Inhibitor of Apoptosis Protein (XIAP) Regulates TRAIL-Induced Apoptosis in Inflammatory Breast Cancer Cells

Abstract TRAIL, a proapoptotic receptor agonist, is a promising tool for anticancer therapy due to its selective triggering of death receptor-mediated apoptosis in cancer cells while sparing the majority of normal cells. Overexpression of X-linked inhibitor of apoptosis protein (XIAP) has been identified as a major mechanism of TRAIL resistance as a result of its ability to inhibit caspase activity, the effector arm of apoptotic cell death. Previous studies in our laboratory in preclinical models of inflammatory breast cancer (IBC), a highly invasive and lethal subtype, have revealed that apoptotic dysregulation mediated by XIAP is a key factor in IBC pathogenesis and acquired therapeutic resistance to epidermal growth factor receptor (ErbB1/2) targeting agents. Characterization of TRAIL efficacy in IBC cell lines derived from primary tumors revealed that SUM149, a triple negative, EGFR activated cell line, is sensitive to TRAIL-induced apoptosis and exhibits a corresponding decrease in XIAP and an increase in caspase3 activation compared to TRAIL-resistant SUM190, ErbB2 overexpressing cells in which XIAP levels are unchanged by TRAIL treatment. Profile from an apoptotic proteomic array revealed that SUM190 cells have low basal levels of the TRAIL receptors DR4 and DR5 in comparison to SUM149 cells. Stable overexpression of XIAP in the TRAIL-sensitive SUM149 cells resulted in a two fold decrease in sensitivity to TRAIL with decreased caspase3 activation. Further, SUM149wtXIAP cells showed low levels of TRAIL receptor expression similar to the TRAIL-insensitive SUM190 line. Conversely, increased cell death was observed in SUM190 cells in which XIAP was knocked down using a lentiviral shRNA expression construct. In order to examine therapeutic strategies aimed at restoring function to the apoptotic pathways in IBC cells, we used the small molecule inhibitor Embelin to modulate XIAP action. Treatment of SUM149wtXIAP cells with Embelin in combination with TRAIL enhanced cell death compared to treatment with TRAIL or Embelin alone. Assessment of the interaction using a derivation of the Chou-Talalay method revealed a combination index of 0.054 in SUM149wtXIAP cells, which is indicative of strong synergism between the two agents. These results reveal that knockdown or antagonism of XIAP allows TRAIL to induce activation of effector caspases efficiently and establishes the feasibility of use of XIAP inhibitors to enhance therapeutic apoptosis in IBC therapy. Funded by American Cancer Society-RSG-08-290-01-CCE (GRD), predoctoral DOD BCRP award (KMA), and the Duke University Chancellor's Scholarship (JLA). Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P1-04-01.

Proapoptotic Agents in Lung Cancer

The session was introduced by Dr. Roy Herbst who defined apoptosis as a physiological process of programmed cell suicide, which eliminates cells that are no longer needed or have become irreparably damaged. Apoptosis is important in embryonic and perinatal development. In the adult-tissue homeostasis, apoptosis helps to replace ineffective or potentially damaging cells. It is distinct from other types of death such as necrosis and autophagy. Apoptosis is defined by specific morphologic and biochemical criteria and mediated by specialized proteases—caspases. Two key apoptosis signaling pathways are involved: the extrinsic pathway engages binding of a proapoptotic ligand to its “death” receptor (DR) and the activation of the caspase cascade. The ligand-independent intrinsic pathway is triggered by the tumor suppressor gene product P53 that acts through the release of proapoptotic proteins that activate caspase enzymes from the mitochondria. Apoptosis is dysregulated in cancer. Some cancer cells acquire genetic changes (e.g., p53, BclII, and inhibitors of apoptosis [IAP]) that circumvent apoptosis, permitting continued, unchecked proliferation. Strategies to reactivate apoptosis selectively in tumor cells have exciting potential for cancer therapy. Current efforts are focused on proapoptotic receptor agonists and on antagonists of apoptosis suppressors (e.g., inhibitors of apoptosis/IAP, survivin, and Bcl-2). SUMMARY

Phase II study of dulanermin plus rituximab in patients with relapsed follicular non-Hodgkin's lymphoma (NHL).

8104 Background: Dulanermin is a pro-apoptotic receptor agonist that induces apoptosis via the extrinsic apoptotic pathway by binding to pro-apoptotic receptors DR4 and DR5. In preclinical studies, adding dulanermin to rituximab enhanced inhibition of NHL tumor xenografts in mice. In a phase Ib study, the combination of rituximab + dulanermin was well tolerated (ASCO 2007 abstract 8078). The present study assessed the safety and activity of multiple doses of rituximab + dulanermin vs. rituximab alone in patients (pts) with follicular NHL who progressed after previous rituximab therapy. Methods: This multicenter, open-label, randomized phase II trial compared rituximab (375 mg/m2/wk × 8) + dulanermin (8 mg/kg for 5 days every 3 wks × 4) (n=26) vs. rituximab alone (n=22). Adverse event (AE) and laboratory data were monitored. The primary efficacy endpoint was objective response rate (ORR) as assessed by blinded, independent review; progression-free survival (PFS) was a key secondary endpoint. Results: Grade 3-5 AEs were more frequent among rituximab + dulanermin pts (n=6) than among rituximab pts (n=2), although most were single occurrences. Among rituximab + dulanermin pts, Grade 3 serum lipase elevation and Grade 4 neutropenia were noted in 2 and 1 pts, respectively. Neither event was dose limiting. ORR results are shown below. PFS data are immature (only 27% of pts have progressed). Conclusions: The rituximab-dulanermin combination was well tolerated. Asymptomatic, transient serum lipase elevations observed in phase II were consistent with findings in phase Ib. Adding dulanermin to rituximab did not improve ORR in these relapsed pts with follicular NHL. Rituximab(n = 22) Rituximab + dulanermin(n = 26) No. (%) of pts with OR 14 (63.6%) 16 (61.5%) 95% CI for ORR (41.8%, 81.3%) (42.1%, 78.8%) Complete response 5 3 Complete response, unconfirmed 0 1 Partial response 9 12 Abbreviation: CI, confidence interval. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Genentech Abbott Laboratories Roche Genentech Abbott Laboratories, Genentech

Combined therapy with the RANKL inhibitor RANK-Fc and rhApo2L/TRAIL/dulanermin reduces bone lesions and skeletal tumor burden in a model of breast cancer skeletal metastasis

In bone metastases, tumor cells interact with the bone microenvironment to induce osteoclastogenesis, leading to bone destruction and the growth factor release. RANK ligand (RANKL) is essential for osteoclast formation, function, and survival. Tumor cell-mediated osteolysis is thought to occur ultimately via induction of RANKL within the bone stroma, and inhibition of RANKL in models of breast cancer bone metastases blocks tumor-induced osteolysis and reduces skeletal tumor burden. In addition, the skeleton is co-opted by tumor cells and functions as a supportive tumor microenvironment. Inhibition of RANKL, by reducing tumor-induced osteoclastogenesis, may reduce the local release of growth factors and calcium which may potentially enhance the anti-tumor activity of cytotoxic or direct tumor apoptotic agents. Recombinant human Apo2 ligand/ TNF-related apoptosis-inducing ligand (rhApo2L/TRAIL/dulanermin) is a dual pro-apoptotic receptor agonist that preferentially induces apoptosis in cancer cells versus normal cells. We therefore examined RANKL inhibition (using RANK-Fc) in combination with rhApo2L/TRAIL on tumor-induced osteolysis and skeletal tumor burden in a murine intracardiac injection model of MDA-MB-231 breast carcinoma bone metastasis. rhApo2L/TRAIL treatment resulted in a rapid reduction of skeletal tumor burden. Treatment with RANK-Fc prevented osteolytic lesions and reduced skeletal tumor burden. Combining RANK-Fc with rhApo2L/TRAIL was superior to either rhApo2L/TRAIL or RANK-Fc alone at reducing skeletal tumor burden in the bone metastasis model. Our findings show that RANKL inhibition effectively inhibits pathologic osteolysis induced by human breast adenocarcinoma MDA-MB-231 cells in animals with established tumors, and also enhances the ability of rhApo2L/TRAIL to reduce skeletal tumor burden in vivo.

Development of Immunohistochemistry Assays to Assess GALNT14 and FUT3/6 in Clinical Trials of Dulanermin and Drozitumab

In vitro sensitivity to the proapoptotic receptor agonists dulanermin (rhApo2L/TRAIL) and drozitumab (DR5-agonist antibody) is strongly predicted by the expression of the O-glycosylation enzymes GALNT14 in non-small cell lung cancer (NSCLC) cell lines (among others) and of FUT3/6 in colorectal cancer (CRC) cell lines. We developed immunohistochemistry (IHC) assays that measure GALNT14 and FUT3/6 levels in archival formalin-fixed, paraffin-embedded human tumor tissue to determine marker prevalence in NSCLC and CRC tissue and to enable the future examination of these markers in clinical trials. GALNT14 or FUT3/6 ELISA-positive hybridoma clones were screened through IHC on cell pellets with known mRNA levels. The specificity of staining was examined in cell lines, normal tissue, and tumor tissue. GALNT14 and FUT3/6 IHC exhibited a golgi staining pattern and correlated with GALNT14 and FUT3/6 (but not GALNT2 and FUT4) mRNA expression levels in cell lines and normal tissues, suggesting specificity. GALNT14 and FUT3/6 H-scores were significantly higher in cell lines sensitive to dulanermin (P = 0.01 and P = 0.0004, respectively) and drozitumab (P = 0.03 and P < 0.0001, respectively) versus resistant cell lines. GALNT14 and FUT3/6 H-scores varied widely, with approximately 45% of NSCLC samples exhibiting weak to moderate GALNT14 staining (H-score of at least 25) and 70% of CRC samples exhibiting moderate to strong FUT3/6 staining (H-score of at least 125). GALNT14 and FUT3/6 expression can be assessed in human tumors using sensitive and specific IHC assays. Both assays are being deployed in ongoing clinical trials of dulanermin and drozitumab to assess potential utility for patient selection.

X Chromosome-linked Inhibitor of Apoptosis Regulates Cell Death Induction by Proapoptotic Receptor Agonists

Proapoptotic receptor agonists cause cellular demise through the activation of the extrinsic and intrinsic apoptotic pathways. Inhibitor of apoptosis (IAP) proteins block apoptosis induced by diverse stimuli. Here, we demonstrate that IAP antagonists in combination with Fas ligand (FasL) or the death receptor 5 (DR5) agonist antibody synergistically stimulate death in cancer cells and inhibit tumor growth. Single-agent activity of IAP antagonists relies on tumor necrosis factor-alpha signaling. By contrast, blockade of tumor necrosis factor-alpha does not affect the synergistic activity of IAP antagonists with FasL or DR5 agonist antibody. In most cancer cells, proapoptotic receptor agonist-induced cell death depends on amplifying the apoptotic signal via caspase-8-mediated activation of Bid and subsequent activation of the caspase-9-dependent mitochondrial apoptotic pathway. In the investigated cancer cell lines, induction of apoptosis by FasL or DR5 agonist antibody can be inhibited by knockdown of Bid. However, knockdown of X chromosome-linked IAP (XIAP) or antagonism of XIAP allows FasL or DR5 agonist antibody to induce activation of effector caspases efficiently without the need for mitochondrial amplification of the apoptotic signal and thus rescues the effect of Bid knockdown in these cells.