Tilsotolimod Exploits the TLR9 Pathway to Promote Antigen Presentation and Type 1 IFN Signaling in Solid Tumors: A Multicenter International Phase I/II Trial (ILLUMINATE-101)

PURPOSE

Tilsotolimod is an investigational synthetic Toll-like receptor 9 (TLR9) agonist that has demonstrated antitumor activity in preclinical models. The ILLUMINATE-101 phase I study explored the safety, dose, efficacy, and immune effects of intratumoral (it) tilsotolimod monotherapy in multiple solid tumors.

PATIENTS AND METHODS

Patients with a diagnosis of refractory cancer not amenable to curative therapies received tilsotolimod in doses escalating from 8 to 32 mg into a single lesion at weeks 1, 2, 3, 5, 8, and 11. Additional patients with advanced malignant melanoma were enrolled into an expansion cohort at the 8 mg dose. Objectives included characterizing the safety, establishing the dose, efficacy, and immunologic assessment. Blood samples and tumor biopsies of injected and noninjected lesions were obtained at baseline and 24 hours after treatment for immune analyses.

RESULTS

Thirty-eight and 16 patients were enrolled into the dose escalation and melanoma expansion cohorts, respectively. Deep visceral injections were conducted in 91% of patients. No dose-limiting toxicities (DLT) or grade 4 treatment-related adverse events were observed. Biopsies 24 hours after treatment demonstrated an increased IFN pathway signature and dendritic cell maturation. Immunologic profiling revealed upregulation of IFN-signaling genes and modulation of genes for checkpoint proteins. In the dose escalation cohort, 12 (34%) of 35 evaluable patients achieved a best overall response rate (ORR) of stable disease (SD), whereas 3 (19%) of 16 evaluable patients in the melanoma cohort achieved stable disease.

CONCLUSIONS

Overall, tilsotolimod monotherapy was generally well tolerated and induced rapid, robust alterations in the tumor microenvironment. See related commentary by Punekar and Weber, p. 5007.

Abstract 5652: Translational evidence of reactivated innate and adaptive immunity with intratumoral IMO-2125 in combination with systemic checkpoint inhibitors from a Phase I/II study in patients with anti-PD-1 refractory metastatic melanoma

Background: While checkpoint inhibitor (CPI) therapy has transformed metastatic melanoma (MM) treatment, many patients remain refractory. We reasoned that combining CPI with an agent that activates antigen presenting cells and improves T-cell priming may result in improved response. Our approach is to modulate the tumor microenvironment through image-guided intratumoral (i.t.) injection of the TLR9 agonist, IMO-2125, in combination with either ipilimumab (ipi) or pembrolizumab (pembro). We hypothesize that this will result in dendritic cell (DC) activation and induction of tumor-specific CD8+T-cells which will synergize with ipilimumab or pembrolizumab to overcome immune-escape. Based on this rationale we initiated a phase I/II clinical trial.

Study Design/Methods: Adults with refractory MM that have had prior PD-1 blockade therapy (with or without a BRAF inhibitor) are eligible. IMO-2125, in doses escalating from 4mg to 32mg, is given i.t. weeks 1, 2, 3, 5, 8, and 11 along with standard doses of ipilimumab or pembrolizumab. Primary endpoints are safety, tumor response, and PK. Multiple biopsies are obtained in both the injected and distant tumor pre- and on-treatment. Immune analyses include DC subsets and their activation status as well as T cell activation, function and proliferation. T-cell repertoire diversity is evaluated by high-throughput CDR3 sequencing and changes in gene expression signatures are assessed by nanoString. Changes in circulating cytokines are also being assessed during therapy.

Results: Enrollment is proceeding on both the IMO-ipilimumab and IMO-pembrolizumab dose-escalation arms of the trial. Safety is acceptable with no DLT recorded to date. Durable clinical responses (including 1 CR) have been observed with IMO-ipilimumab in patients who were refractory to PD-1 inhibitor. Fresh tumor biopsies show maturation (upregulation of HLA-DR) of the myeloid DC1 subset (CD1c+CD303-), upregulation of PD-L1 by malignant cells, as well as an IFNα response gene signature in the IMO-2125 injected tumor lesion 24 hrs post-treatment compared to pre-treatment biopsy. On-treatment biopsy results show a higher expression of CD56+ and Ki67+ effector CD8+ T-cells in responding patients. Initial CDR3 sequencing demonstrates increased diversity in the injected lesions of all patients assessed and expansion of top clones present in the distant lesion in a responding patient. Plasma analysis showed an increase in IFNγ levels in the plasma of responding patients.

Conclusions: These results demonstrate that IMO-2125 with a checkpoint inhibitor is a viable strategy to revive the immune response in tumors that are refractory to PD-1 inhibitors. Further clinical evaluation of both the IMO-ipilimumab and IMO-pembrolizumab combination is planned in a Phase 2 expansion of the current trial.

Citation Format: Cara Haymaker, Marc Uemura, Ravi Murthy, Marihella James, Daqing Wang, Julie Brevard, Suzanne Swann, James Geib, Mark Cornfeld, Srinivas Chunduru, Sudhir Agrawal, Cassian Yee, Jennifer Wargo, Rodabe Amaria, Sapna Patel, Hussein Tawbi, Isabella Glitza, Scott Woodman, Wen-Jen Hwu, Michael A. Davies, Patrick Hwu, Willem Overwjik, Chantale Bernatchez, Adi Diab. Translational evidence of reactivated innate and adaptive immunity with intratumoral IMO-2125 in combination with systemic checkpoint inhibitors from a Phase I/II study in patients with anti-PD-1 refractory metastatic melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5652. doi:10.1158/1538-7445.AM2017-5652

Intratumoral (i.t.) IMO-2125 (IMO), a TLR9 agonist, in combination with ipilimumab (ipi) in PD-(L)1 refractory melanoma (RM)

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Background: Checkpoint inhibitors (CPI) have transformed melanoma treatment but many patients remain refractory. CPI plus i.t. IMO may improve response by activating innate immune function. Based on this we initiated a trial of IMO in combination with ipi or pembrolizumab (pem) in RM. Methods: Adults with RM that progressed during or after ≥ 12 weeks of PD-1 therapy are eligible. IMO, 4 – 32 mg, is given i.t. for 6 doses, along with either ipi or pem. Endpoints are safety, response, biomarkers, and PK. Injected and distant tumors are biopsied pre-treatment and again at 24 hrs (injected tumor), weeks 8 and 13 for immune analyses. Results: As of October 7, 2016, 10 pts have been treated; median age 55 (range: 39-76), 8 with visceral and 1 with brain metastases. Two pts have mucosal histology. 60% have BRAF mutations. Prior duration of anti-PD-(L)1 therapy ranges from 8 to 63 weeks and median time from last PD-1 therapy to onset of study treatment is 6 (4,57) weeks. IMO has been administered at 4, 8, and 16 mg. No DLTs have been observed and there have been no treatment-related discontinuations or deaths. Ipi was discontinued after the second dose in one subject with previous ipi-related hepatitis for recurrent transaminase elevations (grade 4). Grade 3 hypophysitis is the only other immune-related AE (2 pts). Most frequent TEAE (N > 2) are nausea, vomiting, anemia, diarrhea, increases in ALT/AST/GGT/triglycerides, chills, fatigue, pyrexia, and leukopenia; the majority are low-grade. 6 patients are evaluable for response - CR (1), PR (2), SD (2), PD (1) by RECIST1.1. Tumor biopsies show consistent maturation of the myeloid DC1 subset in IMO injected tumors at 24 hrs. Week 8 results are consistent with a higher rate of proliferative (Ki67) effector CD4+ and CD8+ T-cells in responders. Circulating IFNγ shows 2-3 fold increase in responders. Conclusions: The combination of IMO and ipi is tolerable and has activity in PD-1 refractory melanoma. Dose escalation is ongoing and a Phase 2 expansion with both combinations is planned. Updated safety, antitumor activity, PK, and biomarker data will be presented at the meeting. Clinical trial information: NCT02644967.

Abstract 599: Potential biomarkers of Smac mimetic tumor sensitivity: inhibitor of apoptosis protein DNA copy number

The inhibitor of apoptosis (IAP) family of proteins block programmed cell death and promote survival signaling. Birinapant (TL32711) is a bivalent Smac Mimetic that antagonizes multiple IAPs to promote efficient apoptosis and is currently in clinical trials as a single agent and in combination with multiple chemotherapeutics. However, to enrich for patient populations that will maximally benefit from each specific treatment regimen, it is critical to identify predictive biomarkers to achieve maximum response. Based on multiple individual studies, members of IAPs have been reported to be overexpressed in multiple cancers. Therefore, the main focus of this study was to evaluate DNA copy number alterations of different IAPs in a variety of cancer cell lines, and to evaluate their association with birinapant sensitivity. Our initial analysis of the Cancer Cell Line Encyclopedia (CCLE) database revealed that approximately 41% (397/972) of the cancer cell lines carried DNA amplification of different IAPs. Detailed analysis showed copy number amplification of ML-IAP in 214 cell lines (22%), cIAP1/2 in 85 cell lines (∼9%), NAIP (BIRC1) in 37 cell lines (∼4%), BIRC8 (ILP-2) in 39 cell lines (4%) and XIAP in 22 cell lines (∼2%). Tumor-type evaluation indicated that ∼50% pancreatic, ∼25% melanoma, ∼35% colorectal, ∼40% ovarian, and ∼7% AML cancer cell lines carried DNA amplification of different IAPs, indicating that IAPs are frequently amplified in cell lines of various cancer types. To understand the association of IAP amplification and birinapant sensitivity, we analyzed 94 cell lines present in the CCLE for birinapant sensitivity with or without TNF, and with or without TRAIL. Our analyses indicated that approximately 20% (19/94) of cancer cell lines were birinapant single-agent sensitive, and ∼80% (75/94) were single resistant cell lines. Furthermore, ∼50% (37/75) of the birinapant single resistant cell lines showed synergistic induction of apoptosis when birinapant was combined with either TNF or TRAIL ("synergy-positive"). Our analysis showed that the frequency of cIAP1/2 amplification in birinapant single-agent sensitive cell lines was 3-fold higher (4/19, 21%) than in single-agent resistant cancer cell lines (5/75, 7%). However, there was no difference in IAP gene amplification between birinapant "synergy-positive" and "synergy-negative" resistant cell lines. This lack of correlation with the synergistic response observed with the combination of birinapant plus either TNF or TRAIL implies the involvement of additional pathways that we are attempting to define. We will present a comprehensive dataset for the role of IAP gene amplification in birinapant tumor sensitivity.

Citation Format: Gurpreet S. Kapoor, Brian Geier, Eric M. Neiman, Yasuhiro Mitsuuchi, Christopher A. Benetatos, Stephen M. Condon, Srinivas Chunduru, C. Glenn Begley. Potential biomarkers of Smac mimetic tumor sensitivity: inhibitor of apoptosis protein DNA copy number. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 599. doi:10.1158/1538-7445.AM2013-599

Abstract 3333: Birinapant, a novel bivalent Smac mimetic drug, is superior to monovalent Smac mimetics in inhibition of NF-kB by targeting TRAF2-bound cIAP1 and cIAP2

A variety of Smac-mimetic drugs have been developed to target the inhibitor of apoptosis (IAP) proteins including X chromosome-linked IAP (XIAP), cellular IAP proteins (cIAP1 and cIAP2) and ML-IAP whose gene mutations, amplifications and chromosomal translocations have been implicated in various malignancies. The IAPs also play an important role in multiple signaling pathways including the TNFα-mediated NF-kB and MAPK pathways (inflammatory responses) and pattern recognition receptor signaling pathways (innate immunity). Smac-mimetics have been designed to mimic the IAP-binding motif of the second mitochondria-derived activator of caspase (Smac). The IAP-binding motif consists of four amino acids (AVPI) that serve as an endogenous IAP antagonist. Structurally different Smac-mimetic compounds have been published and showed different binding affinity to IAP proteins. These differences in structure and binding have important consequences in terms of biological activity. Here, we present evidence that bivalent Smac-mimetics are superior to monovalent Smac-mimetics in their ability to inhibit NF-kB in cells stimulated with TNFα. Over 300 monovalent and 300 bivalent Smac-mimetics, including compounds whose structures have been published, were tested for ability to degrade cIAP1 and cIAP2, and inhibit NF-kB in cell-based assays. Inhibition of NF-kB by bivalent Smac-mimetics correlated (R²=0.78) with the degradation of cIAP1 over a range of four logs, while monovalent Smac-mimetics did not (R²=0.20). Furthermore, monovalent Smac-mimetics degraded TRAF2-bound cIAP1 and cIAP2 less effectively (1/10-1/100 fold) compared to bivalent Smac-mimetics. While bivalent Smac-mimetics effectively degraded cIAP1 and cIAP2, birinapant (TL32711), a bivalent Smac-mimetic currently in Phase 2 clinical trials, was unique in its ability to preferentially degrade TRAF2-bound cIAP1 and cIAP2. Inhibition of NF-kB by birinapant was further characterized by the ImageStream cytometry, which showed that the nuclear translocation of p65 in response to TNFα stimulation was blocked in both HeLa and HL-60 cells. These data demonstrate that bivalent Smac-mimetics are superior to monovalent Smac-mimetics in degrading TRAF2-bound cIAPs, in inhibition of NF-kB and efficiently mediating cell death. Furthermore, the unique profile of birinapant versus other bivalent Smac-mimetics may explain its preclinical and clinical safety profile.

Citation Format: Yasuhiro Mitsuuchi, Stephen M. Condon, Eric M. Neiman, Christopher A. Benetatos, Martin E. Seipel, Gurpreet Singh Kapoor, Angeline C. Mufalli, Guangyao Yu, Orla Maguire, Hans Minderman, Mark A. Mckinlay, Martin Graham, David Weng, Srinivas Chunduru. Birinapant, a novel bivalent Smac mimetic drug, is superior to monovalent Smac mimetics in inhibition of NF-kB by targeting TRAF2-bound cIAP1 and cIAP2. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3333. doi:10.1158/1538-7445.AM2013-3333

Abstract 3336: The Smac Mimetic Birinapant Synergistically Induces Apoptosis in Combination with Type I Interferons and GM-CSF

The Inhibitor of Apoptosis (IAP) protein family is able to inhibit cell death and promote survival signaling triggered by a wide variety of stimuli. Two members of this family in particular, cIAP1 and cIAP2, play key roles in enabling tumor necrosis factor alpha (TNFα)-induced nuclear factor-kappa beta (NF-kB) activation and inflammatory responses. Birinapant (TL32711) is a bivalent Smac Mimetic that antagonizes multiple IAP family members resulting in the conversion of TNFα-induced survival signaling into an apoptotic response, an effect which is more prominent in tumor cells than their normal counterparts. Combining birinapant with agents capable of increasing the levels of TNFα in the tumor microenvironment represents a novel approach to cancer treatment. We have tested the ability of interferon-alpha/-beta (IFN-α, IFN-β) and granulocyte macrophage colony stimulating factor (GM-CSF), both known to be immunomodulatory agents, for their ability to stimulate TNFα production by peripheral blood mononuclear cells (PBMC). Treatment with each cytokine induced the production of TNFα by cultured PBMC as measured by ELISA. Supernatants of IFN-α/-β and GM-CSF-treated PBMC cultures were able to sensitize resistant tumor cells to Smac Mimetics in a TNFα-dependent manner. Furthermore, the combination of birinapant and either IFN-β or GM-CSF synergistically inhibited the development of RENCA tumors in a syngeneic mouse prevention model. Due to the highly aggressive nature of the syngeneic tumors, this model is performed by simultaneous implantation of tumor cells and initiation of dosing of test agents. Activity in this model is measured by prevention of tumor outgrowth. Birinapant in combination with IFN-β resulted in only 5 of 18 measurable tumors, versus 19 of 20 tumors in vehicle-treated mice, 16 of 20 tumors in IFN-β alone-treated mice and 13 of 20 tumors in birinapant alone-treated mice. In addition, when tumor growth occurred it was delayed in mice treated with the combination. Similarly, the birinapant and GM-CSF combination treatment resulted in 9 of 20 tumors, versus 20 of 20 tumors in the vehicle-treated mice, 20 of 20 tumors in the GM-CSF alone-treated mice, and 16 of 20 tumors in the birinapant alone-treated mice. In addition when tumors did develop in the combination-treated mice, their growth was substantially delayed: 4 of 10 mice treated with the combination of birinapant and GM-CSF were still on study on day 85 post initiation - approximately 40 days post dosing - with no measureable tumor. The combination of birinapant with immunomodulatory agents that induce TNF represents a potential novel therapeutic strategy.

Citation Format: Christopher A. Benetatos, Jennifer M. Burns, Ernest C. Borden, Daniel Lindner, Yasuhiro Mitsuuchi, Mark A. Mckinlay, Gurpreet Singh Kapoor, Eric M. Neiman, Martin E. Seipel, Guangyao Yu, Martin Graham, David Weng, Stephen M. Condon, C. Glenn Begley, Srinivas Chunduru. The Smac Mimetic Birinapant Synergistically Induces Apoptosis in Combination with Type I Interferons and GM-CSF. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3336. doi:10.1158/1538-7445.AM2013-3336

Smac mimetic enables the anticancer action of BCG-stimulated neutrophils through TNF-α but not through TRAIL and FasL

BCG, the current gold standard immunotherapy for bladder cancer, exerts its activity via recruitment of neutrophils to the tumor microenvironment. Many patients do not respond to BCG therapy, indicating the need to understand the mechanism of action of BCG-stimulated neutrophils and to identify ways to overcome resistance to BCG therapy. Using isolated human neutrophils stimulated with BCG, we found that TNF-α is the key mediator secreted by BCG-stimulated neutrophils. RT4v6 human bladder cancer cells, which express TNFR1, CD95/Fas, CD95 ligand/FasL, DR4, and DR5, were resistant to BCG-stimulated neutrophil conditioned medium but effectively killed by the combination of conditioned medium and Smac mimetic. rhTNF-α and rhFasL, but not rhTRAIL, in combination with Smac mimetic, generated signature molecular events similar to those produced by BCG-stimulated neutrophils in combination with Smac mimetic. However, experiments using neutralizing antibodies to these death ligands showed that TNF-α secreted from BCG-stimulated neutrophils was the key mediator of anticancer action. These findings explain the mechanism of action of BCG and identified Smac mimetics as potential combination therapeutic agents for bladder cancer.

Abstract 1939: TL32711, a novel Smac mimetic, exerts significant antitumor efficacy in primary pancreatic adenocarcinoma model

Introduction. Pancreatic cancer is highly resistant to treatment. Inhibitors of apoptosis (IAPs) were overexpressed in pancreatic cancer cells and IAPs downregulation were shown to induce sensitivity to death receptor signaling, cytotoxic agents and radiation. TL32711, a novel Smac mimetic, is a potent IAP antagonist that induces caspase-dependent apoptosis and NFkB canonical pathway inactivation. Here, we investigated the efficacy of TL32711 using a patient-derived primary pancreatic cancer explant model that mirrors the disease's biological heterogeneity. Methods. Effect of TL32711 alone and with TRAIL was evaluated in Panc1 by immunoblotting and Trypan blue staining. Dose escalation studies were performed in 2 primary pancreatic tumors at i.p. 30 mg/kg, 45 mg/kg and 60 mg/kg twice weekly and tumor volume were measured for 28 days. No significant toxicity was observed in tumor-bearing mice at all dose levels. An additional 6 primary pancreatic tumors were evaluated at 60 mg/kg. H&E slides of donor patients for these tumors were evaluated and untreated tumors analyzed by gene microarrays to explore for potential efficacy biomarkers. Tumor, plasma and liver samples were obtained from dose escalation studies for pharmacokinetic analysis. Results. TL32711 treatment resulted in rapid cIAP1 degradation leading to caspase-3 activation in Panc1, and exerted a dose-dependent pro-apoptotic effect that was synergized with TRAIL co-incubation in in vitro studies. In primary tumor explant studies, TL32711 dosed at 60 mg/kg exerted significant growth arrest/inhibition in 6 primary tumors (T/C range −0.1 to 0.2) and suboptimal growth inhibition in 2 (T/C ∼0.4). H&E slides of resected pancreatic cancer specimens for 7 donor patients were available for evaluation, and there was no relationship between histological findings (inflammatory infiltrate, stroma, neutrophil/lymphocyte ratio and necrosis) and in vivo TL32711 efficacy. Dose escalation studies showed a dose-dependent growth inhibitory effect of TL32711 in 2 primary tumors: 30mg/kg achieved significant growth inhibition in #17624 but not #12872. Significant growth inhibition was achieved in both at >= 45 mg/kg. Pharmacokinetic analysis showed that TL32711 efficacy correlated with tumor drug exposure and that tumor concentrations at the effective doses were in the range of what is achievable in patients’ tumors at clinically tolerable doses. Results from gene microarray analysis will be summarized. Conclusions. TL32711 demonstrated significant single agent efficacy in pancreatic cancer that correlated with tumor drug exposure, and the efficacious tumor drug exposure here is achievable in tumors at tolerated doses in clinical studies. Clinical trials evaluating TL32711 in pancreatic cancer are planned.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1939. doi:1538-7445.AM2012-1939

Abstract 3857: Smac mimetic TL32711 and TRAIL synergistically induce apoptosis of germinal center B lymphoma cells

TL32711, a Smac mimetic in clinical testing, potently targets Inhibitor of Apoptosis Proteins (IAPs, including cIAPs and XIAP) to unblock intrinsic and extrinsic pathways, enabling caspase-dependent apoptosis via multiple signals including TRAIL (Tumor Necrosis Factor-Related Apoptosis Inducing Ligand). TL32711 also inactivates canonical and activates non-canonical NF-κB signaling through cIAPs. We investigated the pro-apoptotic effects of TL32711, alone and in combination with TRAIL to activate the extrinsic pathway, in a panel of B cell lymphoma cell lines representing germinal center/follicular (GC) vs activated B cell (ABC) histologies. We hypothesized that the efficacy of this potential combination therapeutic strategy might differ between GC and ABC lymphoma types, as ABC are reported to be NF-kB dependent. We used the following EBV negative cell lines: WSU- FSCCL t(14:18)+ follicular lymphoma (FL), FC-TxFL2 t(14:18)+ transformed FL and SU-DHL4 GC-type diffuse large B cell lymphoma (DLBCL) as examples of GC origin lymphomas. U2932 and TMD8 served as ABC-type DLBCL. Apoptosis was determined by annexin V staining after 48 hr incubation (TL32711 added 2-3 hr after TRAIL). The contribution of the different apoptotic pathways was determined by caspase-3 (common), -8 (extrinsic), and-9 (intrinsic) activity, assessed by flow cytometric methods and Western blot. TL32711 had little effect as a single agent on any of these B cell lymphoma cell lines at ≤ 100nM, though apoptosis was induced at 10-20 µM in GC types. TRAIL alone (10-25 ng/ml) induced apoptosis in the 3 GC lines, but had little effect on the 2 ABC lines. Combination of TL32711 and TRAIL at low concentrations showed marked apoptosis in GC lines, with minimal to no effect for each agent alone. In the combination-treated GC types, caspases -3, -8 and -9 were significantly induced, confirming activation of both pathways. We had previously shown in FSCCL and TxFL2 that caspase-8 induction also cleaved tBID, activating the intrinsic apoptotic pathway via caspase-9. GC subtypes, including FL, transformed FL and GC-DLBCL were sensitive to TRAIL and TL32711 at clinically achievable concentrations for TL32711, with supra-additive combination effects. ABC-type DLBCL were not sensitive to either agent alone or in combination. We are investigating whether ABC-DLBCL are truly dependent on canonical NF-κB activation for survival or have other mechanisms of resistance to TRAIL and IAP inhibition. These data suggest that clinical trials of TL32711 may focus on FL and GC lymphoma in combination with TRAIL or TRAIL-agonists.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3857. doi:1538-7445.AM2012-3857

Sensitization of human bladder tumor cells to TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis with a small molecule IAP antagonist

Urothelial carcinoma of the bladder accounts for approximately 5% of all cancer deaths in humans. The large majority of bladder tumors are non-muscle invasive at diagnosis, but even after local surgical therapy there is a high rate of local tumor recurrence and progression. Current treatments extend time to recurrence but do not significantly alter disease survival. The objective of the present study was to investigate the tumoricidal potential of combining the apoptosis-inducing protein TNF-related apoptosis-inducing ligand (TRAIL) with a small molecule inhibitor of apoptosis proteins (IAP) antagonist to interfere with intracellular regulators of apoptosis in human bladder tumor cells. Our results demonstrate that the IAP antagonist Compound A exhibits high binding affinity to the XIAP BIR3 domain. When Compound A was used at nontoxic concentrations in combination with TRAIL, there was a significant increase in the sensitivity of TRAIL-sensitive and TRAIL-resistant bladder tumor lines to TRAIL-mediated apoptosis. In addition, modulation of TRAIL sensitivity in the TRAIL-resistant bladder tumor cell line T24 with Compound A was reciprocated by XIAP small interfering RNA-mediated suppression of XIAP expression, suggesting the importance of XIAP-mediated resistance to TRAIL in these cells. These results suggest the potential of combining Compound A with TRAIL as an alternative therapy for bladder cancer.

Smac mimetic reverses resistance to TRAIL and chemotherapy in human urothelial cancer cells

PURPOSE

inhibitors of apoptosis proteins (IAPs) have been shown to contribute to resistance of neoplastic cells to chemotherapy and to biologic antineoplastic agents. Consequently, new agents are being developed targeting this family of proteins. In a panel of bladder cancer cell lines, we evaluated a Smac mimetic that antagonizes several IAPs for its suitability for bladder cancer therapy. Experimental design: A panel of seven bladder cancer cell lines were evaluated for sensitivity to the Smac mimetic compound-A alone, TRAIL alone, chemotherapy alone, compound-A plus TRAIL, and compound-A plus chemotherapy by DNA fragmentation analysis. IAP levels and caspase activation were examined by western blotting. Release of caspase-3 from X-linked inhibitor of apoptosis protein (XIAP), the most effective IAP, was assessed by immunoprecipitation and western blotting. Finally, siRNA knockdown of XIAP was correlated with the sensitivity of cells to apoptosis induced by compound-A plus TRAIL by DNA fragmentation and western blotting.

RESULTS

single-agent compound-A had little effect, but compound-A augmented TRAIL- and chemotherapy-induced apoptosis. Immunoblotting showed that combination treatment with compound-A and TRAIL resulted in cleavage of procaspase-3 and procaspase-7, activation of which irreversibly commits cells to apoptosis. Immunoprecipitation of XIAP showed displacement of active caspase-3 fragments from XIAP, supporting the proposed mechanism of action. Furthermore, siRNA-mediated silencing of XIAP similarly sensitized these cells to apoptosis.

EXPERIMENTAL DESIGN

a panel of seven bladder cancer cell lines were evaluated for sensitivity to the Smac mimetic compound-Alone, TRAIL alone, Chemotherapy alone, compound-A plus TRAIL and compound-A plus chemotherapy by DNA fragmentation analysis. IAP levels and caspase activation were examined by western blotting. Release of caspase-3 from X-linked inhibitor of apoptosis protein (XIAP), the most effective IAP, was assessed by immunoprecipitation and western blotting. Finally siRNA knockdown of XIAP was correlated with the sensitivity of cells to apoptosis induced by compound-A plus TRAIL by DNA fragmentation and western blotting.

CONCLUSION

our results suggest that targeting of XIAP with the Smac mimetic compound-A has the potential to augment the effects of a variety of chemotherapeutic and biologic therapies in bladder cancer.

Newly synthesized hepatitis C virus replicon RNA is protected from nuclease activity by a protease-sensitive factor(s)

Biochemical characterization of hepatitis C virus (HCV) replication using purified, membrane-associated replication complexes is hampered by the presence of endogenous nuclease activity that copurifies with the replication complex. In this study, pulse-chase analyses were used to demonstrate that newly synthesized replicon RNA was protected from nuclease activity by a factor(s) that was sensitive to 0.5% NP-40 or protease treatment. Nuclease susceptibility was not related to disruption of lipid membranes, since NP-40 did not significantly affect the buoyant density of HCV replication complexes or protease susceptibility of HCV NS3 and NS5A proteins. These results suggest that a protease-sensitive factor(s) protects newly synthesized RNA from nuclease degradation.

In vivo model of adeno-associated virus vector persistence and rescue

Gene therapy vectors based on human DNA viruses could be mobilized or rescued from individuals who are subsequently infected with the corresponding wild-type (wt) helper viruses. This phenomenon has been effectively modeled in vitro with both adenovirus (Ad) and adeno-associated virus (AAV) vectors but has not previously been studied in vivo. In the current study, we have developed an in vivo model to study the interactions of a recombinant AAV vector (AAV-CFTR) with wt AAV type 2 (AAV2) and a host range mutant Ad (Ad2HR405) for which monkey cells are permissive (D.E.Brough, S.A.Rice, S.Sell, and D.F.Klessig, J. Virol. 55:206-212, 1985). AAV-CFTR was administered to the respiratory epithelium of the nose or lung of rhesus macaques. Primary cells were harvested from the infusion site at time points up to 3 months after vector administration to confirm vector DNA persistence. Vector DNA was present in episomal form and could be rescued in vitro only by addition of wt AAV2 and Ad. In in vivo rescue studies, vector was administered before or after wt-AAV2 and Ad2HR405 infection, and the shedding of AAV-CFTR was examined. Ad2HR405 and wt-AAV2 infections were established in the nose with concomitant administration. wt-AAV2 replication occurred in the lung when virus was administered directly at a high titer to the lower respiratory tract. AAV-CFTR vector rescue was also observed in the latter setting. Although these studies were performed with small numbers of animals within each group, it appears that AAV-CFTR DNA persists in the primate respiratory tract and that this model may be useful for studies of recombinant AAV vector rescue.