Checkpoint Inhibitors In Preclinical Models Research Articles

Abstract 6578: N17465, a systemically deliverable elastase, attenuates tumorigenesis and stimulates anti-tumor immunity

Abstract Background. Neutrophil elastase (ELANE) - a neutrophil-derived serine protease - kills a wide range of cancer cells without harming non-cancer cells through a unique killing program involving histone H1 and the death domain of CD95. Although ELANE attenuates tumor growth and induces anti-tumor immunity following intratumoral delivery (Cui et al., Cell, 2021), systemic delivery is stymied by the presence of serine protease inhibitors in blood (eg. alpha-1-antitrypsin (A1AT) which rapidly inhibit its enzymatic activity essential for its anti-cancer function. To overcome this challenge, we developed N17465, an enzyme that resists serine protease inhibitors in blood, and tested its effects on tumor growth, both as a monotherapy and in combination with checkpoint inhibitors. Methods. Enzymatic properties: N17465 enzymatic activity was quantified in the +/- of A1AT or plasma in vitro, and in blood following intravenous (I.V) injection into tumor-bearing mice. Enzyme activity assays included a fluorogenic substrate AAPV-AMC and the C-terminal domain of CD95 (amino acids212-335). Anti-cancer properties: For in vitro studies, cells were treated with N17465 and viability was quantified by calcein-AM and immunogenic cell death (ICD) markers. Cancer/non-cancer cells included human/murine cell lines and primary cells from ovarian cancer (OvCa) patients. For in vivo studies, N17465 was injected I.V and effects on tumor growth, immunology and survival were assessed as monotherapy or in combination with a checkpoint inhibitor (anti-CTLA4) in pre-clinical models. Results. N17465 maintained enzymatic activity following incubation with A1AT or mouse/human plasma in vitro, and following I.V injection into CT26 tumor-bearing mice in vivo. Importantly, protecting N17465 from serine protease inhibitors did not interfere with its ability to cleave CD95 (therapeutic target) or selectively kill cancer cells in vitro. Indeed, N17465 induced ICD markers, killed a wide range of murine/human cancer cells and also well tolerated by non-cancer cells. Systemically delivered N17465 produced durable tumor regression in a murine CT26 colon cancer model resulting in ~50% tumor-free mice, induced a favorable immune profile, and synergized with anti-CTLA4. N17465 also exhibited efficacy across a range of xenograft models spanning human colon, prostate, and lung cancer, as well as OvCa patient-derived CDX models. Conclusions. Altogether, our data demonstrate that N17465 selectively kills cancer cells, produces durable responses in mice, induces favorable immunology and synergies with checkpoint inhibitors in pre-clinical models. Its ability to maintain enzymatic activity in blood following systemic delivery, selectively kill a wide range of cancer cells, and stimulate anti-tumor immunity warrants further investigation of this unique therapeutic modality across a wide range of solid tumors. Citation Format: Ravindra Gujar, Chang Cui, Christine Lee, Maria Fumagalli, Nicole Martinez, Hannah Liu, Nicole Grigaitis, Sonia Feau, Lev Becker. N17465, a systemically deliverable elastase, attenuates tumorigenesis and stimulates anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6578.

Abstract 1813: Selective ITK blockade induces antitumor responses and enhances efficacy to immune checkpoint inhibitors in preclinical models

Abstract Interleukin 2 inducible T cell kinase (ITK) plays a role in both T cell receptor (TCR) signaling and T helper cell differentiation. ITK-/- mice exhibit defects in Th2 differentiation while retaining the ability to differentiate into Th1 cells that secrete IFNγ. We generated CPI-818, a covalent inhibitor of ITK (KD 2.5nM) with > 100 fold selectivity over resting lymphocyte kinase (RLK) and other TEC family kinases. This drug is now being evaluated as a single agent in an ongoing Phase 1 clinical trial in refractory T cell lymphoma where objective tumor responses have been observed. In the studies reported here, we have investigated the immunomodulatory effects of specific ITK blockade of human T cells with CPI-818 in vitro and in vivo in murine tumor models. Analysis of the cytokine profiles in human CD4 T cells differentiated under non-polarizing, Th1 or Th2 polarizing conditions showed that CPI-818 inhibited generation of Th2-associated cytokines whereas, production of Th1 cytokines such as IFNγ were largely unaffected. Suppression of IL-2-mediated proliferative response occurred only at high concentrations of CPI-818 (>1uM). The effect of CPI-818 on anti-tumor immunity was evaluated in both murine syngeneic CT26 colon cancer and EL4 T cell lymphoma models. In vivo treatment of animals with established tumors showed single-agent anti-tumor activity in both models. Combining CPI-818 with suboptimal doses of anti-PD1 and anti-CTLA4 synergistically inhibited the growth of established CT26 tumors, leading to complete tumor elimination in 100% treated animals. Furthermore, triple combination therapy elicited durable anti-tumor immune memory after animals were rechallenged with a new engraftment of CT26 cells. Enhancement of anti-tumor activity required CD8+ T cells as in vivo antibody-mediated depletion of CD8, but not CD4, abolished the efficacy of CPI-818 monotherapy. Consistent with that, we found increased tumor-infiltrating CD8+ T cells and increased ratio of CD8: Treg in the responding tumors of CPI-818 treated animals. Levels of several exhaustion makers were down-regulated by treatment with CPI-818, suggesting that inhibition of ITK by CPI-818 produces favorable changes in the tumor microenvironment. Our findings provide insights into the effects of selective ITK blockade on tumor immunity and its potential role in immunotherapy. Citation Format: Lih-Yun Hsu, Rahul D. Pawar, Dan Li, Poorva Ghosh, Kevin Nguyen, Carlene Williams, Yuqin Song, Ning Ding, Erik Verner, Richard A. Miller. Selective ITK blockade induces antitumor responses and enhances efficacy to immune checkpoint inhibitors in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1813.

Low-Intensity Pulsed Ultrasound-Mediated Blood-Brain Barrier Opening Increases Anti-Programmed Death-Ligand 1 Delivery and Efficacy in Gl261 Mouse Model

Therapeutic antibodies targeting immune checkpoints have shown limited efficacy in clinical trials in glioblastoma (GBM) patients. Ultrasound-mediated blood-brain barrier opening (UMBO) using low-intensity pulsed ultrasound improved drug delivery to the brain. We explored the safety and the efficacy of UMBO plus immune checkpoint inhibitors in preclinical models of GBM. A blood-brain barrier (BBB) opening was performed using a 1 MHz preclinical ultrasound system in combination with 10 µL/g microbubbles. Brain penetration of immune checkpoint inhibitors was determined, and immune cell populations were evaluated using flow cytometry. The impact of repeated treatments on survival was determined. In syngeneic GL261-bearing immunocompetent mice, we showed that UMBO safely and repeatedly opened the BBB. BBB opening was confirmed visually and microscopically using Evans blue dye and magnetic resonance imaging. UMBO plus anti-PDL-1 was associated with a significant improvement of overall survival compared to anti-PD-L1 alone. Using mass spectroscopy, we showed that the penetration of therapeutic antibodies can be increased when delivered intravenously compared to non-sonicated brains. Furthermore, we observed an enhancement of activated microglia percentage when combined with anti-PD-L1. Here, we report that the combination of UMBO and anti-PD-L1 dramatically increases GL261-bearing mice's survival compared to their counterparts treated with anti-PD-L1 alone. Our study highlights the BBB as a limitation to overcome in order to increase the efficacy of anti-PD-L1 in GBM and supports clinical trials combining UMBO and in GBM patients.

A phase II study of talazoparib plus avelumab in patients with stage IV or recurrent nonsquamous non–small cell lung cancer bearing pathogenic STK11 genomic alterations (SWOG S1900C, LUNG-MAP sub-study, NCT04173507).

9060 Background: Inactivating STK11 genomic alterations are prevalent in non-squamous (nsq) NSCLC and define a patient (pt) subgroup with poor prognosis and inferior response to immune checkpoint inhibitors (CPIs). PARP inhibitors (PARPi) can potentiate response to CPIs in preclinical models. We conducted a single arm Phase II study within Lung-MAP to evaluate the efficacy and safety of talazoparib in combination with avelumab in patients (pts) with previously treated nsq NSCLC harboring pathogenic STK11 genomic alterations. Methods: Eligibility: STK11 pathogenic somatic mutation or bi-allelic loss on tumor identified via LUNGMAP screening; stage IV or recurrent nsq NSCLC, receipt of one prior line of anti-PD-1/anti-PD-L1 therapy and platinum-based chemotherapy for stage IV or recurrent disease (sequentially or in combination) and disease progression > 42 days following treatment initiation, a ECOG PS of 0-1, adequate organ function and no previous PARPi exposure. Pts received talazoparib (1000 mg PO daily) plus avelumab (800 mg IV Q2W). Co-primary objectives were to evaluate the best objective response rate (ORR) and disease control rate at 12 weeks (DCR12) after study registration, assessed by RECISTv1.1. Rejection of an ORR of 10% required ≥ 8 responses or rejection of a DCR12 of 30% required ≥18 w/ disease control at 12 weeks and ≥4 responses. Results: 47 pts enrolled from January 16 - November 16, 2020; 42 pts met eligibility (50% male, 50% female). 54% of pts had PD-L1 TPS < 1%. The median TMB was 8.83 Mut/Mb and 45% of pts had KRAS mutations. 52% of the pts had received ≥2 prior lines of treatment for stage IV disease. As of the November 24, 2021 data cutoff, 3 pts remain on treatment, the ORR was 2% (n = 1) and the DCR12 was 40% (n = 17). 26 pts (62%) had SD as best objective response. One responding pt remained on treatment for > 14 mo. The median progression-free survival (39 events) was 2.7 mo (95% CI, 1.6-3.9 mo) and the median overall survival (30 events) was 7.6 mo (95% CI, 6.3-12.2 mo). There were no reported grade 5 treatment toxicities and most grade 3-4 toxicities were hematologic. Additional biomarker analysis to assess effects of key co-mutations on clinical outcomes will be presented. Conclusions: Treatment with talazoparib and avelumab did not meet the pre-specified threshold for efficacy in previously treated STK11-mutant NSCLC in this biomarker-driven Phase II study, though durable disease stabilization was observed. Further studies are required to determine optimal therapeutic approaches for this challenging subset of NSCLC pts. Funding: NIH/NCI grants U10CA180888, U10CA180819. Talazoparib was provided by Pfizer. Avelumab was provided by Pfizer, as part of an alliance between Pfizer and the healthcare business of Merck KGaA, Darmstadt, Germany (CrossRef Funder ID: 10.13039/100004755). Clinical trial information: NCT04173507.

Abstract P248: The tyrosine kinase inhibitor XL092 promotes an immune-permissive tumor microenvironment and enhances the anti-tumor activity of immune checkpoint inhibitors in preclinical models

Abstract Background: Cabozantinib, an inhibitor of MET, VEGFR2, AXL, and MER, has shown significant clinical activity in multiple solid tumors, both alone and in combination with immune checkpoint inhibitors (ICIs). XL092 has a similar target profile to cabozantinib but with a significantly shorter clinical half-life and pharmacokinetic properties suitable for once daily oral dosing (Hsu, Eur J Cancer, 2020). In preclinical studies, the combination of XL092 and anti–PD-1 exhibited greater anti-tumor activity than either agent alone. Here, we describe further preclinical characterization of XL092 in combination with ICIs, including modulation of immune cells in vivo and in vitro. Methods: Pharmacodynamic activity was evaluated in the MC38 syngeneic tumor model following treatment with XL092 alone or in combination with anti–PD-1 or anti–PD-L1. Tumor CD31+ microvessel density and CD8+ T cell infiltration were assessed by immunohistochemistry, and circulating immune cells were measured by FACS. Macrophage repolarization and efferocytosis were evaluated in vitro using primary human macrophages. Results: Treatment of MC38 tumor-bearing mice with XL092 inhibited tumor angiogenesis in a dose-dependent manner, and combination treatment with XL092 and anti–PD-1 increased CD8+ lymphocyte tumor cell infiltration compared with either agent alone. XL092 and ICIs also promoted significant changes in peripheral immune cell subsets in the MC38 model. Treatment with XL092 alone or in combination with ICIs increased circulating levels of CD4+ and CD8+ T cells and B cells, and combination treatment with anti–PD-1 decreased levels of proliferating and IFNg-producing effector T cells in circulation. While the level of peripheral NK cells was unaffected by these treatments, XL092 alone or in combination with ICIs decreased levels of proliferating and GrzB+ effector cells in circulation. Treatment with XL092 alone or in combination with ICIs reduced the levels of circulating myeloid cells, including myeloid-derived suppressor cells, dendritic cells, and macrophages. In vitro treatment of human macrophages with XL092 inhibited macrophage efferocytosis with IC50 ~81 nM and promoted repolarization from an M2 anti-inflammatory to an M1 pro-inflammatory phenotype. Conclusions: Immune cell profiling showed that treatment with XL092 and ICIs promotes CD8+ T cell tumor infiltration, increases in peripheral lymphocytes, decreases in peripheral myeloid cells, and macrophage repolarization, suggesting that XL092 promotes an immune-permissive tumor microenvironment. Consistent with these immunomodulatory effects, the combination of XL092 and ICIs has shown greater anti-tumor activity in syngeneic tumor models than either agent alone. XL092 is currently being evaluated in multiple solid tumors as a single agent and in combination with ICIs in the phase 1/1b STELLAR trials (NCT03845166). Citation Format: Jeff Hsu, Colin Chong, Jeffrey Serrill, Sharon Wu, Kevin Leong, Ted Yun, Lynne Bannen, Peter Lamb, Wei Xu, Peiwen Yu. The tyrosine kinase inhibitor XL092 promotes an immune-permissive tumor microenvironment and enhances the anti-tumor activity of immune checkpoint inhibitors in preclinical models [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P248.

Abstract 1573: Combinatorial antitumor effects of CD3-based trispecific T cell activating constructs (TriTACs) and checkpoint inhibitors in preclinical models

Abstract Tri-specific T Cell-Activating Constructs (TriTACs) are T-cell engagers that have been developed to redirect T cells to kill tumor cells. TriTAC molecules are currently being investigated in multiple phase 1/2 clinical trials in solid tumors, including HPN424 targeting prostate-specific membrane antigen (PSMA) in prostate cancer (NCT03577028), HPN536 targeting mesothelin (MSLN) in multiple malignancies (NCT03872206) and HPN328 targeting Delta Like Canonical Notch Ligand 3 (DLL3) in small cell lung cancer (SCLC) (NCT04471727). TriTAC molecules consist of a single domain antibody (sdAb) specific for a tumor antigen, a sdAb specific for serum albumin for half-life extension, and a single chain Fv (scFv) specific for the CD3ϵ subunit of the T cell receptor (TCR) complex for T cell engagement. In the presence of antigen expressing tumor cells, TriTAC treatment leads to potent T cell activation, production of proinflammatory cytokines, and re-directed tumor cell killing. Upregulation of co-stimulatory and/or inhibitory receptors during activation can potentially affect the cytolytic functions of TriTAC-activated T cells. We demonstrate that PD-1 can be readily detected on T cells subsequent to the engagement of the TCR by the TriTAC molecules HPN424, HPN536, and HPN328 in the presence of tumor cells expressing the target antigens PSMA, MSLN, and DLL3, respectively. We also demonstrate that TriTAC molecules upregulate PD-L1 on T cells in a dose-dependent manner. While induction of PD-1 on T cells suggests that cytolytic activity of TriTAC-activated T cells may be down-modulated by PD-L1-expressed by target tumor cells, simultaneous upregulation of PD-L1 on T cells suggests a second mechanism through which the functions of TriTAC-activated T cells could be further regulated by the PD1/PD-L1 axis in the tumor microenvironment through T cell-T cell interactions. In addition, in the MSLN-expressing NCI-H292 lung cancer model that co-expresses constitutive, high levels of PD-L1, both anti-PD1 and anti-PDL1 antibodies significantly enhanced the antitumor effects of the MSLN-targeting TriTAC HPN536 in vivo. Together these results demonstrate the potential utility of PD1/PDL1 blockade to enhance the potency of TriTAC-mediated tumor cell killing, supporting further investigation of these combinatorial approaches in patients. Citation Format: Mary Ellen Molloy, Laura B. Valenzuela, Priyanka E. Basak, Che-Leung Law. Combinatorial antitumor effects of CD3-based trispecific T cell activating constructs (TriTACs) and checkpoint inhibitors in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1573.

RX-5902, a novel \u03b2-catenin modulator, potentiates the efficacy of immune checkpoint inhibitors in preclinical models of triple-negative breast Cancer

BackgroundTriple-negative breast cancer (TNBC) is an aggressive breast cancer subtype with limited systemic treatment options. RX-5902 is a novel anti-cancer agent that inhibits phosphorylated-p68 and thus attenuates nuclear β-catenin signaling. The purpose of this study was to evaluate the ability of β-catenin signaling blockade to enhance the efficacy of anti-CTLA-4 and anti-PD-1 immune checkpoint blockade in immunocompetent, preclinical models of TNBC.MethodsTreatment with RX-5902, anti-PD-1, anti-CTLA-4 or the combination was investigated in BALB/c mice injected with the 4 T1 TNBC cell line. Humanized BALB/c-Rag2nullIl2rγnullSIRPαNOD (hu-CB-BRGS) mice transplanted with a human immune system were implanted with MDA-MB-231 cells. Mice were randomized into treatment groups according to human hematopoietic chimerism and treated with RX-5902, anti-PD-1 or the combination. At sacrifice, bone marrow, lymph nodes, spleen and tumors were harvested for flow cytometry analysis of human immune cells.ResultsThe addition of RX-5902 to CTLA-4 or PD-1 inhibitors resulted in decreased tumor growth in the 4 T1 and human immune system and MDA-MB-231 xenograft models. Immunologic analyses demonstrated a significant increase in the number of activated T cells in tumor infiltrating lymphocytes (TILs) with RX-5902 treatment compared to vehicle (p < 0.05). In the RX-5902/nivolumab combination group, there was a significant increase in the percentage of CD4+ T cells in TILs and increased systemic granzyme B production (p < 0.01).ConclusionsConclusions: RX-5902 enhanced the efficacy of nivolumab in a humanized, preclinical model of TNBC. Several changes in immunologic profiles were noted in mice treated with RX-5902 and the combination, including an increase in activated TILs and a decrease in human myeloid populations, that are often associated with immunosuppression in a tumor microenvironment. RX-5902 also was shown to potentiate the effects of checkpoint inhibitors of CTLA4 and the PD-1 inhibitor in the 4 T-1 murine TNBC model. These findings indicate that RX-5902 may have important immunomodulatory, as well as anti-tumor activity, in TNBC when combined with a checkpoint inhibitor.

Abstract 1754: Smac mimetics APG-1387 synergizes with immune checkpoint inhibitors in preclinical models

Abstract APG-1387 is a novel, SMAC-mimetic, small molecule inhibitor for inhibitor of apoptosis proteins (IAPs). IAPs are a class of proteins which negatively regulate caspases and apoptosis. The IAP proteins are frequently dysregulated in many cancers and have been suggested as contributing to apoptosis-resistance of cancer cells to a variety of anticancer drugs. DNA amplification of the cellular IAP-1 (cIAP-1) and cellular IAP-2 (cIAP-2) genes (BIRC2 and BIRC3, respectively) has been observed in various human cancer types, including lung cancer, pancreatic cancer, and liver carcinoma. Dysregulation of IAP proteins has also been frequently observed at the protein level in multiple cancer cell lines and tumor samples. IAPs contribute to tumor cell survival, chemo-resistance, disease progression, and poor prognosis. In addition, IAPs play an important role in immune regulation. For example, IAPs regulate ubiquitin (Ub)-dependent pathways that modulate innate immune signaling via activation of nuclear factor κB (NF-κB). Due to their significant biological functions in cell death and immune responses, IAPs have been emerging as drug targets in a wide range of malignancies. Several IAP inhibitors have been developed and their clinical benefits are currently in investigation in multiple clinical trials in both single agent and combination regimen with immune checkpoint inhibitors. APG-1387 has been developed as a novel drug candidate targeting IAPs. Mechanistically, in both cancer cells and xenograft tumors, APG-1387 induces degradation of cIAP-1 and XIAP proteins, as well as caspase-3 activation and PARP cleavage, which leads to apoptosis. Anti-proliferative and anti-tumor activities of APG-1387 have been well demonstrated in a panel of cancer cell lines and xenograft tumor models. In this study, we explored the synergistic effect of APG-1387 in combination therapy with immune checkpoint inhibitors. We found that APG-1387 enhanced human PBMC co-stimulation of anti-CD3 and anti-CD28, and T cell proliferation in vitro. In syngeneic tumor tissues, the combination treatment with APG-1387 and anti-PD-1 antibody led to an increase in CD3+ and CD8+ T cell populations and a decrease in Treg cell population. Synergistic effect of the combination was further demonstrated in syngeneic tumor models. Taken together, our results suggest that the treatment with APG-1387 may enhance the effect of anti-PD-1 antibody therapy. Consequently, APG-1387 has been approved by FDA for phase I clinical trials as single agent and in combination with anti-PD-1 antibody in solid tumors. Citation Format: Wentao Pan, Douglas D. Fang, Guangfeng Wang, Miaoyi Wu, Yingfeng Li, Keji Lian, Dingxiong Cheng, Yanhui Kong, Guoqin Zhai, Ming Guo, Shaomeng Wang, Dajun Yang, Yifan Zhai. Smac mimetics APG-1387 synergizes with immune checkpoint inhibitors in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1754.

413P - RX-3117, a novel hypomethylating agent, shows promising therapeutic activity in combination with nab-paclitaxel and check-point inhibitors in preclinical models

413P - RX-3117, a novel hypomethylating agent, shows promising therapeutic activity in combination with nab-paclitaxel and check-point inhibitors in preclinical models

Abstract LB-140: Inhibition of cancer stemness sensitizes colorectal cancer to immune checkpoint inhibitors

Abstract Cancer stem cells (CSCs), a highly malignant tumor cell subpopulation capable of self-renewal, are considered to be fundamentally responsible for malignant growth and tumor recurrence. Emerging evidences indicate that CSCs and CSC pathways, such as STAT3, beta-Catenin, CD44 and Nanog pathway, are involved in the immune evasion in cancers. With the exception of a small percentage of colorectal cancers (CRC) patients that display microsatellite instability (MSI), the vast majority of CRC patients have been found to be resistant to immune checkpoint therapies. BBI-608 (napabucasin) is an orally-administered first-in-class cancer stemness inhibitor that works by targeting STAT3, which lead to inhibition of multiple cancer stemness pathways, including Stat3 and β-catenin pathways. In this study, we investigate the effect of cancer stemness inhibition on sensitizing CRC to immune checkpoint inhibitors in preclinical models. In the syngeneic tumor model, anti-PD-1 antibody monotherapy produced low level and temporary antitumor activity with rapid development of complete resistance to anti-PD1 in the MSS CT26 CRC model. The anti-PD-1 antibody treated CT26 tumors exhibited increased p-STAT3 activation and overexpression of a variety of stemness factors, including Nanog, CD44 and CD133, as well as enrichment of sphere-forming stemness-high cancer cells. BBI-608 was able to reduce basal as well as anti-PD1-induced STAT3 activation and other CSC features within CT26 tumors. Combination of stemness inhibitor BBI-608 with anti-PD-1 antibody to treat CT26 tumors led to tumor complete response (CR) virtually in all treated CT26 tumors with 40% of the mice remain tumor-free for 30 days following treatment termination. This combination also had a synergistic effect on the influx of tumor infiltrating CD8+ T cells, which likely contributed to the rapid tumor regression. Finally, mice CR-induced by BBI-608 and anti-PD-1 antibody were able to reject CT26 tumors upon rechallenge, but not the unrelated breast cancer 4T1 tumors. Our data suggests cancer stemness pathways contribute to immunotherapy resistance in MSS CRC and inhibition of cancer stemness by BBI-608 sensitizes colorectal cancer to immune checkpoint inhibition. This study provides compelling preclinical evidence to support the investigation of the combination of BBI608 with immune checkpoint inhibitors in CRC. Citation Format: Yuan Gao, Youzhi Li, Eric Hsu, Yuxin Wang, Janet Huang, Emily Brooks, Chiang J. Li. Inhibition of cancer stemness sensitizes colorectal cancer to immune checkpoint inhibitors [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 LB-140. doi:10.1158/1538-7445.AM2017-LB-140

A phase II study of oral azacitidine (CC-486) in combination with pembrolizumab (PEMBRO) in patients with metastatic melanoma (MM).

TPS9594 Background: Immune checkpoint inhibitors have impressive response rates and improved survival for many pts with MM, offering durable responses in up to 35% of pts while others have short-lived or no response ( &gt; 40%). A potentially targetable mechanism for immune escape is for cancers to subvert the cellular epigenetic machinery, affecting multiple aspects of the immune response from suppression of tumor antigen expression [such as Cancer Testis Antigens (CTA)] to antigen processing and presentation, thus allowing tumor proliferation to continue undetected. In preclinical models, decitabine (DAC), a DNA hypomethylating agent (HMA), has been able to revert heterogeneous CTA expression profiles, increasing cancer cell immunogenicity. HMAs also increased TH1-chemokine expression, T cell tumor infiltration, T cell-mediated tumor killing, and have been shown to be synergistic with checkpoint inhibitors in preclinical models. This suggests that epigenetic therapy with checkpoint inhibition is a rational combination to target MM. Clinical advantages of the HMA CC-486 over DAC include oral bioavailability and potential versatility in dosing and schedule. We hypothesize that CC-486 + PEMBRO will be tolerated at biologically relevant doses; enhance response to PEMBRO in pts with mm who are PD-1 naïve; and reverse resistance to immunotherapy in pts refractory/resistant to PD-1 directed therapy. Methods: This study will evaluate the safety and efficacy of CC-486 + PEMBRO defined by Objective Response Rate (ORR) by RECIST 1.1 in pts with MM. Pts who are PD-1 naïve (Arm A, n = 36) and pts who have progressed on prior PD-1 directed therapy (Arm B, n = 35) will be enrolled. Unlimited prior systemic therapies will be allowed. Pts will receive 300mg PO of CC-486 on days 1-14 and 200mg IV of PEMBRO every 3 weeks. Continuous monitoring for toxicity and futility will be performed and assumes an ORR of &gt; 35% and &gt; 15% for Arms A and B, respectively (95% power). Tumor biopsies at baseline and post treatment are required. Effects of CC-486 + PEMBRO on CTAs, MDSCs and Tregs, and correlation between mutation burden and response will be studied. This study is open for enrollment. Clinical trial information: NCT02816021.

A phase 1 dose escalation study of eFT508, an inhibitor of mitogen-activated protein kinase-interacting serine/threonine kinase-1 (MNK-1) and MNK-2 in patients with advanced solid tumors.

2579 Background: Dysregulated translation of messenger RNA (mRNA) plays a role in the pathogenesis of multiple solid tumors. eFT508, a potent and highly selective small molecule inhibitor of MNK-1 and 2 blocks activation of eIF4E, a key regulator of mRNA translation, and thereby selectively regulates translation of a small set of mRNAs. In addition to direct antitumor activity, eFT508 triggers an anti- tumor immune response and enhances responses to checkpoint inhibitors in preclinical models. Methods: Using a 3+3 dose escalation schema, cohorts of solid tumor patients (pts) were treated with eFT508 administered orally once daily at doses ranging from 50 mg to 600 mg. Results: 28 pts were treated, and the most common tumor types were colorectal cancer (8), prostate cancer (3), and soft tissue sarcoma (3). Median number of prior therapies was 4. The most common observed adverse events (AEs) included nausea (47%), vomiting (47%), dyspepsia (23%), fatigue (20%), and constipation (20%). Two pts treated at 600 mg experienced Gr 3 related AEs, including one pt with Gr3 nausea and vomiting (met criteria for dose limiting toxicity) and one pt with reversible Gr3 AST/ALT elevation. 6 pts achieved stable disease with duration ranging from 82 to 196 days. Pharmacokinetic analysis revealed that eFT508 is bioavailable and rapidly absorbed, with median Tmax of 2 hours and a mean T1/2 of 12 hours. Minimal accumulation was observed between Days 1 and 14/15, with mean accumulation factor of 1.2-fold. Analysis of eIF4E phosphorylation in peripheral blood cells suggested that doses ≥ 300 mg achieved engagement sufficient for maximal efficacy as predicted by preclinical models. Conclusions: Preliminary results suggest that eFT508 is well tolerated, and dose escalation continues with a cohort of pts providing pretreatment and on treatment biopsies for evaluation of target engagement and immunomodulatory effects. After determination of the recommended phase 2 dose, further evaluation will include monotherapy cohorts in specific tumor types as well as cohorts to evaluate efficacy and tolerability in combination with checkpoint inhibitors. Clinical trial information: NCT02605083.

Abstract B92: The tubulin-targeting agent BNC105 potentiates the efficacy of immune checkpoint inhibitors in preclinical models of colorectal cancer

Abstract BNC105 is a tubulin depolymerisation agent. Its activity includes effects on both cancer cells and on solid tumor microvasculature. BNC105 shows evidence of strong anti-cancer efficacy in vitro and in animal models. In solid tumors its efficacy is driven by selective destruction of tumor vasculature (Vascular Disrupting Agent - VDA) and direct action on tumor cells through suppression of their proliferation. In non-proliferating blood cancers (e.g. Chronic Lymphocytic Leukaemia) BNC105 activates pro-apoptotic proteins, which mediate cancer cell death. BNC105P may be useful in the treatment of human cancers both as a monotherapy and also in combination therapies. Two separate in vivo studies were conducted to assess the potential therapeutic utility of combining BNC105 with antibodies that target PD-1 or CTLA4. The in vivo models utilised were xenografts of the murine colorectal cancer cell lines MC38 and CT26. C57/BL6 mice were inoculated subcutaneously with MC38 cells and treatment commenced when tumors reached a volume of approximately 100-150mm3. BNC105 was administered at 10 mg/kg i.v. on Day 1, 8 and 15 andanti-PD-1 antibody (Clone RMP1-14) was administered at 3.5mg/kg i.p. on Day 1, 4, 8, 12 and 16. Tumor growth inhibition was evident as early as Day 8 of the treatment period especially in the combination group compared to control group (p&amp;lt;0.05). On Day 17 of the treatment period, animals treated with BNC105 as a monotherapy experienced 40% inhibition of tumor growth, anti-PD-1 treated animals experienced 74% inhibition in tumor growth. Animals treated with the combination of BNC105+anti-PD-1 therapy experienced 97% inhibition in tumor growth. Balb/c mice were inoculated subcutaneously with CT26 cells. When tumors reached an average volume of approximately 100 - 150mm3 animals were randomised into 5 groups of 10 mice per group. BNC105 (10mg/kg) was administered on Days 1 and 8 and the anti-CTLA4 antibody (Clone 9D9) was administered at 10mg/kg i.p. on Days 2, 5, and 9.. Animals treated with the BNC105+anti-CTLA4 combination experienced greater inhibition of tumor growth compared to animals treated with either BNC105 or anti-CTLA4 alone. On Day 11 of the treatment period, animals treated with BNC105 as a monotherapy experienced 27% inhibition in tumor growth and anti-CTLA4 treated animals experienced 14% inhibition of tumor growth. Animals treated with the combination of BNC105+anti-CTLA4 experienced 70% inhibition in tumor growth. The synergistic relationship for each of the combinations was calculated as previously described (Cancer Biol Ther 2011; 12:837-45). BNC105 displayed synergy with both anti-PD-1 and CTLA4. These findings support the investigation of combining BNC105 with immune checkpoint inhibitors in further preclinical models with the view of progressing such combinations to clinical evaluation. Citation Format: Tina C. Lavranos, Donna Beaumont, Daniel Inglis, Michaela Scherer, Chloe Hawkins, Annabell F. Leske, Gabriel Kremmidiotis. The tubulin-targeting agent BNC105 potentiates the efficacy of immune checkpoint inhibitors in preclinical models of colorectal cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B92.