CT26 Tumor Research Articles

Abstract 5194: BALB/c mice with humanized VISTA: A novel GEMM for preclinical evaluation of therapeutic antibodies against VISTA

Abstract VISTA, also known as PD1H, is an immune-checkpoint receptor mainly expressed in immune cells, including macrophages, conventional dendritic cells, monocytes and circulating neutrophils. As a negative regulator of T cell activation, VISTA inhibits T cell proliferation and attenuates the production of cytokines. Studies have shown that VISTA expression is increased in infiltrating immune cells found in the tumor microenvironment and that blocking pathways that lead to VISTA activation can enhance antitumor immune responses in mice. Based on this, antibodies targeting VISTA are promising leads for cancer therapy. Preclinical efficacy evaluation of antibodies again human VISTA requires the expression of human VISTA in animal models, since difference in extracellular domains may affect antibody recognition while the overall homology between the two proteins is only 77%. To meet this need, we established a humanized mouse model in which the extracellular domain of mVISTA is replaced with that of hVISTA while the trans-membrane and cytoplasmic domains remain intact. In order to confirm the activity of the chimeric protein in our mice, we evaluated the anti-tumor effect of proven VISTA antibodies in homozygous hVISTA mice engrafted with CT26 tumor subcutaneously. Consistent with previous studies, the growth of CT26 tumor was inhibited after VISTA antibody treatment, indicating the humanized VISTA mice are suitable for efficacy evaluation of human VISTA antibodies. Moreover, we evaluated the anti-tumor effect of a combination of PD-L1 antibody and VISTA antibody in these mice. Interestingly, the combined use of PD-L1 antibody and VISTA antibody led to significantly enhanced tumor regression than either antibody. Taken together, BALB/c-hVISTA mouse is a novel non-human animal model appropriate for preclinical efficacy study of human VISTA antibodies. Citation Format: Weiwei Yu, Honghong Bao, Shuai Li, Chao Ju, Hongyan Sun, Hao Qi, Cunxiang Ju, Jing Zhao, Xiang Gao. BALB/c mice with humanized VISTA: A novel GEMM for preclinical evaluation of therapeutic antibodies against VISTA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5194.

Abstract 1333: Dual blockade of the EP2 and EP4 PGE2 receptors with TPST-1495 is an optimal approach for drugging the prostaglandin pathway

Abstract Prostaglandin E2 (PGE2) is a bioactive lipid produced by tumor cells that drives disease progression through stimulating tumor proliferation, enhancing angiogenesis and suppressing immune function in the TME1, 2. PGE2 is also a mediator of adaptive resistance to immune checkpoint inhibitor therapy via the upregulation of cyclooxygenase-2 (COX-2). While the role of PGE2 signaling in cancer is clear, how best to inhibit PGE2 for cancer treatment remains under investigation. Inhibition of COX-1 and/or COX-2 has shown promising results in observational studies and meta-analyses, but inconsistent results in prospective studies. PGE2 signals through four receptors, EP1-4, that are variably expressed on tumor and immune cells and have distinct biological activities. The EP2 and EP4 receptors signal through cAMP and drive pro-tumor activities, while the EP1 and EP3 receptors signal through calcium flux and IP3 and drive immune activation and inflammation. While COX-2 and single EP inhibitors continue to be developed, the nature of PGE2 signaling supports our rationale to inhibit PGE2 by dual antagonism of the pro-tumor EP2/EP4 receptors, while sparing the pro-immune EP1/EP3 receptors. To our knowledge, TPST-1495 is the first clinical-stage dual inhibitor of both the EP2 and EP4 receptors. In mouse and human whole blood assays, dual blockade of EP2 and EP4 receptors with TPST-1495 reversed PGE2-mediated suppression of LPS-induced TNF-α, while single receptor antagonists were unable to block suppression at higher PGE2 concentrations. Similarly, in murine and human T cells in vitro, TPST-1495 inhibited PGE2-mediated suppression, resulting in a significant increase of IFN-γ production in response to stimulation with cognate peptide antigen. In vivo, TPST-1495 monotherapy significantly reduced tumor outgrowth in CT26 tumor-bearing mice and correlated with increased tumor infiltration by NK cells, CD8+ T cells, AH1-specific CD8+ T cells, and other anti-tumor myeloid and adaptive immune cell populations. The relative contribution of increased immune infiltration may be simultaneously dependent on the immunogenicity of the tumor model and on the direct antitumor effect of TPST-1495, because we also observed significant tumor regression in metastatic burden in the LS174T xenograft model in NSG mice as well as CT26 tumors in RAG2-/- animals, both of which are deficient in immune cell development. To that end, TPST- 1495 monotherapy significantly decreased the tumor burden compared to COX2 inhibition and EP2 or EP4 single antagonism in the Adenomatous Polyposis (APCmin/+) model, a model that is hypo-responsive to PD-1 monotherapy. TPST-1495 is currently being evaluated in an ongoing Phase 1 first-in-human study (NCT04344795) to characterize PK, PD, safety, and to identify a recommended phase 2 dose for expansion cohorts in key indications and biomarker-selected patients. Citation Format: Brian Francica, Justine Lopez, Anja Holtz, Dave Freund, Dingzhi Wang, Amanda Enstrom, Raymond Dubois, Francielle Kipper, Dipak Panigrahy, Chan Whiting, Sam Whiting, Thomas W. Dubensky. Dual blockade of the EP2 and EP4 PGE2 receptors with TPST-1495 is an optimal approach for drugging the prostaglandin pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1333.

Abstract 2643: Design and discovery of novel oral INV-88 macrophage migration inhibitory factor (MIF) inhibitors: Potent anti-tumor activity in vitro and in vivo

Abstract Background: MIF is a pleiotropic cytokine critically implicated in tumorigenesis. Tumor cell- and immune effector cell-derived MIF are localized to exosomal, extracellular, cytoplasmic and intranuclear compartments. MIF activates MAPK and PI3K signal transduction, inhibits apoptosis, promotes angiogenesis, elicits premetastatic niche formation and resolves DNA replication stress; contributing to unperturbed cancer cell growth and metastasis. MIF overexpression in several cancers is a negative prognostic indicator associated with poor overall patient survival. Methods & Results: Active novel INV-88 MIF inhibitors were discovered using structure-based drug design against critical MIF pharmacophoric binding sites guided by high-resolution X-ray crystallography (Brookhaven) of INV-88 compound:hu-MIF protein bound complexes. Following an iterative medicinal chemistry campaign; stringent biochemical, pharmacological and ADMET funnel screening identified promising INV-88 lead candidates with potent antitumor activities. Strong MIF binding by INV-88 compounds was demonstrated using thermal shift and fluorescence polarization assays. Profound in vitro antitumor pharmacological properties of INV-88 were established on several murine & human tumor cell lines (HCT116, MeWo, DU145, 4T1, B16-F10, CT26). INV-88 inhibitors demonstrated potent anti-proliferative effects down to nM IC50 potencies and impeded 3D spheroid growth & viability. Disruption of MIF:CD74/CD44-mediated MAPK and PI3K signal transduction pathways by INV-88 compounds blocked ERK and AKT phosphorylation leading to decreased pERK1/2 and pAKT levels. INV-88 inhibitors increased Caspase-3/7, p53 and Bax but decreased Bcl-2 levels. INV-88 lead compounds inhibited tumor MIF protein production in 2D & 3D cell culture systems with concomitant pan-inhibition of tumorigenic proinflammatory cytokine (TNF-α, IL-1β, IL-6, and IL-8) expression by stromal cells. Optimal ADMET properties of INV-88 compounds enabled oral dosing of select INV-88 clinical candidate compounds in mouse syngeneic B16-F10 melanoma and CT26 colon carcinoma models. Mice were dosed daily with INV-88 or vehicle per oral gavage starting in BALB/c and in C57/BL6 mice upon demonstrating palpable tumors after s.c. implantation of CT26 and B16-F10 tumor cells, respectively. Tumor growth inhibition was observed with rates of 71% on Day 24 (CT26) and 75% on Day 20 (B16-F10). INV-88 treatment significantly inhibited CT26 [p<0.0001] and B16-F10 tumor growth [p<0.0001] versus controls. INV-88 was well-tolerated by tumor-bearing mice which exhibited normal body condition scores and body weight. Conclusion: The data presented highlight the potential therapeutic utility of pharmacological MIF inhibition with oral INV-88 new chemical entities as a novel immunotherapeutic treatment modality for cancer. Citation Format: Anderson Gaweco, Vincent Chung, Jefferson Tilley, William Windsor, Terry Stouch, John Ellingboe, Gregg Crichlow, Philipp Sabanas, Christian Sebesta. Design and discovery of novel oral INV-88 macrophage migration inhibitory factor (MIF) inhibitors: Potent anti-tumor activity in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2643.

Abstract 5195: Humanized CD3E,D,G mice: An ideal model for efficacy study of CD3-bispecific antibodies

Abstract CD3-targeting bispecific antibodies (CD3 bsAb) are designed to simultaneously bind to T cells and tumor cell antigens, leading to T-cell activation, proliferation, and tumor cell death. To create a better animal model for studies of CD3-TCBs, we developed the BALBc-hCD3EDG model by gene editing technology, Briefly, a large human genomic fragment containing CD3E,CD3D,CD3G as well as regulatory elements was introduced into the BALBc mouse genome and animals carrying human CD3E,D,G integration were selected to establish the new strain. The BALBc-hCD3EDG mice have a normal immune system and successfully express human CD3E,CD3D,CD3G on the T cell surface. As expected, cytotoxicity of activity T cells by redirecting with CD3-CD20 bsAb was observed in in vitro T cell-mediated killing assays using an A20 cell expressing human CD20. Furthermore, the growth of subcutaneously engrafted CT26 and hCD20-A20 tumors in BALBc-hCD3EDG mice, was strongly inhibited by CD3-TCB antibody treatment. In conclusion, the CD3EDG humanized mice are ideal models for preclinical studies of bispecific antibodies and other immunotherapies. Citation Format: xiaoliu Yang, cunxiang Ju, mingkun zhang, jing zhao. Humanized CD3E,D,G mice: An ideal model for efficacy study of CD3-bispecific antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5195.

Abstract 2881: Proper priming of T cells is crucial for the anti-tumor effect of mPTX-35, an anti-TNFRSF25 agonist antibody

Abstract TNFRSF25, also known as Death Receptor 3 (DR3), is a cell surface receptor of the tumor necrosis factor receptor superfamily (TNFRSF) which is expressed on T cells, innate lymphoid cells, and B cells. Upon binding with TL1A ligand, this co-stimulatory molecule induces T cell activation, leading either to inflammation or cell death. Mouse PTX-35 (mPTX-35) is a TNFRSF25 functional agonist derived from a CDR that was humanized and affinity matured, then fused to a mouse IgG1-Fc backbone. Since costimulatory agonist antibodies have shown limited efficacy in clinical trials, our aims were to (i) determine the anti-tumor efficacy of mPTX-35, (ii) elucidate any mechanisms of resistance, and (iii) identify immune conditions that provide effective anti-tumor immune responses to mPTX-35 treatment. We studied the anti-tumor immune effects of mPTX-35 in both cold and hot tumor models. In a TC-1 cold tumor, we found that treatment with an anti-TNFRSF25 agonist antibody does not affect tumor growth or survival. In contrast, vaccination with an E7 antigen-specific vaccine leads to an environment that reverses primary resistance to the agonist antibody, inhibiting the tumor growth, and enhancing overall survival. Interestingly, we found that similar to other co-stimulatory agonist molecules, the immune effects of the anti-TNFRSF25 agonist are dose-dependent with lower (0.2 mg/kg) and higher (5 mg/kg) doses of mPTX-35 showing a reduced anti-tumor response than a dose of 1 mg/kg, resulting in a bell-shaped response in all tumor models. Similar immune-mediated anti-tumor effects of mPTX-35 were found in a CT26 (hot) tumor model. In conclusion, these results show that anti-TNFRSF25 agonist antibody demonstrates high anti-tumor efficacy in tumors that are infiltrated with T cells while the absence of properly antigen activated CD8 T cells (such as in cold tumors) incurs primary resistance to TNFRSF25 agonist that is reversed by proper priming of CD8 T cells. These results highlight the importance of optimal priming to limit primary resistance mechanisms and drive an efficacious immune response via the TNSFR25 axis. Citation Format: Dareen Sarhan, Lara Rabah, Vikas Tahiliani, Anh M. Trinh, Rahul R. Jasuja, Eric P. Dixon, Matthew Seavey, Vivek Verma, Seema Gupta, Samir N. Khleif. Proper priming of T cells is crucial for the anti-tumor effect of mPTX-35, an anti-TNFRSF25 agonist antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2881.

Abstract 4169: A bifunctional anti-PDL-1 antibody/IL-10 fusion protein targeting exhausted T cells for cancer immunotherapy

Abstract Background: Interleukin-10 (IL-10) has demonstrated utility in aiding CD8 T cell-mediated tumor control in mouse models but phase 2 clinical trials with pegylated IL-10 have so far not been entirely successful. More recent studies revealed that another half-life-extended form of IL-10 (IL10-Fc) can rejuvenate terminally-exhausted CD8+ T cells to boost anti-tumor activity. We investigated whether combination of a PDL-1-blocking antibody with a C-terminal IL-10 fusion may enhance anti-tumor immunity, and possibly achieve synergistic effects. Methods: Recombinant proteins were produced using an expiCHO system (Thermo Fisher). PDL-1 blocking activity was evaluated by ELISA, PD-1/PDL-1 signaling (Eurofins) and mixed lymphocyte reaction assays. IL-10 activity was evaluated by MC/9 cell proliferation and CD8 T cell activation and effector assays. Mouse CT26 colon cancer and EMT6 breast cancer studies employed the services of Oneness Biotech and Crown Bioscience, respectively. Results: To develop a bifunctional anti-PDL-1 antibody/IL-10 fusion protein, anti-human PDL-1 antibodies were first developed by screening an in-house human variable domain phage display library. Three different antibodies were then C-terminally-fused with human IL-10 polypeptide. All three showed high binding affinity to PDL-1 and blocked PD-1 signaling through PD-1/PDL-1 interaction in a dose-dependent manner. In CD4 T cell/dendritic cell co-cultures, the lead anti-PDL1/IL10 protein enhanced IL-2 and IFNγ production, and it enhanced IFNγ and granzyme B production from activated CD8 T cells as well as proliferation of MC/9 cells in an IL-10-dependent manner. Also, a mouse ‘surrogate’ version (BF11, using avelumab anti-PDL-1) showed superior efficacy compared to either IL10-Fc or anti-PDL1/TGFbR in a mouse CT26 colon tumor model, and correlated with increased serum levels of CXCL9 and IL-18. BF11 also allowed greater EMT6 tumor control than anti-PDL-1 alone or anti-PDL1/TGFbR fusion protein. Such BF11-treated mice also showed long-lasting immunity against a secondary EMT6 tumor challenge. This ability of BF11 to enhance tumor control was in part dependent on increased activity of tumor-resident cells as co-treatment with FTY720, which inhibits lymphocyte egress from secondary lymphoid organs, did not appear to reduce anti-tumor activity of BF11 in some, albeit not all, EMT6-tumor-bearing mice. Conclusions: Anti-PDL1/IL10 fusion protein not only targets PDL-1 for checkpoint blockade but also activates the IL-10 pathway to boost T cell response, presumably including revitalization of exhausted T cells as recently reported. Effective anti-tumor activities of a mouse surrogate fusion protein, BF11, are demonstrated in CT26 and EMT6 tumor models. Taken together, our findings support this dual mechanism-strategy to potentiate anti-tumor immunity. Citation Format: Huey-Wen Hsiao, Chih-Lun Hsiao, Pandelakis Koni, Hung-Kai Chen. A bifunctional anti-PDL-1 antibody/IL-10 fusion protein targeting exhausted T cells for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4169.

Abstract 5541: BGB-15025, a potent and selective HPK1 inhibitor, is efficacious as a single agent or in combination with PD-1 antibody in multiple tumor models

Abstract Hematopoietic progenitor kinase 1 (HPK1), a hematopoietic cell-restricted serine/threonine protein kinase, has been reported to serve as a critical negative feedback regulator of T lymphocytes by phosphorylating the adaptor protein SLP76 in the TCR complex. The negative feedback role of HPK1 in TCR signaling makes it a promising target for immuno-oncology therapy. It has been recently demonstrated that the kinase activity of HPK1 is essential for its antitumor activity, and HPK1 inhibitors can be potentially combined with immune checkpoint inhibitor therapy (such as PD-1 antibody) for effective cancer treatment. Here, we report a potent and selective HPK1 inhibitor BGB-15025 which has been identified through in-house high throughput screening and structure-guided drug design. BGB-15025 potently inhibits HPK1 kinase activity in biochemical assay, with a 50% inhibitory concentration (IC50) of 1.04 nM under Km concentration of ATP. Consistently, BGB-15025 can potently reduce SLP76 phosphorylation and increase downstream ERK phosphorylation in a concentration dependent manner in T cells-based assay. As a consequence, BGB-15025 induces TCR activation and IL-2 production in T cells. Based on in-house profiling, BGB-15025 shows good selectivity profile among MAP4K family and does not affect ZAP70 phosphorylation up to 1 μM. Oral administration of BGB-15025 demonstrates dose-dependent pSLP76 inhibition in splenic T cells and induces serum IL-2 in mouse model. In efficacy studies, BGB-15025 exhibits anti-tumor activity in GL261 tumor model as single agent. Moreover, BGB-15025 demonstrated combination effect with anti-PD-1 antibody in CT26 and EMT-6 syngeneic tumor models. BGB-15025 is currently in phase I clinical trial to treat patients with advanced solid tumor, both as a single agent and in combination with anti PD-1 antibody tislelizumab. Citation Format: Ye Liu, Jing Li, Zhuo Li, Qin Wang, Xing Zhou, Xiaoxin Liu, Bo Zhang, Xitao Wang, Sanjia Xu, Hanzi Sun, Xiaomin Song, Xi Yuan, Zhiwei Wang, Xuesong Liu. BGB-15025, a potent and selective HPK1 inhibitor, is efficacious as a single agent or in combination with PD-1 antibody in multiple tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5541.

Abstract 3508: Exosome-mediated delivery of antisense oligonucleotides targeting C/EBPβ reprograms tumor-associated macrophages and induces potent single agent anti-tumor activity

Abstract Background: Tumor-associated macrophages (TAMs) and myeloid derived suppressor cells (MDSCs) promote an immunosuppressive milieu by inhibiting T-cell activation and recruitment, leading to resistance to immune checkpoint therapies. Interleukin 10 (IL10) and prostaglandin E2 (PGE2) promote tumor initiation and spread, in part, through TAM polarization and MDSC recruitment. C/EBPβ is a critical transcription factor that regulates the immunosuppressive state of TAMs and MDSCs and is activated by IL10 and PGE2 signaling. We developed a proprietary engineered exosome loaded with antisense oligonucleotides (ASOs) targeting C/EBPβ (exoASO-C/EBPβ), that selectively delivers ASO to TAMs and MDSCs, thereby inhibiting C/EBPβ expression and inducing reprogramming from an immunosuppressive (M2) to a pro-inflammatory (M1) phenotype. Results: exoASO-C/EBPβ demonstrated dose-dependent target gene knockdown (KD) in primary human M2 macrophages in vitro with a 2-fold higher potency (IC50) compared to free ASO. C/EBPβ KD resulted in profound changes in gene expression and cytokine secretion profile consistent with reprogramming to a M1 phenotype. exoASO-C/EBPβ induced a significant induction of pro-inflammatory cytokines, in M2 macrophages generated with IL10 or PGE2, both of which show prominent activation of the C/EBPβ pathway. Biodistribution in tumor-bearing mice (IT and IV) demonstrate selective uptake by MDSCs and TAMs. Intra-tumoral (IT) administration of exoASO-C/EBPβ in CT26 tumors resulted in a significantly higher KD of C/EBPβ in tumor-associated CD11b+ cells, as compared to CD11b- cells. Additionally, exoASO-C/EBPβ induced changes in Nos2, CD206 and Csf1r mRNA expression in CD11b+ cells, demonstrating in vivo M2 to M1 reprogramming. Furthermore, IT microinjections of exoASO-C/EBPβ in YUMM1.7 tumor-bearing mice resulted in a significant induction of pro-inflammatory M1 markers TNFα and iNOS, in contrast, free C/EBPβ ASO showed limited increase in M1 markers. exoASO-C/EBPβ administered IT as a single agent demonstrated significant anti-tumor activity in multiple tumor models including: the CT26-colorectal cancer (60% complete responses (CRs)), MB49-bladder cancer (70% CRs) and B16F10-melanoma (30% CRs). Combination treatment with anti-PD1 in all these models further increased the anti-tumor efficacy. Finally, we used a myeloid cell specific C/EBPβ/PGE2/IL10 gene signature to identify cancer indications where exoASO-C/EBPβ therapy might have the most therapeutic significance. Conclusion: exoASO-C/EBPβ is a novel therapeutic candidate that selectively targets and attenuates a critical transcription factor in immunosuppressive myeloid cells, resulting in reprogramming of TAMs and potent anti-tumor activity across multiple TAM-rich mouse models as a monotherapy. Citation Format: Sushrut Kamerkar, Charan Leng, Olga Burenkova, SuChul Jang, Kelvin Zhang, Yanyan Liu, William Dahlberg, Kyriakos Economides, Timothy Soos, Dalia Burzyn, Sriram Sathyanarayanan. Exosome-mediated delivery of antisense oligonucleotides targeting C/EBPβ reprograms tumor-associated macrophages and induces potent single agent anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3508.

Abstract 5515: Combination of recombinant murine IL-12 and anti-PD-1 induced synergistic anti-tumor response

Abstract Introduction: Immune-checkpoint inhibitors have become the standard therapy in many types of cancers. The combination of anti-PD-1 and anti-CTLA4 demonstrated better anti-tumor response, but toxicity is a concern. Cytokines including IL-2, IL-12, IL-15, IL-21 that target immune cells have been developed to enhance immune response against tumors. Clinical trials for the combination of cytokines and anti-PD-1 have been proposed (Mohamad et al, 2020). IL-12, a multifunctional cytokine, regulates both innate and adaptive immunity. The role of IL-12 in regulating immune response showed that intra-tumoral electroporation of plasmid IL-12 prime responses to anti-PD-1 treatment (Algazi et al, 2016). IL-12 produced by dendritic cells accompanied with IFN-γ play an important role in anti-tumor response induced by anti-PD-1 (Garris et al, 2018). Therefore, this study aims to explore the synergistic anti-tumor immune response of recombinant murine IL-12 (rmIL-12) and anti-PD-1. Methods: Different doses of rmIL-12 alone or combined with anti-PD-1 were administered in different tumor models. CT26, MC38, Hepa 1-6 that generate hot tumor were used. Tumors were inoculated subcutaneously in syngeneic mouse tumor models and treated when mean tumor volume reach 60-100 mm3. Tumor resection and splenectomy were performed on tumor inoculated mice at termination. Immunocytochemistry stain was used to detect immune cells including CD4, CD8 T cells, regulatory T cells (Treg), myeloid-derived suppressor cells (MDSC) and macrophage. Serum cytokines were checked for immune response and liver enzyme for toxicity. Results: The combination of rmIL-12 and anti-PD-1 (BIW x 3 weeks) showed better tumor control compared to anti-PD-1 alone with CT26, MC38, Hepa 1-6 cell lines. Synergistic effect was observed even with a low dose of rmIL-12 (20 ng/mice). A higher dose of rmIL-12 achieved better tumor control. In the CT26 tumor model, combination therapy suppressed tumor growth up to 73% compared to anti-PD-1 alone. These results demonstrated a clear dose-response relationship. The combination of rmIL-12 and anti-PD-1 induced higher level of IFN-γ compared to anti-PD-1 or rmIL-12 alone. A higher dose of rmIL-12 resulted in higher IFN-γ level. The IFN-γ level peaked about 12 hours after the treatment and returned near baseline in about 48 hours. The combination of rmIL-12 and anti-PD-1 showed higher percentage of CD8 T cells in tumors compared to anti-PD-1 or rmIL-12 alone. Combination group significantly decreased Treg in the tumor microenvironment, but not MDSC. Combination therapy also reprogrammed the macrophages from M2 towards M1 polarization in the tumor. Finally, no significant elevation of AST/ALT level was observed among all the groups. Conclusion: The combination of rmIL-12 and anti-PD-1 demonstrated a synergistic immune response for tumor control. The result needs to be further confirmed in human in the near future. Citation Format: Peiyi Tsou, Wan-Ying Lin, Meng-Na Lee, San-Chi Chen. Combination of recombinant murine IL-12 and anti-PD-1 induced synergistic anti-tumor response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5515.

Abstract 6108: In vivo CRISPR screens identified dual function of MEN1-MLL1 in regulating tumor-microenvironment interactions

Abstract INTRODUCTION: CRISPR functional genomic screens have been widely adopted to identify essential genes and potential drug targets in cell line models. However, it is well known that cell line models studied in vitro do not fully capture the biology in patient tumors due to the lack of the tumor microenvironment. The primary objective of this study was to perform functional genomic screens in in vivo models to identify clinically relevant epigenetic vulnerabilities. METHODS: We designed an EpiDrug sgRNA library that target 357 epigenetic regulators in human, and applied this targeted sgRNA library for essentiality screen in 2D cell culture and 3D xenograft models. We subsequently selected targets that can only be identified in vivo for validation. We also investigated the underlying mechanism of the in vivo specific phenotype caused by target knockouts. Finally, we explored the clinical significance of treating selected target with a small molecule inhibitor. RESULTS: We identified MEN1 as the top hit that confers differential essentialities between in vitro and in vivo models. Knockout of MEN1 has no impact on cell proliferation in 2D cell culture but profoundly promotes tumor growth in human lung and colorectal adenocarcinoma cell line derived xenograft models. In syngeneic colon cancer model CT26, knockout of Men1 resulted in faster tumor growth in immune deficient mice, but reduced tumor growth in immune competent mice. Mechanistically, knockout of MEN1/Men1 can cause the redistribution of its interaction partner MLL1/Mll1, a histone methyl transferase, to repeat regions in chromatin and stimulate the expression of double stranded RNA. This resulted in viral mimicry response, which activates a group of genes involved in cytokine-cytokine receptor interaction. Single-cell RNA-seq and CyTOF analysis revealed that activation of the cytokines induces tumor promoting neutrophil and tumor suppressing CD8+ T cell infiltration in immunodeficient and immunocompetent mice, respectively. Using patient data from TCGA, we identified that the expression level of MEN1 is negatively correlated with neutrophil and CD8+ T cell tumor infiltration in most cancer types including lung and colorectal adenocarcinoma. A small molecular inhibitor targeting Men1-Mll1 interaction dramatically reduced CT26 tumor growth in immunocompetent mice, but its phenotype was reversed by CD8 neutralizing antibody. Finally, we demonstrated the strong synergy of the inhibitor with anti-PD-L1 antibody. CONCLUSION: Our study demonstrated the utility of in vivo CRISPR screen in identifying therapeutic targets that modulate tumor-microenvironment interactions, and identified MEN1 as a promising therapeutic targets alone or in combination with immunotherapy. Citation Format: Peiran Su, Yin Liu, Ming-Sound Tsao, Housheng H. He. In vivo CRISPR screens identified dual function of MEN1-MLL1 in regulating tumor-microenvironment interactions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6108.

Abstract CT526: A Phase 1/2a Study of a PI3Kδγ dual inhibitor ZX-101A in patients with advanced solid tumors

Abstract ZX-101A is a next-generation PI3Kδ/γ dual inhibitor, exerting synergistic effects on PI3Kδ and PI3Kγ-mediated processes through multifaceted mechanisms of actions. Phase 1/2a study, ZX-101A-101 (NCT04504708) is ongoing to assess safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy in patients with advanced hematologic malignancies. Furthermore, recent preclinical studies of ZX-101A showed that dual inhibition of PI3Kδ and PI3Kγ restored the immune surveillance to inhibit solid tumor growth. ZX-101A-201 is a phase 1/2a open-label, multiple-dose ascending study to investigate the safety, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of once daily oral ZX-101A in 28-day cycles in patients with advanced solid tumors.ZX-101A had minimal effects on solid tumor-derived CT26, 4T1 and A20 cells in in vitro cell proliferation assay. In contrast, ZX-101A inhibited tumor growth when CT26 cells were grafted to wild-type syngeneic mice, while only showed a limited tumor growth inhibition when CT26 tumors grew on T-cell deficient nude mice. Thus, in vivo tumor growth inhibition in wild-type mice was attributed to the enhanced anti-tumor immunity by ZX-101A treatment. Flow cytometry analysis on ex vivo tumor tissues from syngeneic mouse demonstrated that ZX-101A decreased regulatory T cells and increased M1/M2 macrophage polarization in the tumor microenvironment. In A20 syngeneic model, ZX-101A in combination of anti-PD1 antibody achieved 99.7% TGI after 18 days of treatment, while anti-PD1 antibody alone only had TGI at 11.7%. Synergistic inhibitory effect of ZX-101A and anti-PD1 antibody was also observed in LLC, CT26 and humanized MC38 syngeneic mouse models. Safety assessment on the mouse spleen, thymus and colon organs indicated minimal side effects by the treatment of the ZX-101A alone and in combination with anti-PD1. These results suggested ZX-101A as a potential immunotherapeutic agent to treat appropriate solid tumor types. ZX-101A-201 study consists of 2 parts, Dose Escalation and Dose Expansion. Part 1 dose escalation is designed to determine the safety, tolerability, and recommended phase 2 dose (RP2D) of ZX-101A monotherapy in patient with advanced solid tumors. Part 2 dose expansion will evaluate ZX-101A activity in up to three disease-specific cohorts. Inclusion of combination therapy is planned after obtaining the initial clinical assessment of ZX-101A on its safety, tolerability, pharmacokinetics, and pharmacodynamics in patients. Citation Format: Xiaoli Qin, Lori Luo, Li Ying-ying, Yin Wang, Shuaijun Sun, Xiaolin Hao, Jinfu Yang. A Phase 1/2a Study of a PI3Kδγ dual inhibitor ZX-101A in patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT526.

Abstract 1718: Characterization of infiltrating immune cells after irradiation using 10x genomics single cell sequencing

Abstract Background: Radiation therapy is delivered to approximately 50% of all cancer patients. It has long been known that radiation causes not only DNA strand breaks, apoptosis, and necrosis, but also immunogenic modulation. Lately, there has been renewed interest in the potential of irradiation in colorectal cancer, not only as an adjuvant and palliative treatment, but also as an immune stimulant. Materials and Methods: CT26 murine colorectal carcinoma cells were subcutaneously implanted on the flank of BALB/c mice. Tumors were exposed to sham, single dose or fractionated radiotherapy regimens via a 300kV, 10mA X-ray with additional filtration to give a radiation quality of 2.3mm Cu half-value layer (HVL). Mice were anaesthetized, restrained and delivered a single uniform dose of radiation at a rate of 0.696Gy/min with the whole mouse being lead shielded except for a 1cm hole in the lead above the tumor site. Tumors were harvested at different timepoints post irradiation and dissociated into single cell suspensions. The tumor microenvironment and immune response within the tumors were analyzed with flow cytometry comparing the different treatment regimens. The individual CD45+ cell profile was investigated using 10x gene expression. 10x sequencing was demultiplexed using CellRanger and data analyzed using Seurat and ACTINN. Results: Following the initial cytotoxicity, flow cytometry showed a clear immune stimulatory effect of radiotherapy with immune cells infiltrating the irradiated tumors. The level of infiltration was dependent on the treatment scheduling. For single cell assessments, we observed approximately 8000 reads/cell and T-SNE cluster analysis using Seurat identified 16 clusters in control and treated samples. Identification of clusters by ACTINN demonstrated that CD8+ T-cells were increased 8-fold in irradiated samples whereas monocytes numbers decreased 3-fold. In irradiated tumors, the main population of CD8+ T-cells with increased numbers also expressed NKG7. Conclusion: These data provide evidence that radiotherapy can enhance immune cell trafficking to locally treated CT26 tumors. Furthermore, 10x genomics single cell sequencing revealed increased levels of cytotoxic T-cells expressing NKG7, a protein implicated in enhanced killing of extracellular targets. This response could prime the tumors such that they may be exploited by immune modulating drugs. Citation Format: Frida Ponthan, Valentina Ubertini, Gary Beale. Characterization of infiltrating immune cells after irradiation using 10x genomics single cell sequencing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1718.

Abstract 590: Humanized PD-1/LAG-3 mice for preclinical evaluation of combination therapy

Abstract Lymphocyte activation gene 3 (LAG-3) is a member of the immunoglobulin superfamily which shares homolog with CD4 and binds to MHC II with higher affinity. It is expressed on activated T cells, regulatory T cells (Tregs), natural killer cells and plasmacytoid dendritic cells, and inhibits their activation. Blocking LAG-3 activity is expected to provide therapeutic benefits in the treatment of cancer, especially when combined with PD-1 blockade. Due to the low homology between human and mouse LAG-3 and PD-1 and in order to enable increased translatability of preclinical in-vivo efficacy evaluation of immune checkpoint antibodies, we generated double humanized mice by replacing the extracellular domain of mouse LAG-3 and PD-1 with the corresponding human sequences. Homozygous double humanized mice express chimeric LAG-3 and PD-1 at comparable levels to mouse LAG-3 and PD-1 respectively in wildtype mice. When treated with human LAG-3 antibody (anti-LAG-3) or human PD-1 antibody (anti-PD-1), CT26 tumor growth was inhibited in a dose-dependent manner, proving that both humanized proteins are functional. However, not all tumor types respond to anti-LAG-3 or anti-PD-1 the same. To identify the suitable tumor models for preclinical efficacy evaluation of anti-LAG-3 and anti-PD-1 combo therapy, we engrafted several syngeneic tumor models onto our mice. The growth of subcutaneously engrafted MC38 colon tumor was mildly inhibited by anti-PD-1, but strongly inhibited in the presence of anti-LAG-3. Similarly, B16F10 melanoma tumor showed modest growth inhibition when treated with anti-PD-1 or anti-LAG-3 separately, while combination therapy significantly repressed tumor growth. However, neither monotherapies of anti-LAG-3 and anti-PD-1 nor combination treatment effectively inhibited tumorigenesis of LLC1 derived lung cancer, indicating that this tumor is likely insensitive to PD-1 and LAG-3 blockade. Collectively, these data indicate that double humanized PD-1 and LAG-3 mice are a powerful tool to evaluate the therapeutic efficacies of anti-hPD-1 and anti-hLAG-3 treatment in different types of tumor in vivo. Citation Format: Feifei Duan, Xiaoliu Yang, Cunxiang Ju, Jing Zhao, Xiang Gao, Santi Suryani Chen. Humanized PD-1/LAG-3 mice for preclinical evaluation of combination therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 590.

Abstract 5622: Preclinical evaluation of humanized PD1/GITR combination therapy using double humanized mouse

Abstract GITR (glucocorticoid-induced TNFR-related protein) is a member of tumor necrosis factor receptor superfamily, expressed on many kinds of cells including T cells, attracting attention as a co-stimulatory immune checkpoint molecule. GITRL, the ligand of GITR is mainly expressed on antigen presenting cells. GITR/GITRL interaction plays an important role on the development of immune response, which can serve as promising anti-tumor target. While more than twenty anti-GITR antibodies are at clinical stages, combination treatments of GITR agonist and PD-1 inhibitor may be a better choice. Thus, there is a need for pre-clinical mouse model to evaluate the anti-tumor effect of humanized PD1/GITR antibodies. Gempharmatech established PD1/GITR double humanized mouse line on a BALB/c background, in which the extracellular domain of mGITR was replaced with its human counterparts while the trans-membrane and cytoplasmic domain kept intact, as well as the same strategy of PD1. BALB/c-hPD1/hGITR mouse could successfully express similar levels of hGITR and hPD1 compared with BALB/c wild type mice. Moreover, no immune or developmental abnormalities were observed in the humanized mouse. Anti-GITR combination with anti-PD1 presented greater tumor growth inhibition than anti-PD1 or anti-GITR monotherapies in PD1/GITR double humanized mouse bearing CT26 tumors. In summary, BALB/c-hPD1/hGITR are valuable models for the pre-cilincal evaluation of candidate humanized PD1/GITR combination treatment or bispecific antibody therapies. Citation Format: Dongdong Yuan, Dongdong zhang, Hongyan Sun, Mingkun Zhang, Liyou Dong, Cunxiang Ju, Shuai Li, Huiyi Wang, Jing Zhao, Xiang Gao. Preclinical evaluation of humanized PD1/GITR combination therapy using double humanized mouse [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5622.

Abstract 2093: PEGylated IL-2 with enhanced anti-tumor efficacy and safety profile

Abstract Introduction: Interleukin-2 (IL-2) can activate and expand tumor killing lymphocytes. High doses of IL-2 are needed to activate CD8+ T cells. Severe toxic side effects associated with high doses, as well as the poor PK profile of IL-2, have limited its clinical usage. Various strategies have been employed to prolong half-lives of IL-2 and enable selectivity or bias towards receptor binding to reduce toxicity and maintain good efficacy. Among these, certain PEGylation strategies have generated promising clinical results, but also showed some major limitations. We report a unique PEGylation strategy to produce PEGylated IL-2 with a therapeutic window more than two times larger than the reference PEGylated IL-2. Methods: CT26 murine syngeneic model was used for evaluation of in vivo efficacy and safety. Each 6-8 weeks old female BALB/c mouse was inoculated subcutaneously in the right front flank region with CT26 tumor cells (5 x 105). Tumors were allowed to grow to mean size ~110 mm3 before randomization and treatment. Body weights and tumor volumes were measured three times per week. The tumor-free mice at the end of the study were re-challenged with CT26 colon tumor cells on the left side. Results: Utilizing our proprietary PEGylation technology, rhIL-2 was covalently connected with multiple PEG polymers through releasable linkers (RL). The releasable linkers are designed to modulate the release rate of the active IL-2 species. In CT26 syngeneic mouse model, CS-PEG-IL-2 showed significantly enhanced efficacy and safety over IL-2 and reference PEGylated IL-2. rhIL-2 (2 mg/kg, bid x 5, two cycles, i.p.) resulted in complete response (CR) in one out of eight (1/8) mice, while 3 mg/kg dose resulted in death in 8/8 mice. With the reference PEGylated IL-2, 3/8 CR were obtained at 3 mg/kg dose (q1w x 4, i.v.), and 6 mg/kg dose resulted in death in 8/8 mice. Whereas, with three CS PEGylated IL-2 analogs, 5/8 and 6/8 CR were achieved at 3 mg/kg and 6 mg/kg dose respectively, and no obvious toxicity was observed even at the highest dose. After re-challenged with another inoculation of CT26 cancer cells, the CR mice remained tumor-free until the end of the study at day 158. Conclusions: CS unique PEGylation strategy generated PEG-IL-2 with superior anti-tumor efficacy and safety profiles. Preclinical results support clinical evaluation of this novel class of PEGylated IL-2 analogs. Citation Format: Yuntao Song, Hui Li, Wei Zhang, Dayan Fu, Meng Xu. PEGylated IL-2 with enhanced anti-tumor efficacy and safety profile [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2093.

Abstract 1283: Single intra-tumoral injection of gaseous nitric oxide induces an adaptive immune response in a mouse CT-26 solid tumor model

Abstract Background: Metastases are responsible for a significant portion of the morbidity and mortality in cancer patients. In situ destruction of tumor mass has been reported to provide the immune system with an antigen source for the induction of antitumor immunity, which can then attack distant metastases. Nitric oxide (NO) acts as a signaling molecule in multiple disease states, including cancer. NO has been shown to activate innate and adaptive responses of the immune system against tumors. In a previous Beyond Air study, 89% of CT26 tumor bearing mice treated with 50,000 parts per million (ppm) gaseous NO (gNO), rejected a secondary tumor induction. Here, we assessed the effects of a single intra-tumoral injection of gNO at concentrations of 20,000-50,000 ppm on immune cell recruitment in the tumor, spleen, and blood. Methods: Mouse colon carcinoma (CT26) tumor bearing Balb/c mice underwent a single intra-tumoral treatment with 20,000 (n=3) or 50,000 (n=4) ppm gNO for 5 minutes. Mice treated with N2 (n=3), under the same conditions, served as a control. Tumors were removed 14 days post treatment and were histologically analyzed to test for immune cell penetration, inflammation, and necrosis. Immune cells from the spleen and blood were harvested 21 days post treatment and assessed via flow cytometry. Results: 1. Treatment with 50,000 ppm gNO resulted in higher levels of inflammation, lymphocytes and T-cell infiltration, and necrosis within the tumor compared to both N2 and 20,000 ppm NO, as viewed histologically. 2. Flow cytometry analysis of immune cells from the spleen revealed a 1.3-fold increase of both B cells and IFN-γ expressing T cells with 50,000 NO treatment, and a 1.3-fold increase of B cells and 1.1-fold increase of IFN-γ expressing T cells with 20,000 NO treatment, compared to N2. 3. A 29% reduction of myeloid-derived suppressor cells (MDSCs) was detected in spleens of mice treated with 50,000 ppm gNO, and 40% for 20,000 ppm, compared to mice treated with N2. Conclusion: Intra-tumoral injection of ultra-high doses of NO at 20,000 and 50,000 ppm gNO led to an increased recruitment and concentration of T and B cells. Additionally, 50,000 ppm NO led to an increase of lymphocyte infiltration to the tumor. Taken together, the data suggest that the increase in lymphocyte infiltration, B and T cell population, and the reduction of MDSCs, are indicative of an adaptive immune response that results in rejection of secondary tumors in gNO-treated mice. Citation Format: Hila Confino, Matan Goldshtein, Yakir Levi, Lidor Malka, Amir Avniel, Steve Lisi, Ido Wolf. Single intra-tumoral injection of gaseous nitric oxide induces an adaptive immune response in a mouse CT-26 solid tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1283.

Abstract 5590: Inhibition of the autophagy protein Vps34 induces tumor cell secretion of proinflammatory chemokines

Abstract Autophagy is the cellular process by which cytoplasmic contents are degraded and recycled through a lysosomal pathway. In cancer, autophagy can contribute to both tumor promotion and tumor suppression, and emerging evidence supports a role in resistance to immunotherapy. We investigated whether inhibition of autophagy with a small molecule inhibitor of the class III phosphoinositide 3-kinase Vps34 could stimulate anti-tumor immune responses and potentiate the efficacy of immune checkpoint blockade (ICB). Treatment with the Vps34 inhibitor (Vps34i) inhibited autophagy and was weakly cytotoxic to B16F10, MC38, EMT6 and CT26 mouse syngeneic tumor cell lines. In certain cancers, autophagy has been linked to lysosomal degradation of MHC I proteins, thereby downregulating expression and contributing to immune evasion. Notably, we observed minimal upregulation of MHC I surface expression on a subset of mouse and human cell lines. We further explored whether autophagy inhibition would result in release of any soluble immune stimulatory factors from mouse tumor cell lines. Inhibition of Vps34 markedly increased the secretion of several proinflammatory chemokines, including CCL5 and CXCL10. Increased chemokine secretion was also observed in a panel of human cancer cell lines, including NCI-H2009 lung cancer and PC-3 prostate cancer, confirming that the response is observed in human cancer cell lines derived from different tissue origins. As the chemokines CCL5 and CXCL10 are critical to the development of robust anti-tumor immunity, we next tested whether Vps34i treatment could potentiate the anti-tumor efficacy of ICB. We explored the activity of Vps34i as a single agent and in combination with anti-PD-1 antibody in three different syngeneic tumor models, including EMT6, CT26 and MC38. No single agent activity was observed in these models, however, combination of anti-PD-1 and Vps34i significantly inhibited the growth of CT26 tumors compared to control. Anti-tumor efficacy of combination treatment was not significantly different compared to single agents, and no complete tumor regressions were observed. No significant increases in CCL5 and CXCL10 were observed in the serum of combination treated mice, potentially explaining the lack of robust efficacy. Our results suggest that inhibition of autophagy promotes the secretion of proinflammatory cytokines from mouse and human cancer cells in vitro. As the autophagy pathway exhibits cross talk with other major cell signaling pathways, the tumor contexture may be a critical determinant of the role of autophagy in anti-tumor immune responses. Future experiments will explore which tumor contexts are sensitive to combination of autophagy inhibition and ICB. Citation Format: Marie Bernardo, Yu-an Zhang, Martin Graf, Jane Cheng, Fangxian Sun, Virna Cortez-Retamozo, Sukhvinder Sidhu, Eladio Marquez, Donald Jackson, Jack Pollard, Timothy R. Wagenaar, Donald Shaffer. Inhibition of the autophagy protein Vps34 induces tumor cell secretion of proinflammatory chemokines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5590.

Abstract 3502: AXA-042 - a novel systemic TLR2/6 agonist for anti-tumor therapy

Abstract Background: Treatment approaches that engage both the innate and adaptive immune response have the potential to transform anti-cancer therapy, especially in settings of checkpoint inhibitor insensitivity or acquired resistance. Toll-like receptors (TLRs) are a class of targets that mediate the initial cellular response to external pathogens or endogenous alarmins, activating downstream pro-inflammatory cascades and leading to the activation and recruitment of key innate subsets. TLR2 is a cell surface receptor, expressed predominantly on macrophages, dendritic cells (DC), neutrophils and subsets of NK and T cells. TLR2 signaling plays important role in NK and T cell cytolytic cell functions, as well as DC and macrophage activation. AXA-042 is a novel synthetic TLR2/6 agonist designed for systemic delivery to re-engage the innate immune response to help overcome tumour immune escape. Methods: In vitro potency and selectivity of AXA-042 was assessed across a panel of human and mouse HEK-blue TLR reporter assays. AXA-042 activity was profiled relative to other TLR agonists in human PBMC cytokine release assays. AXA-042 in vivo efficacy was evaluated in the EMT6 and CT26 syngeneic tumour models. The Nanostring nCounter™ Mouse PanCancer Immune Profiling Panel was used to identify AXA-042 tumour-localized and peripheral response signatures. Results: AXA-042 demonstrated potent and selective activity in murine and human TLR2/6 reporter assays and a differential PBMC cytokine release profile relative to other TLR agonists in vitro. Systemic delivery (QW, IV or IP) of AXA-042 significantly inhibited EMT6 and CT26 tumour growth, which was accompanied by an increase in circulating plasma levels of IL6, IL12 and CXCL10. Combination with anti-PD-1 Ab further potentiated anti-tumour response, resulting in approximately 30-40% tumour regressions. AXA-042 anti-tumour effects were accompanied by increased activation of the tumour-infiltrating myeloid cells, including DCs and macrophages, and a reduction in the M2 TAM subset. Nanostring analysis confirmed TLR and IFNγ pathway engagement and revealed an induction of gene signatures associated with macrophage, DC and NK functions. Longitudinal studies to characterize whole blood biomarkers associated with response are currently in progress. Conclusion: AXA-042 was well tolerated in vivo and demonstrated innate response engagement and anti-tumour efficacy as monotherapy and in combination with anti-PD-1 immunotherapy. AXA-042 has completed GLP toxicology studies and initiation of Phase 1/1b trial is planned for early 2022. Citation Format: Anna V. Galkin, Francesca Mercuri, Nicholas West, Ping Zhang, Weiguang Zeng, Grant McLachlan, Michael Bettess, Ian Holmes, David Jackson, Chris Smith, Christophe Demaison, Tobias Bald, Phil Kearney. AXA-042 - a novel systemic TLR2/6 agonist for anti-tumor therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3502.

Abstract 2862: Novel immune checkpoint protein CNTN4 and the preclinical efficacy of affinity matured anti-CNTN4 antibody GENA-104A16

Abstract The immunotherapeutic treatment has profoundly improved the clinical outcomes in patients with advanced cancers. However, most patients still have not responded to immune checkpoint inhibitor (ICI) treatment. Thus, it is still urgent to find novel treatments for patients who have no response to ICI and acquire ICI resistance. We previously suggested that contactin 4 (CNTN4), known initially to act as an axon guidance molecule during neural development, is a novel inhibitory immune checkpoint protein. In addition, we confirmed that CNTN4 is highly expressed on the various types of human tumor tissue, and anti-CNTN4 antibodies, GENA-104A07 and GENA-104A11, show the anti-tumor efficacy by enhancing T cell activity. In the present study, we describe the role of amyloid precursor protein (APP) expressed on T cells as a binding partner of CNTN4 and the preclinical characterization of GENA-104A16 as an immune-oncology drug candidate targeting CNTN4. Firstly, we investigated the APP expression on T cells and found that APP was detected in T cells' membrane and cytosolic fraction. Its expression level was higher on activated T cells. In addition, we observed that the immune-suppressive activity of CNTN4 on APP KO T cells was significantly decreased compared with APP WT T cells, which means APP as a binding partner of CNTN4 is a core molecule for transmitting immunosuppressive signal of CNTN4 to T cells. GENA-104A16 is a humanized antibody and binds to human and mouse CNTN4 with high binding affinity, which is matured from GENA-104A07 and GENA-104A11. In the in vitro functional assays, GENA-104A16 showed the improved effects on the restoration of T cell proliferation and activation (i.e., inflammatory cytokine releases from T cells and T cell activity-related signaling cascade) suppressed by CNTN4 and on CTL (cytotoxic T lymphocytes)-mediated killing for human cancer cell lines expressing CNTN4. In line with these effects, GENA-104A16 produced higher anti-tumor effects than GENA-104A11 in the CT26 syngeneic mouse colon cancer model. To identify the in vivo immune modulatory function of GENA-104A16, we analyzed the proportion of tumor-infiltrated T cells, Treg cells, and T cell subsets expressing perforin and granzyme B in CT26 tumor tissues. As a result, the population of CD4+ T cells, CD8+ T cells, and cytotoxic CD8+ T cells expressing perforin or granzyme B tended to increase in the tumors of GENA-104A16 treated mice while decreasing the FoxP3+CD25+ Treg population. Interestingly, GENA-104A16 treatment showed better anti-tumor effects together with the elevated level of CD8+ T cells expressing perforin and granzyme B than atezolizumab treatment. Overall, these preclinical studies demonstrate that GENA-104A16 is a promising blocking antibody for CNTN4-mediated immune suppression and can serve as an effective immune-oncology drug for patients with cancer that highly express CNTN4. Citation Format: Mi Young Cha, Hnkyung yu, Bu-Nam Jeon, Hyunuk Kim, Youngeun Ha, Yunyeon Kim, Joo-Yeon Chung, Soojung Moon, Hyunseong Youn, Han-sol Kim, Kyung Mi Park, Hansoo Park. Novel immune checkpoint protein CNTN4 and the preclinical efficacy of affinity matured anti-CNTN4 antibody GENA-104A16 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2862.

Abstract 4236: Temporal inhibition of BCAT1 alters metal homeostasis leading to reversal of terminal exhaustion of CD8 T cells, increased cytotoxicity, and increased efficacy of checkpoint inhibition in cancer

Abstract We have previously demonstrated that BCAT1, the enzyme responsible for the reversible transamination of leucine in the cytosol, is a druggable target in immune-oncology: the small molecule inhibitor ERG245 dramatically increases the efficacy of anti-PD-1 treatment in the moderately immunogenic CT26 colon cancer model. We have also shown that Bcat1 gene expression is enriched in exhausted CD4+ and CD8+ intratumoral cells in cancer patients from diverse cancers. Here, we illustrate that the adoptive cell transfer (ACT) of murine CD8+ T cells treated with ERG245 increased the median survival of CT26 tumor-bearing mice from 25 days, observed with the ACT of untreated CD8+ T cells, to 32 days. This suggested that inhibition of BCAT1 prevented the known exhaustion of adoptively transferred CD8+ T cells, induced by the tumor microenvironment of CT26 tumors. To confirm this hypothesis, we developed an in vitro model of generating terminally exhausted (PD-1+TIM-3+GZMB+CXCL13+) CD8+ T cells by subjecting the cells to consecutive cycles of αCD3/αCD28 activation in the presence of TGF-β. Addition of ERG245 in the last activation cycle decreased terminal exhaustion of the cells. Mechanistically, bulk RNAseq experiments indicated and ICP analysis confirmed that inhibition of BCAT1 interfered with metal homeostasis leading to increased concentrations of Fe in the mitochondria and decreased concentrations of Zn in the nucleus of newly activated CD8+ T cells. The immediate impact of ERG245 treatment on the cells included a general decrease in the genes of processes depending on proper metal equilibrium such as cholesterol biosynthesis and ribosome biogenesis. Withdrawal of BCAT1 restored or reversed the cell phenotype leading to epigenetically altered CD8+ T cells with decreased histone acetyltransferase and histone demethylase presence, increased cytotoxicity, and increased ribosome biogenesis. Collectively, the data suggest that temporal inhibition of BCAT1 inhibition induces profound effects on CD8+ T cells including increased cytotoxicity and suppression of terminal exhaustion, thus rendering the cells rescuable by anti-PD-1 therapy. Citation Format: Adonia E. Papathanassiu, Weixing Li, Hong A. Vu. Temporal inhibition of BCAT1 alters metal homeostasis leading to reversal of terminal exhaustion of CD8 T cells, increased cytotoxicity, and increased efficacy of checkpoint inhibition in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4236.