Abstract 6349: Targeting the CXCR3 pathway with a novel peptide drug candidate mobilizes the immune system to enhance anti-tumor immunity

Immune-checkpoint inhibitor (ICI) therapy releases the molecular “brakes” on the immune system thereby promoting robust anti-tumor immune responses. However, many patients do not respond to ICI therapy due to development of primary and secondary resistance, and this population represents a large unmet medical need. The critical role of C-X-C motif chemokine receptor 3 (CXCR3) signaling in eliciting an effective response to anti-PD-1 therapy has been recently demonstrated. The CXCR3 chemokine system is instrumental in effector cell recruitment to the tumor and augments intratumoral CD8+ T cell proliferation and function, which are key mechanisms driving anti-tumor immunity and responses to ICI therapy.

We used our proprietary peptide discovery platform to identify a unique microbiome-derived peptide, SG-3-00802, from bacterial strains associated with response to anti-PD1 inhibitors in patients with melanoma. We subsequently determined that CXCR3 is the target receptor for SG-3-00802 and demonstrated that SG-3-00802 enhanced the activity of CXCR3 in the presence of its endogenous ligands CXCL9/CXCL10/CXCL11. Optimization of SG-3-00802 pharmacological properties led to the selection of a novel drug development candidate SG-3-00802DC with improved potency and PK properties. Mechanistically, it increases CXCR3 activation by CXCL11 by greater than 10-fold from a nM to a pM range. As a positive allosteric modulator, SG-3-00802DC can potentially alter the conformation of the primary orthosteric binding site of CXCR3 and enhance the binding affinity of CXCL11, causing increased CXCR3 signaling activity, which is known to drive TIL infiltration that improves overall survival in mouse tumor models and cancer patients. Supporting this concept, we demonstrated that SG-3-00802DC showed anti-tumor activity in pre-clinical mouse tumor models, alone and in combination with anti-PD-1, improved overall survival and increased recruitment of CXCR3+ effector cells into the tumor microenvironment.

Numerous strategies are currently undergoing clinical evaluation to improve long-lasting disease control in broader patient populations by combining ICIs with approved and novel therapeutic agents and procedures. SG-3-00802DC, with its well validated and unique mechanism of action to safely target the CXCR3-driven anti-tumor immune response offers a novel orthogonal approach complementary not only to immunotherapies, but also as a combination strategy with chemotherapy or radiotherapy.

Citation Format: Dhwani Haria, Jina Lee, Justy Guagua, Archana Nagaraja, Kyle Roskamp, Bum-Yeol Hwang, Divya Ravichandar, Michi Willcoxon, Todd DeSantis, Karim Dabbagh, Helena Kiefel. Targeting the CXCR3 pathway with a novel peptide drug candidate mobilizes the immune system to enhance anti-tumor immunity [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 6349.

Abstract 3153: Targeting the stress response kinase GCN2 to restore immunity in the tumor microenvironment

Recent advances in cancer metabolism suggest that targeting amino acid metabolism represents a promising strategy for the development of novel therapeutic agents. Tumor, stromal and myeloid-derived suppressor cells (MDSC) within the tumor microenvironment (TME) create a nutrient-poor environment that inhibit immune function and support tumor growth. GCN2 (general control nonderepressible 2), a stress response kinase, plays a key role in maintaining cellular homeostasis under a wide range of stressors. Phosphorylation of GCN2 (pGCN2) in response to stress leads to inhibition of global protein synthesis and subsequently leads to 1) T cell anergy and apoptosis, 2) enhanced MDSC-dependent immune suppression and 3) tumor cell survival. Collectively, these roles suggest that GCN2 inhibition could have both a direct anticancer and an immune-activating effect. Treating nutrient-deprived T cells in vitro with a RAPT GCN2 inhibitor (RPT-GCN2i) rescued CD4+ and CD8+ T cell proliferation and effector functions. The RPT-GCN2i also reversed T cell suppression mediated by MDSCs derived from healthy donors or cancer patients. Using syngeneic mouse tumor models, we demonstrated that translational induction of activating transcription factor 4 (ATF4) is a strong marker of GCN2 pathway activation in vivo. Oral administration of an RPT-GCN2i exhibited notable drug-target occupancy and potently inhibited GCN2 kinase and ATF4 in the TME. RPT-GCN2i as a single agent and in combination with checkpoint blockade or angiogenesis inhibitor (anti-VEGFR) led to delays in tumor growth rate in various syngeneic tumor models. In addition, GCN2 inhibition redirected MDSC within the TME from a suppressive to inflammatory phenotype through downregulation of Arg1 and iNOS. Our results show that inhibition of GCN2 is an attractive approach for enhancing antitumor immune response and therefore GCN2 is a promising therapeutic target for the treatment of cancer.

Citation Format: Lisa Marshall, Buvana Ravishankar, Urvi Kolhatkar, Mengshu Xu, Lavanya Adusumilli, Deepa Pookot, Thant Zaw, Chandru Ramana, Raashi Sreenivasan, Mikhail Zibinsky, Jeffrey Jackson, Grant Shibuya, Paul Leger, Omar Robles, Anqi Ma, Andrew Ng, Anton Shakhmin, Justy Guagua, Scott Jacobson, Steve Wong, Delia Bradford, Tracy L. McGaha, M Teresa Ciudad, James E. Talmadge, Holly C. Britton, George Katibah, Gene Cutler, David Wustrow, Paul D. Kassner, Dirk G. Brockstedt. Targeting the stress response kinase GCN2 to restore immunity in the tumor microenvironment [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 3153.