Abstract Whilst the advent of Immune Checkpoint Blockade has revolutionized the management of cancer, a significant proportion of patients have limited or absent response to these therapies. A key cause of this immune insensitivity is the hostile solid tumor microenvironment (TME) dominated by immunosuppressive myeloid cells. We previously identified the acid sensing G protein coupled receptor (GPCR), GPR65, as a primary determinant of these suppressive cells. In mice, genetic deletion of Gpr65 or oral administration of small molecule GPR65 inhibitors in vivo causes a profound repolarization of immunosuppressive tumor associated macrophages, an increase in infiltrating effector cells and potent anti tumor effects in syngeneic models. In TCGA data, across all tumors, patients homozygous for a hypomorphic coding variant in GPR65 (I231L) show increased overall survival, providing compelling genetic evidence of the clinical potential of GPR65 inhibition. To further explore the translational potential of GPR65 we employed a range of techniques to define the human biology of this receptor in different contexts. At the mechanistic level, single cell RNA sequencing (scRNAseq) of human PBMCs obtained from healthy donors demonstrated a pronounced effect of low pH on the myeloid compartment, with a clear polarization of these cells toward an immunosuppressive character and modulation of GPR65 expression. In parallel, pharmacological inhibition of GPR65 in human monocyte derived macrophages exposed to low pH demonstrated that equivalent gene expression changes are primarily due to GPR65 activation. To examine the relevance of these findings to the intact acidic human TME, we performed studies in fresh primary human tumor histocultures from clear cell renal cell carcinoma (ccRCC) patients with immunohistochemically confirmed high macrophage infiltration and carbonic anhydrase 9 (CA9) expression. In these cultures, GPR65 inhibition caused a dose dependent suppression of a geneset closely overlapping with that modulated by GPR65 in primary macrophages. Furthermore, we observed a marked decrease in immune suppressive IL10 secretion with coincident elevation of specific proinflammatory chemokines. Consistent with these findings, in vivo administration of a small molecule GPR65 inhibitor elicited similar changes in human CA9 expressing RCC PDX tumors implanted in myeloid boosted CD34+ stem cell engrafted NCG mice. In summary, inhibition of GPR65 provides a unique and genetically validated approach to favorably modify the immunosupressive TME with features highly conserved between mouse and human contexts. We propose that GPR65 inhibition holds significant clinical promise, with specific evidence around ccRCC as a potential standout indication. Citation Format: Barbara Cipriani, Alastair Corbin, David Miller, Alan Naylor, Faraz Khan, Gavin Milne, Barbara Young, Rupert Satchell, Sourav Sarkar, Mussa Quareshy, Anastasia Nika, Preeti Singh, Gavin Knox, Darryl Turner, Satish Sankaran, Nandini Pal Basak, Toszka Bohn, Tobia Bopp, Surya Koturan, Bo Sun, Benjamin Fairfax, Tom McCarthy, Stuart Hughes. The translational biology of small molecule GPR65 inhibitors: shared effects between mouse models and human primary tumors highlight the unique transformative potential of targeting a genetically validated innate immune checkpoint [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 668.
American Association for Cancer Research (AACR)
668 - 668