Develop positive allosteric modulators to enhance XCR1 signaling in cancer

Project Summary Our long-term research goal is to develop positive and negative allosteric modulators targeting chemokine receptors as a novel therapeutic approach for cancer treatment by modulating their activities. Towards this goal, the current proposal will focus on XCR1, an important chemokine receptor expressed in conventional dendritic cells subtype 1 (cDC1s). cDC1s are the most potent dendritic cells specialized in cross-presenting exogenous antigens or cancer neoantigens on MHC class I molecules to CD8+ cytotoxic T lymphocytes (CTLs), serving as a pivotal mechanism for initiating CTL responses against tumors in the tumor microenvironment (TME) and playing a critical role in immune checkpoint blockade (ICB) therapy. A defining characteristic of both mouse and human cDC1s is the expression of XCR1, which can respond to its chemokine ligand XCL1 produced by activated CD8+ T cells and natural killer (NK) cells, mediating chemotaxis and activation of cDC1s within the TME. Modulating the XCL1-XCR1 signaling may enhance cDC1 function and CTL responses in the TME. Building on our recent progress obtaining purified XCR1 complexes and determining the first high-resolution cryo-EM structure of the XCL1-XCR1-Gi complex, we propose utilizing DNA-encoded library (DEL) technology to identify small-molecule XCR1 PAMs. We will take a new 'conformation selection' strategy to screen for XCR1 PAMs in a DEL. Extensive signaling assays will validate and characterize DEL screening hits, and we will obtain cryo-EM structures of XCL1-XCR1 with the best candidates. Identifying XCR1 PAMs will provide a novel strategy for enhancing anti-tumor immunity and establish a paradigm for developing PAMs for other chemokine receptors, offering new therapeutic avenues by leveraging native immune mechanisms against tumor.