We discovered that a rabbit polyclonal antibody raised against the second extracellular loop of human G-protein- coupled receptor 160 (hGPR160/ECL2) has two remarkable actions: (1) direct anti-cancer effects on human colon cancer and triple negative breast cancer (TNBC) cell lines that express the receptor without altering the viability of a normal colon cancer cells line, and (2) great potentiation of the cytotoxic effects of the small molecule chemotherapeutic, oxaliplatin, at doses that by themselves have no significant activity. This potentiation indicates that combination with the hGPR160/ECL2 antibody might yield a considerable improvement in the clinical effect with cytotoxin doses that are lower and produce fewer side-effects than those in current use. To translate these observations into a practical therapy, we propose to develop a human monoclonal hGPR160/ECL2 antibody for further characterization of its anticancer effects and as a step towards developing a therapeutically useful human monoclonal hGPR160/ECL2 antibody. The current proposal is in response to PAR-22-216 with aims to develop and test a new biologic agent that both treats cancer and mitigates cancer treatment-related toxicities. We are unaware of any commercially available small molecule ligands for GPR160. Our recent publication1 and preliminary data presented here indicate that an hGPR160/ECL2 monoclonal antibody is a viable chemotherapeutic. However, our preliminary studies used a rabbit polyclonal antibody, which has an irreducible element of uncertainty concerning the locus of binding. Accordingly, a human monoclonal hGPR160/ECL2 antibody will address this issue and permit unambiguous in vitro experiments on anticancer effects in human cancer cell lines and in vivo experiments on human cell line-derived xenografts (CDX) in immunodeficient mice. Success with the work proposed here in three Aims would lead to further work to develop a therapeutic monoclonal antibody. In Aim 1, we will develop human monoclonal antibodies to hGPR160/ECL2 by immunizing transgenic mice expressing human heavy and light genes with the hGPR160’s ECL2 amino acid sequence (or subsequence thereof) conjugated to KLH and developing hybridomas via PEG-fusion. We will screen clonal antibodies by flow cytometry and down-select using a blocking-of-binding assay to a panel of ~10 hGPR160/ECL2 mAbs clones for further in vitro and in vivo studies. We will then test the anti-cancer cell activity of our antibodies with in vitro studies. In Aim 2, the top 2-3 candidates (best binding affinity against the ligand and LC50 in the in vitro cell viability assay) will be advanced for (1) in vivo orthotopic cell line-derived xenograft (CDX) mouse models of colon cancer and TNBC. In Aim 3, the top candidate will be tested in in vitro oxaliplatin and paclitaxel potentiation studies. An hGPR160/ECL2 mAb may prove to be a significant improvement to current anti-cancer treatments that are inadequate for a large percentag...