The Effects of the Proton-Sensing G-Protein Coupled Receptors GPR4 and GPR68 on B16F10 Mouse Melanoma Growth and Responses to Immune Checkpoint Inhibitors.

Abstract

This research delves into the study of proton-sensing G-protein coupled receptors (GPCRs) GPR4 and GPR68 and their relation to the modulation of the tumor microenvironment in metastatic melanoma. Melanoma especially at a higher stage often are harder to treat and have a greater likelihood of recurrence. The main treatment for early-stage melanomas is surgery. Though due to melanomas being an immunogenic tumor, immune checkpoint inhibitors (ICI) and other forms of immunotherapies have been approved for use in treatment of this disease. However, with ICI treatments they are not as effective as they could be, and some patients are removed from treatment due to immune related adverse events (IRAEs). Our aims were three-fold in terms of these GPCRs and tumor treatment. First, we aimed to assess how the absence of these GPCRs in a host body would affect tumor growth and modulate the tumor microenvironment. GPR4 and GPR68 are linked to both inflammatory diseases and cancer, and have been shown to reduce tumor growth when inhibited or knocked-out in a host. With GPR4 it plays a key role in the expression of several key adhesion molecules and chemokines on vascular endothelial cells which are key for immune cell migration and infiltration into the tumor and other tissues. GPR4 is also linked to the promotion of angiogenesis. GPR68 plays a role in immune cell suppression. So when there is a lack of these receptors in the host the B16F10 melanoma lacks key communication targets to stimulate pro-tumoral responses. We observed a significant reduction in tumor growth in the GPR4 KO/GPR68 KO mice alongside a significance both in an increase in CD8+ T-Lymphocyte infiltration into the TME and a reduction in blood vessels in the TME. Next with the ICI treatments we investigated how the tumor growth and IRAEs were affected in the GPR4 knock-out (KO) mice when treated with ICI therapy as compared to wild-type (WT) mice. There was no significant reduction in the efficacy of the ICI treatment on inhibiting tumor growth in the GPR4 KO mice as compared to WT mice. In the GPR4 KO mice there was a reduction in immune cell infiltration into the normal tissues of the mice. Based on these findings, though more work still needs to be done, we can see that there are many possibilities for future antagonists targeting both GPR4 and GPR68, alongside also GPR4 antagonists when paired with ICI treatment.