Abstract Melanoma patients initially respond well to first line immunotherapy. However, cross resistance to immunotherapy and BRAF/MEK inhibitor is a clinical challenge for melanoma care. To investigate drug tolerant and resistant mechanisms promoting cross resistance, we analyzed RNA-sequencing and gene set enrichment targeted therapy resistant melanoma cells revealing an enriched arachidonic acid gene signature. Intracellular arachidonic acid levels were increased in drug resistant and drug tolerant melanoma models. Arachidonic acid is enzymatically converted by COX1 and COX2 to prostaglandins, which is subsequently secreted into the microenvironment. Drug tolerant and resistant cells had increased protein expression of COX1 and COX2 concurrently with increased secretion of prostaglandin E2. COX1/2 inhibition and COX2 knockdown in vitro had no effect on cell growth in drug tolerant or resistant cells compared to parental cells. However, secreted prostaglandins are known immunomodulators, thus we explored how COX1/2 inhibition in combination with BRAF inhibitor plus MEK inhibitor affected immune cell infiltration. COX1/2 inhibition increased CD4+ and CD8+ T cell infiltration as compared to BRAF inhibitor plus MEK inhibitor alone. Under constant BRAF inhibitor plus MEK inhibitor treatment, we found that COX1/2 inhibition upon reaching MRD status prevented tumor relapse in vivo and increased survival dependent on an immune system. Future studies will evaluate the importance of arachidonic acid metabolism in promoting cross resistance to immune checkpoint blockade and whether T cell depletion prevents the delayed tumor relapse. Overall, COX1/2 inhibition delayed tumor relapse and survival in an immune-dependent manner and demonstrated a potential cross resistant mechanism. Citation Format: Casey D. Stefanski, Daniel A. Erkes, Timothy J. Purwin, Glenn L. Mersky, Erica L. Kitterman, Manal Mustafa, Jelan Haj, Diana Melissaratos, Andrew E. Aplin. Arachidonic acid metabolism promoting cross resistance in melanoma cells [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr A023.
Read full abstract