Fatty-acid-binding proteins as a novel target for the treatment of anti-PD-1-resistant tumors.

Abstract

11562 Background: The mechanisms underlying immunosuppression and resistance to PD1 inhibitors in cancer are not well understood. We attempted to fill this gap with an integrated transcriptome analysis in an anti-PD1-resistant lung adenocarcinoma mouse model. The model was created by in vivo passage of 344SQ murine lung cancer cells (p53R172HΔg/+K-rasLA1/+) in a syngeneic host repeatedly dosed with anti-mouse PD1 antibodies. Anti-PD1-resistant 344SQ (344SQ_R) and 344SQ parental (344SQ_P) cells were then inoculated into syngeneic 129Sv/ev mice, which were then dosed twice with anti-PD1 or control IgG antibodies. Methods: Tumor tissues were collected and analyzed as follows: transcriptome with Affymetrix; protein levels by reverse phase protein array analysis; signature enrichment by gene set enrichment analysis; metabolome by mass spectrometry; and lipid content with fluorescent probes Oil O and BODIPY. We also isolated tumor-infiltrating immune cells for flow cytometry and gene expression analyses. Results: We identified lipid-related metabolic pathways as being the most highly enriched in anti-PD1-resistant tumors (344SQ_R) vs. their 344SQ_P counterparts; the resistant cells also had more lipid droplets than the 344SQ_P cells. The anti-PD1-resistant tumors overexpressed several genes involved in lipogenesis and fatty acid pathways, including fatty acid binding proteins (FABPs). Specifically, FABP overexpression promoted fatty acid uptake and lipid-droplet accumulation in resistant tumors. 344SQ_R tumors promoted immune suppressive cells by upregulating FABPs expression in M2-like macrophages, marked by increased fatty acid intake and fatty acid oxidation. Conversely, percentages of CD4+ and CD8+ tumor-infiltrating lymphocytes were reduced in the resistant tumors. Conclusions: These results suggest that lipid metabolic rewiring drives resistance PD1 inhibitors supporting the accumulation of immunosuppressive cells, including M2-like macrophages, preventing type I immune responses elicited by T cells. Collectively, these findings reveal new potential lipid-related targets for drug development or new treatments combining inhibitors of these targets with anti-PD1 therapy.