Abstract 1267: Suppression of pyruvate carboxylase drives PDL1 expression in mouse models of TNBC
Authors: Attaar Numair , Pfeil Alexander J. , Cotul Eylem K. , Teegarden Dorothy , Wendt Michael K. , Coleman Michael F. , Hursting Stephen D. 
Published: June 2023

Background: Programmed death-ligand 1 (PDL1) expression on tumor and other cells dampens T cell activation and promotes exhaustion. Pyruvate carboxylase (PC) converts pyruvate to oxaloacetate which in T cells and tumor associated macrophages supports antitumor immunity. PC is required for lung metastasis in several models of triple negative breast cancer (TNBC); however the role of PC expression in primary tumor growth is less well understood. Suppression of PC in tumor associated macrophages and T cells blunts antitumor immunity. We have shown that suppression of PC in tumor cells is sufficient to promote tumor progression and immune evasion. Here we investigated in murine models of TNBC whether and how PC suppression might alter the expression of PDL1.

Methods: PC was stably suppressed in M-Wnt, metM-Wntlung and E0771 cells using shRNA, and transiently suppressed using siRNA. C57BL6NCrl mice were orthotopically injected with shPC and scram M-Wnt (n=8/group) or E0771 (n=5/group) cells. Transcriptomic analysis of E0771 cells was performed using Clariom D microarray. PC and PDL1 expression was determined in M-Wnt and metM-Wntlung cells by qPCR. Cell signaling was assayed by western blot using pERK and pAKT antibodies. Statistical analysis was performed using two-sided students t-test, with Welch’s correction where variance was not equal.

Results: Suppression of PC in M-Wnt and E0771 cells promotes tumor growth. In vitro, suppression of PC promoted PDL1 expression in E0771 cells. We confirmed similar effects in M-Wnt and metM-Wntlung cells stably expressing shRNA directed against PC using qPCR. Finally we confirmed that transient transfection of siRNA directed against PC similarly induced PDL1 expression. Basal AKT and ERK signaling was induced by stable suppression of PC in M-Wnt cells.

Conclusions: PC suppression in several murine cell models of TNBC promotes PDL1 expression and reveals an underexplored interaction between tumor cell anaplerosis and immune evasion. Through suppression of PC we have identified a reciprocal relationship between PC and PDL1 expression, with a concomitant induction of both AKT and ERK signaling. A better understanding of the mechanisms through which PC-related metabolic reprogramming modulates antitumor immunity will identify new targets for inhibiting TNBC progression. Future studies will address whether targeted restoration of anaplerosis or overexpression of PC can suppress PDL1 and promote antitumor immunity.

Citation Format: Numair Attaar, Alexander J. Pfeil, Eylem K. Cotul, Dorothy Teegarden, Michael K. Wendt, Michael F. Coleman, Stephen D. Hursting. Suppression of pyruvate carboxylase drives PDL1 expression in mouse models of TNBC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1267.