Abstract 6057: Discovery of a novel function for USP7 inhibitors: Reprogramming the tumor microenvironment

Abstract

Abstract During the transition from healthy tissue to cancer and metastasis, the tumor microenvironment (TME) initiates crucial changes that licenses the progression from primary tumors to aggressive and metastatic disease. Our understanding of the specific factors and molecular mechanisms underpinning these transitions in the TME is critical for influencing the potency and scope of existing cancer therapy strategies but is still evolving and subject to substantial and widespread investigations. Here we uncover a novel molecular mechanism actioned by fibroblasts in the TME to modulate the secretion of the vascular endothelial growth factor (VEFG) via the hypoxia-inducible transcription factor (HIF1α). Utilizing primary human cells co-culture systems in combination with highly potent and selective USP7 inhibitors, we demonstrate that the deubiquitinating enzyme USP7 modulates the stability of HIF1α in primary human fibroblasts and secreted VEGF levels in primary fibroblasts as well as cancer-associated fibroblasts. This USP7-mediated modulation of VEGF secretion in the TME does not occur in cancer cells, immune cells or endothelial cells, rather it is restricted to the fibroblastic compartment. Importantly, the modulation of VEGF secretion by USP7 in fibroblasts is not mediated via the Mdm2 axis: Mdm2 antagonists are unable to recapitulate the VEGF modulation in fibroblasts. Knock-down of USP7 in primary fibroblasts validates the phenotype obtained with potent and selective USP7 inhibitors. In line with their effects on the TME in primary cell cultures, potent, selective USP7 inhibitors demonstrated tumour growth inhibition in vivo in a syngeneic cancer xenograft model that does not respond to USP7 inhibitors in vitro. Collectively, our studies reveal a molecular mechanism whereby USP7 inhibition leads to TME reprogramming mediated by an increased destabilization of HIF1α leading to reduced levels of VEGF in the TME and improved anti-tumor activity. Our results support further investigations of combination of a USP7 inhibitor with immune checkpoint inhibitors, as well as other TME modulating agents. Citation Format: Xavier Jacq, Anamarija Jurisic, Julien Daubriac, Ian T. Lobb, Mark Wappett, Aaron Cranston, Peggy Sung, Gerald Gavory, Colin O'Dowd, Tim Harisson. Discovery of a novel function for USP7 inhibitors: Reprogramming the tumor microenvironment [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6057.