Abstract 1284: The tumor scaffold protein SQSTM1 at the crossroads of DNA damage and immunotherapy responses in solid tumors
Authors: Grosjean Iris , D’Andréa Grégoire , Yazbeck Nathalie , Belaid Amine , Roméo Barnabé , Domdom Marie Angela , Guillot Nicolas , Gilson Eric , Chamorey Emmanuel , Milano Gérard , Hofman Véronique , Ilié Marius , Benard-Thiery Isabelle , Heeke Simon , Brest Patrick , Ghiringhelli François , Hofman Paul , Mograbi Baharia 
Published: June 2022

Abstract
Introduction After the recent advent of Immune Checkpoint Inhibitors (ICIs), one of current challenge of clinical cancer trials is certainly to develop the optimal combinations of ICIs with DNA-Damaging Agents (chemotherapy and/or radiotherapy, named DDAs hereafter). Elucidating resistance mechanisms to these different treatments is pivotal to propose new predictive biomarkers and to develop therapeutic strategies to improve ICI efficiency. We hypothesized that resistance to DDA and ICIs is mediated in part by intrinsic tumor mechanisms, some of which may be shared.
Methods To address this knowledge gap, we compared RNA expression signatures, antigen presentation, and PD-L1 expression from cohorts of cancer patients treated with radiotherapy, chemotherapy, and immunotherapy to identify shared molecular pathways that may mediate cross-resistance. Using a panel of lung cancer cell lines, we then confirmed that the tumor-cell-intrinsic expression of SQSTM1 is positively correlated with antigen presentation, and inversely with DNA damage repair and DDA/ICIs resistance gene signatures. This SQSTM1/HERV pathway was then supported in vitro using engineered silenced cell-lines (SQSTM1, MAVS, and STING ShRNA) treated with FDA-approved DDA (cisplatin, oxaliplatin, doxorubicin, and ionizing radiations) or synthetic double-stranded RNA (5’ppp dsRNAs and poly IC).
Results Through three complementary approaches (in silico, ex vivo on patient cohorts, and in vitro), we identify the p62/SQSTM1 scaffold protein as a key molecular mediator able of predicting and controlling sensitivity for DDA and ICIs. Mechanistically, in response to DNA damage, we found that SQSTM1 is essential for the inhibition of DNA repair and the reactivation of human endogenous retroviruses (hERV). Analogous to a “viral alarm”, the hERV are sensed and activate IFN responses that drive the expression of MHC-I and PD-L1, leading to tumor immune evasion. Targeting the hERV pathways in SQSTM1-depleted tumor cells by poly(I:C)/Lyovec, or docetaxel treatment can rescue the hERV, IFN, and MHC pathway, providing a promising therapeutic avenue turning a “cold” into a “hot” tumor in non-responders cancer patients.
Conclusion Depending on its levels, we thus propose SQSTM1 as a predictive biomarker for guiding treatment decisions from i) ICI alone, ii) ICI combined with cisplatin, or; iii) ICI combined with poly(I:C)/Lyovec or docetaxel, with the aim to increase immunotherapy efficacy.
Citation Format: Iris Grosjean, Grégoire D’Andréa, Nathalie Yazbeck, Amine Belaid, Barnabé Roméo, Marie Angela Domdom, Nicolas Guillot, Eric Gilson, Emmanuel Chamorey, Gérard Milano, Véronique Hofman, Marius Ilié, Isabelle Benard-Thiery, Simon Heeke, Patrick Brest, François Ghiringhelli, Paul Hofman, Baharia Mograbi. The tumor scaffold protein SQSTM1 at the crossroads of DNA damage and immunotherapy responses in solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1284.