Abstract Purpose: Epidermal growth factor receptor (EGFR) mutations drive non-small cell lung cancer (NSCLC). Tyrosine kinase inhibitors (TKIs) provide clinical benefit but are limited by resistance. We investigated the role of mono-ADP-ribosyltransferase-1 (ART1) in mediating EGFR signaling, immune suppression, and therapeutic resistance. Methods: ART1 expression was assessed in a human tissue microarray. ART1 function was assessed in vitro in HCC827 and other EGFRmu lines using immunoprecipitation, immunofluorescence, and RNA-seq to define MARylation events and transcriptional changes. In vivo studies tested ART1 blockade with the fully humanized anti-ART1 monoclonal antibody, 22C12, alone or in combination with osimertinib in EGFR-mutant NSCLC GEMMs. These approaches enabled integrated assessment of ART1’s biochemical, transcriptional, and immunologic functions. Results: ART1 protein expression was higher in EGFRmu than EGFRwt human tumors. In vitro, ART1 was increased by osimertinib treatment. ART1 enhanced EGFR signaling through NAD+-dependent mono-ADP-ribosylation (MARylation). ART1 blockade with 22C12 abrogated EGFR MARylation and reduced downstream oncogenic signaling. RNA-seq revealed ART1-dependent regulation of EGFR-related transcriptional programs. In vivo, 22C12 osimertinib and 22C12 each demonstrated single agent efficacy, however small tumors persisted in GEMM models. However, combination therapy with Osimertinib and 22C12 reduced macrophage infiltration, increased tumor-infiltrating CD8+ tissue-resident memory (TRM) T cells, and rendered treated mice tumor-free. This synergy highlighted complementary tumor-intrinsic and immune-modulatory roles of ART1. These dual tumor-intrinsic and immune-modulatory effects identify ART1 as a driver of therapeutic resistance and potential therapeutic target. Conclusions: ART1 promotes EGFR pathway activation and suppresses antitumor immunity in EGFR-mutant NSCLC. Targeting ART1 enhances efficacy of TKIs while decreasing macrophage infiltration and reinvigorating CD8+ T-cell responses. ART1 inhibition represents a promising therapeutic strategy for overcoming resistance, warranting further investigation including ADP-ribosylome mapping and studies on ART1 blockade in modulating receptor signaling and bispecific antibody or antibody-drug conjugate interactions. Overall, these results support ART1 as a targetable mediator of EGFR-driven tumor progression and immune dysfunction in EGFR-mutant lung cancer. 22C12 is being developed to enter phase 1 clinical trials across multiple tumor types. Citation Format: Mimansa., Rajika Jindani, Mukherjee Sumit, Jorge Quintero, Naresh Regmi, Grace Ha, Justin Olivera, Justin Rosario, Melissa Tracy, Brendan Mullaley, Victor Gray, Erik Wennerberg, Lindsay M. LaFave, Brendon Stiles. ART1 as an immune modulating therapeutic target in EGFR-mutated lung cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3086.
Mimansa et al. (Fri,) studied this question.