Abstract 1255: Apoptotic DNase DFFB mediates cancer acquired drug resistance by suppressing persister cell intrinsic interferon signaling

Abstract Tumor adaptation driving cancer acquired drug resistance during oncogene targeted therapy treatment frustrates therapeutic responses and results in patient mortality. Unfortunately, the adaptive mechanisms residual surviving cancer cells utilize to overcome therapeutic stress are not well described. Understanding the processes that drive cancer acquired drug resistance may lead to novel therapeutic strategies to prevent tumor relapses. We used cell culture and mouse xenograft models of chronic, continuous, and toxic oncogene targeted therapy exposure (weeks to months) to study residual surviving “persister” cells and their regrowth into expanded colonies which models acquired drug resistance. Here, we describe how cancer persister cells experience sublethal apoptotic signaling and utilize the caspase-activated DNase DFFB to promote regrowth under drug pressure. We found that while DFFB WT persister cells were able to form colonies in drug, DFFB-deficient cells were severely restricted in their ability to regrow. Mechanistically, DFFB induces persistent DNA damage which both promotes mutagenesis and suppresses growth-arresting interferon signaling. During drug stress, the mitochondrial outer membrane permeabilizes and activates pattern recognition receptors to induce interferon signaling. From single cell RNA sequencing analysis of persister cells, we observed elevated interferon signaling gene sets in DFFB KO cells compared to WT cells. Furthermore, DFFB KO cells also had increased levels of STAT1 and STAT2. This elevated interferon signaling was growth suppressive because colony formation was rescued in DFFB KO cells with a JAK1/2 inhibitor. We then discovered that the stress response transcription factor ATF3 is selectively induced in DFFB WT cells whereas DFFB deficient cells lack ATF3 upregulation. ATF3 is a known modulator of interferon signaling, is induced following DNA damage stress, and has increased expression in patient minimal residual disease tumors on targeted therapy treatment. Consistent with ATF3-mediated interferon suppression, ATF3 depletion in persister cells increased STAT1 levels whereas ATF3 overexpression in DFFB KO persister cells reduced STAT1 levels. This data shows that DFFB-mediated activation of ATF3 promotes residual tumor regrowth by suppressing growth-restricting interferon signaling. This novel tumor adaptation mechanism represents an exciting new therapeutic strategy that could potentially extend the efficacy of targeted therapy treatments and increase patient survival. Importantly, DFFB is a nonessential gene since DFFB knockout mice develop normally. Additionally, increased expression of DFFB and ATF3 correlate with worse patient survival. Therefore, DFFB represents a promising therapeutic target against cancer acquired drug resistance. Citation Format: August (Gus) Finley Williams, David A. Gervasio, Claire E. Turkal, Anna E. Stuhlfire, Michael X. Wang, Brandon E. Mauch, Ariel H. Nguyen, Michelle H. Paw, Rhea Plawat, Mehrshad Hairani, Cooper P. Lathrop, Sophie H. Harris, Jennifer L. Page, Matthew J. Hangauer. Apoptotic DNase DFFB mediates cancer acquired drug resistance by suppressing persister cell intrinsic interferon signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1255.