Abstract 3220: Osimertinib-induced epigenetic and transcriptional reprogramming drives a BRD4-POUF-PDGFRB-YAP-EMT axis of resistance in NSCLC
Authors: Hartley Antja-Voy , Weston Caitlyn , Baldacci Simon , Feng William , Al-Dulaimi Mustafa , Gentile Claudia , Booker Matthew , Tolstorokuv Michael , Kadoch Cigall , Janne Pasi 
Published: March 2024

Abstract
Acquired resistance to Osimertinib continues to pose a major limitation to achieving durable therapeutic responses in EGFR mutant non-small cell lung cancer (NSCLC). While multiple actionable genetic mutations have been identified as the underlying molecular basis of resistance, a genomic mechanism cannot be identified in &gt;50% of Osimertinib resistant tumors and thus an effective combinatorial treatment strategy cannot be deployed for these patients. Recently, we identified YAP/TEAD activation and ERK1/2 reactivation as two major non-mutational counter-regulatory pathways that diminish the efficacy of Osimertinib, promoting establishment of the drug tolerant persister (DTP) and resistant states. Moreover, it is well known that cancer cells escape tyrosine kinase inhibitor (TKI) therapy by developing dependence on alternate, non-mutated receptor tyrosine kinases (RTKs) through a treatment-induced “RTK switch” phenomenon. The link however between alternate RTK signaling and YAP/TEAD/ERK1/2 has never been explored in the context of Osimertinib resistance. In this study, we systemically uncover transcriptional de-repression of, and critical dependence on PDGFRβ as part of a novel “RTK switch” mechanism deployed by cells to evade Osimertinib-induced death. Genetic or pharmacologic co-inhibition of PDGFRβ renders NSCLC cells more sensitive to Osimertinib during drug naïve, DTP and resistant phases of treatment through suppression of ERK1/2 reactivation, YAP activity/nuclear translocation and YAP-mediated induction of EMT factors, SLUG and Zeb2. Importantly, compared to Osimertinib alone, co-targeting EGFR and PDGFRβ robustly suppresses tumor regrowth following treatment cessation both in vitro and in vivo which is consistent with a reduction in the DTP cell population. These data auspiciously demonstrate a two-fold utility of concomitant PDGFRβ inhibition: to enhance the initial efficacy of Osimertinib and to eliminate the DTP and resistant cells following chronic Osimertinib treatment. Further mechanistic studies from integration of ATAC-seq, CUT&RUN and RNA-seq reveal that Osimertinib induces the dynamic cooperativity of chromatin modulator BRD4 with pluripotent POU-domain transcription factors Oct-4, Pit-1 and Brn-3 at putative proximal enhancer elements, facilitating upregulation of PDGFRβ. Collectively, we demonstrate a novel treatment-induced BRD4/POUF epigenetic/transcriptional mediated “RTK switch” that involves co-opting PDGFRβ signaling to activate YAP/TEAD and ERK1/2 as a means of driving adaptive resistance to Osimertinib. These data provide compelling rationale for combined anti-EGFR and PDGFRβ targeted therapy to improve patient outcomes.
Citation Format: Antja-Voy Hartley, Caitlyn Weston, Simon Baldacci, William Feng, Mustafa Al-Dulaimi, Claudia Gentile, Matthew Booker, Michael Tolstorokuv, Cigall Kadoch, Pasi Janne. Osimertinib-induced epigenetic and transcriptional reprogramming drives a BRD4-POUF-PDGFRB-YAP-EMT axis of resistance in NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3220.