Abstract 4735: Targeting CDK1/2-driven mechanisms of resistance to BRAF and EGFR inhibition in BRAF(V600E) colorectal cancer restores therapeutic response

Abstract Purpose: Metastatic colorectal cancer (mCRC) is the second leading cause of cancer death worldwide. Roughly 8% of mCRC tumors harbor a BRAF (V600E) mutation, associated with the worst prognosis and limited treatment options. Most CRC research and most clinical trials of targeted therapies have narrowly focused on targeting vertical mechanisms of MAPK re-activation (i. e. , EGFR-MAPK), with incremental advances for patients. New approaches are needed to address how therapeutic resistance is mediated by coordinated upregulation of multiple signaling pathways. Methods and Recent Advances: Using an innovative high-throughput kinase-activity mapping (HT-KAM) platform and kinase network resource (PhosphoAtlas), we discovered that SRC kinases drive resistance to BRAF ± anti-EGFR therapy independently of ERK signaling by inducing adaptive transcriptional changes via beta-catenin. This compensatory activation of SRC was mediated by an autocrine PGE2-loop that could be blocked with COX2 inhibitors (COX2i). Using patient-derived xenograft (PDX) models established from pre-treatment biopsies in clinical trial participants, we showed that targeting COX2 in combination with standard of care (SOC) BRAFi + EGFRi is an effective drug repurposing strategy to stabilize tumor growth in vivo. New, Unpublished Findings: Building on our drug discovery pipeline to find and target orthogonal modalities of therapeutic resistance, we leveraged our bank of residual PDX tumors collected after 21-day exposure to SOC therapy, and now report that CDK1 and CDK2 are at the center of a stress response program that enables BRAF (V600E) CRC tumor cells to survive under therapeutic pressure. We used HT-KAM to interrogate the activity of 165 kinases and kinase families, and integrated these profiles using computational methods to model signaling pathways. Out of the reprogrammed kinomes of BRAFi + EGFRi resistant tumors, the CDK1/2 kinases and mechanisms of cell cycle checkpoint emerged as critical dependencies. We validated these findings using multiplex immuno-fluorescence in residual tumors, protein/gene expression profile of tissues and cell lines (e. g. , upregulation of Cyclins and CDC25s), and cell viability assay using dinaciclib, a CDK1/2 inhibitor. Considering that COX2i has minimal toxicity, yet improved tumor growth inhibition when added to SOC, we evaluated whether jointly blocking inflammatory pathway (COX2) and cell cycle checkpoints (CDK1/2) could overcome resistance. We found that co-targeting CDK1/2 along with BRAFi + EGFRi ± COX2i is well-tolerated in mice and promotes significant, durable suppression of tumor growth in multiple PDX models, including tumor regression, over 9 weeks of treatment. Conclusion: When tumors progress on SOC BRAFi + EGFRi, a therapeutic window remains open to switch to a CDK1/2i-containing regimen and restore cancer control. Citation Format: Jean-Philippe Coppe, Denise P. Muñoz, Chloe E. Atreya, Yeonjoo Hwang, Mehdi Bouhaddou, Louise E. Heinrich, Mohammad Naser, Ons Zakraoui, Roxana Pirker, Rupa Guha, Christina Moelders, Alessandro Scapozza, Cecilia Schwarzer, Layla Phillips, Changjun Wang, Laura van 't Veer, Veronica Steri, Scott R. VandenBerg. Targeting CDK1/2-driven mechanisms of resistance to BRAF and EGFR inhibition in BRAF (V600E) colorectal cancer restores therapeutic response 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 (6Suppl): Abstract nr 4735.