Mechanistic Dissection and Modulation of Cytoskeletal Regulation to Overcome Innate Resistance to KRAS Inhibition

About This Grant

PROJECT SUMMARY Adaptive mechanisms of resistance are broadly observed across virtually all cancer therapies and contribute to tumor heterogeneity and the emergence drug-tolerant persister cells (DTPs), which limit the upfront efficacy of cytotoxic agents and prevent the full eradication of cancer. KRAS is one of the most commonly observed oncogenic mutations, occurring in approximately 20% of all cancers and at significantly higher rates in pancreatic (~ 75%), colorectal (~40%), and non-small cell lung cancers (~27%). Despite nearly three decades of effort to develop pharmacological agents targeting KRAS, only within the last three years have the first rationally-designed covalent inhibitors for the KRAS G12C mutation been FDA-approved. However, the efficacy has been modest at best, and putative genetic resistance mechanisms have been identified in only ~45% of patients, suggesting that a large percentage of KRAS-driven tumors exhibit innate, non-genetic mechanisms of resistance to these inhibitors. Understanding these adaptive pathways mediating drug resistance to identify new strategies that improve patient survival in KRAS-driven tumors represents a critical unmet need. To study the biology of DTPs, we conducted a genome wide shRNA enrichment screen and discovered that attenuation of the RhoA-ROCK-myosin IIa axis promotes DTP survival through decreased apoptosis and increased cell cycle arrest. This mechanism appears to be conserved across many tumor types, including KRAS-driven tumors treated with KRAS inhibitors, and may represent a therapeutic opportunity to eliminate the residual persister tumor population. In this proposal, we will focus on KRAS inhibition and build upon these key preliminary findings. In Aim 1, we will determine the functional role of the Rho-A/ROCK/myosin IIa axis in promoting DTP survival post-KRAS inhibition in additional 2D and 3D culture systems. Aim 2 will elucidate the mechanism by which attenuation of MYHIIa promotes increased DTP survival by defining the critical cis-acting domains of MYHIIa and the downstream effector pathways required to promote this survival phenotype. Aim 3 will test pharmacological induction of p53 as a therapeutic intervention to enhance DTP killing in KRAS-driven tumors in vivo and also leverage state-of-the-art single cell, barcode tracking to interrogate the origin and transcriptome of DTPs. These studies will 1) provide new biological insight regarding a previously unappreciated link between cytoskeletal regulation, p53 signaling and cellular survival, 2) deploy promising, novel drug combinations specifically targeting the tumor persister population based on biomarker selection, and 3) identify new therapeutic targets for KRAS-mutant tumors to improve clinical responses and patient survival.