Potentiation of EGFR mutant lung cancer treatment targeting replication stress.

Background/ObjectivesOncogene-targeted therapies against growth factor receptors are effective treatment options for driver mutation-positive non-small cell lung cancer (NSCLC). The third-generation EGFR-Tyrosine Kinase inhibitor (TKI) osimertinib, is a standard first-line therapy for patients with EGFR-mutated NSCLC cancer. Acquired resistance to osimertinib is a significant problem that limits survival. In addition to that clinical data show approximately 15% of EGFR mutant non-small cell lung cancer patients have innate resistance to Osimertinib. Tumor heterogeneity and multiple resistance mechanisms add to the complexity of EGFR-mutated NSCLC. Tumor cells that acquire resistance, independent of the mechanism, experience replication stress (RS) as proliferation resumes. MethodsWe have employed a series of non-small cell lung cancer models to assess the efficacy of combining osimertinib with NERx-329, targeting RS via inhibiting RPA, and the impact of these treatments on growth and damage signaling pathways. ResultsWe demonstrate that targeting RS with RPAi treatment induces cell death in multiple EGFR-mutant cell lines alone and when combined with osimertinib. Dissection of signaling pathways revealed that RPAi treatment does not block osimertinib inhibition of EGFR signaling. Analysis of DNA damage response (DDR) signaling reveals that NERx329 potentiates the osimertinib-dependent downregulation of Chk1 activity and expression. The Chk1 loss was shown to be dependent on proteasome degradation as proteasome inhibitor MG-132 restores Chk1 activity and expression. ConclusionsFrom these data, we infer that targeting RS via RPAi NERx-329 in combination with osimertinib is an effective strategy and represents a promising drug combination targeted therapy to enhance efficacy and limit the development of resistance. Simple SummaryThis research aims to assess a new mechanism to potentiate osimertinib treatment of EGFR-mutated non-small cell lung cancer. Targeting replication stress with the small molecule Replication proteins A inhibitor (RPAi), NERx-329, induces cancer cell death and enhance the effectiveness of osimertinib. The findings suggest that combining NERx-329 with osimertinib could be a promising strategy to improve treatment outcomes and reduce resistance. Importantly, we demonstrate that neither RPAi or osimertinib alter the anticancer mechanism of each single agent, providing a new approach to increase therapeutic efficacy and delay or eliminate the development of drug resistance.