Lito, P. | Search bioRxiv

bioRxiv2025

BRAFV600E-Driven Lung Tumorigenesis Requires Ligand-Mediated Activation of ERBB Receptor Signaling

Secretion of ligands of the human epidermal growth factor (EGFR) family of receptors or erythroblastic leukemia viral oncogene family (ERBB1-4) is a feature common to many cancer cells. However, our understanding of the role of autocrine ligands in the aberrant behavior of cancer remains incomplete. Here we demonstrate that, in numerous preclinical models of lung tumorigenesis, BRAFV600E signaling promotes expression of ligands including HB-EGF, TGF, Epi- and Amphiregulin. Moreover, using both genetic or pharmacological approaches, we demonstrate that ligand-mediated activation of EGFR signaling in the tumor cell is required to sustain both early-stage BRAFV600E-driven lung tumorigenesis and supports late-stage BRAFV600E-driven lung cancer maintenance. Unbiased Reverse Phase Protein Analyses (RPPA) analyses, paired with targeted validation, reveals ERBB signaling serves to sustain signaling through the ERK1/2 MAP kinase pathway, through effects on ARAF and CRAF, and on the parallel JUN kinase (JNK) pathway. Furthermore, EGFR is activated in a cohort of BRAF-mutated lung cancer patients both pre- and post-treatment. Finally, we noted significant improvement in the depth and durability of therapeutic responses in preclinical models of BRAFV600E-driven lung cancer by combined inhibition of both BRAFV600E signaling plus pan-ERBB signaling. Collectively, this work provides evidence for an important role for ERBB family signaling in the genesis and maintenance of BRAFV600E-driven lung cancers, and the potential for future therapeutic improvement by rational combination targeting of these pathways. SIGNIFICANCEBRAFT1799A serves as a predictive biomarker for FDA-approved targeted inhibition of BRAFV600E oncoprotein kinase signaling in non-small cell lung cancer (NSCLC). However the occurrence of primary or acquired drug resistance limit the depth and durability of patient responses. Studies described here provide a mechanistic rationale for clinical testing of first-line BRAFV600E inhibition combined with pan-ERBB inhibition to improve the depth and durability of initial patient responses, and delay the emergence of lethal drug resistant disease.

cancer biology↗

bioRxiv2025

Mechanisms of resistance to active state selective tri-complex RAS inhibitors

Tri-complex inhibitors (TCIs) act as molecular glues to recruit cyclophilin A (CYPA) to the active (GTP-bound or ON) conformation of RAS, which in turn prevents the activation of downstream effector proteins like RAF and PI3K. Emerging data demonstrate clinical activity, including tumor regressions, in patients with RAS driven cancers. Despite being promising therapeutic interventions, the mechanisms of resistance in patients treated with these inhibitors remain unknown. Here we studied matched baseline and post-progression specimens from patients treated with the RAS(ON) multi-selective inhibitor daraxonrasib (RMC-6236). Tissue or cell-free DNA specimens were collected from 40 patients with RAS-mutant non-small cell lung, colorectal, or other cancers. Eighteen patients (45%) were found to have acquired alterations in RAS signaling intermediates, including recurrent alterations in KRAS, BRAF, RAF1, MAP2K1/2 and PIK3CA. Preclinical resistance models mirrored the alterations observed in patients. We found that secondary KRAS Y64X mutations caused resistance by disrupting an important pi-pi interaction between KRAS and the indole ring of daraxonrasib, which lowers the affinity of the daraxonrasib:CYPA binary complex for active KRAS. We also identified kinase-dead and low-activity BRAF mutations in samples with acquired resistance. This is puzzling, because TCIs are expected to prevent the interaction between RAS and BRAF, which is needed for hypoactive mutants to dimerize and signal. We now show that RAF dimers are harder to displace from active RAS, as compared to their monomeric forms. Indeed, enhanced RAF dimerization attenuated the ability of TCIs to recruit CYPA to active RAS, resulting in diminished inhibition of oncogenic signaling and tumor growth. Thus, several clinical resistance alterations converge at attenuating the formation of the RAS:daraxonrasib:CYPA tri-complex, either by preventing daraxonrasib binding or by inducing RAF dimers.

cancer biology↗