Ruthenium drug BOLD-100 regulates BRAFmt colorectal cancer cell apoptosis through AhR/ROS/ATR signaling axis modulation

Patients with class I ^V600EBRAF-mutant (MT) colorectal cancer exhibit a poor prognosis, and their response to combined anti-BRAF/EGFR inhibition remains limited. An unmet need exits for further understanding the biology of ^V600EBRAFMT colorectal cancer. We used differential gene expression of BRAFWT and MT colorectal cancer cells to identify pathways underpinning BRAFMT colorectal cancer. We tested a panel of molecularly/genetically subtyped colorectal cancer cells for their sensitivity to the unfolded protein response (UPR) activator BOLD-100. To identify novel combination strategies for BOLD-100, we performed RNA sequencing and high-throughput drug screening. Pathway enrichment analysis identified significant enrichment of the UPR and DNA repair pathways in BRAFMT colorectal cancer. We found that oncogenic BRAF plays a crucial role in mediating the response to BOLD-100. Using a systems biology approach, we identified ^V600EBRAFMT-dependent activation of the replication stress response kinase ataxia telangiectasia and Rad3-related (ATR) as a key mediator of resistance to BOLD-100. Further analysis identified acute increases in BRAFMT-dependent-reactive oxygen species levels following treatment with BOLD-100, which promoted ATR/CHK1 activation and apoptosis. Furthermore, activation of reactive oxygen species/ATR/CHK1 following BOLD-100 was mediated through the AhR transcription factor and CYP1A1. Importantly, pharmacological blockade of this resistance pathway with ATR inhibitors synergistically increased BOLD-100-induced apoptosis and growth inhibition in BRAFMT models. These results highlight a possible novel therapeutic opportunity for BRAFMT colorectal cancer.