Abstract / Summary
Colorectal cancer (CRC) remains a leading cause of cancer mortality, with oxaliplatin resistance driving disease relapse and limiting treatment efficacy. This study investigated transcriptomic signatures of oxaliplatin response in colorectal adenocarcinoma HCT116 cells, comparing sensitive and oxaliplatin-resistant lines to identify survival mechanisms enabling resistance. These signatures reveal potential therapeutic targets for overcoming oxaliplatin resistance in CRC. In contrast to sensitive cells, oxaliplatin-resistant HCT116 cells exhibited a muted transcriptomic response, with twofold fewer differentially expressed genes. This attenuated response was marked by the downregulation of key cell cycle regulators (e.g. E2Fs , FOXM1 and their transcriptional targets), aligning with the observed rapid cell cycle arrest under oxaliplatin exposure. Targeting this adaptive cell cycle arrest with adenoviral E1A expression reactivated proliferation, induced apoptosis, and restored oxaliplatin sensitivity in resistant cells, as evidenced by EdU incorporation, E2F dependent reporter activity, and γH2AX accumulation. The γH2AX signal indicated that forcing cells to replicate oxaliplatin damaged DNA resulted in replication stress, which likely contributed to the observed cell death. Functional analysis revealed that oxaliplatin induced differential expression of genes enriched mostly in pathways associated with cell cycle suppression and DNA replication. Notably, oxaliplatin triggered opposing expression dynamics in 440 genes between sensitive and resistant cells. Among these, ten genes were strongly upregulated in HCT116 cells yet sharply downregulated in HCT116-OX cells. Members of this subset have established roles in promoting proliferation, and their inactivation is known to suppress tumor cell proliferative capacity. Our data reveal that resistant cells evade toxicity primarily through coordinated cell cycle arrest. Cell cycle activation represents a recognised approach for overcoming drug resistance and eliminating drug‑tolerant quiescent cancer cells. Although not yet clinically approved, E1A‑mediated cell cycle activation proves effective in our HCT116‑based model, reversing oxaliplatin resistance through combined cell cycle activation and pro‑apoptotic effects. Mechanistically, forcing resistant cells to re‑enter the cell cycle in the presence of oxaliplatin‑damaged DNA induces replication stress, as evidenced by γH2AX accumulation, which likely contributes to the observed sensitization. Elucidating the precise mechanisms of E1A‑dependent sensitization provides a mechanistic foundation for the future development of small‑molecule or pharmacological cell‑cycle reactivation strategies that mimic E1A’s sensitizing efficacy in refractory CRC.