The role of Ca2+/calmodulin-dependent protein kinase II in oxaliplatin resistance of colorectal cancer: In vitro and in vivo studies.

BACKGROUND: Oxaliplatin (Oxa) resistance is a major barrier in colorectal cancer (CRC) treatment. The Ca2+/CaM/CaMKII pathway is involved in tumor progression, but its role in chemoresistance remains unclear.

METHODS: Oxa-resistant HCT116 and HT29 sublines (HCT116-Oxa and HT29-Oxa) were established through gradual dose escalation. The activation status of the Ca2+/CaM/CaMKII pathway was assessed by measuring intracellular Ca2+ levels and phosphorylation of CaMKII. Functional studies such as CCK-8, clonogenic assays, and flow cytometry-based apoptosis analysis were conducted to assess the impact of CaMKII inhibition by KN-93 on chemosensitivity. Gain-of-function experiments were conducted using CaMKII-overexpressing HT29 cells. The in vivo antitumor efficacy was evaluated using an HCT116-Oxa xenograft model in BALB/c nude mice treated with Oxa, KN-93, or a combination of both.

RESULTS: Oxa-resistant cells exhibited significantly elevated IC50 values, increased basal intracellular Ca2+ levels, and hyperphosphorylation of CaMKII. Pharmacological inhibition of CaMKII with KN-93 enhanced Oxa-induced cytotoxicity, suppressed clonogenic survival, and promoted apoptosis in resistant cells, accompanied by downregulation of p-RAF and p-ERK. Overexpression of CaMKII in parental HT29 cells conferred resistance to Oxa and attenuated drug-induced apoptosis. In vivo, combination therapy with Oxa and KN-93 significantly inhibited tumor growth compared to monotherapy, without increasing systemic toxicity. Western blot analysis confirmed reduced phosphorylation of CaMKII and ERK in tumor tissues from the combination group.

CONCLUSION: Hyperactivation of the Ca2+/CaM/CaMKII pathway contributes to Oxa resistance in CRC, at least in part via RAF-ERK signaling. Targeting CaMKII may be a viable strategy to overcome resistance.