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.