Metformin reverses the drug resistance of cisplatin in irradiated CNE-1 human nasopharyngeal carcinoma cells through PECAM-1 mediated MRPs down-regulation

Objective: To explore a way to reverse the drug resistance for irradiated CNE-1 human nasopharyngeal carcinoma cells and try to develop a new high efficacy with low toxicity therapeutic approach. Methods: 300 Gy irradiated the CNE-1 human nasopharyngeal carcinoma cells, and then treated with single-agent cisplatin or metformin, or combination of both drugs. MTT assay and FCM were applied to detect cell viability and apoptosis. Western blot and RT-PCR were used to characterize the protein and mRNA expression after various drug administrations. Results: The results presented single-agent metformin was capable of arresting the tumor growth and inducing apoptosis in irradiated CNE-1 cells and also demonstrated a synergy effect with cisplatin. Furthermore, metformin down-regulates the PECAM-1 expression, which could regulate Multi-drug Resistance-associate Proteins (MRPs) expression leading to cisplatin resistance of irradiated CNE-1 cells. A pan-MRP inhibitor, probenecid, can resecure cisplatin resistance leading by radiation. Conclusions: Metformin, due to its independent effects on PECAM-1, had a unique anti-proliferative effect on irradiated CNE-1 cells. It would be a new therapeutic option to conquer cisplatin resistance for advanced NPC patients after radiotherapy.