The activity of mTOR inhibitor RAD001 (everolimus) in nasopharyngeal carcinoma and cisplatin-resistant cell lines

Phosphorylated (pi-) protein kinase B (AKT) is commonly expressed in nasopharyngeal carcinoma (NPC) cell lines and tissues, suggesting the involvement of AKT-mammalian target of rapamycin (mTOR) signaling in NPC carcinogenesis. This study evaluated the activity of an mTOR inhibitor, RAD001 (Everolimus, Novartis Pharma AG, Switzerland), in 5 NPC cell lines (HK1, HONE-1, CNE-1, CNE-2, C666-1), 2 cisplatin-resistant NPC cell lines and their respective parental cell lines (HK1-LMP1, HONE-1-EBV). RAD001 inhibited cell growth in a dose-dependent manner at nanomolar concentrations in all cell lines. HONE-1 was most sensitive to RAD001 (IC₅₀ = 0.63 nM, 60% maximal inhibition), while Het-1A (a normal esophageal epithelial cell line) was relatively resistant. No consistent relationship between sensitivity to RAD001 and basal expression of pi-mTOR and pi-p70S6 Kinase-1 (p70S6K) was found. Exposure to RAD001 at picomolar concentrations for 48 h resulted in reduction of pi-mTOR and pi-p70S6K1 expression, but increase in pi-AKT (Ser473) expression in HONE-1 and CNE-1 cell lines. RAD001 significantly induced apoptosis in HONE-1 cells, but has no effect on cell cycle progression. RAD001 exerted an additive to synergistic effect on cisplatin-induced growth inhibition in CNE-1 and HONE-1 cells, and could inhibit the growth of both cisplatin-resistant and cisplatin-sensitive NPC cell lines. In summary, combination of RAD001 and cisplatin maybe a useful therapeutic strategy in NPC. AKT upregulation following RAD001 treatment suggests the presence of a feedback loop on AKT signaling in NPC which warrants further investigation.