Previously, we demonstrated that c-kit and stem cell factors (SCF) commonly co-expressed in primary and metastatic nasophayngeal carcinomas (NPC), and in HONE-1 NPC cells with tyrosine autophosphorylation of c-kit. These findings suggest that the SCF/c-kit signaling may contribute to pathogenesis of NPC. Therefore, the efficacy of STI571 treatment alone and when combined with cisplatin on HONE-1 cells were evaluated. STI571 induced growth inhibition at the IC50 concentration (14.9 µM). When the concentration was at or higher than 30 µM, the induction of cell apoptosis was observed. The effects of STI571 were shown to be mediated by the sustained activation of ERK but did not involve the inhibition of c-kit signal activity. When the STI571 (5 µM) and cisplatin (5 µg/ml) treatments were combined, there were further inductions of ERK activation resulting in obviously enhanced growth inhibition and induction of cell apoptosis. In a xenograft model, STI571 (50 mg/kg/day) showed only a limited ability to inhibit HONE-1 cell growth, but when combined with cisplatin (3 mg/kg/twice a week) treatment, there was a significant improvement in growth inhibition compared with STI571 or cisplatin treatment alone. Our results provide experimental support for the advanced NPC therapeutic trials using the combined STI571 and cisplatin treatment.

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