Secondary c-Kit mutations confer acquired resistance to RTK inhibitors in c-Kit mutant melanoma cells

Activation of the c-Kit receptor tyrosine kinase is rare in melanoma, but occurs in 20-40% of melanoma arising on mucosal membranes, acral skin and skin with chronic sun-induced damage. Many activating c-Kit mutations have been shown to be highly sensitive to imatinib mesylate, although the majority of patients with c-Kit mutant melanoma eventually progress on this inhibitor. We examined acquired resistance to imatinib and the newer generation inhibitor nilotinib in resistant c-kit mutant melanoma sublines. Four imatinib-resistant and six nilotinib-resistant sublines had acquired additional, secondary c-Kit mutations. The secondary A829P c-Kit mutation rendered cells resistant to imatinib, but did not suppress the activity of the tyrosine kinase inhibitors nilotinib and dasatinib. Sublines with an additional T670I c-Kit mutation showed resistance to imatinib, nilotinib and dasatinib, but responded to sunitinib. The concurrent inhibition of the MAPK and PI3K pathways was also effective at promoting apoptosis in the parent and derived resistant sublines. Our data provide a rationale for treating patients with melanoma progressing on imatinib or nilotinib with alternative RTK inhibitors or inhibitors targeting the MAPK and PI3K signalling cascades.