Prospective Investigation of Dynamics of ABL Mutations in Imatinib Failed CML Patients Treated With Nilotinib (AMICAN)

Recently the treatment strategy of Philadelphia chromosome-positive leukemia has undergone groundbreaking changes due to the development of new second-generation cancer-targeting drugs. After 2001, a seven-year survival for leukemia stands at as much as 86 percent due to the oral therapy of cancer-targeting imatinib as a standard treatment, but drug resistance occurs in some patients in the early stage of the treatment. It is known that weakened binding ability of imatinib to BCR-ABL is due to a point mutation in the ATP-binding site of BCR-ABL. This accounts for 70 percent of causes of imatinib resistance. According to the studies so far, there are approximately more than 60 types of BCR-ABL point mutation, which causes imatinib resistance.

The international phase II clinical study of dasatinib and nilotinib, second-generation cancer-targeting therapies, in imatinib failed patients which began in 2005 showed that more than 70 percent of the patients achieved a complete hematological response (CHR) again, and about 50 percent of the patients, a major hematological response (MHR). In the study, it was also observed that kinase activation was inhibited by a second-generation cancer-targeting therapy for most of the major imatinib-resistant point mutations. With regard to peculiar point mutations, V299L, F317L, and E25K/V show relative resistance to dasatinib, and p-loop mutations including G250E, Q252H, Y253F/H and E255K/V and F359C/V show relative resistance to nilotinib. T315I mutation exhibits strong resistance to both of these cancer-targeting therapies. Therefore, it is considered that the second-generation cancer-targeting therapies show therapeutic effects in different domains.

According to the results of the recent studies including the one conducted by our center, it is assumed that imatinib resistance caused by point mutations in patients induces more point mutations and causes selective increase in T315I point mutations during treatment of the second-generation cancer-targeting therapy.

However, in the studies so far, the subjects were selectively chosen in advance for the pharmaceutical company to receive an approval from the health authorities and ABL point mutations were followed up during the limited study period, which indicates that there have been limits to accurately observe and evaluate dynamics of point mutations throughout treatment with the second-generation cancer-targeting drug.

For this reason, this study is designed to examine ABL point mutations in patients with Philadelphia chromosome-positive or BCR-ABL-positive chronic leukemia who are treated with imatinib, to observe dynamics of existing point mutations during treatment with nilotinib, and to confirm the mechanism of resistance including expression of new point mutations and their expression patterns through a long-term follow-up. In addition, this study will confirm whether expression pattern of ABL point mutations associated with nilotinib in Asian is different from that in Western patients.