The emergence of ABL point mutations is the most frequent cause for imatinib resistance in chronic myelogenous leukemia (CML) patients and can occur during any phase of the disease; however, their clinical impact remains controversial. In this study, we retrospectively analyzed the predictive impact of 94 BCR-ABL kinase domain mutations (18 T315I, 26 P-loop, 50 in other sites) found in 89 imatinib-resistant CML patients. At imatinib onset, 64% of patients (57/89) were in chronic phase (CP), 24% (21/89) in accelerated phase (AP) and 12% (11/89) in blastic phase (BP). T315I and P-loop mutations were preferentially discovered in accelerated phase of BP CML, and other types of mutations in CP (P ¼ 0.003). With a median follow-up of 39.2 months (6.3-67.2), since imatinib initiation, overall survival (OS) was significantly worse for P-loop (28.3 months) and for T315I (12.6 months), and not reached for other mutations (P ¼ 0.0004). For CP only, multivariate analysis demonstrated a worse OS for P-loop mutations (P ¼ 0.014), and a worse progression-free survival (PFS) for T315I mutations (P ¼ 0.014). Therefore, P-loop and T315I mutations selectively impair the outcome of imatinib-resistant CML patients, in contrast to other mutations, which may benefit from dose escalation of imatinib, able to improve or stabilize disease response.

The BMI1 polycomb protein regulates self-renewal, proliferation and survival of cancer-initiating cells essentially through epigenetic repression of the CDKN2A tumor suppressor locus. We demonstrate here for the first time that BMI1 also prevents autophagy in chronic myeloid leukemia (CML) cell lines, to support their proliferation and clonogenic activity. Using chromatin immunoprecipitation, we identified CCNG2/cyclin G2 (CCNG2) as a direct BMI1 target. BMI1 downregulation in CD34+ CML cells by PTC-209 pharmacological treatment or shBMI1 transduction triggered CCNG2 expression and decreased clonogenic activity. Also, ectopic expression of CCNG2 in CD34+ CML cells strongly decreased their clonogenicity. CCNG2 was shown to act by disrupting the phosphatase 2A complex, which activates a PKCζ-AMPK-JNK-ERK pathway that engages autophagy. We observed that BMI1 and CCNG2 levels evolved inversely during the progression of CML towards an acute deadly phase, and therefore hypothesized that BMI1 could support acute transformation of CML through the silencing of a CCNG2-mediated tumor-suppressive autophagy response.

Our results are superior to results reported from large multicentre trials (DFS 29-39%). Our study is a relatively large, single-center study involving patients with a low median age at diagnosis. Outcome is often superior in single-center studies compared to multicenter studies, and age is a well-recognized prognostic factor. However, these factors cannot fully account for our favorable results. Our treatment protocol is rather intensive and contains more glucocorticoids, vincristine, L-asparaginase, methotrexate and 6-mercaptopurine than most adult protocols. In this respect, our protocol is in line with pediatric protocols. Favorable outcome for adolescents treated according to pediatric protocols (DFS 64-67%) compared to adult protocols (34-41%) has recently been reported, and the results have been attributed to treatment intensity with particular reference to the drugs specified above. [6][7][8] In patients less than 25 years of age, 8-year DFS is 67% in our study. This fits very well with the results reported in studies in which adolescents have been treated according to pediatric protocols.

Second-generation tyrosine kinase inhibitors (TKI2) often induce molecular remission, and prolonged survival with a better tolerance in imatinib-resistant chronic myelogenous leukaemia (CML) patients. We report the case of a CML in first chronic phase who was diagnosed in August 2003 in a young 24 year-old Caucasian woman. Our patient received first imatinib and then dasatinib and nilotinib. Imatinib was well tolerated and she developed TTP/HUS on dasatinib without documented evolution of CML and finally obtained MR5.0 with nilotinib and without any side effect. This case also illustrates the absence of cross-resistance and side-effects between the different TKIs and the feasibility of kidney transplantation associated with a nilotinib treatment of CML allowing a continuing MR5.0 and no further side effects.