Phase II Front-line Ponatinib in Adult Philadelphia+/BCR-ABL+ Acute Lymphoblastic Leukemia.

Drug resistance resulting from emergence of Imatinib-resistant BCR-ABL clones is a significant problem in Ph positive ALL patients because after a very good initial response to one TKI inhibitor, many patients relapse within one year, relapse being almost always associated with a BCR-ABL kinase domain point mutation. The patients who relapse after treatment with one TKI can be rescued to remission with another TKI, but the second remission is usually shorter than the previous one. A more potent TKI inhibitor, and pan-active not only on all the BCR-ABL variants (including the second generation TKI resistant T315I mutant), but also on others molecular targets can do better. In this context, Ponatinib is a novel synthetic orally active tyrosine kinase inhibitor (TKI), specifically developed to inhibit BCR-ABL, the fusion protein that is the product of the Philadelphia chromosome (Ph) in chronic myeloid leukemia (CML) and in a subset of acute lymphoblastic leukemia (Ph+ ALL). It potently inhibits the BCR-ABL protein as well as mutated forms of the protein that arise in patients resistant to prior therapies with TKIs. Ponatinib has been demonstrated to inhibit all the mutations that have been detected so far, in vitro and in vivo and to uniformly suppress the emerge of single-mutant clones in a mutagenesis assay. In the Phase II study, 41% of Philadelphia chromosome positive acute lymphoblastic leukemia patients treated with Ponatinib achieved major hematologic response, 47% had a major cytogenetic response, 38% obtained a complete cytogenetic response, showing that Ponatinib provides significant benefit despite previous intolerance or refractoriness to other TKIs. The Phase I trial showed that patients with a more recent diagnosis had increased rates of major molecular response: 79% for 14 patients with 0 to 5 years since diagnosis vs. 29% for 14 patients with more than 5 to 9 years since diagnosis (P=0.02) and 27% for 15 patients with more than 9 to 24 years since diag