Treatment Free Remission after Combination Therapy with Asciminib (ABL001) Plus Imatinib in Chronic Phase Chronic Myeloid Leukemia (CP-CML) Patients Who Relapsed after a Prior Attempt at TKI Discontinuation-H Jean Khoury Cure CML Consortium Study

Abstract

Successful tyrosine kinase inhibitor (TKI) discontinuation is currently one of the main goals of CML therapy. Patients who are in sustained deep molecular remission can attempt TKI discontinuation; approximately 50% of such patients will achieve a successful treatment free remission (TFR) and the other 50% will have molecular recurrence , warranting reinitiation of TKI therapy. Molecular recurrence is defined as loss of major molecular response (BCR-ABL1 International Scale ratio >0.1%) . With a goal to increase the ultimate fraction of successful TFR, inquiry has begun into the rate and optimal approach to TFR after a second attempt at TKI discontinuation in patients with molecular recurrence after their first attempt. Molecular recurrence, is suspected to be driven by CML progenitor element(s) capable of, permitted to, and/or signaled to proliferate; different approaches to eradicate such a compartment have been proposed. One such potential means may be through alternative and synergistic BCR::ABL1 inhibition with the allosteric inhibitor asciminib in combination with approved TKIs for CML. Asciminib is a potent BCR::ABL1 inhibitor with a novel, allosteric mode of action. The activity of asciminib is a result of its ability to bind a vacant pocket on the kinase domain that is normally occupied by the myristoylated N-terminus of ABL, a negative regulatory element lost upon the fusion of ABL to BCR. Asciminib has an excellent selectivity profile, is several-fold more potent than current approved TKIs such as nilotinib, and in vitro was active in the low nanomolar range against a spectrum of clinically observed ATP site mutations. Asciminib demonstrated efficacy in phase I studies in resistant/intolerant chronic and accelerated phase CML, including T315I mutation positive and ponatinib pretreated patients. In a phase III trial, asciminib was more active than bosutinib in a phase III trial in patients who had received 2 prior TKIs Our primary objective in this study is to determine the 1-year TFR rate after 12 months of combination therapy with imatinib plus asciminib, followed by treatment cessation, in subjects who have previously had molecular recurrence first TFR attempt. This is a single arm phase II study that will enroll a maximum of 51 patients (NCT04838041). All subjects will have a confirmed diagnosis of CML-CP. Each subject must have previously attempted to discontinue imatinib, and were restarted on imatinib at the time of molecular recurrence in order to be eligible for this trial. This trial will use asciminib 40 mg PO daily plus imatinib at a maximum dose of 400 mg PO once daily in the combination treatment phase of this trial. All eligible subjects will be treated with asciminib and imatinib on cycle 1 day 1 of the combination therapy phase. Patients will remain on imatinib for 12 cycles. RQ-PCR to measure BCR::ABL1 transcripts in the peripheral blood at screening and at specific time points during the first 12 cycles on trial (combination therapy phase). At the end of 12 cycles, asciminib and imatinib will be discontinued in any subject who has continued in stable deep remission and thus meets criteria for TFR. This study will assess a wide range of PROs before and after stopping imatinib. These will be done in conjunction with RQ-PCR testing, though at fewer time points, utilizing online and/or phone questionnaires. The alternative hypothesis of relapse rate after second discontinuation of TKI combination treatment is 35% will be tested against a one-sided alternative of historical control of 55% relapse rate. Simon's two-stage admissible design will be used. The null hypothesis that the true TFR rate (no loss of MMR) is 45% will be tested against a one-sided alternative. In the first stage 29 patients will be accrued. If there are 15 patients or fewer who maintain TFR in these 29 patients, the study will be stopped. Otherwise, 18 additional patients will be accrued for a total of 47. The null hypothesis will be rejected if 27 or more patients maintain TFR in 47 patients. This design yields a type I error rate of 5% and power of 85% when the true TFR rate is 65%. To account for a potential dropout rate of 8% due to adverse events or loss of response, 51 patients will be enrolled to achieve the 47 patients needed.