Ponatinib Efficacy and Safety in Patients with the T315I Mutation: Long-Term Follow-up of Phase 1 and Phase 2 (PACE) Trials

Background: Resistance to tyrosine kinase inhibitors (TKIs) in patients (pts) with chronic myeloid leukemia (CML) and Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) is frequently caused by mutations in the BCR-ABL kinase domain. Ponatinib is the only approved oral TKI that inhibits the T315I mutant, which is uniformly resistant to other TKIs. Here we report long-term follow-up of the efficacy and safety of ponatinib in pts with the T315I mutation at baseline from the Phase 1 (Ph1) and PACE trials.

Methods: The Ph1 trial (NCT01207440) evaluated safety and anti-leukemic activity of ponatinib (2-60 mg qd) in pts with CML or Ph+ ALL (N=81); the PACE trial (NCT00660920) evaluated efficacy and safety of ponatinib (45 mg qd) in CML and Ph+ ALL pts (N=449) resistant/intolerant to dasatinib or nilotinib or with the T315I mutation. Data reported are for pts with the T315I mutation at baseline, detected by Sanger sequencing at a central lab.

Results: The Ph1 and PACE trials included 19 (29%) and 128 (29%) pts with the T315I mutation, respectively. Median age and median time since diagnosis were 47 and 2.7 years for Ph1, and 53 and 3.6 years for PACE.Pts were heavily pretreated: 89% in Ph1 and 84% in PACE had received ≥2 prior TKIs. As of Jan 6, 2014, median follow-up was 42 (1-59) months in Ph1, and 20 (0.1-40) months in PACE; 58% Ph1 (92% CP-CML) and 33% PACE (52% CP-CML) pts remained on study. Most-common reasons for discontinuation: administrative decision (16%) and progressive disease (16%) for Ph1, and progressive disease (31%) and adverse events (AEs; 13%) for PACE. Of the pooled chronic phase (CP)-CML pts, 75%, 72%, and 61% achieved MCyR, CCyR, and MMR, respectively, with deeper responses (MR4, MR4.5) observed in over a third of the pts (Table). MaHR was achieved in 58%, 27% and 38% of pooled AP-CML, BP-CML and Ph+ ALL pts, respectively. For Ph 1 CP-CML pts, 3-year CCyR duration estimates were 80%. For PACE CP-CML pts, 2-year MCyR/CCyR duration, PFS and OS estimates were 93%/79%, 72% and 82%, respectively. Only 1 CP-CML pt in PACE lost MCyR and 1 transformed to AP-CML. For AP-CML, BP-CML, and Ph+ ALL, estimated OS/PFS at 2 years was 69%/54%, 14%/10%, and 10%/N/A, respectively.

The most frequent treatment-emergent AEs (TEAEs) observed in Ph1 CP-CML pts were dry skin (83%), rash (83%), arthralgia (75%), fatigue (75%), headache (67%), abdominal pain (58%), hypertension (58%), hypertriglyceridemia (58%), myalgia (58%), and nausea (58%). None of the 19 serious TEAEs that occurred in Ph1 CP-CML pts occurred in >1 pt. The most common (≥25%) TEAEs in PACE CP-CML pts were rash (48%), dry skin (42%), headache (41%), abdominal pain (39%), nausea (36%), constipation (33%), fatigue (33%), thrombocytopenia (28%), myalgia (28%), hypertension (27%), arthralgia (25%), and upper respiratory tract infection (25%). Most common (≥5 %) serious TEAEs in PACE CP-CML pts were acute myocardial infarction (8%), pancreatitis (8%), atrial fibrillation (6%), coronary artery disease (6%), congestive cardiac failure (5%), pneumonia (5%), cerebral infarction (5%), pyrexia (5%), increased lipase (5%), and dyspnea (5%). Arterial thrombotic events occurred in 1 (8%) Ph1, and 20 (31%) PACE pts. Venous thromboembolic events occurred in 1 (8%) Ph1, and 3 (5%) PACE pts. Despite the higher median dose intensity for T315I CP-CML pts (38 vs 30.8 mg/day overall CP-CML) in PACE, the safety profiles were similar. For CP-CML pts in PACE, responses achieved by 12 months were generally maintained after dose reduction primarily to manage AEs: 100% maintained MCyR; 100% maintained CCyR, and 79% maintained MMR.

Conclusions: In Ph+ leukemia pts with the T315I mutation, where effective treatment options are limited, ponatinib continued to exhibit deep and durable responses with up to 6 years follow-up. Dose reductions to manage AEs did not impact maintenance of cytogenetic responses. The response rates and safety profile of T315I pts were comparable to, if not better than, those observed in the overall population of refractory CML and Ph+ ALL pts in ponatinib clinical trials.