PHA-739358, an Aurora Kinase Inhibitor, Induces Clinical Responses in Chronic Myeloid Leukemia Harboring T315I Mutations of BCR-ABL.

Background. The T315I BCR-ABL mutation confers high level resistance to clinically available ABL kinase inhibitors (i.e., imatinib, nilotinib, dasatinib, bosutinib, INNO-406). PHA-739358 is an aurora kinase inhibitor that selectively inhibits the ATP site of Aurora-A, Aurora-B and Aurora-C kinases, and binds with high affinity to both wild type Abl and Abl/T315I in vitro. A multicenter phase II study of PHA-739358 is being conducted in patients with chronic myeloid leukemia (CML) relapsing on imatinib or other c-ABL therapy.

Methods. Seven consenting CML patients (1 in chronic phase, 1 in accelerated phase, 5 in blast phase) were initially entered in this trial and received PHA-739358 dosed at 250 or 330 mg/m²/day administered by a once-weekly 6-hour infusion for 3 consecutive weeks, every 4 weeks. Six out of seven patients had the BCR-ABL T315I mutation. Pharmacokinetic and pharmacodynamic (PD) samples were collected and analyzed during cycle 1. The PD analyses evaluated BCR-ABL inhibition (phospho-CRKL) and Aurora kinase inhibition (phospho-histone H3).

Results. Two patients with T315I mutated BCR-ABL achieved a complete hematologic response (CHR) to PHA-739358. One of these patients treated in accelerated phase achieved a complete cytogenetic response (CCyR) and a complete molecular response after 3 months on the 330 mg/m² dose level. The CCyR is ongoing after 6 months of treatment. The second patient who achieved a CHR initiated therapy in chronic phase. A minor cytogenetic response was achieved after 3 cycles of therapy at the 330 mg/m², and a minimal cytogenetic response persists after nine months of treatment. Uncomplicated grade 4 neutropenia and an infusion-related reaction requiring acetaminophen, benadryl and hydrocortisone premedication was observed in one patient. No other grade 3/4 non-hematologic toxicity was observed. Patients with blast crisis did not have CHRs at the dose and schedule employed, although suppression of peripheral blood blasts was evident. PHA-739358 pharmacokinetics were in good agreement with those observed in other phase I - II studies. Average exposure, AUC0-t(168h), observed at 330 mg/m²/day was about 45 uM/h with Cmax values around 4 – 6 uM/h. Pharmacodynamic analyses demonstrated treatment-associated decreases of CRKL phosphorylation in 6 out of 7 patients, including both responders. Modulation of histone H3 phosphorylation was observed in 3 of 5 evaluable patients.

Conclusions. Objective clinical responses to PHA-739358 have been observed in two CML patients with T315I mutations of BCR-ABL, with an acceptable tolerability and safety profile. Additional doses and schedules of PHA-739358 are being investigated in patients with advanced phase CML.