A phase 1 dose‐escalation study of ARRY‐520, a kinesin spindle protein inhibitor, in patients with advanced myeloid leukemias

Abstract

BACKGROUND: ARRY‐520 selectively inhibits the mitotic kinesin spindle protein (KSP), which leads to abnormal monopolar spindle formation and apoptosis. METHODS: A phase 1 trial was conducted to establish the safety and the maximum tolerated dose (MTD) of ARRY‐520 given as a 1‐hour infusion in either a single dose or on a day 1, 3, and 5 divided‐dose schedule per cycle in patients with advanced or refractory myeloid leukemias. Additional objectives were to characterize pharmacokinetics, assess preliminary clinical activity, and explore biomarkers of KSP inhibition with ARRY‐520. A total of 36 patients with acute myelogenous leukemia (n = 34) or myelodysplastic syndromes (n = 2) with a median age of 66 years (range, 21‐88 years) were enrolled: 15 in the single‐dose schedule (dose levels: 2.5, 3.75, 4.5, and 5.6 mg/m²) and 21 in the divided‐dose schedule (dose levels: 0.8, 1.2, 1.5, and 1.8 mg/m²/day). RESULTS: The MTD was 4.5 mg/m² total dose per cycle for both dose schedules. Dose‐limiting toxicities included mucositis, exfoliative rash, hand‐foot syndrome, and hyperbilirubinemia. Grades 3 or 4 reversible drug‐related myelosuppression were observed in 33 of 36 patients. Plasma pharmacokinetic analyses revealed low clearance of ARRY‐520 (∼3 L/hour), a volume of distribution of ∼450 L, and a median terminal half‐life of >90 hours. Monopolar spindles were observed in blood mononuclear cells, through use of 4′,6‐diamidino‐2‐phenylindole nucleic acid stain and antitubulin antibodies. CONCLUSIONS: On the basis of the relative lack of clinical activity, further development of ARRY‐520 as an antileukemic agent was halted. (Clinicaltrials.gov identifier NCT00637052). Cancer 2012;3556–3564. © 2011 American Cancer Society.