Continuous 72-h infusion of zosuquidar with chemotherapy in patients with newly diagnosed acute myeloid leukemia stratified for leukemic blast P-glycoprotein phenotype.

ABSTRACT

PURPOSE: To evaluate the safety, tolerability, pharmacodynamics (PD), and potential efficacy of zosuquidar (Zos) in combination with daunorubicin and cytarabine in elderly patients with newly diagnosed acute myeloid leukemia (AML). METHODS: Patients with AML (N = 106) were treated with Zos as a 72-h continuous intravenous (CIV) infusion along with chemotherapy. Leukemic blasts from the patients were assessed for P-glycoprotein (P-gp) function using ex vivo bioassays for screening and PD analyses. Patient outcomes were categorized according to primary (N = 56) and secondary (N = 50) AML cohorts (pAML and sAML, respectively) and stratified into P-gp-high and P-gp-low subgroups. RESULTS: Patients with P-gp-high blasts exhibited comparable overall remission rates (ORR) to those with P-gp-low blasts in both the pAML and sAML cohorts. The P-gp-high and P-gp-low subgroups in the pAML cohort exhibited similar overall survival (OS). Patients with sAML and P-gp-high blasts exhibited significantly better OS than those in the P-gp-low subgroup. PD analyses revealed that Zos infusion provided 82 h of uninterrupted effective ≥ 90% inhibition of P-gp functional activity in leukemic blasts. CONCLUSIONS: These observations provide evidence of Zos efficacy with the 72-h CIV infusion approach. The similarity of ORR in the P-gp-high and P-gp-low subgroups is consistent with Zos-mediated neutralization of P-gp as verified by PD analyses. The bioassay identified sAML patients most likely to respond favorably to Zos co-therapy indicating feasibility as a Zos companion diagnostic. A follow-up placebo-controlled trial is needed to verify these promising results. GOV IDENTIFIER NCT00129168; First posted on August 11, 2005.