Dose Escalation Studies of Cytarabine, Daunorubicin, and Etoposide With and Without Multidrug Resistance Modulation With PSC-833 in Untreated Adults With Acute Myeloid Leukemia Younger Than 60 Years: Final Induction Results of Cancer and Leukemia Group B Study 9621

Abstract

PurposeP-glycoprotein (Pgp) is strongly inhibited by PSC-833. A chemotherapy dose-escalation study was performed with PSC-833 in patients younger than 60 years with untreated acute myeloid leukemia. Clinical rather than pharmacokinetic end points were used to develop two induction therapies containing drugs susceptible to Pgp-mediated efflux and associated with comparable toxicities at the maximum-tolerated doses.Patients and MethodsA total of 410 patients were enrolled. Fifteen induction regimens containing variable doses of daunorubicin (DNR) and etoposide (ETOP) and fixed doses of cytarabine were evaluated with (ADEP) or without (ADE) a fixed dose of PSC-833.ResultsDoses selected for phase III testing were DNR 90 mg/m2and ETOP 100 mg/m2in ADE, and DNR and ETOP each 40 mg/m2in ADEP. Intolerable mucosal toxicity occurred at higher doses of ADEP. Although the design of this study precludes direct comparisons, there was an apparent advantage for receiving ADEP with respect to disease-free and overall survival in patients ≤ 45 years old, despite the significantly lower doses of DNR and ETOP given in ADEP compared with ADE.ConclusionA large clinical data set was used to develop induction regimens containing two drugs susceptible to Pgp-mediated efflux, with and without an inhibitor of Pgp function. The chosen doses have comparable antileukemia activity and toxicity, making them suitable for use in a phase III comparative study of induction chemotherapy for patients with acute myeloid leukemia younger than 60 years. That trial will also clarify whether patients ≤ 45 years old are especially likely to benefit from Pgp inhibition during induction therapy.