PSC833, a Multidrug Resistance Inhibitor, May Improve Efficacy of Chemotherapy in Elderly Patients With AML

SAN DIEGO—Up to 80% of newly diagnosed elderly acute myelogenous leukemia (AML) patients overexpress P-glycoprotein (P-gp), leading to multidrug resistance and a poor prognosis, said Dr. P. Sonneveld, University Hospital, Rotterdam, in a presentation at the American Society of Hematology (ASH) annual meeting.

The addition of a P-gp inhibitor to standard chemotherapy regimens may prevent multidrug resistance in these patients and lead to an improved response to treatment.

In their dose-finding study, Dr. Sonneveld and his colleagues determined the optimum daunorubicin (Cerubidine) dose to be used in conjunction with cytarabine and PSC833, a P-gp inhibitor, in elderly AML patients.

The study included 39 patients over age 60 with newly diagnosed AML, 19 given 35 mg/m2 of daunorubicin on days 1 to 3, and 20 given a 45 mg/m2 dose. PSC833 was given at a daily IV dose of 10 mg/kg on days 1-4, and cytarabine was administered at 200 mg/m2 on days 1 to 7. “Steady state PSC833 blood levels exceeded the level required for inhibition of P-gp,” Dr. Sonneveld said.

Although the higher daunorubicin dose produced a higher complete response rate (60% vs 42% with the lower dose), it came at the cost of increased toxicity. Seven of the patients on the higher dose died of drug-related complications, all while in complete remission, compared with two on the lower dose. Thus, 35 mg/m2 was established as the daunorubicin dose to be used in a randomized controlled phase III trial of PSC833. “This study proves the safety of PSC833 in combination with chemotherapy in elderly patients with AML,” Dr. Sonneveld said.

The researchers also analyzed P-gp expression in 33 patients and found that those who were P-gp positive were just as likely to achieve a complete response as those who were P-gp negative. Thus, use of PSC833 appeared to overcome the negative prognostic effect of P-gp overex-pression.

“Unlike standard treatment, which is less effective in patients with high levels of P-gp, this regimen combining PSC833 with chemotherapy at a reduced dose was equally effective in patients with and without high P-gp levels,” Dr. Sonneveld concluded.