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The treatment of relapsed acute myeloid leukemia (AML) remains unsatisfactory. We conducted a phase II randomized trial where patients received intermediate-dose cytarabine for four days followed by gemtuzumab ozogamicin on day 5 (Arm A), or combined with liposomal daunorubicin for three days (Arm B), or cytarabine given for five days combined with cyclophosphamide for three days and topotecan by continuous infusion for 5 days (Arm C). Eligible patients had primary refractory AML, a first relapse after a remission of less than one year, or a second or greater relapse. The primary objective of this trial was attainment of a conventional complete remission (CR) or a CR without platelet recovery (CRp) in at least 40% of patients. The CR/CRp rates for the 82 eligible patients were 3/26 (12%) in Arm A, 2/29 (7%) in Arm B, and 1/27 (4%) in Arm C. No patients who had relapsed within six months of initial CR or who had suffered multiple relapses responded. More than 95% of patients subsequently died of AML. No unexpected toxicities were encountered. We conclude that none of these three regimens were effective enough in the treatment of high-risk relapsed or refractory AML to warrant further study. This trial was registered at http://www.clinicaltrials.gov as #NCT00005962.

We have conducted a phase I/II trial to determine the maximum tolerated dose, early safety and efficacy of single-agent liposomal daunorubicin in relapsed or refractory acute myeloid leukaemia (AML). Successive cohorts of six patients received escalated doses of 75, 100, 125 or 150 mg/m2 of DaunoXome for three consecutive days. Responding patients received a further consolidation cycle of DaunoXome at a dose identical to the one inducing complete or partial remission at the various dose levels. Twenty-eight patients with a median age of 50.5 years were enrolled. A maximum tolerated dose was determined at 150 mg/m2. Twelve patients received the second cycle. DaunoXome was well tolerated at all administered levels; dose-limiting toxicities included nausea and vomiting, mucositis and two episodes of cardiotoxicity resulting in the death of two patients. The overall response rate was 46% with a median duration of response of 180 d and a median duration of survival of 208 d. Ten patients demonstrated a complete response following cycle 1, and a further four entered partial response with the first cycle (marrow blasts between 5% and 10%). Of these, three attained complete response with the second cycle (total complete response 13/28). Our results indicate that DaunoXome at a dose of 150 mg/m2 displays acceptable toxicity in a 3-d regimen followed by a 3-d consolidation course at 100 mg/m2/d. At this dose schedule, interestingly high remission rates were achieved, justifying further evaluation of DaunoXome for the treatment of relapsed or refractory AML patients.

The possibility that Daunoxome (DNX), a combination of daunorubicin (DNR) with a liposomal targeting system, escapes PGP was tested. Two pairs of leukaemic cell lines, each consisting of the parental non-multidrug resistance (MDR) line and of a MDR variant, were studied for cytotoxicity (MTT test) and for cellular DNR kinetic and accumulation (flow cytometry). DNX and free DNR were equally toxic against non-MDR cells, whereas the liposomal anthracycline was more toxic than the free drug against the MDR variant. Non-MDR cells accumulated DNR more rapidly when they were exposed to free DNR than to DNX, but MDR cells accumulated more DNR when they were exposed to DNX. The kinetics of DNX and free DNR were also studied in the blast cells of 41 cases of acute leukaemia and they were found to be related to blast cell PGP expression. In 15 cases with a low PGP expression intracellular DNR accumulation was faster and higher with free DNR than with DNX. In 26 cases with a high PGP expression the area under the curve was similar with DNX and free DNR, but the kinetics of intracellular DNR accumulation showed an early low plateau with free DNR and a slow and continuous increase with DNX. In MDR cell lines the ratio was more favourable to DNX than to free DNR. We conclude that liposome encapsulated DNR is partially protected from PGP and that it is worth testing for the treatment of PGP-positive acute leukaemia.