Phase I and pharmacokinetic study of a stable, polyethylene-glycolated liposomal doxorubicin in patients with solid tumors: the relation between pharmacokinetic property and toxicity.

BACKGROUND

Compared with free drug, sterically stabilized liposomal drug has prolonged circulation time and, thereby, higher tumor selectivity and antitumor activity. The stability in plasma is an important consideration in the formulation of clinically useful liposomal drug. A Phase I study of a stable liposomal doxorubicin with polyethylene glycol (PEG) coating and phospholipid component of distearoyl phosphatidylcholine (DSPC) was performed to characterize its pharmacokinetic properties, toxicity profile, and maximal tolerated dose.

METHODS

The starting dose was 30 mg/m(2) every 3 weeks with an increment of 10 mg/m(2) for each level. A cohort of at least three patients was entered for each level. Dose escalation stopped when more than one-third of patients had dose limiting toxicity (DLT), which was equal to or more than Grade 3 nonhematologic toxicity. Blood was sampled immediately before and at 5 minutes, 2 hours, 4 hours, 10 hours, 24 hours, 48 hours, 72 hours, and 168 hours after the completion of PEGylated liposomal doxorubicin (PLD) infusion. Plasma level of doxorubicin was determined with fluorometry, and the pharmacokinetic properties were analyzed.

RESULTS

Twenty-six patients were entered, and 101 courses were studied. This DSPC PLD had a steady-state distribution volume (Vss) of 2.4 +/- 0.9 liters (mean +/- standard deviation), a clearance of 0.027 +/- 0.010 liters per hour, and a beta half-life of 65.0 +/- 17.8 per hour. These characteristics were dose independent, and the Vss and clearance were smaller than those of a well characterized PLD comprised of hydrogenated soybean phosphatidylcholine (HSPC). At the dose level of 50 mg/m(2), its plasma area under the concentration time curve was approximately twice that of HSPC PLD. Attenuation of acute toxicity, such as nausea, emesis, and alopecia, was noted in all dose levels. However, stomatitis was common from the dose level of 30 mg/m(2), and its incidence and severity increased with dosage and became dose limiting at 50 mg/m(2). A dose of 45 mg/m(2) every 3 weeks was then given in eight patients, and the side effects were acceptable. This dose was recommended for Phase II clinical trials. Fourteen of 17 patients with a dose level > or = 40 mg/m(2) were evaluable for response, but none achieved partial remission.

CONCLUSIONS

This DSPC PLD had the characteristics of second-generation liposomal drug pharmacokinetically and toxicologically. The incidence of severe stomatitis was higher than that of HSPC PLD, corresponding to the difference in pharmacokinetics. Only limited antitumor activity was observed, although defining its therapeutic application will need further Phase II studies. Further prolongation of plasma stability of PLD may not be clinically beneficial considering the increased stomatitis and the reduced achievable dose intensity.