Dose-Dependent Effect of Phenothiazines as Dynamin II Inhibitors on the Uptake of PEGylated Liposomes by Endocytic Cells and In Vivo Pharmacokinetics of PEGylated Liposomal Doxorubicin in Rats

Dynamin II (dynII) plays a significant role in the internalizationpathways of endocytic cells, by allowing membrane invaginations to"bud off". An important class of dynII inhibitors thatare used clinically are phenothiazines, such as prochlorperazine (PCZ).PCZ is an antipsychotic drug but is also currently in clinical trialsat higher concentrations as an adjuvant in cancer patients that increasesthe efficacy of monoclonal antibodies at high intravenous doses. Itis unknown, however, whether high-dose dynII inhibitors have the potentialto alter the pharmacokinetics of co-administered chemotherapeuticnanomedicines that are largely cleared via the mononuclear phagocytesystem. This work therefore soughtto investigate the impact of clinically relevant concentrations ofphenothiazines, PCZ and thioridazine, on in vitro liposome endocytosisand in vivo liposome pharmacokinetics after PCZ infusion in rats.The uptake of fluorescently labeled PEGylated liposomes into differentiatedand undifferentiated THP-1 and RAW246.7 cells, and primary human peripheralwhite blood cells, was investigated via flow cytometry after co-incubationwith dynII inhibitors. The IV pharmacokinetics of PEGylated liposomeswere also investigated in rats after a 20 min infusion with PCZ. Phenothiazinesand dyngo4a reduced the uptake of PEGylated liposomes by THP-1 andRAW264.7 cells in a concentration-dependent manner in vitro. However,dynII inhibitors did not alter the mean uptake of liposomes by humanperipheral white blood cells, but endocytic white cells from somedonors exhibited sensitivity to phenothiazine exposure. When a clinicallyrelevant dose of PCZ was co-administered with PEGylated liposomaldoxorubicin (Caelyx/Doxil) in rats, the pharmacokinetics and biodistributionof liposomes were unaltered. These data suggest that while clinicallyrelevant doses of dynII inhibitors can inhibit the uptake of liposomesby endocytic cells in vitro, they are unlikely to significantly affectthe pharmacokinetics of long-circulating, co-administered liposomes.