Doxorubicin weekly low dose administration: in vitro cytotoxicity generated by the typical pharmacokinetic profile

Pharmacokinetic/pharmacodynamic modeling of antitumor agents encapsulated into liposomes

Pharmacokinetic/pharmacodynamic (PK/PD) modeling of antitumor agents has been developed for doxorubicin (DOX) in order to predict the optimum conditions for a drug carrier to maximize the antitumor effect. A PK model was constructed for free and liposomal doxorubicin using a hybrid model wherein the disposition in the whole body is described by compartment models, which were linked to the tumor compartment via the blood flow rate. The PD model for doxorubicin was described by a cell-kill kinetic model, which represents the number of tumor cells quantitatively, as a function of the free concentration of doxorubicin in the tumor compartment. The influence of each parameter on the antitumor effects was examined by sensitivity analysis based on the PK/PD model, which clearly showed the importance of optimizing the release rate of DOX from liposomes. The validity of the model has been tested using animal experiments. Preliminary simulations were also performed for humans after scaling up the PK/PD model from rodents to humans. The optimum conditions in the rate of drug release from liposomes were different for rodents vis-a-vis humans, which indicates the limitations involved in extrapolating optimum conditions for experimental animals to those for humans.

Optimization of antitumor effect of liposomally encapsulated doxorubicin based on simulations by pharmacokinetic/pharmacodynamic modeling

It has been reported that long circulating liposomes enhanced the antitumor effect of doxorubicin (DOX) by increasing delivery of DOX to tumor tissues. However, there is no quantitative information on the relationship between the antitumor effect and liposomal characteristics governing the release rate of entrapped drugs, although the importance of drug release-rate control from liposomes has been pointed out. Here, we developed a physiological model for free and liposomal DOX to calculate the time course of free DOX in the extracellular space and linked this with a cell kill kinetic model to quantify the antitumor effect of DOX. Simulations were performed to clarify the relationship between antitumor effect and pharmacokinetic or physicochemical parameters of liposomes, as well as pharmacological or physiological parameters of tumor tissues. The importance of long circulation time of liposomes was confirmed. The optimum rate of drug release from long circulating liposomes was found at the release rate constant of around 0.06 h(-1). This optimum value was not dependent on the tumor proliferation time, sensitivity of tumor cells to DOX, or the tumor blood flow-rate. This simulation indicated that the optimization of the delivery to tumor tissue by long circulating liposomes could be possible by changing the release rate of DOX for the maximum antitumor effect.