Methodology and experimental design for the study of liposome-dependent drugs

This chapter describes the concept of liposome-dependent drugs and the rationale for using them. Subsequently, procedures for studying and identifying liposome-dependent drugs are given. The first procedure described is a simple endpoint assay, and methods are given for both adherent and nonadherent cells. To establish in such a system that a drug is liposome dependent, it is necessary to demonstrate an IC(50) for the encapsulated drug that is less than that of the free drug, preferably with continuous exposure of the cells to drug. Subsequently, a second procedure is described, which is a more rigorous approach able to identify liposome dependency for a drug that is less effective in a carrier system than it is in the free form. This procedure is a multicompartment growth inhibition assay, wherein two cell populations are separated by a semipermeable membrane, through which free drug but not the liposomal carrier system may diffuse. The first population is adherent and is directly exposed to the liposomal or free drug. The second cell population is nonadherent and is exposed only to the drug that diffuses through the membrane. In addition to the methodology, experimental design is discussed and also the calculations needed to determine percent leakage, percent processing, percent metabolism, and the delivery factor, a parameter equivalent to a therapeutic index in an in vivo study.