Screening method for evaluation of bilayer-drug interaction

Medicilon's pharmacokinetics department offers the clients a broad spectrum of high quality of services in the areas of in vitro ADME, in vivo pharmacokinetics study and bioanalysis services, ranging from small molecules to large molecules, such as protein and antibody. The animal species involved in our services are non-human primate, canine, mice, rat, rabbit and hamster. Meanwhile, non-human primate experimental platform and isotope platform for protein/antibody are certified by the Shanghai Government.

A method for generating a correlation between at least one thermal property of a liposomal carrier in the presence of a therapeutic agent and a pharmacokinetic property for the therapeutic agent in the liposomal carrier and using the correlation for predicting the pharmacokinetic property of the liposomal carrier in the presence of any therapeutic agent in a liposomal carrier.

ield of the Invention The invention relates to a screening technique to evaluate drug-lipid interactions using thermal measurements, such as with differential scanning calorimetry (DSC). This technique correlates thermal measurements to the biophysical data of various drugs loaded into STEALTH® liposomes with their respective pharmacokinetic data. A model was constructed that predicts the in vivo pharmacokinetic behavior of drugs loaded into STEALTH®, or long-circulating, liposomes to screen the potential of a drug in a lipidic delivery system, and provides a valuable tool to predict in vivo behavior of a given drug when administered from a liposomal platform.

Background of the Invention Liposomes are closed lipid vesicles used for a variety of purposes, and in particular, for carrying therapeutic agents to a target region or cell by systemic administration of liposomes. Liposomes have proven particularly valuable to buffer drug toxicity and to alter pharmacokinetic parameters of therapeutic compounds. Conventional liposomes are, however, limited in effectiveness because of their rapid uptake by macrophage cells of the immune system, predominantly in the liver and spleen. With regard to the short in vivo half-life of conventional liposomes, a number of companies have overcome this obstacle by designing liposomes that are non- reactive (sterically stabilized) or polymorphic (cationic or fusogenic). For example, the Stealth® liposome is sterically stabilized with a lipid-polymer moiety, typically a phospholipid-polyethylene glycol (PEG) moiety, is included in the liposomal bilayer to prevent the liposomes from sticking to each other and to blood cells or vascular walls. These liposomes appear to be invisible to the immune system and have shown encouraging results in cancer therapy. It has been shown that there is a positive correlation between the amount of liposomal drug accumulation in solid tumors and the blood circulation half-life of the liposomes. However, a challenge with these liposomes is that different drugs exhibit very different drug release profiles upon intravenous administration in vivo. Different drugs may exhibit different pharmacokinetic behaviors even when encapsulated inside the same type of liposomes by the same encapsulation method. Properties of both the lipid and the drug contribute to the drug retention and blood circulation making prediction of the drug retention difficult. However, little is known at present about how drugs interact with the lipid membranes, and furthermore, how the nature of the interaction affects drug leakage. Therefore, achieving prolonged blood circulation for the liposome formulation is a primary focus in formulation feasibility studies, as the circulation half-life may directly relate to the efficacy of the product. Formulation feasibility studies include preparation of liposomes with an entrapped therapeutic agent and evaluation of pharmacokinetic (PK) data for the liposomes. Pharmacokinetic studies are designed to identify and describe one or more of absorption, distribution, metabolism and excretion of drugs. As the pharmacokinetic behavior of the free drug is very different from the same drug entrapped in a liposome, assessing the PK information is not straightforward. This evaluation is a lengthy process and usually takes 6 to 12 months to complete. One can not anticipate the outcome of the PK until the study is completed. A model for identifying suitable carrier systems and predicting the performance of these systems was described by Barenholtz and Cohen (J Liposome Res., 5(4):905-932 (1995)). This system, however, has little use due to the multiple tasks for measuring parameters and does not provide a clear and direct prediction of the pharmacokinetic performance of the liposomal formulations, even with the knowledge of the values of these parameters. Further, Hrynyk et al. proposed a mathematical model describing dose- and time-dependent liposome distribution and elimination to introduce a limited set of parameters, which may be helpful with assessing the in vivo fate of a liposomally encapsulated drug (Hrynyk et al., Cell Mol Biol Lett, 7(2):285, 2002). It would be desirable, therefore, to predict the pharmacokinetics for a liposomal drug formulation. The present invention presents an empirical, predictive model based on an analytical technique such as differential scanning calorimetry. This predictive model is useful for drug screening in order to select drugs with a high potential for long circulation in liposome formulations as well as to identify drug candidates that are potentially problematic. Another use of the model is in designing appropriate lipid formulations for maximum blood circulation time.