The primary goal of this research project is to investigate the molecular mechanisms involved in multidrug resistance (MDR) through the study of naturally occurring MDR-reversing agents. Multidrug resistance is observed in both cancer biology and antibiotic therapy and is characterized by the development of cellular resistance to a broad spectrum of chemotherapeutic agents. One of the major mechanisms involved in this resistance is the over expression of molecular efflux pumps. Several natural product and small-molecule MDR-reversing agents have been identified and are currently under investigation for clinical use. Despite their importance, however, a complete molecular understanding of how these agents function as MDR-reversing agents has not been established. This project is based on the hypothesis that a molecular understanding of multidrug resistance can be obtained through the identification of the specific cellular targets of MDR-reversing agents. It is further hypothesized that we can capitalize on this molecular information to explore the structural determinants of novel MDR-reversing agents, which can be used to further elucidate the common pharmacophores necessary for reversion of the MDR phenotype. The experiments proposed are as follows: 1) To synthesize the known cyclic-depsipeptide MDR-reversing agent, hapalosin, as well as hapalosin-based probe molecules. 2) To use the hapalosin probe-molecules to identify the cellular target of hapalosin, and to investigate additional hapalosin targets through Display Cloning. 3) To synthesize and biologically evaluate hapalosin-like molecules designed to probe the molecular specificity of MDR-reversion using a non-peptidic molecular scaffold. The development of a molecular pharmacophore model for MDR-reversing activity will not only provide a molecular picture of multidrug resistance, but will also provide a novel pharmacological starting point for the development of more potent and specific MDR-reversing agents.
