Paul D. Roepe
Professor  

Department of Chemistry 
Georgetown University
37th and O Streets NW
Washington, DC 20057-1227

Burroughs Wellcome New Initiative Award (1999)  

Biochemistry I & II,  Advanced Topics in Biochemistry

Biochemistry: molecular mechanisms of biological membrane transport; biochemical mechanisms of drug resistance. 
The focus of our laboratory is to elucidate the molecular details of drug resistance pathways.  Two systems that we currently study in depth are "multidrug resistant" tumor cells, and drug resistant malarial parasites.  Although these two topics might seem unrelated, we have found interesting molecular parallels between these two types of drug  resistance.  Thus, we hope to define principles that are applicable to other drug resistance phenomena as well (i.e. various forms of bacterial drug resistance).  Worldwide, approximately 2 million people a year die of malaria, and about half that number die of various cancers.  A substantial fraction of these deaths are attributable to tumors or parasites that have become resistant to various drugs due to sub-lethal exposure to these chemicals.  In one well -studied example, chronic exposure to doxorubicin, vinca alkaloids, or  other natural product chemotherapeutic drugs induces overexpression of a fascinating polytopic integral membrane protein, hu MDR 1, many different types of tumor cells (particularly tumors of hematopoietic lineage).  The function of this protein is controversial.  Our laboratory has championed a model wherein over expression of the protein results in abnormal cellular ion transport that then modulates cellular biophysical parameters (e.g. compartmental pH and membrane potentials) that influence cellular accumulation of drugs as well as the signal transduction associated with their toxicity.  Interestingly, recent work suggests a fundamentally similar mechanism may operate in drug resistant malarial parasites.  The important point is that a variety of proteins involved in transmembrane ion transport reactions likely represent a class of pharmacological targets for "second line" therapy in systems that become drug resistant.  Moreover, elucidation of these physiological parameters provides a reliable set of indicators for the emergence of drug resistance in the clinic. 

In studying these phenomena we use a battery of interdisciplinary techniques, including recombinant DNA methods, yeast genetics, cell culture, and general wet biochemistry.  In addition, we have pioneered the se of novel single-cell fluorescence imaging techniques to analyze membrane transport phenomena for individual living cells under constant perfusion.  For example, in one particularly exciting recent advance we have analyzed the pH of the digestive vacuolar compartment of living malarial parasites growing within human red blood cells.   In collaboration with the Tom Wellems laboratory at NIH, we are now uing this technique to investigate the role of specific genetic mutations associated with the emergence of chloroquine resistance.