Related Experiment Videos
Altered drug translocation mediated by the MDR protein: direct, indirect, or both?
P D Roepe1, L Y Wei, M M Hoffman
1Molecular Pharmacology and Therapeutics Program, Raymond & Beverly Sackler Foundation Laboratory, Memorial Sloan Kettering Cancer Center, New York, New York, USA.
Abstract:
Overexpression of the MDR protein, or p-glycoprotein (p-GP), in cells leads to decreased initial rates of accumulation and altered intracellular retention of chemotherapeutic drugs and a variety of other compounds. Thus, increased expression of the protein is related to increased drug resistance. Since several homologues of the MDR protein (CRP, ItpGPA, PDR5, sapABCDF) are also involved in conferring drug resistance phenomena in microorganisms, elucidating the function of the MDR protein at a molecular level will have important general applications. Although MDR protein function has been studied for nearly 20 years, interpretation of most data is complicated by the drug-selection conditions used to create model MDR cell lines. Precisely what level of resistance to particular drugs is conferred by a given amount of MDR protein, as well as a variety of other critical issues, are not yet resolved. Data from a number of laboratories has been gathered in support of at least four different models for the MDR protein. One model is that the protein uses the energy released from ATP hydrolysis to directly translocate drugs out of cells in some fashion. Another is that MDR protein overexpression perturbs electrical membrane potential (delta psi) and/or intracellular pH (pHi) and thereby indirectly alters translocation and intracellular retention of hydrophobic drugs that are cationic, weakly basic, and/or that react with intracellular targets in a pHi or delta psi-dependent manner. A third model proposes that the protein alternates between drug pump and Cl- channel (or channel regulator) conformations, implying that both direct and indirect mechanisms of altered drug translocation may be catalyzed by MDR protein. A fourth is that the protein acts as an ATP channel. Our recent work has tested predictions of these models via kinetic analysis of drug transport and single-cell photometry analysis of pHi, delta psi, and volume regulation in novel MDR and CFTR transfectants that have not been exposed to chemotherapeutic drugs prior to analysis. This paper reviews these data and previous work from other laboratories, as well as relevant transport physiology concepts, and summarizes how they either support or contradict the different models for MDR protein function.
Insights
Multidrug resistance (MDR) protein, or p-glycoprotein (p-GP), overexpression increases drug resistance. This study investigates MDR protein function models using novel transfectants, analyzing drug transport and cellular parameters.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Overexpression of the multidrug resistance (MDR) protein, also known as p-glycoprotein (p-GP), is linked to decreased drug accumulation and increased cellular drug resistance.
- Homologues of MDR proteins are implicated in drug resistance across various microorganisms, highlighting the broad significance of understanding MDR protein function.
- Previous research interpretations are often complicated by drug-selection methods used to generate MDR cell lines, leaving critical aspects of MDR protein function unresolved.
Purpose of the Study:
- To critically evaluate existing models of MDR protein function.
- To test predictions of these models using kinetic analysis of drug transport and cellular parameter measurements.
- To provide a comprehensive review of data supporting or refuting different MDR protein function models.
Main Methods:
- Kinetic analysis of drug transport in novel MDR and CFTR transfectants.
- Single-cell photometry to analyze intracellular pH (pHi) and electrical membrane potential (delta psi).
- Assessment of volume regulation in transfectants not previously exposed to chemotherapeutic drugs.
Main Results:
- Data from novel transfectants were analyzed to test predictions of four proposed MDR protein function models.
- The study reviewed existing data from multiple laboratories alongside new findings.
- Transport physiology concepts were integrated to interpret results in the context of MDR protein function.
Conclusions:
- The findings contribute to resolving ambiguities surrounding MDR protein function, particularly concerning its role in drug resistance.
- Understanding MDR protein mechanisms has implications for microbial drug resistance and potentially other cellular transport processes.
- The study provides a framework for future research into the precise molecular mechanisms of MDR protein action.