How does P-glycoprotein confer resistance to so many anti-cancer drugs?



Drug efflux pumps confer resistance to chemotherapy in cancer. The project will examine how the pump P-glycoprotein is capable of interacting with its astonishing array of substrates.

Chemotherapy is used in first line management, as an adjunct to surgery/radiotherapy, or in palliative care setting in cancer. Unfortunately, chemotherapy success is severely limited by the inherent or acquired resistant phenotype. Drug resistance in cancer represents an adaptive response that reduces the efficacy of genotoxic and modern cytostatic anti-cancer drugs. The resistant phenotype is multi-factorial and integrated. One of the major strategies to confer drug resistance is the expression of multi-drug efflux pumps on the surface of cancer cells. The pumps are members of the ATP Binding Cassette (ABC) family and prevent sufficient accumulation of anti-cancer drugs inside cells; thereby obviating their cytotoxic effects. The most prominent member of the triad of multidrug efflux pumps is P-glycoprotein (P-gp), which is able to interact with over 200 known chemicals. Moreover, its unwanted activity in cancer cells cannot yet be inhibited in the clinic.

At a molecular level, there is scant understanding of how P-gp is able to recognise such an astonishing array of drugs. Moreover, the precise pharmacophoric region of anti-cancer drugs remains elusive. One of the major objectives of the Callaghan Laboratory is to generate a molecular understanding of drug recognition by multi-drug efflux pumps such as P-gp. This information will enable medicinal chemistry programs to generate potent inhibitors of P-gp to restore sensitivity of chemotherapy in cancer. Alternately, the information will facilitate the design of novel anti-cancer drugs to evade the “molecular clutches” of P-gp.

The honours student will be involved in an existing project aimed at generating molecular and structural information on the drug binding site (or domain) within P-gp. The student will investigate the effects of several mutations within the putative drug binding domain on drug transport by P-gp. The student will purify and reconstitute mutant isoforms of P-gp into lipid vesicles to enable functional assays. The effect of mutations will be assessed on overall transport activity, the characteristics of binding (i.e. affinity) and the coupling between drug binding and ATP hydrolysis. The combination of activities will enable interpretation of the precise involvement of specific amino-acids on the process of drug transport.

The project will suit students with an interest in cancer drug resistance, membrane transport processes and/or molecular studies with proteins. Training will be provided in membrane protein purification, chromatography and reconstitution. Assay systems will involve fluorescence spectroscopy, colorimetric assays and radioligand binding. Further details may be obtained from Associate Professor Callaghan.

Updated:  27 March 2017/Responsible Officer:  Director RSB/Page Contact:  Webmaster RSB