Chemotherapy of cancer is used in first line management, as an adjunct to surgery/radiotherapy, or in palliative care. 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.
This objective of the project is to generate molecular and structural information on the drug binding domain within P-gp. This will involve investigating the effects of several mutations within the putative drug binding domain on drug transport by P-gp. The experimental system will involve purified and reconstituted P-gp and several functional assays. The effect of mutations will be assessed on overall transport activity, binding of drugs to the protein and how drugs alter energy utilisation by Pgp. 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.
Mittra, R., Pavy, M., Subramanian, N., George, A.M., O'Mara, M.L., Kerr, I.D., Callaghan, R., 2017. Location of contact residues in pharmacologically distinct drug binding sites on P-glycoprotein. Biochem Pharmacol 123, 19-28.
van Wonderen, J.H., McMahon, R.M., O'Mara, M.L., McDevitt, C.A., Thomson, A.J., Kerr, I.D., Macmillan, F., Callaghan, R., 2014. The central cavity of ABCB1 undergoes alternating access during ATP hydrolysis. FEBS J 281, 2190-2201.
Callaghan, R., Luk, F., Bebawy, M., 2014. Inhibition of the multidrug resistance P-glycoprotein: time for a change of strategy? Drug Metab Dispos 42, 623-631.
Callaghan, R., 2015. Providing a molecular mechanism for P-glycoprotein; why would I bother? Biochem Soc Trans 43, 995-1002.
Crowley, E., O'Mara, M.L., Kerr, I.D., Callaghan, R., 2010. Transmembrane helix 12 plays a pivotal role in coupling energy provision and drug binding in ABCB1. FEBS J 277, 3974-3985.
Crowley, E., O'Mara, M.L., Reynolds, C., Tieleman, D.P., Storm, J., Kerr, I.D., Callaghan, R., 2009. Transmembrane helix 12 modulates progression of the ATP catalytic cycle in ABCB1. Biochemistry 48, 6249-6258.