Richard A J Darby1,2, Amanda Unsworth1, Stefan Knapp2, Ian D Kerr3, Richard Callaghan4,5. 1. Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, University of Oxford, Headington, UK. 2. Structural Genomics Consortium and Target Discovery Institute, University of Oxford, Old Road Campus, NDM Research Building, Oxford, OX3 7FZ, UK. 3. School of Life Sciences, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, UK. 4. Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, University of Oxford, Headington, UK. richard.callaghan@anu.edu.au. 5. Division of Biomedical Science and Biochemistry, Research School of Biology, The Australian National University, Canberra, ACT, 0200, Australia. richard.callaghan@anu.edu.au.
Abstract
PURPOSE: Multidrug efflux pumps such as ABCG2 confer drug resistance to a number of cancer types, leading to poor prognosis and outcome. To date, the strategy of directly inhibiting multidrug efflux pumps in order to overcome drug resistance in cancer has been unsuccessful. An alternative strategy is to target proteins involved in the regulation of multidrug efflux pump activity or expression. Pim1 kinase has been demonstrated to phosphorylate ABCG2, promote its oligomerisation and contribute to its ability to confer drug resistance. METHODS: In the present manuscript, imidazo-pyridazine-based inhibitors of Pim1 were examined for their ability to overcome ABCG2-mediated drug resistance. Drug efficacy was measured as a cytotoxic response or an effect on transport by ABCG2. Protein expression patterns were assessed using western immuno-blotting. RESULTS: The two Pim1 inhibitors increased the potency of flavopiridol, mitoxantrone, topotecan and doxorubicin, specifically in ABCG2-expressing cells. This effect was associated with an increase in the cellular accumulation of [(3)H]-mitoxantrone, suggesting direct impairment of the transporter. However, prolonged pre-incubation with the studied inhibitors greatly enhanced the effect on mitoxantrone accumulation. The inhibitors caused a significant time-dependent reduction in the expression of ABCG2 in the resistant cells, an effect that would improve drug efficacy. CONCLUSION: Consequently, it appears that the Pim1 inhibitors display a dual-mode effect on ABCG2-expressing cancer cells. This may provide a powerful new strategy in overcoming drug resistance by targeting proteins that regulate expression of efflux pumps.
PURPOSE: Multidrug efflux pumps such as ABCG2 confer drug resistance to a number of cancer types, leading to poor prognosis and outcome. To date, the strategy of directly inhibiting multidrug efflux pumps in order to overcome drug resistance in cancer has been unsuccessful. An alternative strategy is to target proteins involved in the regulation of multidrug efflux pump activity or expression. Pim1 kinase has been demonstrated to phosphorylate ABCG2, promote its oligomerisation and contribute to its ability to confer drug resistance. METHODS: In the present manuscript, imidazo-pyridazine-based inhibitors of Pim1 were examined for their ability to overcome ABCG2-mediated drug resistance. Drug efficacy was measured as a cytotoxic response or an effect on transport by ABCG2. Protein expression patterns were assessed using western immuno-blotting. RESULTS: The two Pim1 inhibitors increased the potency of flavopiridol, mitoxantrone, topotecan and doxorubicin, specifically in ABCG2-expressing cells. This effect was associated with an increase in the cellular accumulation of [(3)H]-mitoxantrone, suggesting direct impairment of the transporter. However, prolonged pre-incubation with the studied inhibitors greatly enhanced the effect on mitoxantrone accumulation. The inhibitors caused a significant time-dependent reduction in the expression of ABCG2 in the resistant cells, an effect that would improve drug efficacy. CONCLUSION: Consequently, it appears that the Pim1 inhibitors display a dual-mode effect on ABCG2-expressing cancer cells. This may provide a powerful new strategy in overcoming drug resistance by targeting proteins that regulate expression of efflux pumps.
Entities:
Keywords:
ABCG2; BCRP; Cancer chemotherapy; Multidrug resistance; Pim1 kinase
Authors: Amanda J Unsworth; Alexander P Bye; Tanya Sage; Renato S Gaspar; Nathan Eaton; Caleb Drew; Alexander Stainer; Neline Kriek; Peter J Volberding; James L Hutchinson; Ryan Riley; Sarah Jones; Stuart J Mundell; Weiguo Cui; Hervé Falet; Jonathan M Gibbins Journal: Haematologica Date: 2021-07-01 Impact factor: 9.941