Overcoming ABCG2-mediated drug resistance with imidazo-[1,2-b]-pyridazine-based Pim1 kinase inhibitors.
OBJECTIVE
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.


CONCLUSIONS
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.
Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, University of Oxford, Headington, UK.|Structural Genomics Consortium and Target Discovery Institute, University of Oxford, Old Road Campus, NDM Research Building, Oxford, OX3 7FZ, UK.
Richard A J
RA
Darby
Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, University of Oxford, Headington, UK.
Amanda
A
Unsworth
Structural Genomics Consortium and Target Discovery Institute, University of Oxford, Old Road Campus, NDM Research Building, Oxford, OX3 7FZ, UK.
Stefan
S
Knapp
School of Life Sciences, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, UK.
Ian D
ID
Kerr
Nuffield Department of Clinical Laboratory Sciences, John Radcliffe Hospital, University of Oxford, Headington, UK. richard.callaghan@anu.edu.au.|Division of Biomedical Science and Biochemistry, Research School of Biology, The Australian National University, Canberra, ACT, 0200, Australia. richard.callaghan@anu.edu.au.
Richard
R
Callaghan
D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D015507:Drugs, Investigational / Q000494:pharmacology*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D007700:Kinetics; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D021381:Protein Transport / Q000187:drug effects; D051573:Proto-Oncogene Proteins c-pim-1 / Q000037:antagonists & inhibitors*; D011724:Pyridazines / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D015507:Drugs, Investigational; D007093:Imidazoles; C000603513:K00135; C000603514:K00486; D009363:Neoplasm Proteins; D047428:Protein Kinase Inhibitors; D011724:Pyridazines; D011994:Recombinant Proteins; C496634:PIM1 protein, human; D051573:Proto-Oncogene Proteins c-pim-1
ABCG2; BCRP; Cancer chemotherapy; Multidrug resistance; Pim1 kinase