title: Identification of dual DNA-PK MDR1 inhibitors for the potentiation of cytotoxic drug activity.
abstract: Inhibition of DNA repair is an attractive therapeutic approach to enhance the activity of DNA-damaging anticancer chemotherapeutic agents. Similarly, blockade of the multidrug-resistance protein 1 (MDR1) can overcome efflux-mediated resistance. DNA-dependent protein kinase (DNA-PK) is essential for the non-homologous end-joining DNA repair pathway. NU7441 is a potent DNA-PK inhibitor (IC50=14nM) that is used widely to study the effects of DNA-PK inhibition in vitro. In growth inhibition studies, 1μM NU7441 sensitised vincristine-resistant CCRF-CEM VCR/R leukaemia cells (1200-fold resistant) to a range of MDR1 substrates, including doxorubicin (8-fold, p=0.03), vincristine (14-fold, p=0.01) and etoposide (63-fold, p=0.02), compared with 1.4-fold (p=0.02), 2.2-fold (p=0.04) and 3.6-fold (p=0.01) sensitisation, respectively, in parental CCRF-CEM cells. This difference in NU7441 sensitivity was confirmed in another two parental and MDR1-overexpressing cell line pairs. A doxorubicin fluorescence assay showed that in MDR1-overexpressing canine kidney MDCKII-MDR1 cells, 1μM NU7441 increased doxorubicin nuclear fluorescence 16-fold. NU7441 and 3 structurally related compounds (NU7742 (an NU7441 analogue that does not inhibit DNA-PK - IC50>10μM), DRN1 (DNA-PK-inhibitory atropisomeric NU7441 derivative - IC50=2nM) and DRN2 (DNA-PK non-inhibitory atropisomeric NU7441 derivative - IC50=7μM)) all increased intracellular vincristine accumulation in the CCRF-CEM VCR/R cells to a level similar to verapamil, as measured by LC-MS. This paper demonstrates that NU7441 is a dual DNA-PK and MDR1 inhibitor, and this extends the therapeutic potential of the compound when used in combination with MDR substrates.
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Medical School, Newcastle University, Paul O'Gorman Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. Electronic address: e.v.a.mould@ncl.ac.uk.
authors.forename: Emily
authors.initials: E
authors.lastname: Mould
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Medical School, Newcastle University, Paul O'Gorman Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. Electronic address: philip.berry@ncl.ac.uk.
authors.forename: Philip
authors.initials: P
authors.lastname: Berry
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Medical School, Newcastle University, Paul O'Gorman Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. Electronic address: david.jamieson@ncl.ac.uk.
authors.forename: David
authors.initials: D
authors.lastname: Jamieson
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Medical School, Newcastle University, Paul O'Gorman Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. Electronic address: chrishill86@gmail.com.
authors.forename: Christopher
authors.initials: C
authors.lastname: Hill
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, School of Chemistry, Newcastle University, Bedson Building, Newcastle upon Tyne NE1 7RU, UK. Electronic address: celine.cano@ncl.ac.uk.
authors.forename: Celine
authors.initials: C
authors.lastname: Cano
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Medical School, Newcastle University, Paul O'Gorman Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. Electronic address: niujinmy@gmail.com.
authors.forename: Niu
authors.initials: N
authors.lastname: Tan
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Medical School, Newcastle University, Paul O'Gorman Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. Electronic address: sarahelliott80@hotmail.com.
authors.forename: Sarah
authors.initials: S
authors.lastname: Elliott
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Medical School, Newcastle University, Paul O'Gorman Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. Electronic address: barbara.durkacz@ncl.ac.uk.
authors.forename: Barbara
authors.initials: B
authors.lastname: Durkacz
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Medical School, Newcastle University, Paul O'Gorman Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. Electronic address: herbie.newell@ncl.ac.uk.
authors.forename: David
authors.initials: D
authors.lastname: Newell
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Medical School, Newcastle University, Paul O'Gorman Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. Electronic address: elaine.willmore@ncl.ac.uk.
authors.forename: Elaine
authors.initials: E
authors.lastname: Willmore
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002867:Chromones / Q000737:chemistry / Q000494:pharmacology*; D051747:DNA-Activated Protein Kinase / Q000037:antagonists & inhibitors*; D004285:Dogs; D018432:Drug Resistance, Multiple / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D006801:Humans; D015394:Molecular Structure; D009025:Morpholines / Q000737:chemistry / Q000494:pharmacology*; D013379:Substrate Specificity
chemical_list: C499693:8-dibenzothiophen-4-yl-2-morpholin-4-yl-chromen-4-one; C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D002867:Chromones; D009025:Morpholines; D051747:DNA-Activated Protein Kinase
keywords: Cancer; DNA-PK; MDR1; Multidrug resistance; NU7441