Further characterisation of the cellular activity of the DNA-PK inhibitor, NU7441, reveals potential cross-talk with homologous recombination
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Inhibition of DNA repair is emerging as a new therapeutic strategy for cancer treatment. One promising target is DNA-PK, a pivotal kinase in double-strand break repair. The purpose of this study was to further characterise the activity of the DNA-PK inhibitor NU7441, giving some new insights into the biology of DNA-PK.
We used NU7441, a potent DNA-PK inhibitor, to evaluate potential pharmacodynamic markers of DNA-PK inhibition, inhibition of DNA repair and chemo- and radio-potentiation in isogenic human cancer cells proficient (M059-Fus1) and deficient (M059 J) in DNA-PK.
NU7441 strongly inhibited DNA-PK in cell lines (IC50 = 0.3 μM) but only weakly inhibited PI3 K (IC50 = 7 μM). The only available anti-phospho-DNA-PK antibody also recognised some phosphoprotein targets of ATM. NU7441 caused doxorubicin- and IR-induced DNA DSBs (measured by γ-H2AX foci) to persist and also slightly decreased homologous recombination activity, as assessed by Rad51 foci. Chemo- and radio-potentiation were induced by NU7441 in M059-Fus-1, but not in DNA-PK-deficient M059 J cells. DNA-PK was highly expressed in a chronic lymphocytic leukaemia sample but undetectable in resting normal human lymphocytes, although it could be induced by PHA-P treatment. In K652 cells, DNA-PK expression was not related to cell cycle phase.
These data confirm NU7441 not only as a potent chemo- and radio-sensitiser clinical candidate but also as a powerful tool to study the biology of DNA-PK.
KeywordsDNA-PK NU7441 Chemo- and radio-potentiation γ-H2AX Rad51 HR
We gratefully acknowledge the financial support of CR UK (NJC, CC and DRN) and AstraZeneca (MT and JMM), Newcastle Cancer Centre-Medicinal Chemistry, Newcastle University, for providing NU7441 and ZSTK474 and Dr GCM Smith, AstraZeneca for providing KU55933.
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