NU7441 (KU-57788)

NU7441 is a selective inhibitor of DNA-dependent protein kinase (DNA-PK) with IC50 value of 13 nM [1].

NU7441 is an ATP-competitive inhibitor of DNA-PK and showed a Ki value of 0.65 nM. The inhibition of DNA-PK was selective. NU7441 showed no inhibition effect on the DNA-PK-related enzymes ATM and ATR at concentration of 100 μM. For mTOR and PI3K, NU7441 exerted inhibition activities with IC50 values of 1.7 and 5 μM, respectively, which were about 100-fold higher than the IC50 value of DNA-PK. In HeLa cells, treatment of NU7441 at concentration of 100 nM significantly enhanced the sensitivity of cells to etoposide and promoted cells to death. In mice bearing SW620 xenografts, coadministration of NU7441 and etoposide caused a tumor growth delay of 5.4 days which was twice longer than that caused by etoposide alone [1, 2].

References:
[1] Hardcastle I R, Cockcroft X, Curtin N J, et al. Discovery of potent chromen-4-one inhibitors of the DNA-dependent protein kinase (DNA-PK) using a small-molecule library approach. Journal of medicinal chemistry, 2005, 48(24): 7829-7846.
[2] Zhao Y, Thomas H D, Batey M A, et al. Preclinical evaluation of a potent novel DNA-dependent protein kinase inhibitor NU7441. Cancer research, 2006, 66(10): 5354-5362.

Pharmacological inhibition of DNA-PK stimulates Cas9-mediated genome editing.[Pubmed:26307031]

Genome Med. 2015 Aug 27;7:93.

BACKGROUND: The ability to modify the genome of any cell at a precise location has drastically improved with the recent discovery and implementation of CRISPR/Cas9 editing technology. However, the capacity to introduce specific directed changes at given loci is hampered by the fact that the major cellular repair pathway that occurs following Cas9-mediated DNA cleavage is the erroneous non-homologous end joining (NHEJ) pathway. Homology-directed recombination (HDR) is far less efficient than NHEJ and makes screening of clones containing directed changes time-consuming and labor-intensive. METHODS: We investigated the possibility of pharmacologically inhibiting DNA-PKcs, a key player in NHEJ, using small molecule inhibitors (NU7441 and KU-0060648), to ameliorate the rates of HDR repair events. These compounds were tested in a sensitive reporter assay capable of simultaneously informing on NHEJ and HDR, as well as on an endogenous gene targeted by Cas9. RESULTS: We find that NU7441 and KU-0060648 reduce the frequency of NHEJ while increasing the rate of HDR following Cas9-mediated DNA cleavage. CONCLUSIONS: Our results identify two small molecules compatible for use with Cas9-editing technology to improve the frequency of HDR.

DNA-dependent protein kinase is a therapeutic target and an indicator of poor prognosis in B-cell chronic lymphocytic leukemia.[Pubmed:18559621]

Clin Cancer Res. 2008 Jun 15;14(12):3984-92.

PURPOSE: del(17p), del(11q), and associated p53 dysfunction predict for short survival and chemoresistance in B-cell chronic lymphocytic leukemia (CLL). DNA-dependent protein kinase (DNA-PK) is activated by DNA damage and mediates DNA double-strand break repair. We hypothesized that inhibiting DNA-PK would sensitize CLL cells to drug-induced DNA damage and that this approach could increase the therapeutic index of agents used to treat CLL. EXPERIMENTAL DESIGN: Fifty-four CLL cases were characterized for poor prognosis markers [del(17p), del(11q), CD38, and ZAP-70]. In selected cases, DNA-PK catalytic subunit (DNA-PKcs) expression and activity and p53 function were also measured. Ex vivo viability assays established sensitivity to fludarabine and chlorambucil and also tested the ability of a novel DNA-PK inhibitor (NU7441) to sensitize CLL cells to these drugs. The effects of NU7441 on fludarabine-induced DNA damage repair were also assessed (Comet assays and detection of gammaH2AX). RESULTS: DNA-PKcs levels correlated with DNA-PK activity and varied 50-fold between cases but were consistently higher in del(17p) (P = 0.01) and del(11q) cases. NU7441 sensitized CLL cells to chlorambucil and fludarabine, including cases with del(17p), del(11q), p53 dysfunction, or high levels of DNA-PKcs. NU7441 increased fludarabine-induced double-strand breaks and abrogated drug-induced autophosphorylation of DNA-PKcs at Ser2056. High DNA-PK levels predicted for reduced treatment-free interval. CONCLUSIONS: These data validate the concept of targeting DNA-PKcs in poor risk CLL, and demonstrate a mechanistic rationale for use of a DNA-PK inhibitor. The novel observation that DNA-PKcs is overexpressed in del(17p) and del(11q) cases indicates that DNA-PK may contribute to disease progression in CLL.

Preclinical evaluation of a potent novel DNA-dependent protein kinase inhibitor NU7441.[Pubmed:16707462]

Cancer Res. 2006 May 15;66(10):5354-62.

DNA double-strand breaks (DSB) are the most cytotoxic lesions induced by ionizing radiation and topoisomerase II poisons, such as etoposide and doxorubicin. A major pathway for the repair of DSB is nonhomologous end joining, which requires DNA-dependent protein kinase (DNA-PK) activity. We investigated the therapeutic use of a potent, specific DNA-PK inhibitor (NU7441) in models of human cancer. We measured chemosensitization by NU7441 of topoisomerase II poisons and radiosensitization in cells deficient and proficient in DNA-PK(CS) (V3 and V3-YAC) and p53 wild type (LoVo) and p53 mutant (SW620) human colon cancer cell lines by clonogenic survival assay. Effects of NU7441 on DSB repair and cell cycle arrest were measured by gammaH2AX foci and flow cytometry. Tissue distribution of NU7441 and potentiation of etoposide activity were determined in mice bearing SW620 tumors. NU7441 increased the cytotoxicity of ionizing radiation and etoposide in SW620, LoVo, and V3-YAC cells but not in V3 cells, confirming that potentiation was due to DNA-PK inhibition. NU7441 substantially retarded the repair of ionizing radiation-induced and etoposide-induced DSB. NU7441 appreciably increased G(2)-M accumulation induced by ionizing radiation, etoposide, and doxorubicin in both SW620 and LoVo cells. In mice bearing SW620 xenografts, NU7441 concentrations in the tumor necessary for chemopotentiation in vitro were maintained for at least 4 hours at nontoxic doses. NU7441 increased etoposide-induced tumor growth delay 2-fold without exacerbating etoposide toxicity to unacceptable levels. In conclusion, NU7441 shows sufficient proof of principle through in vitro and in vivo chemosensitization and radiosensitization to justify further development of DNA-PK inhibitors for clinical use.

Identification of a highly potent and selective DNA-dependent protein kinase (DNA-PK) inhibitor (NU7441) by screening of chromenone libraries.[Pubmed:15546735]

Bioorg Med Chem Lett. 2004 Dec 20;14(24):6083-7.

A solution-phase multiple-parallel synthesis approach was employed for the preparation of 6-, 7- and 8-aryl-substituted chromenone libraries, which were screened as inhibitors of the DNA repair enzyme DNA-dependent protein kinase (DNA-PK). These studies resulted in the identification of 8-dibenzothiophen-4-yl-2-morpholin-4-yl-chromen-4-one (NU7441) as a highly potent and selective DNA-PK inhibitor (IC50=14 nM), exhibiting ATP-competitive inhibition kinetics.

KU-57788 is a potent and selective inhibitor of DNA-PK with an IC50 of 13 nM, with selectivity over a range of kinases including mTOR, PI 3-K, ATM and ATR.

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