DNA-Dependent Protein Kinase Is a Therapeutic Target and an Indicator of Poor Prognosis in B-Cell Chronic Lymphocytic Leukemia

Abstract

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 (DNAPKcs) 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 NU7441on fludarabine-induced DNA damage repair were also assessed (Comet assays and detection of gH2AX). 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 Ser 2056. 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.

NK314 potentiates antitumor activity with adult T-cell leukemia-lymphoma cells by inhibition of dual targets on topoisomerase IIα and DNA-dependent protein kinase

“…48,49 Considering these results, impairment of DNA-PK mediated DNA DSB repair could be associated with genetic instability and cell transformation in the Tax-dependent early stage of ATL, whereas overexpression of DNA-PK or elevated DNA-PK activity could be associated with multidrugresistant phenotypes in overt ATL, as reported in other types of cancers. [42][43][44][45][46][47] In our experiments, it was difficult to analyze the association of Tax expression and effect of NK314 or DNA-PK inhibitor on cell growth inhibition in ATL cells because only one cell line (MT-2) expressed a detectable amount of Tax protein (data not shown). Genetic instability is usually correlated with cell proliferation capacity, and many cancer cell types have a tendency to be genetically unstable.…”

“…[27][28][29] Various agents for inhibiting DNA-PK have been identified and clinical trials have been conducted using both subclinical and clinical approaches. [42][43][44][45][46][47] As for ATL cells, it was reported that transcription factor Tax binds to DNA-PKcs and activates DNA-PK. However, the Tax-DNA-PK complex was incapable of repairing new DNA DSBs induced by genotoxic stimuli in ATL cells.…”

Harnessing the complexity of DNA-damage response pathways to improve cancer treatment outcomes

“…Responses to the combination of DNA-PK inhibitors with DNA-damaging agents include reduced clonogenic survival and cellular proliferation, increased DSBs, G2 arrest and subtle increases in the sub-G1 population (indicative of apoptosis) (Willmore et al, 2004(Willmore et al, , 2008Shinohara et al, 2005), regardless of p53 status (Ismail et al, 2004;Zhao et al, 2006). Recently, Shang et al…”

Inhibition de la réparation des cassures double-brin de l'ADN: quel intérêt en radiothérapie et pharmacologie antitumorale?

“…Les criblages sont réalisés in vitro sur la base de l'activité de phosphorylation du complexe car le manque de résolution des structures ne permet pas une approche in silico. Les molécules sélectionnées montrent une efficacité sur des cellules leucé-miques (LLC) traitées par le chlorambucile (Veuger et al 2003 ;Willmore et al 2008) ou la mithoxantrone (Elliott et al 2011). De plus, ces inhibiteurs conduisent à une action synergique avec l'irinotécan, un inhibiteur de la topoisomérase I dans le traitement in vitro de cellules tumorales coliques (Davidson et al 2011).…”