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

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Clinical Cancer Research 14, 3984-3992, June 15, 2008. doi:

10.1158/1078-0432.CCR-07-5158

DNA-Dependent Protein Kinase Is a Therapeutic Target and an Indicator of Poor

Prognosis in B-Cell Chronic Lymphocytic Leukemia

Elaine Willmore1, L. Elliott1, Tryfonia Mainou-Fowler2, Geoffrey P.

Summerfield2, Graham H. 2, Fran O'Neill3, Lowe3,

5, 5, R. Pettitt5, Celine Cano-Soumillac1, J.

1, Ian G. Cowell4, Caroline A. Austin4 and Barbara W. Durkacz1

Authors' Affiliations: 1 Northern Institute for Cancer Research, 2 Department of

Hematology, 3 Institute of Human Genetics, and 4 Institute for Cell and

Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom

and 5 Department of Hematology, University of Liverpool, Liverpool, United

Kingdom

Requests for reprints: Elaine Willmore, Northern Institute for Cancer Research,

Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom. Phone:

44-191-246-4447; Fax: 44-191-246-4301; E-mail: Elaine.Willmore@... .

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 H2AX).

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.