DNA-dependent protein kinase is a therapeutic target and an indicator of poor prognosis in B-cell chronic lymphocytic leukemia.
OBJECTIVE
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.


METHODS
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.
Northern Institute for Cancer Research, Newcastle University, Newcastle upon Tyne, United Kingdom. Elaine.Willmore@ncl.ac.uk
Elaine
E
Willmore
Sarah L
SL
Elliott
Tryfonia
T
Mainou-Fowler
Geoffrey P
GP
Summerfield
Graham H
GH
Jackson
Fran
F
O'Neill
Christopher
C
Lowe
Anthony
A
Carter
Robert
R
Harris
Andrew R
AR
Pettitt
Celine
C
Cano-Soumillac
Roger J
RJ
Griffin
Ian G
IG
Cowell
Caroline A
CA
Austin
Barbara W
BW
Durkacz
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D002867:Chromones / Q000627:therapeutic use*; D051747:DNA-Activated Protein Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000502:physiology*; D016503:Drug Delivery Systems; D004353:Drug Evaluation, Preclinical; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D005260:Female; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000175:diagnosis* / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D009025:Morpholines / Q000627:therapeutic use*; D011379:Prognosis; D014407:Tumor Cells, Cultured
C499693:8-dibenzothiophen-4-yl-2-morpholin-4-yl-chromen-4-one; D014408:Biomarkers, Tumor; D002867:Chromones; D009025:Morpholines; D051747:DNA-Activated Protein Kinase