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Vol. 303, Issue 2, 753-759, November 2002
Department of Biochemistry & Molecular Biology, Indiana University
Cancer Center, and Walther Cancer Institute, Indiana University School
of Medicine, Indianapolis, Indiana
A major mechanism by which cancer cells become resistant to
ionizing radiation (IR) and chemotherapy drugs is by enhanced DNA
repair of the lesions; therefore, through inhibition of DNA repair
pathways that tumor cells rely on to escape chemotherapy, we expect to
increase the killing of cancer cells and reduce drug resistance.
DNA-dependent protein kinase (DNA-PK) is a nuclear serine/threonine
protein kinase essential for DNA repair as well as sensing and
transmitting a damage signal to downstream targets leading to cell
cycle arrest. We used a peptide cotherapy strategy to see whether a
targeted inhibition of DNA-PK activity sensitizes breast cancer cells
in response to IR or chemotherapy drug. A synthesized peptide
representing the C terminus of Ku80 (HNI-38) selectively
targeted and disrupted interaction between Ku complex and the catalytic
subunit of DNA-dependent protein kinase (DNA-PKcs) as well as the DNA
binding activity of Ku that led to the inhibition of DNA-PK activity
and reduction in double-stranded DNA break (dsb) repair
activity. Furthermore, a peptide-based inhibitor with target sequence
effectively inhibited the growth of breast cancer cells only in the
presence of DNA damage, suggesting that the target peptide sensitizes
cancer cells through blocking dsb DNA repair activity. Together, this
study not only validates the involvement of the C terminus of Ku80 in
Ku's DNA termini binding and interaction with DNA-PKcs, but also a
supports physiological role for DNA-PK in IR or chemotherapy drug
resistance of cancer cells.
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