Potentiation of chlorambucil cytotoxicity in B-cell chronic lymphocytic leukemia by inhibition of DNA-dependent protein kinase activity using wortmannin.
In this study, we examined the ability of wortmannin to modulate chlorambucil (CLB) cytotoxicity in lymphocyte samples from patients with B-cell chronic lymphocytic leukemia (B-CLL). It has been suggested previously that enhanced cross-link repair is a primary mechanism of resistance to nitrogen mustards (NMs) in B-CLL. DNA-dependent protein kinase (DNA-PK) is involved in the repair of double-strand breaks and in rejoining steps in recombination mechanisms. Mutants defective in this process are hypersensitive to alkylating agents. We have recently demonstrated that the activity of DNA-PK is a determinant in the cellular response of B-CLL to CLB. The DNA-PK gene has homology to the P110 phosphatidylinositol 3-kinase (PI 3-K). Wortmannin, an inhibitor of P110 PI 3-K, also inhibits DNA-PK activity in vitro. We investigated the effect of wortmannin on DNA-PK activity and CLB toxicity in the lymphocytes from 11 patients with B-CLL. Our results demonstrate that DNA-PK activity is decreased after exposure to wortmannin in a dose-dependent manner. Wortmannin, at nontoxic concentrations, synergistically sensitized B-CLL lymphocytes to the effects of CLB. Moreover, we observed a significant correlation when we compared the fold decrease in DNA-PK activity and the synergistic value (I), obtained when wortmannin was used at 0.1 microM. In the resistant B-CLL lymphocyte samples, there was a highly significant correlation between the ability of wortmannin at 0.1 and 0.25 microM to decrease the level of DNA-PK activity and to increase CLB sensitivity. In a model of primary human tumor cells, our findings suggest that the inhibition of DNA-PK activity may be a powerful way to overcome resistance to NMs such as CLB and point to new possibilities to improve the effectiveness of NM therapy.
Christodoulopoulos
G
G
Lady Davis Institute for Medical Research, The Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada. gchris1@po-box.mcgill.ca
Muller
C
C
Salles
B
B
Kazmi
R
R
Panasci
L
L
D000730:Androstadienes / Q000494:pharmacology*; D018906:Antineoplastic Agents, Alkylating / Q000633:toxicity*; D002470:Cell Survival / Q000187:drug effects; D002699:Chlorambucil / Q000633:toxicity*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000201:enzymology; D000077191:Wortmannin
D000730:Androstadienes; D018906:Antineoplastic Agents, Alkylating; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D002699:Chlorambucil; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D000077191:Wortmannin