DNA repair mechanisms are involved in the hypoxia-dependent toxicity of NLCQ-1 (NSC 709257) and its synergistic interaction with alkylating agents.
BACKGROUND
The hypoxia selective cytotoxin NLCQ-1 significantly potentiates the antitumor effect of several alkylating agents in vitro and in vivo. Synergy in mice requires administration of NLCQ-1 ca. 1 h before the alkylating agent, a fact that may be related to an in vitro hypoxic pretreatment effect. Since NLCQ-1 targets DNA through weak intercalation, the induction of DNA lesions upon reductive metabolism may be a reasonable mechanism that predisposes cells to further damage by a subsequent alkylating agent.


METHODS
To indirectly identify such lesions, cell lines defective in specific DNA repair genes (EM9 and UV41) and their repair-proficient parental AA8, were exposed to NLCQ-1 +/-L-PAM/cisDDP under hypoxic/aerobic conditions and appropriate administration routes, and assessed for clonogenicity. Selected comparisons with tirapazamine (TPZ) were also performed.


RESULTS
EM9 cells, which lack the functional XRCC1 gene involved in base excision repair, and thus are unable to efficiently repair DNA single-strand breaks (ssbs), were 3.7-fold and 4.5-fold more sensitive to NLCQ-1 and TPZ, respectively, than the parental AA8 cells, under hypoxic conditions. UV41 cells, which are defective in repairing DNA interstrand cross-links (ERCC4/XPF), were 4.5-fold more sensitive than AA8 cells to NLCQ-1. In potentiation studies with melphalan or cisplatin, synergy was observed in AA8 cells but not in EM9 or UV41 cells, with either NLCQ-I or TPZ.


CONCLUSIONS
These results suggest that NLCQ-1 is involved in the formation of DNA ssbs and interstrand crosslinks under hypoxic conditions. The synergistic interaction of NLCQ-1 with L-PAM or cisDDP is probably due to an enhancement in the L-PAM/cisDDP-induced DNA interstrand cross-links, possibly as a result of an inhibited repair mechanism of these lesions.
Papadopoulou
Maria V
MV
Department of Radiation Medicine, Evanston Northwestern Healthcare, Evanston, IL 60201, USA. m-papadopoulou@northwestern.edu
Bloomer
William D
WD
D000477:Alkylating Agents / Q000633:toxicity*; D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity; D016466:CHO Cells; D015687:Cell Hypoxia / Q000187:drug effects; D002945:Cisplatin / Q000633:toxicity; D006224:Cricetinae; D003412:Cricetulus; D004260:DNA Repair / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000172:deficiency; D004357:Drug Synergism; D007093:Imidazoles / Q000633:toxicity*; D011804:Quinolines / Q000633:toxicity*; D000077704:Tirapazamine; D014227:Triazines / Q000633:toxicity; D000076105:X-ray Repair Cross Complementing Protein 1
C434187:4-(3-(2-nitro-1-imidazolyl)-propylamino)-7-chloroquinoline hydrochloride; D000477:Alkylating Agents; D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D007093:Imidazoles; D011804:Quinolines; D014227:Triazines; D000076105:X-ray Repair Cross Complementing Protein 1; C000619352:Xrcc1 protein, mouse; D000077704:Tirapazamine; D002945:Cisplatin