Enhancement of radiation-induced DNA double-strand breaks and micronuclei in human colon carcinoma cells by N-methylformamide.
The differentiation-inducing agent N-methylformamide (NMF) enhances the sensitivity of some cell lines to ionizing radiation. To elucidate the mechanism of NMF-mediated radiosensitization, we examined the effects of this agent on gamma-ray-induced DNA double-strand breaks and micronuclei in two cell lines, clone A (human colon carcinoma) and HCA-1 (murine hepatocarcinoma). Both cell lines form a better differentiated phenotype upon exposure to NMF, yet only clone A is radiosensitized. The neutral (pH 9.6) elution assay was used to evaluate the effects of this maturational agent on radiation-induced double-strand breaks in these cell lines. Exposure of HCA-1 cells to NMF had no effect on the level of DNA double-strand breaks induced by gamma rays. In clone A cells, however, exposure to NMF enhanced the initial formation of gamma-ray-induced double-strand breaks at each dose tested. The repair of double-strand breaks in both cell lines was not influenced by NMF. As a measure of chromosome fragmentation after irradiation, we evaluated micronuclei using the cytokinesis block method. Exposure to NMF had no effect on radiation-induced micronuclei formation in HCA-1 cells yet significantly enhanced the frequency of micronuclei induced by radiation in clone A cells. In clone A cells, the increases in radiation-induced double-strand breaks and micronuclei as a function of NMF exposure time reached maximums by approximately 72 h. These data suggest that NMF-mediated radiosensitization is the result of an increase in the initial level of radiation-induced DNA double-strand breaks.
Department of Experimental Radiotherapy, University of Texas M.D. Anderson Cancer Center, Houston 77030.
P J
PJ
Tofilon
C M
CM
Vines
C A
CA
Bill
D000230:Adenocarcinoma / Q000235:genetics / Q000473:pathology*; D000818:Animals; D003110:Colonic Neoplasms / Q000235:genetics / Q000473:pathology*; D004247:DNA / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000187:drug effects / Q000528:radiation effects*; D005559:Formamides / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008114:Liver Neoplasms, Experimental / Q000235:genetics / Q000473:pathology; D051379:Mice; D015162:Micronucleus Tests; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000528:radiation effects
D004273:DNA, Neoplasm; D005559:Formamides; D011838:Radiation-Sensitizing Agents; D004247:DNA; C002950:methylformamide