COMBINATION THERAPY WITH 5-FLUOROURACIL AND IFN-ALPHA-2A INDUCES A NONRANDOM INCREASE IN DNA FRAGMENTS OF LESS-THAN-3 MEGABASES IN HT29-COLON-CARCINOMA CELLS

We have used pulsed-field gel electrophoresis to examine 5-fluorouraci l (5FU)-induced DNA double-strand breaks (DSBs), both with and without modulation by IFN-alpha 2a (IFN alpha), in HT29 human colon adenocarc inoma cells, Although 24-h treatment with either 10 mu M 5FU or 500 un its/ml IFN alpha did not result in significant DNA fragmentation, the combination of 5FU + IFN alpha resulted in a significant increase in D IVA DSBs versus either drug alone (P < 0.05), The pattern of fragmenta tion induced by treatment with 5FU + IFN alpha was compared to that in duced by gamma-radiation, which generates lesions at random sites, dig estion with NotI restriction endonuclease, which cleaves at the specif ic sequence 5'... GCGGCCGC... 3', and HhaI restriction endonuclease, w hich cleaves at the specific sequence 5'... GCGC... 3', 5FU + IFN alph a resulted in a specific pattern characterized by the accumulation of fragments of <3 Mb in the absence of fragments of >3 Mb, which differe d from that of gamma-radiation and restriction endonuclease digestion, Because neither morphological nor DNA fragmentation characteristic of apoptosis was observed after 5FU + IFN alpha treatment, the nonrandom pattern of DSBs that was observed did not appear to be the result of the initiation of programmed cell death within these cells.