PYRROLIZIDINE ALKALOID-INDUCED DNA-PROTEIN CROSS-LINKS

Pyrrolizidine alkaloids (PAs) are potent carcinogenic and anti-mitotic compounds produced by a large number of plant species. In this study, we investigated in vitro the DNA-protein cross-linking activity of se veral structurally diverse PAs, The DNA cross-linked proteins induced by PAs were also isolated and characterized in mammalian cells. At 300 and 500 mu M, the pyrrolic PAs (dehydrosenecionine, dehydromonocrotal ine, dehydroseneciphylline, dehydroriddelliine) induced potent DNA cro ss-links, Protein-associated DNA cross-links accounted for similar to 50% of the total cellular DNA cross-links at 300 mu M. The simple neci ne pyrrole dehydroretronecine induced few DNA-protein cross-links and none were detected with indicine N-oxide, The major proteins cross-lin ked to DNA from either PA-exposed cells or pyrrolic PA-exposed nuclei were in the molecular weight 40-60 kDa range and were primarily acidic in nature (ca, pI 4.2-5.0), The patterns of the proteins cross-linked to DNA were similar to that induced by standard bifunctional alkylati ng agents mitomycin C, cis-dichlorodiammine platinum(II) and nitrogen mustard. The macrocyclic pyrrole dehydrosenecionine induced DNA cross- links in pBR322 plasmid DNA with BSA as a protein target. Our data ind icated that pyrrolic PAs with a macrocyclic diester such as dehydrosen ecionine, dehydroseneciphylline, dehydroriddelliine and dehydromonocro taline were more potent cross-linkers than the simple necine pyrrolic dehydroretronecine. Cross-linking potency of the PAs examined here coi ncides with known potency differences in animal toxicity and led us to conclude that DNA-protein cross-linking activity is probably involved in PA-related diseases.