Unique pattern of ET-743 activity in different cellular systems with defined deficiencies in DNA-repair pathways

The cytotoxic activity of ecteinascidin 743 (ET-743), a natural product der ived from the marine tunicate Ecteinascidia turbinata that exhibits potent anti-tumor activity in pre-clinical systems and promising activity in phase I and II clinical trials, was investigated in a number of cell systems wit h well-defined deficiencies in DNA-repair mechanisms. ET-743 binds to N2 of guanine in the minor groove, but its activity does not appear to be relate d to DNA-topoisomerase I poisoning as the drug is equally active in wild-ty pe yeast and in yeast with a deletion in the DNA-topoisomerase I gene. Defe cts in the mismatch repair pathway, usually associated with increased resis tance to methylating agents and cisplatin, did not affect the cytotoxic act ivity of ET-743. However, ET-743 did show decreased activity (from 2- to 8- fold) in nucleotide excision repair (NER)-deficient cell lines compared to NER-proficient cell lines, from either hamsters or humans. Restoration of N ER function sensitized cells to ET-743 treatment. The DNA double-strand-bre ak repair pathway was also investigated using human glioblastoma cell lines MO59K and M059J, respectively, proficient and deficient in DNA-dependent p rotein kinase (DNA-PK). ET-743 was more effective in cells lacking DNA-PK; moreover, pre-treatment of HCT-116 colon carcinoma cells with wortmannin, a potent inhibitor of DNA-PK, sensitized cells to ET-743. An increase in ET- 743 sensitivity was also observed in ataxia telangiectasia-mutated cells. O ur data strongly suggest that ET-743 has a unique mechanism of interaction with DNA, (C) 2001 Wiley-Liss, Inc.