CHARACTERIZATION OF ILLUDIN-S SENSITIVITY IN DNA REPAIR-DEFICIENT CHINESE-HAMSTER CELLS - UNUSUALLY HIGH-SENSITIVITY OF ERCC2 AND ERCC3 DNAHELICASE-DEFICIENT MUTANTS IN COMPARISON TO OTHER CHEMOTHERAPEUTIC-AGENTS

Illudins, novel natural products with a structure unrelated to any oth er known chemical, display potent in vitro and in vivo anti-cancer act ivity against even multi-drug resistant tumors, and are metabolically activated to an unstable intermediate that binds to DNA. The DNA damag e produced by illudins, however, appears to differ from that of other known DNA damaging toxins. The sensitivity pattern of the various UV-s ensitive cell lines differs from previously studied DNA cross-linking agents. Normally, the ERCC1- (excision repair cross complementing) and ERCC4-deficient cell lines are most sensitive to DMA cross-linking ag ents, with ERCC2-, ERCC3- and ERCC5-deficient cell lines having minima l sensitivity. With illudins the pattern is reversed, with ERCC2 and E RCC3 being the most sensitive. The sensitivity to illudins in compleme ntation groups 1 through 3 is due to a deficiency of the ERCC1-3 gene products, as cellular drug accumulation studies revealed no difference s in transport capacity or total drug accumulation. Also, a transgenic cell line in which ERCC2 activity was expressed through an expression vector regained its relative resistance to the illudins. The EM9 cell line, which displays sensitivity to monoadduct producing chemicals, w as not sensitive. Thus, excision repair is involved in repair of illud in-induced damage and, unlike other anti-cancer agents, the involvemen t of ERCC2 and ERCC3 helicases is critical for repair to occur. The re quirement for ERCC2, and ERCC3, combined with the finding that ERCC1 b ut not ERCC2, is upregulated in drug-resistant tumors, may explain the efficacy of illudins against drug-resistant tumors. The inhibition of DNA synthesis in cells within minutes after exposure to illudins at n anomolar concentrations may be related to the finding that the ERCC3 g ene product is actually the p89 helicase component of the BTF2 (TFII) basic transcription factor and the high sensitivity of ERCC3-deficient cells to illudins.