Inhibition of O6-alkylguanine-DNA alkyltransferase in animal and human ovarian tumor cell lines by O6-benzylguanine and sensitization to BCNU.

O6-Alkylguanine-DNA alkyltransferase (O6-AGT) activity in rat ovarian tumor lines O-342 and O 342/DDP was 103.4 +/- 18.4 and 240.9 +/- 40.2 fmol/mg protein, respectively; thus, cisplatin (DDP) resistance was paralleled by an increase in O6-AGT activity by a factor of approximately 2.3. The DDP-resistant line expressed a collateral resistance to BCNU. Both lines could be sensitized to BCNU by O6-BG, with sensitization factors of 6.0 and 2.1, respectively. In neither line did depletion of O6-AGT have any sensitizing effect towards DDP. In the human ovarian cancer lines SK-OV-3 and OAW 42, O6-AGT activity was 337.6 +/- 18.2 and 180.0 +/- 39.9 fmol/mg protein, respectively; in these lines depletion of O6-AGT activity by O6-BG treatment resulted in sensitization factors of 3.0 and 4.1, respectively. The increase in sensitivity of ovarian tumor cell lines against a chloroethylating agent by O6-AGT depletion and possible pharmacological advantages of regional (i.p.) administration of this combination might be beneficial in advanced ovarian cancer.