sentence: Anti-cancer agents like adriamycin , mitomycin-C , bleomycin , and etoposide express their cell-killing activity partly through oxygen radicals .
paragraph: Overcoming of cross-resistance to the cell-killing activity of oxygen radicals in VCR-resistant hematologic cell lines with cyclosporin-A.  Anti-cancer agents like adriamycin , mitomycin-C , bleomycin , and etoposide express their cell-killing activity partly through oxygen radicals . Since vincristine (VCR)-resistant cells show cross-resistance to oxygen radicals, this study was designed to study whether the combined effects of oxygen radicals derived from hypoxanthine-xanthine oxidase plus enhancers of anti-cancer drugs such as verapamil (Ver), dipyridamole (Dip), and cyclosporin-A (Cy-A) overcome the cross-resistance for oxygen radicals in VCR-resistant human leukemia/lymphoma cell lines. We found that 3 micrograms/mL Cy-A enhances the cidal effect of oxygen radicals on two of five types of wild type and two of five VCR-resistant cell lines and it could overcome the cross-resistance to oxygen radicals in VCR-resistant cells. Neither Ver nor Dip showed any effect on the cidal activity of oxygen radicals. Thus, it was suggested that Cy-A works with different mechanisms from those of Ver or Dip, and Cy-A may be useful in reducing the doses of anti-neoplastic agents that exert their activity via oxygen radicals in the clinical treatment.