Human mismatch repair and G center dot T mismatch binding by hMutS alpha in vitro is inhibited by adriamycin, actinomycin D, and nogalamycin

Loss of the human DNA mismatch repair pathway confers cross-resistance to s tructurally unrelated anticancer drugs. Examples include cisplatin, doxorub icin (adriamycin), and specific alkylating agents. We focused on defining t he molecular events that link adriamycin to mismatch repair-dependent drug resistance because adriamycin, unlike drugs that covalently modify DNA can interact reversibly with DNA. We found that adriamycin, nogalamycin, and ac tinomycin D comprise a class of drugs that reversibly inhibits human mismat ch repair in vitro at low micromolar concentrations. The substrate DNA was not covalently modified by adriamycin treatment in a way that prevents repa ir, and the inhibition was independent of the number of intercalation sites separating the mismatch and the DNA nick used to direct repair, from 10 to 808 base pairs. Over the broad concentration range tested, there was no ev idence for recognition of intercalated adriamycin by MutS alpha as if it we re an insertion mismatch. Inhibition apparently results from the ability of the intercalated drug to prevent mismatch binding, shown using a defined m obility shift assay, which occurs at drug concentrations that inhibit repai r. These data suggest that adriamycin interacts with the mismatch repair pa thway through a mechanism distinct from the manner by which covalent DNA le sions are processed.