Batracylin reached Stage 3 of the NCI pipeline, but was dropped in 1989 because of concern about the interspecies differences in toxicity and potential for variable oral absorption. It was subsequently shown that the interspecies variation in toxicity was consistent with the pattern of metabolism of the compound by N-acetyltransferase (NAT2) to the highly toxic acetylated form, N-acetyl-batracylin. COMPARE analysis suggested a similarity to topo II inhibitors and the compound was found to be a topo II inhibitor, but the inhibition is not dependent on ATP, which indicates a favorable approach for treating hypoxic tumors. The compound is also not a substrate for P-glycoprotein, thus eliminating this mechanism for resistance. With currently available testing to exclude patients based on pretreatment genotyping for the fast-metabolizing NAT2 allele, an orally dosed Phase I clinical trial is proposed.