A comparative study on the genetic effects of hycanthone and oxamniquine

Oxamniquine (UK-4271; 6-hydroxymethyl-2-isopropylaminomethyl-7-nitro-1,2,3,4-tetrahydroquinoline) is a new schistosomicidal agent currently undergoing clinical investigation in South America. Essentially a complete cure rate against Brazilian Schistosoma mansoni has been seen in adults with a single im dose of 7.5 mg/kg or a single oral dose of 15 mg/kg. These regimens were tolerated without significant toxicity. To assess its mutagenic potential, oxamniquine was examined in a battery of genetic tests designed to detect mutations at the gene and chromosome levels. For comparative purposes, hycanthone, a schistosomicide with extensively studied mutagenic properties, was evaluated in a similar series of tests. Point mutations were measured in a series of histidineless auxotrophs of Salmonella typhimurium in direct plate and host-mediated assays. Gross chromosomal aberrations were assessed in human leucocyte cultures and in bone marrow preparations from drug-treated mice. Effects on germ cells were tested in the dominant-lethal assay. Hycanthone showed significant mutagenic activity in the direct bacterial tests and the in vivo and in vitro cytogenetic assays. No response was detected in the host-mediated or dominant-lethal assays. On the other hand, oxamniquine produced no drug-related mutagenic effects in the cytogenetic, host-mediated, or dominant-lethal tests at doses up to 150 mg/kg administered parenterally. Oxamniquine produced a weak response in the frameshift mutant, TA1538, of Salmonella typhimurium in direct plate tests with and without liver microsomal enzymes. However, this response was achieved only by using a concentration of compound which was several orders of magnitude higher than that required to produce a similar response to hycanthone.