Comparison of the effects of adriamycin and methotrexate on orthotopic and induced heterotopic bone in rats.

The effect of the two antineoplastic drugs, Adriamycin and methotrexate, on orthotopic bone, and on the induction of experimental heterotopic bone in rats was analyzed. The drugs were administered as single injections: Adriamycin in s.c. doses of 0.5 and 2 mg/kg body weight and methotrexate i.v. 100 and 250 mg/kg body weight followed by leucovorin rescue after 2 h. A passing, but significant, decrease in body weights occurred in the methotrexate-treated animals, but not in those given Adriamycin. Analysis of the amount of heterotopic bone formed 4 weeks after induction by demineralized bone matrix revealed a 30-40% decrease in the groups treated with either of the antineoplastic agents, whereas orthotopic bone was unaffected. Six weeks after the treatment the net effect on the induced bone had decreased. The present study shows that the two antineoplastic drugs Adriamycin and methotrexate inhibit heterotopic new bone formation induced by demineralized bone matrix in rats to an equal extent, although their mode of action on the cellular level is entirely different, and that the inhibitory effect of a single treatment diminishes in the presence of a continuous inductive process.