Reduction of chronic doxorubicin cardiotoxicity in beagle dogs by bis-morpholinomethyl derivative of razoxane (ICRF-159).

Addition of morpholinomethyl substituents to razoxane (ICRF-159) produced a compound (bis-4-morpholinomethyl-3,5-dioxopiperazinyl-1,2-propane (MM-159) considerably more water-soluble than razoxane. The increased solubility allowed MM-159 to be examined for protective activity against chronic doxorubicin (DXR) cardiotoxicity. Adult beagle dogs of either sex were given, i.v. at 3-week intervals, either DXR (1.75 mg/kg) alone or DXR 15 min after MM-159 (25 mg/kg). Control animals received MM-159 (25 mg/kg) or saline without DXR. The experiment was terminated 3 weeks after the ninth injection (total DXR dose, 15.75 mg/kg). Of the eight animals given DXR alone, five died after receiving seven to eight injections (12.25-14 mg/kg DXR) and the remaining three were killed after eight injections because they were in poor condition. Marked ascites was noted in four of these eight dogs. When frequency and extent of myocardial lesions (vacuolation and myofibrillar loss) were assessed on a scale from 0 to 4+, severe lesions (3+) were present in all eight dogs given DXR alone, but no abnormalities (lesion score 0) were found in the hearts of three of eight dogs given MM-159 and DXR and the five remaining animals in this group had minimal (1+; four dogs) or mild (2+; one dog) alterations. DXR reduced the erythrocyte count, hemoglobin, and hematocrit when administered alone, but not in combination with MM-159. Such protection against DXR hematologic effects was not noted previously when dogs were pretreated with ICRF-187, the d-isomer of razoxane, despite the fact that pretreatment with ICRF-187 was as effective as MM-159 in reducing chronic DXR cardiotoxicity. It remains to be determined whether there are other differences in biological activity between MM-159 and ICRF-187.