4'-epi-doxorubicin, a new analogue of doxorubicin: a preliminary overview of preclinical and clinical data.

4'-epi-doxorubicin (4'-epi-DX) is a new anthracycline antibiotic. It differs from doxorubicin (DX) by the epimerization of the OH group in position 4' of the aminosugar moiety, and was synthesized in an effort to find agents with a superior therapeutic index to the parent compound doxorubicin (DX). 4'-epi-doxorubicin binds to DNA and inhibits nucleic acid synthesis and function. The antitumor activity of 4'-epi-DX in several experimental tumors (Leukemias L 1210, P 388, Gross Leukemia, Sarcoma 180 ascitic and solid, C3H/HE mammary carcinoma) is similar to that of DX. However, 4'-epi-doxorubicin has greater antitumor activity than doxorubicin in Lewis lung carcinoma, MS-2 sarcoma lung metastasis, and human melanoma in athymic mice. In chronic toxicity studies there were no qualitative differences between 4'-epi-DX and DX; quantitatively, however, 4'-epi-DX was less toxic. In different experimental models 4'-epi-DX has been shown to be less cardiotoxic than its parent compound. In chronic toxicity studies in the rabbit, histopathologic findings revealed the same pattern of cardiotoxicity for both drugs but less marked with 4'-epi-DX. Distribution studies in mice with tumors showed a lower concentration of 4'-epi-DX in the heart, spleen and kidneys; the hepatobiliary metabolism and excretion of 4'-epi-DX investigated in the rat, indicated that the new analogue was more extensively metabolized than the parent compound. Pharmacokinetics of 4'-epi-DX in humans showed a multiexponential decrease of plasma levels; the same pattern was observed for the metabolite 13-OH epidoxorubicinol but with lower concentrations than the unchanged drug. A high plasma clearance (0.9-1.41/min), a terminal half-life of about 30-40 hr and a large volume of distribution were the main pharmacokinetic characteristics of 4'-epi-DX. A reduction of the dose appears to be appropriate in patients with liver function impairment. Phase II studies with 4'-epi-DX have indicated that the drug produces a pattern of acute toxicity, including acute cardiac toxicity, qualitatively similar to that of DX at identical doses but quantitatively lower, with particular regard to leukopenia and gastrointestinal toxicity. The range of single active doses is between 60 and 90 mg/m2, the most frequently employed doses schedules being 75 or 90 mg/m2 i.v. every 3 weeks. 4'-epi-DX has shown activity in a variety of tumors such as breast carcinoma, soft tissues sarcomas, NH lymphomas, leukemias, ovarian cancer and gastric cancer. Preliminary evidence of activity has been found in melanoma, rectal cancer and pancreatic cancer suggesting a broad spectrum of activity. As to chronic cardiac toxicity up to now only 2 mild to moderate and reversible CHF have been observed at doses of 1120 and 1235 mg/m2 in about 700 treated patients. Specific and comparative studies are in progress: preliminary findings from a randomized comparison of 4'-epi-DX vs DX in breast cancer indicated that 4'-epi-DX may have a lower cumulative cardiotoxicity.