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The highly lipophilic cyanomorpholinyl adriamycin (CMA) is the most potent antineoplastic anthracycline yet described. CNS distribution and toxicity were examined after i.v. administration of CMA to mice. At doses greater than or equal to 0.1 mg/kg, a neurotoxic syndrome including ataxia, hypokinesia, and tremors appeared. At doses of less than or equal to 0.05 mg/kg, which have been reported to be antineoplastic, no neurotoxicity was observed. On histopathologic examination, no changes were observed in the brain, spinal cord, or dorsal root ganglia. Unlike adriamycin (ADR), which rapidly appears in the nuclei of several tissues, CMA showed no fluorescence, suggesting a different cellular microcompartmentalization. The i.d. injection of CMA disclosed a 200-fold increase in toxicity compared with that of adriamycin. In comparisons of CMA and ADR, neurotoxicity and cardiotoxicity occurred equally only at higher doses; however, the dermatotoxicity and antineoplastic activity of CMA were increased several hundred-fold.

Plasma and tissue levels of doxorubicin (DXR) and doxorubicinol (DXR-OL) were measured fluorometrically after high-pressure liquid chromatography at 1, 3, and 24 h following one, nine, and 24 doses of 1.0 mg DXR/kg or one and eight doses of 4.0 mg DXR/kg, IP, to rats. Comparison of plasma levels of DXR found following single and multiple doses suggests significant build-up of DXR at 1 h with successive doses, but not at 3 h. Liver exhibited substantially higher levels of DXR (on a per gram of protein basis) than did plasma, and multiple doses did not produce higher levels than did a single dose. In contrast, the heart accumulated DXR slowly, attaining levels after multiple dosing in excess of those found in the liver. Skeletal muscle exhibited dose-related levels similar to those for heart but the absolute levels of DXR in muscle were only about one-tenth of those observed in heart. DXR-OL was at very low levels of less than or equal to 4% of the DXR levels in the tissues; it was, however, a major circulatory metabolite, attaining levels in the plasma as high as 85% of the concentration of DXR.

A series of quinone- and sugar-modified analogs of adriamycin have been tested for growth inhibition of adriamycin-sensitive (P388/S) and -resistant (P388/ADR) sublines of P388 murine leukemia cells in vitro. P388/ADR is less resistant to analogs of adriamycin containing either a 3'-deamino-3'-(4"-morpholinyl) group, MRA; or a -(3"-cyano-4"-morpholinyl) group, MRA-CN, than to adriamycin. However, MRA-CN was the most potent growth inhibitor of either subline. This potency is reduced by either modification of the quinone unit with a 5-imino substituent or restriction of the cyano-morpholinyl ring by an oxygen bridge to the daunosamine sugar. The calcium antagonist verapamil substantially increases the cytotoxicity of adriamycin to P388/ADR but has no appreciable effect on the cytotoxicity of either MRA or MRA-CN. The results suggest that increased uptake and retention by both MRA and MRA-CN may contribute to their increased cytotoxicity, but that the intense potency of the cyano-morpholinyl analogs must be due to other unique properties of these compounds.

We have confirmed that doxorubicin induces irreversible changes in the nucleolar ultrastructure of myocardial cells of rats. Similar changes were not caused by an equal dose of the synthetic analogue, 5-iminodaunomycin. These results combined with previous and current comparative tests with this analogue, doxorubicin, and daunomycin suggest that 5-iminodaunomycin may serve as a less cardiotoxic anthracycline derivative.