Liposomal Annamycin, or L-Annamycin, is a drug from the anthracycline family (chemotherapy drugs which are derived from antibiotics). The in vitro cytotoxicity of L-Annamycin was tested on a panel of 4 different parental cell lines and their respective multidrug-resistant (MDR)-1 expressing cell lines (15). In all MDR cell lines tested (KB-V1, P388/Dox, CEM/Vbl, and 8226/R) there was minimal resistance to L-Annamycin, whereas resistance to doxorubicin was high. Studies with MDR modulators and metabolic inhibitors indicated significant differences in the cellular transmembrane transport systems between doxorubicin and Annamycin and suggest that Annamycin efflux is not mediated by P-glycoprotein MDR.

In vivo, L-Annamycin has shown lack of cross-resistance in KB-VI human xenografts (an MDR-resistant cell line) and enhanced antitumor activity compared with doxorubicin in several mouse tumor models such as leukemia (L-1210), melanoma (B16), reticulosarcoma (M5076), and Lewis lung carcinoma cells. Results in KB and KB-V1 human xenografts demonstrate that L-Annamycin was at least as effective as doxorubicin. L-Annamycin was more active than doxorubicin in a leukemia L-1210 mouse tumor model.