Liposomes as drug carriers for polyene antibiotics

Effective treatment of acute and chronic murine tuberculosis with liposome-encapsulated clofazimine

The therapeutic efficacy of liposomal clofazimine (L-CLF) was studied in mice infected with Mycobacterium tuberculosis Erdman. Groups of mice were treated with either free clofazimine (F-CLF), L-CLF, or empty liposomes twice a week for five treatments beginning on day 1 (acute), day 21 (established), or day 90 (chronic) postinfection. One day after the last treatment, the numbers of CFU of M. tuberculosis in the spleen, liver, and lungs were determined. F-CLF at the maximum tolerated dose of 5 mg/kg of body weight was ineffective; however, 10-fold-higher doses of L-CLF demonstrated a dose response with significant CFU reduction in all tissues without any toxic effects. In acutely infected mice, 50 mg of L-CLF/kg reduced CFU 2 to 3 log units in all three organs. In established or chronic infection, treated mice showed no detectable CFU in the spleen or liver and 1- to 2-log-unit reduction in the lungs. A second series of L-CLF treatments cleared M. tuberculosis in all three tissues. L-CLF appears to be bactericidal in the liver and spleen, which remained negative for M. tuberculosis growth for 2 months. Thus, L-CLF could be useful in the treatment of tuberculosis.

Liposome encapsulation of clofazimine reduces toxicity in vitro and in vivo and improves therapeutic efficacy in the beige mouse model of disseminated Mycobacterium avium-M. intracellulare complex infection

Disseminated infections caused by the Mycobacterium avium-M. intracellulare complex (MAC) are the most frequent opportunistic bacterial infections in patients with AIDS. MAC isolates are resistant to many of the standard antituberculous drugs. Failure to obtain significant activities of certain drugs is due to difficulty in achieving high concentrations at the sites where the infections reside. New and improved agents for the treatment of mycobacterial infections are therefore required. Earlier, the anti-MAC activities of various agents in free or liposomal form were studied; liposomes were used as drug carriers to ultimately target the drugs to macrophages where mycobacterial infections reside. Clofazimine was chosen for further studies because it could be effectively encapsulated and its activity was well maintained in liposomal form. The present studies with both erythrocytes and macrophages as the model systems show that liposomal drug is far less toxic in vitro than the free drug. The in vivo toxicity of clofazimine was also significantly reduced after liposome encapsulation. The therapeutic efficacies of free and liposomal drugs were compared in a beige mouse model of disseminated MAC infection. An equivalent dose of liposomal drug (10 mg/kg of body weight) was more effective in eliminating the bacterial from the various organs studied, particularly from the liver. Moreover, because of the reduced toxicity of liposomal drug, higher doses could be administered, resulting in a significant reduction in the numbers of CFU in the liver, spleen, and kidneys. The data demonstrate that liposomal clofazimine is highly effective in the treatment of MAC infections, even if the treatment is initiated after a disseminated infection has been established. The present studies thus suggest the potential usefulness of liposomal clofazimine for the treatment of disseminated MAC infections.

Mannosylated liposomes as carriers for hamycin in the treatment of experimental aspergillosis in Balb/C mice

Hamycin incorporated into mannosylated liposomes produced less toxicity and enhanced antifungal activity in experimental aspergillosis in balb/c mice in vivo. Incorporation of cholesterol into mannosylated liposomes led to a decrease in hamycin toxicity. The LD50 (mg/kg) values of hamycin contained in SPC/Chol/DPPE-Man (molar ratio 4:5:1) lipsomes was 2.8 whereas that in SPC/DPPE-Man liposomes (molar ratio 9:1) was 1.4. Incorporation of cholesterol into mannosylated liposomes increased the survival rates of infected animals: 70% survival was recorded after 7 days therapy as well as reduced fungal load in lung, liver, spleen and kidney. HPLC studies of distribution of hamycin in various tissues showed a reduction in the concentration of the liposomal drug in circulation compared to that observed for free drug and neutral liposomes after 1 hour.

Clinical experience of targeted therapy

Drug targeting (i.e. administration of a drug-carrier conjugate which delivers active drug selectively to a particular tissue) has recently evolved into a new subdiscipline of experimental pharmacy/pharmacology. However, clinical experience with targeted therapy is very limited to date. This review summarizes human studies of targeted therapy. Indications for which drug targeting has been attempted include neoplastic disorders, fungal infections, enzyme replacement, hematologic and immune disorders, and iron storage disease. To date, no single drug targeting system is recommendable for routine clinical use, but present results justify further clinical evaluation in a number of situations.