One of the approaches for improving drug performance and reducing toxicity is conjugation to a polymeric carrier. Our previous studies have described the conjugation of amphotericin B (AmB) by a Schiff-base reaction with oxidized arabinogalactan (AG) to generate a highly water soluble AmB-AG conjugate (>100 mg/ml) which was formulated for injection. It was much safer than the conventional micellar AmB-deoxycholate (AmB-Doc) (maximal tolerated dose 50 versus 4 mg/kg, respectively). Histopathological evaluation of organs in mice treated with AmB-Doc showed hepatocellular and renal tubular necrosis, whereas no damage was detected in mice treated with the AmB-AG conjugate, even at a much higher dosage (8 vs. 1 mg/kg/day). The use of AmB is limited by adverse effects that may be mediated by AmB induction of pro-inflammatory cytokines such as interleukin-1 (IL-1 ) and tumor necrosis factor- (TNF- ). Therefore, we have tested the expression of these cytokines in various mouse organs, using immunohistochemistry and ELISA. In kidneys, administration of AmB-Doc induced relatively high levels of intracellular TNF- • compared with AmB-AG, which induced mostly extracellular TNF- . IL-1 detected by immunohistochemistry was evident only in renal tubular cells treated with AmB-AG conjugate. These findings may suggest specific TNF- /IL-1 -mediated tissue damage or tissue sparing by AmB-Doc and AmB-AG, respectively. A tissue distribution study performed in immunocompetent uninfected mice, indicated that AmB from the AmB-AG conjugate accumulated preferentially in the lungs compared to AmB from micellar (AmB-Doc) and liposomal (AmBisome TM ) formulations. The high AmB concentration detected in lungs (26 µg/g) was significantly higher than those obtained with AmB-Doc and AmBisome and could be of a great benefit for treatments of invasive fungal infections caused by air-borne conidia, such as aspergillosis. We therefore studied the therapeutic efficacy of the AmB-AG conjugate in a murine invasive aspergillosis model. In this model the mice were immunosuppressed and inoculated intravenously with Aspergillus fumigatus conidia, and treated with once-daily doses of either AmBisome, AmB-Doc and AmB-AG conjugate for 5 consecutive days. Treatment of invasive aspergillosis with a high dose (5 mg/kg/d) of AmB-AG was effective in prolonging survival and in eradicating hyphae from the most commonly involved organs (lungs, kidneys and liver). AmB-AG conjugate was also highly effective in candidiasis, cryptococcosis and leishmaniasis in mouse models. The overall results suggest that after further development AmB-AG conjugate may be a potent and safer agent in the treatment of invasive fungal infections and visceral leishmaniasis.
Full conference title:
The 15 th Congress of the International Society for Human and Animal Mycology
- ISHAM 15th (2003)