Amphotericin B-albumin conjugates: Synthesis, toxicity and anti-fungal activity

Amphotericin B (AmB), a hydrophobic drug with negligible aqueous solubility was conjugated to bovine serum albumin (BSA) via amide bond coupling to give 6 to 8 wt% drug payload. The resulting conjugate was characterized using SDS-PAGE and UV-visible, FTIR and CD spectroscopy. The conjugate was water-soluble to the extent of 150 mg/ml, was non-toxic to HEK 293 T cells at a concentration of 500 μg/ml (equivalent to ~30 μg AmB) and showed hemolysis of <5% at 200 μg/ml (equivalent to ~12 μg AmB) against human erythrocytes in vitro. In vitro release studies at 37 °C demonstrated steady release of AmB up to 20% from the conjugate with little burst effect in phosphate buffered saline whereas thrice the amount was released in human plasma in 72 h. AmBisome® used as a reference showed a very similar release profile in plasma. The conjugate exhibited potential anti-fungal activity against yeast strains such as C. albicans, C. neoformans and C. parapsilosis with the minimum inhibitory concentration (MIC) equivalent to AmB ranging from 0.7 to 1.1 μg/ml while AmBisome® and AmB alone showed the MIC between 0.78 and 1.5 and 0.53-0.78 μg/ml respectively. Although AmB has been conjugated to various natural and synthetic polymers to improve its solubility and reduce its toxicity, the results obtained in this study using the model protein BSA as a carrier point to the possibility of taking this pro-drug approach to human clinical use using human serum albumin (HSA) as the carrier, since HSA has emerged as a versatile drug carrier for treating diabetes and cancer and improving the pharmacokinetic profile of many drugs with US FDA approving HSA as a drug carrier for the anti-cancer drug paclitaxel (Abraxane®) for human use.