RESUMO
Amphotericin B has been an essential drug in the fight against leishmaniasis and fungal pathogens for decades, and has more recently gained attention for the very limited microbial resistance displayed against it. However, its toxicity has restricted its use to only the most severe cases of disease, and attempts to reduce these ill effects via formulation have had only minor success. Genetic engineering has allowed the development of superior amphotericin analogues, notably 16-descarboxyl-16-methyl amphotericin B (MeAmB), which shows a ten-fold reduction in toxicity in addition to a slight improvement in therapeutic activity. However, MeAmB is difficult to extract from its bacterial source and purify. Presented here is an alternative method of MeAmB purification. A biomimetic polymer with a high affinity for MeAmB was designed via computational modelling and synthesised. Prepared as a separation column, the polymer was able to retain the target MeAmB whilst allowing the removal of cell debris from the bacterial extract. Starting with a simple bacterial extract, the relatively simple process allowed the purification of an MeAmB salt complex at approximately 70% MeAmB, and likely higher purification from further extraction. The mean MeAmB recovery between the pre-purification extract sample and the final product was 81%. This is the first successful demonstration of extraction or purification of any amphotericin molecule with any polymeric material. The biomimetic polymer was additionally reusable and simple to fabricate, giving this technique significant advantages over traditional methods of extraction and purification of valuable compounds.
RESUMO
Several polyene macrolides are potent antifungal agents that have severe side effects. Increased glycosylation of these compounds can improve water solubility and reduce toxicity. Three extending glycosyltransferases are known to add hexoses to the mycosaminyl sugar residues of polyenes. The Actinoplanes caeruleus PegA enzyme catalyses attachment of a D-mannosyl residue in a ß-1,4 linkage to the mycosamine of the aromatic heptaene 67-121A to form 67-121C. NppY from Pseudonocardia autotrophica adds an N-acetyl-D-glucosamine to the mycosamine of 10-deoxynystatin. NypY from Pseudonocardia sp. P1 adds an extra hexose to a nystatin, but the identity of the sugar is unknown. Here, we express the nypY gene in Streptomyces nodosus amphL and show that NypY modifies 8-deoxyamphotericins more efficiently than C-8 hydroxylated forms. The modified heptaene was purified and shown to be mannosyl-8-deoxyamphotericin B. This had the same antifungal activity as amphotericin B but was slightly less haemolytic. Chemical modification of this new disaccharide polyene could give better antifungal antibiotics.
