Yukie Kawasaki

Antibacterial to antifungal conversion of neamine aminoglycosides through alkyl modification. Strategy for reviving old drugs into agrofungicides

Many Actinomycetes aminoglycosides are widely used antibiotics. Although mainly antibacterials, a few known aminoglycosides also inhibit yeasts, protozoans and important crop pathogenic fungal oomycetes. Here we show that attachment of a C8 alkyl chain to ring III of a neamine-based aminoglycoside specifically at the 4″-O position yields a broad-spectrum fungicide (FG08) without the antibacterial properties typical for aminoglycosides. Leaf infection assays and greenhouse studies show that FG08 is capable of suppressing wheat fungal infections by Fusarium graminearum—the causative agent of Fusarium head blight—at concentrations that are minimally phytotoxic. Unlike typical aminoglycoside action of ribosomal protein translation miscoding, FG08s antifungal action involves perturbation of the plasma membrane. This antibacterial to antifungal transformation could pave the way for the development of a new class of aminoglycoside-based fungicides suitable for use in crop disease applications. In addition, this strategy is an example of reviving a clinically obsolete drug by simple chemical modification to yield a new application.

Structure–Activity Relationships for Antibacterial to Antifungal Conversion of Kanamycin to Amphiphilic Analogues

Novel fungicides are urgently needed. It was recently reported that the attachment of an octyl group at the O-4″ position of kanamycin B converts this antibacterial aminoglycoside into a novel antifungal agent. To elucidate the structure-activity relationship (SAR) for this phenomenon, a lead compound FG03 with a hydroxyl group replacing the 3″-NH2 group of kanamycin B was synthesized. FG03s antifungal activity and synthetic scheme inspired the synthesis of a library of kanamycin B analogues alkylated at various hydroxyl groups. SAR studies of the library revealed that for antifungal activity the O-4″ position is the optimal site for attaching a linear alkyl chain and that the 3″-NH2 and 6″-OH groups of the kanamycin B parent molecule are not essential for antifungal activity. The discovery of lead compound, FG03, is an example of reviving clinically obsolete drugs like kanamycin by simple chemical modification and an alternative strategy for discovering novel antimicrobials.

Scalable production of biliverdin IXα by Escherichia coli

BackgroundBiliverdin IXα is produced when heme undergoes reductive ring cleavage at the α-methene bridge catalyzed by heme oxygenase. It is subsequently reduced by biliverdin reductase to bilirubin IXα which is a potent endogenous antioxidant. Biliverdin IXα, through interaction with biliverdin reductase, also initiates signaling pathways leading to anti-inflammatory responses and suppression of cellular pro-inflammatory events. The use of biliverdin IXα as a cytoprotective therapeutic has been suggested, but its clinical development and use is currently limited by insufficient quantity, uncertain purity, and derivation from mammalian materials. To address these limitations, methods to produce, recover and purify biliverdin IXα from bacterial cultures of Escherichia coli were investigated and developed.ResultsRecombinant E. coli strains BL21(HO1) and BL21(mHO1) expressing cyanobacterial heme oxygenase gene ho1 and a sequence modified version (mho1) optimized for E. coli expression, respectively, were constructed and shown to produce biliverdin IXα in batch and fed-batch bioreactor cultures. Strain BL21(mHO1) produced roughly twice the amount of biliverdin IXα than did strain BL21(HO1). Lactose either alone or in combination with glycerol supported consistent biliverdin IXα production by strain BL21(mHO1) (up to an average of 23. 5mg L-1 culture) in fed-batch mode and production by strain BL21 (HO1) in batch-mode was scalable to 100L bioreactor culture volumes. Synthesis of the modified ho1 gene protein product was determined, and identity of the enzyme reaction product as biliverdin IXα was confirmed by spectroscopic and chromatographic analyses and its ability to serve as a substrate for human biliverdin reductase A.ConclusionsMethods for the scalable production, recovery, and purification of biliverdin IXα by E. coli were developed based on expression of a cyanobacterial ho1 gene. The purity of the produced biliverdin IXα and its ability to serve as substrate for human biliverdin reductase A suggest its potential as a clinically useful therapeutic.

One-step synthesis of carbohydrate esters as antibacterial and antifungal agents

Carbohydrate esters are biodegradable, and the degraded adducts are naturally occurring carbohydrates and fatty acids which are environmentally friendly and non-toxic to human. A simple one-step regioselective acylation of mono-carbohydrates has been developed that leads to the synthesis of a wide range of carbohydrate esters. Screening of these acylated carbohydrates revealed that several compounds were active against a panel of bacteria and fungi, including Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Candida albicans, Cryptococcus neoformans, Aspergillus flavus and Fusarium graminearum. Unlike prior studies on carbohydrate esters that focus only on antibacterial applications, our compounds are found to be active against both bacteria and fungi. Furthermore, the synthetic methodology is suitable to scale-up production for a variety of acylated carbohydrates. The identified lead compound, MAN014, can be used as an antimicrobial in applications such as food processing and preservation and for treatment of bacterial and fungal diseases in animals and plants.