A new antifungal molecule, devised by modifying the structure of the prominent antifungal drug Amphotericin B, has the potential to harness the drug’s power against fungal infections while eliminating its toxicity, report researchers at the University of Illinois Urbana-Champaign and colleagues at the University of Wisconsin-Madison Journal Report Nature.
Amphotericin B, a naturally occurring small molecule produced by bacteria, is a drug used as a last resort to treat fungal infections. While AmB excels at killing fungi, it is retained as a last line of defense because it is also toxic to the human patient — especially the kidneys.
“Fungal infections are a public health crisis that’s only getting worse. And they have the potential, unfortunately, to break out and have an exponential impact, as COVID-19 did. So let’s take one of nature’s powerful tools to fight fungi and turning them into a powerful ally,” said study leader Dr. Martin D. Burke, an Illinois professor of chemistry, professor at the Illinois Carle College of Medicine, and also a physician.
“This work is a demonstration that, by going deep into fundamental science, you can take a billion years from nature and turn it into something that will hopefully have a big impact on human health,” Burke said.
Burke’s team has spent years exploring AmB in hopes of making a derivative that can kill fungi without harming humans. In previous studies, they developed and used a building block-based approach to molecular synthesis and collaborated with a team specializing in molecular imaging tools called solid-state nuclear magnetic resonance, led by Professor Chad Rienstra at the University of Wisconsin-Madison. Together, the teams uncovered the drug’s mechanism: AmB kills fungi by acting as a sponge to extract ergosterol from fungal cells.
In the new work, Burke’s team teamed up again with Rienstra’s team to find that AmB similarly kills human kidney cells by extracting cholesterol, the most common sterol in humans. The researchers also resolved the atomic-level structure of the AmB sponges when bound to both ergosterol and cholesterol.
“The atomic resolution models were really the key to zoom in and detect these very subtle differences in the binding interactions between AmB and each of these sterols,” said Illinois graduate student Corinne Soutar, co-first author of the paper. .
“Using this structural information along with functional and computational studies, we made a breakthrough in understanding how AmB works as a potent antifungal drug,” said Rienstra. “This provided the insights into modifying AmB and tuning its binding properties, reducing its interaction with cholesterol and thereby reducing toxicity.”
Armed with the information from the NMR studies, the Illinois team began synthesizing and testing derivatives with slight changes in the ergosterol- and cholesterol-binding region, while also enhancing the kinetics of the ergosterol removal process to maintain efficacy.
Made possible by the partners and facilities of the Carl R. Woese Institute of Genomic Biology and U. of I. professor of veterinary clinical medicine, Dr. Timothy Fan, the researchers tested the most promising derivatives — first with in vitro tests, quickly assessing effectiveness in killing fungi; they then move to cell cultures and eventually live mice, assessing toxicity.
One molecule, named AM-2-19, stood out from the rest.
“This molecule is renal, avoids resistance and has broad-spectrum efficacy,” said postdoctoral researcher Arun Maji, co-first author of the paper. “We tested this molecule on more than 500 different clinically relevant pathogen species in four different locations. And this molecule completely surprised us by either mimicking or surpassing the effectiveness of current clinically available antifungal drugs.”
The researchers tested AM-2-19 in human blood and kidney cells to test for toxicity. They also tested AM-2-19 in mouse models of three common, persistent fungal infections and saw high efficacy.
“During my medical rotations, we used to call AmB ‘ambi-terrible,’ because of how hard it was on patients,” Burke said. “Decoupling efficacy from toxicity turns ‘both-terrible’ into ‘both-terrible.’ We are very excited about the potential we see, although a clinical study is needed to see if this potential translates to humans.”
As a first step toward clinical application, AM-2-19 has been licensed to Sfunga Therapeutics and recently entered Phase 1 clinical trials. Sfunga Therapeutics also partially supported the project, and Burke received consulting income and equity in company.
The National Institutes of Health supported this work. Illinois chemistry professor Taras Pogorelov also co-authored the paper under grants 5R01-AI135812-04, R35-GM118185, R01-GM112845 and R01-GM123455, R01-AI0631563M and P33. Fan is also affiliated with Carle Illinois College of Medicine and the Illinois Cancer Center. Burke and Pogorelov are affiliated with the Beckman Institute for Advanced Science and Technology.