Exploring FabK as a Narrow-Spectrum Drug Target Against C. difficile
AUG 27, 2017 | CONTAGION® EDITORIAL STAFF
Julian Hurdle, PhD, associate professor, Center for Infectious and Inflammatory Diseases, Institute of Biosciences and Technology, Texas A&M Health Science Center, explains research focused on validating FabK as an essential enzyme to be used as a narrow-spectrum drug target against Clostridium difficile.
Interview Transcript (slightly modified for readability:
“As for narrow-spectrum drugs, I think that’s what we need to treat [Clostridium] C. difficile infection. One can look at it in this way: you want to treat your ‘bad bug,’ but you want to leave your good bacteria intact, or allow your good bacteria a chance to recover to also control C. difficile as well.
I think when we look at the history of the field, and the history of discovery of narrow-spectrum antibiotics, it has been particularly challenging. Certainly, you can ask, how do you achieve the discovery of a narrow-spectrum antibiotic? Do you go after a particular drug target? What should that drug target be? What should the chemistry of the molecules be? So, this is really my opinion, being a real grey area of this drug discovery versus C. difficile and the discovery of narrow-spectrum antibiotics, in my opinion has been somewhat serendipitous. I love the fact that we are pursuing FabK, this is in collaboration with Dr. Kirk Hevener, at the University of Tennessee Health Sciences Center. Why I think pursuing FabK makes sense, is that C. difficile carries this enzyme known as FabK, which is involved in fatty acid biosynthesis. Other gut microflora, like Bacteroides for example, they carry an alternate isoenzyme, so, in principle, one could inhibit FabK, which is an essential enzyme in C. difficile, while leaving your important gut microbiota intact, such as Bacteroides fragalis.
We have settled on a research plan, where we wanted to first of all, validate that FabK is an essential enzyme and the way that we did that at Texas A&M, was we did some molecular genetics, where we knocked down the FabK from the enzyme, which means that the enzyme is no longer produced within the cells, and, as a result, we saw that when we did that, the bacteria was not able to survive.
Now, since this pathway involves fatty acid biosynthesis, certainly when one thinks about C. difficile as a gastrointestinal disease, one could easily think about the question, well, would the microorganism bypass inhibition with a narrow-spectrum drug targeting fatty acid biosynthesis by simply taking up fatty acids from in the intestines? For example, dietary fatty acids.
What we’ve shown in our studies to date, is that even when FabKis inhibited, C. difficile is unable to take up exogenous fatty acids, including dietary fatty acids, and as a result, what that means is, for C. difficile, fatty acid biosynthesis is essential although it may have within its environment other sources of fatty acids that it can use to generate its cell membrane, and I think that’s extremely important.
When we look at the genetics of the microorganism, the reason why C. difficile is unable to utilize exogenous fatty acids to bypass inhibition of the FASII pathway is because it has this interesting regulator known as FabR, and the possession of this regulator known as FabR actually prevents C. difficile from utilizing exogenous fatty acids to bypass fatty acid synthesis inhibition by a narrow-spectrum molecule.
Now, further aspects of the study that I find particularly important is the concept of recurrence and the population of those patients that recur because of the survival of spores. As Dr. Hevener mentioned earlier, C. difficile uses fatty acids to generate its membrane. Now, during the formation of spores, we call it a process of sporulation, fatty acids are utilized to make the spores. If the organism is unable to utilize fatty acids to make spores, the spore membrane, essentially it’s going to be defunct in sporulation. From our initial studies, we see that when we do inhibit fatty acid biosynthesis, it also affects sporulation. So, in essence, besides having a narrow-spectrum molecule or target that does specifically affect C. difficile, we also have a means of reducing the prospects of recurrence, and also reducing the prospects of spore shedding from patients who have CDI in the hospital environment, so I think it’s a fascinating project; it’s a fascinating concept to pursue for drug discovery for CDI.”
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