The scientists, led by Joseph Vinetz, MD, an infectious diseases specialist, were interested to find out if an oral medication used to treat pancreatitis could reduce the viral load (the amount of virus in your body) of SARS-CoV-2 and improve symptoms in people newly diagnosed with COVID-19.
The study, which is available on a preprint site and has not yet been published in a peer-reviewed journal, ran from June 2020 to April 2021.
It showed that the medication, called camostat mesylate, did little to lessen viral load. But, to the researchers’ surprise, it brought a different type of benefit. “The patients who received the drug didn’t lose any sense of smell or taste. That was a ‘wow’ factor,” says Dr. Vinetz.
This matters because loss of smell, known as anosmia, and loss of taste are common COVID-19 symptoms. For many, the senses return as the infection fades. But for others, the effect lingers in varying degrees. (With the omicron variant, those symptoms can still occur, but not as often as it has with other variants.)
How the ‘surprise’ finding on loss of taste and smell was discovered
Dr. Vinetz says he was originally motivated to look into camostat mesylate after he saw an April 2020 study published in Cell that showed how this medicine could prevent SARS-CoV-2 from entering cells.
Dr. Vinetz recruited several colleagues to collaborate, including Anne Spichler Moffarah, MD, Ph.D., an infectious diseases specialist, and Gary Desir, MD, chair of the Department of Internal Medicine. Geoffrey Chupp, MD, director of the Yale Center for Asthma and Airways Disease, ran the clinical trial.
Although the trial was stopped once it was clear that the main objective of reducing viral load was not occurring, the researchers think the surprise findings about loss of smell and taste warrant additional study.
“My daughter had COVID a year ago and she still has trouble smelling and tasting things,” says Dr. Desir. “This drug seems to be able to modulate that loss of smell and taste. It has very few side effects and has been studied extensively. This could be the type of treatment that is given to someone with COVID at the onset of the infection.”
If the drug were to be approved for this purpose, the doctors believe it could be a game-changer. “It wouldn’t be an expensive medication. Our idea was that everyone would take it if they were diagnosed because it’s hard to predict who will lose their sense of smell or taste, and it’s better to prevent it than to wait for it to happen,” Dr. Desir says.
Additional benefits found for those with COVID-19
There were also other benefits to this medication, as the study showed that those who received it reported notable improvements related to fatigue, compared to those who received a placebo.
“People who got camostat mesylate in the trial started feeling less tired and better overall after day four, which was statistically different from the placebo group,” Dr. Vinetz says. “And there were essentially no adverse effects in the camostat mesylate group.”
Whether camostat mesylate could help restore sense of taste or smell in someone who has lost it is unknown, he adds. “More studies would help us with that,” Dr. Chupp says.
In order for camostat mesylate to become available for use in preventing the COVID-19-related loss of taste or smell, there would need to be a Phase III clinical trial and an application filed to the Food and Drug Administration (FDA) for emergency use authorization. All of this would take some time, Dr. Chupp explains.
Still, the doctors are hopeful their surprise discovery can make a positive impact on the fight against COVID-19. “A drug such as camostat mesylate presents an opportunity,” says Dr. Chupp.
The Camostat mesylate metabolite GBPA shows reduced inhibition of recombinant TMPRSS2
Multiple studies show that Camostat mesylate is rapidly converted into its active metabolite, 4-(4-guanidinobenzoyloxy)phenylacetic acid (GBPA) in animals and humans, followed by further conversion of GBPA into the inactive metabolite 4-guanidinobenzoic acid (GBA) [18, 19, 20,] (Fig. 6a).
However, the capacity of GBPA to inhibit the enzymatic activity of TMPRSS2 has not been examined. To address this question, we compared inhibition of recombinant TMPRSS2 by Camostat mesylate, GBPA and GBA. For this, we used FOY-251, a methanesulfonate of GBPA, which is readily commercially available.
We found that FOY-251 exerted a 10-fold reduced capacity to inhibit TMPRSS2 as compared to Camostat mesylate, although both compounds completely suppressed TMPRSS2 activity at 1 µM or higher (Fig. 4). In contrast, GBA was less active (Fig. 4). Thus, FOY-251 blocks TMPRSS2 activity but with reduced efficiency as compared to Camostat mesylate.
In order to obtain insights into the reduced inhibitory activity of FOY-251, we investigated TMPRSS2 inhibition by GBPA on the molecular level. For this, we used a combination of extensive all-atom molecular dynamics (MD) simulations and Markov modeling of the TMPRSS2-GBPA complex [].
Guanidinobenzoate-containing drugs such as Camostat mesylate and GBPA inhibit TMPRSS2 by first forming a noncovalent precomplex which is then catalyzed to form a long-lived covalent complex that is the main source of inhibition []. However, the population of the short-lived precomplex directly relates to the inhibitory activity [].
By computing the TMPRSS2-GBPA binding kinetics [], we find that (i) the noncovalent TMPRSS2-GBPA complex is metastable, rendering it suitable to form a covalent inhibitory complex, and (ii) its population is 40% lower compared to Camostat at equal drug concentrations, consistent with the finding that FOY-251 is a viable but less potent inhibitor (Fig. 4). Structurally, we find that GBPA binds in the same manner as Camostat (Fig. 5, []).
The main stabilizing interaction is its guanidinium group binding into TMPRSS2’s S1 pocket, which is stabilized by a transient salt bridge with Asp-435. The GBPA ester group can interact with the catalytic Ser-441, making it prone for catalysis and formation of the catalytic complex. The slightly lower stability of the GBPA compared to the Camostat mesylate-TMPRSS2 complex is consistent with GBPA’s shorter tail, which has less possibilities to interact with the hydrophobic patch on the TMPRSS2 binding site shown in Fig. 5, left panel.
Camostat mesylate and FOY-251 inhibit SARS-CoV-2 infection with comparable efficiency
We finally compared the antiviral activity of Camostat mesylate and FOY-251, the methanesulfonate of GBPA, in cell culture. The reduced ability of FOY-251 to block the enzymatic activity of recombinant TMPRSS2 as compared to Camostat mesylate would suggest that the compound should also exert reduced antiviral activity. On the other hand, analysis of antiviral activity encompasses preincubation of target cells with Camostat mesylate for 2 h in the presence of FCS, which allows conversion of Camostat mesylate into GBPA, as demonstrated above.
Indeed, titration experiments with VSV pseudotypes and Calu-3 lung cells as targets revealed that entry inhibition by FOY-251 was only slightly reduced as compared to Camostat mesylate, with EC50 values of 107 nM (Camostat mesylate) and 178 nM (FOY-251) (Fig. 7). Moreover, no marked differences in inhibition of infection of Calu-3 cells with authentic SARS-CoV-2 were observed (Fig. 8a).
Finally, both Camostat mesylate and FOY-251, as well as another promising serine protease inhibitor for treatment of SARS-CoV-2 infections, Nafamostat mesylate, inhibited SARS-CoV-2 infection of human precision-cut-lung slices (PCLS) ex vivo, and again no major differences in inhibition efficiency were observed between Camostat mesylate and FOY-251 (Fig. 8B). Thus, under the conditions chosen Camostat mesylate and GBPA exerted roughly comparable antiviral activity, likely due to conversion of Camostat mesylate into GBPA.
reference link : https://www.thelancet.com/journals/ebiom/article/PIIS2352-3964(21)00048-7/fulltext
More information: Geoffrey Chupp et al, A Phase 2 Randomized, Double-Blind, Placebo-controlled Trial of Oral Camostat Mesylate for Early Treatment of COVID-19 Outpatients Showed Shorter Illness Course and Attenuation of Loss of Smell and Taste (2022). DOI: 10.1101/2022.01.28.22270035