Identification of candidates for drug repurposing. A Selection and validation procedure. B HEp-2 cells were infected with rHRSV-A-GFP29 in the presence of 5 µM compound. 48 hours later, infection and cell viability were quantified via GFP and MTT readouts. The dotted lines indicate the main criteria for success and the points represent the averages of two technical repetitions. VS HEp-2 cells were infected with HRSV-A-Luc29 at MOI 0.01 and treated with the indicated compound concentrations. 24 hours later, the supernatant was transferred to new cells for a second round of infection. Luminescence was quantified 24 hours after inoculation of both infection cycles. Cell viability was measured via MTT reading in treated but uninfected cells. Mean ± SD of three independent experiments. Known RSV inhibitors (F protein: presatovir; N protein: RSV604, IMPDH inhibitors (AVN944, mycophenolic acid), HSP90 inhibitors (radiciol, HSP990). 4-sulfocalix (6)arene hydrate (4SC6AH, target unknown).The source data is provided as a source data file. Natural communications (2024). DOI: 10.1038/s41467-024-45241-y
Every year during the winter months, waves of RSV infection occur. In healthy adults and adolescents, the infection is generally harmless. This is not the case for young children: about 1% of them who are first exposed to the pathogen become so seriously ill that they need to be hospitalized.
It can also cause serious illness in adults over 65 due to pre-existing heart or lung conditions. Vaccines have been authorized since 2023 for the elderly and pregnant women, but there is currently no direct antiviral treatment against the RS virus.
In order to discover new substances active against certain pathogens, researchers search through vast collections of substances already known and clinically tested. This process is known as “drug reuse screening” and examines additional areas of application for already known pharmaceutical products.
A team from the Institute for Experimental Virology at TWINCORE, Center for Experimental and Clinical Infection Research, Hannover, led by Thomas Pietschmann, used this method to search the ReFRAME library at the Scripps Research Institute (USA) of potential new drugs for RSV. This substance bank contains approximately 12,000 active substances in clinical development or already approved.
“To screen the library, we used a so-called reporter virus labeled with the fluorescent protein GFP,” explains Pietschmann. “A lack of fluorescence reaction in this test indicates an antiviral effect.” At the same time, all substances were also analyzed for their toxicity. Only those that have no harmful effect on cells are pre-selected.
The tests were carried out automatically using a pipetting robot in collaboration with the Institute of Virology at the Hannover Medical Faculty. “Otherwise, it is almost impossible to sift through a collection of several thousand substances,” says Sibylle Haid, a scientist at the Institute of Experimental Virology and co-corresponding author of the study.
Among the remaining 21 candidates, scientists focused on the active ingredient lonafarnib, approved for the treatment of Hutchinson-Gilford progeria syndrome. People with this rare genetic disorder age prematurely and die earlier, on average, at 14.5 years old.
“Lonafarnib inhibits a specific step of protein maturation in the cell,” explains Haid. To more precisely characterize the mechanism of action against the RS virus, the researchers tested another farnesylation inhibitor called tipifarnib and compared the results. “Tipifarnib does not work against RSV,” explains Haid. “From this, we could conclude that the antiviral effect of lonafarnib is probably not based on the inhibition of farnesylation.”
With the help of cooperation partners Anna Hirsch from the Helmholtz Institute for Pharmaceutical Research Saarland (HIPS) and Thomas Krey from the University of Lübeck, the team was able to elucidate the molecular structure of the virus-drug complex. Lonafarnib binds to the RSV fusion protein and thus prevents the virus from fusing with the membrane of the target cell. As a result, no new cells can be infected.
In cooperation with French colleagues, a reduction in viral load has already been demonstrated in the mouse model. “However, the dose of lonafarnib required for oral administration is very high, so we also observed side effects,” says Pietschmann. “It is conceivable that local application, for example by inhalation, could improve the effect-to-side effect ratio. This needs to be carefully examined in follow-up studies.”
“With lonafarnib, we have identified an interesting candidate for the treatment of RSV,” explains Svenja Sake, first author of the study. “As the drug has already undergone all clinical trials, approval for the new indication would be much easier, cheaper and faster than for a completely new active substance,” she says.
“This study is also another excellent example of teamwork, as is usual in science,” says study leader Pietschmann. “For example, we are networked with many cooperation partners from the RESIST cluster of excellence.”
The work is published in the journal Natural communications.
More information:
Svenja M. Sake et al, Drug repurposing analysis identifies lonafarnib as respiratory syncytial virus fusion protein inhibitor, Natural communications (2024). DOI: 10.1038/s41467-024-45241-y
Provided by the Zentrum für Experimentelle und Klinische Infektionsforschung
Quote: Drug reuse research offers new hope in fight against RSV (February 9, 2024) retrieved February 9, 2024 from
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