Deciphering the antiviral potential of tomatidine towards mosquito-borne viral infections

Mosquito-borne viruses have rapidly spread around the world, causing millions of clinically apparent infections with various symptoms from rashes and high fever to joint pain that can persist for years. The most common mosquito-borne virus is dengue virus, which causes an estimated 390 million infections each year. To date, there is no specific antiviral compound available to treat these viral diseases. Hence, there is a strong need for the identification and development of new treatment options towards these viruses. In this thesis, we investigated the antiviral potential of tomatidine, a natural compound found in the unripe green tomatoes, towards the mosquito-borne viruses dengue virus, zika virus, west nile virus and chikungunya virus as well as the underlying mode of action. Our work shows that tomatidine is able to reduce the infection of dengue and chikungunya virus in different human cell lines. Moreover, we found a significant but less potent antiviral activity of tomatidine towards zika virus but not towards west nile virus. Regarding the mode of action by which tomatidine exerts its antiviral activity, we found that tomatidine inhibits viral infection by interfering with the production of viral RNA and/or viral proteins which are required for the formation of new virus particles. The exact mechanism by which tomatidine exerts its antiviral activity still remains to be elucidated. Extensive pre-clinical and pharmacokinetic studies are still needed to further evaluate the potential of tomatidine as an antiviral compound in the future

Tomatidine reduces chikungunya virus progeny release by controlling viral protein expression

Author summaryChikungunya fever is a debilitating disease caused by the mosquito-borne Chikungunya virus. Over the past two decades the geographical spread of the virus and its mosquito vector has drastically increased thereby causing millions of infections. To date there is no antiviral drug and no vaccine available to treat/prevent Chikungunya virus infection. We recently showed that the natural steroidal alkaloid tomatidine has potent antiviral activity towards Chikungunya virus at submicromolar concentrations. In this study we dissected how tomatidine reduces the production of Chikungunya virus particles. We show that tomatidine lowers viral protein expression and we hypothesize that the effect of tomatidine on viral protein translation hampers the production of progeny viral RNA copies / number of infected cells thereby leading to a reduced production of secreted virus particles. Also, we show that Chikungunya virus does not readily become resistant to tomatidine. Collectively, we deciphered the mechanism by which tomatidine exerts antiviral activity to Chikungunya virus and our results strengthen the potential of tomatidine as an antiviral treatment strategy towards Chikungunya virus.Tomatidine, a natural steroidal alkaloid from unripe green tomatoes has been shown to exhibit many health benefits. We recently provided in vitro evidence that tomatidine reduces the infectivity of Dengue virus (DENV) and Chikungunya virus (CHIKV), two medically important arthropod-borne human infections for which no treatment options are available. We observed a potent antiviral effect with EC50 values of 0.82 mu M for DENV-2 and 1.3 mu M for CHIKV-LR. In this study, we investigated how tomatidine controls CHIKV infectivity. Using mass spectrometry, we identified that tomatidine induces the expression of p62, CD98, metallothionein and thioredoxin-related transmembrane protein 2 in Huh7 cells. The hits p62 and CD98 were validated, yet subsequent analysis revealed that they are not responsible for the observed antiviral effect. In parallel, we sought to identify at which step of the virus replication cycle tomatidine controls virus infectivity. A strong antiviral effect was seen when in vitro transcribed CHIKV RNA was transfected into Huh7 cells treated with tomatidine, thereby excluding a role for tomatidine during CHIKV cell entry. Subsequent determination of the number of intracellular viral RNA copies and viral protein expression levels during natural infection revealed that tomatidine reduces the RNA copy number and viral protein expression levels in infected cells. Once cells are infected, tomatidine is not able to interfere with active RNA replication yet it can reduce viral protein expression. Collectively, the results delineate that tomatidine controls viral protein expression to exert its antiviral activity. Lastly, sequential passaging of CHIKV in presence of tomatidine did not lead to viral resistance. Collectively, these results further emphasize the potential of tomatidine as an antiviral treatment towards CHIKV infection.Molecular basis of virus replication, viral pathogenesis and antiviral strategie