In 2003 when there was a serious global outbreak of the SARS Coronavirus, it was discovered that the HIV medicine Kaletra was helpful in getting people with the SARS respiratory distress syndrome to recover from this potentially fatal condition. So how could this work?
Kaletra is a combination drug in the class called protease inhibitors. Recall that viruses use our cells as factories to make more viruses. The HIV virus is made up of four structural proteins. HIV maximizes efficiency when it highjacks our cells. Instead of producing the four structural proteins separately, the four proteins are produced as a single long protein.
Then HIV produces an enzyme called the HIV protease and this enzyme acts like a pair of scissors and cuts the single long protein into the four structural proteins. Those four proteins then become assembled into a new HIV virus that will be released from the cell along with thousands of other new viruses to infect other cells. The drug Kaletra blocks the HIV protease, so the HIV structural proteins don’t get produced and new viruses can’t be assembled.
Coronaviruses, while quite different from HIV (lentiviruses), use a similar strategy producing a single protein that requires a coronavirus protease to release the coronavirus structural proteins. In the lab, we can show the ability of Kaletra to block infections with the new coronavirus.
This new coronavirus that causes COVID-19 is closely related to the SARS coronavirus. There are some studies, mainly in China, that showed Kaletra was helpful in patients with SARS coronavirus. So is there any evidence that Kaletra will work against COVID-19? There seem to be isolated reports of a potential benefit, but nothing is conclusive and the reports are somewhat limited. Time will tell. Studies are ongoing.