The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has cost over 2.2 million lives, among the more than 103 million cases. The only definitive control method is the production of herd immunity via vaccination, and the earliest vaccines to receive emergency use approval are now being rolled out. However, many public health authorities project a gap of more than one year before global vaccination can be achieved.
The need for repurposing
During this period, safe and inexpensive drugs that can effectively counter the virus's replication continue to be a necessity. The cumbersome and expensive drug development process can be bypassed by repurposing drugs already approved for other indications, by the Food and Drug Administration (FDA) and the European Medicines Agency (EMA), for instance, as these drugs have already passed safety and toxicity tests.
A new study by researchers at the University of Manchester, UK, reports on the compounds of interest that were identified as having potential for the treatment of COVID-19, from a library of almost 2,000 compounds from the APExBIO DiscoveryProbe library. Their findings have been released on the bioRxiv* preprint server.
Traceable viral particles
Earlier, the researchers developed a technique to measure collagen synthesis using the versatile and powerful gene editor, CRISPR-Cas9, to achieve the insertion of the Nanoluciferase (NLuc) encoding gene into the Col1a2 gene in fibroblasts. This was modified to label the SARS-CoV-2 with NLuc, replacing the Orf7a gene.
The NLuc-tagged virus was structurally identical from the wildtype virus, and both were alike observable within the endosomes of infected cells.
Since NLuc generates bioluminescence in the presence of the enzyme-substrate coelenterazine, it was used as a reporter enzyme to detect the virus's presence in culture. This allows virus replication and cell number to be identified at 72 hours from infection, with close correlation to plaque-forming assays.
Validation and drug screening
After validating the NLuc-tagged virus system for drug effect quantification during viral replication, the labeled virus was then used to screen the compound library in an array of human cell types.
This helped understand the susceptibility of each cell type to infection by the virus, and its ability to support viral replication.
Cell types that support replication
The study shows that many human cell types allow infection with SARS-CoV-2, including lung fibroblasts and epithelial cells. However, all did not allow the virus to replicate.
The researchers found that liver and renal epithelial cells allowed viral replication most efficiently, relative to fibroblasts and lung epithelial cells. This may explain the incidence of liver abnormalities in COVID-19, including abnormal liver enzymes. Also, COVID-19 is more common in patients, especially African Americans, with chronic liver disease.
Acute renal injury associated with proteinuria is also common in COVID-19 patients and is linked to increased morbidity and mortality. The current findings may indicate that such injury is due to direct viral invasion and replication within renal epithelial cells.
Drugs that inhibit replication
The drug screen showed that 35 compounds, including some anti-tumor and antiviral drugs, as well as antimalarials, and antimicrobials, suppressed SARS-CoV-2 infection and replication, such as LY2835219 and Panobinostat. Antihypertensives such as manidipine, and antimicrobials like atovaquone and amodiaquine also showed equivalent inhibition. So did some drugs already being studied for the treatment of this infection.
Since the screen showed inhibition as a result of pretreatment of cells subsequently exposed to the viral challenge, the researchers then repeated the screen with the 35 inhibitors identified, 24 hours after infecting the cells. This showed that viral replication continued unchanged, in most cases, but nine of the compounds inhibited replication of the SARS-CoV-2 virus post-.
The nine compounds are listed here as Panobinostat, LY2835219, Manidipine and Manidipine 2 HCl, ebastine, atovaquone, bedaquiline, vitamin D3 and amodiaquine.
Panobinostat inhibits DNA replication, and produced a completely inhibitory effect on viral replication at all tested doses given before infection, but not after. This could be associated with the ability of this drug to suppress the expression of angiotensin-converting enzyme 2 (ACE2), the host cell receptor for viral binding.
The other drugs have various inhibition mechanisms, ranging from competitive inhibition of the mitochondrial electron transport chain for atovaquone, to the viral main protease inhibitor bedaquiline.
However, manidipine is a calcium channel blocker, while ebastine is an antihistamine, and vitamin D3 a supplement. Their efficacy in suppressing the virus's replication remains a mysterious function of these diverse compounds, but since they are safe and easily available, further evaluation is indicated.
Vitamin D3 receptor is a nuclear hormone receptor and essential for lipid metabolism in the liver, but could also engage vitamin D to regulate liver metabolism, immune responses, and possibly inflammation, fibrosis and cell proliferation.
Finally, the screen showed that some drugs, like aliskiren and lithocholic acid, actually increased viral replication in cells. Aliskiren is a powerful inhibitor of renin, and thus may potentially participate in the virus-driven imbalance of the renin-aldosterone system that enhances viral infection.
What are the implications?
Repurposing of safe, well-tolerated FDA-approved drugs that inhibit SARS-CoV-2 replication is an attractive strategy to reduce the risk of COVID-19 infection prior to receiving an effective vaccine."
In this very early study, the effective doses of these FDA-approved inhibitory compounds against the virus were found, indicating that they can reduce viral replication after infection. These compounds should be studied further to identify their place in managing COVID-19 patients.
Moreover, the study shows, interestingly, that some medications in use today may actually increase the susceptibility of the cells to infection.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.