20 Drugs Evaluated for Repurpose Against COVID-19 in Preclinical Testing

Virologists have taken approved, marketed drugs from in-vitro screening for potential repurposing against SARS-CoV-2, through in-vivo testing in an animal model surrogate of COVID-19, according to a new, pre-print report in bioRxiv.

Matthew Frieman, PhD, Department of Microbiology and Immunology, University of Maryland School of Medicine and colleagues identified 20 drugs as priority candidates from previous screening, for in-vitro testing of their capacity to inhibit SARS-CoV-2 cell entry at concentrations that were not, themselves, cytotoxic.

"We prioritized testing these for antiviral activity against SARS-CoV-2 since they displayed broad-spectrum antiviral activity," Frieman and colleagues explained.

Seventeen of the 20 were found to be viable candidates, and 7 were further tested to confirm their capability to inhibit infectious SARS-CoV-2 production. These included hydroxychloroquine and chloroquine, and the related amodiaquine hydrochloride, amodiaquine dihydrochloride dihydrate, and mefloquine. They were chosen, investigators commented, "because chloroquine has garnered much interest as a potential treatment for COVID-19, and the others are similarly used as anti-malarial compounds."

The 2 other agents subjected to the additional screening were imatinib and chlorpromazine. Frieman and colleagues explained that imatinib has previously been demonstrated to inhibit both SARS-CoV and MERS-CoV, as well as infectious bronchitis virus entry to cells. Chlorpromazine has been found to inhibit clathrin function in cells, and so the researchers posit it might disrupt infection by many viruses that require clathrin-mediated endocytosis.

Frieman and colleagues then selected 2 of the 7 agents, chloroquine and chlorpromazine, to test for efficacy in-vivo. The challenge was how to proceed with that next stage of testing.

"There is currently a lack of an established mouse model for SARS-CoV-2," investigators wrote, "so we used the mouse adapted SARS-CoV strain (cause of 2003 epidemic) as a surrogate to assesses the in-vivo efficacy of these drugs against a closely related coronavirus."

Frieman and colleagues utilized a well-established mouse adapted system for SARS-CoV (MA15 in BALB/c mice). Each drug was administered prior to introduction of the SARS-CoV virus, to ascertain whether it offered any prophylactic effect.

The researchers rationalized the "repurposing" of the animal model from the SARS-CoV strain to test whether a drug might be repurposed against the novel coronavirus, since both viruses use ACE2 as a receptor, and therefore have similar cellular tropism which could be susceptible to inhibition.

In contrast to the in-vitro results, however, neither chloroquine or chlorpromazine were found to inhibit viral replication in mouse lungs. The viral titer was equivalent between drug treated and vehicle control mice. There did appear to be clinical benefit, however, as both drugs were associated with a reduction in the weight loss that occurs in untreated, infected mice.

Mice infected with MA15 without drug treatment lost approximately 15% of their baseline body weight over 4 days, and had other clinical signs of disease including ruffled fur, labored breathing and lethargy. Subsequent examination demonstrated significant inflammation and denuding bronchiolitis, suggesting severe disease.

Mice receiving the higher test doses of either chloroquine or chlorpromazine showed markedly reduced weight loss and less inflammation in the lungs.

"We have demonstrated that...chloroquine and chlorpromazine can protect mice from severe clinical disease from SARS-CoV," Frieman and colleagues concluded. "Future research will be aimed at testing these compounds in SARS-CoV-2 animal models to further assess their potential utility for human treatment."