A long wait for drugs to treat COVID-19 may come to a close, if Phase II trials of the drug niclosamide deliver positive results. The repurposed drug, an antihelminth originally used to treat tapeworm infection, was found to show promise in an exploratory study undertaken by Bengaluru-based National Centre for Biological Sciences (NCBS-TIFR) and Institute for Stem Cell Science and Regenerative Medicine (InSTEM) along with Indian Institute of Integrative Medicine (CSIR-IIIM), Jammu.
Based on the recommendations of this preliminary study, the drug is now under “multi-centric, phase-II, randomized, open label clinical study to evaluate efficacy, safety and tolerability of NIclosamide for the treatment of hospitalized Covid-19 patients,” according to a press release of the Council of Scientific and Industrial Research (CSIR) dated July 5. Since the drug has been used in people earlier for tapeworm infection in adults as well as children, its safety profile is well established and the questions are more about its efficacy in treating COVID-19 and the dosage etc.
Among those following the news about the novel coronavirus, it is well known that the spike protein of the receptor binding domain attaches itself to the ACE2 receptor present in the cell. This is a route the virus uses to enter the cell.
There is also another way of entering the cell, especially in cells that do not carry ACE2.
Alternative route
“The stomach and proximal intestinal epithelium have cells that do not carry the ACE2 receptor but also are infected by the virus, and the cell line we are working with may be a surrogate model for such a system,” explains Satyajit Mayor, Director of NCBS-TIFR, who is an author of the study which has been published in PLOS Pathogens.
To enter such cells the spike glycoprotein finds a different pathway using alternative binding proteins on the surface of the cell. These are not yet fully characterised.
“The other pathway is something that we have been involved in uncovering and working on for the past 20 years at NCBS, and therefore we could immediately deploy our knowledge in seeing how we could influence this route,” says Prof. Mayer.
Blocking the virus
To study the path taken by the virus, the group isolated and purified the spike glycoprotein, attached it to a pseudovirus and tagged it with a fluorescent dye. When the virus tries to enter the cell, it is first engulfed in a membranous vesicle. This vesicle provides an environment of low pH (acidic medium) which is necessary for the virus to infect the cell. Thus, a substance that would alter the pH of the environment would block the entry of the virus. This role can be played by, for instance, niclosamide.
“Niclosamide is a drug used for tapeworm treatment. Other worms, such as pinworms and roundworms, are not affected. It is taken orally so can be used right off the shelf if the dosage and efficacy is proved for Covid,” says Varadharajan Sundaramurthy from NCBS-TIFR, a co-author.
The group has used this method to block the real SARS-CoV-2 virus in culture. “As the pandemic started, we established dedicated space in our biosafety level 3 suite for SARS-CoV-2 infection assays and obtained relevant approvals. So, when bafilomycin and niclosamide showed inhibitory effect in pseudovirus assays, we could immediately test them in real SARS-CoV-2 infection assays,” says Dr Sundaramurthy. “We could further extend these results to the gastric AGS cells with and without ACE2.” Interestingly, AGS cells without ACE2 get infected by the real SARS-Cov2 virus but do not seem to show strong cell death.
Clinical trials
The drug is being taken through a clinical trial by CSIR. Ram Viswakarma, former director of CSIR-IIIM, another co-author, said the following in an email to The Hindu: “CSIR New Delhi (through its constituent laboratory CSIR-IICT, Hyderabad) with an Industry partner received DCGI approval for a Phase II clinical trial, which is currently [underway] in multiple hospitals across India. Once the trial is complete, the results will be submitted to the drug regulator.”
“It was a tremendous effort that students and post doctoral fellows from different labs working on totally different projects came together to focus their energies towards a common goal of understanding the basic biological mechanisms of the virus and exploiting this knowledge for drug discovery,” says Prof Mayor.
