A cancer drug developed to kill tumours could also cure patients hit by Covid-19, researchers say .
Pralatrexate, which is sold under the brand name Folotyn, has been found in lab tests to outperform the current anti-viral drug given to seriously ill patients, remdesivir.
Scientists are now hoping to turn it into a nasal spray for coronavirus patients if side effects of vomiting and fatigue can be solved.
Study lead author Dr Haiping Zhang, of the Shenzhen Institutes of Advanced Technology, said: "Our study discovered it is able to potently inhibit SARS-CoV-2 replication.
"It was stronger than remdesivir within the same experimental conditions."
The study, published in the journal PLOS Computational Biology, offers hope of reformulating it into a nasal spray.
Remdesivir was the first major pharmacalogical breakthrough of the pandemic – speeding up recovery and boosting survival chances.
When someone is infected with SARS-CoV-2 – the virus that causes Covid-19 – a spike-shaped protein attaches to a human cell and then inserts its genetic material.
Pralatrexate acts as a receptor – trapping the virus as it harmlessly degrades.
Experiments on human cells found it worked by homing in on a viral protein known as RdRP – and was more effective than remdesivir.
The Chinese team identified pralatrexate's powers after using artificial intelligence, or machine learning, to screen 1,906 existing drugs.
Dr Zhang said developing new medications is too time consuming to meet the urgent need.
He explained: "Given current emergencies, repurposing approved drugs for Covid-19 may provide a shortcut. They can be immediately tested in clinical trials.
"These findings suggest pralatrexate could potentially be repurposed to treat Covid-19.
"However, this chemotherapy drug can prompt significant side effects and is used for people with terminal lymphoma."
It was approved by the US Food and Drug Administration in 2009 for patients with terminal disease – in spite of its toxicity.
Dr Zhang said: "Therefore, we should be aware it does not guarantee the possibility of immediate use of the drug against Covid-19."
The nose is a main entry point of the disease. Dissolving pralatrexate may offer hope of a nasal spray if side effects can be overcome. They include vomiting and fatigue.
Dr Zhang said: "No effective drug or vaccine is readily available. This work demonstrates the feasibility of accurate virtual drug screening and provides potential therapeutic agents."
It also supports the use of the new strategy to identify drugs that could be repurposed.
Dr Zhang added: "We have demonstrated the value of our novel hybrid approach that combines deep-learning technologies with more traditional simulations of molecular dynamics."
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