The Covid-19 pandemic continues to claim lives around the world and the first vaccine candidates are not expected to be available until 2021 at the earliest.
In the meantime, research on treatments continues to mobilize scientists. In this dynamic, our team has just published in the journal Cell Reports Medicine of promising preclinical results on the combination of remdesivir with a repositioned drug: diltiazem.
An innovative method of research into antiviral treatments
In our laboratory, for several years we have been pursuing a strategy of repositioning drugs already on the market for new therapeutic indications, in particular anti-infectious.
A technical term for a simple reality: a drug is authorized to be marketed for a given medical indication, the idea is to test it, and if necessary reposition it, for the treatment of other pathologies.
You probably know the story of the famous blue pill. Viagra was not originally intended for its current use at all. Pfizer actually intended the molecule (Sildenafil citrate, known for its ability to dilate blood vessels) for the treatment of angina pectoris. In clinical trials, the molecule has been shown to be insufficiently effective in treating this pathology, and unexpected and, to say the least surprising, side effects have been observed. It is therefore based on a fortuitous observation during its clinical development that the molecule has been repositioned for a new therapeutic indication.
In order not to be dependent on the chance discovery of unpredictable effects, we have developed and validated in the laboratory a rational and rationalized scientific screening strategy in silico medication. This strategy is based on the characterization by high throughput sequencing and on the analysis via artificial intelligence tools of chemogenomic and virogenomic signatures, which in a way constitute the cellular fingerprints left by drugs and pathogens, respectively.
Once selected, candidates with high potential for repositioning are evaluated for their supposed anti-infectious property in different preclinical models of infection in vitro (cell lines, human respiratory epithelium reconstituted and cultured in air / liquid interface) and in vivo (animals). Drug repositioning has major advantages over conventional molecule development de novo, in particular that of considerably reducing the duration and costs of development until the marketing authorization for the new indication on the market, but also of being able to respond in a very reactive manner, by drawing on the existing pharmacopoeia, when we are faced with the emergence of a new pathogen against which there is no treatment or vaccine.
Remdesivir is an example of a repositioned drug: a molecule initially in development to fight the Ebola virus, and for which it has been shown to antiviral activity against SARS-CoV-2 (Covid-19 virus) in several preclinical models and a potential to accelerate healing time in hospitalized patients. The clinical results, still incomplete, support the use of remdesivir to treat Covid-19, but, only it is not efficient to decrease the death rate in patients with severe form of the pathology.
A new paradigm: “polypharmacology”
Until recently, the major paradigm in pharmacology was to think that a molecule is associated specifically with a given therapeutic target. Our repositioning strategy is based on a new paradigm, that of “polypharmacology”: a chemical molecule would thus have between 6 and 13 different cell targets ; These are called the “off target” effects of drugs which result in side effects.
Our approach to repositioning drugs for new antiviral therapeutic indications therefore relies on targeting host cells, on which viruses are entirely dependent for their replication, rather than viral determinants, which are constantly mutating as they occur. These are in particular RNA viruses and in particular respiratory viruses such as influenza viruses or coronaviruses.
This strategy may not only reduce the risk of developing viral resistance, but also achieve broad-spectrum antiviral effects. One of our goals is also to be able to combine these repositioned drugs that target respiratory epithelial cells (virus factories), with conventional antivirals to potentiate their effect. A first proof of concept was done on influenza viruses with the identification and repositioning of diltiazem, a drug on the market for its anti-hypertensive properties, as an influenza virus inhibitor in several preclinical models.
Our technological approach has also enabled us to identify its previously unknown mode of action, that of stimulating the innate immune response of the mucous membranes. A phase 2 clinical trial randomized double-blind has been conducted for 3 winters and aims to evaluate the combination Diltiazem + oseltamivir (Tamiflu) in the management of patients with severe influenza in intensive care.
Promising results against SARS-CoV-2
As part of the national consortium REACTing coordinated by Inserm, our team isolated in February several clinical strains of the SARS-CoV-2 virus and developed protocols for viral quantification by molecular biology and infectious titration in cell culture.
To test the therapeutic efficacy of candidate molecules against SARS-CoV-2, we have also implemented and characterized models of infections in vitro, and in particular based on reconstituted human respiratory epithelia of nasal, bronchial and alveolar origin. . Composed of different primary epithelial cells (ciliate, mucus-secreting, Clara cell, basal), organized into tissues, these models are very physiological and predictive, as described in the study recently published in the journal Nature on theineffectiveness of hydroxychloroquine in a model of a non-human primate.
We have evaluated a large number of candidate molecules in these models, including two molecules of interest: remdesivir and diltiazem, as monotherapy and in combination. The results of this study show a significant reduction in viral load in epithelia infected with SARS-CoV-2 when treated with remdesivir. This effect is enhanced when diltiazem is added in combination. By stimulating the innate immune response of the epithelia, diltiazem thus potentiates the effect of remdesivir and offers the opportunity to reduce doses in humans. This molecule does indeed exhibit some toxicity in vivo in addition to being a very expensive drug.
Towards a clinical trial
Our team is continuing its preclinical trials with this dual therapy in animal models and we hope to be able to launch a clinical trial as early as next winter if the positive results are confirmed. Other repositioned drug combinations are also being explored.