Protease Inhibitors: Strategy to Disrupt COVID 19 Contagion


 Background:

The COVID 2019 (Corona Virus Disease) has been currently going pandemic as per WHO (World Health Organisation) situation reports. The major differentiating point in this virus is the presence of a unique furin cleavage site. Our insilico study points out to the effectiveness of a potent plant origin furin inhibitor. We exploited the aspect of the cleavage machinery of furin which is critical and indispensible for the entry of SARS-CoV-2 (Severe Acute Respiratory Syndrome –Corona Virus 2) in human cells and subsequent massive contagion. Most of the drugs are presently targeting ACEII (Angiotensin Converting Enzyme 2) receptor. But these options have injurious effects in diabetics and cardiac patients. Repurposing of old drugs are the current undergoing therapeutic measures as per the EUA (Emergency Usage Administration) of Food and Drug Administration. These aspects could be avoided if we develop a better and safer strategized drug .
Methods

In silico analysis of plant based protein analogs to inhibit furin protein.
Results

Significant interactions of proposed analogs of protease inhibitor of plant origin against furin protein. Furin inhibitors would be incredible drug targets against cancers, MERS CoV (Middle East Respiratory Syndrome) and most urgently SARS- CoV-2.
Conclusion

We report the first of its kind of furin inhibitor and believe that this major finding would fast track arenas for drug trials.


Methods
In silico analysis of plant based protein analogs to inhibit furin protein.

Results
Signi cant interactions of proposed analogs of protease inhibitor of plant origin against furin protein.
Furin inhibitors would be incredible drug targets against cancers, MERS CoV (Middle East Respiratory Syndrome) and most urgently SARS-CoV-2.

Conclusion
We report the rst of its kind of furin inhibitor and believe that this major nding would fast track arenas for drug trials.

Background:
The COVID 2019 outbreak gained a status of "Public Health Emergency of International Concern" on 30th January, 2020. 1 The novel corona virus was found in unknown causes of pneumonia in China in late 2019 and on 11th February, 2020 the World Health Organisation (WHO) named it as Corona virus disease . 2 Eventually, due to the aggressive and massive increase in the number of cases (118,000) spreading across 110 countries and territories around the world, the WHO declared it as a pandemic on 11th March, 2020.The present status of the pandemic can be tracked in real time through the following website (https://www.who.int/emergencies.arcgis.com/experience). 3 Till date, there are 6,38,146 con rmed cases and 30,105 deaths globally ( Data as reported by national authorities by 16:00 CET, 29th March, 2020). This has triggered a lot of research trials related to vaccine development and possible therapeutic measures to combat the disease.
It was in the year 1966 that coronaviruses were morphologically described as spherical having a core shell and surface projections all over. 4 The term "corona" in Latin means "crown". They are categorised into alpha, beta gamma and delta subfamilies. Of these, alpha and beta coronaviruses are of mammalian origin (bats) while gamma and delta have pig and bird origins respectively. SARS CoV-2 belongs to beta-coronaviruses and is a novel relative of SARS CoV classic virus. 5,6 It is also reported to have 96% similarity to bat coronavirus genome. 6 The main structural genes of this novel corona virus are N (nucleocapsid protein), S (spike protein), SM (a small membrane protein), and the (M) membrane glycoprotein. 7 Zhu et al and Wu et al, 2020, published the sequence of the viral genome. 8,9 There has been pandemic episodes in 2003 and 2011 from two other coronaviruses namely (Severe Acute Respiratory syndrome) SARS and MERS (Middle East Respiratory Syndrome) originating in China and Saudi Arabia respectively. 10,11 SARS-CoV-2 is the seventh discovered coronaviruses in humans. 8 The pathogenicity of any virus would largely depend on its mode of entry and sustainability in the host cell. Racaniello, 2020 has elaborated in his virology blog about the novelty in the spike glycoprotein of the virus SARS-CoV-2. He explained the major differences in the behaviour of spike glycoprotein (S) in the SARS-CoV-2 and SARS classic. The furin proteases can potentially cleave the spike protein of the novel coronavirus due the presence of a cleavage site (PRRARS|V).This character varies among the coronaviruses and is also a vital factor for the virus to jump to other species. 12 The most similar bat coronavirus based on sequence homology does not have this cleavage site. It has been being assumed that this "gain of function" in SARS classic helped it to jump into humans from the wildlife market in China.
The pandemic nature of SARS-CoV-2 is due to its ability to bind to ever present furin in many tissues of humans.
Much of the research focus is on the mechanism of cleavage of the spike protein of SARS-CoV-2, its fusion with ACE2 (human angiotensin-converting enzyme 2) receptor in human cells and its entry. Hypothetically, this cleavage is mediated by furin protease. In SARS classic the cleavage occurs with much more di culty. 13 than SARS-CoV-2 whereas SARS classic also uses the ACE2 receptor for its entry. 14 The cellular receptor of MERS coronavirus is dipeptidyl peptidase 4 (DPP4). 15 In the present study, we propose a furin inhibitor through in silico approaches from plant origin which could be a promising therapeutic aspect to disrupt the cleavage of S glycoprotein and hence block its entry into the human cell. Methodology:

Results:
The following computational approaches and bioinformatics tools have been used throughout the study. To measure the effectiveness of receptor and ligand interaction. Discussion: The current study has focussed to nd out a natural protease inhibitor to block the action of furin. In SARS-CoV-2 the furin enzyme plays a key role to cleave the spike glycoprotein which is the rst step to initiate an infection. It is noteworthy to mention that the S glycoprotein is an attractive target for vaccination trials as it projects out on the surface of SARS-CoV-2. 16 Studies have also mentioned that SARS-CoV-2 has a furin cleavage site at the junction of subunits S1 and S2. 17,18,19 The spike protein is made up of two subunits S1 and S2 which have distinct functions. The S1 subunit has the receptor binding machinery and binds to ACE2 receptor in the human cells and helps to stabilize the prefusion stage of the membrane connected to S2 subunit which has the fusion machinery between the viral and cellular membrane. 16 This gives us a clear insight that furin could also be a very important drug or a vaccine target to disrupt the binding and fusion machinery required by coronaviruses.
A correspondence was published saying that the coronaviruses donot survive long on surfaces such as steel, plastic etc but need potential hosts to sustain. 20 This fusion mechanism of SARS-CoV-2 is common to MERS also. 17 Other studies have targeted the ACE2 receptor. 21,22 Xia et al, 2020 have designed furin inhibitors for SARS CoV as well as MERS CoV. 14 However, still a very critical point lies in using ACE2 inhibitors as vaccine or drug targets. It was observed that ACE2 receptor targets are those which have been used in treatments for diabetics, heart disease etc. 23,24 Additionally, ACE2 receptors are present in intestine, kidney, oral mucosa and heart endothelium. 21,24 Eventually, overexpression of ACE receptors result due to administration of ACE inhibitors as reported in rat model experiments. 25,26 As the entry of SARS-Co-2 is mediated by ACE 2 receptor, people undergoing drug therapies for diabetics, hypertension etc would be more susceptible to SARS-CoV-2 as they would be inherently overexpressing ACE2 receptors. 23 This might be the most valid reason why diabetic and heart patients are at larger risk for SARS-Cov-2. 27 Thus, it is the most urgent need to develop a safer and effective therapy. It is noteworthy to mention that besides being anticipated targets for SARS-CoV-2, furin inhibitors have had excellent results in cancer therapy. This matter is beyond the scope of this paper but it clearly exhibits the multipotent therapeutic aspect of a furin inhibitor. Furin was found to overexpress in different cancer cells and its role in cancer related proprotein proteases. 28 Contour et al has enlisted a summary of patent applications in furin inhibitors. 29 Millet and Whittaker 2014, observed that high levels of MERS CoV infection had a correlation with overexpression with furin. 17 They mentioned that MERS CoV entry could be blocked through siRNA silencing.

Conclusion:
Thus it is worth believing that furin inhibitors would be incredible drug targets against cancers, MERS Co V and most urgently SARS-CoV-2. Our study is limited to insilico approaches. Henceforth it is anticipated that puri ed plant protein of analogs that we reported would fast track validation of our ndings.