*2.2.1 Clinical laboratory*


### *2.2.2 Imaging*

Medical imaging, such as Computed Tomography (CT) and X-ray, plays a significant function in the combat against the pandemic. So, the current AI methods can be used to help medical specialists and strengthen imaging tools. Also, AI could also increase work performance by effective detection of CT and X-ray diseases. The Computer-Aided Diagnosis (CAD) models enable physicians to take correct clinical

#### *Perspective Chapter: Repurposing Natural Products to Target COVID-19 – Molecular Targets... DOI: http://dx.doi.org/10.5772/intechopen.103153*

choices on disease diagnosis, monitoring, and prognosis [22]. Many radiological characteristics are used to categorize the disease and help in discovering the treatment, such as the following:


#### **2.3 Therapy**

Therapeutic interferences can be categorized into four main classes: general treatment, antiviral treatments, particular medications, and other medications.

The effectiveness and safety of COVID-19 have been tested using several drugs, such as chloroquine, remdesivir, favipiravir, and hydroxychloroquine. Some of them had presented antiviral impacts against COVID-19 but no conclusive evidences [27].

Although the serious disease has been related to hyperinflammation induced by COVID-19, the immune responses of acute COVID-19 stay ambiguous. Some researchers comprehensively analyzed circumferential immune troubles in blood for 42 recovered and infected by COVID-19. The activation of various immune strains is recognized, including oligoclonal plasmablast expansion, trafficking receptor modulation on granulocytes, innate lymphocytes, and T cell activation, which separated acute COVID-19 patients or moderate-severe patients from healthy donors or COVID-19-recovered. One of the predictive biomarkers is the ratio between neutrophil and lymphocyte of organ failure and disease gravity. Results appeared wide innate and adaptive leukocyte annoyances that characterize dysregulated have an infection in extreme COVID-19 disease, and medication examination is required. There were no efficacious antiviral medications, even common drugs with strong effect as abidol, ritonavir/lopinavir showed no exceptional impact on clinical progression, virus clearance, or deaths [28].

The meta-analysis of corticosteroid treatment and available observational studies suggested maximized death rates and subaltern contagion rates in influenza, maximized viremia, weakened antibody response, and weakened infection riddance MERS-CoV and SARS-CoV, and corticosteroid treatment complications in recovered patients [29]. Therefore, in the medication of COVID-19, corticosteroids should not be supported or even applied for acute patients.

The plasma of convalescent for severe influenza infection and SARS-CoV medication was proposed to minimize the mortality rate and days number in hospital, particularly after symptom appearance and administered plasma early [30].

As for inoculation, if any cross-reactive epitopes were recognized among COVID-19 and SARS-CoV, the preceding vaccine of SARS-CoV might be reused to expedite the COVID-19 vaccine progression. It is recommended for prophylaxis, streptococcus pneumonia, and influenza vaccination, especially in the elderly [31].

#### **2.4 Drug repurposing and COVID-19**

Drug repurposing is also a quick tool that creates a shortcut to find a safe and effective therapy for this exciting pandemic. It depends on the fact that their safety profile, side effects, posology, and drug interactions are well known [27]. Currently, several FDA-approved drugs are tested for their potential to treat COVID-19 infection such as lopinavir, chloroquine, azithromycin, hydroxychloroquine, favipiravir, umifenovir, ribavirin, remdesivir, and darunavir have been tested in many COVID-19 clinical experiments for hopeful use under emergency protocol. Unfortunately, none of these tested drugs showed a conclusive results and satisfactory outcomes among treated patients. Therefore, several studies used in silico tools for prediction of the ability of drugs to interact with molecular targets important for viral replications.

In that aspect, the liver research laboratory (FAB-Lab, Faculty of Pharmacy, Mansoura University, Mansoura, Egypt) has applied several approaches for not only improving the pharmacological effect of easily accessible natural products, but also identifying new applications for them. Drug repositioning or repurposing may reveal a new approach to rediscover new uses for clinically approved existing old drugs [32]. This book revealed the theory, applications, and/or hazardous outcomes on drug discovery in different disciplines in medicine; e.g. dermatology [33, 34], cancer [35–37], and neurological disorders [38].

A hopeful mechanism to cure COVID-19 patients is the reusing of trusted antiviral treatments in opposition to COVID-19. Viral loads are reduced by employing the antiviral treatments that have risen lung allocations, which is helpful to COVID-19 cases. There are a number of antiviral medications such as [39].

#### *2.4.1 Natural products inhibitors for targeting COVID-19*

Some results depended on molecular docking and network direct pharmacology action on COVID-19, for examples:


*Perspective Chapter: Repurposing Natural Products to Target COVID-19 – Molecular Targets... DOI: http://dx.doi.org/10.5772/intechopen.103153*

infection multiplication. On differentiate, shionone (Asteris Radix et Rhizoma), tussilagone, patchouli alcohol, asarinin, ephedrine hydrochloride, and ergosterol might work on steward cells ACE2 to restrain the attack [43–46].


As previously explained, nonstructural proteins of COVID-19 and several factors and receptors in host cells are essential for viral entry and replication, which means that both should be considered in the process of the development of effective antiviral agents as depicted in **Figure 1**. In this section, we will address known natural products inhibitors to the key targets controlling viral entry and replication.

#### *2.4.1.1 Inhibition of viral invasion process*

#### *2.4.1.1.1 Inhibition of SARS-CoV-2 lipid-dependent attachment to host cells*

Targeting host lipids is an intriguing antiviral strategy. Coronaviruses are a class of viruses with a lipid envelope that requires a plasma membrane fusion process mediated by endocytosis, a mechanism that involves certain cholesterol-rich microdomains and its ACE2 receptor [49] and mediates the early stages of internalization of coronaviruses [50].

Macromolecules such as methyl-β-cyclodextrin have been used to inhibit attachment of coronaviruses to host cells. These nontoxic macromolecules mimic attack sites for the enveloped virus, competing with host cell attack sites. It could also decrease ACE2 expression in the cell membrane, thereby reducing the infectivity of coronaviruses, such as SARS-CoV-2 [51].

Natural compounds including phytosterols and triterpenes (**Figure 2**) can exert the same action. For example, betulinic acid also has the same lipophilic properties as cholesterol, so it may therefore compete with cholesterol, replacing it in plasma membranes, or it may bind to the virus instead of raft cholesterol, acting as a soluble competitor [52].

#### *2.4.1.1.2 Blocking the viral entry process by inhibiting TMPRSS2 activity*

TMPRSS2, a human cell surface serine protease, results in membrane fusion. ACE2 and TMPRSS2 are essential in airway cells for SARS-CoV-2 infection [53].

#### **Figure 1.**

*Different approaches for targeting viral entry and replication of the COVID-19. (1) Inhibition of S protein binding to ACE2, (2) disruption of endocytic pathways, (3) inhibition of nuclear translocation of viral RNA and protein by host cell mediators, (4) inhibition of the proteolysis of viral polyprotein to the nonstructural proteins (Nsp), (5) inhibition of transcription and replication of viral RNA.*

#### **Figure 2.**

*Chemical structures of the most common phytosterols. They are considered as potential inhibitors of SARS-CoV-2 lipid-dependent attachment to host cells, a possible approach for decreasing its infectivity.*

ACE2 inhibition should not be tracked as a treatment strategy as ACE inhibitors upregulate the expression of ACE receptors providing more binding sites for SARS-CoV-2. On the other hand, blocking TMPRSS2 is accessible and will prevent the fusion of the envelope of the virus with host cell surface membranes. Nafamostat, an existing safe drug used for pancreatitis, may inhibit SARS-CoV-2 entry by inhibiting TMPRSS2 activity.

*Perspective Chapter: Repurposing Natural Products to Target COVID-19 – Molecular Targets... DOI: http://dx.doi.org/10.5772/intechopen.103153*

In this context, several reported serine protease inhibitors from nature could be repurposed to target TMPRSS2.

Potent serine protease inhibitors have been reported from filamentous marine cyanobacteria. Most of these molecules are 3-amino-6 hydroxy-piperidone (AHPcontaining cyclic depsipeptides). The AHP moiety is crucial for serine protease inhibitory activity, and any structural or conformational variations to this unit will affect activity (**Figure 3**) [54].

#### *2.4.1.1.3 Inhibition of endocytic pathway.*

#### *2.4.1.1.3.1 Increase of the endosomal and lysosomal pH using lysosomotropism agents*

It's now well established that endocytosis is the nick bottle for COVID-19 entry to the host cells, thus inhibiting this pathway could reduce the infectivity of the virus dramatically. This could be achieved by increasing of the endosomal and lysosomal pH using lysosomotropism agents, which disrupt the proteolytic action of host cell proteases, which work optimally in acidic pH and prevent the cleavage of the S Protein of the virus [55]. While chloroquine (CQ ) and its derivative are developed originally for treatment of malaria, but since they demonstrated potent activity by direct acting on the virus and by preventing its endocytosis, they were repurposed for treatment of several viral infection and currently used widely used in therapeutic protocol for treatment of COVID-19 [56]. Bafilomycin A1, a vacuolar-type H+−ATPase inhibitor, lies in the same category and could explain the use of azithromycin, a structurally related macrolide antibiotic for treatment of COVID-19 patients [57].

#### *2.4.1.1.3.2 Cathepsins inhibitors*

Inhibition of cysteine proteases such as cathepsins could be an important approach due to their role in viral entry, and luckily the incorporation of these protein in the pathogenesis of several diseases such as cancer, metabolic conditions, and Alzheimer's has led to the discovery and development of several inhibitors that could be repurposed for treatment of COVID-19 infection. E-64, a compound isolated from the fungus *Aspergillus japonicus*, can bind irreversibly to this target without showing

#### **Figure 3.**

*Serine protease inhibitors isolated from marine cyanobacteria. Potential blockers for the requisite viral entry process (inhibition of the S protein-initiated membrane fusion by inhibiting TMPRSS2 activity).*

toxic activity; also gallinamide A and Miraziridine A marine natural products were reported to possess the same activity. There are a number of natural compounds that possess a promising cathepsins inhibition with IC50 range from 2 to 10 micromolar, such as panduratin A, guttiferone A, ursolic acid, and agathisflavone [58].

#### *2.4.1.1.3.3 Clathrin-mediated endocytosis (CME) pathway blockage*

As addressed earlier, CME is one of the main mechanisms for viral entry; hence, its inhibition could be a reliable method for control of the infection. Ouabain and bufalin cardiotonic steroids, which are used for treatment of cardiovascular diseases, have demonstrated antiviral activity against MERS-CoV infection at nanomolar concentrations by affecting the CME pathway [59]. This is consistent with recent report by Jeon et al., where ouabain, lanatoside C, and digitoxin were able to reduce viral viability of COVID-19 in micromolar concentrations [60].

Bolinaquinone, a sesquiterpenoid derivative with quinone ring, isolated from marine *Dysidea* sp., which is known to possess anti-inflammatory activity, however, affinity chromatography coupled with mass spectrometry revealed the ability of this molecule to inhibit clathrin in a concentration comparable to chlorpromazine, a wellknown inhibitor of this target [61]. Also, ikarugamycin, an antibiotic that was found to specifically inhibit CEM effectively [62].

#### *2.4.1.1.4 Inhibition of translocation mechanisms*

Like other viruses, COVID-19 uses the replication machinery of the host cell for transcription and replication of Viral RNA; this means that viral materials such as nonstructural proteins and negative-strand RNA should be relocated to the nucleus and endoplasmic reticulum.

### *2.4.1.1.4.1 Importin (IMP) α/β1 heterodimer inhibition*

Interestingly, ivermectin, an antiparasitic FDA-approved drug, has been reported to inhibit nuclear transport in host cells such as (IMP) α/β1 heterodimer preventing the translocation of viral DNA integrase in HIV-1 and other viruses. Recently, ivermectin has shown potent antiviral activity against COVID-19 [63]. In fact, such effect was linked to the broad-spectrum antiviral activity of this molecule [64].
