Therapeutic options in coronavirus treatment

Abstract

This chapter details the various therapeutic options available for the treatment of the novel coronavirus, SARS-CoV-2, that has brought the world to a standstill. As at 3.53 CEST, June 28, 2020, WHO reported 9,843,073 confirmed cases of COVID-19, with a death toll of 495,760. The rate of the spread of this disease is alarming posing serious threat to the world healthcare system. Clinical investigations and research are on the way for the development of vaccines or antiviral drugs. Despite this effort, no medication has been found to be very effective for its treatment. In this chapter, emphasis was laid on the need for repurposing of antiviral drugs to combat COVID-19 along with other alternatives such as convalescent plasma therapy and exploitation of drugs from medicinal plants and other natural resources.

6.1. Introduction

Pandemics and epidemics have repeated itself several times in the history of human civilization causing a huge toll of life, of which novel coronavirus disease 2019 (nCOVID-19) needs a special mention due to the severe damage caused by it to human population. It is a threat that has put the entire world to a turmoil. Bats and pangolins are proposed to be its possible biotic reservoir. The extreme contagiousness of the virus promotes its rapid spread and continuous evolution in human population [1].

Coronavirus (CoV) is a member of the enveloped, single-stranded, positive-sense RNA viruses. It was first reported in humans in the mid-1960s mostly causing respiratory tract infection [2]. In the 21st century, three coronaviruses—the severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)—have been a global threat to human health.

SARS-CoV-2 which causes COVID-19 is the product of natural evolution [3]. COVID-19 was reported for the first time on December 27, 2019 at Wuhan hospital, China. Till mid 2020, no vaccine has been reported for the management of the infection, but some treatment options based on previous experiences of viral threats have been proposed for COVID-19.

The RNA genome of SARS-CoV-2 contains a 5′-methyl-guanosine cap, poly (A)-tail, and 29,903 nucleotides according to WH-Human 1 coronavirus. It is classified as a beta-coronavirus (βCoV) (lineage B) and is the seventh coronavirus to infect humans, following 2 αCoV (HCoV-229E and HKU-NL63) and 4 βCoV (HCoV-OC43 [lineage A], HCoV-HKU1 [lineage A]), whereas SARS-CoV and MERS-CoV belong to lineage B and lineage C, respectively [1]. This chapter is an attempt to highlight the initial treatment pattern and strategies to combat COVID-19 . The chapter elaborates the transmission of SARS-CoV and various drugs which acted as initial resort for the treatment of the disease.

6.2. Novel coronavirus 2019

Coronaviruses belong to the Coronaviridae family and the order Nidovirales. They have the capacity of infecting a wide range of hosts namely birds, wild, and domesticated animal species [4]. These viruses have the capability of rapid mutation, alteration of tissue tropism, crossing of species barrier, and adapting to different epidemiological conditions [5]. Coronaviruses are the causal agent of gastrointestinal tract and respiratory infections and are represented by four genera, namely, alpha-CoV, beta-CoV, gamma-CoV, and delta-CoV. Among them, alpha- and beta-coronaviruses are known to infect mammals, gamma-coronavirus infect avians, and delta-coronavirus infects both mammals and avians. Representatives of alpha-coronavirus comprise of HCoV-NL63, TGEV, porcine epidemic diarrhea virus (PEDV), and PRCV, whereas SARS-CoV, MERS-CoV, bat coronavirus HKU4, MHV, BCoV, and human coronavirus OC43 belong to the group of beta-coronavirus. The bronchitis CoV (IBV) and porcine delta CoV (PdCV) falls in the group of delta-coronaviruses [6]. Among all the coronavirus variants, the SARS-CoV and MERS CoV have posed serious public health concerns due to their zoonotic emergence and the ability to cross species barrier, resulting in high pathogenicity and mortality in humans [5]. SARS-CoV-2 is a positive-sense RNA virus that performs its replication through multi-subunit replication/transcription complex composed of nonstructural proteins (NSPs). The NSP12 is the catalytic subunit and forms the core of the complex which is composed of an RNA-dependent RNA polymerase (RdRp). It requires accessory factors such as NSP7 and NSP8 for its full activity [7]. The coronaviruses possess the largest genomes among all RNA viruses with G + C content varying for 32%–43% [8]. The genome of coronavirus ranges from 26,000 bases to 32,000 bases and includes 6–11 open reading frame (ORF). The first ORF is composed of about 67% of the total genome encoding 16 NSPs while the remaining ORFs encode structural and accessory proteins. The crucial structural proteins encoded by the virus are S (spike surface glycoprotein), E (small envelope protein), M (matrix protein), and N (nucleocapsid protein) proteins. The S proteins help in host cell receptor binding and determine the tropism of the host [9]. The spike protein contains three parts, namely, an ectodomain, a membrane spanning anchor, and an intracellular tail. The ectodomain is further cleaved into two parts, namely S1, which helps in attachment to the receptor, and S2, which is responsible for membrane fusion during the process of molecular maturation. The spike proteins either bind to the protein receptors or glycans in different species of coronavirus [10]. The recent pandemic can be traced back to Wuhan, Hubei Province of China, where reports of cluster of patients having pneumonia of undetermined reason which were epidemiologically linked to sea food and wet animal wholesale market of Wuhan in December 2019. Consequently, an unknown beta-coronavirus was discovered from human respiratory epithelial cells through unbiased sequencing in samples of patients suffering from pneumonia. This led to the isolation of a distinct biological group which falls in the subgenus of Sarbecovirus and subfamily Orthocoronavirinae and named as 2019-nCoV, a novel coronavirus [10].

6.2.1. Spread of COVID-19

On December 8, 2019, many patients with pneumonia of unknown cause were reported in Wuhan, Hubei province, China. It was further observed that most of the affected patients were associated to a local wholesale market in Huanan selling seafood and other wet animals. The patients suffered from pneumonia, respiratory infections, and some patients got affected by acute respiratory distress syndrome accompanied by severe respiratory failure. On January 7, novel coronavirus was identified from a throat swab of a patient at the Chinese Center for Disease Control and Prevention [11]. Furthermore, WHO declared the disease a health emergency of global concern in January 2020 and officially named the disease as coronavirus disease 2019 (COVID-19) on February 12, 2020 [12]. During the month of January 2020, about 33 Chinese provinces reported approximately 5900 confirmed and 9000 suspected COVID cases with a death toll of 106 [13]. On January 31, 2020, China reported 11,791 confirmed cases and 17,988 suspected cases in 34 provinces [14]. The spread of COVID-19 was rapid and it crossed the geopolitical borders of China in January 2020 itself and confirmed cases were reported in 19 countries across the globe namely Australia, Canada, Cambodia, France, Finland, Germany, India, Italy, Japan, Nepal, Malaysia, the Philippines, the Republic of Korea, Singapore, Sri Lanka, Thailand, United Arab Emirates, United States of America, and Vietnam [15]. The world experienced a rapid growth of COVID-19 pandemic with 85,403 confirmed cases on a global scale out of which 79,394 confirmed cases were from China with 2838 deaths [16].

Presently, COVID-19 has spread to almost all the countries of the globe and as of July 8, 2020 there is a whopping 11,669,259 cases and 539,906 fatalities across the globe [17]. The present global scenario as of July 8, 2020 is tabulated in Table 6.1 .

Table 6.1.

Continent wise count of COVID-19 cases as on July 8, 2020 [17].

Continents	Total confirmed cases	Total new cases	Total deaths	Total new deaths
Africa	397,942	15,379	7415	276
Americas	6,004,685	89,134	268,828	2092
Eastern Mediterranean	1,204,698	17,078	28,664	562
Europe	2,827,789	17,941	201,255	604
South-East Asia	1,001,655	27,266	26,224	605
Western Pacific	231,749	2159	7507	8
Global	11,669,259	168,957	539,906	4147

6.2.2. Symptoms of COVID-19

COVID-19 positive patients exhibit flu-like symptoms characterized by dry coughs, sore throat, high fever, and breathing problems. These may also be accompanied by fatigue, muscle pain, and sneezing. Under severe condition, there are reports of pneumonia, serious respiratory syndrome, and kidney failure ultimately leading to death [18]. Epidemiological studies suggest that the mortalities are higher in elder populations and the incidence is much lower in children [19]. Respiratory troubles along with elevated white blood cell (WBC) and cytokine levels are reported in patients suffering from COVID-19 [20]. One of the COVID-19 patients reported 5 days of fever accompanied by cough, coarse breathing sounds of both lungs with a body temperature of 39 °C. The WBC differential count exhibited 70.0% neutrophils and 0.1% eosinophils along with elevations in levels of C-reactive protein (16.16 mg/L; normal range 0–10 mg/L), erythrocyte sedimentation rate (29 mm/h; normal range <20 mm/h), and D-dimer (580 ng/mL; normal range 500 ng/mL). Multiple peripheral ground-glass opacities were observed in the lungs through unenhanced chest CT. Analysis of the sputum of the patient showed positive real-time polymerase chain reaction results which confirmed COVID-19 infection [21].

6.2.3. Transmission of COVID-19

Infective particles may spread from their natural hub to a vulnerable host through a variety of pathways which includes the transmission from a human to another human, transmission through air, endogenous infection, common vehicle, and vector spread [22]. The respiratory viruses are assumed to transmit over multiple routes, out of which transmission through droplets and aerosols is of immense significance [23]. There are three potential pathways of transmission of SARS-CoV-2 from an infected host to a susceptible host. The first pathway is transmission from person to person (direct contact) through respiratory droplets. These droplets are capable of traveling a distance of 6 feet through air. The second pathway is transmission through fomites (indirect contact) for the duration it is viable in the surfaces of which it is present. The aerosols form the third way of viral transmission through indirect contact mode for a distance of over six feet in air. To affect a successful infection, SARS-CoV-2 requires to lodge on specific regions namely the eyes, nose, and mouth of a host [24].

As of now, preventive measures are the most effective strategy in limiting the spread of infection of SARS-CoV-2. In this regard, early screening, diagnosis, isolation, and treatment are required to prevent further spread of the disease. In this regard, the most important strategy is frequently washing of hands by soaps and use of alcohol-based hand sanitizers, in addition to avoiding contact with other persons and covering of face and mouth in order to minimize chances of entry of virus through the body opening [25]. The important preventive measures for spread of SARS-CoV are tabulated in Table 6.2 .

Table 6.2.

Measures required to be followed for preventing spread of SARS-CoV.

Quarantine	Other preventive measures
Self-quarantine (practicing lockdown) (a)Mandatory quarantine (b)Private residence (c)Hospitals (d)Public institutions (e)Others (ships)	1.Avoidance of crowding
	2.Frequent hand wash with soaps and use of hand sanitizers
	3.Practicing isolation
	4.Use of personal protective equipment
	5.Closure of schools and colleges (as a protective measure)
	6.Social distancing
	7.Closure of workplaces or measured activities in workplace

6.3. Drug discovery for COVID

The term “drug” originates from “drogue” which means dried herbs in French. Drugs are chemical substances that have the capability to modulate the mental, emotional, and physical state of oneself and have a profound effect on the functions of the brain [26]. Chemicals bind to the protein and are absorbed in the systemic circulation. The efficacy of a drug is due to the difference in pharmacokinetics and pharmacodynamics between ethnicity, age, genetic makeup, and disease state [27]. A group of medicines which have similar molecular structures, the same mechanism of action, a related mode of action, and are used to treat the same disease forms a drug class.

6.3.1. Sources of drug

Drugs are derived mainly from natural sources, but synthetic and semisynthetic drugs are also manufactured owing to their higher yield, purity, quality, and low price [28]. Crude drugs are naturally occurring raw substances obtained from minerals, plants, and animals. It contains pharmacologically active ingredients which do not require any further refinement. Natural sources of drugs comprise plants, animals, microbes, and minerals. Plants as a whole are sources of crude drugs. Whereas, in the case of animals, drugs are mostly obtained from glandular secretions, liver, venoms (polypeptide), nonpeptide toxins, etc. Many life-saving drugs like penicillin, chloramphenicol, streptomycin, etc., are obtained from microbes. Coral (eleutherobin), sponges (discodermolide), and marine microorganisms (curacin A) synthesize biochemical compounds which can attenuate inflammations, inhibit viruses, and prevent cancer. Drugs obtained from minerals may include compounds constituting both metals and nonmetals and are used for treating number of ailments. New drugs are the result of microbiological conversion of precursor molecule, aberrant synthesis in higher plants, as well as through culture of cells and organs. Semisynthetic preparation of drugs involves alteration in chemical structure without any modification of the nucleus, thereby improving the efficiency of natural drugs. Drugs are also prepared synthetically and are also genetically engineered [29].

6.3.2. Antiviral drugs and other alternatives

The application of antiviral drugs includes treating viral infections without harming the host cell by identifying viral proteins, or parts of proteins, that can be disabled. Herpes virus was the first to be treated with an antiviral compound which was produced in 1960s. Various drugs are being developed at an extremely quick pace and new drug targets are being exploited along with clinical trials of newly formulated drugs.

Most of the viral diseases (except HIV) are self-limited illnesses not requiring specific antiviral therapy. Current antiviral drugs target 3 groups of viruses—herpes, hepatitis, and influenza [30].

Natural products such as lycorine, silvestrol, tylophorine, ouabain, and homoharringtonine can interact with key viral proteins that are associated with virulence in nanomolar concentration. These may help in future drug development strategies or may act as drug design templates [31].

Indian medicinal herbs are a promising alternative to combat viral infections. Indian herbs are used as a prophylaxis for a number of viral infections related to respiratory distress. These herbs help to stimulate immune system and modulate inflammatory effects, thereby rendering overall protection against the virus infection.

The homeopathy medicine, Arsenicum album 30, may be a possible preventive against coronavirus infection. It affects HT29 cells and human macrophages. It also showed NF-κB hyperactivity and TNF-α release in macrophage [32].

6.3.3. Role of medicinal plants

In India, the study is rather minimal, where antimouse coronaviral activity is manifested by certain plants such as Allium sativum [33], which target the viral replication of SARS-CoV. Clerodendrum inerme having the potential to inactivate the viral ribosomes may be utilized as a drug targeting SARS-CoV-2 protein translation [34]. Strobilanthes cusia [35] attenuates the RNA synthesis of virus and induces protease activity targeting the HCoV. Andrographis paniculata can treat viral respiratory infections in ayurvedic and medicinal systems [36,37]. Sambucus ebulus [38] has been known to inhibit the activity of enveloped viruses. Methanolic extracts of plants were derived from 22 families and their MIC (minimum inhibitory concentration) values were evaluated. Some of the extracts exhibited antiviral activities which included mouse coronavirus (the surrogate of human SARS virus). Most potent extracts were from Gymnema sylvestre, Pergularia daemia, Sphaeranthus indicus, Cassia alata, Evolvulus alsinoides, Clitoria ternatea, Indigofera tinctoria, Abutilon indicum, Vitex trifolia, C. inerme, and Leucas aspera which revealed anti-MCV and anti-HSV properties at a concentration of 0.4 μg/mL [39].

Camellia japonica, Saposhnikovia divaricata, and Dryopteris crassirhizoma showed potential inhibitory effects on PEDV replication by targeting key structural protein synthesis and relevant gene expression. The anti-PEDV molecules obtained may help in investigating the deadly human coronaviruses, as they share some similar replication mechanisms [40].

6.3.4. Molecular biology and drug target

SARS-CoV-2 targets cells through viral structural spike proteins which binds to angiotensin-converting enzyme 2 (ACE-2) receptor followed by entry into the host using host cell receptors and endosomes [41,42]. S1 unit of S protein helps in adherence of the virus to the surface of the target cells. Serine protease TMPRSS2 promotes viral entry by S protein priming [41]. RdRp, coronavirus main protease, and papain-like protease are nonstructural proteins which are encoded by viral genome. Upon entry to the cell, the virus synthesizes RNA via RdRp. A TMPRSS2 inhibitor thus may be an important target for drugs [41,42]. It is translated to polyproteins of virus within the host cell using the host translation apparatus. They are then broken into effector proteins by coronavirus main protease and papain-like protease which deubiquinates a number of host cell proteins such as interferon factors and NF-κB, which results in suppression of immune system. The cryo-EM structure analysis revealed that the S protein–ACE-2 binding in case of SARS-CoV-2 is in many folds higher than in SARS-CoV [43]. However, drugs that inhibit ACE trigger the expression of ACE-2, thereby intensifying the infection. Thus, drugs that promote ACE inhibition may not be therapeutic in coronavirus treatment [44].

6.4. Drug discovery related to COVID-19

As SARS-CoV-2 wreaks havoc throughout the globe, extensive research was initiated for drug discovery for treating the disease in the first half of 2020. It was revealed that a number of candidates from western medicines, natural substances, and conventional Chinese medicines have potentials to counteract the virus [[45], [46], [47]]. Interferon α (IFN-α), chloroquine phosphate, lopinavir/ritonavir, ribavirin, and Arbidol are the antivirals which are considered as preventive medicine for treatment of SARS-CoV-2 induced pneumonia by the National Health Commission of the People's Republic of China (Table 6.3 ) [48].

Table 6.3.

Names of antivirals recommended by the National Health Commission, People's Republic of China for the treatment of SARS-CoV-2.

Name of the drug	Dosage to be administered	Mode of administration
IFN-α	5 million units or equivalent, twice a day	Vapor inhalation
Lopinavir/ritonavir	200 mg/50 mg/capsule, 2 capsules each time twice a day	Oral
Ribavirin	500 mg in combination with IFN-α or lopinavir/ritonavir, 2–3 times a day	Intravenous infusion
Chloroquine phosphate	500 mg, 2 times a day	Oral
Chloroquine	300 mg, 2 times a day	Oral
Arbidol	200 mg each time, 3 times a day	Oral
The tenure of treatment is recommended for not more than 10 days.

Though a number of antiviral formulations have been recommended for the treatment of SARS-CoV-2, no specific vaccine or therapeutic drugs for COVID-19 were established till the middle of 2020 [49]. This remained a major challenge to narrow down the potential therapeutic regimens for COVID-19 treatment. A potent vaccine is extremely essential for the treatment and cure for ever-increasing cases of COVID-19. From 2020 onwards, a lot of research was being undertaken to develop vaccines throughout the world. Until the development of vaccines, some common antiviral drugs were used for treatment. This section will summarize the status of pharmacotherapeutics that were used for COVID-19 therapy during initial stages of transmission.

6.4.1. Antiviral agents

6.4.1.1. Remdesivir

Remdesivir (Fig. 6.1 ) is one of the potential candidates for treating patients infected with SARS-CoV-2. Chemically, remdesivir is a phosphoramidate prodrug of an adenosine C-nucleoside that functions as broad-spectrum antiviral agent produced by Gilead Sciences in 2017. It was initially used to treat patients infected with Ebola virus [50]. Remdesivir is converted into its active form within the cell which is responsible for obscuring viral RNA polymerase and blocking proofreading by exonuclease of virus. This results in decrease of RNA production of virus. The mechanism by which remdesivir acts is by the delay of chain cessation of nascent viral RNA [51]. Fig. 6.2 depicts the action of remdesivir within the cell.

Figure 6.1.

Molecular structure of remdesivir.

Figure 6.2.

Schematic representation of action of remdesivir inside the cell.

After diffusion, remdesivir is metabolized into nucleoside triphosphate via a series of changes. The nucleoside triphosphate is the active form that inhibits RdRp [52]. In order to evaluate the effectiveness, phase III clinical trials of remdesivir kick-started in China on February 5, 2020 [53]. The trial took place at the Capital Medical University with 308 participants with mild and moderate SARS-CoV infection, but was suspended on April 15, 2020 (NCT04252664, since suspended). A day later, a second trial was also registered on the same location focusing on patients with advanced SARS-CoV-2 related respiratory disease. This trial was undertaken with 237 participants and was terminated in mid-April 2020 (NCT04257656, since terminated). Both trials were designed to monitor the primary outcome of administration of remdesivir in normalization of fever, oxygen saturation, respiratory rate, and remission of cough which is sustained for 72 h [52]. The recommended dose includes a 10-day course of 200 mg loading dose on day 1 followed by 100 mg once-daily maintenance doses of remdesivir for 9 days in both studies [54].

6.4.1.2. Hydroxychloroquine and chloroquine

Hydroxychloroquine and chloroquine (Figure 6.3, Figure 6.4 ) are drugs that are commonly used as a remedy of lupus erythematosus [55], rheumatoid arthritis [56], and malaria [57]. Compared to chloroquine, hydroxychloroquine is less toxic as it possesses a hydroxyl group and performs the same function [58]. Hydroxychloroquine and chloroquine target the lysosomes and are useful to control graft-versus-host disease in humans [59,60]. Chloroquine accumulation in lysosomes results in significant change of pH [61], thereby affecting the activity of protease. This affects degradation of glycosaminoglycans [62,63]. It was reported from several investigations that chloroquine possess the capacity to inhibit the entry of SARS-CoV-2, fusion of virus with cell through interference of glycosylation of ACE-2 receptor, and attachment with spike protein [[64], [65], [66]]. This indicated that chloroquine and hydroxychloroquine are more effective in the early stages of COVID-19 infection (Fig. 6.5 ) [67,68].

Figure 6.3.

Molecular structure of hydroxychloroquine.

Figure 6.4.

Molecular structure of chloroquine.

Figure 6.5.

Probable sites of action of chloroquine (CQ) and hydroxychloroquine (HCQ). (X) Sites of inhibition by CQ and HCQ. (1) CQ and HCQ: inhibition of binding of virus to the specific receptor on cell surface, (2) CQ: inhibition of sialic acid biosynthesis by suppressing activity of quinone reductase 2 which affect activity of ACE-2 receptor, (3) CQ and HCQ: inhibition of pH-dependent endocytosis of virus through increase of pH, (4) CQ: intervention with uncoating of viral particles, (5) CQ: intervention with assembly/budding which results in accumulation of viral vesicles in trans-Golgi network, (6) CQ: interference with degradation of lysosomal protein and fusion of lysosome with autophagosomes. HCQ: Interferes with activity of lysosome which prevents expression of class II MHC, (7) CQ: interference with release of TNF and binding from macrophages and/to monocytes, (8) CQ: attenuation of phosphorylation of P38 MAPK and caspase in Th1 cells thereby inhibiting production of proinflammatory cytokines and replication of virus, (9) HCQ: blocking of MHC expression thereby preventing T cell activation, expression of CD145, and release of cytokines, (10) HCQ: disables TLR signaling through increase of pH of endosomes and interfering with binding of TLR7 and TLR9 to their DNA/RNA ligands, thereby inhibiting transcription of proinflammatory genes, and (11) HCQ: inhibition of binding of DNA to the cGAS resulting in reduction of transcription and production of cytokines [66].

There is evidence that chloroquine and hydroxychloroquine resulted in reduction of cytokine storms which contributed to acute respiratory distress which resulted in majority of deaths among COVID-19 patients [69,70]. There were also reports that hydroxychloroquine effectively inhibits infection of SARS-CoV in vitro [71]. An in vitro study reported that zinc inhibits the activity of RNA polymerase in SARS-CoV and retroviruses [72]. There was also a report that zinc can improve the actions of chloroquine during COVID-19 treatment [73]. In a study conducted at Méditerranée Infection University Hospital Institute in Marseille, France, it was reported that the daily administration of 600 mg of hydroxychloroquine resulted in significant reduction or disappearance of viral load in COVID-19 patients and the effect was further reinforced by azithromycin [74]. A study recommended an initial higher dose of 400 mg two times daily of hydroxychloroquine sulfate followed by a fixed dose of 200 mg, two times a day for 4 days in case of SARS-CoV-2 infection. It was also found that hydroxychloroquine was stronger than chloroquine in inhibiting SARS-CoV-2 in vitro [71]. However, there were reports that hydroxychloroquine exhibited some side effects such as cardiac failure, blindness, and toxicity of kidney [75]. Thus, clinicians are required to be conscious of risks associated with the administration of these drugs for treatment of SARS-CoV infections.

6.4.1.3. Lopinavir-ritonavir

Lopinavir (Fig. 6.6 ) inhibits protease [76] and is reported to possess high affinity for HIV protease I [77]. It is administered in combination with ritonavir and was first launched by Abbott as Kaletra in 2000 [78]. Lopinavir has a poor bioavailability and extensive metabolism [79]. It is thus co-administered with ritonavir to enhance its exposure. Ritonavir (Fig. 6.7 ) boosts the plasma concentration of lopinavir by suppressing its metabolism, thereby increasing the potential of lopinavir [80]. In a trial performed with lopinavir/ritonavir on 199 patients with confirmed SARS-CoV-2 infection, 99 patients were administered with 400 and 100 mg of lopinavir and ritonavir, respectively, twice daily for 2 weeks along with standard care. No significant improvement was observed with lopinavir/ritonavir treatment. Further trials were required to be performed on patients with severe illness in future to determine the best combination of drugs [81]. However, a report from Korea stated that lopinavir/ritonavir administered to a 54-year-old male patient infected with SARS-CoV-2 significantly decreased coronavirus titers [82]. A randomized phase II trial was performed on patients infected with SARS-CoV-2 who were admitted to healthcare facilities in Hong Kong. Out of 127 patients, 86 patients were administered with a combination of 400 mg of lopinavir and 100 mg of ritonavir along with 400 mg of ribavirin every 12 h with three doses of interferon beta-1b (8 million international units) on alternate days. It was observed that the combination group exhibited significantly shorter median time from initiation of study treatment to absence of coronavirus in nasopharyngeal swab which was considered to be the end point of study [83].

Figure 6.6.

Molecular structure of lopinavir.

Figure 6.7.

Molecular structure of ritonavir.

6.4.1.4. Umifenovir (Arbidol)

Umifenovir is a hydrophobic drug with an indole-based chemical structure (Fig. 6.8 ). It is a dual-acting antiviral and host targeting agent which is used for the prevention of influenza and related respiratory infections. It has been in use in Russia for more than two decades and in China from 2006 onwards [84]. It is an oral antiviral drug that is marketed as Arbidol [85]. Umifenovir was also reported to have in vitro antiviral efficacy against Ebola virus, human herpes virus 8, hepatitis C virus, and Tacaribe arenavirus [86]. The main mechanism of umifenovir is blocking of the virus-cell membrane fusion through inhibiting clathrin-mediated endocytosis, thus preventing the virus infection [87]. An in vitro study reported that Arbidol effectively inhibits SARS-CoV-2 infection by blocking the viral entry obstructing attachment of virus and release from endolysosomes [88]. A retrospective cohort study indicates combination of Arbidol with lopinavir/ritonavir resulted in a higher recovery rate (75%) as evident from absence of virus in the nasopharyngeal swab after 7 days of treatment as compared to monotherapy of lopinavir/ritonavir (35%) [89]. Two randomized and open level trials were undertaken in China. A phase IV clinical trial was performed in Guangzhou Eighth People's Hospital which explored the effectiveness of combination of lopinavir, ritonavir, and Arbidol in treating novel coronavirus infection. This trial was initiated on February 5, 2020 and is still on recruitment mode [90]. A second study was initiated on February 7, 2020. It is an interventional clinical trial to study the potential of Arbidol Hydrochloride Tablets along with standard treatment versus standard treatment for pneumonia caused by the novel coronavirus [91].

Figure 6.8.

Molecular structure of umifenovir.

6.4.1.5. Favipiravir

Favipiravir (Fig. 6.9 ) is a derivative of pyrazinecarboxamide and is inhibitory to RNA viruses. Within the host, Favipiravir is modified to ribofuranosyltriphosphate derivative by host's enzyme and this is responsible for the inhibition of RdRp of influenza virus. Toyama Chemical Co Ltd, Japan, introduced Favipiravir and got approval for treating resistant cases of influenza [92]. Favipiravir selectively targets conservative catalytic domains of RdRp, thus preventing nucleotide incorporation replication and transcription of virus [93]. The impairment in replication of virus results in increased number and frequency of transition and transversion mutations inducing lethal mutagenesis in virus [94]. Favipiravir is administered to treat infectious disease such as influenza [95], Ebola [96], and norovirus [97]. A study reported that Favipiravir is effective in SARS-CoV-2 infection of Vero E6 cells (ATCC-1586) with half maximal effective concentration of 61.88 μmol per liter and half maximal cytotoxic concentration (CC50) > 400 μmol per liter and selectivity index > 6.46 [98]. Clinical trials exploring the effectivity of Favipiravir against COVID-19 infection were extensively performed in China and Japan during initial stages of drug developement against COVID-19. The details of the trial were tabulated in Table 6.4 .

Figure 6.9.

Molecular structure of Favipiravir.

Table 6.4.

Selected trials on efficacy of Favipiravir against COVID-19 infection.

Trial registration code	Trial type	Total number of patients enrolled	Objective/Outcome	References
ChiCTR200030254	Randomized control trial	240 120—Favipiravir 120—Arbidol	Comparison of safety and efficacy of Arbidol and Favipiravir in treatment of patients with COVID-19 infection. Higher recovery rate in patients treated with Favipiravir along with faster relief from cough and pyrexia.	[99]
ChiCTR2000030113	Interventional study	15—Control group Intervention: Ritonavir 15—Experimental group Intervention: Favipiravir	Observing the safety and effectiveness of Favipiravir for treating novel coronavirus–related pneumonia with poorly responsive ritonavir.	[100]
ChiCTR2000029600	Interventional study	30—Group A Intervention: Alpha-interferon atomization 30—Group B Intervention: Combination of lopinavir/ritonavir along with Alpha-interferon 30—Group C Intervention: Favipiravir + alpha-interferon atomization	Monitoring safety and effectiveness of Favipiravir for treatment of SARS-CoV-2 infection associated pneumonia.	[101]
ChiCTR2000029544	Interventional study	10—Group 1 Intervention: Current antiviral treatment + baloxavir marboxil tablets 10—Group 2 Intervention: Current antiviral treatment + Favipiravir tablets 10—Group 3 Intervention: Current antiviral treatment	Evaluating the effectiveness and safety of combination of baloxavir marboxil or Fabiravir dipivoxil for treating patients having SARS-CoV-2 infection.	[102]
ChiCTR2000029548	Interventional study	10—Group A Intervention: 80 mg of baloxavir marboxil on first day, 80 mg on fourth day, and 80 mg on seventh day if required. Not to be administered more than three times in total. 10—Group B 600 mg of Favipiravir, three times a day along with 1600 mg first loading up to 14 days. 10—Group C Intervention: 200 mg of lopinavir and 50 mg of ritonavir two times a day for 14 days	Evaluating the effectiveness and safety of baloxavir marboxil, lopinavir/ritonavir, and Favipiravir for treating patients having SARS-CoV-2 infection.	[103]
ChiCTR2000030894	Interventional study	90—Group 1 Intervention: Combination of Favipiravir with tocilizumab 30—Group 2 Intervention: Favipiravir 30—Group 3 Intervention: Tocilizumab	Evaluating the effectiveness and safety of Favipiravir in combination with tocilizumab for treating patients having SARS-CoV-2 infection.	[104].

6.4.1.6. Oseltamivir

Oseltamivir (Fig. 6.10 ) is a drug used to treat influenza A and B [105]. It is a cyclohexene carboxylate ester. Oseltamivir blocks neuraminidases present on the surfaces of influenza viruses and interferes with the release of complete viral particles in the host cell [106]. Several trials were undertaken to check the effectivity of oseltamivir against SARS-CoV-2 (Table 6.5 ).

Figure 6.10.

Molecular structure of oseltamivir.

Table 6.5.

Selected trials for checking the efficacy of oseltamivir against SARS-CoV-2 infection.

Trial registration code	Trial type	Total number of patients enrolled with drug interventions	Objective/Outcome	References
NCT04255017	Interventional (clinical trial)	400 (estimated and recruiting). Intervention: Oseltamivir with various combinations of lopinavir/ritonavir and Arbidol hydrochloride at different doses.	Relief from fever cough and associated symptoms related to SARS-CoV-2 infection along with improvement in lung CT.	[107]
NCT04303299	Interventional (clinical trial)	320 (not recruiting) Intervention: Oseltamivir with various combinations of hhydroxychloroquine, lopinavir, ritonavir, and Favipiravir at different doses.	Eradication of nasopharyngeal SARS-CoV-2.	[108]

6.4.2. Supporting agents

Many concomitant therapies were in use as supporting agents due to the nonavailability of vaccines or antiviral drugs for the treatment of SARS-CoV-2 during the initial months of the pandemic. These included a number of compounds, antibiotics, and antibodies. The mechanism of actions of these therapeutic agents and their role in COVID-19 treatment are tabulated in Table 6.6 while the clinical trials and other scientific studies related to them are tabulated in Table 6.7, Table 6.8 , respectively.

Table 6.6.

Selected supporting agents which are in use for treating SARS-CoV infection.

Name of the supporting agent	IUPAC nomenclature	Mode of action	References
Compounds
Azithromycin	(2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-11-[(2S,3R,4S,6R)-4-(dimethylamino)-3-hydroxy-6-methyloxan-2-yl]oxy-2-ethyl-3,4,10-trihydroxy-13-[(2R,4R,5S,6S)-5-hydroxy-4-methoxy-4,6-dimethyloxan-2-yl]oxy-3,5,6,8,10,12,14-heptamethyl-1-oxa-6-azacyclopentadecan-15-one	Interferes bacterial translation process by attaching to 50S subunit of ribosome, thereby inhibiting translation of mRNA	[109]
Ascorbic acid	(2R)-2-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxy-2H-furan-5-one	Enhances development and proliferation of T lymphocytes and NK (natural killer) cells Involved in the immune response to viral agents	[110]
Corticosteroids (methylprednisolone)	(6S,8S,9S,10R,11S,13S,14S,17R)-11,17-dihydroxy-17-(2-hydroxyacetyl)-6,10,13-trimethyl-7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthren-3-one	Attenuation of cytokine response. Accelerate resolution of pulmonary and systemic inflammation	[111,112]
Nitric oxide	Nitric oxide	Vasodilator	[113]
Sirolimus	(1R,9S,12S,15R,16E,18R,19R,21R,23S,24E,26E,28E,30S,32S,35R)-1,18-dihydroxy-12-[(2R)-1-[(1S,3R,4R)-4-hydroxy-3-methoxycyclohexyl]propan-2-yl]-19,30-dimethoxy-15,17,21,23,29,35-hexamethyl-11,36-dioxa-4-azatricyclo[30.3.1.04,9]hexatriaconta-16,24,26,28-tetraene-2,3,10,14,20-pentone	Immunosuppressant Inhibition of mTOR	[114,115]
Antibodies
Tocilizumab	Monoclonal antibody developed by Roche and Chugai Pharmaceutical	IL-6 receptor antagonist	[116]
Sarilumab	Full human anti–IL-6R monoclonal IgG1 antibody	Binds to both soluble and membrane-bound IL-6Rα, thus blocking the cis- and trans-inflammatory signaling cascades of IL-6	[117,118]

Table 6.7.

Clinical trials performed with the supporting agents.

Trial registration code	Trial type	Total number of patients enrolled/participants	Objective/Outcome	References
2020-000890-25	Randomized clinical trial	36	Azithromycin added to hydroxychloroquine exhibited significantly more efficiency in eliminating virus.	[74,119]
NCT04264533	Randomized trial	140	Number of ventilation-free days determined on the 28th day of enrollment. 28 days mortality monitoring of patient survival. Duration of stay in ICU.	[120]
NCT04341675	Randomized trial	30	Number of patients who are alive and not dependent on advanced respiratory support on 28th day. Number of patients requiring intensification in care. Change in specific biomarkers such as LDH, ferritin, D-dimer, lymphocyte count over time. Number of surviving patients to discharge from hospital.	[121]
NCT03901001	Randomized trail	160	In time frame of 28 days: (a) Respiratory status to normalcy (b) Copies of viral ribonucleic acid (RNA) per milliliter. In time frame of 10 days: Levels of interleukin, chemokine ligand 9, soluble tumor necrosis factor receptor-1, phospho-p38, and phospho-ERK.	[122]
NCT04305457	Randomized, interventional (clinical trial)	240	Decrease in requirement of intubation and mechanical ventilation in patients having mild to moderate COVID-19 symptoms.	[123]
NCT04306393	Randomized, interventional (clinical trial)	200	Change of arterial oxygenation at 48 h from enrollment. Time to reach normoxemia during the first 28 days after enrollment. Proportion of SARS-nCoV-2–free patients during the first 28 days after enrollment.	[124]
ChiCTR2000029765	Interventional study	188	Evaluation of safety and effectiveness of tocilizumab in treatment of regular patients with NCP (including severe risk factors) and critical NCP patients. Outcome: Ventilator utilization.	[125]
NCT04315298	Randomized interventional clinical trial	2500	Evaluation of change in C-reactive protein (CRP) (%) levels in patients with serum interleukin-6 level greater than the upper limit. Proportion of patients with at least 1-point improvement in clinical status using the 7-point ordinal scale in patients with critical COVID-19 treated with mechanical ventilation at baseline.	[126]

Table 6.8.

Other investigations performed with the supporting agents.

Name of the compound	Objectives	Outcome	References
Methylprednisolone	To describe the clinical characteristics and outcomes in patients who have developed ARDS from COVID-19 infection related pneumonia.	Methylprednisolone reduced the mortality incidence among COVID-19 infected patients. Death rate of patients treated with methylprednisolone-46%.	[127]
Methylprednisolone	To evaluate the potential and safety of corticosteroid for treatment of severe COVID-19 pneumonia.	Methylprednisolone administration resulted in improvement of SpO2. Betterment in absorption degree of the focus in chest CT. Less number of days required to normalize body temperature upon treatment with methylprednisolone.	[128]

6.5. Plasma therapy

Plasma therapy was first introduced in the 19th century to treat diphtheria [129]. Clinical trials using antibody-rich plasma from recovered COVID-19 patients to treat COVID-19 positive ones gained a lot of popularity in COVID-19 therapy in some countries including India. Potentiality and lack of side effects in clinical trials related to COVID-19 vaccine development are the main motives of FDA. In India, West Bengal government is collaborating with Council of Scientific and Industrial Research (CSIR), India, and they are conducting clinical trials to cure patients with convalescent plasma therapy (CPT) [130,131].

6.6. Future projections

The unbridled spread of COVID-19 on one hand and the lack of authentic drug or vaccine have put forward a challenge to scientists throughout the world. Immense research is being carried out globally at present to find possible therapeutic options. Thus, this chapter has tried to act as a depository of data for the developments of drug/vaccine formulation against novel coronavirus till June, 2020 .

The chapter has highlighted on different antiviral drugs and supportive agents which undoubtedly created a database for the researchers for its further improvement and administration.

It has also emphasized on natural sources of drugs especially those obtained from medicinal plants to combat COVID-19. This would open up new possibilities for researchers to explore the wide range of phytochemical compounds, acting either directly or after modifications, to formulate drugs or immune booster in the near future.

The chapter also highlighted the recent development in alternative treatments such as homeopathy and plasma therapy which may open up new horizon for researchers to investigate them further.

6.7. Conclusion

SARS-CoV-2 that causes COVID-19 is a single-stranded positive-sense enveloped coronavirus which causes respiratory tract infection in humans. It is closely related to SARS-CoV and MERS-CoV. Being highly contagious, it has caused a global health threat. Till June, 2020, no specific drug or vaccine against this virus is available. During that period, the strategies to combat this deadly virus included:

• 1.Targeting SARS-CoV-2 attachment to the host.
• 2.Targeting SARS-CoV-2 replication inside the host.
• 3.
  Repurposing of already approved drugs which mainly include

  • a.
    Anti-HIV drugs inhibiting the HIV protease (lopinavir/ritonavir, darunavir/cobicistat).
  • b.
    Hydroxychloroquine, a derivative of chloroquine, inhibiting lysosomal functioning.
  • c.
    Inhibition of RdRp—remdesivir.
  • d.
    Favipiravir (Glenmark).

In addition, CPT is an alternative therapy toward SARS-CoV infection and was also investigated. Also, drugs from medicinal plants may be applied for COVID-19 treatment. The ongoing research in this field is also a ray of hope in fighting COVID-19.

The Central Council for Research in Homeopathy under the ministry of AYUSH, Govt. of India, had also proposed the administration of Arsenicum album 30 to boost immunity in order to combat COVID-19.

Moreover, India's first indigenous COVID-19 vaccine “COVAXIN” has been approved for clinical trials (phase I and phase II) by the Drug Controller General of India (DCGI) throughout the country in the month of July 2020. The vaccine is an inactivated one prepared from infectious SARS-CoV-2 virus and is developed by Bharat Biotech with scientific assistance from Indian Council of Medical Research and National Institute of Virology, Pune [132,133].

Although no drug against COVID-19 was certified till the mid of 2020, vigorous research/clinical trials were in full motion for the formulation of a potent drug/vaccine to cure COVID-19. This effort bloomed into success through rolling out of a number of vaccines by several pharmaceutical companies throughout the world. From the last quarter of 2020, the world experienced a massive vaccination drive in stages whose disbursement and administration were meticulously formulated through the concept of ‘equitable disbursement of vaccines’. Till 2022, the world experienced several waves of infection accompanied by transmission with mutant strains of the SARS-CoV surfacing out intermittently. Though the virus has affected the global population but with an efficient vaccination drive coupled with strict precautionary measures, an optimistic condition leading to substantial recovery from the pandemic seems not far off.

List of abbreviations

ACE

Angiotensin-converting protein

AYUSH

Ayurveda, Yoga and Naturopathy, Unani, Siddha, and Homeopathy

BCoV

Bovine coronavirus

c-GAS

Cyclin GMP-AMO synthase

CDC

Chinese Center for Disease Control and Prevention

CEST

Central European Summer Time

CoV

Coronavirus

CPT

Convalescent plasma therapy

CQ

Chloroquine

CRP

C-reactive protein

Cryo-EM

Cryo-electron microscopy

DNA

Deoxyribonucleic acid

EC

Effective concentration

FDA

Food and Drug Administration

HCoV

Human coronavirus

HCV

Hepatitis C virus

HIV

Human immunodeficiency virus

HSV

Herpes simplex virus

HVV

Human herpes virus

IL

Interleukin

MAPK

Mitogen-activated protein kinase

MCV

Mouse coronavirus

MERS-CoV

Middle East respiratory syndrome coronavirus

MHC

Major histocompatibility complex

MHV

Mouse hepatitis coronavirus

nCOVID-19

Novel coronavirus 2019

NF-κB

Nuclear factor kappa light chain enhancer of activated B cells

NK

Neutral killer

NSPs

Nonstructural proteins

ORF

Open reading frame

PdCV

Porcine delta coronavirus

PRCV

Porcine respiratory coronavirus

RdRp

RNA-dependent RNA polymerase

RNA

Ribonucleic acid

SARS-CoV

Severe acute respiratory syndrome coronavirus

TGEV

Transmissible gastroenteritis coronavirus

TLR

Toll-like receptor

TMPRSS2

Transmembrane serine protease 2

TNF

Tumor necrosis factor

UAE

United Arab Emirates

US

United States

WHCV

WH-human coronavirus

WHO

World Health Organization