**14. Experimental therapeutic interventions**

#### **14.1 Convalescent plasma (CP) therapy**

Because an effective vaccine and specific antiviral therapies are no longer available, there is a mandatory demand to develop an alternative approach for COVID-19 treatment, particularly in severe patients. For many centuries, convalescent plasma (CP) therapy, a type of adaptive immunotherapy, has been approved to treat a variety of infectious diseases. CP therapy has been used successfully in the treatment of MERS, SARS, and the H1N1 virus with adequate safety and efficacy [62, 63].

Convalescent plasma received from cured COVID-19 patients with generated humoral response directed toward the virus possesses a high concentration of neutralizing antibodies capable of preventing the viral entry and eliminating the virus from blood stream and lung tissues [64]. The first important determining factor in the success of the CP therapy is the neutralizing antibody titer. It was found in a small sample study of MERS-CoV infection that the titer of the neutralizing antibody should be greater than 1:80% to achieve successful CP therapy [63]. Finding suitable donors with high level of neutralizing antibody represents the cornerstone. Cao et al. [65] revealed that the level of neutralizing antibody to SARS-CoV diminished gradually 4 months after the recovery, eventually reaching undetectable levels in 25.6% (total IgG) and 16.1% t (neutralizing antibodies) of patients 36 months later.

### *Therapeutic Interventions for COVID-19 DOI: http://dx.doi.org/10.5772/intechopen.111543*

According to a study of MERS-CoV infected patients and high risk group, the prevalence of MERS-CoV IgG seroreactivity was estimated to be very low (2.7%), and the antibodies titer decreased rapidly within 3 months [66]. According to these findings, the neutralizing antibodies were a short-lived humoral immune response, and plasma from recently recovered patients should be more effective.

The second key factor that determined the success of treatment is treatment intervention point. The best treatment outcomes were observed in patients with SARS who received CP infusion by day 14 highlighting the necessity of timely rescue therapy. In recent study, they showed that all the transfused patients with neutralizing antibody titer above 1:640 achieved serum SARS-CoV-2 RNA negativity and accompanied with an elevation in lymphocyte counts and oxygen saturation, as well as an improvement in liver function and CRP. The findings suggest that antibodies found in CP alleviated immune system inflammation and overreaction.

Several approaches have been established to isolate and characterize the neutralizing antibodies generated by the convalescent COVID-19 as an attempt to generate effective antibodies as a therapy for COVID-19 [67, 68]. For example, AbCellera, a private Canadian company has developed a human IgG1 monoclonal Abs-based therapeutics for coronavirus infection in collaboration with Eli Lilly. Clinical studies for such antibodies have already been authorized in China.

#### **14.2 Antiviral drugs**

Several antiviral drugs have been adopted as potential candidate to treat SARS-CoV-2. The viral life cycle steps can be used as potential drug targets. The viral entry, nonstructural protein, and immune regulation are the promising drug targets **Figure 3**.

#### **Figure 3.**

*A diagram represents host immune system stimulated by the virus and viral life cycle within target cells. The figure is created by BioRender program.*

#### **14.3 Chloroquine and hydroxychloroquine**

Chloroquine and hydroxychloroquine have been permitted for the treatment of malaria and rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) as they have anti-inflammatory activity. These compounds have the ability to inhibit the virus replication through decreasing the endosomal acidification as SARS-CoV-2 needs the acidic media of the endosome for successful replication [69, 70].

Chloroquine has been shown an antiviral activity against SARS-CoV-2 through *in vitro* study [71]. With the use of chloroquine for the treatment of COVID-19, a clinical trial in China reported efficacy with improved pneumonia severity and an acceptable safety profile [72]. Hydroxychloroquine is a chloroquine derivative that is more stable and has a better clinical safety profile than chloroquine. It also has inhibitory activity toward SARS-CoV-2. When taken in conjunction with azithromycin, it has been proven to provide complete cure and virus clearance in COVID-19 patients [73].

Recent study showed that the combination of azithromycin and hydroxychloroquine has discouraging results in the critically ill SARS-CoV-2 infected patients, which may lead to perform more controlled research before final recommendations for chloroquine/hydroxychloroquine in the treatment of COVID-19 are made [74].

Chloroquine and hydroxychloroquine are zinc ionophores, and zinc has been found to block the activity of coronavirus's RNA-dependent RNA polymerase enzyme [75, 76]. As a result, one reason for some of these clinical trials' limited success might well be the lack of zinc supplementation, which may be required to obtain the medicinal value of these drugs on SARS-CoV-2 and other RNA virus infections [77].

#### **14.4 Lopinavir/ritonavir and other antiretroviral**

Lopinavir/Ritonavir is a combined approved drug used for the treatment of HIV. Lopinavir is a protease inhibitor that prevents virus particle maturation, whereas ritonavir sustains the lopinavir's plasma level by inhibiting CYP3A enzymes, which delays lopinavir's breakdown in the liver [78]. The data obtained from *in vitro*, and animal studies revealed its potential inhibitory effect against SARS-CoV, MERS, and SARS-CoV-2 [78, 79]. For COVID-19 therapy, lopinavir-ritonavir has been administered alone or in combination with alpha interferon or chloroquine/hydroxychloroquine with modest effectiveness [80, 81]. However, contradictory results have been released from China regarding impact of COVID-19 patients who are very unwell [82]. Recently, a randomized study of 199 hospitalized patients with COVID-19 who were treated with lopinavir/ritonavir reported no significant change in viral load, duration of hospital stay, or mortality rate [82]. The study was too small to conclude the potential role of lopinavir/ritonavir on the COVID-19 treatment and experts suggested that further randomized clinical trial to be conducted to confirm or deny the lack of effect.

As a result, more clinical trials are needed to determine the success of this therapy for COVID-19, which is now being conducted.

Furthermore, it has been observed that patients who received lopinavir/ritonavir regimen have had gastrointestinal adverse side includes diarrhea, nausea, and hepatotoxicity [83]. Elevated level of transaminases was commonly noticed in COVID-19 infected patients as one of the side effects, the case that may be worsened by any viral coinfection and/or combined therapy [84]. Recently RCT found that around half of lopinavir/ritonavir patients suffered a lot of unfavorable side effects, and around sixth of patients stopped medication owing to gastrointestinal complications [82]. Elevated transaminases triggered by drugs have special concern since it has the potential to

*Therapeutic Interventions for COVID-19 DOI: http://dx.doi.org/10.5772/intechopen.111543*

worsen COVID-19-induced liver impairment. Notably, the elevation of liver enzyme is an undesired criterion in numerous COVID-19 research study, suggesting that lopinavir/ ritonavir triggered liver toxicity may restrict patients' access to those medications [85].

Darunavir/cobicistat (DRV/c) is a protease inhibitor used for the treatment for HIV. *In vitro* study demonstrated an antiviral activity of darunavir against SARS-CoV-2.

In a randomized controlled clinical trial aimed to monitor the efficacy of DRV in treating COVID-19 patients, the obtained results failed to show a significant benefit of using (DRV/c) therapy beyond the standard care in the mild COVID-19 infected patients [86]. In this regard, HIV1 protease inhibitors may not exhibit clinically significant activity against SARS-CoV-2.

#### **14.5 Favipiravir (Favilavir or Avigan)**

Favipiravir (FPV) is a safe and effective RNA polymerase inhibitor developed in Japan for different RNA viral infection including influenza [87, 88]. The antiviral activity of the FPV against SARS-CoV-2 has been approved in a controlled study conducted in China [89]. Through the COVID-19 patients' medication, the effects of FPV vs. LPV/RTV were examined in this study. The FPV-treated individuals showed a considerably superior therapeutic response, with rapid viral clearance and a higher amelioration in chest radiography. Upon these hopeful data, the FPV therapy has been authorized as first anti-COVID-19 medication by the Chinese National Medical Products Administration [68].

#### **14.6 Remdesivir (GS-5734)**

Remdesivir is a nucleotide analog compound that inhibits the viral RNA-dependent RNA polymerase; its inhibitory effect against MERS CoV, SARS-CoV, and SARS-CoV-2 replication has been confirmed in *in vitro* studies and in animal models [90, 91]. The development company (Gilead Sciences, USA) declared a clinical improvement in more than half of patients (36 of 53) [92]. However, recent study in China did not exhibit significant clinical benefit, with the exception of the diminishment in the time required for recovery [93]. Additionally, in some patients, treatment with remdesivir had to be stopped prematurely due to unfavorable complications in 12% of patients compared to 5% of patients receiving placebo. Similar results were also reported in the first clinical trial in the United States. Repeated clinical trials of remdesivir in multiple countries must be performed to obtain more convincing recommendations for use in COVID-19 patients. Moreover, the efficacy of remdesivir against the novel COVID-19 variants are not well evaluated and the acquired drug resistance to the mutant strains should be monitored.

## **15. Immunomodulatory agents**

Several data pointed out the role of immunosuppressive treatments (e.g., corticosteroids, inhibitors, IL-6 inhibitors, interleukin (IL)-1 inhibitors, and kinase inhibitors) and immunomodulators (e.g., interferon alpha and beta (IFNα), (IFNβ), in COVID-19. The rationale for using these immunomodulatory/immunosuppressive agents for the treatment of COVID-19 is the involvement of the pro-inflammatory mediator with pieces of evidence of cytokine release storm (i.e., critical hyper inflammation and immune imbalance), which is required to induce multi-organ dysfunction and failure, worsening COVID-19 prognosis [94].

The humanized monoclonal antibody (tocilizumab) has been developed to bind with the receptor of IL-6 (IL-6R) that has been licensed by the FDA for the treatment of RA, giant cell arteritis, and systemic juvenile idiopathic arthritis [95]. IL-6 was involved in the production of cytokine storm (CS) found in ICU-admitted COVID-19 patients [95]. As a result, it has been offered as a possible treatment for such individuals [96]. Tocilizumab, for example, has been approved to be used as an immunosuppressive agent in severely ill COVID-19 patients in China and Italy, with promising findings [97, 98]. In a Chinese cohort, the administration of tocilizumab showed an improvement in patients with severe symptoms. While in the Italian cohort, the administration of tocilizumab in a COVID-19 patient with pneumonia revealed good alterations in CT findings within 14 days of therapy [99]. It is proving to be a viable treatment for treating. Several randomized controlled trials (NCT04310228, ChiCTR200002976) of tocilizumab alone or in combination in COVID-19 patients with severe pneumonia are ongoing in China and are included in the current Chinese protocol for the treatment of COVID-19 patients [100].

Sarilumab, another IL6 receptor antagonist approved for the treatment of R, is being investigated in a phase 2/3 clinical trial in hospitalized patients with severe COVID-19 (NCT04315298) [101].

Bevacizumab is monoclonal antibodies directed against vascular endothelial growth factor that are undergoing clinical trials in China and the United States NCT04275414).

Interferon alpha and beta have been studied against nCoV, and interferon beta is active against MERS [102, 103]. The use of interferon for the treatment of SARS-CoV-2 cannot be recommended at this time because of contradictory *in vitro* and animal results and the lack of clinical trials [104]. Current Chinese regulations recommend interferon as an alternative to combination therapy.
