The COVID-19 (Coronavirus Disease 2019) pandemic caused by infection of SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) has caused a global mortality surrounding 3% (1). Multiple studies have found that the hyperinflammatory response induced by SARS-CoV-2 is one of the main causes of severity and death of infected subjects. In severe COVID-19 patients, an association was found between pneumonitis and/or ARDS (Acute Respiratory Distress Syndrome), high serum levels of proinflammatory cytokines, extensive lung damage and microthrombosis (2). The late stage of the disease is difficult to manage and many patients die (3,4). Based on the reports of the Chinese Disease Control Center, Cascella and cols. (5) classified the patients according to clinical severity in three groups (Table 1):
Table 1: Classification of COVID patients according to Cascella and cols. StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; 2020. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554776/
|
Feature
|
% Cases
|
Mild Disease
|
Mild or absent pneumonia
|
81
|
Severe Disease
|
Dyspnea,
Respiratory rate ≥ 30/min,
Oxygen saturation (SpO2) ≤ 93%,
Kirby index (ratio between partial oxygen pressure, PaO2 and oxygen fraction inspired, FiO2) < 300,
Pulmonary infiltrate in thorax imaging > 50%.
|
14
|
Critical Disease
|
Respiratory failure
Septic shock
Multiple organ failure.
|
5
|
It has been proposed that the critical course of the disease that leads to complications and eventually death, is caused by an exacerbated and poorly understood immune response, linked to the phenomenon known as “cytokine storm” or cytokine release syndrome (6). Albeit it is not completely clear what initiates and propagates the cytokine storm, the severity of COVID-19, combined with rapid pandemic spread, has placed unprecedented pressure on the global healthcare system, and therapeutic strategies are urgently needed.
Pathological studies of patients lethally infected by COVID-19 had reported acute pulmonary edema, abundant infiltration of inflammatory cells, multiple organ failure, thromboembolic complications and septicemia (7,8). A better understanding of the sequence and concatenation of these events could help to devise control strategies for the disease. One of the mechanisms that could precede functional and tissue damage is the infiltration of inflammatory cells, which is known to be triggered by the release of chemokines, which are leukocyte-attracting molecules (9,10).
Gene studies in lung samples identified overexpression of CCL2 and CCL3 chemokines (11). Furthermore, Huang and cols. (12) reported that besides leukopenia and lymphopenia, hospitalized patients had higher plasma concentrations of CCL3 and CCL4 upon admission than healthy subjects. They also mention that SARS and MERS physiopathology is outlined by an increase of proinflammatory cytokines and chemokines in serum (IL-Iβ, IL-6, IL-12, IFN-γ and CCL2). Previously, serum CXCL10 and CCL7 were identified as predictors of progression (13). Hence, it is of notice that the cytokine storm is accompanied by chemokine-induced migration of white cells, particularly CCL2, CCL3, CCL7 and CXCL10.
CCR5 is a G-protein-coupled chemokine receptor expressed by dendritic cells, monocytes, macrophages, natural killer (NK) cells, Th1 cells, Th17 cells and Treg cells which has multiple ligands, namely CCL3, CCL4, CCL5, CCL7 and CCL8 (14).
In respiratory diseases, it has been shown that CCR5 is involved in neutrophil recruitment to the lungs (15). In that sense, it has been observed in human subjects with chronic pulmonary inflammatory diseases that infiltrated neutrophils overexpress CCR5, induced by activation of TLRs and NOD2 (16). Neutrophils’ infiltration in pulmonary capillaries, alveolar extravasation and neutrophilic mucositis have already been observed in COVID-19. (17). Despite the precise mechanism that drives such infiltration remains unknown, it is feasible that CCR5 may play a critical role in the immunopathology of COVID-19 (18).
Along with phagocytosis and oxidative burst, neutrophils have another resource to eliminate pathogens: NETosis, a distinct form of programmed, necrotic cell death characterized by the neutrophilic release of network organized protein and DNA structures known as “neutrophil extracellular traps” (NETs), which are able to capture and entangle such pathogens (19). Though beneficial against pathogens, NETs could stimulate certain disease processes, some of them viral (20). Excessive formation of NETs could trigger a chain of inflammatory reactions that destroys surrounding tissue and facilitates micro thrombosis (21). Previous reports associate aberrant formation of NETs to pulmonary disorders, namely ARDS (22). The increase in D dimer described as a severity marker in COVID-19 severe patients, could be related to NETosis, since it has an essential role in the start and progression of thrombosis in veins and arteries (23). Hence, all these neutrophil functions could be part of both the tissue damage and microthrombosis in COVID-19.
As previously mentioned, the chemokines increased in COVID-19 severe patients are CCL3, CCL5 and CCL7. All these are CCR5 ligands; thus, our group hypothesizes that a CCR5 blockade could prevent leukocyte migration to the lung and attenuate the cytokine storm, and can be considered a therapeutic target (24). Moreover, a monoclonal antibody targeted against CCR5 (Leronlimab, also known as PRO140) was able to restore lymphocyte levels and decrease IL-6 in 10 COVID-19 patients (18).
CCR5 targeted drugs have been tested in HIV, multiple sclerosis and hepatic fibrosis clinical trials (25). One of these drugs is Maraviroc (MVC), an oral CCR5 antagonist, mainly used as an anti-retro viral that impedes binding of the gp120 viral protein to CCR5, thus avoiding viral internalization by the cells. (26). MVC has not been widely studied in the context of reduction of hyperinflammatory conditions. However, some reports have found interesting effects in modulation or resolving of general inflammatory conditions, such as reduction of cytokine expression by in vitro human adipocytes (27), and as an alleviating agent of hemorrhage-induced hepatic injury in rats by a PPAR-γ depending pathway (28). Furthermore, it was used in a phase II study to minimize the graft vs. host disease in bone marrow stem cell transplant in pediatric patients (29). It has also been observed that MVC decreases mucosal inflammation (30), VCAM-1 (31), T cell infiltration, neuroinflammation (32) and endothelial dysfunction (33). Regarding the lung, a model of induced hemorrhagic shock in rats reported that MVC has a protective role against pulmonary damage (34). All the aforementioned, along with the broad safety range of MVC, good tolerance an low incidence of adverse effects (35) makes it an excellent candidate to be used as a modulator of the dysregulated immune response in COVID-19.
On the other hand, an in silico study by Shams and cols.(36), aimed to find possible candidates for the treatment of SARS-CoV-2, and found that MVC could have a direct antiviral activity by binding to the main protease of the virus (Mpro). Altogether, this body of evidence suggests that MVC could not only block the CCR5-dependent migration to the lung, but also reduce the viral load. This drug has been available in the market for 10 years, commercialized as Selzentry® (GSK®), and used as anti-retroviral therapy for HIV patients.
We hypothesize that an effective treatment for COVID-19 severe patients could combine a modulator of the immune response with a direct antiviral drug against SARS-CoV-2, in order to address both the hyperinflammatory effects of the immune dysregulation and the viral load, thus yielding best results. One of these antivirals is Favipiravir (FPV), that directly inhibits viral replication and transcription by selective inhibition of the viral enzyme RNA-dependent RNA polymerase (RdRP) (37,38). FPV is a ribonucleotide analogue (fluorinated base analogue with a pyrazine carboxamide) (39). Studies of the nucleotide addition to the elongation complex of the viral RdRP showed that FPV is capable to make RdRP pause during the reading process, which leads to backtracking (an attempt to recover reading errors), that when repetitive, causes the enzyme to interpret them as a prematurely terminated product, thus stopping the elongation and therefore interrupting the viral replication process (40).
FPV has been used successfully against A H1N1 influenza (41,42). Regarding COVID-19, an open randomized study in 80 mild patients found that FPV reduced the time of viral clearance by 50% compared to Lopinavir/Ritonavir with less adverse effects (43); however, the study population had no risk comorbidities and subjects with SpO2 <93% were excluded. Another open randomized study in moderate patients reported FPV to be more effective in clinical recovery compared to Arbidol (44). An in vitro study found that FPV is capable to suppress the SARS-CoV-2 infection at high concentrations (45). Finally, to date there are 37 studies registered in the U.S. National Library of Medicine (ClinicalTrails.gov) that evaluate FPV and 3 studies with MVC in COVID-19 patients, one of which is the present study, which noteworthily, is the only that combines both drugs.