BRD2 inhibition blocks SARS-CoV-2 infection by reducing transcription of the host cell receptor ACE2

COVID-19 and Cardiovascular Diseases: From Cellular Mechanisms to Clinical Manifestations

Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), quickly spread worldwide and led to over 581 million confirmed cases and over 6 million deaths as 1 August 2022. The binding of the viral surface spike protein to the human angiotensin-converting enzyme 2 (ACE2) receptor is the primary mechanism of SARS-CoV-2 infection. Not only highly expressed in the lung, ACE2 is also widely distributed in the heart, mainly in cardiomyocytes and pericytes. The strong association between COVID-19 and cardiovascular disease (CVD) has been demonstrated by increased clinical evidence. Preexisting CVD risk factors, including obesity, hypertension, and diabetes etc., increase susceptibility to COVID-19. In turn, COVID-19 exacerbates the progression of CVD, including myocardial damage, arrhythmia, acute myocarditis, heart failure, and thromboembolism. Moreover, cardiovascular risks post recovery and the vaccination-associated cardiovascular problems have become increasingly evident. To demonstrate the association between COVID-19 and CVD, this review detailly illustrated the impact of COVID-19 on different cells (cardiomyocytes, pericytes, endothelial cells, and fibroblasts) in myocardial tissue and provides an overview of the clinical manifestations of cardiovascular involvements in the pandemic. Finally, the issues related to myocardial injury post recovery, as well as vaccination-induced CVD, has also been emphasized.

Aryl hydrocarbon receptor is a proviral host factor and a candidate pan-SARS-CoV-2 therapeutic target

The emergence of a series of SARS-CoV-2 variants has necessitated the search for broad-spectrum antiviral targets. The aryl hydrocarbon receptor (AhR) senses tryptophan metabolites and is an immune regulator. However, the role of AhR in SARS-CoV-2 infection and whether AhR can be used as the target of antiviral therapy against SARS-CoV-2 and its variants are yet unclear. Here, we show that infection with SARS-CoV-2 activates AhR signaling and facilitates viral replication by interfering with IFN-I-driven antiviral immunity and up-regulating ACE2 receptor expression. The pharmacological AhR blockade or AhR knockout reduces SARS-CoV-2 and its variants' replication in vitro. Drug targeting of AhR with AhR antagonists markedly reduced SARS-CoV-2 and its variants' replication in vivo and ameliorated lung inflammation caused by SARS-CoV-2 infection in hamsters. Overall, AhR was a SARS-CoV-2 proviral host factor and a candidate host-directed broad-spectrum target for antiviral therapy against SARS-CoV-2 and its variants, including Delta and Omicron, and potentially other variants in the future.

Viral E Protein Neutralizes BET Protein-Mediated Post-Entry Antagonism of SARS-CoV-2

Inhibitors of Bromodomain and Extra-terminal domain (BET) proteins are possible anti-SARS-CoV-2 prophylactics as they downregulate angiotensin-converting enzyme 2 (ACE2). Here, we show that BET proteins should not be inactivated therapeutically as they are critical antiviral factors at the post-entry level. Knockouts of BRD3 or BRD4 in cells overexpressing ACE2 exacerbate SARS-CoV-2 infection; the same is observed when cells with endogenous ACE2 expression are treated with BET inhibitors during infection, and not before. Viral replication and mortality are also enhanced in BET inhibitor-treated mice overexpressing ACE2. BET inactivation suppresses interferon production induced by SARS-CoV-2, a process phenocopied by the envelope (E) protein previously identified as a possible "histone mimetic." E protein, in an acetylated form, directly binds the second bromodomain of BRD4. Our data support a model where SARS-CoV-2 E protein evolved to antagonize interferon responses via BET protein inhibition; this neutralization should not be further enhanced with BET inhibitor treatment.

Mutational Landscape and Interaction of SARS-CoV-2 with Host Cellular Components

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its rapid evolution has led to a global health crisis. Increasing mutations across the SARS-CoV-2 genome have severely impacted the development of effective therapeutics and vaccines to combat the virus. However, the new SARS-CoV-2 variants and their evolutionary characteristics are not fully understood. Host cellular components such as the ACE2 receptor, RNA-binding proteins (RBPs), microRNAs, small nuclear RNA (snRNA), 18s rRNA, and the 7SL RNA component of the signal recognition particle (SRP) interact with various structural and non-structural proteins of the SARS-CoV-2. Several of these viral proteins are currently being examined for designing antiviral therapeutics. In this review, we discuss current advances in our understanding of various host cellular components targeted by the virus during SARS-CoV-2 infection. We also summarize the mutations across the SARS-CoV-2 genome that directs the evolution of new viral strains. Considering coronaviruses are rapidly evolving in humans, this enables them to escape therapeutic therapies and vaccine-induced immunity. In order to understand the virus's evolution, it is essential to study its mutational patterns and their impact on host cellular machinery. Finally, we present a comprehensive survey of currently available databases and tools to study viral-host interactions that stand as crucial resources for developing novel therapeutic strategies for combating SARS-CoV-2 infection.

Relevance of BET Family Proteins in SARS-CoV-2 Infection

The recent pandemic we are experiencing caused by the coronavirus disease 2019 (COVID-19) has put the world's population on the rack, with more than 191 million cases and more than 4.1 million deaths confirmed to date. This disease is caused by a new type of coronavirus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A massive proteomic analysis has revealed that one of the structural proteins of the virus, the E protein, interacts with BRD2 and BRD4 proteins of the Bromodomain and Extra Terminal domain (BET) family of proteins. BETs are essential to cell cycle progression, inflammation and immune response and have also been strongly associated with infection by different types of viruses. The fundamental role BET proteins play in transcription makes them appropriate targets for the propagation strategies of some viruses. Recognition of histone acetylation by BET bromodomains is essential for transcription control. The development of drugs mimicking acetyl groups, and thereby able to displace BET proteins from chromatin, has boosted interest on BETs as attractive targets for therapeutic intervention. The success of these drugs against a variety of diseases in cellular and animal models has been recently enlarged with promising results from SARS-CoV-2 infection studies.

Blockade of SARS-CoV-2 infection in vitro by highly potent PI3K-α/mTOR/BRD4 inhibitor

Pathogenic viruses like SARS-CoV-2 and HIV hijack the host molecular machinery to establish infection and survival in infected cells. This has led the scientific community to explore the molecular mechanisms by which SARS-CoV-2 infects host cells, establishes productive infection, and causes life-threatening pathophysiology. Very few targeted therapeutics for COVID-19 currently exist, such as remdesivir. Recently, a proteomic approach explored the interactions of 26 of 29 SARS-CoV-2 proteins with cellular targets in human cells and identified 67 interactions as potential targets for drug development. Two of the critical targets, the bromodomain and extra-terminal domain proteins (BETs): BRD2/BRD4 and mTOR, are inhibited by the dual inhibitory small molecule SF2523 at nanomolar potency. SF2523 is the only known mTOR PI3K-α/(BRD2/BRD4) inhibitor with potential to block two orthogonal pathways necessary for SARS-CoV-2 pathogenesis in human cells. Our results demonstrate that SF2523 effectively blocks SARS-CoV-2 replication in lung bronchial epithelial cells in vitro , showing an IC ₅₀ value of 1.5 µM, comparable to IC ₅₀ value of remdesivir (1.1 µM). Further, we demonstrated that the combination of doses of SF2523 and remdesivir is highly synergistic: it allows for the reduction of doses of SF2523 and remdesivir by 25-fold and 4-fold, respectively, to achieve the same potency observed for a single inhibitor. Because SF2523 inhibits two SARS-CoV-2 driven pathogenesis mechanisms involving BRD2/BRD4 and mTOR signaling, our data suggest that SF2523 alone or in combination with remdesivir could be a novel and efficient therapeutic strategy to block SARS-CoV-2 infection and hence be beneficial in preventing severe COVID-19 disease evolution.

One Sentence Summary

Evidence of in silico designed chemotype (SF2523) targeting PI3K-α/mTOR/BRD4 inhibits SARS-CoV-2 infection and is highly synergistic with remdesivir.