Apabetalone, a BET inhibitor, attenuates inflammation induced by viral RNA mimetic and reduces SARS-CoV-2 spike protein binding regardless of variants

Background/Introduction

Hyperinflammatory responses to SARS-CoV-2 can cause myocarditis and cardiac dysfunction including congestive heart failure [1]. SARS-CoV-2 RNA induces type I interferon (IFN-I), activating IFN regulatory factors (IRFs) and downstream IFN stimulated genes (ISGs) to initiate inflammatory processes. SARS-CoV-2 variants may develop immune escape, undercutting benefits of vaccinations. These challenges highlight the need of variant-independent therapies to improve COVID-19 outcomes. Apabetalone is an epigenetic BD2-selective BET inhibitor in phase 3 trials for cardiovascular disease [2]. Apabetalone has the potential to treat COVID-19. It counters inflammatory signals caused by cytokine storm (CS), preventing cardiac dysfunction associated with severe COVID-19 symptoms in cardiac organoids [3]. It also downregulates angiotensin-converting enzyme 2 (ACE2) expression, the main host cell receptor for SARS-CoV-2 spike protein thus impeding propagation of wild-type SARS-CoV-2 [3,4].

Purpose

1) Evaluate apabetalone's effect on inflammatory processes induced by viral-RNA mimetic in human lung cells; 2) Assess apabetalone's ability to prevent binding of the highly contagious delta variant spike protein to human lung cells.

Methods

Inflammatory gene expression was examined by real-time PCR in apabetalone treated human bronchial epithelial cells (Calu-3) stimulated with poly I:C, a well-accepted viral RNA mimetic that elicits inflammatory signals similar to SARS-CoV-2 RNA [5]. Binding of SARS-CoV-2 delta or wild-type spike protein to apabetalone treated Calu-3 cells was determined by flow cytometry.

Results

In Calu-3 cells, apabetalone dose-dependently downregulated poly I:C induced transcription of key COVID-19 associated cytokines (IL6, CXCL10, CCL2) to a similar extent as baricitinib (up to 86%, p<0.0001), an anti-inflammatory agent in emergency use for COVID-19 treatment. Moreover, apabetalone but not baricitinib diminished IL1B mRNA levels (up to 66%, p<0.0001). Apabetalone and baricitinib opposed poly I:C induced expression of IFNB1 (an IFN-I), IRF1 and IRF9 (upstream regulators) as well as IFIT1 and IFIT2 (downstream ISGs that regulate CXCL10 expression; up to 90%, p<0.0001). Clinically relevant doses of apabetalone did not alter expression of anti-viral IFITM2, an ISG that blocks SARS-CoV-2, particularly omicron, endosomal entry [6]. Therefore, apabetalone counters the expression of inflammatory factors with roles in CS and IFN-I signaling in response to poly I:C. Additionally, apabetalone reduced delta and wild-type spike protein binding to unstimulated Calu-3 cells (up to 72%, p<0.0001).

Conclusions

Apabetalone's dual anti-viral and anti-inflammatory mechanism positions it as a variant-independent COVID-19 therapeutic. Together with an established safety profile from >2000 treatment-years with apabetalone, the data provide rationale for an ongoing clinical trial (NCT04894266) which includes analysis of cardiac damage.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): Resverlogix Corp

P5509Apabetalone (RVX-208) inhibits key drivers of vascular inflammation, calcification, and plaque vulnerability through a BET-dependent epigenetic mechanism

Apabetalone (RVX-208) is an orally available small molecule bromodomain & extraterminal (BET) protein inhibitor that targets the second bromodomain (BD2) of BET proteins. Apabetalone returns dysregulated BET-dependent transcription toward normal physiological levels. In phase 2 trials, apabetalone treatment reduced the incidence of major adverse cardiac events by 44% in CVD patients and by 57% in diabetic CVD patients. Previous studies have highlighted apabetalone's positive impact on vascular calcification (VC) and inflammation (VI) marker expression in vitro, as well as its ability to lower serum alkaline phosphatase (ALP) levels, and improve atherosclerotic plaque stability parameters in treated patients. In CVD, elevated inflammatory mediators and cell surface adhesion molecules drive VI, resulting in leukocyte adhesion, infiltration, uptake of oxLDL, and ultimately plaque formation. Here we show in vitro that THP-1 monocyte adhesion to human aortic endothelial cells (HAECs) increases with TNFα stimulation and is attenuated by apabetalone treatment, with fewer monocytes attaching to HAECs under flow conditions. This functional outcome is attributed to apabetalone's reduction of key endothelial adhesion genes, VCAM-1 (50%, p=0.0001) and SELE (37%, p=9x10–5). Apabetalone also prevents TNFα induction of endothelial recruitment genes (MCP-1; 75%, p=0.0002) and genes involved in plaque rupture (IL8; 24%, p=2x10–5). Basal HAEC ALP expression, a potential contributor to endothelial dysfunction and VC, also decreases with apabetalone treatment (70%, p=0.005). Induction of VI genes by TNFα is BET-dependent as degradation of BET proteins by MZ-1 prevents an increase in transcripts in response to TNFα treatment. Ingenuity® Pathway Analysis (IPA®), GSEA, and GO analysis of HAEC gene expression data predicts apabetalone inhibition of pro-atherogenic pathways, gene sets, and upstream regulators induced by TNFα. These include cytokine and chemokine, Toll-Like Receptor (TLR), NFkβ, Interferon and TNFα signaling. In addition, IPA® disease and biological function analysis predicts inhibition of immune cell activation and recruitment by apabetalone. Plasma proteomics (SOMAscan®) and IPA® analysis from apabetalone-treated CVD patients in ASSERT and ASSURE phase 2 trials indicate that apabetalone inhibits pro-atherogenic upstream regulators (IL-6 and IFNy), canonical pathways, and diseases and functions. Serum ALP also decreases dose dependently with apabetalone treatment (ASSERT). Epigenetic inhibition of VI and VC driven atherogenesis likely contributes to the reduction in MACE observed in phase 2 apabetalone treated patients. The ongoing phase 3 post-acute coronary syndrome (ACS) clinical trial in T2DM patients, BETonMACE, is currently testing this hypothesis.

Endocytic protein intersectin-l regulates actin assembly via Cdc42 and N-WASP

Intersectin-s is a modular scaffolding protein regulating the formation of clathrin-coated vesicles. In addition to the Eps15 homology (EH) and Src homology 3 (SH3) domains of intersectin-s, the neuronal variant (intersectin-l) also has Dbl homology (DH), pleckstrin homology (PH) and C2 domains. We now show that intersectin-l functions through its DH domain as a guanine nucleotide exchange factor (GEF) for Cdc42. In cultured cells, expression of DH-domain-containing constructs cause actin rearrangements specific for Cdc42 activation. Moreover, in vivo studies reveal that stimulation of Cdc42 by intersectin-l accelerates actin assembly via N-WASP and the Arp2/3 complex. N-WASP binds directly to intersectin-l and upregulates its GEF activity, thereby generating GTP-bound Cdc42, a critical activator of N-WASP. These studies reveal a role for intersectin-l in a novel mechanism of N-WASP activation and in regulation of the actin cytoskeleton.

The Ras/Rac Guanine Nucleotide Exchange Factor Mammalian Son-of-sevenless Interacts with PACSIN 1/Syndapin I, a Regulator of Endocytosis and the Actin Cytoskeleton

Mammalian Son-of-sevenless (mSos) functions as a guanine nucleotide exchange factor for Ras and Rac, thus regulating signaling to mitogen-activated protein kinases and actin dynamics. In the current study, we have identified a new mSos-binding protein of 50 kDa (p50) that interacts with the mSos1 proline-rich domain. Mass spectrometry analysis and immunodepletion studies reveal p50 as PACSIN 1/syndapin I, a Src homology 3 domain-containing protein functioning in endocytosis and regulation of actin dynamics. In addition to PACSIN 1, which is neuron-specific, mSos also interacts with PACSIN 2, which is expressed in neuronal and nonneuronal tissues. PACSIN 2 shows enhanced binding to the mSos proline-rich domain in pull-down assays from brain extracts as compared with lung extracts, suggesting a tissue-specific regulation of the interaction. Proline to leucine mutations within the Src homology 3 domains of PACSIN 1 and 2 abolish their binding to mSos, demonstrating the specificity of the interactions. In situ, PACSIN 1 and mSos1 are co-expressed in growth cones and actin-rich filopodia in hippocampal and dorsal root ganglion neurons, and the two proteins co-immunoprecipitate from brain extracts. Moreover, epidermal growth factor treatment of COS-7 cells causes co-localization of PACSIN 1 and mSos1 in actin-rich membrane ruffles, and their interaction is regulated through epidermal growth factor-stimulated mSos1 phosphorylation. These data suggest that PACSINs may function with mSos1 in regulation of actin dynamics.

Retinoic acid affects left-right patterning

Our understanding of the means by which the left-right axis is patterned is not fully understood, although a number of key intermediaries have been recently described. We report here that retinoic acid (RA) excess affects heart situs concomitant with alterations in the expression of genes implicated in the establishment of the left-right axis. Specifically, RA exposure during a specific developmental window evoked bilateral expression of lefty-1, lefty-2, nodal, and pitx-2 in the lateral plate mesoderm. Time course experiments, together with analysis of midline markers, suggest that nascent mesoderm constitutes a predominant RA target involved in this process. These events are likely to underlie the perturbations of heart looping provoked by excess RA and suggest a means by which retinoids influence the early steps in establishment of the left-right embryonic axis.

Dystonin-deficient mice exhibit an intrinsic muscle weakness and an instability of skeletal muscle cytoarchitecture

Dystonia musculorum (dt) was originally described as a hereditary sensory neurodegeneration syndrome of the mouse. The gene defective in dt encodes a cytoskeletal linker protein, dystonin, that is essential for maintaining neuronal cytoskeletal integrity. In addition to the nervous system, dystonin is expressed in a variety of other tissues, including muscle. We now show that dystonin cross-links actin and desmin filaments and that its levels are increased during myogenesis, coinciding with the progressive reorganization of the intermediate filament network. A disorganization of cytoarchitecture in skeletal muscle from dt/dt mice was observed in ultrastructural studies. Myoblasts from dt/dt mice fused to form myotubes in culture; however, terminally differentiated myotubes contained incompletely assembled myofibrils. Another feature observed in dt/dt myotubes in culture and in skeletal muscle in situ was an accumulation and abnormal distribution of mitochondria. The diaphragm muscle from dt/dt mice was weak in isometric contractility measurements in vitro and was susceptible to contraction-induced sarcolemmal damage. Altogether, our data indicate that dystonin is a cross-linker of actin and desmin filaments in muscle and that it is essential for establishing and maintaining proper cytoarchitecture in mature muscle.