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The bromodomain and extra-terminal (BET) family of proteins, consisting of the bromodomains containing protein 2 (BRD2), BRD3, BRD4, and the testis-specific BRDT, are key epigenetic regulators of gene transcription and has emerged as an attractive target for anticancer therapy. Herein, we describe the discovery of a novel potent BET bromodomain inhibitor, using a systematic structure-based approach focused on improving potency, metabolic stability, and permeability. The optimized dimethylisoxazole aryl-benzimidazole inhibitor exhibited high potency towards BRD4 and related BET proteins in biochemical and cell-based assays and inhibited tumor growth in two proof-of-concept preclinical animal models.

The extracellular ATP/adenosine axis in the tumor microenvironment (TME) has emerged as an important immune-regulatory pathway. Nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), otherwise known as CD39, is highly expressed in the TME, both on infiltrating immune cells and tumor cells across a broad set of cancer indications. CD39 processes pro-inflammatory extracellular ATP to ADP and AMP, which is then processed by Ecto-5ʹ-nucleotidase/CD73 to immunosuppressive adenosine. Directly inhibiting the enzymatic function of CD39 via an antibody has the potential to unleash an immune-mediated anti-tumor response via two mechanisms: 1) increasing the availability of immunostimulatory extracellular ATP released by damaged and/or dying cells, and 2) reducing the generation and accumulation of suppressive adenosine within the TME. Tizona Therapeutics has engineered a novel first-in-class fully human anti-CD39 antibody, TTX-030, that directly inhibits CD39 ATPase enzymatic function with sub-nanomolar potency. Further characterization of the mechanism of inhibition by TTX-030 using CD39+ human melanoma cell line SK-MEL-28 revealed an uncompetitive allosteric mechanism (α

Apolipoprotein A-I (ApoA-I), a primary protein component of high-density lipoprotein (HDL), plays an important role in cholesterol metabolism mediating the formation of HDL and the efflux of cellular cholesterol from macrophage foam cells in arterial walls. Lipidation of ApoA-I is mediated by adenosine triphosphate (ATP) binding cassette A1 (ABCA1). Insufficient ABCA1 activity may lead to increased risk of atherosclerosis due to reduced HDL formation and cholesterol efflux. The standard radioactive assay for measuring cholesterol transport to ApoA-I has low throughput and poor dynamic range, and it fails to measure phospholipid transfer. We describe the development of two sensitive, nonradioactive high-throughput assays that report on the lipidation of ApoA-I: a homogeneous assay based on time-resolved fluorescence resonance energy transfer (TR-FRET) and a discontinuous assay that uses the label-free Epic platform. The TR-FRET assay employs HiLyte Fluor 647-labeled ApoA-I with N-terminal biotin bound to streptavidin-terbium. When fluorescent ApoA-I was incorporated into HDL, TR-FRET decreased proportionally to the increase in the ratio of lipids to ApoA-I, demonstrating that the assay was sensitive to the amount of lipid bound to ApoA-I. In the Epic assay, biotinylated ApoA-I was captured on a streptavidin-coated biosensor. Measured resonant wavelength shift was proportional to the amount of lipids associated with ApoA-I, indicating that the assay senses ApoA-I lipidation. © 2012 Society for Laboratory Automation and Screening.

Tegobuvir (TGV) is a novel non-nucleoside inhibitor (NNI) of HCV RNA replication with demonstrated antiviral activity in patients with genotype 1 chronic HCV infection. The mechanism of action of TGV has not been clearly defined despite the identification of resistance mutations mapping to the NS5B polymerase region. TGV does not inhibit NS5B enzymatic activity in biochemical assays in vitro, suggesting a more complex antiviral mechanism with cellular components. Here, we demonstrate that TGV exerts anti-HCV activity utilizing a unique chemical activation and subsequent direct interaction with the NS5B protein. Treatment of HCV subgenomic replicon cells with TGV results in a modified form of NS5B with a distinctly altered mobility on a SDS-PAGE gel. Further analysis reveals that the aberrantly migrating NS5B species contains the inhibitor molecule. Formation of this complex does not require the presence of any other HCV proteins. The intensity of the aberrantly migrating NS5B species is strongly dependent on cellular glutathione levels as well as CYP 1A activity. Furthermore analysis of NS5B protein purified from a heterologous expression system treated with TGV by mass spectrometry suggests that TGV undergoes a CYP- mediated intracellular activation step and the resulting metabolite, after forming a glutathione conjugate, directly and specifically interacts with NS5B. Taken together, these data demonstrate that upon metabolic activation TGV is a specific, covalent inhibitor of the HCV NS5B polymerase and is mechanistically distinct from other classes of the non-nucleoside inhibitors (NNI) of the viral polymerase.

Apolipoprotein A-I (ApoA-I) is the primary protein component of high density lipoproteins (HDL). ApoA-I plays an important role in cholesterol metabolism by mediating the formation of nascent HDL and the efflux of cellular cholesterol from macrophage foam cells in arterial walls. Lipidation of ApoA-I is mediated by the ATP-binding cassette A1 (ABCA1). Insufficient ABCA1 activity my lead to reduced HDL formation, reduced cholesterol efflux and the development of arteriosclerosis. The standard radioactive assay for measuring cholesterol transport to lipid-free ApoA-I has low through-put, poor dynamic range and fails to measure phospholipid transferred with cholesterol. We describe the development of two sensitive, non-radioactive high-throughput assays that report on the lipidation state of ApoA-I and may have applications for studying ABCA1 function and HDL metabolism: a homogenous assay based on the Time Resolved FRET (TR-FRET) and a discontinuous assay that uses the Epic. The TR-FRET assay employs a fluorescent ApoA-I where Cysteine is labeled with the FRET acceptor HiLyte-Fluor-647 and an N-terminal Biotin-AviTag is bound to the streptavidin-Terbium conjugate. When this ApoA-I was incorporated into recombinant HDL, TR-FRET decreased proportionally to the increase in the ratio of lipid to ApoA-I in agreement with the expansion of the surface area of lipids concomitant with the increase in separation of N-terminal and central regions of the protein and demonstrated that the HTRF assay was sensitive to the amount of lipid associated with ApoA-I. The Epic is a label-free platform that allows for the observation of direct biomolecular interactions via a resonant wavelength shift which is proportional to the mass bound to the surface. In the Epic assay, biotinylated ApoA-I was captured on streptavidin-coated sensor. The response was proportional to the amount of lipids associated with ApoA-I indicating that the assay could sense lipidation of ApoA-I.