Multiple subunits of the hepatitis B virus (HBV) core protein (HBc) assemble into an icosahedral capsid that packages the viral pregenomic RNA (pgRNA). The N-terminal domain (NTD) of HBc is sufficient for capsid assembly, in the absence of pgRNA or any other viral or host factors, under conditions of high HBc and/or salt concentrations. The C-terminal domain (CTD) is deemed dispensable for capsid assembly although it is essential for pgRNA packaging. We report here that HBc expressed in a mammalian cell lysate, the rabbit reticulocyte lysate (RRL), was able to assemble into capsids when HBc concentrations (in low nM) mimicked those achieved under conditions of viral replication in vivo and were far below those used previously for capsid assembly in vitro. Furthermore, at physiologically low HBc concentrations in RRL, NTD was insufficient for capsid assembly and CTD was also required. CTD likely facilitated assembly under these conditions via RNA binding and protein-protein interactions. Moreover, CTD underwent phosphorylation and dephosphorylation events in RRL as in vivo, which regulated capsid assembly. Importantly, NTD alone also failed to accumulate in mammalian cells, likely resulting from its failure to assemble efficiently. Co-expression of the full-length HBc rescued NTD assembly in RRL as well as NTD expression and assembly in mammalian cells, resulting in the formation of mosaic capsids containing both full-length HBc and NTD. These results have important implications for HBV assembly during replication and provide a facile cell-free system to study capsid assembly under physiologically relevant conditions including its modulation by host factors.
Hepatitis B virus (HBV) is an important global human pathogen and the main cause of liver cancer worldwide. An essential component of HBV is the spherical capsid composed of multiple copies of a single protein, the core protein (HBc). We have developed a mammalian cell-free system in which HBc is expressed at physiological (low) concentrations and assemble into capsids under near physiological conditions. In this cell-free system, as in mammalian cells, capsid assembly depends on the C-terminal domains (CTD) of HBc, in contrast to other assembly systems in which HBc assembles into capsids independent of CTD under non-physiological protein and salt concentrations. Furthermore, the phosphorylation state of CTD regulates capsid assembly and RNA encapsidation, in the cell-free system as in mammalian cells. This system will facilitate detailed studies on capsid assembly and RNA encapsidation under physiological conditions and identification of antiviral agents that target HBc.
Copyright © 2016, American Society for Microbiology. All Rights Reserved.

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Bromo and extra terminal (BET) proteins (BRD2, BRD3, BRD4 and BRDT) are epigenetic transcriptional regulators required for efficient expression of growth promoting, cell cycle progression and antiapoptotic genes. Through their bromodomain, these proteins bind to acetylated lysine residues of histones and are recruited to transcriptionally active chromatin. Inhibition of the BET-histone interaction provides a tractable therapeutic strategy to treat diseases that may have epigenetic dysregulation. JQ1 is a small molecule that blocks BET interaction with histones. It has been shown to decrease proliferation of patient-derived multiple myeloma in vitro and to decrease tumor burden in vivo in xenograft mouse models. While targeting BET appears to be a viable and efficacious approach, the nonclinical safety profile of BET inhibition remains to be well-defined. We report that mice dosed with JQ1 at efficacious exposures demonstrate dose-dependent decreases in their lymphoid and immune cell compartments. At higher doses, JQ1 was not tolerated and due to induction of significant body weight loss led to early euthanasia. Flow cytometry analysis of lymphoid tissues showed a decrease in both B- and T-lymphocytes with a concomitant decrease in peripheral white blood cells that was confirmed by hematology. Further investigation with the inactive enantiomer of JQ1 showed that these in vivo effects were on-target mediated and not elicited through secondary pharmacology due to chemical structure.
Copyright © 2016 Elsevier Inc. All rights reserved.

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To determine the dose-limiting toxicities, adverse events (AE), pharmacokinetics, and preliminary evidence of antitumor activity of CUDC-427 (formerly GDC-0917), a selective antagonist of inhibitor of apoptosis (IAP) proteins.
Patients with advanced solid malignancies were treated with escalating doses of CUDC-427 orally on a daily14-days on/7 days-off schedule in 21-day cycles using a modified continuous reassessment method design. Blood samples were assayed to determine the pharmacokinetic properties, pharmacodynamic alterations of cellular IAP levels in peripheral blood mononuclear cells (PBMCs), and monocyte chemoattractant protein-1 (MCP-1) levels.
Forty-two patients received 119 cycles of CUDC-427. Overall, the most common treatment-related toxicities were fatigue, nausea, vomiting, and rash. One DLT (Grade 3 fatigue) occurred in a patient at 450 mg dose level during cycle 1; and five patients experienced AEs related to CUDC-427 that led to discontinuation and included Grade 3 pruritis, and fatigue, and Grade 2 drug hypersensitivity, pneumonitis, rash, and QT prolongation. The maximum planned dose of 600 mg po daily × 2 weeks was reached, which allometrically scaled to exceed the IC90 in preclinical xenograft studies. Significant decreases in cIAP-1 levels in PBMCs were observed in all patients 6 hours after initial dosing. Responses included durable complete responses (CR) in one patient with ovarian cancer and one patient with MALT lymphoma.
CUDC-427 can be administered safely at doses up to 600 mg daily for 14 days every 3 weeks. The absence of severe toxicities, inhibition of cIAP-1 in PBMC, and antitumor activity warrant further studies.
Copyright ©2016, American Association for Cancer Research (AACR) (Free AACR Whitepaper).

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The 2015 Annual National Toxicology Program Satellite Symposium, entitled "Pathology Potpourri" was held in Minneapolis, Minnesota, at the American College of Veterinary Pathologists/American Society for Veterinary Clinical Pathology/Society of Toxicologic Pathology combined meeting. The goal of this symposium is to present and discuss diagnostic pathology challenges or nomenclature issues. Because of the combined meeting, both laboratory and domestic animal cases were presented. This article presents summaries of the speakers’ talks, including challenging diagnostic cases or nomenclature issues that were presented, along with select images that were used for audience voting and discussion. Some lesions and topics covered during the symposium included hepatocellular lesions, a proposed harmonized diagnostic approach to rat cardiomyopathy, crop milk in a bird, avian feeding accoutrement, heat exchanger in a tuna, metastasis of a tobacco carcinogen-induced pulmonary carcinoma, neurocytoma in a rat, pituicytoma in a rat, rodent mammary gland whole mounts, dog and rat alveolar macrophage ultrastructure, dog and rat pulmonary phospholipidosis, alveolar macrophage aggregation in a dog, degenerating yeast in a cat liver aspirate, myeloid leukemia in lymph node aspirates from a dog,Trypanosoma cruziin a dog, solanum toxicity in a cow, bovine astrovirus, malignant microglial tumor, and nomenclature challenges from the Special Senses International Harmonization of Nomenclature and Diagnostic Criteria Organ Working Group.
© The Author(s) 2016.

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THIOMAB drug conjugates (TDCs) with engineered cysteine residues allow site-specific drug conjugation and defined Drug-to-Antibody Ratios (DAR). In order to help elucidate the impact of drug-loading, conjugation site, and subsequent deconjugation on pharmacokinetics and efficacy, we have developed an integrated mathematical model to mechanistically characterize pharmacokinetic behavior and preclinical efficacy of MMAE conjugated TDCs with different DARs. General applicability of the model structure was evaluated with two different TDCs.
Pharmacokinetics studies were conducted for unconjugated antibody and purified TDCs with DAR-1, 2 and 4 for trastuzumab TDC and Anti-STEAP1 TDC in mice. Total antibody concentrations and individual DAR fractions were measured. Efficacy studies were performed in tumor-bearing mice.
An integrated model consisting of distinct DAR species (DAR0-4), each described by a two-compartment model was able to capture the experimental data well. Time series measurements of each Individual DAR species allowed for the incorporation of site-specific drug loss through deconjugation and the results suggest a higher deconjugation rate from heavy chain site HC-A114C than the light chain site LC-V205C. Total antibody concentrations showed multi-exponential decline, with a higher clearance associated with higher DAR species. The experimentally observed effects of TDC on tumor growth kinetics were successfully described by linking pharmacokinetic profiles to DAR-dependent killing of tumor cells.
Results from the integrated model evaluated with two different TDCs highlight the impact of DAR and site of conjugation on pharmacokinetics and efficacy. The model can be used to guide future drug optimization and in-vivo studies.

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