1,2,4-Triazoloazine derivatives as a new type of herpes simplex virus inhibitors

A new class of inhibitors of herpes simplex virus replication was found. The compounds under study are derived from condensed 1,2,4-triazolo[5,1-c][1,2,4]triazines and 1,2,4-triazolo[1,5-a]pyrimidines, structural analogues of natural nucleic bases. Antiherpetic activity and cytotoxicity of the compounds were studied. The corresponding triphosphates of several active compounds were prepared and tested as inhibitors of DNA synthesis catalyzed by herpes simplex virus polymerase. The potential mechanism of their action is blocking of DNA dependent DNA polymerase, a key enzyme of viral replication.     

Assembly of the AAA ATPase Vps4 on ESCRT-III

Vps4 is a key enzyme that functions in endosomal protein trafficking, cytokinesis, and retroviral budding. Vps4 activity is regulated by its recruitment from the cytoplasm to ESCRT-III, where the protein oligomerizes into an active ATPase. The recruitment and oligomerization steps are mediated by a complex network of at least 12 distinct interactions between Vps4, ESCRT-III, Ist1, Vta1, and Did2. The order of events leading to active, ESCRT-III–associated Vps4 is poorly understood. In this study we present a systematic in vivo analysis of the Vps4 interaction network. The data demonstrated a high degree of redundancy in the network. Although no single interaction was found to be essential for the localization or activity of Vps4, certain interactions proved more important than others. The most significant among these were the binding of Vps4 to Vta1 and to the ESCRT-III subunits Vps2 and Snf7. In our model we propose the formation of a recruitment complex in the cytoplasm that is composed of Did2-Ist1-Vps4, which upon binding to ESCRT-III recruits Vta1. Vta1 in turn is predicted to cause a rearrangement of the Vps4 interactions that initiates the assembly of the active Vps4 oligomer.     

Co-localization of components of the protein-synthesizing machinery with the cytoskeleton in G0-arrested cells.

The distribution of eukaryotic elongation factor 2 (eEF-2) in G₀-arrested fixed human skin diploid fibroblasts was studied by indirect immunofluorescent microscopy. It was found earlier that the main part of eEF-2 in cycling cells was located near the nucleus in the endoplasm (Gavrilova et al., 1987). It has been demonstrated here that the transition from proliferation to the G₀ phase of the cell cycle leads to the distribution of eEF-2 mainly along the intermediate filaments and/or microtubules. Both in cycling and in G₀-arrested fibroblasts a portion of eEF-2 is also co-localized with actin microfilament bundles. The reversion of the cells from the G₀ phase to proliferation is accompanied by rearrangement of the actin cytoskeleton and reversal to the original pattern of eEF-2 distribution. It is likely that the different types of cytoskeleton in eukaryotic cells can be involved in organization of protein-synthesizing machinery.     

Influence of a natural and a synthetic inhibitor of factor XIIIa on fibrin clot rheology

We investigated the origins of greater clot rigidity associated with FXIIIa-dependent cross-linking. Fibrin clots were examined in which cross-linking was controlled through the use of two inhibitors: a highly specific active-center-directed synthetic inhibitor of FXIIIa, 1,3-dimethyl-4,5-diphenyl-2[2(oxopropyl)thio]imidazolium trifluoromethylsulfonate, and a patient-derived immunoglobulin directed mainly against the thrombin-activated catalytic A subunits of thrombin-activated FXIII. Cross-linked fibrin chains were identified and quantified by one- and two-dimensional gel electrophoresis and immunostaining with antibodies specific for the alpha- and gamma-chains of fibrin. Gamma-dimers, gamma-multimers, alpha(n)-polymers, and alpha(p)gamma(q)-hybrids were detected. The synthetic inhibitor was highly effective in preventing the production of all cross-linked species. In contrast, the autoimmune antibody of the patient caused primarily an inhibition of alpha-chain cross-linking. Clot rigidities (storage moduli, G') were measured with a cone and plate rheometer and correlated with the distributions of the various cross-linked species found in the clots. Our findings indicate that the FXIIIa-induced dimeric cross-linking of gamma-chains by itself is not sufficient to stiffen the fibrin networks. Instead, the augmentation of clot rigidity was more strongly correlated with the formation of gamma-multimers, alpha(n)-polymers, and alpha(p)gamma(q)-hybrid cross-links. A mechanism is proposed to explain how these cross-linked species may enhance clot rigidity.     

Some of eukaryotic elongation factor 2 is colocalized with actin microfilament bundles in mouse embryo fibroblasts

Indirect immunofluorescent microscopy was used to study the distribution of eukaryotic elongation factor 2 (EF-2) in cultured mouse embryo fibroblasts. The perinuclear area (endoplasm) of all the cells and many straight cables running along the whole cytoplasm were stained with monospecific goat or rabbit antibodies to rat liver EF-2. Double staining of the cells with antibodies to EF-2 and rhodaminyl-phalloidin (used for actin microfilament detection) showed that EF-2 containing cables coincided with bundles of actin microfilaments. Not all actin microfilament bundles contained EF-2: sometimes EF-2 was not observed in bundles running along the cell edges or in actin microfilament junctions. Triton X-100 extracted most of EF-2 from the cells and no actin microfilament bundles were stained with the EF-2 antibodies in the Triton-extracted cells. Thus, in mouse embryo fibroblasts EF-2 can be found along actin microfilament bundles, but it is unlikely to be their integral protein.     

Synthesis of antitumor 6-alkylidenepenicillanate sulfones and related 3-alkylidene-2-azetidinones

6-alkylidenepenicillanate sulfoxides and sulfones were synthesized on the base of 6-oxopenicillanate esters. The targeted splitting of their thiazolidine ring led to the formation of 3-alkylidene substituted 4-heteryldithio and 4-methylsulfonyl azetidin-2-ones. Some of mono and bicyclic beta-lactams revealed potent cytotoxic properties towards monolayer tumor cells in <10-microM concentrations.     

Electrophysiological action of ethacizin in acute myocardial ischemia in dogs

The effects of ethacizin on delayed activation of the ischemic myocardium by acute left anterior descending coronary artery occlusion were studied in dogs. Ethacizin, administered intravenously at a dose of 0.5 or 1 mg/kg depressed the conduction of excitation in the ischemic myocardium and significantly increased the incidence of ventricular fibrillation. Electrophysiological effects of ethacizin in acute myocardial ischemia, as well as its antiarrhythmic activity at the advanced stages of experimental myocardial infarction might be related to an intensive influence of ethacizin on fast inward sodium current in the myocardial fibers.