Phenotypic switching in cells transformed with the herpes simplex virus thymidine kinase gene

Biochemical transformation of Ltk- cells with the herpes simplex virus thymidine kinase (tk) gene resulted in numerous TK+ colonies that survived selection in hypoxanthine-aminopterin-thymidine medium. Many of these TK+ cell lines switched phenotypes and reverted to the TK- state. In this report, we describe the biological and biochemical characteristics of three TK- revertant lines. One (K1B5) transiently expressed TK in the presence of bromodeoxyuridine, which selects for the TK- phenotype. Another TK- sibling (K1B6n) expressed TK only after removal from bromodeoxyuridine-containing medium. The last variant (K1B6me) lost the ability to switch to the TK+ phenotype, although it maintained the herpes simplex virus sequences coding for TK. Loss of the ability of K1B6me cells to express TK was correlated with extensive methylation of the sequence recognized by the restriction endonuclease HpaII (pCpCpGpG). After these cells were treated with 5-azacytidine, they regained the ability to clone in hypoxanthine-aminopterin-thymidine medium and reexpressed virus tk mRNA and enzyme. In addition, the HpaII sites that were previously shown to be refractile to enzyme digestion were converted to a sensitive state, demonstrating that they were no longer methylated.

Effects of ibotenic acid-induced loss of neurons in the medial prefrontal cortex of rats on behavioral vigilance: evidence for executive dysfunction

Rats were trained in a previously validated task for the assessment of sustained attention, or vigilance. This task required the animals to discriminate between signals of variable lengths and non-signal events by making an appropriate lever press. The performance of sham-lesioned animals in this task was characterized by a signal-length dependent number of hits. Also, approximately 70 percent of the non-signals were correctly rejected. Ibotenic acid-induced lesions of the medial prefrontal cortex decreased the relative number of hits and correct rejections and, in essence, resulted in random lever selection. The lesion did not affect the number of omissions or side bias. Furthermore, the performance of lesioned animals was insensitive to the detrimental effects of distractors. The effects of the lesions do not support an interpretation in terms of sustained attention. Rather, the pattern of the lesioned animals' performance is speculated to reveal a fundamental disruption of decisional processes, reminiscent of the executive dysfunctions observed in patients with damage to ventromedial prefrontal areas or with schizophrenia.

[Ribonucleoside and 2'-deoxyribonucleoside 5'-phosphonates: synthesis and antiviral activity]

Groups of 5'-phosphonates of natural 2'-deoxynucleosides and ribonucleosides were synthesized by condensation of 3'-acetylated 2'-deoxynucleosides or 2',3'-substituted (2',3'-O-isopropylidene, 2',3'-O-methoxymethylene, or 2',3'-O-ethoxymethylene) ribonucleosides. As condensing agents, either N,N'-dicyclohexylcarbodiimide or 2,4,6-triisopropylbenzenesulphonyl chloride were used. Nucleoside 5'-ethoxycarbonyl-phosphonates were converted into corresponding nucleoside 5'-aminocarbonylphosphonates by the action of ammonia in methanol. All compounds were tested for inhibition of several viruses, including human herpes simplex virus type 2 and cytomegalovirus, but showed no activity. A few compounds insignificantly inhibited human immunodeficiency virus type 1 reproduction. Thymidine 5'-hydrogenphosphonate neutralized the anti HIV action of 3'-azido-3'-deoxythymidine, thus indirectly showing that it could be partly hydrolyzed in cell culture to corresponding thymidine.

Anti-viral activity of human recombinant heparin-binding proteins HBNF and MK

Herpes simplex viruses bind to cell surface heparan sulfate proteoglycans, as a first step of viral infection. We report here that two recombinant heparin-binding proteins HBNF and MK inhibit infectivity of human herpes simplex viruses types 1 and 2 and human cytomegalovirus. Carboxymethylated HBNF and MK, which retain affinity for heparin-Sepharose, do not exhibit anti-viral activities. Arguments are presented that anti-viral effects of HBNF and MK are due to the competition for the specific binding to the cell surface heparan sulfate proteoglycans.

Comparisons of anti-human immunodeficiency virus activities, cellular transport, and plasma and intracellular pharmacokinetics of 3'-fluoro-3'-deoxythymidine and 3'-azido-3'-deoxythymidine

3'-Fluoro-3'-deoxythymidine (FLT), a candidate anti-AIDS compound in clinical trials, showed anti-human immunodeficiency virus type 1 (HIV-1) potency (50% effective concentration, 0.0052 microM) slightly better than or equal to that of 3'-azido-3'-deoxythymidine (AZT) in MT4 cells and was threefold more potent in H9 cells. There was no FLT resistance demonstrable in the AZT-resistant HIV-1 strains. Both FLT and AZT showed low cytotoxicity for MT4 cells, with selectivity indices (efficacy/toxicity ratio) of greater than 47,000 and greater than 33,000, respectively. Cellular permeation of FLT and thymidine (dThd) was greater than that of AZT, and FLT and dThd permeated the cell membranes by a carrier-mediated mechanism as well as by simple diffusion, as indicated by the existence of nitrobenzylthioinosine-5'-monophosphate-sensitive and -insensitive components. By contrast, transport of AZT into cells was by simple diffusion. The intracellular level of the triphosphate of FLT (FLTTP) in MT4 cells was two- to threefold higher than that of AZT (AZTTP) after exposure to 1.8 microM each compound for 12 h. The elimination kinetics of FLTTP and AZTTP in HIV-1-infected MT4 cells in fresh medium showed biphasic patterns, with initial half-lives of 1.03 and 1.09 h, respectively. In phytohemagglutinin-stimulated human peripheral blood lymphocytes, the FLTTP level was increased 59-fold compared with that in unstimulated cells at 12 h, was four- to sixfold higher than the level of AZTTP in stimulated cells at 12 h, and remained four- to fivefold higher during a 4-h elimination period in fresh medium and twofold higher at the end of a 12-h elimination period. Two- to eightfold more [3H]AZT than [3H]FLT was incorporated into the host cell DNA, and both [3H]AZT and [3H]FLT remained persistently incorporated for over 24 h. The incorporated [3H]AZT and [3H]FLT were alkali labile, whereas incorporated [3H]dThd was alkali stable. Pharmacokinetics of FLT in plasma of monkeys after intravenous (i.v.) administration showed that the FLT concentration in plasma declined, with a half-life of 1.19 +/- 0.1 h; the steady-state volume of distribution was 0.93 +/- 0.2 liter/kg of body weight, and total clearance was 0.56 +/- 0.15 liter/kg. Oral bioavailability of FLT was excellent and comparable to i.v. bioavailability in terms of areas under the concentration-time curves for three monkeys. Of the total dose, 41 to 61% was excreted in urine as unchanged FLT, and only 3.2 to 7.4% of the total dose was identified as glucuronide-conjugated FLT in urine 48 h after i.v. administration to monkeys. We conclude that FLT exhibits an anti-HIV-1 potency similar to that of AZT but with slightly better selectivity of effects and with higher intracellular active metabolite levels.

MTX5: a cell line expressing biologically active HSV-1 Vmw65 protein

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Activity of (+)-cyclaradine (Sch 31172) against herpes simplex virus in vitro and in vivo

(+)-Cyclaradine (Sch 31172) is the carbocyclic derivative of adenosine arabinoside (9-beta-D-arabinofuranosyladenine). Because it is not deaminated by deaminase in serum, as is adenosine arabinoside, (+)-cyclaradine is about 2 to 5 times more active in vitro against herpes simplex virus. (+)-Cyclaradine has in vitro activity nearly equivalent to that of phosphonoformate but is significantly less active than acycloguanosine (acyclovir; ACV), trifluorothymidine, or 9-(1,3-dihydroxy-2-propoxymethyl)guanine. The absolute ratios of in vitro activities are difficult to determine because of variability among virus strains, inoculum size, and dependence on the tissue culture cell line in which the comparative test is carried out. (+)-Cyclaradine is active against TK-, ACV-resistant mutants. In the guinea pig model of vaginal herpes simplex virus infection, (+)-cyclaradine is only slightly less active than ACV when both molecules are nearly equivalently bioavailable; thus, the large difference in activity seen in vitro is not reflected in this in vivo model system.

Properties of herpes simplex virus type 1 and type 2 DNA polymerase

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) DNA polymerases were highly purified from infected HeLa BU cells by DEAE cellulose, phosphocellulose and DNA cellulose column chromatography. DNA exonuclease activity but not endonuclease activity was found associated with both types of DNA polymerase. Both DNA polymerase activities could be activated by salt in a similar fashion with the optimal activity in the range of ionic strength between 0.22 and 0.29 alpha. At an ionic strength of 0.14, spermidine and putrescine in the concentration range (0--5 mM) studied could mimic the action of KCI in stimulating DNA polymerase activity. Spermine, in the same concentration range, had a biphasic effect. At an ionic strength of 0.29 all three polyamines were inhibitory. HSV-1 and HSV-2 DNA polymerase are similar in their column chromatographic behavior, sedimentation rate in sucrose gradient centrifugation, and activation energy, but they differ in their heat stability at 45 degrees C with the HSV-2 enzyme more stable than the HSV-1 enzyme. Kinetic behavior of both enzymes is similar, with Km values for deoxyribonucleoside triphosphates in the range of 5 . 10(-7) to 1.8 . 10(-8) M. IdUTP and dUTP served as apparent competitive inhibitors with respect to dTTP, and AraATP acted as an apparent competitive inhibitor with respect to dATP. AraATP could not replace dATP in the DNA polymerization reaction; in contrast, IdUTP could replace TTP. Phosphonoformic acid behaved as an uncompetitive inhibitor with respect to DNA. The ID(50) value estimated was foind to be dependent on the purity of the DNA polymerase used and the ionic strength of the assay condition. Each DNA-polymerase associated DNA exonuclease had the same stability at 45 degrees C as its DNA polymerase. The associated DNAase activity was inhibited by phosphonoformic acid and high ionic strength of the assay condition.

Human chorionic gonadotrophins (hCG) in non-trophoblastic neoplasms. Assessment of abnormalities of hCG and CEA in bronchogenic and digestive neoplasms

Evaluation of plasma hCG measurement in the diagnosis of nontrophoblastic neoplasms and assessment of the value of concomitant measurement of plasma hCG and CEA in patients with bronchogenic carcinoma and neoplasms of the digestive tract were undertaken. Only one of 70 normal control subjects had positive plasma hCG (3.5 ng/ml), whereas 54 of 320 patients with nontrophoblastic neoplasms had measurable plasma hCG (1.9 to 160 ng/ml). Forty of these patients had less than 5.1 ng/ml. Elevated plasma CEA levels of 3.6 to 140 ng/ml were found in 38 of the 70 patients with bronchogenic carcinoma and 30 of the 72 patients with neoplasms of the digestive tract in this series. Concomitant positive hCG was found in only six of the 68 patients who had elevated CEA levels, and positive hCG was found in eight of 74 patients who had normal plasma CEA. The low frequency and the modest elevation of plasma hCG, despite frequent advanced disease, indicate plasma hCG has limited value as a biologic marker for diagnosis and assessment of non-trophoblastic neoplasms.

Deoxythymidine kinase induced in HeLa TK- cells by herpes simplex virus type I and type II. II. Purification and characterization

Deoxythymidine kinase activities were induced in HeLa TK- (deoxythymidine kinase-deficient) cells infected with either herpes simplex virus type I or herpes simplex virus type II. The herpes simplex virus type I-induced enzyme was found in the cytoplasmic and nuclear fractions of the infected cells, whereas the herpes simplex type II-induced deoxythymidine kinase could only be found in the cytoplasm. Herpes simplex virus type I and II specific deoxythymidine kinases were purified by affinity column chromatography. Both purified deoxythymidine kinases retained the deoxycytidine kinase activity present in the crude preparation. The purified herpes simplex virus type I deoxythymidine kinase had a different mobility on electrophoresis, but the same sedimentation rate on a glycerol gradient as the corresponding unpurified enzyme, whereas the purified herpes simplex virus type II deoxythymidine kinase had the same mobility and sedimentation rate as the corresponding unpurified enzyme. In the presence of Mg2+ATP and dithiothreitol, herpes simplex virus type II deoxythymidine kinase was more stable than herpes simplex virus type I deoxythymidine kinase at both 45 degrees and 4 degrees. The deoxycytidine kinase activity present in the purified preparations was inactivated at the same rate as the deoxythymidine kinase activity. In the presence of the other substrate, deoxythymidine, herpes simplex virus type I deoxythymidine kinase was more stable than herpes simplex virus type II kinase. The purified herpes simplex virus type I and II deoxythymidine kinase had different activation energies when Mg2+ATP and deoxythymidine were used as substrates, but showed the same sensitivity toward ammonium sulfate inhibition.

Carcinoembryonic antigen in 228 patients with carcinoma of the lung

Two hundred and twenty-eight patients who were treated for carcinoma of the lung were followed and their plasma CEA levels assessed at intervals during the course of the disease. In addition, plasma samples were taken from 487 healthy blood donors for comparison as a control. CEA assay is not selective or specific enough, at this time, to be used for screening purposes even though 68% of the patients who have lung cancer will have an elevated concentration of CEA regardless of the histological cell type. In patients with plasma levels of CEA above 15 ng/ml the prognosis is uniformly poor. CEA in the author's view does have value as a prognostic marker capable of suggesting the successful resection of a tumor and to a lesser degree confirming the clinical objective response to the radiotherapy or chemotherapy. It was found that the presence of CEA was not necessarily related to the volume of the tumor or the site of organ metastasis, but reflects the metabolic properties and characteristics of the individual tumor as it occurs in the patient.