Cellular and antiviral effects of halogenated deoxyribonucleosides

The effects of 5-bromodeoxyuridine on fusion of the cranial neural folds in the mouse embryo

The effects of 500 and 300 mg/kg bromodeoxyuridine (BUdR) on the process of fusion of the neural folds were tested after injection into pregnant mice on day 8 of gestation (192 hours postcoitum). Various doses of the natural nucleoside, thymidine (TdR), were also tested. Both doses of BUdR retarded growth to the same extent, but only the larger dose caused neural tube defects in 28.8% of embryos. Treatment with the larger dose also caused extensive cell necrosis to appear in the neuroepithelium of the neural folds between 12 and 15 hours after treatment. No changes were detectable with the light microscope up to this time. Measurement of the cell generation time in treated and control embryos indicated that the BUdR prolonged the cycle by about 2 hours and that the dying cells were in the second DNA synthetic phase following incorporation of the analog. Treatment with the smaller dose of BUdR caused minimal cell necrosis. This was taken as evidence for the importance of cell necrosis in the pathogenesis of BUdR-induced neural tube defects. Treatment with excess TdR did not cause either neural tube defects or cell necrosis, and a dose of TdR equimolar with the large dose of BUdR (400 mg/kg TdR) did not retard growth. Doses of 800 and 1,200 mg/kg TdR retarded growth to the same extent as BUdR. The administration of an equimolar amount of TdR, along with the teratogenic dose of BUdR, prevented the occurrence of cell necrosis and neural tube defects. When treatments were given on day 9 of gestation, 500 mg/kg BUdR caused cell necrosis in the neuroepithelium about 15 hours after treatment but no neural tube defects were produced by day 9 after treatment. It is suggested that in this case cell necrosis occurred too late to interfere with neural fold fusion. It was concluded that the ability of BUdR to cause exencephaly in mouse embryos was due to cell necrosis in the neuroepithelium.

Physical and biological consequences of incorporation of antiviral agents into virus DNA

The molecular basis for the antiviral activity is discussed for a variety of nucleoside compounds approved for clinical use in the U.S.A. (5-iodo-2'-deoxyuridine, 5-trifluoromethyl-2'-deoxyuridine, 9-beta-D-arabinofuranosyladenine, 9-(2-hydroxyethoxymethyl)guanine), or in clinical trial (E-5-(2-bromovinyl)-2'-deoxyuridine, 1-(2-deoxy-2-fluoro-beta-D-arabinosyl)-5-iodocytosine, 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide), or of specific interest to our laboratory (5-iodo-5'-amino-2',5'-dideoxyuridine, 5'-amino-5'-deoxythymidine). The consequence of incorporation of idoxuridine, the 5'-amino analog of thymidine or the 5'-amino analog of idoxuridine into the DNA of herpes simplex virus type 1 on transcription and translation is emphasized.

Effects of nucleoside analogues on the expression of herpes simplex type 1-induced proteins

Exposure of herpes simplex virus type 1 (HSV-1)-infected Vero cells to the nucleoside analogues 5-iodo-5'-amino-2',5'-dideoxyuridine (AIdUrd), 5-iodo-2'-deoxyuridine (IdUrd) or 5'-amino-2',5'-dideoxythymidine (5'-AdThd) resulted in altered expression of HSV-1-induced proteins. Infected cell proteins (ICPs) synthesized in the presence of the nucleoside analogues were compared by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis to ICPs from non-drug-treated cells and it was found that there was no effect on HSV-1-induced alpha proteins but beta and gamma proteins were reduced as much as 60%. There were three exceptions: ICP 35 (Mr = 46,000) and ICP 39 (Mr = 36,000) were not reduced and ICP 36 (Mr = 42,000) was increased during drug treatment. Progeny virions were isolated from drug-treated infected Vero cells and were compared to progeny isolated from control cells with respect to their polypeptide make-up and for their ability to induce HSV-1 proteins in non-drug-treated Vero cells. The progeny virus from drug-treated cells exhibited altered protein patterns on SDS-polyacrylamide gels with respect to control HSV-1. The progeny virions from AIdUrd- or IdUrd- but not from 5'-AdThd-treated cells were defective in their abilities to induce proteins upon subsequent infection of non-drug-treated Vero cells. Two unusual phosphoproteins were detected; one with an apparent molecular weight of 30,000 was induced by progeny virus from AIdUrd-treated cells and another at approximately 69,000 was induced by progeny virus from 5'-AdThd-treated cells.

Persistent viral infections as models for research in virus chemotherapy

The acute systemic virus infection is commonly used as an experimental model in chemotherapy research despite the fact that the chance for an effective chemotherapy of acute virus infections is small. In most acute infections, virus multiplication is well advanced before the disease is expressed and treatment will, in many cases, come too late. However, control by chemotherapy might be promising for persistent virus infections, where, owing to the slow progression of the disease, sufficient time for treatment is available. Although there are various ways in which viruses can persist in their hosts, comparative studies in vitro and in vivo reveal common features that shall be briefly reviewed. Animal models with persistent virus infections are usually difficult to experiment with because of the varying length of the incubation period brought about by the complex relationship among virus replication, immune reactions, and disease.

Incorporation of 5-lododeoxyuridine into the DNA of mouse embryos: its relation to embryotoxicity

Pregnant female ICR mice were administered, ip, either a trace (200 muCi/kg) or teratogenic (200 muCi + 300 mg/kg) dose of [6(-3)H] 5-iododeoxyuridine (IdU) on day 10 of gestation. Maternal liver, spleen, intestine, and kidneys, and placentas and embryos were removed at various time intervals after injection, weighed, and homogenized in cold 0.5 m perchloric acid. The half-lives of IdU-derived nucleotides in the acid-soluble fraction ranged from 31-46 min (trace) to 57-131 min (teratogenic) for the tissues analyzed. [3H]IdU was incorporated into the DNA of all mitotically active tissues after both dosages. The presence of the label in iodouracil was demonstrated by thin-layer chromatography of DNA bases extracted from maternal spleen and embryo. Growth of embryos following injection on day 10 resulted in decreased 3H-specific activity in the DNA fraction and concomitant retention of total activity. It is suggested that the previously demonstrated embryotoxicity of IdU is related to its retention at its presumed intracellular site of action.

Deoxyribonucleotide metabolism in Herpes simplex virus infected HeLa cells

The effect of Rolly No. 11 strain herpes simplex virus infection of HeLa cells in culture on deoxynucleotide metabolism and the level of various enzymes concerned with the biosynthesis of DNA has been investigated. Of 18 enzyme activities studied, thymidine kinase, DNA polymerase and deoxyribonuclease were markedly augmented, a finding in agreement with previous reports. Deoxycytidine kinase, ribonucleotide reductase, thymidylate kinase and deoxycytidylate deaminase activities, in contrast with previous reports, did not increase; the activities of the other enzymes studied, also did not increase. Whereas most of the radioactivity derived from [14-C] thymidine in the acid-soluble fraction of the uninfected cells was present as deoxythymidine triphosphate, that present in the infected cells was primarily in the form of deoxythymidine monophosphate. Thus, in the infected cell deoxythymidylate kinase is a rate-limiting enzyme in the biosynthesis of deoxythymidine triphosphate. A marked increase in the pools of the four naturally occurring deoxynucleoside triphosphates (dTTP, dCTP, dATP, dGTP) was found. The rate of formation of the virus-induced enzymes was determined, as were the various nucleoside triphosphate pools and the other phosphorylated derivatives of thymidine; a maximum was reached for all these csmponents between 6 to 8 h post infection. Although an apparent greater synthesis of DNA occurred in the uninefected cells, when the specific activity of the radioactive deoxythymidine triphosphate was taken into account, there was actually a greater rate of DNA synthesis in the infected cells, with the peak at 8 h post infection.

Strand-length measurements of normal and 5-iodo-2'-deoxyuridine-treated vaccinia virus deoxyribonucleic acid released by the Kleinschmidt method

Purified vaccinia virus, which had been grown on chick-embryo chorioallantoic membranes in the presence or in the absence of 5-iodo-2'-deoxyuridine (IUdR), was suspended in 5 m ammonium acetate and subjected to the one-step Kleinschmidt procedure on surfaces of distilled water or salt solutions. Deoxyribonucleic acid (DNA) molecules were clearly revealed, and in many instances accurate length measurements could be made. The longest continuous molecules from normal virus measured 78, 77, and 65 mu. The most frequent length was approximately 30 mu, which corresponds to only one-third to one-half of the total DNA per virus particle predicted from various chemical analyses. These data provide direct evidence that normal vaccinia DNA may occur as a linear molecule of approximately 150 x 10(6) molecular weight units, but, for reasons still unknown, the majority of these molecules appears to break into segments of equal length during release from the virion. There is no evidence for the presence of cyclic DNA. The DNA molecules are typically double-stranded. DNA from IUdR-treated vaccinia presents a markedly different picture: the molecules are mostly fragmented into small pieces, and rosettes or tangled masses equivalent to even one-quarter the length of normal molecules occur very rarely. The possibility is discussed that at least part of the virus-inhibitory effect of IUdR on vaccinia is due to extensive fragmentation of the DNA molecules into which IUdR has been incorporated in place of thymidine.

Herpes simplex encephalitis treated with intravenous idoxuridine

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