Synthesis and anticancer and antiviral activities of various 2'- and 3'-methylidene-substituted nucleoside analogues and crystal structure of 2'-deoxy-2'-methylidenecytidine hydrochloride

Various 2'- and 3'-methylidene-substituted nucleoside analogues have been synthesized and evaluated as potential anticancer and/or antiviral agents. Among these compounds, 2'-deoxy-2'-methylidene-5-fluorocytidine (22) and 2'-deoxy-2'-methylidenecytidine (23) not only demonstrated potent anticancer activity in culture against murine L1210 and P388 leukemias, Sarcoma 180, and human CCRF-CEM lymphoblastic leukemia, producing ED50 values of 1.2 and 0.3 microM, 0.6 and 0.4 microM, 1.5 and 1.5 microM, and 0.05 and 0.03 microM, respectively, but also were active in mice against murine L1210 leukemia. Of all the tested drug dosage levels (25, 50, and 75 mg/kg, respectively) compound 23 had no toxic deaths and compound 22 yielded only one toxic death at the highest dosage level. On the contrary, in the same study, 1-beta-D-arabinofuranosylcytosine (ara-C) resulted in 2/5, 5/5, and 5/5 toxic deaths, respectively. Both compounds 22 and 23 have shown better anticancer activity than ara-C, yielding higher T/C x 100 values and some long-term survivors (greater than 60 days). In addition, compounds 22 and 23 were found to have, respectively, approximately 130 and 40 times lower binding affinity for cytidine/deoxycytidine deaminase derived from human KB cells compared to ara-C, suggesting that the two 2'-methylidene-substituted analogues may be more resistant to deamination. Cytoplasmic deoxycytidine kinase (dCK) was required for compounds 22 and 23 action. Furthermore, compounds 14, 22, 23, and 24 also have antiherpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) activity in cell culture. In addition, the crystal structure of 2'-deoxy-2'-methylidenecytidine hydrochloride (23-HCl) was determined by X-ray crystallography.

Effect of anti-human immunodeficiency virus nucleoside analogs on mitochondrial DNA and its implication for delayed toxicity

The anti-human immunodeficiency virus (-HIV) nucleoside analogs azidothymidine (AZT), dideoxycytidine (ddC), dideoxyinosine (ddl), dideoxydidehydrothymidine (D4T), and dideoxydidehydrocytidine (D4C) and the anticancer drug cytosine arabinoside (AraC) were compared for their effects on the mitochondrial DNA (mtDNA) content in a human lymphoblastoid cell line, CEM. The potency of these compounds in reducing mtDNA content was in the order of ddC greater than D4C greater than D4T greater than AZT greater than ddl. AraC did not have a significant effect on mtDNA content. All of the compounds tested, except AraC, stimulated lactic acid production at concentrations that inhibited mtDNA synthesis. The action of ddC and ddl occurred at concentrations that did not affect cell growth significantly in 4 days but retarded cell growth by day 6. D4T and D4C decreased mtDNA content by 50% at doses lower than those that inhibited cell growth by 50% in 4 days (ID50). However, AZT required a dose higher than the ID50 to exert similar effects on mtDNA content. The decrease of mtDNA content caused by ddC also occurred in nerve growth factor-treated PC12 cells, which differentiate to neuron-like cells upon treatment with nerve growth factor. The preferential inhibition of mtDNA, compared with cell growth, by some of these anti-HIV nucleoside analogs correlates well with their ability to cause drug-limiting delayed toxicity, such as peripheral neuropathy, in patients. These data suggest that the selective mitochondrial toxicity could be responsible for the delayed toxicity caused by these anti-HIV analogs.

Cytogenetic study of twenty-two intracranial tumors

G-banded chromosomal analysis was performed on primary cultures of 22 intracranial tumors, including eight astrocytomas, nine meningiomas, two dermoid cysts, one acoustic neuroma, one pineal teratoma and one eosinophilic granuloma. One or more chromosomally abnormal clones were observed in 6 (75%) gliomas and 5 (56%) meningiomas. There was no chromosomal abnormality found in one of the dermoid cysts, the acoustic neuroma or the eosinophilic granuloma. A teratoma and a grade IV glioma had heterogeneous hyperdiploid karyotypes. Furthermore, astrocytomas displayed nonrandom loss of chromosomes #19, #21, #22 and Y. In meningiomas, characteristic changes involving chromosome 22 were found in 5 tumors. One meningioma had a ring chromosome in addition to chromosomal loss. With our culture and harvesting techniques, cytogenetic studies can be successfully performed on nearly all intracranial tumor explants, including those derived from small biopsy specimens. Also, in our study, specific nonrandom chromosomal anomalies were found.

Effect of 4 beta-arylamino derivatives of 4'-O-demethylepipodophyllotoxin on human DNA topoisomerase II, tubulin polymerization, KB cells, and their resistant variants

Six 4 beta-arylamino derivatives of 4'-O-demethylepipodophyllotoxin were examined for inhibitory activity against human DNA topoisomerase II and tubulin polymerization, their ability to generate protein-linked DNA breaks in cells, and their cytotoxicity toward the KB cell line and its VP-16- and vincristine-resistant variants. Five of these derivatives were 5- to 10-fold more potent than VP-16 as inhibitors of DNA topoisomerase II in vitro, and all of these derivatives could generate the same amount of or more protein-linked DNA breaks in cells than VP-16 at 1-20 microMs. Tubulin polymerization was inhibited by these compounds to different degrees in the order: podophyllotoxin greater than W73 greater than W87 greater than NPF greater than NPC greater than W68 greater than W38 greater than VP-16. These analogues were cytotoxic not only to KB cells but also to their VP-16-resistant and vincristine-resistant variants which showed decreased cellular uptake of VP-16 and a decrease in DNA topoisomerase II content or overexpression of MDR1 phenotype. These characteristics may cause these derivatives to have different spectrums of antitumor activity.

Synthesis and anticancer activity of various 3'-deoxy pyrimidine nucleoside analogues and crystal structure of 1-(3-deoxy-beta-D-threo-pentofuranosyl)cytosine

Various 3'-deoxy pyrimidine nucleoside analogues have been synthesized for evaluation as potential anticancer and antiviral agents. Among these compounds, 1-(3-deoxy-beta-D-threo-pentofuranosyl)cytosine (10, 3'-deoxy-ara-C) and 3'-deoxycytidine (22) had significant anticancer activity against CCRF-CEM, L1210, P388, and S-180 cancer cell lines in vitro, producing ED50 values of 2, 10, 5, and 34 microM, respectively, for 3'-deoxy-ara-C (10); and 25, 5, 2.5, and 15 microM, respectively, for 3'-deoxycytidine (22). Thus, 3'-deoxy-ara-C (10) was 12.5 times more active against CCRF-CEM cells than 3'-deoxycytidine (22). The 2'-O-acetyl, 5'-O-acetyl, and 2',5'-di-O-acetyl derivatives of 3'-deoxy-ara-C (10), compounds 34, 31, and 30, demonstrated anticancer activity in the same range as 3'-deoxy-ara-C (10) against CCRF-CEM, L1210, P388, and S-180 cells. The 5'-O-acetyl derivative (31) had significantly greater activity against CCRF-CEM with an ED50 value of 0.4, but this compound also showed similar activity, as did 3'-deoxy-ara-C, against L1210, P388, and S-180 with ED50 values of 3, 3, and 13 microM, respectively. 3'-Deoxy-ara-C was also evaluated in vitro against HSV-2, HCMV, and GPCMV viruses and was found to be not very active with respective IC50 values of 110, 220, and 1000 microM. The single-crystal structure of 3'-deoxy-ara-C (10) was determined by X-ray crystallography. There are two molecules of the nucleoside and one molecule of water in the asymmetric unit. The sugar moieties of the two nucleoside molecules adopt different conformations. In molecule A, the ring pucker is C3'-endo with P = 18.7 degrees and tau m = 37.3 degrees, while the CH2OH side chain is gauche+. In molecule B, the ring pucker is C2'-endo with P = 156.8 degrees and tau m = 37.8 degrees and the side chain is trans.

Herpes simplex virus-specified DNA polymerase is the target for the antiviral action of 9-(2-phosphonylmethoxyethyl)adenine

9-(2-Phosphonylmethoxyethyl)adenine (PMEA) is a new antiviral compound with activity against herpes simplex virus (HSV) and retroviruses including human immunodeficiency virus. Although it has been suggested that the anti-HSV action of PMEA is through inhibition of the viral DNA polymerase via the diphosphorylated metabolite of PMEA (PMEApp), no conclusive evidence for this has been presented. We report that in cross-resistance studies, a PMEA-resistant HSV variant (PMEAr-1) was resistant to phosphonoformic acid, a compound which directly inhibits the HSV DNA polymerase. In addition, phosphonoformic acid-resistant HSV variants with defined drug resistance mutations within the HSV DNA polymerase gene were resistant to PMEA. Furthermore, the HSV DNA polymerase purified from PMEAr-1 was resistant to PMEApp in comparison with the enzyme from the parental virus. Moreover, PMEA inhibited HSV DNA synthesis in cell culture. These results provide strong evidence that HSV DNA polymerase is the major target for the anti-viral action of PMEA. Further studies showed that HSV DNA polymerase incorporated PMEApp into DNA in vitro, while the HSV polymerase-associated 3'-5' exonuclease was able to remove the incorporated PMEA. Thus, the inhibition of HSV DNA polymerase by PMEApp appears to involve chain termination after its incorporation into DNA.

Mechanism and mode of action of 5-iodo-2-pyrimidinone 2'-deoxyribonucleoside, a potent anti-herpes simplex virus compound, in herpes simplex virus-infected cells

The anti-herpes simplex virus type 2 (-HSV-2) action of 5-iodo-2-pyrimidinone deoxyribonucleoside (IPdR) was found to be exerted through inhibition of HSV DNA synthesis. The inhibition of viral DNA synthesis was not caused by inhibition of the synthesis of HSV-2-specified proteins or HSV-2 mRNA species involved with viral DNA synthesis or by depletion of deoxynucleotides. The inhibition of viral DNA synthesis may be due to damage to the DNA template in the nuclei or to an action at the DNA replication complex, because nuclei isolated from HSV-2-infected cells treated with IPdR could not support DNA synthesis in vitro. Moreover, the addition of exogenous template to the reaction enabled nuclear DNA synthesis to occur at the level of control. The major cellular metabolite of IPdR in HeLa S3 cells infected with HSV-2 was IPdR monophosphate, which was formed through virally specified kinase. Attempts to either identify or synthesize IPdR diphosphate and triphosphate were unsuccessful. The accumulation of IPdR monophosphate was dependent on the extracellular concentration of IPdR. IPdR monophosphate did not have any inhibitory effect on nuclear DNA synthesis, even at 200 microM. Thus, the action of IPdR could be due to an unidentified metabolite of IPdR or the depletion of a cellular metabolite that is essential for viral DNA synthesis.

Mechanisms of inhibition of herpes simplex virus type 2 growth by 28-mer phosphorothioate oligodeoxycytidine

The 28-mer phosphorothioate oligodeoxycytidine (S-(dC)28) has been reported previously to be a strong inhibitor of herpes simplex virus type 2 (HSV-2) DNA polymerase and HSV-2 growth in cell culture. In this study, the mechanism of action of S-(dC)28 was studied. S-(dC)28 was found to interfere with the adsorption of HSV-1 and HSV-2 to HeLa cells. HSV-2 infection, but not HSV-1, was found to potentiate the uptake of S-(dC)28 into HeLa cells. The enhanced uptake reached a plateau at 6-9 h postinfection and appeared to be dose-dependent and saturable at concentrations higher than 1 microM. The amount of S-(dC)28 accumulated in HSV-2 infected cells was found to be 50 pmol/10(6) cells at 6 h postinfection, whereas no significant drug accumulation was found in uninfected cells. S-(dC)28 binding studies suggested that there are several types of tight binding sites associated with HSV-2 virions, which could play a role in the enhancement of S-(dC)28 uptake. Subcellular distribution studies showed that intracellular S-(dC)28 was associated with both nuclei and cytoplasm and remained intact. Mechanism studies suggested three different mechanisms which could be responsible for the anti-HSV-2 action of S-(dC)28; (i) S-(dC)28 could interfere with the uptake of HSV. (ii) HSV-2 infection enhances the uptake of S-(dC)28 into cells. (iii) S-(dC)28 inhibits HSV-2 DNA synthesis, possibly, by inhibiting the viral DNA polymerase. The unique mechanisms of anti-HSV action of S-(dC)28 suggest it could be a potential new agent in anti-HSV-2 chemotherapy.

Antitumor agents. 113. New 4 beta-arylamino derivatives of 4'-O-demethylepipodophyllotoxin and related compounds as potent inhibitors of human DNA topoisomerase II

A number of 4'-O-demethylepipodophyllotoxin derivatives possessing various 4 beta-N-, 4 beta-O- or 4 beta-S-aromatic rings have been synthesized and evaluated for their inhibitory activity against the human DNA topoisomerase II as well as for their activity in causing cellular protein-linked DNA breakage. The results indicated, that for DNA topoisomerase II, a basic unsubstituted 4 beta-anilino moiety is structurally required for the enhanced activity. Substitution on this moiety with CN, COOCH3, COOC2H5, OH and COOCH3, OCH3, COCH3, CH2OH, OCH2O, OCH2CH2O, phenoxy, morpholino, NO2, and NH2 either at the para and/or the meta position yielded compounds which are as potent or more potent than etoposide. Substitution with COOC2H5 and OH at the ortho position afforded inactive compounds. Replacement of the aryl nitrogen with oxygen or sulfur gave compounds which are much less active or inactive. However, replacement of the phenyl ring with a pyridine nucleus furnished compounds which are as active or slightly more active than etoposide. There is a lack of correlation between the ability of these compounds in inhibiting DNA topoisomerase II and in causing protein-linked DNA breaks.

Inhibition of herpes simplex virus type 2 growth by phosphorothioate oligodeoxynucleotides

Phosphorothioate homo-oligodeoxynucleotides were found to be potent inhibitors of herpes simplex virus type 2 (HSV-2) but less potent for HSV-1 in cell culture studies. Oligomers with longer chain lengths were more active against HSV-2 than those with shorter ones. Of all the compounds examined, the 28-mer phosphorothioate homo-oligodeoxynucleotides were the strongest inhibitors of HSV-2. The degree of inhibition was related to the base moiety on the order of deoxycytidine = thymidine greater than deoxyadenosine. The inhibition of HSV-2 growth by S-dC28 was dose dependent with a 90% inhibitory dose of 1 microM. At 50 microM, S-dC28 inhibited HeLa S3 cell growth by less than 10%. The anti-HSV-2 activity was time and schedule dependent. The oligomer was most inhibitory to viral growth when present during the 1-h viral adsorption period, and this effect could be enhanced by continuous drug exposure after the adsorption period. S-dC28 was also an effective inhibitor of two HSV-2 drug-resistant mutants: a phosphonoformate-resistant mutant that induces an altered DNA polymerase and a 9-(1,3-dihydroxy-2-propoxymethyl)guanine-resistant mutant that does not induce the viral thymidine kinase. In drug combination studies, phosphonoformate was shown to potentiate the action of S-dC28 against HSV-2 growth. In conclusion, because of their potency and selectivity, phosphorothioate homo-oligodeoxynucleotides are a promising new class of anti-HSV agents.

Antitumor agents. 111. New 4-hydroxylated and 4-halogenated anilino derivatives of 4'-demethylepipodophyllotoxin as potent inhibitors of human DNA topoisomerase II

A series of C-4 hydroxylated and halogenated anilino derivatives of epipodophyllotoxin or 4'-demethylepipodophyllotoxin have been synthesized and evaluated for their inhibitory activity against the human DNA topoisomerase II as well as for their activity in causing cellular protein-linked DNA breakage. Compounds 11-17 and 22 are more potent than etoposide in causing DNA breakage, while compounds 11-13, 15, 16, and 20 are as active or more active than etoposide in their inhibition of the human DNA topoisomerase II. The cytotoxicity in KB cells appears to have no direct correlation with their ability to inhibit DNA topoisomerase II and to cause protein-linked DNA breaks in cells.

Purification of Epstein-Barr virus associated DNase with affinity chromatography of nasopharyngeal carcinoma patient serum

Epstein-Barr virus associated DNase in the homogeneous form can be purified by chromatographys using CH-sepharose 4B column conjugated with nasopharyngeal carcinoma patient serum, DNA cellulose and phosphocellulose in that sequence. The molecular weight of this enzyme is shown to be 51 kilo-daltons in silver-staining and immunostains. Among various methods for keeping DNase activity, the addition of BSA and dialysis in glycerol or ethylene glycol immediately after the enzyme purification is suggested.

Metabolism and mechanism of action of 5-fluorouracil

This is a review on the mechanism of action of FUra. Three main areas are addressed: metabolism, RNA-directed actions of FUra, and DNA-directed actions of FUra. Key words for bibliographic purposes: metabolism, RNA, rRNA, mRNA, tRNA, DNA primase, DNA, thymidylate synthetase, uracil N-glycosylase, FUra, FUrd, FdUrd, FdUMP, RNA splicing, 5,10-methylene tetrahydrofolate, FUTP.

Incorporation of 3'-azido-3'-deoxythymidine into cellular DNA and its removal in a human leukemic cell line

3'-Azido-3'-deoxythymidine (AZT) is currently used in the treatment of patients with the acquired immunodeficiency syndrome (AIDS); this often, however, results in hematological toxicity. Although the mechanism of toxicity is not clear, it is thought to result in part from incorporation of AZT into DNA, which causes chain termination. In order to investigate the mechanism of AZT toxicity, the relationship between the presence of AZT in DNA of K562 cells, a chronic myelogenous leukemia cell line, and growth inhibition was examined. No growth inhibition was evident at less than 50 microM AZT, although incorporation of AZT into DNA was detected at 10 and 20 microM. This suggested that the presence of AZT in DNA was not sufficient to inhibit cell growth. Removal of AZT from the medium resulted in the removal of AZT from DNA of the cells, indicative of a cellular repair mechanism. Cellular DNA polymerases alpha, beta, gamma, and delta from human leukemic cells were inhibited by AZT trisphosphate to different degrees, polymerase alpha being the least potently inhibited. Furthermore, an enzyme with exonucleolytic activity, capable of removing AZT and dideoxycytidine from the correspondingly terminated DNA (in vitro), was obtained from these cells. In summary, AZT was incorporated into DNA at levels that were not toxic, and it could be removed by an exonuclease, which might play a key role in the susceptibility of cells to AZT.

[Pulmonary barotrauma during anesthesia]

There were three cases of pulmonary barotrauma during anesthesia. The causes of barotrauma were: 1) Undue length of the tube pressed by machine's wheel which connect the ventilator to the anesthesia machine. 2) Inadvertent connection of the breathing tube to the inspiratory side of the machine when using the Bain system. 3) Inadvertent placement of expiratory valve. All resulted in obstruction to air outflow. The condition further aggravated by repeated flushing of the oxygen flush valve, leading to rapid increase in intraluminal pressure and rupture of alveolar. The condition can be rapidly recognized by palpation of the neck, auscultation of breathing sound, and finally, with a portable chest X-ray. When any problem exists in the breathing system of anesthesia machines, disconnecting the patient from the machine is mandatory. The patient can be ventilated with an Ambu bag while checking the system thus lessening the incidence of barotrauma.

Characterization of a novel inhibitor of human DNA polymerases: 3,4,5-tri-O-galloylquinic acid

Various galloyl derivatives of quinic acid were found to be inhibitors of human DNA polymerases. Among them, 3,4,5-tri-O-galloylquinic acid (TGQA) was the most potent inhibitor of DNA polymerase alpha. Under identical conditions, this compound was 60-fold more potent than aphidicolin as an inhibitor of DNA polymerase alpha. The inhibition of DNA polymerase alpha by this compound was not competitive with either the template or any of the deoxynucleoside triphosphates with a Ki of 0.28 microM. Under similar reaction conditions, DNA polymerases beta and gamma were much less sensitive to the effects of these compounds and, in contrast to the effect seen with DNA polymerase alpha, the inhibition of DNA polymerases beta and gamma by TGQA was competitive with respect to the template with Ki values of 44.4 and 7.5 microM respectively. The potency of these compounds against DNA polymerase gamma varied according to the assay conditions used. The inhibition of DNA polymerase gamma by TGQA could be increased substantially by using MnCl2 in place of MgCl2 and by including 50 mM potassium phosphate, pH 7.5, in the assay mixture. DNA polymerase beta was also more sensitive to TGQA when measured with MnCl2. However, potassium phosphate had little, if any, effect on the inhibition by TGQA of either DNA polymerase alpha or beta. DNA polymerase alpha was less sensitive to TGQA when assayed with MnCl2. TGQA was not a potent inhibitor of human KB cell growth in culture, which could be due to its degradation or poor uptake. Nevertheless, this compound could serve as a model for developing antitumor drugs targeted at DNA polymerases.

Human topoisomerase 1 messenger RNA is not destabilized by the herpes simplex virus type 2 virion-associated shut-off function

A cDNA for human topoisomerase I (Topo 1) was used to identify a 4.1 kb polyadenylated Topo 1 mRNA in methotrexate-resistant human KB cells that are permissive for herpes simplex virus type 2 (HSV-2) infection. Using these cells, no effect of the HSV-2-associated early shut-off function on levels of Topo-1 mRNA was observed up to 6 hours postinfection, whereas the actin mRNA level was 22% cellular transcripts are susceptible. The level of several host-cell polyadenylated RNAs detected as cDNA clones (class 3 transcripts) were unchanged 8 hours after HSV-2 infection, and other cellular transcripts (class 2) actually accumulated at postinfection.

Delayed cytotoxicity and selective loss of mitochondrial DNA in cells treated with the anti-human immunodeficiency virus compound 2',3'-dideoxycytidine

The compound 2',3'-dideoxycytidine (ddC) is a potent inhibitor of human immunodeficiency virus replication in vitro and is currently in clinical trials for treatment of acquired immunodeficiency syndrome. The compound was found to exert delayed cytotoxicity against Molt-4F cells, a human T lymphoblastic cell line. At a concentration as low as 0.1 microM, the doubling time of the cells was increased after 8 days of ddC treatment. This concentration is 5-fold lower than plasma levels reached in clinical trials. The cells finally died after a 2-week exposure to 0.1 or 0.2 microM ddC. The delayed cytotoxicity was not due to a greater accumulation of 2',3'-dideoxycytidine triphosphate in cells with longer exposure to the compound. The cellular content of mitochondrial DNA was found to decrease and the rate of glycolysis was found to increase with continuous exposure of cells to ddC. The mitochondrial toxicity and cell growth inhibition were reversed when ddC was removed. The reduction in cellular content of mitochondrial DNA caused by ddC may partially explain the delayed toxicity observed in acquired immunodeficiency syndrome patients treated with the drug.

Characterization of the 3' region of the human DNA topoisomerase I gene

Previous studies suggest that topoisomerase I (Topo I) plays a critical role in cell growth. However, the structure of the Topo I gene has not yet been determined. Two complementary DNA (cDNA) clones for the human Topo I 4.1-kilobase mRNA were isolated independently from HeLa and KB cell cDNA libraries. These clones were identical and they contained 679 base pairs of coding and 1138 base pairs of noncoding sequences. The clones had a two-base difference in the 3' noncoding region compared to the Topo I cDNA from human placenta. The structure of the 3' end of the human Topo I gene from six human tumor cell lines was examined. The Topo I cDNA recognized 16.5, 24.2, and 16.0 kilobases of genomic DNA restricted with EcoRI, HindIII and PstI, respectively. The individual genomic fragments were ordered by double digestion and hybridization with cDNA subclones. digestion and hybridization with cDNA subclones. The results indicate that the human Topo I gene contains several intervening sequences. The gene arrangement was similar in all six cell lines and no polymorphism was observed. However, each digestion contained genomic fragments that hybridized with all the subclones, suggesting that at least one Topo I pseudogene, or another Topo I gene with a different structure, was present in every cell line. As predicted, double digestions generated at 161 base pair fragment that indicates the presence of an intronless pseudogene. In contrast to the DNA topoisomerase I gene, the presumptive pseudogene(s) appears to be hypomethylated. In addition to the 4.1-kilobase Topo I mRNA, a larger 6-kilobase RNA was identified in human KB and HeLa cells which could be a processed Topo I mRNA intermediate.

Effect of phosphorothioate homo-oligodeoxynucleotides on herpes simplex virus type 2-induced DNA polymerase

Effects of phosphorothioate oligodeoxynucleotides of different chain length and base composition on herpes simplex virus (HSV) type 2 (strain 333)-induced DNA polymerase have been examined in vitro. The anti-HSV-2 DNA polymerase activity was related to the base composition of the analogs, with the order of potency: deoxycytidine greater than thymidine greater than deoxyadenosine, for compounds with equal chain length. The potency was also related to oligomer chain length, since it was observed that the longer the chain length, the more potent the inhibition exerted. Among all the compounds tested, the phosphorothioate oligodeoxycytidine 28-mer (S-(dC)28) was the most potent inhibitor of HSV-2-induced DNA polymerase. This inhibition was competitive with an activated DNA template with a Ki value of 7 nM. It was also a competitive inhibitor of the DNA polymerase-associated exonuclease activity with a Ki value of 5 nM. In contrast, this compound showed less inhibition of human DNA polymerase alpha, beta, and gamma, as well as HSV-1 (strain KOS) and Epstein-Barr virus-induced DNA polymerase. The possibility that S-oligomers can serve as primers for DNA elongation was also investigated. Poly(dG).S-(dC)28 and poly(dA).S-(T)28 are poor substrates for DNA elongation catalyzed by HSV-2 DNA polymerase. In summary, phosphorothioate oligonucleotides could be anti-template inhibitors of HSV DNA polymerase. This information may lead to the development of a new class of selective anti-HSV agents.

Podophyllotoxin analogs: effects on DNA topoisomerase II, tubulin polymerization, human tumor KB cells, and their VP-16-resistant variants

Several derivatives of podophyllotoxin with modifications at the C-4 position of ring C, in addition to demethylation at the C-4' position of ring E, were examined for inhibitory activity against DNA topoisomerase II and tubulin polymerization, generation of protein-linked DNA breaks, and cytotoxicity against KB cells and VP-16-resistant KB variants. Substitution of podophyllotoxin with a group in the beta configuration at the C-4 position of ring C resulted in compounds with greater inhibitory activity against DNA topoisomerase II and lower inhibitory activity against tubulin polymerization than those with an alpha configuration. These active analogs exhibited the same mechanism of DNA topoisomerase II inhibition as the epipodophyllotoxin derivative VP-16, which causes protein-linked DNA breaks in vitro as well as in cells. Two analogs selectively inhibited DNA topoisomerases II to a greater extent than tubulin polymerization. These analogs were cytotoxic towards KB cells in addition to VP-16-resistant KB cell lines, which indicated limited cross-resistance with VP-16 in VP-16-resistant KB variants.