The 5'-O-p-tolylsulfonyl derivatives of 5-chloro-, 5-bromo-, and 5-iodo-2'-deoxyuridine were synthesized and converted into the corresponding 5-halo-5'-azido-2',5'-dideoxyuridines (5-7). Reduction of 5-chloro-5'-azido-2',5'-dideoxyuridine (5) afforded 5-chloro-5'-amino-2',5'-dideoxyuridine (10, ACIU); however, similar efforts to prepare 5-bromo-5'-amino-2',5'-dideoxyuridine (11) and 5-iodo-5'-amino-2',5'-dideoxyuridine (12) by reduction of the corresponding 5'-azido precursor resulted in the formation of 5'-amino-2',5'-dideoxyuridine (9). 5-Bromo-5'-amino-2',5'-dideoxyuridine (11, ABrU) and 5-iodo-5'-amino-2',5'-dideoxyuridine (12, AIU) were prepared by halogenation of the 5-mercuriacetate of 5'-amino-2',5'-dideoxyuridine. The 5'-amino-2',5'-dideoxy analogs of 5-methyl-, 5-chloro-, 5-bromo-, and 5-iodo-2'-deoxyuridine possess antiviral activity against herpes simplex virus but exhibit no inhibitory activity against sarcoma 180 (murine) or Vero (monkey) cells in culture.
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.
To date, human immunodeficiency virus infection remains incurable although a variety of antiviral agents have been identified and characterized. Even though nucleoside analogs have been the most successful prodrugs, there remains the need to develop new compounds that exhibit a more favorable toxicity profile, less susceptible to cross-resistance, and greater efficacy. As prodrugs, the nucleoside analogs should be sequentially phosphorylated by cellular kinases to yield triphosphate form before they can inhibit HIV replication at the reverse transcriptase level. The efficiency of phosphorylation of nucleoside analogs is a key factor in their antiviral activity and strongly depends on nucleoside structure and cell type. In recent years, several attempts have been made to improve therapeutic potential of nucleoside analogs by the use of nucleotide prodrugs (pronucleotides), that can avoid the first step of phosphorylation. This review focuses on problems of intracellular phosphorylation of nucleoside analogs and perspectives of developing of a new class of nucleotide analogs modified at phosphate group as a form for the delivery of nucleotide analogs into the cell.
Our previous studies suggested that the dNTP/dNDP transporter systems that exist in mitochondria for transporting dNTP/dNDP from the cytoplasm to the mitochondria for mitochondrial DNA (mtDNA) synthesis play a critical role in delayed cytotoxicity of anti-human immunodeficiency virus (HIV) dideoxynucleoside analogs in mitochondria. A protein, termed mitochondrial deoxynucleotide carrier (DNC), based on its ability to transport dNTPs in reconstituted proteoliposomes, was recently isolated. Lacking cellular information to substantiate DNC's involvement in the delayed cytotoxicity of dideoxynucleoside analogs, we expressed DNC and reconstituted it into proteoliposomes. The K m values for dNTPs uptake by reconstituted DNC were in the millimolar range, which is a thousandfold higher than that of the physiological level. Furthermore, we found that overexpressing DNC (wt and G177A-mutated DNC) in RKO cells did not sensitize the cells to the mtDNA depletion caused by -D-2Ј,3Ј-dideoxycytidine (ddC), 2Ј,3Ј-didehydro-2Ј,3Ј-dideoxythymidine, and 2Ј,3Ј-dideoxyinosine or affect the mtDNA recovery rate after ddC treatment. Mitochondria isolated from DNC-overexpressing cells did not significantly differ from that isolated from RKO cells in terms of the rate of uptake or the incorporation of dTTP into mitochondria DNA. Down-regulation of DNC expression by small interfering RNA was also ineffective in changing the action of dideoxynucleoside analogs on the mtDNA depletion and the rate of dTTP uptake into isolated mitochondria. Down-regulation of both DNC and thymidine kinase-2 also did not cause mtDNA depletion. We conclude that DNC does not play an important role in the delayed cytotoxicity (mtDNA depletion) of anti-HIV dideoxynucleoside analogs and dNTPs uptake into mitochondria.
SUMMARYFour nucleoside analogues, 1-(2'-deoxy-2'-fluoro-fl-~arabinofuranosyl)-5-methyluracil (FMAU), -5-iodouracil (FIAU), -5-methylcytosine (FMAC) and -5-iodocytosine (FIAC), were studied for their effect on human cytomegalovirus (HCMV) replication in vitro. FMAU, FIAU, FMAC and FIAC showed antiviral activities for four strains of HCMV (Major, Clegg, D550 and Towne) in a plaque reduction asssay, with a dose required for 50% inhibition (EDs0) in the range of 0-1 to 0.65 ~tM. At a concentration of 1 ~tM-FMAU or -FIAC, the synthesis of five virus-specific late polypeptides of molecular weights 150000, 120000, 67000, 54000 and 27000 was entirely blocked. Quantification of Towne viral DNA synthesis, using complementary RNA-DNA hybridization with a Towne-specific cRNA probe, demonstrated a complete inhibition of HCMV DNA replication at 1 [.tM of FMAU or FIAC. After the removal of the inhibitors, however, viral DNA synthesis resumed, and infectious virus reappeared, indicating that the inhibition of HCMV replication by these nucleoside analogues was of a virostatic reversible type. INTRODUCTIONHuman cytomegalovirus (HCMV) has become increasingly recognized as an important pathogen having various clinical manifestations ranging from asymptomatic infection to severe diseases such as congenital abnormality, mental retardation and interstitial pneumonia. Owing to the lack of effective treatment of HCMV infections, the search for effective antiviral drugs for chemotherapy of HCMV infection is pivotal.Previously, it has been reported that phosphonoacetic acid (PAA) was effective against HCMV replication by virtue of interference with virus-induced DNA polymerase activity and therefore impeding viral DNA replication (Huang, 1975). However, PAA was found to have limited therapeutic value because of its potential bone deposition effect. Recently, we also examined the effect of a potent antiherpetic nucleoside analogue, namely acycloguanosine (ACV) (Elion et al., 1977), on HCMV replication. The results revealed that HCMV was somewhat resistant to ACV and viral DNA synthesis was not impaired by the drug even at the high concentration of 200 IXM (Mar et al., 1982).With a continuing interest in the search for anti-HCMV drugs, and in view of a rapid development of drug-resistant mutants in herpes simplex systems, we have examined the antiviral activity of four new nucleoside derivatives of deoxyuridine and deoxycytidine on HCMV replication in vitro. These nucleoside analogues were potent anti-HCMV inhibitors, as compared to other existing antiherpetic compounds. Here, we report the study of the inhibitory effect of these nucleoside analogues on HCMV multiplication, at the replication and translation levels.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.