Inhibition of DNA polymerase

One of the simplest molecules found to inhibit the repHcation of DNA vimses in animals is phosphonoformic acid [4428-95-9] (PEA, 1) CH O P. Both PEA (as the trisodium salt CNa O P, foscamet [63585-09-1] audits homologue phosphono acetic acid [4408-78-0] (PAA, 2) C2H O P, were developed by Astra Pharmaceuticals (6) and show selective inhibition of DNA polymerase in various herpes vimses. 

Ficellomycin was found to inhibit semiconservative DNA replication in Eschir-ichia coli, and this was found not to be due to direct inhibition of DNA polymerase [166]. It has been suggested that ficellomycin may exert its biological activity by alkylation of DNA [165], in common with the azinomyins. The biosynthesis of ficellomycin has not been studied, but it seems highly probable that its 1-azabicy-clo[3.1.0]hexane ring system will arise from a pathway related to that for the azinomycins. 

However, not all effects of NRTls on mitochondria can be explained by the DNA polymerase y hypothesis. Other mechanisms, either secondary to or independent of inhibition of DNA polymerase y are involved in NRTI toxicity (Moyle 2000a, 2000b Lewis et al. 2003). AZT is a potent inhibitor of mitochondrial DNA polymerase y but does not cause neuropathy in HIV patients (Dalakas 2001). Keswani and colleagues showed that NRTls caused direct mitochondrial toxicity through... 

The ability of natural products to inhibition of topoisomerase and precipitate apoptosis mentioned in this chapter are two abilities among several others, of which inhibition of microtubule formation, inhibition of DNA polymerase, protein kinases, protein phosphatase and aromatase, and the use of cytokines, interleukins, and tumor necrosis factor and yet uncovered cellular targets. 

Fludarabine (Fludara ) is a 2-fluorocytarabine (Fig. 34) which inhibits the DNA biosynthesis via the inhibition of DNA polymerase a and of RDPR. It is clinically used for the treatment of leukaemia (chronic lymphomytic leukaemia, CLL). 

It was found that 1 acted as an antimitotic agent, not binding to tubulin, but by disorganizing the microtubule network in some fashion. In addition, it is a DNA minor groove guanine-specific alkylating agent [1]. The Et s showed potent inhibition of DNA and RNA synthesis and of RNA polymerase activity, but its inhibition of DNA polymerase activity is much less marked [75]. The potent activity of Et s was attributed, at least in part, to the unit C since the related saframycin A lacks this unit and has lower efficacy than Et 729 in comparable tumor models [74, 75]. More recent structural information on Et 743-DNA adduct was obtained by NMR spectroscopy [78]. An enantioselective total synthesis of Et 743 has been achieved by Corey et al. [79]. 

Fludarabine phosphate (2-fluoro-arabinofuranosyladenine monophosphate) is rapidly dephosphorylated to 2-fluoro-arabinofuranosyladenine and then phosphorylated intracellularly by deoxycytidine kinase to the triphosphate. This metabolite interferes with DNA synthesis through inhibition of DNA polymerase- and ribonucleotide reductase, and it also induces apoptosis. Fludarabine phosphate is used chiefly in the treatment of low-grade non-Hodgkin s lymphoma and chronic lymphocytic leukemia (CLL). Fludarabine phosphate is given parentally and is excreted primarily in the urine its dose-limiting toxicity is myelosuppression. 

Figure 13.14. Cytosine arabinoside Stracture (a), inhibition of DNA polymerase (b), and metabolism (c).

Table 6. Inhibition of DNA-polymerase activity of FL virions by distamycin A and its analogues in the presence of various templates. Figures in brackets are percentages...

It has been recently reported34 that DNA polymerases of several oncogenic viruses are inhibited by ethidium bromide to different degrees according to the nature of the template used and the source of the enzyme. The effect of distamycin derivatives on the DNA polymerase activity of FL virions was therefore studied in the presence of poly (dA—dT), poly (dl dC) and poly (rA) (dT)g (Table 6). The DNA polymerase activity was found to be most sensitive to distamycin inhibition with poly (dA-dT) as primer-template and somewhat less so with poly (rA) (dT)g. In both cases the inhibitory response of the antibiotic increases according to the number of pyrrole rings in the molecule. With poly (dl - dC) as template no significant inhibition of DNA polymerase activity by distamycin derivatives was observed. 

Table 7. Inhibition of DNA polymerase activity of MSV (M) by distamycin A and its derivatives in the presence of various templates. The incorporation in the absence of templates was 157 cpm/reaction mixture for 3H-TMP, and 61 cpm/reaction mixture for 3H-dGMP. - Antibiotic concentration = 20 /ig/reaction mixture. The figures in brackets indicate percent of the control...

The experiments reported here demonstrate that the distamycin inhibition of DNA polymerase activities of FLV and MSV-M are template specific. Templates containing thymine and adenine are highly sensitive to the action of distamycins. This inhibition is dependent on the number of pyrrole rings in the molecule. The inhibition of DNA polymerases of RNA oncogenic viruses and the foci formation by distamycin derivatives conclude that both activities are dependent on the same structural component(s) of the molecule. 

Recently we have thiolated nucleic acid fractions isolated from Ehrlich ascites (EA) cells. The activities of thiolated DNA, ribosomal RNA and transfer RNA were studied in a DNA-polymerase system from Friend leukemia virions. Of all the fractions tested transfer RNA, thiolated 1-3% showed a maximum inhibition of DNA polymerases of oncorna viruses. Table 23 shows some of the results obtained using thiolated tRNA. 

The triphosphate 7V-2-(p-n-octylphenyl)-2 -deoxyguanosine has been synthesised by reaction of the nucleoside 5 -monophosphate with tetrabutylammonium pyrophosphate in HMPA. The compound displays selective inhibition of DNA polymerase a, compared to S and e, but is less selective than the known inhibitor N2-(n-butyl)dGTP. 

ID50 = Concentration of inhibitor giving 50% inhibition of DNA polymerase activity. These inhibitors are the nucleoside 5 -triphosphate derivatives of FNAD. l-(2 -deoxy-2 -fluoro-p-D-arabinoforanosyl)-S-methyluracil FIAC, l-(2 -deoiy-2 -fluoro-p-D-arabinofnranosyl)-S-iodocytosine BVDD. E-5(2-bromovinyl)-2 -deoxynridine Ara-T, l-p-D-arabinofnranosylthymine ACV, 9-(2-hydroxyethoxymethyDguanine Ara-A, 9-p-D-arabinofuranosyl adenine. 

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