Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.7.7.7 (DNA polymerase)
17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The quinone intermediates resulting from tyrosinase-mediated oxidation of tyrosine were evaluated as sulfhydryl reagent inhibitors of purified calf thymus DNA polymerase alpha in order to determine which of these might be cytotoxic. Dopachrome and an oxidation product of 2,4,5-trihydroxyphenylalanine were relatively ineffective as inhibitors of DNA polymerase alpha. On the other hand, a dopaquinone analogue, 4-(2-N-acetylaminoethyl)-1,2-benzoquinone, synthesized from N-acetyl dopamine, was demonstrated to have marked affinity for this sulfhydryl enzyme. This property was shared by 1,2-benzoquinone. These studies point to dopaquinone as a significant toxic metabolite in melanin biosynthesis.
...
PMID:The toxicity of melanin precursors. 41 70

We have examined the killing effect of 4-S-cysteaminylphenol (4-S-CAP), a newly synthesised melanin precursor, on B16 melanoma cell lines possessing different melanin-producing activities and found it to be particularly effective in heavily melanised melanoma cells, but less so in moderately melanised melanoma cells, and having no effect on amelanotic melanoma cells and nonmelanoma cells. Thus, it was found that the killing effect of 4-S-CAP is highly dependent upon the synthesis of melanin and tyrosinase in melanoma cells, suggesting that 4-S-CAP may become toxic to melanoma cells only after oxidation by tyrosinase. The killing activity of 4-S-CAP also was found to be associated with a profound inhibition of the thymidine incorporation in pigmented melanoma cells, as compared to the uridine and leucine incorporation. Further, the inhibition of DNA synthesis was most pronounced in heavily melanised melanoma cells, less so in moderately melanised melanoma cells, and not seen in amelanotic melanoma cells. As a possible mechanism that might account for this action, it may be that 4-S-CAP is oxidised by tyrosinase to the o-quinone form via the catechol derivative and that some of the quinones then conjugate with sulfhydryl enzymes including DNA polymerase, thus exerting a killing activity for pigmented melanoma cells. Thus, 4-S-CAP appears to provide a new, effective cytotoxic agent for rational chemotherapy of malignant melanomas.
...
PMID:The killing effect of 4-S-cysteaminylphenol, a newly synthesised melanin precursor, on B16 melanoma cell lines. 199 95

L-Glutamic acid (gamma-4'-hydroxyanilide) (GHB) is oxidized by tyrosinase to a quinone which inhibits DNA polymerase, RNA polymerase, and mitochondrial energy production within mushrooms. It was previously shown that GHB can kill B16 melanoma cells in culture, but lacks cytotoxicity for nontyrosinase-containing cells. We have conjugated this drug to a superpotent melanotropic peptide and examined the bioactivity of this conjugate to melanoma cells. 4'-Hydroxyaniline was attached to glutamic acid at position 5 in the superpotent melanotropin fragment analogue, Ac-[Nle4, D-Phe7]alpha-MSH4-10-NH2. The melanotropin:anilide conjugate, Ac-[Nle4, Glu(gamma-4'-hydroxyanilide)5, D-Phe7]alpha-MSH4-10-NH2, was not cytotoxic to B16 or Cloudman S91 mouse melanoma cells in culture, as determined by cell counts and protein assays. Interestingly, we also found that GHB stimulated melanoma cell tyrosinase above control levels in both melanoma cell lines. In our study, GHB itself also was found not to be cytotoxic to B16 or S91 melanoma cells in culture. In the frog skin bioassay, the melanotropin conjugate was more potent than alpha-MSH or Ac-[Nle4, D-Phe7]alpha-MSH4-10 in stimulating melanosome dispersion. These results demonstrate that putative chemotherapeutic ligands can be incorporated into active-site fragment analogues of MSH without loss of biological activity.
...
PMID:Synthesis and actions of a melanotropin conjugate, Ac-[Nle4, Glu(gamma-4'-hydroxyanilide)5, D-Phe7]alpha-MSH4-10-NH2, on melanocytes and melanoma cells in vitro. 216 79

A variety of factors were found to modify the toxicity of L-dopa in HeLa cells (D37 16 microM) and in dopa-sensitive, nonpigmented human melanoma cells (MM96) (D37 5 microM) having a similar size and doubling time. Dopa toxicity was decreased by concurrent treatment with superoxide dismutase, peroxidase or catalase, by erythrocytes, or by hypoxia. Toxicity could be increased by the enzyme inhibitors L- and D-penicillamine, sodium diethyldithiocarbamate or 3-amino-1,2,4-triazole. The two cell lines had similar levels of superoxide dismutase and peroxidase; in 6 human melanoma lines, no correlation was found between dopa killing and tyrosinase activity as determined either by formation of dopa from tyrosine or by formation of melanin from dopa. Uptake of L-dopa was similar in HeLa and MM96 cells, and the toxicity of D-dopa was the same in both lines as that of the L-isomer. Dopa decomposed within 12 hr in culture medium, the rate and products being influenced by addition of the above enzymes and by the cell density. Dopa-melanin and medium containing decomposed dopa were also selectively toxic to MM96 cells. Adenovirus 5 was used in two different ways to assess the relative importance of DNA damage and inhibition of DNA synthesis by dopa. Viral replication was found to be unaffected in cells being treated with dopa but was strongly inhibited in cells treated with the DNA polymerase inhibitor cytosine arabinoside. Secondly, the virus was itself inactivated by treatment with dopa for 24 hr (D37 1.3 mM); similar dose response curves were obtained for replication of dopa-treated virus in untreated HeLa or MM96 cells. These results show that the initial events of dopa toxicity occur outside the cell and lead to the formation of a stable, toxic product (probably melanin) which does not strongly inhibit DNA polymerase activity. Melanoma hypersensitivity was not due to differences in oxygen-metabolizing enzymes, dopa uptake, or DNA repair.
...
PMID:Modification of dopa toxicity in human tumour cells. 392 49

Several derivatives of levodopa have been shown to be potent inhibitors of the sulfhydryl enzyme, RNA dependent DNA polymerase, reverse transcriptase (RT). In the presence of the polyphenol oxidase, tyrosinase, the inhibitory values were between 10(-6) M and 10(-5) M. Structure-activity studies revealed that active oxidation or reduction was necessary for this potent inhibitory response. Spectrophotometric analysis showed that the presence of both the quinone and quinol was required for maximum inhibitory activity. These data suggest that the common intermediate of oxidation of quinols or reduction of quinones (i.e., semiquinone) is the active species. The use of tyrosinase provides a convenient model for the detection of the actual inhibitory interaction of a free-radical (semiquinone) with a biologically important macromolecule, reverse transcriptase.
...
PMID:Inhibition of reverse transcriptase by tyrosinase generated quinones related to levodopa and dopamine. 617 37

The dopamine analog 3,4-dihydroxybenzylamine (3,4-DHBA), a novel antitumor agent, was shown to inhibit directly DNA polymerase in cells of the deeply pigmented murine melanoma, S-91A, permeabilized to nucleotides by lysolecithin. In contrast, levodopa and dopamine did not inhibit DNA polymerase in permeabilized cells in the absence of exogenous tyrosinase. Analysis using isolated DNA polymerase showed that the inhibitory activity of the ortho dihydroxy compounds was totally dependent upon enzymatic activation. The enzymatic activation of the ortho derivative 3,4-DHBA by tyrosinase results in two reactive species: a semiquinone intermediate and a less reactive quinone. Inhibition of DNA polymerase by activated 3,4-DHBA was shown by dialysis and kinetic studies to involve an irreversible reaction which occurs at two inhibitor interaction sites as determined by a Hill plot analysis. Double-stranded DNA protected the enzyme from inhibition by 3,4-DHBA, suggesting that the inhibitory sites are at or near the template-initiator binding site.
...
PMID:3,4-Dihydroxybenzylamine: an improved dopamine analog cytotoxic for melanoma cells in part through oxidation products inhibitory to dna polymerase. 640 86

L-glutamic acid, gamma-(p-hydroxyanilide), is a naturally occurring metabolic inhibitor found in mushrooms and shown to be active against B-16 melanoma in vivo. We have prepared and evaluated 2 analogs, the 3,4- and 2,5-dihydroxy derivatives, since these might represent more immediate precursors to the putative biologically active quinone. Both dihydroxy derivatives were more toxic than the parent phenol. The 2,5-dihydroxy derivative was significantly more cytotoxic with a 5-fold decrease in IC50 for both human and B-16 melanoma cells in vitro. In the presence of mushroom tyrosinase, both derivatives were potent inhibitors of isolated DNA polymerase with essentially complete inhibition occurring at concentrations of 10(-5) M. The 3,4-dihydroxy derivative exerted inhibitory effects primarily upon thymidine incorporation into melanoma cells in vitro while the 2,5-dihydroxy derivative also inhibited uridine and leucine incorporation. There was no significant antitumor activity observed in the B-16 system, a fact which might be attributed to the increased toxicity of the compounds.
...
PMID:Antitumor effects of L-glutamic acid dihydroxyanilides against experimental melanoma. 676 71

Levodopa and dopamine are naturally occurring catecholamines with antitumor activity in several experimental tumor systems. Previous studies suggested that their cytotoxic effect was related in part to their inhibitory effect upon DNA polymerase. We have examined the effects of levodopa, dopamine, levodopa methyl ester, norepinephrine, and the analog 3,4-dihydroxybenzylamine upon human and murine melanoma cells. When exponentially growing cells were exposed to these drugs, a characteristic inhibition of thymidine incorporation was observed with much less inhibition of either uridine or leucine incorporation. In order to ascertain that inhibition was occurring at the level of DNA synthesis, we examined the effects of the drugs upon the incorporation of thymidine triphosphate by permeabilized melanoma cells. When melanoma cells were permeabilized by lysolecithin, thereby permitting the direct incorporation of labeled thymidine triphosphate, a similar inhibition of incorporation was observed. Dopamine at a concentration of 4.8 microM caused a 50% reduction in incorporation of label. These results suggested that inhibition did occur at the level of DNA synthesis. In the presence of the melanocyte-specific oxidase, tyrosinase, these derivatives are potent inhibitors of isolated DNA polymerase alpha with 50% inhibitory concentrations between 1 and 10 microM. The inhibition could be completely prevented by the presence of reducing agents such as dithiothreitol (1.0 mM). The quinols themselves were not inhibitors of DNA polymerase. Dopamine analogs represent an interesting class of antitumor agents with inhibitory activity for DNA polymerase.
...
PMID:Levodopa and dopamine analogs as DNA polymerase inhibitors and antitumor agents in human melanoma. 676 47

---