inosine-dialdehyde and 4-methyl-5-amino-1-formylisoquinoline-thiosemicarbazone

Several known inhibitors of mammalian ribonucleotide reductase were studied for their interactions with herpes simplex virus type 1 (HSV-1) ribonucleotide reductase. MAIQ (4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone) produced apparent inactivation of HSV-1 ribonucleotide reductase. Only catalytically cycling, not resting, enzyme could be inactivated. Double reciprocal replots of the rates of inactivation versus the concentration of MAIQ indicated that a reversible complex with the enzyme was formed prior to inactivation. In the presence of 10 microM CDP, the maximum rate of inactivation was 20 per h (t1/2 = 3 min). The half-maximum rate was achieved at about 15 microM MAIQ. INOX (periodate-oxidized inosine) also appeared to inactivate HSV-1 ribonucleotide reductase. In contrast to MAIQ, it readily inactivated resting as well as cycling enzyme. CDP retarded the rates of inactivation by INOX. An initial reversible complex between INOX and enzyme was not detectable under the conditions used. IMPY (2,3-dihydro-1H-pyrazolo(2,3-a)imidazole) and guanazole (3,5-diamino-1,2,4-triazole) produced reversible inhibition. Although the data with both inhibitors were most consistent with the noncompetitive inhibition model (versus CDP), the data with guanazole were also marginally consistent with the uncompetitive model.

Topics: Guanazole; Inosine; Isoquinolines; Kinetics; Pyrazoles; Ribonucleotide Reductases; Simplexvirus; Triazoles

The nature of the inhibition of Ehrlich tumor cell ribonucleotide reductase by combinations of agents directed at the non-heme iron-containing component and the effector-binding component was studied with the use of isobolograms. From these studies, it was determined that the combinations of pyrazoloimidazole (IMPY) and dialdehyde of inosine, IMPY and deoxyguanosine triphosphate (dGTP), IMPY and deoxyadenosine triphosphate (dATP), and IMPY and deoxythymidine triphosphate (dTTP) gave synergistic inhibition of cytidine diphosphate reductase. The combination of dATP and dGTP also gave synergistic inhibition. The combinations of hydroxyurea and IMPY, 4-methyl-5-aminoisoquinoline thiosemicarbazone (MAIQ) and IMPY, and dialdehyde of inosine and dialdehyde derivative of 5'-deoxyinosine gave antagonistic inhibition. Other combinations utilizing MAIQ and dATP, MAIQ and dGTP, MAIQ and dTTP, hydroxyurea and dGTP, and hydroxyurea and dTTP gave inhibition which was additive.

Topics: Aldehydes; Animals; Antineoplastic Agents; Carcinoma, Ehrlich Tumor; Deoxyadenine Nucleotides; Deoxyguanine Nucleotides; Drug Interactions; Drug Synergism; Edetic Acid; Hydroxyurea; Imidazoles; Inosine; Isoquinolines; Mice; Pyrazoles; Ribonucleotide Reductases; Thiosemicarbazones; Thymine Nucleotides

It had been shown previously that the ribonucleotide reductase from mouse tumor consisted of two nonidentical components (Tris and dye fractions, each prepared from the 20 to 40% (NH/)2SO4 protein fraction containing the ribonucleotide reductase activity by blue dextran-Sepharose chromatography). The individual components either separated or present in the intact enzyme can be specifically and independently inhibited by different compounds. The Tris fraction component was inhibited by 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone while the dye fraction component was inactivated by pyridoxal phosphate:BH4- and the dialdehyde derivative of inosine (Inox) and 5'-deoxyinosine prepared by the periodate oxidation of inosine and 5'-deoxyinosine. The intact enzyme could be completely inhibited by any of these compounds. Reductase activity was restored by reconstitution with the exogenous components. The individual components of the reductase in the intact Ehrlich tumor cell could also be specifically inhibited. Activity in the crude cell-free extracts prepared from 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone- or Inox-treated cells was restored by the addition of the appropriate exogenous component. These data suggest that combinations of inhibitors of ribonucleotide reductase which specifically inhibit the components may be useful in the treatment of cancer.

Topics: Aldehydes; Animals; Carcinoma, Ehrlich Tumor; Cells, Cultured; Drug Therapy, Combination; Inosine; Isoquinolines; Mice; Protein Conformation; Pyridoxal Phosphate; Ribonucleotide Reductases; Thiosemicarbazones