mycophenolic-acid and Sarcoma-180

Mycophenolic acid (MA) was demonstrated to be an effective inhibitor of the growth of the intracellular parasitic protozoan Eimeria tenella in tissue culture and guanine was shown to reverse this inhibition as expected for an inhibitor of IMP dehydrogenase (IMP:NAD+ oxidoreductase, EC 1.1.1.205). A high performance liquid chromatography study of the intracellular nucleotide pools labeled with [3H]hypoxanthine was carried out in host cells lacking hypoxanthine-guanine phosphoribosyltransferase, and the depletion of guanine nucleotides demonstrated that the intracellular parasite enzyme was being inhibited by the drug. Kinetic studies carried out on the enzyme derived from E. tenella oocysts demonstrated substrate inhibition by NAD and mycophenolic acid inhibition similar to that found for mammalian enzymes, but different from that for bacterial enzymes. The inhibition by mycophenolic acid was not time-dependent and was immediately reversed upon dilution. As found previously for other IMP dehydrogenases, an Ordered Bi-Bi mechanism prevails with IMP on first followed by NAD, NADH off first, and then XMP. The kinetic patterns are consistent with substrate inhibition at high concentrations of NAD due to the formation of an E X XMP X NAD complex. Uncompetitive inhibition by MA versus IMP, NAD, and K+ was found and this was interpreted as evidence for the formation of an E X XMP X MA complex. A speculative mechanism for the inhibition of the enzyme is offered which is consistent with the fact that E X XMP X MA readily forms, whereas E X IMP X MA does not.

Topics: Animals; Chromatography, High Pressure Liquid; Cricetinae; Cricetulus; Eimeria; Humans; Hypoxanthine Phosphoribosyltransferase; IMP Dehydrogenase; Ketone Oxidoreductases; Kinetics; Liver; Lymphoma; Models, Chemical; Mycophenolic Acid; NAD; Placenta; Rats; Sarcoma 180

The effects of the inhibitors of IMP dehydrogenase, tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide) and mycophenolic acid, on the synthesis of cellular glycoproteins were evaluated in Sarcoma 180 cells. Both tiazofurin and mycophenolic acid decreased the rate of incorporation of [2-3H]mannose and [2-3H]fucose into acid-precipitable glycoproteins within 4 hr of exposure; this inhibitory activity was concentration dependent and occurred in the absence of a significant effect on the incorporation of labeled glucosamine and leucine into acid-insoluble material. Interference with the utilization of [3H]mannose for the formation of glycoproteins was paralleled by an inhibition of [3H] mannose incorporation into their lipid-linked oligosaccharide precursors following treatment with cytotoxic concentrations of tiazofurin (100 microM) or mycophenolic acid (10 microM); these actions occurred within 3 hr of exposure to these agents, with maximal reductions being observed at 12 hr. Under these conditions, intracellular GTP levels were reduced by 80%, whereas ATP pools remained unaffected ant UTP levels were markedly increased. Guanosine (100 microM) prevented the cytotoxic actions of tiazofurin and mycophenolic acid and reversed the drug-induced decrease in GTP pools and in the incorporation of mannose and other metabolic precursors into acid-insoluble material. Inhibition of fucose and mannose incorporation into lipid-linked oligosaccharides and glycoproteins were preceded by decreases in the labeling of their respective guanosine nucleotide sugars and were followed sequentially by alterations in the plasma membrane as detected by both the binding and the rate of cell agglutination caused by the plant lectin, concanavalin A. The findings that tiazofurin and mycophenolic acid produce alterations in the utilization of [3H]mannose for the formation of glycoproteins and in membrane architecture are indicative of metabolic lesions induced by agents that selectively depress guanine nucleotide synthesis through inhibition of IMP dehydrogenase.

Topics: Animals; Cell Division; Cells, Cultured; Dose-Response Relationship, Drug; Glucosamine; Glycoproteins; Guanosine; Guanosine Triphosphate; IMP Dehydrogenase; Ketone Oxidoreductases; Kinetics; Mannose; Mycophenolic Acid; Ribavirin; Ribonucleosides; Sarcoma 180; Tritium

Several derivatives of mycophenolic acid (MA) were tested for their antitumor activity against leukemia L-1210 when administered orally and carbamoyl mycophenolic acid ethylester (CMAE) was selected as the most active antitumor agent in these tests. An oral administration of CMAE also inhibited the growth of Ehrlich solid carcinoma, NF sarcoma, myeloma X-5563 and sarcoma 180 in mice. In comparison with antitumor activity of MA, the improvement in activity of CMAE against leukemia L-1210 and Ehrlich solid carcinoma was indeed remarkable, CMAE seems to be less immunosuppressive than MA.

Topics: Administration, Oral; Animals; Carbamates; Carcinoma, Ehrlich Tumor; Leukemia L1210; Mice; Mycophenolic Acid; Sarcoma 180

Mycophenolic acid, a novel antibiotic of low toxicity containing no nitrogen atoms in its structure, induces tumor regression in several murine solid tumor assays. It has been reported in extensive structure-activity studies that chemical modifications on the antibiotic itself reduce or eliminate antitumor activity. With the objective of antitumor activity enhancement, nitrogen-containing analogs of mycophenolic acid were synthesized according to a program directed toward the ultimate synthesis of close bioisosteres of the antibiotic. Intial efforts reported here describe the terpenoid side-chain degradation of N-geranyl-2(1H)-pyridones and N-geranylglutarimides, where the terminal isopropylidene is replaced with a carboxyl group as it occurs in mycophenolic acid. The resulting nitrogen-containing analogs of the antitumor antibiotic were inactive in the l-1210 and Walker 256 tumor systems.

Topics: Aldehydes; Alkylation; Animals; Antineoplastic Agents; Carboxylic Acids; Leukemia L1210; Magnetic Resonance Spectroscopy; Mycophenolic Acid; Rats; Sarcoma 180; Structure-Activity Relationship