Methylglyoxal bis(guanylhydrazone) analogs: multifunctional inhibitors for polyamine enzymes

S-adenosylmethionine decarboxylase as an enzyme target for therapy

The polyamine biosynthetic pathway has attracted much interest as a therapeutic target. Many studies have shown the potential value of inhibitors of the first enzyme in the biosynthetic pathway, ornithine decarboxylase, which forms putrescine. In order to convert putrescine into the polyamines, spermidine and spermine, the aminopropyl donor, decarboxylated S-adenosylmethionine, is needed. Therefore, S-adenosylmethionine decarboxylase (AdoMetDC, EC 4.1.1.50) is essential for polyamine synthesis. Early studies of the inhibition of this enzyme were carried out with compounds such as methylglyoxal bis(guanylhydrazone) that lack specificity and also lack potency since they are competitive inhibitors whose effects are overcome by a compensatory increase in the amount of the target enzyme. Recently, powerful irreversible inhibitors of AdoMetDC have become available including 5'-([(Z)-4-amino-2-butenyl]methylamino)-5'-deoxyadenosine, an enzyme activated inhibitor and 5'-deoxy-5'-[(3-hydrazinopropyl)methylamino]adenosine which binds to the active site and forms a covalent bond with the pyruvate prosthetic group. This review describes the current state of knowledge of the structure and properties of AdoMetDC, the available inhibitors of this enzyme, their mechanism of action and their effects on polyamines and on the growth of tumors and protozoan parasites. These effects indicate that AdoMetDC inhibitors may be of therapeutic value either alone or in combination with ornithine decarboxylase inhibitors and that further trials of these compounds should be considered.

Evaluation of the antimicrobial activity of methylglyoxal bis(guanylhydrazone) analogues, the inhibitors for polyamine biosynthetic pathway

Metabolic and antiproliferative effects of methylglyoxal bis(butylamidinohydrazone) (MGBB) and methylglyoxal bis(cyclopentylamidinohydrazone) (MGBCP), inhibitors for polyamine biosynthetic pathway, on Escherichia coli, Shigella sonnei, Aeromonas sobria, Aeromonas hydrophila and Vibrio cholerae were investigated. MGBB at the concentration of 100 mumol/l depleted intracellular putrescine and spermidine concentrations of E. coli to 25 and 20% of the controls, respectively, while MGBCP depressed their concentrations to 38 and 24%, respectively. In these polyamine-depleted E. coli cells the syntheses of RNA, DNA and protein decreased to 13, 54 and 29% of the control, respectively, with MGBB and to 23, 71 and 55%, respectively, with MGBCP. The minimum inhibitory concentrations (MIC) of MGBB for the growth of A. sobria, E. coli, A. hydrophila, V. cholerae and Sh. sonnei were estimated to be 50, 160, 240, 285 and 320 mumol/l, respectively, whereas those of MGBCP were slightly higher for respective bacteria.

Synergism through direct covalent bonding between agents: a strategy for rational design of chemotherapeutic combinations

Self-assembling chemotherapeutic agents are mixtures of relatively nontoxic precursors that can combine chemically under physiological conditions to form products with greater cytotoxic and/or antimicrobial activity than either of the precursors. Combinations that form products more rapidly in or near the target (tumor, pathogen, virally infected cell) than in normal tissues will exhibit target-selective synergism, thus exhibiting an antitarget selectivity that is greater than the selectivities of the product (e.g., a hydrazone) and of either precursor (e.g., a hydrazine derivative or ketone) used singly. This paper describes the target-selective cytotoxic synergism of a cationic aldehyde (A) and a cationic acylhydrazine (B) containing a triarylalkylphosphonium moiety against Ehrlich ascites carcinoma cells (ELA) in culture, in addition to reviewing previous work on self-assembling cytotoxins. The synergism between A and B is carcinoma selective when the ELA cells (the target) are compared to CV-1, an untransformed African green monkey kidney epithelial line. Like tetraphenylphosphonium and rhodamine 123, which are selectively concentrated in ELA cells relative to CV-1, A, B and the hydrazone C resulting from their reaction are lipophilic delocalized cations that selectively inhibit ELA growth relative to CV-1 growth. The hydrazone C is more growth inhibitory than either A or B for both cell lines. A combination of A with an unreactive analogue of B and a combination of B with an unreactive analogue of A did not synergistically inhibit ELA proliferation. The degree of synergism is greater against the ELA cells than against the CV-1 cells. These data, together with hydrazone formation kinetics, suggest that A and B are both concentrated together selectively inside the ELA due to the transmembrane potentials, reacting inside the ELA cells at a higher velocity than inside the CV-1 cells to form the more growth-inhibitory hydrazone C.

Stabilization of ornithine decarboxylase in mouse liver and lung by methylglyoxal bis(cyclohexylamidinohydrazone)

The intraperitoneal injection of methylglyoxal bis(cyclohexylamidinohydrazone) (MGBC), an inhibitor of S-adenosylmethionine decarboxylase and spermidine synthase, markedly increased (7-fold of the basal level at 4 hr) ornithine decarboxylase (ODC) activity in normal mouse liver. ODC activity was also increased 2.5-fold over the basal level in mouse lung at 6 hr after the injection. The effect of MGBC on ODC activity occurred in a dose-dependent manner. Measurement of the apparent half-life of ODC induced in the liver and lung by MGBC treatment revealed a clear decrease in the decay rate of the enzyme in both the tissues. Activities of S-adenosylmethionine decarboxylase (AdoMetDC) and spermidine/spermine N1-acetyltransferase (SAT) were not increased by the intraperitoneal injection of MGBC. There was a large rise in putrescine and a fall in spermidine and spermine in the liver and lung except for brain within an 8 hr period in response to MGBC, suggesting that these changes resulted from the stabilization of ODC and inhibitions of AdoMetDC and spermidine synthase.

Difluoro-phenyl-ethyl(4-aminopropylamidinohydrazone): an irreversible inhibitor for both ornithine and S-adenosylmethionine decarboxylases and its effect on human lymphoid leukemia Molt 4B cells

Difluoro-phenyl-ethyl(4-aminopropylamidinohydrazone) (DFPA) was synthesized as an irreversible inhibitor of ornithine and S-adenosylmethionine decarboxylases and analyzed for antiproliferative effects on leukemia cells. The compound irreversibly inhibited ornithine and S-adenosylmethione decarboxylases. This inhibition could not be reversed by dialysis or chromatography on Sephadex G-50. When human lymphoid leukemia Molt 4B cells were cultured in the presence of the inhibitor, the intracellular levels of polyamines (putrescine, spermidine and spermine) and the rate of cell proliferation were markedly depressed. In these polyamine-depleted and growth-retarded cells, the synthesis of protein, but not of DNA or RNA, was observed to be significantly inhibited.