Methyl glyoxal bis(guanylhydrazone) as a potent inhibitor of mammalian and yeast S-adenosylmethionine decarboxylases

The Synergistic Benefit of Combination Strategies Targeting Tumor Cell Polyamine Homeostasis

Mammalian polyamines, including putrescine, spermidine, and spermine, are positively charged amines that are essential for all living cells including neoplastic cells. An increasing understanding of polyamine metabolism, its molecular functions, and its role in cancer has led to the interest in targeting polyamine metabolism as an anticancer strategy, as the metabolism of polyamines is frequently dysregulated in neoplastic disease. In addition, due to compensatory mechanisms, combination therapies are clinically more promising, as agents can work synergistically to achieve an effect beyond that of each strategy as a single agent. In this article, the nature of polyamines, their association with carcinogenesis, and the potential use of targeting polyamine metabolism in treating and preventing cancer as well as combination therapies are described. The goal is to review the latest strategies for targeting polyamine metabolism, highlighting new avenues for exploiting aberrant polyamine homeostasis for anticancer therapy and the mechanisms behind them.

One-Carbon and Polyamine Metabolism as Cancer Therapy Targets

Cancer metabolic reprogramming is essential for maintaining cancer cell survival and rapid replication. A common target of this metabolic reprogramming is one-carbon metabolism which is notable for its function in DNA synthesis, protein and DNA methylation, and antioxidant production. Polyamines are a key output of one-carbon metabolism with widespread effects on gene expression and signaling. As a result of these functions, one-carbon and polyamine metabolism have recently drawn a lot of interest for their part in cancer malignancy. Therapeutic inhibitors that target one-carbon and polyamine metabolism have thus been trialed as anticancer medications. The significance and future possibilities of one-carbon and polyamine metabolism as a target in cancer therapy are discussed in this review.

The RATIOnal Role of Polyamines in Epidermal Differentiation

Polyamines have been implicated in skin tumorigenesis; however, their role in epidermal homeostasis remains obscure. In a new article in the Journal of Investigative Dermatology, Rahim et al. (2021) report that keratinocyte differentiation requires a shift in polyamine ratios that is mediated by AMD1. Results suggest that targeting polyamine availability might be useful in the treatment of hyperproliferative skin disorders.

Metabolism and function of polyamines in cancer progression

Polyamines are essential for the proliferation, differentiation, and development of eukaryotes. They include spermine, spermidine, and the diamine precursor putrescine, and are low-molecular-weight, organic polycations with more than two amino groups. Their intracellular concentrations are strictly maintained within a specific physiological range through several regulatory mechanisms in normal cells. In contrast, polyamine metabolism is dysregulated in many neoplastic states, including cancer. In various types of cancer, polyamine levels are elevated, and crosstalk occurs between polyamine metabolism and oncogenic pathways, such as mTOR and RAS pathways. Thus, polyamines might have potential as therapeutic targets in the prevention and treatment of cancer. The molecular mechanisms linking polyamine metabolism to carcinogenesis must be unraveled to develop novel inhibitors of polyamine metabolism. This overview describes the nature of polyamines, their association with carcinogenesis, the development of polyamine inhibitors and their potential, and the findings of clinical trials.

Methylglyoxal-bis-guanylhydrazone inhibits osteopontin expression and differentiation in cultured human monocytes

Monocyte activation and polarization play essential roles in many chronic inflammatory diseases. An imbalance of M1 and M2 macrophage activation (pro-inflammatory and alternatively activated, respectively) is believed to be a key aspect in the etiology of these diseases, thus a therapeutic approach that regulates macrophage activation could be of broad clinical relevance. Methylglyoxal-bis-guanylhydrazone (MGBG), a regulator of polyamine metabolism, has recently been shown to be concentrated in monocytes and macrophages, and interfere with HIV integration into the DNA of these cells in vitro. RNA expression analysis of monocytes from HIV+ and control donors with or without MGBG treatment revealed the only gene to be consistently down regulated by MGBG to be osteopontin (OPN). The elevated expression of this pro-inflammatory cytokine and monocyte chemoattractant is associated with various chronic inflammatory diseases. We demonstrate that MGBG is a potent inhibitor of secreted OPN (sOPN) in cultured monocytes with 50% inhibition achieved at 0.1 μM of the drug. Furthermore, inhibition of OPN RNA transcription in monocyte cultures occurs at similar concentrations of the drug. During differentiation of monocytes into macrophages in vitro, monocytes express cell surface CD16 and the cells undergo limited DNA synthesis as measured by uptake of BrdU. MGBG inhibited both activities at similar doses to those regulating OPN expression. In addition, monocyte treatment with MGBG inhibited differentiation into both M1 and M2 classes of macrophages at non-toxic doses. The inhibition of differentiation and anti-OPN effects of MGBG were specific for monocytes in that differentiated macrophages were nearly resistant to MGBG activities. Thus MGBG may have potential therapeutic utility in reducing or normalizing OPN levels and regulating monocyte activation in diseases that involve chronic inflammation.

Polyamines and Cancer

This chapter provides an overview of how the polyamine pathway has been exploited as a target for the treatment and prevention of multiple forms of cancer, since this pathway is disrupted in all cancers. It is divided into three main sections. The first explores how the polyamine pathway has been targeted for chemotherapy, starting from the first drug to target it, difluoromethylornithine (DFMO) to the large variety of polyamine analogues that have been synthesised and tested throughout the years with all their potentials and pitfalls. The second section focuses on the use of polyamines as vectors for drug delivery. Knowing that the polyamine transport system is upregulated in cancers and that polyamines naturally bind to DNA, a range of polyamine analogues and polyamine-like structures have been synthesised to target epigenetic regulators, with encouraging results. Furthermore, the use of polyamines as transport vectors to introduce toxic/bioactive/fluorescent agents more selectively to the intended target in cancer cells is discussed. The last section concentrates on chemoprevention, where the different strategies that have been undertaken to interfere with polyamine metabolism and function for antiproliferative intervention are outlined and discussed.

Targeting polyamine metabolism for cancer therapy and prevention

The chemically simple, biologically complex eukaryotic polyamines, spermidine and spermine, are positively charged alkylamines involved in many crucial cellular processes. Along with their diamine precursor putrescine, their normally high intracellular concentrations require fine attenuation by multiple regulatory mechanisms to keep these essential molecules within strict physiologic ranges. Since the metabolism of and requirement for polyamines are frequently dysregulated in neoplastic disease, the metabolic pathway and functions of polyamines provide rational drug targets; however, these targets have been difficult to exploit for chemotherapy. It is the goal of this article to review the latest findings in the field that demonstrate the potential utility of targeting the metabolism and function of polyamines as strategies for both chemotherapy and, possibly more importantly, chemoprevention.

Direct Targeting of Macrophages With Methylglyoxal-Bis-Guanylhydrazone Decreases SIV-Associated Cardiovascular Inflammation and Pathology

BACKGROUND

Despite effective combination antiretroviral therapy, HIV-infected individuals develop comorbidities, including cardiovascular disease, where activated macrophages play a key role. To date, few therapies target activated monocytes and macrophages.

METHODS

We evaluated a novel oral form of the polyamine biosynthesis inhibitor methylglyoxal-bis-guanylhydrazone (MGBG) on cardiovascular inflammation, carotid artery intima-media thickness (cIMT), and fibrosis in a simian immunodeficiency virus infection model of AIDS. Eleven simian immunodeficiency virus-infected animals received MGBG (30 mg/kg) once daily and 8 received a placebo control both beginning at 21 days postinfection (dpi). Animals were time sacrificed at 49 days post infection (dpi), when their matched placebo controls developed AIDS (63, 70, 77, 80), or at the study end-point (84 dpi). Aorta, carotid artery, and cardiac tissues were analyzed. Quantitative analyses of macrophage populations and T lymphocytes were done and correlated with cIMT and fibrosis.

RESULTS

MGBG treatment resulted in 2.19-fold (CD163), 1.86-fold (CD68), 2.31-fold (CD206), and 2.12-fold (MAC387) decreases in macrophages in carotid arteries and significant 2.07-fold (CD163), 1.61-fold (CD68), 1.95-fold (MAC387), and 1.62-fold (CD206) decreases in macrophages in cardiac tissues. cIMT (1.49-fold) and fibrosis (2.05-fold) also were significantly decreased with MGBG treatment. Numbers of macrophage and the degree of fibrosis in treated animals were similar to uninfected animals. A positive correlation between decreased macrophage in the carotid artery and cIMT, and cardiac macrophages and fibrosis was found.

CONCLUSIONS

These data demonstrate that directly targeting macrophages with MGBG can reduce cardiovascular inflammation, cIMT, and fibrosis. They suggest that therapies targeting macrophages with HIV could be used in conjunction with combination antiretroviral therapy.

An oral form of methylglyoxal-bis-guanylhydrazone reduces monocyte activation and traffic to the dorsal root ganglia in a primate model of HIV-peripheral neuropathy

Peripheral neuropathy (PN) is a major comorbidity of HIV infection that is caused in part by chronic immune activation. HIV-PN is associated with infiltration of monocytes/macrophages to the dorsal root ganglia (DRG) causing neuronal loss and formation of Nageotte nodules. Here, we used an oral form of methylglyoxal-bis-guanylhydrazone (MGBG), a polyamine biosynthesis inhibitor, to specifically reduce activation of myeloid cells. MGBG is selectively taken up by monocyte/macrophages in vitro and inhibits HIV p24 expression and DNA viral integration in macrophages. Here, MGBG was administered to nine SIV-infected, CD8-depleted rhesus macaques at 21 days post-infection (dpi). An additional nine SIV-infected, CD8-depleted rhesus macaques were used as untreated controls. Cell traffic to tissues was measured by in vivo BrdU pulse labeling. MGBG treatment significantly diminished DRG histopathology and reduced the number of CD68+ and CD163+ macrophages in DRG tissue. The number of recently trafficked BrdU+ cells in the DRG was significantly reduced with MGBG treatment. Despite diminished DRG pathology, intraepidermal nerve fiber density (IENFD) did not recover after treatment with MGBG. These data suggest that MGBG alleviated DRG pathology and inflammation.

Inhibition of HIV Expression and Integration in Macrophages by Methylglyoxal-Bis-Guanylhydrazone

Macrophages are a target for infection with HIV and represent one of the viral reservoirs that are relatively resistant to current antiretroviral drugs. Here we demonstrate that methylglyoxal-bis-guanylhydrazone (MGBG), a polyamine analog and potent S-adenosylmethionine decarboxylase inhibitor, decreases HIV expression in monocytes and macrophages. MGBG is selectively concentrated by these cells through a mechanism consistent with active transport by the polyamine transporter. Using a macrophage-tropic reporter virus tagged with the enhanced green fluorescent protein, we demonstrate that MGBG decreases the frequency of HIV-infected cells. The effect is dose dependent and correlates with the production of HIV p24 in culture supernatants. This anti-HIV effect was further confirmed using three macrophage-tropic primary HIV isolates. Viral life cycle mapping studies show that MGBG inhibits HIV DNA integration into the cellular DNA in both monocytes and macrophages.

IMPORTANCE

Our work demonstrates for the first time the selective concentration of MGBG by monocytes/macrophages, leading to the inhibition of HIV-1 expression and a reduction in proviral load within macrophage cultures. These results suggest that MGBG may be useful in adjunctive macrophage-targeted therapy for HIV infection.

Polyamines and their metabolites as diagnostic markers of human diseases

Polyamines, putrescine, spermidine and spermine, are ubiquitous in living cells and are essential for eukaryotic cell growth. These polycations interact with negatively charged molecules such as DNA, RNA, acidic proteins and phospholipids and modulate various cellular functions including macromolecular synthesis. Dysregulation of the polyamine pathway leads to pathological conditions including cancer, inflammation, stroke, renal failure and diabetes. Increase in polyamines and polyamine synthesis enzymes is often associated with tumor growth, and urinary and plasma contents of polyamines and their metabolites have been investigated as diagnostic markers for cancers. Of these, diacetylated derivatives of spermidine and spermine are elevated in the urine of cancer patients and present potential markers for early detection. Enhanced catabolism of cellular polyamines by polyamine oxidases (PAO), spermine oxidase (SMO) or acetylpolyamine oxidase (AcPAO), increases cellular oxidative stress and generates hydrogen peroxide and a reactive toxic metabolite, acrolein, which covalently incorporates into lysine residues of cellular proteins. Levels of protein-conjuagated acrolein (PC-Acro) and polyamine oxidizing enzymes were increased in the locus of brain infarction and in plasma in a mouse model of stroke and also in the plasma of stroke patients. When the combined measurements of PC-Acro, interleukin 6 (IL-6), and C-reactive protein (CRP) were evaluated, even silent brain infarction (SBI) was detected with high sensitivity and specificity. Considering that there are no reliable biochemical markers for early stage of stroke, PC-Acro and PAOs present promising markers. Thus the polyamine metabolites in plasma or urine provide useful tools in early diagnosis of cancer and stroke.

Polyamines and cancer: implications for chemotherapy and chemoprevention

Polyamines are small organic cations that are essential for normal cell growth and development in eukaryotes. Under normal physiological conditions, intracellular polyamine concentrations are tightly regulated through a dynamic network of biosynthetic and catabolic enzymes, and a poorly characterised transport system. This precise regulation ensures that the intracellular concentration of polyamines is maintained within strictly controlled limits. It has frequently been observed that the metabolism of, and the requirement for, polyamines in tumours is frequently dysregulated. Elevated levels of polyamines have been associated with breast, colon, lung, prostate and skin cancers, and altered levels of rate-limiting enzymes in both biosynthesis and catabolism have been observed. Based on these observations and the absolute requirement for polyamines in tumour growth, the polyamine pathway is a rational target for chemoprevention and chemotherapeutics. Here we describe the recent advances made in the polyamine field and focus on the roles of polyamines and polyamine metabolism in neoplasia through a discussion of the current animal models for the polyamine pathway, chemotherapeutic strategies that target the polyamine pathway, chemotherapeutic clinical trials for polyamine pathway-specific drugs and ongoing clinical trials targeting polyamine biosynthesis.

Legionella pneumophila requires polyamines for optimal intracellular growth

The Gram-negative intracellular pathogen Legionella pneumophila replicates in a membrane-bound compartment known as the Legionella-containing vacuole (LCV), into which it abundantly releases its chaperonin, HtpB. To determine whether HtpB remains within the LCV or reaches the host cell cytoplasm, we infected U937 human macrophages and CHO cells with L. pneumophila expressing a translocation reporter consisting of the Bordetella pertussisa denylate cyclase fused to HtpB. These infections led to increased cyclic AMP levels, suggesting that HtpB reaches the host cell cytoplasm. To identify potential functions of cytoplasmic HtpB, we expressed it in the yeast Saccharomyces cerevisiae, where HtpB induced pseudohyphal growth. A yeast-two-hybrid screen showed that HtpB interacted with S-adenosylmethionine decarboxylase (SAMDC), an essential yeast enzyme (encoded by SPE2) that is required for polyamine biosynthesis. Increasing the copy number of SPE2 induced pseudohyphal growth in S. cerevisiae; thus, we speculated that (i) HtpB induces pseudohyphal growth by activating polyamine synthesis and (ii) L. pneumophila may require exogenous polyamines for growth. A pharmacological inhibitor of SAMDC significantly reduced L. pneumophila replication in L929 mouse cells and U937 macrophages, whereas exogenously added polyamines moderately favored intracellular growth, confirming that polyamines and host SAMDC activity promote L. pneumophila proliferation. Bioinformatic analysis revealed that most known enzymes required for polyamine biosynthesis in bacteria (including SAMDC) are absent in L. pneumophila, further suggesting a need for exogenous polyamines. We hypothesize that HtpB may function to ensure a supply of polyamines in host cells, which are required for the optimal intracellular growth of L. pneumophila.

Complexes of Thermotoga maritimaS-adenosylmethionine decarboxylase provide insights into substrate specificity

The polyamines putrescine, spermidine and spermine are ubiquitous aliphatic cations and are essential for cellular growth and differentiation. S-Adenosylmethionine decarboxylase (AdoMetDC) is a critical pyruvoyl-dependent enzyme in the polyamine-biosynthetic pathway. The crystal structures of AdoMetDC from humans and plants and of the AdoMetDC proenzyme from Thermotoga maritima have been obtained previously. Here, the crystal structures of activated T. maritima AdoMetDC (TmAdoMetDC) and of its complexes with S-adenosylmethionine methyl ester and 5'-deoxy-5'-dimethylthioadenosine are reported. The results demonstrate for the first time that TmAdoMetDC autoprocesses without the need for additional factors and that the enzyme contains two complete active sites, both of which use residues from both chains of the homodimer. The complexes provide insights into the substrate specificity and ligand binding of AdoMetDC in prokaryotes. The conservation of the ligand-binding mode and the active-site residues between human and T. maritima AdoMetDC provides insight into the evolution of AdoMetDC.

Structural biology of S-adenosylmethionine decarboxylase

S-adenosylmethionine decarboxylase (AdoMetDC) is a critical enzyme in the polyamine biosynthetic pathway and a subject of many structural and biochemical investigations for anti-cancer and anti-parasitic therapy. The enzyme undergoes an internal serinolysis reaction as a post-translational modification to generate the active site pyruvoyl group for the decarboxylation process. The crystal structures of AdoMetDC from Homo sapiens, Solanum tuberosum, Thermotoga maritima, and Aquifex aeolicus have been determined. Numerous crystal structures of human AdoMetDC and mutants have provided insights into the mechanism of autoprocessing, putrescine activation, substrate specificity, and inhibitor design to the enzyme. The comparison of the human and potato enzyme with the T. maritima and A. aeolicus enzymes supports the hypothesis that the eukaryotic enzymes evolved by gene duplication and fusion. The residues implicated in processing and activity are structurally conserved in all forms of the enzyme, suggesting a divergent evolution of AdoMetDC.

S-Adenosylmethionine decarboxylase

S-Adenosylmethionine decarboxylase is a key enzyme for the synthesis of polyamines in mammals, plants and many other species that use aminopropyltransferases for this pathway. It catalyses the formation of S-adenosyl-1-(methylthio)-3-propylamine (decarboxylated S-adenosylmethionine), which is used as the aminopropyl donor. This is the sole function of decarboxylated S-adenosylmethionine. Its content is therefore kept very low and is regulated by variation in the activity of S-adenosylmethionine decarboxylase according to the need for polyamine synthesis. All S-adenosylmethionine decarboxylases have a covalently bound pyruvate prosthetic group, which is essential for the decarboxylation reaction, and have similar structures, although they differ with respect to activation by cations, primary sequence and subunit composition. The present chapter describes these features, the mechanisms for autocatalytic generation of the pyruvate from a proenzyme precursor and for the decarboxylation reaction, and the available inhibitors of this enzyme, which have uses as anticancer and anti-trypanosomal agents. The intricate mechanisms for regulation of mammalian S-adenosylmethionine decarboxylase activity and content are also described.

Divergent regulation of the key enzymes of polyamine metabolism by chiral alpha-methylated polyamine analogues

The natural polyamines are ubiquitous multifunctional organic cations which play important roles in regulating cellular proliferation and survival. Here we present a novel approach to investigating polyamine functions by using optical isomers of MeSpd (alpha-methylspermidine) and Me2Spm (alpha,omega-bismethylspermine), metabolically stable functional mimetics of natural polyamines. We studied the ability of MeSpd and Me2Spm to alter the normal polyamine regulation pathways at the level of polyamine uptake and the major control mechanisms known to affect the key polyamine metabolic enzymes. These include: (i) ODC (ornithine decarboxylase), which catalyses the rate-limiting step of polyamine synthesis; (ii) ODC antizyme, an inhibitor of ODC and polyamine uptake; (iii) SSAT (spermidine/spermine N1-acetyltransferase), the major polyamine catabolic enzyme; and (iv) AdoMetDC (S-adenosyl-L-methionine decarboxylase), which is required for the conversion of putrescine into spermidine, and spermidine into spermine. We show that the stereoisomers differ in their cellular uptake and ability to downregulate ODC and AdoMetDC, and to induce SSAT. These effects are mediated by the ability of the enantiomers to induce +1 ribosomal frameshifting on ODC antizyme mRNA, to suppress the translation of AdoMetDC uORF (upstream open reading frame) and to regulate the alternative splicing of SSAT pre-mRNA. The unique effects of chiral polyamine analogues on polyamine metabolism may offer novel possibilities for studying the physiological functions, control mechanisms, and targets of the natural polyamines, as well as advance therapeutic drug development in cancer and other human health-related issues.

Role of the sulfonium center in determining the ligand specificity of human s-adenosylmethionine decarboxylase

S-Adenosylmethionine decarboxylase (AdoMetDC) is a key enzyme in the polyamine biosynthetic pathway. Inhibition of this pathway and subsequent depletion of polyamine levels is a viable strategy for cancer chemotherapy and for the treatment of parasitic diseases. Substrate analogue inhibitors display an absolute requirement for a positive charge at the position equivalent to the sulfonium of S-adenosylmethionine. We investigated the ligand specificity of AdoMetDC through crystallography, quantum chemical calculations, and stopped-flow experiments. We determined crystal structures of the enzyme cocrystallized with 5'-deoxy-5'-dimethylthioadenosine and 5'-deoxy-5'-(N-dimethyl)amino-8-methyladenosine. The crystal structures revealed a favorable cation-pi interaction between the ligand and the aromatic side chains of Phe7 and Phe223. The estimated stabilization from this interaction is 4.5 kcal/mol as determined by quantum chemical calculations. Stopped-flow kinetic experiments showed that the rate of the substrate binding to the enzyme greatly depends on Phe7 and Phe223, thus supporting the importance of the cation-pi interaction.

New insights into the design of inhibitors of human S-adenosylmethionine decarboxylase: studies of adenine C8 substitution in structural analogues of S-adenosylmethionine

S-adenosylmethionine decarboxylase (AdoMetDC) is a critical enzyme in the polyamine biosynthetic pathway and depends on a pyruvoyl group for the decarboxylation process. The crystal structures of the enzyme with various inhibitors at the active site have shown that the adenine base of the ligands adopts an unusual syn conformation when bound to the enzyme. To determine whether compounds that favor the syn conformation in solution would be more potent AdoMetDC inhibitors, several series of AdoMet substrate analogues with a variety of substituents at the 8-position of adenine were synthesized and analyzed for their ability to inhibit hAdoMetDC. The biochemical analysis indicated that an 8-methyl substituent resulted in more potent inhibitors, yet most other 8-substitutions provided no benefit over the parent compound. To understand these results, we used computational modeling and X-ray crystallography to study C(8)-substituted adenine analogues bound in the active site.

Targeting polyamine metabolism and function in cancer and other hyperproliferative diseases

The polyamines spermidine and spermine and their diamine precursor putrescine are naturally occurring, polycationic alkylamines that are essential for eukaryotic cell growth. The requirement for and the metabolism of polyamines are frequently dysregulated in cancer and other hyperproliferative diseases, thus making polyamine function and metabolism attractive targets for therapeutic intervention. Recent advances in our understanding of polyamine function, metabolic regulation, and differences between normal cells and tumour cells with respect to polyamine biology, have reinforced the interest in this target-rich pathway for drug development.

Involvement of potD in Streptococcus pneumoniae polyamine transport and pathogenesis

Polyamines such as putrescine, spermidine, and cadaverine are small, polycationic molecules that are required for optimal growth in all cells. The intracellular concentrations of these molecules are maintained by de novo synthesis and transport pathways. The human pathogen Streptococcus pneumoniae possesses a putative polyamine transporter (pot) operon that consists of the four pot-specific genes potABCD. The studies presented here examined the involvement of potD in polyamine transport and in pneumococcal pathogenesis. A potD-deficient mutant was created in the mouse-virulent serotype 3 strain WU2 by insertion duplication mutagenesis. The growth of the WU2DeltapotD mutant was identical to that of the wild-type strain WU2 in vitro in rich media. However, WU2DeltapotD possessed severely delayed growth compared to wild-type WU2 in the presence of the polyamine biosynthesis inhibitors DFMO (alpha-dimethyl-fluoroornitithine) and MGBG [methylgloxal-bis (guanyl hydrazone)]. The mutant strain also showed a significant attenuation in virulence within murine models of systemic and pulmonary infection regardless of the inoculation route or location. These data suggest that potD is involved in pneumococcal polyamine transport and is important for pathogenesis within various infection models.

Polyamines and cancer: old molecules, new understanding

The amino-acid-derived polyamines have long been associated with cell growth and cancer, and specific oncogenes and tumour-suppressor genes regulate polyamine metabolism. Inhibition of polyamine synthesis has proven to be generally ineffective as an anticancer strategy in clinical trials, but it is a potent cancer chemoprevention strategy in preclinical studies. Clinical trials, with well-defined goals, are now underway to evaluate the chemopreventive efficacy of inhibitors of polyamine synthesis in a range of tissues.

TATA-binding protein-associated factor 7 regulates polyamine transport activity and polyamine analog-induced apoptosis

Identification of the polyamine transporter gene will be useful for modulating polyamine accumulation in cells and should be a good target for controlling cell proliferation. Polyamine transport activity in mammalian cells is critical for accumulation of the polyamine analog methylglyoxal bis(guanylhydrazone) (MGBG) that induces apoptosis, although a gene responsible for transport activity has not been identified. Using a retroviral gene trap screen, we generated MGBG-resistant Chinese hamster ovary (CHO) cells to identify genes involved in polyamine transport activity. One gene identified by the method encodes TATA-binding protein-associated factor 7 (TAF7), which functions not only as one of the TAFs, but also a coactivator for c-Jun. TAF7-deficient cells had decreased capacity for polyamine uptake (20% of CHO cells), decreased AP-1 activation, as well as resistance to MGBG-induced apoptosis. Stable expression of TAF7 in TAF7-deficient cells restored transport activity (55% of CHO cells), AP-1 gene transactivation (100% of CHO cells), and sensitivity to MGBG-induced apoptosis. Overexpression of TAF7 in CHO cells did not increase transport activity, suggesting that TAF7 may be involved in the maintenance of basal activity. c-Jun NH2-terminal kinase inhibitors blocked MGBG-induced apoptosis without alteration of polyamine transport. Decreased TAF7 expression, by RNA interference, in androgen-independent human prostate cancer LN-CaP104-R1 cells resulted in lower polyamine transport activity (25% of control) and resistance to MGBG-induced growth arrest. Taken together, these results reveal a physiological function of TAF7 as a basal regulator for mammalian polyamine transport activity and MGBG-induced apoptosis.

Catalytic Properties of the Archaeal S-Adenosylmethionine Decarboxylase from Methanococcus jannaschii

S-Adenosylmethionine decarboxylase (AdoMetDC) is a pyruvoyl cofactor-dependent enzyme that participates in polyamine biosynthesis. AdoMetDC from the Archaea Methanococcus jannaschii is a prototype for a recently discovered class that is not homologous to the eucaryotic enzymes or to a distinct group of microbial enzymes. M. jannaschii AdoMetDC has a Km of 95 microm and the turnover number (kcat) of 0.0075 s(-1) at pH 7.5 and 22 degrees C. The turnover number increased approximately 38-fold at a more physiological temperature of 80 degrees C. AdoMetDC was inactivated by treatment with the imine reductant NaCNBH3 only in the presence of substrate. Mass spectrometry of the inactivated protein showed modification solely of the pyruvoyl-containing subunit, with a mass increase corresponding to reduction of a Schiff base adduct with decarboxylated AdoMet. The presteady state time course of the AdoMetDC reaction revealed a burst of product formation; thus, a step after CO2 formation is rate-limiting in turnover. Comparable D2O kinetic isotope effects of were seen on the first turnover (1.9) and on kcat/Km (1.6); there was not a significant D2O isotope effect on kcat, suggesting that product release is rate-limiting in turnover. The pH dependence of the steady state rate showed participation of acid and basic groups with pK values of 5.3 and 8.2 for kcat and 6.5 and 8.3 for kcat/Km, respectively. The competitive inhibitor methylglyoxal bis(guanylhydrazone) binds at a single site per (alphabeta) heterodimer. UV spectroscopic studies show that methylglyoxal bis(guanylhydrazone) binds as the dication with a 23 microm dissociation constant. Studies with substrate analogs show a high specificity for AdoMet.

A phase I human trial of mitoguazone and gemcitabine sequential bi-weekly treatment of cancer patients

Our previous studies have demonstrated the existence of synergism in a combination therapy using mitoguazone and gemcitabine when the mitoguazone is administered 24 hours before gemcitabine. Based on the cell culture and animal experimental results, a phase I clinical trial was performed in order to determine the toxicity of the combined treatment. Mitoguazone and gemcitabine were administered sequentially: mitoguazone on day 1 and gemcitabine on day 2. This cycle was repeated every 2 weeks. The dosages of these two drugs were varied between patients. Ten patients were enrolled in the study. Six patients began treatment at dose level 1 (mitoguazone 500 mg/m2, gemcitabine 1500 mg/m2), three at dose level 2 (mitoguazone 500 mg/m2, gemcitabine 2000 mg/m2), and one at dose level 3 (mitoguazone 600 mg/m2, gemcitabine 2000 mg/m2). Dose-limiting toxicity (DLT) was only observed in two patients treated at dose level 1 and one patient treated at dose level 3, while all the other patients only experienced nonhematologic toxicity, such as asthenia and mucositis. Two melanoma patients showed responses (one partial and one minor) to the treatment. One lymphoma patient also showed a brief partial response. This phase I trial indicated that the combination of mitoguazone and gemcitabine had limited but noticeable activity for treatment of cancer patients. Further study on the toxicity and on the effect of the scheduled mitoguazone-gemcitabine combination is needed.

Synergistic effect of sequential administration of mitoguazone (MGBG) and gemcitabine in treating tissue cultured human breast cancer cells and mammary rat tumors

Modulation of cancer chemotherapeutic drugs has been attempted to increase efficacy and overcome resistance to the chemotherapeutic agent. Studies have shown schedule-dependent interactions in combined use of chemotherapeutic drugs. Mitoguazone (MGBG), an old drug with possible modulating activity, was used in combination with gemcitabine, a relatively new cancer drug, in treating tissue cultured human breast cancer cells and mammary rat tumors. Tissue cultured BOT-2 cancer cells were first treated with varying concentrations of gemcitabine and MGBG, independently. Combinations of the two drugs were then used with different scheduled administrations. Marked synergistic activity was found between gemcitabine and MGBG when the MGBG was given first, followed by gemcitabine 24 hours later. A non-toxic dose of MGBG enhanced the toxicity of gemcitabine by eight orders of magnitude using MTT assays in the tissue cultured human breast cancer cell study. The sequential administration of MGBG and gemcitabine also increased the survival rate of rats bearing mammary tumors in our pilot animal study.

Polyamine metabolism and cancer

Polyamines are aliphatic cations present in all cells. In normal cells, polyamine levels are intricately controlled by biosynthetic and catabolic enzymes. The biosynthetic enzymes are ornithine decarboxylase, S-adenosylmethionine decarboxylase, spermidine synthase, and spermine synthase. The catabolic enzymes include spermidine/spermine acetyltransferase, flavin containing polyamine oxidase, copper containing diamine oxidase, and possibly other amine oxidases. Multiple abnormalities in the control of polyamine metabolism and uptake might be responsible for increased levels of polyamines in cancer cells as compared to that of normal cells. This review is designed to look at the current research in polyamine biosynthesis, catabolism, and transport pathways, enumerate the functions of polyamines, and assess the potential for using polyamine metabolism or function as targets for cancer therapy.

Analysis of polyamines as markers of (patho)physiological conditions

The aliphatic polyamines, putrescine, spermidine and spermine, are normal cell constituents that play important roles in cell proliferation and differentiation. The equilibrium between cellular uptake and release and the balanced activities of biosynthetic and catabolic enzymes of polyamines are essential for normal homeostasis in the proliferation and functions of cells and tissues. However, the intracellular polyamine content increases in hyperplastic or neoplastic growth. Although the involvement of polyamines in physiological and pathological cell proliferation and differentiation has been well established, the role they play is quite different in relation to cell systems and animal models and is dependent on inducer agents and stimuli. Also, the experimental procedures used to deplete polyamines have been shown to influence the cell responses. In this paper, the assay methods currently in use for polyamines are reviewed and compared with respect to sensitivity, reproducibility and applicability to routine analysis. The relevance of polyamine metabolism and the uptake/release process in many physiological and pathological processes is highlighted, and the cellular polyamine pathways are discussed in relation to the possible diagnostic and therapeutic significance of these mediators.

Enhanced susceptibility of photosynthesis to low-temperature photoinhibition due to interruption of chill-induced increase of S-adenosylmethionine decarboxylase activity in leaves of spinach (Spinacia oleracea L.)

The possible involvement of polyamines in the chilling tolerance of spinach (Spinacia oleracea L.) was investigated focusing on photosynthesis. During chilling at 8/5C (day/night) for 6 d, S-adenosylmethionine decarboxylase (SAMDC) activity increased significantly in leaves in parallel with the increase in putrescine and spermidine (Spd) content in leaves and chloroplasts. Treatment of leaves with methylglyoxal-bis(guanylhydrazone) (MGBG), an SAMDC inhibitor, resulted in the deterioration of plant growth and photosynthesis under chilling conditions, which was reversed by the concomitant treatment with Spd through the roots. Plants treated with MGBG showed lower photochemical efficiency of PSII than either the control or plants treated with MGBG plus Spd during chilling and even after transfer to warm conditions, suggesting an increase of photoinhibition due to low Spd in chloroplasts. Indeed, MGBG-treated plants had much lower activities of thylakoid electron transport and enzymes in carbon metabolism as well as higher degrees of lipid peroxidation of thylakoid membranes compared to the control. These results indicate that the enhanced activity of SAMDC with a consequential rise of Spd in chloroplasts is crucial for the cold acclimation of the photosynthetic apparatus in spinach leaves.

Guanidino-containing drugs in cancer chemotherapy: biochemical and clinical pharmacology

The pharmacology and clinical application of three guanidino-containing compounds are reviewed in this commentary with special focus on a new member of this group of drugs, CHS 828 [N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N"-4-pyridylguanidine]. m-Iodobenzylguanidine (MIBG) and methylglyoxal bis(guanylhydrazone) (MGBG) have been extensively studied, preclinically as well as clinically, and have established use as anticancer agents. MIBG has structural similarities to the neurotransmitter, norepinephrine, and MGBG is a structural analog of the natural polyamine spermidine. CHS 828 is a pyridyl cyanoguanidine newly recognized as having cytotoxic effects when screening antihypertensive compounds. Apart from having the guanidino groups in common, there are many differences between these drugs in both structure and their mechanisms of action. However, they all inhibit mitochondrial function, a seemingly unique feature among chemotherapeutic drugs. In vitro in various cell lines and primary cultures of patient tumor cells and in vivo in various tumor models, CHS 828 has cytotoxic properties unlike any of the standard cytotoxic drugs with which it has been compared. Among these are non-cross-resistance to standard drugs and pronounced activity in tumor models acknowledged to be highly drug-resistant. Similar to MIBG, CHS 828 induces an early increase in extracellular acidification, due to stimulation of the glycolytic flux. Furthermore, ATP levels decrease, and the syntheses of DNA and protein are shut off after approximately 30 hr of exposure, indicating active cell death. CHS 828 is now in early clinical trials, the results of which are eagerly awaited.

Cellular pharmacodynamics of the cytotoxic guanidino-containing drug CHS 828. Comparison with methylglyoxal-bis(guanylhydrazone)

N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N"-4-pyridylguanidine (CHS 828) is a new guanidino-containing compound with antitumoral activity both in vitro and in vivo. Its activity profile differs from those of standard cytotoxic drugs but the mechanism of action is not yet fully understood. CHS 828 is presently in early phase I and II clinical trials. In the present study, the pharmacodynamic effects at the cellular level of CHS 828 was compared to another compound containing two guanidino groups, methylglyoxal-bis(guanylhydrazone) (MGBG). MGBG is known to inhibit the synthesis of polyamines, which are important in, e.g., proliferation and macromolecular synthesis. The concentration-response relationship of CHS 828 closely resembled that of MGBG and the drugs were similar with respect to inhibition of DNA and protein synthesis. On the other hand, CHS 828 induced a significant increase in cellular metabolism while MGBG did not. The cytotoxic effect of MGBG was reversed by the addition of exogenous polyamines, while that of CHS 828 was unaffected. Unlike MGBG, there was also no effect of CHS 828 on the levels of decarboxylating enzymes in the polyamine biosynthesis. In conclusion, CHS 828 does not appear to share any major mechanisms of action with the polyamine synthesis inhibitor MGBG. Further studies will be required to define the exact mechanism of action of CHS 828.

Spermine deficiency resulting from targeted disruption of the spermine synthase gene in embryonic stem cells leads to enhanced sensitivity to antiproliferative drugs

Polyamines are known to be essential for normal cell growth and differentiation. However, despite numerous studies, specific cellular functions of polyamines in general and individual polyamines in particular have remained only tentative, because of a lack of appropriate cell lines in which genes of polyamine-synthesizing enzymes have been disrupted by gene targeting. With the use of homologous recombination technique, we disrupted the gene encoding spermine synthase in mouse embryonic stem cells. The spermine synthase gene is located on X chromosome in mouse and, because the cells used in this study were of XY karyotype, a single targeting event was sufficient to result in null genotype. The targeted cells did not have any measurable spermine synthase activity and were totally devoid of the polyamine spermine. Spermine deficiency led to a substantial increase in spermidine content, but the total polyamine content was nearly unchanged. Despite the lack of spermine, these cells displayed a growth rate that was nearly similar to that of the parental cells and showed no overt morphological changes. However, the spermine-deficient cells were significantly more sensitive to the growth inhibition exerted by 2-difluoromethylornithine, an inhibitor of ornithine decarboxylase. Similarly, methylglyoxal bis(guanylhydrazone), an inhibitor of S-adenosylmethionine decarboxylase, and diethylnorspermine, a polyamine analog, although exerting cytostatic growth inhibition on wild-type cells, were clearly cytotoxic to the spermine-deficient cells. The spermine-deficient cells were also much more sensitive to etoposide-induced DNA damage than their wild-type counterparts.

Molecular correlates of the action of bis(ethyl)polyamines in breast cancer cell growth inhibition and apoptosis

Polyamines are known to be involved in cell growth regulation in breast cancer. To evaluate the efficacy of bis(ethyl)polyamine analogs for breast cancer therapy and to understand their mechanism of action we measured the effects of a series of polyamine analogs on cell growth, activities of enzymes involved in polyamine metabolism, intracellular polyamine levels, and the uptake of putrescine and spermidine using MCF-7 breast cancer cells. The IC50 values for cell growth inhibition of three of the compounds, N1,N12-bis(ethyl)spermine, N1,N11-bis(ethyl)norspermine, and N1,N14-bis(ethyl)homospermine, were in the range of 1-2 microM. Another group of three compounds showed antiproliferative activity at about 5 microM level. These compounds are also capable of suppressing colony formation in soft agar assay and inducing apoptosis of MCF-7 cells. The highly effective growth inhibitory agents altered the activity of polyamine biosynthetic and catabolic enzymes and down-regulated the transport of natural polyamines, although each compound produced a unique pattern of alterations in these parameters. HPLC analysis showed that cellular uptake of bis(ethyl)polyamines was highest for bis(ethyl)spermine. We also analyzed polyamine analog conformations and their binding to DNA minor or major grooves by molecular modelling and molecular dynamics simulations. Results of these analyses indicate that tetramine analogs fit well in the minor groove of DNA whereas, larger compounds extend out of the minor groove. Although major groove binding was also possible for the short tetramine analogs, this interaction led to a predominantly bent conformation. Our studies show growth inhibitory activities of several potentially important analogs on breast cancer cells and indicate that multiple sites are involved in the mechanism of action of these analogs. While the activity of an analog may depend on the sum of these different effects, molecular modelling studies indicate a correlation between antiproliferative activity and stable interactions of the analogs with major or minor grooves of DNA.

Polyamines, and effects from reducing their synthesis during egg development in the yellow fever mosquito, Aedes aegypti

Development of eggs after a blood meal in the yellow fever mosquito Aedes aegypti involves hormonal changes, synthesis of nucleic acids, activation of the digestive enzyme trypsin, and production of the yolk protein vitellogenin. Polyamines have been implicated in growth processes and were here examined for possible involvement during egg development. The data suggest that polyamines are important for normal vitellogenesis in the mosquito. Polyamine levels and activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase, key enzymes in the polyamine pathway, were determined in the fat body for two days after a blood meal. During the time that the macromolecules required for vitellogenesis were being synthesized, polyamine levels increased as did the activities of their rate-limiting enzymes. Administration of suicide inhibitors of ornithine decarboxylase, alpha-difluoromethylornithine (DFMO) and alpha-monofluoromethyldehydroornithine methylester (MDME), limited increased polyamine levels and disrupted macromolecular syntheses, particularly during the first twenty-four hours after blood feeding. Specific metabolic processes reduced by DFMO included trypsin activity, and production of RNA, DNA and vitellogenin. MDME had differential effects on transcription of some mRNA species made after an oogenic meal. The level of actin mRNA was not affected by inhibiting polyamine synthesis, but the mRNA levels of vitellogenin, trypsin, and the vitelline membrane protein were decreased. Adding polyamines to a meal containing DFMO or MDME partially reversed the effects of these inhibitors. Increases in spermidine and spermine were associated with these reversals.

The effects of methylglyoxal-bis(guanylhydrazone) on spermine binding and transport in liver mitochondria

This study evaluated the effect of the anticancer drug methylglyoxal-bis(guanylhydrazone) (MGBG) on the binding of the polyamine spermine to the mitochondrial membrane and its transport into the inner compartment of this organelle. Spermine binding was studied by applying a new thermodynamic treatment of ligand-receptor interactions (Di Noto et al., Macromol Theory Simul 5: 165-181, 1996). Results showed that MGBG inhibited the binding of spermine to the site competent for the first step in polyamine transport; the interaction of spermine with this site, termed S1, also mediates the inhibitory effect of the polyamine on the mitochondrial permeability transition (Dalla Via et al., Biochim Biophys Acta 1284: 247-252, 1996). In the presence of 1 mM MGBG, the binding capacity and affinity of this site were reduced by about 2.6-fold; on the contrary, the binding capacity of the S2 site, which is most likely responsible for the internalization of cytoplasmic proteins (see Dalla Via et al., reference cited above), increased by about 1.3-fold, and its binding affinity remained unaffected. MGBG also inhibited the initial rate of spermine transport in a dose-dependent manner by establishing apparently sigmoidal kinetics. Consequently, the total extent of spermine accumulation inside mitochondria was inhibited. This inhibition in transport seems to reflect a conformational change at the level of the channel protein constituting the polyamine transport system, rather than competitive inhibition at the inner active site of the channel, thereby excluding the possibility that the polyamine and drug use the same transport pathway. Furthermore, it is suggested that, in the presence of MGBG, the S2 site is able to participate in residual spermine transport. MGBG also strongly inhibits deltapH-dependent spermine efflux, resulting in a complete block in the bidirectional flux of the polyamine and its sequestration inside the matrix space. The effects of MGBG on spermine accumulation are consistent with in vivo disruption of the regulator of energy metabolism and replication of the mitochondrial genome.

MGBG analogues as potent inhibitors of S-adenosylmethionine decarboxylase of Onchocerca volvulus

Polyamines are essential for cell growth and differentiation and therefore, S-adenosylmethionine decarboxylase (SAMDC), a key regulatory enzyme of the polyamine biosynthesis, is considered as a potentially important target for chemotherapy of filarial infections. Recombinant Onchocerca volvulus SAMDC was expressed in Escherichia coli and characterised. The enzyme activity was found to be stimulated 15-fold by addition of 1 mM putrescine. The Km-value for S-adenosylmethionine was determined to be 36 microM. Furthermore, the efficiencies of SAMDC inhibitors were analysed: Berenil inhibits the enzyme activity competitively with a Ki-value of 0.1 microM. MDL 73811 acts as an irreversible inhibitor with a Ki-value of 1.4 microM. Recently synthesised aromatic methylglyoxal bis(guanylhydrazone) analogues demonstrated high efficacy as inhibitors of the SAMDCs. Some of these analogues exhibited Ki-values of 5 and 14 nM for the Onchocerca enzyme, a result which shows an up to 100-fold increase in specificity compared to the value of 0.47 microM for methylglyoxal bis(guanylhydrazone). These inhibitors might have potential as drug candidates against filarial worms.

Selective sites for polyamine binding to rabbit intestinal brush-border membranes

The intestinal polyamine transporters have not yet been identified. Our aim was to characterize specific polyamine binding sites in rabbit intestinal brush-border membranes (IBBM) as a starting step for identification of polyamine transporters. This was investigated at 4 degrees and at low membrane concentration. Saturation isotherms for [3H]putrescine (PUT) binding indicated a single population of sites (puT) with a dissociation equilibrium constant Kd of 3.8 microM and a density of sites Bmax of 58 pmol/mg of protein. [3H]spermidine (SPD) binding also involved only one class of sites (spD), albeit with a lower affinity (Kd = 106 microM) and higher abundance (Bmax = 1240 pmol/mg of protein) than puT. On the contrary, [14C]spermine (SPM) bound two classes of sites (spM1 and spM2) differing in their affinity (Kd = 2.5 and 31.4 microM) and abundance (Bmax = 467 and 1617 pmol/mg of protein, respectively). Membrane association of SPM at 4 degrees was much faster than that of SPD and PUT, both of which proceeded at a similar rate. In contrast to PUT and SPD dissociation, SPM dissociation at 23 degrees did not follow a first-order reaction. Specifically bound [3H]PUT, unlike [3H]SPD and [14C]SPM, dissociated at 23 degrees independently of the addition of nonradioactive polyamine. Methylglyoxal-bis-(guanylhydrazone) was an extremely potent inhibitor of PUT binding (Ki = 3.2 +/- 1.5 nM), but as with PUT and cadaverine (CAD), it did not alter [3H]SPD and [14C]SPM binding substantially. The intestinal brush-border membrane may contain at least three sites specific for polyamine binding and exhibiting different ligand selectivity. Site puT might be associated with the transport system already described for intestinal uptake of PUT.

Trypanosoma cruzi has not lost its S-adenosylmethionine decarboxylase: characterization of the gene and the encoded enzyme

All attempts to identify ornithine decarboxylase in the human pathogen Trypanosoma cruzi have failed. The parasites have instead been assumed to depend on putrescine uptake and S-adenosylmethionine decarboxylase (AdoMetDC) for their synthesis of the polyamines spermidine and spermine. We have now identified the gene encoding AdoMetDC in T. cruzi by PCR cloning, with degenerate primers corresponding to conserved amino acid sequences in AdoMetDC proteins of other trypanosomatids. The amplified DNA fragment was used as a probe to isolate the complete AdoMetDC gene from a T. cruzi genomic library. The AdoMetDC gene was located on chromosomes with a size of approx. 1.4 Mbp, and contained a coding region of 1110 bp, specifying a sequence of 370 amino acid residues. The protein showed a sequence identity of only 25% with human AdoMetDC, the major differences being additional amino acids present in the terminal regions of the T. cruzi enzyme. As expected, a higher sequence identity (68-72%) was found in comparison with trypanosomatid AdoMetDCs. When the coding region was expressed in Escherichia coli, the recombinant protein underwent autocatalytic cleavage, generating a 33-34 kDa alpha subunit and a 9 kDa beta subunit. The encoded protein catalysed the decarboxylation of AdoMet (Km 0.21 mM) and was stimulated by putrescine but inhibited by the polyamines, weakly by spermidine and strongly by spermine. Methylglyoxal-bis(guanylhydrazone) (MGBG), a potent inhibitor of human AdoMetDC, was a poor inhibitor of the T. cruzi enzyme. This differential sensitivity to MGBG suggests that the two enzymes are sufficiently different to warrant the search for compounds that might interfere with the progression of Chagas' disease by selectively inhibiting T. cruzi AdoMetDC.

Unusual central nervous system toxicity in a phase I study of N1N11 diethylnorspermine in patients with advanced malignancy

The objectives of this study were to determine the dose limiting toxicity (DLT) and other major toxicities, the maximum tolerated dose (MTD) and the human pharmacokinetics of N1N11 diethylnorspermine (DENSPM), a new polyamine analog which in experimental systems inhibits the biosynthesis of intracellular polyamines and promotes their degradation by inducing the enzyme spermine/spermidine N-acetyl transferase. These objectives were incompletely achieved because of the occurrence of an unusual syndrome of acute central nervous system toxicity which forms the basis of the present report. Fifteen patients with advanced solid tumors were entered into a phase I study of DENSPM given by a 1 h i.v. infusion every 12 h for 5 days (10 doses). The starting dose was 25 mg/m2/day (12.5 mg/m2/dose) with escalation by a modified Fibonacci search. Doses of 25 and 50 mg/m2/day were tolerated with only minor side effects of facial flushing, nausea, headache and dizziness (all grade I). At doses of 83 and 125 mg/m2/day, a symptom complex of headache, nausea and vomiting, unilateral weakness, dysphagia, dysarthria, numbness, paresthesias, and ataxia, was seen in 3 patients, one after 2 courses of 83 and 2 after 1 course of 125 mg/m2/day. This syndrome occurred after drug administration was complete and the patients had returned home. Lesser CNS toxicity was seen in 2 other patients at lower daily doses. Preliminary pharmacokinetics of DESPM measured in plasma by HPLC in 8 patients showed linearity with dose and a rapid plasma decay with a t1/2 of 0.12 h. We conclude that great caution is warranted in administering DENSPM on this schedule at doses of > or = 83 mg/m2/day.

A comparison of structure-activity relationships between spermidine and spermine analogue antineoplastics

A systematic investigation of the impact of spermidine analogues both in vitro and in vivo is described. The study characterizes the effects of these analogues on L1210 cell growth, polyamine pools, ornithine decarboxylase, S-adenosyl-L-methionine decarboxylase, spermidine/spermine N1-acetyltransferase, the maintenance of cellular charge, i.e., cationic equivalence associated with the polyamines and their analogues, and compares their ability to compete with spermidine for transport. The findings clearly demonstrate that the activity of the linear polyamine analogues is highly dependent on the length of the triamines and the size of the N(alpha),N(omega)-substituents. It appears that there is an optimum chain length for various activities and that the larger the N(alpha),N(omega)-alkyls, the less active the compound. Metabolic transformation including N-dealkylation of these compounds is also evaluated. While there is no monotonic relationship between chain length and the ability of the analogue to be metabolized, the dipropyl triamines are clearly more actively catabolized than the corresponding methyl and ethyl systems. A comparison of the triamines with the corresponding tetraamines is made throughout the text regarding both in vitro activity against L1210 cells and in vivo toxicity measurements, suggesting that several triamine analogues may offer therapeutic advantages over the corresponding tetraamines.

Interference with DNA methyltransferase activity and genome methylation during F9 teratocarcinoma stem cell differentiation induced by polyamine depletion

When ornithine decarboxylase, the initial and highly regulated enzyme in polyamine biosynthesis, is irreversibly inactivated by alpha-difluoromethylornithine, F9 teratocarcinoma stem cells are depleted of putrescine and spermidine and as a result differentiate into a cell type which phenotypically resembles the parietal endoderm cells of the early mouse embryo. Simultaneously the level of decarboxylated S-adenosylmethionine (dcAdoMet), the aminopropyl group donor in spermidine and spermine synthesis, increases dramatically, as the aminopropyl group acceptor molecules (putrescine and spermidine) become limiting. When this excessive accumulation of dcAdoMet is prevented by specific inhibition of the AdoMet decarboxylase activity, the differentiative effect is counteracted, despite the fact that the extent of polyamine depletion remains almost identical. Therefore, it may be concluded that dcAdoMet plays an important role in the induction of differentiation. Moreover, this key metabolite acts as a competitive inhibitor of DNA methyltransferase and is therefore capable of interfering with the maintenance methylation of newly replicated DNA. During the course of F9 cell differentiation, the highly methylated genome is gradually demethylated, and its pattern of gene expression is changed. Our present findings, that the DNA remains highly methylated and that the differentiative process is counteracted when the build-up of dcAdoMet is prevented, provide strong evidence for a causative relation between the level of dcAdoMet and the state of DNA methylation as well as cell differentiation.

Combined action of inhibitors of S-adenosylmethionine decarboxylase with an antimalarial drug, chloroquine, on Plasmodium falciparum

Methylglyoxal bis (guanylhydrazone), (MGBG) a potent competitive inhibitor of S-adenosyl-L-methionine decarboxylase activity, Berenil, a trypanocidal agent and chloroquine, the commonly used antimalarial resulted in a dose dependent inhibition of Plasmodium falciparum in vitro. The IC50 values of MGBG, Berenil and chloroquine were 224 microM, 40 microM and 42 nM respectively. Parasites treated with different concentrations of MGBG or Berenil were arrested at the trophozoite stage of the erythrocytic cycle. The combined action of chloroquine (10 nM) with either Berenil (0.1 mM) or MGBG (0.1 mM) on P. falciparum growth showed an additive inhibitory effect. The effect of these inhibitors alone and in combination on polyamine biosynthesis is also reported.

Formation of cadaverine derivatives in Saccharomyces cerevisiae

The higher homologues of cadaverine, aminopropylcadaverine (APC) and N,N-bis(3-aminopropyl)cadaverine (3APC) were formed by a wild-type strain of Saccharomyces cerevisiae, and by two mutant strains, spe 3-1 and spe 4-1, exhibiting point mutations in the genes for spermidine synthase and spermine synthase, respectively. This, together with the incomplete inhibition of APC and 3APC formation in the presence of inhibitors of S-adenosylmethionine decarboxylase and spermidine synthase, suggests that the cadaverine derivatives are formed partly by the operation of a different route. However, the yeast strains were unable to utilise [14C]aspartate and lysine to form APC and 3APC. Since the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO) greatly reduced the formation of APC and 3APC, it is suggested that these compounds are formed preferentially in these yeast strains from cadaverine formed by ODC. APC and 3APC formation in the yeast strains was increased substantially following exposure to 37 degrees C for 2 h.

Determination of the antileukemic drug mitoguazone and seven other closely related bis(amidinohydrazones) in human blood serum by high-performance liquid chromatography

A reversed-phase (C18) HPLC method with diode-array detection was developed for the separation and determination of methylglyoxal bis(amidinohydrazone) (mitoguazone) and seven closely related aliphatic analogs thereof, namely the bis(amidinohydrazones) of glyoxal, dimethylglyoxal, ethylmethylglyoxal, methylpropylglyoxal, butylmethylglyoxal, diethylglyoxal and dipropylglyoxal. The mobile phase consisted of a non-linear binary gradient of methanol and 0.03 M aqueous sodium acetate buffer (pH 4.3). Good separation of the eight congeners was achieved. On increasing the methanol content of the eluent, the bis(amidinohydrazones) eluted in the order of increasing number of carbon atoms in the side-chains. The method was also applied to the quantitative analysis of the compounds in aqueous solution and, combined with ultrafiltration, for the separation of the eight congeners in spiked human blood serum. A separate simplified method for the quantitative determination of each of the compounds in spiked human blood serum samples was also developed. The methods developed made for the first time possible the simultaneous HPLC analysis of more than one bis(amidinohydrazones). The results obtained indicate that the bis(amidinohydrazones) studied obviously have a distinct tendency to form ion associates with acetate ions and probably also other carboxylate ions in aqueous solution. This aspect may be of biochemical significance, especially concerning the intracellular binding of the compounds. Each one of the compounds studied invariably gave rise to one peak only, this result supporting the theory that the conventional synthesis of each of the compounds gives rise to one geometrical isomer only. This result is completely in agreement with the results of previous proton and carbon NMR spectroscopic as well as X-ray diffraction studies.

Structure-activity relations of S-adenosylmethionine decarboxylase inhibitors on the growth of MCF-7 breast cancer cells

SAMDC is a key enzyme in the biosynthesis of spermidine and spermine, 2 polyamines that are essential for cell proliferation. Inhibition of polyamine biosynthesis is often targeted as a therapeutic strategy to suppress cancer cell growth as these cells contain elevated levels of polyamines. We examined the effect of a new group of SAMDC inhibitors, CGP33829, CGP35753, CGP36958, CGP39937, and CGP48664, (obtained from Ciba-Geigy, Basel, Switzerland), and their parent compound, MGBG, on the proliferation of MCF-7 breast cancer cells. MGBG had minimal effects on the proliferation of MCF-7 cells up to 6 microM concentration. In contrast, CGP48664 and CGP39937, containing 2 aromatic rings that delocalize the pi electron system of the backbone of MGBG, were potent inhibitors with 50% growth inhibition at 0.5 microM concentration. Other CGP compounds were less effective in inhibiting cell growth. The ability of CGP48664 to inhibit MCF-7 cell proliferation was related to its ability to inhibit SAMDC and to consequently deplete spermidine and spermine levels in the cell. Exogenous spermidine and spermine could reverse the growth inhibitory effects of this compound. CGP compounds also increased the activity of ODC, another enzyme involved in polyamine biosynthesis. Northern blot analysis of mRNA from MCF-7 cells progressing in cell cycle after G1 synchronization did not show an increase in ODC mRNA level by CGP48664. These data demonstrate structure-activity relationships of a series of MGBG derivatives on cell growth, enzyme activities, and polyamine biosynthesis in a hormone-responsive breast cancer cell line and suggest potential application of SAMDC inhibitors as therapeutic agents.