Cytotoxicity of methoctramine and methoctramine-related polyamines

Identification and Characterization of Novel Small-Molecule SMOX Inhibitors

The major intracellular polyamines spermine and spermidine are abundant and ubiquitous compounds that are essential for cellular growth and development. Spermine catabolism is mediated by spermine oxidase (SMOX), a highly inducible flavin-dependent amine oxidase that is upregulated during excitotoxic, ischemic, and inflammatory states. In addition to the loss of radical scavenging capabilities associated with spermine depletion, the catabolism of spermine by SMOX results in the production of toxic byproducts, including H₂O₂ and acrolein, a highly toxic aldehyde with the ability to form adducts with DNA and inactivate vital cellular proteins. Despite extensive evidence implicating SMOX as a key enzyme contributing to secondary injury associated with multiple pathologic states, the lack of potent and selective inhibitors has significantly impeded the investigation of SMOX as a therapeutic target. In this study, we used a virtual and physical screening approach to identify and characterize a series of hit compounds with inhibitory activity against SMOX. We now report the discovery of potent and highly selective SMOX inhibitors 6 (IC₅₀ 0.54 μM, Ki 1.60 μM) and 7 (IC₅₀ 0.23 μM, K_i 0.46 μM), which are the most potent SMOX inhibitors reported to date. We hypothesize that these selective SMOX inhibitors will be useful as chemical probes to further elucidate the impact of polyamine catabolism on mechanisms of cellular injury.

Exploring the activity of polyamine analogues on polyamine and spermine oxidase: methoctramine, a potent and selective inhibitor of polyamine oxidase

Fourteen polyamine analogues, asymmetric or symmetric substituted spermine (1-9) or methoctramine (10-14) analogues, were evaluated as potential inhibitors or substrates of two enzymes of the polyamine catabolic pathway, spermine oxidase (SMOX) and acetylpolyamine oxidase (PAOX). Compound 2 turned out to be the best substrate for PAOX, having the highest affinity and catalytic efficiency with respect to its physiological substrates. Methoctramine (10), a well-known muscarinic M2 receptor antagonist, emerged as the most potent competitive PAOX inhibitor known so far (Ki = 10 nM), endowed with very good selectivity compared with SMOX (Ki=1.2 μM vs SMOX). The efficacy of methoctramine in inhibiting PAOX activity was confirmed in the HT22 cell line. Methoctramine is a very promising tool in the design of drugs targeting the polyamine catabolism pathway, both to understand the physio-pathological role of PAOX vs SMOX and for pharmacological applications, being the polyamine pathway involved in various pathologies.

Benextramine and derivatives as novel human monoamine oxidases inhibitors: an integrated approach

The two human monoamine oxidase isoforms (namely MAO A and MAO B) are enzymes involved in the catabolism of monoamines, including neurotransmitters, and for this reason are well-known and attractive pharmacological targets in neuropsychiatric and neurodegenerative diseases, for which novel pharmacological approaches are necessary. Benextramine is a tetraamine disulfide mainly known as irreversible α-adrenergic antagonist, but able to hit additional targets involved in neurodegeneration. As the molecular structures of monoamine oxidases contain nine cysteine residues, the aim of this study was to evaluate benextramine and eleven structurally related polyamine disulfides as potential MAO inhibitors. Most of the compounds were found to induce irreversible inactivation of MAOs with inactivation potency depending on both the polyamine structure and the enzyme isoform. The more effective compounds generally showed preference for MAO B. Structure-activity relationships studies revealed the key role played by the disulfide core of these molecules in the inactivation mechanism. Docking experiments pointed to Cys323, in MAO A, and Cys172, in MAO B, as target of this type of inhibitors thus suggesting that their covalent binding inside the MAO active site sterically impedes the entrance of substrate towards the FAD cofactor. The effectiveness of benextramine in inactivating MAOs was demonstrated in SH-SY5Y neuroblastoma cell line. These results demonstrated for the first time that benextramine and its derivatives can inactivate human MAOs exploiting a mechanism different from that of the classical MAO inhibitors and could be a starting point for the development of pharmacological tools in neurodegenerative diseases.

Identification of Deregulated Signaling Pathways in Jurkat Cells in Response to a Novel Acylspermidine Analogue-N4-Erucoyl Spermidine

Natural polyamines such as putrescine, spermidine, and spermine are crucial in the cell proliferation and maintenance in all the eukaryotes. However, the requirement of polyamines in tumor cells is stepped up to maintain tumorigenicity. Many synthetic polyamine analogues have been designed recently to target the polyamine metabolism in tumors to induce apoptosis. N⁴-Erucoyl spermidine (designed as N⁴-Eru), a novel acylspermidine derivative, has been shown to exert selective inhibitory effects on both hematological and solid tumors, but its mechanisms of action are unknown. In this study, RNA sequencing was performed to investigate the anticancer mechanisms of N⁴-Eru-treated T-cell acute lymphoblastic leukemia (ALL) cell line (Jurkat cells), and gene expression was examined through different tools. We could show that many key oncogenes including NDRG1, CACNA1G, TGFBR2, NOTCH1,2,3, UHRF1, DNMT1,3, HDAC1,3, KDM3A, KDM4B, KDM4C, FOS, and SATB1 were downregulated, whereas several tumor suppressor genes such as CDKN2AIPNL, KISS1, DDIT3, TP53I13, PPARG, FOXP1 were upregulated. Data obtained through RNA-Seq further showed that N⁴-Eru inhibited the NOTCH/Wnt/JAK-STAT axis. This study also indicated that N⁴-Eru-induced apoptosis could involve several key signaling pathways in cancer. Altogether, our results suggest that N⁴-Eru is a promising drug to treat ALL.

Coumarin derivatives as potential antitumor agents: Growth inhibition, apoptosis induction and multidrug resistance reverting activity

A small library of coumarins, carrying butynyl-amino chains, was synthesized continuing our studies in the field of MDR reverting ageEnts and in order to obtain multipotent agents to combat malignancies. In particular, the reported anticancer and chemopreventive natural product 7-isopentenyloxycoumarin was linked to different terminal amines, selected on the basis of our previously reported results. The anticancer behaviour and the MDR reverting ability of the new compounds were evaluated on human colon cancer cells, particularly prone to develop the MDR phenotype. Some of the new derivatives showed promising effects, directly acting as cytotoxic compounds and/or counteracting MDR phenomenon. Compound 1e emerged as the most interesting of this series, showing a multipotent biological profile and suggesting that conjugation of an appropriate coumarin core with a properly selected butynyl-amino chain allows to obtain novel hybrid molecules endowed with improved in vitro antitumor activity.

Substituted E-3-(3-indolylmethylene)1,3-dihydroindol-2-ones with antiproliferative activity. Study of the effects on HL-60 leukemia cells

The synthesis of new substituted E-3-(3-indolylmethylene)1,3-dihydroindol-2-ones is reported. The antiproliferative activity was evaluated according to protocols available at the National Cancer Institute (NCI), Bethesda, MD. The action of the most active compound 10 was further investigated in HL-60 leukemia cells. Results obtained show that it causes a block in cell cycle progression, with cell arrest in the G2/M phase, associated with activation of apoptosis accompanied with increased oxidative stress and deregulation of the homeostasis of divalent cations, with significant increase in the cellular concentrations of free Ca(2+) and Mg(2+).

Synthetic polyamines activating autophagy: effects on cancer cell death

The ability of symmetrically substituted long chain polymethylene tetramines, methoctramine (1) and its analogs 2-4 to kill cancer cells was studied. We found that an elevated cytotoxicity was correlated with a 12 methylene chain length separating the inner amine functions (6-12-6 carbon backbone), together with the introduction of diphenylethyl moieties on the terminal nitrogen atoms (compound 4) of a tetramine backbone. Compound 4 triggered dissipation of mitochondrial transmembrane potential and increased intracellular peroxide levels, leading to a caspase-independent HeLa cell death associated with a rapid activation of autophagy. The antioxidant N-acetylcysteine inhibited cell death and activation of autophagy, indicating a link between oxidative stress and autophagy. Autophagy was rapidly triggered even by tetramines 2 and 3, indicating that is related to their polyamine structure. Autophagy did not protect HeLa cells against cytotoxicity elicited by compound 4. The present study shows that, by modifications of the methoctramine structure, it is possible to design polyamine derivatives highly cytotoxic against tumor cells and that the appropriate design of molecules bearing polyamine-like structures leads to powerful inducers of autophagy.

Network-based assessment of the selectivity of metabolic drug targets in Plasmodium falciparum with respect to human liver metabolism

Background

The search for new drug targets for antibiotics against Plasmodium falciparum, a major cause of human deaths, is a pressing scientific issue, as multiple resistance strains spread rapidly. Metabolic network-based analyses may help to identify those parasite’s essential enzymes whose homologous counterparts in the human host cells are either absent, non-essential or relatively less essential.

Results

Using the well-curated metabolic networks PlasmoNet of the parasite Plasmodium falciparum and HepatoNet1 of the human hepatocyte, the selectivity of 48 experimental antimalarial drug targets was analyzed. Applying in silico gene deletions, 24 of these drug targets were found to be perfectly selective, in that they were essential for the parasite but non-essential for the human cell. The selectivity of a subset of enzymes, that were essential in both models, was evaluated with the reduced fitness concept. It was, then, possible to quantify the reduction in functional fitness of the two networks under the progressive inhibition of the same enzymatic activity. Overall, this in silico analysis provided a selectivity ranking that was in line with numerous in vivo and in vitro observations.

Conclusions

Genome-scale models can be useful to depict and quantify the effects of enzymatic inhibitions on the impaired production of biomass components. From the perspective of a host-pathogen metabolic interaction, an estimation of the drug targets-induced consequences can be beneficial for the development of a selective anti-parasitic drug.

Substituted E-3-(3-indolylmethylene)-1,3-dihydroindol-2-ones with antitumor activity. In depth study of the effect on growth of breast cancer cells

The synthesis of new substituted E-3-(3-indolylmethylene)-1,3-dihydroindol-2-ones is reported. The antitumor activity was evaluated according to protocols available at the National Cancer Institute (NCI), Bethesda, MD. Structure-activity relationships are discussed. The action of selected compounds was investigated in MCF-7 breast cancer cells. The ability of these derivatives to inhibit cellular proliferation was accompanied by increased level of p53 and its transcriptional targets p21 and Bax, interference in the cell cycle progression with cell accumulation in the G2/M phase, and activation of apoptosis.