Synthesis and biological characterization of novel charge-deficient spermine analogues

Synthesis of a new water-soluble hexacarboxylated tribenzotriquinacene derivative and its competitive host–guest interaction for drug delivery

A new water-soluble hexacarboxylated tribenzotriquinacene derivative (TBTQ-CB6) was synthesized and used as a supramolecular drug carrier to load the model anticancer drugs dimethyl viologen (MV) and doxorubicin (DOX) via host–guest interactions. The drugs could be effectively released by spermine (SM), a molecule overexpressed in cancer cells, through host–guest competitive substitution since TBTQ-CB6 has a stronger binding affinity toward SM than MV and DOX. The host–guest interactions of the complexes of TBTQ-CB6 with MV, DOX and SM were investigated by NMR spectroscopy and fluorescence spectroscopy. The association stoichiometry of the complexes of TBTQ-CB6 with MV, DOX, and SM was found to be 1:1 with association constants of K_a = (7.67 ± 0.34) × 10⁴ M⁻¹, K_a = (6.81 ± 0.33) × 10⁴ M⁻¹, and K_a = (5.09 ± 0.98) × 10⁵ M⁻¹, respectively. The competitive substitution process was visualized by NMR titration. This novel TBTQ-based host–guest drug delivery system may have potential use in supramolecular chemotherapy.

Role of Polyamine-Induced Dimerization of Antizyme in Its Cellular Functions

The polyamines, spermine (Spm) and spermidine (Spd), are important for cell growth and function. Their homeostasis is strictly controlled, and a key downregulator of the polyamine pool is the polyamine-inducible protein, antizyme 1 (OAZ1). OAZ1 inhibits polyamine uptake and targets ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis, for proteasomal degradation. Here we report, for the first time, that polyamines induce dimerization of mouse recombinant full-length OAZ1, forming an (OAZ1)₂-Polyamine complex. Dimerization could be modulated by functionally active C-methylated spermidine mimetics (MeSpds) by changing the position of the methyl group along the Spd backbone—2-MeSpd was a poor inducer as opposed to 1-MeSpd, 3-MeSpd, and Spd, which were good inducers. Importantly, the ability of compounds to inhibit polyamine uptake correlated with the efficiency of the (OAZ1)₂-Polyamine complex formation. Thus, the (OAZ1)₂-Polyamine complex may be needed to inhibit polyamine uptake. The efficiency of polyamine-induced ribosomal +1 frameshifting of OAZ1 mRNA could also be differentially modulated by MeSpds—2-MeSpd was a poor inducer of OAZ1 biosynthesis and hence a poor downregulator of ODC activity unlike the other MeSpds. These findings offer new insight into the OAZ1-mediated regulation of polyamine homeostasis and provide the chemical tools to study it.

Case Study 10: A Case to Investigate Acetyl Transferase Kinetics

Major routes of metabolism for marketed drugs are predominately driven by enzyme families such as cytochromes P450 and UDP-glucuronosyltransferases. Less studied conjugative enzymes, like N-acetyltransferases (NATs), are commonly associated with detoxification pathways. However, in the clinic, the high occurrence of NAT polymorphism that leads to slow and fast acetylator phenotypes in patient populations has been linked to toxicity for a multitude of drugs. A key example of this is the observed clinical toxicity in patients who exhibit the slow acetylator phenotype and were treated with isoniazid. Toxicity in patients has led to detailed characterization of the two NAT isoforms and their polymorphic genotypes. Investigation in recombinant enzymes, genotyped hepatocytes, and in vivo transgenic models coupled with acetylator status-driven clinical studies have helped understand the role of NATs in drug development, clinical study design and outcomes, and potential roles in human disease models. The selected case studies herein document NAT enzyme kinetics to explore substrate overlap from two human isoforms, preclinical species considerations, and clinical genotype population concerns.

Unforeseen Possibilities To Investigate the Regulation of Polyamine Metabolism Revealed by Novel C-Methylated Spermine Derivatives

The biogenic polyamines, spermine (Spm) and spermidine, are organic polycations present in millimolar concentrations in all eukaryotic cells participating in the regulation of vital cellular functions including proliferation and differentiation. The design and biochemical evaluation of polyamine analogues are cornerstones of polyamine research. Here we synthesized and studied novel C-methylated Spm analogues: 2,11-dimethylspermine (2,11-Me2Spm), 3,10-dimethylspermine (3,10-Me2Spm), 2-methylspermine, and 2,2-dimethylspermine. The tested analogues overcame growth arrest induced by a 72 h treatment with α-difluoromethylornithine, an ornithine decarboxylase (ODC) inhibitor, and entered into DU145 cells via the polyamine transporter. 3,10-Me2Spm was a poor substrate of spermine oxidase and spermidine/spermine-N1-acetyltransferase (SSAT) when compared with 2,11-Me2Spm, thus resembling 1,12-dimethylspermine, which lacks the substrate properties required for the SSAT reaction. The antizyme (OAZ1)-mediated downregulation of ODC and inhibition of polyamine transport are crucial in the maintenance of polyamine homeostasis. Interestingly, 3,10-Me2Spm was found to be the first Spm analogue that did not induce OAZ1 and, consequently, was a weak downregulator of ODC activity in DU145 cells.

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.

Inhibitor of polyamine catabolism MDL72.527 restores the sensitivity to doxorubicin of monocytic leukemia Thp-1 cells infected with human cytomegalovirus

Leukemic cells from different patients exhibit different sensitivity to anticancer drugs including doxorubicin (DOX). Resistance to chemotherapy decreases efficacy of the treatment and promotes cancer recurrence and metastases. One of the approaches to overcome drug resistance includes E2F1-mediated regulation of the р73 protein that belongs to the р53 family. Its ΔNp73 isoform exhibits pro-oncogenic effects, and TAp73 - anti-oncogenic effects. Human cytomegalovirus (HCMV), often found in tumors, suppresses pro-apoptotic pathways and E2F1/p73 in particular. The activity of E2F1 and p73 transcription factors is linked to metabolism of biogenic polyamines. Therefore, it could be suggested that compounds that target polyamine-metabolizing enzymes can sensitize HCMV-infected hematological malignancies to doxorubicin. Here we report that HCMV infection of ТНР-1 monocytic leukemic cells considerably elevates E2F1 levels and shifts the balance between the р73 isoforms towards ΔNp73 leading to survival of DOX-treated leukemic cells. In contrast, MDL72.527, an inhibitor of polyamine catabolism, decreases ΔNp73/ТАр73 ratio and thus restores sensitivity of the cells to DOX. Our findings indicate the combination of doxorubicin and MDL72.527 may present a novel strategy for therapy of leukemia in patients with and without HCMV infection.

The old and new biochemistry of polyamines

Polyamines are ubiquitous positively charged amines found in all organisms. These molecules play a crucial role in many biological functions including cell growth, gene regulation and differentiation. The three major polyamines produced in all mammalian cells are putrescine, spermidine and spermine. The intracellular levels of these polyamines depend on the interplay of the biosynthetic and catabolic enzymes of the polyamine and methionine salvage pathway, as well as the involvement of polyamine transporters. Polyamine levels are observed to be high in cancer cells, which contributes to malignant transformation, cell proliferation and poor patient prognosis. Considering the critical roles of polyamines in cancer cell proliferation, numerous anti-polyaminergic compounds have been developed as anti-tumor agents, which seek to suppress polyamine levels by specifically inhibiting polyamine biosynthesis, activating polyamine catabolism, or blocking polyamine transporters. However, in terms of the development of effective anti-cancer therapeutics targeting the polyamine system, these efforts have unfortunately resulted in little success. Recently, several studies using the iron chelators, O-trensox and ICL670A (Deferasirox), have demonstrated a decline in both iron and polyamine levels. Since iron levels are also high in cancer cells, and like polyamines, are required for proliferation, these latter findings suggest a biochemically integrated link between iron and polyamine metabolism.

Comparative study of polyethylene polyamines as activator molecules for a structurally unstable group I ribozyme

Polyamines are a promising class of molecules that can modulate RNA enzyme activities. To analyze the effects of the number of amine moieties systematically, we employed four polyamines sharing dimethylene units to connect amine moieties. As a model RNA enzyme, we used a structurally unstable group I ribozyme, which was activated most and least efficiently by tetraethylenepentamine and diethylenetriamine respectively.

Synthesis and Biological Evaluation of Novel Aromatic Imide-Polyamine Conjugates

Three types of conjugates in which aromatic imide scaffolds were coupled to diverse amine/polyamine motifs were synthesized, and their antitumor activities were evaluated in vitro and in vivo. Results showed that the conjugate 11e of 1,8-naphthilimide with spermine had pronounced effects on inhibiting tumor cell proliferation and inducing tumor cell apoptosis via ROS-mediated mitochondrial pathway. The in vivo assays on three H22 tumor transplant models revealed that compound 11e exerted potent ability in preventing lung cancer metastasis and extending lifespan. Furthermore, the efficacy of 11e in inhibiting tumor growth and improving body weight index were better than that of positive control, amonafide. Our study demonstrates that compound 11e is a valuable lead compound for further investigation.

Tamoxifen metabolite endoxifen interferes with the polyamine pathway in breast cancer

Tamoxifen is the most widely used drug to treat women with estrogen receptor α (ERα)-positive breast cancer. Endoxifen is recognized as the active metabolite of tamoxifen in humans. We studied endoxifen effects on ERα-positive MCF-7 breast cancer cells. Estradiol increased the proliferation of MCF-7 cells by two- to threefold and endoxifen suppressed its effects. Endoxifen suppressed c-myc, c-fos and Tff1 oncogene expression, as revealed by RT-PCR. Estradiol increased the activity of ornithine decarboxylase (ODC) and adenosyl methioninedecarboxylase (AdoMetDC), whereas endoxifen suppressed these enzyme activities. Endoxifen increased activities of spermine oxidase (SMO) and acetyl polyamine oxidase (APAO) significantly, and reduced the levels of putrescine and spermidine. These data suggest a possible mechanism for the antiestrogenic effects of tamoxifen/endoxifen, involving the stimulation of polyamine oxidase enzymes. Therefore, SMO and APAO stimulation might be useful biomarkers for the efficacy of endoxifen treatment of breast cancer.

Triethylenetetramine modulates polyamine and energy metabolism and inhibits cancer cell proliferation

Copper chelators show anticancer effects by preventing neo-angiogenesis. In the present study, we show that triethylenetetramine (TETA) is a multi-targeting drug, which modulates several key regulatory proteins of polyamine metabolism that contributes to its anticancer effect.

A novel enzyme with spermine oxidase properties in bovine liver mitochondria: identification and kinetic characterization

The uptake of spermine into mammalian mitochondria indicated the need to identify its catabolic pathway in these organelles. Bovine liver mitochondria were therefore purified and their capacity for natural polyamine uptake was verified. A kinetic approach was then used to determine the presence of an MDL 72527-sensitive enzyme with spermine oxidase activity in the matrix of bovine liver mitochondria. Western blot analysis of mitochondrial fractions and immunogold electron microscopy observations of purified mitochondria unequivocally confirmed the presence of a protein recognized by anti-spermine oxidase antibodies in the mitochondrial matrix. Preliminary kinetic characterization showed that spermine is the preferred substrate of this enzyme; lower activity was detected with spermidine and acetylated polyamines. Catalytic efficiency comparable to that of spermine was also found for 1-aminododecane. The considerable effect of ionic strength on the Vmax/KM ratio suggested the presence of more than one negatively charged zone inside the active site cavity of this mitochondrial enzyme, which is probably involved in the docking of positively charged substrates. These findings indicate that the bovine liver mitochondrial matrix contains an enzyme belonging to the spermine oxidase class. Because H2O2 is generated by spermine oxidase activity, the possible involvement of the latter as an important signaling transducer under both physiological and pathological conditions should be considered.

Synthesis and evaluation of cationically modified poly(styrene-alt-maleic anhydride) nanocarriers for intracellular gene delivery

The paper discusses the intracellular gene delivery efficacy of various cationic PSMA derivatives.

Star-shaped tetraspermine enhances cellular uptake and cytotoxicity of T-oligo in prostate cancer cells

PURPOSE

An oligonucleotide termed 'T-oligo' having sequence homology with telomere overhang has shown cytotoxicity in multiple cancers. We have demonstrated that T-oligo can induce apoptosis in androgen independent prostate cancer cell line DU-145. In this report, we evaluate the use of star-shaped tetraspermine (SSTS) for delivery of T-oligo.

METHODS

SSTS was synthesized from spermine and its intrinsic cytotoxicity towards DU-145 cells was compared with spermine and branched polyethyleneimine (bPEI). Atomistic molecular dynamic (MD) simulations were conducted to understand binding and complexation of spermine and SSTS with T-oligo. Complexation was also determined using gel electrophoresis and SYBR gold assay. Complexes were characterized for size, cellular uptake and antiproliferative effect.

RESULTS

SSTS exhibited significantly lower toxicity than spermine and bPEI. Its affinity towards T-oligo was significantly higher than spermine as determined by experimental studies and confirmed by MD simulations and it formed stable complexes (TONPs) with T-oligo. TONPs facilitated cellular uptake and nuclear accumulation of T-oligo and their cytotoxic potential was observed at concentration several folds lower than that required for T-oligo alone.

CONCLUSION

SSTS significantly enhanced therapeutic benefits associated with the use of T-oligo and can be developed as a delivery vehicle for its in-vivo therapeutic applications.

SPECT/CT imaging of radiolabeled cubosomes and hexosomes for potential theranostic applications

We have developed a highly efficient method for the radiolabeling of phytantriol (PHYT)/oleic acid (OA)-based hexosomes based on the surface chelation of technetium-99m ((99m)Tc) to preformed hexosomes using the polyamine 1, 12-diamino-3, 6, 9-triazododecane (SpmTrien) as chelating agent. We also report on the unsuccessful labeling of cubosomes using the well-known chelating agent hexamethylpropyleneamine oxime (HMPAO). The (99m)Tc-labeled SpmTrien-hexosomes ((99m)Tc-SpmTrien-hexosomes) were synthesized with good radiolabeling (84%) and high radiochemical purity (>90%). The effect of radiolabeling on the internal nanostructure and the overall size of these aqueous dispersions was investigated by using synchrotron small angle X-ray scattering (SAXS), dynamic light scattering (DLS), and transmission electron cryo microscopy (cryo-TEM). Further, we show the utility of (99m)Tc-SpmTrien-hexosomes for the in vivo imaging of healthy mice using single photon emission computed tomography (SPECT) in combination with computed tomography (CT), i.e. SPECT/CT. SPECT/CT experiments of subcutaneously administered (99m)Tc-SpmTrien-hexosomes to the flank of mice showed a high stability in vivo allowing imaging of the distribution of the radiolabeled hexosomes for up to 24 h. These injected (99m)Tc-SpmTrien-hexosomes formed a deposit within the subcutaneous adipose tissue, displaying a high biodistribution of ≈ 343% injected dose/g tissue (%ID/g), with negligible uptake in other organs and tissues. The developed (99m)Tc labeling method for PHYT/OA-based hexosomes could further serve as a useful tool for investigating and imaging the in vivo performance of cubosomal and hexosomal drug nanocarriers.

Biogenic polyamines spermine and spermidine activate RNA polymerase and inhibit RNA helicase of hepatitis C virus

Influence of the biogenic polyamines spermine, spermidine, and putrescine as well as their derivatives on the replication enzymes of hepatitis C virus (HCV) was investigated. It was found that spermine and spermidine activate HCV RNA-dependent RNA polymerase (NS5B protein). This effect was not caused by the stabilization of the enzyme or by competition with template-primer complex, but rather it was due to achievement of true maximum velocity V(max). Natural polyamines and their derivatives effectively inhibited the helicase reaction catalyzed by another enzyme of HCV replication - helicase/NTPase (NS3 protein). However, these compounds affected neither the NTPase reaction nor its activation by polynucleotides. Activation of the HCV RNA polymerase and inhibition of the viral helicase were shown at physiological concentrations of the polyamines. These data suggest that biogenic polyamines may cause differently directed effects on the replication of the HCV genome in an infected cell.

Complex N-acetylation of triethylenetetramine

Triethylenetetramine (TETA) is an efficient copper chelator that has versatile clinical potential. We have recently shown that spermidine/spermine-N(1)-acetyltransferase (SSAT1), the key polyamine catabolic enzyme, acetylates TETA in vitro. Here, we studied the metabolism of TETA in three different mouse lines: syngenic, SSAT1-overexpressing, and SSAT1-deficient (SSAT1-KO) mice. The mice were sacrificed at 1, 2, or 4 h after TETA injection (300 mg/kg i.p.). We found only N(1)-acetyltriethylenetetramine (N(1)AcTETA) and/or TETA in the liver, kidney, and plasma samples. As expected, SSAT1-overexpressing mice acetylated TETA at an accelerated rate compared with syngenic and SSAT1-KO mice. It is noteworthy that SSAT1-KO mice metabolized TETA as syngenic mice did, probably by thialysine acetyltransferase, which had a K(m) value of 2.5 ± 0.3 mM and a k(cat) value of 1.3 s(-1) for TETA when tested in vitro with the human recombinant enzyme. Thus, the present results suggest that there are at least two N-acetylases potentially metabolizing TETA. However, their physiological significance for TETA acetylation requires further studies. Furthermore, we detected chemical intramolecular N-acetyl migration from the N(1) to N(3) position of N(1)AcTETA and N(1),N(8)-diacetyltriethylenetetramine in an acidified high-performance liquid chromatography sample matrix. The complex metabolism of TETA together with the intramolecular N-acetyl migration may explain the huge individual variations in the acetylation rate of TETA reported earlier.

Tissue-specific alternative splicing of spermidine/spermine N1-acetyltransferase

The polyamines, spermidine and spermine, are abundant organic cations participating in many important cellular processes. We have previously shown that the rate-limiting enzyme of polyamine catabolism, spermidine/spermine N(1)-acetyltransferase (SSAT), has an alternative mRNA splice variant (SSATX) which undergoes degradation via nonsense-mediated mRNA decay (NMD) pathway, and that the intracellular polyamine level regulates the ratio of the SSATX and SSAT splice variants. The aim of this study was to investigate the effect of SSATX level manipulation on SSAT activity in cell culture, and to examine the in vivo expression levels of SSATX and SSAT mRNA. Silencing SSATX expression with small interfering RNA led to increased SSAT activity. Furthermore, transfection of SSAT-deficient cells with mutated SSAT gene (which produced only trace amount of SSATX) yielded higher SSAT activity than transfection with natural SSAT gene (which produced both SSAT and SSATX). Blocking NMD in vivo by protein synthesis inhibitor cycloheximide resulted in accumulation of SSATX mRNA, and like in cell culture, the increase of SSATX mRNA was prevented by administration of polyamine analog N(1),N(11)-diethylnorspermine. Although SSATX/total SSAT mRNA ratio did not correlate with polyamine levels or SSAT activity between different tissues, increasing polyamine levels in a given tissue led to decreased SSATX/total SSAT mRNA ratio and vice versa. Taken together, the regulated unproductive splicing and translation of SSAT has a physiological relevance in modulating SSAT activity. However, in addition to polyamine level there seems to be additional factors regulating tissue-specific alternative splicing of SSAT.

The use of novel C-methylated spermidine derivatives to investigate the regulation of polyamine metabolism

The polyamines are organic polycations present at millimolar concentrations in eukaryotic cells where they participate in the regulation of vital cellular functions including proliferation and differentiation. Biological evaluation of rationally designed polyamine analogs is one of the cornerstones of polyamine research. Here we have synthesized and characterized novel C-methylated spermidine analogs, that is, 2-methylspermidine, 3-methylspermidine, and 8-methylspermidine. 3-Methylspermidine was found to be metabolically stable in DU145 cells, while 8-methylspermidine was a substrate for spermidine/spermine N(1)-acetyltransferase (SSAT) and 2-methylspermidine was a substrate for both SSAT and acetylpolyamine oxidase. All the analogs induced the splicing of the productive mRNA splice variant of SSAT, overcame growth arrest induced by 72-h treatment with ornithine decarboxylase (ODC) inhibitor α-difluoromethylornithine, and were transported via the polyamine transporter. Surprisingly, 2-methylspermidine was a weak downregulator of ODC activity in DU145 cells. Our data demonstrates that it is possible to radically alter the biochemical properties of a polyamine analog by changing the position of the methyl group.