2,2'-Dithiobis(N-ethyl-spermine-5-carboxamide) is a high affinity, membrane-impermeant antagonist of the mammalian polyamine transport system

Polyamines in cancer: integrating organismal metabolism and antitumour immunity

The natural mammalian polyamines putrescine, spermidine and spermine are essential for both normal and neoplastic cell function and replication. Dysregulation of metabolism of polyamines and their requirements is common in many cancers. Both clinical and experimental depletion of polyamines have demonstrated their metabolism to be a rational target for therapy; however, the mechanisms through which polyamines can establish a tumour-permissive microenvironment are only now emerging. Recent data indicate that polyamines can play a major role in regulating the antitumour immune response, thus likely contributing to the existence of immunologically 'cold' tumours that do not respond to immune checkpoint blockade. Additionally, the interplay between the microbiota and associated tissues creates a tumour microenvironment in which polyamine metabolism, content and function can all be dramatically altered on the basis of microbiota composition, dietary polyamine availability and tissue response to its surrounding microenvironment. The goal of this Perspective is to introduce the reader to the many ways in which polyamines, polyamine metabolism, the microbiota and the diet interconnect to establish a tumour microenvironment that facilitates the initiation and progression of cancer. It also details ways in which polyamine metabolism and function can be successfully targeted for therapeutic benefit, including specifically enhancing the antitumour immune response.

Quantitative detection of 8-Oxo-7,8-dihydro-2'-deoxyguanosine using chemical tagging and qPCR

8-Oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo) is a commonly formed DNA lesion that is useful as a biomarker for oxidative stress. Although methods for selective quantification of 8-oxodGuo exist, there is room for additional methods that are sensitive and utilize instrumentation that is widely available. We previously took advantage of the reported reactivity of 8-oxodGuo to develop a method for detecting the lesion by selectively covalently tagging it with a molecule equipped with a biotin label that can be used subsequently with a reporting method (XueL., and GreenbergM. M. (2007) J. Am. Chem. Soc.129, 701017497789). We now report a method that can detect as little as 14 amol of 8-oxodGuo by tagging DNA with a reagent containing a disulfide that reduces background due to nonspecific binding. The reagent also contains biotin that enables capturing target DNA on streptavidin-coated magnetic beads. The captured DNA is quantified using quantitative PCR. The method is validated by comparing the amount of 8-oxodGuo detected as a function of Fe²⁺/H₂O₂/ascorbate-dose to that reported previously using mass spectrometry.

Recent advances in the molecular biology of metazoan polyamine transport

Very limited molecular knowledge exists about the identity and protein components of the ubiquitous polyamine transporters found in animal cells. However, a number of reports have been published over the last 5 years on potential candidates for metazoan polyamine permeases. We review the available evidence on these putative polyamine permeases, as well as establish a useful "identikit picture" of the general polyamine transport system, based on its properties as found in a wide spectrum of mammalian cells. Any molecular candidate encoding a putative "general" polyamine permease should fit that provided portrait. The current models proposed for the mechanism of polyamine internalization in mammalian cells are also briefly reviewed.

Polyamine transport as a target for treatment of Pneumocystis pneumonia

Polyamine levels are greatly increased in alveolar macrophages (AMs) during Pneumocystis pneumonia (PCP), leading to increased production of H(2)O(2), which causes AMs to undergo apoptosis. One of the mechanisms by which polyamine levels in AMs are elevated is enhanced uptake of exogenous polyamines. In this study, the possibility of targeting polyamine uptake as a treatment for PCP was examined. Four anthracene- and one benzene-polyamine conjugates that are potential polyamine transport inhibitors, including N1-anthracen-9-ylmethyl-butane-1,4-diamine; N-(4-aminobutyl)-N-anthracen-9-ylmethylbutane-1,4-diamine; N-[4-(4-aminobutylamino)butyl]-N-anthracen-9-ylmethylbutane-1,4-diamine; N-(4-amino-butyl)-N'-(10-[[4-(4-amino-butylamino)butylamino]-methyl]anthracen-9-ylmethyl)butane-1,4-diamine (44-Ant-44); and benzene-polyamine conjugate N-(4-amino-butyl)-N'-(4-[[4-(4-amino-butylamino)butylamino]-methyl]benzyl)butane-1,4-diamine (44-Bn-44), were tested. Compounds 44-Ant-44 and 44-Bn-44 were found to have a very low toxicity to AMs in vitro and were evaluated for their therapeutic effect on PCP in vivo. Sprague-Dawley rats infected with P. carinii for 28 days were intranasally instilled with 50 microl of a 1 mM solution of 44-Bn-44 or 44-Ant-44 every 2 days. Twenty-one days after initiation of the treatment, three to five rats from each group were sacrificed and examined for lung pathology, organism burden, and apoptosis of AMs. Both 44-Bn-44 and 44-Ant-44 reduced organism burdens; however, only 44-Ant-44 decreased the severity of the infection with reduced lung inflammation, increased clearance of exudates, increased air space, and decreased apoptosis of AMs. 44-Ant-44 also significantly prolonged the survival of treated animals. These results suggest that polyamine uptake is a potential target for treatment of PCP.

Lipophilic lysine-spermine conjugates are potent polyamine transport inhibitors for use in combination with a polyamine biosynthesis inhibitor

Cancer cells can overcome the ability of polyamine biosynthesis inhibitors to completely deplete their internal polyamines by the importation of polyamines from external sources. This paper discusses the development of a group of lipophilic polyamine analogues that potently inhibit the cellular polyamine uptake system and greatly increase the effectiveness of polyamine depletion when used in combination with DFMO, a well-studied polyamine biosynthesis inhibitor. The attachment of a length-optimized C(16) lipophilic substituent to the epsilon-nitrogen atom of an earlier lead compound, D-Lys-Spm (5), has produced an analogue, D-Lys(C(16)acyl)-Spm (11) with several orders of magnitude more potent cell growth inhibition on a variety of cultured cancer cell types including breast (MDA-MB-231), prostate (PC-3), melanoma (A375), and ovarian (SK-OV-3), among others. These results are discussed in the context of a possible membrane-catalyzed interaction with the extracellular polyamine transport apparatus. The resulting novel two-drug combination therapy targeting cellular polyamine metabolism has shown exceptional efficacy against cutaneous squamous cell carcinomas (SCC) in a transgenic ornithine decarboxylase (ODC) mouse model of skin cancer. A majority (88%) of large, aggressive SCCs exhibited complete or nearly complete remission to this combination therapy, whereas responses to each agent alone were poor. The availability of a potent polyamine transport inhibitor allows, for the first time, for a real test of the hypothesis that starving cells of polyamines will lead to objective clinical response.

Designing the polyamine pharmacophore: influence of N-substituents on the transport behavior of polyamine conjugates

N-Ethylated N-arylmethyl polyamine conjugates were synthesized and evaluated for their ability to target the polyamine transporter (PAT). To understand the effect of N-ethylation upon PAT selectivity, ethyl groups were appended onto a PAT-selective N (1)-anthracenenylmethyl homospermidine derivative, 1b. Bioevaluation in L1210 murine leukemia cells and in two Chinese hamster ovary cell lines (PAT-active CHO and PAT-deficient CHO-MG) revealed a dramatic decrease in PAT targeting ability upon N (1) or N (5) ethylation of the pharmacophore 1b. Experiments using the amine oxidase inhibitor, aminoguanidine (AG, 2 mM), revealed that the N (9)-ethyl and N (9)-methyl analogues were able to retain their PAT selectivity and cytotoxicity properties in the presence or absence of AG. In contrast, the lead compound 1b (containing a terminal NH 2 group) revealed a dramatic reduction in both its PAT-targeting ability and cytotoxicity in the absence of AG. An improved balance between these three properties of PAT-targeting, cytotoxicity and metabolic stability can be attained via N-methylation at the N (9)-position.

Structure-activity investigations of polyamine-anthracene conjugates and their uptake via the polyamine transporter

A series of polyamine conjugates were synthesized and evaluated for their ability to target the polyamine transporter (PAT) in two Chinese hamster ovary (CHO) cell lines (PAT-active CHO and PAT-inactive CHOMG). This systematic study identified salient features of the polyamine architecture required to target and enter cells via the PAT. Indeed, the separation of charges, the degree of N-alkylation, and the spacer unit connecting the N(1)-terminus to the appended cytotoxic component (anthracene) were found to be key contributors to optimal delivery via the PAT. Using the CHO screen, the homospermidine motif (e.g., 4,4-triamine) was identified as a polyamine vector, which could enable the selective import of large N(1)-substituents (i.e., naphthylmethyl, anthracenylmethyl and pyrenylmethyl), which were cytotoxic to cells. The cell selectivity of this approach was demonstrated in B-16 murine melanoma cells and normal melanocytes (Mel-A). Three polyamine areas (recognition and transport, vesicle sequestration and polyamine-target interactions) were identified for future research.

Dendritic Cationic Lipids with Highly Charged Headgroups for Efficient Gene Delivery

Gene therapy is expected to lead to powerful new approaches for curing many diseases, a potential that is currently explored in worldwide clinical trials. Nonviral DNA delivery systems are desirable to overcome the inherent problems of viral vectors, but their current efficiency requires improvement and the understanding of their mechanism of action is incomplete. We have synthesized new multivalent cationic lipids with highly charged dendritic headgroups to probe the structure-transfection efficiency relationships of cationic liposome (CL)-DNA complexes, a prevalent nonviral vector. The lipid headgroups are constructed from ornithine cores and ornithine or carboxyspermine endgroups. The dendritic lipids were prepared on a gram scale, using a synthetic scheme that permits facile variation of the lipid building blocks headgroup, spacer, and hydrophobic moiety. They carry four to sixteen positive charges in their headgroups. Complexes of DNA with mixtures of the dendritic lipids and neutral 1,2-dioleoyl-sn-glycero phosphatidylcholine (DOPC) exhibit novel structures at high contents of the highly charged lipids, while the well-known lamellar phase is formed at high contents of DOPC. DNA complexes of the new dendritic lipids efficiently transfect mammalian cells in culture without cytotoxicity and, in contrast to lamellar complexes, maintain high transfection efficiency over a broad range of composition.

Synthesis and biological activities of bisnaphthalimido polyamines derivatives: cytotoxicity, DNA binding, DNA damage and drug localization in breast cancer MCF 7 cells

New bisoxynaphthalimidopolyamines (BNIPOPut, BNIPOSpd and BNIPOSpm) were synthesized. Their cytotoxic properties were evaluated against breast cancer MCF 7 cells and compared with bisnaphthalimidopolyamines BNIPSpd and BNIPSpm. Among the bisoxynaphthalimido polyamines, BNIPOSpm and BNIPOSpd exhibited cytotoxic activity with an IC50 f 29.55 and 27.22 microM, respectively, while BNIPOPut failed to exert significant cytotoxicity after 48-h drug exposure. DNA binding was determined by midpoint of thermal denaturation (Tm) measurement, ethidium bromide displacement and DNA gel mobility. Both BNIPOSpm and BNIPOSpd exhibited strong binding affinities with DNA. BNIPOPut had the least effect. The results were compared with other cytotoxic bisnaphthalimido compounds (BNIPSpm and BNIPSpd) previously reported by us. Using the single cell gel electrophoresis assay, it was found that BNIPSpm and BNIPSpd caused substantial DNA damage to MCF 7 treated cells while BNIPOSpm showed no significant effect over a range of drug concentrations after 4-h drug exposure. However, after 12-h drug exposure, BNIPOSpm had induced significant DNA damage similar to that of BNIPSpm (after 4-h drug exposure). Fluorescence microscopic analysis revealed that at 1 microM drug concentration and after 6-h drug exposure, both BNIPSpm and BNIPSpd were located within the cell while the presence of BNIPOSpm, was not observed. Therefore, we conclude that BNIPSpd, BNIPSpm and BNIPOSpm induce DNA damage consistent with their rate of uptake into the cells.

Uptake of polyamines by the unicellular green alga Chlamydomonas reinhardtii and their effect on ornithine decarboxylase activity

Uptake of exogenous polyamines by the unicellular green alga Chlamydomonas reinhardtii and their effects on polyamine metabolism were investigated. Our data show that, in contrast to mammalian cells, Chlamydomonas reinhardtii does not contain short-living, high-affinity polyamine transporters whose cellular level is dependent on the polyamine concentration. However, exogenous polyamines affect polyamine metabolism in Chlamydomonas cells. Exogenous putrescine caused a slow increase of both putrescine and spermidine and, vice versa, exogenous spermidine also led to an increase of the intracellular levels of both spermidine and putrescine. No intracellular spermine was detected under any conditions. Exogenous spermine was taken up by the cells and caused a decrease in their putrescine and spermidine levels. As in other organisms, exogenous polyamines led to a decrease in the activity of ornithine decarboxylase, a key enzyme of polyamine synthesis. In contrast to mammalian cells, this polyamine-induced decrease in ornithine decarboxylase activity is not mediated by a polyamine-dependent degradation or inactivation, but exclusively due to a decreased synthesis of ornithine decarboxylase. Translation of ornithine decarboxylase mRNA, but not overall protein biosynthesis is slowed by increased polyamine levels.

Xylylated dimers of putrescine and polyamines: influence of the polyamine backbone on spermidine transport inhibition

Dimeric norspermidine and spermidine derivatives are strong competitive inhibitors of polyamine transport. A xylyl tether was used for the dimerization of various triamines and spermine via a secondary amino group, and of putrescine via an ether or an amino group. Dimerization of putrescine moieties potentiates their ability to compete against spermidine transport to a much greater extent than for triamine dimers.

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.

Synthesis of bis-spermine dimers that are potent polyamine transport inhibitors

A series of novel spermine dimer analogues was synthesized and assessed for their ability to inhibit spermidine transport into MDA-MB-231 breast carcinoma cells. Two spermine molecules were tethered via their N(1) primary amines with naphthalenedisulfonic acid, adamantanedicarboxylic acid and a series of aliphatic dicarboxylic acids. The linked spermine analogues were potent polyamine transport inhibitors and inhibited cell growth cytostatically in combination with a polyamine synthesis inhibitor. Variation in the linker length did not alter polyamine transport inhibition. The amount of charge on the molecule may influence the molecular interaction with the transporter since the most potent spermidine transport inhibitors contained 5-6 positive charges.

Novel lysine-spermine conjugate inhibits polyamine transport and inhibits cell growth when given with DFMO

Polyamines are ubiquitous molecules with multiple intracellular functions. Cells tightly regulate their levels through feedback mechanisms affecting synthesis, intracellular conversion, and transport. Because polyamines have an important role in regulating cell growth, they are a target for cancer therapeutic development. However, to effectively inhibit cell growth through polyamine depletion one needs to inhibit both polyamine synthesis and import. Although the mammalian polyamine transporter has not been cloned, we have identified ORI 1202, an N(1)-spermine-L-lysinyl amide, as an effective polyamine transport inhibitor. ORI 1202 prevents the cellular accumulation of [(3)H]spermidine over a 20-h test period. ORI 1202 (30-100 microM) effectively inhibits cell growth when used in conjunction with the polyamine synthesis inhibitor alpha-difluoromethylornithine (DFMO; > or =230 microM). Human breast, prostate, and bladder carcinoma cell lines and melanoma cell lines show ORI 1202 EC(50) values in the low micromolar range when tested in conjunction with DFMO. This cytostatic effect correlates with a reduction in the intracellular levels of putrescine and spermidine. When ORI 1202 (45 mg/kg, i.p., tidx5) and DFMO (1% in drinking water) were delivered over 14 days, MDA-MB-231 breast tumor xenografts in nude mice showed 50% growth inhibition. Polyamine depletion therapy provides a cytostatic therapy that could be useful against cancer and other diseases resulting from uncontrolled cell growth.

Elevated levels of polyamines and trypanothione resulting from overexpression of the ornithine decarboxylase gene in arsenite-resistant Leishmania

The levels of trypanothione, a glutathione-spermidine conjugate, are increased in the protozoan parasite Leishmania selected for resistance to the heavy metal arsenite. The levels of putrescine and spermidine were increased in resistant mutants. This increase is mediated by overexpression of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis. Gene overexpression is generally mediated by gene amplification in Leishmania but, here, the mRNA and the enzymatic activity of ODC are increased without gene amplification. This RNA overexpression is stable when cells are grown in the absence of the drug and does not result from gene rearrangements or from an increased rate of RNA synthesis. Transient transfections suggest that mutations in the revertant cells contribute to these elevated levels of RNA. Stable transfection of the ODC gene increases the level of trypanothione, which can contribute to arsenite resistance. In addition to ODC overexpression, the gene for the ABC transporter PGPA is amplified in the mutants. The co-transfection of the ODC and PGPA genes confers resistance in a synergistic fashion in partial revertants, also suggesting that PGPA recognizes metals conjugated to trypanothione.

Synthesis of spermidine and norspermidine dimers as high affinity polyamine transport inhibitors

A series of novel spermidine and sym-norspermidine dimers was synthesized by crosslinking the polyamine backbones via alkylation of their secondary amino groups to butyl, trans-2-butenyl, 2-butynyl or p-xylyl bridges. The resulting hexamines behaved as high-affinity antagonists of polyamine uptake, with a relative potency that was dependent on the geometry of the linker structure.

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.