Development of Polyamine Transport Ligands with Improved Metabolic Stability and Selectivity against Specific Human Cancers

Polyamine Signal through HCC Microenvironment: A Key Regulator of Mitochondrial Preservation and Turnover in TAMs

Hepatocellular carcinoma (HCC) is the most common primary liver cancer, and, with increasing research on the tumor immune microenvironment (TIME), the immunosuppressive micro-environment of HCC hampers further application of immunotherapy, even though immunotherapy can provide survival benefits to patients with advanced liver cancer. Current studies suggest that polyamine metabolism is not only a key metabolic pathway for the formation of immunosuppressive phenotypes in tumor-associated macrophages (TAMs), but it is also profoundly involved in mitochondrial quality control signaling and the energy metabolism regulation process, so it is particularly important to further investigate the role of polyamine metabolism in the tumor microenvironment (TME). In this review, by summarizing the current research progress of key enzymes and substrates of the polyamine metabolic pathway in regulating TAMs and T cells, we propose that polyamine biosynthesis can intervene in the process of mitochondrial energy metabolism by affecting mitochondrial autophagy, which, in turn, regulates macrophage polarization and T cell differentiation. Polyamine metabolism may be a key target for the interactive dialog between HCC cells and immune cells such as TAMs, so interfering with polyamine metabolism may become an important entry point to break intercellular communication, providing new research space for developing polyamine metabolism-based therapy for HCC.

Modulating the polyamine/hypusine axis controls generation of CD8+ tissue-resident memory T cells

Glutaminolysis is a hallmark of the activation and metabolic reprogramming of T cells. Isotopic tracer analyses of antigen-activated effector CD8+ T cells revealed that glutamine is the principal carbon source for the biosynthesis of polyamines putrescine, spermidine, and spermine. These metabolites play critical roles in activation-induced T cell proliferation, as well as for the production of hypusine, which is derived from spermidine and is covalently linked to the translation elongation factor eukaryotic translation initiation factor 5A (eIF5A). Here, we demonstrated that the glutamine/polyamine/hypusine axis controlled the expression of CD69, an important regulator of tissue-resident memory T cells (Trm). Inhibition of this circuit augmented the development of Trm cells ex vivo and in vivo in the BM, a well-established niche for Trm cells. Furthermore, blocking the polyamine/hypusine axis augmented CD69 expression as well as IFN-γ and TNF-α production in (a) human CD8+ T cells from peripheral blood and sarcoma tumor infiltrating lymphocytes and (b) human CD8+ CAR-T cells. Collectively, these findings support the notion that the polyamine-hypusine circuit can be exploited to modulate Trm cells for therapeutic benefit.

Older but Stronger: Development of Platinum-Based Antitumor Agents and Research Advances in Tumor Immunity

Platinum (Pt) drugs have developed rapidly in clinical applications because of their broad and highly effective antitumor effects. In recent years, with the rapid development of immunotherapy, Pt-based antitumor agents have gained new challenges and opportunities. Since the discovery of their pharmacological effects in immunotherapy and tumor microenvironment regulation, research into Pt drugs has progressed to multi-ligand and multi-functional Pt precursors and their own shortcomings have been further highlighted. With the development of antitumor immunotherapy and the rise of combination therapy, the development of Pt-based drugs has started to move in the direction of multi-targeting, nanocarrier modification, immunotherapy and photodynamic therapy. In this paper, we first overview the recent applications of Pt-based drugs in antitumor inorganic chemistry, with a focus on summarizing the application of Pt-based drugs and their precursors in the anticancer immune response. The paper also provides a reasonable outlook on the future development of Pt-based drugs from the chemical and immunological perspectives, relying on the existing content and problems of Pt-based drug development. On the basis of the gathered information, joint multidisciplinary programs on implementing comprehensive immune analyses for the future development of novel anticancer metal compounds should be initiated.

Melanoma-targeted photodynamic therapy based on hypericin-loaded multifunctional P123-spermine/folate micelles

Multifunctional P123 micelle linked covalently with spermine (SM) and folic acid (FA) was developed as a drug delivery system of hypericin (HYP). The chemical structures of the modified copolymers were confirmed by spectroscopy and spectrophotometric techniques (UV-vis, FTIR, and ¹H NMR). The copolymeric micelles loading HYP were prepared by solid dispersion and characterized by UV-vis, fluorescence, dynamic light scattering (DLS), ζ potential, and transmission electron microscopy (TEM). The results provided a good level of stability for HYP-loaded P123-SM, P123-FA, and P123-SM/P123-FA in the aqueous medium. The morphology analysis showed that all copolymeric micelles are spherical. Well-defined regions of different contrast allow us to infer that SM and FA were localized on the surface of micelles, and the HYP molecules are located in the core region of micelles. The uptake potential of multifunctional P123 micelle was accessed by exposing the micellar systems loading HYP to two cell lines, B16-F10 and HaCaT. HYP-loaded P123 micelles reveal a low selectivity for melanoma cells, showing significant photodamage for HaCat cells. However, the exposition of B16-F10 cells to Hyp-loaded SM- and FA-functionalized P123 micelles under light irradiation revealed the lowest CC₅₀ values. The interpretation of these results suggested that the combination of SM and FA on P123 micelles is the main factor in enhancing the HYP uptake by melanoma cells, consequently leading to its photoinactivation.

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.

Polyamine and Ethanolamine Metabolism in Bacteria as an Important Component of Nitrogen Assimilation for Survival and Pathogenicity

Nitrogen is an essential element required for bacterial growth. It serves as a building block for the biosynthesis of macromolecules and provides precursors for secondary metabolites. Bacteria have developed the ability to use various nitrogen sources and possess two enzyme systems for nitrogen assimilation involving glutamine synthetase/glutamate synthase and glutamate dehydrogenase. Microorganisms living in habitats with changeable availability of nutrients have developed strategies to survive under nitrogen limitation. One adaptation is the ability to acquire nitrogen from alternative sources including the polyamines putrescine, cadaverine, spermidine and spermine, as well as the monoamine ethanolamine. Bacterial polyamine and monoamine metabolism is not only important under low nitrogen availability, but it is also required to survive under high concentrations of these compounds. Such conditions can occur in diverse habitats such as soil, plant tissues and human cells. Strategies of pathogenic and non-pathogenic bacteria to survive in the presence of poly- and monoamines offer the possibility to combat pathogens by using their capability to metabolize polyamines as an antibiotic drug target. This work aims to summarize the knowledge on poly- and monoamine metabolism in bacteria and its role in nitrogen metabolism.

Development of Polyamine Lassos as Polyamine Transport Inhibitors

Nine- and twelve-membered triaza-macrocycles were appended to one end of homospermidine to make polyamine lassos. These compounds were shown to be potent polyamine transport inhibitors (PTIs) using pancreatic ductal adenocarcinoma L3.6pl cells, which have high polyamine transport activity. The smaller triazacyclononane-based lasso significantly reduced the uptake of a fluorescent polyamine probe and inhibited spermidine uptake and reduced intracellular polyamine levels in difluoromethylornithine (DFMO)-treated L3.6pl cells. Both designs were shown to be effective inhibitors of ³H-spermidine uptake, with the smaller lasso outperforming the larger lasso. When the smaller lasso was challenged to inhibit each of the three radiolabeled native polyamines, it had similar K _i values as those of the known PTIs, Trimer44NMe and AMXT1501. Because of these promising properties, these materials may have future anticancer applications in polyamine blocking therapy, an approach that couples a polyamine biosynthesis inhibitor (DFMO) with a PTI to lower intracellular polyamines and suppress cell growth.

Polyamine homeostasis-based strategies for cancer: The role of combination regimens

Spermine, spermidine and putrescine polyamines are naturally occurring ubiquitous positively charged amines and are essential metabolites for biological functions in our life. These compounds play a crucial role in many cell processes, including cellular proliferation, growth, and differentiation. Intracellular levels of polyamines depend on their biosynthesis, transport and degradation. Polyamine levels are high in cancer cells, which leads to the promotion of tumor growth, invasion and metastasis. Targeting polyamine metabolism as an anticancer strategy is considerably rational. Due to compensatory mechanisms, a single strategy does not achieve satisfactory clinical effects when using a single agent. Combination regimens are more clinically promising for cancer chemoprevention because they work synergistically with causing little or no adverse effects due to each individual agent being used at lower doses. Moreover, bioactive substances have advantages over single chemical agents because they can affect multiple targets. In this review, we discuss anticancer strategies targeting polyamine metabolism and describe how combination treatments and effective natural active ingredients are promising therapies. The existing research suggests that polyamine metabolic enzymes are important therapeutic targets and that combination therapies can be more effective than monotherapies based on polyamine depletion.

Polyamines: Functions, Metabolism, and Role in Human Disease Management

Putrescine, spermine, and spermidine are the important polyamines (PAs), found in all living organisms. PAs are formed by the decarboxylation of amino acids, and they facilitate cell growth and development via different cellular responses. PAs are the integrated part of the cellular and genetic metabolism and help in transcription, translation, signaling, and post-translational modifications. At the cellular level, PA concentration may influence the condition of various diseases in the body. For instance, a high PA level is detrimental to patients suffering from aging, cognitive impairment, and cancer. The levels of PAs decline with age in humans, which is associated with different health disorders. On the other hand, PAs reduce the risk of many cardiovascular diseases and increase longevity, when taken in an optimum quantity. Therefore, a controlled diet is an easy way to maintain the level of PAs in the body. Based on the nutritional intake of PAs, healthy cell functioning can be maintained. Moreover, several diseases can also be controlled to a higher extend via maintaining the metabolism of PAs. The present review discusses the types, important functions, and metabolism of PAs in humans. It also highlights the nutritional role of PAs in the prevention of various diseases.

A naphthalimide-polyamine conjugate preferentially accumulates in hepatic carcinoma metastases as a lysosome-targeted antimetastatic agent

Disseminated tumors lead to approximately 90% of cancer-associated deaths especially for hepatocellular carcinoma (HCC), indicating the imperative need of antimetastatic drugs and the ineffectiveness of current therapies. Recently polyamine derivatives have been identified as a promising prospect in dealing with metastatic tumors. Herein, a novel class of naphthalimide-polyamine conjugates 8a-8d, 13a-13c, 17 and 21 were synthesized and the mechanism was further determined. The polyamine conjugate 13b displayed remarkably elevated anti-tumor and anti-metastatic effects (76.01% and 75.02%) than the positive control amonafide (46.91% and 55.77%) at 5 mg/kg in vivo. The underlying molecular mechanism indicated that in addition to induce DNA damage by up-regulating p53 and γH2AX, 13b also targeted lysosome to modulate polyamine metabolism and function in a totally different way from that of amonafide. Furthermore, the HMGB1/p62/LC3II/LC3I and p53/SSAT/β-catenin pathways were mainly involved in the inhibition of 13b-induced HCC metastasis by targeting polyamine transporters (PTs) overexpressed in HCC. At last, 13b down-regulated the concentrations of Put, Spd and Spm by modulating polyamine metabolism key enzymes SSAT and PAO, which favored the suppression of fast growing tumor cells. Taken together, our study implies a promising strategy for naphthalimide conjugates to treat terminal cancer of HCC by targeting autophagy and tumor microenvironment with reduced toxicities and notable activities.

Harnessing the polyamine transport system to treat BRAF inhibitor-resistant melanoma

BRAF mutations are present in over half of all melanoma tumors. Although BRAF inhibitors significantly improve survival of patients with metastatic melanoma, recurrences occur within several months. We previously reported that BRAF mutant melanoma cells are more sensitive to a novel arylmethyl-polyamine (AP) compound that exploits their increased polyamine uptake compared to that of BRAF wildtype cells. Using an animal model of BRAF inhibitor-resistant melanoma, we show that co-treatment with the BRAF inhibitor, PLX4720, and AP significantly delays the recurrence of PLX4720-resistant melanoma tumors and decreases tumor-promoting macrophages. Development of BRAF inhibitor-resistance enriches for metastatic cancer stem cells (CSC) and increases tumor-promoting macrophages. In vitro studies demonstrated that CD304⁺, CXCR4⁺ spheroid cultures of BRAF mutant melanoma cells are resistant to PLX4720 but are more sensitive to AP compared to monolayer cultures of the same cells. AP significantly inhibited YUMM1.7 melanoma cell invasiveness across a Matrigel-coated filter using the CXCR4 ligand, SDF-1α, as the chemoattractant. AP also blocked the chemotactic effect of SDF-1α on CXCR4⁺ macrophages and inhibited M2 polarization of macrophages. In melanoma-macrophage co-cultures, AP prevented the PLX4720-induced release of pro-tumorigenic growth factors, such as VEGF, from macrophages and prevented the macrophage rescue of BRAF mutant melanoma cells treated with PLX4720. Our study offers a novel therapy (AP) to treat chemo-resistant melanoma. AP is unique because it targets the polyamine transport system in BRAF inhibitor-resistant CSCs and also blocks CXCR4 signaling in invasive melanoma cells and pro-tumorigenic macrophages.

A Polyamine-Based Dinitro-Naphthalimide Conjugate as Substrates for Polyamine Transporters Preferentially Accumulates in Cancer Cells and Minimizes Side Effects in vitro and in vivo

Naphthalimides, such as amonafide and mitonafide in clinical trials, have been developed as antitumor agents for orthotopic tumor. However, the serious side effects in cancer patients limit their applications. Herein, a new class of polyamine-based naphthalimide conjugates 5a-5c, 7a-7b, and 11a-11b with and without the alkylation of the distant nitrogen in the polyamine chain were synthesized and the mechanism was determined. Compared with amonafide, dinitro-naphthalimide conjugate 5c with a 4,3-cyclopropyl motif preferentially accumulates in cancer cells and minimizes side effects in vitro and in vivo. More importantly, 5c at the dosage of as low as 3 mg/kg (57.97%) displays better antitumor effects than the positive control amonafide (53.27%) at 5 mg/kg in vivo. And a remarkably elevated antitumor activity and a reduced toxicity are also observed for 5c at 5 mg/kg (65.90%). The upregulated p53 and the apoptotic cells (73.50%) indicate that the mechanism of 5c to induce apoptosis may result from its enhanced DNA damage. Further investigation indicates that in addition to target DNA, 5c can modulate the polyamine homeostasis by upregulating polyamine oxidase (PAO) in a different way from that of amonafide. And also by targeting PTs overexpressed in most of cancer cells, 5c downregulates the contents of Put, Spd, and Spm, which are in favor of suppressing fast-growing tumor cells. Our study implies a promising strategy for naphthalimide conjugates to treat hepatic carcinoma with notable activities and reduced toxicities at a low dosage.

Serendipitous Discovery of Leucine and Methionine Depletion Agents during the Search for Polyamine Transport Inhibitors

Targeting polyamine metabolism is a proven anticancer strategy. Cancers often escape the polyamine biosynthesis inhibitors by increased polyamine import. Therefore, there is much interest in identifying polyamine transport inhibitors (PTIs) to be used in combination therapies. In a search for new PTIs, we serendipitously discovered a LAT-1 efflux agonist, which induces intracellular depletion of methionine, leucine, spermidine, and spermine, but not putrescine. Because S-adenosylmethioninamine is made from methionine, a loss of intracellular methionine leads to an inability to biosynthesize spermidine, and spermine. Importantly, we found that this methionine-depletion approach to polyamine depletion could not be rescued by exogenous polyamines, thereby obviating the need for a PTI. Using ³H-leucine (the gold standard for LAT-1 transport studies) and JPH-203 (a specific LAT-1 inhibitor), we showed that the efflux agonist did not inhibit the uptake of extracellular leucine but instead facilitated the efflux of intracellular leucine pools.

Toward a Rational Design of Polyamine-Based Zinc-Chelating Agents for Cancer Therapies

In vitro viability assays against a representative panel of human cancer cell lines revealed that polyamines L1a and L5a displayed remarkable activity with IC₅₀ values in the micromolar range. Preliminary research indicated that both compounds promoted G1 cell cycle arrest followed by cellular senescence and apoptosis. The induction of apoptotic cell death involved loss of mitochondrial outer membrane permeability and activation of caspases 3/7. Interestingly, L1a and L5a failed to activate cellular DNA damage response. The high intracellular zinc-chelating capacity of both compounds, deduced from the metal-specific Zinquin assay and ZnL²⁺ stability constant values in solution, strongly supports their cytotoxicity. These data along with quantum mechanical studies have enabled to establish a precise structure-activity relationship. Moreover, L1a and L5a showed appropriate drug-likeness by in silico methods. Based on these promising results, L1a and L5a should be considered a new class of zinc-chelating anticancer agents that deserves further development.

Polyamine-Based Pt(IV) Prodrugs as Substrates for Polyamine Transporters Preferentially Accumulate in Cancer Metastases as DNA and Polyamine Metabolism Dual-Targeted Antimetastatic Agents

Diverse platinum drug candidates have been designed to improve inhibitory potency and overcome resistance for orthotopic tumors. However, the antimetastatic properties have rarely been reported. We herein report that homospermidineplatin (4a), a polyamine-Pt(IV) prodrug, can potently inhibit tumor growth in situ and reverse cisplatin resistance as expected, and more importantly, 4a displays remarkably elevated antimetastatic activity in vivo (65.7%), compared to those of cisplatin (27.0%) and oxaliplatin (19.6%). The underlying molecular mechanism indicates that in addition to targeting nuclear DNA, 4a can modulate polyamine metabolism and function in a manner different from that of cisplatin. By upregulating SSAT and PAO, 4a downregulates the concentrations of Put, Spd, and Spm, which favors the suppression of fast-growing tumor cells. Moreover, the p53/SSAT/β-catenin and PAO/ROS/GSH/GSH-Px pathways are involved in the inhibition of 4a-induced tumor metastasis. Our study implies a promising strategy for the design of platinum drugs for the treatment of terminal cancer.

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.

Synthesis and antiproliferative evaluation of some iron chelators as polyamine transporter targeting agents

A series of kojic acid derivatives based on monoamines, diamines, and triamines have been synthesized in good yield and purity. A spermidine (spd) rescue experiment was applied against MCF-7 cells to evaluate the polyamine transporter selectivity, and in vitro antiproliferative effects were determined against Hela and DU-145 cell lines. Overall, 5b showed the best selectivity for the polyamine transporter and antiproliferative effects. Therefore, the in-silico metabolism profile and ADMET properties of the title compounds were calculated by the PreADMET server. Additionally, physicochemical properties of ligands were predicted by using the Molinspiration online property calculation server.

A Novel Polyamine-Targeted Therapy for BRAF Mutant Melanoma Tumors

Mutant serine/threonine protein kinase B-Raf (BRAF) protein is expressed in over half of all melanoma tumors. Although BRAF inhibitors (BRAFi) elicit rapid anti-tumor responses in the majority of patients with mutant BRAF melanoma, the tumors inevitably relapse after a short time. We hypothesized that polyamines are essential for tumor survival in mutant BRAF melanomas. These tumors rely on both polyamine biosynthesis and an upregulated polyamine transport system (PTS) to maintain their high intracellular polyamine levels. We evaluated the effect of a novel arylpolyamine (AP) compound that is cytotoxic upon cellular entry via the increased PTS activity of melanoma cells with different BRAF mutational status. Mutant BRAF melanoma cells demonstrated greater PTS activity and increased sensitivity to AP compared to wild type BRAF (BRAF^WT) melanoma cells. Treatment with an inhibitor of polyamine biosynthesis, α-difluoromethylornithine (DFMO), further upregulated PTS activity in mutant BRAF cells and increased their sensitivity to AP. Furthermore, viability assays of 3D spheroid cultures of mutant BRAF melanoma cells demonstrated greater resistance to the BRAFi, PLX4720, compared to 2D monolayer cultures. However, co-treatment with AP restored the sensitivity of melanoma spheroids to PLX4720. These data indicate that mutant BRAF melanoma cells are more dependent on the PTS compared to BRAF^WT melanoma cells, resulting in greater sensitivity to the PTS-targeted cytotoxic AP compound.

A minimalistic approach to develop new anti-apicomplexa polyamines analogs

The development of new chemical entities against the major diseases caused by parasites is highly desired. A library of thirty diamines analogs following a minimalist approach and supported by chemoinformatics tools have been prepared and evaluated against apicomplexan parasites. Different member of the series of N,N'-disubstituted aliphatic diamines shown in vitro activities at submicromolar concentrations and high levels of selectivity against Toxoplasma gondii and in chloroquine-sensitive and resistant-strains of Plasmodium falciparum. In order to demonstrate the importance of the secondary amines, ten N,N,N',N'-tetrasubstituted aliphatic diamines derivatives were synthesized being considerably less active than their disubstituted counterpart. Theoretical studies were performed to establish the electronic factors that govern the activity of the compounds.

Investigation of Polyamine Metabolism and Homeostasis in Pancreatic Cancers

Pancreatic cancers are currently the fourth leading cause of cancer-related death and new therapies are desperately needed. The most common pancreatic cancer is pancreatic ductal adenocarcinoma (PDAC). This report describes the development of therapies, which effectively deplete PDAC cells of their required polyamine growth factors. Of all human tissues, the pancreas has the highest level of the native polyamine spermidine. To sustain their high growth rates, PDACs have altered polyamine metabolism, which is reflected in their high intracellular polyamine levels and their upregulated import of exogenous polyamines. To understand how these cancers respond to interventions that target their specific polyamine pools, L3.6pl human pancreatic cancer cells were challenged with specific inhibitors of polyamine biosynthesis. We found that pancreatic cell lines have excess polyamine pools, which they rebalance to address deficiencies induced by inhibitors of specific steps in polyamine biosynthesis (e.g., ornithine decarboxylase (ODC), spermidine synthase (SRM), and spermine synthase (SMS)). We also discovered that combination therapies targeting ODC, SMS, and polyamine import were the most effective in reducing intracellular polyamine pools and reducing PDAC cell growth. A combination therapy containing difluoromethylornithine (DFMO, an ODC inhibitor) and a polyamine transport inhibitor (PTI) were shown to significantly deplete intracellular polyamine pools. The additional presence of an SMS inhibitor as low as 100 nM was sufficient to further potentiate the DFMO + PTI treatment.

Synthesis and Bioevaluation of Macrocycle-Polyamine Conjugates as Cell Migration Inhibitors

The motuporamines are natural products isolated from the New Guinea sea sponge Xestospongia exigua. Dihydromotuporamine C contains a large macrocycle and an appended polyamine component and was shown to be both antimetastatic and cytotoxic to human L3.6pl pancreatic cancer cells. A series of macrocycle-polyamine conjugates were prepared, and the sequence of the polyamine component was varied to optimize the antimigration properties (as measured in L3.6pl cells) of this molecular class. A one-carbon spacer between the 15-membered carbocycle and the appended polyamine showed improved antimigration properties. A survey of different polyamine sequences containing two, three, or four carbon spacers revealed that the natural polyamine sequence (norspermidine, a 3,3-triamine) was superior in terms of inhibiting the migration of L3.6pl cells in vitro. An investigation of the respective ceramide and sphingomyelin populations in L3.6pl cells revealed that these molecules can modulate both ceramide and sphingomyelin pools in cells and inhibit cell migration.

A novel polyamine blockade therapy activates an anti-tumor immune response

Most tumors maintain elevated levels of polyamines to support their growth and survival. This study explores the anti-tumor effect of polyamine starvation via both inhibiting polyamine biosynthesis and blocking the upregulated import of polyamines into the tumor. We demonstrate that polyamine blockade therapy (PBT) co-treatment with both DFMO and a novel polyamine transport inhibitor, Trimer PTI, significantly inhibits tumor growth more than treatment with DFMO or the Trimer PTI alone. The anti-tumor effect of PBT was lost in mice where CD4⁺ and CD8⁺ T cells were antibody depleted, implying that PBT stimulates an anti-tumor immune effect that is T-cell dependent. The PBT anti-tumor effect was accompanied by an increase in granzyme B⁺, IFN-γ⁺ CD8⁺ T-cells and a decrease in immunosuppressive tumor infiltrating cells including Gr-1⁺CD11b⁺ myeloid derived suppressor cells (MDSCs), CD4⁺CD25⁺ Tregs, and CD206⁺F4/80⁺ M2 macrophages. Stimulation with tumor-specific peptides elicited elevated antigen-specific IFN-γ secretion in splenocytes from PBT-treated mice, indicating that PBT treatment stimulates the activation of T-cells in a tumor-specific manner. These data show that combined treatment with both DFMO and the Trimer PTI not only deprives polyamine-addicted tumor cells of polyamines, but also relieves polyamine-mediated immunosuppression in the tumor microenvironment, thus allowing the activation of tumoricidal T-cells.

Guanosine-5'-Monophosphate Polyamine Hybrid Hydrogels: Enhanced Gel Strength Probed by z-Spectroscopy

The self-assembling tendencies of guanosine-5'-monophosphate (GMP) can be drastically increased using polyamines, with potential applications in the production of biocompatible smart materials, as well as for the design of antitumor drugs based on G-quadruplex stabilization. Results from scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), rheology, and nuclear magnetic resonance (NMR) z-spectroscopy studies are presented.

Surface spermidine functionalized PEGylated poly(lactide-co-glycolide) nanoparticles for tumor-targeted drug delivery

SPD functionalized nanoparticles could target the delivery of a drug into tumor cells by binding specifically with PTS.

Polyamine transport inhibitors: design, synthesis, and combination therapies with difluoromethylornithine

The development of polyamine transport inhibitors (PTIs), in combination with the polyamine biosynthesis inhibitor difluoromethylornithine (DFMO), provides a method to target cancers with high polyamine requirements. The DFMO+PTI combination therapy results in sustained intracellular polyamine depletion and cell death. A series of substituted benzene derivatives were evaluated for their ability to inhibit the import of spermidine in DFMO-treated Chinese hamster ovary (CHO) and L3.6pl human pancreatic cancer cells. Several design features were discovered which strongly influenced PTI potency, sensitivity to amine oxidases, and cytotoxicity. These included changes in (a) the number of polyamine chains appended to the ring system, (b) the polyamine sequence, (c) the attachment linkage of the polyamine to the aryl core, and (d) the presence of a terminal N-methyl group. Of the series tested, the optimal design was N(1),N(1'),N(1″)-(benzene-1,3,5-triyltris(methylene))tris(N(4)-(4-(methylamino)butyl)butane-1,4-diamine, 6b, which contained three N-methylhomospermidine motifs. This PTI exhibited decreased sensitivity to amine oxidases and low toxicity as well as high potency (EC50 = 1.4 μM) in inhibiting the uptake of spermidine (1 μM) in DFMO-treated L3.6pl human pancreatic cancer cells.