Inhibition Of Polyamine Biosynthesis Research Articles

Discordant Effects of Polyamine Depletion by DENSpm and DFMO on β-cell Cytokine Stress and Diabetes Outcomes in Mice.

Type 1 diabetes (T1D) is an autoimmune disease leading to dysfunction and loss of insulin-secreting β cells. In β cells, polyamines have been implicated in causing cellular stress and dysfunction. An inhibitor of polyamine biosynthesis, difluoromethylornithine (DFMO), has been shown to delay T1D in mouse models and preserve β-cell function in humans with recent-onset T1D. Another small molecule, N1,N11-diethylnorspermine (DENSpm), both inhibits polyamine biosynthesis and accelerates polyamine metabolism and is being tested for efficacy in cancer clinical trials. In this study, we show that DENSpm depletes intracellular polyamines as effectively as DFMO in mouse β cells. RNA-sequencing analysis, however, suggests that the cellular responses to DENSpm and DFMO differ, with both showing effects on cellular proliferation but the latter showing additional effects on mRNA translation and protein-folding pathways. In the low-dose streptozotocin-induced mouse model of T1D, DENSpm, unlike DFMO, did not prevent or delay diabetes outcomes but did result in improvements in glucose tolerance and reductions in islet oxidative stress. In nonobese diabetic (NOD) mice, short-term DENSpm administration resulted in a slight reduction in insulitis and proinflammatory Th1 cells in the pancreatic lymph nodes. Longer term treatment resulted in a dose-dependent increase in mortality. Notwithstanding the efficacy of both DFMO and DENSpm in reducing potentially toxic polyamine levels in β cells, our results highlight the discordant T1D outcomes that result from differing mechanisms of polyamine depletion and, more importantly, that toxic effects of DENSpm may limit its utility in T1D treatment.

THU277 Deletion Or inhibition Of Ornithine Decarboxylase Protects Islet β-cell Health And Is Associated With Preserved Residual C-peptide In Persons With Recent Onset Type 1 Diabetes

Abstract Disclosure: B. Hammoud: None. L.A. DiMeglio: None. A. Kulkarni: None. A. Hull: None. S. Woerner: None. S. Cabrera: None. L.D. Mastrandrea: None. F. Ouyang: None. S.N. Perkins: None. C. Evans-Molina: None. T.L. Mastracci: None. S.A. Tersey: None. S. Sarkar: None. E. Nakayasu: None. B. Webb-Robertson: None. E. Gerner: None. R.G. Mirmira: None. E.K. Sims: None. Inhibition of polyamine biosynthesis using α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, reduces β cell stress and type 1 diabetes (T1D) incidence in preclinical animal models. However, the cellular and molecular mechanisms by which polyamines promote β-cell stress and the tolerability and effectiveness of their depletion by DFMO in humans with T1D remain unknown. We hypothesized that β-cell protection from stress occurs via cell-autonomous effects of polyamine depletion. To test this hypothesis, we generated β-cell specific knockout of ornithine decarboxylase in mice, performed comprehensive proteomics and transcriptomics on human islets treated with DFMO under inflammatory conditions in vitro, and performed a clinical study of DFMO tolerability, safety, and efficacy in persons with new-onset T1D. β-cell-specific deletion of the gene encoding ornithine decarboxylase in mice demonstrated protection of these animals against toxin (streptozotocin)-induced β-cell loss and hyperglycemia, implicating a cell-autonomous role for ornithine decarboxylase in β-cell stress. RNA sequencing and proteomics analyses of human islets exposed to a cytokine mix (1000 U/mL IFNγ + 50 U/mL IL-1β) +/- 5 mM DFMO identified 130 differentially regulated transcripts and 701 differentially regulated proteins. Pathway analysis implicated endosomal transport, vesicle organization and regulation of exocytosis, mRNA processing, and antigen cross presentation as mechanisms underlying DFMO effects on the islet response. To test DFMO in humans, we performed a 3-site randomized, placebo-controlled, double masked dose-ranging study of 3 months daily oral DFMO in persons with recent-onset T1D (<100 days). Dosing at 125, 250, 500, 750 or 1000 mg/m2/day was tested in 41 persons (12-34 y/o, 59% male, mean HbA1c 7.3%), with 6-10 participants/dosing group. Only mild and moderate adverse effects (AEs) were noted. Possible drug-related AEs included mild-moderate gastrointestinal symptoms, headache, upper respiratory infections, a pump site infection, and anemia. Urinary levels of the ODC product putrescine were decreased (p=0.05) in the 1000 mg/m2 dosing group. Compared to placebo, individuals receiving 750 and 1000 mg/m2 doses had significantly higher mixed-meal C-peptide area under the curve values at the 6-month post-randomization visit (p<0.05 vs. placebo). In conclusion, β-cell ODC inhibition protects β-cell health and function in the context of the proinflammatory T1D milieu. A 3-month course of oral DFMO was well tolerated with a favorable AE profile in persons with recent-onset T1D. Higher doses were associated with greater β-function compared to placebo. DFMO may have utility as a β-cell preservation therapy in recent-onset T1D. Presentation: Thursday, June 15, 2023

Difluoromethylornithine rebalances aberrant polyamine ratios in Snyder-Robinson syndrome.

Snyder-Robinson syndrome (SRS) results from mutations in spermine synthase (SMS), which converts the polyamine spermidine into spermine. Affecting primarily males, common manifestations of SRS include intellectual disability, osteoporosis, hypotonia, and seizures. Symptom management is the only treatment. Reduced SMS activity causes spermidine accumulation while spermine levels are reduced. The resulting exaggerated spermidine:spermine ratio is a biochemical hallmark of SRS that tends to correlate withsymptom severity. Our studies aim to pharmacologically manipulate polyamine metabolism to correct this imbalance as a therapeutic strategy for SRS. Here we report the repurposing of 2-difluoromethylornithine (DFMO), an FDA-approved inhibitor of polyamine biosynthesis, in rebalancing spermidine:spermine ratios in SRS patient cells. Mechanistic in vitro studies demonstrate that, while reducing spermidine biosynthesis, DFMO also stimulates the conversion of spermidine into spermine in hypomorphic SMS cells and induces uptake of exogenous spermine, altogether reducing the aberrant ratios. In a Drosophila SRS model characterized by reduced lifespan, DFMO improves longevity. As nearly all SRS patient mutations are hypomorphic, these studies form a strong foundation for translational studies with significant therapeutic potential.

MDB-03. DFMO AS A TREATMENT STRATEGY IN GROUP 3 MEDULLOBLASTOMA

Abstract Medulloblastomas, the most common malignant brain tumor in children, are subdivided into 4 major molecular subgroups. Among these, Group 3 medulloblastomas have one of the worst prognoses. We have recently identified the LIN28B pathway as being critically important in Group 3 medulloblastoma growth in vitro and in vivo. There are few targeted inhibitors of the LIN28B pathway and none are currently in clinical practice. Recently DFMO has been identified as an indirect inhibitor of the LIN28B-let-7 axis through its inhibition of polyamine biosynthesis. Another recent study identified ornithine, a precursor to polyamines, as being upregulated in MYC amplified Group 3 medulloblastoma. Importantly, DFMO has been demonstrated to achieve high concentrations in brain tumors in a rat glioma model with minimal systemic toxicity. Based on this we hypothesize that DFMO would be attractive agent for Group 3 medulloblastoma treatment as it would inhibit both polyamine synthesis and LIN28B and potentially achieve high tumor concentrations. Here we demonstrate that treatment with increasing concentration of DFMO leads to significant reduction in Group 3 medulloblastoma viability, increased apoptosis and reduced levels of LIN28B and its downstream targets. We are currently investigating whether this drug can effectively inhibit in vivo tumor growth in orthotopic xenograft models of Group 3 medulloblastoma.

Understanding the Polyamine and mTOR Pathway Interaction in Breast Cancer Cell Growth.

The polyamines putrescine, spermidine and spermine are nutrient-like polycationic molecules involved in metabolic processes and signaling pathways linked to cell growth and cancer. One important pathway is the PI3K/Akt pathway where studies have shown that polyamines mediate downstream growth effects. Downstream of PI3K/Akt is the mTOR signaling pathway, a nutrient-sensing pathway that regulate translation initiation through 4EBP1 and p70S6K phosphorylation and, along with the PI3K/Akt, is frequently dysregulated in breast cancer. In this study, we investigated the effect of intracellular polyamine modulation on mTORC1 downstream protein and general translation state in two breast cancer cell lines, MCF-7 and MDA-MB-231. The effect of mTORC1 pathway inhibition on the growth and intracellular polyamines was also measured. Results showed that polyamine modulation alters 4EBP1 and p70S6K phosphorylation and translation initiation in the breast cancer cells. mTOR siRNA gene knockdown also inhibited cell growth and decreased putrescine and spermidine content. Co-treatment of inhibitors of polyamine biosynthesis and mTORC1 pathway induced greater cytotoxicity and translation inhibition in the breast cancer cells. Taken together, these data suggest that polyamines promote cell growth in part through interaction with mTOR pathway. Similarly intracellular polyamine content appears to be linked to mTOR pathway regulation. Finally, dual inhibition of polyamine and mTOR pathways may provide therapeutic benefits in some breast cancers.

The role of polyamine metabolism in remodeling immune responses and blocking therapy within the tumor immune microenvironment.

The study of metabolism provides important information for understanding the biological basis of cancer cells and the defects of cancer treatment. Disorders of polyamine metabolism is a common metabolic change in cancer. With the deepening of understanding of polyamine metabolism, including molecular functions and changes in cancer, polyamine metabolism as a new anti-cancer strategy has become the focus of attention. There are many kinds of polyamine biosynthesis inhibitors and transport inhibitors, but not many drugs have been put into clinical application. Recent evidence shows that polyamine metabolism plays essential roles in remodeling the tumor immune microenvironment (TIME), particularly treatment of DFMO, an inhibitor of ODC, alters the immune cell population in the tumor microenvironment. Tumor immunosuppression is a major problem in cancer treatment. More and more studies have shown that the immunosuppressive effect of polyamines can help cancer cells to evade immune surveillance and promote tumor development and progression. Therefore, targeting polyamine metabolic pathways is expected to become a new avenue for immunotherapy for cancer.

Histone deacetylase-10 liberates spermidine to support polyamine homeostasis and tumor cell growth

Cytosolic histone deacetylase-10 (HDAC10) specifically deacetylates the modified polyamine N8-acetylspermidine (N8-AcSpd). Although intracellular concentrations of N8-AcSpd are low, extracellular sources can be abundant, particularly in the colonic lumen. Extracellular polyamines, including those from the diet and microbiota, can support tumor growth both locally and at distant sites. However, the contribution of N8-AcSpd in this context is unknown. We hypothesized that HDAC10, by converting N8- AcSpd to spermidine, may provide a source of this growth-supporting polyamine in circumstances of reduced polyamine biosynthesis, such as in polyamine-targeting anticancer therapies. Inhibitors of polyamine biosynthesis, including α-difluoromethylornithine (DFMO), inhibit tumor growth, but compensatory uptake of extracellular polyamines has limited their clinical success. Combining DFMO with inhibitors of polyamine uptake have improved the antitumor response. However, acetylated polyamines may use different transport machinery than the parent molecules. Here, we use CRISPR/Cas9-mediated HDAC10-knockout cell lines and HDAC10-specific inhibitors to investigate the contribution of HDAC10 in maintaining tumor cell proliferation. We demonstrate inhibition of cell growth by DFMO-associated polyamine depletion is successfully rescued by exogenous N8-AcSpd (at physiological concentrations), which is converted to spermidine and spermine, only in cell lines with HDAC10 activity. Furthermore, we show loss of HDAC10 prevents both restoration of polyamine levels and growth rescue, implicating HDAC10 in supporting polyamine-associated tumor growth. These data suggest the utility of HDAC10-specific inhibitors as an antitumor strategy that may have value in improving the response to polyamine-blocking therapies. Additionally, the cell-based assay developed in this study provides an inexpensive, high-throughput method of screening potentially selective HDAC10 inhibitors.

Abstract 5812: Histone deacetylase 10 supports tumor growth under polyamine-limiting conditions

Abstract Cytosolic histone deacetylase 10 (HDAC10) is specifically deacetylates the modified polyamine N8-acetylspermidine (N8-AcSpd). Although intracellular concentrations of N8-AcSpd are low, extracellular sources can be abundant, particularly in the colonic lumen. Extracellular polyamines, including those from the diet and microbiota, can support tumor growth both locally and at distant sites. However, the contribution of N8-AcSpd is unknown. We hypothesized that HDAC10, by converting N8-AcSpd to spermidine, may provide a source of this growth-supporting polyamine in circumstances of reduced polyamine biosynthesis, such as in polyamine-targeting, anticancer therapies. Inhibitors of polyamine biosynthesis, such as difluoromethylornithine (DFMO), inhibit tumor growth but with compensatory uptake of extracellular polyamines that have limited their clinical success. Combining DFMO with inhibitors of polyamine uptake have improved the antitumor response. However, acetylated polyamines may use different transport machinery than the parent molecules. The current study uses CRISPR/Cas9-mediated HDAC10-knockout cell lines and recently developed, selective HDAC10 inhibitors to investigate the contribution of HDAC10 in maintaining tumor cell proliferation. Inhibition of cell growth by DFMO-associated polyamine depletion is successfully rescued by the provision of physiological concentrations of exogenous N8-AcSpd, which is converted to spermidine and spermine, only in cell lines with HDAC10 activity. Loss of HDAC10 prevents both restoration of polyamine levels and growth rescue, implicating HDAC10 in supporting polyamine-associated tumor growth. These data suggest the utility of HDAC10-specific inhibitors as an antitumor strategy that may have particular value in improving the response to polyamine-blocking therapies. Citation Format: Tracy Murray Stewart, Raphael R. Steimbach, Jackson R. Foley, Aubry K. Miller, Robert A. Casero. Histone deacetylase 10 supports tumor growth under polyamine-limiting conditions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5812.

The KRAS-G12D mutation induces metabolic vulnerability in B-cell acute lymphoblastic leukemia

SummaryMutations in RAS pathway genes are highly prevalent in acute lymphoblastic leukemia (ALL). However, the effects of RAS mutations on ALL cell growth have not been experimentally characterized, and effective RAS-targeting therapies are being sought after. Here, we found that Reh ALL cells bearing the KRAS-G12D mutation showed increased proliferation rates in vitro but displayed severely compromised growth in mice. Exploring this divergence, proliferation assays with multiple ALL cell lines revealed that the KRAS-G12D rewired methionine and arginine metabolism. Isotope tracing results showed that KRAS-G12D promotes catabolism of methionine and arginine to support anabolism of polyamines and proline, respectively. Chemical inhibition of polyamine biosynthesis selectively killed KRAS-G12D B-ALL cells. Finally, chemically inhibiting AKT/mTOR signaling abrogated the altered amino acid metabolism and strongly promoted the in vivo growth of KRAS-G12D cells in B-ALL xenograft. Our study thus illustrates how hyperactivated AKT/mTOR signaling exerts distinct impacts on hematological malignancies vs. solid tumors.

Conjugated polyamines are involved in conformation stability of plasma membrane from maturing maize grain embryos under drought stress

Polyamines are closely associated with drought stress in plants. However, the function which polyamines play in the maturing maize grain under drought is not still clear. Especially, whether the conjugated polyamines are involved in H + -ATPase activity and conformation of plasma membrane remains to be answered. Therefore, in the study, the contents of conjugated polyamines, H + -ATPase activity and conformation of plasma membrane were detected with maturing grain embryos of two maize ( Zea mays L.) cultivars, which were different in drought stress-tolerance. Under drought stress, the cell plasmolysis of the drought-sensitive Xundan No. 22 cv. was more marked than that of the drought-tolerant Yedan No. 13 cv., while the increases in the contents of conjugated non-covalently spermidine and spermine, conjugated covalently putrescine and spermidine in plasma membrane from Yedan 13 were more obvious than those in Xundan 22. The results suggested that these conjugated polyamines might be involved in stability of plasma membrane. Furthermore, H + -ATPase activity in plasma membrane from Yedan 13 increased more significantly than that in Xundan 22, indicating that these conjugated polyamines were closely correlated with the activity of H + -ATPase. To justify further the inferences, the additional experiments with exogenous spermidine, spermine and polyamine biosynthesis inhibitors were carried out in the study. The results showed that the application of exogenous spermidine or spermine increased the levels of conjugated polyamines in plasma membrane, coupled with alleviating cell plasmolysis and increasing H + -ATPase activity. The application of inhibitors decreased the levels of conjugated polyamines, coupled with aggravating cell plasmolysis and decreasing H + -ATPase activity. From these results together, it could be concluded that non-covalently conjugated spermidine and spermine, conjugated covalently putrescine and spermidine in plasma membrane functioned in increasing H + -ATPase activity, mitigating cell plasmolysis and maintaining the plasma membrane conformation of the maturing maize grain embryos under drought stress. • Drought stress increased the levels of conjugated PAs in plasma membrane. • Conjugated PAs in plasma membrane mitigated cell plasmolysis induced by drought. • Conjugated PAs enhanced the H + -ATPase activity in plasma membrane under drought. • Conjugated PAs in plasma membrane were closely associated with drought tolerance.

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.

The discovery of indolone GW5074 during a comprehensive search for non-polyamine-based polyamine transport inhibitors.

The native polyamines putrescine, spermidine, and spermine are essential for cell development and proliferation. Polyamine levels are often increased in cancer tissues and polyamine depletion is a validated anticancer strategy. Cancer cell growth can be inhibited by the polyamine biosynthesis inhibitor difluoromethylornithine (DFMO), which inhibits ornithine decarboxylase (ODC), the rate-limiting enzyme in the polyamine biosynthesis pathway. Unfortunately, cells treated with DFMO often replenish their polyamine pools by importing polyamines from their environment. Several polyamine-based molecules have been developed to work as polyamine transport inhibitors (PTIs) and have been successfully used in combination with DFMO in several cancer models. Here, we present the first comprehensive search for potential non-polyamine based PTIs that work in human pancreatic cancer cells in vitro. After identifying and testing five different categories of compounds, we have identified the c-RAF inhibitor, GW5074, as a novel non-polyamine based PTI. GW5074 inhibited the uptake of all three native polyamines and a fluorescent-polyamine probe into human pancreatic cancer cells. GW5074 significantly reduced pancreatic cancer cell growth in vitro when treated in combination with DFMO and a rescuing dose of spermidine. Moreover, GW5074 alone reduced tumor growth when tested in a murine pancreatic cancer mouse model in vivo. In summary, GW5074 is a novel non-polyamine-based PTI that potentiates the anticancer activity of DFMO in pancreatic cancers.

The KRAS-G12D Mutation Induces Metabolic Vulnerability in B-Cell Acute Lymphoblastic Leukemia

Mutations in RAS pathway genes are highly prevalent in acute lymphoblastic leukemia (ALL). However, the effects of RAS mutations on ALL cell growth have not been experimentally characterized, and effective RAS-targeting therapies are being sought after. Here, we found that Reh ALL cells bearing the KRAS-G12D mutation showed increased proliferation rates in vitro but displayed severely compromised growth in mice. Exploring this divergence, proliferation assays with multiple ALL cell lines revealed that the KRAS-G12D mutation drives rewiring of methionine and arginine metabolism. Our isotope tracing results showed that mutant KRAS promotes catabolism of methionine and arginine to support anabolism of polyamines and proline, respectively. Chemical inhibition of polyamine biosynthesis selectively killed KRAS-G12D B-ALL cells, implicating the ornithine decarboxylase 1 (ODC1) enzyme as a potential vulnerability for RAS mutant B-ALL. Finally, chemically inhibiting AKT/mTOR signaling abrogated the altered amino acid metabolism and strongly promoted the in vivo growth of KRAS-G12D cells in B-ALL xenograft model. Our study thus illustrates how hyperactivated AKT/mTOR signaling exerts distinct impacts on hematological malignancies vs. solid tumors.

Difluoromethylornithine (DFMO), an Inhibitor of Polyamine Biosynthesis, and Antioxidant N-Acetylcysteine Potentiate Immune Response in Mice to the Recombinant Hepatitis C Virus NS5B Protein

Hepatitis C virus (HCV) is one of the main triggers of chronic liver disease. Despite tremendous progress in the HCV field, there is still no vaccine against this virus. Potential vaccines can be based on its recombinant proteins. To increase the humoral and, especially, cellular immune response to them, more effective adjuvants are needed. Here, we evaluated a panel of compounds as potential adjuvants using the HCV NS5B protein as an immunogen. These compounds included inhibitors of polyamine biosynthesis and urea cycle, the mTOR pathway, antioxidants, and cellular receptors. A pronounced stimulation of cell proliferation and interferon-γ (IFN-γ) secretion in response to concanavalin A was shown for antioxidant N-acetylcysteine (NAC), polyamine biosynthesis inhibitor 2-difluoromethylornithine (DFMO), and TLR9 agonist CpG ODN 1826 (CpG). Their usage during the immunization of mice with the recombinant NS5B protein significantly increased antibody titers, enhanced lymphocyte proliferation and IFN-γ production. NAC and CpG decreased relative Treg numbers; CpG increased the number of myeloid-derived suppressor cells (MDSCs), whereas neither NAC nor DFMO affected MDSC counts. NAC and DFMO suppressed NO and interleukin 10 (IL-10) production by splenocytes, while DFMO increased the levels of IL-12. This is the first evidence of immunomodulatory activity of NAC and DFMO during prophylactic immunization against infectious diseases.

Inhibition of Polyamine Biosynthesis Using Difluoromethylornithine Acts as a Potent Immune Modulator and Displays Therapeutic Synergy With PD-1-blockade.

Polyamines are known to play a significant role in cancer progression and treatment using difluoromethylornithine (DFMO), an inhibitor of polyamine biosynthesis, has shown some clinical promise. It is interesting to note that, while DFMO is directly cytostatic in vitro, recent work has suggested that it achieves its antitumor efficacy in vivo by enhancing adaptive antitumor immune responses. On the basis of these data, we hypothesized that DFMO might act as an immune sensitizer to increase tumor responsiveness to checkpoint blockade. To test this hypothesis, we treated tumors with DFMO, in either the presence or absence of additional PD-1 blockade, and subsequently analyzed their immunological and therapeutic responses. Our data demonstrates that treatment with DFMO significantly enhances both the viability and activation status of intratumoral CD8+ T cells, most likely through an indirect mechanism. When combined with PD-1 blockade, this increased viability resulted in unique proinflammatory cytokine profiles and transcriptomes within the tumor microenvironment and improved therapeutic outcomes. Taken together, these data suggest that DFMO might represent a potential immunomodulatory agent that can enhance current PD-1-based checkpoint therapies.

α-Difluoromethylornithine-Induced Cytostasis is Reversed by Exogenous Polyamines, Not by Thymidine Supplementation.

Polyamine spermidine is essential for the proliferation of eukaryotic cells. Administration of polyamine biosynthesis inhibitor α-difluoromethylornithine (DFMO) induces cytostasis that occurs in two phases; the early phase which can be reversed by spermidine, spermine, and some of their analogs, and the late phase which is characterized by practically complete depletion of cellular spermidine pool. The growth of cells at the late phase can be reversed by spermidine and by very few of its analogs, including (S)-1-methylspermidine. It was reported previously (Witherspoon et al. Cancer Discovery 3(9); 1072–81, 2013) that DFMO treatment leads to depletion of cellular thymidine pools, and that exogenous thymidine supplementation partially prevents DFMO-induced cytostasis without affecting intracellular polyamine pools in HT-29, SW480, and LoVo colorectal cancer cells. Here we show that thymidine did not prevent DFMO-induced cytostasis in DU145, LNCaP, MCF7, CaCo2, BT4C, SV40MES13, HepG2, HEK293, NIH3T3, ARPE19 or HT-29 cell lines, whereas administration of functionally active mimetic of spermidine, (S)-1-methylspermidine, did. Thus, the effect of thymidine seems to be specific only for certain cell lines. We conclude that decreased polyamine levels and possibly also distorted pools of folate-dependent metabolites mediate the anti-proliferative actions of DFMO. However, polyamines are necessary and sufficient to overcome DFMO-induced cytostasis, while thymidine is generally not.

Impact of nicotine pathway downregulation on polyamine biosynthesis and leaf ripening in tobacco.

Traditional breeding and molecular approaches have been used to develop tobacco varieties with reduced nicotine and secondary alkaloid levels. However, available low‐alkaloid tobacco varieties have impaired leaf quality likely due to the metabolic consequences of nicotine biosynthesis downregulation. Recently, we found evidence that the unbalanced crosstalk between nicotine and polyamine pathways is involved in impaired leaf ripening of a low‐alkaloid (LA) Burley 21 line having a mutation at the Nic1 and Nic2 loci, key biosynthetic regulators of nicotine biosynthesis. Since the Nic1 and Nic2 loci are comprised of several genes, all phenotypic changes seen in LA Burley 21 could be due to a mixture of genetics‐based responses. Here, we investigated the commercial burley variety TN90 LC and its transgenic versions with only one downregulated gene, either putrescine methyl transferase (PMT‐RNAi) or PR50‐protein (PR50‐RNAi). Nicotine levels of cured lamina of TN90 LC, TN90 PMT‐RNAi and TN90 PR50‐RNAi, were 70.5 ± 3.8, 2.4 ± 0.5, and 6.0 ± 1.1 mg/g dry weight, respectively. Low‐alkaloid transgenic lines showed delayed leaf maturation and impaired leaf quality. We analyzed polyamine contents and ripening markers in wild‐type TN90 control plants (WT) and the two transgenic lines. The ripening markers revealed that the PMT‐RNAi line showed the most pronounced impaired leaf maturation phenotype at harvest, characterized by higher chlorophyll (19%) and glucose (173%) contents and more leaf mesophyll cells per area (25%), while the ripening markers revealed that maturation of PR50‐RNAi plants was intermediate between PMT‐RNAi and WT lines. Comparative polyamine analyses showed an increase in free and conjugated polyamines in roots of both transgenic lines, this being most pronounced in the PMT‐RNAi plants. For PMT‐RNAi plants, there were further perturbations of polyamine content in the leaves, which mirrored the general phenotype, as PR50‐RNAi transgenic plants looked more similar to the WT than PMT‐RNAi transgenic plants. Activity of ornithine decarboxylase, the enzyme that catalyzes the committing step of polyamine biosynthesis, was significantly higher in roots and mature leaves of PMT‐RNAi plants in comparison to WT, while there was no increase observed for arginine decarboxylase. Treatment of both transgenic lines with polyamine biosynthesis inhibitors decreased the polyamine content and ameliorated the phenotype, confirming the intricate interplay of polyamine and nicotine biosynthesis in tobacco and the influence of this interplay on leaf ripening.

The Emerging Clinical Role of Spermine in Prostate Cancer.

Spermine, a member of polyamines, exists in all organisms and is essential for normal cell growth and function. It is highly expressed in the prostate compared with other organs and is detectable in urine, tissue, expressed prostatic secretions, and erythrocyte. A significant reduction of spermine level was observed in prostate cancer (PCa) tissue compared with benign prostate tissue, and the level of urinary spermine was also significantly lower in men with PCa. Decreased spermine level may be used as an indicator of malignant phenotype transformation from normal to malignant tissue in prostate. Studies targeting polyamines and key rate-limiting enzymes associated with spermine metabolism as a tool for PCa therapy and chemoprevention have been conducted with various polyamine biosynthesis inhibitors and polyamine analogues. The mechanism between spermine and PCa development are possibly related to the regulation of polyamine metabolism, cancer-driving pathways, oxidative stress, anticancer immunosurveillance, and apoptosis regulation. Although the specific mechanism of spermine in PCa development is still unclear, ongoing research in spermine metabolism and its association with PCa pathophysiology opens up new opportunities in the diagnostic and therapeutic roles of spermine in PCa management.

ATP13A3 is a major component of the enigmatic mammalian polyamine transport system

Polyamines, such as putrescine, spermidine, and spermine, are physiologically important polycations, but the transporters responsible for their uptake in mammalian cells remain poorly characterized. Here, we reveal a new component of the mammalian polyamine transport system using CHO-MG cells, a widely used model to study alternative polyamine uptake routes and characterize polyamine transport inhibitors for therapy. CHO-MG cells present polyamine uptake deficiency and resistance to a toxic polyamine biosynthesis inhibitor methylglyoxal bis-(guanylhydrazone) (MGBG), but the molecular defects responsible for these cellular characteristics remain unknown. By genome sequencing of CHO-MG cells, we identified mutations in an unexplored gene, ATP13A3, and found disturbed mRNA and protein expression. ATP13A3 encodes for an orphan P5B-ATPase (ATP13A3), a P-type transport ATPase that represents a candidate polyamine transporter. Interestingly, ATP13A3 complemented the putrescine transport deficiency and MGBG resistance of CHO-MG cells, whereas its knockdown in WT cells induced a CHO-MG phenotype demonstrated as a decrease in putrescine uptake and MGBG sensitivity. Taken together, our findings identify ATP13A3, which has been previously genetically linked with pulmonary arterial hypertension, as a major component of the mammalian polyamine transport system that confers sensitivity to MGBG.

Tpo3 and dur3, Aspergillus fumigatus Plasma Membrane Regulators of Polyamines, Regulate Polyamine Homeostasis and Susceptibility to Itraconazole.

Aspergillus fumigatus is a well-known opportunistic pathogen that causes invasive aspergillosis (IA) infections, which have high mortality rates in immunosuppressed individuals. Long-term antifungal drug azole use in clinical treatment and agriculture results in loss of efficacy or drug resistance. Drug resistance is related to cellular metabolites and the corresponding gene transcription. In this study, through untargeted metabolomics and transcriptomics under itraconazole (ITC) treatment, we identified two plasma membrane-localized polyamine regulators tpo3 and dur3, which were important for polyamine homeostasis and susceptibility to ITC in A. fumigatus. In the absence of tpo3 and/or dur3, the levels of cytoplasmic polyamines had a moderate increase, which enhanced the tolerance of A. fumigatus to ITC. In comparison, overexpression of tpo3 or dur3 induced a drastic increase in polyamines, which increased the sensitivity of A. fumigatus to ITC. Further analysis revealed that polyamines concentration-dependently affected the susceptibility of A. fumigatus to ITC by scavenging reactive oxygen species (ROS) at a moderate concentration and promoting the production of ROS at a high concentration rather than regulating drug transport. Moreover, inhibition of polyamine biosynthesis reduced the intracellular polyamine content, resulted in accumulation of ROS and enhanced the antifungal activity of ITC. Interestingly, A. fumigatus produces much lower levels of ROS under voriconazole (VOC) treatment than under ITC-treatment. Accordingly, our study established the link among the polyamine regulators tpo3 and dur3, polyamine homeostasis, ROS content, and ITC susceptibility in A. fumigatus.