Impaired polyamine metabolism causes behavioral and neuroanatomical defects in a mouse model of Snyder-Robinson Syndrome

Snyder-Robinson Syndrome (SRS) is a rare X-linked recessive disorder caused by a mutation in the SMS gene encoding spermine synthase and aberrant polyamine metabolism. SRS is characterized by intellectual disability, thin habitus, seizure, low muscle tone/hypotonia, and osteoporosis. Progress towards understanding and treating SRS requires a model that recapitulates human mutations and disease presentations. Here, we evaluated molecular and neurological presentations in the G56S mouse model carrying a missense mutation in the Sms gene. The lack of SMS protein in the G56S mice resulted in increased spermidine/spermine ratio, failure to thrive, short stature, and reduced bone density. They showed impaired learning capacity, increased anxiety, reduced mobility, and heightened fear responses, accompanied by reduced total and regional brain volumes. Furthermore, impaired mitochondrial oxidative phosphorylation was evident in G56S cerebral cortex, G56S fibroblasts, and Sms-null hippocampal cells, and may serve as a future therapeutic target. Collectively, our study establishes the suitability of the G56S mice as a preclinical model for SRS and provides a set of molecular and functional outcome measures that can be used to evaluate therapeutic interventions for SRS.

LSD1 inhibition suppresses ASCL1 and de-represses YAP1 to drive potent activity against neuroendocrine prostate cancer

Lysine-specific demethylase 1 (LSD1 or KDM1A ) has emerged as a critical mediator of tumor progression in metastatic castration-resistant prostate cancer (mCRPC). Among mCRPC subtypes, neuroendocrine prostate cancer (NEPC) is an exceptionally aggressive variant driven by lineage plasticity, an adaptive resistance mechanism to androgen receptor axis-targeted therapies. Our study shows that LSD1 expression is elevated in NEPC and associated with unfavorable clinical outcomes. Using genetic approaches, we validated the on-target effects of LSD1 inhibition across various models. We investigated the therapeutic potential of bomedemstat, an orally bioavailable, irreversible LSD1 inhibitor with low nanomolar potency. Our findings demonstrate potent antitumor activity against CRPC models, including tumor regressions in NEPC patient-derived xenografts. Mechanistically, our study uncovers that LSD1 inhibition suppresses the neuronal transcriptional program by downregulating ASCL1 through disrupting LSD1:INSM1 interactions and de-repressing YAP1 silencing. Our data support the clinical development of LSD1 inhibitors for treating CRPC - especially the aggressive NE phenotype.

Statement of Significance

Neuroendocrine prostate cancer presents a clinical challenge due to the lack of effective treatments. Our research demonstrates that bomedemstat, a potent and selective LSD1 inhibitor, effectively combats neuroendocrine prostate cancer by downregulating the ASCL1- dependent NE transcriptional program and re-expressing YAP1.

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 with symptom 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.

Polyamine transport inhibition and cisplatin synergistically enhance tumor control through oxidative stress in murine head and neck cancer models

Background

Surgery and/or platinum-based chemoradiation remain standard of care for patients with head and neck squamous cell carcinoma (HNSCC). While these therapies are effective in a subset of patients, a substantial proportion experience recurrence or treatment resistance. As cisplatin mediates cytotoxicity through oxidative stress while polyamines play a role in redox regulation, we posited that combining cisplatin with polyamine transport inhibitor, AMXT-1501, would increase oxidative stress and tumor cell death in HNSCC cells.

Methods

Cell proliferation was measured in syngeneic mouse HNSCC cell lines treated with cisplatin ± AMXT-1501. Synergy was determined by administering cisplatin and AMXT-1501 at a ratio of 1:10 to cancer cells in vitro . Cancer cells were transferred onto mouse flanks to test the efficacy of treatments in vivo . Reactive oxygen species (ROS) were measured. Cellular apoptosis was measured with flow cytometry using Annexin V/PI staining. High-performance liquid chromatography (HPLC) was used to quantify polyamines in cell lines. Cell viability and ROS were measured in the presence of exogenous cationic amino acids.

Results

The combination of cisplatin and AMXT-1501 synergize in vitro on HNSCC cell lines. In vivo combination treatment resulted in tumor growth inhibition greater than either treatment individually. The combination treatment increased ROS production and induced apoptotic cell death. HPLC revealed the synergistic mechanism was independent of intracellular polyamine levels. Supplementation of cationic amino acids partially rescued cancer cell viability and reduced ROS.

Conclusion

AMXT-1501 enhances the cytotoxic effects of cisplatin in vitro and in vivo in aggressive HNSCC cell lines through a polyamine-independent mechanism.

Deoxyhypusine synthase mutations alter the post-translational modification of eukaryotic initiation factor 5A resulting in impaired human and mouse neural homeostasis

DHPS deficiency is a rare genetic disease caused by biallelic hypomorphic variants in the Deoxyhypusine synthase (DHPS) gene. The DHPS enzyme functions in mRNA translation by catalyzing the post-translational modification, and therefore activation, of eukaryotic initiation factor 5A (eIF5A). The observed clinical outcomes associated with human mutations in DHPS include developmental delay, intellectual disability, and seizures. Therefore, to increase our understanding of this rare disease, it is critical to determine the mechanisms by which mutations in DHPS alter neurodevelopment. In this study, we have generated patient-derived lymphoblast cell lines and demonstrated that human DHPS variants alter DHPS protein abundance and impair enzyme function. Moreover, we observe a shift in the abundance of the post-translationally modified forms of eIF5A; specifically, an increase in the nuclear localized acetylated form (eIF5A^AcK47) and concomitant decrease in the cytoplasmic localized hypusinated form (eIF5A^HYP). Generation and characterization of a mouse model with a genetic deletion of Dhps in the brain at birth shows that loss of hypusine biosynthesis impacts neuronal function due to impaired eIF5A^HYP-dependent mRNA translation; this translation defect results in altered expression of proteins required for proper neuronal development and function. This study reveals new insight into the biological consequences and molecular impact of human DHPS deficiency and provides valuable information toward the goal of developing treatment strategies for this rare disease.

Difluoromethylornithine rebalances aberrant polyamine ratios in Snyder-Robinson syndrome: mechanism of action and therapeutic potential

Snyder-Robinson Syndrome (SRS) is caused by mutations in the spermine synthase (SMS) gene, the enzyme product of which converts the polyamine spermidine into spermine. Affecting primarily males, common manifestations of SRS include intellectual disability, osteoporosis, hypotonic musculature, and seizures, along with other more variable symptoms. Currently, medical management focuses on treating these symptoms without addressing the underlying molecular cause of the disease. Reduced SMS catalytic activity in cells of SRS patients causes the accumulation of spermidine, while spermine levels are reduced. The resulting exaggeration in spermidine-to-spermine ratio is a biochemical hallmark of SRS that tends to correlate with symptom severity in the patient. Our studies aim to pharmacologically manipulate polyamine metabolism to correct this polyamine imbalance and investigate the potential of this approach as a therapeutic strategy for affected individuals. Here we report the use of difluoromethylornithine (DFMO; eflornithine), an FDA-approved inhibitor of polyamine biosynthesis, in re-establishing normal spermidine-to-spermine ratios in SRS patient cells. Through mechanistic studies, we demonstrate that, while reducing spermidine biosynthesis, DFMO also stimulates the conversion of existing spermidine into spermine in cell lines with hypomorphic variants of SMS. Further, DFMO treatment induces a compensatory uptake of exogenous polyamines, including spermine and spermine mimetics, cooperatively reducing spermidine and increasing spermine levels. In a Drosophila SRS model characterized by reduced lifespan, adding DFMO to the feed extended lifespan. As nearly all known SRS patient mutations are hypomorphic, these studies form a foundation for future translational studies with significant therapeutic potential.

Abstract 4944: Evaluating the efficacy of spermine analogue ivospemin (SBP-101) in combination with chemotherapy in ovarian cancer

Polyamines are small cationic alkylamines that play critical roles in essential cellular processes governing growth and proliferation. As such, cancers are fully reliant on increased polyamine pools maintained through dysregulation of polyamine metabolism. Pharmaceutical modulation of polyamine metabolism is a promising avenue in cancer therapeutics and has been attempted with enzyme inhibitors, including DFMO (difluoromethylornithine), and polyamine analogues. Ivospemin is a spermine analogue that has shown efficacy in slowing pancreatic and ovarian tumor progression both in vitro and in vivo and demonstrated encouraging results in pancreatic cancer clinical trials. We have shown that ivospemin decreases polyamine content through depression of the activity of the polyamine biosynthetic enzyme ornithine decarboxylase (ODC) in a variety of cancer cell lines. Treatment of the VDID8+ murine ovarian cancer model with ivospemin resulted in a marked increase in survival. Here we examine the potential of combining ivospemin and chemotherapeutic agents that are used to treat cisplatin-resistant ovarian cancer. Treatment with gemcitabine, topotecan, and doxorubicin increased the in vitro toxicity of ivospemin, while paclitaxel and docetaxel did not have any added benefit over ivospemin alone. Using the VDID8+ model, we further evaluated the efficacy of ivospemin in combination with gemcitabine, topotecan, and doxorubicin in vivo. Ascites fluid was used as a marker of tumor burden and evaluated for polyamine content. Addition of ivospemin improved the survival of mice treated with any of the three chemotherapeutics. The ivospemin and doxorubicin combination mice had the greatest median survival time; this combination is being further evaluated in mechanistic studies and additional murine studies. Ovarian cancers have extremely immunosuppressive tumor microenvironments (TME) and metabolic reprogramming of the TME to reduce immunosuppressive phenotypes is a promising approach for treatment. Sustained elevation of polyamine levels supports an immunosuppressive TME, and evidence suggests that pharmacologic depletion of polyamines may reduce immunosuppressive phenotypes. DFMO treatment in the immunosuppressive VDID8+ model influences the immune cells of the TME, and we therefore are investigating the combination of ivospemin and DFMO in ovarian cancer. In addition to the cooperativity of ivospemin and chemotherapeutic agents, we have observed a cooperative antiproliferative response in ovarian cancer cells following DFMO and ivospemin cotreatment. Together, these studies suggest the potential of polyamine modulation by ivospemin and DFMO in combination with standard of care chemotherapy. Future studies will determine influences on the immune microenvironment and will evaluate cooperativity between ivospemin, DFMO, and chemotherapy.

Citation Format: Cassandra E. Holbert, Jackson R. Foley, Tracy Murray Stewart, Michael J. Walker, Elizabeth Bruckheimer, Jennifer K. Simpson, Robert A. Casero. Evaluating the efficacy of spermine analogue ivospemin (SBP-101) in combination with chemotherapy in ovarian cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4944.

Reduction of Spermine Synthase Suppresses Tau Accumulation Through Autophagy Modulation in Tauopathy

Tauopathy, including Alzheimer Disease (AD), is characterized by Tau protein accumulation and autophagy dysregulation. Emerging evidence connects polyamine metabolism with the autophagy pathway, however the role of polyamines in Tauopathy remains unclear. In the present study we investigated the role of spermine synthase (SMS) in autophagy regulation and tau protein processing in Drosophila and human cellular models of Tauopathy. Our previous study showed that Drosophila spermine synthase (dSms) deficiency impairs lysosomal function and blocks autophagy flux. Interestingly, partial loss-of-function of SMS in heterozygous dSms flies extends lifespan and improves the climbing performance of flies with human Tau (hTau) overexpression. Mechanistic analysis showed that heterozygous loss-of-function mutation of dSms reduces hTau protein accumulation through enhancing autophagic flux. Measurement of polyamine levels detected a mild elevation of spermidine in flies with heterozygous loss of dSms. SMS knock-down in human neuronal or glial cells also upregulates autophagic flux and reduces Tau protein accumulation. Proteomics analysis of postmortem brain tissue from AD patients showed a significant albeit modest elevation of SMS protein level in AD-relevant brain regions compared to that of control brains consistently across several datasets. Taken together, our study uncovers a correlation between SMS protein level and AD pathogenesis and reveals that SMS reduction upregulates autophagy, promotes Tau clearance, and reduces Tau protein accumulation. These findings provide a new potential therapeutic target of Tauopathy.

Impaired polyamine metabolism causes behavioral and neuroanatomical defects in a novel mouse model of Snyder-Robinson Syndrome

Polyamines (putrescine, spermidine, and spermine) are essential molecules for normal cellular functions and are subject to strict metabolic regulation. Mutations in the gene encoding spermine synthase (SMS) lead to accumulation of spermidine in an X-linked recessive disorder known as Snyder-Robinson syndrome (SRS). Presently, no treatments exist for this rare disease that manifests with a spectrum of symptoms including intellectual disability, developmental delay, thin habitus, and low muscle tone. The development of therapeutic interventions for SRS will require a suitable disease-specific animal model that recapitulates many of the abnormalities observed in patients. Here, we characterize the molecular, behavioral, and neuroanatomical features of a mouse model with a missense mutation in Sms gene that results in a glycine-to-serine substitution at position 56 (G56S) of the SMS protein. Mice harboring this mutation exhibit a complete loss of SMS protein and elevated spermidine/spermine ratio in skeletal muscles and the brain. In addition, the G56S mice demonstrate increased anxiety, impaired learning, and decreased explorative behavior in fear conditioning, Morris water maze, and open field tests, respectively. Furthermore, these mice failed to gain weight over time and exhibit abnormalities in brain structure and bone density. Transcriptomic analysis of the cerebral cortex revealed downregulation of genes associated with mitochondrial oxidative phosphorylation and ribosomal protein synthesis. Our findings also revealed impaired mitochondrial bioenergetics in fibroblasts isolated from the G56S mice, indicating a correlation between these processes in the affected mice. Collectively, our findings establish the first in-depth characterization of an SRS preclinical mouse model that identifies cellular processes that could be targeted for future therapeutic development.

Aza-SAHA Derivatives Are Selective Histone Deacetylase 10 Chemical Probes That Inhibit Polyamine Deacetylation and Phenocopy HDAC10 Knockout

We report the first well-characterized selective chemical probe for histone deacetylase 10 (HDAC10) with unprecedented selectivity over other HDAC isozymes. HDAC10 deacetylates polyamines and has a distinct substrate specificity, making it unique among the 11 zinc-dependent HDAC hydrolases. Taking inspiration from HDAC10 polyamine substrates, we systematically inserted an amino group ("aza-scan") into the hexyl linker moiety of the approved drug Vorinostat (SAHA). This one-atom replacement (C→N) transformed SAHA from an unselective pan-HDAC inhibitor into a specific HDAC10 inhibitor. Optimization of the aza-SAHA structure yielded the HDAC10 chemical probe DKFZ-748, with potency and selectivity demonstrated by cellular and biochemical target engagement, as well as thermal shift assays. Cocrystal structures of our aza-SAHA derivatives with HDAC10 provide a structural rationale for potency, and chemoproteomic profiling confirmed exquisite cellular HDAC10-selectivity of DKFZ-748 across the target landscape of HDAC drugs. Treatment of cells with DKFZ-748, followed by quantification of selected polyamines, validated for the first time the suspected cellular function of HDAC10 as a polyamine deacetylase. Finally, in a polyamine-limiting in vitro tumor model, DKFZ-748 showed dose-dependent growth inhibition of HeLa cells. We expect DKFZ-748 and related probes to enable further studies on the enigmatic biology of HDAC10 and acetylated polyamines in both physiological and pathological settings.

Elucidating the Role of Chmp1 Overexpression in the Transport of Polyamines in Drosophila melanogaster

Polyamines are small organic cations that are essential for many biological processes such as cell proliferation and cell cycle progression. While the metabolism of polyamines has been well studied, the mechanisms by which polyamines are transported into and out of cells are poorly understood. Here, we describe a novel role of Chmp1, a vesicular trafficking protein, in the transport of polyamines using a well-defined leg imaginal disc assay in Drosophila melanogaster larvae. We show that Chmp1 overexpression had no effect on leg development in Drosophila, but does attenuate the negative impact on leg development of Ant44, a cytotoxic drug known to enter cells through the polyamine transport system (PTS), suggesting that the overexpression of Chmp1 downregulated the PTS. Moreover, we showed that the addition of spermine did not rescue the leg development in Chmp1-overexpressing leg discs treated with difluoromethylornithine (DFMO), an inhibitor of polyamine metabolism, while putrescine and spermidine did, suggesting that there may be unique mechanisms of import for individual polyamines. Thus, our data provide novel insight into the underlying mechanisms that are involved in polyamine transport and highlight the utility of the Drosophila imaginal disc assay as a fast and easy way to study potential players involved in the PTS.

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.

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.

Phenylbutyrate modulates polyamine acetylase and ameliorates Snyder-Robinson syndrome in a Drosophila model and patient cells

Polyamine dysregulation plays key roles in a broad range of human diseases from cancer to neurodegeneration. Snyder-Robinson syndrome (SRS) is the first known genetic disorder of the polyamine pathway, caused by X-linked recessive loss-of-function mutations in spermine synthase. In the Drosophila SRS model, altered spermidine/spermine balance has been associated with increased generation of ROS and aldehydes, consistent with elevated spermidine catabolism. These toxic byproducts cause mitochondrial and lysosomal dysfunction, which are also observed in cells from SRS patients. No efficient therapy is available. We explored the biochemical mechanism and discovered acetyl-CoA reduction and altered protein acetylation as potentially novel pathomechanisms of SRS. We repurposed the FDA-approved drug phenylbutyrate (PBA) to treat SRS using an in vivo Drosophila model and patient fibroblast cell models. PBA treatment significantly restored the function of mitochondria and autolysosomes and extended life span in vivo in the Drosophila SRS model. Treating fibroblasts of patients with SRS with PBA ameliorated autolysosome dysfunction. We further explored the mechanism of drug action and found that PBA downregulates the first and rate-limiting spermidine catabolic enzyme spermidine/spermine N1-acetyltransferase 1 (SAT1), reduces the production of toxic metabolites, and inhibits the reduction of the substrate acetyl-CoA. Taken together, we revealed PBA as a potential modulator of SAT1 and acetyl-CoA levels and propose PBA as a therapy for SRS and potentially other polyamine dysregulation-related diseases.

Interrogation of T Cell-Enriched Tumors Reveals Prognostic and Immunotherapeutic Implications of Polyamine Metabolism

Metabolic features of the tumor microenvironment (TME) antagonize anti-tumor immunity. We hypothesized that T cell infiltrated tumors with a known antigen should exhibit superior clinical outcomes, though some fare worse given unfavorable metabolic features leveraging T cell-infiltrated (Thi), human papillomavirus-related (HPV+) head and neck squamous cell carcinomas (HNSC) to test this hypothesis. Expression of 2,520 metabolic genes were analyzed among Thi HPV+ HNSCs stratified by high-risk molecular subtype. RNAseq data from The Cancer Genome Atlas (TCGA; 10 cancer types), single cell RNAseq data, and an immunotherapy-treated melanoma cohort were used to test the association between metabolic gene expression and clinical outcomes and contribution of tumor versus stromal cells to metabolic gene expression. Polyamine (PA) metabolism genes were overexpressed in high-risk, Thi HPV+ HNSCs. Genes involved in PA biosynthesis and transport were associated with T cell infiltration, recurrent or persistent cancer, overall survival status, primary site, molecular subtype, and MYC genomic alterations. PA biogenesis gene sets were associated with tumor intrinsic features while myeloid cells in HPV+ HNSCs were enriched in PA catabolism, regulatory, transport, putrescine, and spermidine gene set expression. PA gene set expression also correlated with IFNγ or cytotoxic T cell ssGSEA scores across TCGA tumor types. PA transport ssGSEA scores were associated with poor survival whereas putrescine ssGSEA scores portended better survival for several tumor types. Thi melanomas enriched in PA synthesis or combined gene set expression exhibited worse anti-PD-1 responses. These data address hurdles to anti-tumor immunity warranting further investigation of divergent polyamine metabolism in the TME.

Expanded Potential of the Polyamine Analogue SBP-101 (Diethyl Dihydroxyhomospermine) as a Modulator of Polyamine Metabolism and Cancer Therapeutic

Naturally occurring polyamines are absolutely required for cellular growth and proliferation. Many neoplastic cells are reliant on elevated polyamine levels and maintain these levels through dysregulated polyamine metabolism. The modulation of polyamine metabolism is thus a promising avenue for cancer therapeutics and has been attempted with numerous molecules, including enzyme inhibitors and polyamine analogues. SBP-101 (diethyl dihydroxyhomospermine) is a spermine analogue that has shown efficacy in slowing pancreatic tumor progression both in vitro and in vivo; however, the mechanisms underlying these effects remain unclear. We determined the effects of the SBP-101 treatment on a variety of cancer cell types in vitro, including lung, pancreatic, and ovarian. We evaluated the activity of enzymes involved in polyamine metabolism and the effect on intracellular polyamine pools following the SBP-101 treatment. The SBP-101 treatment produced a modest but variable increase in polyamine catabolism; however, a robust downregulation of the activity of the biosynthetic enzyme, ornithine decarboxylase (ODC), was seen across all of the cell types studied and indicates that SBP-101 likely exerts its effect predominately through the downregulation of ODC, with a minor upregulation of catabolism. Our in vitro work indicated that SBP-101 was most toxic in the tested ovarian cell lines. Therefore, we evaluated the efficacy of SBP-101 as a monotherapy in the immunosuppressive VDID8⁺ murine ovarian model. Mice treated with SBP-101 demonstrated a delay in tumor progression, a decrease in the overall tumor burden, and a marked increase in median survival.

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

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.

Polyamine Depletion Strategies in Cancer: Remodeling the Tumor Immune Microenvironment to Enhance Anti-Tumor Responses

Polyamine biosynthesis is frequently dysregulated in cancers, and enhanced flux increases intracellular polyamines necessary for promoting cell growth, proliferation, and function. Polyamine depletion strategies demonstrate efficacy in reducing tumor growth and increasing survival in animal models of cancer; however, mechanistically, the cell-intrinsic and cell-extrinsic alterations within the tumor microenvironment underlying positive treatment outcomes are not well understood. Recently, investigators have demonstrated that co-targeting polyamine biosynthesis and transport alters the immune landscape. Although the polyamine synthesis-targeting drug 2-difluoromethylornithine (DFMO) is well tolerated in humans and is FDA-approved for African trypanosomiasis, its clinical benefit in treating established cancers has not yet been fully realized; however, combination therapies targeting compensatory mechanisms have shown tolerability and efficacy in animal models and are currently being tested in clinical trials. As demonstrated in pre-clinical models, polyamine blocking therapy (PBT) reduces immunosuppression in the tumor microenvironment and enhances the therapeutic efficacy of immune checkpoint blockade (ICB). Thus, DFMO may sensitize tumors to other therapeutics, including immunotherapies and chemotherapies.

Hyaluronate-coated perfluoroalkyl polyamine prodrugs as bioactive siRNA delivery systems for the treatment of peritoneal cancers

RNA interference (RNAi) is an emerging therapeutic modality for cancer, which remains in critical need of effective delivery vectors due to the unfavorable biopharmaceutical properties of small RNAs. Polyamines are essential for functioning of mammalian cells. Dysregulated polyamine metabolism is found in many cancers and has been an attractive therapeutic target in combination therapies. Combination therapies based on drugs that affect polyamine metabolism and nucleic acids promise to enhance anticancer activity due to a cooperative effect on multiple oncogenic pathways. Here, we report bioactive polycationic prodrug (F-PaP) based on an anticancer polyamine analog bisethylnorspermine (BENSpm) modified with perfluoroalkyl moieties. Following encapsulation of siRNA, F-PaP/siRNA nanoparticles were coated with hyaluronic acid (HA) to form ternary nanoparticles HA@F-PaP/siRNA. The presence of perfluoroalkyl moieties and HA reduced cell membrane toxicity and improved stability of the particles with cooperatively enhanced siRNA delivery in pancreatic and colon cancer cell lines. We then tested a therapeutic hypothesis that combining BENSpm with siRNA silencing of polo-like kinase 1 (PLK1) would result in cooperative cancer cell killing. HA@F-PaP/siPLK1 induced polyamine catabolism and cell cycle arrest, leading to enhanced apoptosis in the tested cell lines. The HA-coated nanoparticles facilitated tumor accumulation and contributed to strong tumor inhibition and favorable modulation of the immune tumor microenvironment in orthotopic pancreatic cancer model. Combination anticancer therapy with polyamine prodrug-mediated delivery of siRNA. Hyaluronate coating of the siRNA nanoparticles facilitates selective accumulation in orthotopic pancreatic tumors. Perfluoroalkyl conjugation reduces toxicity and improves gene silencing effect. Nanoparticle treatment induces polyamine catabolism and cell cycle arrest leading to strong tumor inhibition and favorable modulation of immune tumor microenvironment.

A new class of cytotoxic agents targets tubulin and disrupts microtubule dynamics

Despite the advances in treatment strategies, cancer is still the second leading cause of death in the USA. A majority of the currently used cancer drugs have limitations in their clinical use due to poor selectivity, toxic side effects and multiple drug resistance, warranting the development of new anticancer drugs of different mechanisms of action. Here we describe the design, synthesis and initial biological evaluation of a new class of antimitotic agents that modulate tubulin polymerization. Structurally, these compounds are chalcone mimics containing a 1-(1H-imidazol-2-yl)ethan-1-one moiety, which was initially introduced to act as a metal-binding group and inhibit histone deacetylase enzymes. Although several analogues selectively inhibited purified HDAC8 with IC₅₀ values in low micromolar range, tissue culture studies suggest that HDAC inhibition is not a major mechanism responsible for cytotoxicity. The compounds demonstrated cell growth inhibition with GI₅₀ values of upper nanomolar to low micromolar potency with significant selectively for cancer over normal cells. Interestingly, several compounds arrested HeLaM cells in mitosis and seem to target tubulin to cause mitotic arrest. For example, when combined with inhibitors of Aurora B kinase, they led to dramatic disassembly of the mitotic spindle. In-vitro tubulin polymerization studies showed that the compounds reduced the rate of polymerization of microtubules during the elongation phase and lowered the amount of polymerized tubulin during the plateau phase. Finally, in silico docking studies identified binding of IPE-7 to the colchicine site with similar affinity as the test compound D64131. These compounds represent a new antimitotic pharmacophore with limited HDAC inhibitory activity.

Spermidine is not an independent factor regulating limb muscle mass in mice following androgen deprivation

Maintaining a critical amount of skeletal muscle mass is linked to reduced morbidity and mortality. In males, testicular androgens regulate muscle mass with a loss of androgens being critical as it is associated with muscle atrophy. Atrophy of the limb muscles is particularly important, but the pathways by which androgens regulate limb muscle mass remain equivocal. We used microarray analysis to identify changes to genes involved with polyamine metabolism in the tibialis anterior (TA) muscle of castrated mice. Of the polyamines, the concentration of spermidine (SPD) was significantly reduced in the TA of castrated mice. To assess whether SPD was an independent factor by which androgens regulate limb muscle mass, we treated castrated mice with SPD for 8 weeks and compared them with sham operated mice. Though this treatment paradigm effectively restored SPD concentrations in the TA muscles of castrated mice, mass of the limb muscles (i.e., TA, gastrocnemius, plantaris, and soleus) were not increased to the levels observed in sham animals. Consistent with those findings, muscle force production was also not increased by SPD treatment. Overall, these data demonstrate for the first time that SPD is not an independent factor by which androgens regulate limb skeletal muscle mass. Novelty: Polyamines regulate growth in various cells/tissues. Spermidine concentrations are reduced in the limb skeletal muscle following androgen depletion. Restoring spermidine concentrations in the limb skeletal muscle does not increase limb muscle mass or force production.

A Phase Ib multicenter, dose-escalation study of the polyamine analogue PG-11047 in combination with gemcitabine, docetaxel, bevacizumab, erlotinib, cisplatin, 5-fluorouracil, or sunitinib in patients with advanced solid tumors or lymphoma

PURPOSE

Polyamines are absolutely essential for maintaining tumor cell proliferation. PG-11047, a polyamine analogue, is a nonfunctional competitor of the natural polyamine spermine that has demonstrated anticancer activity in cells and animal models of multiple cancer types. Preclinical investigations into the effects of common chemotherapeutic agents have revealed overlap with components of the polyamine metabolic pathway also affected by PG-11047. This report describes a Phase Ib clinical trial investigating PG-11047 in combination with cytotoxic and anti-angiogenic chemotherapeutic agents in patients with advanced refractory metastatic solid tumors or lymphoma.

METHODS

A total of 172 patients were assigned to treatment arms based on cancer type to receive the appropriate standard-of-care therapy (gemcitabine, docetaxel, bevacizumab, erlotinib, cisplatin, 5-fluorouracil (5-FU), or sunitinib as directed) along with once weekly intravenous infusions of PG-11047. PG-11047 dose escalation ranged from 50 to 590 mg.

RESULTS

The maximum tolerated dose (MTD) of PG-11047 in combination with bevacizumab, erlotinib, cisplatin, and 5-FU was 590 mg. Dose-limiting toxicities (DLTs) in these groups were rare (5 of 148 patients). Overall partial responses (PR) were observed in 12% of patients treated with PG-11047 and bevacizumab, with stable disease documented in an additional 40%. Stable disease occurred in 71.4% of patients in the 5-FU arm, 54.1% in the cisplatin arm, and 33.3% in the erlotinib arm. Four of the patients receiving cisplatin + PG-11047 (20%) had unconfirmed PRs. MTDs for gemcitabine, docetaxel, and sunitinib could not be determined due to DLTs at low doses of PG-11047 and small sample size.

CONCLUSIONS

Results of this Phase Ib trial indicate that PG-11047 can be safely administered to patients in combination with bevacizumab, erlotinib, cisplatin, and 5-FU on the once weekly dosing schedule described and may provide therapeutic benefit. The manageable toxicity profile and high MTD determination provide a safety profile for further clinical studies.

Ablation of polyamine catabolic enzymes provokes Purkinje cell damage, neuroinflammation, and severe ataxia

BACKGROUND

Polyamine catabolism plays a key role in maintaining intracellular polyamine pools, yet its physiological significance is largely unexplored. Here, we report that the disruption of polyamine catabolism leads to severe cerebellar damage and ataxia, demonstrating the fundamental role of polyamine catabolism in the maintenance of cerebellar function and integrity.

METHODS

Mice with simultaneous deletion of the two principal polyamine catabolic enzymes, spermine oxidase and spermidine/spermine N1-acetyltransferase (Smox/Sat1-dKO), were generated by the crossbreeding of Smox-KO (Smox-/-) and Sat1-KO (Sat1-/-) animals. Development and progression of tissue injury was monitored using imaging, behavioral, and molecular analyses.

RESULTS

Smox/Sat1-dKO mice are normal at birth, but develop progressive cerebellar damage and ataxia. The cerebellar injury in Smox/Sat1-dKO mice is associated with Purkinje cell loss and gliosis, leading to neuroinflammation and white matter demyelination during the latter stages of the injury. The onset of tissue damage in Smox/Sat1-dKO mice is not solely dependent on changes in polyamine levels as cerebellar injury was highly selective. RNA-seq analysis and confirmatory studies revealed clear decreases in the expression of Purkinje cell-associated proteins and significant increases in the expression of transglutaminases and markers of neurodegenerative microgliosis and astrocytosis. Further, the α-Synuclein expression, aggregation, and polyamination levels were significantly increased in the cerebellum of Smox/Sat1-dKO mice. Finally, there were clear roles of transglutaminase-2 (TGM2) in the cerebellar pathologies manifest in Smox/Sat1-dKO mice, as pharmacological inhibition of transglutaminases reduced the severity of ataxia and cerebellar injury in Smox/Sat1-dKO mice.

CONCLUSIONS

These results indicate that the disruption of polyamine catabolism, via coordinated alterations in tissue polyamine levels, elevated transglutaminase activity and increased expression, polyamination, and aggregation of α-Synuclein, leads to severe cerebellar damage and ataxia. These studies indicate that polyamine catabolism is necessary to Purkinje cell survival, and for sustaining the functional integrity of the cerebellum.

Ornithine decarboxylase, the rate-limiting enzyme of polyamine synthesis, modifies brain pathology in a mouse model of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a rare autosomal dominant neurodevelopmental disorder characterized by variable expressivity. TSC results from inactivating variants within the TSC1 or TSC2 genes, leading to constitutive activation of mechanistic target of rapamycin complex 1 signaling. Using a mouse model of TSC (Tsc2-RG) in which the Tsc2 gene is deleted in radial glial precursors and their neuronal and glial descendants, we observed increased ornithine decarboxylase (ODC) enzymatic activity and concentration of its product, putrescine. To test if increased ODC activity and dysregulated polyamine metabolism contribute to the neurodevelopmental defects of Tsc2-RG mice, we used pharmacologic and genetic approaches to reduce ODC activity in Tsc2-RG mice, followed by histologic assessment of brain development. We observed that decreasing ODC activity and putrescine levels in Tsc2-RG mice worsened many of the neurodevelopmental phenotypes, including brain growth and neuronal migration defects, astrogliosis and oxidative stress. These data suggest a protective effect of increased ODC activity and elevated putrescine that modify the phenotype in this developmental Tsc2-RG model.

Autophagy induction by exogenous polyamines is an artifact of bovine serum amine oxidase activity in culture serum

Polyamines are small polycationic alkylamines involved in many fundamental cellular processes, including proliferation, nucleic acid synthesis, apoptosis, and protection from oxidative damage. It has been proposed that in addition to these functions, elevated levels of polyamines promote longevity in various biological systems, including yeast, Drosophila, and murine models. A series of in vitro mechanistic studies by multiple investigators has led to the conclusion that addition of exogenous spermidine promotes longevity through autophagy induction; however, these experiments were confounded by the use of mammalian cell culture systems supplemented with fetal bovine serum. Using cell viability assays, LC3B immunoblots, and live-cell fluorescence microscopy, we report here that in the presence of ruminant serum, exogenously added polyamines are quickly oxidized by the copper-containing bovine serum amine oxidase. This polyamine oxidation resulted in the production of harmful byproducts including hydrogen peroxide, ammonia, and reactive aldehydes. Our data demonstrate that it is critically important to prevent confounding bovine serum amine oxidase-induced cytotoxicity in mechanistic studies of the roles of polyamines in autophagy.

Epigenetic Reexpression of Hemoglobin F Using Reversible LSD1 Inhibitors: Potential Therapies for Sickle Cell Disease

Sickle cell disease (SCD) is caused by a single nucleotide polymorphism on chromosome 11 in the β-globin gene. The resulting mutant hemoglobin S (HbS) is a poor oxygen transporter and causes a variety of vascular symptoms and organ failures. At birth, the DRED epigenetic complex forms and silences the γ-globin gene, and fetal hemoglobin (HbF, 2 α-, and 2 γ-subunits) is replaced by adult HbA (α2β2) or HbS (α2βs 2) in SCD patients. HbF is a potent inhibitor of HbS polymerization, thus alleviating the symptoms of SCD. The current therapy, hydroxyurea (HU), increases γ-globin and the HbF content in sickle cells but is highly underutilized due to concern for adverse effects and other complications. The DRED complex contains the epigenetic eraser lysine-specific demethylase 1 (LSD1), which appears to serve as a scaffolding protein. Our recently discovered 1,2,4-triazole derivatives and cyclic peptide LSD1 inhibitors promote the upregulation of γ-globin production in vitro without significant toxicity. Herein, we demonstrate that these LSD1 inhibitors can be used to disrupt the DRED complex and increase the cellular HbF content in vitro and in vivo. This approach could lead to an innovative and effective treatment for SCD.

Inhibition of the polyamine synthesis enzyme ornithine decarboxylase sensitizes triple-negative breast cancer cells to cytotoxic chemotherapy

Treatment of patients with triple-negative breast cancer (TNBC) is limited by a lack of effective molecular therapies targeting this disease. Recent studies have identified metabolic alterations in cancer cells that can be targeted to improve responses to standard-of-care chemotherapy regimens. Using MDA-MB-468 and SUM-159PT TNBC cells, along with LC-MS/MS and HPLC metabolomics profiling, we found here that exposure of TNBC cells to the cytotoxic chemotherapy drugs cisplatin and doxorubicin alter arginine and polyamine metabolites. This alteration was because of a reduction in the levels and activity of a rate-limiting polyamine biosynthetic enzyme, ornithine decarboxylase (ODC). Using gene silencing and inhibitor treatments, we determined that the reduction in ODC was mediated by its negative regulator antizyme, targeting ODC to the proteasome for degradation. Treatment with the ODC inhibitor difluoromethylornithine (DFMO) sensitized TNBC cells to chemotherapy, but this was not observed in receptor-positive breast cancer cells. Moreover, TNBC cell lines had greater sensitivity to single-agent DFMO, and ODC levels were elevated in TNBC patient samples. The alterations in polyamine metabolism in response to chemotherapy, as well as DFMO-induced preferential sensitization of TNBC cells to chemotherapy, reported here suggest that ODC may be a targetable metabolic vulnerability in TNBC.

Spermine oxidase mediates Helicobacter pylori-induced gastric inflammation, DNA damage, and carcinogenic signaling

Helicobacter pylori infection is the main risk factor for the development of gastric cancer, the third leading cause of cancer death worldwide. H. pylori colonizes the human gastric mucosa and persists for decades. The inflammatory response is ineffective in clearing the infection, leading to disease progression that may result in gastric adenocarcinoma. We have shown that polyamines are regulators of the host response to H. pylori, and that spermine oxidase (SMOX), which metabolizes the polyamine spermine into spermidine plus H2O2, is associated with increased human gastric cancer risk. We now used a molecular approach to directly address the role of SMOX, and demonstrate that Smox-deficient mice exhibit significant reductions of gastric spermidine levels and H. pylori-induced inflammation. Proteomic analysis revealed that cancer was the most significantly altered functional pathway in Smox-/- gastric organoids. Moreover, there was also less DNA damage and β-catenin activation in H. pylori-infected Smox-/- mice or gastric organoids, compared to infected wild-type animals or gastroids. The link between SMOX and β-catenin activation was confirmed in human gastric organoids that were treated with a novel SMOX inhibitor. These findings indicate that SMOX promotes H. pylori-induced carcinogenesis by causing inflammation, DNA damage, and activation of β-catenin signaling.

(R,R)-1,12-Dimethylspermine can mitigate abnormal spermidine accumulation in Snyder-Robinson syndrome

Snyder-Robinson syndrome (SRS) is an X-linked intellectual disability syndrome caused by a loss-of-function mutation in the spermine synthase (SMS) gene. Primarily affecting males, the main manifestations of SRS include osteoporosis, hypotonic stature, seizures, cognitive impairment, and developmental delay. Because there is no cure for SRS, treatment plans focus on alleviating symptoms rather than targeting the underlying causes. Biochemically, the cells of individuals with SRS accumulate excess spermidine, whereas spermine levels are reduced. We recently demonstrated that SRS patient-derived lymphoblastoid cells are capable of transporting exogenous spermine and its analogs into the cell and, in response, decreasing excess spermidine pools to normal levels. However, dietary supplementation of spermine does not appear to benefit SRS patients or mouse models. Here, we investigated the potential use of a metabolically stable spermine mimetic, (R,R)-1,12-dimethylspermine (Me₂SPM), to reduce the intracellular spermidine pools of SRS patient-derived cells. Me₂SPM can functionally substitute for the native polyamines in supporting cell growth while stimulating polyamine homeostatic control mechanisms. We found that both lymphoblasts and fibroblasts from SRS patients can accumulate Me₂SPM, resulting in significantly decreased spermidine levels with no adverse effects on growth. Me₂SPM administration to mice revealed that Me₂SPM significantly decreases spermidine levels in multiple tissues. Importantly, Me₂SPM was detectable in brain tissue, the organ most affected in SRS, and was associated with changes in polyamine metabolic enzymes. These findings indicate that the (R,R)-diastereomer of 1,12-Me₂SPM represents a promising lead compound in developing a treatment aimed at targeting the molecular mechanisms underlying SRS pathology.

Elevation of cellular Mg2+ levels by the Mg2+ transporter, Alr1, supports growth of polyamine-deficient Saccharomyces cerevisiae cells

The polyamines putrescine, spermidine, and spermine are required for normal eukaryotic cellular functions. However, the minimum requirement for polyamines varies widely, ranging from very high concentrations (mm) in mammalian cells to extremely low in the yeast Saccharomyces cerevisiae Yeast strains deficient in polyamine biosynthesis (spe1Δ, lacking ornithine decarboxylase, and spe2Δ, lacking SAM decarboxylase) require externally supplied polyamines, but supplementation with as little as 10^-8 m spermidine restores their growth. Here, we report that culturing a spe1Δ mutant or a spe2Δ mutant in a standard polyamine-free minimal medium (SDC) leads to marked increases in cellular Mg²⁺ content. To determine which yeast Mg²⁺ transporter mediated this increase, we generated mutant strains with a deletion of SPE1 or SPE2 combined with a deletion of one of the three Mg²⁺ transporter genes, ALR1, ALR2, and MNR2, known to maintain cytosolic Mg²⁺ concentration. Neither Alr2 nor Mnr2 was required for increased Mg²⁺ accumulation, as all four double mutants (spe1Δ alr2Δ, spe2Δ alr2Δ, spe1Δ mnr2Δ, and spe2Δ mnr2Δ) exhibited significant Mg²⁺ accumulation upon polyamine depletion. In contrast, a spe2Δ alr1Δ double mutant cultured in SDC exhibited little increase in Mg²⁺ content and displayed severe growth defects compared with single mutants alr1Δ and spe2Δ under polyamine-deficient conditions. These findings indicate that Alr1 is required for the up-regulation of the Mg²⁺ content in polyamine-depleted cells and suggest that elevated Mg²⁺ can support growth of polyamine-deficient S. cerevisiae mutants. Up-regulation of cellular polyamine content in a Mg²⁺-deficient alr1Δ mutant provided further evidence for a cross-talk between Mg²⁺ and polyamine metabolism.

DFMO and 5-Azacytidine Increase M1 Macrophages in the Tumor Microenvironment of Murine Ovarian Cancer

Although ovarian cancer has a low incidence rate, it remains the most deadly gynecologic malignancy. Previous work has demonstrated that the DNMTi 5-Azacytidine (5AZA-C) activates type I interferon signaling to increase IFNγ⁺ T cells and natural killer (NK) cells and reduce the percentage of macrophages in the tumor microenvironment. To improve the efficacy of epigenetic therapy, we hypothesized that the addition of α-difluoromethylornithine (DFMO), an ornithine decarboxylase inhibitor, may further decrease immunosuppressive cell populations improving outcome. We tested this hypothesis in an immunocompetent mouse model for ovarian cancer and found that in vivo, 5AZA-C and DFMO, either alone or in combination, significantly increased survival, decreased tumor burden, and caused recruitment of activated (IFNγ⁺) CD4⁺ T cells, CD8⁺ T cells, and NK cells. The combination therapy had a striking increase in survival when compared with single-agent treatment, despite a smaller difference in recruited lymphocytes. Instead, combination therapy led to a significant decrease in immunosuppressive cells such as M2 polarized macrophages and an increase in tumor-killing M1 macrophages. In this model, depletion of macrophages with a CSF1R-blocking antibody reduced the efficacy of 5AZA-C + DFMO treatment and resulted in fewer M1 macrophages in the tumor microenvironment. These observations suggest our novel combination therapy modifies macrophage polarization in the tumor microenvironment, recruiting M1 macrophages and prolonging survival. SIGNIFICANCE: Combined epigenetic and polyamine-reducing therapy stimulates M1 macrophage polarization in the tumor microenvironment of an ovarian cancer mouse model, resulting in decreased tumor burden and prolonged survival.

Dual inhibitors of LSD1 and spermine oxidase

We have previously described the synthesis and evaluation of 3,5-diamino-1,2,4-triazole analogues as inhibitors of the flavin-dependent histone demethylase LSD1. These compounds are potent inhibitors of LSD1 without activity against monoamine oxidases A and B, and promote the elevation of H3K4me2 levels in tumor cells in vitro. We now report that the cytotoxicity of these analogues in pancreatic tumor cells correlates with the overexpression of LSD1 in each tumor type. In addition, we show that a subset of these 3,5-diamino-1,2,4-triazole analogues inhibit a related flavin-dependent oxidase, the polyamine catabolic enzyme spermine oxidase (SMOX) in vitro.

Polyamine catabolism and oxidative damage

Polyamines (PAs) are indispensable polycations ubiquitous to all living cells. Among their many critical functions, PAs contribute to the oxidative balance of the cell. Beginning with studies by the Tabor laboratory in bacteria and yeast, the requirement for PAs as protectors against oxygen radical-mediated damage has been well established in many organisms, including mammals. However, PAs also serve as substrates for oxidation reactions that produce hydrogen peroxide (H2O2) both intra- and extracellularly. As intracellular concentrations of PAs can reach millimolar concentrations, the H2O2 amounts produced through their catabolism, coupled with a reduction in protective PAs, are sufficient to cause the oxidative damage associated with many pathologies, including cancer. Thus, the maintenance of intracellular polyamine homeostasis may ultimately contribute to the maintenance of oxidative homeostasis. Again, pioneering studies by Tabor and colleagues led the way in first identifying spermine oxidase in Saccharomyces cerevisiae. They also first purified the extracellular bovine serum amine oxidase and elucidated the products of its oxidation of primary amine groups of PAs when included in culture medium. These investigations formed the foundation for many polyamine-related studies and experimental procedures still performed today. This Minireview will summarize key innovative studies regarding PAs and oxidative damage, starting with those from the Tabor laboratory and including the most recent advances, with a focus on mammalian systems.

Polyamine metabolism and cancer: treatments, challenges and opportunities

Advances in our understanding of the metabolism and molecular functions of polyamines and their alterations in cancer have led to resurgence in the interest of targeting polyamine metabolism as an anticancer strategy. Increasing knowledge of the interplay between polyamine metabolism and other cancer-driving pathways, including the PTEN-PI3K-mTOR complex 1 (mTORC1), WNT signalling and RAS pathways, suggests potential combination therapies that will have considerable clinical promise. Additionally, an expanding number of promising clinical trials with agents targeting polyamines for both therapy and prevention are ongoing. New insights into molecular mechanisms linking dysregulated polyamine catabolism and carcinogenesis suggest additional strategies that can be used for cancer prevention in at-risk individuals. In addition, polyamine blocking therapy, a strategy that combines the inhibition of polyamine biosynthesis with the simultaneous blockade of polyamine transport, can be more effective than therapies based on polyamine depletion alone and may involve an antitumour immune response. These findings open up new avenues of research into exploiting aberrant polyamine metabolism for anticancer therapy.

Targeting the aryl hydrocarbon receptor/polyamine biosynthesis axis of evil for cancer therapy

The polyamine metabolic pathway has been considered a rational target for antineoplastic therapy since it was discovered that polyamines are absolute requirements for tumor initiation, growth, and, in some instances, survival. Although several promising preclinical studies have demonstrated the critical nature of polyamines for tumor growth, the clinical success of agents targeting polyamine metabolism have been lacking. In the accompanying article, Bianchi-Smiraglia et al. identify both a new target and new drug that inhibits polyamine biosynthesis, reduces intracellular polyamines, and inhibits the growth of several models of human multiple myeloma. These results are both intriguing and provide promise for moving such a strategy to the clinic.

Efficacy and Safety of Curcumin in Treatment of Intestinal Adenomas in Patients With Familial Adenomatous Polyposis

BACKGROUND & AIMS

Familial adenomatous polyposis is an autosomal dominant disorder characterized by the development of hundreds of colorectal adenomas and eventually colorectal cancer. Oral administration of the spice curcumin has been followed by regression of polyps in patients with this disorder. We performed a double-blinded randomized trial to determine the safety and efficacy of curcumin in patients with familial adenomatous polyposis.

METHODS

This study included 44 patients with familial adenomatous polyposis (18-85 years old) who had not undergone colectomy or had undergone colectomy with ileorectal anastomosis or ileal anal pouches, had at least 5 intestinal adenomatous polyps, and had enrolled in Puerto Rico or the United States from September 2011 through November 2016. Patients were randomly assigned (1:1) to groups given 100% pure curcumin (1,500 mg orally, twice per day) or identical-appearing placebo capsules for 12 months. The number and size of lower gastrointestinal tract polyps were evaluated every 4 months for 1 year. The primary outcome was the number of polyps in the curcumin and placebo groups at 12 months or at the time of withdrawal from the study according to the intention-to-treat principle.

RESULTS

After 1 year of treatment, the average rate of compliance was 83% in the curcumin group and 91% in the placebo group. After 12 weeks, there was no significant difference in the mean number of polyps between the placebo group (18.6; 95% CI, 9.3-27.8) and the curcumin group (22.6; 95% CI, 12.1-33.1; P = .58). We found no significant difference in mean polyp size between the curcumin group (2.3 mm; 95% CI, 1.8-2.8) and the placebo group (2.1 mm; 95% CI, 1.5-2.7; P = .76). Adverse events were few, with no significant differences between groups.

CONCLUSIONS

In a double-blinded randomized trial of patients with familial adenomatous polyposis, we found no difference in the mean number or size of lower intestinal tract adenomas between patients given curcumin 3,000 mg/day and those given placebo for 12 weeks. Clinicaltrials.gov ID NCT00641147.

Curcumin mediates polyamine metabolism and sensitizes gastrointestinal cancer cells to antitumor polyamine-targeted therapies

Curcumin, a natural polyphenol that contributes to the flavor and yellow pigment of the spice turmeric, is known for its antioxidant, anti-inflammatory, and anticarcinogenic properties. Capable of affecting the initiation, promotion, and progression of carcinogenesis through multiple mechanisms, curcumin has potential utility for both chemoprevention and chemotherapy. Previous studies demonstrated that curcumin can inhibit ornithine decarboxylase (ODC) activity in human leukemia and breast cancer cells, and pretreatment with dietary curcumin blocks carcinogen-induced ODC activity in rodent models of skin, colon, and renal cancer. The current study investigated the regulation of polyamine metabolism in human gastric and colon carcinoma cell lines in response to curcumin. Curcumin treatment significantly induced spermine oxidase (SMOX) mRNA and activity, which results in the generation of hydrogen peroxide, a source of ROS. Simultaneously, curcumin down regulated spermidine/spermine N1-acetyltransferase (SSAT) activity and the biosynthetic enzymes ODC and S-adenosylmethionine decarboxylase (SAMDC), thereby diminishing intracellular polyamine pools. Combination treatments using curcumin with the ODC inhibitor 2-difluoromethylornithine (DFMO), an agent currently in clinical chemoprevention trials, significantly enhanced inhibition of ODC activity and decreased growth of GI cancer cell lines beyond that observed with either agent alone. Similarly, combining curcumin with the polyamine analogue bis(ethyl)norspermine enhanced growth inhibition that was accompanied by enhanced accumulation of the analogue and decreased intracellular polyamine levels beyond those observed with either agent alone. Importantly, cotreatment with curcumin permitted the lowering of the effective dose of ODC inhibitor or polyamine analogue. These studies provide insight into the polyamine-related mechanisms involved in the cancer cell response to curcumin and its potential as a chemopreventive or chemotherapeutic agent in the GI tract.

Abstract B052: Leveraging the metabolic stress of polyamine biosynthesis in prostate cancer towards a novel therapeutic approach

Prostatic epithelial cells secrete high levels of acetylated polyamines into the prostatic lumen. This distinctive characteristic places added strain on connected pathways, forcing increased metabolite production from both one-carbon metabolism and the methionine cycle to maintain nucleotide and S-adenosylmethionine (SAM) pools, respectively. More importantly, this stress is increased in prostate cancer (CaP) due to increased polyamine biosynthesis, DNA synthesis, and proliferation. The metabolic flux is driven by the activity of spermidine/spermine N1-acetyltransferase (SSAT), which acetylates the polyamines leading to their secretion into the lumen, which drives demand for biosynthesis of polyamines. To overcome this stress, the methionine salvage pathway (MSP) recycles the one-carbon unit lost to polyamine biosynthesis back to the methionine cycle, allowing for replenishment of SAM pools. The rate-limiting enzyme involved in this process is methylthioadenosine phosphorylase (MTAP). We have found that CaP relies on the MSP to relieve the strain caused by high polyamine biosynthesis and that both genetic and pharmacologic inhibition of MTAP blocks CaP xenograft growth. We hypothesized that this dependence can be enhanced by increasing the activity of SSAT. Recent results from our lab have shown that pharmacologic inhibition of MTAP alongside SSAT upregulation is synergistic in multiple androgen-sensitive and castration-recurrent CaP cell lines. We are currently exploring the effects of our combination treatment in castration-recurrent xenografts in vivo as well as in human CaP treatment-naïve tumors from radical prostatectomies grown as ex vivo explants. Preliminary results reveal that our treatments are effective at slowing growth in a subset of xenografts in vivo as well as impacting our target enzymes, polyamine levels, and increasing apoptosis in our ex vivo system. We expect that simultaneous targeting of multiple, converging pathways that are exceptionally important for prostate will lead to significant delay or prevention of disease recurrence.

Citation Format: Hayley C. Affronti, Anthony J. Pellerite, Aryn Rowsam, Spencer R. Rosario, Robert A. Casero, Mikhail A. Nikiforov, James Phillips, Dominic J. Smiraglia. Leveraging the metabolic stress of polyamine biosynthesis in prostate cancer towards a novel therapeutic approach [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr B052.

Polymeric Prodrugs Targeting Polyamine Metabolism Inhibit Zika Virus Replication

The Zika virus (ZIKV) is primarily transmitted via an infected mosquito bite, during sexual intercourse, or in utero mother to child transmission. When a fetus is infected, both neurological malformations and deficits in brain development are frequently manifested. As such, there is a need for vaccines or drugs that may be used to cure ZIKV infections. Metabolic pathways play a crucial role in cell differentiation and development. More importantly, polyamines play a key role in replication and translation of several RNA viruses, including ZIKV, Dengue virus, and Chikungunya virus. Here, we present polyamine analogues (BENSpm and PG11047) and their corresponding polymer prodrug derivatives for inhibiting ZIKV infection by intersecting with polyamine catabolism pathways. We tested the compounds against ZIKV African (MR766) and Asian (PRVABC59) strains in human kidney epithelial (Vero) and glioblastoma derived (SNB-19) cell lines. Our results demonstrate potent inhibition of ZIKV viral replication in both cell lines tested. This antiviral effect was mediated by the upregulation of two polyamine catabolic enzymes, spermine oxidase, and spermidine (SMOX)/spermine N1-acetyltransferase (SAT1) as apparent reduction of the ZIKV infection following heterologous expression of SMOX and SAT1. On the basis of these observations, we infer potential use of these polyamine analogues to treat ZIKV infections.

Placental polyamine metabolism differs by fetal sex, fetal growth restriction, and preeclampsia

Preeclampsia and fetal growth restriction (FGR) are major causes of the more than 5 million perinatal and infant deaths occurring globally each year, and both are associated with placental dysfunction. The risk of perinatal and infant death is greater in males, but the mechanisms are unclear. We studied data and biological samples from the Pregnancy Outcome Prediction (POP) study, a prospective cohort study that followed 4,212 women having first pregnancies from their dating ultrasound scan through delivery. We tested the hypothesis that fetal sex would be associated with altered placental function using multiomic and targeted analyses. We found that spermine synthase (SMS) escapes X-chromosome inactivation (XCI) in the placenta and is expressed at lower levels in male primary trophoblast cells, and male cells were more sensitive to polyamine depletion. The spermine metabolite N1,N12-diacetylspermine (DiAcSpm) was higher in the female placenta and in the serum of women pregnant with a female fetus. Higher maternal serum levels of DiAcSpm increased the risk of preeclampsia but decreased the risk of FGR. To our knowledge, DiAcSpm is the first maternal biomarker to demonstrate opposite associations with preeclampsia and FGR, and this is the first evidence to implicate polyamine metabolism in sex-related differences in placentally related complications of human pregnancy.

Metabolomic studies identify changes in transmethylation and polyamine metabolism in a brain-specific mouse model of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant neurodevelopmental disorder and the quintessential disorder of mechanistic Target of Rapamycin Complex 1 (mTORC1) dysregulation. Loss of either causative gene, TSC1 or TSC2, leads to constitutive mTORC1 kinase activation and a pathologically anabolic state of macromolecular biosynthesis. Little is known about the organ-specific metabolic reprogramming that occurs in TSC-affected organs. Using a mouse model of TSC in which Tsc2 is disrupted in radial glial precursors and their neuronal and glial descendants, we performed an unbiased metabolomic analysis of hippocampi to identify Tsc2-dependent metabolic changes. Significant metabolic reprogramming was found in well-established pathways associated with mTORC1 activation, including redox homeostasis, glutamine/tricarboxylic acid cycle, pentose and nucleotide metabolism. Changes in two novel pathways were identified: transmethylation and polyamine metabolism. Changes in transmethylation included reduced methionine, cystathionine, S-adenosylmethionine (SAM-the major methyl donor), reduced SAM/S-adenosylhomocysteine ratio (cellular methylation potential), and elevated betaine, an alternative methyl donor. These changes were associated with alterations in SAM-dependent methylation pathways and expression of the enzymes methionine adenosyltransferase 2A and cystathionine beta synthase. We also found increased levels of the polyamine putrescine due to increased activity of ornithine decarboxylase, the rate-determining enzyme in polyamine synthesis. Treatment of Tsc2+/- mice with the ornithine decarboxylase inhibitor α-difluoromethylornithine, to reduce putrescine synthesis dose-dependently reduced hippocampal astrogliosis. These data establish roles for SAM-dependent methylation reactions and polyamine metabolism in TSC neuropathology. Importantly, both pathways are amenable to nutritional or pharmacologic therapy.

Distinct Immunomodulatory Effects of Spermine Oxidase in Colitis Induced by Epithelial Injury or Infection

Polyamines have been implicated in numerous biological processes, including inflammation and carcinogenesis. Homeostatic regulation leads to interconversion of the polyamines putrescine and the downstream metabolites spermidine and spermine. The enzyme spermine oxidase (SMOX), which back-converts spermine to spermidine, contributes to regulation of polyamine levels, but can also have other effects. We have implicated SMOX in gastric inflammation and carcinogenesis due to infection by the pathogen Helicobacter pylori. In addition, we reported that SMOX can be upregulated in humans with inflammatory bowel disease. Herein, we utilized Smox-deficient mice to examine the role of SMOX in two murine colitis models, Citrobacter rodentium infection and dextran sulfate sodium (DSS)-induced epithelial injury. In C. rodentium-infected wild-type (WT) mice, there were marked increases in colon weight/length and histologic injury, with mucosal hyperplasia and inflammatory cell infiltration; these changes were ameliorated in Smox-/- mice. In contrast, with DSS, Smox-/- mice exhibited substantial mortality, and increased body weight loss, colon weight/length, and histologic damage. In C. rodentium-infected WT mice, there were increased colonic levels of the chemokines CCL2, CCL3, CCL4, CXCL1, CXCL2, and CXCL10, and the cytokines IL-6, TNF-α, CSF3, IFN-γ, and IL-17; each were downregulated in Smox-/- mice. In DSS colitis, increased levels of IL-6, CSF3, and IL-17 were further increased in Smox-/- mice. In both models, putrescine and spermidine were increased in WT mice; in Smox-/- mice, the main effect was decreased spermidine and spermidine/spermine ratio. With C. rodentium, polyamine levels correlated with histologic injury, while with DSS, spermidine was inversely correlated with injury. Our studies indicate that SMOX has immunomodulatory effects in experimental colitis via polyamine flux. Thus, SMOX contributes to the immunopathogenesis of C. rodentium infection, but is protective in DSS colitis, indicating the divergent effects of spermidine.

Coupling of the polyamine and iron metabolism pathways in the regulation of proliferation: Mechanistic links to alterations in key polyamine biosynthetic and catabolic enzymes

Many biological processes result from the coupling of metabolic pathways. Considering this, proliferation depends on adequate iron and polyamines, and although iron-depletion impairs proliferation, the metabolic link between iron and polyamine metabolism has never been thoroughly investigated. This is important to decipher, as many disease states demonstrate co-dysregulation of iron and polyamine metabolism. Herein, for the first time, we demonstrate that cellular iron levels robustly regulate 13 polyamine pathway proteins. Seven of these were regulated in a conserved manner by iron-depletion across different cell-types, with four proteins being down-regulated (i.e., acireductone dioxygenase 1 [ADI1], methionine adenosyltransferase 2α [MAT2α], Antizyme and polyamine oxidase [PAOX]) and three proteins being up-regulated (i.e., S-adenosyl methionine decarboxylase [AMD1], Antizyme inhibitor 1 [AZIN1] and spermidine/spermine-N¹-acetyltransferase 1 [SAT1]). Depletion of iron also markedly decreased polyamine pools (i.e., spermidine and/or spermine, but not putrescine). Accordingly, iron-depletion also decreased S-adenosylmethionine that is essential for spermidine/spermine biosynthesis. Iron-depletion additionally reduced ³H-spermidine uptake in direct agreement with the lowered levels of the polyamine importer, SLC22A16. Regarding mechanism, the "reprogramming" of polyamine metabolism by iron-depletion is consistent with the down-regulation of ADI1 and MAT2α, and the up-regulation of SAT1. Moreover, changes in ADI1 (biosynthetic) and SAT1 (catabolic) partially depended on the iron-regulated changes in c-Myc and/or p53. The ability of iron chelators to inhibit proliferation was rescuable by putrescine and spermidine, and under some conditions by spermine. Collectively, iron and polyamine metabolism are intimately coupled, which has significant ramifications for understanding the integrated role of iron and polyamine metabolism in proliferation.

N1-Nonyl-1,4-diaminobutane ameliorates brain infarction size in photochemically induced thrombosis model mice

Inhibitors for polyamine oxidizing enzymes, spermine oxidase (SMOX) and N1-acetylpolyamine oxidase (PAOX), were designed and evaluated for their effectiveness in a photochemically induced thrombosis (PIT) mouse model. N1-Nonyl-1,4-diaminobutane (C9-4) and N1-tridecyl-1,4-diaminobutane (C13-4) competitively inhibited the activity of PAOX and SMOX in a manner comparable to N1,N4-bis(2,3-butadienyl)-1,4-butanediamine (MDL72527), an irreversible inhibitor of both enzymes. The two compounds were then tested for their effects in the PIT model. Both intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration of C9-4 decreased infarct volumes significantly. By contrast, C13-4 reduced the volume of brain infarction by i.c.v. administration, but no reduction was observed after i.p. administration. C9-4 administered by i.p. injection reduced the volume of brain infarction significantly at doses of more than 3 mg/kg, and the dosage of 5 mg/kg or 10 mg/kg demonstrated the most potent effect and were more effective than equivalent doses of the other inhibitors such as MDL72527 and N-benzylhydroxylamine. I.P. injection of 5 mg/kg of C9-4 provided a therapeutic time window of longer than 12 h. This report demonstrates that C9-4 is a potent inhibitor of the polyamine oxidizing enzymes and is useful lead compound for candidate drugs with a long therapeutic time window, to be used in the treatment of ischemic stroke.

Activation of endoplasmic reticulum stress response by enhanced polyamine catabolism is important in the mediation of cisplatin-induced acute kidney injury

Cisplatin-induced nephrotoxicity limits its use in many cancer patients. The expression of enzymes involved in polyamine catabolism, spermidine/spermine N1-acetyltransferase (SSAT) and spermine oxidase (SMOX) increase in the kidneys of mice treated with cisplatin. We hypothesized that enhanced polyamine catabolism contributes to tissue damage in cisplatin acute kidney injury (AKI). Using gene knockout and chemical inhibitors, the role of polyamine catabolism in cisplatin AKI was examined. Deficiency of SSAT, SMOX or neutralization of the toxic products of polyamine degradation, H2O2 and aminopropanal, significantly diminished the severity of cisplatin AKI. In vitro studies demonstrated that the induction of SSAT and elevated polyamine catabolism in cells increases the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) and enhances the expression of binding immunoglobulin protein BiP/GRP78) and CCAAT-enhancer-binding protein homologous protein (CHOP/GADD153). The increased expression of these endoplasmic reticulum stress response (ERSR) markers was accompanied by the activation of caspase-3. These results suggest that enhanced polyamine degradation in cisplatin AKI may lead to tubular damage through the induction of ERSR and the consequent onset of apoptosis. In support of the above, we show that the ablation of the SSAT or SMOX gene, as well as the neutralization of polyamine catabolism products modulate the onset of ERSR (e.g. lower BiP and CHOP) and apoptosis (e.g. reduced activated caspase-3). These studies indicate that enhanced polyamine catabolism and its toxic products are important mediators of ERSR and critical to the pathogenesis of cisplatin AKI.