Phase 1 study of N1-N11-diethylnorspermine (DENSPM) administered TID for 6 days in patients with advanced malignancies

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

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

Polyamine-Based Nanostructures Share Polyamine Transport Mechanisms with Native Polyamines and Their Analogues: Significance for Polyamine-Targeted Therapy

Polyamines are small polycationic alkylamines involved in many fundamental cellular processes, including cell proliferation, survival, and protection from oxidative stress. Polyamine homeostasis is tightly regulated through coordinated biosynthesis, catabolism, and transport. Due to their continual proliferation, cancer cells maintain elevated intracellular polyamine pools. Both polyamine metabolism and transport are commonly dysregulated in cancer, and as such, polyamine analogues are a promising strategy for exploiting the increased polyamine requirement of cancer cells. One potential polyamine analogue resistance mechanism is the downregulation of the poorly defined polyamine transport system. Recent advances in nanomedicine have produced nanostructures with polyamine analogue-based backbones (nanopolyamines). Similar nanostructures with non-polyamine backbones have been shown to be transported by endocytosis. As these polyamine-based nanoparticles could be a method for polyamine analogue delivery that bypasses polyamine transport, we designed the current studies to determine the efficacy of polyamine-based nanoparticles in cells lacking intact polyamine transport. Utilizing polyamine transport-deficient derivatives of lung adenocarcinoma lines, we demonstrated that cells unable to transport natural polyamines were also resistant to nanopolyamine-induced cytotoxicity. This resistance was a result of transport-deficient cells being incapable of importing and accumulating nanopolyamines. Pharmacological modulation of polyamine transport confirmed these results in polyamine transport competent cells. These studies provide additional insight into the polyamine transport pathway and suggest that receptor-mediated endocytosis is a likely mechanism of transport for higher-order polyamines, polyamine analogues and the nanopolyamines.

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.

Natural and synthetic compounds in Ovarian Cancer: A focus on NRF2/KEAP1 pathway

Among gynecologic malignancies, ovarian cancer is one of the most dangerous, with a high fatality rate and relapse due to the occurrence of chemoresistance. Many researchers demonstrated that oxidative stress is involved in tumor occurrence, development and procession. Nuclear factor erythroid 2-related factor 2 (NRF2) is an important transcription factor playing an important role in protecting against oxidative damage. Increased levels of Reactive Oxygen Species (ROS) activate NRF2 signaling inducing the expression of antioxidant enzymes such as heme oxygenase (HO-1), catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD) that protect cells against oxidative stress. However, NRF2 activation in cancer cells is responsible for the development of chemoresistance inactivating drug-mediated oxidative stress that normally leads cancer cells to death. In this review we analyzed the current literature regarding the role of natural and synthetic compounds in modulating NRF2/KEAP1 (Kelch Like ECH Associated Protein 1) pathway in in vitro models of ovarian cancer. In particular, we reported how these compounds can modulate chemotherapy response.

Self-Assembled Alkylated Polyamine Analogs as Supramolecular Anticancer Agents

Conformationally restrained polyamine analog PG11047 is a well-known drug candidate that modulates polyamine metabolism and inhibits cancer cell growth in a broad spectrum of cancers. Here, we report a structure–activity relationship study of the PG11047 analogs (HPGs) containing alkyl chains of varying length, while keeping the unsaturated spermine backbone unchanged. Synthesis of higher symmetrical homologues was achieved through a synthetic route with fewer steps than the previous route to PG11047. The amphiphilic HPG analogs underwent self-assembly and formed spherically shaped nanoparticles whose size increased with the hydrophobic alkyl group’s increasing chain length. Assessment of the in vitro anticancer activity showed more than an eight-fold increase in the cancer cell inhibition activity of the analogs with longer alkyl chains compared to PG11047 in human colon cancer cell line HCT116, and a more than ten-fold increase in human lung cancer cell line A549. Evaluation of the inhibition of spermine oxidase (SMOX) showed no activity for PG11047, but activity was observed for its higher symmetrical homologues. Comparison with a reference SMOX inhibitor MDL72527 showed nine-fold better activity for the best performing HPG analog.

Metabolism and function of polyamines in cancer progression

Polyamines are essential for the proliferation, differentiation, and development of eukaryotes. They include spermine, spermidine, and the diamine precursor putrescine, and are low-molecular-weight, organic polycations with more than two amino groups. Their intracellular concentrations are strictly maintained within a specific physiological range through several regulatory mechanisms in normal cells. In contrast, polyamine metabolism is dysregulated in many neoplastic states, including cancer. In various types of cancer, polyamine levels are elevated, and crosstalk occurs between polyamine metabolism and oncogenic pathways, such as mTOR and RAS pathways. Thus, polyamines might have potential as therapeutic targets in the prevention and treatment of cancer. The molecular mechanisms linking polyamine metabolism to carcinogenesis must be unraveled to develop novel inhibitors of polyamine metabolism. This overview describes the nature of polyamines, their association with carcinogenesis, the development of polyamine inhibitors and their potential, and the findings of clinical trials.

Polyamine Homeostasis in Development and Disease

Polycationic polyamines are present in nearly all living organisms and are essential for mammalian cell growth and survival, and for development. These positively charged molecules are involved in a variety of essential biological processes, yet their underlying mechanisms of action are not fully understood. Several studies have shown both beneficial and detrimental effects of polyamines on human health. In cancer, polyamine metabolism is frequently dysregulated, and elevated polyamines have been shown to promote tumor growth and progression, suggesting that targeting polyamines is an attractive strategy for therapeutic intervention. In contrast, polyamines have also been shown to play critical roles in lifespan, cardiac health and in the development and function of the brain. Accordingly, a detailed understanding of mechanisms that control polyamine homeostasis in human health and disease is needed to develop safe and effective strategies for polyamine-targeted therapy.

A phase I dose-escalation study of the polyamine analog PG-11047 in patients with advanced solid tumors

PURPOSE

Polyamines are essential for the sustained proliferation and biomass required by tumor cells. Bis-alkylated polyamine analogs are nonfunctional competitors of natural polyamines. Of these, PG-11047, a second-generation unsaturated analog of the polyamine spermine, has demonstrated anticancer activity in cell lines and animal models of multiple cancer types. This report describes the first phase I clinical trial to investigate PG-11047 in patients with advanced refractory metastatic solid tumors.

METHODS

Forty-six patients were treated with 60-min intravenous infusions of PG-11047 using a 28-day dosing cycle with treatments on days 1, 8, and 15. Doses ranged from 50 to 750 mg. The treatment period consisted of at least two cycles.

RESULTS

The maximum tolerated dose of PG-11047 administered at this dosing schedule was 610 mg. Dose-limiting toxicities (DLT) were mainly gastrointestinal, including oral/anal mucositis and diarrhea; other DLTs included one case each of angioedema and a grade 3 alanine aminotransferase (ALT) increase. The most common adverse effects were fatigue and anorexia. Stable disease was documented in 30% of patients.

CONCLUSION

Results of this phase I trial suggest that PG-11047 can be safely administered to patients on the once weekly dosing schedule described. The manageable toxicity profile and high MTD determination provide a safety profile for further clinical studies, including those in combination with current chemotherapeutic agents.

Pharmacological polyamine catabolism upregulation with methionine salvage pathway inhibition as an effective prostate cancer therapy

Prostatic luminal epithelial cells secrete high levels of acetylated polyamines into the prostatic lumen, sensitizing them to perturbations of connected metabolic pathways. Enhanced flux is driven by spermidine/spermine N1-acetyltransferase (SSAT) activity, which acetylates polyamines leading to their secretion and drives biosynthetic demand. The methionine salvage pathway recycles one-carbon units lost to polyamine biosynthesis to the methionine cycle to overcome stress. Prostate cancer (CaP) relies on methylthioadenosine phosphorylase (MTAP), the rate-limiting enzyme, to relieve strain. Here, we show that inhibition of MTAP alongside SSAT upregulation is synergistic in androgen sensitive and castration recurrent CaP models in vitro and in vivo. The combination treatment increases apoptosis in radical prostatectomy ex vivo explant samples. This unique high metabolic flux through polyamine biosynthesis and connected one carbon metabolism in CaP creates a metabolic dependency. Enhancing this flux while simultaneously targeting this dependency in prostate cancer results in an effective therapeutic approach potentially translatable to the clinic.

Prostate cancer cells depend on MTAP, the rate-limiting enzyme involved in the methionine salvage pathway, to cope with increased polyamine biosynthesis. Here, the authors show that inducing upregulation of polyamine biosynthesis and targeting MTAP synergize to increase apoptosis in prostate cancer cells.

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.

Polyamines and Cancer

This chapter provides an overview of how the polyamine pathway has been exploited as a target for the treatment and prevention of multiple forms of cancer, since this pathway is disrupted in all cancers. It is divided into three main sections. The first explores how the polyamine pathway has been targeted for chemotherapy, starting from the first drug to target it, difluoromethylornithine (DFMO) to the large variety of polyamine analogues that have been synthesised and tested throughout the years with all their potentials and pitfalls. The second section focuses on the use of polyamines as vectors for drug delivery. Knowing that the polyamine transport system is upregulated in cancers and that polyamines naturally bind to DNA, a range of polyamine analogues and polyamine-like structures have been synthesised to target epigenetic regulators, with encouraging results. Furthermore, the use of polyamines as transport vectors to introduce toxic/bioactive/fluorescent agents more selectively to the intended target in cancer cells is discussed. The last section concentrates on chemoprevention, where the different strategies that have been undertaken to interfere with polyamine metabolism and function for antiproliferative intervention are outlined and discussed.

Oil for the cancer engine: The cross-talk between oncogenic signaling and polyamine metabolism

The study of metabolism has provided remarkable information about the biological basis and therapeutic weaknesses of cancer cells. Classic biochemistry established the importance of metabolic alterations in tumor biology and revealed the importance of various metabolite families to the tumorigenic process. We have evidence of the central role of polyamines, small polycatonic metabolites, in cell proliferation and cancer growth from these studies. However, how cancer cells activate this metabolic pathway and the molecular cues behind the oncogenic action of polyamines has remained largely obscure. In contrast to the view of metabolites as fuel (anabolic intermediates) for cancer cells, polyamines are better defined as the oil that lubricates the cancer engine because they affect the activity of biological processes. Modern research has brought back to the limelight this metabolic pathway, providing a strong link between genetic, metabolic, and signaling events in cancer. In this review, we enumerate and discuss current views of the regulation and activity of polyamine metabolism in tumor cell biology.

Targeting polyamine metabolism for cancer therapy and prevention

The chemically simple, biologically complex eukaryotic polyamines, spermidine and spermine, are positively charged alkylamines involved in many crucial cellular processes. Along with their diamine precursor putrescine, their normally high intracellular concentrations require fine attenuation by multiple regulatory mechanisms to keep these essential molecules within strict physiologic ranges. Since the metabolism of and requirement for polyamines are frequently dysregulated in neoplastic disease, the metabolic pathway and functions of polyamines provide rational drug targets; however, these targets have been difficult to exploit for chemotherapy. It is the goal of this article to review the latest findings in the field that demonstrate the potential utility of targeting the metabolism and function of polyamines as strategies for both chemotherapy and, possibly more importantly, chemoprevention.

Self-immolative nanoparticles for simultaneous delivery of microRNA and targeting of polyamine metabolism in combination cancer therapy

Combination of anticancer drugs with therapeutic microRNA (miRNA) has emerged as a promising anticancer strategy. However, the promise is hampered by a lack of desirable delivery systems. We report on the development of self-immolative nanoparticles capable of simultaneously delivering miR-34a mimic and targeting dysregulated polyamine metabolism in cancer. The nanoparticles were prepared from a biodegradable polycationic prodrug, named DSS-BEN, which was synthesized from a polyamine analog N1,N11-bisethylnorspermine (BENSpm). The nanoparticles were selectively disassembled in the cytoplasm where they released miRNA. Glutathione (GSH)-induced degradation of self-immolative linkers released BENSpm from the DSS-BEN polymers. MiR-34a mimic was effectively delivered to cancer cells as evidenced by upregulation of intracellular miR-34a and downregulation of Bcl-2 as one of the downstream targets of miR-34a. Intracellular BENSpm generated from the degraded nanoparticles induced the expression of rate-limiting enzymes in polyamine catabolism (SMOX, SSAT) and depleted cellular natural polyamines. Simultaneous regulation of polyamine metabolism and miR-34a expression by DSS-BEN/miR-34a not only enhanced cancer cell killing in cultured human colon cancer cells, but also improved antitumor activity in vivo. The reported findings validate the self-immolative nanoparticles as delivery vectors of therapeutic miRNA capable of simultaneously targeting dysregulated polyamine metabolism in cancer, thereby providing an elegant and efficient approach to combination nanomedicines.

Activation of SAT1 engages polyamine metabolism with p53-mediated ferroptotic responses

Although p53-mediated cell-cycle arrest, senescence, and apoptosis remain critical barriers to cancer development, the emerging role of p53 in cell metabolism, oxidative responses, and ferroptotic cell death has been a topic of great interest. Nevertheless, it is unclear how p53 orchestrates its activities in multiple metabolic pathways into tumor suppressive effects. Here, we identified the SAT1 (spermidine/spermine N¹-acetyltransferase 1) gene as a transcription target of p53. SAT1 is a rate-limiting enzyme in polyamine catabolism critically involved in the conversion of spermidine and spermine back to putrescine. Surprisingly, we found that activation of SAT1 expression induces lipid peroxidation and sensitizes cells to undergo ferroptosis upon reactive oxygen species (ROS)-induced stress, which also leads to suppression of tumor growth in xenograft tumor models. Notably, SAT1 expression is down-regulated in human tumors, and CRISPR-cas9-mediated knockout of SAT1 expression partially abrogates p53-mediated ferroptosis. Moreover, SAT1 induction is correlated with the expression levels of arachidonate 15-lipoxygenase (ALOX15), and SAT1-induced ferroptosis is significantly abrogated in the presence of PD146176, a specific inhibitor of ALOX15. Thus, our findings uncover a metabolic target of p53 involved in ferroptotic cell death and provide insight into the regulation of polyamine metabolism and ferroptosis-mediated tumor suppression.

One-Carbon Metabolism in Prostate Cancer: The Role of Androgen Signaling

Cancer cell metabolism differs significantly from the metabolism of non-transformed cells. This altered metabolic reprogramming mediates changes in the uptake and use of nutrients that permit high rates of proliferation, growth, and survival. The androgen receptor (AR) plays an essential role in the establishment and progression of prostate cancer (PCa), and in the metabolic adaptation that takes place during this progression. In its role as a transcription factor, the AR directly affects the expression of several effectors and regulators of essential catabolic and biosynthetic pathways. Indirectly, as a modulator of the one-carbon metabolism, the AR can affect epigenetic processes, DNA metabolism, and redox balance, all of which are important factors in tumorigenesis. In this review, we focus on the role of AR-signaling on one-carbon metabolism in tumorigenesis. Clinical implications of one-carbon metabolism and AR-targeted therapies for PCa are discussed in this context.

Self-immolative polycations as gene delivery vectors and prodrugs targeting polyamine metabolism in cancer

Polycations are explored as carriers to deliver therapeutic nucleic acids. Polycations are conventionally pharmacological inert with the sole function of delivering therapeutic cargo. This study reports synthesis of a self-immolative polycation (DSS-BEN) based on a polyamine analogue drug N(1),N(11)-bisethylnorspermine (BENSpm). The polycation was designed to function dually as a gene delivery carrier and a prodrug targeting dysregulated polyamine metabolism in cancer. Using a combination of NMR and HPLC, we confirm that the self-immolative polycation undergoes intracellular degradation into the parent drug BENSpm. The released BENSpm depletes cellular levels of spermidine and spermine and upregulates polyamine catabolic enzymes spermine/spermidine N(1)-acetyltransferase (SSAT) and spermine oxidase (SMO). The synthesized polycations form polyplexes with DNA and facilitate efficient transfection. Taking advantage of the ability of BENSpm to sensitize cancer cells to TNFα-induced apoptosis, we show that DSS-BEN enhances the cell killing activity of TNFα gene therapy. The reported findings validate DSS-BEN as a dual-function delivery system that can deliver a therapeutic gene and improve the outcome of gene therapy as a result of the intracellular degradation of DSS-BEN to BENSpm and the subsequent beneficial effect of BENSpm on dysregulated polyamine metabolism in cancer.

Polyamines metabolism and breast cancer: state of the art and perspectives

Breast cancer (BC) is a common disease that generally occurs in women over the age of 50, and the risk is especially high for women over 60 years of age. One of the major BC therapeutic problems is that tumors initially responsive to chemotherapeutic approaches can progress to more aggressive forms poorly responsive to therapies. Polyamines (PAs) are small polycationic alkylamines, naturally occurring and essential for normal cell growth and development in eukaryotes. The intracellular concentration of PA is maintained within strongly controlled contents, while a dysregulation occurs in BC cells. Polyamines facilitate the interactions of transcription factors, such as estrogen receptors with their specific response element, and are involved in the proliferation of ER-negative and highly invasive BC tumor cells. Since PA metabolism has a critical role in cell death and proliferation, it represents a potential target for intervention in BC. The goal of this study was to perform a literature search reviewing the association between PA metabolism and BC, and the current evidence supporting the BC treatment targeting PA metabolism. We here describe in vitro and in vivo models, as well as the clinical trials that have been utilized to unveil the relationship between PA metabolism and BC. Polyamine pathway is still an important target for the development of BC chemotherapy via enzyme inhibitors. Furthermore, a recent promising strategy in breast anticancer therapy is to exploit the self-regulatory nature of PA metabolism using PA analogs to affect PA homeostasis. Nowadays, antineoplastic compounds targeting the PA pathway with novel mechanisms are of great interest and high social impact for BC chemotherapy.

Phase 1 study of N(1),N(11)‑diethylnorspermine (DENSPM) in patients with advanced hepatocellular carcinoma

PURPOSE

N(1),N(11)-diethylnorspermine (DENSPM), a synthetic analog of the naturally occurring polyamine spermine, can induce polyamine depletion and inhibit tumor cell growth. The objectives of this phase I study were to assess the safety, maximum-tolerated dose (MTD), pharmacokinetics, and preliminary antitumor activity of DENSPM in advanced HCC.

METHODS

Patients with measurable advanced HCC, Child-Pugh A or B cirrhosis, CLIP score ≤3, and Karnofsky score ≥60 % were eligible. DENSPM was given as a short intravenous infusion on days 1, 3, 5, 8, 10, and 12 of each 28-day cycle. The starting dose of 30 mg/m(2) was escalated at a fixed increment of 15 mg/m(2) until the MTD was identified. The plasma pharmacokinetics of DENSPM for the first and last doses given in cycle 1 was characterized.

RESULTS

Thirty-eight patients (male 79 %; median age 61 years; Child-Pugh A 84 %; ≥1 prior systemic therapy 45 %) were enrolled and treated. The most common adverse events (AEs) ≥grade 1 were fatigue (53 %), nausea (34 %), diarrhea (32 %), vomiting (32 %), anemia (29 %), and elevated AST (29 %). The most common grade 3-4 AEs were fatigue/asthenia (13 %), elevated AST (13 %), hyperbilirubinemia (11 %), renal failure (8 %), and hyperglycemia (8 %). The MTD was 75 mg/m(2). There were no objective responses, although 7/38 (18 %) patients achieved stable disease for ≥16 weeks. The overall mean (±SD) total body clearance for the initial dose, 66.3 ± 35.9 L/h/m(2) (n = 16), was comparable to the clearance in patients with normal to near normal hepatic function. Drug levels in plasma decayed rapidly immediately after the infusion but remained above 10 nM for several days after dosing at the MTD.

CONCLUSIONS

N(1),N(11)-diethylnorspermine treatment at the MTD of 75 mg/m(2), given intravenously every other weekday for two consecutive weeks of each 28-day cycle, was relatively well tolerated in patients with advanced HCC including those with mild-to-moderate liver dysfunction. This administration schedule provided prolonged systemic exposure to potentially effective concentrations of the drug. Stable disease was seen in 18 % of patients receiving DENSPM treatment. Further evaluation of DENSPM monotherapy for advanced HCC does not appear to be justified because of insufficient evidence of clinical benefit in the patients evaluated in this study.

A novel assay platform for the detection of translation modulators of spermidine/spermine acetyltransferase

Spermidine/spermine-N1-acetyltransferase (SSAT) is a mitochondrial-localized enzyme that is highly inducible and tightly controlled and is the rate-limiting enzyme in polyamine catabolism. It is known that SSAT is induced when polyamine level increases. Although multiple mechanisms have been implicated, translational control is thought to be paramount. Previous studies with transgenic and knockout mice suggested that for certain human conditions, the modulation of SSAT levels could offer therapeutic benefits. Besides polyamines and their analogs, certain stimuli can increase SSAT levels, suggesting that the development of reporters for high throughput screening can lead to the identification of novel pharmacophores that can modulate SSAT translation. Here we report the development and validation of a luciferase-based biosensor system for the identification of compounds that are able to either promote or prevent the translation of SSAT. The system uses HEK293T cells transfected with a construct composed of SSAT mRNA modified to lack upstream open reading frame (uORF) function, is mutated to reduce translational repression and is linked with luciferase. As a proof of principle of the utility of the SSAT translation sensor, we screened the Prestwick drug library (1,200 FDA Approved compounds). The library contained 15 compounds that activated SSAT translation by at least 40% more than the basal expression, but none exceeded the positive control N1, N11-diethylnorspermine. On the other hand, 38 compounds were found to strongly inhibit SSAT translation. We conclude that this biosensor can lead to the identification of novel pharmacophores that are able to modulate the translation of SSAT.

Polyamines and cancer: implications for chemotherapy and chemoprevention

Polyamines are small organic cations that are essential for normal cell growth and development in eukaryotes. Under normal physiological conditions, intracellular polyamine concentrations are tightly regulated through a dynamic network of biosynthetic and catabolic enzymes, and a poorly characterised transport system. This precise regulation ensures that the intracellular concentration of polyamines is maintained within strictly controlled limits. It has frequently been observed that the metabolism of, and the requirement for, polyamines in tumours is frequently dysregulated. Elevated levels of polyamines have been associated with breast, colon, lung, prostate and skin cancers, and altered levels of rate-limiting enzymes in both biosynthesis and catabolism have been observed. Based on these observations and the absolute requirement for polyamines in tumour growth, the polyamine pathway is a rational target for chemoprevention and chemotherapeutics. Here we describe the recent advances made in the polyamine field and focus on the roles of polyamines and polyamine metabolism in neoplasia through a discussion of the current animal models for the polyamine pathway, chemotherapeutic strategies that target the polyamine pathway, chemotherapeutic clinical trials for polyamine pathway-specific drugs and ongoing clinical trials targeting polyamine biosynthesis.

A potential estrogen mimetic effect of a bis(ethyl)polyamine analogue on estrogen receptor positive MCF-7 breast cancer cells

BE-3-3-3-3 (1,15-(ethylamino)4,8,12-triazapentadecane) is a bis(ethyl)polyamine analogue under investigation as a therapeutic agent for breast cancer. Since estradiol (E(2)) is a critical regulatory molecule in the growth of breast cancer, we examined the effect of BE-3-3-3-3 on estrogen receptor α (ERα) positive MCF-7 cells in the presence and absence of E(2). In the presence of E(2), a concentration-dependent decrease in DNA synthesis was observed using [(3)H]-thymidine incorporation assay. In the absence of E(2), low concentrations (2.5-10 μM) of BE-3-3-3-3 increased [(3)H]-thymidine incorporation at 24 and 48 h. BE-3-3-3-3 induced the expression of early response genes, c-myc and c-fos, in the absence of E(2), but not in its presence, as determined by real-time quantitative polymerase chain reaction (qPCR). BE-3-3-3-3 had no significant effect on these genes in an ERα-negative cell line, MDA-MB-231. Chromatin immunoprecipitation assay demonstrated enhanced promoter occupation by either E(2) or BE-3-3-3-3 of an estrogen-responsive gene pS2/Tff1 by ERα and its co-activator, steroid receptor co-activator 3 (SRC-3). Confocal microscopy of BE-3-3-3-3-treated cells revealed membrane localization of ERα, similar to that induced by E(2). The failure of BE-3-3-3-3 to inhibit cell proliferation was associated with autophagic vacuole formation, and the induction of Beclin 1 and MAP LC3 II. These results indicate a differential effect of BE-3-3-3-3 on MCF-7 cells in the absence and presence of E(2), and suggest that pre-clinical and clinical development of polyamine analogues might require special precautions and selection of sensitive subpopulation of patients.

Overexpression of spermidine/spermine N1-acetyltransferase or treatment with N1-N11-diethylnorspermine attenuates the severity of zinc-induced pancreatitis in mouse

Depletion of pancreatic intracellular polyamine pools has been observed in acute pancreatitis both in the animal models and in humans. In this study, the wild-type mice, polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase overexpressing (SSAT mice) and SSAT-deficient mice were used to characterize the new zinc-induced acute pancreatitis mouse model and study the role of polyamines and polyamine catabolism in this model. Intraperitoneal zinc injection induced acute necrotizing pancreatitis in wild-type mice as well as in SSAT-overexpressing and SSAT-deficient mice. Serum α-amylase activity was significantly increased in all zinc-treated mice compared with the untreated controls. However, the α-amylase activities in SSAT mice were constantly lower than those in the other groups. Histopathological examination of pancreatic tissue revealed edema, acinar cell necrosis and necrotizing inflammation, typical for acute pancreatitis. Compared with the other zinc-treated mice less damage according to the histopathological analysis was observed in the pancreatic tissue of SSAT mice. Levels of intracellular spermidine, and occasionally spermine, were significantly decreased in pancreases of all zinc-treated animals and SSAT enzyme activity was enhanced both in wild-type and SSAT mice. Interestingly, a spermine analog, N(1), N(11)-diethylnorspermine (DENSpm), enhanced the proliferation of pancreatic cells and reduced the severity of zinc-induced pancreatitis in wild-type mice. The results show that in mice a single intraperitoneal zinc injection causes acute necrotizing pancreatitis accompanied by decrease of intracellular polyamine pools. The study supports the important role of polyamines for the integrity and function of the pancreas. In addition, the study suggests that whole body overexpression of SSAT obtained in SSAT mice reduces inflammatory pancreatic cell injury.

Spermine oxidase (SMO) activity in breast tumor tissues and biochemical analysis of the anticancer spermine analogues BENSpm and CPENSpm

BACKGROUND

Polyamine metabolism has a critical role in cell death and proliferation representing a potential target for intervention in breast cancer (BC). This study investigates the expression of spermine oxidase (SMO) and its prognostic significance in BC. Biochemical analysis of Spm analogues BENSpm and CPENSpm, utilized in anticancer therapy, was also carried out to test their property in silico and in vitro on the recombinant SMO enzyme.

METHODS

BC tissue samples were analyzed for SMO transcript level and SMO activity. Student's t test was applied to evaluate the significance of the differences in value observed in T and NT samples. The structure modeling analysis of BENSpm and CPENSpm complexes formed with the SMO enzyme and their inhibitory activity, assayed by in vitro experiments, were examined.

RESULTS

Both the expression level of SMO mRNA and SMO enzyme activity were significantly lower in BC samples compared to NT samples. The modeling of BENSpm and CPENSpm complexes formed with SMO and their inhibition properties showed that both were good inhibitors.

CONCLUSIONS

This study shows that underexpression of SMO is a negative marker in BC. The SMO induction is a remarkable chemotherapeutical target. The BENSpm and CPENSpm are efficient SMO inhibitors. The inhibition properties shown by these analogues could explain their poor positive outcomes in Phases I and II of clinical trials.

Characterization of Pt-, Pd-spermine complexes for their effect on polyamine pathway and cisplatin resistance in A2780 ovarian carcinoma cells

We have previously showed that platinum drugs up-regulate SSAT and SMO and down-regulate ODC and SAMDC in the polyamine pathway. Several studies including our own established that platinum drugs combined with polyamine analog DENSPM produces synergistic increase in SSAT activity with polyamine depletion. Since polyamine pathway is an important therapeutic target, we investigated whether agents containing both platinum and polyamines have similar effects on the polyamine pathway. Two complexes i) Pt-spermine with two cisplatin molecules linked to a spermine in the center and ii) Pd-spermine with similar structure i, but Pd (II) substituted for Pt (II) were analyzed with respect to their effect on the expression of genes in polyamine pathway, SSAT and SMO protein expression, SSAT activity and polyamine pools. Pt-, Pd-spermine complexes induced significant down-regulation of SMO, arginase 2 and NRF-2, with no change in SSAT, while cisplatin as a single agent or in combination with DENSPM induced significant up-regulation of SSAT and SMO. The SSAT activity was not induced by either Pt- or Pd-spermine in A2780 cells; SMO protein levels were significantly elevated compared to the no-drug control and to a similar extent as cisplatin/DENSPM. The Pd-spm treatment induced a fall in putrescine levels to 33%, spermidine to 62% and spermine to 72% while Pt-spm did not induce such a decline. Comparative cytotoxicity studies in A2780 cells indicated the potency to be cisplatin> Pd-Spm>Pt-Spm. Although both complexes exhibit a lower potency, the degree of resistance itself is much lower for Pt-spermine and Pd-spermine in that order (2.5 and 7.5, respectively) compared to cisplatin ( approximately 12) as tested in cisplatin resistant A2780/CP cells. These studies suggest that Pd (II)-polyamine complexes may constitute a promising group of inorganic compounds for further studies in the development of novel chemotherapy/adjuvant chemotherapy strategies.

Combination effects of platinum drugs and N1, N11 diethylnorspermine on spermidine/spermine N1-acetyltransferase, polyamines and growth inhibition in A2780 human ovarian carcinoma cells and their oxaliplatin and cisplatin-resistant variants

Purpose

To understand the mechanisms behind platinum drug/DENSPM-induced inhibition of cancer cell growth, we compared the effects of oxaliplatin and cisplatin when combined with DENSPM on the induction of SSAT mRNA, activity, polyamines and cell growth in A2780 human ovarian carcinoma cells and their oxaliplatin- and cisplatin-resistant variants A2780/C10B and A2780/CP, respectively.

Methods

Parental and Pt-resistant cells were treated with platinum agent alone, DENSPM alone or combination (10 μM each, 20 h). QRT–PCR, radioactive product measurement and HPLC were used for mRNA, activity and polyamine pools, respectively; drug interaction on cell growth was by SRB and isobologram analysis.

Results

Both platinum agents induced SSAT mRNA in parental A2780 cells, but not in resistant cells. Platinum drug/DENSPM combinations produced high levels of SSAT activity in parental cells with significant depletion of spermine and spermidine, but not in resistant cells. Co-treatment with platinum agents increased the levels of DENSPM in all cell lines. Oxaliplatin/DENSPM combination was superior to cisplatin/DENSPM in the inhibition of cell growth in parental cells. No synergy was observed in the resistant cells.

Conclusions

Increased DENSPM levels following co-treatment with Pt agents enhances the translation and stability of SSAT protein leading to polyamine pool depletion, facilitating more Pt–DNA adduct formation in parental cells. Oxaliplatin/DENSPM combination is superior to cisplatin/DENSPM in cell growth inhibition as DACH-Pt DNA adducts are cytotoxic even at relatively fewer numbers. Reduced platinum uptake in Pt-resistant cells contributes to reduced SSAT mRNA induction and absence of synergy when combined with DENSPM.

Design of polyamine-based therapeutic agents: new targets and new directions

Enzymes in the biosynthetic and catabolic polyamine pathway have long been considered targets for drug development, and early drug discovery efforts in the polyamine area focused on the design and development of specific inhibitors of the biosynthetic pathway, or polyamine analogues that specifically bind DNA. More recently, it has become clear that the natural polyamines are involved in numerous known and unknown cellular processes, and disruption of polyamine functions at their effector sites can potentially produce beneficial therapeutic effects. As new targets for polyamine drug discovery continue to evolve, the rational design of polyamine analogues will result in more structurally diverse agents. In addition, the physical linkage of polyamine-like structures to putative drug molecules can have beneficial effects resulting from increases in DNA affinity and selective cellular uptake. The present chapter will summarize recent advances in the development of alkylpolyamine analogues as antitumour agents, and describe subsequent advances that have resulted from incorporating polyamine character into more diverse drug molecules. Specifically, new polyamine analogues, and the role of polyamine fragments in the design of antiparasitic agents, antitumour metal complexes, histone deacetylase inhibitors and lysine-specific demethylase 1 inhibitors, will be described.

Polyamine catabolism in colorectal cancer cells following treatment with oxaliplatin, 5-fluorouracil and N1, N11 diethylnorspermine

PURPOSE

Our previous studies showed that combined treatment of oxaliplatin and N(1), N(11) diethyl-norspermine (DENSPM) results in massive induction of spermidine/spermine N(1)-acetyltransferase (SSAT) mRNA and activity. Since oxaliplatin and 5-fluorouracil (5FU) are used clinically in treatment of colorectal cancers, this study examines the effect of adding DENSPM to oxaliplatin/5FU combination on SSAT and spermine oxidase (SMO) in HCT-116 cells.

METHODS

HCT-116 cells were treated with clinically relevant concentrations of drugs for 20 h followed by 24 h in drug free medium. SSAT and SMO mRNA and protein were assayed by QRT-PCR and Westerns respectively; polyamine pools were measured by HPLC. SSAT and SMO mRNA in tumor biopsies from patients with rectal cancer receiving oxaliplatin, capecitabine and radiation were measured by QRT-PCR.

RESULTS

Oxaliplatin + 5FU + DENSPM produced significantly higher levels of SSAT and SMO mRNA, protein and activity than those seen with oxaliplatin+5FU with a significant depletion of cellular spermine and spermidine pools. Oxaliplatin/DENSPM was superior to 5FU/DENSPM in SSAT induction but similar for SMO. Oxaliplatin + DENSPM revealed synergistic growth inhibition at >IC(50) concentrations and antagonism at

CONCLUSIONS

These studies demonstrated that combining DENSPM with oxaliplatin + 5FU provides an added benefit by aiming at the clinically relevant therapeutic target, the polyamine catabolism. Further, we show for the first time, that SMO and SSAT induction could be measured in tumor biopsies in patients receiving chemo-radiation. Optimization of treatment conditions in vivo should facilitate a clinical evaluation of the three drug combination.

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Key Words Collapse

MESH Headings

• Acetyltransferases/genetics
• Acetyltransferases/metabolism
• Antineoplastic Combined Chemotherapy Protocols/pharmacology
• Antineoplastic Combined Chemotherapy Protocols/therapeutic use
• Blotting, Western
• Cell Line, Tumor
• Colonic Neoplasms/drug therapy
• Colonic Neoplasms/metabolism
• Colonic Neoplasms/pathology
• Drug Synergism
• Fluorouracil/pharmacology
• Fluorouracil/therapeutic use
• Gene Expression/drug effects
• Humans
• Organoplatinum Compounds/pharmacology
• Organoplatinum Compounds/therapeutic use
• Oxaliplatin
• Oxidoreductases Acting on CH-NH Group Donors/genetics
• Oxidoreductases Acting on CH-NH Group Donors/metabolism
• Polyamines/metabolism
• Rectal Neoplasms/drug therapy
• Rectal Neoplasms/metabolism
• Rectal Neoplasms/pathology
• Spermine/analogs & derivatives
• Spermine/pharmacology
• Spermine/therapeutic use
• Polyamine Oxidase

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Grants

• CA 10656 NCI NIH HHS
• CA 109619 NCI NIH HHS

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Affiliation(s)

Suzanne Hector Department of Medicine, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263, USA
Ramakumar Tummala
Nicholas D Kisiel
Paula Diegelman
Slavoljub Vujcic
Kimberly Clark
Marwan Fakih
Debora L Kramer
Carl W Porter
Lakshmi Pendyala

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In vitro and in vivo effects of the conformationally restricted polyamine analogue CGC-11047 on small cell and non-small cell lung cancer cells

PURPOSE

Polyamines are essential for normal growth; however, the requirement for, and the metabolism of, polyamines are frequently dysregulated in cancer. Polyamine analogues have demonstrated promising preclinical results in multiple model systems of cancer, but their clinical utility has been limited by apparent toxicity. A representative compound of a new generation of short chain, conformationally restricted polyamine analogues, CGC-11047 has been synthesized and ongoing phase I clinical trials indicate it to be well tolerated at weekly doses of 610 mg (dose escalation is still in progress). Therefore, studies were designed to gain a better understanding of its effects on cellular polyamine biochemistry and efficacy in the treatment of human lung cancer models in vitro and in vivo.

METHODS

Human lung cancers cell lines representing non-small cell and small cell lung cancers were investigated for their growth and biochemical response to CGC-11047. Effects of in vitro treatment with CGC-11047 on cell growth, the activity of the polyamine biosynthetic enzyme ornithine decarboxylase (ODC), and the expression and activity of the polyamine catabolic enzymes spermidine/spermine N(1)-acetyltransferase (SSAT) and spermine oxides (SMO) were measured. Additionally, the overall effects on intracellular polyamine pools were monitored. Finally, the in vivo efficacy of CGC-11047 in the treatment of a nude mouse model of human non-small cell lung cancer was evaluated.

RESULTS

CGC-11047 effectively inhibited the growth of both small cell and non-small cell lung cancer cells in vitro. The greatest biochemical effects were observed in the non-small cell lung cancer cells where in addition to a profound down regulation of ODC activity, there was a significant increase in polyamine catabolism leading to a greater degree of polyamine pool depletion and greater accumulation of CGC-11047 when compared with the changes observed for the small cell lines. Importantly, CGC-11047 was found to be highly significant (P < 0.0001) in delaying the progression of established tumors in an in vivo model of human non-small cell lung cancer.

CONCLUSION

CGC-11047 represents a promising new polyamine analogue that warrants further preclinical and, potentially, clinical evaluation in lung cancer.

Measurement of spermidine/spermine-N1-acetyltransferase activity by high-performance liquid chromatography with N1-dansylnorspermine as the substrate

We developed a nonradioactive assay to measure spermidine/spermine N(1)-acetyltransferase (SSAT) activity by high-performance liquid chromatography (HPLC). N(1)-dansylnorspermine was prepared and evaluated as a substrate of acetylation with acetyl-CoA by SSAT in rat hepatoma (HTC) cells. Kinetic studies revealed that the K(m) values of N(1)-dansylnorspermine and acetyl-CoA were approximately 11 and 13 microM, respectively. When the assay method was applied to HTC cell samples, the SSAT activity, even at the control level, could easily be detected in as few as 20 microg protein of cell extract corresponding to 1 x 10(5) cells per determination, and 100 samples could be analyzed overnight. Thus, our HPLC method is a rapid and sensitive assay for the measurement of SSAT activity.

Targeting polyamine metabolism: a viable therapeutic/preventative solution for cancer?

The polyamine pathway has been identified as a target for the design of new antiproliferative drugs, due to the strong positive relationship between intracellular polyamine content and cell, particularly cancer cell growth. A number of single enzyme inhibitors have been synthesised against the two key biosynthetic enzymes, ornithine decarboxylase and S-adenosylmethionine decarboxylase, but their success in the clinic has been limited due to incomplete polyamine depletion and induction of compensatory mechanisms that counteract the effects of enzyme inhibition. Overall, clinical trials of these agents as chemotherapeutic drugs have proved disappointing, with either little clinical efficacy or unacceptable toxicity. The polyamine analogues provide an alternative strategy that shows promise, particularly against diseases other than cancer. Combination of the polyamine inhibitors with classic cytotoxic agents may be an alternative strategy that is showing some promise, at least in vitro. An avenue that is, however, presently more promising is the use of polyamine inhibitors or analogues as chemopreventative agents against a range of human cancers. It seems likely that the future use of these drugs will be in disease prevention rather than treatment. With regard to the newer agents with restricted conformation that are now undergoing clinical trials, it is too early to say whether they will be chemotherapeutic and/or chemopreventative. This article focuses on the clinical use and responses to inhibitors of polyamine metabolism.

Polyamine-dependent Regulation of Spermidine-Spermine N1-Acetyltransferase mRNA Translation

Spermidine-spermine N(1)-acetyltransferase (SSAT) is induced in response to an elevation in intracellular polyamine pools. The increased enzyme activity is the result of an increase in gene transcription, mRNA translation, and protein stability. Induction of SSAT by polyamine analogues can lead to intracellular polyamine depletion and apoptosis. The mechanism by which polyamines alter the translational efficiency of SSAT mRNA is not well understood. In this study, we investigated the regulation of SSAT translation by the polyamine analogue N(1),N(11)-diethylnorspermine (DENSPM). DENSPM induced expression of both FLAG-tagged SSAT and SSAT fused to Renilla luciferase in a time- and concentration-dependent manner. This effect was not inhibited by actinomycin D indicating that changes in gene transcription did not explain the enhanced expression in the presence of DENSPM. Furthermore, because FLAG-SSAT did not contain the 5'- or 3'-untranslated regions of SSAT, translational regulation involved the coding sequence only. By contrast, cycloheximide completely inhibited induction by DENSPM, indicating a requirement for new protein synthesis. Deletion constructs identified two regions of the SSAT protein-coding RNA sequence that conferred polyamine responsiveness. Using these regions as probes in RNA electrophoretic mobility shift assays, we observed specific binding of a cytoplasmic protein. In addition, we found that the interaction between the RNA probes and the binding protein could be inhibited by DENSPM in a concentration-dependent manner. These results suggest that polyamines regulate SSAT mRNA translational efficiency by inhibiting a repressor protein from binding to regions of the coding sequence of the SSAT transcript.

Targeting polyamine metabolism and function in cancer and other hyperproliferative diseases

The polyamines spermidine and spermine and their diamine precursor putrescine are naturally occurring, polycationic alkylamines that are essential for eukaryotic cell growth. The requirement for and the metabolism of polyamines are frequently dysregulated in cancer and other hyperproliferative diseases, thus making polyamine function and metabolism attractive targets for therapeutic intervention. Recent advances in our understanding of polyamine function, metabolic regulation, and differences between normal cells and tumour cells with respect to polyamine biology, have reinforced the interest in this target-rich pathway for drug development.

Polyamine analogues – an update

The polyamines are growth factors in both normal and cancer cells. As the intracellular polyamine content correlates positively with the growth potential of that cell, the idea that depletion of polyamine content will result in inhibition of cell growth and, particularly tumour cell growth, has been developed over the last 15 years. The polyamine pathway is therefore a target for development of rationally designed, antiproliferative agents. Following the lessons from the single enzyme inhibitors (alpha-difluoromethylornithine DFMO), three generations of polyamine analogues have been synthesised and tested in vitro and in vivo. The analogues are multi-site inhibitors affecting multiple reactions in the pathway and thus prevent the up-regulation of compensatory reactions that have been the downfall of DFMO in anticancer chemotherapy. Although the initial concept was that the analogues may provide novel anticancer drugs, it now seems likely that the analogues will have wider applications in diseases involving hyperplasia.

Concentration-dependent effects ofN1,N11-diethylnorspermine on melanoma cell proliferation

N1, N11-diethylnorspermine (DENSPM) is a polyamine analog that is currently under investigation as a novel anticancer drug. Although it has shown promising preclinical activity, there has been large variation in responsiveness reported between different human cancers. During our studies into the causes of this variation, we observed a consistent increase in cell proliferation at low drug concentrations (<10 microM) in human melanoma cells resistant to the drug. At higher concentrations, growth inhibition was seen in all cell lines, with IC50 values ranging 2-180 microM. We hypothesized that DENSPM may mimic endogenous polyamines at low concentrations, supporting cell growth in resistant lines. We also observed that DENSPM downregulated polyamine transport in a manner similar to that for spermidine, a finding that confirms previous reports. Finally, DENSPM could rescue cells from growth arrest by the ornithine decarboxylase inhibitor difluoromethylornithine, which depletes intracellular polyamines. Taken together, these results suggest that DENSPM, at clinically relevant concentrations, can mimic endogenous polyamines and induce proliferation in resistant human melanoma cells.

Pharmacological aspects of cytotoxic polyamine analogs and derivatives for cancer therapy

During the past 20 years, numerous derivatives and analogues of spermidine (Spd) and spermine (Spm) were synthesized with the aim to generate a new type of anticancer drug. The common denominator of most cytotoxic polyamine analogues is their lipophilicity, which is superior to that of the parent amines. The natural polyamines bind to polyanions and to proteins with anionic binding sites. Their hydrophilicity/hydrophobicity is balanced, allowing them to perform physiological functions by interacting with some of these anionic structures, without impairing the functionality of others. Because the attachment of lipophilic substituents to the polyamine backbone increases the binding energy, lipophilic polyamine derivatives affect secondary and tertiary structures of a larger number of macromolecules than do their natural counterparts. In addition, lipophilicity improves the blood-brain barrier transport and thus enhances CNS toxicity. Close structural analogues of spermidine and spermine mimic the natural polyamines in regulatory functions. The cytotoxic mechanisms of analogues with a less close structural resemblance to spermidine or spermine have not been completely clarified. The displacement of spermidine from functional binding sites and the consequent prevention of its physiological roles is a likely mechanism, but many others may play a role as well. Up to now, polyamine analogues were conceived without specific growth-related targets in mind. To develop therapeutically useful drugs, it will be imperative to identify specific targets and to design compounds that interact selectively with the target molecules. It will also be necessary to include, at an early state of the work, pharmacological and toxicological considerations, to avoid unproductive directions.

Small Interfering RNA Suppression of Polyamine Analog-Induced Spermidine/SpermineN1-Acetyltransferase

N1,N11-diethylnorspermine (DENSPM) is a polyamine analog that down-regulates polyamine biosynthesis and potently upregulates the polyamine catabolic enzyme spermidine/spermine N1-acetyltransferase (SSAT). In certain cells, such as SKMEL-28 human melanoma cells, induction of SSAT is associated with rapid apoptosis. In this study, we used small interfering RNA (siRNA) to examine the role of SSAT induction in mediating polyamine pool depletion and apoptosis. siRNA duplexes were designed to target three independent sites in the SSAT mRNA coding region (siSSAT). When transfected under nontoxic conditions, two of the duplexes selectively reduced basal SSAT mRNA in HEK-293 cells by >80% and prevented DENSPM-induced SSAT mRNA by 95% in SK-MEL-28 cells. Treatment of SK-MEL-28 cells with 10 muM DENSPM in the presence of 83 nM siSSAT selectively prevented the 1400-fold induction of SSAT activity by approximately 90% and, in turn, prevented analog depletion of spermine (Spm) pools by approximately 35%. siSSAT also prevented DENSPM-induced cytochrome c release and caspase-3 cleavage at 36 h and apoptosis at 48 h as measured by annexin V staining. Overall, the data directly link analog induction of SSAT to Spm pool depletion and to caspase-dependent apoptosis in DENSPM-treated SK-MEL-28 cells. This represents the first use of siRNA technology directed toward a polyamine gene and the first unequivocal demonstration that SSAT induction initiates events leading to polyamine analog-induced apoptosis.

Loss of inhibitor of apoptosis proteins as a determinant of polyamine analog-induced apoptosis in human melanoma cells

We have previously shown that the clinically relevant polyamine analog N1,N11-diethylnorspermine (DENSPM) causes rapid apoptosis in human melanoma SK-MEL-28 cells via a series of events that include mitochondrial release of cytochrome c and activation of the caspase cascade. Upstream to these events, DENSPM downregulates polyamine biosynthesis and potently upregulates polyamine catabolism at the level of spermidine/spermine N1-acetyltransferase (SSAT). In searching for downstream effectors that either contribute to or abrogate the apoptotic response, we observed that DENSPM treatment of SK-MEL-28 cells for 30 h led to cytosolic release of Smac/Diablo, a mitochondrial protein known to bind and inhibit the function of inhibitor of apoptosis proteins (IAPs). Subsequently, we found that DENSPM markedly lowered survivin and ML-IAP protein (but not XIAP) levels by 18 h via an apparently Smac/Diablo-independent pathway. Proteasome inhibitors fully prevented survivin and ML-IAP protein loss as well as apoptosis, suggesting that the proteasome-mediated degradation of survivin and ML-IAP is causally linked to the cellular outcome. We also observed that structural analogs of DENSPM which differentially induced SSAT and apoptosis lowered survivin and ML-IAP levels in a manner that correlated with enzyme activity. The linkage between IAPs and SSAT was more directly established by the finding that selective prevention of SSAT induction by small interfering RNA prevented survivin and ML-IAP loss as well as apoptosis during DENSPM treatment. Among the melanoma cell lines (SK-MEL-28, MALME-3M, A375 and LOX), survivin degradation correlated temporally with the onset of DENSPM induced apoptosis or growth inhibition. By contrast, ML-IAP degradation occurred only during rapid apoptosis seen in SK-MEL-28 cells. These data suggest a sequence of events whereby DENSPM induction of SSAT leads to loss of IAP proteins and a more fulminate apoptotic response. The findings implicate survivin and ML-IAP as important determinants of polyamine analog drug action in melanoma cells.