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

Quantification of spermine oxidase (SMOX) activity in tissues by HPLC

The polyamine oxidases, SMOX and PAOX, are enzymes involved in the normal metabolism of polyamines. Both enzymes are implicated in numerous human diseases including cancer, reperfusion injury, and neurodegenerative diseases. The ability to directly measure the activity of these enzymes is imperative in understanding their role in human health and disease. Most assays currently used to measure both SMOX and PAOX activity use a coupled reaction with horse radish peroxidase (HRP). These assays cannot be used when evaluating certain compounds for potential polyamine oxidase inhibition if these compouds also affect HRP activity. Additionally, since most assays use H2O2 production as an indicator of oxidase activity they cannot be used to evaluate polyamine oxidase activity in the presence of iron or other divalent metals. This prevents the use of these assays to evaluate polyamine oxidase activity in tissue samples. Here we describe the protocols for determining polyamine oxidase activity in an HRP-independent manner via an HPLC-based assay allowing for evaluation of both compounds that may interfere with HRP activity and polyamine oxidase activity in tissue samples.

The Synergistic Benefit of Combination Strategies Targeting Tumor Cell Polyamine Homeostasis

Mammalian polyamines, including putrescine, spermidine, and spermine, are positively charged amines that are essential for all living cells including neoplastic cells. An increasing understanding of polyamine metabolism, its molecular functions, and its role in cancer has led to the interest in targeting polyamine metabolism as an anticancer strategy, as the metabolism of polyamines is frequently dysregulated in neoplastic disease. In addition, due to compensatory mechanisms, combination therapies are clinically more promising, as agents can work synergistically to achieve an effect beyond that of each strategy as a single agent. In this article, the nature of polyamines, their association with carcinogenesis, and the potential use of targeting polyamine metabolism in treating and preventing cancer as well as combination therapies are described. The goal is to review the latest strategies for targeting polyamine metabolism, highlighting new avenues for exploiting aberrant polyamine homeostasis for anticancer therapy and the mechanisms behind them.

A PET probe targeting polyamine transport system for precise tumor diagnosis and therapy

Polyamine metabolism dysregulation is a hallmark of many cancers, offering a promising avenue for early tumor theranostics. This study presents the development of a nuclear probe derived from spermidine (SPM) for dual-purpose tumor PET imaging and internal radiation therapy. The probe, radiolabeled with either [68Ga]Ga for diagnostic applications or [177Lu]Lu for therapeutic use, was synthesized with exceptional purity, stability, and specific activity. Extensive testing involving 12 different tumor cell lines revealed remarkable specificity towards B16 melanoma cells, showcasing outstanding tumor localization and target-to-non-target ratio. Mechanistic investigations employing polyamines, non-labeled precursor, and polyamine transport system (PTS) inhibitor, consistently affirmed the probe's targetability through recognition of the PTS. Notably, while previous reports indicated PTS upregulation in various tumor types for targeted therapy, this study observed no positive signals, highlighting a concentration-dependent discrepancy between targeting for therapy and diagnosis. Furthermore, when labeled with [177Lu], the probe demonstrated its therapeutic potential by effectively controlling tumor growth and extending mouse survival. Investigations into biodistribution, excretion, and biosafety in healthy humans laid a robust foundation for clinical translation. This study introduces a versatile SPM-based nuclear probe with applications in precise tumor theranostics, offering promising prospects for clinical implementation.

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.

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.

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.

The Potential Role of Spermine and Its Acetylated Derivative in Human Malignancies

Polyamines are essential biomolecules for normal cellular metabolism in humans. The roles of polyamines in cancer development have been widely discussed in recent years. Among all, spermine alongside with its acetylated derivative, N¹, N¹²-Diacetylspermine, demonstrate a relationship with the diagnosis and staging of various cancers, including lung, breast, liver, colorectal and urogenital. Numerous studies have reported the level of spermine in different body fluids and organ tissues in patients with different types of cancers. Currently, the role and the underlying mechanisms of spermine in cancer development and progression are still under investigation. This review summarized the roles of spermine in cancer development and as a diagnostic, prognostic and therapeutic tool in various cancers.

Recent Advances in the Synthesis of Polyamine Derivatives and Their Applications

Biogenic polyamines (PAs) are involved in the growth and development of normal cells, and their intracellular concentration is stable. The concentration of PAs in cancer cells is significantly increased to promote and sustain their rapid proliferation. Over the years, synthetic PAs, which differ in their structure, have demonstrated high antitumor activity and are involved in clinical trials. The chemical synthesis of PAs and their conjugates require the correct choice of synthetic pathways-methods for constructing conjugates and the orthogonal protection of amino groups. The most common methods of synthesis of PA conjugates are acylation of regioselectively protected PAs or their alkylation under the conditions of the Fukuyama reaction. One of the most promising methods of PA synthesis is the use of a multicomponent Ugi reaction, which allows various PAs to be obtained in high yields. In this review, we describe and analyze various approaches that are used in the synthesis of polyamines and their conjugates.

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.

Antimicrobial and antitumor activity of peptidomimetics synthesized from amino acids

Thirteen cationic peptidomimetics derived from amino acids bearing an alkyl or ethynylphenyl moiety that mimic the structure of cationic antibacterial peptides were designed and synthesized using a simple coupling reaction of an amino acid with a substituted amine. Antibacterial activities of the resulting peptidomimetics against drug-sensitive bacteria, such as Gram-positive Staphylococcus aureus (S. aureus) and Bacillus subtilis, Gram-negative Escherichia coli (E. coli) and Salmonella enterica, and a drug-resistant bacterium, methicillin-resistant S. aureus (MRSA), were systematically evaluated. Most peptidomimetics show significant broad-spectrum antibacterial activity. A-L-Iso-C₁₂ (isoleucine derivative bearing a dodecyl moiety) show MICs of 2.5 μg/mL against S. aureus and 4 μg/mL against MRSA and A-L-Val-C₁₂ (valine derivative bearing a dodecyl moiety) show MICs of 1.67 μg/mL against E. coli and 8.3 μg/mL against MRSA. A-L-Val-C₁₂ showed low cytotoxicity toward L929 cells in comparison with SGC 7901 cells, indicating tumor-directed killing by peptidomimetics while avoiding toxicity to normal cells. The influences of type of amino acid and substituent, length of substituent, and stereochemistry of amino acids on antibacterial activity and cytotoxicity of peptidomimetics were systematically investigated. The results indicate that this series of cationic peptidomimetics derived from amino acids display antitumor activity and may be useful for treatment of bacterial infections.

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.

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.

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.

The old and new biochemistry of polyamines

Polyamines are ubiquitous positively charged amines found in all organisms. These molecules play a crucial role in many biological functions including cell growth, gene regulation and differentiation. The three major polyamines produced in all mammalian cells are putrescine, spermidine and spermine. The intracellular levels of these polyamines depend on the interplay of the biosynthetic and catabolic enzymes of the polyamine and methionine salvage pathway, as well as the involvement of polyamine transporters. Polyamine levels are observed to be high in cancer cells, which contributes to malignant transformation, cell proliferation and poor patient prognosis. Considering the critical roles of polyamines in cancer cell proliferation, numerous anti-polyaminergic compounds have been developed as anti-tumor agents, which seek to suppress polyamine levels by specifically inhibiting polyamine biosynthesis, activating polyamine catabolism, or blocking polyamine transporters. However, in terms of the development of effective anti-cancer therapeutics targeting the polyamine system, these efforts have unfortunately resulted in little success. Recently, several studies using the iron chelators, O-trensox and ICL670A (Deferasirox), have demonstrated a decline in both iron and polyamine levels. Since iron levels are also high in cancer cells, and like polyamines, are required for proliferation, these latter findings suggest a biochemically integrated link between iron and polyamine metabolism.

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.

Biochemical evaluation of the anticancer potential of the polyamine-based nanocarrier Nano11047

Synthesizing polycationic polymers directly from existing drugs overcomes the drug-loading limitations often associated with pharmacologically inert nanocarriers. We recently described nanocarriers formed from a first-generation polyamine analogue, bis(ethyl)norspermine (BENSpm), that could simultaneously target polyamine metabolism while delivering therapeutic nucleic acids. In the current study, we describe the synthesis and evaluation of self-immolative nanocarriers derived from the second-generation polyamine analogue PG-11047. Polyamines are absolutely essential for proliferation and their metabolism is frequently dysregulated in cancer. Through its effects on polyamine metabolism, PG-11047 effectively inhibits tumor growth in cancer cell lines of multiple origins as well as in human tumor mouse xenografts. Promising clinical trials have been completed verifying the safety and tolerance of this rotationally restricted polyamine analogue. We therefore used PG-11047 as the basis for Nano11047, a biodegradable, prodrug nanocarrier capable of targeting polyamine metabolism. Following exposure of lung cancer cell lines to Nano11047, uptake and intracellular degradation into the parent compound PG-11047 was observed. The release of PG-11047 highly induced the polyamine catabolic enzyme activities of spermidine/spermine N1-acetyltransferase (SSAT) and spermine oxidase (SMOX). By contrast, the activity of ornithine decarboxylase (ODC), a rate-limiting enzyme in polyamine biosynthesis and a putative oncogene, was decreased. Consequently, intracellular levels of the natural polyamines were depleted concurrent with tumor cell growth inhibition. This availability of Nano11047 as a novel drug form and potential nucleic acid delivery vector will potentially benefit and encourage future clinical studies.

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.

Histone deacetylase inhibition overcomes drug resistance through a miRNA-dependent mechanism

The treatment of specific tumor cell lines with poly- and oligoamine analogs results in a superinduction of polyamine catabolism that is associated with cytotoxicity; however, other tumor cells show resistance to analog treatment. Recent data indicate that some of these analogs also have direct epigenetic effects. We, therefore, sought to determine the effects of combining specific analogs with an epigenetic targeting agent in phenotypically resistant human lung cancer cell lines. We show that the histone deacetylase inhibitor MS-275, when combined with (N(1), N(11))-bisethylnorspermine (BENSpm) or (N(1), N(12))-bis(ethyl)-cis-6,7-dehydrospermine tetrahydrochloride (PG-11047), synergistically induces the polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase (SSAT), a major determinant of sensitivity to the antitumor analogs. Evidence indicates that the mechanism of this synergy includes reactivation of miR-200a, which targets and destabilizes kelch-like ECH-associated protein 1 (KEAP1) mRNA, resulting in the translocation and binding of nuclear factor (erythroid-derived 2)-like 2 (NRF2) to the polyamine-responsive element of the SSAT promoter. This transcriptional stimulation, combined with positive regulation of SSAT mRNA and protein by the analogs, results in decreased intracellular concentrations of natural polyamines and growth inhibition. The finding that an epigenetic targeting agent is capable of inducing a rate-limiting step in polyamine catabolism to overcome resistance to the antitumor analogs represents a completely novel chemotherapeutic approach. In addition, this is the first demonstration of miRNA-mediated regulation of the polyamine catabolic pathway. Furthermore, the individual agents used in this study have been investigated clinically; therefore, translation of these combinations into the clinical setting holds promise.

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.

Polyamine pathway inhibition as a novel therapeutic approach to treating neuroblastoma

Polyamines are highly regulated essential cations that are elevated in rapidly proliferating tissues, including diverse cancers. Expression analyses in neuroblastomas suggest that up-regulation of polyamine pro-synthetic enzymes and down-regulation of catabolic enzymes is associated with poor prognosis. Polyamine sufficiency may be required for MYCN oncogenicity in MYCN amplified neuroblastoma, and targeting polyamine homeostasis may therefore provide an attractive therapeutic approach. ODC1, an oncogenic MYCN target, is rate-limiting for polyamine synthesis, and is overexpressed in many cancers including neuroblastoma. Inhibition of ODC1 by difluoromethylornithine (DFMO) decreased tumor penetrance in TH-MYCN mice treated pre-emptively, and extended survival and synergized with chemotherapy in treating established tumors in both TH-MYCN and xenograft models. Efforts to augment DFMO activity, or otherwise maximally reduce polyamine levels, are focused on antagonizing polyamine uptake or augmenting polyamine export or catabolism. Since polyamine inhibition appears to be clinically well tolerated, these approaches, particularly when combined with chemotherapy, have great potential for improving neuroblastoma outcome in both MYCN amplified and non-MYCN amplified neuroblastomas.

Sulforaphane potentiates RNA damage induced by different xenobiotics

Background

The isothiocyanate sulforaphane (SFN) possesses interesting anticancer activities. However, recent studies reported that SFN promotes the formation of reactive oxygen species (ROS) as well as DNA breakage.

Methodology/Principal Findings

We investigated whether SFN is able to damage RNA, whose loss of integrity was demonstrated in different chronic diseases. Considering the ability of SFN to protect from genotoxicity, we also examined whether SFN is able to protect from RNA damage induced by different chemicals (doxorubicin, spermine, S-nitroso-N-acetylpenicillamine, H₂O₂). We observed that SFN was devoid of either RNA damaging and RNA protective activity in human leukemic cells. It was able to potentiate the RNA damage by doxorubicin and spermine. In the first case, the effect was attributable to its ability of modulating the bioreductive activation of doxorubicin. For spermine, the effects were mainly due to its modulation of ROS levels produced by spermine metabolism. As to the cytotoxic relevance of the RNA damage, we found that the treatment of cells with a mixture of spermine or doxorubicin plus SFN increased their proapoptotic potential. Thus it is conceivable that the presence of RNA damage might concur to the overall toxic response induced by a chemical agent in targeted cells.

Conclusions/Significance

Since RNA is emerging as a potential target for anticancer drugs, its ability to enhance spermine- and doxorubicin-induced RNA damage and cytotoxicity could represent an additional mechanism for the potentiating effects of SFN associated with anticancer drugs.

Initial testing (stage 1) of the polyamine analog PG11047 by the pediatric preclinical testing program

BACKGROUND

PG11047 is a novel conformationally restricted analog of the natural polyamine, spermine that lowers cellular endogenous polyamine levels and competitively inhibits natural polyamine functions leading to cancer cell growth inhibition. The activity of PG11047 was evaluated against the PPTP's in vitro and in vivo panels.

PROCEDURES

PG11047 was evaluated against the PPTP in vitro panel using 96 hr exposure at concentrations ranging from 10 nM to 100 µM. It was tested against the PPTP in vivo panels at a dose of 100 mg/kg administered by the intraperitoneal route weekly for 6 weeks.

RESULTS

In vitro PG11047 demonstrated a concentration-response pattern consistent with cytostatic activity. The median EC(50) for PG11047 was 71 nM. Cell lines of the Ewing sarcoma panel had a lower median EC(50) value compared to the remaining cell lines in the panel, while cell lines of the neuroblastoma panel had a higher median EC(50) value. In vivo PG11047 induced significant differences in EFS distribution compared to control in 5 of 32 (15.6%) of the evaluable solid tumor xenografts and in 0 of 7 (0%) of the evaluable ALL xenografts. The single case of tumor regression occurred in an ependymoma xenograft.

CONCLUSIONS

Further pediatric development of PG11047 will require better defining a target population and identifying combinations for which there is a tumor-selective cytotoxic effect. The regression observed for an ependymoma xenograft and the exquisite sensitivity of some Ewing sarcoma cell lines to the antiproliferative effects of PG11047 provide leads for further preclinical investigations.

Reduction of the putative CD44+CD24- breast cancer stem cell population by targeting the polyamine metabolic pathway with PG11047

Cancer stem cells (CSCs) are considered to be of particular concern in cancer as they possess inherent properties of self-renewal and differentiation, along with expressing certain genes related to a mesenchymal phenotype. These features favour the promotion of tumour recurrence and metastasis in cancer patients. Thus, the optimal chemotherapeutic treatment should target the CSC population, either by killing these cells and/or by inducing their transition to a more differentiated epithelial-like phenotype. Experiments were carried out on the trastuzumab-resistant human epidermal growth factor receptor 2-overexpressing breast cancer cell line JIMT-1 to unravel the chemotherapeutic effects of the polyamine analogue [1N,12N]bis(ethyl)-cis-6,7-dehydrospermine (PG11047) and of the polyamine biosynthetic inhibitor 2-difluoromethylornithine (DFMO) on the CD44+CD24- CSC population. Furthermore, effects on the properties of self-renewal and epithelial/mesenchymal markers were also investigated. Treatment with PG11047 reduced the CD44+CD24- subpopulation of JIMT-1 cells by approximately 50%, inhibited and/or reduced self-renewal capability of the CSC population, decreased cell motility and induced expression of mesenchymal to epithelial transition-associated proteins that are involved in promoting an epithelial phenotype. By contrast, DFMO slightly increased the CD44+CD24- subpopulation, increased cell motility and the level of mesenchymal-related proteins. DFMO treatment reduced the self-renewal capability of the CSC population. Both PG11047 and DFMO reduced the expression of the human epidermal growth factor receptor 2 protein, which is correlated to malignancy and resistance to trastuzumab in JIMT-1 cells. Our findings indicate that treatment with PG11047 targeted the CSC population by interfering with several stem cell-related properties, such as self-renewal, differentiation, motility and the mesenchymal phenotype.

Current status of the polyamine research field

This chapter provides an overview of the polyamine field and introduces the 32 other chapters that make up this volume. These chapters provide a wide range of methods, advice, and background relevant to studies of the function of polyamines, the regulation of their content, their role in disease, and the therapeutic potential of drugs targeting polyamine content and function. The methodology provided in this new volume will enable laboratories already working in this area to expand their experimental techniques and facilitate the entry of additional workers into this rapidly expanding field.

The role of the polyamine catabolic enzymes SSAT and SMO in the synergistic effects of standard chemotherapeutic agents with a polyamine analogue in human breast cancer cell lines

INTRODUCTION

Polyamine analogues have demonstrated significant activity against human breast cancer cell lines as single agents as well as in combination with other cytotoxic drugs. This study evaluates the ability of a polyamine analogue N (1),N (11)-bis(ethyl)norspermine (BENSpm) to synergize with six standard chemotherapeutic agents, 5-fluorouracil (FU), fluorodeoxyuridine, cis-diaminechloroplatinum(II) (C-DDP), paclitaxel, docetaxel, and vinorelbine.

MATERIALS AND METHODS

Four human breast cancer cell lines (MDA-MB-231, MCF-7, Hs578t, and T47D) and one immortalized, non-tumorigenic mammary epithelial cell line (MCF-10A) were used for in vitro combination studies with BENSpm and cytotoxic drugs. Xenograft mice models generated with MDA-MB-231 cells were used for in vivo studies with BENSpm and paclitaxel.

RESULTS AND CONCLUSION

BENSpm exhibited synergistic inhibitory effect on cell proliferation in combination with 5-FU or paclitaxel in human breast cancer cell lines (MDA-MB-231 and MCF-7) and was either antagonistic or less effective in the non-tumorigenic MCF-10A cell line. Synergism was highest with 120 h concomitant treatment or pre-treatment with BENSpm for 24 h followed by concomitant treatment for 96 additional hours. Since the cytotoxic effects of many polyamine analogues and cytotoxic agents are believed to act, in part, through induction of the polyamine catabolic enzymes SSAT and SMO, the role of these enzymes on synergistic response was evaluated in MDA-MB-231 and MCF-7 treated with BENSpm and 5-FU or paclitaxel. Combination treatments of BENSpm with 5-FU or paclitaxel resulted in induction of SSAT mRNA and activity in both cell lines compared to either drug alone, while SMO mRNA and activity were increased only in MDA-MB-231 cells. Induction was greater with BENSpm/paclitaxel combination than BENSpm/5-FU. Further, RNAi studies demonstrated that both SSAT and SMO play a significant role in the response of MDA-MB-231 cells to treatment with BENSpm and 5-FU or paclitaxel. In MCF-7 cells, only SSAT appears to be involved in the response to these treatments. In an effort to translate combination studies from in vitro to in vivo, and to form a basis for clinical setting, the in vivo therapeutic efficacy of BENSpm alone and in combination with paclitaxel on tumor regression was evaluated in xenograft mice models generated with MDA-MB-231 cells. Intraperitoneal exposure to BENSpm or taxol singly and in combination for 4 weeks resulted in significant inhibition in tumor growth. These findings help elucidate the mechanisms involved in synergistic drug response and support combinations of polyamine analogues with chemotherapeutic agents which could potentially be used in the treatment of breast cancer.

A systems analysis of the chemosensitivity of breast cancer cells to the polyamine analogue PG-11047

BACKGROUND

Polyamines regulate important cellular functions and polyamine dysregulation frequently occurs in cancer. The objective of this study was to use a systems approach to study the relative effects of PG-11047, a polyamine analogue, across breast cancer cells derived from different patients and to identify genetic markers associated with differential cytotoxicity.

METHODS

A panel of 48 breast cell lines that mirror many transcriptional and genomic features present in primary human breast tumours were used to study the antiproliferative activity of PG-11047. Sensitive cell lines were further examined for cell cycle distribution and apoptotic response. Cell line responses, quantified by the GI50 (dose required for 50% relative growth inhibition) were correlated with the omic profiles of the cell lines to identify markers that predict response and cellular functions associated with drug sensitivity.

RESULTS

The concentrations of PG-11047 needed to inhibit growth of members of the panel of breast cell lines varied over a wide range, with basal-like cell lines being inhibited at lower concentrations than the luminal cell lines. Sensitive cell lines showed a significant decrease in S phase fraction at doses that produced little apoptosis. Correlation of the GI50 values with the omic profiles of the cell lines identified genomic, transcriptional and proteomic variables associated with response.

CONCLUSIONS

A 13-gene transcriptional marker set was developed as a predictor of response to PG-11047 that warrants clinical evaluation. Analyses of the pathways, networks and genes associated with response to PG-11047 suggest that response may be influenced by interferon signalling and differential inhibition of aspects of motility and epithelial to mesenchymal transition.

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.

Disrupting polyamine homeostasis as a therapeutic strategy for neuroblastoma

MYC genes are deregulated in a plurality of human cancers. Through direct and indirect mechanisms, the MYC network regulates the expression of > 15% of the human genome, including both protein-coding and noncoding RNAs. This complexity has complicated efforts to define the principal pathways mediating MYC's oncogenic activity. MYC plays a central role in providing for the bioenergetic and biomass needs of proliferating cells, and polyamines are essential cell constituents supporting many of these functions. The rate-limiting enzyme in polyamine biosynthesis, ODC, is a bona fide MYC target, as are other regulatory enzymes in this pathway. A wealth of data link enhanced polyamine biosynthesis to cancer progression, and polyamine depletion may limit the malignant transformation of preneoplastic lesions. Studies with transgenic cancer models also support the finding that the effect of MYC on tumor initiation and progression can be attenuated through the repression of polyamine production. High-risk neuroblastomas (an often lethal embryonal tumor in which MYC activation is paramount) deregulate numerous polyamine enzymes to promote the expansion of intracellular polyamine pools. Selective inhibition of key enzymes in this pathway, e.g., using DFMO and/or SAM486, reduces tumorigenesis and synergizes with chemotherapy to regress tumors in preclinical models. Here, we review the potential clinical application of these and additional polyamine depletion agents to neuroblastoma and other advanced cancers in which MYC is operative.

Polyamine catabolism and disease

In addition to polyamine homoeostasis, it has become increasingly clear that polyamine catabolism can play a dominant role in drug response, apoptosis and the response to stressful stimuli, and contribute to the aetiology of several pathological states, including cancer. The highly inducible enzymes SSAT (spermidine/spermine N1-acetyltransferase) and SMO (spermine oxidase) and the generally constitutively expressed APAO (N1-acetylpolyamine oxidase) appear to play critical roles in many normal and disease processes. The dysregulation of polyamine catabolism frequently accompanies several disease states and suggests that such dysregulation may both provide useful insight into disease mechanism and provide unique druggable targets that can be exploited for therapeutic benefit. Each of these enzymes has the potential to alter polyamine homoeostasis in response to multiple cell signals and the two oxidases produce the reactive oxygen species H2O2 and aldehydes, each with the potential to produce pathological states. The activity of SSAT provides substrates for APAO or substrates for the polyamine exporter, thus reducing the intracellular polyamine concentration, the net effect of which depends on the magnitude and rate of any increase in SSAT. SSAT may also influence cellular metabolism via interaction with other proteins and by perturbing the content of acetyl-CoA and ATP. The goal of the present review is to cover those aspects of polyamine catabolism that have an impact on disease aetiology or treatment and to provide a solid background in this ever more exciting aspect of polyamine biology.

Gene expression analysis of HCT116 colon tumor-derived cells treated with the polyamine analog PG-11047

BACKGROUND

The conformationally restricted polyamine analog PG-11047 has significant growth inhibitory activity against prostate and lung cancer cell lines and is currently under evaluation in several clinical trials, both alone and in combination with other drugs, for the treatment of relapsed or refractory cancer. The objective of this study was to identify the molecular signature of genes responsive to PG-11047 treatment and the biochemical effects of this drug in the HCT116 colon cancer cell line.

MATERIALS AND METHODS

Gene expression analysis was performed using Affymetrix GeneChip human genome U133 Plus 2.0 arrays. Changes in protein expression were evaluated using 2D polyacrylamide gels followed by LCMS/MS.

RESULTS

Treatment of cells with PG-11047 at concentrations ranging from 0.1 to 10 microM caused inhibition of cell growth. The activity of PG-11047 was found to correlate with its transcriptional effects on cell cycle control, focal adhesion, adherent and gap junction genes, MAPK-, Wnt- and, TGF-beta signaling pathways, transport and DNA/RNA transcription factor genes. PG-11047 caused depletion of polyamine pools. Proteomics analysis showed that PG-11047 restricts the modification of eukaryotic translation initiation factor 5A (eIF5A), resulting in suppression of general protein synthesis in PG-11047-treated cells.

CONCLUSION

These data show that PG-11047 has a broad spectrum of anticancer activity in colon cancer cells.