Phase I-II clinical trial with alpha-difluoromethylornithine--an inhibitor of polyamine biosynthesis

Polyamine Catabolism Revisited: Acetylpolyamine Oxidase Plays a Minor Role due to Low Expression

Biogenic polyamines are ubiquitous compounds. Dysregulation of their metabolism is associated with the development of various pathologies, including cancer, hyperproliferative diseases, and infections. The canonical pathway of polyamine catabolism includes acetylation of spermine and spermidine and subsequent acetylpolyamine oxidase (PAOX)-mediated oxidation of acetylpolyamines (back-conversion) or their direct efflux from the cell. PAOX is considered to catalyze a non-rate-limiting catabolic step. Here, we show that PAOX transcription levels are extremely low in various tumor- and non-tumor cell lines and, in most cases, do not change in response to altered polyamine metabolism. Its enzymatic activity is undetectable in the majority of cell lines except for neuroblastoma and low passage glioblastoma cell lines. Treatment of A549 cells with N1,N11-diethylnorspermine leads to PAOX induction, but its contribution to polyamine catabolism remains moderate. We also describe two alternative enzyme isoforms and show that isoform 4 has diminished oxidase activity and isoform 2 is inactive. PAOX overexpression correlates with the resistance of cancer cells to genotoxic antitumor drugs, indicating that PAOX may be a useful therapeutic target. Finally, PAOX is dispensable for the replication of various viruses. These data suggest that a decrease in polyamine levels is achieved predominantly by the secretion of acetylated spermine and spermidine rather than by back-conversion.

Salmonella Typhimurium employs spermidine to exert protection against ROS-mediated cytotoxicity and rewires host polyamine metabolism to ameliorate its survival in macrophages

Salmonella infection entails a cascade of attacks and defence measures. After breaching the intestinal epithelial barrier, Salmonella is phagocytosed by macrophages, where the bacteria encounter multiple stresses, to which it employs relevant countermeasures. Our study shows that, in Salmonella, the polyamine spermidine activates a stress response mechanism by regulating critical antioxidant genes. Salmonella Typhimurium mutants for spermidine transport and synthesis cannot mount an antioxidative response, resulting in high intracellular ROS levels. These mutants are also compromised in their ability to be phagocytosed by macrophages. Furthermore, it regulates a novel enzyme in Salmonella, Glutathionyl-spermidine synthetase (GspSA), which prevents the oxidation of proteins in E. coli. Moreover, the spermidine mutants and the GspSA mutant show significantly reduced survival in the presence of hydrogen peroxide in vitro and reduced organ burden in the mouse model of Salmonella infection. Conversely, in macrophages isolated from gp91phox-/- mice, we observed a rescue in the attenuated fold proliferation previously observed upon infection. We found that Salmonella upregulates polyamine biosynthesis in the host through its effectors from SPI-1 and SPI-2, which addresses the attenuated proliferation observed in spermidine transport mutants. Thus, inhibition of this pathway in the host abrogates the proliferation of Salmonella Typhimurium in macrophages. From a therapeutic perspective, inhibiting host polyamine biosynthesis using an FDA-approved chemopreventive drug, D, L-α-difluoromethylornithine (DFMO), reduces Salmonella colonisation and tissue damage in the mouse model of infection while enhancing the survival of infected mice. Therefore, our work provides a mechanistic insight into the critical role of spermidine in stress resistance of Salmonella. It also reveals a bacterial strategy in modulating host metabolism to promote their intracellular survival and shows the potential of DFMO to curb Salmonella infection.

Phase 1 study of high-dose DFMO, celecoxib, cyclophosphamide and topotecan for patients with relapsed neuroblastoma: a New Approaches to Neuroblastoma Therapy trial

BACKGROUND

MYC genes regulate ornithine decarboxylase (Odc) to increase intratumoral polyamines. We conducted a Phase I trial [NCT02030964] to determine the maximum tolerated dose (MTD) of DFMO, an Odc inhibitor, with celecoxib, cyclophosphamide and topotecan.

METHODS

Patients 2-30 years of age with relapsed/refractory high-risk neuroblastoma received oral DFMO at doses up to 9000 mg/m2/day, with celecoxib (500 mg/m2 daily), cyclophosphamide (250 mg/m2/day) and topotecan (0.75 mg/m2/day) IV for 5 days, for up to one year with G-CSF support.

RESULTS

Twenty-four patients (median age, 6.8 years) received 136 courses. Slow platelet recovery with 21-day courses (dose-levels 1 and 2) led to subsequent dose-levels using 28-day courses (dose-levels 2a-4a). There were three course-1 dose-limiting toxicities (DLTs; hematologic; anorexia; transaminases), and 23 serious adverse events (78% fever-related). Five patients (21%) completed 1-year of therapy. Nine stopped for PD, 2 for DLT, 8 by choice. Best overall response included two PR and four MR. Median time-to-progression was 19.8 months, and 3 patients remained progression-free at >4 years without receiving additional therapy. The MTD of DFMO with this regimen was 6750 mg/m2/day.

CONCLUSION

High-dose DFMO is tolerable when added to chemotherapy in heavily pre-treated patients. A randomized Phase 2 trial of DFMO added to chemoimmunotherapy is ongoing [NCT03794349].

Ototoxicity Review: A Growing Number of Non-Platinum-Based Chemo- and Immunotherapies

OBJECTIVE

To raise awareness of the growing list of non-platinum-based chemo- and immunotherapeutic agents that have been associated with ototoxicity and to introduce the possible mechanism of ototoxicity of these agents.

DATA SOURCES

PubMed, Embase, and Web of Science.

REVIEW METHODS

A systematic review was performed following the PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-analyses). PubMed, Embase, and Web of Science databases were searched for published reports of ototoxicity from non-platinum-based chemo- and immunotherapeutic agents in adult and pediatric patients. Therapies that utilized any platinum-based agent were excluded.

CONCLUSIONS

Ototoxicity from non-platinum-based chemo- and immunotherapies is an evolving problem. There were 54 reports-39 case reports and 15 cohort studies-documenting ototoxicity from 7 agents/combination therapies. Of these reports, 37 (69%) were published within the last 15 years (after 2005). No recovery of hearing was documented in 21 of 56 cases (38%). Pretreatment audiograms were uncommon (19/54 studies, 35%), despite documented ototoxic associations.

IMPLICATIONS FOR PRACTICE

There is a growing number of novel, ototoxic, non-platinum-based chemo- and immunotherapeutic agents with various potential mechanisms of action. Otolaryngologists will need to prioritize awareness of these agents. This growing list of agents, many of which have reversible effects, suggest a need for standardized ototoxicity monitor protocols so that appropriate and timely management options can be implemented.

Ototoxicity of Long-Term α-Difluoromethylornithine for Skin Cancer Prevention

OBJECTIVE

Evaluate the effects of α-difluoromethylornithine (DFMO) on hearing thresholds as part of a randomized, double-blind, placebo-controlled trial.

METHODS

Subjects were randomized and assigned to the control (placebo) or experimental (DFMO) group. DFMO or placebo were administered orally (500 mg/m2 /day) for up to 5 years.

RESULTS

Subjects taking DFMO had, on average, increased hearing thresholds from baseline across the frequency range compared to subjects in the control group. Statistical analysis revealed this was significant in the lower frequency range.

CONCLUSIONS

This randomized controlled trial revealed the presence of increased hearing thresholds associated with long-term DFMO use. As a whole, DFMO may help prevent and treat certain types of cancers; however, it can result in some degree of hearing loss even when administered at low doses. This study further highlights the importance of closely monitoring hearing thresholds in subjects taking DFMO. Laryngoscope, 133:676-682, 2023.

One-Carbon and Polyamine Metabolism as Cancer Therapy Targets

Cancer metabolic reprogramming is essential for maintaining cancer cell survival and rapid replication. A common target of this metabolic reprogramming is one-carbon metabolism which is notable for its function in DNA synthesis, protein and DNA methylation, and antioxidant production. Polyamines are a key output of one-carbon metabolism with widespread effects on gene expression and signaling. As a result of these functions, one-carbon and polyamine metabolism have recently drawn a lot of interest for their part in cancer malignancy. Therapeutic inhibitors that target one-carbon and polyamine metabolism have thus been trialed as anticancer medications. The significance and future possibilities of one-carbon and polyamine metabolism as a target in cancer therapy are discussed in this review.

A structural model of a Ras-Raf signalosome

The protein K-Ras functions as a molecular switch in signaling pathways regulating cell growth. In the human mitogen-activated protein kinase (MAPK) pathway, which is implicated in many cancers, multiple K-Ras proteins are thought to assemble at the cell membrane with Ras effector proteins from the Raf family. Here we propose an atomistic structural model for such an assembly. Our starting point was an asymmetric guanosine triphosphate-mediated K-Ras dimer model, which we generated using unbiased molecular dynamics simulations and verified with mutagenesis experiments. Adding further K-Ras monomers in a head-to-tail fashion led to a compact helical assembly, a model we validated using electron microscopy and cell-based experiments. This assembly stabilizes K-Ras in its active state and presents composite interfaces to facilitate Raf binding. Guided by existing experimental data, we then positioned C-Raf, the downstream kinase MEK1 and accessory proteins (Galectin-3 and 14-3-3σ) on and around the helical assembly. The resulting Ras-Raf signalosome model offers an explanation for a large body of data on MAPK signaling.

Difluoromethylornithine Induces Apoptosis through Regulation of AP-1 Signaling via JNK Phosphorylation in Epithelial Ovarian Cancer

Difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), has promising activity against various cancers and a tolerable safety profile for long-term use as a chemopreventive agent. However, the anti-tumor effects of DFMO in ovarian cancer cells have not been entirely understood. Our study aimed to identify the effects and mechanism of DFMO in epithelial ovarian cancer cells using SKOV-3 cells. Treatment with DFMO resulted in a significantly reduced cell viability in a time- and dose-dependent manner. DFMO treatment inhibited the activity and downregulated the expression of ODC in ovarian cancer cells. The reduction in cell viability was reversed using polyamines, suggesting that polyamine depletion plays an important role in the anti-tumor activity of DFMO. Additionally, significant changes in Bcl-2, Bcl-xL, Bax protein levels, activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase were observed, indicating the apoptotic effects of DFMO. We also found that the effect of DFMO was mediated by AP-1 through the activation of upstream JNK via phosphorylation. Moreover, DFMO enhanced the effect of cisplatin, thus showing a possibility of a synergistic effect in treatment. In conclusion, treatment with DFMO alone, or in combination with cisplatin, could be a promising treatment for ovarian cancer.

The role of polyamines in gastric cancer

Advancements in our understanding of polyamine molecular and cellular functions have led to increased interest in targeting polyamine metabolism for anticancer therapeutic benefits. The polyamines putrescine, spermidine, and spermine are polycationic alkylamines commonly found in all living cells and are essential for cellular growth and survival. This review summarizes the existing research on polyamine metabolism and function, specifically the role of polyamines in gastric immune cell and epithelial cell function. Polyamines have been implicated in a multitude of cancers, but in this review, we focus on the role of polyamine dysregulation in the context of Helicobacter pylori-induced gastritis and subsequent progression to gastric cancer. Due to the emerging implication of polyamines in cancer development, there is an increasing number of promising clinical trials using agents to target the polyamine metabolic pathway for potential chemoprevention and anticancer therapy.

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.

Characterising the Response of Human Breast Cancer Cells to Polyamine Modulation

Breast cancer is a complex heterogeneous disease with multiple underlying causes. The polyamines putrescine, spermidine, and spermine are polycationic molecules essential for cell proliferation. Their biosynthesis is upregulated in breast cancer and they contribute to disease progression. While elevated polyamines are linked to breast cancer cell proliferation, there is little evidence to suggest breast cancer cells of different hormone receptor status are equally dependent on polyamines. In this study, we characterized the responses of two breast cancer cells, ER+ (oestrogen receptor positive) MCF-7 and ER- MDA-MB-231 cell lines, to polyamine modulation and determined the requirement of each polyamine for cancer cell growth. The cells were exposed to DFMO (a polyamine pathway inhibitor) at various concentrations under different conditions, after which several growth parameters were determined. Exposure of both cell lines to DFMO induced differential growth responses, MCF-7 cells showed greater sensitivity to polyamine pathway inhibition at various DFMO concentrations than the MDA-MB-231 cells. Analysis of intracellular DFMO after withdrawal from growth medium showed residual DFMO in the cells with concomitant decreases in polyamine content, ODC protein level, and cell growth. Addition of exogenous polyamines reversed the cell growth inhibition, and this growth recovery appears to be partly dependent on the spermidine content of the cell. Similarly, DFMO exposure inhibits the global translation state of the cells, with spermidine addition reversing the inhibition of translation in the breast cancer cells. Taken together, these data suggest that breast cancer cells are differentially sensitive to the antitumour effects of polyamine depletion, thus, targeting polyamine metabolism might be therapeutically beneficial in breast cancer management based on their subtype.

The Emerging Clinical Role of Spermine in Prostate Cancer

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

Chiral Chromatographic Isolation on Milligram Scale of the Human African Trypanosomiasis Treatment d- and l-Eflornithine

Eflornithine is a recommended treatment against the otherwise fatal parasitic disease late stage human African trypanosomiasis (HAT), also known as Gambian sleeping sickness. It is administered repeatedly as a racemic mixture intravenously (IV) together with oral nifurtimox. Racemic eflornithine has been investigated in clinical trials for oral dosing. However, due to low systemic exposures at a maximum tolerated oral dose, the drug is continued to be administered IV. The eflornithine enantiomers, d- and l-eflornithine, have different affinities to the target enzyme ornithine decarboxylase, suggesting that the pharmacodynamics of the enantiomers may differ. The aim of this study was to develop a method for isolation of d- and l-eflornithine from a racemic mixture. Several chiral stationary phases (CSPs) were evaluated for enantioselectivity using supercritical fluid chromatography (SFC) or high-performance liquid chromatography (HPLC). None of the tested CSPs rendered separation of the enantiomers in SFC mode. Separation of the enantiomers with SFC on the CSP Chiralpak IG was only achieved on an analytical scale after derivatization with ortho-phthalaldehyde (OPA). This was the first reported enantioselective SFC method for an eflornithine derivate. However, due to poor stability, the eflornithine-OPA derivates degraded and no chemically pure enantiomers were obtained. The CSP that showed enantioselectivity in HPLC mode was Chirobiotic R, which resulted in a successful isolation on a semipreparative milligram scale. The isolated eflornithine enantiomers will be tested in nonclinical in vitro and in vivo studies to support and assess the feasibility of a future clinical program with an oral HAT treatment.

Spermidine as a target for cancer therapy

Spermidine, as a natural component from polyamine members, is originally isolated from semen and also existed in many natural plants, and can be responsible for cell growth and development in eukaryotes. The supplementation of spermidine can extend health and lifespan across species. Although the elevated levels of polyamines and the regulation of rate-limiting enzymes for polyamine metabolism have been identified as the biomarkers in many cancers, recent epidemiological data support that an increased uptake of spermidine as a caloric restriction mimic can reduce overall mortality associated with cancers. The possible mechanisms between spermidine and cancer development may be related to the precise regulation of polyamine metabolism, anti-cancer immunosurveillance, autophagy, and apoptosis. Increased intake of polyamine seems to suppress tumorigenesis, but appears to accelerate the growth of established tumors. Based on these observations and the absolute requirement for polyamines in tumor growth, spermidine could be a rational target for chemoprevention and clinical therapeutics of cancers.

PGC1α Inhibits Polyamine Synthesis to Suppress Prostate Cancer Aggressiveness

Although tumorigenesis is dependent on the reprogramming of cellular metabolism, the metabolic pathways engaged in the formation of metastases remain largely unknown. The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) plays a pleiotropic role in the control of cancer cell metabolism and has been associated with a good prognosis in prostate cancer. Here, we show that PGC1α represses the metastatic properties of prostate cancer cells via modulation of the polyamine biosynthesis pathway. Mechanistically, PGC1α inhibits the expression of c-MYC and ornithine decarboxylase 1 (ODC1), the rate-limiting enzyme for polyamine synthesis. Analysis of in vivo metastases and clinical data from patients with prostate cancer support the proposition that the PGC1α/c-MYC/ODC1 axis regulates polyamine biosynthesis and prostate cancer aggressiveness. In conclusion, downregulation of PGC1α renders prostate cancer cells dependent on polyamine to promote metastasis. SIGNIFICANCE: These findings show that a major regulator of mitochondrial metabolism controls polyamine synthesis and prostate cancer aggressiveness, with potential applications in therapy and identification of new biomarkers.

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

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

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.

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.

Difluoromethylornithine in cancer: new advances

Difluoromethylornithine (DFMO; eflornithine) is an irreversible suicide inhibitor of the enzyme ornithine decarboxylase which is involved in polyamine synthesis. Polyamines are important for cell survival, thus DFMO was studied as an anticancer agent and as a chemoprevention agent. DFMO exhibited mainly cytostatic activity and had single agent efficacy as well as activity in combination with other chemotherapeutic drugs for some cancers and leukemias. Herewith, we summarize the current knowledge of the anticancer and chemopreventive properties of DFMO and assess the status of clinical trials.

Herbacetin Is a Novel Allosteric Inhibitor of Ornithine Decarboxylase with Antitumor Activity

Ornithine decarboxylase (ODC) is a rate-limiting enzyme in the first step of polyamine biosynthesis that is associated with cell growth and tumor formation. Existing catalytic inhibitors of ODC have lacked efficacy in clinical testing or displayed unacceptable toxicity. In this study, we report the identification of an effective and nontoxic allosteric inhibitor of ODC. Using computer docking simulation and an in vitro ODC enzyme assay, we identified herbacetin, a natural compound found in flax and other plants, as a novel ODC inhibitor. Mechanistic investigations defined aspartate 44 in ODC as critical for binding. Herbacetin exhibited potent anticancer activity in colon cancer cell lines expressing high levels of ODC. Intraperitoneal or oral administration of herbacetin effectively suppressed HCT116 xenograft tumor growth and also reduced the number and size of polyps in a mouse model of APC-driven colon cancer (ApcMin/+). Unlike the well-established ODC inhibitor DFMO, herbacetin treatment was not associated with hearing loss. Taken together, our findings defined the natural product herbacetin as an allosteric inhibitor of ODC with chemopreventive and antitumor activity in preclinical models of colon cancer, prompting its further investigation in clinical trials.

Dietary polyamine intake and colorectal cancer risk in postmenopausal women

BACKGROUND

Putrescine, spermidine, and spermine (i.e., polyamines) are small cationic amines synthesized by cells or acquired from the diet or gut bacteria. Polyamines are required for both normal and colorectal cancer (CRC) cell growth.

OBJECTIVE

We investigated the association between dietary polyamines and risk of CRC incidence and mortality.

DESIGN

The study was a prospective analysis in 87,602 postmenopausal women in the Women's Health Initiative Observational Study. Multivariate Cox regression was used to calculate HRs and 95% CIs.

RESULTS

Total dietary polyamine intake (mean ± SD: 289.2 ± 127.4 μmol/d) was not positively associated with CRC in fully adjusted models. Instead, intake ≥179.67 μmol/d was associated with reduced risk of CRC [HR (95% CI): 0.82 (0.68, 1.00), 0.81 (0.66, 0.99), 0.91 (0.74, 1.12), and 0.80 (0.62, 1.02) for quintiles 2-5, respectively, compared with quintile 1]. Reduced risk was not significant across all quintiles. Polyamines were not significantly associated with CRC-specific mortality in fully adjusted models. When stratified by risk factors for CRC, only body mass index (BMI) and fiber intake significantly modified the association between polyamine intake and CRC. In women with BMI (in kg/m²) ≤25 or fiber consumption above the median, polyamine intake was associated with significantly lower risk of CRC.

CONCLUSIONS

No positive association between dietary polyamines and CRC or CRC-specific mortality risk in women was observed. Instead, a protective effect of dietary polyamines was suggested in women with some CRC risk-lowering behaviors in particular. These results are consistent with emerging evidence that exogenous polyamines may be beneficial in colon health and warrant additional study.

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.

Difluoromethylornithine: the proof is in the polyamines

In this issue (beginning on page 1368), Kreul and colleagues report a retrospective review of long-term efficacy and toxicity for subjects participating in a phase III study of difluoromethylornithine (DFMO) for prevention of nonmelanoma skin cancer (NMSC). They conclude that those treated with DFMO had a nonsignificant, persistent decrease in NMSC after completion of treatment and that treatment with DFMO did not result in late toxicity after the discontinuation of treatment. We review the data on DFMO as a chemopreventive agent for skin and other cancers, discuss the necessary qualities of a cancer chemopreventive agent, and reflect on the requirements for a well-conducted cancer chemoprevention study, including the rationale for long-term follow-up in cancer prevention studies.

Ornithine decarboxylase inhibition by alpha-difluoromethylornithine activates opposing signaling pathways via phosphorylation of both Akt/protein kinase B and p27Kip1 in neuroblastoma

Ornithine decarboxylase (ODC) is a key enzyme in mammalian polyamine biosynthesis that is up-regulated in various types of cancer. We previously showed that treating human neuroblastoma (NB) cells with the ODC inhibitor alpha-difluoromethylornithine (DFMO) depleted polyamine pools and induced G1 cell cycle arrest without causing apoptosis. However, the precise mechanism by which DFMO provokes these changes in NB cells remained unknown. Therefore, we further examined the effects of DFMO, alone and in combination with phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 or Akt/protein kinase B (PKB) inhibitor IV, on the regulation of cell survival and cell cycle-associated pathways in LAN-1 NB cells. In the present study, we found that the inhibition of ODC by DFMO promotes cell survival by inducing the phosphorylation of Akt/PKB at residue Ser473 and glycogen synthase kinase-3beta at Ser9. Intriguingly, DFMO also induced the phosphorylation of p27Kip1 at residues Ser10 (nuclear export) and Thr198 (protein stabilization) but not Thr187 (proteasomal degradation). The combined results from this study provide evidence for a direct cross-talk between ODC-dependent metabolic processes and well-established cell signaling pathways that are activated during NB tumorigenesis. The data suggest that inhibition of ODC by DFMO induces two opposing pathways in NB: one promoting cell survival by activating Akt/PKB via the PI3K/Akt pathway and one inducing p27Kip1/retinoblastoma-coupled G1 cell cycle arrest via a mechanism that regulates the phosphorylation and stabilization of p27Kip1. This study presents new information that may explain the moderate efficacy of DFMO monotherapy in clinical trials and reveals potential new targets for DFMO-based combination therapies for NB treatment.

Spermine synthase deficiency leads to deafness and a profound sensitivity to alpha-difluoromethylornithine

Male gyro (Gy) mice, which have an X chromosomal deletion inactivating the SpmS and Phex genes, were found to be profoundly hearing impaired. This defect was due to alteration in polyamine content due to the absence of spermine synthase, the product of the SpmS gene. It was reversed by breeding the Gy strain with CAG/SpmS mice, a transgenic line that ubiquitously expresses spermine synthase under the control of a composite cytomegalovirus-IE enhancer/chicken beta-actin promoter. There was an almost complete loss of the endocochlear potential in the Gy mice, which parallels the hearing deficiency, and this was also reversed by the production of spermine from the spermine synthase transgene. Gy mice showed a striking toxic response to treatment with the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO). Within 2-3 days of exposure to DFMO in the drinking water, the Gy mice suffered a catastrophic loss of motor function resulting in death within 5 days. This effect was due to an inability to maintain normal balance and was also prevented by the transgenic expression of spermine synthase. DFMO treatment of control mice or Gy-CAG/SpmS had no effect on balance. The loss of balance in Gy mice treated with DFMO was due to inhibition of polyamine synthesis because it was prevented by administration of putrescine. Our results are consistent with a critical role for polyamines in regulation of Kir channels that maintain the endocochlear potential and emphasize the importance of normal spermidine:spermine ratio in the hearing and balance functions of the inner ear.

The novel polyamine analogue CGC-11093 enhances the antimyeloma activity of bortezomib

Multiple myeloma (MM) is an incurable plasma cell malignancy. The recent successes of the proteasome inhibitor bortezomib in MM therapy have prompted investigations of its efficacy in combination with other anticancer agents. Polyamines play important roles in regulating tumor cell proliferation and angiogenesis and represent an important therapeutic target. CGC-11093 is a novel polyamine analogue that has completed a phase I clinical trial for the treatment of cancer. Here, we report that CGC-11093 selectively augments the in vitro and in vivo antimyeloma activity of bortezomib. Specifically, the combination of CGC-11093 and bortezomib compromised MM viability and clonogenic survival, and increased drug-induced apoptosis over that achieved by either single agent. Xenografts of MM tumors treated with this combination had marked increases in phospho-c-Jun-NH(2)-kinase (JNK)-positive cells and apoptosis, and corresponding reductions in tumor burden, tumor vasculature, and the expression of proliferating cell nuclear antigen and the proangiogenic cytokine vascular endothelial growth factor. Furthermore, inhibition of JNK with a pharmacologic inhibitor or by selective knockdown blunted the efficacy of CGC-11093 and bortezomib. Therefore, CGC-11093 enhances the anticancer activity of bortezomib by augmenting JNK-mediated apoptosis and blocking angiogenesis. These findings support the study of the use of the combination of bortezomib and CGC-11093 in MM patients that fail to respond to frontline therapy.

Mechanism and tissue specificity of nicotine-mediated lung S-adenosylmethionine reduction

We previously reported that chronic nicotine infusion blocks development of Pneumocystis pneumonia. This discovery developed from our work demonstrating the inability of this fungal pathogen to synthesize the critical metabolic intermediate S-adenosylmethionine and work by others showing nicotine to cause lung-specific reduction of S-adenosylmethionine in guinea pigs. We had found nicotine infusion to cause increased lung ornithine decarboxylase activity (rate-controlling enzyme of polyamine synthesis) and hypothesized that S-adenosylmethionine reduction is driven by up-regulated polyamine biosynthesis. Here we report a critical test of our hypothesis; inhibition of ornithine decarboxylase blocks the effect of nicotine on lung S-adenosylmethionine. Further support is provided by metabolite analyses showing nicotine to cause a strong diversion of S-adenosylmethionine toward polyamine synthesis and away from methylation reactions; these shifts are reversed by inhibition of ornithine decarboxylase. Because the nicotine effect on Pneumocystis is so striking, we considered the possibility of tissue specificity. Using laser capture microdissection, we collected samples of lung alveolar regions (site of infection) and respiratory epithelium for controls. We found nicotine to cause increased ornithine decarboxylase protein in alveolar regions but not airway epithelium; we conclude that tissue specificity likely contributes to the effect of nicotine on Pneumocystis pneumonia. Earlier we reported that the full effect of nicotine requires 3 weeks of treatment, and here we show recovery is symmetrical, also requiring 3 weeks after treatment cessation. Because this time frame is similar to pneumocyte turnover time, the shift in polyamine metabolism may occur as new pneumocytes are produced.

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.

Regulation of intracellular polyamine biosynthesis and transport by NO and cytokines TNF-alpha and IFN-gamma

Nitric oxide (NO) has been described to exert cytostatic effects on cellular proliferation; however the mechanisms responsible for these effects have yet to be fully resolved. Polyamines, conversely, are required components of cellular proliferation. In experimental models of inflammation, a relationship between these two pathways has been suggested by the temporal regulation of a common precursor, arginine. This study was undertaken to determine the effects NO and the NO synthase (NOS)-inducing cytokines, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), exert on polyamine regulation. The transformed kidney proximal tubule cell line, MCT, maintains high constitutive levels of the first polyamine biosynthetic enzyme, ornithine decarboxylase (ODC). NO donors markedly suppressed ODC activity in MCT and all other cell lines examined. TNF-alpha and IFN-gamma induction of NO generation resulted in suppressed ODC activity, an effect prevented by the inducible NOS inhibitor L-N6-(1-iminoethyl)lysine (L-NIL). Dithiothreitol reversal of NO-mediated ODC suppression supports nitrosylation as the mechanism of inactivation. We also evaluated polyamine uptake, inasmuch as inhibition of ODC can result in a compensatory induction of polyamine transporters. Administration of NO donors, or TNF-alpha and IFN-gamma, suppressed [3H]putrescine uptake, thereby preventing transport-mediated reestablishment of intracellular polyamine levels. This study demonstrates the capacity of NO and inflammatory cytokines to regulate both polyamine biosynthesis and transport.

A novel cytotoxic agent for human carcinoid tumors

BACKGROUND

Conventional adjuvant therapy for advanced carcinoid tumors remains disappointing; novel therapeutic agents are needed. We have shown previously that inhibiting polyamine biosynthesis with alpha-difluoromethylornithine (DFMO) slows the growth of carcinoid tumors. However, the clinical utility of DFMO has been limited by its cytostatic property. Synthetic polyamine analogs such as 1,19-bis(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4) appear to be cytotoxic against several human tumors. The purpose of our study was to determine whether BE-4-4-4-4 is a more effective antiproliferative and cytotoxic agent than DFMO on human carcinoid (BON) cells in vitro.

METHODS

BON cells were treated with either 5 mmol/L DFMO, 0.5 to 10 mumol/L BE-4-4-4-4, or vehicle (control). Ornithine decarboxylase activity was determined by the rate of 14CO2 production, and intracellular polyamine levels were determined by chromatography. Cell number and viability were determined by Coulter counter and trypan blue exclusion, respectively.

RESULTS

BE-4-4-4-4 inhibited ornithine decarboxylase activity and depleted all 3 polyamines. BE-4-4-4-4 decreased cell numbers by 81% compared with control and 27% compared with DFMO. BE-4-4-4-4 also induced a 2-fold increase in cell death compared with control or DFMO.

CONCLUSIONS

BE-4-4-4-4 is cytotoxic and more effective than DFMO in inhibiting growth of BON cells. Polyamine analogs such as BE-4-4-4-4 may be effective adjuvant therapeutic agents for advanced carcinoid tumors.

Inhibition of gastric tumorigenesis by alpha-difluoromethylornithine in rats treated with N-methyl-N'-nitro-N-nitrosoguanidine

Male Wistar rats were treated concurrently with a combination of the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG; CAS 70-25-7) and the polyamine-synthesis inhibitor alpha-difluoromethylornithine (DFMO) at two different doses of 0.5% and 1.0% (w/v). Experimental groups were treated with (I) MNNG alone (n = 25), (II) MNNG plus 0.5% (w/v) DFMO (n = 25), (III) MNNG plus 1.0% (w/v) DFMO (n = 25), (IV) 1.0% (w/v) DFMO alone (n = 25). Group V represented untreated controls (n = 20). Both the carcinogen and DFMO were administered in drinking water. The treatment time with the carcinogen and DFMO was 35 weeks. After treatment was completed animals were followed for an additional 50 weeks to cover a total observation time of 85 weeks. Significantly fewer animals developed gastric adenocarcinoma in the two groups of animals that received a combined treatment of MNNG plus DFMO compared to animals treated with the carcinogen alone (P < 0.05 and 0.005). No benign or malignant neoplastic lesions were observed in the stomach or duodenum of animals treated with DFMO alone or in untreated controls. It is concluded that concurrent treatment with DFMO prevents the development of malignant gastric epithelial tumors induced by MNNG in rats.

Pharmacological properties of the ornithine decarboxylase inhibitor 3-aminooxy-1-propanamine and several structural analogues

Analogues of 3-aminooxy-1-propanamine proved to be highly potent and selective inhibitors of ornithine decarboxylase (ODC). The compounds competed with ornithine for the substrate binding site of ODC, but resulted in progressive and apparently irreversible inactivation of the enzyme. Diamine oxidase was inhibited by these compounds to a lesser extent than ODC; the compounds were not metabolized by this enzyme. Several derivatives were growth-inhibitory for human T24 cells and for other mammalian cells, the most active compound being 3-aminooxy-2-fluoro-1-propanamine (AFPA). Growth-arrested cells were largely depleted of putrescine and spermidine. Cellular growth arrest could be antagonized by supplementation with spermidine. Selection for resistance against AFPA led to cells with amplified ODC genes and overexpression of the message. Some of the derivatives were tumoristatic at well-tolerated doses in mice bearing solid T24 tumours. The antiproliferative activity of these compounds appears to be mediated by polyamine depletion.

Successful treatment of lupus nephritis in MRL-lpr/lpr mice by inhibiting ornithine decarboxylase

Ornithine decarboxylase (ODC) is a key enzyme in the biosynthesis of cellular polyamines, putrescine, spermidine and spermine. Difluoromethylornithine (DFMO) is an irreversible inhibitor of ODC and thereby depletes putrescine and spermidine levels in vivo and in vitro. Previous studies in lupus-prone MRL-lpr/lpr mice treated with 1% DFMO in drinking water have been associated with improved lifespan, and reduced anti-DNA antibody production, lymphadenopathy, and splenic polyamine levels. Since glomerulonephritis is a major cause of morbidity and mortality in lupus, we studied the effect of DFMO on renal histology of MRL-lpr/lpr mice. Female BALB/c and MRL-(+)/+ mice were used as controls. Dose response studies revealed that 1.5% DFMO in drinking water had maximum therapeutic efficacy and produced a significant 79% increase in the median lifespan of a group of 20 mice compared to an equal number of controls (P less than 0.001). Renal histologic studies were performed on kidney sections from four to five mice each from DFMO-treated and untreated groups at 12, 16, 20, 24 and 29 weeks of age. Sections were read blinded to duration and treatment and scored by four major histologic criteria (glomerulonephritis, interstitial inflammation, perivascular inflammation, and vasculitis) and showed significant reduction in all these parameters in DFMO-treated mice when compared to age- and sex-matched untreated mice of the same strain. DFMO treatment had no significant effect on pulmonary histologic findings on these mice. DFMO treatment reduced ODC activity and polyamine concentrations in treated mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary polyamine levels in cancer patients treated with D,L-alpha-difluoromethylornithine, an inhibitor of polyamine biosynthesis

The polyamine biosynthesis inhibitor D,L-alpha-Difluoromethylornithine hydrochloride monohydrate (DFMO) has cytostatic and cytotoxic effects against various human tumor cell lines in vitro. We measured levels of the polyamines putrescine and spermidine in the urine of cancer patients undergoing "conventional" chemotherapy in a two-arm randomized phase I-II study with and without additional DFMO administered orally at a dose of 1.7 g/sq.m. t.i.d. The study group included 38 patients with carcinoma of the breast, stomach, prostate, or female genital organs or metastatic carcinoma of unknown origin. A control group of 32 patients with similar malignancies received "conventional" chemotherapy without DFMO. Polyamine levels were determined periodically in the urine of all patients. In DFMO-treated patients, a significant decrease in putrescine and spermidine levels was observed after 3 weeks of DFMO therapy (the first time point evaluated) that usually persisted throughout the course of treatment. Significant differences in polyamine levels between DFMO-treated and control patients were observed for patients in remission. Less significant differences were noted, however, for patients with static or progressive disease between DFMO-treated and control groups. DFMO activity appears to be reflected by a long-term decrease in urinary polyamine levels.