Effect of alpha-difluoromethylornithine on rectal mucosal levels of polyamines in a randomized, double-blinded trial for colon cancer prevention

Antitumor potential of polyamines in cancer

The dysregulation of polyamines in tumors has made polyamine metabolism an appealing target for cancer therapy. Gene mutations drive the reprogramming of polyamine metabolism in tumors, presenting promising opportunities for clinical treatment. The proposed strategies involve inhibiting polyamine biosynthesis while also targeting the polyamine transport system as antitumor approaches. A growing number of drugs aimed at polyamine biosynthesis and transport systems are undergoing clinical trials. Polyamine metabolism plays a role in regulating cancer signaling pathways, suggesting potential combination therapies for cancer treatment. Furthermore, supplemental polyamine substances have demonstrated antitumor activity, indicating that combining polyamines with downstream targets or immunotherapy could offer significant clinical benefits. These discoveries open new avenues for leveraging polyamine metabolism in anticancer therapy.

Evaluating Difluoromethylornithine Safety and Efficacy for Non-Melanoma Skin Cancer Chemoprevention: A Systematic Review

INTRODUCTION

Recent FDA approval of difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase for the prevention of neuroblastoma in children, has renewed interest in this medication for the prevention of other cancers including keratinocyte carcinomas (KCs). It has been investigated for cancer chemoprevention, including neoplasms of the colon, breast, and prostate.

METHODS

We assessed the current body of literature that determines DFMO efficacy and safety in non-melanoma skin cancer prevention. A systematic search of PubMed Central, and Web of Sciences was performed.

RESULTS

In this analysis, 12 studies were included evaluating 1618 patients. Most patients were Caucasian 90% (1452/1618) with a mean age of 61 years, and 73% (1214/1618) had previously been diagnosed with KC. For oral DFMO, reduction in KC was significant in 24% (291/1214) of patients. Nonsignificant reduction was observed in 17% (207/1214) of patients. The remaining studies, representing 59% (716/1214) of patients explored DFMO's pharmacological/biological effects without elucidating its direct impact on KC. Topical DFMO shows modest efficacy in reducing the number of actinic keratosis (AK), as indicated in 4 studies representing 38.12% (154/404) of patients. For patients taking the oral eflornithine, the most frequently reported adverse events included reversible ototoxicity (11% of patients) gastrointestinal disturbances (10.39%). For the topical DFMO transient local cutaneous eruptions were common impacting 28.76% (111/386) of patients.

CONCLUSION

Current evidence highlights the lack of conclusive data supporting the efficacy of oral DFMO, making it difficult to recommend its use. Conversely, topical DFMO demonstrates more promising outcomes in preventing AKs, presenting a potentially useful alternative in select patients.

P53-dependent hypusination of eIF5A affects mitochondrial translation and senescence immune surveillance

Cellular senescence is characterized by a permanent growth arrest and is associated with tissue aging and cancer. Senescent cells secrete a number of different cytokines referred to as the senescence-associated secretory phenotype (SASP), which impacts the surrounding tissue and immune response. Here, we find that senescent cells exhibit higher rates of protein synthesis compared to proliferating cells and identify eIF5A as a crucial regulator of this process. Polyamine metabolism and hypusination of eIF5A play a pivotal role in sustaining elevated levels of protein synthesis in senescent cells. Mechanistically, we identify a p53-dependent program in senescent cells that maintains hypusination levels of eIF5A. Finally, we demonstrate that functional eIF5A is required for synthesizing mitochondrial ribosomal proteins and monitoring the immune clearance of premalignant senescent cells in vivo. Our findings establish an important role of protein synthesis during cellular senescence and suggest a link between eIF5A, polyamine metabolism, and senescence immune surveillance.

Phase IIa Clinical Biomarker Trial of Dietary Arginine Restriction and Aspirin in Colorectal Cancer Patients

After potentially curative treatment, colorectal cancer (CRC) patients remain at high risk for recurrence, second primary CRC, and high-risk adenomas. In combination with existing data, our previous findings provide a rationale for reducing tissue polyamines as tertiary prevention in non-metastatic CRC patients. The goal of this study was to demonstrate rectal tissue polyamine reduction in optimally treated stage I-III CRC patients after intervention with daily oral aspirin + dietary arginine restriction. A single-institution phase IIa clinical trial was conducted. Patients were treated with aspirin 325 mg/day and an individualized dietary regimen designed to reduce arginine intake by ≥30% over a 12-week study period. Dietary intake, endoscopy with rectal biopsies, and phlebotomy were performed pre- and post-intervention. The primary endpoint was to demonstrate ≥50% decrease in rectal tissue putrescine levels from baseline as a measure of polyamine reduction in the target tissue. Twenty eligible patients completed the study. After study intervention, mean dietary arginine intake decreased from 3.7 g/day ± 1.3 SD to 2.6 g/day ± 1.2 SD (29.7% decrease, p < 0.02 by Sign test). Mean plasma arginine levels decreased from 46.0 ng/mL ± 31.5 SD at baseline to 35 ng/mL ± 21.7 SD (p < 0.001). Rectal tissue putrescine levels were 0.90 nMol/mg-protein pre-intervention and 0.99 nMol/mg-protein post-intervention (p < 0.64, NS). No significant differences were observed for the other tissue polyamines investigated: spermidine (p < 0.13), spermine (p < 0.21), spermidine:spermine ratio (p < 0.71). Among CRC survivors, treatment with daily oral aspirin and an individualized dietary arginine restriction intervention resulted in lower calculated dietary arginine intake and plasma arginine levels but did not affect rectal tissue polyamine levels.

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.

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.

Chemoprevention with low-dose aspirin, mesalazine, or both in patients with familial adenomatous polyposis without previous colectomy (J-FAPP Study IV): a multicentre, double-blind, randomised, two-by-two factorial design trial

BACKGROUND

The only established treatment for preventing colorectal cancer in patients with familial adenomatous polyposis (FAP) is colectomy, which greatly reduces patient quality of life. Thus, an alternative method is warranted. In this trial, we aimed to clarify the individual and joint effects of low-dose aspirin and mesalazine on the recurrence of colorectal polyps in Japanese patients with FAP.

METHODS

This was a randomised, double-blind, placebo-controlled, multicentre trial with a two-by-two factorial design done in 11 centres in Japan. Eligible patients were aged 16-70 years and had a history of more than 100 adenomatous polyps in the large intestine, without a history of colectomy. Before the study, patients underwent endoscopic removal of all colorectal polyps of at least 5·0 mm in diameter. Randomisation was done with a minimisation method with a random component to balance the groups with respect to the adjustment factors of sex, age (<30 years vs ≥30 years), or smoking status at the time of entry. Patients and researchers were masked to the treatment group. There were four groups: aspirin (100 mg per day) plus mesalazine (2 g per day), aspirin (100 mg per day) plus mesalazine placebo, aspirin placebo plus mesalazine (2 g per day), or aspirin placebo plus mesalazine placebo. Treatment was continued until 1 week before 8 month colonoscopy. The primary endpoint was the incidence of colorectal polyps of at least 5·0 mm at 8 months and was assessed in the intention-to-treat population. Safety was assessed in the ITT population. We also did a per-protocol analysis including only patients who took at least 70% of the allocated study drug. This trial is registered with the UMIN Clinical Trials Registry, number UMIN000018736, and is complete.

FINDINGS

Between Sept 25, 2015, and March 13, 2017, 104 patients were randomly assigned to receive either aspirin or aspirin placebo (n=52) or mesalazine or mesalazine placebo (n=52). Two patients withdrew from the aspirin plus mesalazine placebo group. 26 (50%) of 52 patients who received no aspirin had colorectal polyps of at least 5·0 mm at 8 months, as did 15 (30%) of the 50 patients who received any aspirin, 21 (42%) of the 50 patients who received no mesalazine, and 20 (38%) of the 52 patients who received any mesalazine. The adjusted odds ratio for polyp recurrence was 0·37 (95% CI 0·16-0·86) in the patients who received any aspirin and 0·87 (95% CI 0·38-2·00) in any who received mesalazine. The most common adverse events were grade 1-2 upper gastrointestinal symptoms in three (12%) of 26 patients who received aspirin plus mesalazine, one (4%) of 24 patients who received aspirin plus mesalazine placebo, and one (4%) of 26 patients who received mesalazine plus aspirin placebo. There was one grade 4 event in the mesalazine plus aspirin placebo group, but not related to the treatment.

INTERPRETATION

Low-dose aspirin safely suppressed the recurrence of colorectal polyps larger than 5·0 mm in patients with FAP. These results suggest an effect of low-dose aspirin for FAP and could be an alternative method for preventing colorectal cancer in FAP.

FUNDING

Japan Agency for Medical Research and Development.

Metformin Inhibits the Urea Cycle and Reduces Putrescine Generation in Colorectal Cancer Cell Lines

The urea cycle (UC) removes the excess nitrogen and ammonia generated by nitrogen-containing compound composites or protein breakdown in the human body. Research has shown that changes in UC enzymes are not only related to tumorigenesis and tumor development but also associated with poor survival in hepatocellular, breast, and colorectal cancers (CRC), etc. Cytoplasmic ornithine, the intermediate product of the urea cycle, is a specific substrate for ornithine decarboxylase (ODC, also known as ODC1) for the production of putrescine and is required for tumor growth. Polyamines (spermidine, spermine, and their precursor putrescine) play central roles in more than half of the steps of colorectal tumorigenesis. Given the close connection between polyamines and cancer, the regulation of polyamine metabolic pathways has attracted attention regarding the mechanisms of action of chemical drugs used to prevent CRC, as the drug most widely used for treating type 2 diabetes (T2D), metformin (Met) exhibits antitumor activity against a variety of cancer cells, with a vaguely defined mechanism. In addition, the influence of metformin on the UC and putrescine generation in colorectal cancer has remained unclear. In our study, we investigated the effect of metformin on the UC and putrescine generation of CRC in vivo and in vitro and elucidated the underlying mechanisms. In nude mice bearing HCT116 tumor xenografts, the administration of metformin inhibited tumor growth without affecting body weight. In addition, metformin treatment increased the expression of monophosphate (AMP)-activated protein kinase (AMPK) and p53 in both HCT116 xenografts and colorectal cancer cell lines and decreased the expression of the urea cycle enzymes, including carbamoyl phosphate synthase 1 (CPS1), arginase 1 (ARG1), ornithine trans-carbamylase (OTC), and ODC. The putrescine levels in both HCT116 xenografts and HCT116 cells decreased after metformin treatment. These results demonstrate that metformin inhibited CRC cell proliferation via activating AMPK/p53 and that there was an association between metformin, urea cycle inhibition and a reduction in putrescine generation.

Updates in chemoprevention research for hereditary gastrointestinal and polyposis syndromes

PURPOSE OF REVIEW

To critically examine recently published research in the area of chemoprevention in hereditary polyposis and gastrointestinal cancers, and to briefly review several ongoing chemoprevention trials testing novel agents in this population.

RECENT FINDINGS

Four recent chemoprevention trials in patients with familial adenomatous polyposis (FAP) were identified and reviewed. In the FAPEST trial, the combination of erlotinib+sulindac (compared to placebo) met its primary outcome of decreased duodenal polyp burden. A secondary analysis of lower gastrointestinal tract outcomes also demonstrated significant benefits. Two randomized trials in FAP patients examining combination regimens (celecoxib+DFMO and sulindac+DFMO) failed to meet their primary endpoints. Benefits of further research into these combinations was suggested by efficacy signals seen in secondary and post-hoc analyses. Finally, a randomized trial found curcumin (vs placebo) to have no benefit in reducing colorectal polyp count or size in patients with FAP.

SUMMARY

Progress in developing new and more effective preventive options for patients with hereditary gastrointestinal syndromes continues to be made through the efforts of investigators conducting chemoprevention research.

Metabolic changes in the brain and blood of rats following acoustic trauma, tinnitus and hyperacusis

It has been increasingly recognized that tinnitus is likely to be generated by complex network changes. Acoustic trauma that causes tinnitus induces significant changes in multiple metabolic pathways in the brain. However, it is not clear whether those metabolic changes in the brain could also be reflected in blood samples and whether metabolic changes could discriminate acoustic trauma, hyperacusis and tinnitus. We analyzed brain and serum metabolic changes in rats following acoustic trauma or a sham procedure using metabolomics. Hearing levels were recorded before and after acoustic trauma and behavioral measures to quantify tinnitus and hyperacusis were conducted at 4 weeks following acoustic trauma. Tissues from 11 different brain regions and serum samples were collected at about 3 months following acoustic trauma. Among the acoustic trauma animals, eight exhibited hyperacusis-like behavior and three exhibited tinnitus-like behavior. Using Gas chromatography-mass spectrometry and multivariate statistical analysis, significant metabolic changes were found in acoustic trauma animals in both the brain and serum samples with a number of metabolic pathways significantly perturbated. Furthermore, metabolic changes in the serum were able to differentiate sham from acoustic trauma animals, as well as sham from hyperacusis animals, with high accuracy. Our results suggest that serum metabolic profiling in combination with machine learning analysis may be a promising approach for identifying biomarkers for acoustic trauma, hyperacusis and potentially, tinnitus.

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.

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

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

Alpha-Difluoromethylornithine, an Irreversible Inhibitor of Polyamine Biosynthesis, as a Therapeutic Strategy against Hyperproliferative and Infectious Diseases

The fluorinated ornithine analog α-difluoromethylornithine (DFMO, eflornithine, ornidyl) is an irreversible suicide inhibitor of ornithine decarboxylase (ODC), the first and rate-limiting enzyme of polyamine biosynthesis. The ubiquitous and essential polyamines have many functions, but are primarily important for rapidly proliferating cells. Thus, ODC is potentially a drug target for any disease state where rapid growth is a key process leading to pathology. The compound was originally discovered as an anticancer drug, but its effectiveness was disappointing. However, DFMO was successfully developed to treat African sleeping sickness and is currently one of few clinically used drugs to combat this neglected tropical disease. The other Food and Drug Administration (FDA) approved application for DFMO is as an active ingredient in the hair removal cream Vaniqa. In recent years, renewed interest in DFMO for hyperproliferative diseases has led to increased research and promising preclinical and clinical trials. This review explores the use of DFMO for the treatment of African sleeping sickness and hirsutism, as well as its potential as a chemopreventive and chemotherapeutic agent against colorectal cancer and neuroblastoma.

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.

Regulation of Polyamine Metabolism by Curcumin for Cancer Prevention and Therapy

Curcumin (diferuloylmethane), the natural polyphenol responsible for the characteristic yellow pigment of the spice turmeric (Curcuma longa), is traditionally known for its antioxidant, anti-inflammatory, and anticarcinogenic properties. Capable of affecting the initiation, promotion, and progression of carcinogenesis through multiple mechanisms, curcumin has potential utility for both chemoprevention and chemotherapy. In human cancer cell lines, curcumin has been shown to decrease ornithine decarboxylase (ODC) activity, a rate-limiting enzyme in polyamine biosynthesis that is frequently upregulated in cancer and other rapidly proliferating tissues. Numerous studies have demonstrated that pretreatment with curcumin can abrogate carcinogen-induced ODC activity and tumor development in rodent tumorigenesis models targeting various organs. This review summarizes the results of curcumin exposure with regard to the modulation of polyamine metabolism and discusses the potential utility of this natural compound in conjunction with the exploitation of dysregulated polyamine metabolism in chemopreventive and chemotherapeutic settings.

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.

An international randomised trial of celecoxib versus celecoxib plus difluoromethylornithine in patients with familial adenomatous polyposis

BACKGROUND AND AIM

Although Non-steroidal anti-inflammatory drugs reduce colorectal adenoma burden in familial adenomatous polyposis (FAP), the utility of combining chemopreventive agents in FAP is not known. We conducted a randomised trial of celecoxib (CXB) versus CXB+diflouromethylornithine (DFMO) to determine the synergistic effect, if any.

METHODS

The primary endpoint was % change in adenoma count in a defined field. Secondary endpoints were adenoma burden (weighted by adenoma diameter) and video review of entire colon/rectal segments. Adverse event (AEs) were monitored by National Cancer Institution toxicity criteria.

RESULTS

112 subjects were randomised: 60 men and 52 women at a mean age of 38 years. For the 89 patients who had landmark-matched polyp counts available at baseline and 6 months, the mean % change in adenoma count over the 6 months of trial was -13.0% for CXB+DFMO and -1.0% for CXB (p=0.69). Mean % change in adenoma burden was -40% (CXB+DFMO) vs -27% (CXB) (p=0.13). Video-based global polyp change was -0.80 for CXB+DFMO vs -0.33 for CXB (p=0.03). Fatigue was the only significant AE, worse on the CXB arm (p=0.02).

CONCLUSIONS

CXB combined with DFMO yielded moderate synergy according to a video-based global assessment. No significant difference in adenoma count, the primary endpoint, was seen between the two study arms. No evidence of DFMO-related ototoxicity was seen. There were no adverse cardiovascular outcomes in either trial arm and no significant increase in AEs in the CXB+DFMO arm of the trial. Differences in outcomes between primary and secondary endpoints may relate to sensitivity of the endpoint measures themselves.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov number N01-CN95040.

Time-serial Assessment of Drug Combination Interventions in a Mouse Model of Colorectal Carcinogenesis Using Optical Coherence Tomography

Optical coherence tomography (OCT) is a high-resolution, nondestructive imaging modality that enables time-serial assessment of adenoma development in the mouse model of colorectal cancer. In this study, OCT was utilized to evaluate the effectiveness of interventions with the experimental antitumor agent α-difluoromethylornithine (DFMO) and a nonsteroidal anti-inflammatory drug sulindac during early [chemoprevention (CP)] and late stages [chemotherapy (CT)] of colon tumorigenesis. Biological endpoints for drug interventions included OCT-generated tumor number and tumor burden. Immunochistochemistry was used to evaluate biochemical endpoints [Ki-67, cleaved caspase-3, cyclooxygenase (COX)-2, β-catenin]. K-Ras codon 12 mutations were studied with polymerase chain reaction-based technique. We demonstrated that OCT imaging significantly correlated with histological analysis of both tumor number and tumor burden for all experimental groups (P < 0.0001), but allows more accurate and full characterization of tumor number and burden growth rate because of its time-serial, nondestructive nature. DFMO alone or in combination with sulindac suppressed both the tumor number and tumor burden growth rate in the CP setting because of DFMO-mediated decrease in cell proliferation (Ki-67, P < 0.001) and K-RAS mutations frequency (P = 0.04). In the CT setting, sulindac alone and DFMO/sulindac combination were effective in reducing tumor number, but not tumor burden growth rate. A decrease in COX-2 staining in DFMO/sulindac CT groups (COX-2, P < 0.01) confirmed the treatment effect. Use of nondestructive OCT enabled repeated, quantitative evaluation of tumor number and burden, allowing changes in these parameters to be measured during CP and as a result of CT. In conclusion, OCT is a robust minimally invasive method for monitoring colorectal cancer disease and effectiveness of therapies in mouse models.

Eflornithine (DFMO) prevents progression of pancreatic cancer by modulating ornithine decarboxylase signaling

Ornithine decarboxylase (ODC) is the key rate-limiting enzyme in the polyamine synthesis pathway and it is overexpressed in a variety of cancers. We found that polyamine synthesis and modulation of ODC signaling occurs at early stages of pancreatic precursor lesions and increases as the tumor progresses in Kras-activated p48(Cre/+)-LSL-Kras(G12D/+) mice. Interest in use of the ODC inhibitor eflornithine (DFMO) as a cancer chemopreventive agent has increased in recent years since ODC was shown to be transactivated by the c-myc oncogene and to cooperate with the ras oncogene in malignant transformation of epithelial tissues. We tested the effects of DFMO on pancreatic intraepithelial neoplasias (PanIN) and their progression to pancreatic ductal adenocarcinoma (PDAC) in genetically engineered Kras mice. The Kras(G12D/+) mice fed DFMO at 0.1% and 0.2% in the diet showed a significant inhibition (P < 0.0001) of PDAC incidence compared with mice fed control diet. Pancreatic tumor weights were decreased by 31% to 43% (P < 0.03-0.001) with both doses of DFMO. DFMO at 0.1% and 0.2% caused a significant suppression (27% and 31%; P < 0.02-0.004) of PanIN 3 lesions (carcinoma in situ). DFMO-treated pancreas exhibited modulated ODC pathway components along with decreased proliferation and increased expression of p21/p27 as compared with pancreatic tissues derived from mice fed control diet. In summary, our preclinical data indicate that DFMO has potential for chemoprevention of pancreatic cancer and should be evaluated in other PDAC models and in combination with other drugs in anticipation of future clinical trials.

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.

At the Bench: Helicobacter pylori, dysregulated host responses, DNA damage, and gastric cancer

Helicobacter pylori infection is the strongest known risk factor for the development of gastric cancer. Given that ∼50% of the global population is infected with this pathogen, there is great impetus to elucidate underlying causes that mediate progression from infection to cancer. Recent evidence suggests that H. pylori-induced chronic inflammation and oxidative stress create an environment conducive to DNA damage and tissue injury. DNA damage leads to genetic instability and eventually, neoplastic transformation. Pathogen-encoded virulence factors induce a robust but futile immune response and alter host pathways that lower the threshold for carcinogenesis, including DNA damage repair, polyamine synthesis and catabolism, antioxidant responses, and cytokine production. Collectively, such dysregulation creates a protumorigenic microenvironment within the stomach. This review seeks to address each of these aspects of H. pylori infection and to call attention to areas of particular interest within this field of research. This review also seeks to prioritize areas of translational research related to H. pylori-induced gastric cancer based on insights garnered from basic research in this field. See related review by Dalal and Moss, At the Bedside: H. pylori, dysregulated host responses, DNA damage, and gastric cancer.

Colorectal cancer predicted risk online (CRC-PRO) calculator using data from the multi-ethnic cohort study

BACKGROUND

Better risk predictions for colorectal cancer (CRC) could improve prevention strategies by allowing clinicians to more accurately identify high-risk individuals. The National Cancer Institute's CRC risk calculator was created by Freedman et al using case control data.

METHODS

An online risk calculator was created using data from the Multi-Ethnic Cohort Study, which followed >180,000 patients for the development of CRC for up to 11.5 years through linkage with cancer registries. Forward stepwise regression tuned to the c statistic was used to select the most important variables for use in separate Cox survival models for men and women. Model accuracy was assessed using 10-fold cross-validation.

RESULTS

Patients in the cohort experienced 2762 incident cases of CRC. The final model for men contained age, ethnicity, pack-years of smoking, alcoholic drinks per day, body mass index, years of education, regular use of aspirin, family history of colon cancer, regular use of multivitamins, ounces of red meat intake per day, history of diabetes, and hours of moderate physical activity per day. The final model for women included age, ethnicity, years of education, use of estrogen, history of diabetes, pack-years of smoking, family history of colon cancer, regular use of multivitamins, body mass index, regular use of nonsteroidal anti-inflammatory drugs, and alcoholic drinks per day. The calculator demonstrated good accuracy with a cross-validated c statistic of 0.681 in men and 0.679 in women, and it seems to be well calibrated graphically. An electronic version of the calculator is available at http://rcalc.ccf.org.

CONCLUSION

This calculator seems to be accurate, is user friendly, and has been internally validated in a diverse population.

Unbiased metabolite profiling indicates that a diminished thymidine pool is the underlying mechanism of colon cancer chemoprevention by alpha-difluoromethylornithine

The ornithine decarboxylase inhibitor α-difluoromethylornithine (DFMO) is a highly effective chemopreventive agent for colorectal cancer thought to act via polyamine depletion. However, in DFMO-treated patients, mucosal polyamine levels do not directly correlate with colorectal cancer risk. Untargeted metabolite profiling was used to broadly survey DFMO actions on colon cancer cell metabolism. We found that DFMO treatment of Apc(Min) intestinal tumors and human colorectal cancer cells is associated with reduced levels of folate-dependent metabolites, including S-adenosylmethionine (SAM), thymidine pools, and related pathway intermediates. We hypothesized that unrestrained SAM consumption/regeneration constitutes a futile DFMO-triggered cascade that can steal tetrahydrofolate from thymidylate synthase and thereby diminish thymidine pools. In accord with this hypothesis, DFMO treatment altered the folate cofactor balance and thymidine supplementation prevented DFMO-elicited cytostasis without restoring polyamine levels. These findings suggest that thymidine metabolite pool insufficiency is a fundamental mechanism of DFMO cytostatic activity.

SIGNIFICANCE

A previously unappreciated metabolic linkage between polyamine and thymidine biosynthesis is revealed, based on the competing requirement of these pathways for a limited pool of tetrahydrofolate cofactor. This study identifies the fi rst shared mechanism for colorectal cancer chemoprevention and chemotherapy, suggesting a common metabolic target for both premalignant and malignant colon cells.

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.

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.

Role of dietary polyamines in a phase III clinical trial of difluoromethylornithine (DFMO) and sulindac for prevention of sporadic colorectal adenomas

Background:

The polyamine-inhibitory regimen difluoromethylornithine (DFMO)+sulindac has marked efficacy in preventing metachronous colorectal adenomas. Polyamines are synthesised endogenously and obtained from dietary sources. Here we investigate dietary polyamine intake and outcomes in the DFMO+sulindac colorectal adenoma prevention trial.

Methods:

Dietary polyamine data were available for 188 of 267 patients completing the study. Total dietary polyamine content was derived by the sum of dietary putrescine, spermine and spermidine values and categorised into two groups: highest (>75–100%) vs the lower three quartiles (0–25, 25–50 and 50–75%). Baseline tissue polyamine concentration and ODC1 genotype were determined. Logistic regression models were used for risk estimation.

Results:

A significant interaction was detected between dietary polyamine group and treatment with regard to adenoma recurrence (P=0.012). Significant metachronous adenoma risk reduction was observed after DFMO+sulindac treatment in dietary polyamine quartiles 1–3 (risk ratio (RR) 0.19; 95% confidence interval (CI) 0.08–0.42; P<0.0001) but not in quartile 4 (RR 1.51; 95% CI 0.53–4.29; P=0.44). However, a lower number of events in the placebo group within dietary quartile 4 confound the aforementioned risk estimates.

Conclusion:

These preliminary findings reveal complex relationships between diet and therapeutic prevention, and they support further clinical trial-based investigations where the dietary intervention itself is controlled.

Dietary polyamine intake and risk of colorectal adenomatous polyps

BACKGROUND

Putrescine, spermidine, and spermine are the polyamines required for human cell growth. The inhibition of ornithine decarboxylase (ODC), which is the rate-limiting enzyme of polyamine biosynthesis, decreases tumor growth and the development of colorectal adenomas. A database was developed to estimate dietary polyamine exposure and relate exposure to health outcomes.

OBJECTIVE

We hypothesized that high polyamine intake would increase risk of colorectal adenoma and that the allelic variation at ODC G>A +316 would modify the association.

DESIGN

Polyamine exposure was estimated in subjects pooled (n = 1164) from the control arms of 2 randomized trials for colorectal adenoma prevention [Wheat Bran Fiber low-fiber diet arm (n = 585) and Ursodeoxycholic Acid placebo arm (n = 579)] by using baseline food-frequency questionnaire data. All subjects had to have a diagnosis of colorectal adenoma to be eligible for the trial.

RESULTS

A dietary intake of polyamines above the median amount in the study population was associated with 39% increased risk of colorectal adenoma at follow-up (adjusted OR: 1.39; 95% CI: 1.06, 1.83) in the pooled sample. In addition, younger participants (OR: 1.94; 95% CI: 1.23, 3.08), women (OR: 2.43; 95% CI: 1.48, 4.00), and ODC GG genotype carriers (OR: 1.59; 95% CI: 1.00, 2.53) had significantly increased odds of colorectal adenoma if they consumed above-median polyamine amounts.

CONCLUSIONS

This study showed a role for dietary polyamines in colorectal adenoma risk. Corroboration of these findings would confirm a previously unrecognized, modifiable dietary risk factor for colorectal adenoma.

Aspirin in the chemoprevention of colorectal neoplasia: an overview

Considerable evidence supports the effectiveness of aspirin for chemoprevention of colorectal cancer (CRC) in addition to its well-established benefits in the prevention of vascular disease. Epidemiologic studies have consistently observed an inverse association between aspirin use and risk of CRC. A recent pooled analysis of a long-term posttrial follow-up of nearly 14,000 patients from four randomized, cardiovascular disease prevention trials showed that daily aspirin treatment for about five years was associated with a 34% reduction in 20-year CRC mortality. A separate metaanalysis of nearly 3,000 patients with a history of colorectal adenoma or cancer in four randomized adenoma prevention trials showed that aspirin reduced the occurrence of advanced adenomas by 28% and any adenoma by 17%. Aspirin has also been shown to be beneficial in a clinical trial of patients with Lynch syndrome, a hereditary CRC syndrome; in those treated with aspirin for at least two years, there was a 50% or more reduction in the risk of CRC commencing five years after randomization and after aspirin had been discontinued. A few observational studies have shown an increase in survival among patients with CRC who use aspirin. Taken together, these findings strengthen the case for consideration of long-term aspirin use in CRC prevention. Despite these compelling data, there is a lack of consensus about the balance of risks and benefits associated with long-term aspirin use, particularly in low-risk populations. The optimal dose to use for cancer prevention and the precise mechanism underlying aspirin's anticancer effect require further investigation.

Cellular diamine levels in cancer chemoprevention: modulation by ibuprofen and membrane plasmalogens

Background

To develop effective strategies in cancer chemoprevention, an increased understanding of endogenous biochemical mediators that block metastatic processes is critically needed. Dietary lipids and non-steroidal anti-inflammatory drugs (NSAIDs) have a published track record of providing protection against gastrointestinal malignancies. In this regard, we examined the effects of membrane plasmalogens and ibuprofen on regulation of cellular levels of diamines, polyamine mediators that are augmented in cancer cells. For these studies we utilized Chinese hamster ovary (CHO) cells and NRel-4 cells, a CHO cell line with defective plasmalogen synthesis.

Results

NRel-4 cells, which possess cellular plasmalogen levels that are 10% of control CHO cells, demonstrated 2- to 3-fold increases in cellular diamine levels. These diamine levels were normalized by plasmalogen replacement and significantly reduced by ibuprofen. In both cases the mechanism of action appears to mainly involve increased diamine efflux via the diamine exporter. The actions of ibuprofen were not stereospecific, supporting previous studies that cyclooxygenase (COX) inhibition is unlikely to be involved in the ability of NSAIDs to reduce intracellular diamine levels.

Conclusions

Our data demonstrate that ibuprofen, a drug known to reduce the risk of colorectal cancer, reduces cellular diamine levels via augmentation of diamine efflux. Similarly, augmentation of membrane plasmalogens can increase diamine export from control and plasmalogen-deficient cells. These data support the concept that membrane transporter function may be a therapeutic point of intervention for dietary and pharmacological approaches to cancer chemoprevention.

Evaluation of difluoromethylornithine for the chemoprevention of Barrett's esophagus and mucosal dysplasia

Patients with Barrett's esophagus (BE) and dysplasia are candidates for chemopreventive strategies to reduce cancer risk. We determined the effects of difluoromethylornithine (DMFO) on mucosal polyamines, gene expression, and histopathology in BE. Ten patients with BE and low-grade dysplasia participated in a single-arm study of DFMO (0.5 g/m(2)/d) given continuously for 6 months. Esophagoscopy with biopsies was conducted at baseline, 3, 6, and 12 months. Dysplasia was graded by a gastrointestinal pathologist. Audiology was assessed (at baseline and at 6 months). Mucosal polyamines were measured by high-performance liquid chromatography. Microarray-based gene expression was analyzed using a cDNA two-color chip. DFMO suppressed levels of the polyamines putrescine (P = 0.02) and spermidine (P = 0.02) and the spermidine/spermine ratio (P < 0.01) in dysplastic BE (6 months vs. baseline) that persisted at 6 months following drug cessation. Among the top 25 modulated genes, we found those regulating p53-mediated cell signaling (RPL11), cell-cycle regulation (cyclin E2), and cell adhesion and invasion (Plexin1). DFMO downregulated Krüppel-like factor 5 (KLF5), a transcription factor promoting cell proliferation, and suppressed RFC5 whose protein interacts with proliferating cell nuclear antigen. Histopathology showed regression of dysplasia (n = 1), stable disease (n = 8), and progression to high-grade dysplasia (n = 1). Polyamines were suppressed in the responder to a greater extent than in stable cases. DFMO was well tolerated, and one patient had subclinical, unilateral ototoxicity. DFMO suppressed mucosal polyamines and modulated genes that may be mechanistically related to its chemopreventive effect. Further study of DFMO for the chemoprevention of esophageal cancer in BE patients is warranted.

DFMO: targeted risk reduction therapy for colorectal neoplasia

Strategies to decrease intracellular polyamine levels have been studied for their efficacy in reducing colorectal cancer (CRC) risk. A successful strategy combined agents that decreased polyamine synthesis by inhibiting ornithine decarboxylase with difluoromethylornithine (DFMO), and increased cellular export of polyamines by activating the spermidine/spermine acetyl transferase with non-steroidal anti-inflammatory drugs (NSAIDs). A Phase III trial treating resected adenoma patients with DFMO plus sulindac demonstrated marked reduction of metachronous adenomas, advanced adenomas and multiple adenomas compared to placebo. This combination regimen was well-tolerated, however there was a non-significant excess of cardiovascular events in the treatment arm compared to placebo as well as modest ototoxicity. Targeting this therapy to people at elevated risk of CRC, and employing clinical and genetic predictors, should improve patient benefit and reduce the risk of side effects to improve the acceptability of this strategy.

Polyamines in cancer

Polyamines are organic cations shown to control gene expression at the transcriptional, posttranscriptional, and translational levels. Multiple cellular oncogenic pathways are involved in regulation of transcription and translation of polyamine-metabolizing enzymes. As a consequence of genetic alterations, expression levels and activities of polyamine-metabolizing enzymes change rapidly during tumorigenesis resulting in high levels of polyamines in many human epithelial tumors. This review summarizes the mechanisms of polyamine regulation by canonical tumor suppressor genes and oncogenes, as well as the role of eukaryotic initiation factor 5A (EIF5A) in cancer. The importance of research utilizing pharmaceutical inhibitors and cancer chemopreventive strategies targeting the polyamine pathway is also discussed.

Levels of rectal mucosal polyamines and prostaglandin E2 predict ability of DFMO and sulindac to prevent colorectal adenoma

BACKGROUND & AIMS

Combination of polyamine and prostaglandin E2 (PGE2)-synthesis inhibitors reduced the risk of colorectal adenoma (CRA) by 70% in patients who received polypectomies. We studied effects of the combination of difluoromethylornithine (DFMO) and sulindac on biomarkers and investigated factors that modify their efficacy.

METHODS

We analyzed rectal mucosal levels of polyamines (spermidine, spermine, and putrescine) and PGE2, treatment regimens, and risk of CRA in 267 participants of a phase IIb/III chemoprevention trial of DFMO/sulindac.

RESULTS

In the group that received DFMO/sulindac, spermidine-to-spermine ratio (Spd:Spm) in rectal mucosa decreased between baseline and 12- and 36-month follow-up examinations (0.30, 0.23, and 0.24, respectively; P < .001 for both comparisons to baseline). Putrescine levels decreased between baseline and 12 months (0.46 vs 0.15 nmol/mg protein; P < .001) but rebounded between 12 and 36 months (0.15 vs 0.36 nmol/mg protein; P = .001). PGE2 levels did not change, although aspirin use was significantly associated with lower baseline levels of PGE2. No significant associations were observed between changes in biomarker levels and efficacy. However, drug efficacy was greatest in subjects with low Spd:Spm and high PGE2 at baseline; none of these subjects, versus 39% of those given placebo, developed CRA (P < .001). Efficacy was lowest in subjects with high Spd:Spm and low PGE2 at baseline; 28% developed CRA, compared with 36% of patients given placebo (P = .563).

CONCLUSIONS

A combination of DFMO and sulindac significantly suppressed production of rectal mucosal polyamines but not PGE2. No relationship was found between changes in biomarker levels and response. However, baseline biomarker levels modified the effect of DFMO/sulindac for CRA prevention.

Ornithine decarboxylase-1 polymorphism, chemoprevention with eflornithine and sulindac, and outcomes among colorectal adenoma patients

The ornithine decarboxylase-1 (ODC1) polymorphism at position +316 affects binding by transcriptional activators and repressors and modulates the risk of metachronous colorectal adenomas, particularly in association with aspirin use. We investigated the effects of ODC1 after treatment with difluoromethylornithine (eflornithine)/sulindac or placebo. Two hundred twenty-eight colorectal adenoma patients in a randomized phase III trial were genotyped for ODC1. We used Wilcoxon rank sums tests on non-normally distributed continuous variables across two genotype groups, χ(2) or Fisher exact test to assess the association between baseline categorical variables and genotype group, and log binomial regression for the primary (adenoma recurrence) and secondary outcomes (tissue polyamine response, cardiovascular toxicity, gastrointestinal toxicity, and ototoxicity). All statistical tests were two-sided. In binomial regression models with variables age, sex, race, aspirin use, treatment, and ODC1 genotype, treatment was the only statistically significant factor associated with differences in adenoma recurrence or tissue polyamine response. A statistically significant interaction was detected between ODC1 genotype and treatment with respect to adenoma recurrence (placebo group: GG, 50%, AA/GA: 34%; treatment group: GG, 11%, AA/GA, 21%; P(interaction) = .038). Excess ototoxicity was observed among ODC1 AA patients receiving treatment, but the interaction of genotype and treatment on ototoxicity was not statistically significant (P = .45).

Primary prevention of colorectal cancer

Colorectal cancer has been strongly associated with a Western lifestyle. In the past several decades, much has been learned about the dietary, lifestyle, and medication risk factors for this malignancy. Although there is controversy about the role of specific nutritional factors, consideration of dietary pattern as a whole appears useful for formulating recommendations. For example, several studies have shown that high intake of red and processed meats, highly refined grains and starches, and sugars is related to increased risk of colorectal cancer. Replacing these factors with poultry, fish, and plant sources as the primary source of protein; unsaturated fats as the primary source of fat; and unrefined grains, legumes and fruits as the primary source of carbohydrates is likely to lower risk of colorectal cancer. Although a role for supplements, including vitamin D, folate, and vitamin B6, remains uncertain, calcium supplementation is likely to be at least modestly beneficial. With respect to lifestyle, compelling evidence indicates that avoidance of smoking and heavy alcohol use, prevention of weight gain, and maintenance of a reasonable level of physical activity are associated with markedly lower risks of colorectal cancer. Medications such as aspirin and nonsteroidal anti-inflammatory drugs and postmenopausal hormones for women are associated with substantial reductions in colorectal cancer risk, though their utility is affected by associated risks. Taken together, modifications in diet and lifestyle should substantially reduce the risk of colorectal cancer and could complement screening in reducing colorectal cancer incidence.

A randomized, double-blind, placebo-controlled phase 3 skin cancer prevention study of {alpha}-difluoromethylornithine in subjects with previous history of skin cancer

Preclinical studies have shown that the inhibition of ornithine decarboxylase (ODC) by alpha-difluoromethylornithine (DFMO) and resultant decreases in tissue concentrations of polyamines (putrescine and spermidine) prevents neoplastic developments in many tissue types. Clinical studies of oral DFMO at 500 mg/m(2)/day revealed it to be safe and tolerable and resulted in significant inhibition of phorbol ester-induced skin ODC activity. Two hundred and ninety-one participants (mean age, 61 years; 60% male) with a history of prior nonmelanoma skin cancer (NMSC; mean, 4.5 skin cancers) were randomized to oral DFMO (500 mg/m(2)/day) or placebo for 4 to 5 years. There was a trend toward a history of more prior skin cancers in subjects randomized to placebo, but all other characteristics including sunscreen and nonsteroidal anti-inflammatory drug use were evenly distributed. Evaluation of 1,200 person-years of follow-up revealed a new NMSC rate of 0.5 events/person/year. The primary end point, new NMSCs, was not significantly different between subjects taking DFMO and placebo (260 versus 363 cancers, P = 0.069, two-sample t test). Evaluation of basal cell (BCC) and squamous cell cancers separately revealed very little difference in squamous cell cancer between treatment groups but a significant difference in new BCC (DFMO, 163 cancers; placebo, 243 cancers; expressed as event rate of 0.28 BCC/person/year versus 0.40 BCC/person/year, P = 0.03). Compliance with DFMO was >90% and it seemed to be well tolerated with evidence of mild ototoxicity as measured by serial audiometric examination when compared with placebo subjects. The analysis of normal skin biopsies revealed a significant (P < 0.05) decrease in 12-0-tetradecanoylphorbol-13-acetate-induced ODC activity (month 24, 36, and 48) and putrescine concentration (month 24 and 36 only) in DFMO subjects. Subjects with a history of skin cancer taking daily DFMO had an insignificant reduction (P = 0.069) in new NMSC that was predominantly due to a marked reduction in new BCC. Based on these data, the potential of DFMO, alone or in combination, to prevent skin cancers should be explored further.

Polyamines as mediators of APC-dependent intestinal carcinogenesis and cancer chemoprevention

Combination chemoprevention for cancer was proposed a quarter of a century ago, but has not been implemented in standard medical practice owing to limited efficacy and toxicity. Recent trials have targeted inflammation and polyamine biosynthesis, both of which are increased in carcinogenesis. Preclinical studies have demonstrated that DFMO (difluoromethylornithine), an irreversible inhibitor of ODC (ornithine decarboxylase) which is the first enzyme in polyamine biosynthesis, combined with NSAIDs (non-steroidal anti-inflammatory drugs) suppresses colorectal carcinogenesis in murine models. The preclinical rationale for combination chemoprevention with DFMO and the NSAID sulindac, was strengthened by the observation that a SNP (single nucleotide polymorphism) in the ODC promoter was prognostic for adenoma recurrence in patients with prior sporadic colon polyps and predicted reduced risk of adenoma in those patients taking aspirin. Recent results from a phase III clinical trial showed a dramatic reduction in metachronous adenoma number, size and grade. Combination chemoprevention with DFMO and sulindac was not associated with any serious toxicity. A non-significant trend in subclinical ototoxicity was detected by quantitative audiology in a subset of patients identified by a genetic marker. These preclinical, translational and clinical data provide compelling evidence for the efficacy of combination chemoprevention. DFMO and sulindac is a rational strategy for the prevention of metachronous adenomas, especially in patients with significant risk for colorectal cancer. Toxicities from this combination may be limited to subsets of patients identified by either past medical history or clinical tests.

Associations of a polymorphism in the ornithine decarboxylase gene with colorectal cancer survival

PURPOSE

Activity of ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis, is required for normal growth and is elevated in many cancers, including colorectal cancer. We examined associations of the +316 ODC1 single nucleotide polymorphism (SNP) with colorectal cancer-specific survival among colorectal cancer cases, and then investigated its functional significance in colon cancer cells.

EXPERIMENTAL DESIGN

The study included 400 incident stage I-III colorectal cancer cases from the population-based University of California Irvine Gene-Environment Study of Familial Colorectal Cancer (diagnosed from 1994 to 1996 with follow-up through March 2008). The primary outcome was colorectal cancer-specific survival dependent on ODC1 (rs2302615) genotype (GG versus GA/AA). In human colon cancer cell lines, ODC1 allele-specific binding of E-box transcription factors was determined via Western blotting and chromatin immunoprecipitation assays. ODC1 allele-specific promoter activity was determined using promoter constructs in combination with vectors expressing either the transcriptional activator c-MYC or the repressor MAD1.

RESULTS

Genotype-specific survival differences were observed among colorectal cancer cases: compared with cases with the ODC1 GG genotype (hazards ratio, 1; reference) the adjusted colorectal cancer-specific survival hazards ratio was 2.02 (95% confidence interval, 1.17-3.50) for ODC1 GA/AA cases (P = 0.012). In colon cancer cells, the ODC1 SNP, flanked by two E-boxes, predicts ODC1 promoter activity. The E-box activator c-MYC and repressors MAD1 and MAD4 preferentially bind to ODC1 minor A-alleles, compared with major G-alleles, in cultured cells.

CONCLUSIONS

These results have implications for conditional regulation of polyamine homeostasis and suggest a model in which the ODC1 SNP may be protective for colon adenoma recurrence and detrimental for survival after colon cancer diagnosis.

Current concepts in colorectal cancer prevention

Colorectal cancer chemoprevention, or chemoprophylaxis, is a drug-based approach to prevent colorectal cancer. Preventing colorectal adenomas with currently available agents demonstrates the promise of pharmacologic strategies directed at critical regulatory pathways. However, agent toxicity, lesion breakthrough and competing efficacy from endoscopy procedures challenge population-based implementation. This article reviews the role of colorectal cancer chemoprevention in the context of existing screening and surveillance guidelines and practice. Emphasis is placed on the role of the colorectal adenoma as a cancer precursor and its surrogacy in assessing individual risk and for evaluating chemoprevention efficacy. We discuss the importance of risk stratification for identifying subjects at moderate-to-high risk for colorectal cancer who are most likely to benefit from chemoprevention at an acceptable level of risk.

Colon cancer: preventive agents and the present status of chemoprevention

BACKGROUND

Colorectal cancer (CRC) is one of the most common cancers worldwide and a prevalent cause of morbidity and mortality. CRC has a natural history of transition from a precursor lesion, ie adenomatous polyp to cancer, that spans over 10 to 15 years providing an extended opportunity for intervention and cancer prevention. Suppression of the carcinogenic process by use of pharmacological or natural agents is the cornerstone of chemoprevention.

OBJECTIVES

The aim of this review was to give an up-to-date overview on the different agents that had been studied, over the last decade, as chemopreventive agents and the current status of chemoprevention.

METHODS

Articles were identified by searches of PubMed and the Internet and reviewed. All articles and other referenced materials were retrieved using the keywords "colon cancer", "adenoma", "chemoprevention", "non steroidal anti-inflammatory drugs", "aspirin", "HMG-CoA reductase inhibitors", "bile acids", "Difluoromethylornithine", "hormone replacement therapy", "mesalamine", "curcumin", and "calcium". Papers were published between 1960 and 2008, with older references selected for historical significance. Only papers published in English were reviewed.

RESULTS

Recent preclinical as well as clinical trials have provided data on the potential benefit of a number of drugs and nutritional elements in the field of CRC prevention. Currently, only celecoxib is FDA approved for chemoprevention of CRC and only for high-risk patients with Familial Adenomatous Polyposis (FAP). This is mainly due to cardiovascular toxicity reported in individuals with a personal history of sporadic adenomas. Aspirin and sulindac have also repeatedly demonstrated efficacy in this setting. However, due to increased risk of associated GI toxicity their benefit will have to be weighed against their risk. Combination therapy, using lower doses of each medication, is drawing a great deal of attention and many studies utilizing a variety of chemopreventive agents are presently under study. Promising results have recently been published using sulindac and DFMO.

CONCLUSION

Many agents have shown positive results in the field of chemoprevention however, the ideal chemopreventive agent remains to be discovered with great emphasis on need not to harm. Combining different agents may maximize effectiveness while limiting drug toxicity.

Difluoromethylornithine plus sulindac for the prevention of sporadic colorectal adenomas: a randomized placebo-controlled, double-blind trial

Preclinical studies of chemoprevention drugs given in combination at low doses show remarkable efficacy in preventing adenomas with little additional toxicities, suggesting a strategy to improve risk to benefit ratios for preventing recurrent adenomas. Three hundred seventy-five patients with history of resected (> or =3 mm) adenomas were randomly assigned to receive oral difluoromethylornithine (DFMO) 500 mg and sulindac 150 mg once daily or matched placebos for 36 months, stratified by use of low-dose aspirin (81 mg) at baseline and clinical site. Follow-up colonoscopy was done 3 years after randomization or off-study. Colorectal adenoma recurrence was compared among the groups with log-binomial regression. Comparing the outcome in patients receiving placebos to those receiving active intervention, (a) the recurrence of one or more adenomas was 41.1% and 12.3% (risk ratio, 0.30; 95% confidence interval, 0.18-0.49; P < 0.001); (b) 8.5% had one or more advanced adenomas, compared with 0.7% of patients (risk ratio, 0.085; 95% confidence interval, 0.011-0.65; P < 0.001); and (c) 17 (13.2%) patients had multiple adenomas (>1) at the final colonoscopy, compared with 1 (0.7%; risk ratio, 0.055; 0.0074-0.41; P < 0.001). Serious adverse events (grade > or =3) occurred in 8.2% of patients in the placebo group, compared with 11% in the active intervention group (P = 0.35). There was no significant difference in the proportion of patients reporting hearing changes from baseline. Recurrent adenomatous polyps can be markedly reduced by a combination of low oral doses of DFMO and sulindac and with few side effects.

The effect of difluoromethylornithine on decreasing prostate size and polyamines in men: results of a year-long phase IIb randomized placebo-controlled chemoprevention trial

BACKGROUND

Prostate cancer is a major health issue, and prevention of prostate cancer and/or its progression will yield benefits for men. Difluoromethylornithine (DFMO) is an antiproliferative agent, inhibiting ornithine decarboxylase, the first enzyme in the polyamine pathway, and has been studied as a therapeutic and chemopreventive agent. The prostate has high levels of tissue polyamines and has shown sensitivity to DFMO both in vitro and in vivo.

METHODS

Eighty-one men participated in a 1-year randomized trial of placebo or DFMO. Prostate volume determination and biopsy of the prostate for histology and polyamine content were done at baseline and after 12 months. Other biomarker variables were assessed, including total and free prostate-specific antigen and prostate-specific antigen doubling time.

RESULTS

Compared with baseline, men receiving DFMO had a smaller increase in prostate volume (0.14 cm(3)) than those on placebo (2.95 cm(3); P = 0.0301) at 1 year. In addition, DFMO caused a 60.8% reduction of prostate putrescine levels compared with a 139.5% increase in the placebo arm (P = 0.0014). Stratification by ornithine decarboxylase genotype showed that DFMO reduced prostate volume (P = 0.029) and putrescine levels (P = 0.0053) in the AA + GA group but not in the GG group. There were no grade 3 or 4 toxicities. There was no clinical ototoxicity, with one subclinical grade 2 hearing decline on audiogram.

CONCLUSION

In this randomized placebo-controlled trial, DFMO induced a decrease of prostate putrescine levels and rate of prostate growth. The potential of this compound for prostate cancer or hyperplasia should be further studied.

Chemoprevention of colorectal neoplasia: the potential for personalized medicine

CRC development is a multi-step process that spans 10 to 15 years, thereby providing an opportunity for early detection and even prevention. The poor survival rate of advanced CRC has prompted the emphasis on prevention of this disease. CRC screening and removal of adenomas is an effective intervention, and is the cornerstone of prevention. However, screening efforts have had limited impact due to less than optimal compliance with guidelines. Chemoprevention involves the long-term use of a variety of oral agents that can delay, prevent or even reverse the development of adenomas in the large bowel, thus interfering with the multi-step progessing from adenoma to carcinoma. This effect is of particular importance to individuals with a hereditary prediposition to colorectal neoplasia and to those who are especially susceptile to the environmental causes of CRC. NSAIDs have drawn the most attention as chemoprevention agents. Sulindac and celecoxib are effective in promoting poly regression in high risk individuals with Familial Adenomatous Polyposis (FAP). In the more common sporadic setting the APROVe (refecoxib), APC and PreSAP (Celecoxib) trials have shown a significant reduction in adenoma recurrence but important concerns exist regarding cardiovascular toxicity associated with selective COX-2 inhibitors. These landmark studies are very important, as they provide a proof of concept that we can prevent high risk adenomas that can lead to CRC development. The ideal chemopreventive agent remains to be discovered with great emphasis on need not to harm. Possibly, combinations of agents will maximize effectiveness while limiting drug toxicity. Finally, personalized approaches will include the ability to predict risk and toxicity.