A phase III skin cancer chemoprevention study of DFMO: long-term follow-up of skin cancer events and toxicity

Polyamine Derived Photosensitizer: A Novel Approach for Photodynamic Therapy of Cancer

Polyamines play a pivotal role in cancer cell proliferation. The excessive polyamine requirement of these malignancies is satisfied through heightened biosynthesis and augmented extracellular uptake via the polyamine transport system (PTS) present on the cell membrane. Meanwhile, photodynamic therapy (PDT) emerges as an effective anti-cancer treatment devoid of drug resistance. Recognizing these intricacies, our study devised a novel polyamine-derived photosensitizer (PS) for targeted photodynamic treatment, focusing predominantly on pancreatic cancer cells. We synthesized and evaluated novel spermine-derived fluorescent probes (N2) and PS (N3), exhibiting selectivity towards pancreatic cancer cells via PTS. N3 showed minimal dark toxicity but significant phototoxicity upon irradiation, effectively causing cell death in vitro. A significant reduction in tumor volume was observed post-treatment with no pronounced dark toxicity using the pancreatic cancer CDX mouse model, affirming the therapeutic potential of N3. Overall, our findings introduce a promising new strategy for cancer treatment, highlighting the potential of polyamine-derived PSs in PDT.

The MUC1-HIF-1α signaling axis regulates pancreatic cancer pathogenesis through polyamine metabolism remodeling

Dysregulation of polyamine metabolism has been implicated in cancer initiation and progression; however, the mechanism of polyamine dysregulation in cancer is not fully understood. In this study, we investigated the role of MUC1, a mucin protein overexpressed in pancreatic cancer, in regulating polyamine metabolism. Utilizing pancreatic cancer patient data, we noted a positive correlation between MUC1 expression and the expression of key polyamine metabolism pathway genes. Functional studies revealed that knockdown of spermidine/spermine N1-acetyltransferase 1 (SAT1), a key enzyme involved in polyamine catabolism, attenuated the oncogenic functions of MUC1, including cell survival and proliferation. We further identified a regulatory axis whereby MUC1 stabilized hypoxia-inducible factor (HIF-1α), leading to increased SAT1 expression, which in turn induced carbon flux into the tricarboxylic acid cycle. MUC1-mediated stabilization of HIF-1α enhanced the promoter occupancy of the latter on SAT1 promoter and corresponding transcriptional activation of SAT1, which could be abrogated by pharmacological inhibition of HIF-1α or CRISPR/Cas9-mediated knockout of HIF1A. MUC1 knockdown caused a significant reduction in the levels of SAT1-generated metabolites, N1-acetylspermidine and N8-acetylspermidine. Given the known role of MUC1 in therapy resistance, we also investigated whether inhibiting SAT1 would enhance the efficacy of FOLFIRINOX chemotherapy. By utilizing organoid and orthotopic pancreatic cancer mouse models, we observed that targeting SAT1 with pentamidine improved the efficacy of FOLFIRINOX, suggesting that the combination may represent a promising therapeutic strategy against pancreatic cancer. This study provides insights into the interplay between MUC1 and polyamine metabolism, offering potential avenues for the development of treatments against pancreatic cancer.

Inhibition of polyamine biosynthesis preserves β cell function in type 1 diabetes

In preclinical models, α-difluoromethylornithine (DFMO), an ornithine decarboxylase (ODC) inhibitor, delays the onset of type 1 diabetes (T1D) by reducing β cell stress. However, the mechanism of DFMO action and its human tolerability remain unclear. In this study, we show that mice with β cell ODC deletion are protected against toxin-induced diabetes, suggesting a cell-autonomous role of ODC during β cell stress. In a randomized controlled trial (ClinicalTrials.gov: NCT02384889) involving 41 recent-onset T1D subjects (3:1 drug:placebo) over a 3-month treatment period with a 3-month follow-up, DFMO (125-1,000 mg/m2) is shown to meet its primary outcome of safety and tolerability. DFMO dose-dependently reduces urinary putrescine levels and, at higher doses, preserves C-peptide area under the curve without apparent immunomodulation. Transcriptomics and proteomics of DFMO-treated human islets exposed to cytokine stress reveal alterations in mRNA translation, nascent protein transport, and protein secretion. These findings suggest that DFMO may preserve β cell function in T1D through islet cell-autonomous effects.

Recent Advances in Clinical Research for Skin Cancer Chemoprevention

Neoplasm arising from the keratinocytes or melanocytes in the skin is the most prevalent type of cancer in the United States and worldwide. Since ultraviolet (UV) radiation may be a causing factor for several types of skin cancer, effective strategies to manage skin cancer include preventive measures such as minimizing exposure to UV and applying sunscreens. However, the effect of sunscreen in reducing skin cancer incidence remains uncertain. An alternative approach to prevent skin cancer is chemoprevention, which is defined as using either natural products or synthetic compounds to inhibit, delay, or reverse the development of cancer. Preclinical studies have demonstrated the effectiveness of multiple pharmacological agents and dietary supplements. However, whether preclinical findings can be translated into clinical application is unknown. This review evaluates the state of recent clinical trials investigating chemopreventive agents focusing on skin cancer to compare the target populations, interventions, endpoints, and outcomes of these trials. The ClinicalTrials and PubMed databases were searched for their available literature using the key words "skin cancer" and "chemoprevention". The objective of this review is to provide updated information on the effectiveness and side effects of promising chemopreventive agents in human subjects and to identify research gaps.

An update on clinical trials for chemoprevention of human skin cancer

The pathophysiology of skin cancer is complex, with multiple factors contributing to its development. The proactive treatment of skin cancer has been investigated in the form of chemoprevention of cutaneous malignancies in clinical trials. Chemoprevention is the use of natural or pharmacologic agents that prevent or reverse skin cancer development. Multiple trials have arisen over the past decades to explore the efficacy of specific agents to halt the progression of UV radiation damage. This comprehensive review article aims to assess clinical trials performed with chemopreventive agents for melanoma and nonmelanoma skin cancers. The following compounds were most often used in these trials: nicotinamide, retinoids, polyphenolic antioxidants, COX-2 selective inhibitors, non-steroidal anti-inflammatory drugs, difluoromethylornithine, and 5-fluorouracil. Many agents show promise in their ability to prevent nonmelanoma skin cancer formation, with few melanoma trials demonstrating efficacy. The chemoprevention efforts aimed at skin cancer are complex; current and future trials will be instrumental in identifying therapeutic agents that pose efficacy in halting cancer development and assessing whether long-term administration is tolerable.

Protective Role of Spermidine in Colitis and Colon Carcinogenesis

BACKGROUND & AIMS

Because inflammatory bowel disease is increasing worldwide and can lead to colitis-associated carcinoma (CAC), new interventions are needed. We have shown that spermine oxidase (SMOX), which generates spermidine (Spd), regulates colitis. Here we determined whether Spd treatment reduces colitis and carcinogenesis.

METHODS

SMOX was quantified in human colitis and associated dysplasia using quantitative reverse-transcription polymerase chain reaction and immunohistochemistry. We used wild-type (WT) and Smox-/- C57BL/6 mice treated with dextran sulfate sodium (DSS) or azoxymethane (AOM)-DSS as models of colitis and CAC, respectively. Mice with epithelial-specific deletion of Apc were used as a model of sporadic colon cancer. Animals were supplemented or not with Spd in the drinking water. Colonic polyamines, inflammation, tumorigenesis, transcriptomes, and microbiomes were assessed.

RESULTS

SMOX messenger RNA levels were decreased in human ulcerative colitis tissues and inversely correlated with disease activity, and SMOX protein was reduced in colitis-associated dysplasia. DSS colitis and AOM-DSS-induced dysplasia and tumorigenesis were worsened in Smox-/- vs WT mice and improved in both genotypes with Spd. Tumor development caused by Apc deletion was also reduced by Spd. Smox deletion and AOM-DSS treatment were both strongly associated with increased expression of α-defensins, which was reduced by Spd. A shift in the microbiome, with reduced abundance of Prevotella and increased Proteobacteria and Deferribacteres, occurred in Smox-/- mice and was reversed with Spd.

CONCLUSIONS

Loss of SMOX is associated with exacerbated colitis and CAC, increased α-defensin expression, and dysbiosis of the microbiome. Spd supplementation reverses these phenotypes, indicating that it has potential as an adjunctive treatment for colitis and chemopreventive for colon carcinogenesis.

Cutaneous Squamous Cell Carcinoma: The Frontier of Cancer Immunoprevention

Cutaneous squamous cell carcinoma (cSCC) is the second most common cancer, with its incidence rising steeply. Immunosuppression is a well-established risk factor for cSCC, and this risk factor highlights the critical role of the immune system in regulating cSCC development and progression. Further highlighting the nature of cSCC as an immunological disorder, substantial evidence demonstrates a tight association between cSCC risk and age-related immunosenescence. Besides the proven efficacy of immune checkpoint blockade therapy for advanced cSCC, novel immunotherapy that targets cSCC precursor lesions has shown efficacy for cSCC prevention. Furthermore, the appreciation of the interplay between keratinocytes, commensal papillomaviruses, and the immune system has revealed the possibility for the development of a preventive cSCC vaccine. cSCC shares fundamental aspects of its origin and pathogenesis with mucosal SCCs. Therefore, advances in the field of cSCC immunoprevention will inform our approach to the management of mucosal SCCs and potentially other epithelial cancers.

NSAIDs: Old Acquaintance in the Pipeline for Cancer Treatment and Prevention─Structural Modulation, Mechanisms of Action, and Bright Future

The limitations of current chemotherapeutic drugs are still a major issue in cancer treatment. Thus, targeted multimodal therapeutic approaches need to be strategically developed to successfully control tumor growth and prevent metastatic burden. Inflammation has long been recognized as a hallmark of cancer and plays a key role in the tumorigenesis and progression of the disease. Several epidemiological, clinical, and preclinical studies have shown that traditional nonsteroidal anti-inflammatory drugs (NSAIDs) exhibit anticancer activities. This Perspective reports the most recent outcomes for the treatment and prevention of different types of cancers for several NSAIDs alone or in combination with current chemotherapeutic drugs. Furthermore, an extensive review of the most promising structural modifications is reported, such as phospho, H₂S, and NO releasing-, selenium-, metal complex-, and natural product-NSAIDs, among others. We also provide a perspective about the new strategies used to obtain more efficient NSAID- or NSAID derivative- formulations for targeted delivery.

S-adenosylmethionine: A metabolite critical to the regulation of autophagy

Autophagy is a mechanism that enables cells to maintain cellular homeostasis by removing damaged materials and mobilizing energy reserves in conditions of starvation. Although nutrient availability strongly impacts the process of autophagy, the specific metabolites that regulate autophagic responses have not yet been determined. Recent results indicate that S-adenosylmethionine (SAM) represents a critical inhibitor of methionine starvation-induced autophagy. SAM is primarily involved in four key metabolic pathways: transmethylation, transsulphuration, polyamine synthesis and 5'-deoxyadenosyl 5'-radical-mediated biochemical transformations. SAM is the sole methyl group donor involved in the methylation of DNA, RNA and histones, modulating the autophagic process by mediating epigenetic effects. Moreover, the metabolites of SAM, such as homocysteine, glutathione, decarboxylated SAM and spermidine, also exert important influences on the regulation of autophagy. From our perspective, nuclear-cytosolic SAM is a conserved metabolic inhibitor that connects cellular metabolic status and the regulation of autophagy. In the future, SAM might be a new target of autophagy regulators and be widely used in the treatment of various diseases.

Photocarcinogenesis

Purpose of Review

Skin cancers account for more than 40% of all cancers in the USA and continue to rise in incidence. It is prudent to understand the current burden and pathogenesis of photocarcinogenesis and preventive measures.

Recent Findings

Insights into recently discovered mechanisms have paved way for potential targets for prevention and therapeutics. Nicotinamide has shown promising results as an oral chemopreventive agent. UVB affects the DHODH pathway of pyrimidine synthesis via STAT 3. DHODH inhibition by leflunomide may be a potential targeted chemoprevention strategy. A photolyase containing sunscreen, which repairs UV-damaged DNA, effectively reduced new precancerous lesions. Several antioxidants and anti-inflammatory agents including many phytochemicals ameliorate the process of photocarcinogenesis in preclinical and clinical studies, e.g., green tea polyphenols, Polypodium leucotomos extract, and Timosaponin A III. Diet can potentially affect skin cancer risk by its ability to modify oxidative stress and cell signaling pathways.

Summary

Photocarcinogenesis is a multi-step process. An in-depth understanding is instrumental in development of novel agents for prevention and treatment of skin cancers.

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.

Inhibition of polyamine synthesis and uptake reduces tumor progression and prolongs survival in mouse models of neuroblastoma

Amplification of the MYCN oncogene is associated with an aggressive phenotype and poor outcome in childhood neuroblastoma. Polyamines are highly regulated essential cations that are frequently elevated in cancer cells, and the rate-limiting enzyme in polyamine synthesis, ornithine decarboxylase 1 (ODC1), is a direct transcriptional target of MYCN. Treatment of neuroblastoma cells with the ODC1 inhibitor difluoromethylornithine (DFMO), although a promising therapeutic strategy, is only partially effective at impeding neuroblastoma cell growth due to activation of compensatory mechanisms resulting in increased polyamine uptake from the surrounding microenvironment. In this study, we identified solute carrier family 3 member 2 (SLC3A2) as the key transporter involved in polyamine uptake in neuroblastoma. Knockdown of SLC3A2 in neuroblastoma cells reduced the uptake of the radiolabeled polyamine spermidine, and DFMO treatment increased SLC3A2 protein. In addition, MYCN directly increased polyamine synthesis and promoted neuroblastoma cell proliferation by regulating SLC3A2 and other regulatory components of the polyamine pathway. Inhibiting polyamine uptake with the small-molecule drug AMXT 1501, in combination with DFMO, prevented or delayed tumor development in neuroblastoma-prone mice and extended survival in rodent models of established tumors. Our findings suggest that combining AMXT 1501 and DFMO with standard chemotherapy might be an effective strategy for treating neuroblastoma.

Polyamine Metabolism as a Therapeutic Target inHedgehog-Driven Basal Cell Carcinomaand Medulloblastoma

Hedgehog (Hh) signaling is a critical developmental regulator and its aberrant activation,due to somatic or germline mutations of genes encoding pathway components, causes Basal CellCarcinoma (BCC) and medulloblastoma (MB). A growing effort has been devoted at theidentification of druggable vulnerabilities of the Hedgehog signaling, leading to the identificationof various compounds with variable efficacy and/or safety. Emerging evidence shows that anaberrant polyamine metabolism is a hallmark of Hh-dependent tumors and that itspharmacological inhibition elicits relevant therapeutic effects in clinical or preclinical models ofBCC and MB. We discuss here the current knowledge of polyamine metabolism, its role in cancerand the available targeting strategies. We review the literature about the connection betweenpolyamines and the Hedgehog signaling, and the potential therapeutic benefit of targetingpolyamine metabolism in two malignancies where Hh pathways play a well-established role: BCCand MB.

Essential oils: from prevention to treatment of skin cancer

The increasing incidence of cutaneous malignancies signifies the need for multiple treatment options. Several available reviews have emphasized the potential role of various botanical extracts and naturally occurring compounds as anti-skin-cancer agents. Few studies relate to the role of chemoprevention and therapeutic activity of essential oils (EOs) and EO components. The present review summarizes an overview of chemopreventive, anti-melanoma and anti-nonmelanoma activities of EOs from various plants and EO components in in vitro and in vivo models with special emphasis on skin cancer. Also, the mechanisms by which EOs and EO components exert their effects to induce cell death are presented.

Guidelines of care for the management of cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the second most common form of human cancer and has an increasing annual incidence. Although most cSCC is cured with office-based therapy, advanced cSCC poses a significant risk for morbidity, impact on quality of life, and death. This document provides evidence-based recommendations for the management of patients with cSCC. Topics addressed include biopsy techniques and histopathologic assessment, tumor staging, surgical and nonsurgical management, follow-up and prevention of recurrence, and management of advanced disease. The primary focus of these recommendations is on evaluation and management of primary cSCC and localized disease, but where relevant, applicability to recurrent cSCC is noted, as is general information on the management of patients with metastatic disease.

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.

N-ω-chloroacetyl-L-ornithine has in-vitro activity against cancer cell lines and in-vivo activity against ascitic and solid tumors

N-ω-chloroacetyl-L-ornithine (NCAO) is an ornithine decarboxylase (ODC) inhibitor that is known to exert cytotoxic and antiproliferative effects on three neoplastic human cancer cell lines (HeLa, MCF-7, and HepG2). Here, we show that NCAO has antiproliferative activity in 13 cancer cell lines, of diverse tissue origin from human and mice, and in a mouse cancer model in vivo. All cell lines were sensitive to NCAO after 72 h of treatment (the EC50 ranged from 1 to 50.6 µmol/l). The Ca Ski cell line was the most sensitive (EC50=1.18±0.07 µmol/l) and MDA-MB-231 was the least sensitive (EC50=50.6±0.3 µmol/l). This ODC inhibitor showed selectivity for cancer cells, exerting almost no cytotoxic effect on the normal Vero cell line (EC50>1000 µmol/l). NCAO induced apoptosis and inhibited tumor cell migration in vitro. Furthermore, in vivo, this compound (at 50 and 100 mg/kg, daily intraperitoneal injection for 7 days) exerted potent antitumor activity against both solid and ascitic tumors in a mouse model using the myeloma (Ag8) cell line. At these same two doses, the toxicological evaluation showed that NCAO has no obvious systemic toxicity. The current results suggest that the antitumor activity is exerted by apoptosis related not only to a local but also a systemic cytotoxic effect exerted by NCAO on tumor cells. The applications for NCAO as an antitumor agent may be extensive; however, further studies are needed to ascertain the antitumor activity on other types of tumor in vivo and to determine the precise molecular mechanism of its activity.

Targeting ornithine decarboxylase (ODC) inhibits esophageal squamous cell carcinoma progression

To explore the function of ornithine decarboxylase in esophageal squamous cell carcinoma progression and test the effectiveness of anti-ornithine decarboxylase therapy for esophageal squamous cell carcinoma. In this study, we examined the expression pattern of ornithine decarboxylase in esophageal squamous cell carcinoma cell lines and tissues using immunohistochemistry and Western blot analysis. Then we investigated the function of ornithine decarboxylase in ESCC cells by using shRNA and an irreversible inhibitor of ornithine decarboxylase, difluoromethylornithine. To gather more supporting pre-clinical data, a human esophageal squamous cell carcinoma patient-derived xenograft mouse model (C.B-17 severe combined immunodeficient mice) was used to determine the antitumor effects of difluoromethylornithine in vivo. Our data showed that the expression of the ornithine decarboxylase protein is increased in esophageal squamous cell carcinoma tissues compared with esophagitis or normal adjacent tissues. Polyamine depletion by ODC shRNA not only arrests esophageal squamous cell carcinoma cells in the G2/M phase, but also induces apoptosis, which further suppresses esophageal squamous cell carcinoma cell tumorigenesis. Difluoromethylornithine treatment decreases proliferation and also induces apoptosis of esophageal squamous cell carcinoma cells and implanted tumors, resulting in significant reduction in the size and weight of tumors. The results of this study indicate that ornithine decarboxylase is a promising target for esophageal squamous cell carcinoma therapy and difluoromethylornithine warrants further study in clinical trials to test its effectiveness against esophageal squamous cell carcinoma.

Blocking an enzyme involved in the cellular synthesis of essential compounds called polyamines could help treat esophageal cancer. Zigang Dong from the University of Minnesota’s Hormel Institute, USA, and colleagues showed that this enzyme, called ornithine decarboxylase (ODC), is expressed at elevated levels in tumor tissues taken from patients with esophageal squamous cell carcinoma. The researchers blocked ODC activity in esophageal cancer cells using either RNA interference techniques or a drug called difluoromethylornithine (DFMO). In both cases, the treatment suppressed further growth and induced cell death. DFMO treatment also reduced the size and weight of tumors in mice implanted with human patient-derived esophageal cancer tissue. The findings point DFMO, which is already used as a medication to treat African sleeping sickness and excessive hair growth, as a potential therapy for cancer patients.

Cutaneous squamous cell carcinoma: an epidemiological review

Cutaneous squamous cell carcinoma (SCC) is a common cancer in white populations and its disease burden is often substantially underestimated. SCC occurs more often in men than women and increases dramatically with age; those affected often develop multiple primaries over time, which increases the burden. The main external cause is solar ultraviolet radiation (UVR), with immunosuppression being the other established risk factor, shown by the high SCC rates in organ transplant recipients. Sunbed use and certain genetic disorders and medical conditions are also associated with SCC, while associations with human papillomavirus infection and high bodyweight are not established. The presence of actinic keratoses (AKs) on sun-damaged skin is one of the strongest predictors of SCC in unaffected people and a very small proportion of AKs are SCC precursors, although the true rate of malignant transformation of AKs is unknown. The mainstay of SCC prevention is protection of the skin from undue sun exposure by use of clothing cover and sunscreen during summer or in sunny places. Educational, behavioural and multicomponent interventions directed at individuals ranging from parents of newborns, to school children and adolescents, to outdoor workers, have repeatedly been shown to be effective in improving sun-protective behaviours. Health policies can facilitate SCC prevention by setting standards for relevant behaviours to reduce UVR exposure, for example, by legislated restriction of the tanning industry. Skin cancer prevention initiatives are generally highly cost-effective and public investment should be encouraged to control the growing public health problems caused by SCC.

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.

Chemoprevention of Keratinocyte Carcinomas: An Updated Review

A well-established link between ultraviolet exposure and the carcinogenesis of keratinocyte carcinomas exists. Despite increased sun protection efforts, skin cancer remains the most common cancer in the USA. Numerous studies on the topic of chemoprevention investigate alternative topical, oral, and injectable agents to reduce skin cancer incidence in those at risk. Such agents include sunscreen, numerous vitamins and minerals, difluoromethylornithine, non-steroidal anti-inflammatory drugs, various peptides, field therapy, statins, and polyphenols. In this focused review, we discuss the risks and benefits of chemoprotective agents reported in clinical studies conducted in humans. We report several agents that may reduce skin cancer incidence in those at risk.

Molecular cancer prevention: Current status and future directions

The heterogeneity and complexity of advanced cancers strongly support the rationale for an enhanced focus on molecular prevention as a priority strategy to reduce the burden of cancer. Molecular prevention encompasses traditional chemopreventive agents as well as vaccinations and therapeutic approaches to cancer-predisposing conditions. Despite challenges to the field, we now have refined insights into cancer etiology and early pathogenesis; successful risk assessment and new risk models; agents with broad preventive efficacy (eg, aspirin) in common chronic diseases, including cancer; and a successful track record of more than 10 agents approved by the US Food and Drug Administration for the treatment of precancerous lesions or cancer risk reduction. The development of molecular preventive agents does not differ significantly from the development of therapies for advanced cancers, yet it has unique challenges and special considerations given that it most often involves healthy or asymptomatic individuals. Agents, biomarkers, cohorts, overall design, and endpoints are key determinants of molecular preventive trials, as with therapeutic trials, although distinctions exist for each within the preventive setting. Progress in the development and evolution of molecular preventive agents has been steadier in some organ systems, such as breast and skin, than in others. In order for molecular prevention to be fully realized as an effective strategy, several challenges to the field must be addressed. Here, the authors provide a brief overview of the context for and special considerations of molecular prevention along with a discussion of the results from major randomized controlled trials.

Skin Carcinogenesis Studies Using Mouse Models with Altered Polyamines

Nonmelanoma skin cancer (NMSC) is a major health concern worldwide. With increasing numbers in high-risk groups such as organ transplant recipients and patients taking photosensitizing medications, the incidence of NMSC continues to rise. Mouse models of NMSC allow us to better understand the molecular signaling cascades involved in skin tumor development in order to identify novel therapeutic strategies. Here we review the models designed to determine the role of the polyamines in NMSC development and maintenance. Elevated polyamines are absolutely required for tumor growth, and dysregulation of their biosynthetic and catabolic enzymes has been observed in NMSC. Studies using mice with genetic alterations in epidermal polyamines suggest that they play key roles in tumor promotion and epithelial cell survival pathways, and recent clinical trials indicate that pharmacological inhibitors of polyamine metabolism show promise in individuals at high risk for NMSC.

Chemopreventive opportunities to control basal cell carcinoma: Current perspectives

Basal cell carcinoma (BCC) is a major health problem with approximately 2.8 million new cases diagnosed each year in the United States. BCC incidences have continued to rise due to lack of effective chemopreventive options. One of the key molecular characteristics of BCC is the sustained activation of hedgehog signaling through inactivating mutations in the tumor suppressor gene patch (Ptch) or activating mutations in Smoothened. In the past, several studies have addressed targeting the activated hedgehog pathway for the treatment and prevention of BCC, although with toxic effects. Other studies have attempted BCC chemoprevention through targeting the promotional phase of the disease especially the inflammatory component. The compounds that have been utilized in pre-clinical and/or clinical studies include green and black tea, difluoromethylornithine, thymidine dinucleotide, retinoids, non-steroidal anti-inflammatory drugs, vitamin D3, and silibinin. In this review, we have discussed genetic and epigenetic modifications that occur during BCC development as well as the current state of BCC pre-clinical and clinical chemoprevention studies.

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.

Tazarotene: randomized, double-blind, vehicle-controlled, and open-label concurrent trials for basal cell carcinoma prevention and therapy in patients with basal cell nevus syndrome

Sporadic human basal cell carcinomas (BCC) are generally well managed with current surgical modalities. However, in the subset of high-risk patients predisposed to developing large numbers of BCCs, there is an unmet need for effective, low-morbidity chemoprevention. This population includes fair-skinned patients with extensive sun exposure and those with genodermatoses such as the basal cell nevus (Gorlin) syndrome (BCNS). Tazarotene (Tazorac, Allergan) is a topical retinoid with relative specificity for RAR-β and RAR-γ receptors. We previously demonstrated tazarotene's robust anti-BCC efficacy in Ptch1(+/-) mice, a murine equivalent of BCNS, and others have found it to have some efficacy against sporadic human BCCs. We report here results of a randomized, double-blind, vehicle-controlled study in patients with BCNS evaluating the efficacy of topically applied tazarotene for BCC chemoprevention (N = 34 subjects), along with an open-label trial evaluating tazarotene's efficacy for chemotherapy of BCC lesions (N = 36 subjects) for a maximum follow-up period of 3 years. We found that only 6% of patients had a chemopreventive response and that only 6% of treated BCC target lesions were clinically cured. Our studies provide no evidence for either chemopreventive or chemotherapeutic effect of tazarotene against BCCs in patients with BCNS.

Chemoprevention of prostate cancer with the polyamine synthesis inhibitor difluoromethylornithine

In vitro and in vivo preclinical results suggest that inhibition of polyamine synthesis inhibits the progression of prostate cancer. These findings has led to two clinical trials in patients at risk for invasive prostate cancer with difluoromethylornithine which specifically and irreversibly inhibits ornithine decarboxylase which catalyses the conversion of ornithine to putrescine the rate limiting step in polyamines synthesis. We have conducted a phase IIa one month and placebo randomized phase IIb 12 months trials in patients at increased risk for invasive prostate cancer. Favorable reduction in prostate polyamine levels and prostate volume was documented with no difference in clinical hearing changes. Patients with Gleason's VI lesions in a surveillance cohort would be appropriate candidates for a definitive risk reduction trial although the unavailability of validated biomarkers for invasive progression would require a large and lengthy study.

Inhibiting cycloxygenase and ornithine decarboxylase by diclofenac and alpha-difluoromethylornithine blocks cutaneous SCCs by targeting Akt-ERK axis

Non-melanoma skin cancer (NMSC) is the most common type of skin cancer in Caucasian populations. Its increasing incidence has been a major public health concern. Elevated expressions of ODC and COX-2 are associated with both murine and human NMSCs. Inhibition of these molecular targets singly employing their respective small molecule inhibitors showed limited success. Here, we show that combined blockade of ODC and COX-2 using their potent inhibitors, DFMO and diclofenac respectively abrogates growth of A431 epidermal xenograft tumors in nu/nu mice by more than 90%. The tumor growth inhibition was associated with a diminution in the proliferation and enhancement in apoptosis. The proliferation markers such as PCNA and cyclin D1 were reduced. TUNEL-positive apoptotic cells and cleaved caspase-3 were increased in the residual tumors. These agents also manifested direct target-unrelated effects. Reduced expression of phosphorylated MAPKAP-2, ERK, and Akt (ser(473) & thr(308)) were noticed. The mechanism by which combined inhibition of ODC/COX attenuated tumor growth and invasion involved reduction in EMT. Akt activation by ODC+COX-2 over-expression was the key player in this regard as Akt inhibition manifested effects similar to those observed by the combined inhibition of ODC+COX-2 whereas forced over-expression of Akt resisted against DFMO+diclofenac treatment. These data suggest that ODC+COX-2 over-expression together leads to pathogenesis of aggressive and invasive cutaneous carcinomas by activating Akt signaling pathway, which through augmenting EMT contributes to tumor invasion.

Chemoprevention of gastrointestinal neoplasia

Cancer chemoprevention is defined as the pharmacologic intervention, by drugs or nutrient-components, with the process of carcinogenesis, in order to prevent the development of invasive malignant neoplasms. This preventive attempt is particularly challenging in cancer types, which have a long subclinical developmental phase, because of their low cellular proliferation rate and their slow pre-clinical evolution, until they become clinically detectable and therapeutically as well as prognostically relevant. Therefore, only certain specific cancer types are presently in the focus of clinical chemoprevention. Among the GI tract cancer, colorectal (CRC) as well as esophageal cancer have raised the most attention over the past decades, as they both share a long precancerous stage (the adenoma in CRC and Barrett's esophagus in the case of esophageal adenocarcinoma) which provides a window of opportunity to intervene and prevent development of cancer.In this review, we will focus on both CRC as well as esophageal adenocarcinoma (EAC).

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.