Iron as a target of chemoprevention for longevity in humans

Abstract

Iron is universally abundant and no life can exist without it. However, iron levels should be maintained within a narrow range. Iron deficiency causes anaemia, whereas excessive iron increases cancer risk, presumably by free radical generation. Several pathological conditions such as genetic haemochromatosis, chronic viral hepatitis B and C, conditions related to asbestos fibre exposure and ovarian endometriosis have been recognized as iron overload-associated conditions that also increase human cancer risks. Iron's carcinogenicity has been documented in animal experiments. Surprisingly, these studies have revealed that the homozygous deletion of CDKN2A/2B is a major hallmark of iron-induced carcinogenesis. Recently, the hormonal regulation of iron metabolism has been elucidated. A commonly hypothesized mechanism may be the lack of any iron disposal pathway other than for bleeding and a mechanism of iron re-uptake as catechol chelate has been discovered. Iron overload in neurons via the ferroportin block may play a role in Alzheimer's disease. Furthermore, a recent epidemiological study reported that iron reduction by phlebotomy was associated with decreased cancer risks in a general population. Given that the required amounts of iron decrease during ageing, the fine control of body iron stores would be a wise strategy for chemoprevention of several diseases.     

Iron requirement for longevity ofPseudomonas cultures

Cultures of five out of six strains ofPseudomonas species grown in shaken flasks at 37 C needed tenfold more iron for longevity than for growth. At 30 C, the iron requirement was present in only two, and at 25 C in only one, of the six strains. The metal acted during early stationary phase and, to function, required protein synthesis. In a variety of microorganisms, qualitative and quantitative trace metal requirements for secondary metabolism and culture longevity are identical; we propose that successful completion of the former is a prerequisite of the latter.This work was supported in part by grant HD-03038-02 from the National Institute of Child Health and Human Development, U. S. Public Health Service.We express our appreciation to Miss Patsy Linn Person for performing preliminary experiments. A portion of the material was presented at the Annual Meeting of the American Society for Microbiology in Miami Beach, Florida, 4–9 May, 1969.     

Iron trafficking as an antimicrobial target

Iron is essential for the survival of most organisms. Microbial iron acquisition depends on multiple, sometimes complex steps, many of which are not shared by higher eukaryotes. Depriving pathogenic microbes of iron is therefore a potential antimicrobial strategy. The following minireview briefly describes general elements in microbial iron uptake pathways and summarizes some of the current work aiming at their medicinal inhibition.     

beta-Catenin-mediated signaling: a novel molecular target for chemoprevention with anti-inflammatory substances

Inflammation is thought to play a role in the pathophysiology of cancer. Accumulating evidence from clinical and laboratory-based studies suggests that substances with anti-inflammatory activities are potential candidates for chemoprevention. Recent advances in cellular and molecular biology of cancer shed light on components of intracellular signaling cascades that can be potential molecular targets of chemoprevention with various anti-inflammatory substances. Although cyclooxygenase-2, a primary enzyme that mediates inflammatory responses, has been well recognized as a molecular target for chemoprevention by both synthetic and natural anti-inflammatory agents, the cellular signaling mechanisms that associate inflammation and cancer are not still clearly illustrated. Recent studies suggest that beta-catenin-mediated signaling, which regulates developmental processes, may act as a potential link between inflammation and cancer. This review aims to focus on beta-catenin-mediated signaling pathways, particularly in relation to its contribution to carcinogenesis, and the modulation of inappropriately activated beta-catenin-mediated signaling by nonsteroidal anti-inflammatory drugs and chemopreventive phytochemicals possessing anti-inflammatory properties.     

Genetic signatures of exceptional longevity in humans

Like most complex phenotypes, exceptional longevity is thought to reflect a combined influence of environmental (e.g., lifestyle choices, where we live) and genetic factors. To explore the genetic contribution, we undertook a genome-wide association study of exceptional longevity in 801 centenarians (median age at death 104 years) and 914 genetically matched healthy controls. Using these data, we built a genetic model that includes 281 single nucleotide polymorphisms (SNPs) and discriminated between cases and controls of the discovery set with 89% sensitivity and specificity, and with 58% specificity and 60% sensitivity in an independent cohort of 341 controls and 253 genetically matched nonagenarians and centenarians (median age 100 years). Consistent with the hypothesis that the genetic contribution is largest with the oldest ages, the sensitivity of the model increased in the independent cohort with older and older ages (71% to classify subjects with an age at death>102 and 85% to classify subjects with an age at death>105). For further validation, we applied the model to an additional, unmatched 60 centenarians (median age 107 years) resulting in 78% sensitivity, and 2863 unmatched controls with 61% specificity. The 281 SNPs include the SNP rs2075650 in TOMM40/APOE that reached irrefutable genome wide significance (posterior probability of association = 1) and replicated in the independent cohort. Removal of this SNP from the model reduced the accuracy by only 1%. Further in-silico analysis suggests that 90% of centenarians can be grouped into clusters characterized by different “genetic signatures” of varying predictive values for exceptional longevity. The correlation between 3 signatures and 3 different life spans was replicated in the combined replication sets. The different signatures may help dissect this complex phenotype into sub-phenotypes of exceptional longevity.     

Mitochondria: A novel target for the chemoprevention of cancer

The mitochondria have emerged as a novel target for anticancer chemotherapy. This tenet is based on the observations that several conventional and experimental chemotherapeutic agents promote the permeabilization of mitochondrial membranes in cancerous cells to initiate the release of apoptogenic mitochondrial proteins. This ability to engage mitochondrial-mediated apoptosis directly using chemotherapy may be responsible for overcoming aberrant apoptosis regulatory mechanisms commonly encountered in cancerous cells. Interestingly, several putative cancer chemopreventive agents also possess the ability to trigger apoptosis in transformed, premalignant, or malignant cells in vitro via mitochondrial membrane permeabilization. This process may occur through the regulation of Bcl-2 family members, or by the induction of the mitochondrial permeability transition. Thus, by exploiting endogenous mitochondrial-mediated apoptosis-inducing mechanisms, certain chemopreventive agents may be able to block the progression of premalignant cells to malignant cells or the dissemination of malignant cells to distant organ sites as means of modulating carcinogenesis in vivo. This review will examine cancer chemoprevention with respect to apoptosis, carcinogenesis, and the proapoptotic activity of various chemopreventive agents observed in vitro. In doing so, I will construct a paradigm supporting the notion that the mitochondria are a novel target for the chemoprevention of cancer.     

Butyrate as a model for "gene-regulating chemoprevention and chemotherapy."

Recent progress in molecular genetics has facilitated understanding of the mechanisms of carcinogenesis. However, there is not yet any effective therapy or prevention for cancer based on the molecular mechanisms of carcinogenesis. So-called "gene therapy" for cancer is expected to become a new method of treatment, but there are still several serious problems with gene therapy. As a matter of fact, it seems impossible to adopt gene therapy for prevention. We therefore tried to develop a different method of cancer prevention or therapy based on the molecular mechanisms of carcinogenesis. For instance, the tumor-suppressor gene p53 is mutated in about 50% of human malignancies. It is known that p53 stimulates the promoter activities of p21/WAF1, gadd45 and bax genes, resulting in cell cycle arrest, DNA repair and apoptosis, respectively. Therefore, chemical compounds that can stimulate these genes should compensate for the function of p53. As a model of this, we found that histone deacetylase inhibitors such as butyrate or trichostatin A dramatically stimulate the p21/WAF1 gene promoter through the Spl sites, resulting in cell cycle arrest. Interestingly, another group has recently reported that phenylbutyrate, which is also known as a histone deacetylase inhibitor, is very effective for leukemia patients. We therefore consider methods of up-regulating p21/WAF, gadd45 or bax genes should be useful for cancer therapy and termed this method "Gene-regulating chemotherapy". Theoretically, the chemicals up-regulating such genes should be also useful for chemoprevention, and we also termed it as "Gene-regulating chemoprevention". In conclusion, we propose that "Gene-regulating chemotherapy or chemoprevention" may be a promising new method for cancer therapy or prevention and histone deacetylase inhibitor is a good candidate for this method.     

Epididymis as a target for contraception

Advantage of using a vaccine based on sperm antigens is that it can be used both in males and females as individuals who have antisperm antibodies are usually infertile but otherwise healthy. Several sperm specific antigens identified as prospective candidates for immunocontraception are of testicular origin. For the purpose of immunocontraception it may be desirable not to disrupt spermatogenesis and testicular function. Concept of post testicular maturation of spermatozoa has been very well established. During post testicular voyage spermatozoa undergo a series of complex and sequential events which transforms the immature immotile spermatozoa into mature sperm. Acquisition of functional maturity is necessary for progressive motility, zona pellucida recognition culminating in sperm egg binding. Importance of epididymal maturation is highlighted by the fact that high percentage of male infertility in human originates from the malfunction of the epididymis. The epididymis has also shown to be involved in sperm storage and provides an adequate environment for final maturation of the sperm. It provides a conducive microenvironment by virtue of which the spermatozoa are protected during the storage. In view of this it is imperative that more attention needs to be focused on epididymal antigens. The information obtained will enable us to identify epididymal antigens relevant to fertility and also help in infertility diagnosis.     

Cholesterol as a target for toxins

A mechanism is proposed for the way in which cholesterol facilitates channel formation by polyene antibiotics and bacterial protein toxins. Central elements of the model are: (i) interactions between the ring system of the sterol and rigid elements of the polyene or toxin molecule, and (ii) the specific orientation of cholesterol within the membrane.     

Mitochondria as a target for neuroprotection

Despite all the efforts of modern medical and biomedical sciences, the effective therapeutic treatments that would restore the brain functions lost after stroke have not been found yet. At the same time, experimental preclinical studies revealed an arsenal of effectors having potential for clinical applications. Identification of the key signaling pathways, both damaging and protective, can accelerate the development and implementation of new effective neuroprotectors. One of the key elements of these pathways is mitochondrion. In this context, we studied various therapeutic approaches to the treatment and prevention of cerebral ischemia, which are aimed at modulation of mitochondrial functions. The spectrum of tested neuroprotectors included antioxidants, uncouplers of respiration and phosphorylation, as well as ischemic, remote, and pharmacological preconditioning. Their efficacy and therapeutic windows were compared and the possibility of combining different methods in order to maximize their efficiency was considered.     

Connexins as targets for cancer chemoprevention and chemotherapy

Cells within a tissue continuously interact to coordinate normal tissue functions and maintain homeostasis. Gap junctional communication (GJC), mediated by the connexin protein family, allows this type of intercellular crosstalk resulting in synchronized and cooperative tissue behavior such as cardiac contraction. In cancer, loss of these types of cell:cell interactions has been shown to facilitate tumorigenesis and enable the autonomous cell behavior associated with transformed cells. Indeed, many human tumor lines demonstrate deficient or aberrant GJC and/or loss of connexin expression. Restoration of exogenous connexin expression/GJC function is correlated with increased cell growth control both in vitro and in vivo. In support of this growth regulatory hypothesis, decreased connexin expression has been observed in situ in early human neoplasia of various organs. Additionally, genetically engineered mice lacking particular connexins (Connexins 32 or 43) exhibit increased susceptibility to radiation and chemically-induced liver and/or lung tumorigenesis. These studies strongly suggest that connexins and GJC serve a tumor suppressor role. Consistent with this proposed role, in a model cell culture system, retinoids and carotenoids up-regulate Connexin43 (Cx43) expression in direct proportion to their ability to suppress carcinogen-induced neoplastic transformation. Here, we discuss the important role of connexins and GJC in tumorigenesis and suggest the possibility of connexins as potential anti-oncogenic targets for chemoprevention and/or chemotherapy.     

Omics underpins novel clues on VDR chemoprevention target in breast cancer

Breast cancer is the commonest form of female malignancy among women in Western countries. The advent of genomic technologies has enhanced the diagnosis and the biological classification of such pathology. It has been demonstrated that cancer takes many years to be fully established. This long dormancy could represent a potential window for intervening with chemoprevention studies. Cancer chemoprevention is by definition the use of natural, synthetic, or biological chemical agents to reverse, suppress, or delay the genetic or other alterations that culminate in the appearance of the tumor phenotype. An important step for the success of chemoprevention is the identification of molecularly targeted agents to prevent cancer development. Currently, only two chemoprevention agents, raloxifene and tamoxifen, are used in clinical practice to prevent breast cancer. In this review, we will mainly focus on: (1) the application of genomic technologies for the identification and validation of molecular targets for chemoprevention; (2) the role of vitamin D and its cognate receptor VDR (vitamin D receptor) as a model for the molecularly targeted chemoprevention of breast cancer.     

MYCN as a target for cancer immunotherapy

MYCN is a potential target for cancer immunotherapy by virtue of its overexpression in numerous human malignancies and its functional role in tumour progression. Here we show limited expression of MYCN in normal human tissues indicating that anti-MYCN immune responses are unlikely to cross react with self tissues. An HLA-A2 restricted ten amino acid peptide epitope from MYCN, VILKKATEYV, was used to stimulate cytotoxic T cell lines from the peripheral blood of normal blood donors, and from a patient with MYCN amplified neuroblastoma. Strong and specific activity was seen against each MYCN overexpressing cell line and against autologous tumour cells. We generated two CTL clones capable of killing cells pulsed with as low as 0.5 nM of VIL peptide. Therefore strong and specific immune responses against MYCN expressing tumours are possible in patients with the most common HLA class 1 type in the Caucasian population.     

K-ras as a target for cancer therapy

The central role K-, H- and N-Ras play in regulating diverse cellular pathways important for cell growth, differentiation and survival is well established. Dysregulation of Ras proteins by activating mutations, overexpression or upstream activation is common in human tumors. Of the Ras proteins, K-ras is the most frequently mutated and is therefore an attractive target for cancer therapy. The complexity of K-ras signaling presents many opportunities for therapeutic targeting. A number of different approaches aimed at abrogating K-ras activity have been explored in clinical trials. Several of the therapeutic agents tested have demonstrated clinical activity, supporting ongoing development of K-ras targeted therapies. However, many of the agents currently being evaluated have multiple targets and their antitumor effects may not be due to K-Ras inhibition. To date, no selective, specific inhibitor of K-ras is available for routine clinical use. In this review, we will summarize the structure and function of K-ras with attention to its role in tumorigenesis and discuss the successes and failures of the various strategies designed to therapeutically target this important oncogene.     

Actin as a potential target for decavanadate

ATP prevents G-actin cysteine oxidation and vanadyl formation specifically induced by decavanadate, suggesting that the oxometalate-protein interaction is affected by the nucleotide. The ATP exchange rate is increased by 2-fold due to the presence of decavanadate when compared with control actin (3.1 × 10^− 3 s^− 1), and an apparent dissociation constant (k_dapp) of 227.4 ± 25.7 μM and 112.3 ± 8.7 μM was obtained in absence or presence of 20 μM V₁₀, respectively. Moreover, concentrations as low as 50 μM of decameric vanadate species (V₁₀) increases the relative G-actin intrinsic fluorescence intensity by approximately 80% whereas for a 10-fold concentration of monomeric vanadate (V₁) no effects were observed. Upon decavanadate titration, it was observed a linear increase in G-actin hydrophobic surface (2.6-fold), while no changes were detected for V₁ (0-200 μM). Taken together, three major ideas arise: i) ATP prevents decavanadate-induced G-actin cysteine oxidation and vanadate reduction; ii) decavanadate promotes actin conformational changes resulting on its inactivation, iii) decavanadate has an effect on actin ATP binding site. Once it is demonstrated that actin is a new potential target for decavanadate, being the ATP binding site a suitable site for decavanadate binding, it is proposed that some of the biological effects of vanadate can be, at least in part, explained by decavanadate interactions with actin.     

Reliability and validity of a histologic score as a marker for skin cancer chemoprevention studies

OBJECTIVE: To develop a reliable and valid scoring system for grading skin biopsies from actinic keratosis (AK) and sun-damaged skin for use in evaluating the efficacy of skin cancer chemopreventive agents. STUDY DESIGN: A panel of dermatopathologists developed histologic criteria and diagnostic definitions for the progression of lesions from early AK to AK. The criteria were then applied to a sample of 335 histologic slides from an ongoing chemoprevention study. A 10% sample of 35 slides was reread in order to assess intrarater reliability. RESULTS: Six of the 7 criteria demonstrated high reliability (> 85%). The total histologic score, calculated using the 6 criteria, was found to significantly differentiate between (blinded) biopsy location (normal, pre-AK, AK and adjacent to squamous cell carcinoma) and histologic diagnosis (normal, pre- or early AK, AK and squamous cell carcinoma). CONCLUSION: The total histologic score, having demonstrated reliability on repeated readings and validity in its association with biopsy location and histologic score, is a reliable and valid end point for judging the efficacy of agents in skin cancer chemoprevention studies. Additional interrater reliability tests utilizing larger test sets and a rigorous statistical design should be undertaken to establish its portability.