Modulation of the insulin-like growth factor-I system by N-(4-hydroxyphenyl)-retinamide in human breast cancer cell lines

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Acceptability of chemoprevention trials in high-risk subjects

The development and current widespread acceptance of clinical trials is one of the major conceptual advances in research medicine introduced during the second half of the 20th century. Despite general agreement on the scientific merits of randomization, many patients and physicians are however reluctant to participate in randomized, controlled trials. If we focus on chemoprevention in healthy subjects, it is even more essential to evaluate the ethics, logistics, patient's and doctor's acceptability, acute and late toxic effect, patient accrual and compliance of treatment. Furthermore, the decision-making process about participating in a cancer chemoprevention trial is often poorly understood. Adherence to a cancer prevention trial requires in fact a strong sense of awareness and an ability to carefully assess risks and benefits. We review the main aspects in the chemo-preventive approach to patients at high risk for breast and ovarian cancer, focusing on different pharmacological risk reduction strategies, ongoing phase III chemoprevention studies in carriers of BRCA1/2 germline mutation, the psychological and clinical factors implicated in decision making about a trial, and the possible impact of the trial design on the overall acceptability and adherence.

Synthetic retinoid fenretinide in breast cancer chemoprevention

Preclinical models suggest that retinoids inhibit mammary carcinogenesis. The induction of apoptosis is a unique feature of fenretinide, the most-studied retinoid in clinical trials of breast cancer chemoprevention, owing to its selective accumulation in breast tissue and its favorable toxicological profile. In a Phase III breast cancer prevention trial, fenretinide showed a strong trend of reduction of incidence of second breast malignancies in premenopausal women, which was confirmed by 15 years of follow-up. This warrants further research on the mechanisms of action and potential efficacy of fenretinide and provides the rationale for a Phase III primary prevention trial in young women at high risk for breast cancer. This review will highlight the role of fenretinide in breast cancer chemoprevention.

The science behind vitamins and natural compounds for breast cancer prevention. Getting the most prevention out of it

This review highlights the role of vitamins and natural compounds in breast cancer prevention, with a particular focus on Vitamin D. In the last decades, both encouraging and discouraging results about the association between antioxidant supplementation and cancer have been reported to public and scientific community. Their safe and favorable toxicity profile makes them suitable to be investigated in a preventive setting. However, a recent large meta-analysis showed that treatment with beta carotene, vitamin A, and vitamin E may increase mortality, whereas the potential roles of vitamin C and selenium on mortality need further study. Likewise, folate levels were not associated with reduced breast cancer risk in a recent meta-analysis. Several studies have shown that a high proportion of women at-risk for breast cancer or affected by the disease have deficient vitamin D levels, i.e., 250 H-D <20 ng/ml or 50 nmol/L. While the association between Vitamin D levels and breast cancer risk/prognosis is still controversial, the U-shaped relationship between 250 H-D levels observed in different studies suggests the need to avoid both deficient and too high levels. Further trials using an optimal dose range are needed to assess the preventive and therapeutic effect of vitamin D. Finally, Fenretinide, a pro-apoptotic and pro-oxidant vitamin A derivative, has shown promise in several trials and its preventive potential is being assessed in young women at very high risk for breast cancer.

Fenretinide (4-HPR): a preventive chance for women at genetic and familial risk?

The incidence and mortality of breast cancer have been recently influenced by several new therapeutic strategies. In particular our knowledge on cancer precursors, risk biomarkers, and genetics has considerably increased, and prevention strategies are being successfully explored. Since their discovery, retinoids, the natural and synthetic derivatives of vitamin A, have been known to play a crucial role in cell and tissue differentiation and their ability to inhibit carcinogenesis has made them the ideal chemopreventive agents studied in several preclinical and clinical trials. Fenretinide (4-HPR) is the most studied retinoid in breast cancer chemoprevention clinical trials due to its selective accumulation in breast tissue and its favorable toxicological profile. This agent showed a significative reduction of the incidence of second breast tumors in premenopausal women confirmed after 15-year followups. Considering Fenretinide protective action, a similar trend on ovarian cancer, this drug warrants reevaluations as a preventive agent for high-risk young women, such as BRCA-1 and 2 mutation carriers or with a high familial risk. This favorable effect therefore provides a strong rationale for a primary prevention trial in these unaffected cohort of women.

Phase III double-blind, placebo-controlled, prospective randomized trial of adjuvant tamoxifen vs. tamoxifen and fenretinide in postmenopausal women with positive receptors (EB193): an intergroup trial coordinated by the Eastern Cooperative Oncology Group

Fenretinide and tamoxifen have additive antitumor effects preclinically. We performed a randomized, placebo-controlled, double-blind adjuvant trial in breast cancer patients treated for 5 years with tamoxifen, with or without fenretinide. Between October 1995 and October 1999, 426 postmenopausal women with hormone receptor-positive breast cancer were randomized. Patients were monitored for efficacy and toxicity. Four hundred and nineteen patients were evaluable. The study was terminated early due to slow accrual. There were no significant differences between treatment groups in DFS, TTR or survival. More patients stopped treatment early on the fenretinide arm than on placebo (P = 0.02). Grade 3/4 toxicities, including visual problems and musculoskeletal complaints were more common in patients receiving fenretinide (P = 0.007). A Night Blindness Questionnaire was used to monitor nyctalopia, which was slightly, but not significantly, more common on fenretinide. In this underpowered study, no significant difference was observed in efficacy between treatment groups. This trial provides important toxicity information about fenretinide, a retinoid that has been used in the prevention setting, because it is the only placebo-controlled, double-blind randomized study ever performed.

Progress in chemoprevention drug development: the promise of molecular biomarkers for prevention of intraepithelial neoplasia and cancer--a plan to move forward

This article reviews progress in chemopreventive drug development, especially data and concepts that are new since the 2002 AACR report on treatment and prevention of intraepithelial neoplasia. Molecular biomarker expressions involved in mechanisms of carcinogenesis and genetic progression models of intraepithelial neoplasia are discussed and analyzed for how they can inform mechanism-based, molecularly targeted drug development as well as risk stratification, cohort selection, and end-point selection for clinical trials. We outline the concept of augmenting the risk, mechanistic, and disease data from histopathologic intraepithelial neoplasia assessments with molecular biomarker data. Updates of work in 10 clinical target organ sites include new data on molecular progression, significant completed trials, new agents of interest, and promising directions for future clinical studies. This overview concludes with strategies for accelerating chemopreventive drug development, such as integrating the best science into chemopreventive strategies and regulatory policy, providing incentives for industry to accelerate preventive drugs, fostering multisector cooperation in sharing clinical samples and data, and creating public-private partnerships to foster new regulatory policies and public education.

Targeting cyclin D1, a downstream effector of INI1/hSNF5, in rhabdoid tumors

Rhabdoid tumors (RTs) are aggressive and currently incurable pediatric malignancies. INI1/hSNF5 is a tumor suppressor biallelically inactivated in RTs. Our previous studies have indicated that cyclin D1 is a key downstream target of INI1/hSNF5 and genesis and/or survival of RTs in vivo is critically dependent on the presence of cyclin D1. In this report, we have tested the hypothesis that therapeutic targeting of cyclin D1 is an effective means of treating RTs. We found that RNA interference of cyclin D1 in rhabdoid cells was sufficient to induce G1 arrest and apoptosis. Furthermore, we found that pharmacological intervention with low micromolar concentrations of N-(4-hydroxyphenyl)retinamide (4-HPR), which downmodulates cyclin D1, induced G1 arrest and apoptosis in rhabdoid cell lines. 4-HPR in combination with 4-hydroxy-tamoxifen (4OH-Tam), synergistically inhibited survival as well as anchorage-dependent and -independent growth of rhabdoid cells and caused synergistic induction of cell cycle arrest and apoptosis. 4-HPR and tamoxifen exhibited synergistic growth inhibition of RTs in xenograft models in vivo. The effects of combination of drugs were correlated to the depletion of cyclin D1 levels both in in vitro and in vivo tumor models. These results demonstrate that 4-HPR and tamoxifen are effective chemotherapeutic agents for RTs. We propose that downmodulation of cyclin D1 is a novel and effective therapeutic strategy for RTs.

Breast cancer and sex steroids: critical review of epidemiological, experimental and clinical investigations on etiopathogenesis, chemoprevention and endocrine treatment of breast cancer

There is strong epidemiological, experimental and clinical evidence that the etiology of breast cancer is closely related to long-term exposure of breast epithelium to sex steroid hormones. Estrogens can enhance the development of breast cancer by stimulating cell proliferation rate and thereby increasing the number of errors occurring during DNA replication, as well as by causing DNA damage via their genotoxic metabolites produced during oxidation reactions. Anti-estrogenic drugs, including tamoxifen, raloxifene and anastrozole, have been tested with promising results in the chemoprevention of breast cancer in high-risk women. As for the use of exogenous sex-steroids in the gynecological practice, data about breast cancer risk associated with oral contraception are reassuring, and available data on oral hormone replacement therapy (HRT) use for not more than 5 years have failed to detect a significant increase in the risk of developing a breast cancer. Long-term HRT administration increases the incidence of this tumor slightly, with a relative risk ranging from 1 to 2 depending on hormone preparation. Estrogens alone, even if taken for long periods of time, seem to be safer than estrogen/progestin combinations. New administration routes and novel hormone regimens are currently under evaluation, and these new HRT modalities could have different impact on breast cancer risk because of their metabolic and pharmacodynamic effects.

Activation of p53, inhibition of telomerase activity and induction of estrogen receptor beta are associated with the anti-growth effects of combination of ovarian hormones and retinoids in immortalized human mammary epithelial cells

Background

A full-term pregnancy has been associated with reduced risk for developing breast cancer. In rodent models, the protective effect of pregnancy can be mimicked with a defined regimen of estrogen and progesterone combination (E/P). However, the effects of pregnancy levels of E/P in humans and their underlying mechanisms are not fully understood. In this report, we investigated the growth inhibitory effects of pregnancy levels of E/P and both natural and synthetic retinoids in an immortalized human mammary epithelial cell line, 76N TERT cell line.

Results

We observed that cell growth was modestly inhibited by E/P, 9-cis-retinoic acid (9-cis RA) or all-trans-retinoic acid (ATRA), and strongly inhibited by N-(4-hydroxyphenyl) retinamide (HPR). The growth inhibitory effects of retinoids were further increased in the presence of E/P, suggesting their effects are additive. In addition, our results showed that both E/P and retinoid treatments resulted in increased RARE and p53 gene activity. We further demonstrated that p53 and p21 protein expression were induced following the E/P and retinoid treatments. Furthermore, we demonstrated that while the telomerase activity was moderately inhibited by E/P, 9-cis RA and ATRA, it was almost completely abolished by HPR treatment. These inhibitions on telomerase activity by retinoids were potentiated by co-treatment with E/P, and correlated well with their observed growth inhibitory effects. Finally, this study provides the first evidence that estrogen receptor beta is up-regulated in response to E/P and retinoid treatments.

Conclusion

Taken together, our studies show that part of the anti-growth effects of E/P and retinoids is p53 dependent, and involve activation of p53 and subsequent induction of p21 expression. Inhibition of telomerase activity and up-regulation of estrogen receptor beta are also associated with the E/P- and retinoid-mediated growth inhibition. Our studies also demonstrate that the potency of retinoids on cell growth inhibition may be increased through combination of estrogen and progesterone treatment.

Race is a Fundamental Prognostic Indicator for 2325 Northeastern Ohio Women with Infiltrating Breast Cancer

The goal of this research was to determine if race, independent of socioeconomic status, is a prognostic indicator for women diagnosed with infiltrating breast cancer. We hypothesized that black patients would present with breast cancers having less favorable prognostic indicators relative to white patients, regardless of socioeconomic status. Using data collected prospectively in our institutional review board approved breast center patient registry and 2000 Census Tract data for northeastern Ohio, we compared tumor size, node status, hormone receptor status, clinical outcomes, and socioeconomic status for patients who were self-described as either black or white and who had been diagnosed with infiltrating breast cancer. The chi-square test, t-test, log-rank test, and Cox proportional hazards analysis were used to analyze the data. Kaplan-Meier outcome curves were generated. Data were available for 2325 women, including 313 who were black and 2012 who were white. Compared to white patients, black patients were more likely to have positive axillary nodes and to have hormone receptor-negative tumors. Black patients were also more likely to have positive axillary nodes associated with smaller tumors. Independent of socioeconomic status, black patients were more likely to have poorer overall survival and disease-free survival rates for breast cancer relative to white patients. The prognostic significance of race was not dependent on a concomitant relationship with socioeconomic status.

A two-by-two factorial trial comparing oral with transdermal estrogen therapy and fenretinide with placebo on breast cancer biomarkers

PURPOSE

Oral conjugated equine estrogen (CEE) and medroxyprogesterone acetate (MPA) increase breast cancer risk, whereas the effect of transdermal estradiol (E2) and MPA is less known. Fenretinide may decrease second breast malignancies in premenopausal women but not in postmenopausal women, suggesting a hormone-sensitizing effect. We compared the 6 and 12-month changes in insulin-like growth factor-I (IGF-I), IGF-binding protein-3 (IGFBP-3), IGF-I:IGFBP-3 ratio, sex-hormone binding-globulin, and computerized mammographic percent density during oral CEE or transdermal E2 with sequential MPA and fenretinide or placebo.

EXPERIMENTAL DESIGN

A total of 226 recent postmenopausal healthy women were randomly assigned in a two-by-two factorial design to either oral CEE 0.625 mg/day (n = 111) or transdermal E2, 50 microg/day (n = 115) and to fenretinide 100 mg/twice a day (n = 112) or placebo (n = 114) for 12 months. Treatment effects were investigated by the Kruskall-Wallis test and analysis of covariance. P values were two-sided.

RESULTS

After 12 months, oral CEE decreased IGF-I by 26% [95% confidence interval (CI), 22-30%] and increased sex-hormone binding-globulin by 96% (95% CI, 79-112%) relative to baseline, whereas no change occurred with transdermal E2 (P < 0.001 between groups). Fenretinide decreased IGFBP-3 relative to placebo (P = 0.04). Percentage of breast density showed an absolute increase of 3.5% (95% CI, 2.5-4.6%) during hormone therapy without differences between groups (P = 0.39).

CONCLUSIONS

Oral CEE has more favorable changes than transdermal E2 on circulating breast cancer risk biomarkers but gives similar effects on mammographic density. Fenretinide exerted little modulation on most biomarkers. The clinical implications of these findings require additional studies.

Progress in chemoprevention of breast cancer

Primary prevention trials have shown that tamoxifen lowers breast cancer incidence by 30-40%. Because of the endometrial risk of tamoxifen and the pro-thrombotic effects of tamoxifen and raloxifene, different strategies are being pursued to improve the risk:benefit ratio of breast cancer chemoprevention. Thus, raloxifene is being compared with tamoxifen in a phase III trial, while the minimal active dose of tamoxifen is being assessed in phase I-II trials. Also, the combination of hormone replacement therapy (HRT) and tamoxifen may reduce the risks while retaining the benefits of either agent. Anastrozole holds promise as a preventive agent based on preliminary results on contralateral breast cancer. The identification of women at increased risk for estrogen receptor (ER)-positive breast cancer due to hormonal and reproductive factors may maximize the therapeutic index of hormonal agents. Finally, new targets that interfere with ER-negative breast carcinogenesis are being sought as one-third of breast cancers will not be preventable by hormonal interventions.

Pharmacological prevention of breast cancer: quo vadis?

Although tamoxifen reduces breast cancer incidence by 30-40% in at-risk subjects, its adverse events may be a limiting factor. Thus, different strategies are being pursued to improve the risk:benefit ratio of breast cancer chemoprevention intervention. Firstly, raloxifene is being compared with tamoxifen in a phase-III trial, whereas the minimal active dose of tamoxifen is being assessed in phase I-II trials. The combination of HRT and tamoxifen may also reduce the risks while retaining the benefits of either agent. Anastrozole holds promise as a preventive agent based on preliminary data on contralateral breast cancer. Another important area is the appropriate identification of women at increased risk for ER-positive breast cancer due to reproductive factors, which may maximize the therapeutic index of hormonal agents. Finally, new targets that interfere with the onset of ER-negative breast cancer are being sought since one-third of breast cancers will not be modulated by hormonal interventions.

Enhanced effectiveness of last generation antiblastic compounds vs. cisplatin on malignant pleural mesothelioma cell lines

The purpose of this study was to examine the antiproliferative potentialities of a pool of new generation compounds (Paclitaxel, Docetaxel, Gemcitabine, Topotecan, SN-38) together with fenretinide, a synthetic derivative of retinoic acid, in comparison with the current first choice treatment cisplatin molecule, on a pool of human malignant pleural mesothelioma cell lines derived from either bioptic and pleural effusions samples. To evaluate the chemosensitivity features of malignant mesothelioma cells in vitro, we resorted to a rapid and reproducible colorimetric assay, a useful widely recognized tool for preclinical drug screening. In addition, by DNA content analysis and cellular morphologic assessment, we focused on the apoptosis as a potential mechanism of drug activity. The main results clearly indicate that, in all the models of malignant mesothelioma we handled in vitro, each tested antineoplastic agent is more powerful than cisplatin in inhibiting cell proliferation. Moreover, on experimental evidences basis, we can assume that the cytotoxic activity of tested compounds could be related, at least partially, to the drug-induced programmed cell death. This experimental study gives substance to the expected pharmacologic worth of the second generation antineoplastic drugs even if, in order to afford the most satisfactory biopharmacological approach, allowing to bypass the refractoriness to chemotherapy of this highly lethal tumour, further investigations at preclinical level are required.

Breast cancer prevention trials using retinoids

Retinoids have been studied as chemopreventive agents in clinical trials. Given their ability to inhibit mammary carcinogenesis in preclinical models. Fenretinide has extensively been investigated because of its favorable toxicological profile in humans. In a phase III secondary prevention trial, fenretinide showed a trend to a reduction of second breast malignancies in premenopausal women but not in postmenopausal women. This pattern was associated with a similar modulation of circulating IGF-I. A trend towards a reduction of ovarian cancer was also noted. Biomarker studies of fenretinide or novel selective retinoids alone and in combination with different nuclear receptor ligands are being conducted. These studies provide a model for testing the safety and tolerability, pharmacokinetics and pharmacodynamics, and biomarker modulation in high-risk women, and offer clues as to both the pathophysiology of carcinogenesis and the drug mechanisms of action, and help select new compounds and doses for testing in large randomized studies.

Upregulation of GADD153 expression in the apoptotic signaling of N-(4-hydroxyphenyl)retinamide (4HPR)

The molecular basis for the pharmacologic effects of N-(4-hydroxyphenyl)retinamide (4HPR) was investigated by studying the gene(s) that this compound may upregulate in cultured human epithelial tumor cells. Treatment of the cultured human nasopharyngeal carcinoma-derived cells (CNE3) with 4HPR caused modest cell-cycle arrest at G(1) and apoptosis. The mRNA levels of a total of 20 genes were downregulated with the majority of them involved in cell cycle-related functions. Only the mRNA level of the growth arrest and DNA-damage inducible gene (gadd153) was upregulated by approximately 7-fold, with a concomitant increase in intracellular protein level. Similar upregulation of gadd153 by 4HPR was observed in HeLa and 2 other tumor cell lines. The 4HPR-induced apoptosis was markedly enhanced in the CNE3 cells that transiently overexpressed the gadd153 protein. Unlike 4HPR, all-trans-retinoic acid (ATRA) had no effect on the mRNA or protein level of gadd153. The ability of 4HPR and ATRA to stimulate the promoter activity of gadd153 was then examined. In the HeLa cells, both 4HPR and ATRA caused a 2- to 4-fold stimulation of the promoter activity of gadd153, but similar to the CNE3 cells, ATRA was incapable of upregulating the protein level of gadd153. This is the first demonstration that gadd153 is a 4HPR-responsive gene in tumor cells and may have a functional role to play in 4HPR-induced apoptosis. Furthermore, our data suggest that the expression of gadd153 can be regulated by 4HPR at the transcriptional level.

Is growth inhibition and induction of apoptosis in lung cancer cell lines by fenretinide [N-(4-hydroxyphenyl)retinamide] sufficient for cancer therapy?

The synthetic retinoid fenretinide [N-(4-hydroxyphenyl)retinamide, 4-HPR] has demonstrated growth inhibition and induction of apoptosis of various malignant cells, including lung cancer cell lines. 4-HPR is now being investigated in several clinical trials. In our study, we show that 4-HPR inhibits growth on a broad panel of lung cancer cell lines (12/12 small cell lung cancer and 9/12 nonsmall cell lung cancer cell lines), including cell lines unresponsive to all-trans-retinoic acid (ATRA). 4-HPR revealed a higher potency than ATRA in inhibiting cell growth with IC(50) values ranging from 3.3-8.5 microM. Furthermore, 4-HPR induces apoptosis in lung cancer cell lines as proven by TUNEL and annexin V assay. Despite this, we observed stimulation of growth in 2 SCLC cell lines at 1 microM 4-HPR. In advance to the clinical application of 4-HPR, we demonstrate that growth inhibition is reversible after removal of 4-HPR and that long-term application is necessary. Through long-term stimulation with 4-HPR, we cultivated 3 resistant cell lines that were still inhibited by 4-HPR after several weeks, however, exhibited almost no apoptosis. These cell lines exhibited morphologic changes, which in the case of the SCLC cell lines suggested differentiation. Our data show that 4-HPR inhibits growth in lung cancer cell lines by varying mechanisms including (i) cytostasis, (ii) apoptosis and (iii) presumably, differentiation. In contrast, the observed growth stimulation, reversibility of growth inhibition and development of resistance to apoptosis make successful cancer therapy uncertain and may limit clinical application of 4-HPR in lung cancer patients, although its inhibitory effects last over several weeks.

Regulation of cell proliferation by insulin-like growth factor 1 in hyperoxia-exposed neonatal rat lung

Hyperoxic exposure of the developing lung leads to characteristic peribronchial and mesenchymal fibroproliferative changes. We hypothesize that O2-induced changes in the neonatal lung are mediated by Insulin-like growth factor 1 (IGF-1) and IGF-1 receptor (IGF-1R). Lung explant cultures were prepared from 3-day-old neonatal rat pups and exposed to room air or 95% O2 for 72 h. Western blots and immunohistochemistry were used to determine if hyperoxia stimulated IGF-1 and IGF-1R, and to identify the cell types involved. Retinoic acid was used to learn if this would inhibit oxygen-induced cell proliferation. Hyperoxia induced a significant increase in thymidine incorporation (control, 54 +/- 9; hyperoxia, 254 +/- 24 dpm/nM DNA; mean +/- SEM; N = 3; P < 0.05). This was inhibited by 5 x 10(-5) M RA (149 +/- 18 dpm/nM DNA; P < 0.05) and by anti-IGF-1 antibody (115 +/- 25 dpm/nM DNA; P < 0.05; N = 3). BrdU labeling in the mesenchymal cells was significantly increased in mesenchymal cells after exposure to oxygen (91% higher than the room air control) but not in epithelial cells. This increase was inhibited in the presence of retinoic acid. Western blots showed IGF-1 protein was increased after 72 h of O2 exposure compared to room air exposure (57 +/- 7 compared to 32 +/- 5 densitometric units; P < 0.05; N = 3). The increase was inhibited when the cultures were exposed to 95% O2 in the presence of anti-IGF-1 antibody (28 +/- 4; P < 0.05; N = 3). IGF-1 protein decreased in the presence of retinoic acid after oxygen exposure but not in room air. Immunostaining of O2-exposed lung showed IGF-1 was most abundant in airway and alveolar epithelial cells. We conclude that hyperoxia increases cell proliferation by stimulating IGF-1 in the neonatal rat lung. Interaction of IGF-1 and IGF-1R is an important cell-cell communication mechanism in the developmental and repair processes of hyperoxic neonatal lung injury.

Chemoprevention of breast cancer with fenretinide

Chemoprevention of cancer represents a challenge for oncology during this new millennium. Substantial advances have been accomplished in the last decade, especially for primary and secondary prevention of breast cancer. In addition to tamoxifen, raloxifene and other selective estrogen receptor modulators, retinoids are among the most promising agents, given their ability to inhibit mammary carcinogenesis in preclinical models. Fenretinide, the synthetic amide of retinoic acid, inhibits cell growth mostly through the induction of apoptosis with mechanisms which may partly involve the retinoid receptors. Because it has a favourable toxicological profile, fenretinide has been extensively investigated in clinical trials. A large randomised phase III trial for secondary breast cancer prevention has been recently carried out in Italy. Results showed a reduction of second breast malignancies in premenopausal women. In addition, a significant decrease of circulating insulin-like growth factor (IGF)-1, a known risk factor for premenopausal breast cancer, was observed after 1 year of fenretinide administration in premenopausal women with breast cancer. Ongoing studies on the validation of the circulating IGF-1 as a surrogate endpoint biomarker of fenretinide activity and on the effectiveness of the combination with low dose tamoxifen may provide further insight into the future clinical application of fenretinide.

Novel non-isotopic method for the localization of receptors in tissue sections

We describe a novel fluorescent method for the detection of receptors for chimeric proteins in tissue sections. The technique was developed using a recombinant human insulin-like growth factor (IGF-1) chimera, bearing six additional histidine residues at the carboxy-terminal end (IGF-1-His). We demonstrated that dehydration of the tissue sections was detrimental for binding and that its prevention dramatically increased sensitivity. The specificity of IGF-1-His interaction was shown by gradual abolition of the fluorescent signal in the presence of increasing concentrations of IGF-1. Combining immunofluorescence with in situ ligand binding, we showed that IGF-1-His binding corresponded to the IGF-1 receptor (IGFR-1) distribution in human fetal kidney. Moreover, incubation of the tissue sections with an anti-IGFR-1 blocking antibody abolished IGF-1-His binding, demonstrating that the interaction was mediated by the IGFR-1. The method was also used to localize the IGFR-1 in E18 rat embryo sagittal sections. The IGF-1-His binding pattern was observed in brain, cartilage, lung, skin, heart, diaphragm, and tongue, and paralleled the previously reported IGFR-1 distribution. We believe that this new non-isotopic in situ ligand binding method will facilitate rapid and accurate localization of receptors in tissue sections.

Effect of low dose tamoxifen on the insulin-like growth factor system in healthy women

The use of tamoxifen as a preventive agent may be limited by the increased risk of endometrial cancer and venous thromboembolic events observed in postmenopausal women. We have recently shown a comparable activity of lower doses of tamoxifen on several surrogate biomarkers of cardiovascular disease and breast cancer, including Insulin-like Growth Factor-I (IGF-I). To provide further insight into the effect of tamoxifen at low doses on the IGF system, we have correlated the drug serum levels attained after 2 months of either placebo (n = 32), tamoxifen 20 mg/day (n = 26), 10 mg/day (n = 23) or 10 mg/every other day (n = 29) with the changes in IGF-I, Insulin-like Growth Factor-II (IGF-II), Insulin-like Growth Factor Binding Protein-1 (IGFBP-1), Insulin-like Growth Factor Binding Protein-3 (IGFBP-3), and IGF-I/IGFBP-3 ratio. Compared with placebo, tamoxifen induced a mean +/- standard error (SE) reduction of IGF-I of 16.9 +/- 7.8%, p < 0.05, a non-significant increase of 22.9 +/- 12.2% in IGF-II, an increase in IGFBP-1 of 49.3 +/- 22.7%, p < 0.05, and a non-significant change of IGFBP-3 (-4.0% +/- 9.2). No significant concentration-response relationship was observed between serum tamoxifen concentrations and the biomarker changes except for the ratio of IGF-I/IGFBP-3, which decreased by 1.53 +/- 0.68% for any increase by 10 ng/ml of serum tamoxifen concentration (p = 0.02). Although low tamoxifen concentrations induce a comparable modulation of the IGF family relative to the conventional dose, the lower decrements in the IGF-I/IGFBP-3 ratio observed at low drug concentrations might be associated with a reduced preventive activity. Further studies on the search of the minimal active dose of tamoxifen are warranted.

Chemoprevention of breast cancer: the Italian experience

The activity of our group is focused on the conduction of chemoprevention clinical trials of breast cancer in at-risk subjects, among which we include women on hormone replacement therapy (HRT). The role of the insulin-like growth factor (IGF) system and of mammographic breast density as surrogate biomarkers for breast cancer prevention is also being investigated. The IGF system is involved in human carcinogenesis of several solid tumors. IGF-I is a potent mitogen for breast cancer cells; elevated circulating IGF-I levels have been associated with a higher risk of premenopausal breast cancer, prostate and colorectal cancer in prospective studies. Both tamoxifen and the synthetic retinoid fenretinide (4-HPR) have been shown to decrease plasma IGF-I levels. A trial of their combination is ongoing in premenopausal women with increased risk for breast cancer. Mammographic breast density has also been associated with an increased risk of breast cancer in several prospective studies. In this article, we discuss the rationale for selection of appropriate cohorts, candidate agents, and putative surrogate biomarkers in our breast cancer prevention trials. Moreover, updated results of the secondary prevention trial of 4-H PR and of the primary prevention trial of tamoxifen are presented. Finally, the rationale for a reduction of tamoxifen dose in future prevention trials is provided.

Inhibition of aromatase activity and expression in MCF-7 cells by the chemopreventive retinoid N-(4-hydroxy-phenyl)-retinamide

The effect of the chemopreventive synthetic retinoid N-(4-hydroxyphenyl)-retinamide (4-HPR) on aromatase activity and expression was examined. 4-HPR caused a dose-dependent inhibition of aromatase activity in microsomes isolated from JEG-3 human placental carcinoma cells. The kinetics of inhibition were analysed by double-reciprocal plot. The Km of the substrate increased and the Vmax of the reaction decreased in the presence of 4-HPR, indicating that enzyme inhibition involved both competition for the substrate-binding site and non-competitive mechanisms. To determine whether 4-HPR would also inhibit aromatase activity in intact cells, MCF-7 human breast cancer cells were incubated with or without cAMP in the presence of 4-HPR. 4-HPR inhibited both basal and cAMP-induced aromatase activity in intact MCF-7 cells. The induction of aromatase mRNA expression in MCF-7 cells by cAMP was inhibited in cells treated with 4-HPR. These results indicate that 4-HPR inhibits both the enzymatic activity and expression of aromatase. These activities may play an important role in the known chemopreventive effect of 4-HPR towards breast cancer.

Toward checkmate: biology and breast cancer therapy for the new millennium

A better understanding of the biology of breast cancer should lead to the rational development of new treatments and the ability to customize therapy for individual patients. Though promising in theory, translating advances in biological knowledge to the clinic has been difficult. Recently several areas of research have produced treatments which have entered clinical trials: three will be reviewed here. The growth of breast cancer is regulated by growth factors and their receptors; amplification or overexpression is associated with poor prognosis. As such inhibition of growth factors and/or growth factor receptors may provide an ideal therapeutic target. Herceptin binds to c-erbB-2, a member of the epidermal growth factor receptor family. Significant responses were seen in patients with c-erbB-2 overexpressing breast cancer with Herceptin administered as a single agent or in combination with chemotherapy. Herceptin was approved by the Food and Drug Administration in late 1998. Breast cancer invasion and metastasis requires degradation of the surrounding basement membrane by matrix metalloproteinases and other proteolytic enzymes. Synthetic inhibitors of these enzymes are now in clinical trials. Breast cancers must stimulate angiogenesis, the growth of new blood vessels, in order to grow beyond a few millimeters in diameter. This nascent vascular network provides another opportunity for therapy. Preclinical models support the critical role of angiogenesis and the therapeutic benefit of angiogenesis inhibition; clinical trials are underway.

Fenretinide and cancer prevention

A characteristic feature of fenretinide is the ability to inhibit cell growth through the induction of apoptosis with mechanisms that may be both receptor-dependent and receptor-independent. Chemopreventive efficacy of fenretinide has been investigated in clinical trials targeted at different organs. Results of a phase III secondary prevention trial suggest a benefit in preventing second breast malignancies in premenopausal women with early breast cancer. A potential benefit of fenretinide with ovarian cancer and a reduction of new occurrences of leukoplakia have also been observed in clinical trials with this agent. However, no effects on DNA content of urothelial cells from bladder washings and on recurrence rate were noted in a study of patients with superficial bladder tumors. Future trials using surrogate biomarkers may aid in rapid evaluation of the chemopreventive activity of fenretinide with various targeted organs.

Recent advances in cancer chemoprevention, with emphasis on breast and colorectal cancer

Chemoprevention is a recently introduced and rapidly growing area of oncology that is identifying agents with a potentially preventive role in cancer. Several clinical trials have recently shown the feasibility of this approach in reducing the risk of major human cancers. In the USA, a large trial that demonstrated a reduction of approximately 50% in the risk of developing breast cancer led to Food and Drug Administration (FDA) approval of tamoxifen as a preventive agent in women at increased risk. Although the results could not be reproduced in two smaller European trials, further investigations into this agent are clearly warranted. Raloxifene, another selective oestrogen receptor modulator which has reduced the risk of breast cancer in a trial in women with osteoporosis, is being compared with tamoxifen in a large primary prevention trial in at-risk women. Retinoids are a group of compounds that have proved especially effective in reducing the occurrence of second primary tumours in subjects with skin, head and neck or liver cancer. Fenretinide, a synthetic retinoic acid derivative, has recently been shown to decrease the occurrence of a second breast malignancy in premenopausal women. Results with non-steroidal anti-inflammatory drugs (NSAIDs) have proved consistently encouraging in epidemiological studies in lowering the incidence of colorectal cancer. Clinical trials with selective cyclo-oxygenase inhibitors potentially devoid of gastrointestinal (GI) toxicity are currently underway in at-risk subjects. Calcium and selenium have also received much attention as chemopreventive agents. Originally investigated against skin cancer, selenium showed efficacy in reducing prostate, lung and colon cancer incidence. Similarly, vitamin E was effective in reducing prostate cancer incidence and mortality in a lung cancer prevention trial in heavy smokers. The challenges of conducting well-designed and unequivocal chemoprevention trials are considerable, but advances in techniques of identification of at-risk subjects and establishing surrogate endpoint biomarkers should contribute greatly to future studies. Current knowledge suggests that a pharmacological approach to preventing cancer, using natural or synthetic agents, could become an important way forward.