Phase I Clinical Trial of Alitretinoin and Tamoxifen in Breast Cancer Patients: Toxicity, Pharmacokinetic, and Biomarker Evaluations

Interactive effects of 9-cis-retinoic acid and androgen on proliferation, differentiation, and apoptosis of LNCaP prostate cancer cells

9-cis-Retinoic acid (9cRA), which binds to both retinoic acid receptors and retinoic X receptors, inhibits prostate cancer induction in rats and reduces growth of prostate cancer cells. However, the nature of this growth inhibition and the interactive influence of androgens are not well defined and are the subject of this report. LNCaP and PC-3 cells were cultured and treated with a range of 9cRA concentrations for 3-6 days in the absence or presence of 5α-dehydrotestosterone. 9cRA inhibited cell proliferation in a dose-dependent manner, plateauing at 10 mol/l. Treatment of cells with 10 mol/l 9cRA inhibited 5α-dihydroxytestosterone (DHT)-stimulated proliferation, the effect of which was maximal at 10 mol/l DHT. Treatment of DHT (10 mol/l)-exposed cells with 9cRA caused a dose-dependent increase in prostate-specific antigen in the medium after 6 days, but not 3 days. 9cRA caused a dose-dependent increase in apoptotic cells stained with H33258 after 3 days, but not 6 days; however, on using flow cytometry, apoptosis was apparent at both 3 and 6 days. Flow cytometry also revealed interference of G0/G1 to S phase transition by 9cRA. Inhibition by 9cRA of anchorage-independent growth of PC-3 cells was also found; LNCaP cells did not grow colonies in soft agar. 9cRA inhibited growth and induced differentiation of human LNCaP prostate cancer cells in vitro and inhibited anchorage-independent growth of PC-3 cells. Because 9cRA and 13-cis-retinoic acid, which is retinoic acid receptor-selective, prevent prostate carcinogenesis in rats, and 13-cis-retinoic acid also inhibits growth of human prostate cancer cells, the RAR is a potential molecular target for prostate cancer prevention and therapy.

Reverse ethnopharmacology and drug discovery

ETHNOPHARMACOLOGICAL RELEVANCE

Ethnopharmacological investigations of traditional medicines have made significant contributions to plant-derived drugs, as well as the advancement of pharmacology. Drug discovery from medicinal flora is more complex than generally acknowledged because plants are applied for different therapeutic indications within and across cultures. Therefore we propose the concept of "reverse ethnopharmacology" and compare biomedical uses of plant taxa with their ethnomedicinal and popular uses and test the effect of these on the probability of finding biomedical and specifically anticancer drugs.

MATERIALS AND METHODS

For this analysis we use data on taxonomy and medical indications of plant derived biomedical drugs, clinical trial, and preclinical trial drug candidates published by Zhu et al. (2011) and compare their therapeutic indications with their ethnomedicinal and popular uses as reported in the NAPRALERT^® database. Specifically, we test for increase or decrease of the probability of finding anticancer drugs based on ethnomedicinal and popular reports with Bayesian logistic regression analyses.

RESULTS

Anticancer therapy resulted as the most frequent biomedicinal indication of the therapeutics derived from the 225 drug producing higher plant taxa and showed an association with ethnomedicinal and popular uses in women's medicine, which was also the most important popular use-category. Popular remedies for dysmenorrhoea, and uses as emmenagogues, abortifacients and contraceptives showed a positive effect on the probability of finding anticancer drugs. Another positive effect on the probability of discovering anticancer therapeutics was estimated for popular herbal drugs associated with the therapy of viral and bacterial infections, while the highest effect was found for popular remedies used to treat cancer symptoms. However, this latter effect seems to be influenced by the feedback loop and divulgence of biomedical knowledge on the popular level.

CONCLUSION

We introduce the concept of reverse ethnopharmacology and show that it is possible to estimate the probability of finding biomedical drugs based on ethnomedicinal uses. The detected associations confirm the classical ethnopharmacological approach where a popular remedy for disease category X results in a biomedical drug for disease category X but does also point out the existence of cross-over relationships where popular remedies for disease category X result in biomedical therapeutics for disease category Y (Zhu et al., 2011).

Selective brain penetrable Nurr1 transactivator for treating Parkinson's disease

Parkinson's disease (PD) is one of the most common movement disorders, and currently there is no effective treatment that can slow disease progression. Preserving and enhancing DA neuron survival is increasingly regarded as the most promising therapeutic strategy for treating PD. IRX4204 is a second generation retinoid X receptor (RXR) agonist that has no cross reactivity with retinoic acid receptors, farnesoid X receptor, liver X receptors or peroxisome proliferator-activated receptor PPARγ. We found that IRX4204 promotes the survival and maintenance of nigral dopaminergic (DA) neurons in a dose-dependent manner in primary mesencephalic cultures. Brain bioavailability studies demonstrate that IRX4204 can cross the blood brain barrier and reach the brain at nM concentration. Oral administration of IRX4204 can activate nuclear receptor Nurr1 downstream signaling in the substantia nigra (SN) andattenuate neurochemical and motor deficits in a rat model of PD. Our study suggests that IRX4204 represents a novel, potent and selective pharmacological means to activate cellular RXR-Nurr1 signaling and promote SN DA neuron survival in PD prevention and/or treatment.

All-Trans-Retinoic Acid Enhances Mitochondrial Function in Models of Human Liver

All-trans-retinoic acid (atRA) is the active metabolite of vitamin A. The liver is the main storage organ of vitamin A, but activation of the retinoic acid receptors (RARs) in mouse liver and in human liver cell lines has also been shown. AlthoughatRA treatment improves mitochondrial function in skeletal muscle in rodents, its role in modulating mitochondrial function in the liver is controversial, and little data are available regarding the human liver. The aim of this study was to determine whetheratRA regulates hepatic mitochondrial activity.atRA treatment increased the mRNA and protein expression of multiple components of mitochondrialβ-oxidation, tricarboxylic acid (TCA) cycle, and respiratory chain. Additionally,atRA increased mitochondrial biogenesis in human hepatocytes and in HepG2 cells with and without lipid loading based on peroxisome proliferator activated receptor gamma coactivator 1αand 1βand nuclear respiratory factor 1 mRNA and mitochondrial DNA quantification.atRA also increasedβ-oxidation and ATP production in HepG2 cells and in human hepatocytes. Knockdown studies of RARα, RARβ, and PPARδrevealed that the enhancement of mitochondrial biogenesis andβ-oxidation byatRA requires peroxisome proliferator activated receptor delta. In vivo in mice,atRA treatment increased mitochondrial biogenesis markers after an overnight fast. Inhibition ofatRA metabolism by talarozole, a cytochrome P450 (CYP) 26 specific inhibitor, increased the effects ofatRA on mitochondrial biogenesis markers in HepG2 cells and in vivo in mice. These studies show thatatRA regulates mitochondrial function and lipid metabolism and that increasingatRA concentrations in human liver via CYP26 inhibition may increase mitochondrial biogenesis and fatty acidβ-oxidation and provide therapeutic benefit in diseases associated with mitochondrial dysfunction.

Systematic Prioritization of Druggable Mutations in ∼5000 Genomes Across 16 Cancer Types Using a Structural Genomics-based Approach

A massive amount of somatic mutations has been cataloged in large-scale projects such as The Cancer Genome Atlas (TCGA) and the International Cancer Genome Consortium projects. The majority of the somatic mutations found in tumor genomes are neutral 'passenger' rather than damaging "driver" mutations. Now, understanding their biological consequences and prioritizing them for druggable targets are urgently needed. Thanks to the rapid advances in structural genomics technologies (e.g. X-ray), large-scale protein structural data has now been made available, providing critical information for deciphering functional roles of mutations in cancer and prioritizing those alterations that may mediate drug binding at the atom resolution and, as such, be druggable targets. We hypothesized that mutations at protein-ligand binding-site residues are likely to be druggable targets. Thus, to prioritize druggable mutations, we developed SGDriver, a structural genomics-based method incorporating the somatic missense mutations into protein-ligand binding-site residues using a Bayes inference statistical framework. We applied SGDriver to 746,631 missense mutations observed in 4997 tumor-normal pairs across 16 cancer types from The Cancer Genome Atlas. SGDriver detected 14,471 potential druggable mutations in 2091 proteins (including 1,516 recurrently mutated proteins) across 3558 cancer genomes (71.2%), and further identified 298 proteins harboring mutations that were significantly enriched at protein-ligand binding-site residues (adjusted p value < 0.05). The identified proteins are significantly enriched in both oncoproteins and tumor suppressors. The follow-up drug-target network analysis suggested 98 known and 126 repurposed druggable anticancer targets (e.g. SPOP and NR3C1). Furthermore, our integrative analysis indicated that 13% of patients might benefit from current targeted therapy, and this -proportion would increase to 31% when considering drug repositioning. This study provides a testable strategy for prioritizing druggable mutations in precision cancer medicine.

Activation of the retinoid X receptor modulates angiotensin II-induced smooth muscle gene expression and inflammation in vascular smooth muscle cells

The retinoid X receptor (RXR) partners with numerous nuclear receptors, such as the peroxisome proliferator activated receptor (PPAR) family, liver X receptors (LXRs), and farnesoid X receptor (FXR). Although each heterodimer can be activated by specific ligands, a subset of these receptors, defined as permissive nuclear receptors, can also be activated by RXR agonists known as rexinoids. Many individual RXR heterodimers have beneficial effects in vascular smooth muscle cells (SMCs). Because rexinoids can potently activate multiple RXR pathways, we hypothesized that treating SMCs with rexinoids would more effectively reverse the pathophysiologic effects of angiotensin II than an individual heterodimer agonist. Cultured rat aortic SMCs were pretreated with either an RXR agonist (bexarotene or 9-cis retinoic acid) or vehicle (dimethylsulfoxide) for 24 hours before stimulation with angiotensin II. Compared with dimethylsulfoxide, bexarotene blocked angiotensin II-induced SM contractile gene induction (calponin and smooth muscle-α-actin) and protein synthesis ([(3)H]leucine incorporation). Bexarotene also decreased angiotensin II-mediated inflammation, as measured by decreased expression of monocyte chemoattractant protein-1 (MCP-1). Activation of p38 mitogen-activated protein (MAP) kinase but not extracellular signal-related kinase (ERK) or protein kinase B (Akt) was also blunted by bexarotene. We compared bexarotene to five agonists of nuclear receptors (PPARα, PPARγ, PPARδ, LXR, and FXR). Bexarotene had a greater effect on calponin reduction, MCP-1 inhibition, and p38 MAP kinase inhibition than any individual agonist. PPARγ knockout cells demonstrated blunted responses to bexarotene, indicating that PPARγ is necessary for the effects of bexarotene. These data demonstrate that RXR is a potent modulator of angiotensin II-mediated responses in the vasculature, partially through inhibition of p38.

Interplay between estrogen and retinoid signaling in breast cancer--current and future perspectives

All-trans-retinoic acid (RA) is a promising agent for breast cancer treatment, but it induces several adverse effects and the few clinical trials performed up to now in breast cancer patients have provided disappointing results. The combination of RA and antiestrogenic compounds, such as tamoxifen, synergistically decreases the proliferation of breast cancer cells and an interplay between retinoid and estrogen signaling has begun to be unraveled, turning these combinations into an appealing strategy for breast cancer treatment. This review focus on the current knowledge regarding the interplay between retinoid and estrogen signaling in breast cancer and the combinations of RA with antiestrogens, aiming their future utilization in cancer therapy.

Antitumoral effects of 9-cis retinoic acid in adrenocortical cancer

The currently available medical treatment options of adrenocortical cancer (ACC) are limited. In our previous meta-analysis of adrenocortical tumor genomics data, ACC was associated with reduced retinoic acid production and retinoid X receptor-mediated signaling. Our objective has been to study the potential antitumoral effects of 9-cis retinoic acid (9-cisRA) on the ACC cell line NCI-H295R and in a xenograft model. Cell proliferation, hormone secretion, and gene expression have been studied in the NCI-H295R cell line. A complex bioinformatics approach involving pathway and network analysis has been performed. Selected genes have been validated by real-time qRT-PCR. Athymic nude mice xenografted with NCI-H295R have been used in a pilot in vivo xenograft model. 9-cisRA significantly decreased cell viability and steroid hormone secretion in a concentration- and time-dependent manner in the NCI-H295R cell line. Four major molecular pathways have been identified by the analysis of gene expression data. Ten genes have been successfully validated involved in: (1) steroid hormone secretion (HSD3B1, HSD3B2), (2) retinoic acid signaling (ABCA1, ABCG1, HMGCR), (3) cell-cycle damage (GADD45A, CCNE2, UHRF1), and the (4) immune response (MAP2K6, IL1R2). 9-cisRA appears to directly regulate the cell cycle by network analysis. 9-cisRA also reduced tumor growth in the in vivo xenograft model. In conclusion, 9-cisRA might represent a promising new candidate in the treatment of hormone-secreting adrenal tumors and adrenocortical cancer.

Retinoids and breast cancer: from basic studies to the clinic and back again

All-trans retinoic acid (ATRA) is the most important active metabolite of vitamin A controlling segmentation in the developing organism and the homeostasis of various tissues in the adult. ATRA as well as natural and synthetic derivatives, collectively known as retinoids, are also promising agents in the treatment and chemoprevention of different types of neoplasia including breast cancer. The major aim of the present article is to review the basic knowledge acquired on the anti-tumor activity of classic retinoids, like ATRA, in mammary tumors, focusing on the underlying cellular and molecular mechanisms and the determinants of retinoid sensitivity/resistance. In the first part, an analysis of the large number of pre-clinical studies available is provided, stressing the point that this has resulted in a limited number of clinical trials. This is followed by an overview of the knowledge acquired on the role played by the retinoid nuclear receptors in the anti-tumor responses triggered by retinoids. The body of the article emphasizes the potential of ATRA and derivatives in modulating and in being influenced by some of the most relevant cellular pathways involved in the growth and progression of breast cancer. We review the studies centering on the cross-talk between retinoids and some of the growth-factor pathways which control the homeostasis of the mammary tumor cell. In addition, we consider the cross-talk with relevant intra-cellular second messenger pathways. The information provided lays the foundation for the development of rational and retinoid-based therapeutic strategies to be used for the management of breast cancer.

[Off-label use of alitretinoin]

Oral alitretinoin (9-cis retinoic acid) is an endogenous retinoid related to vitamin A. Studies have shown that oral alitretinoin is effective and well-tolerated in the treatment of severe chronic hand eczema, so that it is approved for this indication. This review summarizes new studies and clinical experience on the off-label use of alitretinoin.

Targeted therapy for breast cancer prevention

With a better understanding of the etiology of breast cancer, molecularly targeted drugs have been developed and are being testing for the treatment and prevention of breast cancer. Targeted drugs that inhibit the estrogen receptor (ER) or estrogen-activated pathways include the selective ER modulators (tamoxifen, raloxifene, and lasofoxifene) and aromatase inhibitors (AIs) (anastrozole, letrozole, and exemestane) have been tested in preclinical and clinical studies. Tamoxifen and raloxifene have been shown to reduce the risk of breast cancer and promising results of AIs in breast cancer trials, suggest that AIs might be even more effective in the prevention of ER-positive breast cancer. However, these agents only prevent ER-positive breast cancer. Therefore, current research is focused on identifying preventive therapies for other forms of breast cancer such as human epidermal growth factor receptor 2 (HER2)-positive and triple-negative breast cancer (TNBC, breast cancer that does express ER, progesterone receptor, or HER2). HER2-positive breast cancers are currently treated with anti-HER2 therapies including trastuzumab and lapatinib, and preclinical and clinical studies are now being conducted to test these drugs for the prevention of HER2-positive breast cancers. Several promising agents currently being tested in cancer prevention trials for the prevention of TNBC include poly(ADP-ribose) polymerase inhibitors, vitamin D, and rexinoids, both of which activate nuclear hormone receptors (the vitamin D and retinoid X receptors). This review discusses currently used breast cancer preventive drugs, and describes the progress of research striving to identify and develop more effective preventive agents for all forms of breast cancer.

Potential therapeutic approaches for modulating expression and accumulation of defective lamin A in laminopathies and age-related diseases

Scientific understanding of the genetic components of aging has increased in recent years, with several genes being identified as playing roles in the aging process and, potentially, longevity. In particular, genes encoding components of the nuclear lamina in eukaryotes have been increasingly well characterized, owing in part to their clinical significance in age-related diseases. This review focuses on one such gene, which encodes lamin A, a key component of the nuclear lamina. Genetic variation in this gene can give rise to lethal, early-onset diseases known as laminopathies. Here, we analyze the literature and conduct computational analyses of lamin A signaling and intracellular interactions in order to examine potential mechanisms for altering or slowing down aberrant Lamin A expression and/or for restoring the ratio of normal to aberrant lamin A. The ultimate goal of such studies is to ameliorate or combat laminopathies and related diseases of aging, and we provide a discussion of current approaches in this review.

Structure, energetics, and dynamics of binding coactivator peptide to the human retinoid X receptor α ligand binding domain complex with 9-cis-retinoic acid

Retinoid X receptors (RXRs) are ligand-dependent nuclear receptors, which are activated by the potent agonist 9-cis-retinoic acid (9cRA). 9cRA binds to the ligand binding domain (LBD) of RXRs and recruits coactivator proteins for gene transcription. Using isothermal titration calorimetry, the binding of a 13-mer coactivator peptide, GRIP-1, to the hRXRα-LBD homodimer complex containing 9cRA (hRXRα-LBD:9cRA:GRIP-1) is reported between 20 and 37 °C. ΔG is temperature independent (-8.5 kcal/mol), and GRIP-1 binding is driven by ΔH (-9.2 kcal/mol) at 25 °C. ΔC(p) is large and negative (-401 cal mol(-1) K(-1)). The crystal structure of hRXRα-LBD:9cRA:GRIP-1 is reported at 2.05 Å. When the structures of hRXRα-LBD:9cRA:GRIP-1 and hRXRα-LBD:9cRA ( 1FBY ) homodimers are compared, E453 and E456 on helix 12 bury and form ionic interactions with GRIP-1. R302 on helix 4 realigns to form new salt bridges to both E453 and E456. F277 (helix 3), F437 (helix 11), and F450 (helix 12) move toward the hydrophobic interior. The changes in the near-UV spectrum at 260 nm of the hRXRα-LBD:9cRA:GRIP-1 support this structural change. Helix 11 tilts toward helix 12 by ≈1 Å, modifying the ring conformation of 9cRA. Hydrogen-deuterium exchange mass spectroscopy indicates GRIP-1 binding to hRXRα-LBD:9cRA significantly decreases the exchange rates for peptides containing helices 3 (F277), 4 (R302), 11 (F437), and 12 (E453, E456). The structural changes and loss of dynamics of the GRIP-1-bound structure are used to interpret the energetics of coactivator peptide binding to the agonist-bound hRXRα-LBD.

Anti-tumor effects of retinoids combined with trastuzumab or tamoxifen in breast cancer cells: induction of apoptosis by retinoid/trastuzumab combinations

INTRODUCTION

HER2 and estrogen receptor (ER) are important in breast cancer and are therapeutic targets of trastuzumab (Herceptin) and tamoxifen, respectively. Retinoids inhibit breast cancer growth, and modulate signaling by HER2 and ER. We hypothesized that treatment with retinoids and simultaneous targeting of HER2 and/or ER may have enhanced anti-tumor effects.

METHODS

The effects of retinoids combined with trastuzumab or tamoxifen were examined in two human breast cancer cell lines in culture, BT474 and SKBR3. Assays of proliferation, apoptosis, differentiation, cell cycle distribution, and receptor signaling were performed.

RESULTS

In HER2-overexpressing/ER-positive BT474 cells, combining all-trans retinoic acid (atRA) with tamoxifen or trastuzumab synergistically inhibited cell growth, and altered cell differentiation and cell cycle. Only atRA/trastuzumab-containing combinations induced apoptosis. BT474 and HER2-overexpressing/ER-negative SKBR3 cells were treated with a panel of retinoids (atRA, 9-cis-retinoic acid, 13-cis-retinoic acid, or N-(4-hydroxyphenyl) retinamide (fenretinide) (4-HPR)) combined with trastuzumab. In BT474 cells, none of the single agents except 4-HPR induced apoptosis, but again combinations of each retinoid with trastuzumab did induce apoptosis. In contrast, the single retinoid agents did cause apoptosis in SKBR3 cells; this was only modestly enhanced by addition of trastuzumab. The retinoid drug combinations altered signaling by HER2 and ER. Retinoids were inactive in trastuzumab-resistant BT474 cells.

CONCLUSIONS

Combining retinoids with trastuzumab maximally inhibits cell growth and induces apoptosis in trastuzumab-sensitive cells. Treatment with such combinations may have benefit for breast cancer patients.

A pilot phase II trial of all-trans retinoic acid (Vesanoid) and paclitaxel (Taxol) in patients with recurrent or metastatic breast cancer

PURPOSE

We investigated a combination therapy with weekly paclitaxel and all trans-retinoic acid (ATRA) for tolerability, response to treatment, time to progression and survival in previously treated patients with metastatic or recurrent breast cancer. Our rationale was based on preclinical studies demonstrating potentiation of the cytotoxic effects of taxanes and induction of differentiation by ATRA.

PATIENTS AND METHODS

Seventeen patients with previously treated metastatic or recurrent breast cancer were enrolled to a regimen of all-trans retinoic acid (Vesanoid, tretinoin, Hoffman-La Roche, Inc.) 45 mg/m(2) PO daily for 4 days starting 2 days before a 1 h treatment with paclitaxel (Taxol, Bristol-Myers Squibb, Plainsboro, NJ) 80 mg/m(2) IV administered weekly for 3 weeks, repeated in 28 day cycles until disease progression or until no longer tolerated. Patients were evaluated for toxicity, response, time to progression and survival. Patients were primarily African American and Latino, representative of the population served by our Cancer Center.

RESULTS

The regimen was relatively well tolerated. There were nine grade 3 and one grade 4 toxic events. We administered 162 treatment cycles with a mean of 7.5 per patient (range 1-22, median 5). Three patients had a partial response (17.6%) and ten patients had stable disease (58.8%), with an overall clinical benefit of 76.4%. Median time to progression was 6.0 months (range 1-21, mean 7.7 months). Fourteen evaluable patients had a median survival of 16 months (range 1-68 months, mean 25.2 months).

CONCLUSIONS

The data suggest this is a well tolerated regimen with modest response rates but with time to progression and survival rates similar to those reported for paclitaxel alone and relatively high rates of stable disease in this sample of patients.

13-cis-Retinoic acid in combination with gemcitabine in the treatment of locally advanced and metastatic pancreatic cancer--report of a pilot phase II study

AIMS

Adenocarcinoma of the pancreas is a cancer with extremely poor prognosis and limited therapeutic options. Retinoids are derivatives of vitamin A involved in the control of many biological functions, including cell growth and differentiation and the induction of apoptosis. On the basis of pre-clinical evidence and some clinical data, we conducted a phase II study of 13-cis-retinoic acid (13-cis-RA) in combination with gemcitabine in patients with unresectable pancreatic carcinoma.

MATERIALS AND METHODS

Patients with histologically confirmed unresectable pancreatic carcinoma were treated with gemcitabine 1000 mg/m2 on days 8, 15, 22 plus 13-cis-RA 1 mg/kg on days 1-14 for six cycles. The end points included the objective response rate and median survival.

RESULTS

Thirty patients were recruited, 15 men and 15 women; 20 patients were evaluable. The median age was 65 years (range 44-79 years) and the median Karnofsky performance status was 80% (range 60-100%). The median follow-up was 21 months. One patient achieved a partial remission, seven patients had stable disease and 12 patients developed progressive disease. Toxicity was mainly haematological, with eight cases of grade 3 and four cases of grade 4 neutropenia, thrombocytopenia and anaemia. The median survival was 7.8 months (range 2.6-21.6 months).

CONCLUSIONS

The combination of gemcitabine and 13-cis-RA was well tolerated, but we did not see improvement in the response rate. Further studies with other retinoids may be beneficial to patients with unresectable pancreatic cancer.

Efficacy of new retinoids in the prevention of mammary cancers and correlations with short-term biomarkers

A number of retinoid X receptor (RXR) agonists have proven to be highly effective in preventing methylnitrosourea (MNU) induced mammary cancers. However, these agonists have side effects; particularly causing an increase in serum triglyceride levels. A series of ligands for RXR were designed based on computer modeling to the ligand binding domain (LBD) of the RXR receptors and on structure-activity relationships. The chemopreventive effects of these retinoids were evaluated in the relatively long-term MNU model. As a short-term assay to predict their efficacy, the ability of the retinoids to modulate cell proliferation and apoptosis was also determined in mammary cancers after only 7 days of treatment. The five UAB retinoids evaluated included two Class I UAB retinoids (UAB20, UAB112) and three Class II UAB retinoids (UAB30, 4-methyl-UAB30 and the benzosuberone-analog of UAB30). The previously evaluated RXR agonist targretin and the pan-agonist 9-cis-retinoic acid (9-cis-RA), which interacts with both RAR and RXR receptors, were included as positive agonists known to prevent cancer in the MNU model. In the prevention studies, in which the agents were administered beginning 5 days after MNU until the end of the study, targretin (150 mg/kg diet) and 4-methyl-UAB30 (200 mg/kg diet) were highly effective in decreasing cancer numbers by 75-85%. UAB30 (200 mg/kg diet) and 9-cis-RA (60 mg/kg diet) gave intermediate inhibitions of 60 and 45%, respectively. Targretin (15 mg/kg diet), UAB20 (200 mg/kg diet) and the benzosuberone analog of UAB30 (200 mg/kg diet) showed limited activity by decreasing cancer multiplicity 25-30%, while UAB112 had no effect on mammary cancer multiplicity. A direct correlation was observed between the long-term chemopreventive efficacy of these agents and their ability to decrease cell proliferation in mammary cancers after short-term treatment. Furthermore, the highly effective agents (4-methyl-UAB30 and targretin at 150 mg/kg diet) increased apoptosis 3-5 times, while agents with moderate or limited preventive efficacy failed to significantly increase apoptosis. Although the more effective retinoid treatments increased serum triglycerides 2.5- to 4.0-fold, one moderately effective agent (UAB30) had no significant effect on lipid levels. In summary, a short-term in vivo method has been identified for screening newly synthesized retinoids both for chemopreventive efficacy and for their adverse effect on serum triglycerides.

Are gene expression microarray analyses reliable? A review of studies of retinoic acid responsive genes

Microarray analyses of gene expression are widely used, but reports of the same analyses by different groups give widely divergent results, and raise questions regarding reproducibility and reliability. We take as an example recent published reports on microarray experiments that were designed to identify retinoic acid responsive genes. These reports show substantial differences in their results. In this article, we review the methodology, results, and potential causes of differences in these applications of microarrays. Finally, we suggest practices to improve the reliability and reproducibility of microarray experiments.

Retinoic Acid Inhibits the Proliferative Response Induced by CD40 Activation and Interleukin-4 in Mantle Cell Lymphoma

Mantle cell lymphoma (MCL) is an aggressive B-cell non-Hodgkin's lymphoma with poor response to therapy and unfavorable prognosis. Here, we show that retinoic acid (RA) isomers significantly inhibit the proliferation of both primary MCL cultures (n = 7) and established cell lines (Granta 519 and SP-53) as shown by [3H]thymidine uptake and carboxyfluorescein diacetate succinimidyl ester labeling coupled with cyclin D1 staining. RA induces cell accumulation in G0-G1 together with a marked up-regulation of p27Kip1 by inhibiting ubiquitination and proteasome-dependent degradation of the protein. The p21Cip1 inhibitor was also up-regulated by RA in Granta 519 cells, whereas the expression of cyclin D1 is unaffected. Most of RA-induced p27Kip1 was bound to cyclin D1/cyclin-dependent kinase 4 complexes, probably contributing to the decreased cyclin-dependent kinase 4 kinase activity and pRb hypophosphorylation observed in RA-treated cells. Experiments with receptor-selective ligands indicate that RA receptor α cooperates with retinoid X receptors in mediating RA-dependent MCL cell growth inhibition. Notably, RA isomers, and particularly 9-cis-RA, also inhibited the growth-promoting effect induced in primary MCL cells by CD40 activation alone or in combination with interleukin-4. Immunohistochemical analysis showed that significant numbers of CD40L-expressing lymphoid cells are present in lymph node biopsies of MCL patients. These results therefore further strengthen the possibility that triggering of CD40 by infiltrating CD40L+ cells may continuously promote the growth of MCL cells in vivo. On these grounds, our findings that RA inhibits basal MCL proliferation as well as MCL growth-promoting effects exerted by microenvironmental factors make these compounds highly attractive in terms of potential clinical efficacy in this setting.

Application of retinoids in the treatment of renal cell carcinoma–a futile effort?

The therapeutic benefit of adding retinoids such as all-trans retinoic acid (RA), 9-cis-RA or 13-cis-RA to established single-agent or combination immuno/chemotherapy regimens for the treatment of metastatic renal cell carcinoma (RCC) has been extensively investigated during the last decade. However, at present results are contradictory and their application controversial. Moreover, recent studies indicated a significantly higher incidence of toxic side-effects in patients treated with retinoids in addition to established bio/chemotherapy. This Commentary summarizes preclinical and clinical trials investigating efficacy and toxicity of retinoids in the treatment of RCC.

Drug-induced pulmonary edema and acute respiratory distress syndrome

Noncardiogenic pulmonary edema, and, to a lesser extent, acute respiratory distress syndrome (ARDS), are common clinical manifestations of drug-induced lung diseases. Clinical features and radiographic appearances are generally indistinguishable from other causes of pulmonary edema and ARDS. Typical manifestations include dyspnea, chest discomfort, tachypnea, and hypoxemia. Chest radiographs commonly reveal interstitial and alveolar filling infiltrates. Unlike pulmonary edema that is due to congestive heart failure, cardiomegaly and pulmonary vascular redistribution are generally absent in cases that are drug-related. Rare cases of drug-induced myocarditis with heart failure and pulmonary edema have been described. Results from laboratory evaluation and respiratory function tests are nonspecific.

Cell growth inhibition by all-trans retinoic acid in SKBR-3 breast cancer cells: Involvement of protein kinase C? and extracellular signal-regulated kinase mitogen-activated protein kinase

All-trans retinoic acid (ATRA), a synthetic derivative of vitamin A, inhibits the growth of breast cancer cells. To elucidate the mechanism by which ATRA causes cell growth inhibition, we examined changes in cell cycle and intracellular signaling pathways, focusing on protein kinase C (PKC) and mitogen-activated protein kinase (MAPK). Using the estrogen receptor-negative, retinoid receptor-positive breast cancer cell line SKRB-3, we found that treatment with ATRA significantly decreased the expression of PKCalpha, as well as reducing ERK MAPK phosphorylation. ATRA treatment leads to dephosphorylation of Rb, and consequently to G(1) arrest. Marked changes in the expression of cyclins (particularly cyclins A and E) were observed in SKBR-3 cells treated with ATRA. Using a series of pharmacological and molecular approaches, we found evidence that ATRA-induced SKBR-3 cell growth inhibition involves the deregulation of the PKCalpha-MAPK pathway. These data suggest that retinoids interfered with signal transduction pathways that are crucial for cell cycle progression, and highlight the complexities of the biological effects of retinoid derivatives.

A phase 1 study of tazarotene in adults with advanced cancer

Tazarotene is an acetylenic retinoid which is metabolised to tazarotenic acid and which binds selectively to the retinoid receptors RARbeta and RARgamma. The safety, toxicity and pharmacokinetics of oral tazarotene were determined over 12 weeks of treatment in 34 patients with advanced cancer. Commonly seen toxicities were mucocutaneous symptoms, musculoskeletal pain and headache. Dose-limiting toxicities were hypercalcaemia, hypertriglyceridaemia and musculoskeletal pain. The maximum tolerated dose of tazarotene in this schedule is 25.2 mg day(-1). Plasma concentrations of tazarotenic acid were found to peak rapidly within 1-3 h of dosing and thereafter declined quickly. The C(max) and AUC values on day 0, and weeks 2 and 4 were similar indicating no drug accumulation. The dose-normalised C(max) and AUC values at different dose levels and different study days appeared to be similar indicating linear pharmacokinetics. No objective responses were seen, although stable disease was seen in six out of eight evaluable patients receiving the three highest dose levels of tazarotene (16.8, 25.2 or 33.4 mg day(-1)). We conclude that oral tazarotene is well tolerated when administered daily for 12 weeks, has a favourable toxicity profile compared with other retinoids and merits further investigation as an anticancer therapy.

Differentiation, proliferation and retinoid receptor status of papillary carcinoma of the thyroid

Messenger RNA expression of retinoic acid receptors (RARalpha, RARbeta and RARgamma) and retinoid X receptors (RXRalpha, RXRbeta and RXRgamma) was examined using reverse transcription-polymerase chain reaction in 42 papillary thyroid carcinomas (PTCs). A loss of mRNA expression was observed in 18 cases of the 42 PTCs, including three cases for RARalpha, 14 cases for RARbeta, six cases for RXRalpha and five cases for RXRbeta. The expressions of RARgamma and RXRgamma were found in all 42 PTCs. Based on Ki 67/MIB1 labeling index (LI), the 42 PTCs were classified into Group A (20 cases; LI = 0-2%), Group B (17 cases; LI = 2-5%) and Group C (5 cases; LI > 5%). The PTCs of groups B and C showed solid, trabecular or scirrhous arrangements, infiltrative growth, loss of cellular polarity and cohesiveness more frequently, but capsulated growth pattern less frequently, when compared with PTCs of Group A. They also showed more frequent extrathyroidal extension than Group A. However, no significant differences were identified in sex, age, nodal status and tumor size. Loss of expression for one or more retinoid receptors frequently occurred in groups B and C. These results suggest that the loss of retinoid receptors might occur during the loss of differentiation and tumor progression of PTC.

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.

Retinoids in combination therapies for the treatment of cancer: mechanisms and perspectives

Retinoid derivatives have been of special interest in cancer research because of their antiproliferative and differentiation-inducing activities in premalignant and malignant cells. Some retinoids are clinically effective in cancer therapy and prevention, and all-trans-retinoic acid is being used for the treatment of acute promyelocytic leukemia. Unfortunately, classical retinoids are not effective against most advanced solid tumors and cause undesirable side effects, which have limited the full development of retinoids as chemopreventive and chemotherapeutic drugs. The recent identification of selective retinoid derivatives capable of inducing apoptosis and their combination with other anticancer therapies promises a more effective and less toxic manner to the successful use of retinoids in cancer therapy.

Human cytochrome P450s involved in the metabolism of 9-cis- and 13-cis-retinoic acids

The purpose of this work was to identify the principal human cytochrome P450s (CYPs) involved in the metabolism of the retinoic acid (RA) isomers, 9-cis- and 13-cis-RA, by using a combination of techniques including human liver microsomes (correlation of activity and inhibition), and lymphoblast microsomes expressing a single CYP. Concerning the 9-cis-RA, 4-OH- and 4-oxo-9-cis-RA were formed with human liver microsomes, and their formation correlated with activities linked to CYPs 3A4/5, 2B6, 2C8, 2A6, and 2C9. The use of lymphoblast microsomes expressing a single human CYP identified CYPs 2C9>2C8>3A7 as the most active in the formation of 4-OH-9-cis-RA. With regard to 13-cis-RA, specific P450 activities linked to CYPs 2B6, 2C8, 3A4/5, and 2A6 were correlated with the formation of 4-OH- and 4-oxo-13-cis-RA. Microsomes expressing a single CYP identified CYPs 3A7, 2C8, 4A11, 1B1, 2B6, 2C9, 2C19, 3A4 (decreasing activity) in the formation of 4-OH-13-cis-RA. The use of CYP-specific inhibitors in human liver microsomes disclosed that the formation of the 4-OH-9-cis-RA was best inhibited by sulfaphenazole (72%) and quercetin (66%), whereas ketoconazole and troleandomycin inhibited its formation by 55 and 38%, respectively; the formation of 4-OH-13-cis-RA was best inhibited by troleandomycin (54%) and ketoconazole (46%), whereas quercetin was a weak inhibitor (14%). In conclusion, adult human CYPs 2C9, 2C8, 3A4 have been identified as active in the 9-cis-RA metabolism, whereas CYPs 3A4 and 2C8 were active in 13-cis-RA metabolism. The fetal form CYP3A7 was also identified as very active in either 9-cis- or 13-cis-RA metabolism. The role of these human CYPs in the biological response or resistance to RA isomers remains to be determined.

Lavage and nipple aspiration of breast ductal fluids: a source of biomarkers for environmental mutagenesis

The acquisition of breast ductal fluid by nipple aspiration and ductal lavage are simple noninvasive procedures to sample breast tissue. Nipple aspiration fluid (NAF) obtained with gentle suction and a simple syringe-adapted apparatus may evaluate the secretory components that bathe the ductal epithelial cells. Evaluations have included the quantification of soluble markers (carcinoembryonic antigen and prostatic-specific antigen), DNA amplification, protein gel electrophoresis, and mutagenesis assays. It has been suggested that environmental mutagens in the breast ductal system may contribute to carcinogenesis. The feasibility of mutagenesis assays on NAF has been limited by the small size of the samples obtained. Three small clinical studies detected mutagens in 6-14% of the samples using the Salmonella Ames assay. Ductal lavage collects more of a cellular aspirate from the ductal system utilizing a microcatheter. Early studies on ductal lavage fluid have included cytology and methylation-specific PCR. Ductal lavage in a high-risk group has identified cellular atypia in 21% of those sampled. Samples obtained through the nipple, by aspiration or lavage, are the proteinaceous secretions from the ductal system and ductal epithelial cells. The fluid represents the cellular events and the dynamic secretory process of the breast and may include potential initiators of the carcinogenesis process in the cellular microenvironment. Fluid obtained by ductal lavage may allow for more detailed studies of the role of mutagens in breast cancer.

Selective estrogen receptor modulators (SERMs) and retinoids in breast cancer chemoprevention

Tamoxifen has been shown to decrease the risk of invasive breast cancer by 49% and noninvasive breast cancer by 50%. Tamoxifen is also associated with a threefold increased risk of endometrial cancer. Raloxifene, a second-generation selective estrogen receptor modulator (SERM), has not been associated with endometrial cancer risk, and is currently under study in a large, multi-institutional, randomized Study of Tamoxifen and Raloxifene (STAR) for breast cancer prevention in postmenopausal women. A pilot trial of raloxifene in premenopausal women to assess the safety, tolerability, effects on bone mineral density, mammographic density, and other biological endpoints is ongoing. The retinoids have been shown to decrease mammary tumors in rodent carcinogenesis models. The Italian trial of fenretinide (4-HPR) in women with stage I breast cancer randomized women to fenretinide or no intervention. This study did not show an overall effect of decreasing the risk of contralateral breast cancer. However, a protective effect was suggested in premenopausal women. It has been suggested that this effect may be related to insulin-like growth factor 1 (IGF-1), which has been shown to be modulated by fenretinide in premenopausal but not postmenopausal women. Pilot studies of SERMs alone and in combination with retinoids or other agents provide a model for testing the safety and tolerability, pharmacokinetics and pharmacodynamics, and biomarker modulation in high-risk women. These studies can provide information as to both the pathophysiology of carcinogenesis and the mechanism of action of chemopreventive agents, and help select agents and doses for testing in large randomized studies.

Nuclear receptors in cell life and death

The balance between cell proliferation and programmed cell death (apoptosis) determines body patterns during animal development and controls compartment sizes, tissue architecture and remodeling. The removal of primordial structures by apoptosis allows the organism to develop sex specifically and to adapt for novel functions at later stages; apoptosis also limits the size of evolving structures. It is a ubiquitous function that is essential for all cells. Although inappropriate regulation or execution of apoptosis leads to disease, such as cancer, there is now evidence for its great therapeutic potential. This would be particularly true if apoptosis could be targeted at defined cell compartments, rather than acting ubiquitously like chemotherapy. Here, we discuss the potential of nuclear receptor ligands, many of which act through their cognate receptors in defined body compartments as modulators of cell life and death, with special emphasis on the molecular pathways by which these receptors affect cell-cycle progression, survival and apoptosis.

The promise of retinoids to fight against cancer

Retinoids have a reputation for being both detrimental and beneficial: they are teratogens, but they also have tumour-suppressive capacity. Cell biology and genetics have significantly improved our understanding of the mechanisms that underlie the anti-proliferative action of retinoids. Recent elucidation of the pathways that are activated by retinoids will help us to exploit the beneficial aspects of this powerful class of compounds for cancer therapy and prevention.

Systemic therapy

A large body of data on systemic therapy has been presented and published in the past year, including new information on primary risk reduction, patient selection for adjuvant systemic therapy, and anthracycline-analogs. New data on ongoing adjuvant trials (including taxane studies), unpublished updates from the fourth Oxford Overview in September 2000, and provocative data on ovarian ablation were important features of the November 2000 National Institutes of Health Consensus Development Conference on Adjuvant Therapy for Breast Cancer. Important new data on anti-estrogen therapy, including aromatase inhibitors and pure antiestrogens, further expand the role of the oldest targeted breast cancer therapy. Trastuzumab and other novel compounds are being investigated as single-agents and in combination with conventional systemic approaches. Discussions on the long-term effects of adjuvant therapy have taken center stage also. These and other important ongoing developments since 2000 are examined in this review article.