Expression of retinoic acid receptor gamma correlates with retinoic acid sensitivity and metabolism in head and neck squamous cell carcinoma cell lines

High RAB25 expression is associated with good clinical outcome in patients with locally advanced head and neck squamous cell carcinoma

Currently there are no molecular markers able to predict clinical outcome in locally advanced head and neck squamous cell carcinoma (HNSCC). In a previous microarray study, RAB25 was identified as a potential prognostic marker. The aim of this study was to analyze the association between RAB25 expression and clinical outcome in patients with locally advanced HNSCC treated with standard therapy. In a retrospective immunohistochemical study (n = 97), we observed that RAB25-negative tumors had lower survival (log-rank, P = 0.01) than patients bearing positive tumors. In an independent prospective mRNA study (n = 117), low RAB25 mRNA expression was associated with poor prognosis. Using classification and regression tree analysis (CART) we established two groups of patients according to their RAB25 mRNA level and their risk of death. Low mRNA level was associated with poor local recurrence-free (log-rank, P = 0.005), progression-free (log-rank, P = 0.002) and cancer-specific (log-rank, P < 0.001) survival. Multivariate Cox model analysis showed that low expression of RAB25 was an independent poor prognostic factor for survival (hazard ratio: 3.84, 95% confidence interval: 1.93-7.62, P < 0.001). Patients whose tumors showed high RAB25 expression had a low probability of death after treatment. We also found lower RAB25 expression in tumors than in normal tissue (Mann-Whitney U, P < 0.001). Moreover, overexpression of RAB25 in the UM-SCC-74B HNSCC cell line increased cisplatin sensitivity, and reduced cell migration and invasion. Our findings support a tumor suppressor role for RAB25 in HNSCC and its potential use to identify locally advanced patients with a high probability of survival after genotoxic treatment.

All-trans-retinoic acid modulates ICAM-1 N-glycan composition by influencing GnT-III levels and inhibits cell adhesion and trans-endothelial migration

Changes in the expression of glycosyltransferases directly influence the oligosaccharide structures and conformations of cell surface glycoproteins and consequently cellular phenotype transitions and biological behaviors. In the present study, we show that all-trans-retinoic acid (ATRA) modulates the N-glycan composition of intercellular adhesion molecule-1 (ICAM-1) by manipulating the expression of two N-acetylglucosaminyltransferases, GnT-III and GnT-V, via the ERK signaling pathway. Exposure of various cells to ATRA caused a remarkable gel mobility down-shift of ICAM-1. Treatment with PNGase F confirmed that the reduction of the ICAM-1 molecular mass is attributed to the decreased complexity of N-glycans. We noticed that the expression of the mRNA encoding GnT-III, which stops branching, was significantly enhanced following ATRA exposure. In contrast, the level of the mRNA encoding GnT-V, which promotes branching, was reduced following ATRA exposure. Silencing of GnT-III prevented the molecular mass shift of ICAM-1. Moreover, ATRA induction greatly inhibited the adhesion of SW480 and U937 cells to the HUVEC monolayer, whereas knock-down of GnT-III expression effectively restored cell adhesion function. Treatment with ATRA also dramatically reduced the trans-endothelial migration of U937 cells. These data indicate that the alteration of ICAM-1 N-glycan composition by ATRA-induced GnT-III activities hindered cell adhesion and cell migration functions simultaneously, pinpointing a unique regulatory role of specific glycosyltransferases in the biological behaviors of tumor cells and a novel function of ATRA in the modulation of ICAM-1 N-glycan composition.

Signalling with retinoids in the human lung: validation of new tools for the expression study of retinoid receptors

Background

Retinoid Receptors are involved in development and cell homeostasis. Alterations of their expressions have been observed in lung cancer. However, retinoid chemoprevention trials in populations at risk to develop such tumors have failed. Therefore, the pertinence of new clinical trials using second generation retinoid requires prior better understanding of retinoid signalling. This is our aim when validating extensively research tools, focused on Retinoic Acid Receptor beta, whose major role in lung cancer is documented.

Methods

Biocomputing was used to assess the genomic organization of RAR beta. Its putative RAR-beta1' promoter features were investigated experimentally. Specific measures realized, with qRT-PCR Syber Green assays and a triplex of Taqman probes, were extensively validated to establish Retinoid Receptors mRNAs reference values for in vivo normal human bronchial cells, lung tumors and cell lines. Finally, a pan-RAR-beta antibody was generated and extensively validated by western-blot and immunoprecipitation.

Results

No promoter-like activity was found for RAR-beta1'. RAR-beta2 mRNAs increase signs the normal differentiation of the human bronchial epithelium while a decrease is observed in most lung cancer cell lines. Accordingly, it is also, along with RXR beta, down-regulated in lung tumors. When using nuclear extracts of BEAS-2B and normal lung cells, only the RAR-beta2 long protein isoform was recognized by our antibody.

Conclusion

Rigorous samples processing and extensive biocomputing, were the key factors for this study. mRNA reference values and validated tools can now be used to advance researches on retinoid signalling in the lung.

Monitoring response to radiotherapy in human squamous cell cancer bearing nude mice: comparison of 2'-deoxy-2'-[18F]fluoro-D-glucose (FDG) and 3'-[18F]fluoro-3'-deoxythymidine (FLT)

Objective

The uptake of 3′-[¹⁸F]fluoro-3′-deoxythymidine (FLT), a proliferation marker, was measured before and during fractionated radiotherapy to evaluate the potential of FLT-positron emission tomography (PET) imaging as an indicator of tumor response compared to 2′-deoxy-2′-[¹⁸F]fluoro-d-glucose (FDG).

Materials and Methods

Nude mice bearing established human head and neck xenografts (HNX-OE; nu/nu mice) were locally irradiated (three fractions/week; 22 Gy) using a 150-kV_p unit. Multiple FDG- and FLT-PET scans were acquired during treatment. Tumor volume was determined regularly, and tissue was analyzed for biomarkers involved in tracer uptake.

Results

Both groups revealed a significant decline in tumor volume (P < 0.01) compared to untreated tumors. For FDG as well as for FLT, a significant decline in retention was observed at day 4. For FLT, most significant decline in retention was observed at day 12; whereas, for FDG, this was already noted at day 4. Maximum decline in tumor-to-nontumor ratios (T/NT) for FDG and FLT was 42 ± 18% and 49 ± 16% (mean ± SD), respectively. FLT uptake was higher then that of FDG. For FLT, statistical significant correlations were found for both tumor volume at baseline and at day 29 with T/NT and ΔT/NT. All tumors demonstrated expression of glucose transporter-1, thymidine kinase-1, and hexokinase II. No differences were found for amount of tumor cells and necrosis at the end of treatment.

Conclusion

This new experimental in vivo model supports the promise of using FLT-PET, as with FDG-PET, to monitor response to external radiotherapy. This warrants further clinical studies to compare these two tracers especially in cancers treated with radiotherapy.

Cytodifferentiation by retinoids, a novel therapeutic option in oncology: rational combinations with other therapeutic agents

Retinoic acid (RA) and derivatives are promising antineoplastic agents endowed with both therapeutic and chemopreventive potential. Although the treatment of acute promyelocytic leukemia with all-trans retinoic acid is an outstanding example, the full potential of retinoids in oncology has not yet been explored and a more generalized use of these compounds is not yet a reality. One way to enhance the therapeutic and chemopreventive activity of RA and derivatives is to identify rational combinations between these compounds and other pharmacological agents. This is now possible given the information available on the biochemical and molecular mechanisms underlying the biological activity of retinoids. At the cellular level, the antileukemia and anticancer activity of retinoids is the result of three main actions, cytodifferentiation, growth inhibition, and apoptosis. Cytodifferentiation is a particularly attractive modality of treatment and differentiating agents promise to be less toxic and more specific than conventional chemotherapy. This is the result of the fact that cytotoxicity is not the primary aim of differentiation therapy. At the molecular level, retinoids act through the activation of nuclear retinoic acid receptor-dependent and -independent pathways. The cellular pathways and molecular networks relevant for retinoid activity are modulated by a panoply of other intracellular and extracellular pathways that may be targeted by known drugs and other experimental therapeutics. This chapter aims to summarize and critically discuss the available knowledge in the field.

Retinoic acid receptors and tissue-transglutaminase mediate short-term effect of retinoic acid on migration and invasion of neuroblastoma SH-SY5Y cells

Long-term treatment with all trans-retinoic acid (RA) induces neuronal differentiation and apoptosis. However, the effect of short-term RA treatment on cell proliferation, migration and invasion of neuroblastoma cell lines (SH-SY5Y and IMR-32) remains unclear. RA induces expression of tissue-transglutaminase (TGase) and promotes migration and invasion after 24 h of treatment in SH-SY5Y cells, but not in IMR-32 cells. RA receptor (RAR) agonist (4-(E-2-[5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl]-1-propenyl) benzoic acid) and RAR/retinoid X receptor (RXR) agonist (9-cis-RA) promote expression of TGase, migration and invasion of SH-SY5Y cells, while RXR agonist has no significant effect. RAR antagonist blocks RA effect on migration and invasion, indicating that RAR receptors are required. Retinoid receptors are expressed and activated by RA in both cell lines. However, only transient activation of RAR is observed in IMR-32 cells. These findings suggest that different responses observed in SH-SY5Y and IMR-32 cells could be due to differential activation of retinoid receptors. Overexpression of TGase has no effect on migration or invasion, while overexpression of antisense TGase blocks RA-induced migration and invasion, indicating that other molecules along with TGase mediate RA effects. In addition to the long-term effects of RA that are coupled with cell differentiation, short-term effects involve migration and invasion of neuroblastoma SH-SY5Y cells.

Retinoid-induced mu opioid receptor expression by phytohemagglutinin-stimulated U937 cells

Opioid use may be associated with an increased risk of neurological disease in human immunodeficiency virus (HIV) infection through effects on immune cell function. Studies were performed to examine the effects of specific retinoid receptor activation on mu opioid receptor (MOR) production by phytohemagglutinin (PHA)-stimulated U937 cells, a mononuclear cell line. PHA stimulation increased activation of the MOR promoter as well as levels of MOR mRNA, total receptor protein in cell lysates, and surface and cytoplasmic receptor expression. Retinoid X receptor (RXR) agonist and retinoic acid receptor (RAR) antagonist further increased MOR expression by the PHA-stimulated cells. In contrast, MOR expression was suppressed by RAR agonist and by RXR antagonist. Finally, opioid receptor binding was also increased by RXR agonist and RXR antagonist; no increase in binding occurred in the presence of RAR agonists and RXR antagonist. All together, these studies suggest that MOR expression in U937 cells can be differentially regulated by specific retinoid receptor activation. Such effects may have important clinical relevance for opioid users with HIV infection, including individuals with neurological disease.

Clinical significance of altered expression of retinoid receptors in oral precancerous and cancerous lesions: Relationship with cell cycle regulators

Alterations in expression of retinoid receptors are implicated in human cancers. We hypothesized that altered expression of retinoic acid receptors (RARalpha,beta,gamma) and retinoid X receptor RXRalpha and their relationship with cell cycle regulators (p53, p16, p21) is associated with development, progression and prognosis of oral cancer. Immunohistochemical analysis of RAR alpha, beta, gamma and RXRalpha proteins was carried out on serial sections from 244 oral squamous cell carcinomas (OSCCs), 102 potentially malignant lesions (65 hyperplasias, 37 dysplasias), 83 matched histologically normal oral tissues and 29 normal mucosa from non-exposed individuals without oral lesions and correlated with expression of cell cycle regulators p53, p16 and p21 as well as with clinicopathological parameters. Expression of retinoid receptors RARbeta, RARgamma, RXRalpha and cell cycle regulators p16 and p21 was decreased in majority of oral SCCs as well as in potentially malignant lesions. Multivariate stepwise logistic regression analysis carried out for comparison of non-exposed normal oral mucosa with histologically normal oral tissues from patients with oral lesions showed significant loss of RARbeta or p53 accumulation (RARbeta(-)/p53(+) Odd's ratio, OR = 266.6, p = 0.000); non-exposed normal mucosa from individuals without oral lesions with potentially malignant lesion was RARbeta(-)/p21(-)/p53(+) (OR = 215.7, p = 0.000); matched normal to potentially malignant stage was RARalpha(+)/p21(-) (OR = 4.414, p = 0.005); hyperplasia to dysplasia was RARalpha(+)/p53(+) (OR = 4.72, p = 0.005) and potentially malignant to malignant phenotype was RARalpha(+) (OR = 2.061, p = 0.004). The prognostic relevance of these factors was assessed in 115 of these SCC patients who were followed-up for a maximum period of 94 months (median 21 months). Multivariate analysis using Cox's proportional Hazard's model showed that RARalpha(+)/p21(-) phenotype was associated with shorter disease-free survival (Hazard's ratio, HR = 1.863, p = 0.0471). To our knowledge, this is the first large study showing alterations in expression of retinoid receptors at the protein level at different stages in development and progression of oral SCC. It also underscored the prognostic significance of retinoid receptors and their interactions with cell cycle regulators in multistep oral tumorigenesis.

Retinoic acid receptors and cancers

Studies utilizing experimental animals, epidemiological approaches, cellular models, and clinical trials all provide evidence that retinoic acid and some of its synthetic derivatives (retinoids) are useful pharmacological agents in cancer therapy and prevention. In this chapter, we first review the current knowledge of retinoic acid receptors (RARs) and their role in mediating the actions of retinoic acid. We then focus on a discussion of RARalpha and acute promyelocytic leukemia followed by a discussion of the role of RARs, in particular RARbeta expression, in other cancer types. Loss of normal RAR function in the presence of physiological levels of RA (either due to alterations in the protein structure or level of expression) is associated with a variety of different cancers. In some cases treatment with pharmacological doses of RA can be effective.

RARgamma acts as a tumor suppressor in mouse keratinocytes

All-trans retinoic acid (RA), the principle biologically active form of vitamin A, is essential for many developmental process as well as homeostasis in the adult. Many lines of evidence also suggest that RA, acting through the RA receptors (RARs), can also suppress growth of tumors of diverse origin. To assess directly the role of the RARs in a model of epidermal tumorigenesis, we investigated the incidence of tumor formation using keratinocytes lacking specific RAR types. Our data suggest that loss of RARgamma, but not RARalpha, predisposed keratinocytes to v-Ha-Ras-induced squamous cell carcinoma. We also found that ablation of RARgamma, but not RARalpha, abolished RA-induced cell cycle arrest and apoptosis in these keratinocytes. Reconstitution of receptor expression into RAR-null cells restored sensitivity to RA, and reversed the tumorigenic potential of receptor-deficient keratinocytes. These data strongly support a tumor suppressor effect for the RARs, in particular endogenous RARgamma, in murine keratinocytes.

Induction of apoptosis in oral cancer cells: agents and mechanisms for potential therapy and prevention

Oral cancer is one of the most disfiguring types of cancer, since the surgical removal of the tumor may result in facial distortion. Oral cancer is also known to exhibit "field cancerization", resulting in the development of a second primary tumor. Furthermore, the five-year survival rate of this disease has remained approximately 50% during the past 30 years. Prevention and early detection/treatment of oral cancer could significantly improve the quality of life for individuals at risk. Recently, the targeted elimination of oral squamous cell carcinoma cells by inducing apoptosis has emerged as a valued strategy to combat oral cancer. Studies utilizing a variety of chemical or biological interventions demonstrated promising results for induction of apoptosis in oral malignant cells. This review summarizes the results of a number of investigations focused specifically on induction of apoptosis in oral cancer cells by synthetic compounds and naturally occurring chemopreventive agents with apoptotic potential.

Retinoic acid causes cell growth arrest and an increase in p27 in F9 wild type but not in F9 retinoic acid receptor β2 knockout cells

We have previously shown that an F9 teratocarcinoma retinoic acid receptor beta(2) (RARbeta(2)) knockout cell line exhibits no growth arrest in response to all-trans-retinoic acid (RA), whereas F9 wild type (Wt), F9 RARalpha(-/-), and F9 RARgamma(-/-) cell lines do growth arrest in response to RA. To examine the role of RARbeta(2) in growth inhibition, we analyzed the cell cycle regulatory proteins affected by RA in F9 Wt and F9 RARbeta(2)(-/-) cells. Flow microfluorimetry analyses revealed that RA treatment of F9 Wt cells greatly increased the percentage of cells in the G1/G0 phase of the cell cycle. In contrast, RA did not alter the cell cycle distribution profile of RARbeta(2)(-/-) cells. In F9 Wt cells, cyclin D1, D3, and cyclin E protein levels decreased, while cyclin D2 and p27 levels increased after RA treatment. Compared to the F9 Wt cells, the F9 RARbeta(2)(-/-) cells exhibited lower levels of cyclins D1, D2, D3, and E in the absence of RA, but did not exhibit further changes in the levels of these cell cycle regulators after RA addition. Since RA significantly increased the level of p27 protein (approximately 24-fold) in F9 Wt as compared to the F9 RARbeta(2)(-/-) cells, we chose to study p27 in greater detail. The p27 mRNA level and the rate of p27 protein synthesis were increased in RA-treated F9 Wt cells, but not in F9 RARbeta(2)(-/-) cells. Moreover, RA increased the half-life of p27 protein in F9 Wt cells. Reduced expression of RARbeta(2) is associated with the process of carcinogenesis and RARbeta(2) can mediate the growth arrest induced by RA in a variety of cancer cells. Using both genetic and molecular approaches, we have identified some of the molecular mechanisms, such as the large elevation of p27, through which RARbeta(2) mediates these growth inhibitory effects of RA in F9 cells.

Establishment and characterization of a cell line from smokeless tobacco associated oral squamous cell carcinoma

A cell line, AMOS-III has been established from the surgically resected specimen of an untreated primary human oral squamous cell carcinoma of the floor of mouth from a chronic smokeless tobacco consumer. Immunocytochemical analysis showed epithelial specific antigen, cytokeratins 5, 10, 13 and 16 and integrin alpha(6) markers in AMOS-III cells, confirming the epithelial lineage of the cell line. Analyses of morphology, ultrastructure, karyotype, anchorage independent growth and immunocytochemical properties of the cell line demonstrated the transformed phenotype of epithelial cells. AMOS-III cells have doubling time of 42-44 h. Giemsa-banding patterns of chromosomes confirmed the human origin of the AMOS-III cells. Molecular analysis of cancer-related gene products, p53 and p21(cip1/waf1) showed the presence of wild type p21(cip1/waf1) and truncated p53 proteins. The molecular mechanism underlying the action of retinoids in preventing the occurrence of second primary tumors in oral cancer patients remain to be clearly defined. Treatment of AMOS-III cells with all-trans retinoic acid (ATRA) at 10(-4) microM resulted in 81% cell death. ATRA treatment resulted in enhanced expression of p21(cip1/waf1), nuclear translocation of retinoic acid receptors and apoptotic cell death. Thus, this cell line provides an in vitro model for elucidating the mechanism involving p53 inactivation and p21(cip1/waf1) overexpression in smokeless tobacco-induced oral cancer. Furthermore, the ATRA responsiveness of the cell line underscores its potential utility in identifying the retinoid responsive molecular targets in oral cancer cells.

Inhibition of tumor growth by biodegradable microspheres containing all-trans-retinoic acid in a human head-and-neck cancer xenograft

Retinoids play essential roles in the regulation of cell differentiation and in the proliferation of various epithelial tissues, and atRA is one such active metabolite of retinoids. However, despite the known functions of atRA, its clinical applications are limited due to the induced metabolism by the specific cytochrome P-450s in the liver. To overcome the limitation, parenteral administration of atRA-loaded biodegradable microspheres, the PDLLA/PLE microspheres containing atRA, was suggested previously. We evaluated chemotherapeutic efficacy of atRA-loaded microspheres in a human head-and-neck xenograft/nude mouse model. When atRA-loaded microspheres were administered s.c. at 200 mg/kg body weight to athymic nude mice, plasma concentration of atRA could be maintained in a range of 1.2 to 3.7 x 10(-8) M for 4 weeks. As a result, the tumor volume of human head-and-neck cancer was reduced compared to the control group by 51.3% (p < 0.01) at 14 days and by 49.2% (p < 0.05) at 28 days.

Anticancer activity and mechanism of action of retinoids in oral and pharyngeal cancer

Retinoids are the natural and synthetic derivatives of vitamin A. Epidemiological studies indicate that a low intake of vitamin A is associated with an increased risk of squamous cancer. In vitro studies on cancer cells show that exposure to retinoids results in the inhibition of growth, by blocking the cell cycle or by inducing apoptosis. With respect to the clinical efficacy of retinoids some positive effects have been observed in early stage oral and oropharyngeal cancer. Administration of retinoids has been shown to elicit responses in leukoplakia, a premalignant lesion of the oral mucosa that frequently develops into invasive cancer. Furthermore, it has been possible with a retinoid, 13-cis-retinoic acid, to delay or inhibit the development of second primary tumors in patients who have been curatively treated for a first primary tumor in the oral cavity or oropharynx. Recent trials, however, failed to show protective effects on the development of second primary tumors. Because of the short duration of the response, the intrinsic resistance to retinoids and the toxic side effects, the treatment with this class of compounds has not become a standard therapy. Recent studies have shed light on how preneoplastic and neoplastic cells defend themselves against the growth inhibiting action of retinoids. An increased retinoid breakdown and an inactivation of nuclear retinoid receptor appear to be the cause of acquired or intrinsic resistance. This knowledge can be used to develop novel tumor-selective strategies. This review gives an update on the role of retinoids in oral and oropharyngeal cancer and their precursor lesions. The focus will be on the anticancer activity, the mechanism of action and future directions.

The roles of JNK1 and Stat3 in the response of head and neck cancer cell lines to combined treatment with all-trans-retinoic acid and 5-fluorouracil

We have used a combination of vitamin A (all-trans-retinyl palmitate), 5-fluorouracil (5-FU) and radiation to treat human head and neck squamous cell carcinoma (HNSCC). This chemoradiotherapy is called "FAR therapy." In this study we examined the effects of all-trans-retinoic acid (ATRA), the active metabolite of vitamin A, and ATRA plus 5-FU on two HNSCC cell lines (YCU-N861 and YCU-H891) to gain insight into the molecular mechanisms of FAR therapy. ATRA at 1 mM (the order of concentration found in HNSCC tumors treated with FAR therapy) inhibited cell proliferation and caused G1 cell cycle arrest in both cell lines. This was associated with a decrease in cyclin D1, an increase in p27(Kip1) and a reduction in the hyperphosphorylated form of retinoblastoma protein (pRB). With YCU-N861 cells, ATRA also caused a decrease in Bcl-2 and Bcl-X(L) and an increase in Bax. Both ATRA and 5-FU activated c-Jun N-terminal kinase (JNK) 1 and the combination of both agents resulted in additive or synergistic activation of JNK1, and also enhanced the induction of apoptosis. The YCU-H891 cells, in which the epidermal growth factor receptor (EGFR)-signal transducer and activator of transcription 3 (Stat3) pathway is constitutively activated, were more resistant to treatments with ATRA, 5-FU and the combination of both agents than YCU-N861 cells. A dominant negative Stat3 construct strongly enhanced the cellular sensitivity of this cell line to 5-FU but not to ATRA. In addition there is evidence that activation of Stat3 is associated with cellular resistance to radiation in HNSCC. Therefore, the addition to FAR therapy of agents that inhibit activation of the Stat3 pathway may enhance the clinical response of patients with HNSCC to FAR therapy.

Metabolism and growth inhibition of four retinoids in head and neck squamous normal and malignant cells

Isotretinoin (13-cis-retinoic acid, 13cRA) has proven to be active in chemoprevention of head and neck squamous cell carcinoma (HNSCC). Moreover, both all-trans-retinoic acid (ATRA) and 13cRA induce objective responses in oral premalignant lesions. After binding of retinoids to retinoic acid receptors (RARs and RXRs) dimers are formed that are able to regulate the expression of genes involved in growth and differentiation. We compared the metabolism and level of growth inhibition of 13cRA with that of ATRA, 9cRA and retinol in four HNSCC cell lines and normal oral keratinocyte cultures (OKC). These retinoid compounds are known to bind with different affinities to the retinoic acid receptors. We observed that all retinoids were similar with respect to their capacity to induce growth inhibition. One HNSCC line could be ranked as sensitive, one as moderately sensitive and the remaining two were totally insensitive; OKC were moderately sensitive. The rate at which the cells were able to catabolize the retinoid was similar for all compounds. Retinoid metabolism in HNSCC cells resulted in a profile of metabolites that was unique for each retinoid. These metabolic profiles were different in OKC. Our findings indicate that differences in retinoid receptor selectivity of these retinoids do not influence the level of growth inhibition and rate of metabolism.