The impact of retinoic acid treatment on the sensitivity of neuroblastoma cells to fenretinide

Despite the successful introduction of 13-cis retinoic acid (13cisRA) therapy for the treatment of neuroblastoma, approximately 50% patients do not respond or experience relapse. A retinoid analogue, fenretinide [N-(4-hydroxyphenyl) retinamide; 4-HPR] can induce apoptosis in neuroblastoma cell lines and could have clinical use after therapy with 13cisRA. However, there are important questions concerning potential retinoid drug interactions which need to be addressed. The aim of this study was to investigate the influence of retinoic acid pre-treatment on fenretinide-induced apoptosis and fenretinide metabolism in neuroblastoma cell lines. Apoptosis was measured by flow cytometry of propidium iodide-stained neuroblastoma cells and a live-cell imaging assay. Intracellular fenretinide metabolism was determined by HPLC analysis. Pre-treatment of neuroblastoma cell lines with retinoic acid (RA) resulted in a significant decrease in the apoptotic response to fenretinide in three of the four lines tested. Comparison between responsive and non-responsive cell lines suggested that RA sensitivity was required to promote fenretinide resistance, and that this was mediated by up-regulation of Bcl-2 and the inhibition of pro-apoptotic fenretinide signalling pathways. Induction of the oxidative metabolism of fenretinide after RA pre-treatment did not significantly impact on intracellular parent drug levels and is unlikely to explain the decreased apoptotic response observed. The interaction between RA and fenretinide could have important implications for the scheduling of fenretinide in therapeutic protocols for neuroblastoma.     

9-cis retinoic acid — a better retinoid for the modulation of differentiation,proliferation and gene expression in human neuroblastoma

To date, the clinical success of 13-cis or all-trans retinoic acid in the treatment of neuroblastoma has been disappointing. In vivo, 13-cis will isomerise to both all-trans and 9-cis retinoic acid, believed to be the main biologically-active isomers. In vitro studies with an N-type neuroblastoma cell line, SH SY 5Y, show that 9-cis is better than other isomers at both inducing morphological differentiation and inhibiting proliferation. RAR-, a gene which may mediate retinoic acid responsiveness and be of prognostic significance, is also more-effectively induced by 9-cis retinoic acid. 9-cis and all-trans retinoic acid do not have synergistic effects on SH SY 5Y cell proliferation and gene expression. A retinoid X receptor (RXR)-specific analogue of 9-cis retinoic acid had similar effects on gene expression to 9-cis retinoic acid alone. In view of these results, 9-cis retinoic acid or stable analogues of this retinoid may have potential for the treatment of neuroblastoma.     

Fenretinide and its relation to cancer.

Retinoids, natural or synthetic substances which have vitamin A activity, have a well-known reputation for their antitumour and differention-inducing activity in vitro and in vivo. More than 1500 retinoids have been tested so far but very few of them have been entered into clinical trials because of their side-effects. All-trans-N-(4-hydroxyphenyl)retinamide (4HPR or fenretinide) is a synthetic retinoid that is reported to have fewer side-effects compared to naturally occurring retinoids such as all-trans retinoic acid (ATRA) and 9-cis retinoic acid. In addition, fenretinide has been shown to induce cell death (apoptosis) even in ATRA-resistant cell lines. Although the mechanism by which fenretinide acts is not entirely known it is considered to be a promising drug and seems to induce apoptosis via different pathway(s) from classical retinoids. In this review, we discuss possible mechanisms of fenretinide action and summarize results of clinical trials.     

The synthetic retinoid RO 13-6307 induces neuroblastoma differentiation in vitro and inhibits neuroblastoma tumour growth in vivo

Retinoids modulate cell proliferation, differentiation and apoptosis in a variety of tumour cells including leukaemia and neuroblastoma, a childhood tumour of the sympathetic nervous system. 13-cis retinoic acid is in clinical use against minimal residual disease in neuroblastoma, where the effect seems to depend on dose, scheduling and tumour mass. Novel retinoids are searched for, to improve potency and lower toxicity. We investigated the effect of the synthetic retinoid Ro 13-6307 on neuroblastoma growth in vitro on SK-N-BE(2) and SH-SY5Y cells. Furthermore, effects on tumour growth and the toxicity profile were investigated in a rat xenograft model. Effects of Ro 13-6307 were compared to 13-cis RA (retinoic acid) in vitro and in vivo. Neuroblastoma cells treated with 1 microM Ro 13-6307 exhibited neuronal differentiation, decreased proliferation and accumulation of cells in G1 phase in at least the same magnitude as 5 microM 13-cis RA. No apoptosis was detected in vitro. Treatment of nude rats with neuroblastoma using Ro 13-6307, 0.12 mg p.o. daily, decreased neuroblastoma growth in vivo, in terms of tumour volume during treatment and tumour weight at sacrifice (p < 0.05). In contrast, Ro 13-6307, 0.08 mg p.o. daily, resulted in no significant reduction in tumour growth. All rats treated with Ro 13-6307 gained less weight than control rats, but they exhibited no other signs of toxicity. The toxicity profile of Ro 13-6307 was similar to what we found with 13-cis RA. Our preclinical results suggest that Ro 13-6307 may be a candidate retinoid for clinical oral therapy of neuroblastoma in children.     

Death receptor signaling regulatory function for telomerase: hTERT abolishes TRAIL-induced apoptosis, independently of telomere maintenance

Human telomerase has been implicated in cell immortalization and cancer. Recent works suggest that telomerase confers additional function required for tumorigenesis that does not depend on its ability to maintain telomeres. This new action may influence tumor therapy outcomes by yet unraveled mechanisms. Here, we show that overexpression of the catalytic subunit of telomerase (hTERT) protects a maturation-resistant acute promyelocytic leukemia (APL) cell line from apoptosis induced by the tumor necrosis factor (TNF) or TNF-related apoptosis-inducing ligand (TRAIL) and not from apoptosis induced by chemotherapeutic drugs such as etoposide or cisplatin. Conversely, in these cells, TRAIL-induced cell death is magnified by all-trans retinoic acid (ATRA) treatment, independently of telomerase activity on telomeres. Of note, this response is subordinated neither to maturation nor to telomere shortening. This work underlines that retinoids and death receptor signaling cross-talks offer new perspectives for antitumor therapy.     

Identification of a unique binding protein specific for a novel retinoid inducing cellular apoptosis

The retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalenecarboxylic acid (AHPN, CD437) induces apoptosis in a variety of cell types, many of which are cancer cells that resist the antiproliferative and/or differentiating effects of retinoids. While the retinoids exert their effects by binding to the retinoic acid nuclear receptors (RARs) or retinoid X receptors (RXRs), AHPN (CD437) binds to another protein with different ligand specificity. In nuclear extracts from HL-60R cells the binding of AHPN (CD437) was only minimally competed by either retinoic acid (tRA)or 9-cis-retinoic acid (9-cis-RA), the natural ligands for the RARs and RXRs, respectively. Moreover, AHPN (CD437) was unable to compete with either tRA or 9-cis-RA for binding to endogenous retinoid receptors in nuclear extracts from the MDA-MB-468 breast carcinoma cell line. Size exclusion chromatography revealed AHPN binding to a 95 kDa protein(s) which is neither an RAR or RXR. Our results suggest that apoptosis induction by AHPN (CD437) may occur through interaction with another protein and is independent of the RAR/RXR-signaling pathways.     

The RARgamma selective agonist CD437 inhibits gastric cell growth through the mechanism of apoptosis.

Retinoids are differentiation-inducing agents that exhibit multiple functions. Their activities are mediated through interaction with nuclear retinoic acid receptors (RAR) and retinoid X receptors (RXR). We have investigated the activities of synthetic retinoids on the growth of five gastric cancer cell lines. The effects of agonists selective for RARalpha, RARbeta and RARgamma (AM580, CD2019 and CD437, respectively) on cell growth were determined, in comparison to all-trans retinoic acid, by measuring total cellular DNA. AM580 and CD2019 had little or no effect on the growth of all five cell lines. In contrast, the RARgamma agonist CD437 inhibited cell growth up to 90-99% in both retinoic acid sensitive and resistant gastric cancer cells at a concentration of 1 microM. The growth suppression caused by CD437 was accompanied by the induction of apoptosis as judged by morphological criteria and DNA ladder formation. However, the extent of CD437-induced growth suppression was not correlated with RARgamma mRNA levels, which indicates that CD437 induces apoptosis in gastric cancer cells via an RARgamma independent pathway.     

Synergistic effect of retinoids and interferon α on tumor-induced angiogenesis: Anti-angiogenic effect on HPV-harboring tumor-cell lines

Various retinoids and interferons exert anti-tumor effects both in experimental studies and in clinical trials. Recent reports indicate that they have a synergistic antineoplastic activity. Our study aimed to determine whether these synergistic anti-tumor effects are related to inhibition of tumor-cell-induced angiogenesis. A further aim was to compare the anti-angiogenic activity of various retinoids including 9-cis retinoic acid, a ligand for nuclear retinoic acid receptor RXR, given alone and in combination with interferon α-2a (IFNα-2a). An in vivo experimental model of cutaneous angiogenesis in the mouse was used. Angiogenesis was induced by intradermal injection of HPVI6-or HPVI8 DNA-harboring tumor-cell lines. All-trom retinoic acid (all-trans RA), 13-cis retinoic acid (13-cis RA) and 9-cis retinoic acid (9-cis RA) as well as 1FNα-2a applied to mice intra-peritoneally for S consecutive days before induction of angiogen-esis resulted in significant inhibition of angiogenesis. Combination of retinoids with IFNα-2a led to a synergistic inhibition of angiogenesis, as compared to the effects of the drugs given alone. Similar results were obtained when tumor cells were preincubated in vitro with the compounds, before injection into untreated mice. Our findings on synergistic anti-angiogenic effects of retinoids and IFNα-2a could explain, at least partially, the anti-tumor efficacy of combined therapy with these agents, and provide support for the role of angiogenesis in tumor growth. © Wiley-Liss, Inc.     

Plasma retinoid levels in head and neck cancer patients: a comparison with healthy controls and the effect of retinyl palmitate treatment

Vitamin A and related compounds, also known as retinoids are thought to play a role in the development of head and neck cancer. We measured levels of the major retinoids, retinol, all-trans retinoic acid, 13-cis retinoic acid and 13-cis-4-oxo retinoic acid in plasma of head and neck cancer patients in comparison with controls without cancer. No differences were found between plasma levels of these retinoids between 25 head and neck cancer patients and 21 controls. Mean baseline levels for the patients were 2458. 6.0, 6.4 and 8.6 nM for retinol, all-trans retinoic acid, 13-cis retinoic acid and 13-cis-4-oxo retinoic acid, respectively. In addition, we selected 10 patients from the chemoprevention trial Euroscan and measured the effect on retinoid levels of 300,000 I.U. daily retinyl palmitate intake during 1 month. Medication caused significant elevations in retinol levels (1.2 fold), all-trans retinoic acid (2.2 fold) and its metabolites 13-cis retinoic acid (5.8 fold) and 13-cis-4-oxo retinoic acid (8.9 fold). Because of its high increase in levels, 13-cis-4-oxo retinoic acid seems a good candidate to serve as a suitable marker to monitor patient compliance in future chemo-prevention trials involving retinoids. No relations were found between the occurrence of side-effects of retinyl palmitate and retinoid levels during treatment. However, the two patients who developed side-effects had the highest pre-treatment levels of 13-cis retinoic acid and 13-cis-4-oxo retinoic acid, suggesting that retinoid toxicity is associated with relatively high basal retinoid metabolism.     

Evaluation of anti-tumour effects of oral fenretinide (4-HPR) in rats with human neuroblastoma xenografts

Neuroblastoma, the most common extracranial solid tumour in children, may undergo spontaneous differentiation or regression, but the majority of metastatic neuroblastomas have poor prognosis despite intensive treatment. Retinoic acid and its analogues regulate growth and differentiation of neuroblastoma cells in vitro, and 13-cis retinoic acid has shown activity against human neuroblastomas in vivo. Fenretinide [N-(4-hydroxyphenyl)retinamide] has been identified as a synthetic retinoid able to induce apoptosis of numerous malignant cell lines in vitro, including neuroblastoma. Furthermore, in animal models, fenretinide has shown chemopreventive and therapeutic efficacy against several malignancies without any obvious signs of toxicity. To investigate the anti-neuroblastoma tumour growth effects of oral fenretinide in vivo we used a human neuroblastoma xenograft model. Nude rats with established neuroblastoma xenograft tumours were treated orally with fenretinide for 10 days. Five different doses of fenretinide were used ranging from 2.5 to 75 mg/rat/day (10-300 mg/kg). Tumour volumes and toxic side effects were monitored during treatment and tumour weights were recorded at autopsy. In this study we found no significant anti-tumour growth effects of fenretinide in vivo, when used as oral treatment of rats with established neuroblastoma xenograft tumours. Furthermore, there were no intra tumoural differences in treated compared to untreated tumours. However, because of the promising results of fenretinide on neuroblastoma growth in vitro, further in vivo studies are warranted using other modalities of drug administration.     

Positive and negative interaction of 1,25-dihydroxyvitamin D3 and the retinoid CD437 in the induction of human melanoma cell apoptosis

The natural ligands of the nuclear receptors vitamin D receptor (VDR) and retinoic acid receptor (RAR), i.e., 1alpha,25-dihydroxyvitamin D3 (VD) and all-trans retinoic acid, have important effects on the proliferation, differentiation and apoptosis of a variety of malignant cells, including melanoma. The therapeutic potential of the 2 nuclear hormones can be enhanced by the use of synthetic analogues. In this study, the 2 human melanoma cell lines WM1341 and MeWo were compared for the combined effect of VD and synthetic retinoids. Both cell lines expressed reasonable amounts of VDR, RARgamma and retinoid X receptor alpha and differed only in the relative expression of RARalpha and beta. From 9 functional variants of retinoids, only the RARgamma-selective retinoid CD437 showed, in both cell lines, a significant anti-proliferative effect. In MeWo cells, but not in WM1341 cells, VD induced growth arrest but showed no synergistic interaction with the effects of CD437. In contrast, VD induced apoptosis in WM1341, but not in MeWo, cells. CD437 was a strong inducer of apoptosis in both melanoma cell lines. Parallel treatment with CD437 and VD resulted in synergistic enhancement of apoptosis in WM1341 cells, whereas a clear decrease in induction of apoptosis in MeWo cells occurred. Our results indicate that a combined treatment of melanoma with VD and selected retinoids is promising but should be adapted to individual types of tumor.     

Differential responses of normal, premalignant, and malignant human bronchial epithelial cells to receptor-selective retinoids.

Using an in vitro lung carcinogenesis model consisting of normal, premalignant, and malignant human bronchial epithelial (HBE) cells, we analyzed the growth inhibitory effects of 26 novel synthetic retinoic acid receptor (RAR)- and retinoid X receptor (RXR)-selective retinoids. RAR-selective retinoids such as CD271, CD437, CD2325, and SR11364 showed potent activity in inhibiting the growth of either normal or premalignant and malignant HBE cells (IC50s mostly <1 microM) and were much more potent than RXR-selective retinoids. Nonetheless, the combination of RAR- and RXR-selective retinoids exhibited additive effects in HBE cells. As the HBE cells became progressively more malignant, they exhibited decreased or lost sensitivity to many retinoids. The activity of the RAR-selective retinoids, with the exception of the most potent retinoid, CD437, could be suppressed by an RAR panantagonist. These results suggest that: (a) RAR/RXR heterodimers play an important role in mediating the growth inhibitory effects of most retinoids in HBE cells; (b) CD437 may act through an RAR-independent pathway; (c) some of the RAR-selective retinoids may have the potential to be used in the clinic as chemopreventive and chemotherapeutic agents for lung cancer; and (d) early stages of lung carcinogenesis may be responsive targets for chemoprevention by retinoids, as opposed to later stages.     

Evidence supporting a role for mitochondrial respiration in apoptosis induction by the synthetic retinoid CD437

Retinoids have been shown to modulate cell proliferation, differentiation, and apoptosis. It is thought that these effects mediate the chemopreventive and therapeutic effects of retinoids. Recently, some synthetic retinoids, including 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437), have been found to induce apoptosis even in tumor cell lines that are resistant to all-trans retinoic acid. The proapoptotic activity of CD437 has been attributed to mitochondrial dysfunction via the induction of mitochondrial permeability transition (P. Marchetti et al., Cancer Res. 59: 6257-6266, 1999). The mechanistic aspects pertaining to how CD437 promotes changes in mitochondrial function are unclear. This study investigated the role of mitochondrial respiration in CD437-induced apoptosis. Human cutaneous squamous cell carcinoma COLO 16 cells were chronically exposed to ethidium bromide to inhibit mitochondrial DNA synthesis and produce respiration-deficient clones. These clones were exposed to CD437 (相似文献   

Increasing the intracellular availability of all-trans retinoic acid in neuroblastoma cells

Recent data indicate that isomerisation to all-trans retinoic acid (ATRA) is the key mechanism underlying the favourable clinical properties of 13-cis retinoic acid (13cisRA) in the treatment of neuroblastoma. Retinoic acid (RA) metabolism is thought to contribute to resistance, and strategies to modulate this may increase the clinical efficacy of 13cisRA. The aim of this study was to test the hypothesis that retinoids, such as acitretin, which bind preferentially to cellular retinoic acid binding proteins (CRABPs), or specific inhibitors of the RA hydroxylase CYP26, such as R116010, can increase the intracellular availability of ATRA. Incubation of SH-SY5Y cells with acitretin (50 microM) or R116010 (1 or 10 microM) in combination with either 10 microM ATRA or 13cisRA induced a selective increase in intracellular levels of ATRA, while 13cisRA levels were unaffected. CRABP was induced in SH-SY5Y cells in response to RA. In contrast, acitretin had no significant effect on intracellular retinoid concentrations in those neuroblastoma cell lines that showed little or no induction of CRABP after RA treatment. Both ATRA and 13cisRA dramatically induced the expression of CYP26A1 in SH-SY5Y cells, and treatment with R116010, but not acitretin, potentiated the RA-induced expression of a reporter gene and CYP26A1. The response of neuroblastoma cells to R116010 was consistent with inhibition of CYP26, indicating that inhibition of RA metabolism may further optimise retinoid treatment in neuroblastoma.     

Bortezomib as a therapeutic candidate for neuroblastoma

Outcomes remain poor in neuroblastoma despite intensive treatment. Agents with potential efficacy can be drawn from anti-neoplastic drugs introduced for other malignancies. Bortezomib, a proteasome inhibitor, modulates cell-signaling molecules leading to apoptosis. Bortezomib, alone and in combination with other agents, was tested across an in vitro panel of neuroblastic, stromal, and chemo-resistant neuroblastoma cell types to determine its effect on cell viability and to assess for interactions between bortezomib and other chemotherapeutic agents that either limit or increase overall response. Each subtype of neuroblastoma was sensitive to bortezomib and killing occurred with EC50 values of approximately 50 nM. When bortezomib was combined with other agents (doxorubicin, etoposide, SN-38, carboplatin, or cisplatin), no antagonism was observed. The bortezomib-doxorubicin combination was especially effective, demonstrating synergy on isobolographic analysis and resulting in a decrease in EC50 from 50 ng/mL with doxorubicin alone to 5 ng/mL with 25 nM bortezomib. Interestingly, the different cell types exhibited varying response patterns to treatment with bortezomib alone and in combination with other drugs suggesting different mechanisms may be engaged. A decision analysis, incorporating these results showing efficacy in all cell types, the synergy obtained in combination, and the available toxicity data, supports a phase II clinical trial of bortezomib in neuroblastoma.     

Mechanisms of apoptosis induced by the synthetic retinoid CD437 in human non-small cell lung carcinoma cells.

The novel synthetic retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) has been shown to induce apoptosis in various tumor cell lines including human non-small cell lung carcinoma (NSCLC) cells, which are resistant to the natural all-trans retinoic acid and to many synthetic receptor-selective retinoids. Although the mechanism of this effect was not elucidated, it was found to be independent of nuclear retinoid receptors. In the present study, we analysed the mechanisms by which CD437 induces apoptosis in two human NSCLC cell lines: H460 with wild-type p53 and H1792 with mutant p53. Both cell lines underwent apoptosis after exposure to CD437, although the cell line with wild-type p53 (H460) was more sensitive to the induction of apoptosis. CD437 increased the activity of caspase in both cell lines, however, the effect was much more pronounced in the H460 cells. The caspase inhibitors (Z-DEVD-FMK and Z-VAD-FMK) suppressed CD437-induced CPP32-like caspase activation and apoptosis in both cell lines. CD437 induced the expression of the p53 gene and its target genes, p21, Bax, and Killer/DR5, only in the H460 cells. These results suggest that CD437-induced apoptosis is more extensive in NSCLC cells that express wild-type p53, possibly due to the involvement of the p53 regulated genes Killer/DR5, and Bax although CD437 can also induce apoptosis by means of a p53-independent mechanism. Both pathways of CD437-induced apoptosis appear to involve activation of CPP32-like caspase.