Differentiating agents in pediatric malignancies: retinoids in neuroblastoma

Ago1 and Ago2 differentially affect cell proliferation, motility and apoptosis when overexpressed in SH-SY5Y neuroblastoma cells

Argonaute are a conserved class of proteins central to the microRNA pathway. We have highlighted a novel and non-redundant function of Ago1 versus Ago2; the two core factors of the miRNA-associated RISC complex. Stable overexpression of Ago1 in neuroblastoma cells causes the cell cycle to slow down, a decrease in cellular motility and a stronger apoptotic response upon UV irradiation. These effects, together with a significant increase in p53 levels, suggest that Ago1 may act as a tumor-suppressor factor, a function also supported by GEO Profiles microarrays that inversely correlate Ago1 expression levels with cell proliferation rates.

Retinoids, retinoic acid receptors, and cancer

Retinoids (i.e., vitamin A, all-trans retinoic acid, and related signaling molecules) induce the differentiation of various types of stem cells. Nuclear retinoic acid receptors mediate most but not all of the effects of retinoids. Retinoid signaling is often compromised early in carcinogenesis, which suggests that a reduction in retinoid signaling may be required for tumor development. Retinoids interact with other signaling pathways, including estrogen signaling in breast cancer. Retinoids are used to treat cancer, in part because of their ability to induce differentiation and arrest proliferation. Delivery of retinoids to patients is challenging because of the rapid metabolism of some retinoids and because epigenetic changes can render cells retinoid resistant. Successful cancer therapy with retinoids is likely to require combination therapy with drugs that regulate the epigenome, such as DNA methyltransferase and histone deacetylase inhibitors, as well as classical chemotherapeutic agents. Thus, retinoid research benefits both cancer prevention and cancer treatment.

From carrot to clinic: an overview of the retinoic acid signaling pathway

Vitamin A is essential for the formation and maintenance of many body tissues. It is also important for embryonic growth and development and can act as a teratogen at critical periods of development. Retinoic acid (RA) is the biologically active form of vitamin A and its signaling is mediated by the RA and retinoid X receptors. In addition to its role as an important molecule during development, RA has also been implicated in clinical applications, both as a potential anti-tumor agent as well as for the treatment of skin diseases. This review presents an overview of how dietary retinoids are converted to RA, hence presenting the major players in RA metabolism and signaling, and highlights examples of treatment applications of retinoids. Moreover, we discuss the origin and diversification of the retinoid pathway, which are important factors for understanding the evolution of ligand-specificity among retinoid receptors.

Effect of cytotoxic agents and retinoic acid on Myc-N protein expression in neuroblastoma

AIM

Neuroblastoma is an important pediatric tumor in which Myc-N amplification is a well-known poor prognostic indicator. It has a great diversity in clinical behavior. The effect of pharmacologic agents used in neuroblastoma treatment on Myc-N expression is still unclear.

METHOD

We analyzed Myc-N expression changes by immunocytochemistry in Myc-N-positive Kelly human neuroblastoma cell line using retinoic acid and cytotoxic drugs (cisplatin, vincristine, cyclophosphamide, etoposide, and doxorubicin) and their combinations compared with control conditions. First, concentration of drugs were determined as LD50 doses. Kelly cells and drugs were incubated for 24 hours in 5% CO2, 37 degrees C in 96-well plates. Myc-N expression was scored semiquantitatively as negative, mild, moderate, or high positive.

RESULTS

Myc-N amplification did not change with any agent or combination. It was higher than 20 copies in all conditions. Myc-N protein expression was high in control and doxorubicin group. It was moderate in retinoic acid, cyclophosphamide, retinoic acid combined with cyclophosphamide and retinoic acid combined with doxorubicin groups. The expression was mild in cisplatin, vincristine, etoposide, retinoic acid combined with etoposide, and retinoic acid combined with cisplatin groups. Myc-N expression was negative in retinoic acid combined with vincristine group.

CONCLUSIONS

Myc-N expression is reduced with cytotoxic agents and retinoic acid in neuroblastoma although Myc-N amplification remains the same. Retinoic acid combined with vincristine is the most effective combination to reduce Myc-N expression. Our results suggest that therapeutic applications of these agents as low dose maintenance therapy might be useful.

All-trans retinoic acid arrests neuroblastoma cells in a dormant state. Subsequent nerve growth factor/brain-derived neurotrophic factor treatment adds modest benefit

BACKGROUND

Therapies aiming at inducing differentiation or apoptosis of neuroblastoma (NB) are an important research topic. Although retinoic acid showed promising antitumoral results, its effects against refractory disease are limited. Putative candidates for combination therapies are nerve growth factor (NGF; Tebu-Bio/Peprotech, Offenbach, Germany) and brain-derived neurotrophic factor (BDNF; Tebu-Bio/Peprotech, Offenbach, Germany) because their receptors are of prognostic clinical value in clinical neuroblastoma. Another clinical prognostic factor is the number of Schwann cells. Substances secreted by Schwann cells proved antitumoral capacities in vitro. The aim of the study was to analyze whether retinoic acid may offer an additional line of attack acting independent from Schwann cells and whether additive treatment with the neurotrophin-receptor ligands NGF/BDNF confers additional benefit.

METHODS

Human SHSY-5Y NB cells were cultured in vitro. After a 7-day all-trans retinoic acid (ATRA; Sigma-Aldrich Chemie, Taufkirchen, Germany) treatment (15 mumol/L of ATRA), NB proliferation was proportional to extinction in dimethyl-thiazol-diphenyltetrazoliumbromide (MTT) tests. Fluorescence-activated cell sorter (FACS) analysis for annexin and propidium iodide determined the degree of apoptosis and necrosis as well as the expression of the Schwann type cell marker S100. The S100 messenger RNA was assessed by reverse transcriptase polymerase chain reaction. In addition, the effect on NB proliferation was investigated when ATRA was combined with a 7-day treatment with NGF or BDNF (10, 50, 100 ng/mL) either before or after the 7-day ATRA treatment.

RESULTS

All-trans retinoic acid reduced proliferation (0.116 +/- 0.006 SEM vs 0.359 +/- 0.010 SEM in the untreated control group; P < .001). After ATRA treatment, 95% +/- 1.82% SEM were still viable, with only 2.61% +/- 1.17% SEM apoptotic and 2.38% +/- 0.69% SEM necrotic cells. All-trans retinoic acid induced a remarkable decrease in S100 expression in FACS (16.91% +/- 1.72% SEM vs 32.33% +/- 2.54% SEM in controls; P = .009). The S100 messenger RNA levels were not increased by ATRA (DeltaDeltaT values: 1.73, 2.77, and 1.43; n = 3). Both NGF and BDNF had only a modest synergistic effect when given after ATRA treatment. No effect was seen when they were administered before ATRA treatment.

CONCLUSIONS

All-trans retinoic proved to be a vigorous inhibitor of NB proliferation in vitro. However, because most NB cells remained viable combination therapies are required. Treatment with NGF and BDNF showed only a modest benefit and did not reflect the strong prognostic impact of tyrosine kinase receptors in clinical NB. The ATRA-induced proliferation arrest is not related to Schwann type subdifferentiation. This suggests that substances secreted by Schwann cells could be possible independent combination partners. We suggest studies using combinations of ATRA and substances secreted by Schwann cells.

p-Dodecylaminophenol derived from the synthetic retinoid, fenretinide: antitumor efficacy in vitro and in vivo against human prostate cancer and mechanism of action

Fenretinide, N-(4-hydroxyphenyl)retinamide (4-HPR) is an aminophenol-containing synthetic retinoid derivative of all-trans-retinoic acid, which is a potent chemopreventive and antiproliferative agent against various cancers. Clinical studies of 4-HPR have shown side effects consisting of night blindness and ocular toxicity. To maintain potent anticancer activity without side effects, p-dodecylaminophenol (p-DDAP) was designed based on structure-activity relationships of 4-HPR. In our study, we investigate whether p-DDAP shows anticancer activity against human prostate cancer cell line PC-3 when compared with 4-HPR. p-DDAP inhibited PC-3 cell growth progressively from low to high concentration in a dose-dependent manner. p-DDAP was the most potent antiproliferative agent in vitro among 6 p-alkylaminophenols and 3 4-hydroxyphenyl analogs examined including 4-HPR. Cells treated with p-DDAP were shown to undergo apoptosis, based on condensation nuclei, cytofluorimetric analysis, propidium iodide staining and the expression of bcl-2 and caspase 3. p-DDAP arrested the S phase of the cell cycle, while 4-HPR arrested the G(0)/G(1) phase. In addition, both the i.v. and i.p. administration of p-DDAP suppressed tumor growth in PC-3-implanted mice in vivo. p-DDAP showed no effects on blood retinol concentrations, in contrast to reductions after 4-HPR administration. These results indicate that p-DDAP exhibits excellent anticancer efficacy against hormonal independent prostate cancer in vitro and in vivo, and it may have great potential for clinical use in the treatment of prostate cancer with reduced side effects.

ArrayCGH-based classification of neuroblastoma into genomic subgroups

High-resolution array comparative genomic hybridization (arrayCGH) profiling was performed on 75 primary tumors and 29 cell lines to gain further insight into the genetic heterogeneity of neuroblastoma and to refine genomic subclassification. Using a novel data-mining strategy, three major and two minor genomic subclasses were delineated. Eighty-three percent of tumors could be assigned to the three major genomic subclasses, corresponding to the three known clinically and biologically relevant subsets in neuroblastoma. The remaining subclasses represented (1) tumors with no/few copy number alterations or an atypical pattern of aberrations and (2) tumors with 11q13 amplification. Inspection of individual arrayCGH profiles showed that recurrent genomic imbalances were not exclusively associated with a specific subclass. Of particular notice were tumors with numerical imbalances typically observed in subtype 1 neuroblastoma, in association with genomic features of subtype 2A or 2B. A search for prognostically relevant genomic alterations disclosed 1q gain as a predictive marker for therapy failure within the group of subtype 2A and 2B tumors. In cell lines, a high incidence of 6q loss was observed, with a 3.87-5.32 Mb region of common loss within 6q25.1-6q25.2. Our study clearly illustrates the importance of genomic profiling in relation to tumor behavior in neuroblastoma. We propose that genome-wide assessment of copy number alterations should ideally be included in the genetic workup of neuroblastoma. Further multicentric studies on large tumor series are warranted in order to improve therapeutic stratification in conjunction with other features such as age at diagnosis, tumor stage, and gene expression signatures.

A rapid, sensitive and selective liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry method for determination of fenretinide (4-HPR) in plasma

A simple and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method using an atmospheric pressure chemical ionization source (APCI) for the quantification of fenretinide (4-HPR) in mouse plasma was developed and validated. After a simple protein precipitation of plasma sample by acetonitrile, 4-HPR was analyzed by LC-APCI-MS/MS. High-performance liquid chromatography (HPLC) separation was conducted on a Hypurity C18 column (50mmx2.1mm, 5microm) with a flow rate 0.60mL/min using a gradient mobile phase comprised of 0.05% formic acid in water (A) and methanol (B), and a run time of 4.5min. The elimination of a tedious sample preparation process and a shorter run time substantially reduced total analysis time. The method was linear over the range 0.5-100ng/mL, with r>0.998. The intra- and inter-assay precisions were 1.4-9.2% and 5.1-8.2%, respectively, and the intra- and inter-assay accuracies were 93.9-98.6% and 92.7-95.3%, respectively. The absolute recoveries were 90.3% (1.5ng/mL), 97.0% (7.5ng/mL) and 92.1% (75.0ng/mL) for 4-HPR, and 99.1% for the internal standard (150ng/mL). The analytical method had excellent sensitivity using a small sample volume (30microL) with the lower limit of quantification (LLOQ) 0.5ng/mL. This method is robust and has been successfully employed in a pharmacokinetic study of 4-HPR in a mouse xenograft model of neuroblastoma.

Neuroblastoma

The clinical hallmark of neuroblastoma is heterogeneity, with the likelihood of cure varying widely according to age at diagnosis, extent of disease, and tumour biology. A subset of tumours will undergo spontaneous regression while others show relentless progression. Around half of all cases are currently classified as high-risk for disease relapse, with overall survival rates less than 40% despite intensive multimodal therapy. This Seminar focuses on recent advances in our understanding of the biology of this complex paediatric solid tumour. We outline plans for the development of a uniform International Neuroblastoma Risk Group (INRG) classification system, and summarise strategies for risk-based therapies. We also update readers on new discoveries related to the underlying molecular pathogenesis of this tumour, with special emphasis on advances that are translatable to the clinic. Finally, we discuss new approaches to treatment, including recently discovered molecular targets that might provide more effective treatment strategies with the potential for less toxicity.

Retinoic acid elicits cytostatic, cytotoxic and immunomodulatory effects on uveal melanoma cells

The current therapy of uveal melanoma (UM) metastases remains inefficient, which warrants the development of new treatment modalities. For the first time we investigated the effects of retinoic acid (RA) on a panel of UM cell lines and found that RA induces morphological changes compatible with differentiation, suppresses proliferation and causes apoptosis in these cells. RA treatment resulted in an increase of p21, p27 and p53 protein levels and G1 arrest in UM cells, which correlated with significant down-modulation of surface Her2/neu proto-oncogene expression. In addition, RA-treated UM cells exhibited increased sensitivity to both MHC class I-restricted killing by cytotoxic T lymphocytes and NK cell-mediated lysis that were accompanied by more efficient conjugate formation between UM cells and killer lymphocytes. Taken together, our results implicate UM as a new target for treatment with retinoids and suggest that retinoids and T- or NK-cell based immunotherapy can have mutually enhancing effects in UM patients.

Potent anticancer activities of novel aminophenol analogues against various cancer cell lines

Novel aminophenol analogues were synthesized based on the structure of fenretinide (N-(4-hydroxyphenyl)retinamide, 5), which is a potent anticancer agent. Our findings showed that the anticancer activities of 5 were due to the side chain attached to the aminophenol moiety. A p-octylaminophenol (p-OAP) provided the most potent anticancer activity among p-alkylaminophenols examined. In this study, we investigated anticancer activities against various cancer cell lines by the new aminophenols, p-dodecylaminophenol (1), p-decylaminophenol (2), N-(4-hydroxyphenyl)dodecananamide (3), and N-(4-hydroxyphenyl)decananamide (4), which exhibits a side chain as long as 5. Cell growth of breast cancer (MCF-7, MCF-7/Adr(R)), prostate cancer (DU-145), and leukemia (HL60) cells was suppressed by 1 and 2 in a fashion dependent on the length of the alkyl chain attached to the aminophenol. In contrast, 3 and 4 were extremely weak. Compound 5 was less potent than 1. Cell growth of liver cancer (HepG2) was not markedly affected by these compounds. In addition, apoptosis of HL60 cells was induced by 1 and 2 in a chain length-dependent manner, but not by 3 and 4. Incorporation of compounds into HL60 cells was in the order 1>2=3>4. These results indicated that anticancer activities for 1 and 2 are correlated with their incorporation into cancer cells and their capability to induce apoptosis, but not for 3 and 4. Compound 1, a potent anticancer agent with potency strikingly greater than 5, may potentially be useful in clinic.

Retinol induces the ERK1/2-dependent phosphorylation of CREB through a pathway involving the generation of reactive oxygen species in cultured Sertoli cells

The ability to regulate cell cycle progression and apoptosis through the activation of nuclear receptors and gene transcription has been generally accepted as a potential chemopreventive and therapeutic property of retinoids. However, recent studies suggest that retinol and related compounds can exert rapid and non-genomic effects, which may increase the production of reactive oxygen species (ROS) and lead to cell cycle disruption and malignant transformation. In this work, we report that, in Sertoli cells, retinol (7 microM) induces the Src-dependent activation of ERK1/2 MAPK and the ERK1/2-mediated phosphorylation of the transcription factor CREB. We found that these retinol-induced effects were completely blocked by the antioxidant Trolox 100 microM (a hydrophilic analogue of alpha-tocopherol), the hydroxyl radical scavenger mannitol (1 mM) and the addition of native superoxide dismutase (200 U/ml), and also that retinol increased the production of ROS and several other parameters indicative of oxidative stress during the same incubation periods in which ERK1/2 and CREB were phosphorylated. The activation of the ERK1/2-CREB pathway appears to be involved in the onset of some of the malignant effects caused by retinol in Sertoli cells since inhibition of ERK1/2 activation blocked the retinol-induced cell transformation and proliferation.

Antioxidant and anticancer activities of novel p-alkylaminophenols and p-acylaminophenols (aminophenol analogues)

Novel compounds were designed based on fenretinide, N-(4-hydroxyphenyl)retinamide (2), which is a synthetic amide of all-trans-retinoic acid (1) that is a potent antioxidant and anticancer agent. Our recent findings indicated that antioxidant and anticancer activities were due to p-methylaminophenol moiety (8) in 2, and that p-octylaminophenol (7), which has an elongated alkyl chain, was more potent than 8. This finding lets us to investigate whether compounds containing alkyl or acyl chains linked to an aminophenol residue as long as 2 and 1, would show activities greater than 2. For this purpose, we prepared p-dodecanoylaminophenol (3), p-decanoylaminophenol (4), p-dodecylaminophenol (5), and p-decylaminophenol (6). The p-alkylaminophenols, 5 and 6, exhibited superoxide scavenging activities, but not p-acylaminophenols, 3 and 4. Elongation of the alkyl chain length reduced superoxide trapping capability (8>7>6>5). In contrast, lipid peroxidation in rat liver microsomes was reduced by 5 and 6 in dose-dependent manner. Compounds 3 and 4 were poor lipid peroxidation inhibitors, being approximately 400- to 1300-fold lower than 5 and 6. In addition, all compounds inhibited cell growth of human leukemia cell lines, HL60 and HL60R, in dose-dependent manners (5>6>3=4). The HL60R cell line is resistant against 1. Growth of both cell lines was suppressed by 5 and 6 in a fashion dependent on the length of the aminophenol alkyl chain, but not by 3 and 4. These results indicate that 5, a potent anticancer agent greater than 2, may potentially have clinical utility, and that its anticancer activity is correlated with inhibitory potency against lipid peroxidation, but not with superoxide scavenging activity.

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

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

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.

Anticancer and superoxide scavenging activities of p-alkylaminophenols having various length alkyl chains

A series of p-alkylaminophenols including 3, p-butylaminophenol; 4, p-hexylaminophenol; 5, p-octylaminophenol; and 6, N-(p-methoxybenzyl)aminophenol were synthesized based on the structure of fenretinide, N-(4-hydroxyphenyl)retinamide (1). This latter agent is a synthetic amide of all-trans-retinoic acid (RA), which is a cancer chemopreventive and antiproliferative agent. It was found that elongation of the alkyl chain length in these compounds increased antioxidative activity and inhibition of lipid peroxidation. These findings led us to investigate whether antiproliferative activity against cancer cells was effected by the length of alkyl chains linked to the aminophenol residue. All p-alkylaminophenols inhibited growth of HL60 and HL60R cells in a dose-dependent manners. The HL60R line is a resistant clone against RA. Growth of various cancer cell lines (HL60, HL60R, MCF-7, MCF-7/Adr(R), HepG2, and DU-145) was suppressed by p-alkylaminophenols in a fashion dependent on the aminophenol alkyl chain length (5>4>3>p-methylaminophenol (2)), with 5 being the most potent inhibitor of cell growth against HL60R, MCF-7/Adr(R), and DU-145 cells among p-alkylaminophenols tested, including 1. In particular, with the exception of compound 2, antiproliferative activity against DU-145 cells by these p-alkylaminophenols was greater than by 1. In HL60 cells, growth inhibition was associated with apoptosis. On the other hand, elongation of the alkyl chain length reduced superoxide trapping capability (2>3>4>5) in contrast to the effects on inhibition of lipid peroxidation. These results indicate that anticancer activity of p-alkylaminophenols correlated with the inhibitory activity of lipid peroxidation, but not with the superoxide scavenging activity.

Factores de riesgo para el neuroblastoma

INTRODUCTION

NB is the most frequent pediatric cancer arising in the sympathetic nervous system and represents a serious healthcare challenge because: 1) it is the most frequent neoplasm in the first decades of life; 2) it biological behavior is unpredictable (spontaneous regression, maturation to ganglioneuroma, and localized and metastasized variants); and 3) little is known about most of the risk factors involved in its etiopathogenesis. The objective of this study was to disseminate knowledge of constitutional and environmental (physical, chemical, biological and social) risk factors linked to the development of neuroblastoma (NB), with various levels of scientific evidence. To seek collaboration among pediatricians in the research project "Environment and Pediatric Cancer".

MATERIAL AND METHODS

We performed a systematic review of the literature published in the previous 25 years on risk factors for NB diagnosed in the first two decades of life, using Medline, the Science Citation Index and Embase. Search profiles were: "neuroblastoma/childhood sympathetic nervous system neoplasms and risk factors/etiology/epidemiology". The most interesting articles and the most relevant references contained therein were selected.

RESULTS

With greater or lesser scientific evidence, the following risk factors increase the risk of developing NB: genetic factors; geographic factors; ethnic factors; socioeconomic factors; infectious factors; physical factors; parental occupational exposure; gestational factors; and perinatal and maternal factors. Preventive factors associated with a lower risk of developing NB are breastfeeding and intake of vitamin supplements during pregnancy.

CONCLUSIONS

The main barriers to the identification of evidence-based risk factors involved in the development of NB are its complex biology and clinical course, its relative rarity and the difficulty of performing epidemiological studies. Research on constitutional and environmental factors involved in its etiopathogenesis should be stimulated. The best preventive strategy is to recommend breastfeeding for more than 6 months.

Results of a Phase I study utilizing monocyte-derived dendritic cells pulsed with tumor RNA in children with Stage 4 neuroblastoma

BACKGROUND

A Phase I study of 11 pediatric patients with newly diagnosed, Stage 4 neuroblastoma was conducted using monocyte-derived dendritic cells (DC) pulsed with tumor RNA to produce antitumor vaccines (DC(RNA)).

METHODS

Patients received two courses of induction with carboplatin followed by standard chemotherapy, surgery, radiation, high-dose therapy, stem cell rescue, and DC(RNA) vaccine therapy.

RESULTS

The results showed that this method for producing and administering DC(RNA) from a single leukapheresis product was both feasible and safe in this pediatric neuroblastoma population. Two courses of carboplatin maintained lymphocyte counts at normal levels. However, immune function 6 weeks after high-dose chemotherapy and stem cell rescue and prior to receiving DC(RNA) was impaired in all patients tested. There was an alteration in the ratio of CD4-positive and CD80-positive T cells. CD4-positive cell numbers were below normal, whereas CD8-positive cell numbers were above normal for all patients. In addition, CD19-positive cell numbers were below normal for all but one patient. It was found that humoral responses to recall antigens (diphtheria and tetanus) and cellular responses to mitogen and recall antigens were below normal in most patients. Despite this, two of three patients tested showed a tumor-specific humoral immune response to DC(RNA). Among the patients who had measurable disease at the time of DC(RNA) vaccine, none showed any objective tumor response.

CONCLUSIONS

DC(RNA) vaccines were both safe and feasible in children with Stage 4 neuroblastoma. Humoral responses to tumor were detected, although remained immunosuppressed at the time of administration, limiting efficacy.

Effect of cytochrome P450 inhibitors (diethyl dithiocarbamate, ketoconazole and grapefruit juice) on the pharmacokinetics of all-trans-retinoic acid

Diethyl dithiocarbamate (DEDTC) has been reported to be a more powerful inhibitor of all-trans-retinoic acid (ATRA) in vitro metabolism than the well-established cytochrome P450 (CYP) inhibitor ketoconazole (KC). In recent years grapefruit juice (GJ) has been shown to be able to increase the oral bioavailability of several drugs by inhibiting intestinal CYP. This study investigated the in vivo effect of these CYP inhibitors on the pharmacokinetics of ATRA. The latter was administered to rats as a constant-rate intravenous (i.v.) infusion (0.48 mg h(-1) kg(-1)) during 10 h and orally (1.6 mg kg(-1)). DEDTC (320 mg kg(-1) x 2 i.v., 6.4 and 32 mg kg(-1) per os (p.o.)) did not change the ATRA concentration-time profiles, whereas KC (320 and 32 mg kg(-1) p.o.)--with i.v. infused or orally dosed ATRA--increased the mean concentration-time curve value by 160% and 78%, respectively. A high dose of DEDTC (320 mg kg(-1) p.o.) caused a marked decrease in plasma levels of ATRA. GJ (6.4 ml kg(-1) p.o.) did not affect the plasma levels of ATRA. It is concluded that the in vivo effect of CYP inhibitors (DEDTC and KC) on the elimination rate of ATRA is qualitatively different from that expected from in vitro studies.

Pediatric neuroblastomas: genetic and epigenetic 'danse macabre'

Neuroblastomas are the most frequently occurring solid tumors in children under 5 years. Spontaneous regression is more common in neuroblastomas than in any other tumor type, especially in young patients under 12 months. Unfortunately, the full clinical spectrum of neuroblastomas also includes very aggressive tumors, unresponsive to multi-modality treatment and accounting for most of the pediatric cancer mortalities under 5 years of age. It is generally emphasized that more than one biological entity of neuroblastoma exists. Structural genetic defects such as amplification of MYCN, gain of chromosome 17q and LOH of 1p and several other chromosomal regions have proven to be valuable as prognostic factors and will be discussed in relation to their clinical relevance. Recent research is starting to uncover important molecular pathways involved in the pathogenesis of neuroblastomas. The aim of this review is to discuss several important aspects of the biology of the neuroblast, such as the role of overexpressed oncogenes like MYCN and cyclin D1, the mechanisms leading to decreased apoptosis, like overexpression of BCL-2, survivin, NM23, epigenetic silencing of caspase 8 and the role of tumor suppressor genes, like p53, p73 and RASSF1A. In addition, the role of specific proteins overexpressed in neuroblastomas, such as the neurotrophin receptors TrkA, B and C in relation to spontaneous regression and anti-angiogenesis will be discussed. Finally, we will try to relate these pathways to the embryonal origin of neuroblastomas and discuss possible new avenues in the therapeutic approach of future neuroblastoma patients.

Retinoic acid-induced neuritogenesis of human neuroblastoma SH-SY5Y cells is ERK independent and PKC dependent

Retinoic acid (RA), an active metabolite of vitamin A, is a natural morphogen involved in development and differentiation of the nervous system. To elucidate signaling mechanisms involved in RA-induced neuritogenesis, we used human neuroblastoma SH-SY5Y cells, an established in vitro model for studying RA action, to examine the role of extracellular signal-regulated kinase (ERK) 1 and 2 in RA-induced neuritogenesis and cell survival. From immunoblotting experiments, we observed that RA induced delayed but persistent ERK1 and ERK2 phosphorylation (until 96 hr) that was reduced significantly by the specific mitogen-activated protein kinase (MAPK)/ERK kinase (MEK) inhibitor U0126. For the subsequent studies we chose 24 hr as the reference time. Inhibition of ERK activation did not affect RA-induced neuritogenesis (percentage of neurite-bearing cells and neurite length) but significantly reduced cell survival. In addition, we analyzed the signaling pathway that mediates ERK activation. Our results suggest that RA-induced ERK phosphorylation does not follow the classic Raf kinase-dependent pathway. Protein kinase C (PKC) and phosphatidylinositol 3-kinase (PI 3-K) are possible alternative kinases involved in the ERK signaling pathway. In fact, in the presence of the specific PKC inhibitor GF 109203X, or the specific PI 3-K inhibitor wortmannin, we observed a significant dose-dependent reduction in ERK phosphorylation. RA-induced neuritogenesis and cell survival were reduced by GF 109203X in a concentration-dependent manner. These results suggest that rather than ERK1 and ERK2, it is PKC that plays an important role during early phases of RA-induced neuritogenesis.

Potent cytotoxic effects of novel retinamide derivatives in ovarian cancer cells

4-(N-Hydroxyphenyl)retinamide (also known as 4-HPR or fenretinide), a synthetic amide of all-trans retinoic acid (RA), has been implicated as a promising anticancer agent associated with reducing the toxicity related to RA. However, the low plasma levels of 4-HPR in patients limited clinical trials, leading to a search for derivatives with better efficacy. In this study, we synthesized a series of 4-HPR derivatives in good yields by introducing acetate (compound 1). propionate (2). pyruvate (3). butyrate (4). or stearate (5). to the 4-hydroxylphenyl moiety of 4-HPR. In our initial proliferation assays, we identified compound 3 as the most cytotoxic of the series against four ovarian cancer cell lines (OVCAR-3, PA-1, 2774, and SKOV-3). Dose-response curves yielded IC(50) values of 3.75-7.75 microM for AtRA, 2.80-5.50 microM for 9-cis RA, 0.65-4.05 microM for 4-HPR, and 0.25-0.75 microM for compound 3, depending on the cell type treated. Nuclear staining with 4',6-diamidino-2-phenylindole (DAPI) and DNA fragmentation assays clearly indicated that the antiproliferative effect of compound 3 was mediated by apoptosis. In contrast to natural retinoids, both 4-HPR and compound 3 activated two (RARbeta and RARgamma) of the three retinoic acid receptor (RAR) subtypes tested, but did not activate any of the three retinoid X receptors (RXRs), as determined by transcription assays in OVCAR-3 cells. However, like natural retinoids, 4-HPR and compound 3 actively suppressed c-Jun transcriptional activity. Thus, compound 3 not only showed more potent antiproliferative activity than any other retinoid derivatives tested, but also effectively inhibited the c-Jun activity that has been implicated in tumor promotion and invasion. These results, together with compound 3's selectivity for RAR subtypes, suggest that compound 3 could be an effective anticancer drug for ovarian cancer, with less toxicity than RA.

Pharmacokinetics of the time-dependent elimination of all-trans-retinoic acid in rats

The time-dependent elimination kinetics of all-trans-retinoic acid (ATRA) has been associated with autoinduction of its metabolism and has led to the hypothesis that rapid development of acquired clinical resistance to ATRA may be prevented by coadministration of metabolic inhibitors. This study in rats was performed to investigate the pharmacokinetics and onset of time-dependent elimination of ATRA, with the purpose of establishing an animal model suitable for in vivo preclinical studies of compounds capable of inhibiting ATRA metabolism. After the intravenous (IV) bolus administration of single doses of ATRA (1.60 mg kg(-1) and 0.40 mg kg(-1)), the plasma concentration-time curves showed an accelerated decline at 180 minutes after dosing. The plasma clearance (Cl) of ATRA, determined after IV administration of a second dose (1.60 mg kg(-1)), at 180 minutes was greater than Cl after a single dose, thus indicating the existence of a time-dependent elimination process detectable 180 minutes after administration of the first dose. Such time-dependent elimination was confirmed by means of an IV constant-rate infusion of 0.48 mg h(-1) kg(-1) of ATRA during 10 hours. Peak plasma ATRA concentration was achieved at 180 minutes, after which the plasma concentration decreased to reach a much lower apparent steady-state drug concentration at 420 minutes. The area under the plasma concentration-time curve (AUC) obtained after oral administration of a second ATRA dose (1.60 mg kg(-1)) was approximately 8% of the AUC obtained after a single oral dose; consistent with a time-dependent increase in the elimination of ATRA, as was observed after IV administration.

Potent effect of 5-HPBR, a butanoate derivative of 4-HPR, on cell growth and apoptosis in cancer cells

Fenretinide, 4-(N-hydroxyphenyl) retinamide (4-HPR), has demonstrated anticancer activity associated with a favorable toxicity profile and is now being investigated in several clinical trials. However, its plasma levels in patients have been far lower than the effective concentration required to induce apoptosis (usually 10 microM). This result has led to the synthesis of derivatives with better efficacy. Sodium butyrate's potential as an anticancer agent prompted us to synthesize a butanoate derivative of 4-HPR, 5-hydroxyphenyl butanoate retinamide (5-HPBR) and compare it to the parent compound for antitumor potential in vitro. The cytotoxicity of 5-HPBR was 2- to 6-fold greater than that of 4-HPR against cancer cell lines derived from various tissues. In premalignant bronchial cells (BEAS2B), 5-HPBR exhibited about a 10-fold stronger cytotoxicity than did 4-HPR. Normal CHANG liver cells were unaffected by either 4-HPR or 5-HPBR. Subsequent assays using DNA fragmentation, DAPI staining, FACS and Western blotting suggested that the potent inhibitory effect of 5-HPBR is mediated by apoptosis; the exact mechanism appears to differ among cancer cell types. In transcription assays with COS-1 cells, 5-HPBR selectively activated RARbeta and RARgamma but was a weaker ligand for all 3 subtypes of RAR than either all-trans retinoic acid or 4-HPR. Overall, these data suggest that 4-BHPR may be a promising retinoid with enhanced antitumor activity and reduced toxicity.

Involvement of endogenous ceramide in the inhibition of telomerase activity and induction of morphologic differentiation in response to all-trans-retinoic acid in human neuroblastoma cells

In this study, we examined the role of endogenous ceramide in the inhibition of telomerase and induction of morphologic differentiation in response to all-trans-retinoic acid (ATRA) in the SK-N-SH and SK-N-AS human neuroblastoma cell lines. The results showed that ATRA inhibited the activity of telomerase significantly in a time- and dose-dependent manner, as determined by telomere repeat amplification protocol (TRAP). The inhibition of telomerase by ATRA was maximum (about 50-80% of untreated controls) at 5-10 microM for 4-8 days. Treatment of cells with ATRA (5 microM) also resulted in the inhibition of growth by about 30-70% after 4 and 8 days of treatment, respectively, which was measured by trypan blue exclusion method. Measurement of accumulation of endogenous ceramide by high pressure liquid chromatography coupled with mass spectroscopy (LC/MS) showed that treatment of cells with ATRA resulted in increased levels of mainly C24:0 and C24:1 ceramides at days 2, 4, and 8, respectively. Also, treatment of cells with ATRA in the presence of myriocin blocked the accumulation of ceramide significantly, and more importantly, presence of myriocin partially prevented the inhibition of telomerase. Mechanistically, inhibition of telomerase by endogenous ceramide in response to ATRA treatment involves, at least in part, down-regulation of the expression of telomerase reverse transcriptase (hTERT) mRNA, as determined by semi-quantitative RT-PCR, in these cells. In addition, the modulation of telomerase activity by ATRA correlated with the induction of morphologic differentiation, which was also blocked by myriocin, as determined by extension of neurites using phase-contrast microscopy. These results, therefore, reveal an important effect of ATRA on telomerase inhibition and induction of morphologic differentiation in human neuroblastoma cells. These data also demonstrate that endogenous ceramide is one of the upstream regulators of telomerase activity in human neuroblastoma cells in response to ATRA.

Effects on M5076-hepatic metastasis of retinoic acid and N-(4-hydroxyphenyl) retinamide, fenretinide entrapped in SG-liposomes

Retinoic acid (RA), a potent inducer of cell differentiation, and N-(4-hydroxyphenyl)retinamide (4-HPR, fenretinide), a potent inducer of apoptosis, are well known as anticancer agents that are administered orally to patients for leukemia, breast and prostate cancer, respectively. However, it has not been studied whether both retinoids are effective on metastatic cancer. In mice implanted with M5076 cells, murine reticulum cell sarcoma survival times were prolonged by i.v. treatment of RA and 4-HPR entrapped in liposomes containing soybean-derived sterylglucoside mixture (SG), which accumulates in liver. In contrast, free RA and 4-HPR were inactive. These results indicate that RA and 4-HPR in SG-liposomes exhibit anticancer efficacy on metastatic cancers, and may have great potential for clinical use in the treatment of various cancers.

Specificity of photosensitizer accumulation in undifferentiated versus differentiated colon carcinoma cells

The relationship between tumor cell differentiation and photosensitizer accumulation used in PDT is poorly defined. In the present work, specific cell differentiation of colon carcinoma CT26 cells induced by sodium butyrate was manifested by morphological changes, proliferation and protein expression and was correlated with the accumulation of endogenous and exogenous photosensitizes. Reduced accumulation of the endogenous protoporphyrin IX and the exogenous hypericin and MC540 was detected in differentiated cells. In contrast, a differentiation-dependent increase was measured with TPPS4, TMPyP, the pheophorbides (C5, C6, C12), HypS4 and helianthrone. In conclusion, PpIX, Hypericin and MC540 show specific binding and accumulation in poorly differentiated tumors, giving these tumors tissue-specific advantage in photo-diagnostic PDT applications.

Differentiation of human retinal pigment epithelial cells into neuronal phenotype by N-(4-hydroxyphenyl)retinamide

ARPE-19, a human retinal pigment epithelial (RPE) cell line, has been widely used in studies of RPE function as well as gene expression. Here, we report the novel finding that N-(4-hydroxyphenyl)retinamide (fenretinide), a synthetic retinoic acid derivative and a potential chemopreventive agent against cancer, induced the differentiation of ARPE-19 cells into a neuronal phenotype. The treated cells lost their epithelial phenotype and exhibited a typical neuronal shape with long processes (four to five times longer than the cell body). The onset of fenretinide-induced neuronal differentiation was dose and time dependent, started within 1-2 days, and lasted at least 4 weeks. Immunohistochemical studies indicated that the expression of neurofilament proteins (NF160 and NF200), calretinin and neural cell adhesion molecule was increased in these differentiated cells. Western blot analysis indicated that cellular retinaldehyde-binding protein, which is normally expressed in RPE cells, was decreased in treated cells. Protein analysis on a two-dimensional gel followed by matrix-assisted laser desorption ionization-time of flight mass spectrometric analysis demonstrated that heat-shock protein 70 was increased after fenretinide treatment. Thus, fenretinide, a synthetic retinoid, is able to induce neuronal differentiation of human RPE cells in culture.

N-(4-hydroxyphenyl)retinamide inhibits retinoblastoma growth through reactive oxygen species-mediated cell death

Retinoblastoma arises from a subset of developing retinal cells lacking the RB-1 gene product pRB, which have lost the ability to respond to apoptotic signals. A better understanding of retinoblastoma biological response to therapeutic agents with low toxicity could improve the development of novel approaches for treatment and prevention of the disease. Naturally occurring retinoids inhibit growth and induce differentiation of Y79 human retinoblastoma cells in vitro. The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) has been shown to induce apoptosis and/or necrosis of tumor cells of neuroectodermal origin. We examined the sensitivity of Y79 retinoblastoma cells to 4HPR in vitro, and in a xenograft model of tumor growth in nude mice in vivo. 4HPR treatment in the range 2.5 to 10 microM induced a loss of Y79 cell viability, as determined by crystal violet, trypan blue exclusion, and long-term clonogenic assays, and impairment of mitochondrial function detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Reactive oxygen species were elevated in 4HPR-treated cells and antioxidants rescued cell viability, indicating that 4HPR-induced cell death was mediated by oxidative stress. 4HPR inhibited growth of Y79 xenografts in vivo in both chemoprevention and intervention settings. Tumor growth inhibition by 4HPR was also associated with significant inhibition of angiogenesis in vivo. These findings could have an important translational value for chemoprevention or early intervention in the treatment of retinoblastoma.

Neuroblastoma: biological insights into a clinical enigma

Neuroblastoma is a tumour derived from primitive cells of the sympathetic nervous system and is the most common solid tumour in childhood. Interestingly, most infants experience complete regression of their disease with minimal therapy, even with metastatic disease. However, older patients frequently have metastatic disease that grows relentlessly, despite even the most intensive multimodality therapy. Recent advances in understanding the biology and genetics of neuroblastomas have allowed classification into low-, intermediate- and high-risk groups. This allows the most appropriate intensity of therapy to be selected - from observation alone to aggressive, multimodality therapy. Future therapies will focus increasingly on the genes and biological pathways that contribute to malignant transformation or progression.

Activation of the phosphatidylinositol 3-kinase/Akt signaling pathway by retinoic acid is required for neural differentiation of SH-SY5Y human neuroblastoma cells

Retinoic acid (RA) induces neural differentiation of SH-SY5Y neuroblastoma cells. We show that the mRNA levels of the differentiation-inhibiting basic helix-loop-helix transcription factors ID1, ID2, and ID3 are down-regulated during RA-induced differentiation of SH-SY5Y cells. The levels of ID proteins decreased in parallel to the observed transcriptional repression. The expression of other basic helix-loop-helix genes changed during RA-induced differentiation: expression of neuroblast-specific ASCL1 (HASH-1) gene was promptly reduced after RA treatment, whereas expression of differentiation-promoting genes NEUROD6 (NEX-1, HATH-2) and NEUROD1 was increased. Treatments with 12-O-tetradecanoylphorbol-13-acetate, another inducer of neuroblastoma cell differentiation, also resulted in coordinated down-regulation of ID gene expression, underscoring the role of ID genes in differentiation. Down-regulation of ID gene expression by RA involves a complex mechanism because full transcriptional repression required newly synthesized proteins and signaling by phosphatidylinositol 3-kinase (PI3K). RA treatment activates the PI3K/Akt signaling pathway, resulting in increased PI3K activity in extracts from RA-treated cells and a rapid increase in phosphorylation of Akt in Ser-473. Inhibition of PI3K by LY294002 impaired RA-induced differentiation, as assessed by morphological and biochemical criteria. We propose that RA, by activating the PI3K/Akt signaling pathway, plays an important role in the regulation of neuronal cell survival.

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.

Retinoid therapy of childhood cancer

In vitro studies that showed RA could cause growth arrest and differentiation of myelogenous leukemia and neuroblastoma led to clinical trials of retinoids in APL and neuroblastoma that increased survival for both of those diseases. In the case of APL, ATRA has been the drug of choice, and preclinical and clinical data support direct combinations of ATRA with cytotoxic chemotherapy. For neuroblastoma, a phase I study defined a dose of 13-cis-RA, which was tolerable in patients after myeloablative therapy, and a phase III trial that showed postconsolidation therapy with 13-cis-RA improved EFS for patients with high-risk neuroblastoma. Preclinical studies in neuroblastoma indicate that ATRA or 13-cis-RA can antagonize cytotoxic chemotherapy and radiation, so use of 13-cis-RA in neuroblastoma is limited to maintenance after completion of cytotoxic chemotherapy and radiation. A limitation on the antitumor benefit of ATRA in APL is the marked decrease in drug levels that occurs during therapy as a result of induction of drug metabolism, resulting in a shorter drug half-life and decreased plasma levels. Although early studies sought to overcome the pharmacologic limitations of ATRA therapy in APL, the demonstration that ATO is active against APL in RA-refractory patients has led to a focus on studies employing ATO. Use of 13-cis-RA in neuroblastoma has avoided the decreased plasma levels seen with ATRA. It is likely that recurrent disease seen during or after 13-cis-RA therapy in neuroblastoma is due to tumor cell resistance to retinoid-mediated differentiation induction. Studies in neuroblastoma cell lines resistant to 13-cis-RA and ATRA have shown that they can be sensitive, and in some cases collaterally hypersensitive, to the cytotoxic retinoid fenretinide. Fenretinide induces tumor cell cytotoxicity rather than differentiation, acts independently from RA receptors, and in initial phase I trials has been well tolerated. Clinical trials of fenretinide, alone and in combination with ceramide modulators, are in development.

Distinct mechanisms of cell cycle arrest control the decision between differentiation and senescence in human neuroblastoma cells

Retinoic acid (RA) induces cell cycle arrest and differentiation of human neuroblastoma (NB) cells. Typically, NB cells differentiate along the neuronal lineage, but quiescent, "flat" cell types frequently have been described after treatment with differentiating agents. Two indistinguishable subclones of the cell line SK-N-SH, SK-N-SH-N (SH-N) and SK-N-SH-F (SH-F), display dramatically different responses to RA. In SH-N, RA induces neuronal differentiation, but in SH-F it transforms the small neuroblastic cells into large, flattened, epithelium-like cells. Here we analyze the mechanistic basis for the different effects of RA in the two NB subclones. First, we show that the flattened RA-treated SH-F expresses markers of cells undergoing replicative senescence. Inhibition of DNA synthesis by RA is significantly more rapid in SH-F than in SH-N. SH-F, which expresses basal amounts of p16(INK4A), responds to RA with elevation of p18(INK4C), marked down-regulation of cyclin D1, and swift inhibition of cyclin D-dependent kinases (cdks). Conversely, after addition of RA, SH-N retains cell cycling due to high expression of cyclin D1, the absence of Ink4 inhibitors, and accumulation of p21(Cip1). These changes result in sustained cdk activity. Accordingly, overexpression of p21(Cip1) but not p16(INK4A) induces neuronal differentiation of untreated NB cells. We propose that rapid inhibition of cdks by RA in NB leads to early cell cycle arrest, prevents neuronal differentiation, and results in a senescence-like state.