N-(4-hydroxyphenyl)retinamide: a potent inducer of apoptosis in human neuroblastoma cells

Design, Synthesis, Radiosynthesis and Biological Evaluation of Fenretinide Analogues as Anticancer and Metabolic Syndrome-Preventive Agents

Fenretinide (4-HPR) is a synthetic derivative of all-trans-retinoic acid (ATRA) characterised by improved therapeutic properties and toxicological profile relative to ATRA. 4-HPR has been mostly investigated as an anti-cancer agent, but recent studies showed its promising therapeutic potential for preventing metabolic syndrome. Several biological targets are involved in 4-HPR's activity, leading to the potential use of this molecule for treating different pathologies. However, although 4-HPR displays quite well-understood multitarget promiscuity with regards to pharmacology, interpreting its precise physiological role remains challenging. In addition, despite promising results in vitro, the clinical efficacy of 4-HPR as a chemotherapeutic agent has not been satisfactory so far. Herein, we describe the preparation of a library of 4-HPR analogues, followed by the biological evaluation of their anti-cancer and anti-obesity/diabetic properties. The click-type analogue 3 b showed good capacity to reduce the amount of lipid accumulation in 3T3-L1 adipocytes during differentiation. Furthermore, it showed an IC₅₀ of 0.53±0.8 μM in cell viability tests on breast cancer cell line MCF-7, together with a good selectivity (SI=121) over noncancerous HEK293 cells. Thus, 3 b was selected as a potential PET tracer to study retinoids in vivo, and the radiosynthesis of [¹⁸ F]3b was successfully developed. Unfortunately, the stability of [¹⁸ F]3b turned out to be insufficient to pursue imaging studies.

Novel retinoic acid derivative induces differentiation and growth arrest in neuroblastoma

INTRODUCTION

Retinoic acid (RA) is a differentiating agent utilized as maintenance therapy for high-risk neuroblastoma (NB), but associated toxicities limit its use. We have previously shown that a non-toxic, novel rexinoid, 9-cis-UAB30 (UAB30), decreased NB cell proliferation and in vivo tumor growth. A second generation, mono-methylated compound, 6-Methyl-UAB30 (6-Me), has been recently designed having greater potency compared with UAB30. In the current study, we hypothesized that 6-Me would inhibit NB cell proliferation and survival and induce differentiation and cell-cycle arrest.

METHODS

Proliferation and viability were measured in four human NB cell lines following treatment with UAB30 or 6-Me. Cell-cycle was analyzed and tumor cell stemness was evaluated with extreme limiting dilution assays and immunoblotting for expression of stem cell markers. A xenograft murine model was utilized to study the effects of 6-Me in vivo.

RESULTS

Treatment with 6-Me led to decreased proliferation and viability, induced cell cycle arrest, and increased neurite outgrowth, indicating differentiation of surviving cells. Furthermore, treatment with 6-Me decreased tumorsphere formation and expression of stem cell markers. Finally, inhibition of tumor growth and increased animal survival was observed in vivo following treatment with 6-Me.

CONCLUSION

These results indicate a potential therapeutic role for this novel rexinoid in neuroblastoma treatment.

Clinical development of fenretinide as an antineoplastic drug: Pharmacology perspectives

Fenretinide (4-HPR) is a synthetic retinoid that has cytotoxic activity against cancer cells. Despite substantial in vitro cytotoxicity, response rates in early clinical trials with 4-HPR have been less than anticipated, likely due to the low bioavailability of the initial oral capsule formulation. Several clinical studies have shown that the oral capsule formulation at maximum tolerated dose (MTD) achieved <10 µmol/L concentrations in patients. To improve bioavailability of 4-HPR, new oral powder (LYM-X-SORB®, LXS) and intravenous lipid emulsion (ILE) formulations are being tested in early-phase clinical trials. ILE 4-HPR administered as five-day continuous infusion achieved over 50 µmol/L at MTD with minimal systemic toxicities; multiple complete and partial responses were observed in peripheral T cell lymphomas. The LXS oral powder 4-HPR formulation increased plasma levels approximately two-fold at MTD in children without dose-limiting toxicities and demonstrated multiple complete responses in recurrent neuroblastoma. The clinical activity observed with new 4-HPR formulations is attributed to increased bioavailability. Phase I and II clinical trials of both LXS 4-HPR and ILE 4-HPR are in progress as a single agent or in combination with other drugs. Impact statement One of the critical components in drug development is understanding pharmacology (especially pharmacokinetics) of the drugs being developed. Often the pharmacokinetic properties, such as poor solubility leading to poor bioavailability, of the drug can limit further development of the drug. The development of numerous drugs has often halted at clinical testing stages, and several of them were due to the pharmacological properties of the agents, resulting in increased drug development cost. The current review provides an example of how improved clinical activity can be achieved by changing the formulations of a drug with poor bioavailability. Thus, it emphasizes the importance of understanding pharmacologic characteristics of the drug in drug development.

Vitamin A, cancer treatment and prevention: the new role of cellular retinol binding proteins

Retinol and vitamin A derivatives influence cell differentiation, proliferation, and apoptosis and play an important physiologic role in a wide range of biological processes. Retinol is obtained from foods of animal origin. Retinol derivatives are fundamental for vision, while retinoic acid is essential for skin and bone growth. Intracellular retinoid bioavailability is regulated by the presence of specific cytoplasmic retinol and retinoic acid binding proteins (CRBPs and CRABPs). CRBP-1, the most diffuse CRBP isoform, is a small 15 KDa cytosolic protein widely expressed and evolutionarily conserved in many tissues. CRBP-1 acts as chaperone and regulates the uptake, subsequent esterification, and bioavailability of retinol. CRBP-1 plays a major role in wound healing and arterial tissue remodelling processes. In the last years, the role of CRBP-1-related retinoid signalling during cancer progression became object of several studies. CRBP-1 downregulation associates with a more malignant phenotype in breast, ovarian, and nasopharyngeal cancers. Reexpression of CRBP-1 increased retinol sensitivity and reduced viability of ovarian cancer cells in vitro. Further studies are needed to explore new therapeutic strategies aimed at restoring CRBP-1-mediated intracellular retinol trafficking and the meaning of CRBP-1 expression in cancer patients' screening for a more personalized and efficacy retinoid therapy.

Fenretinide: a novel treatment for endometrial cancer

Resistance to progestin treatment is a major hurdle in the treatment of advanced and reoccurring endometrial cancer. Fenretinide is a synthetic retinoid that has been evaluated in clinical trials as a cancer therapeutic and chemo-preventive agent. Fenretinide has been established to be cytotoxic to many kinds of cancer cells. In the present study, we demonstrate that fenretinide decreased cell viability and induced apoptosis in Ishikawa cells, which are an endometrial cancer cell line, in dose dependent manner in-vitro. This effect was found to be independent of retinoic acid nuclear receptor signaling pathway. Further, we have shown that this induction of apoptosis by fenretinide may be caused by increased retinol uptake via STRA6. Silencing of STRA6 was shown to decrease apoptosis which was inhibited by knockdown of STRA6 expression in Ishikawa cells. Results of an in-vivo study demonstrated that intraperitoneal injections of fenretinide in endometrial cancer tumors (created using Ishikawa cells) in mice inhibited tumor growth effectively. Immunohistochemistry of mice tumors showed a decrease in Ki67 expression and an increase in cleaved caspase-3 staining after fenretinide treatment when compared to vehicle treated mice. Collectively, our results are the first to establish the efficacy of fenretinide as an antitumor agent for endometrial cancer both in-vitro and in-vivo, providing a valuable rationale for initiating more preclinical studies and clinical trials using fenretinide for the treatment of endometrial cancer.

Cell-based small-molecule compound screen identifies fenretinide as potential therapeutic for translocation-positive rhabdomyosarcoma

A subset of paediatric sarcomas are characterized by chromosomal translocations encoding specific oncogenic transcription factors. Such fusion proteins represent tumor specific therapeutic targets although so far it has not been possible to directly inhibit their activity by small-molecule compounds. In this study, we hypothesized that screening a small-molecule library might identify already existing drugs that are able to modulate the transcriptional activity of PAX3/FOXO1, the fusion protein specifically found in the pediatric tumor alveolar rhabdomyosarcoma (aRMS). Towards this end, we established a reporter cell line based on the well characterized PAX3/FOXO1 target gene AP2ß. A library enriched in mostly FDA approved drugs was screened using specific luciferase activity as read-out and normalized for cell viability. The most effective inhibitor identified from this screen was Fenretinide. Treatment with this compound resulted in down-regulation of PAX3/FOXO1 mRNA and protein levels as well as in reduced expression of several of its direct target genes, but not of wild-type FOXO1, in a dose- and time-dependent manner. Moreover, fenretinide induced reactive oxygen species and apoptosis as shown by caspase 9 and PARP cleavage and upregulated miR-9. Importantly, it demonstrated a significant anti-tumor effect in vivo. These results are similar to earlier reports for two other pediatric tumors, namely neuroblastoma and Ewing sarcoma, where fenretinide is under clinical development. Our results suggest that fenretinide might represent a novel treatment option also for translocation-positive rhabdomyosarcoma.

p75NTR: an enhancer of fenretinide toxicity in neuroblastoma

OBJECTIVE

Neuroblastoma is a common, frequently fatal, neural crest tumor of childhood. Chemotherapy-resistant neuroblastoma cells typically have Schwann cell-like ("S-type") morphology and express the p75 neurotrophin receptor (p75NTR). p75NTR has been previously shown to modulate the redox state of neural crest tumor cells. We, therefore, hypothesized that p75NTR expression level would influence the effects of the redox-active chemotherapeutic drug fenretinide on neuroblastoma cells.

METHODS

Transfection and lentiviral transduction were used to manipulate p75NTR expression in these cell lines. Sensitivity to fenretinide was determined by concentration- and time-cell survival studies. Apoptosis incidence was determined by morphological assessment and examination of cleavage of poly-ADP ribose polymerase and caspase-3. Generation and subcellular localization of reactive oxygen species were quantified using species- and site-specific stains and by examining the effects of site-selective antioxidants on cell survival after fenretinide treatment. Studies of mitochondrial electron transport employed specific inhibitors of individual proteins in the electron transport chain.

RESULTS

Knockdown of p75NTR attenuates fenretinide-induced accumulation of mitochondrial superoxide and apoptosis. Overexpression of p75NTR has the opposite effects. Pretreatment of cells with 2-thenoyltrifluoroacetone or dehydroascorbic acid uniquely prevents mitochondrial superoxide accumulation and cell death after fenretinide treatment, indicating that mitochondrial complex II is the likely site of fenretinide-induced superoxide generation and p75NTR-induced potentiation of these phenomena.

CONCLUSION

Modification of expression of p75NTR in a particular neuroblastoma cell line modifies its susceptibility to fenretinide. Enhancers of p75NTR expression or signaling could be potential drugs for use as adjuncts to chemotherapy of neural tumors.

Fenretinide metabolism in humans and mice: utilizing pharmacological modulation of its metabolic pathway to increase systemic exposure

BACKGROUND AND PURPOSE

High plasma levels of fenretinide [N-(4-hydroxyphenyl)retinamide (4-HPR)] were associated with improved outcome in a phase II clinical trial. Low bioavailability of 4-HPR has been limiting its therapeutic applications. This study characterized metabolism of 4-HPR in humans and mice, and to explore the effects of ketoconazole, an inhibitor of CYP3A4, as a modulator to increase 4-HPR plasma levels in mice and to increase the low bioavailability of 4-HPR.

EXPERIMENTAL APPROACH

4-HPR metabolites were identified by mass spectrometric analysis and levels of 4-HPR and its metabolites [N-(4-methoxyphenyl)retinamide (4-MPR) and 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR)] were quantified by high-performance liquid chromatography (HPLC). Kinetic analysis of enzyme activities and the effects of enzyme inhibitors were performed in pooled human and pooled mouse liver microsomes, and in human cytochrome P450 (CYP) 3A4 isoenzyme microsomes. In vivo metabolism of 4-HPR was inhibited in mice.

KEY RESULTS

Six 4-HPR metabolites were identified in the plasma of patients and mice. 4-HPR was oxidized to 4-oxo-4-HPR, at least in part via human CYP3A4. The CYP3A4 inhibitor ketoconazole significantly reduced 4-oxo-4-HPR formation in both human and mouse liver microsomes. In two strains of mice, co-administration of ketoconazole with 4-HPR in vivo significantly increased 4-HPR plasma concentrations by > twofold over 4-HPR alone and also increased 4-oxo-4-HPR levels.

CONCLUSIONS AND IMPLICATIONS

Mice may serve as an in vivo model of human 4-HPR pharmacokinetics. In vivo data suggest that the co-administration of ketoconazole at normal clinical doses with 4-HPR may increase systemic exposure to 4-HPR in humans.

Phase II study of oral capsular 4-hydroxyphenylretinamide (4-HPR/fenretinide) in pediatric patients with refractory or recurrent neuroblastoma: a report from the Children's Oncology Group

PURPOSE

To determine the response rate to oral capsular fenretinide in children with recurrent or biopsy proven refractory high-risk neuroblastoma.

EXPERIMENTAL DESIGN

Patients received 7 days of fenretinide: 2,475 mg/m(2)/d divided TID (<18 years) or 1,800 mg/m(2)/d divided BID (≥18 years) every 21 days for a maximum of 30 courses. Patients with stable or responding disease after course 30 could request additional compassionate courses. Best response by course 8 was evaluated in stratum 1 (measurable disease on CT/MRI ± bone marrow and/or MIBG avid sites) and stratum 2 (bone marrow and/or MIBG avid sites only).

RESULTS

Sixty-two eligible patients, median age 5 years (range 0.6-19.9), were treated in stratum 1 (n = 38) and stratum 2 (n = 24). One partial response (PR) was seen in stratum 2 (n = 24 evaluable). No responses were seen in stratum 1 (n = 35 evaluable). Prolonged stable disease (SD) was seen in 7 patients in stratum 1 and 6 patients in stratum 2 for 4 to 45+ (median 15) courses. Median time to progression was 40 days (range 17-506) for stratum 1 and 48 days (range 17-892) for stratum 2. Mean 4-HPR steady-state trough plasma concentrations were 7.25 μmol/L (coefficient of variation 40-56%) at day 7 course 1. Toxicities were mild and reversible.

CONCLUSIONS

Although neither stratum met protocol criteria for efficacy, 1 PR + 13 prolonged SD occurred in 14/59 (24%) of evaluable patients. Low bioavailability may have limited fenretinide activity. Novel fenretinide formulations with improved bioavailability are currently in pediatric phase I studies.

Promising effects of the 4HPR-BSO combination in neuroblastoma monolayers and spheroids

To enhance the efficacy of fenretinide (4HPR)-induced reactive oxygen species (ROS) in neuroblastoma, 4HPR was combined with buthionine sulfoximine (BSO), an inhibitor of glutathione (GSH) synthesis, in neuroblastoma cell lines and spheroids, the latter being a three-dimensional tumor model. 4HPR exposure (2.5-10 μM, 24 h) resulted in ROS induction (114-633%) and increased GSH levels (68-120%). A GSH depletion of 80% of basal levels was observed in the presence of BSO (25-100 μM, 24 h). The 4HPR-BSO combination resulted in slightly increased ROS levels (1.1- to 1.3-fold) accompanied by an increase in cytotoxicity (110-150%) compared to 4HPR treatment alone. A correlation was observed between the ROS-inducing capacity of each cell line and the increase in cytotoxicity induced by 4HPR-BSO compared to 4HPR. No significant correlation between baseline antioxidant levels and sensitivity to 4HPR or BSO was observed. In spheroids, 4HPR-BSO induced a strong synergistic growth retardation and induction of apoptosis. Our data show that BSO increased the cytotoxic effects of 4HPR in neuroblastoma monolayers and spheroids in ROS-producing cell lines. This indicates that the 4HPR-BSO combination might be a promising new strategy in the treatment of neuroblastoma.

Preclinical evaluation of lestaurtinib (CEP-701) in combination with retinoids for neuroblastoma

PURPOSE

Lestaurtinib (CEP-701), a multi-kinase inhibitor with potent activity against the Trk family of receptor tyrosine kinases, has undergone early phase clinical evaluation in children with relapsed neuroblastoma. We studied the interaction of CEP-701 with isotretinoin (13cRA) and fenretinide (4HPR), two retinoids that have been studied in children with high-risk neuroblastoma.

METHODS

In vitro growth inhibition was assessed following a 72-hour drug exposure using the sulforhodamine B (SRB) assay in eight neuroblastoma cell lines with variable TrkB expression. When appropriate, the combination index (CI) of Chou-Talalay was used to characterize the interaction of 13cRA (non-constant ratio) or 4HPR (constant ratio) with CEP-701.

RESULTS

The median (range) IC(50) of single-agent CEP-701 across all cell lines was 0.09 (0.08-0.3) μM. The combination of 13cRA and CEP-701 resulted in additive to synergistic interactions in four of the five cell lines studied. Addition of 1 or 5 μM of 13cRA decreased the median (range) CEP-701 IC(50) 1.5-fold (1.1-2.8-fold) and 1.7-fold (1.5-1.8-fold), respectively. With 10 μM 13cRA, less than 50% of cells survived when combined with various concentrations of CEP-701. The combination of 4HPR and CEP-701 trended toward being antagonistic, with a median (range) CI at the ED(50) of 1.3 (1.1-1.5).

CONCLUSIONS

The combination of 13cRA and CEP-701 was additive or synergistic in a spectrum of neuroblastoma cell lines, suggesting that these agents can be potentially studied together in the setting of minimal residual disease following intensive chemoradiotherapy for children with high-risk neuroblastoma.

Pharmacotherapy of neuroblastoma

IMPORTANCE OF THE FIELD

Neuroblastoma, a tumor of the sympathetic nervous system, is the most common extracranial solid tumor of early life. High risk disease in older children remains a therapeutic challenge, despite high-intensity therapy with correspondingly significant short- and long-term toxicities.

AREAS COVERED IN THIS REVIEW

We have reviewed therapy for neuroblastoma over the last three decades. This includes cytotoxic chemotherapy, immunotherapy, radionuclides, antiangiogenic compounds, and molecularly targeted agents. We provide a perspective on the incorporation of these drugs into therapy for neuroblastoma.

WHAT THE READER WILL GAIN

The reader will gain a better understanding of these novel agents and their targets in neuroblastoma. The reader will also gain insight into the need to define through sequential, carefully designed clinical trials, the roles and toxicities of these therapies, especially if the combination of targeted and conventional cytotoxic agents is used.

TAKE HOME MESSAGE

Advanced-stage neuroblastoma in older infants and children remains a disease that is difficult to cure. New, targeted agents may improve both the therapeutic index and the outcome, but are, for the most part, in early development and present a challenge for clinical trial design given both the rarity of this disease and its responsiveness (albeit incomplete) to currently used cytotoxic agents.

Fenretinide induces mitochondrial ROS and inhibits the mitochondrial respiratory chain in neuroblastoma

Fenretinide induces apoptosis in neuroblastoma by induction of reactive oxygen species (ROS). In this study, we investigated the role of mitochondria in fenretinide-induced cytotoxicity and ROS production in six neuroblastoma cell lines. ROS induction by fenretinide was of mitochondrial origin, demonstrated by detection of superoxide with MitoSOX, the scavenging effect of the mitochondrial antioxidant MitoQ and reduced ROS production in cells without a functional mitochondrial respiratory chain (Rho zero cells). In digitonin-permeabilized cells, a fenretinide concentration-dependent decrease in ATP synthesis and substrate oxidation was observed, reflecting inhibition of the mitochondrial respiratory chain. However, inhibition of the mitochondrial respiratory chain was not required for ROS production. Co-incubation of fenretinide with inhibitors of different complexes of the respiratory chain suggested that fenretinide-induced ROS production occurred via complex II. The cytotoxicity of fenretinide was exerted through the generation of mitochondrial ROS and, at higher concentrations, also through inhibition of the mitochondrial respiratory chain.

Oral fenretinide in biochemically recurrent prostate cancer: a California cancer consortium phase II trial

BACKGROUND

Fenretinide is a synthetic retinoid that is cytotoxic to a variety of cancers. We conducted a phase II trial of oral fenretinide in patients with biochemically recurrent prostate cancer.

PATIENTS AND METHODS

Eligible patients had histologically confirmed prostate cancer and a confirmed rising prostate-specific antigen (PSA) >or= 2 ng/mL following either radical prostatectomy and/or pelvic radiation therapy, without clinical or radiographic evidence of metastasis. The primary endpoint was PSA response, which was defined as a confirmed decrease by >or=50%, and >or=5 ng/mL, from the pretreatment value. Treatment comprised oral fenretinide 900 mg/m2 twice daily for 1 week, every 3 weeks, for 1 year.

RESULTS

After a median follow-up of 17.7 months, out of 23 patients, 7 (30%) patients had PSA stable disease (SD), 11 (48%) patients had PSA progression within 3 months, 4 patients had minimal increases over 3 months that did not qualify as SD or progression (17%), and one patient (4%) was not evaluable. Median time to PSA progression was 4.6 months (95% CI, 3.2-8.2 months). Observed grade 3 toxicities included fatigue, pain, hypermagnesemia, a rise in lipase, and nyctalopia.

CONCLUSION

Although well-tolerated, oral fenretinide did not meet prespecified PSA criteria for response in biochemically recurrent prostate cancer; however, 30% of patients had SD, which suggests modest single-agent clinical activity. The role of different formulations of fenretinide, which might allow for higher serum concentrations of the drug, is currently under investigation.

High-dose fenretinide in oral leukoplakia

We previously showed that low-dose fenretinide (200 mg/d) had limited activity in retinoid-resistant oral leukoplakia (34% response rate) possibly because serum drug levels were insufficient to induce retinoid receptor-independent apoptosis. Therefore, we designed the single-arm phase II trial reported here to investigate whether higher-dose fenretinide would improve leukoplakia response over that of our previous study. Leukoplakia patients received fenretinide (900 mg/m(2) twice daily) in four 3-week cycles (1 week on drug followed by 2 weeks off). At week 12, clinical responses were determined and blood samples were collected for serum drug level assessments. A planned interim futility analysis led to early trial closure after the initial 15 (of 25 planned) patients because only 3 (20%) had a partial response (stopping rule: <or=4 responses in first 16 patients). Fenretinide was well tolerated--only one grade 3 adverse event (diarrhea) occurred. Serum fenretinide levels changed from 0 (baseline) to 0.122 +/- 0.093 micromol/L (week 12). In correlative in vitro studies, high-dose fenretinide inhibited the growth of head and neck cancer cells more and oral leukoplakia cells less than did lower doses of fenretinide. This result is consistent with our clinical finding that high-dose fenretinide did not improve on the historical response rate of lower-dose fenretinide in our previous oral leukoplakia trial.

Mechanisms of fenretinide-induced apoptosis

Fenretinide, a synthetic retinoid, has emerged as a promising anticancer agent based on numerous in vitro and animal studies, as well as chemoprevention clinical trials. In vitro observations suggest that the anticancer activity of fenretinide may arise from its ability to induce apoptosis in tumor cells. Diverse signaling molecules including reactive oxygen species, ceramide, and ganglioside GD3 can mediate apoptosis induction by fenretinide in transformed, premalignant, and malignant cells. In many cell types, these signaling intermediates appear to be induced by mechanisms that are independent of retinoic acid receptor activation, and ultimately initiate the intrinsic or mitochondrial-mediated pathway of cell elimination. Numerous investigations conducted during the past 10 years have discovered a great deal about the apoptogenic activity of fenretinide. In this review we explore the mechanisms associated with fenretinide-induced apoptosis and highlight certain mechanistic underpinnings of fenretinide-induced cell death that remain poorly understood and thus warrant further characterization.

Phase I trial of oral fenretinide in children with high-risk solid tumors: a report from the Children's Oncology Group (CCG 09709)

PURPOSE

To determine the maximal tolerated dosage (MTD) of oral fenretinide given as intact capsules for 7 days, repeated every 21 days, in children with high-risk solid tumors.

METHODS

Children 21 years of age or younger received daily doses from 350 mg/m2 to 3,300 mg/m2 (divided into two or three doses), with pharmacokinetics during course one. The MTD was defined as zero to one of six patients with dose-limiting toxicity (DLT), with at least two of three or two of six DLT at next higher dose.

RESULTS

Fifty-four patients, age 2 years to 20 years (median, 9 years), were treated: neuroblastoma (n = 39), Ewing sarcoma (n = 5), and other (n = 10). Prior therapy included autologous stem cell transplantation (n = 42), 13-cis-RA (n = 35), and 9-cis-RA (n = 1). One of four patients at 1,050 mg/m2 with prior liver transplant had grade 3 ALT/abdominal pain/nausea/dehydration and grade 4 AST/emesis. At 1,860 mg/m2, one of seven patients had grade 3 hypoalbuminemia/hypophosphatemia. At 2,475 mg/m2, one of eight patients had grade 3 alkaline phosphatase; three of five patients had DLT at 3,300 mg/m2: grade 3 AST/ALT (n = 1), grade 4 bilirubin/grade 3 AST/ALT (n = 1), pseudotumor cerebri (n = 1). Pseudotumor cerebri also occurred at 600 mg/m2 and 800 mg/m2. There was one complete response and 13 patients with stable disease (SD) for 8 or more courses in 30 assessable neuroblastoma patients. SD for 8 or more courses was seen in one of five Ewing sarcoma patients and one melanoma patient. Mean N-4-hydroxyphenyl retinamide plasma level (day 7, steady-state concentration) was 9.9 mumol/L at MTD.

CONCLUSION

The pediatric MTD of oral capsular fenretinide was 2,475 mg/m2 per day, which achieved levels active against neuroblastoma in vitro with minimal toxicity. Response data support a phase II trial in neuroblastoma.

A phase I clinical and pharmacokinetic study of fenretinide combined with paclitaxel and cisplatin for refractory solid tumors

BACKGROUND

Fenretinide is a semi-synthetic retinoid that has pro-apoptotic effects as a single agent and synergistically with chemotherapy in vitro. We performed this study to determine the toxicity of cisplatin, paclitaxel and fenretinide in patients with advanced cancer, the recommended phase II dose of these agents together, and the pharmacokinetics (PK) of fenretinide when administered with chemotherapy.

PATIENTS AND METHODS

Fourteen patients (mean age 57.3) were assessable for pharmacokinetics, toxicity and response. Fenretinide was given orally in 2 divided daily doses for 7 days, starting 24 hours prior to cisplatin and paclitaxel. Cisplatin and paclitaxel were given in standard fashion. Cycles were repeated every 3 weeks. Cycle one fenretinide PK was obtained on days 2 and 8.

RESULTS

Dose limiting toxicity (Gr 3 diarrhea and Gr 4 neutropenia) was encountered in two patients during cycle one at 80/175/1,800 mg/m(2) of cisplatin/paclitaxel/fenretinide (dose level 2), respectively. Seven patients received 2-8 cycles at the recommended level of 60/135/1,800 (dose level 1). Severe cumulative toxicities included fatigue, nausea/vomiting, neuropathy, and dehydration. Two patients had a partial response and 4 patients had stable disease for up to 8 cycles. PK analysis demonstrated a reduction in fenretinide Cmax on day 8 compared to day 2, accompanying a decrease in AUC.

CONCLUSIONS

Cisplatin/paclitaxel/fenretinide can be administered safely at 60/135/1,800 mg/m(2) respectively on an every three-week schedule. This combination may have activity in a variety of tumors, however, the number of pills required complicates oral dosing of fenretinide, and limits the applicability of this regimen.

Receptor-selective retinoids inhibit the growth of normal and malignant breast cells by inducing G1 cell cycle blockade

Despite advances in treatment, breast cancer continues to be the second leading cause of cancer mortality in women. Statistics suggest that while focus on treatment should continue, chemopreventive approaches should also be pursued. Previous studies have demonstrated that naturally occurring retinoids such as 9-cis retinoic acid (9cRA) can prevent breast cancer in animal models. However, these studies have also shown that these compounds are too toxic for general use. Work from our laboratory showed that an RXR-selective retinoid LGD1069 prevented tumor development in animal models of cancer with reduced toxicity as compared to an RAR-selective retinoid TTNPB. In the present study, we investigated the mechanisms by which receptor-selective retinoids inhibit the growth of normal and malignant breast cells. Our results demonstrate that the synthetic retinoids tested are as effective as 9cRA in suppressing the growth of normal human mammary epithelial cells (HMECs) and estrogen receptor-positive (ER-positive) breast cancer cells. Although the receptor-selective retinoids induce minimal amounts of apoptosis in T47D breast cancer cells, the predominant factor that leads to growth arrest is G1 cell cycle blockade. Our data indicate that this blockade results from the downregulation of Cyclin D1 and Cyclin D3, which in turn causes Rb hypophosphorylation. Non-toxic retinoids that are potent inducers of cell cycle arrest may be particularly useful for the prevention of breast cancer.

N-(4-Hydroxyphenyl)Retinamide Inhibits Invasion, Suppresses Osteoclastogenesis, and Potentiates Apoptosis through Down-regulation of IκBα Kinase and Nuclear Factor-κB–Regulated Gene Products

N-(4-hydroxyphenyl) retinamide [4-HPR], a synthetic retinoid, has been shown to inhibit tumor cell growth, invasion, and metastasis by a mechanism that is not fully understood. Because the nuclear factor-kappaB (NF-kappaB) has also been shown to regulate proliferation, invasion, and metastasis of tumor cells, we postulated that 4-HPR modulates the activity of NF-kappaB. To test this postulate, we examined the effect of this retinoid on NF-kappaB and NF-kappaB-regulated gene products. We found that 4-HPR potentiated the apoptosis induced by tumor necrosis factor (TNF) and chemotherapeutic agents, suppressed TNF-induced invasion, and inhibited RANKL-induced osteoclastogenesis, all of which are known to require NF-kappaB activation. We found that 4-HPR suppressed both inducible and constitutive NF-kappaB activation without interfering with the direct DNA binding of NF-kappaB. 4-HPR was found to be synergistic with Velcade, a proteasome inhibitor. Further studies showed that 4-HPR blocked the phosphorylation and degradation of IkappaBalpha through the inhibition of activation of IkappaBalpha kinase (IKK), and this led to suppression of the phosphorylation and nuclear translocation of p65. 4-HPR also inhibited TNF-induced Akt activation linked with IKK activation. NF-kappaB-dependent reporter gene expression was also suppressed by 4-HPR, as was NF-kappaB reporter activity induced by TNFR1, TRADD, TRAF2, NIK, and IKK but not that induced by p65 transfection. The expression of NF-kappaB-regulated gene products involved in antiapoptosis (IAP1, Bfl-1/A1, Bcl-2, cFLIP, and TRAF1), proliferation (cyclin D1 and c-Myc), and angiogenesis (vascular endothelial growth factor, cyclooxygenase-2, and matrix metalloproteinase-9) were also down-regulated by 4-HPR. This correlated with potentiation of apoptosis induced by TNF and chemotherapeutic agents.

Phase II trial of fenretinide in advanced renal carcinoma

PURPOSE

Fenretinide, a synthetic form of retinoid, induced apoptosis even in chemotherapy resistant cell lines. A phase II study was hence conducted to evaluate toxicity and efficacy of fenretinide in metastatic renal cancer.

METHODS

Eligibility included unresectable or metastatic renal cell carcinoma (RCC), adequate organ function and Zubrod performance status < or =2. Prior immunotherapy and a maximum of one prior chemotherapy regimen were allowed. Fenretinide was administered at a dose of 900 mg/m(2) twice daily orally for 7 days in a 21-day cycle. Toxicity was assessed at the start of each cycle, and response every 2 cycles.

RESULTS

Nineteen eligible patients enrolled of which fifteen had visceral/bone metastases. Seventeen patients had prior nephrectomy and 11 had prior immunotherapy. 76 cycles of therapy were delivered. Therapy was very well tolerated with few severe toxicities consisting of thrombosis in 1 individual and grade 3 fatigue, nausea and diarrhea in 1 patient. 5 patients had grade 2 nyctalopia and 3 patients had transient grade 2 visual toxicity. No objective responses were noted. Stable disease was seen in seven of nineteen cases (37%, 90% C.I. 0.21-0.59). Median time to progression was 1.5 months and median duration of stable disease was 5.8 months (90% C.I. 3.0-8.4). Median survival was 10 months. Tumor fenretinide levels were obtained in three patients and were in the lower end of the therapeutic range.

CONCLUSION

Fenretinide was well tolerated but demonstrated minimal activity that was consistent with results of intratumoral drug measurements. Strategies are needed that will increase systemic and tumor levels of fenretinide.

Hydrolysis of 4-HPR to atRA occurs in vivo but is not required for retinamide-induced apoptosis

The retinamide, N-(4-hydroxyphenyl)retinamide (4-HPR), has shown promising anti-tumor activity, but it is unclear whether this compound is hydrolyzed to all-trans retinoic acid (atRA) and if so, whether this plays any role in its chemotherapeutic activity. To address this issue, the ability of 4-hydroxybenzylretinone (4-HBR), a carbon-linked analog of 4-HPR, to support growth in vitamin A-deficient (VAD) animals and to activate an atRA-responsive gene in vivo was compared to 4-HPR and atRA. Further, the non-hydrolyzable 4-HBR analog was used to determine whether the presence of the labile amide linkage in 4-HPR is essential for the induction of apoptosis in cultured MCF-7 breast cancer cells. Studies in VAD rats showed that 4-HPR, like atRA, supports animal growth and induces CYP26B1 mRNA expression in lung whereas 4-HBR does not. Analysis of plasma from 4-HPR- and atRA-treated VAD animals revealed the presence of atRA whereas it was not detected in plasma from animals given 4-HBR. To determine whether hydrolysis to atRA is necessary for apoptosis induced by 4-HPR in MCF-7 breast cancer cells, morphological and biochemical assays for apoptosis were performed. 4-HBR, like 4-HPR, induced apoptosis in MCF-7 cells. Apoptosis was not induced even at high concentrations of atRA, showing that 4-HPR and 4-HBR act in cells via a distinct signaling pathway. These results show that although limited hydrolysis of 4-HPR occurs in vivo, the ability to liberate atRA is not required for these 4-hydroxyphenyl retinoids to induce apoptosis in MCF-7 breast cancer cells. Thus the non-hydrolyzable analog, 4-HBR, may have significant therapeutic advantage over 4-HPR because it does not liberate atRA that can contribute to the adverse side effects of drug administration in vivo.

N-(4-hydroxyphenyl)retinamide increases ceramide and is cytotoxic to acute lymphoblastic leukemia cell lines, but not to non-malignant lymphocytes

The retinoid, N-(4-hydroxyphenyl)retinamide (4-HPR), mediates p53-independent cytotoxicity and can increase reactive oxygen species and ceramide in solid tumor cell lines. We determined changes in ceramide and cytotoxicity upon treatment with 4-HPR (3-12 microM) in six human acute lymphoblastic leukemia (ALL) cell lines: T cell (MOLT-3, MOLT-4, CEM), pre-B-cell (NALM-6, SMS-SB), and null cell (NALL-1). Exposure to 4-HPR (12 microM) for 96 h caused 4.7 (MOLT-3), 3.5 (MOLT-4), 3.9 (CEM), 2.9 (NALM-6), 4.7 (SMS-SB), AND 4.5 (NALL-1) logs of cell kill. The average 4-HPR concentration that killed 99% of cells (LC(99)) for all six lines was 4.8 microM (range: 1.5-8.9 microM). Treatment with 4-HPR (9 microM) for 24 h resulted in an 8.9 +/- 1.0-fold (range: 4.9-15.7-fold) increase of ceramide. Ceramide increase was time- and dose-dependent and abrogated by inhibitors of de novo ceramide synthesis. Concurrent inhibition of ceramide glycosylation/acylation by d,l-threo-(1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol) (PPMP) further increased ceramide levels, and synergistically increased 4-HPR cytotoxicity in four of six ALL cell lines. 4-HPR was minimally cytotoxic to peripheral blood mononuclear cells and a lymphoblastoid cell line, and increased ceramide <2-fold. Thus, 4-HPR was cytotoxic and increased ceramide in ALL cell lines, but not in non-malignant lymphoid cell types.

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.

Retinoic-acid-resistant neuroblastoma cell lines show altered MYC regulation and high sensitivity to fenretinide

BACKGROUND

High-dose, pulse-13-cis-retinoic acid (13-cis-RA) given after intensive cytotoxic therapy improves event-free survival for high-risk neuroblastoma (NB), but more than 50% of patients have tumor recurrence.

PROCEDURE

We conducted multistep selection for resistance to all-trans-retinoic acid (ATRA) in NB cell lines with (SMS-KCNR and LA-N-5) or without (SMS-LHN) MYCN genomic amplification.

RESULTS

After 12 exposures to 10 microM ATRA, the two MYCN-amplified cell lines (KCNR 12X RR and LA-N-5 12X RR) showed partial resistance to the cytostatic/differentiation effects of ATRA; complete resistance was seen in LHN 12X RR. ATRA-selected cells showed general RA resistance (cross-resistance to 13-cis-RA). Transient (KCNR 12 X RR, LA-N-5 12X RR) or sustained (LHN 12X RR) novel overexpression of c-myc was associated with RA resistance. RA-insensitive overexpression of MYCN by transduction in SMS-LHN also conferred RA resistance. Both parental and RA-resistant lines showed 2-4 logs of cell kill in response to N-(4-hydroxyphenyl)retinamide (4- HPR, fenretinide). Compared to parental lines, 4-HPR achieved 1-3 log greater cell kills in RA-resistant LHN 12X RR, LA-N-5 12X RR, KCNR 12X RR, and MYCN-transduced SMS-LHN or SK-N-RA. NB cell lines (n = 26) from 21 different patients showed that 16 of 26 (62%) were sensitive to 4-HPR (LC(90) < 10 microM), including lines established at relapse after myeloablative and/or 13-cis-RA therapy.

CONCLUSION

Thus, RA-resistant NB cell lines can be sensitive (and in some cases collaterally hypersensitive) to 4-HPR.

Differentiating agents in pediatric malignancies: retinoids in neuroblastoma

Retinoids are derivatives of vitamin A that include all- trans-retinoic acid (ATRA), 13-cis-retinoic acid, (13-cis-RA), and fenretinide (4-HPR). High levels of either ATRA or 13-cis-RA can cause arrest of cell growth and morphologic differentiation of human neuroblastoma cell lines. Phase I trials have shown that higher and more sustained drug levels were obtained with 13-cis-RA relative to ATRA. A phase III randomized trial showed that high-dose pulse therapy with 13-cis-RA given after completion of intensive chemoradiotherapy (with or without autologous bone marrow transplantation) significantly improves event-free survival in high-risk neuroblastoma. Because 4-HPR achieves multi-log cell kills in neuroblastoma cell lines that are resistant to ATRA and 13-cis-RA, a pediatric phase I trial is in progress to determine the maximum tolerated dose of 4-HPR, with a view toward giving 4-HPR after completion of myeloablative therapy and 13-cis-RA.

Effector mechanisms of fenretinide-induced apoptosis in neuroblastoma

Fenretinide is an effective inducer of apoptosis in many malignancies but its precise mechanism(s) of action in the induction of apoptosis in neuroblastoma is unclear. To characterize fenretinide-induced apoptosis, neuroblastoma cell lines were treated with fenretinide and flow cytometry was used to measure apoptosis, free radical generation, and mitochondrial permeability changes. Fenretinide induced high levels of caspase-dependent apoptosis accompanied by an increase in free radicals and the release of cytochrome c in the absence of mitochondrial permeability transition. Apoptosis was blocked by two retinoic acid receptor (RAR)-beta/gamma-specific antagonists, but not by an RARalpha-specific antagonist. Free radical induction in response to fenretinide was not blocked by the caspase inhibitor ZVAD or by RAR antagonists and was only marginally reduced in cells selected for resistance to fenretinide. Therefore, free radical generation may be only one of a number of intracellular mechanisms of apoptotic signaling in response to fenretinide. These results suggest that the effector pathway of fenretinide-induced apoptosis of neuroblastoma is caspase dependent, involving mitochondrial release of cytochrome c independently of permeability changes, and mediated by specific RARs. As the mechanism of action of fenretinide may be different from other retinoids, this compound may be a valuable adjunct to neuroblastoma therapy with retinoic acid and conventional chemotherapeutic drugs.

pRb and Cdk regulation by N-(4-hydroxyphenyl)retinamide

The cancer chemopreventive synthetic retinoid N-(4-hydroxyphenyl)retinamide (HPR) can inhibit the growth and induce apoptosis of tumor cells. In this study we analysed the growth suppressive effect of HPR on human breast cancer cell lines in vitro and the role of the retinoblastoma protein (pRb) in this response. Treatment of MCF7, T47D and SKBR3 for 24 - 48 h with 3 microM HPR, a concentration attainable in vivo, resulted in growth inhibition and marked dephosphorylation of pRb involving Ser612, Thr821, Ser795 and Ser780, target residues for cyclin-dependent kinase 2 (Cdk2) the former two, and Cdk4 the latter two. Interestingly, this dephosphorylation of pRb occurred in S-G2-M phase cells, as revealed by experiments on cells fractionated by FACS according to the cell cycle phase, hence suggesting that the retinoid interferes with the regulation of pRb phosphorylation. The in vitro phosphorylation of a GST-pRb recombinant substrate by Cdk2 immunocomplexes from MCF7, T47D and SKBR3 was markedly suppressed after HPR treatment, whereas that by Cdk4 complexes was suppressed in T47D and SKBR3 but not in MCF7. The steady-state levels of Cdk2, Cdk4 and Cyclin A proteins were unaffected by HPR, while those of Cyclin D1 were significantly reduced in all three cell lines. Interestingly, Cyclin D1 downregulation by HPR correlated with transcriptional repression, but not with enhanced proteolysis of Cyclin D1 typically elicited by other retinoids. Collectively, our data suggest that the antiproliferative activity of HPR arises from its capacity to maintain pRb in a de-phosphorylated growth-suppressive status in S-G2/M, possibly through Cyclin D1 downregulation and inhibition of pRb-targeting Cdks. Oncogene (2000) 19, 4035 - 41.

Increase of ceramide and induction of mixed apoptosis/necrosis by N-(4-hydroxyphenyl)- retinamide in neuroblastoma cell lines

BACKGROUND

The synthetic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR or fenretinide) is toxic to myeloid leukemia and cervical carcinoma cell lines, probably in part due to its ability to increase levels of reactive oxygen species (ROS). We have studied the effects of 4-HPR on neuroblastoma cell lines. Since neuroblastomas commonly relapse in bone marrow, a hypoxic tissue compartment, and many chemotherapeutic agents are antagonized by hypoxia, our purpose was to study in these cell lines several factors influencing 4-HPR-induced cytotoxicity, including induced levels of ROS, effects of physiologic hypoxia and antioxidants, levels of ceramide, and the mechanism of cell death.

METHODS

ROS generation was measured by carboxydichlorofluorescein diacetate fluoresence. Ceramide was quantified by radiolabeling and thin-layer chromatography. Immunoblotting was used to assess p53 protein levels. Apoptosis (programmed cell death) and necrosis were analyzed by nuclear morphology and internucleosomal DNA fragmentation patterns. Cytotoxicity was measured by a fluorescence-based assay employing digital imaging microscopy in the presence or absence of the pancaspase enzyme inhibitor BOC-d-fmk. Statistical tests were two-sided.

RESULTS/CONCLUSIONS

In addition to increasing ROS, 4-HPR (2.5-10 microM) statistically significantly increased the level of intracellular ceramide (up to approximately 10-fold; P<.001) in a dose-dependent manner in two neuroblastoma cell lines, one of which is highly resistant to alkylating agents and to etoposide. Cell death induced by 4-HPR was reduced but not abrogated by hypoxia in the presence or absence of an antioxidant, N-acetyl-L-cysteine. Expression of p53 protein was not affected by 4-HPR. Furthermore, the pan-caspase enzyme inhibitor BOC-d-fmk prevented apoptosis, but not necrosis, and only partially decreased cytotoxicity induced by 4-HPR, indicating that 4-HPR induced both apoptosis and necrosis in neuroblastoma cells.

IMPLICATIONS

4-HPR may form the basis for a novel, p53-independent chemotherapy that operates through increased intracellular levels of ceramide and that retains cytotoxicity under reduced oxygen conditions.

N-(4-hydroxyphenyl)retinamide-induced death in human lymphoblastoid cells: 50 kb DNA breakage as a means of distinguishing apoptosis from necrosis

Experimental studies of N-(4-hydroxyphenyl)retinamide, a potential cancer chemopreventive agent, have primarily involved breast cancer and neuroblastoma cell populations together with an investigation of myeloid leukemia cells and have principally been concerned with the induction of apoptosis. This investigation of N-(4-hydroxyphenyl)retinamide-induced apoptosis using T-cell-derived human lymphoblastoid lines extends these studies by indicating distinctive features associated with this drug. The induction of apoptosis is restricted to a limited concentration range, which, if exceeded, results in cell death by necrosis. While morphological changes typical of apoptosis induced by many agents are readily demonstrable after treatment of lymphoblastoid cells with 3 microM N-(4-hydroxyphenyl)retinamide, distinctive features evident using the retinoid include the absence of cell cycle arrest along with the mode and pattern of DNA breakage. Analysis by conventional gel electrophoresis indicated that internucleosomal fragmentation of DNA was an unreliable indicator of apoptosis. On the other hand, higher order DNA breakage was consistently detected during drug-induced apoptosis, but not as a result of treatment causing necrosis.

Fenretinide-induced apoptosis of human head and neck squamous carcinoma cell lines

BACKGROUND

Squamous cell carcinoma of the head and neck (HNSCC) has a high incidence of recurrence and associated second primary malignancy. The retinoid 13-cis-retinoic acid has been shown to be effective as both a chemopreventive and chemotherapeutic agent for HNSCC, but often with treatment-limiting toxicity. The synthetic retinoid fenretinide (N-(4-hydroxyphenyl)retinamide) (HPR) has significant antiproliferative activity against a number of animal and human malignancies and has been used in clinical trials as a chemopreventive agent in patients with breast and prostate cancer and oral leukoplakia. HPR has been shown to have a toxicity profile lower than that for other retinoids used in clinical trials.

PURPOSE

The aim of this study was to investigate the effect of HPR on the growth of HNSCC cell lines in vitro.

METHODS

Four HNSCC cell lines (JHU-011-SCC, JHU-020-SCC, JHU-022-SCC, and FaDu) were treated with a range of concentrations of HPR for various times. After HPR exposure, cell viability was determined by tetrazolium dye (MTT) colorimetric assay, comparing cell survival with that of untreated control cells. HPR-induced apoptosis was determined by flow-cytometric deoxyribonucleic acid cell-cycle analysis, ultrastructural analysis with electron microscopy, and deoxyribonucleic acid fragmentation detected by gel electrophoresis.

RESULTS

HPR caused significant growth inhibition in three of the four HNSCC cell lines in a dose- and time-dependent fashion. In two cell lines (JHU-011-SCC, JHU-020-SCC) a significant antiproliferative effect was achieved between 1 and 2.5 micromol/L HPR after 72 hours of treatment. By deoxyribonucleic acid cell-cycle analysis, electron microscopy, and gel electrophoresis, HPR was shown to induce apoptosis in the JHU-011-SCC and JHU-020-SCC cell lines, but not in the FaDu cell line, which was insensitive to the growth inhibitory effect of HPR.

CONCLUSIONS

This study has demonstrated that HPR reduces cell viability in HNSCC cells in vitro at clinically relevant doses, with the growth inhibition occurring through the induction of apoptosis.

Apoptosis in neurological disease

Enormous interest in cell death in the past several years has moved apoptosis to the forefront of scientific research. Apoptosis has been found to mediate cell deletion in tissue homeostasis, embryological development, and immunological functioning. It also occurs in pathological conditions, including cancer and acquired immunodeficiency syndrome, and is implicated in neurodegenerative diseases. Claims of neuronal apoptosis induced by various agents and conditions are published regularly, but in many instances the data are questionable because they are incomplete. This review presents a brief history of apoptosis and describes the evidence required before claims of apoptosis are made. Summaries and critiques of important investigations concerning the genetic and biochemical regulation of neuronal apoptosis are presented, as are other studies describing connections between apoptosis and neuronal cell death in physiological and pathological situations. There is a realization that apoptosis can be programmed and is distinguishable from necrotic cell death. Combining apoptosis with programmed cell death produces misleading terminology and confusion over these two forms of cell degeneration. Further investigations into neuronal apoptosis should focus on all of the criteria that the original investigators outlined 25 years ago, to clarify whether apoptosis and/or another form of cell death mediates neuronal degeneration in physiological settings and in neurological diseases such as Alzheimer's disease, Parkinson's disease, epilepsy, and ischemia/stroke.

Effects of fenretinide (4-HPR) on prostate LNCaP cell growth, apoptosis, and prostate-specific gene expression

BACKGROUND

Although fenretinide (4-HPR) is currently being evaluated in a phase II clinical study for the chemoprevention of prostate cancer [Greenwald et al.: CA 45:31-49, 1995], the mechanism underlying its antineoplastic activity has not been elucidated.

METHODS

Androgen-dependent human prostatic LNCaP cells cultured with fetal bovine serum (FBS) were treated with 4-HPR and evaluated for effects on cell growth and cell cycle phase distribution, induction of apoptosis, and changes in proliferating cell nuclear antigen (PCNA), prostate-specific antigen (PSA), and androgen receptor (AR) levels.

RESULTS

LNCaP cells treated with 4-HPR for 6 days showed 82-95% suppression of cell growth, with accompanying time- and dose-dependent downregulation of PCNA, a partial arrest in G1 phase of the cell cycle, and a marked increase in the percentage of apoptotic cells. Apoptosis was demonstrated by the characteristic DNA fragmentation pattern seen on agarose gels, and by flow cytometric analysis. 4-HPR-induced prostate-specific phenotype changes included significant downregulated expression of both intracellular and secreted forms of PSA, which were preceded by a reduction of AR expression.

CONCLUSIONS

These data suggest that 4-HPR acts as a pleiotropic effector of prostate cell growth and specific gene expression.

Specific activation of retinoic acid receptors (RARs) and retinoid X receptors reveals a unique role for RARgamma in induction of differentiation and apoptosis of S91 melanoma cells

Retinoic acid (RA) and 9-cis-RA induce growth arrest and differentiation of S91 melanoma cells. RA activates retinoic acid receptors (RARs), whereas 9-cis-RA activates both RARs and retinoid X receptors (RXRs). Both classes of receptors function as ligand-dependent transcription factors. S91 melanoma cells contain mRNA for RXRalpha, RXRbeta, RARalpha, RARgamma, and RARbeta in low levels. Among these, only RARbeta gene transcription is induced by retinoids. However, at present the individual role(s) for each RXR and RAR isoform in these processes is unclear. We assessed the function of all isoforms in the S91 melanoma model by using RXR and RAR isoform-specific retinoids to study their effects on cell growth, RARbeta expression, and differentiation. Activation of each of the endogenous RXR or RAR isoforms induces RARbeta gene expression, and blocks cellular proliferation. However, only the RARgamma-ligands cause additional differentiation toward a melanocytic phenotype, which coincides with substantial apoptosis well before morphological changes are apparent. Apoptosis is completely dependent on de novo protein synthesis but cannot be induced by changes in activities of AP-1, protein kinase C, and protein kinase A, nor can it be blocked by the presence of the antioxidant glutathione. These results argue against a specific role for RARbeta, but suggest that RARgamma has a critical role in a genetic switch between melanocytes and melanoma, and induction of ligand-dependent apoptosis.

Identification of a novel human kinesin-related gene (HK2) by the cDNA differential display technique

We have used the cDNA differential display technique to isolate genes regulated by the synthetic retinoid N-(4-hydroxyphenyl)-all-trans-retinamide (HPR), a cancer chemopreventive agent in vivo and a powerful inducer of apoptotic cell death in vitro. Here we report the identification of a novel gene, the expression of which is markedly up-regulated in tumor cells after treatment for 30-60 min with HPR. The full-length cDNA of this gene, determined by screening of a human placenta cDNA, is 3.5 kb long and contains an open reading frame of 2037 nt. The gene is > 90% homologous to the mouse KIF2, a gene belonging to the family of kinesin-related motor proteins, and we therefore named it HK2 (human kinesin 2). A shorter form of the HK2 mRNA (HK2s), containing a 57-nt deletion in the open reading frame, has also been detected. Northern analysis revealed that HK2 is widely expressed among hemopoietic and nonhemopoietic cell lines and tissues. By the use of radiation hybrids, HK2 has been localized to chromosome 5q12-q13. Kinesins constitute a superfamily of motor proteins that use energy liberated from ATP hydrolysis to move cargo along microtubules and are implicated in mechanisms of mitosis or meiosis. The role of HK2 in the growth-inhibitory and apoptotic responses elicited by HPR remains to be established.

N-(4-hydroxyphenyl)retinamide induces apoptosis in T lymphoma and T lymphoblastoid leukemia cells

We demonstrate that N-(4-hydroxyphenyl)-all-trans-retinamide (4-HPR), a synthetic retinoic acid (RA) derivative, is a potent and selective inducer of apoptosis in malignant T lymphoid cells, but has little effect on normal lymphoid cells of the thymus or spleen. 4-HPR and its stereoisomer, 9-cis-4-HPR, are 50 to > 150 times more potent than 7 other retinoids in killing CEM-C7 human T lymphoblastoid leukemia cells and P1798-C7 murine T lymphoma cells. 4-HPR's apoptotic action requires the intact molecule bearing both the retinoid moiety and the hydroxyphenol ring; 4-HPR remains unmetabolized after uptake into CEM-C7 and P1798-C7 cells for up to 24 hours. We also show that glucocorticoid (GC)-resistant variants are equally susceptible to 4-HPR as are GC-sensitive cells. Thus, 4-HPR may be potentially important as a new chemotherapeutic drug for use as alternative to, or in combination with, conventional drugs for treating lymphoid malignancies.

Induction of apoptosis in human neuroblastoma cells by abrogation of integrin-mediated cell adhesion

The survival, proliferation and differentiation of neuroblastoma (NB) cells are largely dependent on adhesion to extracellular matrix (ECM) proteins. Integrin occupancy seems to play a primary role. To elucidate the role of integrin heterodimers during neuronal cell death, we have analysed the changes in integrin expression in 2 human NB cell lines which represent different stages of neuronal maturation. Retinoic acid (RA) had different effects on the 2 NB cell lines: on LAN-5 cells it acted as a differentiation-promoting agent, while it had an anti-proliferative effect on GI-LI-N cells, driving them to apoptosis. Indeed, this occurrence was evidenced by the visualization of a "DNA ladder" on gel electrophoresis, by propidium iodide staining, and by DNA flow cytofluorimetric analysis. RA treatment rapidly and drastically decreased integrin expression and cell adhesion on GI-LI-N cells. These findings were also obtained by treating both NB cell lines with the apoptotic agent fenretinide. Furthermore, treatment of NB cells with anti-sense oligonucleotides to beta 1 integrin chain specifically induced chromatin condensation and nucleosomal DNA laddering. Moreover, blocking cell-matrix interactions by means of perturbing antibody against beta 1 subunit resulted in the induction of typical features of apoptotic cells. In conclusion, these findings indicate that abrogation of cell adhesion through down-modulation of integrin receptors plays a crucial role in the induction of neuroblastoma programmed cell death.

Current status of retinoids in chemoprevention of oral squamous cell carcinoma: an overview

Squamous cell carcinoma of the oral cavity and oropharynx may be amenable to chemoprevention. This review focuses on current concepts of mechanisms in oral carcinogenesis, as well as the evidence that retinoids have a role in the primary and secondary prevention of this malignancy.

Inhibition of proliferation and induction of apoptosis in cervical carcinoma cells by retinoids: implications for chemoprevention

The effects of retinoids including all-trans-retinoic acid (ATRA), 13-CIS-RETINOIC ACID (13CRA), and N-(4-hydroxyphenyl)retinamide (4-HPR) on several cervical carcinoma cell lines in culture were investigated as a prelude to investigating the mechanisms underlying the chemopreventive potential of retinoids in cervical cancer. We found that when used at a concentration of 1 microM, 13CRA and ATRA inhibited the proliferation of three cell lines (ME-180 [HPV 68], SiHa [HPV 18], and HT-3 [HPV-]) by about 80% after a seven-day treatment. Three other cell lines (MS-751 [HPV 18], HeLa [HPV 18], C-33A [HPV-]) were moderately inhibited (30-48%), and two (C-4 II [HPV 18], CaSki [HPV 16]) responded poorly (< 25% inhibition). 4-HPR failed to inhibit the growth of any of these cell lines when used at 1 microM; however, when used at 5 or 10 microM, it induced apoptosis as evidenced by DNA fragmentation in several of the cell lines and was more potent in this effect than 10 microM ATRA. Retinoids that induce apoptosis in malignant cells may be able to exert similar effects on premalignant cells. Such retinoids would be expected to exhibit greater potency as chemopreventive agents than retinoids that exert only cytostatic effects.