Phase I and pharmacokinetic evaluation of all-trans-retinoic acid in pediatric patients with cancer

Mitochondrial uncoupler and retinoic acid synergistically induce differentiation and inhibit proliferation in neuroblastoma

Neuroblastoma is a leading cause of death in childhood cancer cases. Unlike adult malignancies, which typically develop from aged cells through accumulated damage and mutagenesis, neuroblastoma originates from neural crest cells with disrupted differentiation. This distinct feature provides novel therapeutic opportunities beyond conventional cytotoxic methods. Previously, we reported that the mitochondrial uncoupler NEN (niclosamide ethanolamine) activated mitochondria respiration to reprogram the epigenome, promoting neuronal differentiation. In the current study, we further combine NEN with retinoic acid (RA) to promote neural differentiation both in vitro and in vivo. The treatment increased the expression of RA signaling and neuron differentiation-related genes, resulting in a global shift in the transcriptome towards a more favorable prognosis. Overall, these results suggest that the combination of a mitochondrial uncoupler and the differentiation agent RA is a promising therapeutic strategy for neuroblastoma.

Expression and activation of nuclear hormone receptors result in neuronal differentiation and favorable prognosis in neuroblastoma

BACKGROUND

Neuroblastoma (NB), a childhood tumor derived from the sympathetic nervous system, presents with heterogeneous clinical behavior. While some tumors regress spontaneously without medical intervention, others are resistant to therapy, associated with an aggressive phenotype. MYCN-amplification, frequently occurring in high-risk NB, is correlated with an undifferentiated phenotype and poor prognosis. Differentiation induction has been proposed as a therapeutic approach for high-risk NB. We have previously shown that MYCN maintains an undifferentiated state via regulation of the miR-17 ~ 92 microRNA cluster, repressing the nuclear hormone receptors (NHRs) estrogen receptor alpha (ERα) and the glucocorticoid receptor (GR).

METHODS

Cell viability was determined by WST-1. Expression of differentiation markers was analyzed by Western blot, RT-qPCR, and immunofluorescence analysis. Metabolic phenotypes were studied using Agilent Extracellular Flux Analyzer, and accumulation of lipid droplets by Nile Red staining. Expression of angiogenesis, proliferation, and neuronal differentiation markers, and tumor sections were assessed by immunohistochemistry. Gene expression from NB patient as well as adrenal gland cohorts were analyzed using GraphPad Prism software (v.8) and GSEA (v4.0.3), while pseudo-time progression on post-natal adrenal gland cells from single-nuclei transcriptome data was computed using scVelo.

RESULTS

Here, we show that simultaneous activation of GR and ERα potentiated induction of neuronal differentiation, reduced NB cell viability in vitro, and decreased tumor burden in vivo. This was accompanied by a metabolic reprogramming manifested by changes in the glycolytic and mitochondrial functions and in lipid droplet accumulation. Activation of the retinoic acid receptor alpha (RARα) with all-trans retinoic acid (ATRA) further enhanced the differentiated phenotype as well as the metabolic switch. Single-cell nuclei transcriptome analysis of human adrenal glands indicated a sequential expression of ERα, GR, and RARα during development from progenitor to differentiated chromaffin cells. Further, in silico analysis revealed that patients with higher combined expression of GR, ERα, and RARα mRNA levels had elevated expression of neuronal differentiation markers and a favorable outcome.

CONCLUSION

Together, our findings suggest that combination therapy involving activation of several NHRs could be a promising pharmacological approach for differentiation treatment of NB patients.

Restoration of dysbiotic human gut microbiome for homeostasis

The human microbiome is a complex and dynamic ecosystem, and the imbalance of its microbial community structure from the normal state is termed dysbiosis. The dysbiotic gut microbiome has been proved to be related to several pathological conditions like Inflammatory Bowel Disease (IBD), Irritable Bowel Syndrome (IBS), Colorectal Cancer (CRC), etc., and several other extra-intestinal conditions like Type 1 & 2 diabetes, obesity, etc. The complex gut microbial ecosystem starts to build before the birth of an individual. It is known to get affected by several factors such as birth mode, individual lifestyle, dietary practices, medications, and antibiotics. A dysbiotic microbiome can potentially hamper host homeostasis due to its role in immune modulation, metabolism, nutrient synthesis, etc. Restoration of the dysbiotic gut microbiome has emerged as a promising aid and a better therapeutic approach. Several approaches have been investigated to achieve this goal, including prebiotics and probiotics, Fecal Microbiota Transplantation (FMT), extracellular vesicles, immune modulation, microbial metabolites, dietary interventions, and phages. This review discusses the various factors that influence the human microbiome with respect to their cause-effect relationship and the effect of gut microbiome compositional changes on the brain through the gut-brain axis. We also discuss the practices used globally for gut microbiome restoration purposes, along with their effectiveness.

Targeting Protein Folding: A Novel Approach for the Treatment of Pathogenic Bacteria

Infectious diseases are a major cause of morbidity and mortality worldwide, exacerbated by increasing antibiotic resistance in many bacterial species. The development of drugs with new modes of action is essential. A leading strategy is antivirulence, with the aim to target bacterial proteins that are important in disease causation and progression but do not affect growth, resulting in reduced selective pressure for resistance. Immunophilins, a superfamily of peptidyl-prolyl cis-trans isomerase (PPIase) enzymes have been shown to be important for virulence in a broad-spectrum of pathogenic bacteria. This Perspective will provide an overview of the recent advances made in understanding the role of each immunophilin family, cyclophilins, FK506 binding proteins (FKBPs), and parvulins in bacteria. Inhibitor design and medicinal chemistry strategies for development of novel drugs against bacterial FKBPs will be discussed. Furthermore, drugs against human cyclophilins and parvulins will be reviewed in their current indication as antiviral and anticancer therapies.

Retinoic Acids in the Treatment of Most Lethal Solid Cancers

Although the use of oral administration of pharmacological all-trans retinoic acid (ATRA) concentration in acute promyelocytic leukaemia (APL) patients was approved for over 20 years and used as standard therapy still to date, the same use in solid cancers is still controversial. In the present review the literature about the top five lethal solid cancers (lung, stomach, liver, breast, and colon cancer), as defined by The Global Cancer Observatory of World Health Organization, and retinoic acids (ATRA, 9-cis retinoic acid, and 13-cis retinoic acid, RA) was compared. The action of retinoic acids in inhibiting the cell proliferation was found in several cell pathways and compartments: from membrane and cytoplasmic signaling, to metabolic enzymes, to gene expression. However, in parallel in the most aggressive phenotypes several escape routes have evolved conferring retinoic acids-resistance. The comparison between different solid cancer types pointed out that for some cancer types several information are still lacking. Moreover, even though some pathways and escape routes are the same between the cancer types, sometimes they can differently respond to retinoic acid therapy, so that generalization cannot be made. Further studies on molecular pathways are needed to perform combinatorial trials that allow overcoming retinoic acids resistance.

The Antagonist of Retinoic Acid Receptor α, ER-50891 Antagonizes the Inhibitive Effect of All-Trans Retinoic Acid and Rescues Bone Morphogenetic Protein 2-Induced Osteoblastogenic Differentiation

Background

Hypervitaminosis A, alcoholism or medical treatment for acute promyelocytic leukaemia may cause unphysiologically high accumulation of all-trans retinoic acid (ATRA), which could inhibit osteoblastogenesis, thereby triggering osteoporosis. We have shown that bone morphogenetic protein-2 (BMP-2) can only partially antagonize the inhibitive effects of ATRA. In this study, we hypothesized that antagonists of retinoic acid receptors (RARs) could further antagonize the inhibitive effect of ATRA and rescue BMP2-induced osteoblastogenesis.

Materials and Methods

We first screened the dose-dependent effects of the specific antagonists of RAR α, β and γ and transforming growth factor-beta receptor (ER-50891, LE-135, MM11253, and SB-43142, respectively) on ATRA-induced inhibition of the total cell metabolic activity and proliferation of preosteoblasts. We selected ER-50891 and tested its effects on osteoblastogenesis with the presence or absence of 1 μM ATRA and/or 200 ng/mL BMP-2. We measured the following parameters: Alkaline phosphatase activity (ALP), osteocalcin (OCN) expression and extracellular matrix mineralization as well as the level of phosphorylated Smad1/5.

Results

ER-50891 but not LE-135, MM11253, or SB-431542 significantly antagonized the inhibition of ATRA and enhanced the total cell metabolic activity and proliferation of preosteoblasts. Dose-dependent assays show ER-50891 could also rescue ATRA inhibited OCN expression and mineralization with or without the induction of BMP. ER-50891 also suppressed the ALP activity that was synergistically enhanced by BMP and ATRA. Neither ATRA, nor ER-50891 or their combination significantly affected the level of BMP-induced phosphorylated Smad1/5.

Conclusion

The antagonist of RARα, ER-50891 could significantly attenuate ATRA’s inhibitive effects on BMP 2-induced osteoblastogenesis.

Targeting PIN1 exerts potent antitumor activity in pancreatic ductal carcinoma via inhibiting tumor metastasis

The human prolyl isomerase PIN1, best known for its association with carcinogenesis, has recently been indicated in the disease of pancreatic ductal adenocarcinoma (PDAC). However, the functions of PIN1 and the feasibility of targeting PIN1 in PDAC remain elusive. For this purpose, we examined the expression of PIN1 in cancer, related paracarcinoma and metastatic cancer tissues by immunohistochemistry and analyzed the associations with the pathogenesis of PDAC in 173 patients. The functional roles of PIN1 in PDAC were explored in vitro and in vivo using both genetic and chemical PIN1 inhibition. We showed that PIN1 was upregulated in pancreatic cancer and metastatic tissues. High PIN1 expression is significantly association with poor clinicopathological features and shorter overall survival and disease‐free survival. Further stratified analysis showed that PIN1 phenotypes refined prognostication in PDAC. Inhibition of PIN1 expression with RNA interference or with all trans retinoic acid decreased not only the growth but also the migration and invasion of PDAC cells through regulating the key molecules of multiple cancer‐driving pathways, simultaneously resulting in cell cycle arrest and mesenchymal‐epithelial transition in vitro. Furthermore, genetic and chemical PIN1 ablation showed dramatic inhibition of the tumorigenesis and metastatic spread and then reduced the tumor burden in vivo. We provided further evidence for the use of PIN1 as a promising therapeutic target in PDAC. Genetic and chemical PIN1 ablation exerted potent antitumor effects through blocking multiple cancer‐driving pathways in PDAC. More potent and specific PIN1 targeted inhibitors could be exploited to treat this aggressive cancer.

The path toward using microbial metabolites as therapies

Metabolites have emerged as the quintessential effectors mediating the impact of the commensal microbiome on human physiology, both locally at the sites of microbial colonization and systemically. The endocrine activity of the microbiome and its involvement in a multitude of complex diseases has made microbiome-modulated metabolites an attractive target for the development of new therapies. Several properties make metabolites uniquely suited for interventional strategies: natural occurrence in a broad range of concentrations, functional pleiotropy, ease of administration, and tissue bioavailability. Here, we provide an overview of recently discovered physiological effects of microbiome-associated small molecules that may serve as the first examples of metabolite-based therapies. We also highlight challenges and obstacles that the field needs to overcome on the path toward successful clinical trials of microbial metabolites for human disease.

A 3D bioprinted hydrogel mesh loaded with all-trans retinoic acid for treatment of glioblastoma

Treatment of glioblastoma (GBM), as the most lethal type of brain tumor, still remains a major challenge despite the various therapeutic approaches developed over the recent decades. GBM is considered as one of the most therapy-resistant human tumors. Treatment with temozolomide (TMZ) chemotherapy and radiotherapy in GBM patients has led to 30% of two-year survival rate (American Brain Tumor Association), representing a demanding field to develop more effective therapeutic strategies. This study presents a novel method for local delivery of all-trans retinoic acid (ATRA) for targeting GBM cells as a possible adjuvant therapeutic strategy for this disease. We have used 3D bioprinting to fabricate hydrogel meshes laden with ATRA-loaded polymeric particles. The ATRA-loaded meshes have been shown to facilitate a sustained release of ATRA with tunable release rate. Cell viability assay was used to demonstrate the ability of fabricated meshes in reducing cell growth in U-87 MG cell line. We later showed that the developed meshes induced apoptotic cell death in U-87 MG. Furthermore, the use of hydrogel for embedding the ATRA-loaded particles can facilitate the immobilization of the drug next to the tumor site. Our current innovative approach has shown the potential to open up new avenues for treatment of GBM, benefiting patients who suffer from this debilitating disease.

Arsenic targets Pin1 and cooperates with retinoic acid to inhibit cancer-driving pathways and tumor-initiating cells

Arsenic trioxide (ATO) and all-trans retinoic acid (ATRA) combination safely cures fatal acute promyelocytic leukemia, but their mechanisms of action and efficacy are not fully understood. ATRA inhibits leukemia, breast, and liver cancer by targeting isomerase Pin1, a master regulator of oncogenic signaling networks. Here we show that ATO targets Pin1 and cooperates with ATRA to exert potent anticancer activity. ATO inhibits and degrades Pin1, and suppresses its oncogenic function by noncovalent binding to Pin1's active site. ATRA increases cellular ATO uptake through upregulating aquaporin-9. ATO and ATRA, at clinically safe doses, cooperatively ablate Pin1 to block numerous cancer-driving pathways and inhibit the growth of triple-negative breast cancer cells and tumor-initiating cells in cell and animal models including patient-derived orthotopic xenografts, like Pin1 knockout, which is substantiated by comprehensive protein and microRNA analyses. Thus, synergistic targeting of Pin1 by ATO and ATRA offers an attractive approach to combating breast and other cancers.

Pin1 inhibition exerts potent activity against acute myeloid leukemia through blocking multiple cancer-driving pathways

Background

The increasing genomic complexity of acute myeloid leukemia (AML), the most common form of acute leukemia, poses a major challenge to its therapy. To identify potent therapeutic targets with the ability to block multiple cancer-driving pathways is thus imperative. The unique peptidyl-prolyl cis-trans isomerase Pin1 has been reported to promote tumorigenesis through upregulation of numerous cancer-driving pathways. Although Pin1 is a key drug target for treating acute promyelocytic leukemia (APL) caused by a fusion oncogene, much less is known about the role of Pin1 in other heterogeneous leukemia.

Methods

The mRNA and protein levels of Pin1 were detected in samples from de novo leukemia patients and healthy controls using real-time quantitative RT-PCR (qRT-PCR) and western blot. The establishment of the lentiviral stable-expressed short hairpin RNA (shRNA) system and the tetracycline-inducible shRNA system for targeting Pin1 were used to analyze the biological function of Pin1 in AML cells. The expression of cancer-related Pin1 downstream oncoproteins in shPin1 (Pin1 knockdown) and Pin1 inhibitor all-trans retinoic acid (ATRA) treated leukemia cells were examined by western blot, followed by evaluating the effects of genetic and chemical inhibition of Pin1 in leukemia cells on transformed phenotype, including cell proliferation and colony formation ability, using trypan blue, cell counting assay, and colony formation assay in vitro, as well as the tumorigenesis ability using in vivo xenograft mouse models.

Results

First, we found that the expression of Pin1 mRNA and protein was significantly increased in both de novo leukemia clinical samples and multiple leukemia cell lines, compared with healthy controls. Furthermore, genetic or chemical inhibition of Pin1 in human multiple leukemia cell lines potently inhibited multiple Pin1 substrate oncoproteins and effectively suppressed leukemia cell proliferation and colony formation ability in cell culture models in vitro. Moreover, tetracycline-inducible Pin1 knockdown and slow-releasing ATRA potently inhibited tumorigenicity of U937 and HL-60 leukemia cells in xenograft mouse models.

Conclusions

We demonstrate that Pin1 is highly overexpressed in human AML and is a promising therapeutic target to block multiple cancer-driving pathways in AML.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0611-7) contains supplementary material, which is available to authorized users.

Pin1-Targeted Therapy for Systemic Lupus Erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) is a debilitating autoimmune disease affecting multiple organs in the body, but therapeutic options are still very limited and often come with adverse effects. Increasing evidence has underlined an important role of the Toll-like receptor 7 (TLR-7)/TLR-9/interleukin-1 receptor-associated kinase 1 (IRAK-1)/interferon regulatory factor 7 (IRF-7) pathway in the development and progression of SLE. Notably, the prolyl isomerase Pin1 is an essential regulator of IRAK-1 in TLR-7/TLR-9 signaling, but its role in SLE is unknown. We undertook this study to determine whether Pin1 is activated and plays any role in the development and treatment of SLE.

METHODS

Activation of Pin1 and TLR-7/TLR-9/IRAK-1/IRF-7 signaling was determined in various cell types among peripheral blood mononuclear cells from healthy controls and SLE patients. The effects of Pin1 and TLR signaling on SLE development were determined using validated Pin1 short hairpin RNA (shRNA), Pin1 genetic knockout, and the small-molecule Pin1 inhibitor all-trans-retinoic acid (ATRA) in immune cells and in several strains of lupus-prone mice.

RESULTS

We found abnormal activation of Pin1 and its downstream targets IRAK-1 and IRF-7 in SLE patients. Furthermore, inhibition of Pin1 using either validated Pin1 shRNA or ATRA blocked TLR-7-induced activation of IRAK-1 and IRF-7 in SLE patient-derived immune cells. Moreover, in multiple lupus-prone animals, both Pin1 knockout and ATRA strikingly attenuated the expression of autoimmunity, including skin lesions, lymphadenopathy, splenomegaly, glomerulonephritis, proteinuria, and production of anti-double-stranded DNA antibodies and CD4-CD8- T cells, and also prolonged overall survival in MRL/lpr and B6.lpr mice.

CONCLUSION

Pin1 plays a critical role in the development of SLE, and Pin1-targeted therapy offers a promising new strategy for treating SLE.

Physiologically Based Pharmacokinetic Model of All-trans-Retinoic Acid with Application to Cancer Populations and Drug Interactions

All-trans retinoic acid (atRA) is a front-line treatment of acute promyelocytic leukemia (APL). Due to its activity in regulating the cell cycle, it has also been evaluated for the treatment of other cancers. However, the efficacy of atRA has been limited by atRA inducing its own metabolism during therapy, resulting in a decrease of atRA exposure during continuous dosing. Frequent relapse occurs in patients receiving atRA monotherapy. In an attempt to combat therapy resistance, inhibitors of atRA metabolism have been developed. Of these, ketoconazole and liarozole have shown some benefits, but their usage is limited by side effects and low potency toward the cytochrome P450 26A1 isoform (CYP26A1), the main atRA hydroxylase. We determined the pharmacokinetic basis of therapy resistance to atRA and tested whether the complex disposition kinetics of atRA could be predicted in healthy subjects and in cancer patients in the presence and absence of inhibitors of atRA metabolism using physiologically based pharmacokinetic (PBPK) modeling. A PBPK model of atRA disposition was developed and verified in healthy individuals and in cancer patients. The population-based PBPK model of atRA disposition incorporated saturable metabolic clearance of atRA, induction of CYP26A1 by atRA, and the absorption and distribution kinetics of atRA. It accurately predicted the changes in atRA exposure after continuous dosing and when coadministered with ketoconazole and liarozole. The developed model will be useful in interpretation of atRA disposition and efficacy, design of novel dosing strategies, and development of next-generation atRA metabolism inhibitors.

Chemical or genetic Pin1 inhibition exerts potent anticancer activity against hepatocellular carcinoma by blocking multiple cancer-driving pathways

Hepatocellular carcinoma (HCC) is one of the most prevalent and malignant cancers with high inter- and intra-tumor heterogeneity. A central common signaling mechanism in cancer is proline-directed phosphorylation, which is further regulated by the unique proline isomerase Pin1. Pin1 is prevalently overexpressed in human cancers including ~70% of HCC, and promotes tumorigenesis by activating multiple cancer-driving pathways. However, it was challenging to evaluate the significance of targeting Pin1 in cancer treatment until the recent identification of all-trans retinoic acid (ATRA) as a Pin1 inhibitor. Here we systematically investigate functions of Pin1 and its inhibitor ATRA in the development and treatment of HCC. Pin1 knockdown potently inhibited HCC cell proliferation and tumor growth in mice. ATRA-induced Pin1 degradation inhibited the growth of HCC cells, although at a higher IC50 as compared with breast cancer cells, likely due to more active ATRA metabolism in liver cells. Indeed, inhibition of ATRA metabolism enhanced the sensitivity of HCC cells to ATRA. Moreover, slow-releasing ATRA potently and dose-dependently inhibited HCC growth in mice. Finally, chemical or genetic Pin1 ablation blocked multiple cancer-driving pathways simultaneously in HCC cells. Thus, targeting Pin1 offers a promising therapeutic approach to simultaneously stop multiple cancer-driving pathways in HCC.

A comparison of safety and efficacy of cytotoxic versus molecularly targeted drugs in pediatric phase I solid tumor oncology trials

BACKGROUND

Prior reviews of phase I pediatric oncology trials involving primarily cytotoxic agents have reported objective response rates (ORRs) and toxic death rates of 7.9-9.6% and 0.5%, respectively. These data may not reflect safety and efficacy in phase I trials of molecularly targeted (targeted) drugs.

METHODS

A systematic review of pediatric phase I solid tumor trials published in 1990-2013 was performed. The published reports were evaluated for patient characteristics, toxicity information, and response numbers.

RESULTS

A total of 143 phase I pediatric clinical trials enrolling 3,896 children involving 53 targeted and 48 cytotoxic drugs were identified. A meta-analysis demonstrated that the ORR is 2.1-fold higher with cytotoxic drugs (0.066 vs. 0.031 per subject; P = 0.007). By contrast, the pooled estimate of the stable disease rate (SDR) is similar for cytotoxic and targeted drugs (0.2 vs. 0.23 per subject; P = 0.27).  The pooled estimate of the dose-limiting toxicity rate is 1.8-fold larger with cytotoxic drugs (0.24 vs. 0.13 per subject; P = 0.0003). The hematologic grade 3-4 (G3/4) toxicity rate is 3.6-fold larger with cytotoxic drugs (0.43 vs. 0.12 per treatment course; P = 0.0001); however, the nonhematologic G3/4 toxicities and toxic deaths occur at similar rates for cytotoxic and targeted drugs.

CONCLUSIONS

In phase I pediatric solid tumor trials, ORRs were significantly higher for cytotoxic versus targeted agents. SDRs were similar in targeted and cytotoxic drug trials. Patients treated with cytotoxic agents were more likely to experience hematologic G3/4 toxicities than those patients receiving targeted drugs.

Pseudotumor Cerebri in Acute Promyelocytic Leukemia Patients on Intergroup Protocol 0129: Clinical Description and Recommendations for New Diagnostic Criteria

BACKGROUND

Multiple randomized trials have demonstrated a benefit for all-trans retinoic acid (ATRA) in patients with acute promyelocytic leukemia (APL). Pseudotumor cerebri (PTC) is an infrequently reported adverse effect of ATRA.

METHODS

We examined the incidence, clinical course, and outcomes of patients with APL treated on Intergroup Protocol 0129 (I0129) who developed PTC. This trial evaluated the role of ATRA alone during induction and/or as maintenance therapy.

RESULTS

Of the patients on trial, 240 received ATRA during induction, maintenance, or both; 8 had a clinical suspicion for PTC. Upon review of individual cases, this was felt to be "probable" in 4 patients, "possible" in 1 and "unlikely" in 3 due to lack of diagnostic criteria or presence of a more likely alternate diagnosis.

CONCLUSIONS

"Probable" PTC occurred in 1.7% of patients who received ATRA during induction and/or maintenance therapy. In agreement with previous reports, the incidence of PTC in APL patients receiving ATRA was higher in the pediatric population. Here, we discuss the method for diagnosing PTC in the setting of ATRA therapy and management strategies.

Treatment of paediatric APL: how does the therapeutic approach differ from adults?

Acute promyelocytic leukaemia (APL) in children and adolescents shares many features with APL in adults. There are important distinctions, however, between these age groups in the presentation, complications and treatment outcomes. Paediatric patients are more likely to present with high risk features including elevated WBC count or microgranular variant (M3v). Yet the early death rate is lower in paediatric patients compared to adult patients. Overall outcomes such as CR, OS and EFS appear similar in paediatric and adult patients treated on similar regimens except that very young children may have a higher risk of relapse. While contemporary studies have clearly demonstrated improved survival in adults receiving ATO therapy, currently there is more limited data on the role of ATO in paediatric patients. Here we highlight the similarities and important distinctions between paediatric and adult APL while reviewing available data on treatment of paediatric APL.

Bortezomib sensitizes human acute myeloid leukemia cells to all-trans-retinoic acid-induced differentiation by modifying the RARα/STAT1 axis

All-trans-retinoic acid (ATRA) has held great promise for differentiation-based therapy but reportedly downregulates retinoic acid receptor-α (RARα) in a proteasome-dependent manner, which leads to decreased acute myeloid leukemia (AML) cell differentiation efficiency. Therefore, research strategies that seek to further sensitize cells to retinoids and extend the range of retinoid-affected myeloid malignancies beyond acute promyelocytic leukemia (APL) are key investigative avenues. Here, we show that bortezomib, the first proteasome inhibitor approved for newly diagnosed and relapsed multiple myeloma, exhibited strong synergism with ATRA to promote HL60 and NB4 AML cell differentiation. We observed that bortezomib sensitized AML cells to ATRA-induced morphologic, biochemical, and functional changes, indicative of myeloid differentiation without cell death. In addition, treatment of human leukemia HL60 xenografts with bortezomib and ATRA together did not increase bortezomib-induced progressive weight loss but resulted in significant tumor growth inhibition in addition to increased differentiation (P < 0.05). These enhanced differentiation effects were accompanied by RARα stabilization and STAT1 activation. Taken together, our study was the first to evaluate bortezomib and ATRA synergy in AML cell differentiation and to assess new opportunities for bortezomib and ATRA combination as a promising approach for future differentiation therapy.

All-Trans Retinoic Acid-Induced Pseudotumor Cerebri during Induction Therapy for Acute Promyelocytic Leukemia: A Case Report and Literature Review

All-trans retinoic acid (ATRA), a derivative of vitamin A, is an essential component in the treatment of acute promyelocytic leukemia (APL). Though considered to be a relatively safe drug, use of ATRA can lead to several side effects such as retinoic acid syndrome and pseudotumor cerebri (PC). PC is a rare disorder characterized by neurologic and ocular signs and symptoms of increased intracranial pressure, but with normal cerebrospinal fluid composition and normal brain imaging. Most of the previous studies suggest that PC, as a complication of ATRA therapy, occurs predominantly in the pediatric age group. Herein, we report a rare case of ATRA-induced PC in a 38-year-old woman undergoing induction treatment for APL. Symptoms improved with discontinuation of ATRA and treatment with acetazolamide. Concomitant administration of medications such as triazole antifungals which influence the cytochrome P-450 system can exacerbate this potential complication of ATRA. In this paper, we also review the current literature, provide a descriptive analysis of clinical features, and discuss the principles of management of ATRA-induced PC.

Targeted therapy in pediatric and adolescent oncology

Cancers in children and adolescents are fortunately infrequent. Overall, cure rates are good, approximately 80%, although this varies by histology and stage. Targeted therapies aim to improve efficacy and decrease toxicity by more specifically affecting malignant cells or their supporting stroma. Cancers of early life are often of different histology than those seen in adults. Sometimes, the same pathway is affected, even if the histology is different. Toxicities may also be different, particularly in younger children. These factors render drug development in young people challenging. This article reviews some successes and challenges to that development, including brief discussions of imatinib, lestaurtinib, antiangiogenesis, and anti-GD2 therapies.

All-trans retinoic acid downregulates ALK in neuroblastoma cell lines and induces apoptosis in neuroblastoma cell lines with activated ALK

Recently, gene amplification and gain-of-function mutations of ALK have been found in some neuroblastoma cell lines and clinical tumor samples. We have previously reported that knockdown of ALK by RNAi induced apoptosis in neuroblastoma cells with gene amplification of ALK. We report that all-trans retinoic acid (ATRA) downregulates ALK in neuroblastoma cell lines. Downregulation of ALK protein by ATRA was accompanied by apoptosis in neuroblastoma cells with gene amplification or gain-of-function mutation of ALK but not in neuroblastoma cells without these genetic alterations. These results suggest that ALK downregulation by ATRA might lead to apoptosis in neuroblastoma cells with activated ALK.

Central nervous system involvement at the time of presentation in acute promyelocytic leukemia

Central nervous system (CNS) involvement is rarely observed in acute promyelocytic leukemia (APML). Most cases of CNS involvement occur at relapse rather than at presentation. Because of the extremely low incidence of CNS disease, diagnostic lumbar puncture is not routinely required and prophylactic intrathecal chemotherapy is not routinely administered. Here, we describe a teenage patient with newly diagnosed APML, chloromas, and symptomatic CNS involvement confirmed by MRI and cerebrospinal fluid (CSF) findings.

Single-agent arsenic trioxide in the treatment of children with newly diagnosed acute promyelocytic leukemia

The aim of this study was to determine the efficacy and safety of treatment of pediatric acute promyelocytic leukemia (APL) with single-agent arsenic trioxide (ATO). A total of 19 children (≤ 15 years of age) with newly diagnosed APL were treated with single-agent ATO for remission induction and postremission therapy. Seventeen of the children (89.5%) achieved complete hematologic remission, and 2 early deaths occurred from intracranial hemorrhage. ATO-induced leukocytosis was observed in 13 (68.4%) patients. Other ATO-related toxicities were minimal and transient. Postremission ATO therapy continued for 3 years; the most common side effect was ATO-induced neutropenia. With a median follow-up of 53 months (range, 23-76 months), the calculated 5-year overall survival and event-free survival were 83.9% and 72.7%, respectively, which are comparable with results achieved by the use of ATRA plus chemotherapy, which is the standard therapy for APL. No chronic arsenic toxicity or second malignancies were found during the follow-up period, and arsenic retention was not significant in patients off treatment more than 24 months. ATO resistance was observed in only 1 patient with a complex karyotype. The results indicate the high efficacy and safety of single-agent ATO regimens in the treatment of children with de novo APL.

Potential of retinoic acid derivatives for the treatment of corticotroph pituitary adenomas

Cushing's disease is a severe clinical condition caused by hypersecretion of corticosteroids due to excessive ACTH secretion from a pituitary adenoma. This complex endocrine disorder still represents a major challenge for the physician in terms of efficient treatment. In the last years there was only little progress in elucidating the molecular mechanisms responsible for the constitutive and autonomous ACTH secretion of pituitary corticotrophinomas. As a consequence, no effective drug therapy is currently available, particularly if surgical excision is not successful. In the present article we examine recent studies that have investigated the therapeutic potential of retinoic acid receptors as nuclear receptor targets for the treatment of Cushing's disease. Retinoic acid is an efficient drug used for the treatment of different types of cancers and it proved to act in animal models of Cushing's disease. The efficiency of this treatment in patients with this disorder still needs to be tested in clinical trials.

Pediatric idiopathic intracranial hypertension

Our understanding of pediatric idiopathic intracranial hypertension has been refined since Dr. Simmons Lessell's review in 1992. The use of rigorous methodologies and standard definitions in recent studies has demonstrated distinct demographic trends. Specifically, the incidence of idiopathic intracranial hypertension seems to be increasing among adolescent children, and among older children its clinical picture is similar to that of adult idiopathic intracranial hypertension (female and obese). Within younger age groups there are more boys and nonobese children who may develop idiopathic intracranial hypertension. The pathogenesis of the disease has yet to be elucidated. Idiopathic intracranial hypertension among young children has been associated with several new etiologies, including recombinant growth hormone and all-trans-retinoic acid. More modern neuroimaging techniques such as MRI and MRI-venograms are being used to exclude intracranial processes. Although most cases of pediatric idiopathic intracranial hypertension improve with medical treatment, those who have had visual progression despite medical treatment have undergone optic nerve sheath fenestration and lumboperitoneal shunting. Because idiopathic intracranial hypertension in young children appears to be a different disorder than in adolescents and adults, separate diagnostic criteria for younger children are warranted. We propose new criteria for pediatric idiopathic intracranial hypertension in which children should have signs or symptoms consistent with elevated intracranial pressure, be prepubertal, have normal sensorium, can have reversible cranial nerve palsies, and have an opening cerebrospinal fluid pressure greater than 180 mm H(2)O if less than age 8 and papilledema is present, but greater than 250 mm H(2)0 if age 8 or above or less than 8 without papilledema.

Chronic vitamin A status and acute repletion with retinyl palmitate are determinants of the distribution and catabolism of all-trans-retinoic acid in rats

The relation between vitamin A (VA) nutritional status and the metabolism of all-trans-retinoic acid (RA) is not well understood. In this study, we determined the tissue distribution and metabolism of a test dose of [(3)H]-RA in rats with graded, diet-dependent, differences in VA status. The design included 3 groups, designated VA-deficient, VA-marginal, and VA-adequate, with liver total retinol concentrations of 9.7, 35.7 and 359 nmol/g, respectively, (P < 0.05), and an additional group of VA-deficient rats treated with a single oral dose of retinyl palmitate (RP) 20 h before the injection of [(3)H]-RA. Plasma, liver, lung, and small intestines, collected 30 min after [(3)H]-RA, were analyzed for total (3)H, unmetabolized [(3)H]-RA, polar organic-phase metabolites of [(3)H]-RA, and aqueous phase [(3)H]-labeled metabolites. In all groups, [(3)H]-RA was rapidly removed from plasma and concentrated in the liver. VA deficiency did not prevent the oxidative metabolism of RA. Nevertheless, the quantity of [(3)H]-RA metabolites in plasma and the ratio of total [(3)H]-polar metabolites to unmetabolized [(3)H]-RA in liver varied directly with VA status (VA-adequate > VA-marginal > VA-deficient, P < 0.05). Moreover, supplementation of VA-deficient rats with RP reduced the metabolism of [(3)H]-RA, similar to that in VA-adequate or VA-marginal rats. Liver retinol concentration, considered a proxy for VA status, was correlated (P < 0.05) with [(3)H]-RA metabolites in liver (R(2) = 0.54), plasma (R(2) = 0.44), lung (R(2) = 0.40), intestine (R(2) = 0.62), and all combined (R(2) = 0.655). Overall, the results demonstrate close linkage between dietary VA intake, hepatic storage of VA, and the degradation of RA and suggest that measuring plasma retinoid metabolites after a dose of RA may provide insight into the metabolism of this bioactive retinoid by visceral organs.

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.

All-trans-retinoic acid distribution and metabolism in vitamin A-marginal rats

Retinoids, including all-trans-retinoic acid (RA), are considered to have anti-inflammatory properties and are used therapeutically for diseases of the skin and certain cancers. However, few studies have addressed the effects of disease states on RA metabolism. The present study was conducted to better understand the effects of exogenous RA, both in the absence and presence of inflammation, on the distribution and metabolism of a dose of [3H]RA. Female Sprague-Dawley rats fed a low vitamin A diet were pretreated with RA (po), a low dose of lipopolysaccharide (LPS, ip), or their combination. Twelve hours later, albumin-bound [3H]RA was injected intravenously, and tissue organic- and aqueous-phase 3H was determined after 10 and 30 min. In liver and plasma, 3H-labeled organic metabolites (e.g., 4-oxo- and 4-hydroxy-RA) were isolated by solid-phase extraction. LPS-induced inflammation significantly reduced plasma retinol by 47%, increased total 3H in plasma at 10 min, and reduced total 3H in liver at both times. In contrast, RA pretreatment did not affect plasma retinol, significantly increased total 3H in plasma at both times, and did not affect liver total 3H. However, by 30 min, RA significantly increased [3H]RA metabolism in plasma, liver, lung, and small intestine, as indicated by greater 3H-labeled aqueous-phase and 3H-labeled organic-phase metabolites. The results presented here demonstrate that, although LPS-induced inflammation affects the organ distribution of RA, the ability of RA to induce its own catabolism is maintained during inflammation. Thus we conclude that RA and LPS act independently to alter RA metabolism in vitamin A-marginal rats.

Retinoic acid metabolism blocking agents (RAMBAs) for treatment of cancer and dermatological diseases

The naturally occurring retinoids and their synthetic analogs play a key role in differentiation, proliferation, and apoptosis, and their use/potential in oncology, dermatology and a variety of diseases are well documented. This review focuses on the role of all-trans-retinoic acid (ATRA), the principal endogenous metabolite of vitamin A (retinol) and its metabolism in oncology and dermatology. ATRA has been used successfully in differentiated therapy of acute promyelocytic leukemia, skin cancer, Kaposi's sarcoma, and cutaneous T-cell lymphoma, and also in the treatment of acne and psoriasis. However, its usefulness is limited by the rapid emergence of acquired ATRA resistance involving multifactoral mechanisms. A key mechanism of resistance involves ATRA-induced catabolism of ATRA. Thus, a novel strategy to overcome the limitation associated with exogenous ATRA therapy has been to modulate and/or increase the levels of endogenous ATRA by inhibiting the cytochrome P450-dependent ATRA-4-hydroxylase enzymes (particularly CYP26s) responsible for ATRA metabolism. These inhibitors are also referred to as retinoic acid metabolism blocking agents (RAMBAs). This review highlights development in the design, synthesis, and evaluation of RAMBAs. Major emphasis is given to liarozole, the most studied and only RAMBA in clinical use and also the new RAMBAs in development and with clinical potential.

Inhibitory effects of retinoic acid metabolism blocking agents (RAMBAs) on the growth of human prostate cancer cells and LNCaP prostate tumour xenografts in SCID mice

In recent studies, we have identified several highly potent all-trans-retinoic acid (ATRA) metabolism blocking agents (RAMBAs). On the basis of previous effects of liarozole (a first-generation RAMBA) on the catabolism of ATRA and on growth of rat Dunning R3227G prostate tumours, we assessed the effects of our novel RAMBAs on human prostate tumour (PCA) cell lines. We examined three different PCA cell lines to determine their capacity to induce P450-mediated oxidation of ATRA. Among the three different cell lines, enhanced catabolism was detected in LNCaP, whereas it was not found in PC-3 and DU-145. This catabolism was strongly inhibited by our RAMBAs, the most potent being VN/14-1, VN/50-1, VN/66-1, and VN/69-1 with IC50 values of 6.5, 90.0, 62.5, and 90.0 nM, respectively. The RAMBAs inhibited the growth of LNCaP cells with IC50 values in the microM-range. In LNCaP cell proliferation assays, VN/14-1, VN/50-1, VN/66-1, and VN/69-1 also enhanced by 47-, 60-, 70-, and 65-fold, respectively, the ATRA-mediated antiproliferative activity. We then examined the molecular mechanism underlying the growth inhibitory properties of ATRA alone and in combination with RAMBAs. The mechanism appeared to involve the induction of differentiation, cell-cycle arrest, and induction of apoptosis (TUNEL), involving increase in Bad expression and decrease in Bcl-2 expression. Treatment of LNCaP tumours growing in SCID mice with VN/66-1 and VN/69-1 resulted in modest but statistically significant tumour growth inhibition of 44 and 47%, respectively, while treatment with VN/14-1 was unexpectedly ineffective. These results suggest that some of our novel RAMBAs may be useful agents for the treatment of prostate cancer.

Regulation of a highly specific retinoic acid-4-hydroxylase (CYP26A1) enzyme and all-trans-retinoic acid metabolism in human intestinal, liver, endothelial, and acute promyelocytic leukemia cells

The recently identified retinoic acid (RA)-metabolizing cytochrome P450RAI-1 (CYP26A1) has been implicated in accelerated metabolism and rapid clearance of all-trans-retinoic acid (ATRA) during prolonged oral administration in patients with acute promyelocytic leukemia (APL), leading to a progressive decline in plasma drug levels. We studied induction and regulation of CYP26A1 expression and ATRA metabolism in human intestinal (Caco-2), liver (HepG2), endothelial (HUVEC), and APL (NB4) cell lines. ATRA rapidly induced upregulation of CYP26A1 mRNA expression in a dose-dependent manner. Other retinoids (retinol, 9-cis-RA, and 13-cis-RA) also induced significant CYP26A1 expression in HepG2 and NB4 cells. CYP26A1 mRNA expression in HepG2 cells returned to baseline in 48 h upon removal of ATRA from the culture medium, suggesting that the expression is reversible and requires the presence of ATRA. In endothelial cells, however, a higher concentration of ATRA (10 microM) was required to induce expression of CYP26A1. A specific RA receptor-alpha antagonist totally inhibited ATRA-induced expression of CYP26A1, indicating that RA receptor-alpha plays a major role in CYP26A1 expression in HepG2 cells. Liposomal incorporation of ATRA has been shown to alter its metabolism. Therefore, we also tested CYP26A1 expression after administration of free ATRA and liposomal ATRA (L-ATRA). L-ATRA induced lower CYP26A1 expression and metabolic activity in HepG2 and NB4 cells when compared with free ATRA. Pretreatment of cells with free ATRA resulted in higher metabolic activity as indicated by conversion of radiolabeled [3H]-ATRA into its metabolites (4-oxo-RA and 4-hydroxy-RA), which was associated with lower nuclear localization of [3H]-ATRA when compared with pretreatment with L-ATRA. Our data suggest that upregulation of CYP26A1 expression in intestinal, endothelial, liver, and APL cells and metabolism of ATRA may play a role in rapid clearance of ATRA after continuous oral administration. Therapeutic strategies such as liposomal encapsulation and intermittent administration of ATRA may circumvent accelerated ATRA metabolism and improve the treatment of APL.

Pediatric Phase I Trials in Oncology: An Analysis of Study Conduct Efficiency

Purpose

To determine the efficacy and safety of pediatric phase I oncology trials in the era of dose-intensive chemotherapy and to analyze how efficiently these trials are conducted.

Methods

Phase I pediatric oncology trials published from 1990 to 2004 and their corresponding adult phase I trials were reviewed. Dose escalation schemes using fixed 30% dose increments were studied to theoretically determine whether trials could be completed utilizing fewer patients and dose levels.

Results

Sixty-nine pediatric phase I oncology trials enrolling 1,973 patients were identified. The pediatric maximum-tolerated dose (MTD) was strongly correlated with the adult MTD (r = 0.97). For three-fourths of the trials, the pediatric and adult MTD differed by no more than 30%, and for more than 85% of the trials, the pediatric MTD was less than or equal to 1.6 times the adult MTD. The median number of dose levels studied was four (range, two to 13). The overall objective response rate was 9.6%, the likelihood of experiencing a dose-limiting toxicity was 24%, and toxic death rate was 0.5%.

Conclusion

Despite the strong correlation between the adult and pediatric MTDs, more than four dose levels were studied in 40% of trials. There appeared to be little value in exploring dose levels greater than 1.6 times the adult MTD. Limiting pediatric phase I trials to a maximum of four doses levels would significantly shorten the timeline for study conduct without compromising safety.

Outcome of Childhood Acute Promyelocytic Leukemia With All-Trans-Retinoic Acid and Chemotherapy

Purpose

To determine the results of treatment combining all-trans-retinoic acid (ATRA) and chemotherapy (CT) in childhood acute promyelocytic leukemia (APL).

Patients and Methods

Children (< 18 years) with newly diagnosed APL were included in the APL93 trial, treated by ATRA followed or combined with daunorubicin-cytarabine, and then randomly assigned between no maintenance, intermittent ATRA, continuous CT, or both.

Results

Of the 576 patients included in APL93 trial, 31 (5%) were children, including 22 girls (71%) and nine boys (29%). Thirty of the children (97%) obtained complete remission (CR). ATRA syndrome occurred in four children (13%), who all achieved CR, and headaches occurred in 12 children (39%), with signs of pseudotumor cerebri in five children (16%). Seven patients (23%) relapsed. None of the eight patients who received both ATRA and CT for maintenance relapsed. All relapsing patients achieved a second CR. Twenty-two patients remained in first CR after 43+ to 96+ months, six remained in second CR after 17+ to 66+ months, and three patients had died. The 5-year event-free survival (EFS), relapse, and overall survival rates were 71%, 27%, and 90%, respectively. No difference between adults and children included in the APL93 trial was seen for CR rate, 5-year relapse rate, EFS, and overall survival, but significantly better survival was seen in children after adjustment on WBC counts (P = .02) and incidence of microgranular M3 variant (P = .04).

Conclusion

ATRA combined with CT for induction and also probably for maintenance provides as favorable results in children with APL as in adults and currently constitutes the reference first-line treatment in both age groups.

Acute promyelocytic leukaemia in children

Acute promyelocytic leukaemia (APL), designated M3, is a particularly interesting subtype of acute myeloid leukaemia (AML) that has unique molecular and clinical characteristics. It is characterized by an arrest of myeloid differentiation at the promyelocyte stage with abnormal proliferation of these cells. Recent paediatric and adult trials which included all-trans retinoic acid (ATRA) have shown that APL has significantly better survival rates than other subtypes of AML. While there is extensive literature on APL in adults, articles dedicated to describing solely paediatric patients are limited. This chapter focuses on the incidence, diagnosis, clinical characteristics, treatment, and survival rates of children with APL.

A phase 1 study of tazarotene in adults with advanced cancer

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

Retinoid therapy of high-risk 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 morphological differentiation of human neuroblastoma cell lines, and phase I trials showed 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 improved event-free survival in high-risk neuroblastoma. The cytotoxic retinoid 4-HPR achieved multi-log cell kills in neuroblastoma cell lines resistant to ATRA and 13-cis-RA, and a pediatric phase I trial has shown it to be well tolerated. Cytotoxicity of 4-HPR is mediated at least in part by increasing tumor cell ceramide levels and combining 4-HPR with ceramide modulators increased anti-tumor activity in pre-clinical models. Thus, further clinical trials of 4-HPR in neuroblastoma, and of 4-HPR in combination with ceramide modulators, are warranted.

Interaction of all-trans-retinoic acid with fluconazole in acute promyelocytic leukemia

All-trans-retinoic acid (ATRA) has a dramatic antitumor effect in patients with acute promyelocytic leukemia (APL). It is hepatically metabolized by cytochrome P-450, and there are known toxicities associated with high levels of this drug. The effects of ATRA can be potentiated by inhibition of cytochrome P-450, which is known to occur with certain drugs. We report a case of a patient with ATRA toxicity thought to be secondary to interaction with fluconazole.

Pharmacology of all-trans-retinoic acid in children with acute promyelocytic leukemia

BACKGROUND

Due to severe side effects in virtually all children treated with a standard dose of 45 mg/m(2)/day all-trans-retinoic acid (ATRA) for acute promyelocytic leukemia (APL) the AML-BFM study group reduced the dosage to 25 mg/m(2)/day. For the lack of data on the use of ATRA at this dosage in children with APL, the study group further decided to evaluate the pharmacokinetics and metabolism of ATRA in children.

PROCEDURE

Twenty-three pharmacokinetic and metabolic profiles of ATRA were studied in 14 children (aged 0.9-18.4 years) with APL. Eleven plasma samples were collected over a period of 8 hr and analyzed for ATRA and its metabolites by high-performance liquid chromatography.

RESULTS

Peak plasma concentrations of ATRA were characterized by wide interpatient variability (range: 28.6-513.0 nM). Compared to adults the same metabolic pathways were observed in children. Even though peak plasma concentrations were in the lower range of those considered effective in vitro, ATRA side effects, notably neurotoxicity, still required dose reduction, treatment break, or drug withdrawal in eight patients. In this small number of patients, neurotoxicity could not be related to age or any specific level of ATRA or metabolites in the plasma. Plasma concentrations of vitamin A, however, were significantly higher in those patients, who developed signs of neurotoxicity (P = 0.03, Mann-Whitney Rank Sum test).

CONCLUSIONS

Considering the low plasma concentrations and the persistence of toxicity in spite of dose reduction intermittent dosing schedules might be considered as an alternative to further dose reduction of ATRA in the treatment of APL especially in children, who might be at risk of ATRA-induced neurotoxicity.

Retinoic acid reduces the cytotoxicity of cyclopentenyl cytosine in neuroblastoma cells

In this paper, it is demonstrated that all-trans, 9-cis and 13-cis retinoic acid (RA) decreased the sensitivity of SK-N-BE(2)c neuroblastoma cells towards the chemotherapeutic agent cyclopentenyl cytosine (CPEC), a potent inhibitor of cytosine-5'-triphosphate synthetase. Retinoic acid attenuated CPEC-induced apoptosis as reflected by a decreased caspase-3 induction. Retinoic acid decreased the accumulation of CPEC, whereas the salvage of cytidine was strongly increased. Metabolic labeling studies using [(3)H]uridine showed a strongly decreased biosynthesis of CTP via CTP synthetase. Retinoic acid likely confers resistance of neuroblastoma cells to CPEC in part by slowing down proliferation, and in part by shifting the synthesis of CTP towards the salvage of cytidine, thereby bypassing CTP synthetase.

Acute promyelocytic leukemia: evolving therapeutic strategies

Acute promyelocytic leukemia (APL) is now the most curable subtype of acute myeloid leukemia in adults. All-trans retinoic acid (ATRA), which induces differentiation of the leukemic cells into mature granulocytes, represents the important advance. The incorporation of ATRA in induction results in a high complete remission rate, leads to rapid resolution of the characteristic life-threatening coagulopathy, and, most importantly, decreases the relapse rate compared with treatment with chemotherapy alone. However, ATRA is associated with unique toxicities not observed with conventional cytotoxic chemotherapy. A number of clinical trials have been performed to define the optimal role of ATRA in the treatment of patients. The therapeutic strategies have rapidly evolved as a result of both single institution and large cooperative group trials. Arsenic trioxide and stem cell transplantation are effective treatments for patients with APL who relapse after or are refractory to ATRA-based therapy. As experience with ATRA and arsenic trioxide in patients with APL accumulates, a number of important questions arise that need to be addressed.

Influence of isomerisation on the growth inhibitory effects and cellular activity of 13-cis and all-trans retinoic acid in neuroblastoma cells

Treatment with 13-cis retinoic acid (13-cis RA) has been shown to significantly improve the clinical outcome of children with high-risk neuroblastoma. Despite the large number of studies investigating the cellular effects of retinoids in neuroblastoma cells, the influence of RA isomerisation and the factors that determine the extent of RA isomerisation and uptake are unknown. The aim of this study was to establish the extent of extra- and intracellular isomerisation of 13-cis RA and all-trans retinoic acid (ATRA) in neuroblastoma cell lines, and to investigate the influence of isomerisation on their growth inhibitory effects and on the regulation of expression of cellular retinoic acid binding protein II (CRABP II) and RAR-beta. Limited extracellular isomerisation was observed up to 72 hr after incubation of four neuroblastoma cell lines with 10 microM 13-cis RA or ATRA. The retinoic acid isomer present initially in the medium accounted for >75% of extracellular retinoid exposure. By contrast, incubation with 13-cis RA resulted in intracellular levels of ATRA comparable to those of 13-cis RA. This degree of intracellular isomerisation was not observed after ATRA incubations, with 13-cis RA accounting for <10% of total intracellular retinoids. No differences were observed in the sensitivity of three N-type neuroblastoma cell lines to either 13-cis RA (IC(50): 11.2-13.9 microM) or ATRA (IC(50): 12.9-14.4 microM), despite 10-fold differences in intracellular retinoid levels. A decrease in sensitivity to 13-cis RA (IC(50)=137 microM), as compared to ATRA (IC(50)=41 microM), was observed in the S-type cell line SH S EP. RAR-beta was induced in a dose-dependent manner in SH SY 5Y cells following incubation with ATRA, whereas a weaker and delayed induction was observed with 13-cis RA. Similarly, incubation with ATRA resulted in a greater induction of CRABP II in these cells. In summary, these results indicate either an intracellular conversion of 13-cis RA to ATRA or a selective uptake of ATRA and suggest that this may mediate the differential activity of 13-cis RA in neuroblastoma cell subtypes.

Interferon-gamma cooperates with retinoic acid and phorbol ester to induce differentiation and growth inhibition of human neuroblastoma cells

The prognosis of patients with advanced stages of neuroblastoma with N-myc amplification remains poor despite escalated therapy, a situation that has called for alternative therapeutic approaches. Neuroblastoma cells, which represent immature peripheral neuronal cells, treated with certain physiologic and nonphysiologic agents such as retinoic acid (RA), phorbol esters and interferons (IFN) in vitro undergo cellular differentiation and stop to divide, a process that mimics normal neuronal development. Such "differentiation therapy" using RA after autologous bone marrow transplantation has recently given encouraging results in neuroblastoma patients with advanced disease. Considering approaches for improved differentiation therapy, we investigated possible synergistic effects of combining agents known to influence neuroblastoma growth and differentiation in vitro. Our results show that combined treatment with IFN-gamma and RA or the phorbol ester 12-O-tetradecanoyl-phorbol acetate (TPA) had synergistic or enhancing effects on morphologic differentiation and neurite outgrowth in 5 of 5 neuroblastoma cell lines, 3 of which expressed very high levels of N-myc mRNA due to N-myc amplification. The combinations RA+IFN-gamma or TPA+IFN-gamma also enhanced induced growth inhibition in all 5 cell lines, in several cases resulting in complete growth arrest under conditions where cells stimulated with either agent alone continued to grow. The phenotypic effects of the combined RA+IFN-gamma or TPA+IFN-gamma treatments were in most, but not all, investigated cases accompanied by moderate reductions in N-myc expression, suggesting that the cooperative signals may counteract N-Myc activity at several levels. The cooperativity between IFN-gamma and other differentiation signals may be relevant for approaches to improve the therapy for high-risk neuroblastoma with N-myc-amplification.

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.

Developmental therapeutics in childhood cancer. A perspective from the Children's Oncology Group and the US Food and Drug Administration

Drug development in pediatric oncology has been reviewed, concentrating on overall development issues and COG studies of cytotoxic compounds. A variety of interesting molecules with more specific targeting are becoming available. The challenges that remain include the availability of such compounds for pediatric trial and their study in a timely fashion, and the subsequent incorporation of the new agents into more up-front regimens, with the ultimate shared goal of curing more children with less toxicity.