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

Sphingosine 1-Phosphate Stimulates ER to Golgi Ceramide Traffic to Promote Survival in T98G Glioma Cells

Glioblastoma multiforme is the most common and fatal brain tumor among human cancers. Ceramide (Cer) and Sphingosine 1-phosphate (S1P) have emerged as bioeffector molecules that control several biological processes involved in both cancer development and resistance. Cer acts as a tumor suppressor, inhibiting cancer progression, promoting apoptosis, enhancing immunotherapy and sensitizing cells to chemotherapy. In contrast, S1P functions as an onco-promoter molecule, increasing proliferation, survival, invasiveness, and resistance to drug-induced apoptosis. The pro-survival PI3K/Akt pathway is a recognized downstream target of S1P, and we have previously demonstrated that in glioma cells it also improves Cer transport and metabolism towards complex sphingolipids in glioma cells. Here, we first examined the possibility that, in T98G glioma cells, S1P may regulate Cer metabolism through PI3K/Akt signaling. Our research showed that exogenous S1P increases the rate of vesicular trafficking of Cer from the endoplasmic reticulum (ER) to the Golgi apparatus through S1P receptor-mediated activation of the PI3K/Akt pathway. Interestingly, the effect of S1P results in cell protection against toxicity arising from Cer accumulation in the ER, highlighting the role of S1P as a survival factor to escape from the Cer-generating cell death response.

The mechanisms of ferroptosis in the pathogenesis of kidney diseases

The pathological features of acute and chronic kidney diseases are closely associated with cell death in glomeruli and tubules. Ferroptosis is a form of programmed cell death characterized by iron overload-induced oxidative stress. Ferroptosis has recently gained increasing attention as a pathogenic mechanism of kidney damage. Specifically, the ferroptosis signaling pathway has been found to be involved in the pathological process of acute and chronic kidney injury, potentially contributing to the development of both acute and chronic kidney diseases. This paper aims to elucidate the underlying mechanisms of ferroptosis and its role in the pathogenesis of kidney disease, highlighting its significance and proposing novel directions for its treatment.

Ceramide Is Involved in Temozolomide Resistance in Human Glioblastoma U87MG Overexpressing EGFR

Glioblastoma multiforme (GBM) is the most frequent and deadly brain tumor. Many sphingolipids are crucial players in the regulation of glioma cell growth as well as in the response to different chemotherapeutic drugs. In particular, ceramide (Cer) is a tumor suppressor lipid, able to induce antiproliferative and apoptotic responses in different types of tumors including GBM, most of which overexpress the epidermal growth factor receptor variant III (EGFRvIII). In this paper, we investigated whether Cer metabolism is altered in the U87MG human glioma cell line overexpressing EGFRvIII (EGFR+ cells) to elucidate their possible interplay in the mechanisms regulating GBM survival properties and the response to the alkylating agent temozolomide (TMZ). Notably, we demonstrated that a low dose of TMZ significantly increases Cer levels in U87MG cells but slightly in EGFR+ cells (sensitive and resistant to TMZ, respectively). Moreover, the inhibition of the synthesis of complex sphingolipids made EGFR+ cells sensitive to TMZ, thus involving Cer accumulation/removal in TMZ resistance of GBM cells. This suggests that the enhanced resistance of EGFR+ cells to TMZ is dependent on Cer metabolism. Altogether, our results indicate that EGFRvIII expression confers a TMZ-resistance phenotype to U87MG glioma cells by counteracting Cer increase.

Phase I trial of intravenous fenretinide (4-HPR) plus safingol in advanced malignancies

PURPOSE

Fenretinide (4-HPR) is a synthetic retinoid that induces cytotoxicity through dihydroceramide production. Safingol, a stereochemical-variant dihydroceramide precursor, exhibits synergistic effects when administered with fenretinide in preclinical studies. We conducted a phase 1 dose-escalation clinical trial of this combination.

METHODS

Fenretinide was administered as a 600 mg/m2 24-h infusion on Day 1 of a 21-day cycle followed by 900 mg/m2/day on Days 2 and 3. Safingol was concurrently administered as a 48-h infusion on Day 1 and 2 using 3 + 3 dose escalation. Primary endpoints were safety and maximum tolerated dose (MTD). Secondary endpoints included pharmacokinetics and efficacy.

RESULTS

A total of 16 patients were enrolled (mean age 63 years, 50% female, median three prior lines of therapy), including 15 patients with refractory solid tumors and one with non-Hodgkin lymphoma. The median number of treatment cycles received was 2 (range 2-6). The most common adverse event (AE) was hypertriglyceridemia (88%; 38% ≥ Grade 3), attributed to the fenretinide intralipid infusion vehicle. Other treatment-related AEs occurring in ≥ 20% of patients included anemia, hypocalcemia, hypoalbuminemia, and hyponatremia. At safingol dose 420 mg/m2, one patient had a dose-limiting toxicity of grade 3 troponinemia and grade 4 myocarditis. Due to limited safingol supply, enrollment was halted at this dose level. Fenretinide and safingol pharmacokinetic profiles resembled those observed in monotherapy trials. Best radiographic response was stable disease (n = 2).

CONCLUSION

Combination fenretinide plus safingol commonly causes hypertriglyceridemia and may be associated with cardiac events at higher safingol levels. Minimal activity in refractory solid tumors was observed.

TRIAL REGISTRATION NUMBER

NCT01553071 (3.13.2012).

Ceramide Kinase Inhibition Drives Ferroptosis and Sensitivity to Cisplatin in Mutant KRAS Lung Cancer by Dysregulating VDAC-Mediated Mitochondria Function

Ceramide kinase (CERK) is the mammalian lipid kinase from which the bioactive sphingolipid, ceramide-1-phosphate (C1P), is derived. CERK has been implicated in several promalignant phenotypes with little known as to mechanistic underpinnings. In this study, the mechanism of how CERK inhibition decreases cell survival in mutant (Mut) KRAS non-small cell lung cancer (NSCLC), a major lung cancer subtype, was revealed. Specifically, NSCLC cells possessing a KRAS mutation were more responsive to inhibition, downregulation, and genetic ablation of CERK compared with those with wild-type (WT) KRAS regarding a reduction in cell survival. Inhibition of CERK induced ferroptosis in Mut KRAS NSCLC cells, which required elevating VDAC-regulated mitochondria membrane potential (MMP) and the generation of cellular reactive oxygen species (ROS). Importantly, through modulation of VDAC, CERK inhibition synergized with the first-line NSCLC treatment, cisplatin, in reducing cell survival and in vivo tumor growth. Further mechanistic studies indicated that CERK inhibition affected MMP and cell survival by limiting AKT activation and translocation to mitochondria, and thus, blocking VDAC phosphorylation and tubulin recruitment.

IMPLICATIONS

Our findings depict how CERK inhibition may serve as a new key point in combination therapeutic strategy for NSCLC, specifically precision therapeutics targeting NSCLC possessing a KRAS mutation.

One-Step, Low-Cost, Operator-Friendly, and Scalable Procedure to Synthetize Highly Pure N-(4-ethoxyphenyl)-retinamide in Quantitative Yield without Purification Work-Up

It is widely reported that N-(4-hydroxyphenyl)-retinamide or fenretinide (4-HPR), which is a synthetic amide of all-trans-retinoic acid (ATRA), inhibits in vitro several types of tumors, including cancer cell lines resistant to ATRA, at 1–10 µM concentrations. Additionally, studies in rats and mice have confirmed the potent anticancer effects of 4-HPR, without evidencing hemolytic toxicity, thus demonstrating its suitability for the development of a new chemo-preventive agent. To this end, the accurate determination of 4-HPR levels in tissues is essential for its pre-clinical training, and for the correct determination of 4-HPR and its metabolites by chromatography, N-(4-ethoxyphenyl)-retinamide (4-EPR) has been suggested as an indispensable internal standard. Unfortunately, only a consultable old patent reports the synthesis of 4-EPR, starting from dangerous and high-cost reagents and using long and tedious purification procedures. To the best of our knowledge, no article existed so far describing the specific synthesis of 4-EPR. Only two vendors worldwide supply 4-ERP, and its characterization was incomplete. Here, a scalable, operator-friendly, and one-step procedure to synthetize highly pure 4-EPR without purification work-up and in quantitative yield is reported. Additionally, a complete characterization of 4-EPR using all possible analytical techniques has been provided.

The unfolding role of ceramide in coordinating retinoid-based cancer therapy

Sphingolipid-mediated regulation in cancer development and treatment is largely ceramide-centered with the complex sphingolipid metabolic pathways unfolding as attractive targets for anticancer drug discovery. The dynamic interconversion of sphingolipids is tightly controlled at the level of enzymes and cellular compartments in response to endogenous or exogenous stimuli, such as anticancer drugs, including retinoids. Over the past two decades, evidence emerged that retinoids owe part of their potency in cancer therapy to modulation of sphingolipid metabolism and ceramide generation. Ceramide has been proposed as a 'tumor-suppressor lipid' that orchestrates cell growth, cell cycle arrest, cell death, senescence, autophagy, and metastasis. There is accumulating evidence that cancer development is promoted by the dysregulation of tumor-promoting sphingolipids whereas cancer treatments can kill tumor cells by inducing the accumulation of endogenous ceramide levels. Resistance to cancer therapy may develop due to a disrupted equilibrium between the opposing roles of tumor-suppressor and tumor-promoter sphingolipids. Despite the undulating effect and complexity of sphingolipid pathways, there are emerging opportunities for a plethora of enzyme-targeted therapeutic interventions that overcome resistance resulting from perturbed sphingolipid pathways. Here, we have revisited the interconnectivity of sphingolipid metabolism and the instrumental role of ceramide-biosynthetic and degradative enzymes, including bioactive sphingolipid products, how they closely relate to cancer treatment and pathogenesis, and the interplay with retinoid signaling in cancer. We focused on retinoid targeting, alone or in combination, of sphingolipid metabolism nodes in cancer to enhance ceramide-based therapeutics. Retinoid and ceramide-based cancer therapy using novel strategies such as combination treatments, synthetic retinoids, ceramide modulators, and delivery formulations hold promise in the battle against cancer.

Ceramide Metabolism Enzymes-Therapeutic Targets against Cancer

Sphingolipids are both structural molecules that are essential for cell architecture and second messengers that are involved in numerous cell functions. Ceramide is the central hub of sphingolipid metabolism. In addition to being the precursor of complex sphingolipids, ceramides induce cell cycle arrest and promote cell death and inflammation. At least some of the enzymes involved in the regulation of sphingolipid metabolism are altered in carcinogenesis, and some are targets for anticancer drugs. A number of scientific reports have shown how alterations in sphingolipid pools can affect cell proliferation, survival and migration. Determination of sphingolipid levels and the regulation of the enzymes that are implicated in their metabolism is a key factor for developing novel therapeutic strategies or improving conventional therapies. The present review highlights the importance of bioactive sphingolipids and their regulatory enzymes as targets for therapeutic interventions with especial emphasis in carcinogenesis and cancer dissemination.

Glucosylceramide and galactosylceramide, small glycosphingolipids with significant impact on health and disease

Numerous clinical observations and exploitation of cellular and animal models indicate that glucosylceramide (GlcCer) and galactosylceramide (GalCer) are involved in many physiological and pathological phenomena. In many cases, the biological importance of these monohexosylcermides has been shown indirectly as the result of studies on enzymes involved in their synthesis and degradation. Under physiological conditions, GalCer plays a key role in the maintenance of proper structure and stability of myelin and differentiation of oligodendrocytes. On the other hand, GlcCer is necessary for the proper functions of epidermis. Such an important lysosomal storage disease as Gaucher disease (GD) and a neurodegenerative disorder as Parkinson’s disease are characterized by mutations in the GBA1 gene, decreased activity of lysosomal GBA1 glucosylceramidase and accumulation of GlcCer. In contrast, another lysosomal disease, Krabbe disease, is associated with mutations in the GALC gene, resulting in deficiency or decreased activity of lysosomal galactosylceramidase and accumulation of GalCer and galactosylsphingosine. Little is known about the role of both monohexosylceramides in tumor progression; however, numerous studies indicate that GlcCer and GalCer play important roles in the development of multidrug-resistance by cancer cells. It was shown that GlcCer is able to provoke immune reaction and acts as a self-antigen in GD. On the other hand, GalCer was recognized as an important cellular receptor for HIV-1. Altogether, these two molecules are excellent examples of how slight differences in chemical composition and molecular conformation contribute to profound differences in their physicochemical properties and biological functions.

Nanomicellar Lenalidomide-Fenretinide Combination Suppresses Tumor Growth in an MYCN Amplified Neuroblastoma Tumor

Purpose

In a previous study, we demonstrated that the combination of fenretinide with lenalidomide, administered by a novel nanomicellar formulation (FLM), provided a strong antitumor effect in a neuroblastoma TrkB-expressing tumor. In this study, we tested the nanomicellar combination in an MYCN amplified neuroblastoma xenograft to assess its efficacy in different tumor genotypes and evaluate the interactions of the nanomicelles with the tumor cells.

Experimental Design

FLM was administered to mice bearing human NLF xenografts to evaluate its efficacy in comparison with the nanomicelles containing fenretinide alone (FM). Confocal laser-scanning fluorescence microscopy images of the NLF cells treated with FLM and FM allowed us to estimate the nanomicelle ability to transport the encapsulated drugs inside the tumor cells. Flow cytometric analysis of the cells from treated tumors was performed to assess the effect of treatment on GD2 expression and NK cell infiltration.

Results

FLM and FM decreased the growth of NLF xenografts at comparable extents during the treatment period. Afterwards, FLM induced a progressive tumor regression without regrowth, while FM treatment was followed by regrowth within 15-20 days after the end of treatment. Both FLM and FM were able to penetrate the tumor cells transporting the encapsulated drugs. FLM transported higher amount of fenretinide inside the cells. Also, FLM treatment strongly increased GD2 expression in treated tumors and slightly decreased the NK infiltration compared to FM.

Conclusion

FLM treatment induced a superior antitumor response than FM in NLF xenografts, presumably due to the combined effects of fenretinide cytotoxicity and lenalidomide antiangiogenic activity. The ability of FLM to penetrate tumor cells, transporting the encapsulated drugs, substantially improved the therapeutic efficiency of this system. Moreover, the enhancement of GD2 expression in FLM treated tumors offers the possibility to further increase the antitumor effect by the use of anti-GD2 CAR-T cells and anti-GD2 antibodies in combination with FLM in multimodal therapies.

Antineoplastic Agents Targeting Sphingolipid Pathways

Emerging studies in the enigmatic area of bioactive lipids have made many exciting new discoveries in recent years. Once thought to play a strictly structural role in cellular function, it has since been determined that sphingolipids and their metabolites perform a vast variety of cellular functions beyond what was previously believed. Of utmost importance is their role in cellular signaling, for it is now well understood that select sphingolipids serve as bioactive molecules that play critical roles in both cancer cell death and survival, as well as other cellular responses such as chronic inflammation, protection from intestinal pathogens, and intrinsic protection from intestinal contents, each of which are associated with oncogenesis. Importantly, it has been demonstrated time and time again that many different tumors display dysregulation of sphingolipid metabolism, and the exact profile of said dysregulation has been proven to be useful in determining not only the presence of a tumor, but also the susceptibility to various chemotherapeutic drugs, as well as the metastasizing characteristics of the malignancies. Since these discoveries surfaced it has become apparent that the understanding of sphingolipid metabolism and profile will likely become of great importance in the clinic for both chemotherapy and diagnostics of cancer. The goal of this paper is to provide a comprehensive review of the current state of chemotherapeutic agents that target sphingolipid metabolism that are undergoing clinical trials. Additionally, we will formulate questions involving the use of sphingolipid metabolism as chemotherapeutic targets in need of further research.

A Cationic Nanomicellar Complex of the Quaternary Amphiphilic Amine RC16+ with Fenretinide as a New Multitasking System for Antitumor Therapy

OBJECTIVES

This study investigated the antitumor effect of a new nanomicellar complex obtained by combining the antitumor agent fenretinide with a quaternary amphiphilic amine RC16+ also endowed with antitumor activity.

METHODS

The complex (Fen-RC16+) strongly improved the aqueous solubility of fenretinide (from 1,71 ± 0.08 µg/ml, pure fenretinide to 1500 ± 164 µg /ml, Fen-RC16+ complex) and provided a cytotoxic effect on SH-SY5Y neuroblastoma cell lines resulting from the intrinsic activity of both the complex components. Moreover, the mean size of the nanomicellar complex (ranging from 20 ± 1.97 nm to 40 ± 3.05 nm) was suitable for accumulation to the tumor site by the enhanced permeability and retention effect and the positive charge provided by the quaternary RC16+ induced adsorption of the complex on the tumor cell surface improving the intracellular concentration of fenretinide.

RESULTS

All these characteristics made the Fen-RC16+ complex a multitasking system for antitumor therapy.

CONCLUSION

Indeed its in vivo activity, evaluated on SH-SY5Y xenografts, was strong, and the tumor growth did not resume after the treatment withdrawal.

A Novel Nanomicellar Combination of Fenretinide and Lenalidomide Shows Marked Antitumor Activity in a Neuroblastoma Xenograft Model

Purpose

Currently >50% of high-risk neuroblastoma (NB) patients, despite intensive therapy and initial partial or complete response, develop recurrent NB due to the persistence of minimal residual disease (MRD) that is resistant to conventional antitumor drugs. Indeed, their low therapeutic index prevents drug-dose escalation and protracted administration schedules, as would be required for MRD treatment. Thus, more effective and less toxic therapies are urgently needed for the management of MRD. To address this aim, we evaluated a new combination of fenretinide and lenalidomide, both endowed with antitumor activity and low-toxicity profiles. New nanomicelles were prepared as carriers for this combination to maximize bioavailability and accumulation at the tumor site because of the enhanced permeability and retention (EPR) effect.

Experimental design

New nanomicelles containing the fenretinide–lenalidomide combination (FLnMs) were prepared by a one-step method, providing high drug encapsulation and micelle dimensions suitable for tumor accumulation. Their administration to mice bearing human NB xenografts allowed us to evaluate their efficacy in comparison with the nanomicelles containing fenretinide alone (FnMs).

Results

Treatment by FLnMs significantly decreased the tumor growth of NB xenografts. FLnMs were more active than FnMs despite comparable fenretinide concentrations in tumors, and lenalidomide alone did not show cytotoxic activity in vitro against NB cells. The tumor mass at the end of treatment with FLnMs was predominantly necrotic, with a decreased Ki-67 proliferation index.

Conclusion

FLnMs provided superior antitumor efficacy in NB xenografts compared to FnMs. The enhanced efficacy of the combination was likely due to the antiangiogenic effect of lenalidomide added to the cytotoxic effect of fenretinide. This new nanomicellar combination is characterized by a low-toxicity profile and offers a novel therapeutic option for the treatment of high-risk tumors where the persistence of MRD requires repeated administrations of therapeutic agents over long periods of time to avoid recurrent disease.

A novel oral micellar fenretinide formulation with enhanced bioavailability and antitumour activity against multiple tumours from cancer stem cells

Background

An increasing number of anticancer agents has been proposed in recent years with the attempt to overcome treatment-resistant cancer cells and particularly cancer stem cells (CSC), the major culprits for tumour resistance and recurrence. However, a huge obstacle to treatment success is the ineffective delivery of drugs within the tumour environment due to limited solubility, short circulation time or inconsistent stability of compounds that, together with concomitant dose-limiting systemic toxicity, contribute to hamper the achievement of therapeutic drug concentrations. The synthetic retinoid Fenretinide (4-hydroxy (phenyl)retinamide; 4-HPR) formerly emerged as a promising anticancer agent based on pre-clinical and clinical studies. However, a major limitation of fenretinide is traditionally represented by its poor aqueous solubility/bioavailability due to its hydrophobic nature, that undermined the clinical success of previous clinical trials.

Methods

Here, we developed a novel nano-micellar fenretinide formulation called bionanofenretinide (Bio-nFeR), based on drug encapsulation in an ion-pair stabilized lipid matrix, with the aim to raise fenretinide bioavailability and antitumour efficacy.

Results

Bio-nFeR displayed marked antitumour activity against lung, colon and melanoma CSC both in vitro and in tumour xenografts, in absence of mice toxicity. Bio-nFeR is suitable for oral administration, reaching therapeutic concentrations within tumours and an unprecedented therapeutic activity in vivo as single agent.

Conclusion

Altogether, our results indicate Bio-nFeR as a novel anticancer agent with low toxicity and high activity against tumourigenic cells, potentially useful for the treatment of solid tumours of multiple origin.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1383-9) contains supplementary material, which is available to authorized users.

Cytotoxic activity of difluoromethylornithine compared with fenretinide in neuroblastoma cell lines

BACKGROUND

Maintenance therapy with 13-cis-retinoic acid and immunotherapy (given after completion of intensive cytotoxic therapy) improves outcome for high-risk neuroblastoma patients. The synthetic retinoid fenretinide (4-HPR) achieved multiple complete responses in relapse/refractory neuroblastoma in early-phase clinical trials, has low systemic toxicity, and has been considered for maintenance therapy clinical trials. Difluoromethylornithine (DFMO, an irreversible inhibitor of ornithine decarboxylase with minimal single-agent clinical response data) is being used for maintenance therapy of neuroblastoma. We evaluated the cytotoxic activity of DFMO and fenretinide in neuroblastoma cell lines.

PROCEDURE

We tested 16 neuroblastoma cell lines in bone marrow-level hypoxia (5% O₂ ) using the DIMSCAN cytotoxicity assay. Polyamines were measured by HPLC-mass spectrometry and apoptosis by transferase dUTP nick end labeling (TUNEL) using flow cytometry.

RESULTS

At clinically achievable levels (100 μM), DFMO significantly decreased (P < 0.05) polyamine putrescine and achieved modest cytotoxicity (<1 log (90% cytotoxicity). Prolonged exposures (7 days) or culture in 2% and 20% O₂ did not enhance DFMO cytotoxicity. However, fenretinide (10 μM) even at a concentration lower than clinically achievable in neuroblastoma patients (20 μM) induced ≥ 1 log cell kill in 14 cell lines. The average IC₉₀ and IC₉₉ of fenretinide was 4.7 ± 1 μM and 9.9 ± 1.8 μM, respectively. DFMO did not induce a significant increase (P > 0.05) in apoptosis (TUNEL assay). Apoptosis by fenretinide was significantly higher (P < 0.001) compared with DFMO or controls.

CONCLUSIONS

DFMO as a single agent has minimal cytotoxic activity for neuroblastoma cell lines.

Efficiency of All-Trans Retinoic Acid on Gastric Cancer: A Narrative Literature Review

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide with a five-year survival rate of around 25%, and 4% when diagnosed at a metastatic stage. Cancer stem cells (CSC) have recently been characterized as being responsible for resistance to radio/chemotherapies and metastasis formation, opening up perspectives for new targeted therapies. Those CSCs express biomarkers such as cluster of differentiation 44 (CD44) and display high aldehyde dehydrogenase activity that converts vitamin A-derived retinal into retinoic acids. All-trans retinoic acid (ATRA), which has pro-differentiating properties, has revolutionized the prognosis of acute promyelotic leukemia by increasing its remission rate from 15% to 85%. Recent studies have started to show that ATRA also has an anti-tumoral role on solid cancers such as GC. The purpose of this review is therefore to summarize the work that evaluated the effects of ATRA in GC and to evaluate whether its anti-cancerous action involves gastric CSCs targeting. It has been demonstrated that ATRA can block the cell cycle, enhance apoptosis, and decrease gastric CSCs properties in GC cell lines, tumorspheres, and patient-derived xenograft mice models. Therefore, retinoids and new synthetic retinoids seem to be a promising step forward in targeted therapy of gastric CSC in combination with existing chemotherapies. Future studies should probably focus on these points.

Antiglioma via regulating oxidative stress and remodeling tumor-associated macrophage using lactoferrin-mediated biomimetic codelivery of simvastatin/fenretinide

Effective treatment of malignant glioma still remains a formidable challenge due to lack of the effective BBB-permeable drugs and efficient brain delivery methods, and the pharmacotherapy options are very limited. Therefore, to develop an effective therapeutic strategy is a pressing need. In this work, a noncytotoxic drug combination (i.e., simvastatin and fenretinide) was revealed to be potent for treating glioma, which was co-encapsulated into a TPGS-TAT-embedded lactoferrin nanoparticle system for achieving brain-targeted biomimetic delivery via the LRP-1 receptor. It was shown that the lactoferrin nanoparticle repolarized the tumor-associated macrophages from the M2 phenotype to M1 via regulating the STAT6 pathway, as well as induced the ROS-mediated mitochondrial apoptosis by inhibiting the Ras/Raf/p-Erk pathway in the glioma cells. The antiglioma efficacy was further demonstrated in both the subcutaneous and orthotopic glioma models. The repolarization of tumor-associated macrophages not only prompted the ROS generation but also induced the innate immunity (e.g., antitumor cytokine release). This delivery and therapeutic strategy provides a novel modality for the glioma treatment.

Investigational drugs in phase II clinical trials for the treatment of neuroblastoma

INTRODUCTION

Neuroblastoma (NB) is an embryonal tumor originating from undifferentiated neural crest cell, highly heterogeneous ranging from spontaneous regression to progression despite multimodal treatments. Approximately, 20% of patients are refractory to frontline therapy and 50% will relapse/progress after an initial response. The overall five year survival for high-risk neuroblastoma ranges from 35-45%. Despite enhanced understanding of NB biology and the addition of myeloablative chemotherapy, isotretinoin and immunotherapy, survival for high risk NB remains less than 50%. Areas covered: This review summarizes and gives a critical overview of phase II trials investigating therapies for relapsed-refractory and high risk neuroblastoma. Expert opinion: Several novel molecules have been developed and are currently under investigation for the treatment of NB. The trend of novel targeted agents is one towards individualized, tailored therapy, based on the molecular and biological differences that characterize tumors that seem similar based solely on histological analysis. The task of developing new molecules is particularly difficult for NB, given the recurrent development of new patterns of drug resistance. However, even if current research is focused towards identifying the best treatments for each children and young adult with a NB defined disease, a deeper knowledge of the molecular biology and genetics is needed.

P450 inhibitor ketoconazole increased the intratumor drug levels and antitumor activity of fenretinide in human neuroblastoma xenograft models

We previously reported that concurrent ketoconazole, an oral anti-fungal agent and P450 enzyme inhibitor, increased plasma levels of the cytotoxic retinoid, fenretinide (4-HPR) in mice. We have now determined the effects of concurrent ketoconazole on 4-HPR cytotoxic dose-response in four neuroblastoma (NB) cell lines in vitro and on 4-HPR activity against two cell line-derived, subcutaneous NB xenografts (CDX) and three patient-derived NB xenografts (PDX). Cytotoxicity in vitro was assessed by DIMSCAN assay. Xenografted animals were treated with 4-HPR/LXS (240 mg/kg/day) + ketoconazole (38 mg/kg/day) in divided oral doses in cycles of five continuous days a week. In one model, intratumoral levels of 4-HPR and metabolites were assessed by HPLC assay, and in two models intratumoral apoptosis was assessed by TUNEL assay, on Day 5 of the first cycle. Antitumor activity was assessed by Kaplan-Meier event-free survival (EFS). The in vitro cytotoxicity of 4-HPR was not affected by ketoconazole (p ≥ 0.06). Ketoconazole increased intratumoral levels of 4-HPR (p = 0.02), of the active 4-oxo-4-HPR metabolite (p = 0.04), and intratumoral apoptosis (p ≤ 0.0006), compared to 4-HPR/LXS-alone. Concurrent ketoconazole increased EFS in both CDX models compared to 4-HPR/LXS-alone (p ≤ 0.008). 4-HPR + ketoconazole also increased EFS in PDX models compared to controls (p ≤ 0.03). Thus, concurrent ketoconazole decreased 4-HPR metabolism with resultant increases of plasma and intratumoral drug levels and antitumor effects in neuroblastoma murine xenografts. These results support the clinical testing of concurrent ketoconazole and oral fenretinide in neuroblastoma.

Phase I Study of Fenretinide Delivered Intravenously in Patients with Relapsed or Refractory Hematologic Malignancies: A California Cancer Consortium Trial

Purpose: A phase I study was conducted to determine the MTD, dose-limiting toxicities (DLT), and pharmacokinetics of fenretinide delivered as an intravenous emulsion in relapsed/refractory hematologic malignancies.Experimental Design: Fenretinide (80-1,810 mg/m²/day) was administered by continuous infusion on days 1 to 5, in 21-day cycles, using an accelerated titration design.Results: Twenty-nine patients, treated with a median of three prior regimens (range, 1-7), were enrolled and received the test drug. Ninety-seven courses were completed. An MTD was reached at 1,280 mg/m²/day for 5 days. Course 1 DLTs included 6 patients with hypertriglyceridemia, 4 of whom were asymptomatic; 2 patients experienced DLT thrombocytopenia (asymptomatic). Of 11 patients with response-evaluable peripheral T-cell lymphomas, two had complete responses [CR, progression-free survival (PFS) 68+ months; unconfirmed CR, PFS 14+ months], two had unconfirmed partial responses (unconfirmed PR, PFS 5 months; unconfirmed PR, PFS 6 months), and five had stable disease (2-12 cycles). One patient with mature B-cell lymphoma had an unconfirmed PR sustained for two cycles. Steady-state plasma levels were approximately 10 mcg/mL (mid-20s μmol/L) at 640 mg/m²/day, approximately 14 mcg/mL (mid-30s μmol/L) at 905 mg/m²/day, and approximately 22 mcg/mL (mid-50s μmol/L) at 1,280 mg/m²/day.Conclusions: Intravenous fenretinide obtained significantly higher plasma levels than a previous capsule formulation, had acceptable toxicities, and evidenced antitumor activity in peripheral T-cell lymphomas. A recommended phase II dosing is 600 mg/m² on day 1, followed by 1,200 mg/m² on days 2 to 5, every 21 days. A registration-enabling phase II study in relapsed/refractory PTCL (ClinicalTrials.gov identifier: NCT02495415) is ongoing. Clin Cancer Res; 23(16); 4550-5. ©2017 AACR.

Reactive Oxygen Species Mediates the Synergistic Activity of Fenretinide Combined with the Microtubule Inhibitor ABT-751 against Multidrug-Resistant Recurrent Neuroblastoma Xenografts

ABT-751 is a colchicine-binding site microtubule inhibitor. Fenretinide (4-HPR) is a synthetic retinoid. Both agents have shown activity against neuroblastoma in laboratory models and clinical trials. We investigated the antitumor activity of 4-HPR + the microtubule-targeting agents ABT-751, vincristine, paclitaxel, vinorelbine, or colchicine in laboratory models of recurrent neuroblastoma. Drug cytotoxicity was assessed in vitro by a fluorescence-based assay (DIMSCAN) and in subcutaneous xenografts in nu/nu mice. Reactive oxygen species levels (ROS), apoptosis, and mitochondrial depolarization were measured by flow cytometry; cytochrome c release and proapoptotic proteins were measured by immunoblotting. 4-HPR + ABT-751 showed modest additive or synergistic cytotoxicity, mitochondrial membrane depolarization, cytochrome c release, and caspase activation compared with single agents in vitro; synergism was inhibited by antioxidants (ascorbic acid, α-tocopherol). 4-HPR + ABT-751 was highly active against four xenograft models, achieving multiple maintained complete responses. The median event-free survival (days) for xenografts from 4 patients combined was control = 28, 4-HPR = 49, ABT-751 = 77, and 4-HPR + ABT-751 > 150 (P < 0.001). Apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, TUNEL) was significantly higher in 4-HPR + ABT-751-treated tumors than with single agents (P < 0.01) and was inhibited by ascorbic acid and α-tocopherol (P < 0.01), indicating that ROS from 4-HPR enhanced the activity of ABT-751. 4-HPR also enhanced the activity against neuroblastoma xenografts of vincristine or paclitaxel, but the latter combinations were less active than 4-HPR + ABT-751. Our data support clinical evaluation of 4-HPR combined with ABT-751 in recurrent and refractory neuroblastoma. Mol Cancer Ther; 15(11); 2653-64. ©2016 AACR.

Ceramide-tamoxifen regimen targets bioenergetic elements in acute myelogenous leukemia

The objective of our study was to determine the mechanism of action of the short-chain ceramide analog, C6-ceramide, and the breast cancer drug, tamoxifen, which we show coactively depress viability and induce apoptosis in human acute myelogenous leukemia cells. Exposure to the C6-ceramide-tamoxifen combination elicited decreases in mitochondrial membrane potential and complex I respiration, increases in reactive oxygen species (ROS), and release of mitochondrial proapoptotic proteins. Decreases in ATP levels, reduced glycolytic capacity, and reduced expression of inhibitors of apoptosis proteins also resulted. Cytotoxicity of the drug combination was mitigated by exposure to antioxidant. Cells metabolized C6-ceramide by glycosylation and hydrolysis, the latter leading to increases in long-chain ceramides. Tamoxifen potently blocked glycosylation of C6-ceramide and long-chain ceramides. N-desmethyltamoxifen, a poor antiestrogen and the major tamoxifen metabolite in humans, was also effective with C6-ceramide, indicating that traditional antiestrogen pathways are not involved in cellular responses. We conclude that cell death is driven by mitochondrial targeting and ROS generation and that tamoxifen enhances the ceramide effect by blocking its metabolism. As depletion of ATP and targeting the "Warburg effect" represent dynamic metabolic insult, this ceramide-containing combination may be of utility in the treatment of leukemia and other cancers.

Novel mechanisms of action of classical chemotherapeutic agents on sphingolipid pathways

The prevailing mechanisms of action of traditional chemotherapeutic agents have been challenged by sphingolipid cancer research. Many studies have shown that ceramide generation in response to cytotoxic agents is central to tumor cell death. Ceramide can be generated either via hydrolysis of cell-membrane sphingomyelin by sphingomyelinases, hydrolysis of cerebrosides, or via de novo synthesis by ceramide synthases. Ceramide can act as a second messenger for apoptosis, senescence or autophagy. Inherent or acquired alterations in the sphingolipid pathway can account for resistance to the classic chemotherapeutic agents. In particular, it has been shown that activation of the acid ceramidase can lead to the formation of sphingosine 1-phosphate, which then antagonizes ceramide signaling by initiating a pro-survival signaling pathway. Furthermore, ceramide glycosylation catalyzed by glucosylceramide synthase converts ceramide to glucosylceramide, thus eliminating ceramide and consequently protecting cancer cells from apoptosis. In this review, we describe the effects of some of the most commonly used chemotherapeutic agents on ceramide generation, with a particular emphasis on strategies used to enhance the efficacy of these agents.

Thymosin-β4 is a determinant of drug sensitivity for Fenretinide and Vorinostat combination therapy in neuroblastoma

Retinoids are an important component of neuroblastoma therapy at the stage of minimal residual disease, yet 40-50% of patients treated with 13-cis-retinoic acid (13-cis-RA) still relapse, indicating the need for more effective retinoid therapy. Vorinostat, or Suberoylanilide hydroxamic acid (SAHA), is a potent inhibitor of histone deacetylase (HDAC) classes I & II and has antitumor activity in vitro and in vivo. Fenretinide (4-HPR) is a synthetic retinoid which acts on cancer cells through both nuclear retinoid receptor and non-receptor mechanisms. In this study, we found that the combination of 4-HPR + SAHA exhibited potent cytotoxic effects on neuroblastoma cells, much more effective than 13-cis-RA + SAHA. The 4-HPR + SAHA combination induced caspase-dependent apoptosis through activation of caspase 3, reduced colony formation and cell migration in vitro, and tumorigenicity in vivo. The 4-HPR and SAHA combination significantly increased mRNA expression of thymosin-beta-4 (Tβ4) and decreased mRNA expression of retinoic acid receptor α (RARα). Importantly, the up-regulation of Tβ4 and down-regulation of RARα were both necessary for the 4-HPR + SAHA cytotoxic effect on neuroblastoma cells. Moreover, Tβ4 knockdown in neuroblastoma cells increased cell migration and blocked the effect of 4-HPR + SAHA on cell migration and focal adhesion formation. In primary human neuroblastoma tumor tissues, low expression of Tβ4 was associated with metastatic disease and predicted poor patient prognosis. Our findings demonstrate that Tβ4 is a novel therapeutic target in neuroblastoma, and that 4-HPR + SAHA is a potential therapy for the disease.

Dynamics of ceramide generation and metabolism in response to fenretinide--Diversity within and among leukemia

Fenretinide, N-(4-hydroxyphenyl)retinamide, (4-HPR), a synthetic retinoid, owes its cancer-toxic effects in part to the generation of ceramide, a potent tumor-suppressing sphingolipid. As such, 4-HPR has garnered considerable interest as a chemotherapeutic. Cancer cells, however, via various metabolic routes, inactivate ceramide, and this can limit 4-HPR efficacy. As relatively little is known regarding 4-HPR-induced ceramide management in acute myelogeneous leukemia (AML), we undertook the present study to evaluate the impact of 4-HPR on ceramide production, metabolism, and cytotoxicity. In KG-1, HL-60, and HL-60/VCR (multidrug resistant) human leukemia cells, 4-HPR induced 15-, 2-, and 20-fold increases in ceramide (measured using [3H]palmitic acid), respectively. By use of specific inhibitors we show that ceramide was produced by sphingomyelinase and de novo pathways in response to 4-HPR exposure. HL-60/VCR cells metabolized ceramide to glucosylceramide (GC). 4-HPR exposure (1.25-10 μM) reduced viability in all cell lines, with approximate IC50's ranging from 1 to 8.0 μM. Reactive oxygen species (ROS) were generated in response to 4-HPR treatment, and the concomitant cytotoxicity was reversed by addition of vitamin E. 4-HPR was not cytotoxic nor did it elicit ceramide formation in K562, a chronic myeloid leukemia cell line; however, K562 cells were sensitive to a cell-deliverable form of ceramide, C6-ceramide. Treatment of Molt-3, an acute lymphoblastic leukemia cell line, with 4-HPR revealed moderate ceramide production (5-fold over control), robust conversion of ceramide to GC and sphingomyelin, and resistance to 4-HPR and C6-ceramide. In conclusion, this work demonstrates diversity within and among leukemia in 4-HPR sensitivity and ceramide generation and subsequent metabolism. As such, knowledge of these metabolic pathways can provide guidance for enhancing ceramide-driven effects of 4-HPR in treatment of leukemia.

Anti-tumor activity of fenretinide complexed with human serum albumin in lung cancer xenograft mouse model

Sufficient knowledge regarding cellular and molecular basis of lung cancer progression and metastasis would help in the development of novel and effective strategies for the treatment of lung cancer. 4HPR is a synthetic retinoid with potential anti-tumor activity but is still limited because of its poor bioavailability. The use of albumin as a complexing agent for a hydrophobic drug is expected to improve the water solubility and consequently their bioavailability.This study investigated the antitumor activity of a novel complex between albumin and 4-HPR in a mouse model of human lung cancer and focuses on role and mechanism of Cav-1 mainly involved in regulating cancer and Acsvl3 mainly connected with tumor growth.

Their expressions were assayed by immunohistochemistry and qRT-PCR, to demonstrate the reduction of the tumor growth following the drug treatment. Our results showed a high antitumor activity of 4HPR-HSA by reduction of the volume of tumor mass and the presence of a high level of apoptotic cell by TUNEL assay. The downregulation of Cav-1 and Acsvl3 suggested a reduction of tumor growth.

In conclusion, we demonstrated the great potential of 4HPR-HSA in the treatment of lung cancer. More data about the mechanism of drug delivery the 4HPR-HSA are necessary.

Tamoxifen regulation of sphingolipid metabolism--Therapeutic implications

Tamoxifen, a triphenylethylene antiestrogen and one of the first-line endocrine therapies used to treat estrogen receptor-positive breast cancer, has a number of interesting, off-target effects, and among these is the inhibition of sphingolipid metabolism. More specifically, tamoxifen inhibits ceramide glycosylation, and enzymatic step that can adventitiously support the influential tumor-suppressor properties of ceramide, the aliphatic backbone of sphingolipids. Additionally, tamoxifen and metabolites N-desmethyltamoxifen and 4-hydroxytamoxifen, have been shown to inhibit ceramide hydrolysis by the enzyme acid ceramidase. This particular intervention slows ceramide destruction and thereby depresses formation of sphingosine 1-phosphate, a mitogenic sphingolipid with cancer growth-promoting properties. As ceramide-centric therapies are becoming appealing clinical interventions in the treatment of cancer, agents like tamoxifen that can retard the generation of mitogenic sphingolipids and buffer ceramide clearance via inhibition of glycosylation, take on new importance. In this review, we present an abridged, lay introduction to sphingolipid metabolism, briefly chronicle tamoxifen's history in the clinic, examine studies that demonstrate the impact of triphenylethylenes on sphingolipid metabolism in cancer cells, and canvass works relevant to the use of tamoxifen as adjuvant to drive ceramide-centric therapies in cancer treatment. The objective is to inform the readership of what could be a novel, off-label indication of tamoxifen and structurally-related triphenylethylenes, an indication divorced from estrogen receptor status and one with application in drug resistance.

Dihydroceramides: From Bit Players to Lead Actors

Sphingolipid synthesis involves a highly conserved biosynthetic pathway that produces fundamental precursors of complex sphingolipids. The final reaction involves the insertion of a double bond into dihydroceramides to generate the more abundant ceramides, which are converted to sphingomyelins and glucosylceramides/gangliosides by the addition of polar head groups. Although ceramides have long been known to mediate cellular stress responses, the dihydroceramides that are transiently produced during de novo sphingolipid synthesis were deemed inert. Evidence published in the last few years suggests that these dihydroceramides accumulate to a far greater extent in tissues than previously thought. Moreover, they have biological functions that are distinct and non-overlapping with those of the more prevalent ceramides. Roles are being uncovered in autophagy, hypoxia, and cellular proliferation, and the lipids are now implicated in the etiology, treatment, and/or diagnosis of diabetes, cancer, ischemia/reperfusion injury, and neurodegenerative diseases. This minireview summarizes recent findings on this emerging class of bioactive lipids.

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.

Modification of sphingolipid metabolism by tamoxifen and N-desmethyltamoxifen in acute myelogenous leukemia--Impact on enzyme activity and response to cytotoxics

The triphenylethylene antiestrogen, tamoxifen, can be an effective inhibitor of sphingolipid metabolism. This off-target activity makes tamoxifen an interesting ancillary for boosting the apoptosis-inducing properties of ceramide, a sphingolipid with valuable tumor censoring activity. Here we show for the first time that tamoxifen and metabolite, N-desmethyltamoxifen (DMT), block ceramide glycosylation and inhibit ceramide hydrolysis (by acid ceramidase, AC) in human acute myelogenous leukemia (AML) cell lines and in AML cells derived from patients. Tamoxifen (1-10 μM) inhibition of AC in AML cells was accompanied by decreases in AC protein expression. Tamoxifen also depressed expression and activity of sphingosine kinase 1 (SphK1), the enzyme-catalyzing production of mitogenic sphingosine 1-phosphate (S1-P). Results from mass spectroscopy showed that tamoxifen and DMT (i) increased the levels of endogenous C16:0 and C24:1 ceramide molecular species, (ii) nearly totally halted production of respective glucosylceramide (GC) molecular species, (iii) drastically reduced levels of sphingosine (to 9% of control), and (iv) reduced levels of S1-P by 85%, in vincristine-resistant HL-60/VCR cells. The co-administration of tamoxifen with either N-(4-hydroxyphenyl)retinamide (4-HPR), a ceramide-generating retinoid, or a cell-deliverable form of ceramide, C6-ceramide, resulted in marked decreases in HL-60/VCR cell viability that far exceeded single agent potency. Combination treatments resulted in synergistic apoptotic cell death as gauged by increased Annexin V binding and DNA fragmentation and activation of caspase-3. These results show the versatility of adjuvant triphenylethylene with ceramide-centric therapies for magnifying therapeutic potential in AML. Such drug regimens could serve as effective strategies, even in the multidrug-resistant setting.

The bioactive lipid 4-hydroxyphenyl retinamide inhibits flavivirus replication

Dengue virus (DENV), a member of the Flaviviridae family, is a mosquito-borne pathogen and the cause of dengue fever. The increasing prevalence of DENV worldwide heightens the need for an effective vaccine and specific antivirals. Due to the dependence of DENV upon the lipid biosynthetic machinery of the host cell, lipid signaling and metabolism present unique opportunities for inhibiting viral replication. We screened a library of bioactive lipids and modulators of lipid metabolism and identified 4-hydroxyphenyl retinamide (4-HPR) (fenretinide) as an inhibitor of DENV in cell culture. 4-HPR inhibits the steady-state accumulation of viral genomic RNA and reduces viremia when orally administered in a murine model of DENV infection. The molecular target responsible for this antiviral activity is distinct from other known inhibitors of DENV but appears to affect other members of the Flaviviridae, including the West Nile, Modoc, and hepatitis C viruses. Although long-chain ceramides have been implicated in DENV replication, we demonstrate that DENV is insensitive to the perturbation of long-chain ceramides in mammalian cell culture and that the effect of 4-HPR on dihydroceramide homeostasis is separable from its antiviral activity. Likewise, the induction of reactive oxygen species by 4-HPR is not required for the inhibition of DENV. The inhibition of DENV in vivo by 4-HPR, combined with its well-established safety and tolerability in humans, suggests that it may be repurposed as a pan-Flaviviridae antiviral agent. This work also illustrates the utility of bioactive lipid screens for identifying critical interactions of DENV and other viral pathogens with host lipid biosynthesis, metabolism, and signal transduction.

The oxidation states of DJ-1 dictate the cell fate in response to oxidative stress triggered by 4-hpr: autophagy or apoptosis?

AIM

Chemotherapy-induced reactive oxygen species (ROS) not only contribute to apoptosis, but also trigger autophagy. Since autophagy is reported to protect cancer cells from apoptosis, this weakens the therapeutic effect of chemotherapy. This study aimed at identifying the key molecules that determine the cellular response to ROS and, therefore, provide better strategies to increase chemotherapeutic efficiency.

RESULTS

Increasing concentrations of N-(4-hydroxyphenyl) retinamide (4-HPR)-treatment pushed autophagy down to apoptosis in a dose-dependent manner, and 4-HPR-induced ROS contribute to this process. Since we found that ASK1-regulated JNK1 and p38 are responsible for 4-HPR-induced autophagy and apoptosis, respectively, we further utilized co-immunoprecipitation followed by liquid chromatography-tandem mass spectrometry analysis to identify proteins that specifically bind to ASK1 under different oxidative states. Of note, DJ-1, a crucial antioxidant protein, was identified. Interestingly, DJ-1 functions as a redox sensor that senses ROS levels and determines the cellular response to 4-HPR: Under mild oxidative stress, moderate oxidation of DJ-1 is recruited to inhibit the activity of ASK1 and maintain cell viability by activating autophagy; under a lethal level of oxidative stress, excessive oxidized DJ-1 dissociates from ASK1 and activates it, thereby initiating p38 activation and enabling the cells to commit to apoptosis. Moreover, the depletion of DJ-1 increases the sensitivity of tumor cells to 4-HPR both in vitro and in vivo.

INNOVATION

Our results reveal that the different oxidation states of DJ-1 function as a cellular redox sensor of ROS caused by 4-HPR and determine the cell fate of autophagy or apoptosis. Moreover, the results suggest that DJ-1 might be a potent therapeutic target for cancer treatment.

CONCLUSION

ROS-mediated changes in the oxidation state of DJ-1 are involved in 4-HPR's effect on pushing autophagy down to apoptosis. Consequently, this change mediates ASK1 activation by regulating DJ-1-ASK1 complex formation and determines the cell fate of autophagy or apoptosis.

Molecular profiling of childhood cancer: Biomarkers and novel therapies

BACKGROUND

Technological advances including high-throughput sequencing have identified numerous tumor-specific genetic changes in pediatric and adolescent cancers that can be exploited as targets for novel therapies.

SCOPE OF REVIEW

This review provides a detailed overview of recent advances in the application of target-specific therapies for childhood cancers, either as single agents or in combination with other therapies. The review summarizes preclinical evidence on which clinical trials are based, early phase clinical trial results, and the incorporation of predictive biomarkers into clinical practice, according to cancer type.

MAJOR CONCLUSIONS

There is growing evidence that molecularly targeted therapies can valuably add to the arsenal available for treating childhood cancers, particularly when used in combination with other therapies. Nonetheless the introduction of molecularly targeted agents into practice remains challenging, due to the use of unselected populations in some clinical trials, inadequate methods to evaluate efficacy, and the need for improved preclinical models to both evaluate dosing and safety of combination therapies.

GENERAL SIGNIFICANCE

The increasing recognition of the heterogeneity of molecular causes of cancer favors the continued development of molecularly targeted agents, and their transfer to pediatric and adolescent populations.

A mechanically-induced colon cancer cell population shows increased metastatic potential

Background

Metastasis accounts for the majority of deaths from cancer. Although tumor microenvironment has been shown to have a significant impact on the initiation and/or promotion of metastasis, the mechanism remains elusive. We previously reported that HCT-8 colon cancer cells underwent a phenotypic transition from an adhesive epithelial type (E-cell) to a rounded dissociated type (R-cell) via soft substrate culture, which resembled the initiation of metastasis. The objective of current study was to investigate the molecular and metabolic mechanisms of the E-R transition.

Methods

Global gene expressions of HCT-8 E and R cells were measured by RNA Sequencing (RNA-seq); and the results were further confirmed by real-time PCR. Reactive oxygen species (ROS), anoikis resistance, enzyme activity of aldehyde dehydrogenase 3 family, member A1 (ALDH3A1), and in vitro invasion assay were tested on both E and R cells. The deformability of HCT-8 E and R cells was measured by atomic force microscopy (AFM). To study the in vivo invasiveness of two cell types, athymic nude mice were intra-splenically injected with HCT-8 E or R cells and sacrificed after 9 weeks. Incidences of tumor development and metastasis were histologically evaluated and analyzed with Fisher’s exact test.

Results

Besides HCT-8, E-R transition on soft substrates was also seen in three other cancer cell lines (HCT116, SW480 colon and DU145 prostate cancer). The expression of some genes, such as ALDH3A1, TNS4, CLDN2, and AKR1B10, which are known to play important roles in cancer cell migration, invasion, proliferation and apoptosis, were increased in HCT-8 R cells. R cells also showed higher ALDH3A1 enzyme activity, higher ROS, higher anoikis resistance, and higher softness than E cells. More importantly, in vitro assay and in vivo animal models revealed that HCT-8 R cells were more invasive than E cells.

Conclusions

Our comprehensive comparison of HCT-8 E and R cells revealed differences of molecular, phenotypical, and mechanical signatures between the two cell types. To our knowledge, this is the first study that explores the molecular mechanism of E-R transition, which may greatly increase our understanding of the mechanisms of cancer mechanical microenvironment and initiation of cancer metastasis.

Sphingolipids: key regulators of apoptosis and pivotal players in cancer drug resistance

Drug resistance elicited by cancer cells still constitutes a huge problem that frequently impairs the efficacy of both conventional and novel molecular therapies. Chemotherapy usually acts to induce apoptosis in cancer cells; therefore, the investigation of apoptosis control and of the mechanisms used by cancer cells to evade apoptosis could be translated in an improvement of therapies. Among many tools acquired by cancer cells to this end, the de-regulated synthesis and metabolism of sphingolipids have been well documented. Sphingolipids are known to play many structural and signalling roles in cells, as they are involved in the control of growth, survival, adhesion, and motility. In particular, in order to increase survival, cancer cells: (a) counteract the accumulation of ceramide that is endowed with pro-apoptotic potential and is induced by many drugs; (b) increase the synthesis of sphingosine-1-phosphate and glucosylceramide that are pro-survivals signals; (c) modify the synthesis and the metabolism of complex glycosphingolipids, particularly increasing the levels of modified species of gangliosides such as 9-O acetylated GD3 (αNeu5Ac(2-8)αNeu5Ac(2-3)βGal(1-4)βGlc(1-1)Cer) or N-glycolyl GM3 (αNeu5Ac (2-3)βGal(1-4)βGlc(1-1)Cer) and de-N-acetyl GM3 (NeuNH(2)βGal(1-4)βGlc(1-1)Cer) endowed with anti-apoptotic roles and of globoside Gb3 related to a higher expression of the multidrug resistance gene MDR1. In light of this evidence, the employment of chemical or genetic approaches specifically targeting sphingolipid dysregulations appears a promising tool for the improvement of current chemotherapy efficacy.

Synthetic retinoid fenretinide in breast cancer chemoprevention

Preclinical models suggest that retinoids inhibit mammary carcinogenesis. The induction of apoptosis is a unique feature of fenretinide, the most-studied retinoid in clinical trials of breast cancer chemoprevention, owing to its selective accumulation in breast tissue and its favorable toxicological profile. In a Phase III breast cancer prevention trial, fenretinide showed a strong trend of reduction of incidence of second breast malignancies in premenopausal women, which was confirmed by 15 years of follow-up. This warrants further research on the mechanisms of action and potential efficacy of fenretinide and provides the rationale for a Phase III primary prevention trial in young women at high risk for breast cancer. This review will highlight the role of fenretinide in breast cancer chemoprevention.

Phase I trial of fenretinide delivered orally in a novel organized lipid complex in patients with relapsed/refractory neuroblastoma: a report from the New Approaches to Neuroblastoma Therapy (NANT) consortium

BACKGROUND

A phase I study was conducted to determine the maximum-tolerated dose, dose-limiting toxicities (DLTs), and pharmacokinetics of fenretinide (4-HPR) delivered in an oral powderized lipid complex (LXS) in patients with relapsed/refractory neuroblastoma.

PROCEDURE

4-HPR/LXS powder (352-2,210 mg/m(2) /day) was administered on Days 0-6, in 21-day courses, by standard 3 + 3 design.

RESULTS

Thirty-two patients (median age = 8 years, range 3-27 years) enrolled with 30 evaluable for dose escalation. Prior therapies included stem cell transplantation/support (n = 26), 13-cis-retinoic acid (n = 22), (125/131) I-MIBG (n = 13), and anti-GD2 antibody (n = 6). 170+ courses were delivered. Course 1 DLTs were a Grade 3 (n = 1) alkaline phosphatase at 352 mg/m(2) /day. Other major toxicities were Grade 4 (n = 1) alkaline phosphatases on Courses 5 and 6 at 774 mg/m(2) /day, and Grade 3 (n = 1) ALT/AST elevation on Course 2 at 1,700 mg/m(2) /day. Of 29 response-evaluable patients, six had stable disease (SD) (4-26 courses); four with marrow- or bone disease-only had complete responses (CR) (10-46 courses). 4-HPR plasma levels were several folds higher (P < 0.05) than previously reported using capsular fenretinide. The Day 6 mean peak 4-HPR plasma level at 1,700 mg/m(2) /day was 21 µM. An MTD was not reached.

CONCLUSIONS

4-HPR/LXS oral powder obtained higher plasma levels, with minimal toxicity and evidence of anti-tumor activity, than a previous capsule formulation. A recommended phase II schedule of 4-HPR/LXS powder is 1,500 mg/m(2) /day, TID, on Days 0-6, of a 21-day course.

Fenretinide corrects the imbalance between omega-6 to omega-3 polyunsaturated fatty acids and inhibits macrophage inflammatory mediators via the ERK pathway

We previously identified Fragile X-related protein 1 (FXR1) as an RNA-binding protein involved in the post-transcriptional control of TNF and other cytokines in macrophages. Macrophages derived from FXR1-KO mice overexpress several inflammatory cytokines including TNF. Recently, we showed that fenretinide (4HPR) is able to inhibit several inflammatory cytokines in the lungs of cystic fibrosis mice, which also have abnormal immune responses. Therefore, we hypothesized that 4HPR might also be able to downregulate excessive inflammation even in macrophages with ablated FXR1. Indeed, our results demonstrate that 4HPR inhibited the excessive production of inflammatory mediators, including TNF, IL-6, CCL2 and CCL-5 in LPS-stimulated FXR1-KO macrophages, by selectively inhibiting phosphorylation of ERK1/2, which is naturally more phosphorylated in FXR1-KO cells. We also found that LPS stimulation of FXR1-KO macrophages led to significantly higher ratio of arachidonic acid/docosahexaenoic acid than observed in FXR1-WT macrophages. Interestingly, treatment with 4HPR was associated with the normalization of arachidonic acid/docosahexaenoic acid ratio in macrophages, which we found to impact phosphorylation of ERK1/2. Overall, this study shows for the first time that 4HPR modulates inflammatory cytokine expression in macrophages by correcting a phospholipid-bound fatty acid imbalance that impacts the phosphorylation of ERK1/2.

C22:0- and C24:0-dihydroceramides confer mixed cytotoxicity in T-cell acute lymphoblastic leukemia cell lines

We previously reported that fenretinide (4-HPR) was cytotoxic to acute lymphoblastic leukemia (ALL) cell lines in vitro in association with increased levels of de novo synthesized dihydroceramides, the immediate precursors of ceramides. However, the cytotoxic potentials of native dihydroceramides have not been defined. Therefore, we determined the cytotoxic effects of increasing dihydroceramide levels via de novo synthesis in T-cell ALL cell lines and whether such cytotoxicity was dependent on an absolute increase in total dihydroceramide mass versus an increase of certain specific dihydroceramides. A novel method employing supplementation of individual fatty acids, sphinganine, and the dihydroceramide desaturase-1 (DES) inhibitor, GT-11, was used to increase de novo dihydroceramide synthesis and absolute levels of specific dihydroceramides and ceramides. Sphingolipidomic analyses of four T-cell ALL cell lines revealed strong positive correlations between cytotoxicity and levels of C22:0-dihydroceramide (ρ = 0.74–0.81, P ≤ 0.04) and C24:0-dihydroceramide (ρ = 0.84–0.90, P ≤ 0.004), but not between total or other individual dihydroceramides, ceramides, or sphingoid bases or phosphorylated derivatives. Selective increase of C22:0- and C24:0-dihydroceramide increased level and flux of autophagy marker, LC3B-II, and increased DNA fragmentation (TUNEL assay) in the absence of an increase of reactive oxygen species; pan-caspase inhibition blocked DNA fragmentation but not cell death. C22:0-fatty acid supplemented to 4-HPR treated cells further increased C22:0-dihydroceramide levels (P ≤ 0.001) and cytotoxicity (P ≤ 0.001). These data demonstrate that increases of specific dihydroceramides are cytotoxic to T-cell ALL cells by a caspase-independent, mixed cell death mechanism associated with increased autophagy and suggest that dihydroceramides may contribute to 4-HPR-induced cytotoxicity. The targeted increase of specific acyl chain dihydroceramides may constitute a novel anticancer approach.

Glioma cell death induced by irradiation or alkylating agent chemotherapy is independent of the intrinsic ceramide pathway

BACKGROUND/AIMS

Resistance to genotoxic therapy is a characteristic feature of glioma cells. Acid sphingomyelinase (ASM) hydrolyzes sphingomyelin to ceramide and glucosylceramide synthase (GCS) catalyzes ceramide metabolism. Increased ceramide levels have been suggested to enhance chemotherapy-induced death of cancer cells.

METHODS

Microarray and clinical data for ASM and GCS in astrocytomas WHO grade II-IV were acquired from the Rembrandt database. Moreover, the glioblastoma database of the Cancer Genome Atlas network (TCGA) was used for survival data of glioblastoma patients. For in vitro studies, increases in ceramide levels were achieved either by ASM overexpression or by the GCS inhibitor DL-threo-1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP) in human glioma cell lines. Combinations of alkylating chemotherapy or irradiation and ASM overexpression, PPMP or exogenous ceramide were applied in parental cells. The anti-glioma effects were investigated by assessing proliferation, metabolic activity, viability and clonogenicity. Finally, viability and clonogenicity were assessed in temozolomide (TMZ)-resistant cells upon treatment with PPMP, exogenous ceramide, alkylating chemotherapy, irradiation or their combinations.

RESULTS

Interrogations from the Rembrandt and TCGA database showed a better survival of glioblastoma patients with low expression of ASM or GCS. ASM overexpression or PPMP treatment alone led to ceramide accumulation but did not enhance the anti-glioma activity of alkylating chemotherapy or irradiation. PPMP or exogenous ceramide induced acute cytotoxicity in glioblastoma cells. Combined treatments with chemotherapy or irradiation led to additive, but not synergistic effects. Finally, no synergy was found when TMZ-resistant cells were treated with exogenous ceramide or PPMP alone or in combination with TMZ or irradiation.

CONCLUSION

Modulation of intrinsic glioma cell ceramide levels by ASM overexpression or GCS inhibition does not enhance the anti-glioma activity of alkylating chemotherapy or irradiation.

CXCR4-tropic, but not CCR5-tropic, human immunodeficiency virus infection is inhibited by the lipid raft-associated factors, acyclic retinoid analogs, and cholera toxin B subunit

Development of an effective low-cost anti-acquired immunodeficiency syndrome (AIDS) drugs is needed for treatment of AIDS patients in developing countries. Host cell lipid raft microdomains, which are enriched with cholesterol, glycolipids, ceramide, and gangliosides, are important for human immunodeficiency virus type 1 (HIV-1) entry. Retinoid analogs have been shown to modulate ceramide levels in the cell membrane, while cholera toxin B subunit (CT-B) specifically binds to the ganglioside GM1. In this study, we found that the acyclic retinoid analogs geranylgeranoic acid (GGA) and NIK-333 as well as CT-B efficiently attenuate CXCR4-tropic, but not CCR5-tropic, HIV-1 vector infection. We also found that GGA and NIK-333 suppress CXCR4-tropic HIV-1 infection by attenuating CXCR4 expression. CT-B also attenuated CXCR4-tropic HIV-1 infection, but did not suppress CXCR4 expression. These results suggest a distinct role for lipid raft microdomains in CXCR4- and CCR5-tropic HIV-1 infections and illuminate novel agents for the development of AIDS therapy.

Novel chemotherapeutic drugs in sphingolipid cancer research

Sphingolipid-metabolizing enzymes are becoming targets for chemotherapeutic development with an increasing interest in the recent years. In this chapter we introduce the sphingolipid family of lipids, and the role of individual species in cell homeostasis. We also discuss their roles in several rare diseases and overall, in cancer transformation. We follow the biosynthesis pathway of the sphingolipid tree, focusing on the enzymes in order to understand how using small molecule inhibitors makes it possible to modulate cancer progression. Finally, we describe the most used and historically significant inhibitors employed in cancer research, their relationships to sphingolipid metabolism, and some promising results found in this field.

Fenretinide inhibited de novo ceramide synthesis and proinflammatory cytokines induced by Aggregatibacter actinomycetemcomitans

Ceramides play an essential role in modulating immune signaling pathways and proinflammatory cytokine production in response to infectious pathogens, stress stimuli, or chemotherapeutic drugs. In this study, we demonstrated that Aggregatibacter actinomycetemcomitans, the pathogen for aggressive periodontitis, induced de novo synthesis of ceramide in Raw 264.7 cells. In addition, we identified that fenretinide, a synthetic retinoid, suppressed the de novo synthesis of ceramide induced by A. actinomycetemcomitans. Moreover, fenretinide attenuated interleukin (IL)-1β, IL-6, and cyclooxygenase-2 mRNA expression induced by A. actinomycetemcomitans. Fenretinide also decreased IL-1β, IL-6, and prostaglandin E2 proinflammatory cytokine levels in Raw 264.7 cells induced by A. actinomycetemcomitans. However, fenretinide had no significant effects on tumor necrosis factor alpha mRNA or protein levels. Furthermore, we showed that fenretinide inhibited the janus kinase-signal transducer and activator of transcription, phosphatidylinositol 3-kinase-Akt, protein kinase C, and nuclear factor-kappaB signaling pathways, whereas fenretinide up-regulated the mitogen-activated protein kinase signaling pathways after bacterial stimulation. This study emphasizes the de novo ceramide synthesis pathway in response to bacterial stimulation and demonstrates the anti-inflammatory role of fenretinide in the bacteria-induced immune response.

Natural products as platforms for the design of sphingolipid-related anticancer agents

Modulation of sphingolipid metabolism is a promising strategy for cancer therapy that has already opened innovative approaches for the development of pharmacological tools and rationally designed new drugs. On the other hand, natural products represent a classical and well-established source of chemical diversity that has guided medicinal chemists on the development of new chemical entities with potential therapeutic use. Based on these premises, the aim of this chapter is to provide the reader with a general overview of some of the most representative families of sphingolipid-related natural products that have been described in the recent literature as lead compounds for the design of new modulators of sphingolipid metabolism. Special emphasis is placed on the structural aspects of natural sphingoids and synthetic analogs that have found application as anticancer agents. In addition, their cellular targets and/or their mode of action are also considered.