4-oxo-N-(4-hydroxyphenyl)retinamide: two independent ways to kill cancer cells

Encapsulation of 4-oxo-N-(4-hydroxyphenyl) retinamide in human serum albumin nanoparticles promotes EZH2 degradation in preclinical neuroblastoma models

Neuroblastoma is the most prevalent and aggressive solid tumor that develops extracranially in children between the ages of 0-14 years, which accounts for 8-10% of all childhood malignancies and ∼15% of pediatric cancer-related mortality. The polycomb repressive complex 2 (PRC2) protein, EZH2, is overexpressed in neuroblastoma and mediates histone H3 methylation at lysine 27 (K27) positions through its methyl transferase activity and is a potential epigenetic silencer of many tumor suppressor genes in cancer. Phosphorylation of EZH2 decreases its stability and leads to proteasomal degradation. The 4-oxo-N-(4-hydroxyphenyl) retinamide (4O4HPR) promotes EZH2 degradation via activation of PKC-δ, but its limited solubility and physiological instability limit its application. In the current study, the encapsulation of 4O4HPR in Human Serum Albumin Nanoparticles (HSANPs) enhanced the solubility and physiological stability of the nanoformulation, leading to improved therapeutic efficacy through G2-M cell cycle arrest, depolarization of mitochondrial membrane potential, generation of reactive oxygen species and caspase 3 mediated apoptosis activation. The molecular mechanistic approach of 4O4HPR loaded HSANPs has activated caspase 3, which further cleaves PKC-δ into two fragments wherein the cleaved fragment of PKC-δ possesses the kinase activity that phosphorylates EZH2 and decreases the protein stability leading to its further ubiquitination in SH-SY5Y cells. Co-immunoprecipitation experiments revealed the direct interaction between PKC-δ and EZH2 phosphorylation, followed by ubiquitination. Moreover, 4O4HPR loaded HSANPs demonstrated improved in vivo biodistribution, greater dispersibility, and biocompatibility and exhibited enhanced protein instability and degradation of EZH2 in the neuroblastoma xenograft mouse model.

Biological evaluation of octahydropyrazin[2,1-a:5,4-a']diisoquinoline derivatives as potent anticancer agents

In this study, we evaluated the cytotoxic activity and antiproliferative potency of novel octahydropyrazin[2,1-a:5,4-a']diisoquinoline derivatives (1-7) in MCF-7 and MDA-MB-231 breast cancer cell lines. Annexin V binding assay and disruption of the mitochondrial potential were performed to determine apoptosis. The activity of caspases 3, 8, 9, and 10 was measured after 24 h of incubation with tested compounds to explain detailed molecular mechanism of induction of apoptosis. The results from experiments were compared with effects obtained after incubation in the presence of camptothecin and etoposide. Our study demonstrated that the most active compounds in both analyzed breast cancer cell lines were compounds 3 and 4. We also observed that all compounds induced apoptosis. We demonstrated the higher activity of caspases 3, 8, 9, and 10, which confirmed that induction of apoptosis is associated with external and internal cell death pathway. Our study revealed that the novel compounds in group of diisoquinoline derivatives are promising candidates in anticancer treatment by activation of both extrinsic and intrinsic apoptotic pathways.

Inhibitory effects of fenretinide metabolites N-[4-methoxyphenyl]retinamide (MPR) and 4-oxo-N-(4-hydroxyphenyl)retinamide (3-keto-HPR) on fenretinide molecular targets β-carotene oxygenase 1, stearoyl-CoA desaturase 1 and dihydroceramide Δ4-desaturase 1

The therapeutic capacity of fenretinide (N-[4-hydroxyphenyl] retinamide; 4-HPR) has been demonstrated for several conditions, including cancer, obesity, diabetes, and ocular disease. Yet, the mechanisms of action for its pleiotropic effects are still undefined. We hypothesized that investigation of two of the major physiological metabolites of fenretinide, N-[4-methoxyphenyl]retinamide (MPR) and 4-oxo-N-(4-hydroxyphenyl)retinamide (3-keto-HPR), might begin to resolve the multifaceted effects of this synthetic retinoid. We analyzed the effects of fenretinide, MPR, 3-keto-HPR, and the non-retinoid RBP4 ligand A1120, on the activity of known targets of fenretinide, stearoyl-CoA desaturase 1 (SCD1) and dihydroceramide Δ4-desaturase 1 (DES1) in ARPE-19 cells, and purified recombinant mouse beta-carotene oxygenase 1 (BCO1) in vitro. Lipids and retinoids were extracted and quantified by liquid chromatography-mass spectrometry and reversed phase HPLC, respectively. The data demonstrate that while fenretinide is an inhibitor of the activities of these three enzymes, that 3-keto-HPR is a more potent inhibitor of all three enzymes, potentially mediating most of the in vivo beneficial effects of fenretinide. However, while MPR does not affect SCD1 and DES1 activity, it is a potent specific inhibitor of BCO1. We conclude that a deeper understanding of the mechanisms of action of fenretinide and its metabolites provides new avenues for therapeutic specificity. For example, administration of 3-keto-HPR instead of fenretinide may be preferential if inhibition of SCD1 or DES1 activity is the goal (cancer), while MPR may be better for BCO1 modulation (carotenoid metabolism). Continued investigation of fenretinide metabolites in the context of fenretinide’s various therapeutic uses will begin to resolve the pleotropic nature of this compound.

Sodium 4-Carboxymethoxyimino-(4-HPR) a Novel Water-Soluble Derivative of 4-Oxo-4-HPR Endowed with In Vivo Anticancer Activity on Solid Tumors

4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR), an active polar metabolite of the synthetic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR), was shown to exert promising antitumor activity through at least two independent mechanisms of action. Specifically, differently from 4-HPR and other retinoids, 4-oxo-4-HPR targets microtubules and inhibits tubulin polymerization causing mitotic arrest and on the other hand, analogously to the parent drug, it induces apoptosis through the activation of a signaling cascade involving the generation of reactive oxygen species (ROS). However, the potential in vivo use of 4-oxo-4-HPR is impaired by its poor solubility. By chemical modification of 4-oxo-4-HPR, a new class of compounds with improved solubility and in vivo bioavailability was obtained. We demonstrated here that, among them, the most promising molecule, sodium 4-carboxymethoxyimino-(4-HPR), was endowed with in vitro antitumor efficacy and entirely preserved the double mechanism of action of the parent drug in cancer cells of different histotypes. In fact, the retinoid induced the activation of the apoptotic cascade related to the generation of ROS through endoplasmic reticulum stress response and upregulation of phospho c-Jun N-terminal kinases and PLAcental Bone morphogenetic protein, leading to cell death through caspase-3 cleavage. Otherwise, sodium 4-carboxymethoxyimino-(4-HPR) caused a marked mitotic arrest coupled with multipolar spindle formation and tubulin depolymerization. To assess the compound antitumor activity, in vivo experiments were performed in three mouse xenograft models (ovarian and breast cancers and mesothelioma). The in vivo results demonstrated that retinoid administration as single agent significantly increased the survival in ovarian cancer xenografts, induced a statistically significant decrease in tumor growth in breast cancer xenografts, and caused a 30% reduction in tumor growth in a mesothelioma mouse model. Even though further studies investigating sodium 4-carboxymethoxyimino-(4-HPR) toxicity and in vitro and in vivo activities in combination with other drugs are required, the double mechanism of action of the retinoid coupled with its in vivo antitumor efficacy and potential low toxicity suggest a promising therapeutic potential for the compound in different solid tumors.

Molecular mechanisms of apoptosis and roles in cancer development and treatment

Programmed cell death (PCD) or apoptosis is a mechanism which is crucial for all multicellular organisms to control cell proliferation and maintain tissue homeostasis as well as eliminate harmful or unnecessary cells from an organism. Defects in the physiological mechanisms of apoptosis may contribute to different human diseases like cancer. Identification of the mechanisms of apoptosis and its effector proteins as well as the genes responsible for apoptosis has provided a new opportunity to discover and develop novel agents that can increase the sensitivity of cancer cells to undergo apoptosis or reset their apoptotic threshold. These novel targeted therapies include those targeting anti-apoptotic Bcl-2 family members, p53, the extrinsic pathway, FLICE-inhibitory protein (c-FLIP), inhibitor of apoptosis (IAP) proteins, and the caspases. In recent years a number of these novel agents have been assessed in preclinical and clinical trials. In this review, we introduce some of the key regulatory molecules that control the apoptotic pathways, extrinsic and intrinsic death receptors, discuss how defects in apoptotic pathways contribute to cancer, and list several agents being developed to target apoptosis.

Fenretinide Perturbs Focal Adhesion Kinase in Premalignant and Malignant Human Oral Keratinocytes. Fenretinide's Chemopreventive Mechanisms Include ECM Interactions

The membrane-associated protein, focal adhesion kinase (FAK), modulates cell-extracellular matrix interactions and also conveys prosurvival and proliferative signals. Notably, increased intraepithelial FAK levels accompany transformation of premalignant oral intraepithelial neoplasia (OIN) to oral squamous cell carcinoma (OSCC). OIN chemoprevention is a patient-centric, optimal strategy to prevent OSCC's comorbidities and mortality. The cancer chemopreventive and synthetic vitamin A derivative, fenretinide, has demonstrated protein-binding capacities, for example, mTOR- and retinol-binding protein interactions. These studies used a continuum of human oral keratinocytes (normal-HPV E6/E7-transduced-OSCC) to assess potential fenretinide-FAK drug protein interactions and functional consequences on cellular growth regulation and motility. Molecular modeling studies demonstrated that fenretinide has approximately 200-fold greater binding affinity relative to the natural ligand (ATP) at FAK's kinase domain. Fenretinide also shows intermediate binding at FAK's FERM domain and interacts at the ATP-binding site of the closest FAK analogue, PYK2. Fenretinide significantly suppressed proliferation via induction of apoptosis and G2-M cell-cycle blockade. Fenretinide-treated cells also demonstrated F-actin disruption, significant inhibition of both directed migration and invasion of a synthetic basement membrane, and decreased phosphorylation of growth-promoting kinases. A commercially available FAK inhibitor did not suppress cell invasion. Notably, although FAK's FERM domain directs cell invasion, FAK inhibitors target the kinase domain. In addition, FAK-specific siRNA-treated cells showed an intermediate cell migration capacity; data which suggest cocontribution of the established migrating-enhancing PYK2. Our data imply that fenretinide is uniquely capable of disrupting FAK's and PYK2's prosurvival and mobility-enhancing effects and further extend fenretinide's chemopreventive contributions beyond induction of apoptosis and differentiation.

AF1q: a novel mediator of basal and 4-HPR-induced apoptosis in ovarian cancer cells

Background

Fenretinide (4-HPR) is a synthetic retinoid that exhibits potent antitumor and chemopreventive activities against different malignancies, including ovarian tumors. We previously showed that in ovarian cancer cells, 4-HPR induces apoptosis through a signaling cascade starting from reactive oxygen species (ROS) generation and involving endoplasmic reticulum (ER) stress response, Jun N-terminal Kinase (JNK) activation, and induction of the proapoptotic PLAcental Bone morphogenetic protein (PLAB). Since recent studies have shown that the oncogene ALL1-fused from chromosome 1q (AF1q), a retinoic acid target gene, is implicated in apoptosis induction by several therapeutic agents, we investigated its possible involvement in the apoptosis induced by 4-HPR in ovarian cancer cells.

Methodology/Principal Findings

Protein expression analysis, performed in ovarian cancer cells and extended to other histotypes (breast, neuroblastoma, and cervical), revealed that 4-HPR enhanced AF1q expression in cancer cells sensitive to the retinoid but not in resistant cells. Through gene silencing, AF1q was found functionally involved in 4-HPR-induced apoptosis in A2780, an ovarian cancer cell line highly sensitive to retinoid growth inhibitory and apoptotic effects. Inhibition of the signaling intermediates of the 4-HPR apoptotic cascade showed that AF1q upregulation was depended on prior generation of ROS, induction of ER stress response, JNK activation, and PLAB upmodulation. Finally, we found that direct overexpression of AF1q, in the absence of external stimuli, increased apoptosis in ovarian cancer cell lines.

Conclusions/Significance

The study expands the knowledge of the 4-HPR mechanism of action, which has not yet been completely elucidated, identifying AF1q as a novel mediator of retinoid anticancer activity. In addition, we demonstrate, for the first time, that AF1q plays a role in the onset of basal apoptosis in ovarian cancer cells, thus providing new information about the activity of this protein whose biologic functions are mostly unknown.