Combination of all-trans retinoic acid and paclitaxel-induced differentiation and apoptosis in human glioblastoma U87MG xenografts in nude mice

Monitoring alterations of all-trans-retinal in human brain cancer cells by label-free confocal Raman imaging: regulation of the redox status of cytochrome c

This article has shown the impact of all-trans-retinal on human brain cancer, which is apparent in the shifts in the redox status of cytochrome c in a single cell. The connection between cytochrome c expression and its role in cancer development remains relatively unexplored. To assess this, we employed Raman spectroscopy and imaging to determine the redox state of the iron ion in cytochrome c across different cellular locations, including mitochondria, cytoplasm, lipid droplets, and the endoplasmic reticulum within human brain cancer cells. We have analyzed normal human astrocytes (NHA) and two brain cancer cell lines (astrocytoma - CRL-1718 and glioblastoma - U-87 MG) without and supplemented with all-trans-retinal. Our results confirmed that human brain cancer cells demonstrate varying redox status compared to normal cells based on the established correlation between the intensity of the cytochrome c Raman band at 1583 cm-1 and the malignancy grade of brain cancer cells. Our research unveiled that all-trans-retinal induces remarkable changes in the mitochondrial functional activity (redox status) of cancer cells, which were measured by confocal Raman spectroscopy and imaging.

pH-Sensitive nanodiamond co-delivery of retinal and doxorubicin boosts breast cancer chemotherapy

Herein for the first time we take the advantage of nanodiamonds (NDs) to covalently immobilize all-trans retinal (NPA) by an imine bond, allowing pH-mediated drug release. DOX is then physically adsorbed onto NPA to form an NPA@D co-loaded double drug in the sodium citrate medium, which is also susceptible to pH-triggered DOX dissociation. The cytotoxicity results showed that NPA@D could markedly inhibit the growth of DOX-sensitive MCF-7 cells in a synergetic way compared to the NP@D system of single-loaded DOX, while NPA basically showed no cytotoxicity and weak inhibition of migration. In addition, NPA@D can overcome the drug resistance of MCF-7/ADR cells, indicating that this nanodrug could evade the pumping of DOX by drug-resistant cells, but free DOX is nearly ineffective against these cells. More importantly, the fluorescence imaging of tumor-bearing mice in vivo and ex vivo demonstrated that the NPA@D was mainly accumulated in the tumor site rather than any other organ by intraperitoneal injection after 24 h, in which the fluorescence intensity of NPA@D was 19 times that of the free DOX, suggesting that a far reduced off-target effect and side effects would be expected. Therefore, this work presents a new paradigm for improving chemotherapy and reversing drug resistance using the ND platform for co-delivery of DOX and ATR.

Lipid-polymer hybrid nanoparticle with cell-distinct drug release for treatment of stemness-derived resistant tumor

Drug resistance presents one of the major causes for the failure of cancer chemotherapy. Cancer stem-like cells (CSCs), a population of self-renewal cells with high tumorigenicity and innate chemoresistance, can survive conventional chemotherapy and generate increased resistance. Here, we develop a lipid-polymer hybrid nanoparticle for co-delivery and cell-distinct release of the differentiation-inducing agent, all-trans retinoic acid and the chemotherapeutic drug, doxorubicin to overcome the CSC-associated chemoresistance. The hybrid nanoparticles achieve differential release of the combined drugs in the CSCs and bulk tumor cells by responding to their specific intracellular signal variation. In the hypoxic CSCs, ATRA is released to induce differentiation of the CSCs, and in the differentiating CSCs with decreased chemoresistance, DOX is released upon elevation of reactive oxygen species to cause subsequent cell death. In the bulk tumor cells, the drugs are released synchronously upon the hypoxic and oxidative conditions to exert potent anticancer effect. This cell-distinct drug release enhances the synergistic therapeutic efficacy of ATRA and DOX with different anticancer mechanism. We show that treatment with the hybrid nanoparticle efficiently inhibit the tumor growth and metastasis of the CSC-enriched triple negative breast cancer in the mouse models.

Current Opportunities for Targeting Dysregulated Neurodevelopmental Signaling Pathways in Glioblastoma

Glioblastoma (GBM) is the most common and highly lethal type of brain tumor, with poor survival despite advances in understanding its complexity. After current standard therapeutic treatment, including tumor resection, radiotherapy and concomitant chemotherapy with temozolomide, the median overall survival of patients with this type of tumor is less than 15 months. Thus, there is an urgent need for new insights into GBM molecular characteristics and progress in targeted therapy in order to improve clinical outcomes. The literature data revealed that a number of different signaling pathways are dysregulated in GBM. In this review, we intended to summarize and discuss current literature data and therapeutic modalities focused on targeting dysregulated signaling pathways in GBM. A better understanding of opportunities for targeting signaling pathways that influences malignant behavior of GBM cells might open the way for the development of novel GBM-targeted therapies.

miR-221/222 suppression induced by activation of the cAMP/PKA/CREB1 pathway is required for cAMP-induced bidirectional differentiation of glioma cells

Factors that increase cAMP levels can induce lineage-specific differentiation of glioma cells into astrocyte-like cells. However, the differentiation pattern and underlying mechanisms remain unclear. Here, we find that cAMP/protein kinase A (PKA)/cAMP responsive element binding protein 1 (CREB1)-induced miR-221/222 suppression contributes to the neuron-like differentiation of gliomas. cAMP agonists selectively induced neuron- and astrocyte-like but not oligodendrocyte-like differentiation of C6 glioma cells. PKA inhibitors and CREB1 knockout blocked neuron-like differentiation of glioma cells. cAMP inhibited miR-221/222 in a PKA/CREB1-dependent manner. Importantly, both in vitro and in vivo assays demonstrated that transcriptional suppression of miR-221/222 is required for neuronal differentiation of glioma cells. Our findings suggest that increasing cAMP levels can induce bidirectional differentiation of glioma cells. Furthermore, the miR-221/222 cluster acts as an epigenetic brake during glioma differentiation.

Synergistic Antiproliferative Effects of All-Trans Retinoic Acid and Paclitaxel on Autosomal Dominant Polycystic Kidney Disease Epithelial Cells

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by uncontrollable epithelial cell growth, cyst formation, and kidney malfunction. In the present study, we investigated the antiproliferative effects of the treatment with the combination of paclitaxel (PAC) and all-trans retinoic acid (ATRA) on ADPKD epithelial cells. Our results show that the combined treatment with 1 nM PAC and 10 nM ATRA significantly suppressed ADPKD cell proliferation (20%), while the treatment with ATRA or PAC alone had no such effect. Treatment with PAC and ATRA induced cell cycle arrest at the G2/M phase and apoptosis by upregulating p53 and caspase-8 expression and increased the intracellular calcium (Ca²⁺) level possibly by enhancing Ca²⁺ uptake via plasma membrane channels. In addition, this treatment suppressed extracellular signal-regulated kinase signaling possibly through mitogen-activated protein kinase phosphatase-1 activation. Thus, the combination of PAC and ATRA can be explored as a potential treatment regimen for ADPKD.

All-Trans Retinoic Acid Enhances Chemosensitivity to 5-FU by Targeting miR-378c/E2F7 Axis in Colorectal Cancer

Colorectal carcinoma (CRC), a life-threatening malignancy, has been found to present resistance to 5-fluorouracil (5-FU) and cause a poor prognosis for patients. Previous studies have proved that all-trans retinoic acid (ATRA) could inhibit the development of CRC cells. In addition, miR-378c was discovered to exert a vital role in various cancers. In this study, we utilized MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), transwell assay, and flow cytometry to confirm that ATRA was able to enhance the inhibitory effects of 5-FU on HCT116 cells effectively by promoting cell apoptosis. Then, ENCORI database (http://starbase.sysu.edu.cn/) was employed to predict that miR-378c was downregulated dramatically in CRC and E2F7 was the direct target of miR-378c. QRT-PCR (quantitative real-time polymerase chain reaction) was conducted to verify that the expression level of miR-378c was decreased while E2F7 expression was upregulated in CRC tissues compared with para-carcinoma tissues. Additionally, treatment of 5-FU combined with ATRA could increase miR-378c expression, whereas it decreased the expression of E2F7. Dual-Luciferase Reporter assay results revealed that miR-378c could regulate the load of E2F7 by binding to its 3′UTR directly. Furthermore, miR-378c inhibitor or vector with E2F7 partially counteracted the effects of 5-FU combined with ATRA on viability, migration, invasion, and apoptosis of HCT116 cells. In conclusion, our study aims to confirm that ATRA enhances chemosensitivity to 5-FU of patients with CRC and expound the potential molecular mechanisms.

Combined effect of (-)-epigallocatechin-3-gallate and all-trans retinoic acid in FLT3-mutated cell lines

Patents diagnosed with acute promyelocytic leukemia were treated with Vesanoid^® [all-trans retinoic acid (ATRA)]. ATRA promotes the maturation and differentiation of leukemia cells and is therefore capable of reducing the symptoms of leukemia by preventing aggregation of myeloid cells. However, the clinical applications of ATRA are limited by its side effects, including acute retinoid resistance, hypertriglyceridemia, mucocutaneous dryness, nausea, brief recovery time relapse and drug resistance. Therefore, combinations of ATRA and other anticancer drugs are being investigated to overcome these limitations. In our previous study it was shown that in leukemia cells, (-)-epigallocatechin-3-gallate (EGCG) reduced cell proliferation and induced apoptotic cell death. In the present study, an in vitro evaluation of the effects of the combination of EGCG and ATRA on FLT3-mutated cell lines was performed using the isobologram method. The results showed that there was an additive effect in leukemic cells when treated with a combination of ATRA and EGCG. Thus, it was concluded that the cytotoxic effects of EGCG were improved by ATRA.

Current Trends in ATRA Delivery for Cancer Therapy

All-Trans Retinoic Acid (ATRA) is the most active metabolite of vitamin A. It is critically involved in the regulation of multiple processes, such as cell differentiation and apoptosis, by activating specific genomic pathways or by influencing key signaling proteins. Furthermore, mounting evidence highlights the anti-tumor activity of this compound. Notably, oral administration of ATRA is the first choice treatment in Acute Promyelocytic Leukemia (APL) in adults and NeuroBlastoma (NB) in children. Regrettably, the promising results obtained for these diseases have not been translated yet into the clinics for solid tumors. This is mainly due to ATRA-resistance developed by cancer cells and to ineffective delivery and targeting. This up-to-date review deals with recent studies on different ATRA-loaded Drug Delivery Systems (DDSs) development and application on several tumor models. Moreover, patents, pre-clinical, and clinical studies are also reviewed. To sum up, the main aim of this in-depth review is to provide a detailed overview of the several attempts which have been made in the recent years to ameliorate ATRA delivery and targeting in cancer.

Combinational treatment of all-trans retinoic acid (ATRA) and bisdemethoxycurcumin (BDMC)-induced apoptosis in liver cancer Hep3B cells

The effects of two-drug combination, all-trans retinoic acid (ATRA) and bisdemethoxycurcumin (BDMC), on apoptosis induction of liver cancer cells were investigated in human liver Hep 3B cells. Two-drug combination caused a more effective decrease in cell viability and in induction of S phase arrest, DNA damage, and cell apoptosis than that of ATRA or BDMC only. Also, the two-drug combination caused more cells to undergo significantly increased ROS productions when compared to that of ATRA or BDMC only. Results of Western blotting demonstrated that two-drug combination increased expressions of Fas, pro-apoptotic proteins, and active form of caspase-3 and -9, but decreased that of anti-apoptotic proteins and XIAP than that of ATRA or BDMC only in Hep 3B cells. In conclusion, ATRA combined with BDMC enhance cell apoptosis and associated protein expression in Hep 3B cells. PRACTICAL APPLICATIONS: Bisdemethoxycurcumin (BDMC) derived from natural plants, turmeric (Curcuma longa), which had been used for Asia food for thousands of years. All-trans retinoid acid (ATRA) is currently used as a primary treatment for patients with acute promyelocytic leukemia. In previous study, ATRA and BDMC were reported to have anti-inflammatory and anticancer effects. Our results showed that treatment of ATRA combined with BDMC showed more effectively apoptosis than that of ATRA or BDMC only in Hep 3B cells. The findings also provided possible pathways concerning the induction of liver cancer cell apoptosis. We conclude that ATRA combined with BDMC may be potent anticancer agents or adjuvants for liver cancer therapy in the future.

UAB30, A Novel Rexinoid Agonist, Decreases Stemness In Group 3 Medulloblastoma Human Cell Line Xenografts

PURPOSE: In spite of advances in therapy for some subtypes, group 3 medulloblastoma continues to portend a poor prognosis. A subpopulation of medulloblastoma cells expressing the cell surface marker CD133 have been posited as possible stem cell like cancer cells (SCLCC), a potential source of drug resistance and relapse. Retinoids have been shown to affect SCLCC in other brain tumors. Based on these findings, we hypothesized that the CD133-enriched cell population group 3 medulloblastoma cells would be sensitive to the novel rexinoid, UAB30. METHODS: Human medulloblastoma cell lines were studied. Cell sorting based on CD133 expression was performed. Both in vitro and in vivo extreme limiting dilution assays were completed to establish CD133 as a SCLCC marker in these cell lines. Cells were treated with either retinoic acid (RA) or UAB30 and sphere forming capacity and CD133 expression were assessed. Immunoblotting was used to assess changes in stem cell markers. Finally, mice injected with CD133-enriched or CD133-depleted cells were treated with UAB30. RESULTS: CD133-enriched cells more readily formed tumorspheres in vitro at lower cell concentrations and formed tumors in vivo at low cell numbers. Treatment with RA or UAB30 decreased CD133 expression, decreased tumorsphere formation, and decreased expression of cancer stem cell markers. In vivo studies demonstrated that tumors from both CD133-enriched and CD133-depleted cells were sensitive to treatment with UAB30. CONCLUSIONS: CD133 is a marker for medulloblastoma SCLCCs. Both CD133-enriched and CD133-depleted medulloblastoma cell populations demonstrated sensitivity to UAB30, indicating its potential as a therapeutic option for group 3 medulloblastoma.

The Cytoskeleton-A Complex Interacting Meshwork

The cytoskeleton of animal cells is one of the most complicated and functionally versatile structures, involved in processes such as endocytosis, cell division, intra-cellular transport, motility, force transmission, reaction to external forces, adhesion and preservation, and adaptation of cell shape. These functions are mediated by three classical cytoskeletal filament types, as follows: Actin, microtubules, and intermediate filaments. The named filaments form a network that is highly structured and dynamic, responding to external and internal cues with a quick reorganization that is orchestrated on the time scale of minutes and has to be tightly regulated. Especially in brain tumors, the cytoskeleton plays an important role in spreading and migration of tumor cells. As the cytoskeletal organization and regulation is complex and many-faceted, this review aims to summarize the findings about cytoskeletal filament types, including substructures formed by them, such as lamellipodia, stress fibers, and interactions between intermediate filaments, microtubules and actin. Additionally, crucial regulatory aspects of the cytoskeletal filaments and the formed substructures are discussed and integrated into the concepts of cell motility. Even though little is known about the impact of cytoskeletal alterations on the progress of glioma, a final point discussed will be the impact of established cytoskeletal alterations in the cellular behavior and invasion of glioma.

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.

Curcumin potentiates the antitumor activity of Paclitaxel in rat glioma C6 cells

BACKGROUND

Glioma is the most common primary cancer in central nervous system, especially in brain. Paclitaxel (PTX) is a microtubule stabilizing agent with anticancer potential, but its clinical application to brain tumours is limited by drug resistance, side effects, and lower brain penetration.

PURPOSE

Herein we explored the in vitro effects, in glioma C6 cells, of the combination of PTX with curcumin, a natural compound with chemotherapeutic activity, in order to improve cytotoxic effects and overcome PTX limitations.

RESULTS

Our data confirmed PTX antiproliferative activity that was improved by curcumin. These effects were confirmed by clonogenic assay and G0/G1 cell cycle arrest. PTX significantly promoted generation of intracellular reactive species (RS), while curcumin did not affect RS production; the combination of the two drugs resulted in a slight but significant increase in RS levels. Furthermore, we found a constitutive activation of NF-κB in C6 cell line that was inhibited by PTX and curcumin. Interestingly, combination of the drugs totally inhibited NF-κB nuclear translocation and reduced IκB phosphorylation. Our results also supported the involvement of p53-p21 axis in the anticancer effects of curcumin and PTX. The combination of the two drugs further increased p53 and p21 levels enhancing the antiproliferative effects. Furthermore, PTX plus curcumin most impressively activated caspase-3, effector of apoptosis pathways, and reduced the expression of the anti-apoptotic protein Bcl-2.

CONCLUSION

In conclusion, our findings demonstrated that combination of PTX and curcumin exerts a potentiated anti-glioma efficacy in vitro that may help in reducing dosage and/or minimizing side effects of cytotoxic therapy.

Templated Macroporous Polyethylene Glycol Hydrogels for Spheroid and Aggregate Cell Culture

Macroporous cell-laden hydrogels have recently gained recognition for a wide range of biomedical and bioengineering applications. There are various approaches to create porosity in hydrogels, including lyophilization or foam formation. However, many do not allow a precise control over pore size or are not compatible with in situ cell encapsulation. Here, we developed novel templated macroporous hydrogels by encapsulating uniform degradable hydrogel microspheres produced via microfluidics into a hydrogel slab. The microspheres degraded completely leaving macropores behind. Microsphere degradation was dependent on the incubation medium, microsphere size, microsphere confinement in the hydrogel as well as cell encapsulation. Uniquely, the degradable microspheres were biocompatible and when laden with cells, the cells were deposited in the macropores upon microsphere degradation and formed multicellular aggregates. The hydrogel-encapsulated cell aggregates were used in a small drug screen to demonstrate the relevance of cell-matrix interactions for multicellular spheroid drug responsiveness. Hydrogel-grown spheroid cultures are increasingly important in applications such as in vitro tumor, hepatocellular, and neurosphere cultures and drug screening; hence, the templated cell aggregate-laden hydrogels described here would find utility in various applications.

Nonradioactive and Radioactive Telomerase Assays for Detecting Diminished Telomerase Activity in Cancer Cells after Treatment with Retinoid

Detection of any decrease in telomerase activity in cancer cells and tumor tissues is an important part in assessing overall therapeutic outcomes of a treatment agent in the laboratory and clinical settings. Almost 85% of cancers have activation of telomerase activity that promotes cell proliferation and discourages differentiation to sustain growth of the cancers. Retinoids are highly regarded as the anti-proliferation and pro-differentiation agents that cause down regulation of telomerase activity in the cancer cells. Two (nonradioactive and radioactive) telomeric repeat amplification protocol (TRAP) assays are optimized and fully described for detection of the diminished or abolished telomerase activity in a very low amount of protein extracts from cancer cells after treatment with a natural retinoid or a synthetic retinoid. These highly optimized and improved nonradioactive and radioactive TRAP assays can also be used for determining the presence or absence of telomerase activity in a small amount of any tumor tissue. The results from these TRAP assays can also help decide appropriate therapeutic options for the cancers with or without telomerase activity.

All-trans retinoic acid reverses epithelial-mesenchymal transition in paclitaxel-resistant cells by inhibiting nuclear factor kappa B and upregulating gap junctions

Paclitaxel is a widely used chemotherapy drug, but development of resistance leads to treatment failure. Tumor cells that are treated with a sublethal dose of paclitaxel for a long period of time show the epithelial‐mesenchymal transition (EMT) phenotype, which leads to metastasis and resistance. All‐trans retinoic acid (ATRA) is always used in combination with paclitaxel and can reverse EMT in many types of cancer cells. The ability of ATRA to reverse EMT in chemoresistant cells is still unknown. In the present study, the ability of ATRA to reverse EMT in paclitaxel‐resistant cells was investigated. Three colorectal cancer cell lines, HCT116, LoVo and CT26, were treated with sublethal doses of paclitaxel to create resistant cell lines. Western blotting, immunocytochemistry, and “parachute” dye‐coupling assays showed that ATRA reverses EMT, inhibits nuclear factor kappa B (NF‐κΒ), and upregulates gap junctions in paclitaxel‐resistant cells. Scratch wound‐healing and Transwell assays showed that ATRA decreases the migration and invasion abilities of paclitaxel‐resistant cells. In addition, the CT26 cell line was used in the Balb/c pulmonary metastasis model to show that ATRA reduces metastasis of paclitaxel‐resistant cells in vivo. Given these data, ATRA may reverse EMT by inhibiting NF‐κΒ and upregulating gap junctions in paclitaxel‐resistant cells.

UAB30, a novel RXR agonist, decreases tumorigenesis and leptomeningeal disease in group 3 medulloblastoma patient-derived xenografts

BACKGROUND

Group 3 tumors account for approximately 25-30% of medulloblastomas and have the worst prognosis. UAB30 is a novel synthetic rexinoid shown to have limited toxicities in humans and significant efficacy in the pediatric neuroectodermal tumor, neuroblastoma. We hypothesized that treatment with UAB30 would decrease tumorigenicity in medulloblastoma patient-derived xenografts (PDXs).

METHODS

Three group 3 medulloblastoma PDXs (D341, D384 and D425) were utilized. Cell viability, proliferation, migration and invasion assays were performed after treatment with UAB30 or 13-cis-retinoic acid (RA). Cell cycle analysis was completed using flow cytometry. A flank model, a cerebellar model, and a model of leptomeningeal metastasis using human medulloblastoma PDX cells was used to assess the in vivo effects of UAB30 and RA.

RESULTS

UAB30 treatment led to cell differentiation and decreased medulloblastoma PDX cell viability, proliferation, migration and invasion and G1 cell cycle arrest in all three PDXs similar to RA. UAB30 and RA treatment of mice bearing medulloblastoma PDX tumors resulted in a significant decrease in tumor growth and metastasis compared to vehicle treated animals.

CONCLUSIONS

UAB30 decreased viability, proliferation, and motility in group 3 medulloblastoma PDX cells and significantly decreased tumor growth in vivo in a fashion similar to RA, suggesting that further investigations into the potential therapeutic application of UAB30 for medulloblastoma are warranted.

Redox-sensitive micelles for targeted intracellular delivery and combination chemotherapy of paclitaxel and all-trans-retinoid acid

The application of paclitaxel (PTX) in clinic has been restricted due to its poor solubility. Several traditional nano-medicines have been developed to improve this defect, while they are still lack of tumor targeting ability and rapid drug release. In this work, an amphiphilic polymeric micelle of hyaluronic acid (HA) – all-trans-retinoid acid (ATRA) with a disulfide bond, was developed successfully for the co-delivery of PTX and ATRA. The combination chemotherapy of PTX and ATRA can strengthen the anti-tumor activity. Along with self-assembling to micelles in water, the delivery system displayed satisfying drug loading capacities for both PTX (32.62% ± 1.39%) and ATRA, due to directly using ATRA as the hydrophobic group. Rapid drug release properties of the PTX-loaded redox-sensitive micelles (HA-SS-ATRA) in vitro were confirmed under reducing condition containing GSH. Besides, HA-CD44 mediated endocytosis promoted the uptake of HA-SS-ATRA micelles by B16F10 cells. Due to these properties, cytotoxicity assay verified that PTX-loaded HA-SS-ATRA micelles showed concentration-dependent cytotoxicity and displayed obvious combination therapy of PTX and ATRA. Importantly, HA-SS-ATRA micelles could remarkably prolong plasma circulation time after intravenously administration. Therefore, redox-sensitive HA-SS-ATRA micelles could be utilized and explored as a promising drug delivery system for cancer combination chemotherapy.

Retinoic acid receptor α expression exerts an anti-apoptosis effect on PC12 cells following oxygen-glucose deprivation

It has been established that the primary form of neuron death following hypoxic ischemic brain damage is apoptosis. Imbalances in the expression of genes in the B-cell lymphoma 2 (Bcl-2) family located in the mitochondrion, and in the expression of their encoded proteins, are key events in the mitochondrial apoptotic pathway, which lead to damage of cellular structure and function. The present study aimed to explore the regulatory effect of retinoic acid receptor α (RAR-α) on the apoptosis of PC12 cells induced by oxygen-glucose deprivation (OGD) in the retinoic acid signaling pathway. Recombinant adenovirus RAR-α small interfering RNA (Ad-siRAR-α) was used to transduce PC12 cells, and the efficiency of RAR-α expression inhibition was detected by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). An empty adenovirus vector was transfected in PC12 cells, which were used as the control. Flow cytometry with Annexin V-propidium iodide (PI) and fluorescence probe JC-1 staining was used to detect the apoptosis rate and mitochondrial transmembrane potential (MMP), respectively, of PC12 cells after transduction with Ad-siRAR-α. Furthermore, the expression levels of key genes in the RAR-α and mitochondrial apoptotic pathway, Bcl-2 and Bcl-2-associated protein (Bax) were analyzed by RT-quantitative (q)PCR and western blot analysis. RAR-α mRNA expression was observed to be decreased in PC12 cells following OGD-induced injury, and this decrease can be reversed by 4 µmol/l ATRA treatment. After 36 h transfection with Ad-siRAR-α, RAR-α gene expression was significantly inhibited compared with the control (P<0.05). The results of Annexin V-PI, fluorescence probe JC-1 staining and flow cytometry demonstrated that the apoptosis rate significantly increased and MMP significantly decreased in OGD-induced PC12 cells following transduction with Ad-siRAR-α compared with the control (both P<0.05). RT-qPCR and western blot analysis indicated that Bax expression was significantly increased and Bcl-2 expression was significantly decreased in PC12 cells transduced with Ad-siRAR-α after OGD-induced injury at the mRNA and protein level (P<0.05). In conclusion, Ad-siRAR-α transduction could promote apoptosis in OGD-induced PC12 cells. This suggests that the expression of Bax and Bcl-2 in the mitochondrial apoptosis signaling pathway is, at least in part, mediated by RAR-α expression, thereby indicating that RAR-α expression exerts an anti-apoptotic effect on OGD-damaged PC12 cells.

Saponins isolated from Schizocapsa plantaginea inhibit human hepatocellular carcinoma cell growth in vivo and in vitro via mitogen-activated protein kinase signaling

The underground cane of Schizocapsa plantaginea (Hance) has long been used by Chinese ethnic minority as a constituent of anti-cancer formulae. Saponins are abundant secondary metabolic products located in the underground cane of this plant. The potential therapeutic effects of total saponins isolated from Schizocapsa plantaginea (Hance) (SSPH) on human hepatocellular carcinoma (HCC) were tested in vitro in human liver cancer cell lines, SMMC-7721 and Bel-7404. Apoptosis and cell cycle arrest were determined using flow cytometry, caspase activation was determined by ELISA, and PARP, cleaved PARP, mitogen-activated protein kinase (MAPK) expression and phosphorylation were measured using Western blotting analysis. In vivo anti-HCC effects of SSPH were verified in nude mouse xenograft model. SSPH exerted markedly inhibitory effect on HCC cell proliferation in time- and concentration-dependent manner. Moreover, SSPH significantly induced apoptosis through caspase-dependent signaling and arrested cell cycle at G₂/M phase. These anti-proliferation effects of SSPH were associated with up-regulated phosphorylation of extracellular signal-regulated kinase-1/2 (Erk1/2) and c-jun-NH2-kinase-1/2 (JNK1/2) and reduced phosphorylation of p38MAPK. Furthermore, inhibitors of ERK, UO126, and JNK, SP600125 inhibited the anti-proliferation effects by SSPH, suggesting that Erk and JNK were the effector molecules in SSPH induced anti-proliferative action. During in vivo experiments, SSPH was found to inhibit xenograft tumor growth in nude mice, with a similar mechanism in vitro. Our study confirmed that SSPH exerted antagonistic effects on human liver cancer cells both in vitro and in vivo. Molecular mechanisms underlying SSPH action might be closely associated with MAPK signaling pathways. These results indicated that SSPH has potential therapeutic effects on HCC.

The protective role of all-transretinoic acid (ATRA) against colorectal cancer development is achieved via increasing miR-3666 expression and decreasing E2F7 expression

OBJECTIVE

Colorectal cancer (CRC) is one of the most common malignancies with high morbidity and mortality rates worldwide. This study aimed to investigate whether miR-3666 was involved in inhibitory effects of all-transretinoic acid (ATRA) on the development of colorectal cancer (CRC).

MATERIAL AND METHODS

Surgical specimens of CRC tissues and adjacent non-tumor mucosa were collected for determining miR-3666 expression. Human CRC HCT116 cells were treated with different doses of ATRA (10, 20, 40, and 60 μM, respectively) and/or transfected with miR-3666 mimic, miR-3666 inhibitor, E2F7 siRNAs or their controls, respectively. After different treatments, cell viability, apoptosis, migration and invasion were detected. The regulatory relationship between miR-3666 and E2F7 was investigated. Furthermore, the association between MAPK/ERK pathway and ATRA or miR-3666/E2F7 was explored.

RESULTS

The miR-3666 was lowly expressed in CRC tissues, while E2F7 was highly expressed. ATRA decreased HCT116 cell viability, migration, and invasion, and induced apoptosis, indicating that ATRA inhibited the malignant behaviors of HCT116 cells. Moreover, ATRA increased miR-3666 expression, and effects of ATRA on the malignant behaviors of HCT116 cells were achieved by positive regulating miR-3666 expression. Furthermore, E2F7 was a target gene of miR-3666, and knockdown of E2F7 reversed the combined effects of ATRA and miR-3666 inhibitor on the malignant behaviors of HCT116 cells. Besides, ATRA inhibited the activation of MAPK/ERK signaling pathway, which was reversed by inhibition of miR-3666.

CONCLUSIONS

Our results reveal that ATRA protects against CRC development possible via increasing miR-3666 expression and decreasing E2F7 expression. MiR-3666/E2F7 may play a key role in regulating the inhibitory effects of ATRA on HCT116 cells via suppressing the activation of MAPK/ERK signaling pathway.

Pegylated liposomal‑paclitaxel induces ovarian cancer cell apoptosis via TNF‑induced ERK/AKT signaling pathway

Ovarian cancer is one of the most common gynecological types of cancer and is characterized by a relatively high incidence and high mortality rate. Evidence has demonstrated that paclitaxel (PTX) is an effective therapeutic treatment for human ovarian cancer. In the present study, the inhibitory effects of pegylated liposomal (PL)-PTX on the growth of ovarian cancer cells were investigated in vitro; a CAOV-3-bearing mouse model was established to investigate the in vivo effects of PL-PTX on ovarian tumor growth. In the present study, the underlying mechanism of tumor necrosis factor (TNF)-induced inhibition of extracellular signal-regulated kinase (ERK)/protein kinase B (AKT) signaling pathway mediated by PL-PTX was analyzed within ovarian cancer cells. The results of the present study revealed that PL-PTX significantly inhibited the growth and aggressiveness of ovarian cancer cells in vitro and in vivo and apoptotic ability increased upon administration of PL-PTX. The expression levels of caspase-3/9 were significantly upregulated within PL-PTX-treated ovarian cancer cells. The expression and phosphorylation levels of ERK and AKT were markedly increased in response to PL-PTX treatment. In addition, the inhibitory effects of PL-PTX on ovarian cancer cells were eliminated by neutralizing antibodies against TNF. The observations of the present study revealed that PL-PTX induced ovarian cell apoptosis via the TNF-dependent pathway, which was significantly inhibited with the employment of antibodies against TNF. In vivo analysis demonstrated that PL-PTX treatment significantly inhibited ovarian tumor growth and prolonged the survival of tumor bearing mice. In conclusion, the findings of the present study have provided an insight into the potential mechanism of PL-PTX-induced apoptosis of ovarian cancer cells. As PL-PTX has been reported to induce ovarian tumor cell apoptosis via the TNF-induced ERK/AKT signaling pathway, PL-PTX may serve as an efficient anticancer drug for the treatment of ovarian cancer.

A novel retinoid X receptor agonist, UAB30, inhibits rhabdomyosarcoma cells in vitro

BACKGROUND

While patients with early-stage rhabdomyosarcoma (RMS) have seen steady improvement in prognosis over the last 50 y, those with advanced-stage or high-grade disease continue to have a dismal prognosis. Retinoids have been shown to cause growth suppression and terminal differentiation in RMS cells, but the toxicities associated with retinoic acid limit its use. Rexinoids provide an alternative treatment approach to retinoic acid. Rexinoids primarily bind the retinoid X receptor with minimal retinoic acid receptor binding, the entity responsible for many of the toxicities of retinoid therapies. UAB30 is a novel rexinoid with limited toxicities. We hypothesized that UAB30 would lead to decreased cell survival in RMS.

MATERIALS AND METHODS

Two RMS cell lines, one embryonal (RD) subtype and one alveolar (St. Jude Cancer Research Hospital 30) subtype, were used. Cells were treated with UAB30, and cytotoxicity, proliferation, mobility, and apoptosis were evaluated.

RESULTS

UAB30 significantly decreased RMS tumor cell viability and proliferation. Invasion, migration, and attachment-independent growth were reduced following UAB30 treatment. UAB30 also resulted in apoptosis and G1 cell cycle arrest. UAB30 affected both the alveolar and embryonal RMS cell lines in a similar fashion.

CONCLUSIONS

The results of these studies suggest a potential therapeutic role for the low-toxicity synthetic retinoid X receptor selective agonist, UAB30, in RMS treatment.

Filomicelles Deliver a Chemo-Differentiation Combination of Paclitaxel and Retinoic Acid That Durably Represses Carcinomas in Liver to Prolong Survival

Drug resistance and relapse is common in cancer treatments with chemotherapeutics, and while drug combinations with naturally occurring, differentiation-inducing retinoic acid (RA) provide remission-free cures for one type of liquid tumor, solid tumors present major problems for delivery. Here, inspired by filoviruses that can be microns in length, flexible filomicelles that self-assemble from an amphiphilic block copolymer (PEG-PCL) are shown to effectively deliver RA and paclitaxel (TAX) to several solid tumor models, particularly in the liver. These hydrophobic compounds synergistically load into the cores of the elongated micelles, and the coloaded micelles prove most effective at causing cell death, ploidy, and durable regression of tumors compared to free drugs or to separately loaded drugs. RA-TAX filomicelles also reduce mortality of human lung or liver derived cancers engrafted at liver, intraperitoneal, and subcutaneous sites in immunodeficient mice. In vitro studies show that the dual drug micelles effectively suppress proliferation while upregulating a generic differentiation marker. The results highlight the potency of dual-loaded filomicelles in killing cancer cells or else driving their differentiation away from growth.

Paclitaxel inhibits breast cancer metastasis via suppression of Aurora kinase-mediated cofilin-1 activity

The main problem in breast cancer treatment is the recurrence of tumor growth and metastases. Previous studies have suggested that Paclitaxel is widely used to treat various cancers. The present study analyzed the potential signaling pathway of Paclitaxel-inhibited breast cancer metastasis. It was demonstrated that Paclitaxel treatment significantly inhibited growth of breast cancer cell lines including MCF-7 and SKBR3 cells. Results demonstrated that Paclitaxel significantly inhibited breast cancer cell migration and invasion. Results additionally demonstrated that Paclitaxel treatment suppressed Aurora kinase and cofilin-1 activity in breast cancer cells. The potential mechanism indicated that activation of Aurora kinase activity stimulated cofilin-1 activity, which canceled Paclitaxel-inhibited growth and aggressiveness of breast cancer cells. An in vivo assay revealed that Paclitaxel treatment significantly inhibited breast cancer growth. Immunohistochemistry demonstrated that Paclitaxel treatment increased apoptosis of tumor cells in tumor tissue. Notably, Aurora kinase and cofilin-1 activity were downregulated by Paclitaxel in tumor tissues. In conclusion, these results indicated that Paclitaxel inhibited breast cancer cell growth and metastasis via suppression of Aurora kinase-mediated cofilin-1 activity, suggesting Paclitaxel may be an efficient anticancer agent for the treatment of this disease.

Real-Time Apoptosis and Viability High-Throughput Screening of 3D Multicellular Tumor Spheroids Using the Celigo Image Cytometer

Three-dimensional tumor spheroid models have been increasingly used to investigate and characterize cancer drug compounds. Previously, the Celigo image cytometer has demonstrated its utility in a high-throughput screening manner for evaluating potential drug candidates in a 3D multicellular tumor spheroid (MCTS) primary screen. In addition, we have developed real-time kinetic caspase 3/7 apoptosis and propidium iodide viability 3D MCTS assays, both of which can be used in a secondary screen to better characterize the hit compounds. In this work, we monitored the kinetic apoptotic and cytotoxic effects of 14 compounds in 3D MCTS produced from the glioblastoma cell line U87MG in 384-well plates for 9 days. The kinetic results allowed the categorization of the effects from 14 drug compounds into early and late cytotoxic, apoptotic, cytostatic, and no effects. The real-time apoptosis and viability screening method can serve as an improved secondary screen to better understand the mechanism of action of these potential drug candidates identified from the primary screen, allowing one to identify a more qualified drug candidate and streamline the drug discovery process of research and development.

Fabrication of all-trans-retinoic acid-loaded biocompatible precirol: A strategy for escaping dose-dependent side effects of doxorubicin

BACKGROUND

Drug delivery-based nanoparticles have been emerged to be an alternative and efficient approach to cancer therapy compared to conventional systems. Here, we investigated the role of all-trans retinoic acid (ATRA) formulated with precirol in increasing doxorubicin (Dox) induced apoptosis and cell cycle arrest in MDA-MB-231 breast cancer cells.

METHODS

ATRA-loaded Nano structured lipid carriers (NLCs) were evaluated in terms of particle size, zeta potential, Fourier transforms infrared spectroscopy (FTIR), cell internalization, and scanning electron microscope (SEM). To understand molecular mechanism of apoptosis and cell cycle progression flow cytometric assay, MTT and DAPI staining was applied. Real time (RT)-PCR analysis was employed to investigate the expression of apoptosis related genes, including Survivin, Bcl-2 and Bax.

RESULTS

The optimized ATRA formulation exhibited average particle size of 95±5nm with nearly narrow size distribution. The IC50 values for ATRA and doxorubicin were 48±0.4μM and 0.81±0.02μM, respectively. ATRA-loaded NLCs decreased percentage of cell proliferation from 51±7.2% to 36±4.1% (p <0.05). Co-treatment of the MDA-MB-231 cells with ATRA formulation and doxorubicin caused two-fold increase in the percentage of apoptosis (p<0.05). The results from gene expression exhibited a significant decrease in survivin along with increase at Bax mRNA levels accompanied by a slight increase in Bax/Bcl-2 ratio.

CONCLUSION

Our results propose that ATRA encapsulated in precirol as a biocompatible compound augments the efficacy of Dox in cancer therapy.

A Novel Multiparametric Drug-Scoring Method for High-Throughput Screening of 3D Multicellular Tumor Spheroids Using the Celigo Image Cytometer

Three-dimensional (3D) tumor models have been increasingly used to investigate and characterize cancer drug compounds. The ability to perform high-throughput screening of 3D multicellular tumor spheroids (MCTS) can highly improve the efficiency and cost-effectiveness of discovering potential cancer drug candidates. Previously, the Celigo Image Cytometer has demonstrated a novel method for high-throughput screening of 3D multicellular tumor spheroids. In this work, we employed the Celigo Image Cytometer to examine the effects of 14 cancer drug compounds on 3D MCTS of the glioblastoma cell line U87MG in 384-well plates. Using parameters such as MCTS diameter and invasion area, growth and invasion were monitored for 9 and 3 d, respectively. Furthermore, fluorescent staining with calcein AM, propidium iodide, Hoechst 33342, and caspase 3/7 was performed at day 9 posttreatment to measure viability and apoptosis. Using the kinetic and endpoint data generated, we created a novel multiparametric drug-scoring system for 3D MCTS that can be used to identify and classify potential drug candidates earlier in the drug discovery process. Furthermore, the combination of quantitative and qualitative image data can be used to delineate differences between drugs that induce cytotoxic and cytostatic effects. The 3D MCTS-based multiparametric scoring method described here can provide an alternative screening method to better qualify tested drug compounds.

Carbohydrate-based amphiphilic nano delivery systems for cancer therapy

Nanoparticles (NPs) are novel drug delivery systems that have been attracting more and more attention in recent years, and have been used for the treatment of cancer, infection, inflammation and other diseases. Among the numerous classes of materials employed for constructing NPs, organic polymers are outstanding due to the flexibility of design and synthesis and the ease of modification and functionalization. In particular, NP based amphiphilic polymers make a great contribution to the delivery of poorly-water soluble drugs. For example, natural, biocompatible and biodegradable products like polysaccharides are widely used as building blocks for the preparation of such drug delivery vehicles. This review will detail carbohydrate based amphiphilic polymeric systems for cancer therapy. Specifically, it focuses on the nature of the polymer employed for the preparation of targeted nanocarriers, the synthetic methods, as well as strategies for the application and evaluation of biological activity. Applications of the amphiphilic polymer systems include drug delivery, gene delivery, photosensitizer delivery, diagnostic imaging and specific ligand-assisted cellular uptake. As a result, a thorough understanding of the relationship between chemical structure and biological properties facilitate the optimal design and rational clinical application of the resulting carbohydrate based nano delivery systems for cancer therapy.

Induction of neural differentiation in rat C6 glioma cells with taxol

BACKGROUND

Glioblastoma is a common and aggressive type of primary brain tumor. Several anticancer drugs affect GBM (glioblastoma multiforme) cells on cell growth and morphology. Taxol is one of the widely used antineoplastic drugs against many types of solid tumors, such as breast, ovarian, and prostate cancers. However, the effect of taxol on GBM cells remains unclear and requires further investigation.

METHODS

Survival rate of C6 glioma cells under different taxol concentrations was quantified. To clarify the differentiation patterns of rat C6 glioma cells under taxol challenge, survived glioma cells were characterized by immunocytochemical, molecular biological, and cell biological approaches.

RESULTS

After taxol treatment, not only cell death but also morphological changes, including cell elongation, cellular processes thinning, irregular shapes, and fragmented nucleation or micronuclei, occurred in the survived C6 cells. Neural differentiation markers NFL (for neurons), β III-tubulin (for neurons), GFAP (for astrocytes), and CNPase (for oligodendrocytes) were detected in the taxol-treated C6 cells. Quantitative analysis suggested a significant increase in the percentage of neural differentiated cells. The results exhibited that taxol may trigger neural differentiation in C6 glioma cells. Increased expression of neural differentiation markers in C6 cells after taxol treatment suggest that some anticancer drugs could be applied to elimination of the malignant cancer cells as well as changing proliferation and differentiation status of tumor cells.

Broad targeting of resistance to apoptosis in cancer

Apoptosis or programmed cell death is natural way of removing aged cells from the body. Most of the anti-cancer therapies trigger apoptosis induction and related cell death networks to eliminate malignant cells. However, in cancer, de-regulated apoptotic signaling, particularly the activation of an anti-apoptotic systems, allows cancer cells to escape this program leading to uncontrolled proliferation resulting in tumor survival, therapeutic resistance and recurrence of cancer. This resistance is a complicated phenomenon that emanates from the interactions of various molecules and signaling pathways. In this comprehensive review we discuss the various factors contributing to apoptosis resistance in cancers. The key resistance targets that are discussed include (1) Bcl-2 and Mcl-1 proteins; (2) autophagy processes; (3) necrosis and necroptosis; (4) heat shock protein signaling; (5) the proteasome pathway; (6) epigenetic mechanisms; and (7) aberrant nuclear export signaling. The shortcomings of current therapeutic modalities are highlighted and a broad spectrum strategy using approaches including (a) gossypol; (b) epigallocatechin-3-gallate; (c) UMI-77 (d) triptolide and (e) selinexor that can be used to overcome cell death resistance is presented. This review provides a roadmap for the design of successful anti-cancer strategies that overcome resistance to apoptosis for better therapeutic outcome in patients with cancer.

Polymeric nanoparticles based on chitooligosaccharide as drug carriers for co-delivery of all-trans-retinoic acid and paclitaxel

An amphiphilic all-trans-retinoic acid (ATRA)-chitooligosaccharide (RCOS) conjugate was synthesized to form self-assembled polymeric nanoparticles to facilitate the co-delivery of ATRA and paclitaxel (PTX). The blank RCOS nanoparticles possessed low hemolytic activity and cytotoxicity, and could efficiently load PTX with a drug loading of 22.2% and a high encapsulation efficiency of 71.3%. PTX-loaded RCOS nanoparticles displayed a higher cytotoxicity to HepG2 cells compared to PTX plus ATRA solution when corrected by the accumulated drug release. Cellular uptake profiles of RCOS nanoparticles were evaluated via confocal laser scanning microscope and flow cytometry with FITC as a fluorescent mark. The RCOS nanoparticles could be rapidly and continuously taken up by HepG2 cells via endocytosis and transported into the nucleus, and the uptake rates increased with particle concentration. These results revealed the promising potential of RCOS nanoparticles as drug carriers for co-delivery of ATRA and PTX or other hydrophobic therapeutic agents.

All-trans retinoic acid inhibits migration, invasion and proliferation, and promotes apoptosis in glioma cells in vitro

All-trans retinoic acid (ATRA) is a derivative of vitamin A that can induce differentiation and apoptosis, as well as inhibit proliferation, in glioma cells. However, the effect of ATRA on the migration and invasiveness of glioma remains poorly understood. In addition, although it is universally accepted that ATRA can induce apoptosis and inhibit proliferation in glioma cells, the association between the concentration and effects of ATRA remain unclear. Therefore, the present study investigated the effects of ATRA treatment on the migration, invasion, apoptosis and proliferation of glioma cells. The U87 and SHG44 glioma cell lines were treated with various concentrations of ATRA, consisting of 0, 5, 10, 20 and 40 µmol/l. A scratch wound healing assay and a Matrigel invasion assay were used to investigate cell migration and invasion, respectively. Flow cytometry was performed to investigate apoptosis and cell cycle distribution. Reverse transcription-quantitative polymerase chain reaction and western blotting were used to investigate the expression of matrix metalloproteinase (MMP)-2 and -9 in each cell treatment group. Following treatment with ATRA, the migration, invasion and proliferation of the glioma cells were significantly inhibited, and the apoptosis rate was significantly increased compared with that of the blank control group. Furthermore, a dose-effect association was identified between each effects and ATRA treatment. The mRNA and protein expression of MMP-2 in U87 glioma cells was not significantly affected following treatment with low concentrations of ATRA, consisting of 5 and 10 µmol/l ATRA, compared with the expression in the control group (P>0.05). However, treatment with high concentrations of ATRA, consisting of 20 and 40 µmol/l ATRA, significantly downregulated the expression levels of MMP-2 in U87 cells. In contrast to U87 cells, the administration of ATRA treatment to SHG44 glioma cells resulted in a significant and dose-dependent downregulation in MMP-2 mRNA and protein expression (P<0.01). In addition, significant downregulation of MMP-9 expression was identified in the two glioma cell lines (P<0.01). The results of the present study indicate that treatment with ATRA may inhibit migration, invasion and proliferation, and promote apoptosis in glioma cells. Furthermore, the current study indicates that the inhibition of glioma cell invasion by ATRA may be partially associated with its effect ability to downregulate MMP expression.

Enhanced cell growth inhibition by thiacremonone in paclitaxel-treated lung cancer cells

Activation of nuclear factor kappa-B (NF-κB) is implicated in drug resistant of lung cancer cells. Our previous data showed that thiacremonone inhibited activation of NF-κB. In the present study, we investigated whether thiacremonone enhanced susceptibility of lung cancer cells to a common anti-cancer drug paclitaxel by further inhibition of NF-κB. Thus, we used the threefold lower doses of IC50 values (50 μg/ml thiacremonone and 2.5 nM paclitaxel). We found that combination treatment with thiacremonone and paclitaxel was more susceptible (combination index; 0.40 in NCI-H460 cells and 0.46 in A549 cells) in cell growth inhibition of two types of lung cancer cell lines compared to a single agent treatment. Consistent with the combination effect on cancer cell growth inhibition, the combination treatment further induced apoptotic cell death and arrested the cancer cells in G2/M phase accompanied with a much lower expression of cdc2 and cyclin B1, and inhibited colony formation. Much more inactivation of NF-κB and greater expression of NF-κB target apoptosis regulated genes such as caspase-8 and PARPs were found by the combination treatment. Molecular model and pull down assay as well as MALDI-TOF analysis demonstrated that thiacremonone directly binds to p50. These data indicated that thiacremonone leads to increased apoptotic cell death in lung cancer cell lines through greater inhibition of NF-κB by the combination treatment with paclitaxel.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Synergistic effect of all‑trans retinoic acid in combination with protein kinase C 412 in FMS-like tyrosine kinase 3-mutated acute myeloid leukemia cells

Acute myeloid leukemia (AML) is a heterogeneous disease. Numerous molecular abnormalities have been identified in AML and, amongst these, FMS‑like tyrosine kinase 3 (FLT3) mutations are one of the most common somatic alterations detected. In the present study, an in vitro investigation was performed to evaluate the effects of all‑trans retinoic acid (ATRA) and PKC412, alone and in combination, in FLT3‑mutated AML cell lines. Trypan blue exclusion test, as well as morphological, western blot and isobologram analyses were conducted. The results indicated that the combined ATRA and PKC412 treatment exhibited additive or synergistic effects in FLT3‑mutated AML cell lines. These results provided in vitro evidence for the future clinical trials evaluating the effects of a combination treatment using PKC412 and ATRA on AML patients with FLT3‑mutations.

Biological parameters influencing the human umbilical cord-derived mesenchymal stem cells' response to retinoic acid

Human umbilical cord-derived mesenchymal stem cells (HUCMSCs) are multipotent fetal stem cells that differentiate into various cell lineages. In recent years, they have gained attention for therapeutic applications but very little is known about their sensitivity to chemical agents such as widely used retinoic acid (RA). As a morphogen inducing differentiation of mesenchymal stem cells, RA has for a long time been known to be a potent teratogen promoting craniofacial and limb abnormality in vertebrate embryos. Here, using MTT assay and EB/AO staining as well as TUNEL assay we show that RA in a concentration-dependent manner induces apoptosis through upregulating Caspase expression and increasing Bax/Bcl2 ratio. Moreover, different biological parameters such as initial time seeding, cell density, passage number and duration of RA treatment play a major role in HUCMSCs cytotoxic response to this agent.

The effects of ponatinib, a multi-targeted tyrosine kinase inhibitor, against human U87 malignant glioblastoma cells

Glioblastoma is one of the most common malignant tumors in the nervous system in both adult and pediatric patients. Studies suggest that abnormal activation of receptor tyrosine kinases contributes to pathological development of glioblastoma. However, current therapies targeting tyrosine kinase receptors have poor therapeutic outcomes. Here, we examined anticancer effects of ponatinib, a multi-targeted tyrosine kinase inhibitor, on glioblastoma cells both in the U87MG cell line and in the mouse xenograft model. We showed that ponatinib treatment reduced cell viability and induced cell apoptosis in a dose-dependent manner in U87MG cells. In addition, ponatinib suppressed migration and invasion of U87MG cells effectively. Furthermore, ponatinib-treated tumors showed an obvious reduction of tumor volume and an increase of apoptosis as compared with vehicle-treated tumors in the mouse xenograft model. These findings support a potential application of ponatinib as a chemotherapeutic option against glioblastoma cells.

Responsiveness of stem-like human glioma cells to all-trans retinoic acid and requirement of retinoic acid receptor isotypes α, β and γ

Retinoic acid (RA) is required for development and homeostasis of the normal mammalian brain and may play a role in the initiation and progression of malignant brain tumors, such as the glioblastoma multiforme (GBM) and the gliosarcoma (Gsarc). The subpopulation of stem-like glioma cells (SLGCs) was shown to resist standard glioma radio-/chemotherapy and to propagate tumor regrowth. We used phenotypically distinct, self-renewing SLGC lines from six human GBMs, two Gsarcs, and two subcloned SLGC derivatives in order to investigate their responsiveness to all-trans retinoic acid (atRA) and to identify the RA-receptor (RAR) isotypes involved. In general, atRA exerted a pro-proliferative and pro-survival effect on SLGCs, though the efficacy was distinct. By means of RAR isotype-selective retinoids we disclosed that these effects were mediated by RARα and RARγ, except for one SLGC line, in which the pro-proliferative signal was induced by the RARβ-selective retinoid. Only one GBM-derived cell line (T1338) and a subpopulation of another (T1389) displayed neural differentiation in response to atRA. Differentiation of T1338 was induced by RARα and RARγ isotype-selective retinoids, associated with down-regulation of Sox2, and the failure to induce orthotopic tumors in the brains of SCID mice. The differential responsiveness of the SLGC lines appeared unrelated to the expression of RARβ, as (i) atRA augmented RAR isotype mRNA expression and particularly rarβ mRNA in all SLGC lines, (ii) rarβ promoter hypomethylation in the SLGC lines was not related to differentiation and (iii) the induction of T1338 differentiation was by RARα- and RARγ-selective ligands.

All-trans retinoic acid suppresses apoptosis in PC12 cells injured by oxygen and glucose deprivation via the retinoic acid receptor α signaling pathway

Vitamin A (VA) has a number of important biological functions in human growth and development. Previous studies by our group demonstrated that the normal VA levels improved recovery of learning and memory function and decreased apoptosis in rats with hypoxic‑ischemic brain damage (HIBD). However, it has not been fully elucidated how VA regulates the apoptosis of neuronal cells. To investigate the anti‑apoptotic effect of VA, an in vitro oxygen glucose deprivation (OGD) model in PC12 cells was treated with four concentrations of all‑trans‑retinoic acid (ATRA), an active in vivo product of VA. Following in vitro OGD injury in PC12 cells, the percentage of apoptosis and the fluorescence intensity of the mitochondrial membrane potential (MMP) were increased in the cells, and the expression levels of B-cell lymphoma-associated X (Bax) were enhanced. ATRA treatment at 2‑4 µmol/l for 24 h decreased the percentage of apoptosis and the MMP of the PC12 cells injured by OGD. ATRA at 4 µmol/l also reduced the expression levels of Bax and enhanced the expression of B-cell lymphoma 2. Furthermore, RNA interference with retinoic acid receptor α (RARα) reversed the observed effect in PC12 cells following ATRA treatment at 4 µmol/l alone. In conclusion, the present study suggested that treatment with ATRA at 4 µmol/l suppressed apoptosis of PC12 cells following OGD injury, potentially through regulation of the RARα signaling pathway.

Effects of all‑trans retinoic acid on VEGF and HIF‑1α expression in glioma cells under normoxia and hypoxia and its anti‑angiogenic effect in an intracerebral glioma model

All‑trans retinoic acid (ATRA) is one of the most potent inducers of differentiation and is capable of inducing differentiation and apoptosis in glioma cells. However, the effect of ATRA on glioma angiogenesis is yet to be elucidated. The present study investigated the effects of ATRA on the expression of vascular endothelial growth factor (VEGF) and hypoxia‑inducible factor‑1α (HIF‑1α) in various glioma cell lines under normoxia and hypoxia. The effect of ATRA on angiogenesis in a rat intracerebral glioma model was also investigated, with the aim of revealing the effect of ATRA on glioma angiogenesis. In the present study, U‑87 MG and SHG44 glioma cells were treated with ATRA at various concentrations (0, 5, 10, 20 and 40 µmol/l) under normoxia or hypoxia. Quantitative polymerase chain reaction and western blot analysis were used to investigate VEGF and HIF‑1α mRNA and protein expression, respectively. An intracerebral glioma model was generated using intracerebral implantation of C6 glioma cells into rats. Tumor‑bearing rats were treated with ATRA at different doses (0, 5 and 10 mg/kg/day) for two weeks, and immunohistochemical assays were performed to detect the cluster of differentiation 34‑positive cells in order to evaluate the microvessel density (MVD) in each group. Following ATRA treatment, the expression of VEGF and HIF‑1α was found to vary among the different concentration groups. In the glioma cells in the lower concentration groups (5 and 10 µmol/l ATRA), a significant increase in VEGF and HIF‑1α expression was observed. Conversely, a significant decrease in VEGF and HIF‑1α expression was found in the glioma cells in the high ATRA concentration group (40 µmol/l), compared with that in the cells in the control group. Furthermore, in the rat intracerebral glioma model, ATRA decreased glioma MVD, particularly in the high‑dose group (10 mg/kg/day), compared with the control group. These results suggest that ATRA may exhibit a dose‑dependent effect on glioma angiogenesis and may inhibit glioma angiogenesis in vivo.

MicroRNA-302b-inhibited E2F3 transcription factor is related to all trans retinoic acid-induced glioma cell apoptosis

All-trans retinoic acid (ATRA), a derivative of retinoid, is involved in the onset of differentiation and apoptosis in a wide variety of normal and cancer cells. MicroRNAs (miRNAs) are small non-coding RNAs that control gene expression. Several miRNAs were identified to participate in ATRA-mediated cell differentiation. However, no studies have demonstrated whether miRNA can enhance ATRA cytotoxicity, thereby resulting in cell apoptosis. This study investigated the effects of ATRA-mediated miRNA expression in activating apoptotic pathways in glioblastoma. First, we found that high-dose ATRA treatment significantly reduced cell viability, caspase-dependent apoptosis, endoplasmic reticular (ER) stress activation, and intracellular reactive oxygen species accumulation. From microarray data, miR-302b was analyzed as a putative downstream regulator upon ATRA treatment. Furthermore, we found that ATRA up-regulated miR-302b expression in a dose- and time-dependent manner through retinoic acid receptor α-mediated pathway. Overexpression and knockdown of miR-302b significantly influenced ATRA-mediated cytotoxicity. E2F3, an important transcriptional regulator of glioma proliferation, was validated to be a direct target gene of miR-302b. The miR-302b-reduced E2F3 levels were also identified to be associated with ATRA-mediated glioma cell death. These results emphasize that an ATRA-mediated miR-302b network may provide novel therapeutic strategies for glioblastoma therapy. We propose that high-dose all-trans retinoic acid (ATRA) treatment, a derivative of retinoid, significantly induces glioblastoma cell apoptosis via caspase-dependent apoptosis, endoplasmic reticular (ER) stress, and intracellular reactive oxygen species (ROS) accumulation. The miR-302b overexpression enhanced by ATRA-mediated retinoic acid receptor (RAR)α pathway was also identified. The E2F3 repression, a novel target gene of miR-302b, was involved in ATRA-induced glioblastoma cell cytotoxicity.

Nanoparticle delivery and combination therapy of gambogic acid and all-trans retinoic acid

In order to enhance the in vivo codelivery efficiency of gambogic acid (GA) and all-trans retinoic acid (ATRA), our strategy was to entrap GA in the self-assembled nanoparticles based on amphiphilic hyaluronic acid (HA)-ATRA (HRA) conjugate. In this way, GA and ATRA were loaded simultaneously in a nanocarrier and codelivered into the tumor cell through HA receptor-mediated endocytosis. GA-loaded HRA nanoparticles (GA-HRA) were prepared by a dialysis method, and their physicochemical characteristics were investigated as well. GA-HRA exhibited a high drug loading capacity (31.1%), had a particle size in the range of 100–150 nm, and good biocompatibility. HRA nanoparticles were effectively internalized by MCF-7 cells and translocated into the nucleus in a time-dependent manner. The in vivo imaging analysis demonstrated that the fluorescent signals in the tumor were markedly increased with DiR-loaded nanoparticles after intravenous administration compared to free DiR solution, suggesting it has excellent tumor targeting properties. More importantly, GA-HRA exhibited excellent in vivo efficacy with dramatically reduced toxicity. In conclusion, with the assistance of HRA nanoparticles, GA and ATRA can successfully realize an effective combination chemotherapy as well as tumor-targeted delivery.

In vitro anticancer drug test: A new method emerges from the model of glioma stem cells

Glioblastoma multiforme (GBM) is a grade IV astrocytoma and the most common malignant brain tumor. Current therapies provide a median survival of 12–15 months after diagnosis, due to the high recurrence rate. The failure of current therapies may be due to the presence, within the tumor, of cells characterized by enhanced self-renewal capacity, multilineage differentiation potential and elevated invasive behavior, called glioma stem cells (GSCs). To evaluate the pharmacological efficacy of selected drugs on six GSC lines, we set up a multiple drug responsivity assay based on the combined evaluation of cytomorphological and functional parameters, including the analysis of polymorphic nuclei, mitotic index and cell viability. In order to understand the real pharmacological efficacy of the tested drugs, we assigned a specific drug responsivity score to each GSC line, integrating the data produced by multiple assays. In this work we explored the antineoplastic effects of paclitaxel (PTX), an inhibitor of microtubule depolymerization, utilized as standard treatment in several cancers, and of valproic acid (VPA), an inhibitor of histone deacetylases (HDACs) with multiple anticancer properties. We classified the six GSC lines as responsive or resistant to these drugs, on the basis of their responsivity scores. This method can also be useful to identify the best way to combine two or more drugs. In particular, we utilized the pro-differentiating effect of VPA to improve the PTX effectiveness and we observed a significant reduction of cell viability compared to single treatments.

Vitamin D in thyroid tumorigenesis and development

Besides its classical role in bone and calcium homeostasis, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D, has many non-classical effects; antiproliferative, anti-apoptotic and prodifferentiating effects of 1,25(OH)2D3 have been described in several tumour types in preclinical models. This review focuses on the insights gained in the elucidation of the role of 1,25(OH)2D3 in the normal thyroid and in the pathogenesis, progression and treatment of thyroid cancer, the most common endocrine malignancy. An increasing amount of observations points towards a role for impaired 1,25(OH)2D3-VDR signalling in the occurrence and progression of thyroid cancer, and a potential for structural analogues in the multimodal treatment of dedifferentiated iodine-resistant thyroid cancer. A role for vitamin D in thyroid-related autoimmunity is less convincing and needs further study. Altered 1,25(OH)2D3-VDR signalling does not influence normal thyroid development nor thyrocyte function, but does affect C-cell function, at least in rodents. If these findings also apply to humans deserves further study.

Effect of all-trans retinoic acid on the differentiation of U87 glioma stem/progenitor cells

GSPCs (glioma stem/progenitor cells) were isolated from U87 glioma cell lines by serum-free neural stem cell medium. Four concentrations (1, 2, 4, and 8 μmol/L) of ATRA (all-trans retinoic acid) were used to induce the differentiation of GSPCs in the medium with or without growth factors. The effect of ATRA on the differentiation of GSPCs was analyzed by flow cytometry, real-time-PCR, and immunofluorescence. The differentiation of GSPCs could be induced by 1 or 2 μmol/L ATRA when GSPCs were cultured in growth factor-free medium. The detection of real-time-PCR showed that the level of GFAP (glial fibrillary acidic protein) mRNA of differentiated GSPCs in the growth factor-free medium containing 1 μmol/L ATRA group was significantly higher than that in the control group, and there was no significant difference in the level of TUBB-3 mRNA between the two groups. The GSPCs suffered apoptosis in the growth factor-free medium containing 4 or 8 μmol/L ATRA. The differentiation of GSPCs could not be induced by ATRA when GSPCs were cultured in the medium containing growth factors. The percentage of cells in G0/G1 phase was 84.26 ± 2.24 %, and the percentage of apoptosis was 18.95 ± 2.53 % in experimental groups which was similar to those in the control group. In conclusion, ATRA has certain capacity to induce differentiation of GSPCs, while its effective concentration should be controlled strictly. The differentiation of GSPCs induced by ATRA cannot antagonize the formidable differential inhibition of epidermal growth factor and basic fibroblast growth factor.

All-trans retinoic acid upregulates the expression of p53 via Axin and inhibits the proliferation of glioma cells

All-trans retinoic acid (ATRA) is a potent chemopreventive and therapeutic agent and exerts its effects by inducing growth arrest. In the present study, we demonstrated that ATRA activated the expression of p53 via Axin and induced cell cycle arrest at the G1/S phase and apoptosis of glioma cells. Briefly, C6 cells were treated with ATRA, and the levels of p53 mRNA and protein were determined by RT-PCR, western blotting and immunohistochemistry. The results showed that ATRA activated the expression of p53. In addition, ectopic expression of Axin by transient transfection of C6 cells with rAxin revealed that overexpression of Axin induced cell cycle arrest and apoptosis with an upregulation of p53. Furthermore, loss-of-function of Axin in glioma cells by RNAi blocked ATRA-induced cell cycle phase arrest and apoptosis via downregulation of p53. The present study revealed a novel function of Axin and identified it as an important regulator of ATRA-activated p53 expression.