Targeted inhibition of HDAC8 increases the doxorubicin sensitivity of neuroblastoma cells via up regulation of miR-137

MiRNAs: main players of cancer drug resistance target ABC transporters

Chemotherapy remains the cornerstone of cancer treatment; however, its efficacy is frequently compromised by the development of chemoresistance. Multidrug resistance (MDR), characterized by the refractoriness of cancer cells to a wide array of chemotherapeutic agents, presents a significant barrier to achieving successful and sustained cancer remission. One critical factor contributing to this chemoresistance is the overexpression of ATP-binding cassette (ABC) transporters. Furthermore, additional mechanisms, such as the malfunctioning of apoptosis, alterations in DNA repair systems, and resistance mechanisms inherent to cancer stem cells, exacerbate the issue. Intriguingly, microRNAs (miRNAs) have demonstrated potential in modulating chemoresistance by specifically targeting ABC transporters, thereby offering promising new avenues for overcoming drug resistance. This narrative review aims to elucidate the molecular underpinnings of drug resistance, with a particular focus on the roles of ABC transporters and the regulatory influence of miRNAs on these transporters.

miRNAs as short non-coding RNAs in regulating doxorubicin resistance

The treatment of cancer patients has been prohibited by chemoresistance. Doxorubicin (DOX) is an anti-tumor compound disrupting proliferation and triggering cell cycle arrest via inhibiting activity of topoisomerase I and II. miRNAs are endogenous RNAs localized in cytoplasm to reduce gene level. Abnormal expression of miRNAs changes DOX cytotoxicity. Overexpression of tumor-promoting miRNAs induces DOX resistance, while tumor-suppressor miRNAs inhibit DOX resistance. The miRNA-mediated regulation of cell death and hallmarks of cancer can affect response to DOX chemotherapy in tumor cells. The transporters such as P-glycoprotein are regulated by miRNAs in DOX chemotherapy. Upstream mediators including lncRNAs and circRNAs target miRNAs in affecting capacity of DOX. The response to DOX chemotherapy can be facilitated after administration of agents that are mostly phytochemicals including curcumol, honokiol and ursolic acid. These agents can regulate miRNA expression increasing DOX's cytotoxicity. Since delivery of DOX alone or in combination with other drugs and genes can cause synergistic impact, the nanoparticles have been introduced for drug sensitivity. The non-coding RNAs determine the response of tumor cells to doxorubicin chemotherapy. microRNAs play a key role in this case and they can be sponged by lncRNAs and circRNAs, showing interaction among non-coding RNAs in the regulation of doxorubicin sensitivity.

HDAC8 as an emerging target in drug discovery with special emphasis on medicinal chemistry

HDAC8 catalyzes the deacetylation of both histones and nonhistone proteins. The abnormal expression of HDAC8 is associated with various pathological conditions causing cancer and other diseases like myopathies, Cornelia de Lange syndrome, renal fibrosis, and viral and parasitic infections. The substrates of HDAC8 are involved in diverse molecular mechanisms of cancer such as cell proliferation, invasion, metastasis and drug resistance. Based on the crystal structures and the key residues at the active site, HDAC8 inhibitors have been designed along the canonical pharmacophore. This article details the importance, recent advancements, and the structural and functional aspects of HDAC8 with special emphasis on the medicinal chemistry aspect of HDAC8 inhibitors that will help in developing novel epigenetic therapeutics.

MicroRNAs as prospective biomarkers, therapeutic targets and pharmaceuticals in neuroblastoma

Neuroblastomas, the most prevalent malignant solid neoplasms of childhood, originate from progenitor cells of the sympathetic nervous system. Their genetic causation is diverse and involves multiple molecular mechanisms. This review highlights multiple roles of microRNA in neuroblastoma pathogenesis and discusses the prospects of harnessing these important natural regulator molecules as biomarkers, therapeutic targets and pharmaceuticals in neuroblastoma.

Therapy resistance in neuroblastoma: Mechanisms and reversal strategies

Neuroblastoma is one of the most common pediatric solid tumors that threaten the health of children, accounting for about 15% of childhood cancer-related mortality in the United States. Currently, multiple therapies have been developed and applied in clinic to treat neuroblastoma including chemotherapy, radiotherapy, targeted therapy, and immunotherapy. However, the resistance to therapies is inevitable following long-term treatment, leading to treatment failure and cancer relapse. Hence, to understand the mechanisms of therapy resistance and discover reversal strategies have become an urgent task. Recent studies have demonstrated numerous genetic alterations and dysfunctional pathways related to neuroblastoma resistance. These molecular signatures may be potential targets to combat refractory neuroblastoma. A number of novel interventions for neuroblastoma patients have been developed based on these targets. In this review, we focus on the complicated mechanisms of therapy resistance and the potential targets such as ATP-binding cassette transporters, long non-coding RNAs, microRNAs, autophagy, cancer stem cells, and extracellular vesicles. On this basis, we summarized recent studies on the reversal strategies to overcome therapy resistance of neuroblastoma such as targeting ATP-binding cassette transporters, MYCN gene, cancer stem cells, hypoxia, and autophagy. This review aims to provide novel insight in how to improve the therapy efficacy against resistant neuroblastoma, which may shed light on the future directions that would enhance the treatment outcomes and prolong the survival of patients with neuroblastoma.

Design, Synthesis and Biological Characterization of Histone Deacetylase 8 (HDAC8) Proteolysis Targeting Chimeras (PROTACs) with Anti-Neuroblastoma Activity

In addition to involvement in epigenetic gene regulation, histone deacetylases (HDACs) regulate multiple cellular processes through mediating the activity of non-histone protein substrates. The knockdown of HDAC8 isozyme is associated with the inhibition of cell proliferation and apoptosis enhancement in several cancer cell lines. As shown in several studies, HDAC8 can be considered a potential target in the treatment of cancer forms such as childhood neuroblastoma. The present work describes the development of proteolysis targeting chimeras (PROTACs) of HDAC8 based on substituted benzhydroxamic acids previously reported as potent and selective HDAC8 inhibitors. Within this study, we investigated the HDAC8-degrading profiles of the synthesized PROTACs and their effect on the proliferation of neuroblastoma cells. The combination of in vitro screening and cellular testing demonstrated selective HDAC8 PROTACs that show anti-neuroblastoma activity in cells.

MicroRNA as a Potential Therapeutic Molecule in Cancer

Small noncoding RNAs, as post-translational regulators of many target genes, are not only markers of neoplastic disease initiation and progression, but also markers of response to anticancer therapy. Hundreds of miRNAs have been identified as biomarkers of drug resistance, and many have demonstrated the potential to sensitize cancer cells to therapy. Their properties of modulating the response of cells to therapy have made them a promising target for overcoming drug resistance. Several methods have been developed for the delivery of miRNAs to cancer cells, including introducing synthetic miRNA mimics, DNA plasmids containing miRNAs, and small molecules that epigenetically alter endogenous miRNA expression. The results of studies in animal models and preclinical studies for solid cancers and hematological malignancies have confirmed the effectiveness of treatment protocols using microRNA. Nevertheless, the use of miRNAs in anticancer therapy is not without limitations, including the development of a stable nanoconstruct, delivery method choices, and biodistribution. The aim of this review was to summarize the role of miRNAs in cancer treatment and to present new therapeutic concepts for these molecules. Supporting anticancer therapy with microRNA molecules has been verified in numerous clinical trials, which shows great potential in the treatment of cancer.

Histone deacetylase HDAC2 regulates microRNA-125a expression in neuroblastoma

BACKGROUND

Neuroblastoma (NB) is an infrequent childhood malignancy of the peripheral sympathetic nervous system and is accountable for about 10% of pediatric tumors. microRNA (miR)-125a has been implicated to serve as a tumor suppressor in various cancers. Herein, we set out to ascertain whether miR-125a exerts antitumor effects in NB.

METHODS

Downregulated miRNAs were identified by miRNA microarray analysis of NB tissues and paracancerous tissues. The expression of miR-125a in NB tissues and cells was detected by reverse transcription-quantitative (RT-q) PCR, followed by prognostic analysis. Gene Ontology (GO) enrichment analysis was performed on target genes of differentially expressed miRNAs. Cell proliferation, apoptosis, and differentiation were detected by cell counting kit-8 (CCK-8), Hoechst staining, immunofluorescence, and western blot. NB cells were injected into nude mice to detect tumorigenic, apoptotic, and differentiation activities in vivo. Dual-luciferase assay and chromatin immunoprecipitation (ChIP) were carried out to verify the binding relationship between miR-125a and PHOX2B or histone deacetylases 2 (HDAC2), respectively. Finally, rescue experiments were conducted.

RESULTS

miR-125a was downregulated in NB tissues and cells, which was associated with poor prognosis. miR-125a reduced NB cell proliferation and augmented apoptosis and differentiation. NB cells with miR-125a overexpression decreased cell tumorigenesis and increased apoptosis and differentiation in xenograft tumor tissues. miR-125a targeted PHOX2B, which was highly expressed in NB tissues and cells. HDAC2, highly expressed in NB tissues and cells, repressed miR-125a transcription through histone deacetylation. Overexpression of HDAC2 or PHOX2B rescued the effects of miR-125a on NB cell proliferation, apoptosis, and differentiation.

CONCLUSION

HDAC2 inhibited miR-125a transcription through deacetylation, and miR-125a suppressed NB development through binding to PHOX2B.

NBM-BMX, an HDAC8 Inhibitor, Overcomes Temozolomide Resistance in Glioblastoma Multiforme by Downregulating the β-Catenin/c-Myc/SOX2 Pathway and Upregulating p53-Mediated MGMT Inhibition

Although histone deacetylase 8 (HDAC8) plays a role in glioblastoma multiforme (GBM), whether its inhibition facilitates the treatment of temozolomide (TMZ)-resistant GBM (GBM-R) remains unclear. By assessing the gene expression profiles from short hairpin RNA of HDAC8 in the new version of Connectivity Map (CLUE) and cells treated by NBM-BMX (BMX)-, an HDAC8 inhibitor, data analysis reveals that the Wnt signaling pathway and apoptosis might be the underlying mechanisms in BMX-elicited treatment. This study evaluated the efficacy of cotreatment with BMX and TMZ in GBM-R cells. We observed that cotreatment with BMX and TMZ could overcome resistance in GBM-R cells and inhibit cell viability, markedly inhibit cell proliferation, and then induce cell cycle arrest and apoptosis. In addition, the expression level of β-catenin was reversed by proteasome inhibitor via the β-catenin/ GSK3β signaling pathway to reduce the expression level of c-Myc and cyclin D1 in GBM-R cells. BMX and TMZ cotreatment also upregulated WT-p53 mediated MGMT inhibition, thereby triggering the activation of caspase-3 and eventually leading to apoptosis in GBM-R cells. Moreover, BMX and TMZ attenuated the expression of CD133, CD44, and SOX2 in GBM-R cells. In conclusion, BMX overcomes TMZ resistance by enhancing TMZ-mediated cytotoxic effect by downregulating the β-catenin/c-Myc/SOX2 signaling pathway and upregulating WT-p53 mediated MGMT inhibition. These findings indicate a promising drug combination for precision personal treating of TMZ-resistant WT-p53 GBM cells.

HDAC8 Activates AKT through Upregulating PLCB1 and Suppressing DESC1 Expression in MEK1/2 Inhibition-Resistant Cells

Inhibition of the RAF-MEK1/2-ERK signaling pathway is an ideal strategy for treating cancers with NRAS or BRAF mutations. However, the development of resistance due to incomplete inhibition of the pathway and activation of compensatory cell proliferation pathways is a major impediment of the targeted therapy. The anthrax lethal toxin (LT), which cleaves and inactivates MEKs, is a modifiable biomolecule that can be delivered selectively to tumor cells and potently kills various tumor cells. However, resistance to LT and the mechanism involved are yet to be explored. Here, we show that LT, through inhibiting MEK1/2-ERK activation, inhibits the proliferation of cancer cells with NRAS/BRAF mutations. Among them, the human colorectal tumor HT-29 and murine melanoma B16-BL6 cells developed resistance to LT in 2 to 3 days of treatment. These resistant cells activated AKT through a histone deacetylase (HDAC) 8-dependent pathway. Using an Affymetrix microarray, followed by qPCR validation, we identified that the differential expression of the phospholipase C-β1 (PLCB1) and squamous cell carcinoma-1 (DESC1) played an important role in HDAC8-mediated AKT activation and resistance to MEK1/2-ERK inhibition. By using inhibitors, small interference RNAs and/or expression vectors, we found that the inhibition of HDAC8 suppressed PLCB1 expression and induced DESC1 expression in the resistant cells, which led to the inhibition of AKT and re-sensitization to LT and MEK1/2 inhibition. These results suggest that targeting PLCB1 and DESC1 is a novel strategy for inhibiting the resistance to MEK1/2 inhibition.

Identification of potential histone deacetylase inhibitory biflavonoids from Garcinia kola (Guttiferae) using in silico protein-ligand interaction

Overactivity of histone deacetylases (HDACs) is the underlying cause of some cancers, thus, inhibiting their overactivities is a rational treatment option. However, endeavors to employ current anti-HDACs agents in cancer treatment have yielded limited success. Consequently, there is need to explore anti-HDACs natural products, especially from plants sources, because of the intimate relationship plant products and drug discovery have enjoyed over the centuries. To identify possible HDACs inhibitors, Garcinia kola (Guttiferae) seed-derived compounds were screened in silico for HDAC-inhibitory tendencies because of their reported anticancer potentials. Fifteen G. kola-derived compounds and givinostat were docked with five selected HDACs using AutodockVina, while the binding interactions of the compounds with high binding affinities for the five HDACs were viewed with Discovery Studio Visualizer BIOVIA, 2016. Results indicated that four of the compounds studied, including amentoflavone, Garcinia biflavonoid 1, Garcinia biflavonoid 2 and kolaflavanone have higher binding propensity for all the five HDACs relative to givinostat, the standard HDAC inhibitor. This study indicated that inhibition of HDAC might be another key mechanism accountable for the bioactivities of G. kola and its intrinsic compounds. The results from this study implied that the compounds could be further investigated as drugable HDAC inhibitors with potential pharmacological applications in the treatment of cancers.

Circular RNA circPVT1 Contributes to Doxorubicin (DXR) Resistance of Osteosarcoma Cells by Regulating TRIAP1 via miR-137

Background

Chemoresistance is a major obstacle to the treatment of osteosarcoma patients. Circular RNA (circRNA) circPVT1 has been reported to be related to the doxorubicin (DXR) resistance in osteosarcoma. This study is designed to explore the role and mechanism of circPVT1 in the DXR resistance of osteosarcoma.

Methods

circPVT1, microRNA-137 (miR-137), and TP53-regulated inhibitor of apoptosis 1 (TRIAP1) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). The protein levels of ATP-binding cassette, subfamily C, member 1 (ABCC1), multidrug resistance-associated protein 1 (MRP-1), cleaved- (c-) caspase-3, B-cell lymphoma-2 (Bcl-2), and TRIAP1 were examined by a western blot assay. Cell viability, proliferation, and apoptosis were detected by cell counting kit-8 (CCK-8), colony formation, and flow cytometry assays, severally. The binding relationship between miR-137 and circPVT1 or TRIAP1 was predicted by starbase 3.0 and then verified by dual-luciferase reporter and RNA Immunoprecipitation (RIP) assays. The biological role of circPVT1 in osteosarcoma tumor growth and drug resistance was examined by the xenograft tumor model in vivo. Results. circPVT1 and TRIAP1 were highly expressed, and miR-137 was decreased in DXR-resistant osteosarcoma tissues and cells. Moreover, circPVT1 knockdown could boost DXR sensitivity by inhibiting DXR-caused proliferation and DXR-induced apoptosis in DXR-resistant osteosarcoma cells in vitro. The mechanical analysis discovered that circPVT1 acted as a sponge of miR-137 to regulate TRIAP1 expression. circPVT1 silencing increased the drug sensitivity of osteosarcoma in vivo. Conclusion. circPVT1 boosted DXR resistance of osteosarcoma cells partly by regulating the miR-137/TRIAP1 axis, hinting a promising therapeutic target for the osteosarcoma treatment.

The role of miRNAs and lncRNAs in conferring resistance to doxorubicin

Doxorubicin is a chemotherapeutic agent that inhibits topoisomerase II, intercalates within DNA base pairs and results in oxidative DNA damage, thus inducing cell apoptosis. Although it is effective in the treatment of a wide range of human cancers, the emergence of resistance to this drug can increase tumour growth and impact patients' survival. Numerous molecular mechanisms and signalling pathways have been identified that induce resistance to doxorubicin via stimulation of cell proliferation, cell cycle switch and preclusion of apoptosis. A number of microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) have also been identified that alter sensitivity to doxorubicin. Understanding the particular impact of these non-coding RNAs in conferring resistance to doxorubicin has considerable potential to improve selection of chemotherapeutic regimens for cancer patients. Moreover, modulation of expression of these transcripts is a putative strategy for combating resistance. In the current paper, the influence of miRNAs and lncRNAs in the modification of resistance to doxorubicin is discussed.

Neuroblastoma and the epigenome

Neuroblastoma (NB) is a pediatric cancer of the sympathetic nervous system and one of the most common solid tumors in infancy. Amplification of MYCN, copy number alterations, numerical and segmental chromosomal aberrations, mutations, and rearrangements on a handful of genes, such as ALK, ATRX, TP53, RAS/MAPK pathway genes, and TERT, are attributed as underlying causes that give rise to NB. However, the heterogeneous nature of the disease-along with the relative paucity of recurrent somatic mutations-reinforces the need to understand the interplay of genetic factors and epigenetic alterations in the context of NB. Epigenetic mechanisms tightly control gene expression, embryogenesis, imprinting, chromosomal stability, and tumorigenesis, thereby playing a pivotal role in physio- and pathological settings. The main epigenetic alterations include aberrant DNA methylation, disrupted patterns of posttranslational histone modifications, alterations in chromatin composition and/or architecture, and aberrant expression of non-coding RNAs. DNA methylation and demethylation are mediated by DNA methyltransferases (DNMTs) and ten-eleven translocation (TET) proteins, respectively, while histone modifications are coordinated by histone acetyltransferases and deacetylases (HATs, HDACs), and histone methyltransferases and demethylases (HMTs, HDMs). This article focuses predominately on the crosstalk between the epigenome and NB, and the implications it has on disease diagnosis and treatment.

Non-Coding RNAs Participate in the Pathogenesis of Neuroblastoma

Neuroblastoma is one of the utmost frequent neoplasms during the first year of life. This pediatric cancer is believed to be originated during the embryonic life from the neural crest cells. Previous studies have detected several types of chromosomal aberrations in this tumor. More recent studies have emphasized on expression profiling of neuroblastoma samples to identify the dysregulated genes in this type of cancer. Non-coding RNAs are among the mostly dysregulated genes in this type of cancer. Such dysregulation has been associated with a number of chromosomal aberrations that are frequently detected in neuroblastoma. In this study, we explain the role of non-coding transcripts in the malignant transformation in neuroblastoma and their role as biomarkers for this pediatric cancer.

LncRNA NORAD accelerates the progression and doxorubicin resistance of neuroblastoma through up-regulating HDAC8 via sponging miR-144-3p

The dysregulation of non-coding RNAs (ncRNAs) often caused aberrant cell behaviors. In the present study, we focused on the role of long noncoding RNA (lncRNA) non-coding RNA activated by DNA damage (NORAD) in the development of neuroblastoma (NB). The enrichment of NORAD, miRNA-144-3p (miR-144-3p) and histone deacetylase 8 (HDAC8) was measured by quantitative real time polymerase chain reaction (qRT-PCR). The proliferation, chemoresistance, apoptosis, metastasis and autophagy of NB cells were determined by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), flow cytometry, transwell migration and invasion assays and Western blot assay, respectively. The target relationship between miR-144-3p and NORAD or HDAC8 was predicted by Starbase software and validated through dual-luciferase reporter assay, RIP and RNA-pull down assays. The protein expression of HDAC8 was measured by Western blot assay. Murine xenograft model was used to verify the function of NORAD in vivo. We found that the level of NORAD was up-regulated in NB tissues and cells, and the level of NORAD was negatively correlated with the prognosis of NB patients. NORAD promoted the proliferation, metastasis and doxorubicin (DOX) resistance while inhibited the apoptosis and autophagy of NB cells. MiR-144-3p was a target of NORAD in NB cells, and NORAD accelerated the progression and DOX resistance of NB through sponging miR-144-3p. HDAC8 was a direct target of miR-144-3p in NB cells, and miR-144-3p suppressed the progression of NB through down-regulating HDAC8. NORAD up-regulated the expression of HDAC8 through sponging miR-144-3p in NB cells. NORAD accelerated the growth of NB tumors at least partly through miR-144-3p/HDAC8 signaling in vivo. In conclusion, NORAD promoted the progression and DOX resistance of NB through miR-144-3p/HDAC8 axis in vivo and in vitro.

Epigenetic Regulation of Multidrug Resistance Protein 1 and Breast Cancer Resistance Protein Transporters by Histone Deacetylase Inhibition

Multidrug resistance protein 1 (MDR1, ABCB1, P-glycoprotein) and breast cancer resistance protein (BCRP, ABCG2) are key efflux transporters that mediate the extrusion of drugs and toxicants in cancer cells and healthy tissues, including the liver, kidneys, and the brain. Altering the expression and activity of MDR1 and BCRP influences the disposition, pharmacodynamics, and toxicity of chemicals, including a number of commonly prescribed medications. Histone acetylation is an epigenetic modification that can regulate gene expression by changing the accessibility of the genome to transcriptional regulators and transcriptional machinery. Recently, studies have suggested that pharmacological inhibition of histone deacetylases (HDACs) modulates the expression and function of MDR1 and BCRP transporters as a result of enhanced histone acetylation. This review addresses the ability of HDAC inhibitors to modulate the expression and the function of MDR1 and BCRP transporters and explores the molecular mechanisms by which HDAC inhibition regulates these transporters. While the majority of studies have focused on histone regulation of MDR1 and BCRP in drug-resistant and drug-sensitive cancer cells, emerging data point to similar responses in nonmalignant cells and tissues. Elucidating epigenetic mechanisms regulating MDR1 and BCRP is important to expand our understanding of the basic biology of these two key transporters and subsequent consequences on chemoresistance as well as tissue exposure and responses to drugs and toxicants. SIGNIFICANCE STATEMENT: Histone deacetylase inhibitors alter the expression of key efflux transporters multidrug resistance protein 1 and breast cancer resistance protein in healthy and malignant cells.

MicroRNA dysregulation interplay with childhood abdominal tumors

Abdominal tumors (AT) in children account for approximately 17% of all pediatric solid tumor cases, and frequently exhibit embryonal histological features that differentiate them from adult cancers. Current molecular approaches have greatly improved the understanding of the distinctive pathology of each tumor type and enabled the characterization of novel tumor biomarkers. As seen in abdominal adult tumors, microRNAs (miRNAs) have been increasingly implicated in either the initiation or progression of childhood cancer. Moreover, besides predicting patient prognosis, they represent valuable diagnostic tools that may also assist the surveillance of tumor behavior and treatment response, as well as the identification of the primary metastatic sites. Thus, the present study was undertaken to compile up-to-date information regarding the role of dysregulated miRNAs in the most common histological variants of AT, including neuroblastoma, nephroblastoma, hepatoblastoma, hepatocarcinoma, and adrenal tumors. Additionally, the clinical implications of dysregulated miRNAs as potential diagnostic tools or indicators of prognosis were evaluated.

HDAC8 affects MGMT levels in glioblastoma cell lines via interaction with the proteasome receptor ADRM1

Temozolomide (TMZ) is an alkylating agent chemotherapy drug used as a first-line treatment for glioblastoma multiforme (GBM). O⁶-methyl-guanine DNA methyltransferase (MGMT) repairs DNA damage induced by TMZ; hence, elevated MGMT levels usually correlate with TMZ resistance. MGMT promoter methylation is a key regulatory mechanism for MGMT expression and is important in overcoming TMZ therapy resistance. To date, little is known about how MGMT expression is regulated beyond promoter methylation. In this work, we show an alternative mechanism by which MGMT levels are regulated independent of its promoter methylation status. We found that inhibition of the histone deacetylase HDAC8 by either HDAC8-specific inhibitor PCI34051 or HDAC8 shRNA decreases MGMT levels in GBM cell lines. Furthermore, the proteasome receptor ADRM1 participates in this MGMT regulation by interacting with HDAC8. Interestingly, this interaction is disrupted by TMZ exclusively in TMZ sensitive cells, suggesting that this MGMT regulatory pathway might be inactivated in TMZ resistant cells. Consequently, HDAC8 inhibition in GBM cell lines increases DNA damage and cell cycle arrest and, eventually, decreases cell viability, likely due to the decrease in MGMT protein levels.

Implication for Cancer Stem Cells in Solid Cancer Chemo-Resistance: Promising Therapeutic Strategies Based on the Use of HDAC Inhibitors

Resistance to therapy in patients with solid cancers represents a daunting challenge that must be addressed. Indeed, current strategies are still not effective in the majority of patients; which has resulted in the need for novel therapeutic approaches. Cancer stem cells (CSCs), a subset of tumor cells that possess self-renewal and multilineage differentiation potential, are known to be intrinsically resistant to anticancer treatments. In this review, we analyzed the implications for CSCs in drug resistance and described that multiple alterations in morphogenetic pathways (i.e., Hippo, Wnt, JAK/STAT, TGF-β, Notch, Hedgehog pathways) were suggested to be critical for CSC plasticity. By interrogating The Cancer Genome Atlas (TCGA) datasets, we first analyzed the prevalence of morphogenetic pathways alterations in solid tumors with associated outcomes. Then, by highlighting epigenetic relevance in CSC development and maintenance, we selected histone deacetylase inhibitors (HDACi) as potential agents of interest to target this subpopulation based on the pleiotropic effects exerted specifically on altered morphogenetic pathways. In detail, we highlighted the role of HDACi in solid cancers and, specifically, in the CSC subpopulation and we pointed out some mechanisms by which HDACi are able to overcome drug resistance and to modulate stemness. Although, further clinical and preclinical investigations should be conducted to disclose the unclear mechanisms by which HDACi modulate several signaling pathways in different tumors. To date, several lines of evidence support the testing of novel combinatorial therapeutic strategies based on the combination of drugs commonly used in clinical practice and HDACi to improve therapeutic efficacy in solid cancer patients.

Targeting of epigenetic regulators in neuroblastoma

Approximately 15,000 new cases of pediatric cancer are diagnosed yearly in Europe, with 8–10% corresponding to neuroblastoma, a rare disease with an incidence of 8–9 cases per million children <15 years of age. Although the survival rate for low-risk and intermediate-risk patients is excellent, half of children with high-risk, refractory, or relapsed tumors will be cured, and two-thirds of the other half will suffer major side effects and life-long disabilities. Epigenetic therapies aimed at reversing the oncogenic alterations in chromatin structure and function are an emerging alternative against aggressive tumors that are or will become resistant to conventional treatments. This approach proposes targeting epigenetic regulators, which are proteins that are involved in the creation, detection, and interpretation of epigenetic signals, such as methylation or histone post-translational modifications. In this review, we focused on the most promising epigenetic regulators for targeting and current drugs that have already reached clinical trials.

Treatments that target chromatin, the combination of DNA and proteins, are emerging as alternative ways to treat aggressive neuroblastomas, cancers of neural tissue. Altering the structure and function of chromatin is a form of “epigenetic therapy”, treatment that affects inheritable molecular signals controlling the activity of genes, rather than targeting the genes directly. Researchers in Spain led by Miguel Segura at the Vall d’Hebron Research Institute in Barcelona review progress in developing epigenetic therapies for neuroblastomas. A growing body of fundamental research and evidence from clinical trials suggest this approach could open promising new avenues to treating aggressive and drug-resistant cancers. The authors recommend an increased effort to identify and explore the activities of small molecules that could form the basis of effective epigenetic therapies for various cancers.

Doxorubicin synergism and resistance reversal in human neuroblastoma BE(2)C cell lines: An in vitro study with dextran-catechin nanohybrids

Hybrid nanocarrier consisting in nanographene oxide coated by a dextran-catechin conjugate was proposed in the efforts to find more efficient Neuroblastoma treatment with Doxorubicin chemotherapy. The dextran-catechin conjugate was prepared by immobilized laccase catalysis and its peculiar reducing ability exploited for the synthesis of the hybrid carrier. Raman spectra and DSC thermograms were recorded to check the physicochemical properties of the nanohybrid, while DLS measurements, SEM, TEM, and AFM microscopy allowed the determination of its morphological and dimensional features. A pH dependent Doxorubicin release was observed, with 30 and 75% doxorubicin released at pH 7.4 and 5.0, respectively. Viability assays on parental BE(2)C and resistant BE(2)C/ADR cell lines proved that the high anticancer activity of dextran-catechin conjugate (IC₅₀ 19.9 ± 0.6 and 18.4 ± 0.7 µg mL^-1) was retained upon formation of the nanohybrids (IC₅₀ 24.8 ± 0.7 and 22.9 ± 1 µg mL^-1). Combination therapy showed a synergistic activity between doxorubicin and either bioconjugate or nanocarrier on BE(2)C. More interestingly, on BE(2)C/ADR we recorded both the reversion of doxorubicin resistance mechanism as a consequence of decreased P-gp expression (Western Blot analysis) and a synergistic effect on cell viability, confirming the proposed nanohybrid as a very promising starting point for further research in neuroblastoma treatment.

HDAC2 was involved in placental P-glycoprotein regulation both in vitro and vivo

INTRODUCTION

Placental P-glycoprotein (P-gp) plays a significant role in regulating drugs' transplacental transfer rates. Investigations on placental P-gp regulation could provide more therapeutic targets for individualized and safe pharmacotherapy during pregnancy. Currently, the epigenetic regulation of placental P-gp is rare. Our previous study has demonstrated that HDACs inhibition could up-regulate placental P-gp and HDAC1/2/3 might be involved in this process. The present study was carried out to further explore whether HDAC1/2/3 were indeed involved in the regulation of placental P-gp or not and screen out the subtype engaged in this process.

METHODS

BeWo and JAR cells were transfected with HDAC1/2/3 specific siRNA. After 48 h of transfection, cells were harvested for real-time quantitative PCR (qRT-PCR), Western blot, immunofluorescence and fluorescent dye efflux assay to evaluate P-gp expression, localization, and efflux activity, respectively. Hdac2 siRNA was intraperitoneally injected to pregnant mice every 48 h from E7.5 to E15.5 and digoxin was administered by gavages 1 h prior to euthanasia at E16.5. Placental Hdac1/2/3 and P-gp expression were determined by qRT-PCR and Western blot. Maternal plasma and fetal-unit digoxin concentrations were detected by enzyme-multiplied immunoassay.

RESULTS

In vitro, HDAC2 inhibition could significantly elevate P-gp expression and reduce intracellular accumulation of P-gp substrates (DiOC₂ (3) and Rh 123) both in BeWo and JAR, while knockdown of HDAC1/3 had no influence on P-gp expression and its efflux activity. Additionally, in vivo, Hdac2 silencing in pregnant mice also elevated placental P-gp expression and decreased digoxin transplacental transfer rate.

CONCLUSION

HDAC2 inhibition could result in induction of placental P-gp expression and functionality both in vitro and in vivo.