Panobinostat reduces hypoxia-induced cisplatin resistance of non-small cell lung carcinoma cells via HIF-1α destabilization

Turning on the Radio: Epigenetic Inhibitors as Potential Radiopriming Agents

First introduced during the late 1800s, radiation therapy is fundamental to the treatment of cancer. In developed countries, approximately 60% of all patients receive radiation therapy (also known as the sixty percenters), which makes radioresistance in cancer an important and, to date, unsolved, clinical problem. Unfortunately, the therapeutic refractoriness of solid tumors is the rule not the exception, and the ubiquity of resistance also extends to standard chemotherapy, molecularly targeted therapy and immunotherapy. Based on extrapolation from recent clinical inroads with epigenetic agents to prime refractory tumors for maximum sensitivity to concurrent or subsequent therapies, the radioresistant phenotype is potentially reversible, since aberrant epigenetic mechanisms are critical contributors to the evolution of resistant subpopulations of malignant cells. Within the framework of a syllogism, this review explores the emerging link between epigenetics and the development of radioresistance and makes the case that a strategy of pre- or co-treatment with epigenetic agents has the potential to, not only derepress inappropriately silenced genes, but also increase reactive oxygen species production, resulting in the restoration of radiosensitivity.

Sequential pathogenesis of metastatic VHL mutant clear cell renal cell carcinoma: putting it together with a translational perspective

Clear cell renal cell carcinoma (ccRCC) accounts for ∼80% of all RCC, and biallelic Von Hippel-Lindau (VHL) gene defects occur in ∼75% of sporadic ccRCC. The etiopathogenesis of VHL mutant metastatic RCC, based on our understanding to date of molecular mechanisms involved, is a sequence of events which can be grouped under the following: (i) loss of VHL activity (germline/somatic mutation + inactivation of the wild-type copy); (ii) constitutive activation of the hypoxia-inducible factor (HIF) pathway due to loss of VHL activity and transcription of genes involved in angiogenesis, epithelial-mesenchymal transition, invasion, metastasis, survival, anaerobic glycolysis and pentose phosphate pathway; (iii) interactions of the HIF pathway with other oncogenic pathways; (iv) genome-wide epigenetic changes (potentially driven by an overactive HIF pathway) and the influence of epigenetics on various oncogenic, apoptotic, cell cycle regulatory and mismatch repair pathways (inhibition of multiple tumor suppressor genes); (v) immune evasion, at least partially caused by changes in the epigenome. These mechanisms interact throughout the pathogenesis and progression of disease, and also confer chemoresistance and radioresistance, making it one of the most difficult metastatic cancers to treat. This article puts together the sequential pathogenesis of VHL mutant ccRCC by elaborating these mechanisms and the interplay of oncogenic pathways, epigenetics, metabolism and immune evasion, with a perspective on potential therapeutic strategies. We reflect on the huge gap between our understanding of the molecular biology and currently accepted standard of care in metastatic ccRCC, and present ideas for better translational research involving therapeutic strategies with combinatorial drug approach, targeting different aspects of the pathogenesis.

The predictive value of ERCC1 and p53 for the effect of panobinostat and cisplatin combination treatment in NSCLC

Cisplatin is one of the most common chemotherapeutic drugs for non-small cell lung cancer (NSCLC). However, the response rate is limited because of drug resistance. Histone deacetylase inhibitors (HDACis), which can alter DNA accessibility by regulating chromatin structure and inducing apoptosis, exhibit a synergistic action with cisplatin. However, no biomarkers that can predict the efficacy of the combination of HDACis and cisplatin have been reported. Our study found that panobinostat, an HDAC inhibitor, increased the cisplatin sensitivity of several NSCLC cell lines with low ERCC1 expression but not those with high ERCC1 expression or gain-of-function (GOF) p53 mutation despite of ERCC1 expression level. ERCC1 knockdown increased the cisplatin sensitivity of NSCLC cell lines with high ERCC1 expression without GOF p53 mutations. In addition, in low ERCC1 expression NSCLC cell lines, knockdown of GOF mutant p53 enhanced cisplatin sensitivity. Further double knockdown of ERCC1 and GOF mutant p53 but not ERCC1 knockdown alone increased the cisplatin sensitivity of cells with both high ERCC1 expression and GOF p53 mutations. Therefore, this study demonstrated that ERCC1 expression combined with p53 mutation status may determine the efficacy of cisplatin and HDACi combined therapy and guide the development of future NSCLC therapies.

Cisplatin treatment increases stemness through upregulation of hypoxia-inducible factors by interleukin-6 in non-small cell lung cancer

Cisplatin‐resistant A549 and H157 (A549CisR and H157CisR) non‐small cell lung cancer cells show increased stemness of cancer stem cells (CSCs) compared to their parental cells. We investigated whether interleukin‐6 (IL‐6) signaling contributes to this increased stemness in cisplatin‐resistant cells. When A549CisR and H157CisR cells were treated with neutralizing IL‐6 antibody, decreased cisplatin resistance was observed, whereas IL‐6 treatment of parental cells resulted in increased cisplatin resistance. Expression of the CSC markers was significantly upregulated in IL‐6‐expressing scramble cells (in vitro) and scramble cell‐derived tumor tissues (in vivo) after cisplatin treatment, but not in IL‐6 knocked down (IL‐6si) (in vitro) cells and in IL‐6si cell‐derived tumor tissues (in vivo), suggesting the importance of IL‐6 signaling in triggering increased stemness during cisplatin resistance development. Hypoxia inducible factors (HIFs) were upregulated by IL‐6 and responsible for the increased CSC stemness on cisplatin treatment. Mechanism dissection studies found that upregulation of HIFs by IL‐6 was through transcriptional control and inhibition of HIF degradation. Treatment of HIF inhibitor (FM19G11) abolished the upregulation of CSC markers and increased sphere formations in IL‐6 expressing cells on cisplatin treatment. In all, IL‐6‐mediated HIF upregulation is important in increasing stemness during cisplatin resistance development, and we suggest that the strategies of inhibiting IL‐6 signaling or its downstream HIF molecules can be used as future therapeutic approaches to target CSCs after cisplatin treatment for lung cancer.

Epigenetic Therapy for Solid Tumors: Highlighting the Impact of Tumor Hypoxia

In the last few decades, epigenetics has emerged as an exciting new field in development and disease, with a more recent focus towards cancer. Epigenetics has classically referred to heritable patterns of gene expression, primarily mediated through DNA methylation patterns. More recently, it has come to include the reversible chemical modification of histones and DNA that dictate gene expression patterns. Both the epigenetic up-regulation of oncogenes and downregulation of tumor suppressors have been shown to drive tumor development. Current clinical trials for cancer therapy include pharmacological inhibition of DNA methylation and histone deacetylation, with the aim of reversing these cancer-promoting epigenetic changes. However, the DNA methyltransferase and histone deacetylase inhibitors have met with less than promising results in the treatment of solid tumors. Regions of hypoxia are a common occurrence in solid tumors. Tumor hypoxia is associated with increased aggressiveness and therapy resistance, and importantly, hypoxic tumor cells have a distinct epigenetic profile. In this review, we provide a summary of the recent clinical trials using epigenetic drugs in solid tumors, discuss the hypoxia-induced epigenetic changes and highlight the importance of testing the epigenetic drugs for efficacy against the most aggressive hypoxic fraction of the tumor in future preclinical testing.

MicroRNA-338 inhibits migration and proliferation by targeting hypoxia-induced factor 1α in nasopharyngeal carcinoma

Nasopharyngeal cancer (NPC) is an endemic type of head and neck cancer with a high rate of cervical lymph node metastasis. An increasing number of studies have shown that microRNAs (miRNAs) play a key role in the development and progression of NPC. miR-338-3p has been demonstrated as an anti-oncogene in different solid tumors. The aim of the present study was to investigate the potential role of miR‑338-3p in the development and progression of NPC. Compared with normal samples, our data showed that miR-338-3p were downregulated in NPC tissues and cells. The luciferase assay demonstrated that HIF-1α was a direct target of miR-338-3p. We also found that miR-338-3p regulated the expression levels of HIF-1α, respectively. Overexpression of miR-338-3p in NPC cells significantly inhibited cell proliferation, and migration. Conversely, miR-338-3p knockdown in cells with lower endogenous expression levels significantly reduced antitumor behavior. Furthermore, enforced expression of miR-338-3p led to a decline in ERK phosphorylation as well as inhibited the hypoxia induced epithelial to mesenchymal transition. Cells pre-transfected with miR-338-3p can overcome hypoxia-mediated cisplatin resistance. Taken together, we found that miR-338-3p directly targeted HIF-1α, and we provide insight into NPC initiation and progression, possibly representing a novel therapeutic target.