Proteasome inhibitors in glioblastoma

Production of Epoxyketone Peptide-Based Proteasome Inhibitors by Streptomyces sp. BRA-346: Regulation and Biosynthesis

Streptomyces sp. BRA-346 is an Actinobacteria isolated from the Brazilian endemic tunicate Euherdmania sp. We have reported that this strain produces epoxyketone peptides, as dihydroeponemycin (DHE) and structurally related analogs. This cocktail of epoxyketone peptides inhibits the proteasome chymotrypsin-like activity and shows high cytotoxicity to glioma cells. However, low yields and poor reproducibility of epoxyketone peptides production by BRA-346 under laboratory cultivation have limited the isolation of epoxyketone peptides for additional studies. Here, we evaluated several cultivation methods using different culture media and chemical elicitors to increase the repertoire of peptide epoxyketone production by this bacterium. Furthermore, BRA-346 genome was sequenced, revealing its broad genetic potential, which is mostly hidden under laboratory conditions. By using specific growth conditions, we were able to evidence different classes of secondary metabolites produced by BRA-346. In addition, by combining genome mining with untargeted metabolomics, we could link the metabolites produced by BRA-346 to its genetic capacity and potential regulators. A single biosynthetic gene cluster (BGC) was related to the production of the target epoxyketone peptides by BRA-346. The candidate BGC displays conserved biosynthetic enzymes with the reported eponemycin (EPN) and TMC-86A (TMC) BGCs. The core of the putative epoxyketone peptide BGC (ORFs A-L), in which ORF A is a LuxR-like transcription factor, was cloned into a heterologous host. The recombinant organism was capable to produce TMC and EPN natural products, along with the biosynthetic intermediates DH-TMC and DHE, and additional congeners. A phylogenetic analysis of the epn/tmc BGC revealed related BGCs in public databases. Most of them carry a proteasome beta-subunit, however, lacking an assigned specialized metabolite. The retrieved BGCs also display a diversity of regulatory genes and TTA codons, indicating tight regulation of this BGC at the transcription and translational levels. These results demonstrate the plasticity of the epn/tmc BGC of BRA-346 in producing epoxyketone peptides and the feasibility of their production in a heterologous host. This work also highlights the capacity of BRA-346 to tightly regulate its secondary metabolism and shed light on how to awake silent gene clusters of Streptomyces sp. BRA-346 to allow the production of pharmacologically important biosynthetic products.

Role of stress granules in modulating senescence and promoting cancer progression: Special emphasis on glioma

Stress granules (SGs) contain mRNAs and proteins stalled in translation during stress; these are increasingly being implicated in diseases, including neurological disorders and cancer. The dysregulated assembly, persistence, disassembly and clearance of SGs contribute to the process of senescence. Senescence has long been a mysterious player in cellular physiology and associated diseases. The systemic process of aging has been pivotal in the development of various neurological disorders like age-related neuropathy, Alzheimer's disease and Parkinson's disease. Glioma is a cancer of neurological origin with a very poor prognosis and high rate of recurrence, SGs have only recently been implicated in its pathogenesis. Senescence has long been established to play an antitumorigenic role, however, relatively less studied is its protumorigenic importance. Here, we have evaluated the existing literature to assess the crosstalk of the two biological phenomena of senescence and SG formation in the context of tumorigenesis. In this review, we have attempted to analyze the contribution of senescence in regulating diverse cellular processes, like, senescence associated secretory phenotype (SASP), microtubular reorganization, telomeric alteration, autophagic clearance and how intricately these phenomena are tied with the formation of SGs. Finally, we propose that interplay between senescence, its contributing factors and the genesis of SGs can drive tumorigenicity of gliomas, which can potentially be utilized for therapeutic intervention.

A Systematic Review of Glioblastoma-Targeted Therapies in Phases II, III, IV Clinical Trials

Glioblastoma (GBM), the most frequent and aggressive glial tumor, is currently treated as first line by the Stupp protocol, which combines, after surgery, radiotherapy and chemotherapy. For recurrent GBM, in absence of standard treatment or available clinical trials, various protocols including cytotoxic drugs and/or bevacizumab are currently applied. Despite these heavy treatments, the mean overall survival of patients is under 18 months. Many clinical studies are underway. Based on clinicaltrials.org and conducted up to 1 April 2020, this review lists, not only main, but all targeted therapies in phases II-IV of 257 clinical trials on adults with newly diagnosed or recurrent GBMs for the last twenty years. It does not involve targeted immunotherapies and therapies targeting tumor cell metabolism, that are well documented in other reviews. Without surprise, the most frequently reported drugs are those targeting (i) EGFR (40 clinical trials), and more generally tyrosine kinase receptors (85 clinical trials) and (ii) VEGF/VEGFR (75 clinical trials of which 53 involving bevacizumab). But many other targets and drugs are of interest. They are all listed and thoroughly described, on an one-on-one basis, in four sections related to targeting (i) GBM stem cells and stem cell pathways, (ii) the growth autonomy and migration, (iii) the cell cycle and the escape to cell death, (iv) and angiogenesis.

In vitro models of molecular and nano-particle transport across the blood-brain barrier

The blood-brain barrier (BBB) is the tightest endothelial barrier in humans. Characterized by the presence of tight endothelial junctions and adherens junctions, the primary function of the BBB is to maintain brain homeostasis through the control of solute transit across the barrier. The specific features of this barrier make for unique modes of transport of solutes, nanoparticles, and cells across the BBB. Understanding the different routes of traffic adopted by each of these is therefore critical in the development of targeted therapies. In an attempt to move towards controlled experimental assays, multiple groups are now opting for the use of microfluidic systems. A comprehensive understanding of bio-transport processes across the BBB in microfluidic devices is therefore necessary to develop targeted and efficient therapies for a host of diseases ranging from neurological disorders to the spread of metastases in the brain.

Combination Therapy With Histone Deacetylase Inhibitors (HDACi) for the Treatment of Cancer: Achieving the Full Therapeutic Potential of HDACi

Genetic and epigenetic changes in DNA are involved in cancer development and tumor progression. Histone deacetylases (HDACs) are key regulators of gene expression that act as transcriptional repressors by removing acetyl groups from histones. HDACs are dysregulated in many cancers, making them a therapeutic target for the treatment of cancer. Histone deacetylase inhibitors (HDACi), a novel class of small-molecular therapeutics, are now approved by the Food and Drug Administration as anticancer agents. While they have shown great promise, resistance to HDACi is often observed and furthermore, HDACi have shown limited success in treating solid tumors. The combination of HDACi with standard chemotherapeutic drugs has demonstrated promising anticancer effects in both preclinical and clinical studies. In this review, we summarize the research thus far on HDACi in combination therapy, with other anticancer agents and their translation into preclinical and clinical studies. We additionally highlight the side effects associated with HDACi in cancer therapy and discuss potential biomarkers to either select or predict a patient's response to these agents, in order to limit the off-target toxicity associated with HDACi.