A novel cell-permeable peptide prevents protein SUMOylation and supports the mislocalization and aggregation of TDP-43

SUMOylation is a post-translational modification (PTM) that exerts a regulatory role in different cellular processes, including protein localization, aggregation, and biological activities. It consists of the dynamic formation of covalent isopeptide bonds between a family member of the Small Ubiquitin Like Modifiers (SUMOs) and the target proteins. Interestingly, it is a cellular mechanism implicated in several neurodegenerative pathologies and potentially it could become a new therapeutic target; however, there are very few pharmacological tools to modulate the SUMOylation process. In this study, we have designed and tested the activity of a novel small cell-permeable peptide, COV-1, in a neuroblastoma cell line that specifically prevents protein SUMOylation. COV-1 inhibits UBC9-protein target interaction and efficiently decreases global SUMO-1ylation. Moreover, it can perturb RanGAP-1 perinuclear localization by inducing the downregulation of UBC9. In parallel, we found that COV-1 causes an increase in the ubiquitin degradation system up to its engulfment while enhancing the autophagic flux. Surprisingly, COV-1 modifies protein aggregation, and specifically it mislocalizes TDP-43 within cells, inducing its aggregation and co-localization with SUMO-1. These data suggest that COV-1 could be taken into future consideration as an interesting pharmacological tool to study the cellular cascade effects of SUMOylation prevention.

Peptide-based LDH5 inhibitors enter cancer cells and impair proliferation

Lactate dehydrogenase 5 (LDH5) is overexpressed in many cancers and is a potential target for anticancer therapy due to its role in aerobic glycolysis. Small-molecule drugs have been developed as competitive inhibitors to bind substrate/cofactor sites of LDH5, but none reached the clinic to date. Recently, we designed the first LDH5 non-competitive inhibitor, cGmC9, a peptide that inhibits protein-protein interactions required for LDH5 enzymatic activity. Peptides are gaining a large interest as anticancer agents to modulate intracellular protein-protein interactions not targetable by small molecules; however, delivery of these peptides to the cytosol, where LDH5 and other anticancer targets are located, remains a challenge for this class of therapeutics. In this study, we focused on the cellular internalisation of cGmC9 to achieve LDH5 inhibition in the cytosol. We designed cGmC9 analogues and compared them for LDH5 inhibition, cellular uptake, toxicity, and antiproliferation against a panel of cancer cell lines. The lead analogue, [R/r]cGmC9, specifically impairs proliferation of cancer cell lines with high glycolytic profiles. Proteomics analysis showed expected metabolic changes in response to decreased glycolysis. This is the first report of a peptide-based LDH5 inhibitor able to modulate cancer metabolism and kill cancer cells that are glycolytic. The current study demonstrates the potential of using peptides as inhibitors of intracellular protein-protein interactions relevant for cancer pathways and shows that active peptides can be rationally designed to improve their cell permeation.

Rabphilin 3A: A novel target for the treatment of levodopa-induced dyskinesias

N-methyl-d-aspartate receptor (NMDAR) subunit composition strictly commands receptor function and pharmacological responses. Changes in NMDAR subunit composition have been documented in brain disorders such as Parkinson's disease (PD) and levodopa (L-DOPA)-induced dyskinesias (LIDs), where an increase of NMDAR GluN2A/GluN2B subunit ratio at striatal synapses has been observed. A therapeutic approach aimed at rebalancing NMDAR synaptic composition represents a valuable strategy for PD and LIDs. To this, the comprehension of the molecular mechanisms regulating the synaptic localization of different NMDAR subtypes is required. We have recently demonstrated that Rabphilin 3A (Rph3A) is a new binding partner of NMDARs containing the GluN2A subunit and that it plays a crucial function in the synaptic stabilization of these receptors. Considering that protein-protein interactions govern the synaptic retention of NMDARs, the purpose of this work was to analyse the role of Rph3A and Rph3A/NMDAR complex in PD and LIDs, and to modulate Rph3A/GluN2A interaction to counteract the aberrant motor behaviour associated to chronic L-DOPA administration. Thus, an array of biochemical, immunohistochemical and pharmacological tools together with electron microscopy were applied in this study. Here we found that Rph3A is localized at the striatal postsynaptic density where it interacts with GluN2A. Notably, Rph3A expression at the synapse and its interaction with GluN2A-containing NMDARs were increased in parkinsonian rats displaying a dyskinetic profile. Acute treatment of dyskinetic animals with a cell-permeable peptide able to interfere with Rph3A/GluN2A binding significantly reduced their abnormal motor behaviour. Altogether, our findings indicate that Rph3A activity is linked to the aberrant synaptic localization of GluN2A-expressing NMDARs characterizing LIDs. Thus, we suggest that Rph3A/GluN2A complex could represent an innovative therapeutic target for those pathological conditions where NMDAR composition is significantly altered.

Photosensitizer and polycationic peptide-labeled streptavidin as a nano-carrier for light-controlled protein transduction

Transductions of exogenous proteins into cells enable the precise study of the effect of the transduced proteins on cellular functions. Accordingly, the protein transduction technique, which can control the release of proteins into the cytosol with certainty and high-throughput, is highly desired in various research fields. In this study, streptavidin (SA) labeled with a photosensitizer and cell-permeable peptides (CPP) was proposed as a nano-carrier for light-controlled protein transduction. SA was modified with biotinylated oligo-arginine peptides (Rpep), which were functionalized with Alexa Fluor 546 (AF546), to achieve cell penetrating and endosomal escape functionalities. The SA-Rpep complex was efficiently internalized into living HeLa cells corresponding to the length and the modification number of Rpep. SA conjugated with more than three equimolar AF546-modified Rpep consisting of fifteen arginine residues was achieved to diffuse throughout the cytosol without cytotoxicity by irradiation of the excitation light for AF546. The optimized nano-carrier was confirmed to transduce a biotinylated model cargo protein, enhanced green fluorescent protein fused with thioredoxin (tEGFP) into the cytosol at the light-irradiated area. The results provided proof-of-principle that SA possessing multiple AF546-modified Rpep has the potential to be a versatile and facile carrier for light-controlled protein transduction into the cytosol of mammalian cells.

Cell-based peptide screening to access the undruggable target space

Only 20-30% of drug target proteins can be accessed by common drug classes, like small molecules or therapeutic antibodies. The vast majority of the remaining proteins are considered "undruggable" and include drug target proteins, like transcription factors, scaffold or adapter proteins, which play important roles in disease. However over the last years innovative compound classes including nucleotide derived drugs (e.g. siRNA, antisense), macrocyclic compounds and cell-permeable peptides matured significantly and hold now the potential to modulate these hard to access target proteins for therapeutic use. This article will focus on the discovery of cell-permeable peptides and discuss intracellular screening systems for peptides, which yield highly relevant peptides, because peptide selection takes place in eukaryotic cells, under conditions, which are very similar to the later therapeutic use.

Modulation of NMDA receptor at the synapse: promising therapeutic interventions in disorders of the nervous system

There is general agreement that excessive activation of N-methyl-D-aspartate (NMDA) receptors plays a key role in mediating at least some aspects of synaptic dysfunction in several central nervous system disorders. On this view, in the last decades, research focused on the discovery of different compounds able to reduce NMDA receptor activity, such as classical and/or subunit-specific antagonists. However, the increasing body of knowledge on specific signaling pathways downstream NMDA receptors led to the identification of new pharmacological targets for NMDA receptor-related pathological conditions. Moreover, besides over-activation, several studies indicated that also abnormal NMDA receptor trafficking, resulting in the modification of the receptor subunit composition at the synapse, has a major role in the pathogenesis of several brain disorders. For this reason, the discovery of the molecular mechanisms regulating the abundance of synaptic versus extra-synaptic NMDA receptors as well as the activation of the specific signaling pathways downstream the different NMDA receptor subtypes is needed for the development of novel therapeutic approaches for NMDA receptor-dependent synaptic dysfunction.