News about non-secretory exocytosis: mechanisms, properties, and functions

Insights on the molecular targets of cardiotoxicity induced by anticancer drugs: A systematic review based on proteomic findings

Several anticancer agents have been associated with cardiac toxic effects. The currently proposed mechanisms to explain cardiotoxicity differ among anticancer agents, but in fact, the specific modulation is not completely elucidated. Thus, this systematic review aims to provide an integrative perspective of the molecular mechanisms underlying the toxicity of anticancer agents on heart muscle while using a high-throughput technology, mass spectrometry (MS)-based proteomics. A literature search using PubMed database led to the selection of 27 studies, of which 13 reported results exclusively on animal models, 13 on cardiomyocyte-derived cell lines and only one included both animal and a cardiomyocyte line. The reported anticancer agents were the proteasome inhibitor carfilzomib, the anthracyclines daunorubicin, doxorubicin, epirubicin and idarubicin, the antimicrotubule agent docetaxel, the alkylating agent melphalan, the anthracenedione mitoxantrone, the tyrosine kinase inhibitors (TKIs) erlotinib, lapatinib, sorafenib and sunitinib, and the monoclonal antibody trastuzumab. Regarding the MS-based proteomic approaches, electrophoretic separation using two-dimensional (2D) gels coupled with tandem MS (MS/MS) and liquid chromatography-MS/MS (LC-MS/MS) were the most common. Overall, the studies highlighted 1826 differentially expressed proteins across 116 biological processes. Most of them were grouped in larger processes and critically analyzed in the present review. The selection of studies using proteomics on heart muscle allowed to obtain information about the anticancer therapy-induced modulation of numerous proteins in this tissue and to establish connections that have been disregarded in other studies. This systematic review provides interesting points for a comprehensive understanding of the cellular cardiotoxicity mechanisms of different anticancer drugs.

Endocytosis and exocytosis protect cells against severe membrane tension variations

The ability of cells to regulate their shape and volume is critical for many cell functions. How endocytosis and exocytosis, as important ways of membrane trafficking, affect cellular volume regulation is still unclear. Here, we develop a theoretical framework to study the dynamics of cell volume, endocytosis, and exocytosis in response to osmotic shocks and mechanical loadings. This model can not only explain observed dynamics of endocytosis and exocytosis during osmotic shocks but also predict the dynamics of endocytosis and exocytosis during cell compressions. We find that a hypotonic shock stimulates exocytosis, while a hypertonic shock stimulates endocytosis; and exocytosis in turn allows cells to have a dramatic change in cell volume but a small change in membrane tension during hyposmotic swelling, protecting cells from rupture under high tension. In addition, we find that cell compressions with various loading speeds induce three distinct dynamic modes of endocytosis and exocytosis. Finally, we show that increasing endocytosis and exocytosis rates reduce the changes in cell volume and membrane tension under fast cell compression, whereas they enhance the changes in cell volume and membrane tension under slow cell compression. Together, our findings reveal critical roles of endocytosis and exocytosis in regulating cell volume and membrane tension.

Relationships and Interactions between Ionotropic Glutamate Receptors and Nicotinic Receptors in the CNS

Although ionotropic glutamate receptors and nicotinic receptors for acetylcholine (ACh) have usually been studied separately, they are often co-localized and functionally inter-dependent. The objective of this review is to survey the evidence for interactions between the two receptor families and the mechanisms underlying them. These include the mutual regulation of subunit expression, which change the NMDA:AMPA response balance, and the existence of multi-functional receptor complexes which make it difficult to distinguish between individual receptor sites, especially in vivo. This is followed by analysis of the functional relationships between the receptors from work on transmitter release, cellular electrophysiology and aspects of behavior where these can contribute to understanding receptor interactions. It is clear that nicotinic receptors (nAChRs) on axonal terminals directly regulate the release of glutamate and other neurotransmitters, α7-nAChRs generally promoting release. Hence, α7-nAChR responses will be prevented not only by a nicotinic antagonist, but also by compounds blocking the indirectly activated glutamate receptors. This accounts for the apparent anticholinergic activity of some glutamate antagonists, including the endogenous antagonist kynurenic acid. The activation of presynaptic nAChRs is by the ambient levels of ACh released from pre-terminal synapses, varicosities and glial cells, acting as a 'volume neurotransmitter' on synaptic and extrasynaptic sites. In addition, ACh and glutamate are released as CNS co-transmitters, including 'cholinergic' synapses onto spinal Renshaw cells. It is concluded that ACh should be viewed primarily as a modulator of glutamatergic neurotransmission by regulating the release of glutamate presynaptically, and the location, subunit composition, subtype balance and sensitivity of glutamate receptors, and not primarily as a classical fast neurotransmitter. These conclusions and caveats should aid clarification of the sites of action of glutamate and nicotinic receptor ligands in the search for new centrally-acting drugs.

Novel vertebrate- and brain-specific driver of neuronal outgrowth

During the process of neuronal outgrowth, developing neurons produce new projections, neurites, that are essential for brain wiring. Here, we discover a relatively late-evolved protein that we denote Ac45-related protein (Ac45RP) and that, surprisingly, drives neuronal outgrowth. Ac45RP is a paralog of the Ac45 protein that is a component of the vacuolar proton ATPase (V-ATPase), the main pH regulator in eukaryotic cells. Ac45RP mRNA expression is brain specific and coincides with the peak of neurogenesis and the onset of synaptogenesis. Furthermore, Ac45RP physically interacts with the V-ATPase V₀-sector and colocalizes with V₀ in unconventional, but not synaptic, secretory vesicles of extending neurites. Excess Ac45RP enhances the expression of V₀-subunits, causes a more elaborate Golgi, and increases the number of cytoplasmic vesicular structures, plasma membrane formation and outgrowth of actin-containing neurites devoid of synaptic markers. CRISPR-cas9n-mediated Ac45RP knockdown reduces neurite outgrowth. We conclude that the novel vertebrate- and brain-specific Ac45RP is a V₀-interacting constituent of unconventional vesicular structures that drives membrane expansion during neurite outgrowth and as such may furnish a tool for future neuroregenerative treatment strategies.

Polymer Pro-Drug Nanoparticles for Sustained Release of Cytotoxic Drugs Evaluated in Patient-Derived Glioblastoma Cell Lines and In Situ Gelling Formulations

Glioblastoma (GBM) is the most common, malignant and aggressive brain tumour in adults. Despite the use of multimodal treatments, involving surgery, followed by concomitant radiotherapy and chemotherapy, the median survival for patients remains less than 15 months from diagnosis. Low penetration of drugs across the blood-brain barrier (BBB) is a dose-limiting factor for systemic GBM therapies, and as a result, post-surgical intracranial drug delivery strategies are being developed to ensure local delivery of drugs within the brain. Here we describe the effects of PEGylated poly(lactide)-poly(carbonate)-doxorubicin (DOX) nanoparticles (NPs) on the metabolic activity of primary cancer cell lines derived from adult patients following neurosurgical resection, and the commercially available GBM cell line, U87. The results showed that non-drug-loaded NPs were well tolerated at concentrations of up to 100 µg/mL while tumour cell-killing effects were observed for the DOX-NPs at the same concentrations. Further experiments evaluated the release of DOX from polymer-DOX conjugate NPs when incorporated in a thermosensitive in situ gelling poly(DL-lactic-co-glycolic acid) and poly(ethylene glycol) (PLGA/PEG) matrix paste, in order to simulate the clinical setting of a locally injected formulation for GBM following surgical tumour resection. These assays demonstrated drug release from the polymer pro-drugs, when in PLGA/PEG matrices of two formulations, over clinically relevant time scales. These findings encourage future in vivo assessment of the potential capability of polymer-drug conjugate NPs to penetrate brain parenchyma efficaciously, when released from existing interstitial delivery systems.

Enhancement of Anticancer Efficacy and Tumor Penetration of Sorafenib by Ionic Liquids

Ionic liquids (ILs) possess unique solvation and biological properties for drug delivery. Choline and geranic acid (CAGE) in particular, has been successfully formulated to orally deliver insulin and hydrophobic therapeutics such as sorafenib (SRF). However, relatively little is known about the effect of CAGE on intracellular delivery of drugs. Here the effect of low-concentration CAGE (<2 mg mL^-1 ) on the delivery of SRF into cancer cells (4T1, PANC-1, and HT29) as well as intestine epithelium cells (Caco-2) is studied. The anti-cancer effect of SRF is enhanced by up to fivefold in the presence of CAGE (0.5 mg mL^-1 ). The effect is mediated not by enhancing the cellular uptake of SRF but by improving intracellular SRF retention by inhibiting exocytosis. Moreover, CAGE improves the anti-tumor effect of SRF by increasing apoptosis and blocking cell-cycle progression. Moreover, CAGE significantly enhances the penetration of SRF into and across multicellular constructs with multiple mechanisms involved. Collectively, the administration of ILs such as CAGE combined with SRF may offer a novel therapy to better inhibit tumor progression.