Oxidation and inactivation of low molecular weight protein tyrosine phosphatase by the anticancer drug Aplidin

From Beach to the Bedside: Harnessing Mitochondrial Function in Human Diseases Using New Marine-Derived Strategies

Mitochondria are double-membrane organelles within eukaryotic cells that act as cellular power houses owing to their ability to efficiently generate the ATP required to sustain normal cell function. Also, they represent a "hub" for the regulation of a plethora of processes, including cellular homeostasis, metabolism, the defense against oxidative stress, and cell death. Mitochondrial dysfunctions are associated with a wide range of human diseases with complex pathologies, including metabolic diseases, neurodegenerative disorders, and cancer. Therefore, regulating dysfunctional mitochondria represents a pivotal therapeutic opportunity in biomedicine. Marine ecosystems are biologically very diversified and harbor a broad range of organisms, providing both novel bioactive substances and molecules with meaningful biomedical and pharmacological applications. Recently, many mitochondria-targeting marine-derived molecules have been described to regulate mitochondrial biology, thus exerting therapeutic effects by inhibiting mitochondrial abnormalities, both in vitro and in vivo, through different mechanisms of action. Here, we review different strategies that are derived from marine organisms which modulate specific mitochondrial processes or mitochondrial molecular pathways and ultimately aim to find key molecules to treat a wide range of human diseases characterized by impaired mitochondrial function.

The effects of two gold-N-heterocyclic carbene (NHC) complexes in ovarian cancer cells: a redox proteomic study

PURPOSE

Ovarian cancer is the fifth leading cause of cancer-related deaths in women. Standard treatment consists of tumor debulking surgery followed by platinum and paclitaxel chemotherapy; yet, despite the initial response, about 70-75% of patients develop resistance to chemotherapy. Gold compounds represent a family of very promising anticancer drugs. Among them, we previously investigated the cytotoxic and pro-apoptotic properties of Au(NHC) and Au(NHC)2PF6, i.e., a monocarbene gold(I) complex and the corresponding bis(carbene) complex. Gold compounds are known to alter the redox state of cells interacting with free cysteine and selenocysteine residues of several proteins. Herein, a redox proteomic study has been carried out to elucidate the mechanisms of cytotoxicity in A2780 human ovarian cancer cells.

METHODS

A biotinylated iodoacetamide labeling method coupled with mass spectrometry was used to identify oxidation-sensitive protein cysteines.

RESULTS

Gold carbene complexes cause extensive oxidation of several cellular proteins; many affected proteins belong to two major functional classes: carbohydrate metabolism, and cytoskeleton organization/cell adhesion. Among the affected proteins, Glyceraldehyde-3-phosphate dehydrogenase inhibition was proved by enzymatic assays and by ESI-MS studies. We also found that Au(NHC)2PF6 inhibits mitochondrial respiration impairing complex I function. Concerning the oxidized cytoskeletal proteins, gold binding to the free cysteines of actin was demonstrated by ESI-MS analysis. Notably, both gold compounds affected cell migration and invasion.

CONCLUSIONS

In this study, we deepened the mode of action of Au(NHC) and Au(NHC)2PF6, identifying common cellular targets but confirming their different influence on the mitochondrial function.

Biomaterials and Bioactive Natural Products from Marine Invertebrates: From Basic Research to Innovative Applications

Aquatic invertebrates are a major source of biomaterials and bioactive natural products that can find applications as pharmaceutics, nutraceutics, cosmetics, antibiotics, antifouling products and biomaterials. Symbiotic microorganisms are often the real producers of many secondary metabolites initially isolated from marine invertebrates; however, a certain number of them are actually synthesized by the macro-organisms. In this review, we analysed the literature of the years 2010–2019 on natural products (bioactive molecules and biomaterials) from the main phyla of marine invertebrates explored so far, including sponges, cnidarians, molluscs, echinoderms and ascidians, and present relevant examples of natural products of interest to public and private stakeholders. We also describe omics tools that have been more relevant in identifying and understanding mechanisms and processes underlying the biosynthesis of secondary metabolites in marine invertebrates. Since there is increasing attention on finding new solutions for a sustainable large-scale supply of bioactive compounds, we propose that a possible improvement in the biodiscovery pipeline might also come from the study and utilization of aquatic invertebrate stem cells.

Electrochemical Monitoring of Paclitaxel-Induced ROS Release from Mitochondria inside Single Cells

Mitochondria are believed to be the major source of intracellular reactive oxygen species (ROS). However, in situ, real-time and quantitative monitoring of ROS release from mitochondria that are present in their cytosolic environment remains a great challenge. In this work, a platinized SiC@C nanowire electrode is placed into a single cell for in situ detection of ROS signals from intracellular mitochondria, and antineoplastic agent (paclitaxel) induced ROS production is successfully recorded. Further investigations indicate that complex IV (cytochrome c oxidase, COX) is the principal site for ROS generation, and significantly more ROS are generated from mitochondria in cancer cells than that from normal cells. This work provides an effective approach to directly monitor intracellular mitochondria by nanowire electrodes, and consequently obtains important physiological evidence on antineoplastic agent-induced ROS generation, which will be of great benefit for better understanding of chemotherapy at subcellular levels.

Exploring the effect of aplidin on low molecular weight protein tyrosine phosphatase by molecular docking and molecular dynamic simulation study

The low molecular weight protein tyrosine phosphatase (LMW-PTP) could regulate many signaling pathways, and it had drawn attention as a potential target for cancer. As previous report has indicated that the aplidin could inhibit the LMW-PTP, and thus, the relevant cancer caused by the abnormal regulation of the LMW-PTP could be remission. However, the molecular mechanism of inhibition of the LMW-PTP by the aplidin had not been fully understood. In this study, various computational approaches, namely molecular docking, MDs and post-dynamic analyses were utilized to explore the effect of the aplidin on the LMW-PTP. The results suggested that the intramolecular interactions of the residues in the two sides of the active site (Ser43-Ala55 and Pro121-Asn134) and the P-loop region (Leu13-Ser19) in the LMW-PTP was disturbed owing to the aplidin, meanwhile, the π-π interaction between Tyr131 and Tyr132 might be broken. The Asn15 might be the key residue to break the residues interactions. In a word, this study may provide more information for understanding the effect of inhibition of the aplidin on the LMW-PTP.

Daedophamide, a Cytotoxic Cyclodepsipeptide from a Daedalopelta sp. Sponge Collected in Indonesia

A new cyclodepsipeptide, daedophamide (1), has been isolated from a Daedalopelta sp. marine sponge collected from Alor Island (Indonesia). The planar structure of 1 was assigned on the basis of extensive 1D and 2D NMR spectroscopy and mass spectrometry. Daedophamide (1) contains 11 amino acid residues and an amide-linked 3-hydroxy-2,4,6,8-tetramethylnonanoic acid (Htemna). The amino acid constituents were identified as l-Leu, N-Me-l-Gln, d-Arg, d-Asp, d-allo-Thr, l-Pip, d-Ala, d-Ser, 3,4-dimethyl-Gln, O-MeThr, and 4-amino-7-guanidino-2,3-dihydroxyheptanoic acid (Agdha). The absolute configurations of eight of the amino acid residues in 1 were determined by application of the Marfey's method after acid-catalyzed hydrolysis, with the relative configurations of the remaining three amino acid residues and the Htemna unit being assigned by comparison of the NMR data with those reported for other similar peptides. Compound 1 displayed strong cytotoxic activity against a panel of four human tumor cell lines with GI₅₀ values in the submicromolar range.

Low molecular weight protein tyrosine phosphatase: Multifaceted functions of an evolutionarily conserved enzyme

Originally identified as a low molecular weight acid phosphatase, LMW-PTP is actually a protein tyrosine phosphatase that acts on many phosphotyrosine-containing cellular proteins that are primarily involved in signal transduction. Differences in sequence, structure, and substrate recognition as well as in subcellular localization in different organisms enable LMW-PTP to exert many different functions. In fact, during evolution, the LMW-PTP structure adapted to perform different catalytic actions depending on the organism type. In bacteria, this enzyme is involved in the biosynthesis of group 1 and 4 capsules, but it is also a virulence factor in pathogenic strains. In yeast, LMW-PTPs dephosphorylate immunophilin Fpr3, a peptidyl-prolyl-cis-trans isomerase member of the protein chaperone family. In humans, LMW-PTP is encoded by the ACP1 gene, which is composed of three different alleles, each encoding two active enzymes produced by alternative RNA splicing. In animals, LMW-PTP dephosphorylates a number of growth factor receptors and modulates their signalling processes. The involvement of LMW-PTP in cancer progression and in insulin receptor regulation as well as its actions as a virulence factor in a number of pathogenic bacterial strains may promote the search for potent, selective and bioavailable LMW-PTP inhibitors.

Low molecular weight protein tyrosine phosphatase isoforms regulate breast cancer cells migration through a RhoA dependent mechanism

Low molecular weight protein tyrosine phosphatase (LMW-PTP) has been associated with cell proliferation control through dephosphorylation and inactivation of growth factor receptors such as PDGF-R and EphA2, and with cellular adhesion and migration through p190RhoGap and RhoA. We aim to clarify the role of two main LMW-PTP isoforms in breast cancer tumorigenesis. We used a siRNA-mediated loss-of-function in MDA-MB-435 breast cancer cell line to study the role of the two main LMW-PTP isoforms, fast and slow, in breast cancer tumorigenesis and migration. Our results show that the siRNAs directed against total LMW-PTP and LMW-PTP slow isoform enhanced cell motility in an invasive breast cancer cell line, MDA-MB-435, with no changes in the proliferation and invasive potential of cells. The total LMW-PTP knockdown caused a more pronounced increase of cell migration. Suppression of total LMW-PTP decreased RhoA activation and suppression of the LMW-PTP slow isoform caused a small but significant increase in RhoA activation. We propose that the increase or decrease in RhoA activation induces changes in stress fibers formation and consequently alter the adhesive and migratory potential of cells. These findings suggest that the two main isoforms of LMW-PTP may act differentially, with the fast isoform having a more prominent role in tumor cell migration. In addition, our results highlight functional specificity among LMW-PTP isoforms, suggesting hitherto unknown roles for these proteins in breast cancer biology. Novel therapeutic approaches targeting LMW-PTP, considering the expression of these two isoforms and not LMW-PTP as a whole, should be investigated.

Didemnins, tamandarins and related natural products

Since the discovery and isolation of the didemnin family of marine depsipeptides in 1981, the synthesis and biological activity of its congeners have been of great interest to the scientific community. The didemnins have demonstrated antitumor, antiviral, and immunosuppressive activity at low nano- and femtomolar levels. Of the congeners, didemnin B was the first marine natural product to reach phase II clinical trials in the United States, stimulating many analogue syntheses to date. About two decades later, tamandarins A and B were isolated, and were found to possess very similar structure and biological activity to that of the didemnin B. These compounds have shown impressive biological activity and some progress has been made in establishing structure-activity relationships. However, their molecular mechanism of action still remains unclear. This review highlights the long-standing study of didemnins and its critical application towards the understanding of the molecular mechanism of action of tamandarins and their potential use as therapeutic agents.

Differential regulation of endothelial cell permeability by high and low doses of oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine

The generation of phospholipid oxidation products in atherosclerosis, sepsis, and lung pathologies affects endothelial barrier function, which exerts significant consequences on disease outcomes in general. Our group previously showed that oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (OxPAPC) at low concentrations increases endothelial cell (EC) barrier function, but decreases it at higher concentrations. In this study, we determined the mechanisms responsible for the pulmonary endothelial cell barrier dysfunction induced by high OxPAPC concentrations. OxPAPC at a range of 5-20 μg/ml enhanced EC barriers, as indicated by increased transendothelial electrical resistance. In contrast, higher OxPAPC concentrations (50-100 μg/ml) rapidly increased EC permeability, which was accompanied by increased total cell protein tyrosine (Tyr) phosphorylation, phosphorylation at Tyr-418, the activation of Src kinase, and the phosphorylation of adherens junction (AJ) protein vascular endothelial cadherin (VE-cadherin) at Tyr-731 and Tyr-658, which was not observed in ECs stimulated with low OxPAPC doses. The early tyrosine phosphorylation of VE-cadherin was linked to the dissociation of VE-cadherin-p120-catenin/β-catenin complexes and VE-cadherin internalization, whereas low OxPAPC doses promoted the formation of VE-cadherin-p120-catenin/β-catenin complexes. High but not low doses of OxPAPC increased the production of reactive oxygen species (ROS) and protein oxidation. The inhibition of Src by PP2 and ROS production by N-acetyl cysteine inhibited the disassembly of VE-cadherin-p120-catenin complexes, and attenuated high OxPAPC-induced EC barrier disruption. These results show the differential effects of OxPAPC doses on VE-cadherin-p120-catenin complex assembly and EC barrier function. These data suggest that the rapid tyrosine phosphorylation of VE-cadherin and other potential targets mediated by Src and ROS-dependent mechanisms plays a key role in the dissociation of AJ complexes and EC barrier dysfunction induced by high OxPAPC doses.

The cytotoxic activity of Aplidin in chronic lymphocytic leukemia (CLL) is mediated by a direct effect on leukemic cells and an indirect effect on monocyte-derived cells

Aplidin is a novel cyclic depsipeptide, currently in Phase II/III clinical trials for solid and hematologic malignancies. The aim of this study was to evaluate the effect of Aplidin in chronic lymphocytic leukemia (CLL), the most common leukemia in the adult. Although there have been considerable advances in the treatment of CLL over the last decade, drug resistance and immunosuppression limit the use of current therapy and warrant the development of novel agents. Here we report that Aplidin induced a dose- and time-dependent cytotoxicity on peripheral blood mononuclear cells (PBMC) from CLL patients. Interestingly, Aplidin effect was markedly higher on monocytes compared to T lymphocytes, NK cells or the malignant B-cell clone. Hence, we next evaluated Aplidin activity on nurse-like cells (NLC) which represent a cell subset differentiated from monocytes that favors leukemic cell progression through pro-survival signals. NLC were highly sensitive to Aplidin and, more importantly, their death indirectly decreased neoplasic clone viability. The mechanisms of Aplidin-induced cell death in monocytic cells involved activation of caspase-3 and subsequent PARP fragmentation, indicative of death via apoptosis. Aplidin also showed synergistic activity when combined with fludarabine or cyclophosphamide. Taken together, our results show that Aplidin affects the viability of leukemic cells in two different ways: inducing a direct effect on the malignant B-CLL clone; and indirectly, by modifying the microenvironment that allows tumor growth.

Human health benefits supplied by Mediterranean marine biodiversity

This paper summarizes the overall benefits supplied by Mediterranean marine biodiversity to human health and highlights the anthropogenic and environmental causes that are threatening these benefits. First, the Mediterranean Sea is a valuable source of seafood, which is an important component of the so-called "Mediterranean diet". This type of diet has several health benefits, including cardio and cancer protective effects, which are attributed to the high intake of seafood-derived n-3 (omega-3) fatty acids. Second, the Mediterranean marine organisms, particularly the benthic ones, have furnished a large variety of bioactive metabolites, some of which are being developed into new drugs to threat major human diseases such as cancer. Third, the Mediterranean coastal areas provide environments for practising maritime leisure activities that provide physical and psychological benefits to users. Despite all this, fishing, tourism, contamination and sea warming are deteriorating this rich marine ecosystem, which needs to be protected to assure human welfare.

Marine pharmacology in 2005-2006: antitumour and cytotoxic compounds

During 2005 and 2006, marine pharmacology research directed towards the discovery and development of novel antitumour agents was reported in 171 peer-reviewed articles. The purpose of this article is to present a structured review of the antitumour and cytotoxic properties of 136 marine natural products, many of which are novel compounds that belong to diverse structural classes, including polyketides, terpenes, steroids and peptides. The organisms yielding these bioactive marine compounds included invertebrate animals, algae, fungi and bacteria. Antitumour pharmacological studies were conducted with 42 structurally defined marine natural products in a number of experimental and clinical models which further defined their mechanisms of action. Particularly potent in vitro cytotoxicity data generated with murine and human tumour cell lines were reported for 94 novel marine chemicals with as yet undetermined mechanisms of action. Noteworthy is the fact that marine anticancer research was sustained by a global collaborative effort, involving researchers from Australia, Belgium, Benin, Brazil, Canada, China, Egypt, France, Germany, India, Indonesia, Italy, Japan, Mexico, the Netherlands, New Zealand, Panama, the Philippines, Slovenia, South Korea, Spain, Sweden, Taiwan, Thailand, United Kingdom (UK) and the United States of America (USA). Finally, this 2005-2006 overview of the marine pharmacology literature highlights the fact that the discovery of novel marine antitumour agents continued at the same active pace as during 1998-2004.

Low molecular weight protein tyrosine phosphatase genetic polymorphism and susceptibility to cancer development

Low molecular weight protein tyrosine phosphatases (LMW-PTPs) are a family of 18-kDa enzymes involved in cell growth regulation. Human acid phosphatase 1 (ACP1) is genetically polymorphic, and three common alleles segregating at the ACP1 locus on the short arm of chromosome 2 give rise to six phenotypes. Each allele appears to encode two electrophoretically different isozymes, fast and slow, which are produced in allele-specific ratios. Fast isozymes are related with cytoskeletal organization, cellular organization, and spreading. Slow isozymes are associated with growth factor receptors and dephosphorylation. In this study, ACP1 genetic polymorphisms were determined by polymerase chain reaction-restriction fragment length polymorphism on 74 subjects with various cancers; the control group was 236 healthy subjects randomly selected. With genotypes cumulated according to fast isoform concentration, [A + AC] < [AB + BC] < [BB], subjects with cancer presented an increase of fast isozyme concentration (BB 38.2%; P = 0.002, chi2), relative to the control sample (19.8%). The increase of fast isozyme concentration increased the invasive capacity of cancer cells, whereas a decrease of slow isozyme concentration in cancer did not cause growth inhibition and so resulted in cancer cell proliferation.

Marine natural products

This review covers the literature published in 2006 for marine natural products, with 758 citations (534 for the period January to December 2006) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, cnidaria, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (779 for 2006), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Plitidepsin has a dual effect inhibiting cell cycle and inducing apoptosis via Rac1/c-Jun NH2-terminal kinase activation in human melanoma cells

Melanoma is the most aggressive skin cancer and a serious health problem worldwide because of its increasing incidence and the lack of satisfactory chemotherapy for late stages of the disease. The marine depsipeptide Aplidin (plitidepsin) is an antitumoral agent under phase II clinical development against several neoplasias, including melanoma. We report that plitidepsin has a dual effect on the human SK-MEL-28 and UACC-257 melanoma cell lines; at low concentrations (</=45 nM), it inhibits the cell cycle by inducing G(1) and G(2)/M arrest, whereas at higher concentrations it induces apoptosis as assessed by poly-(ADP-ribose) polymerase cleavage and the appearance of a hypodiploid peak in flow cytometry analyses. Plitidepsin activates Rac1 GTPase and c-Jun NH(2)-terminal kinase (JNK). In addition, it induces AKT and p38 mitogen-activated protein kinase (MAPK) phosphorylation. By using inhibitors, we found that JNK and p38 MAPK activation depends on Rac1 but not on phosphatidylinositol 3-kinase (PI3K), whereas AKT activation is independent of Rac1 but requires PI3K activity. Plitidepsin cytotoxicity diminishes by Rac1 inhibition or by the blockage of JNK and p38 MAPK using 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), but not by PI3K inhibition using wortmannin or 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002). It is remarkable that plitidepsin and dacarbazine, the alkylating agent most active for treating metastatic melanoma, show a synergistic antiproliferative effect that was paralleled at the level of JNK activation. These results indicate that Rac1/JNK activation is critical for cell cycle arrest and apoptosis induction by plitidepsin in melanoma cells. They also support the combined use of plitidepsin and dacarbazine in in vivo studies.

Aplidin synergizes with cytosine arabinoside: functional relevance of mitochondria in Aplidin-induced cytotoxicity

Aplidin (plitidepsin) is a novel marine-derived antitumor agent presently undergoing phase II clinical trials in hematological malignancies and solid tumors. Lack of bone marrow toxicity has encouraged further development of this drug for treatment of leukemia and lymphoma. Multiple signaling pathways have been shown to be involved in Aplidin-induced apoptosis and cell cycle arrest in G1 and G2 phase. However, the exact mechanism(s) of Aplidin action remains to be elucidated. Here we demonstrate that mitochondria-associated or -localized processes are the potential cellular targets of Aplidin. Whole genome gene-expression profiling (GEP) revealed that fatty acid metabolism, sterol biosynthesis and energy metabolism, including the tricarboxylic acid cycle and ATP synthesis are affected by Aplidin treatment. Moreover, mutant MOLT-4, human leukemia cells lacking functional mitochondria, were found to be resistant to Aplidin. Cytosine arabinoside (araC), which also generates oxidative stress but does not affect the ATP pool, showed synergism with Aplidin in our leukemia and lymphoma models in vitro and in vivo. These studies provide new insights into the mechanism of action of Aplidin. The efficacy of the combination of Aplidin and araC is currently being evaluated in clinical phase I/II program for the treatment of patients with relapsed leukemia and high-grade lymphoma.