Nose-to-brain selective drug delivery to glioma via ferritin-based nanovectors reduces tumor growth and improves survival rate

Gliomas are among the most fatal tumors, and the available therapeutic options are very limited. Additionally, the blood-brain barrier (BBB) prevents most drugs from entering the brain. We designed and produced a ferritin-based stimuli-sensitive nanocarrier with high biocompatibility and water solubility. It can incorporate high amounts of the potent topoisomerase 1 inhibitor Genz-644282. Here, we show that this nanocarrier, named The-0504, can cross the BBB and specifically deliver the payload to gliomas that express high amounts of the ferritin/transferrin receptor TfR1 (CD71). Intranasal or intravenous administration of The-0504 both reduce tumor growth and improve the survival rate of glioma-bearing mice. However, nose-to-brain administration is a simpler and less invasive route that may spare most of the healthy tissues compared to intravenous injections. For this reason, the data reported here could pave the way towards a new, safe, and direct ferritin-based drug delivery method for brain diseases, especially brain tumors.

AI is a viable alternative to high throughput screening: a 318-target study

High throughput screening (HTS) is routinely used to identify bioactive small molecules. This requires physical compounds, which limits coverage of accessible chemical space. Computational approaches combined with vast on-demand chemical libraries can access far greater chemical space, provided that the predictive accuracy is sufficient to identify useful molecules. Through the largest and most diverse virtual HTS campaign reported to date, comprising 318 individual projects, we demonstrate that our AtomNet® convolutional neural network successfully finds novel hits across every major therapeutic area and protein class. We address historical limitations of computational screening by demonstrating success for target proteins without known binders, high-quality X-ray crystal structures, or manual cherry-picking of compounds. We show that the molecules selected by the AtomNet® model are novel drug-like scaffolds rather than minor modifications to known bioactive compounds. Our empirical results suggest that computational methods can substantially replace HTS as the first step of small-molecule drug discovery.

Widespread in vivo efficacy of The-0504: A conditionally-activatable nanoferritin for tumor-agnostic targeting of CD71-expressing cancers

Background

Cancer is still among the leading causes of death all over the world. Improving chemotherapy and minimizing associated toxicities are major unmet medical needs. Recently, we provided a preliminary preclinical evaluation of a human ferritin (HFt)-based drug carrier (The-0504) that selectively delivers the wide-spectrum topoisomerase I inhibitor Genz-644282 to CD71-expressing tumors. The-0504 has so far been evaluated on four different human tumor xenotransplant models (breast, colorectal, pancreatic and liver cancers).

Methods

Herein, we extend our studies, by: (a) testing DNA damage in vitro, (b) treating eight additional tumor xenograft models in vivo with The-0504; (c) performing pharmacokinetic (PK) studies in rats; and (d) evaluating The-0504 anti-tumor xenotransplant efficacy by optimizing its administration schedule based on PK considerations.

Results

Immunofluorescence demonstrated that The-0504 induces foci expressing the DNA double-strand break marker γH2AX. Expression increases up to 4-fold and is more persistent as compared to free Genz-644282. In vivo studies confirmed a remarkable anti-tumor activity of The-0504, resulting in tumor eradication in most murine xenograft models, regardless of embryological origin (e.g. epithelial, mesenchymal or neuroendocrine), and molecular subtypes. PK studies demonstrated a long persistence of The-0504 in rat serum (half-life of about 40 h as compared to 15 h of the free drug), with a 400-fold increase in peak concentrations as compared to the free drug. On this basis, we reduced The-0504 administration frequency from twice to once per week, with no appreciable loss in therapeutic efficacy in mice.

Conclusion

The results presented here confirm that The-0504 is highly active against several human tumor xenotransplants, even when administered less frequently than previously reported. The-0504 may be a good candidate for further clinical development in a tumor histotype-agnostic setting.

Doxorubicin and other anthracyclines in cancers: Activity, chemoresistance and its overcoming

Anthracyclines have been important and effective treatments against a number of cancers since their discovery. However, their use in therapy has been complicated by severe side effects and toxicity that occur during or after treatment, including cardiotoxicity. The mode of action of anthracyclines is complex, with several mechanisms proposed. It is possible that their high toxicity is due to the large set of processes involved in anthracycline action. The development of resistance is a major barrier to successful treatment when using anthracyclines. This resistance is based on a series of mechanisms that have been studied and addressed in recent years. This work provides an overview of the anthracyclines used in cancer therapy. It discusses their mechanisms of activity, toxicity, and chemoresistance, as well as the approaches used to improve their activity, decrease their toxicity, and overcome resistance.

Bcl-2 family inhibitors sensitize human cancer models to therapy

BH3 mimetics, targeting the Bcl-2 family anti-apoptotic proteins, represent a promising therapeutic opportunity in cancers. ABT-199, the first specific Bcl-2 inhibitor, was approved by FDA for the treatment of several hematological malignancies. We have recently discovered IS21, a novel pan BH3 mimetic with preclinical antitumor activity in several tumor types. Here, we evaluated the efficacy of IS21 and other BH3 mimetics, both as single agents and combined with the currently used antineoplastic agents in T-cell acute lymphoblastic leukemia, ovarian cancer, and melanoma. IS21 was found to be active in T-cell acute lymphoblastic leukemia, melanoma, lung, pancreatic, and ovarian cancer cell lines. Bcl-xL and Mcl-1 protein levels predicted IS21 sensitivity in melanoma and ovarian cancer, respectively. Exploring IS21 mechanism of action, we found that IS21 activity depends on the presence of BAX and BAK proteins: complexes between Bcl-2 and Bcl-xL proteins and their main binding partners were reduced after IS21 treatment. In combination experiments, BH3 mimetics sensitized leukemia cells to chemotherapy, ovarian cancer cells and melanoma models to PARP and MAPK inhibitors, respectively. We showed that this enhancing effect was related to the potentiation of the apoptotic pathway, both in hematologic and solid tumors. In conclusion, our data suggest the use of inhibitors of anti-apoptotic proteins as a therapeutic strategy to enhance the efficacy of anticancer treatment.

Novel 1,4-Dihydropyridines as Specific Binders and Activators of SIRT3 Impair Cell Viability and Clonogenicity and Downregulate Hypoxia-Induced Targets in Cancer Cells

The mitochondrial SIRT3 modulates several biological pathways such as cancer, metabolism, and hypoxia-related diseases. Recently, we discovered new 1,4-dihydropyridines, compounds 2 and 3, the latter being a SIRT3-specific activator. In the present work, a novel 2- and 3-related small series of compounds have been developed, with 3c displaying the strongest SIRT3 binding and activation, with a K_D of 29 μM and 387% of enzyme activation. Differently, 3d was the best in enhancing glutamate dehydrogenase activity and deacetylating K68- and K122-acMnSOD in triple-negative MDA-MB-231 breast cancer cells. Tested in CAL-62 thyroid cancer and MDA-MB-231 cells, 3d displayed the strongest time- and dose-dependent reduction of cell viability and clonogenicity at a single-digit micromolar level, along with cell death, in both normoxia and hypoxia conditions. Moreover, 3d downregulated not only hypoxia-induced factors, such as HIF-1α, EPAS-1, and CA-IX, but also epithelial-mesenchymal transition master regulators and extracellular matrix components such as SNAIL1, ZEB1, SLUG, COL1A2, MMP2, and MMP9, markedly hampering MDA-MB-231 cell migration.

Sorcin promotes migration in cancer and regulates the EGF-dependent EGFR signaling pathways

The epidermal growth factor receptor (EGFR) is one of the main tumor drivers and is an important therapeutic target for many cancers. Calcium is important in EGFR signaling pathways. Sorcin is one of the most important calcium sensor proteins, overexpressed in many tumors, that promotes cell proliferation, migration, invasion, epithelial-to-mesenchymal transition, malignant progression and resistance to chemotherapeutic drugs. The present work elucidates a functional mechanism that links calcium homeostasis to EGFR signaling in cancer. Sorcin and EGFR expression are significantly correlated and associated with reduced overall survival in cancer patients. Mechanistically, Sorcin directly binds EGFR protein in a calcium-dependent fashion and regulates calcium (dys)homeostasis linked to EGF-dependent EGFR signaling. Moreover, Sorcin controls EGFR proteostasis and signaling and increases its phosphorylation, leading to increased EGF-dependent migration and invasion. Of note, silencing of Sorcin cooperates with EGFR inhibitors in the regulation of migration, highlighting calcium signaling pathway as an exploitable target to enhance the effectiveness of EGFR-targeting therapies.

Investigation of the Entry Pathway and Molecular Nature of σ1 Receptor Ligands

The σ1 receptor (σ1-R) is an enigmatic endoplasmic reticulum resident transmembrane protein implicated in a variety of central nervous system disorders and whose agonists have neuroprotective activity. In spite of σ1-R’s physio-pathological and pharmacological importance, two of the most important features required to fully understand σ1-R function, namely the receptor endogenous ligand(s) and the molecular mechanism of ligand access to the binding site, have not yet been unequivocally determined. In this work, we performed molecular dynamics (MD) simulations to help clarify the potential route of access of ligand(s) to the σ1-R binding site, on which discordant results had been reported in the literature. Further, we combined computational and experimental procedures (i.e., virtual screening (VS), electron density map fitting and fluorescence titration experiments) to provide indications about the nature of σ1-R endogenous ligand(s). Our MD simulations on human σ1-R suggested that ligands access the binding site through a cavity that opens on the protein surface in contact with the membrane, in agreement with previous experimental studies on σ1-R from Xenopus laevis. Additionally, steroids were found to be among the preferred σ1-R ligands predicted by VS, and 16,17-didehydroprogesterone was shown by fluorescence titration to bind human σ1-R, with significantly higher affinity than the prototypic σ1-R ligand pridopidine in the same essay. These results support the hypothesis that steroids are among the most important physiological σ1-R ligands.

Characterization of the Escherichia coli pyridoxal 5'-phosphate homeostasis protein (YggS): Role of lysine residues in PLP binding and protein stability

The pyridoxal 5'-phosphate (PLP) homeostasis protein (PLPHP) is a ubiquitous member of the COG0325 family with apparently no catalytic activity. Although the actual cellular role of this protein is unknown, it has been observed that mutations of the PLPHP encoding gene affect the activity of PLP-dependent enzymes, B6 vitamers and amino acid levels. Here we report a detailed characterization of the Escherichia coli ortholog of PLPHP (YggS) with respect to its PLP binding and transfer properties, stability, and structure. YggS binds PLP very tightly and is able to slowly transfer it to a model PLP-dependent enzyme, serine hydroxymethyltransferase. PLP binding to YggS elicits a conformational/flexibility change in the protein structure that is detectable in solution but not in crystals. We serendipitously discovered that the K36A variant of YggS, affecting the lysine residue that binds PLP at the active site, is able to bind PLP covalently. This observation led us to recognize that a number of lysine residues, located at the entrance of the active site, can replace Lys36 in its PLP binding role. These lysines form a cluster of charged residues that affect protein stability and conformation, playing an important role in PLP binding and possibly in YggS function.

Optimization of Potent and Specific Trypanothione Reductase Inhibitors: A Structure-Based Drug Discovery Approach

Leishmania spp. are responsible for up to 1 million new cases each year. The current therapeutic arsenal against Leishmania is largely inadequate, and there is an urgent need for better drugs. Trypanothione reductase (TR) represents a druggable target since it is essential for the parasite and not shared by the human host. Here, we report the optimization of a novel class of potent and selective LiTR inhibitors realized through a concerted effort involving X-ray crystallography, synthesis, structure-activity relationship (SAR) investigation, molecular modeling, and in vitro phenotypic assays. 5-Nitrothiophene-2-carboxamides 3, 6e, and 8 were among the most potent and selective TR inhibitors identified in this study. 6e and 8 displayed leishmanicidal activity in the low micromolar range coupled to SI > 50. Our studies could pave the way for the use of TR inhibitors not only against leishmaniasis but also against other trypanosomatidae due to the structural similarity of TR enzymes.

Innovative Approach for a Classic Target: Fragment Screening on Trypanothione Reductase Reveals New Opportunities for Drug Design

Trypanothione reductase (TR) is a key factor in the redox homeostasis of trypanosomatid parasites, critical for survival in the hostile oxidative environment generated by the host to fight infection. TR is considered an attractive target for the development of new trypanocidal agents as it is essential for parasite survival but has no close homolog in humans. However, the high efficiency and turnover of TR challenging targets since only potent inhibitors, with nanomolar IC50, can significantly affect parasite redox state and viability. To aid the design of effective compounds targeting TR, we performed a fragment-based crystal screening at the Diamond Light Source XChem facility using a library optimized for follow-up synthesis steps. The experiment, allowing for testing over 300 compounds, resulted in the identification of 12 new ligands binding five different sites. Interestingly, the screening revealed the existence of an allosteric pocket close to the NADPH binding site, named the “doorstop pocket” since ligands binding at this site interfere with TR activity by hampering the “opening movement” needed to allow cofactor binding. The second remarkable site, known as the Z-site, identified by the screening, is located within the large trypanothione cavity but corresponds to a region not yet exploited for inhibition. The fragments binding to this site are close to each other and have some remarkable features making them ideal for follow-up optimization as a piperazine moiety in three out of five fragments.

ERp57 Chaperon Protein Protects Neuronal Cells from Aβ-induced toxicity

Alzheimer's disease (AD) is a neurodegenerative disorder whose main pathological hallmark is the accumulation of Amyloid-β peptide (Aβ) in the form of senile plaques. Aβ can cause neurodegeneration and disrupt cognitive functions by several mechanisms, including oxidative stress. ERp57 is a protein disulfide isomerase involved in the cellular stress response and known to be present in the cerebrospinal fluid of normal individuals as a complex with Aβ peptides, suggesting that it may be a carrier protein which prevents aggregation of Aβ. Although several studies show ERp57 involvement in neurodegenerative diseases, no clear mechanism of action has been identified thus far. In this work we gain insights into the interaction of Aβwith ERp57, with a special focus on the contribution of ERp57 to the defence system of the cell. Here we show that recombinant ERp57 directly interacts with the Aβ_25-35 fragment in vitro with high affinityvia two in silico-predicted main sites of interaction. Furthermore, we used human neuroblastoma cells to show that short-term Aβ_25-35 treatment induces ERp57 decrease in intracellular protein levels, different intracellular localization and ERp57 secretion in the cultured medium. Finally, we demonstrate that recombinant ERp57 counteracts the toxic effects of Aβ_25-35 and restores cellular viability, by preventing Aβ_25-35 aggregation. Overall, the present study shows thatextracellular ERp57 can exert a protective effect from Aβ toxicity and highlights it as a possible therapeutic tool in the treatment of AD.

Targeting the anti-apoptotic Bcl-2 family proteins: machine learning virtual screening and biological evaluation of new small molecules

Bcl-2 family anti-apoptotic proteins are overexpressed in several hematological and solid tumors, and contribute to tumor formation, progression, and resistance to therapy. They represent a promising therapeutic avenue to explore for cancer treatment. Venetoclax, a Bcl-2 inhibitor is currently used for hematological malignancies or is undergoing clinical trials for either hematological or solid tumors. Despite these progresses, ongoing efforts are focusing on the identification and development of new molecules targeting Bcl-2 protein and/or other family members.

Methods: Machine learning guided virtual screening followed by surface plasmon resonance, molecular docking and pharmacokinetic analyses were performed to identify new inhibitors of anti-apoptotic members of Bcl-2 family and their pharmacokinetic profile. The sensitivity of cancer cells from different origin to the identified compounds was evaluated both in in vitro (cell survival, apoptosis, autophagy) and in vivo (tumor growth in nude mice) preclinical models.

Results: IS20 and IS21 were identified as potential new lead compounds able to bind Bcl-2, Bcl-xL and Mcl-1 recombinant proteins. Molecular docking investigation indicated IS20 and IS21 could bind into the Beclin-1 BH3 binding site of wild type Bcl-2, Bcl-xL and Mcl-1 proteins. In particular, although the IS21 docked conformation did not show a unique binding mode, it clearly showed its ability in flexibly adapting to either BH3 binding sites. Moreover, both IS20 and IS21 reduced cell viability, clonogenic ability and tumor sphere formation, and induced apoptosis in leukemic, melanoma and lung cancer cells. Autophagosome formation and maturation assays demonstrated induction of autophagic flux after treatment with IS20 or IS21. Experiments with z-VAD-fmk, a pan-caspase inhibitor, and chloroquine, a late-stage autophagy inhibitor, demonstrated the ability of the two compounds to promote apoptosis by autophagy. IS21 also reduced in vivo tumor growth of both human leukemia and melanoma models.

Conclusion: Virtual screening coupled with in vitro and in vivo experimental data led to the identification of two new promising inhibitors of anti-apoptotic proteins with good efficacy in the binding to recombinant Bcl-2, Bcl-xL and Mcl-1 proteins, and against different tumor histotypes.

Neuropilin-1 is required for endothelial cell adhesion to soluble vascular endothelial growth factor receptor 1

Neuropilin‐1 (NRP‐1) is a semaphorin receptor involved in neuron guidance, and a co‐receptor for selected isoforms of the vascular endothelial growth factor (VEGF) family. NRP‐1 binding to several VEGF‐A isoforms promotes growth factor interaction with VEGF receptor (VEGFR)‐2, increasing receptor phosphorylation. Additionally, NRP‐1 directly interacts with VEGFR‐1, but this interaction competes with NRP‐1 binding to VEGF‐A165 and does not enhance VEGFR‐1 activation. In this work, we investigated in detail the role of NRP‐1 interaction with the soluble isoform of VEGFR‐1 (sVEGFR‐1) in angiogenesis. sVEGFR‐1 acts both as a decoy receptor for VEGFs and as an extracellular matrix protein directly binding to α5β1 integrin on endothelial cells. By combining cell adhesion assays and surface plasmon resonance experiments on purified proteins, we found that sVEGFR‐1/NRP‐1 interaction is required both for α5β1 integrin binding to sVEGFR‐1 and for endothelial cell adhesion to a sVEGFR‐1‐containing matrix. We also found that a previously reported anti‐angiogenic peptide (Flt_2‐11), which maps in the second VEGFR‐1 Ig‐like domain, specifically binds NRP‐1 and inhibits NRP‐1/sVEGFR‐1 interaction, a process that likely contributes to its anti‐angiogenic activity. In view of potential translational applications, we developed a five‐residue‐long peptide, derived from Flt_2‐11, which has the same ability as the parent Flt_2‐11 peptide to inhibit cell adhesion to, and migration towards, sVEGFR‐1. Therefore, the Flt_2‐5 peptide represents a potential anti‐angiogenic compound per se, as well as an attractive lead for the development of novel angiogenesis inhibitors acting with a different mechanism with respect to currently used therapeutics, which interfere with VEGF‐A165 binding.

Known Drugs Identified by Structure-Based Virtual Screening Are Able to Bind Sigma-1 Receptor and Increase Growth of Huntington Disease Patient-Derived Cells

Huntington disease (HD) is a devastating and presently untreatable neurodegenerative disease characterized by progressively disabling motor and mental manifestations. The sigma-1 receptor (σ1R) is a protein expressed in the central nervous system, whose 3D structure has been recently determined by X-ray crystallography and whose agonists have been shown to have neuroprotective activity in neurodegenerative diseases. To identify therapeutic agents against HD, we have implemented a drug repositioning strategy consisting of: (i) Prediction of the ability of the FDA-approved drugs publicly available through the ZINC database to interact with σ1R by virtual screening, followed by computational docking and visual examination of the 20 highest scoring drugs; and (ii) Assessment of the ability of the six drugs selected by computational analyses to directly bind purified σ1R in vitro by Surface Plasmon Resonance and improve the growth of fibroblasts obtained from HD patients, which is significantly impaired with respect to control cells. All six of the selected drugs proved able to directly bind purified σ1R in vitro and improve the growth of HD cells from both or one HD patient. These results support the validity of the drug repositioning procedure implemented herein for the identification of new therapeutic tools against HD.

Structural basis of ubiquitination mediated by protein splicing in early Eukarya

BACKGROUND

Inteins are intervening proteins, which are known to perform protein splicing. The reaction results in the production of an intein domain and an inteinless protein, which shows no trace of the insertion. BIL2 is part of the polyubiquitin locus of Tetrahymena thermophila (BUBL), where two bacterial-intein-like (BIL) domains lacking the C + 1 nucleophile, are flanked by two independent ubiquitin-like domains (ubl4/ubl5).

METHODS

We solved the X-ray structures of BIL2 in both the inactive and unprecedented, zinc-induced active, forms. Then, we characterized by mass spectrometry the BUBL splicing products in the absence and in the presence of T.thRas-GTPase. Finally, we investigated the effect of ubiquitination on T.thRas-GTPase by molecular dynamics simulations.

RESULTS

The structural analysis demonstrated that zinc-induced conformational change activates protein splicing. Moreover, mass spectrometry characterization of the splicing products shed light on the possible function of BIL2, which operates as a "single-ubiquitin-dispensing-platform", allowing the conjugation, via isopeptide bond formation (K(εNH₂)-C-ter), of ubl4 to either ubl5 or T.thRas-GTPase. Lastly, we demonstrated that T.thRas-GTPase ubiquitination occurs in proximity of the nucleotide binding pocket and stabilizes the protein active state.

CONCLUSIONS

We demonstrated that BIL2 is activated by zinc and that protein splicing induced by this intein does not take place through classical or aminolysis mechanisms but via formation of a covalent isopeptide bond, causing the ubiquitination of endogenous substrates such as T.thRas-GTPase.

GENERAL SIGNIFICANCE

In this "enzyme-free" ubiquitination mechanism the isopeptide formation, which canonically requires E1-E2-E3 enzymatic cascade and constitutes the alphabet of ubiquitin biology, is achieved in a single, concerted step without energy consumption.

Taxanes in cancer treatment: Activity, chemoresistance and its overcoming

Since 1984, when paclitaxel was approved by the FDA for the treatment of advanced ovarian carcinoma, taxanes have been widely used as microtubule-targeting antitumor agents. However, their historic classification as antimitotics does not describe all their functions. Indeed, taxanes act in a complex manner, altering multiple cellular oncogenic processes including mitosis, angiogenesis, apoptosis, inflammatory response, and ROS production. On the one hand, identification of the diverse effects of taxanes on oncogenic signaling pathways provides opportunities to apply these cytotoxic drugs in a more rational manner. On the other hand, this may facilitate the development of novel treatment modalities to surmount anticancer drug resistance. In the latter respect, chemoresistance remains a major impediment which limits the efficacy of antitumor chemotherapy. Taxanes have shown impact on key molecular mechanisms including disruption of mitotic spindle, mitosis slippage and inhibition of angiogenesis. Furthermore, there is an emerging contribution of cellular processes including autophagy, oxidative stress, epigenetic alterations and microRNAs deregulation to the acquisition of taxane resistance. Hence, these two lines of findings are currently promoting a more rational and efficacious taxane application as well as development of novel molecular strategies to enhance the efficacy of taxane-based cancer treatment while overcoming drug resistance. This review provides a general and comprehensive picture on the use of taxanes in cancer treatment. In particular, we describe the history of application of taxanes in anticancer therapeutics, the synthesis of the different drugs belonging to this class of cytotoxic compounds, their features and the differences between them. We further dissect the molecular mechanisms of action of taxanes and the molecular basis underlying the onset of taxane resistance. We further delineate the possible modalities to overcome chemoresistance to taxanes, such as increasing drug solubility, delivery and pharmacokinetics, overcoming microtubule alterations or mitotic slippage, inhibiting drug efflux pumps or drug metabolism, targeting redox metabolism, immune response, and other cellular functions.

Isolation and preliminary characterization of a human 'phage display'-derived antibody against neural adhesion molecule-1 antigen interfering with fibroblast growth factor receptor-1 binding

BACKGROUND

The NCAM or CD56 antigen is a cell surface glycoprotein belonging to the immunoglobulin super-family involved in cell-cell and cell-matrix adhesion. NCAM is also over-expressed in many tumour types and is considered a tumour associated antigen, even if its role and biological mechanisms implicated in tumour progression and metastasis have not yet to be elucidated. In particular, it is quite well documented the role of the interaction between the NCAM protein and the fibroblast growth factor receptor-1 in metastasis and invasion, especially in the ovarian cancer progression.

OBJECTIVE

Here we describe the isolation and preliminary characterization of a novel human anti-NCAM single chain Fragment variable antibody able to specifically bind NCAM-expressing cells, including epithelial ovarian cancer cells.

METHODS

The antibody was isolate by phage display selection and was characterized by ELISA, FACS analysis and SPR experiments. Interference in EOC migration was analyzed by scratch test.

RESULTS

It binds a partially linear epitope lying in the membrane proximal region of two fibronectin-like domains with a dissociation constant of 3.43 × 10-8 M. Interestingly, it was shown to interfere with the NCAM-FGFR1 binding and to partially decrease migration of EOC cells.

CONCLUSIONS

According to our knowledge, this is the first completely human antibody able to interfere with this newly individuated cancer mechanism.

Sorcin is an early marker of neurodegeneration, Ca2+ dysregulation and endoplasmic reticulum stress associated to neurodegenerative diseases

Dysregulation of calcium signaling is emerging as a key feature in the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and Huntington’s disease (HD), and targeting this process may be therapeutically beneficial. Under this perspective, it is important to study proteins that regulate calcium homeostasis in the cell. Sorcin is one of the most expressed calcium-binding proteins in the human brain; its overexpression increases endoplasmic reticulum (ER) calcium concentration and decreases ER stress in the heart and in other cellular types. Sorcin has been hypothesized to be involved in neurodegenerative diseases, since it may counteract the increased cytosolic calcium levels associated with neurodegeneration. In the present work, we show that Sorcin expression levels are strongly increased in cellular, animal, and human models of AD, PD, and HD, vs. normal cells. Sorcin partially colocalizes with RyRs in neurons and microglia cells; functional experiments with microsomes containing high amounts of RyR2 and RyR3, respectively, show that Sorcin is able to regulate these ER calcium channels. The molecular basis of the interaction of Sorcin with RyR2 and RyR3 is demonstrated by SPR. Sorcin also interacts with other ER proteins as SERCA2 and Sigma-1 receptor in a calcium-dependent fashion. We also show that Sorcin regulates ER calcium transients: Sorcin increases the velocity of ER calcium uptake (increasing SERCA activity). The data presented here demonstrate that Sorcin may represent both a novel early marker of neurodegenerative diseases and a response to cellular stress dependent on neurodegeneration.

Discovery of the First Human Arylsulfatase A Reversible Inhibitor Impairing Mouse Oocyte Fertilization

Arylsulfatase A (ARSA) plays a crucial role in the reproduction of mammals due to its involvement in the specific gamete interaction preceding sperm and egg fusion leading to fertilization. Recently, it has been shown that zona pellucida (ZP) sperm binding and in vivo fertilization in mice are markedly hampered by using a specific anti-ARSA antibody. Herein, the design and discovery of the first ARSA small molecule inhibitor based on a coumarin-containing polycycle are presented. Through a structure-based approach applied on our in-house library, compound 1r was identified as an ARSA reversible inhibitor (ARSAi); then its activity was validated through both surface plasmon resonance and biochemical inhibition experiments, the first providing a K_D value of 21 μM and the latter an IC₅₀ value of 13.2 μM. Further investigations highlighted that compound 1r induced 20% sperm death at 25 μM and also impaired sperm motility; nevertheless both the effects were mediated by ROS production, since they were rescued by the cotreatment of 1r and N-acetyl cysteine (NAC). Interestingly, while 1r was not able to hamper the ZP/sperm binding, it markedly decreased the in vitro oocyte fertilization by mouse sperm up to 60%. Notably, this effect was not hampered by 1r/NAC coadministration, hence allowing the ruling out of an ROS-dependent mechanism. In conclusion, herein is reported the first ever hit of ARSAi as a chemical tool that will enable better exploration of ARSA's biological role in fertilization as well as provide a starting point for developing 1r structure optimization aimed at increasing enzyme inhibition potency but also providing a deeper understanding of the involvement of ARSA in the fertilization pathway mechanism.

Spiro-containing derivatives show antiparasitic activity against Trypanosoma brucei through inhibition of the trypanothione reductase enzyme

Trypanothione reductase (TR) is a key enzyme that catalyzes the reduction of trypanothione, an antioxidant dithiol that protects Trypanosomatid parasites from oxidative stress induced by mammalian host defense systems. TR is considered an attractive target for the development of novel anti-parasitic agents as it is essential for parasite survival but has no close homologue in humans. We report here the identification of spiro-containing derivatives as inhibitors of TR from Trypanosoma brucei (TbTR), the parasite responsible for Human African Trypanosomiasis. The hit series, identified by high throughput screening, was shown to bind TbTR reversibly and to compete with the trypanothione (TS₂) substrate. The prototype compound 1 from this series was also found to impede the growth of Trypanosoma brucei parasites in vitro. The X-ray crystal structure of TbTR in complex with compound 1 solved at 1.98 Å allowed the identification of the hydrophobic pocket where the inhibitor binds, placed close to the catalytic histidine (His 461’) and lined by Trp21, Val53, Ile106, Tyr110 and Met113. This new inhibitor is specific for TbTR and no activity was detected against the structurally similar human glutathione reductase (hGR). The central spiro scaffold is known to be suitable for brain active compounds in humans thus representing an attractive starting point for the future treatment of the central nervous system stage of T. brucei infections.

Trypanosoma brucei is a parasite responsible for neglected pathologies such as human African trypanosomiasis, also known as sleeping sickness. This disease is endemic in sub-Saharan Africa, with 70 million people at risk of infection. Current treatments for this type of disease are limited by their toxicity, administration in endemic countries and treatment resistance. Therapies against infectious diseases typically rely on targeting one or more components of the parasite that are not present in humans to ensure the best possible therapeutic window. In this case we aimed at targeting the Trypanosoma brucei trypanothione reductase (TR), one enzyme that synthesize the reduced trypanothione a key molecule for preserving the parasite redox balance. This enzyme does not exist in humans that have glutathione instead of trypanothione. Past attempts to identify novel inhibitors of this target has failed to generate drug-like molecules. To overcome this limitation we employed a recent, higher quality, TR activity assay to test a collection of compounds previously reported to be active against these parasites. This approach led to the identification and validation of a new chemotype with a unique mode of inhibition of TR. This chemical series is a drug-like starting point, in fact its core (spiro) is present in drugs approved for human use.

Targeting Trypanothione Reductase, a Key Enzyme in the Redox Trypanosomatid Metabolism, to Develop New Drugs against Leishmaniasis and Trypanosomiases

The protozoans Leishmania and Trypanosoma, belonging to the same Trypanosomatidae family, are the causative agents of Leishmaniasis, Chagas disease, and human African trypanosomiasis. Overall, these infections affect millions of people worldwide, posing a serious health issue as well as socio-economical concern. Current treatments are inadequate, mainly due to poor efficacy, toxicity, and emerging resistance; therefore, there is an urgent need for new drugs.

Exogenous peptides are able to penetrate human cell and mitochondrial membranes, stabilize mitochondrial tRNA structures, and rescue severe mitochondrial defects

Mutations in mitochondrial transfer RNA (mt-tRNA) genes are responsible for a wide range of syndromes, for which no effective treatment is available. We previously reported that transfection of the nucleotide sequence encoding for the 16-residue β32_33 peptide from mitochondrial leucyl-tRNA synthetase ameliorates the cell phenotype caused by the mitochondrial tRNA mutations. In this work, we demonstrated that both the β32_33 peptide linked with the known (L)-Phe-(D)-Arg-(L)-Phe-(L)-Lys (FrFK) mitochondrial penetrating sequence and, strikingly, the β32_33 peptide per se, are able to penetrate both the plasma and mitochondrial membranes and exert the rescuing activity when exogenously administered to cells bearing the mutations m.3243A > G and m.8344A > G. These mutations are responsible for the most common and severe mt-tRNA-related diseases. In addition, we dissected the molecular determinants of constructs activity by showing that both the order of amino acids along the sequence and presence of positive charges are essential determinants of the peptide activity in cells and mt-tRNA structures stabilization in vitro. In view of future in vivo studies, this information may be required to design of β32_33 peptide-mimetic derivatives. The β32_33 and FrFK-β32_33 peptides are, therefore, promising molecules for the development of therapeutic agents against diseases caused by the mt-tRNA point mutations.

Profiling calcium-dependent interactions between Sorcin and intrinsically disordered regions of human proteome

BACKGROUND

Sorcin is a calcium sensor that exerts many calcium-related functions in the cells, e.g. it regulates calcium concentration in the cytoplasm, endoplasmic reticulum (ER) and mitochondria, by interacting with calcium pumps, exchangers and channels. Albeit Sorcin is an interesting potential cancer target, little is known about its interactors upon calcium-mediated activation. Our previous study suggested that Sorcin may recognize short linear binding motifs as the crystal structure revealed a self-interaction with a GYYPGG stretch in its N-terminus, and combinatorial peptide-phage display provided support for peptide-mediated interactions.

METHODS

In this study we screened for motif-based interactions between Sorcin and intrinsically disordered regions of the human proteome using proteomic peptide phage display (ProP-PD). We identified a peptide belonging to protein phosphatase 1 regulatory subunit 3G (PPP1R3G) as a potential novel interactor and confirm the interaction through biophysical and cell-based approaches, and provide structural information through molecular dynamics simulations.

RESULTS

Altogether, we identify a preferred motif in the enriched pool of binders and a peptide belonging to protein phosphatase 1 regulatory subunit 3G (PPP1R3G) as a preferred ligand.

CONCLUSION

Through this study we gain information on a new Sorcin binding partner and profile Sorcin's motif-based interaction.

GENERAL SIGNIFICANCE

The interaction between Sorcin and PPP1R3G may suggest a close dependence between glucose homeostasis and calcium concentration in the different cell compartments, opening a completely new and interesting scenery yet to be fully disclosed.

Roles of Sorcin in Drug Resistance in Cancer: One Protein, Many Mechanisms, for a Novel Potential Anticancer Drug Target

The development of drug resistance is one of the main causes of failure in anti-cancer treatments. Tumor cells adopt many strategies to counteract the action of chemotherapeutic agents, e.g., enhanced DNA damage repair, inactivation of apoptotic pathways, alteration of drug targets, drug inactivation, and overexpression of ABC (Adenosine triphosphate-binding cassette, or ATP-binding cassette) transporters. These are broad substrate-specificity ATP-dependent efflux pumps able to export toxins or drugs out of cells; for instance, ABCB1 (MDR1, or P-glycoprotein 1), overexpressed in most cancer cells, confers them multidrug resistance (MDR). The gene coding for sorcin (SOluble Resistance-related Calcium-binding proteIN) is highly conserved among mammals and is located in the same chromosomal locus and amplicon as the ABC transporters ABCB1 and ABCB4, both in human and rodent genomes (two variants of ABCB1, i.e., ABCB1a and ABCB1b, are in rodent amplicon). Sorcin was initially characterized as a soluble protein overexpressed in multidrug (MD) resistant cells and named "resistance-related" because of its co-amplification with ABCB1. Although for years sorcin overexpression was thought to be only a by-product of the co-amplification with ABC transporter genes, many papers have recently demonstrated that sorcin plays an important part in MDR, indicating a possible role of sorcin as an oncoprotein. The present review illustrates sorcin roles in the generation of MDR via many mechanisms and points to sorcin as a novel potential target of different anticancer molecules.

Bioinformatics analysis of Ras homologue enriched in the striatum, a potential target for Huntington's disease therapy

Huntington's disease (HD) is a lethal neurodegenerative disorder for which no cure is available yet. It is caused by abnormal expansion of a CAG triplet in the gene encoding the huntingtin protein (Htt), with consequent expansion of a polyglutamine repeat in mutated Htt (mHtt). This makes mHtt highly unstable and aggregation prone. Soluble mHtt is linked to cytotoxicity and neurotoxicity, whereas mHtt aggregates are thought to be neuroprotective. While Htt and mHtt are ubiquitously expressed throughout the brain and peripheral tissues, HD is characterized by selective degradation of the corpus striatum, without notable alterations in peripheral tissues. Screening for mRNAs preferentially expressed in rodent striatum led to the discovery of a GTP binding protein homologous to Ras family members. Due to these features, the newly discovered protein was termed Ras Homolog Enriched in Striatum (RHES). The aetiological role of RHES in HD has been ascribed to its small ubiquitin-like modifier (SUMO)-E3 ligase function. RHES sumoylates mHtt with higher efficiency than wild-type Htt, thereby protecting mHtt from degradation and increasing the amounts of the soluble form. Although RHES is an attractive target for HD treatment, essential information about protein structure and function are still missing. With the aim of investigating RHES 3D structure and function, bioinformatic analyses and molecular modelling have been performed in the present study, based on which, RHES regions predicted to be involved in the interaction with mHtt or the SUMO-E2 ligase Ubc9 have been identified. These regions have been used to design peptides aimed at inhibiting RHES interactions and, therefore, mHtt sumoylation; in turn, these peptides will be used to develop small molecule inhibitors by both rational design and virtual screening of large compound libraries. Once identified, RHES sumoylation inhibitors may open the road to the development of therapeutic agents against the severe, and currently untreatable, HD.

Abstract 2502: Targeting anti-apoptotic Bcl-2 family for cancer therapy

Introduction: Despite the recent advancement in treating melanoma, options are still limited for patients without BRAF mutations or in relapse from current treatments, and promising, immunotherapies are not without caveats. Thus, alternative options are still in need.

Bcl-2 protein is the main member of a family whose best-characterized function is to regulate apoptosis in several pathologies, including melanoma. To evade apoptotic checkpoints, melanoma cells often overexpress Bcl-2 and other antiapoptotic proteins. Consequently, along with the fact that antiapoptotic proteins play a critical role in the efficacy of most chemotherapeutics and play a relevant role in melanoma progression, they have emerged as attractive targets for therapeutic development. Structure-based efforts led to the development of ABT-199 (also known as venetoclax), recently approved by the Food and Drug Administration for the treatment of chronic lymphocytic leukaemia patients.

Experimental procedures: To identify new possible selective inhibitors towards antiapoptotic proteins belonging to the bcl-2 family, a computational medicinal chemistry protocol was set up. Both the PubMed/ChEMBL databases, containing known ligands for bcl-2, bcl-w and bcl-xL proteins and their associated affinities, and the RCSB Protein Data Bank listing 65 bcl-2 family protein structures, were used to build preliminary Quantitative Structure-Activity Relationships (QSAR) models. The QSAR models were used to screen the VITAS-M Laboratory database to select 60 chemical scaffolds as hypothetical novel Bcl-2 inhibitors. Surface Plasmon Experiments were carried out to assess affinity of compounds for Bcl-2. The sensitivity of human leukemia and melanoma cells to these compounds was evaluated in terms of cell survival, cell cycle distribution and apoptosis induction, by using different concentrations and time exposure.

Results: 9 out of 60 compounds (15%) were able to reduce cell viability at concentrations lower than 50µM, and to induce cell death in a dose-dependent manner, even though at different extend depending on the compound tested. Inclusion of the 60 selected compounds led to a new QSAR model to perform a second virtual screen on the NIH database from which 40 putative Bcl-2 target molecules were selected and whose efficacy to inhibit cell viability of both leukemia and melanoma cells was measured. 11 compounds are endowed with high affinity for Bcl-2, 2 out of 40 compounds were demonstrated to induce apoptosis in both tumor histotypes in a dose-dependent manner, while they did not affect cell viability of human normal fibroblasts.

Conclusion: Machine learning application coupled with experimental data have provided new insights into bcl-2 family's regulation of the apoptotic pathway both in leukemia and in melanoma, and suggest that inhibiting the major anti-apoptotic proteins is sufficient to induce cell death.

Note: This abstract was not presented at the meeting.

Citation Format: Elisabetta Valentini, Marta Di Martile, Marianna Desideri, Simona Carcasole, Alexandros Patsilinakos, Manuela Sabatino, Antonello Mai, Gianni Colotti, Rino Ragno, Daniela Trisciuoglio, Donalella Del Bufalo. Targeting anti-apoptotic Bcl-2 family for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2502.

Small Molecule Inhibitors of KDM5 Histone Demethylases Increase the Radiosensitivity of Breast Cancer Cells Overexpressing JARID1B

Background: KDM5 enzymes are H3K4 specific histone demethylases involved in transcriptional regulation and DNA repair. These proteins are overexpressed in different kinds of cancer, including breast, prostate and bladder carcinomas, with positive effects on cancer proliferation and chemoresistance. For these reasons, these enzymes are potential therapeutic targets. Methods: In the present study, we analyzed the effects of three different inhibitors of KDM5 enzymes in MCF-7 breast cancer cells over-expressing one of them, namely KDM5B/JARID1B. In particular we tested H3K4 demethylation (western blot); radio-sensitivity (cytoxicity and clonogenic assays) and damage accumulation (COMET assay and kinetics of H2AX phosphorylation). Results: we show that all three compounds with completely different chemical structures can selectively inhibit KDM5 enzymes and are capable of increasing sensitivity of breast cancer cells to ionizing radiation and radiation-induced damage. Conclusions: These findings confirm the involvement of H3K4 specific demethylases in the response to DNA damage, show a requirement of the catalytic function and suggest new strategies for the therapeutic use of their inhibitors.

Structure-guided approach to identify a novel class of anti-leishmaniasis diaryl sulfide compounds targeting the trypanothione metabolism

Leishmania protozoans are the causative agent of leishmaniasis, a neglected tropical disease consisting of three major clinical forms: visceral leishmaniasis (VL), cutaneous leishmaniasis, and mucocutaneous leishmaniasis. VL is caused by Leishmania donovani in East Africa and the Indian subcontinent and by Leishmania infantum in Europe, North Africa, and Latin America, and causes an estimated 60,000 deaths per year. Trypanothione reductase (TR) is considered to be one of the best targets to find new drugs against leishmaniasis. This enzyme is fundamental for parasite survival in the human host since it reduces trypanothione, a molecule used by the tryparedoxin/tryparedoxin peroxidase system of Leishmania to neutralize the hydrogen peroxide produced by host macrophages during infection. Recently, we solved the X-ray structure of TR in complex with the diaryl sulfide compound RDS 777 (6-(sec-butoxy)-2-((3-chlorophenyl)thio)pyrimidin-4-amine), which impairs the parasite defense against the reactive oxygen species by inhibiting TR with high efficiency. The compound binds to the catalytic site and engages in hydrogen bonds the residues more involved in the catalysis, namely Glu466', Cys57 and Cys52, thereby inhibiting the trypanothione binding. On the basis of the RDS 777-TR complex, we synthesized structurally related diaryl sulfide analogs as TR inhibitors able to compete for trypanothione binding to the enzyme and to kill the promastigote in the micromolar range. One of the most active among these compounds (RDS 562) was able to reduce the trypanothione concentration in cell of about 33% via TR inhibition. RDS 562 inhibits selectively Leishmania TR, while it does not inhibit the human homolog glutathione reductase.

Toward a Drug Against All Kinetoplastids: From LeishBox to Specific and Potent Trypanothione Reductase Inhibitors

Leishmaniasis, Chagas disease, and sleeping sickness affect millions of people worldwide and lead to the death of about 50 000 humans per year. These diseases are caused by the kinetoplastids Leishmania, Trypanosoma cruzi, and Trypanosoma brucei, respectively. These parasites share many general features, including gene conservation, high amino acid identity among proteins, the presence of subcellular structures as glycosomes and the kinetoplastid, and genome architecture, that may make drug development family specific, rather than species-specific, i.e., on the basis of the inhibition of a common, conserved parasite target. However, no optimal molecular targets or broad-spectrum drugs have been identified to date to cure these diseases. Here, the LeishBox from GlaxoSmithKline high-throughput screening, a 192-molecule set of best antileishmanial compounds, based on 1.8 million compounds, was used to identify specific inhibitors of a validated Leishmania target, trypanothione reductase (TR), while analyzing in parallel the homologous human enzyme glutathione reductase (GR). We identified three specific highly potent TR inhibitors and performed docking on the TR solved structure, thereby elucidating the putative molecular basis of TR inhibition. Since TRs from kinetoplastids are well conserved, and these compounds inhibit the growth of Leishmania, Trypanosoma cruzi, and Trypanosoma brucei, the identification of a common validated target may lead to the development of potent antikinetoplastid drugs.

Identification of chalcone-based antileishmanial agents targeting trypanothione reductase

All currently used first-line and second-line drugs for the treatment of leishmaniasis exhibit several drawbacks including toxicity, high costs and route of administration. Furthermore, some drugs are associated with the emergence of drug resistance. Thus, the development of new treatments for leishmaniasis is a priority in the field of neglected tropical diseases. The present work highlights the use of natural derived products, i.e. chalcones, as potential source of antileishmanial agents. Thirty-one novel chalcone compounds have been synthesized and their activity has been evaluated against promastigotes of Leishmania donovani; 16 compounds resulted active against L. donovani in a range from 3.0 to 21.5 μM, showing low toxicity against mammalian cells. Among these molecules, 6 and 16 showed good inhibitory activity on both promastigotes and intracellular amastigotes, coupled with an high selectivity index. Furthermore, compounds 6 and 16 inhibited the promastigote growth of other leishmanial species, including L. tropica, L. major and L. infantum. Finally, 6 and 16 interacted with high affinity with trypanothione reductase (TR), an essential enzyme for the leishmanial parasite and compound 6 inhibited TR with sub-micromolar potency. Thus, the effective inhibitory activity against Leishmania, the lack of toxicity on mammalian cells and the ability to block a crucial parasite's enzyme, highlight the potential for compound 6 to be optimized as novel drug candidate against leishmaniasis.

Identification of small molecule inhibitors of the Aurora-A/TPX2 complex

Aurora kinases are a family of cell division regulators that govern the correct assembly of a bipolar mitotic spindle and the fidelity of chromosome segregation. Their overexpression is associated with genomic instability and aneuploidy, and is frequently observed in cancer. Accordingly, competitive inhibitors targeting Aurora kinase activity at the ATP-binding site are being investigated for therapeutic purposes. Despite promising pre-clinical data, these molecules display moderate effects in clinical trials and incomplete selectivity, either against distinct family members, or other kinases. As an alternative approach, protein-protein interaction inhibitors targeting mitotic kinases and their activators can be exploited to achieve increased specificity of action. In this study, a virtual screening of small molecules led to the identification of 25 potential inhibitors of the interaction between Aurora-A and its activator TPX2. In vitro experiments confirmed that 4 hits bind Aurora-A in the low micromolar range and compete for TPX2 binding. Immunofluorescence assays showed that 2 compounds also yield lowered Aurora-A activity and spindle pole defects in cultured osteosarcoma cells. The identified protein-protein interaction inhibitors of the Aurora-A/TPX2 complex might represent lead compounds for further development towards pioneering anti-cancer drugs and provide the proof-of-concept for a new exploitable strategy to target mitotic kinases.

The presence of glutamate residues on the PAS sequence of the stimuli-sensitive nano-ferritin improves in vivo biodistribution and mitoxantrone encapsulation homogeneity

A genetically engineered human ferritin heavy chain (HFt)-based construct has been recently shown by our group to efficiently entrap and deliver doxorubicin to cancer cells. This construct, named HFt-MP-PAS, contained a tumor-selective sequence (MP) responsive to proteolytic cleavage by tumor proteases (MMPs), located between each HFt subunit and an outer shielding polypeptide sequence rich in proline (P), serine (S) and alanine (A) residues (PAS). HFt-MP-PAS displayed excellent therapeutic efficacy in xenogenic pancreatic and head and neck cancer models in vivo, leading to a significant increase in overall animal survivals. Here we report a new construct obtained by the genetic insertion of two glutamate residues in the PAS sequence of HFt-MP-PAS. Such new construct, named HFt-MP-PASE, is characterized by improved performances as drug biodistribution in a xenogenic pancreatic cancer model in vivo. Moreover, HFt-MP-PASE efficiently encapsulates the anti-cancer drug mitoxantrone (MIT), and the resulting MIT-loaded nanoparticles proved to be more soluble and monodispersed than the HFt-MP-PAS counterparts. Importantly, in vitro MIT-loaded HFt-MP-PASE kills several cancer cell lines of different origin (colon, breast, sarcoma and pancreas) at least as efficiently as the free drug. Finally, our MIT loaded protein nanocages allowed in vivo an impressive incrementing of the drug accumulation in the tumor with respect to the free drug.

Peptide-based development of PKA activators

Activation of the PKA catalytic unit by small peptide (SE1). Development of peptidomimetics.

Metal- and metalloid-containing drugs for the treatment of trypanosomatid diseases

The trypanosomatid-induced diseases are considered as neglected, because the countries where they kill people are not important markets for western big pharmaceutical companies. However, recently some effort has been made to translate the use of already known drugs to neglected infectious disease. Although many metals are essential to life, many disorders affecting metal homeostasis and bioavailability are responsible for several human diseases. Metals can be toxic even at very low concentrations and semimetals are classified as toxic and dangerous for the environment. However, metal- and metalloid-based therapeutic drugs have existed for centuries. Some of them, as antimony and arsenic compounds, are still the first line drugs used for the treatment of leishmaniasis and trypanosomiases in developing countries. Other metal complexes (as those of Ag, Pt, Pd and Au), already present in the market for cancer therapies or to cure bacterial infection or for anti-inflammatory treatments, have been proposed also against the vector-borne infections caused by trypanosomatids. The use of novel approaches based on nanotechnologies, allowing selective targeting, may represent a promising strategy to decrease the toxicity of these drugs.

N6L pseudopeptide interferes with nucleophosmin protein-protein interactions and sensitizes leukemic cells to chemotherapy

NPM1 is a multifunctional nucleolar protein implicated in several processes such as ribosome maturation and export, DNA damage response and apoptotic response to stress stimuli. The NPM1 gene is involved in human tumorigenesis and is found mutated in one third of acute myeloid leukemia patients, leading to the aberrant cytoplasmic localization of NPM1. Recent studies indicated that the N6L multivalent pseudopeptide, a synthetic ligand of cell-surface nucleolin, is also able to bind NPM1 with high affinity. N6L inhibits cell growth with different mechanisms and represents a good candidate as a novel anticancer drug for a number of malignancies of different histological origin. In this study we investigated whether N6L treatment could drive antitumor effect in acute myeloid leukemia cell lines. We found that N6L binds NPM1 at the N-terminal domain, co-localizes with cytoplasmic, mutated NPM1, and interferes with its protein-protein associations. N6L toxicity appears to be p53 dependent but interestingly, the leukemic cell line harbouring the mutated form of NPM1 is more resistant to treatment, suggesting that NPM1 cytoplasmic delocalization confers protection from p53 activation. Moreover, we show that N6L sensitizes AML cells to doxorubicin and cytarabine treatment. These studies suggest that N6L may be a promising option in combination therapies for acute myeloid leukemia treatment.

Binding of doxorubicin to Sorcin impairs cell death and increases drug resistance in cancer cells

Sorcin is a calcium binding protein that plays an important role in multidrug resistance (MDR) in tumors, since its expression confers resistance to doxorubicin and to other chemotherapeutic drugs. In this study, we show that Sorcin is able to bind doxorubicin, vincristine, paclitaxel and cisplatin directly and with high affinity. The high affinity binding of doxorubicin to sorcin has been demonstrated with different techniques, that is, surface plasmon resonance, fluorescence titration and X-ray diffraction. Although the X-ray structure of sorcin in complex with doxorubicin has been solved at low resolution, it allows the identification of one of the two doxorubicin binding sites, placed at the interface between the EF5 loop the G helix and the EF4 loop. We show that Sorcin cellular localization changes upon doxorubicin treatment, an indication that the protein responds to doxorubicin and it presumably binds the drug also inside the cell, soon after drug entrance. We also demonstrate that Sorcin is able to limit the toxic effects of the chemotherapeutic agent in the cell. In addition, Sorcin silencing increases cell death upon treatment with doxorubicin, increases the accumulation of doxorubicin in cell nucleus, decreases the expression of MDR1 and doxorubicin efflux via MDR1.

Inhibition of Leishmania infantum trypanothione reductase by diaryl sulfide derivatives

The study presented here aimed at identifying a new class of compounds acting against Leishmania parasites, the causative agent of Leishmaniasis. For this purpose, the thioether derivatives of our in-house library have been evaluated in whole-cell screening assays in order to determine their in vitro activity against Leishmania protozoan. Among them, promising results have been achieved with compound RDS 777 (6-(sec-butoxy)-2-((3-chlorophenyl)thio)pyrimidin-4-amine) (IC₅₀=29.43 µM), which is able to impair the mechanism of the parasite defence against the reactive oxygen species by inhibiting the trypanothione reductase (TR) with high efficiency (K_i 0.25 ± 0.18 µM). The X-ray structure of L. infantum TR in complex with RDS 777 disclosed the mechanism of action of this compound that binds to the catalytic site and engages in hydrogen bonds the residues more involved in the catalysis, namely Glu466', Cys57 and Cys52, thereby inhibiting the trypanothione binding and avoiding its reduction.

Small Molecules Targeting the miRNA-Binding Domain of Argonaute 2: From Computer-Aided Molecular Design to RNA Immunoprecipitation

The development of small-molecule-based target therapy design for human disease and cancer is object of growing attention. Recently, specific microRNA (miRNA) mimicking compounds able to bind the miRNA-binding domain of Argonaute 2 protein (AGO2) to inhibit miRNA loading and its functional activity were described. Computer-aided molecular design techniques and RNA immunoprecipitation represent suitable approaches to identify and experimentally determine if a compound is able to impair the loading of miRNAs on AGO2 protein. Here, we describe these two methodologies that we recently used to select a specific compound able to interfere with the AGO2 functional activity and able to improve the retinoic acid-dependent myeloid differentiation of leukemic cells.

Short peptides from leucyl-tRNA synthetase rescue disease-causing mitochondrial tRNA point mutations

Mutations in mitochondrial (mt) genes coding for mt-tRNAs are responsible for a range of syndromes, for which no effective treatment is available. We recently showed that the carboxy-terminal domain (Cterm) of human mt-leucyl tRNA synthetase rescues the pathologic phenotype associated either with the m.3243A>G mutation in mt-tRNA^Leu(UUR) or with mutations in the mt-tRNA^Ile, both of which are aminoacylated by Class I mt-aminoacyl-tRNA synthetases (mt-aaRSs). Here we show, by using the human transmitochondrial cybrid model, that the Cterm is also able to improve the phenotype caused by the m.8344A>G mutation in mt-tRNA^Lys, aminoacylated by a Class II aaRS. Importantly, we demonstrate that the same rescuing ability is retained by two Cterm-derived short peptides, β30_31 and β32_33, which are effective towards both the m.8344A>G and the m.3243A>G mutations. Furthermore, we provide in vitro evidence that these peptides bind with high affinity wild-type and mutant human mt-tRNA^Leu(UUR) and mt-tRNA^Lys, and stabilize mutant mt-tRNA^Leu(UUR). In conclusion, we demonstrate that small Cterm-derived peptides can be effective tools to rescue cellular defects caused by mutations in a wide range of mt-tRNAs.

Targeting polyamine metabolism for finding new drugs against leishmaniasis: a review

Leishmaniasis is a neglected disease affecting more than 12 million people worldwide. The most used drugs are pentavalent antimonials that are very toxic and display the problem of drug resistance, especially in endemic regions such as Bihar in India. For this reason, it is urgent to find new and less toxic drugs against leishmaniasis. To this end, the understanding of pathways affecting parasite survival is of prime importance for targeted drug discovery. The parasite survival inside the macrophage is strongly dependent on polyamine metabolism. Polyamines are, in fact, very important for cell growth and proliferation. In particular, spermidine (Spd), the final product of the polyamine biosynthesis pathway, serves as a precursor for trypanothione (N1,N8- bis(glutathionyl)spermidine, T(SH)2) and hypusine (N(ε)-(4-amino-2-hydroxybutyl)lysine). T(SH)2 is a key molecule for parasite defense against the hydrogen peroxide produced by macrophages during the infection. Hypusination is a posttranslational modification occurring exclusively in the eukaryotic initiation factor 5A (eIF5A), which has an important role in avoiding the ribosome stalling during the biosynthesis of protein containing polyprolines sequences. The enzymes, belonging to the spermidine metabolism, i.e. arginase (ARG), ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (AdoMetDC), spermidine synthase (SpdS), trypanothione synthetase (TryS or TSA), trypanothione reductase (TryR or TR), tryparedoxin peroxidase (TXNPx), deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH) are promising targets for the development of new drugs against leishmaniasis. This minireview furnishes a picture of the structural, functional and inhibition studies on polyamine metabolism enzymes that could guide the discovery of new drugs against leishmaniasis.

Leishmania infantum trypanothione reductase is a promiscuous enzyme carrying an NADPH:O2 oxidoreductase activity shared by glutathione reductase

BACKGROUND

Leishmania infantum is a protozoan of the trypanosomatid family causing visceral leishmaniasis. Leishmania parasites are transmitted by the bite of phlebotomine sand flies to the human host and are phagocyted by macrophages. The parasites synthesize N1-N8-bis(glutationyl)-spermidine (trypanothione, TS2), which furnishes electrons to the tryparedoxin-tryparedoxin peroxidase couple to reduce the reactive oxygen species produced by macrophages. Trypanothione is kept reduced by trypanothione reductase (TR), a FAD-containing enzyme essential for parasite survival.

METHODS

The enzymatic activity has been studied by stopped-flow, absorption spectroscopy, and amperometric measurements.

RESULTS

The study reported here demonstrates that the steady-state parameters change as a function of the order of substrates addition to the TR-containing solution. In particular, when the reaction is carried out by adding NADPH to a solution containing the enzyme and trypanothione, the KM for NADPH decreases six times compared to the value obtained by adding TS2 as last reagent to start the reaction (1.9 vs. 12μM). More importantly, we demonstrate that TR is able to catalyze the oxidation of NADPH also in the absence of trypanothione. Thus, TR catalyzes the reduction of O2 to water through the sequential formation of C(4a)-(hydro)peroxyflavin and sulfenic acid intermediates. This NADPH:O2 oxidoreductase activity is shared by Saccharomyces cerevisiae glutathione reductase (GR).

CONCLUSIONS

TR and GR, in the absence of their physiological substrates, may catalyze the electron transfer reaction from NADPH to molecular oxygen to yield water.

GENERAL SIGNIFICANCE

TR and GR are promiscuous enzymes.

The multiple cellular functions of the oncoprotein Golgi phosphoprotein 3

The highly conserved Golgi phosphoprotein 3 (GOLPH3) protein, a component of Trans-Golgi Network (TGN), has been defined as a "first-in-class Golgi oncoprotein" and characterized as a Phosphatidylinositol 4-phosphate [PI(4)P] effector at the Golgi. GOLPH3 is commonly amplified in several solid tumors. Furthermore this protein has been associated with poor prognosis in many cancers. Highly conserved from yeast to humans, GOLPH3 provides an essential function in vesicle trafficking and Golgi structure. Recent data have also implicated this oncoprotein in regulation of cytokinesis, modulation of mitochondrial mass and cellular response to DNA damage. A minute dissection of the molecular pathways that require GOLPH3 protein will be helpful to develop new therapeutic cancer strategies.

Sorcin, a calcium binding protein involved in the multidrug resistance mechanisms in cancer cells

Sorcin is a penta-EF hand calcium binding protein, which participates in the regulation of calcium homeostasis in cells. Sorcin regulates calcium channels and exchangers located at the plasma membrane and at the endo/sarcoplasmic reticulum (ER/SR), and allows high levels of calcium in the ER to be maintained, preventing ER stress and possibly, the unfolded protein response. Sorcin is highly expressed in the heart and in the brain, and overexpressed in many cancer cells. Sorcin gene is in the same amplicon as other genes involved in the resistance to chemotherapeutics in cancer cells (multi-drug resistance, MDR) such as ABCB4 and ABCB1; its overexpression results in increased drug resistance to a number of chemotherapeutic agents, and inhibition of sorcin expression by sorcin-targeting RNA interference leads to reversal of drug resistance. Sorcin is increasingly considered a useful marker of MDR and may represent a therapeutic target for reversing tumor multidrug resistance.

A small-molecule targeting the microRNA binding domain of argonaute 2 improves the retinoic acid differentiation response of the acute promyelocytic leukemia cell line NB4

Argonaute proteins are pivotal regulators of gene expression mediating miRNAs function. Modulating their activity would be extremely useful to elucidate the processes governing small-RNAs-guided gene silencing. We report the identification of a chemical compound able to compete with Argonaute 2 miRNAs binding, and we demonstrate that this functional inhibition determines effects similar to Argonaute 2 shRNA-mediated down-regulation, favoring granulocytic differentiation of the acute promyelocytic leukemia cell line NB4 in response to retinoic acid.

The isolated carboxy-terminal domain of human mitochondrial leucyl-tRNA synthetase rescues the pathological phenotype of mitochondrial tRNA mutations in human cells

Mitochondrial (mt) diseases are multisystem disorders due to mutations in nuclear or mtDNA genes. Among the latter, more than 50% are located in transfer RNA (tRNA) genes and are responsible for a wide range of syndromes, for which no effective treatment is available at present. We show that three human mt aminoacyl-tRNA syntethases, namely leucyl-, valyl-, and isoleucyl-tRNA synthetase are able to improve both viability and bioenergetic proficiency of human transmitochondrial cybrid cells carrying pathogenic mutations in the mt-tRNA(Ile) gene. Importantly, we further demonstrate that the carboxy-terminal domain of human mt leucyl-tRNA synthetase is both necessary and sufficient to improve the pathologic phenotype associated either with these "mild" mutations or with the "severe" m.3243A>G mutation in the mt-tRNA(L)(eu(UUR)) gene. Furthermore, we provide evidence that this small, non-catalytic domain is able to directly and specifically interact in vitro with human mt-tRNA(Leu(UUR)) with high affinity and stability and, with lower affinity, with mt-tRNA(Ile). Taken together, our results sustain the hypothesis that the carboxy-terminal domain of human mt leucyl-tRNA synthetase can be used to correct mt dysfunctions caused by mt-tRNA mutations.

Sorcin links calcium signaling to vesicle trafficking, regulates Polo-like kinase 1 and is necessary for mitosis

Sorcin, a protein overexpressed in many multi-drug resistant cancers, dynamically localizes to distinct subcellular sites in 3T3-L1 fibroblasts during cell-cycle progression. During interphase sorcin is in the nucleus, in the plasma membrane, in endoplasmic reticulum (ER) cisternae, and in ER-derived vesicles localized along the microtubules. These vesicles are positive to RyR, SERCA, calreticulin and Rab10. At the beginning of mitosis, sorcin-containing vesicles associate with the mitotic spindle, and during telophase are concentrated in the cleavage furrow and, subsequently, in the midbody. Sorcin regulates dimensions and calcium load of the ER vesicles by inhibiting RYR and activating SERCA. Analysis of sorcin interactome reveals calcium-dependent interactions with many proteins, including Polo-like kinase 1 (PLK1), Aurora A and Aurora B kinases. Sorcin interacts physically with PLK1, is phosphorylated by PLK1 and induces PLK1 autophosphorylation, thereby regulating kinase activity. Knockdown of sorcin results in major defects in mitosis and cytokinesis, increase in the number of rounded polynucleated cells, blockage of cell progression in G2/M, apoptosis and cell death. Sorcin regulates calcium homeostasis and is necessary for the activation of mitosis and cytokinesis.

Inhibition of Leishmania infantum trypanothione reductase by azole-based compounds: a comparative analysis with its physiological substrate by X-ray crystallography

Herein we report a study aimed at discovering a new class of compounds that are able to inhibit Leishmania donovani cell growth. Evaluation of an in-house library of compounds in a whole-cell screening assay highlighted 4-((1-(4-ethylphenyl)-2-methyl-5-(4-(methylthio)phenyl)-1H-pyrrol-3-yl)methyl)thiomorpholine (compound 1) as the most active. Enzymatic assays on Leishmania infantum trypanothione reductase (LiTR, belonging to the Leishmania donovani complex) shed light on both the interaction with, and the nature of inhibition by, compound 1. A molecular modeling approach based on docking studies and on the estimation of the binding free energy aided our rationalization of the biological data. Moreover, X-ray crystal structure determination of LiTR in complex with compound 1 confirmed all our results: compound 1 binds to the T(SH)2 binding site, lined by hydrophobic residues such as Trp21 and Met113, as well as residues Glu18 and Tyr110. Analysis of the structure of LiTR in complex with trypanothione shows that Glu18 and Tyr110 are also involved in substrate binding, according to a competitive inhibition mechanism.

Green tea catechins can bind and modify ERp57/PDIA3 activity

BACKGROUND

Green tea is a rich source of polyphenols, mainly catechins (flavanols), which significantly contribute to the beneficial health effects of green tea in the prevention and treatment of various diseases. In this study the effects of four green tea catechins on protein ERp57, also known as protein disulfide isomerase isoform A3 (PDIA3), have been investigated in an in vitro model.

METHODS

The interaction of catechins with ERp57 was explored by fluorescence quenching and surface plasmon resonance techniques and their effect on ERp57 activities was investigated.

RESULTS

A higher affinity was observed for galloylated cathechins, which bind close to the thioredoxin-like redox-sensitive active sites of the protein, with a preference for the oxidized form. The effects of these catechins on ERp57 properties were also investigated and a moderate inhibition of the reductase activity of ERp57 was observed as well as a strong inhibition of ERp57 DNA binding activity.

CONCLUSIONS

Considering the high affinity of galloylated catechins for ERp57 and their capability to inhibit ERp57 binding to other macromolecular ligands, some effects of catechins interaction with this protein on eukaryotic cells may be expected.

GENERAL SIGNIFICANCE

This study provides information to better understand the molecular mechanisms underlying the biological activities of catechins and to design new polyphenol-based ERp57-specific inhibitors.