Adeno-Associated Virus-Mediated Dorsal Root Ganglion Toxicity in the New Zealand White Rabbit

Recombinant adeno-associated virus (AAV)-mediated degeneration of sensory neurons in the dorsal root ganglia (DRG) and trigeminal ganglia (TG) has been observed in non-human primates (NHPs) following intravenous (IV) and intrathecal (IT) delivery. Administration of recombinant AAV encoding a human protein transgene via a single intra-cisterna magna (ICM) injection in New Zealand white rabbits resulted in histopathology changes very similar to NHPs: mononuclear cell infiltration, degeneration/necrosis of sensory neurons, and nerve fiber degeneration of sensory tracts in the spinal cord and of multiple nerves. AAV-associated clinical signs and incidence/severity of histologic findings indicated that rabbits were equally or more sensitive than NHPs to sensory neuron damage. Another study using human and rabbit transgene constructs of the same protein demonstrated comparable changes suggesting that the effects are not an immune response to the non-self protein transgene. Rabbit has not been characterized as a species for general toxicity testing of AAV gene therapies, but these studies suggest that it may be an alternative model to investigate mechanisms of AAV-mediated neurotoxicity and test novel AAV designs mitigating these adverse effects.

A multi-parametric high throughput assay for detecting beta-cell proliferation in dispersed primary islets

Identification of novel compounds to selectively induce pancreatic beta-cell proliferation has the potential to restore functional beta-cell mass and insulin secretory demand in type 2 diabetes. The rarity of islet cell clusters (comprising of only 1% of the total pancreas mass) makes such a discovery a challenge. To address this obstacle a high throughput, 384 well, plate-based multi-parametric imaging assay was developed to capture ex vivo primary islet proliferation, allowing positive identification of compounds that can selectively enhance islet beta-cell proliferation. The use of microscopy-based, high-content imaging technology enables acquisition of additional multi-parametric information such as proliferating populations in the islet beta and non beta-cells, insulin intensity, and cell counts, improving understanding of on and off target effects in primary tissue. The protocol requires access to a high-throughput microscopy platform for automated image acquisition of treated islet cells in assay plates. High content image analysis software is required to extract multiparametric cellular features and aid identification of therapeutically relevant small molecules and perturbants. Several putative beta-cell proliferative compounds have validated in this high throughput assay format, including the pleiotropic hormone prolactin [1] and the small molecule DYRK1A inhibitor harmine [2]. It is recommended to include one, or both, as positive controls to provide a reference for image analysis, give confidence in assay performance and capture potential assay variability during experimental runs. The protocol outlined specifically focuses on the multiparametric assessment of betacell proliferation in mouse and rat ex vivo islets and provides the methodology required for the collection of high quality cellular material. The high throughput, plate based assay can additionally be adapted to evaluate and quantify other disease relevant endpoints by high content microscopy and be applied to other downstream measurements. One of the caveats of a high-throughput, 384 microplate beta-cell proliferative assay is its limitations to facilitate human beta-cell proliferation detection, especially for weak activators. Adult human beta-cell proliferation is an extremely rare biological event and assessment experimentally can be donor dependent. In addition lower human islet beta-cell subpopulations require large numbers of cells for accurate rare event measurement.

Highly scalable arrayed CRISPR mediated gene silencing in primary lung small airway epithelial cells

Small airway epithelial cells (SAECs) play a central role in the pathogenesis of lung diseases and are now becoming a crucial cellular model for target identification and validation in drug discovery. However, primary cell lines such as SAECs are often difficult to transfect using traditional lipofection methods; therefore, gene editing using CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 is often carried out through ribonucleoprotein (RNP) electroporation. Here we have established a robust, scalable, and automated arrayed CRISPR nuclease (CRISPRn) screening workflow for SAECs which can be combined with a myriad of disease-specific endpoint assays.

Selecting the right therapeutic target for kidney disease

Kidney disease is a complex disease with several different etiologies and underlying associated pathophysiology. This is reflected by the lack of effective treatment therapies in chronic kidney disease (CKD) that stop disease progression. However, novel strategies, recent scientific breakthroughs, and technological advances have revealed new possibilities for finding novel disease drivers in CKD. This review describes some of the latest advances in the field and brings them together in a more holistic framework as applied to identification and validation of disease drivers in CKD. It uses high-resolution ‘patient-centric’ omics data sets, advanced in silico tools (systems biology, connectivity mapping, and machine learning) and ‘state-of-the-art‘ experimental systems (complex 3D systems in vitro, CRISPR gene editing, and various model biological systems in vivo). Application of such a framework is expected to increase the likelihood of successful identification of novel drug candidates based on strong human target validation and a better scientific understanding of underlying mechanisms.

Selective inhibition of protein secretion by abrogating receptor-coat interactions during ER export

Protein secretion is an essential process that drives cell growth, movement, and communication. Protein traffic within the secretory pathway occurs via transport intermediates that bud from one compartment and fuse with a downstream compartment to deliver their contents. Here, we explore the possibility that protein secretion can be selectively inhibited by perturbing protein-protein interactions that drive capture into transport vesicles. Human proprotein convertase subtilisin/kexin type 9 (PCSK9) is a determinant of cholesterol metabolism whose secretion is mediated by a specific cargo adaptor protein, SEC24A. We map a series of protein-protein interactions between PCSK9, its endoplasmic reticulum (ER) export receptor SURF4, and SEC24A that mediate secretion of PCSK9. We show that the interaction between SURF4 and SEC24A can be inhibited by 4-phenylbutyrate (4-PBA), a small molecule that occludes a cargo-binding domain of SEC24. This inhibition reduces secretion of PCSK9 and additional SURF4 clients that we identify by mass spectrometry, leaving other secreted cargoes unaffected. We propose that selective small-molecule inhibition of cargo recognition by SEC24 is a potential therapeutic intervention for atherosclerosis and other diseases that are modulated by secreted proteins.

Fragment-based screening: A new paradigm for ligand and target discovery

Significant advances in fragment-based screening, including the emergence of Fully Functionalised Fragments (FFFs) and innovations in Covalent Fragment screening are providing a new paradigm for ligand and target discovery. FFFs offer some key distinct advantages over other screening modalities such as small molecules and genetic screens, including 1) An ability to access diverse chemical space employing a relatively small compound set 2) Ease of screen optimisation given there is no requirement for genetic manipulation and 3) Built-in proteomics tools to facilitate rapid target deconvolution directly in cells. Covalent fragments enable exploration of novel druggable nodes through irreversible fragment-cysteine interactions, complementing their fully functionalized counterparts. Both FFFs and Covalent fragments present the phenotypic screening community with an additional and complementary approach for disease centric target identification.

Abstract P066: Gain and loss of function genome-wide CRISPR screens identify Hippo signalling as an important driver of resistance in EGFR mutant lung cancer

Drug resistance is ultimately the cause of death for most cancer patients – even initially strong responses to treatment are usually followed by the emergence of resistance over time. This suggests the existence of residual or persistent cancer cells, creating a reservoir that ultimately gives rise to stable resistance. These drug tolerant persisters (‘the deadly survivors’) have been described for over a decade in numerous studies; they are often present as a minor fraction of the total tumour population and may exploit non-genetic (transcriptional) programs to allow the cells to survive drug treatment. 10-20% of lung adenocarcinoma patients harbour activating mutations in EGFR. Although treatment with the EGFR kinase inhibitor osimertinib has improved overall survival in such patients, almost all patients ultimately develop drug resistance. We carried out parallel genome-wide CRISPR gain and loss of function screens in EGFR mutant lung cancer cell lines treated with EGFR inhibitors, to identify the genes and pathways that may be important in enabling the survival of persister cells. We observed recurrent resistant genes in previously identified resistance pathways including PI3K (PTEN, TSC1, TSC2), MAPK (KRAS, NF1, MET), cell death (BCL2L11, BAX), the mediator complex (MED24, MED19) and ubiquitination (KCTD5, KEAP1). A secondary screen of 63 resistance genes that combined high content microscopy with CRISPR gene knockout demonstrated that 21% (13/63) of genes were associated with increased nuclear localisation of YAP1/WWTR1, key activators of the Hippo pathway. A closer review of the CRISPR screen data confirmed that many resistance hits are members of this pathway - upstream regulators (NF2, AMOTL2), core signalling genes (LATS1, LATS2), main effectors (WWTR1, YAP1), transcriptional co-effectors (TEAD3, FOSL1, VGLL4) and the SWI/SNF complex (ARID2, SMARCA4, SMARCB1, PBRM1). Hippo signalling is mediated through YAP1 and WWTR1 which bind to TEAD transcription factors and activate transcriptional programs affecting cell proliferation and apoptosis. We confirmed using CRISPR that knockout (NF2) or overexpression (YAP1, WWTR1) of key Hippo genes in the EGFR mutant lung cancer cell lines PC-9, HCC827 and HCC4006 resulted in up to 60-fold increased resistance to osimertinib and increased expression of canonical Hippo transcriptional targets. We therefore reasoned that the Hippo pathway might be involved in maintaining the survival of drug tolerant persister cells in this setting. Acute treatment of EGFR mutant cell lines with osimertinib was associated with increased nuclear localisation of YAP1 and WWTR1 and increased expression of canonical Hippo transcriptional targets. Furthermore, the combination of osimertinib and a TEAD inhibitor (K-975) almost completely abolished the survival of drug tolerant persister cells following treatment, indicating that this pathway is an important survival mechanism following drug treatment. Consequently, we propose Hippo signalling as an important target mechanism for the prevention of resistance to osimertinib.

Citation Format: Matthias Pfeifer, Jonathan Brammeld, Stacey Price, Matthew Martin, Hannah Thorpe, Aurelie Bornot, Ercia Banks, Nin Guan, Shanade Dunn, Maria Lisa Guerriero, Daniel O'Neill, James Pilling, Davide Gianni, James Brownell, Paul Smith, Ultan McDermott. Gain and loss of function genome-wide CRISPR screens identify Hippo signalling as an important driver of resistance in EGFR mutant lung cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P066.

Abstract 1100: Gain and loss of function genome-wide CRISPR screens identify Hippo signaling as an important driver of resistance in EGFR mutant lung cancer

10-20% of lung adenocarcinoma patients harbour activating mutations in EGFR. Although treatment with the EGFR kinase inhibitor osimertinib has improved overall survival in such patients, almost all patients ultimately develop drug resistance. In many cases the molecular resistance mechanisms remain unknown. A systematic identification of the involved genes and pathways is critical to overcome osimertinib resistance. To define the resistance landscape of EGFR kinase inhibition we performed genome-wide gain and loss of function CRISPR screens in EGFR mutant lung cancer cell lines treated with osimertinib. Resistance hits were enriched for genes in previously identified resistance pathways including PI3K (PTEN, TSC2), MAPK (NF1, MET), cell death (BCL2L11, BAX), the mediator complex (MED24, MED19) and ubiquitination (KCTD5, LZTR1). A secondary screen of 63 resistance genes that combined high content microscopy with CRISPR gene knockouts demonstrated that 21% (13/63) of genes were associated with increased nuclear localisation of YAP1/WWTR1, indicating transcriptional activation of the Hippo pathway. According to our screening data, many resistance hits mapped onto the Hippo signaling axis - upstream regulators (NF2, AMOTL2), core signaling genes (LATS1, LATS2), main effectors (WWTR1, YAP1), transcriptional co-effectors (TEAD3, FOSL1, VGLL4) and the SWI/SNF complex (ARID2, SMARCA4, SMARCB1, PBRM1). Hippo signaling is mediated through YAP1 and WWTR1 which bind to TEAD transcription factors and activate transcriptional programs affecting cell proliferation and apoptosis. We confirmed using CRISPR that knockout (NF2) or overexpression (YAP1, WWTR1) of key Hippo genes in the EGFR mutant lung cancer cell lines PC-9, HCC827 and HCC4006 resulted in up to 60-fold increased resistance to osimertinib and elevated activity of a TEAD reporter system, indicating activation of Hippo transcriptional programs. To maintain osimertinib resistance, expression of both YAP1 and WWTR1 was necessary, suggesting non-redundant roles for both Hippo main effectors in mediating osimertinib resistance. The combination of osimertinib and a TEAD inhibitor (MYF-01-37) reversed the resistance phenotype in NF2 KO cell line models in long-term proliferation assays and also substantially repressed the emergence of drug-tolerant persister cells in PC-9, HCC827 and HCC4006 cell lines following osimertinib treatment. These cells exhibited an enhanced apoptotic response when treated with combination of osimertinib and TEAD inhibitor. Consequently, we propose Hippo signaling as an important target mechanism for the prevention of resistance to osimertinib.

Citation Format: Matthias Pfeifer, Jonathan S. Brammeld, Stacey Price, Matthew Martin, Hannah Thorpe, Aurelie Bornot, Erica Banks, Nin Guan, Shanade Dunn, Maria Luisa Guerriero, Daniel O'Neill, James Pilling, Davide Gianni, James Brownell, Paul Smith, Ultan McDermott. Gain and loss of function genome-wide CRISPR screens identify Hippo signaling as an important driver of resistance in EGFR mutant lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1100.

CGRP, adrenomedullin and adrenomedullin 2 display endogenous GPCR agonist bias in primary human cardiovascular cells

Agonist bias occurs when different ligands produce distinct signalling outputs when acting at the same receptor. However, its physiological relevance is not always clear. Using primary human cells and gene editing techniques, we demonstrate endogenous agonist bias with physiological consequences for the calcitonin receptor-like receptor, CLR. By switching the receptor-activity modifying protein (RAMP) associated with CLR we can “re-route” the physiological pathways activated by endogenous agonists calcitonin gene-related peptide (CGRP), adrenomedullin (AM) and adrenomedullin 2 (AM2). AM2 promotes calcium-mediated nitric oxide signalling whereas CGRP and AM show pro-proliferative effects in cardiovascular cells, thus providing a rationale for the expression of the three peptides. CLR-based agonist bias occurs naturally in human cells and has a fundamental purpose for its existence. We anticipate this will be a starting point for more studies into RAMP function in native environments and their importance in endogenous GPCR signalling.

Clark et al. explore the ability of ligands to activate the calcitonin-like receptor (CLR) in primary endothelial cells, and the influence of co-expressed receptor-activity modifying proteins (RAMPs). Their study reveals that GPCR agonist bias occurs naturally in human cells and plays a fundamental role in providing unique functions to endogenous agonists.

Next-generation Bruton's tyrosine kinase inhibitor BIIB091 selectively and potently inhibits B cell and Fc receptor signaling and downstream functions in B cells and myeloid cells

Objectives

Bruton's tyrosine kinase (BTK) plays a non-redundant signaling role downstream of the B-cell receptor (BCR) in B cells and the receptors for the Fc region of immunoglobulins (FcR) in myeloid cells. Here, we characterise BIIB091, a novel, potent, selective and reversible small-molecule inhibitor of BTK.

Methods

BIIB091 was evaluated in vitro and in vivo in preclinical models and in phase 1 clinical trial.

Results

In vitro, BIIB091 potently inhibited BTK-dependent proximal signaling and distal functional responses in both B cells and myeloid cells with IC₅₀s ranging from 3 to 106 nm, including antigen presentation to T cells, a key mechanism of action thought to be underlying the efficacy of B cell-targeted therapeutics in multiple sclerosis. BIIB091 effectively sequestered tyrosine 551 in the kinase pocket by forming long-lived complexes with BTK with t _1/2 of more than 40 min, thereby preventing its phosphorylation by upstream kinases. As a key differentiating feature of BIIB091, this property explains the very potent whole blood IC₅₀s of 87 and 106 nm observed with stimulated B cells and myeloid cells, respectively. In vivo, BIIB091 blocked B-cell activation, antibody production and germinal center differentiation. In phase 1 healthy volunteer trial, BIIB091 inhibited naïve and unswitched memory B-cell activation, with an in vivo IC₅₀ of 55 nm and without significant impact on lymphoid or myeloid cell survival after 14 days of dosing.

Conclusion

Pharmacodynamic results obtained in preclinical and early clinical settings support the advancement of BIIB091 in phase 2 clinical trials.

CRISPR gRNA phenotypic screening in zebrafish reveals pro-regenerative genes in spinal cord injury

Zebrafish exhibit robust regeneration following spinal cord injury, promoted by macrophages that control post-injury inflammation. However, the mechanistic basis of how macrophages regulate regeneration is poorly understood. To address this gap in understanding, we conducted a rapid in vivo phenotypic screen for macrophage-related genes that promote regeneration after spinal injury. We used acute injection of synthetic RNA Oligo CRISPR guide RNAs (sCrRNAs) that were pre-screened for high activity in vivo. Pre-screening of over 350 sCrRNAs allowed us to rapidly identify highly active sCrRNAs (up to half, abbreviated as haCRs) and to effectively target 30 potentially macrophage-related genes. Disruption of 10 of these genes impaired axonal regeneration following spinal cord injury. We selected 5 genes for further analysis and generated stable mutants using haCRs. Four of these mutants (tgfb1a, tgfb3, tnfa, sparc) retained the acute haCR phenotype, validating the approach. Mechanistically, tgfb1a haCR-injected and stable mutant zebrafish fail to resolve post-injury inflammation, indicated by prolonged presence of neutrophils and increased levels of il1b expression. Inhibition of Il-1β rescues the impaired axon regeneration in the tgfb1a mutant. Hence, our rapid and scalable screening approach has identified functional regulators of spinal cord regeneration, but can be applied to any biological function of interest.

Different Fumaric Acid Esters Elicit Distinct Pharmacologic Responses

Objective

To test the hypothesis that dimethyl fumarate (DMF, Tecfidera) elicits different biological changes from DMF combined with monoethyl fumarate (MEF) (Fumaderm, a psoriasis therapy), we investigated DMF and MEF in rodents and cynomolgus monkeys. Possible translatability of findings was explored with lymphocyte counts from a retrospective cohort of patients with MS.

Methods

In rodents, we evaluated pharmacokinetic and pharmacodynamic effects induced by DMF and MEF monotherapies or in combination (DMF/MEF). Clinical implications were investigated in a retrospective, observational analysis of patients with MS treated with DMF/MEF (n = 36).

Results

In rodents and cynomolgus monkeys, monomethyl fumarate (MMF, the primary metabolite of DMF) exhibited higher brain penetration, whereas MEF was preferentially partitioned into the kidney. In mice, transcriptional profiling for DMF and MEF alone identified both common and distinct pharmacodynamic responses, with almost no overlap between DMF- and MEF-induced differentially expressed gene profiles in immune tissues. The nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated oxidative stress response pathway was exclusively regulated by DMF, whereas apoptosis pathways were activated by MEF. DMF/MEF treatment demonstrated that DMF and MEF functionally interact to modify DMF- and MEF-specific responses in unpredictable ways. In patients with MS, DMF/MEF treatment led to early and pronounced suppression of lymphocytes, predominantly CD8⁺ T cells. In a multivariate regression analysis, the absolute lymphocyte count (ALC) was associated with age at therapy start, baseline ALC, and DMF/MEF dosage but not with previous immunosuppressive medication and sex. Furthermore, the ALC increased in a small cohort of patients with MS (n = 6/7) after switching from DMF/MEF to DMF monotherapy.

Conclusions

Fumaric acid esters exhibit different biodistribution and may elicit different biological responses; furthermore, pharmacodynamic effects of combinations differ unpredictably from monotherapy. The strong potential to induce lymphopenia in patients with MS may be a result of activation of apoptosis pathways by MEF compared with DMF.

Developing an Arrayed CRISPR-Cas9 Co-Culture Screen for Immuno-Oncology Target ID

Immunotherapies including PD-L1 blockade have shown remarkable increases in the T cell-directed antitumor response; however, efficacy is seen only in a minority of patients. Recently, pooled CRISPR-Cas9 knockout (CRISPRn) screens in tumor/immune co-culture systems have identified a number of genes that confer resistance to T cell killing in pathways including antigen presentation and cytokine signaling, providing insight into tumor mechanisms that cause resistance to immunotherapies. The development of an arrayed CRISPRn screen in a tumor/immune co-culture system would allow the identification of novel targets for immuno-oncology, characterization of hits from pooled screens, and multiple assay endpoints to be measured per gene. Here, a small-scale arrayed CRISPRn screen was successfully developed to investigate the effects on a co-culture of T cells and Cas9-expressing PC9 lung adenocarcinoma cells modified to express anti-CD3 antibody on the cell surface (PC9-OKT3 T cell system). A focused CRISPRn library was designed to target genes involved in known resistance mechanisms (including antigen presentation, cytokine signaling, and apoptosis) as well as genes involved in immune synapse interactions. The viability of PC9 cells was assessed in two-dimensional adherent co-cultures via longitudinal imaging analysis. Knockout of epidermal growth factor receptor (EGFR) and PLK1 in tumor cells cultured alone or with T cells resulted in increased tumor cell death, as expected, whereas knockout of the test gene ICAM1 showed subtle donor-specific resistance to T cell killing. Taken together, these data provide proof of concept for arrayed CRISPRn screens in tumor/immune co-culture systems and warrant further investigation of in vitro co-culture models.

Arrayed CRISPR Screening Identifies Novel Targets That Enhance the Productive Delivery of mRNA by MC3-Based Lipid Nanoparticles

Modified messenger RNAs (mRNAs) hold great potential as therapeutics by using the body’s own processes for protein production. However, a key challenge is efficient delivery of therapeutic mRNA to the cell cytosol and productive protein translation. Lipid nanoparticles (LNPs) are the most clinically advanced system for nucleic acid delivery; however, a relatively narrow therapeutic index makes them unsuitable for many therapeutic applications. A key obstacle to the development of more potent LNPs is a limited mechanistic understanding of the interaction of LNPs with cells. To address this gap, we performed an arrayed CRISPR screen to identify novel pathways important for the functional delivery of MC3 lipid-based LNP encapsulated mRNA (LNP-mRNA). Here, we have developed and validated a robust, high-throughput screening–friendly phenotypic assay to identify novel targets that modulate productive LNP-mRNA delivery. We screened the druggable genome (7795 genes) and validated 44 genes that either increased (37 genes) or inhibited (14 genes) the productive delivery of LNP-mRNA. Many of these genes clustered into families involved with host cell transcription, protein ubiquitination, and intracellular trafficking. We show that both UDP-glucose ceramide glucosyltransferase and V-type proton ATPase can significantly modulate the productive delivery of LNP-mRNA, increasing and decreasing, respectively, with both genetic perturbation and by small-molecule inhibition. Taken together, these findings shed new light into the molecular machinery regulating the delivery of LNPs into cells and improve our mechanistic understanding of the cellular processes modulating the interaction of LNPs with cells.

Developing an Arrayed CRISPR-Cas9 Co-Culture Screen for Immuno-Oncology Target ID

Immunotherapies including PD-L1 blockade have shown remarkable increases in the T cell-directed antitumor response; however, efficacy is seen only in a minority of patients. Recently, pooled CRISPR-Cas9 knockout (CRISPRn) screens in tumor/immune co-culture systems have identified a number of genes that confer resistance to T cell killing in pathways including antigen presentation and cytokine signaling, providing insight into tumor mechanisms that cause resistance to immunotherapies. The development of an arrayed CRISPRn screen in a tumor/immune co-culture system would allow the identification of novel targets for immuno-oncology, characterization of hits from pooled screens, and multiple assay endpoints to be measured per gene. Here, a small-scale arrayed CRISPRn screen was successfully developed to investigate the effects on a co-culture of T cells and Cas9-expressing PC9 lung adenocarcinoma cells modified to express anti-CD3 antibody on the cell surface (PC9-OKT3 T cell system). A focused CRISPRn library was designed to target genes involved in known resistance mechanisms (including antigen presentation, cytokine signaling, and apoptosis) as well as genes involved in immune synapse interactions. The viability of PC9 cells was assessed in two-dimensional adherent co-cultures via longitudinal imaging analysis. Knockout of epidermal growth factor receptor (EGFR) and PLK1 in tumor cells cultured alone or with T cells resulted in increased tumor cell death, as expected, whereas knockout of the test gene ICAM1 showed subtle donor-specific resistance to T cell killing. Taken together, these data provide proof of concept for arrayed CRISPRn screens in tumor/immune co-culture systems and warrant further investigation of in vitro co-culture models.

Positioning High-Throughput CETSA in Early Drug Discovery through Screening against B-Raf and PARP1

Methods to measure cellular target engagement are increasingly being used in early drug discovery. The Cellular Thermal Shift Assay (CETSA) is one such method. CETSA can investigate target engagement by measuring changes in protein thermal stability upon compound binding within the intracellular environment. It can be performed in high-throughput, microplate-based formats to enable broader application to early drug discovery campaigns, though high-throughput forms of CETSA have only been reported for a limited number of targets. CETSA offers the advantage of investigating the target of interest in its physiological environment and native state, but it is not clear yet how well this technology correlates to more established and conventional cellular and biochemical approaches widely used in drug discovery. We report two novel high-throughput CETSA (CETSA HT) assays for B-Raf and PARP1, demonstrating the application of this technology to additional targets. By performing comparative analyses with other assays, we show that CETSA HT correlates well with other screening technologies and can be applied throughout various stages of hit identification and lead optimization. Our results support the use of CETSA HT as a broadly applicable and valuable methodology to help drive drug discovery campaigns to molecules that engage the intended target in cells.

Determining direct binders of the Androgen Receptor using a high-throughput Cellular Thermal Shift Assay

Androgen Receptor (AR) is a key driver in prostate cancer. Direct targeting of AR has valuable therapeutic potential. However, the lack of disease relevant cellular methodologies capable of discriminating between inhibitors that directly bind AR and those that instead act on AR co-regulators has made identification of novel antagonists challenging. The Cellular Thermal Shift Assay (CETSA) is a technology enabling confirmation of direct target engagement with label-free, endogenous protein in living cells. We report the development of the first high-throughput CETSA assay (CETSA HT) to identify direct AR binders in a prostate cancer cell line endogenously expressing AR. Using this approach, we screened a pharmacology library containing both compounds reported to directly engage AR, and compounds expected to target AR co-regulators. Our results show that CETSA HT exclusively identifies direct AR binders, differentiating them from co-regulator inhibitors where other cellular assays measuring functional responses cannot. Using this CETSA HT approach we can derive apparent binding affinities for a range of AR antagonists, which represent an intracellular measure of antagonist-receptor Ki performed for the first time in a label-free, disease-relevant context. These results highlight the potential of CETSA HT to improve the success rates for novel therapeutic interventions directly targeting AR.

Triple Angiokinase Inhibitor Nintedanib Directly Inhibits Tumor Cell Growth and Induces Tumor Shrinkage via Blocking Oncogenic Receptor Tyrosine Kinases

The triple-angiokinase inhibitor nintedanib is an orally available, potent, and selective inhibitor of tumor angiogenesis by blocking the tyrosine kinase activities of vascular endothelial growth factor receptor (VEGFR) 1-3, platelet-derived growth factor receptor (PDGFR)-α and -β, and fibroblast growth factor receptor (FGFR) 1-3. Nintedanib has received regulatory approval as second-line treatment of adenocarcinoma non-small cell lung cancer (NSCLC), in combination with docetaxel. In addition, nintedanib has been approved for the treatment of idiopathic lung fibrosis. Here we report the results from a broad kinase screen that identified additional kinases as targets for nintedanib in the low nanomolar range. Several of these kinases are known to be mutated or overexpressed and are involved in tumor development (discoidin domain receptor family, member 1 and 2, tropomyosin receptor kinase A (TRKA) and C, rearranged during transfection proto-oncogene [RET proto oncogene]), as well as in fibrotic diseases (e.g., DDRs). In tumor cell lines displaying molecular alterations in potential nintedanib targets, the inhibitor demonstrates direct antiproliferative effects: in the NSCLC cell line NCI-H1703 carrying a PDGFRα amplification (ampl.); the gastric cancer cell line KatoIII and the breast cancer cell line MFM223, both driven by a FGFR2 amplification; AN3CA (endometrial carcinoma) bearing a mutated FGFR2; the acute myeloid leukemia cell lines MOLM-13 and MV-4-11-B with FLT3 mutations; and the NSCLC adenocarcinoma LC-2/ad harboring a CCDC6-RET fusion. Potent kinase inhibition does not, however, strictly translate into antiproliferative activity, as demonstrated in the TRKA-dependent cell lines CUTO-3 and KM-12. Importantly, nintedanib treatment of NCI-H1703 tumor xenografts triggered effective tumor shrinkage, indicating a direct effect on the tumor cells in addition to the antiangiogenic effect on the tumor stroma. These findings will be instructive in guiding future genome-based clinical trials of nintedanib.

Atad2 is a generalist facilitator of chromatin dynamics in embryonic stem cells

Although the conserved AAA ATPase and bromodomain factor, ATAD2, has been described as a transcriptional co-activator upregulated in many cancers, its function remains poorly understood. Here, using a combination of ChIP-seq, ChIP-proteomics, and RNA-seq experiments in embryonic stem cells where Atad2 is normally highly expressed, we found that Atad2 is an abundant nucleosome-bound protein present on active genes, associated with chromatin remodelling, DNA replication, and DNA repair factors. A structural analysis of its bromodomain and subsequent investigations demonstrate that histone acetylation guides ATAD2 to chromatin, resulting in an overall increase of chromatin accessibility and histone dynamics, which is required for the proper activity of the highly expressed gene fraction of the genome. While in exponentially growing cells Atad2 appears dispensable for cell growth, in differentiating ES cells Atad2 becomes critical in sustaining specific gene expression programmes, controlling proliferation and differentiation. Altogether, this work defines Atad2 as a facilitator of general chromatin-templated activities such as transcription.

Transcriptional plasticity promotes primary and acquired resistance to BET inhibition

Following the discovery of BRD4 as a non-oncogene addiction target in acute myeloid leukaemia (AML), bromodomain and extra terminal protein (BET) inhibitors are being explored as a promising therapeutic avenue in numerous cancers. While clinical trials have reported single-agent activity in advanced haematological malignancies, mechanisms determining the response to BET inhibition remain poorly understood. To identify factors involved in primary and acquired BET resistance in leukaemia, here we perform a chromatin-focused RNAi screen in a sensitive MLL-AF9;Nras(G12D)-driven AML mouse model, and investigate dynamic transcriptional profiles in sensitive and resistant mouse and human leukaemias. Our screen shows that suppression of the PRC2 complex, contrary to effects in other contexts, promotes BET inhibitor resistance in AML. PRC2 suppression does not directly affect the regulation of Brd4-dependent transcripts, but facilitates the remodelling of regulatory pathways that restore the transcription of key targets such as Myc. Similarly, while BET inhibition triggers acute MYC repression in human leukaemias regardless of their sensitivity, resistant leukaemias are uniformly characterized by their ability to rapidly restore MYC transcription. This process involves the activation and recruitment of WNT signalling components, which compensate for the loss of BRD4 and drive resistance in various cancer models. Dynamic chromatin immunoprecipitation sequencing and self-transcribing active regulatory region sequencing of enhancer profiles reveal that BET-resistant states are characterized by remodelled regulatory landscapes, involving the activation of a focal MYC enhancer that recruits WNT machinery in response to BET inhibition. Together, our results identify and validate WNT signalling as a driver and candidate biomarker of primary and acquired BET resistance in leukaemia, and implicate the rewiring of transcriptional programs as an important mechanism promoting resistance to BET inhibitors and, potentially, other chromatin-targeted therapies.

Cofilin-2 phosphorylation and sequestration in myocardial aggregates: novel pathogenetic mechanisms for idiopathic dilated cardiomyopathy

BACKGROUND

Recently, tangles and plaque-like aggregates have been identified in certain cases of dilated cardiomyopathy (DCM), traditionally labeled idiopathic (iDCM), where there is no specific diagnostic test or targeted therapy. This suggests a potential underlying cause for some of the iDCM cases. [Corrected]

OBJECTIVES

This study sought to identify the make-up of myocardial aggregates to understand the molecular mechanisms of these cases of DCM; this strategy has been central to understanding Alzheimer's disease.

METHODS

Aggregates were extracted from human iDCM samples with high congophilic reactivity (an indication of plaque presence), and the findings were validated in a larger cohort of samples. We tested the expression, distribution, and activity of cofilin in human tissue and generated a cardiac-specific knockout mouse model to investigate the functional impact of the human findings. We also modeled cofilin inactivity in vitro by using pharmacological and genetic gain- and loss-of-function approaches.

RESULTS

Aggregates in human myocardium were enriched for cofilin-2, an actin-depolymerizing protein known to participate in neurodegenerative diseases and nemaline myopathy. Cofilin-2 was predominantly phosphorylated, rendering it inactive. Cardiac-specific haploinsufficiency of cofilin-2 in mice recapitulated the human disease's morphological, functional, and structural phenotype. Pharmacological stimulation of cofilin-2 phosphorylation and genetic overexpression of the phosphomimetic protein promoted the accumulation of "stress-like" fibers and severely impaired cardiomyocyte contractility.

CONCLUSIONS

Our study provides the first biochemical characterization of prefibrillar myocardial aggregates in humans and the first report to link cofilin-2 to cardiomyopathy. The findings suggest a common pathogenetic mechanism connecting certain iDCMs and other chronic degenerative diseases, laying the groundwork for new therapeutic strategies.

Stanniocalcin1 is a key mediator of amyloidogenic light chain induced cardiotoxicity

Immunoglobulin light chain (LC) amyloidosis (AL) results from overproduction of circulating amyloidogenic LC proteins and subsequent amyloid fibril deposition in organs. Mortality in AL amyloidosis patients is highly associated with a rapidly progressive AL cardiomyopathy, marked by profound impairment of diastolic and systolic cardiac function and significant early mortality. While myocardial fibril deposition contributes to the severe diastolic dysfunction seen in AL cardiomyopathy patients, the degree of fibril deposition has not been found to correlate with prognosis. Previously, we and others showed a direct cardiotoxic effect of amyloidogenic LC proteins (AL-LC), which may contribute to the pathophysiology and mortality observed in AL cardiomyopathy patients. However, the mechanisms underlying AL-LC related cardiotoxicity remain unknown. Mammalian stanniocalcin1 (STC1) is associated with a number of cellular processes including oxidative stress and cell death. Herein, we find that STC1 expression is elevated in cardiac tissue from AL cardiomyopathy patients, and is induced in isolated cardiomyocytes in response to AL-LC, but not non-amyloidogenic LC. STC1 overexpression in vitro recapitulates the pathophysiology of AL-LC mediated cardiotoxicity, with increased ROS production, contractile dysfunction and cell death. Overexpression of STC1 in vivo results in significant cardiac dysfunction and cell death. Genetic silencing of STC1 prevents AL-LC induced cardiotoxicity in cardiomyocytes and protects against AL-LC induced cell death and early mortality in zebrafish. The cardiotoxic effects of STC1 appears to be mediated via mitochondrial dysfunction as indicated by loss of mitochondrial membrane potential, ROS production and increased mitochondrial calcium levels. Collectively, this work identifies STC1 as a critical determinant of AL-LC cardiotoxicity.

Stochastic model of Tsc1 lesions in mouse brain

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder due to mutations in either TSC1 or TSC2 that affects many organs with hamartomas and tumors. TSC-associated brain lesions include subependymal nodules, subependymal giant cell astrocytomas and tubers. Neurologic manifestations in TSC comprise a high frequency of mental retardation and developmental disorders including autism, as well as epilepsy. Here, we describe a new mouse model of TSC brain lesions in which complete loss of Tsc1 is achieved in multiple brain cell types in a stochastic pattern. Injection of an adeno-associated virus vector encoding Cre recombinase into the cerebral ventricles of mice homozygous for a Tsc1 conditional allele on the day of birth led to reduced survival, and pathologic findings of enlarged neurons, cortical heterotopias, subependymal nodules, and hydrocephalus. The severity of clinical and pathologic findings as well as survival was shown to be dependent upon the dose and serotype of Cre virus injected. Although several other models of TSC brain disease exist, this model is unique in that the pathology reflects a variety of TSC-associated lesions involving different numbers and types of cells. This model provides a valuable and unique addition for therapeutic assessment.

Regression of schwannomas induced by adeno-associated virus-mediated delivery of caspase-1

Schwannomas are tumors formed by proliferation of dedifferentiated Schwann cells. Patients with neurofibromatosis 2 (NF2) and schwannomatosis develop multiple schwannomas in peripheral and cranial nerves. Although benign, these tumors can cause extreme pain and compromise sensory/motor functions, including hearing and vision. At present, surgical resection is the main treatment modality, but it can be problematic because of tumor inaccessibility and risk of nerve damage. We have explored gene therapy for schwannomas, using a model in which immortalized human NF2 schwannoma cells expressing a fluorescent protein and luciferase are implanted in the sciatic nerve of nude mice. Direct injection of an adeno-associated virus (AAV) serotype 1 vector encoding caspase-1 (ICE) under the Schwann-cell specific promoter, P0, leads to regression of these tumors with essentially no vector-mediated neuropathology, and no changes in sensory or motor function. In a related NF2 xenograft model designed to cause measurable pain behavior, the same gene therapy leads to tumor regression and concordant resolution of tumor-associated pain. This AAV1-P0-ICE vector holds promise for clinical treatment of schwannomas by direct intratumoral injection to achieve reduction in tumor size and normalization of neuronal function.

Microvesicle-associated AAV vector as a novel gene delivery system

Adeno-associated virus (AAV) vectors have shown remarkable efficiency for gene delivery to cultured cells and in animal models of human disease. However, limitations to AAV vectored gene transfer exist after intravenous transfer, including off-target gene delivery (e.g., liver) and low transduction of target tissue. Here, we show that during production, a fraction of AAV vectors are associated with microvesicles/exosomes, termed vexosomes (vector-exosomes). AAV capsids associated with the surface and in the interior of microvesicles were visualized using electron microscopy. In cultured cells, vexosomes outperformed conventionally purified AAV vectors in transduction efficiency. We found that purified vexosomes were more resistant to a neutralizing anti-AAV antibody compared to conventionally purified AAV. Finally, we show that vexosomes bound to magnetic beads can be attracted to a magnetized area in cultured cells. Vexosomes represent a unique entity which offers a promising strategy to improve gene delivery.

Direct interaction between Tks proteins and the N-terminal proline-rich region (PRR) of NoxA1 mediates Nox1-dependent ROS generation

NADPH oxidase (Nox) family enzymes are one of the main sources of cellular reactive oxygen species (ROS), which have been implicated in several physiological and pathophysiological processes. To date seven members of this family have been reported, including Nox1-5 and Duox1 and 2. With the exception of Nox2, the regulation of the Nox enzymes is still poorly understood. Nox1 is highly expressed in the colon, and requires two cytosolic regulators, the organizer subunit NoxO1 and the activator subunit NoxA1, as well as the binding of Rac1 GTPase, for its activity. Recently, we identified the c-Src substrate proteins Tks4 and Tks5 as functional members of a p47(phox)-related organizer superfamily. As a functional consequence of this interaction, Nox1 localizes to invadopodia, actin-rich membrane protrusions of cancer cells which facilitate pericellular proteolysis and invasive behavior. Here, we report that Tks4 and Tks5 directly bind to NoxA1. Moreover, the integrity of the N-terminal PRR of NoxA1 is essential for this direct interaction with the Tks proteins. When the PRR in NoxA1 is disrupted, Tks proteins cannot bind NoxA1 and lose their ability to support Nox1-dependent ROS generation. Consistent with this, Tks4 and Tks5 are unable to act as organizers for Nox2 because of their inability to interact with p67(phox), which lacks the N-terminal PRR, thus conferring a unique specificity to Tks4 and 5. Taken together, these results clarify the molecular basis for the interaction between NoxA1 and the Tks proteins and may provide new insights into the pharmacological design of a more effective anti-metastatic strategy.

A novel and specific NADPH oxidase-1 (Nox1) small-molecule inhibitor blocks the formation of functional invadopodia in human colon cancer cells

The NADPH oxidase (Nox) proteins catalyze the regulated formation of reactive oxygen species (ROS), which play key roles as signaling molecules in several physiological and pathophysiological processes. ROS generation by the Nox1 member of the Nox family is necessary for the formation of extracellular matrix (ECM)-degrading, actin-rich cellular structures known as invadopodia. Selective inhibition of Nox isoforms can provide reversible, mechanistic insights into these cellular processes in contrast to scavenging or inhibition of ROS production. Currently no specific Nox inhibitors have been described. Here, by high-throughput screening, we identify a subset of phenothiazines, 2-acetylphenothiazine (here referred to as ML171) (and its related 2-(trifluoromethyl)-phenothiazine) as nanomolar, cell-active, and specific Nox1 inhibitors that potently block Nox1-dependent ROS generation, with only marginal activity on other cellular ROS-producing enzymes and receptors including the other Nox isoforms. ML171 also blocks the ROS-dependent formation of ECM-degrading invadopodia in colon cancer cells. Such effects can be reversed by overexpression of Nox1 protein, which is suggestive of a selective mechanism of inhibition of Nox1 by this compound. These results elucidate the relevance of Nox1-dependent ROS generation in mechanisms of cancer invasion and define ML171 as a useful Nox1 chemical probe and potential therapeutic agent for inhibition of cancer cell invasion.

c-Src-mediated phosphorylation of NoxA1 and Tks4 induces the reactive oxygen species (ROS)-dependent formation of functional invadopodia in human colon cancer cells

Reactive oxygen species (ROS) generated by the NADPH oxidase system have been shown to be necessary for the invadopodia formation and function. We show here that the abolishment of Src-mediated phosphorylation of NoxA1 and Tks4 blocks their binding, decreases Nox1-dependent ROS generation, and inhibits the invadopodia formation and ECM degradation.

The NADPH oxidase family, consisting of Nox1-5 and Duox1-2, catalyzes the regulated formation of reactive oxygen species (ROS). Highly expressed in the colon, Nox1 needs the organizer subunit NoxO1 and the activator subunit NoxA1 for its activity. The tyrosine kinase c-Src is necessary for the formation of invadopodia, phosphotyrosine-rich structures which degrade the extracellular matrix (ECM). Many Src substrates are invadopodia components, including the novel Nox1 organizer Tks4 and Tks5 proteins. Nox1-dependent ROS generation is necessary for the maintenance of functional invadopodia in human colon cancer cells. However, the signals and the molecular machinery involved in the redox-dependent regulation of invadopodia formation remain unclear. Here, we show that the interaction of NoxA1 and Tks proteins is dependent on Src activity. Interestingly, the abolishment of Src-mediated phosphorylation of Tyr110 on NoxA1 and of Tyr508 on Tks4 blocks their binding and decreases Nox1-dependent ROS generation. The contemporary presence of Tks4 and NoxA1 unphosphorylable mutants blocks SrcYF-induced invadopodia formation and ECM degradation, while the overexpression of Tks4 and NoxA1 phosphomimetic mutants rescues this phenotype. Taken together, these results elucidate the role of c-Src activity on the formation of invadopodia and may provide insight into the mechanisms of tumor formation in colon cancers.

Targeting HSV-1 virions for specific binding to epidermal growth factor receptor-vIII-bearing tumor cells

Oncolytic herpes simplex virus (HSV) vectors have been used in early phase human clinical trials as a therapy for recurrent malignant glioblastoma. This treatment proved safe but limited improvements in patient survival were observed. The potency of these vectors might be enhanced by targeting vector infectivity to tumor cells. Glioma tumors often express a mutant form (vIII) of the epidermal growth factor receptor (EGFR) resulting in the presence of a novel epitope on the cell surface. This epitope is specifically recognized by a single chain antibody designated MR1-1. HSV-1 infection involves initial binding to heparan sulfate (HS) on the cell surface mediated primarily by the viral envelope, glycoprotein C (gC). Here we joined the MR1-1 single chain antibody (scFv) to the gC sequence deleted for the HS binding domain (HSBD) as a means of targeting viral attachment to EGFRvIII on glial tumor cells. Virions bearing MR1-1-modified-gC had 5-fold increased infectivity for EGFRvIII-bearing human glioma U87 cells compared to mutant receptor-deficient cells. Further, MR1-1/EGFRvIII mediated infection was more efficient for EGFRvIII-positive cells than was wild-type virus for either positive or negative cells. Sustained infection of EGFRvIII+ glioma cells by MR1-1-modified-gC bearing oncolytic virus, as compared to wild-type gC oncolytic virus, was also shown in subcutaneous tumors in vivo using firefly luciferase as a reporter of infection. These data demonstrate that HSV tropism can be manipulated so that virions recognize a cell specific binding site with increased infectivity for the target cell. The retargeting of HSV infection to tumor cells should enhance vector specificity, tumor cell killing and vector safety.

Protein aggregates and novel presenilin gene variants in idiopathic dilated cardiomyopathy

BACKGROUND

Heart failure is a debilitating condition resulting in severe disability and death. In a subset of cases, clustered as idiopathic dilated cardiomyopathy (iDCM), the origin of heart failure is unknown. In the brain of patients with dementia, proteinaceous aggregates and abnormal oligomeric assemblies of beta-amyloid impair cell function and lead to cell death.

METHODS AND RESULTS

We have similarly characterized fibrillar and oligomeric assemblies in the hearts of iDCM patients, pointing to abnormal protein aggregation as a determinant of iDCM. We also showed that oligomers alter myocyte Ca(2+) homeostasis. Additionally, we have identified 2 new sequence variants in the presenilin-1 (PSEN1) gene promoter leading to reduced gene and protein expression. We also show that presenilin-1 coimmunoprecipitates with SERCA2a.

CONCLUSIONS

On the basis of these findings, we propose that 2 mechanisms may link protein aggregation and cardiac function: oligomer-induced changes on Ca(2+) handling and a direct effect of PSEN1 sequence variants on excitation-contraction coupling protein function.

Directed evolution of adeno-associated virus for glioma cell transduction

Glioblastoma multiforme (GBM) is a serious form of brain cancer for which there is currently no effective treatment. Alternative strategies such as adeno-associated virus (AAV) vector mediated-genetic modification of brain tumor cells with genes encoding anti-tumor proteins have shown promising results in preclinical models of GBM, although the transduction efficiency of these tumors is often low. As higher transduction efficiency of tumor cells should lead to enhanced therapeutic efficacy, a means to rapidly engineer AAV vectors with improved transduction efficiency for individual tumors is an attractive strategy. Here we tested the possibility of identifying high-efficiency AAV vectors for human U87 glioma cells by selection in culture of a newly constructed chimeric AAV capsid library generated by DNA shuffling of six different AAV cap genes (AAV1, AAV2, AAV5, AAVrh.8, AAV9, AAVrh.10). After seven rounds of selection, we obtained a chimeric AAV capsid that transduces U87 cells at high efficiency (97% at a dose of 10(4) genome copies/cell), and at low doses it was 1.45-1.6-fold better than AAV2, which proved to be the most efficient parental capsid. Interestingly, the new AAV capsid displayed robust gene delivery properties to all glioma cells tested (including primary glioma cells) with relative fluorescence indices ranging from 1- to 14-fold higher than AAV2. The selected vector should be useful for in vitro glioma research when efficient transduction of several cell lines is required, and provides proof-of-concept that an AAV library can be used to generate AAV vectors with enhanced transduction efficiency of glioma cells.

Emerging evidence for the importance of phosphorylation in the regulation of NADPH oxidases

The NADPH oxidase (Nox) enzyme family generates reactive oxygen species (ROS) that contribute to cell signaling, innate immune responses, proliferation, and transcription. The signaling mechanisms that regulate this important enzyme family are only beginning to be understood. Evidence is emerging which suggests that phosphorylation of Nox and/or their regulatory components may be important means of modulating their activity. We describe here the evidence for Nox regulation through the action of kinases, and speculate on how such regulatory mechanisms might contribute to the development of pathological disease states.

Novel p47(phox)-related organizers regulate localized NADPH oxidase 1 (Nox1) activity

The mechanisms that determine localized formation of reactive oxygen species (ROS) through NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase (Nox) family members in nonphagocytic cells are unknown. We show that the c-Src substrate proteins Tks4 (tyrosine kinase substrate with four SH3 domains) and Tks5 are functional members of a p47(phox)-related organizer superfamily. Tks proteins selectively support Nox1 and Nox3 (and not Nox2 and Nox4) activity in reconstituted cellular systems and interact with the NoxA1 activator protein through an Src homology 3 domain-mediated interaction. Endogenous Tks4 is required for Rac guanosine triphosphatase- and Nox1-dependent ROS production by DLD1 colon cancer cells. Our results are consistent with the Tks-mediated recruitment of Nox1 to invadopodia that form in DLD1 cells in a Tks- and Nox-dependent fashion. We propose that Tks organizers represent previously unrecognized members of an organizer superfamily that link Nox to localized ROS formation.

Prevention of ventricular arrhythmias with sarcoplasmic reticulum Ca2+ ATPase pump overexpression in a porcine model of ischemia reperfusion

BACKGROUND

Ventricular arrhythmias are life-threatening complications of heart failure and myocardial ischemia. Increased diastolic Ca2+ overload occurring in ischemia leads to afterdepolarizations and aftercontractions that are responsible for cellular electric instability. We inquired whether sarcoplasmic reticulum Ca2+ ATPase pump (SERCA2a) overexpression could reduce ischemic ventricular arrhythmias by modulating Ca2+ overload.

METHODS AND RESULTS

SERCA2a overexpression in pig hearts was achieved by intracoronary gene delivery of adenovirus in the 3 main coronary arteries. Homogeneous distribution of the gene was obtained through the left ventricle. After gene delivery, the left anterior descending coronary artery was occluded for 30 minutes to induce myocardial ischemia followed by reperfusion. We compared this model with a model of permanent coronary artery occlusion. Twenty-four-hour ECG Holter recordings showed that SERCA2a overexpression significantly reduced the number of episodes of ventricular tachycardia after reperfusion, whereas no significant difference was found in the occurrence of sustained or nonsustained ventricular tachycardia and ventricular fibrillation in pigs undergoing permanent occlusion.

CONCLUSIONS

We show that Ca2+ cycling modulation using SERCA2a overexpression reduces ventricular arrhythmias after ischemia-reperfusion. Strategies that modulate postischemic Ca2+ overload may have clinical promise for the treatment of ventricular arrhythmias.

The involvement of the tyrosine kinase c-Src in the regulation of reactive oxygen species generation mediated by NADPH oxidase-1

NADPH oxidase (Nox) family enzymes are one of the main sources of cellular reactive oxygen species (ROS), which have been shown to function as second messenger molecules. To date, seven members of this family have been reported, including Nox1-5 and Duox1 and -2. With the exception of Nox2, the regulation of the Nox enzymes is still poorly understood. Nox1 is highly expressed in the colon, and it requires two cytosolic regulators, NoxO1 and NoxA1, as well as the binding of Rac1 GTPase, for its activity. In this study, we investigate the role of the tyrosine kinase c-Src in the regulation of ROS formation by Nox1. We show that c-Src induces Nox1-mediated ROS generation in the HT29 human colon carcinoma cell line through a Rac-dependent mechanism. Treatment of HT29 cells with the Src inhibitor PP2, expression of a kinase-inactive form of c-Src, and c-Src depletion by small interfering RNA (siRNA) reduce both ROS generation and the levels of active Rac1. This is associated with decreased Src-mediated phosphorylation and activation of the Rac1-guanine nucleotide exchange factor Vav2. Consistent with this, Vav2 siRNA that specifically reduces endogenous Vav2 protein is able to dramatically decrease Nox1-dependent ROS generation and abolish c-Src-induced Nox1 activity. Together, these results establish c-Src as an important regulator of Nox1 activity, and they may provide insight into the mechanisms of tumor formation in colon cancers.

Identification of a conserved Rac-binding site on NADPH oxidases supports a direct GTPase regulatory mechanism

The NADPH oxidases (Noxs) are a family of superoxide-generating enzymes implicated in a variety of biological processes. Full activity of Nox1, -2, and -3 requires the action of a Rac GTPase. A direct regulatory interaction of Rac with Nox2 has been proposed as part of a two-step mechanism for regulating electron transfer during superoxide formation. Using truncation analysis of Rac binding to the cytoplasmic tail of Nox2, along with peptides derived from this region in cell-free assays, we identify a Rac interaction site within amino acids 419-430 of Nox2. This region is required for binding Rac2 but not p47(phox) or p67(phox) cytosolic regulatory factors. A cell-permeant version of the peptide encompassing amino acids 419-430 specifically inhibits NADPH oxidase activation in intact human neutrophils. Mutational analysis of the putative Rac-binding site revealed specific residues, particularly Lys-421, Tyr-425, and Lys-426, individually required for Rac-dependent NADPH oxidase activity that are conserved in the Rac-regulated Nox1, Nox2, and Nox3 enzymes but not in Nox4 or Nox5. Mutation of the conserved residues in the Rac-binding site of Nox1 also result in the loss of Rac-dependent activity. Our data identify a functional Rac interaction site conserved in Rac-dependent Noxs and support a direct regulatory interaction of Rac GTPases to promote activation of these NADPH oxidases.

Depletion of peripheral macrophages and brain microglia increases brain tumor titers of oncolytic viruses

Clinical trials have proven oncolytic virotherapy to be safe but not effective. We have shown that oncolytic viruses (OV) injected into intracranial gliomas established in rodents are rapidly cleared, and this is associated with up-regulation of markers (CD68 and CD163) of cells of monocytic lineage (monocytes/microglia/macrophages). However, it is unclear whether these cells directly impede intratumoral persistence of OV through phagocytosis and whether they infiltrate the tumor from the blood or the brain parenchyma. To investigate this, we depleted phagocytes with clodronate liposomes (CL) in vivo through systemic delivery and ex vivo in brain slice models with gliomas. Interestingly, systemic CL depleted over 80% of peripheral CD163+ macrophages in animal spleen and peripheral blood, thereby decreasing intratumoral infiltration of these cells, but CD68+ cells were unchanged. Intratumoral viral titers increased 5-fold. In contrast, ex vivo CL depleted only CD68+ cells from brain slices, and intratumoral viral titers increased 10-fold. These data indicate that phagocytosis by both peripheral CD163+ and brain-resident CD68+ cells infiltrating tumor directly affects viral clearance from tumor. Thus, improved therapeutic efficacy may require modulation of these innate immune cells. In support of this new therapeutic paradigm, we observed intratumoral up-regulation of CD68+ and CD163+ cells following treatment with OV in a patient with glioblastoma.

Cyclophosphamide increases transgene expression mediated by an oncolytic adenovirus in glioma-bearing mice monitored by bioluminescence imaging

Approaches to improve the oncolytic potency of replication-competent adenoviruses include the insertion of therapeutic transgenes into the viral genome. Little is known about the levels and duration of in vivo transgene expression by cells infected with such "armed" viruses. Using a tumor-selective adenovirus encoding firefly luciferase (AdDelta24CMV-Luc) we investigated these questions in an intracranial mouse model for malignant glioma. Luciferase expression was detected by bioluminescence imaging, and the effect of the immunosuppressive agent cyclophosphamide (CPA) on transgene expression was assessed. Intratumoral AdDelta24CMV-Luc injection led to a localized dose-dependent expression of luciferase. Surprisingly, this expression decreased rapidly during the course of 14 days. In contrast, mice injected with nonreplicating Ad.CMV-Luc demonstrated stable transgene expression. Treatment of mice with CPA in combination with AdDelta24CMV-Luc retarded the loss of transgene expression. Staining of mouse brains for inflammatory cells demonstrated decreased tumor infiltration by immune cells in CPA-treated mice. Moreover, in immunodeficient NOD/SCID mice loss of transgene expression was less rapid and not prevented by CPA treatment. Together, our data demonstrate that transgene expression and viral replication decrease rapidly after intratumoral injection of oncolytic adenovirus in mouse brains and that treatment with the immunomodulator CPA prolongs viral-mediated gene expression.

Cyclophosphamide enhances glioma virotherapy by inhibiting innate immune responses

Clinical trials are testing oncolytic viruses (OVs) as therapies for cancer. We have shown that animals that have brain tumors and are treated with a herpes simplex virus (HSV)-derived OV live significantly longer when cyclophosphamide (CPA) is preadministered. Here, we explore the mechanisms behind this finding. In a syngeneic rat glioma model, intratumoral HSV administration is associated with rapid increase of natural killer cells, microglia/macrophages (CD68+ and CD163+), and IFN-gamma. Pretreatment with CPA enhances HSV replication and oncolysis and reduces an HSV-mediated increase in CD68+ and CD163+ cells and intratumoral IFN-gamma. Molecular imaging shows CPA pretreatment to inhibit HSV-induced infiltration of tumor-associated phagocytic cells. Our results reveal molecular and cellular mechanisms that inhibit intratumoral spread of HSV and suggest a therapeutic path for improving the efficacy of virotherapy as a treatment for cancer.

SERCA2a in heart failure: role and therapeutic prospects

Ca(2+) is a key molecule controlling several cellular processes, from fertilization to cell death, in all cell types. In excitable and contracting cells, such as cardiac myocytes, Ca(2+) controls muscle contractility. The spatial and temporal segregation of Ca(2+) concentrations are central to maintain its concentration gradients across the cells and the cellular compartments for proper function. SERCA2a is a cornerstone molecule for maintaining a balanced concentration of Ca(2+) during the cardiac cycle, since it controls the transport of Ca(2+) to the sarcoplasmic reticulum (SR) during relaxation. Alterations of the activity of this pump have been widely investigated, emphasizing its central role in the control of Ca(2+) homeostasis and consequently in the pathogenesis of the contractile defect seen with heart failure. This review focuses on the molecular characteristics of the pump, its role during the cardiac cycle and the prospects derived from the manipulation of SERCA2a for heart failure treatment.

Tissue inhibitor of metalloproteinase-3 expression from an oncolytic adenovirus inhibits matrix metalloproteinase activity in vivo without affecting antitumor efficacy in malignant glioma

Oncolytic adenoviruses exhibiting tumor-selective replication are promising anticancer agents. Insertion and expression of a transgene encoding tissue inhibitor of metalloproteinase-3 (TIMP-3), which has been reported to inhibit angiogenesis and tumor cell infiltration and induce apoptosis, may improve the antitumor activity of these agents. To assess the effects of TIMP-3 gene transfer to glioma cells, a replication-defective adenovirus encoding TIMP-3 (Ad.TIMP-3) was employed. Ad.TIMP-3 infection of a panel of glioma cell cultures decreased the proliferative capacity of these cells and induced morphologic changes characteristic for apoptosis. Next, a conditionally replicating adenovirus encoding TIMP-3 was constructed by inserting the TIMP-3 expression cassette into the E3 region of the adenoviral backbone containing a 24-bp deletion in E1A. This novel oncolytic adenovirus, AdDelta24TIMP-3, showed enhanced oncolytic activity on a panel of primary cell cultures and two glioma cell lines compared with the control oncolytic virus AdDelta24Luc. In vivo inhibition of matrix metalloproteinase (MMP) activity by AdDelta24TIMP-3 was shown in s.c. glioma xenografts. The functional activity of TIMP-3 was imaged noninvasively using a near-IR fluorescent MMP-2-activated probe. Tumoral MMP-2 activity was significantly reduced by 58% in the AdDelta24TIMP-3-treated tumors 24 hours after infection. A study into the therapeutic effects of combined oncolytic and antiproteolytic therapy was done in both a s.c. and an intracranial model for malignant glioma. Treatment of s.c. (U-87MG) or intracranial (U-87deltaEGFR) tumors with AdDelta24TIMP-3 and AdDelta24Luc both significantly inhibited tumor growth and prolonged survival compared with PBS-treated controls. However, expression of TIMP-3 in the context of AdDelta24 did not significantly affect the antitumor efficacy of this oncolytic agent.

Transcription regulation by the adaptor protein Fe65 and the nucleosome assembly factor SET

Fe65 protein interacts with the cytosolic domain of the amyloid precursor APP. Its possible involvement in gene regulation is suggested by numerous observations, including those demonstrating that it activates transcription. Here, we show that the Fe65 transcription activation domain overlaps with the WW domain of Fe65 and binds to the nucleosome assembly factor SET. This protein is required for the Fe65-mediated transactivation of a reporter gene. Two-step chromatin immunoprecipitation experiments demonstrate that a complex including Fe65/AICD/Tip60 and SET is associated with the KAI1 gene promoter. Suppression of SET levels by RNA interference shows that this protein is required for full levels of basal transcription of the KAI1 gene. These results further support the function of Fe65 and APP in gene regulation and show a new role for the SET factor.

Mutation of the feh-1 gene, the Caenorhabditis elegans orthologue of mammalian Fe65, decreases the expression of two acetylcholinesterase genes

The molecular adaptor Fe65 is one of the cytosolic ligands of the Alzheimer's beta-amyloid precursor protein (APP), and this complex is believed to play important roles in mammalian cells. Upon cleavage of APP by specific processing activities, the complex between Fe65 and the APP intracellular domain (AICD) translocates to the nucleus. Experimental evidence suggests that the Fe65-AICD complex regulates gene transcription. In Caenorhabditis elegans the orthologue of the Fe65 gene, feh-1, regulates pharyngeal activity. In fact, the rate of pharyngeal contraction is increased following transient or stable suppression of the feh-1 gene expression. Here we show that the increased contraction rate of the pharynx in feh-1 mutant worms is associated to decreased acetylcholinesterase activity. The decreased activity is accompanied by reduced expression of ace-1 and ace-2 transcripts, coding for the two major acetylcholinesterase activities in the nematode. These results indicate a target of the regulatory mechanisms based on the Fe65-APP complex that could be relevant for the pathogenesis of Alzheimer's disease.