Engineering human pluripotent stem cell lines to evade xenogeneic transplantation barriers.

Successful allogeneic human pluripotent stem cell (hPSC)-derived therapies must overcome immunological rejection by the recipient. To build reagents to define these barriers, we genetically ablated ß2M, TAP1, CIITA, CD74, MICA, and MICB to limit expression of HLA-I, HLA-II, and natural killer (NK) cell activating ligands in hPSCs. Transplantation of these cells that also expressed covalent single chain trimers of Qa1 and H2-Kb to inhibit NK cells and CD55, Crry, and CD59 to inhibit complement deposition led to persistent teratomas in wild-type mice. Transplantation of HLA-deficient hPSCs into mice genetically deficient in complement and depleted of NK cells also led to persistent teratomas. Thus, T cell, NK cell, and complement evasion are necessary to prevent immunological rejection of hPSCs and their progeny. These cells and versions expressing human orthologs of immune evasion factors can be used to define cell type-specific immune barriers and conduct preclinical testing in immunocompetent mouse models.

Engineering Human Pluripotent Stem Cell Lines to Evade Xenogeneic Transplantation Barriers.

Allogeneic human pluripotent stem cell (hPSC)-derived cells and tissues for therapeutic transplantation must necessarily overcome immunological rejection by the recipient. To define these barriers and to create cells capable of evading rejection for preclinical testing in immunocompetent mouse models, we genetically ablated ß2m, Tap1, Ciita, Cd74, Mica, and Micb to limit expression of HLA-I, HLA-II, and natural killer cell activating ligands in hPSCs. Though these and even unedited hPSCs readily formed teratomas in cord blood-humanized immunodeficient mice, grafts were rapidly rejected by immunocompetent wild-type mice. Transplantation of these cells that also expressed covalent single chain trimers of Qa1 and H2-Kb to inhibit natural killer cells and CD55, Crry, and CD59 to inhibit complement deposition led to persistent teratomas in wild-type mice. Expression of additional inhibitory factors such as CD24, CD47, and/or PD-L1 had no discernible impact on teratoma growth or persistence. Transplantation of HLA-deficient hPSCs into mice genetically deficient in complement and depleted of natural killer cells also led to persistent teratomas. Thus, T cell, NK cell, and complement evasion are necessary to prevent immunological rejection of hPSCs and their progeny. These cells and versions expressing human orthologs of immune evasion factors can be used to refine tissue- and cell type-specific immune barriers, and to conduct preclinical testing in immunocompetent mouse models.

The nutritional supplement taurine activates p53-dependent and independent tumor suppressor mechanisms in various cellular models of ovarian cancer.

Loss of treatment-induced ovarian carcinoma (OC) growth suppression poses a major clinical challenge because it leads to disease recurrence. Therefore, there is a compelling need for well- -tolerated approaches that can support tumor growth-suppression after therapy is stopped. We have profiled ascites as OC tumor microenvironments to search for potential non-toxic soluble components that would activate tumor suppressor pathways in OC cells. Our investigations revealed that low levels of taurine, a non-proteogenic sulfonic amino acid, were present within OC ascites. Taurine supplementation, beyond levels found in ascites, induced growth suppression without causing cytotoxicity in various OC cells, including chemotherapy-resistant cell clones and patient-derived organoids representing primary or chemotherapy recovered disease. Inhibition of proliferation by taurine was linked to increased mutant or wild-type p53 proteins binding to DNA, induction of p21, and independently of p53, TIGAR expression. Taurine-induced activation of p21 and TIGAR was associated with suppression of cell-cycle progression, glycolysis, and mitochondrial respiration. Expression of p21 or TIGAR in OC cells mimicked taurine-induced growth suppression. Our studies support the potential therapeutic value of taurine supplementation in OC.

Integrating deep learning and unbiased automated high-content screening to identify complex disease signatures in human fibroblasts.

Drug discovery for diseases such as Parkinson's disease are impeded by the lack of screenable cellular phenotypes. We present an unbiased phenotypic profiling platform that combines automated cell culture, high-content imaging, Cell Painting, and deep learning. We applied this platform to primary fibroblasts from 91 Parkinson's disease patients and matched healthy controls, creating the largest publicly available Cell Painting image dataset to date at 48 terabytes. We use fixed weights from a convolutional deep neural network trained on ImageNet to generate deep embeddings from each image and train machine learning models to detect morphological disease phenotypes. Our platform's robustness and sensitivity allow the detection of individual-specific variation with high fidelity across batches and plate layouts. Lastly, our models confidently separate LRRK2 and sporadic Parkinson's disease lines from healthy controls (receiver operating characteristic area under curve 0.79 (0.08 standard deviation)), supporting the capacity of this platform for complex disease modeling and drug screening applications.

Discovery of [11C]MK-6884: A Positron Emission Tomography (PET) Imaging Agent for the Study of M4Muscarinic Receptor Positive Allosteric Modulators (PAMs) in Neurodegenerative Diseases.

The measurement of receptor occupancy (RO) using positron emission tomography (PET) has been instrumental in guiding discovery and development of CNS directed therapeutics. We and others have investigated muscarinic acetylcholine receptor 4 (M4) positive allosteric modulators (PAMs) for the treatment of symptoms associated with neuropsychiatric disorders. In this article, we describe the synthesis, in vitro, and in vivo characterization of a series of central pyridine-related M4 PAMs that can be conveniently radiolabeled with carbon-11 as PET tracers for the in vivo imaging of an allosteric binding site of the M4 receptor. We first demonstrated its feasibility by mapping the receptor distribution in mouse brain and confirming that a lead molecule 1 binds selectively to the receptor only in the presence of the orthosteric agonist carbachol. Through a competitive binding affinity assay and a number of physiochemical properties filters, several related compounds were identified as candidates for in vivo evaluation. These candidates were then radiolabeled with 11C and studied in vivo in rhesus monkeys. This research eventually led to the discovery of the clinical radiotracer candidate [11C]MK-6884.

A Diffusion-Based and Dynamic 3D-Printed Device That Enables Parallel in Vitro Pharmacokinetic Profiling of Molecules.

The process of bringing a drug to market involves many steps, including the preclinical stage, where various properties of the drug candidate molecule are determined. These properties, which include drug absorption, distribution, metabolism, and excretion, are often displayed in a pharmacokinetic (PK) profile. While PK profiles are determined in animal models, in vitro systems that model in vivo processes are available, although each possesses shortcomings. Here, we present a 3D-printed, diffusion-based, and dynamic in vitro PK device. The device contains six flow channels, each with integrated porous membrane-based insert wells. The pores of these membranes enable drugs to freely diffuse back and forth between the flow channels and the inserts, thus enabling both loading and clearance portions of a standard PK curve to be generated. The device is designed to work with 96-well plate technology and consumes single-digit milliliter volumes to generate multiple PK profiles, simultaneously. Generation of PK profiles by use of the device was initially performed with fluorescein as a test molecule. Effects of such parameters as flow rate, loading time, volume in the insert well, and initial concentration of the test molecule were investigated. A prediction model was generated from this data, enabling the user to predict the concentration of the test molecule at any point along the PK profile within a coefficient of variation of ∼ 5%. Depletion of the analyte from the well was characterized and was determined to follow first-order rate kinetics, indicated by statistically equivalent (p > 0.05) depletion half-lives that were independent of the starting concentration. A PK curve for an approved antibiotic, levofloxacin, was generated to show utility beyond the fluorescein test molecule.

HIV cell fusion assay: phenotypic screening tool for the identification of HIV entry inhibitors via CXCR4.

The health and disease-related biology of the CXCR4 chemokine receptor presents the challenge of finding a small molecule that can bind CXCR4 and block T-cell tropic human immunodeficiency virus type 1 (HIV-1) cell entry, while preserving the ability of CXCR4 to respond to its native ligand, CXCL12. HIV entry into the host cell involves the interaction of the viral envelope glycoprotein gp120 binding to CD4, followed by a rearrangement in gp120, and subsequent interaction with the chemokine receptor CXCR4 or CCR5. These initial events can be re-created in a cell fusion assay that represents a surrogate system, mimicking the early stages of viral entry via these host cell receptors. In the current study, a T-tropic HIV cell fusion assay was established using U2OS cells expressing the envelope glycoprotein gp160 from the T-tropic HIV NL4-3 and HeLa cells expressing CD4 and CXCR4. Detection of the cell fusion event was based on a Gal4/VP16-activated ß-lactamase signal and was measured by automated microscopy or laser scanning plate cytometry. Changes in morphology associated with cell fusion were combined with ß-lactamase activity to generate results with robust assay statistics in both 384-well and 1536-well plates. Compounds were subsequently characterized by CXCR4 signaling assays to eliminate functional antagonists and allow the identification of a function-sparing HIV entry inhibitor.

Murgocil is a highly bioactive staphylococcal-specific inhibitor of the peptidoglycan glycosyltransferase enzyme MurG.

Modern medicine is founded on the discovery of penicillin and subsequent small molecules that inhibit bacterial peptidoglycan (PG) and cell wall synthesis. However, the discovery of new chemically and mechanistically distinct classes of PG inhibitors has become exceedingly rare, prompting speculation that intracellular enzymes involved in PG precursor synthesis are not 'druggable' targets. Here, we describe a ß-lactam potentiation screen to identify small molecules that augment the activity of ß-lactams against methicillin-resistant Staphylococcus aureus (MRSA) and mechanistically characterize a compound resulting from this screen, which we have named murgocil. We provide extensive genetic, biochemical, and structural modeling data demonstrating both in vitro and in whole cells that murgocil specifically inhibits the intracellular membrane-associated glycosyltransferase, MurG, which synthesizes the lipid II PG substrate that penicillin binding proteins (PBPs) polymerize and cross-link into the cell wall. Further, we demonstrate that the chemical synergy and cidality achieved between murgocil and the ß-lactam imipenem is mediated through MurG dependent localization of PBP2 to the division septum. Collectively, these data validate our approach to rationally identify new target-specific bioactive ß-lactam potentiation agents and demonstrate that murgocil now serves as a highly selective and potent chemical probe to assist our understanding of PG biosynthesis and cell wall biogenesis across Staphylococcal species.

SCH 1473759, a novel Aurora inhibitor, demonstrates enhanced anti-tumor activity in combination with taxanes and KSP inhibitors.

PURPOSE: Aurora kinases are required for orderly progression of cells through mitosis, and inhibition of these kinases by siRNA or small molecule inhibitors results in cell death. We previously reported the synthesis of SCH 1473759, a novel sub-nanomolar Aurora A/B inhibitor. METHODS: We utilized SCH 1473759 and a panel of tumor cell lines and xenograft models to gain knowledge about optimal dosing schedule and chemotherapeutic combinations for Aurora A/B inhibitors. RESULTS: SCH 1473759 was active against a large panel of tumor cell lines from different tissue origin and genetic backgrounds. Asynchronous cells required 24-h exposure to SCH 1473759 for maximal induction of >4 N DNA content and inhibition of cell growth. However, following taxane- or KSP inhibitor-induced mitotic arrest, less than 4-h exposure induced >4 N DNA content. This finding correlated with the ability of SCH 1473759 to accelerate exit from mitosis in response to taxane- and KSP inhibitor-induced arrest. We tested various dosing schedules in vivo and demonstrated SCH 1473759 dose- and schedule-dependent anti-tumor activity in four human tumor xenograft models. Further, the efficacy was enhanced in combination with taxanes and found to be most efficacious when SCH 1473759 was dosed 12-h post-taxane treatment. CONCLUSIONS: SCH 1473759 demonstrated potent mechanism-based activity, and activity was shown to be enhanced in combination with taxanes and KSP inhibitors. This information may be useful for optimizing the clinical efficacy of Aurora inhibitors.

Discovery of novel chemotypes to a G-protein-coupled receptor through ligand-steered homology modeling and structure-based virtual screening.

Melanin-concentrating hormone receptor 1 (MCH-R1) is a G-protein-coupled receptor (GPCR) and a target for the development of therapeutics for obesity. The structure-based development of MCH-R1 and other GPCR antagonists is hampered by the lack of an available experimentally determined atomic structure. A ligand-steered homology modeling approach has been developed (where information about existing ligands is used explicitly to shape and optimize the binding site) followed by docking-based virtual screening. Top scoring compounds identified virtually were tested experimentally in an MCH-R1 competitive binding assay, and six novel chemotypes as low micromolar affinity antagonist "hits" were identified. This success rate is more than a 10-fold improvement over random high-throughput screening, which supports our ligand-steered method. Clearly, the ligand-steered homology modeling method reduces the uncertainty of structure modeling for difficult targets like GPCRs.

P518/Qrfp sequence polymorphisms in SAMP6 osteopenic mouse.

Mice lacking GPR103A expression display osteopenia. Analysis of mouse quantitative trait loci literature associated with bone mineral density suggested GPR103A ligand P518/Qrfp (chromosome 2qB) as a candidate osteoporosis gene. Promoter and coding regions of mouse P518/Qrfp were sequenced from genomic DNA obtained from the osteoporosis-prone strain SAMP6 and control strains SAMR1, A/J, AKR/J, BALB/c, C3H/HeJ, C57BL/6J, and DBA/2J. Four single-nucleotide polymorphisms (SNPs) were identified in only SAMP6 genomic DNA, g.-1773 T-->C, g.110 A-->G (N37S), g.188 G-->A (R63K), and g.135 T-->C (H45H). The promoter SNP generated a novel neuron-restrictive silencing factor binding site, a repressor that decreases gene expression in nonneuronal tissues. TaqMan analysis demonstrated fivefold lower P518/Qrfp liver expression in SAMP6 versus SAMR1 or C57BL/6J control strains. Tissue distribution of human, mouse, and rat P518/Qrfp and its receptors showed expression in bone and spinal cord. A direct role for P518/Qrfp function in maintaining bone mineral density is suggested.

The KiSS-1 receptor GPR54 is essential for the development of the murine reproductive system.

GPR54 is a G-protein-coupled receptor that displays a high percentage of identity in the transmembrane domains with the galanin receptors. The ligand for GPR54 has been identified as a peptide derived from the KiSS-1 gene. KiSS-1 has been shown to have anti-metastatic effects, suggesting that KiSS-1 or its receptor represents a potential therapeutic target. To further our understanding of the physiological function of this receptor, we have generated a mutant mouse line with a targeted disruption of the GPR54 receptor (GPR54 -/-). The analysis of the GPR54 mutant mice revealed developmental abnormalities of both male and female genitalia and histopathological changes in tissues which normally contain sexually dimorphic features. These data suggest a role for GPR54/KiSS-1 in normal sexual development, and indicate that study of the GPR54 mutant mice may provide valuable insights into human reproductive syndromes.

Cloning and characterization of murine neuromedin U receptors.

Neuromedin U (NmU) is a neuropeptide involved in various physiological functions such as feeding behavior, muscle contractile activity, and regulation of intestinal ion transport. Recently, two human G protein-coupled receptors have been identified as NmU-specific receptors, NmU-R1 and NmU-R2, which share 55% amino acid identity. It is unclear however, which of the two receptors mediates responses to NmU observed in rodent models. Attempts to define the pharmacological profile of the two receptors are confounded by overlapping expression of the two receptors and a lack of subtype-selective compounds. In order to establish a basis to further our understanding of the function of these receptors, we cloned and characterized the mouse homologues of the two human NmU receptors. Mouse NmU-R1 and mouse NmU-R2 are 79 and 81% identical to their respective human homologues. Expression of NmU-R1 was mainly observed in testis, gastrointestinal (GI) tract, and immune system, while NmU-R2 was primarily expressed in brain tissues. Each mouse receptor was independently expressed in HEK293 cells and demonstrated a dose-dependent calcium flux in response to NmU-8, NmU-23 and NmU-25. In an attempt to identify a synthetic NmU peptide that would exhibit selectivity at one of the two receptors, we examined the functional activity of eight alanine-substituted NmU-8 peptides. These experiments demonstrated that alanine substitution at positions 5 and 7 affects the functional activity of the peptide at both receptors. The arginine residue at position 7 is required for NmU-8 activity at either receptor while alanine substitution at position 5 selectively affects the potency and the efficacy at mNmU-R1. These experiments validate the use of rodent models to characterize NmU function relative to humans and suggest that substitution at Arginine-5 of NmU-8 may provide a receptor selective peptide.

Molecular modeling and site-specific mutagenesis of the histamine-binding site of the histamine H4 receptor.

The histamine H4 receptor is a novel G-protein-coupled receptor with a unique pharmacological profile. The distribution of H4 mRNA suggests that it may play a role in the regulation of immune function, particularly with respect to allergy and asthma. To define the histamine-binding site of this receptor, molecular modeling and site-directed mutagenesis were used to predict and alter amino acids residing in the histamine-binding pocket. The effects of these alterations on histamine binding and receptor activation were then assessed. Our results indicate that Asp94 (3.32) in transmembrane region (TM) 3 and Glu182 (5.46) in TM5 are critically involved in histamine binding. Asp94 probably serves as a counter-anion to the cationic amino group of histamine, whereas Glu182 (5.46) interacts with the N(tau) nitrogen atom of the histamine imidazole ring via an ion pair. In contrast, Thr178 (5.42) and Ser179 (5.43) in TM5 are not significantly involved in either histamine binding or receptor activation. These results resemble those for the analogous residues in the H1 histamine receptor but contrast with findings regarding the H2 histamine receptor. Our results also demonstrate that Asn147 (4.57) in TM4 and Ser320 (6.52) in TM6 play a role in receptor activation but are not involved in histamine binding. Taken together, these data indicate that although histamine seems to bind to the H4 receptor in a fashion similar to that predicted for the other histamine receptor subtypes, there are also important differences that can probably be exploited for the discovery of novel H4-selective compounds.