A Perfused In Vitro Human iPSC-Derived Blood-Brain Barrier Faithfully Mimics Transferrin Receptor-Mediated Transcytosis of Therapeutic Antibodies

Delivering biologics to elicit a therapeutic response in the central nervous system (CNS) remains challenging due to the presence of the blood-brain barrier (BBB). Receptor-mediated transcytosis is a strategy to improve brain exposure after systemic drug administration. The availability of a clinically relevant in vitro BBB model is crucial to investigate transcytosis pathways and to predict the penetration of biologics into the CNS. We created a perfused human in vitro BBB model made of induced pluripotent stem cells (iPSC)-derived brain microvascular endothelial cells (BMEC) for studying transferrin receptor-mediated transcytosis. iPSC-derived BMEC were seeded in the top channel of a three-lane microfluidic device (OrganoPlate®). After 2 days in culture, the established cell model exhibited relevant BBB features, including physiological transendothelial electrical resistance in a transwell setting (1500 Ω*cm2), reduced apparent permeability (Papp) to the fluorescence tracer Lucifer yellow (20-fold less than cell-free chips), expression of key BBB markers such as tight junctions proteins, transporters, receptors and functional P-gp efflux pump. Moreover, the model exhibited functional transferrin receptor-mediated uptake and transcytosis. To assess selective transferrin receptor-mediated transcytosis, a mixture of anti-human transferrin receptor (MEM-189) and control (sheep IgG anti-bovine serum albumin) antibodies was perfused in the top channel for 2 h. The Papp of MEM-189 was 11-fold higher than that of the control antibody, demonstrating facilitated receptor-mediated transcytosis. Compared to published work reporting a 2-fold ratio, this result is remarkable and establishes the suitability of our model for exploring receptor-mediated transcytosis and screening of antibodies for putative brain shuttle application. A perfused in vitro human model made of iPSC-derived BMEC with the chief characteristics (barrier tightness, functionality) of the human BBB can be applied to study transferrin receptor (TfR)-mediated transcytosis of therapeutic antibodies. This may bring critical advances in drug shuttle technology. Graphical abstract generated with biorender.com.

Ligand-Specific Allosteric Coupling Controls G-Protein-Coupled Receptor Signaling

Allosteric coupling describes a reciprocal process whereby G-protein-coupled receptors (GPCRs) relay ligand-induced conformational changes from the extracellular binding pocket to the intracellular signaling surface. Therefore, GPCR activation is sensitive to both the type of extracellular ligand and intracellular signaling protein. We hypothesized that ligand-specific allosteric coupling may result in preferential (i.e., biased) engagement of downstream effectors. However, the structural basis underlying ligand-dependent control of this essential allosteric mechanism is poorly understood. Here, we show that two sets of extended muscarinic acetylcholine receptor M₁ agonists, which only differ in linker length, progressively constrain receptor signaling. We demonstrate that stepwise shortening of their chemical linker gradually hampers binding pocket closure, resulting in divergent coupling to distinct G-protein families. Our data provide an experimental strategy for the design of ligands with selective G-protein recognition and reveal a potentially general mechanism of ligand-specific allosteric coupling.

Direct targeting of Gαq and Gα11 oncoproteins in cancer cells

Somatic gain-of-function mutations of GNAQ and GNA11, which encode α subunits of heterotrimeric Gαq/11 proteins, occur in about 85% of cases of uveal melanoma (UM), the most common cancer of the adult eye. Molecular therapies to directly target these oncoproteins are lacking, and current treatment options rely on radiation, surgery, or inhibition of effector molecules downstream of these G proteins. A hallmark feature of oncogenic Gαq/11 proteins is their reduced intrinsic rate of hydrolysis of guanosine triphosphate (GTP), which results in their accumulation in the GTP-bound, active state. Here, we report that the cyclic depsipeptide FR900359 (FR) directly interacted with GTPase-deficient Gαq/11 proteins and preferentially inhibited mitogenic ERK signaling rather than canonical phospholipase Cβ (PLCβ) signaling driven by these oncogenes. Thereby, FR suppressed the proliferation of melanoma cells in culture and inhibited the growth of Gαq-driven UM mouse xenografts in vivo. In contrast, FR did not affect tumor growth when xenografts carried mutated B-RafV600E as the oncogenic driver. Because FR enabled suppression of malignant traits in cancer cells that are driven by activating mutations at codon 209 in Gαq/11 proteins, we envision that similar approaches could be taken to blunt the signaling of non-Gαq/11 G proteins.

Repurposing HAMI3379 to Block GPR17 and Promote Rodent and Human Oligodendrocyte Differentiation

Identification of additional uses for existing drugs is a hot topic in drug discovery and a viable alternative to de novo drug development. HAMI3379 is known as an antagonist of the cysteinyl-leukotriene CysLT₂ receptor, and was initially developed to treat cardiovascular and inflammatory disorders. In our study we identified HAMI3379 as an antagonist of the orphan G protein-coupled receptor GPR17. HAMI3379 inhibits signaling of recombinant human, rat, and mouse GPR17 across various cellular backgrounds, and of endogenous GPR17 in primary rodent oligodendrocytes. GPR17 blockade by HAMI3379 enhanced maturation of primary rat and mouse oligodendrocytes, but was without effect in oligodendrocytes from GPR17 knockout mice. In human oligodendrocytes prepared from inducible pluripotent stem cells, GPR17 is expressed and its activation impaired oligodendrocyte differentiation. HAMI3379, conversely, efficiently favored human oligodendrocyte differentiation. We propose that HAMI3379 holds promise for pharmacological exploitation of orphan GPR17 to enhance regenerative strategies for the promotion of remyelination in patients.

Allosteric modulators targeting CNS muscarinic receptors

Muscarinic acetylcholine receptors are G protein-coupled receptors (GPCRs) which are broadly expressed in the central nervous system (CNS) and other tissues in the periphery. They emerge as important drug targets for a number of diseases including Alzheimer's disease, Parkinson's disease, and schizophrenia. Muscarinic receptors are divided into five subtypes (M₁-M₅) of which M₁-M₄ have been crystalized. All subtypes possess at least one allosteric binding site which is located in the extracellular region of the receptor on top of the ACh (i.e. orthosteric) binding site. The former can be specifically targeted by chemical compounds (mostly small molecules) and binding of such allosteric modulators affects the affinity and/or efficacy of orthosteric ligands. This allows highly specific modulation of GPCR function and, from a drug discovery point of view, may be advantageous in terms of subtype selectivity and biased signaling. There is a plethora of allosteric modulators for all five muscarinic receptor subtypes. This review presents the basic principles of allosteric modulation of GPCRs on both the molecular and structural level focusing on allosteric modulators of the muscarinic receptor family. Further we discuss dualsteric (i.e. bitopic orthosteric/allosteric) ligands emphasizing their potential in modulating muscarinic receptor dynamics and signaling. The common mechanisms of muscarinic receptor allosteric modulation have been proven to be generalizable and are at play at many, if not all GPCRs. Given this paradigmatic role of muscarinic receptors we suggest that also new developments in muscarinic allosteric modulation may also be extended to other members of the GPCR superfamily. This article is part of the Special Issue entitled 'Neuropharmacology on Muscarinic Receptors'.

The Orphan Receptor GPR17 Is Unresponsive to Uracil Nucleotides and Cysteinyl Leukotrienes

Pairing orphan G protein–coupled receptors (GPCRs) with their cognate endogenous ligands is expected to have a major impact on our understanding of GPCR biology. It follows that the reproducibility of orphan receptor ligand pairs should be of fundamental importance to guide meaningful investigations into the pharmacology and function of individual receptors. GPR17 is an orphan receptor characterized by some as a dualistic uracil nucleotide/cysteinyl leukotriene receptor and by others as inactive toward these stimuli altogether. Whereas regulation of central nervous system myelination by GPR17 is well established, verification of activity of its putative endogenous ligands has proven elusive so far. Herein we report that uracil nucleotides and cysteinyl leukotrienes do not activate human, mouse, or rat GPR17 in various cellular backgrounds, including primary cells, using eight distinct functional assay platforms based on labelfree pathway-unbiased biosensor technologies, as well as canonical second-messenger or biochemical assays. Appraisal of GPR17 activity can neither be accomplished with co-application of both ligand classes, nor with exogenous transfection of partner receptors (nucleotide P2Y12, cysteinyl-leukotriene CysLT1) to reconstitute the elusive pharmacology. Moreover, our study does not support the inhibition of GPR17 by the marketed antiplatelet drugs cangrelor and ticagrelor, previously suggested to antagonize GPR17. Whereas our data do not disagree with a role of GPR17 per se as an orchestrator of central nervous system functions, they challenge the utility of the proposed (ant)agonists as tools to imply direct contribution of GPR17 in complex biologic settings.

Engineered Context-Sensitive Agonism: Tissue-Selective Drug Signaling through a G Protein-Coupled Receptor

Drug discovery strives for selective ligands to achieve targeted modulation of tissue function. Here we introduce engineered context-sensitive agonism as a postreceptor mechanism for tissue-selective drug action through a G protein-coupled receptor. Acetylcholine M₂-receptor activation is known to mediate, among other actions, potentially dangerous slowing of the heart rate. This unwanted side effect is one of the main reasons that limit clinical application of muscarinic agonists. Herein we show that dualsteric (orthosteric/allosteric) agonists induce less cardiac depression ex vivo and in vivo than conventional full agonists. Exploration of the underlying mechanism in living cells employing cellular dynamic mass redistribution identified context-sensitive agonism of these dualsteric agonists. They translate elevation of intracellular cAMP into a switch from full to partial agonism. Designed context-sensitive agonism opens an avenue toward postreceptor pharmacologic selectivity, which even works in target tissues operated by the same subtype of pharmacologic receptor.

Superagonism at G protein-coupled receptors and beyond

Ligands targeting GPCRs can be categorized according to their intrinsic efficacy to trigger a specific, receptor-mediated response. A ligand endowed with the same level of efficacy as the endogenous agonist can be classified as a full agonist, whereas a compound that displays greater efficacy, that is, higher receptor signalling output than the endogenous agonist, can be called a superagonist. Subsequent to GPCR activation, an intracellular signalling cascade is set in motion, which may generate substantial amplification of the signal. This may obscure superagonism in pharmacological assays and, therefore, the definition of superagonism necessitates a combination of operational approaches, reduction of spare receptors or estimation of receptor activation close to the receptor level to quantify relative agonist efficacies in a particular system. The first part of this review will compare GPCR superagonism with superagonism in the field of immunology, where this term is well established. In the second part, known GPCR superagonists will be reviewed. Then, the experimental and analytical challenges in the deconvolution of GPCR superagonism will be addressed. Finally, the potential benefit of superagonism is discussed. The molecular mechanisms behind GPCR superagonism are not completely understood. However, crystallography shows that agonist binding alone is not sufficient for a fully active receptor state and that binding of the G protein is at least equally important. Accordingly, the emerging number of reported superagonists implies that ligand-induced receptor conformations more active than the ones stabilized by the endogenous agonist are indeed feasible. Superagonists may have therapeutic potential when receptor function is impaired or to induce negative feedback mechanisms. Linked Articles This article is part of a themed section on Molecular Pharmacology of G Protein-Coupled Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.20/issuetoc.

A cell-permeable inhibitor to trap Gαq proteins in the empty pocket conformation

In spite of the crucial role of heterotrimeric G proteins as molecular switches transmitting signals from G protein-coupled receptors, their selective manipulation with small molecule, cell-permeable inhibitors still remains an unmet challenge. Here, we report that the small molecule BIM-46187, previously classified as pan-G protein inhibitor, preferentially silences Gαq signaling in a cellular context-dependent manner. Investigations into its mode of action reveal that BIM traps Gαq in the empty pocket conformation by permitting GDP exit but interdicting GTP entry, a molecular mechanism not yet assigned to any other small molecule Gα inhibitor to date. Our data show that Gα proteins may be "frozen" pharmacologically in an intermediate conformation along their activation pathway and propose a pharmacological strategy to specifically silence Gα subclasses with cell-permeable inhibitors.

Agonists with supraphysiological efficacy at the muscarinic M2 ACh receptor

BACKGROUND AND PURPOSE

Artificial agonists may have higher efficacy for receptor activation than the physiological agonist. Until now, such 'superagonism' has rarely been reported for GPCRs. Iperoxo is an extremely potent muscarinic receptor agonist. We hypothesized that iperoxo is a 'superagonist'.

EXPERIMENTAL APPROACH

Signalling of iperoxo and newly synthesized structural analogues was compared with that of ACh at label-free M2 muscarinic receptors applying whole cell dynamic mass redistribution, measurement of G-protein activation, evaluation of cell surface agonist binding and computation of operational efficacies.

KEY RESULTS

In CHO-hM2 cells, iperoxo significantly exceeds ACh in Gi /Gs signalling competence. In the orthosteric loss-of-function mutant M2 -Y104(3.33) A, the maximum effect of iperoxo is hardly compromised in contrast to ACh. 'Superagonism' is preserved in the physiological cellular context of MRC-5 human lung fibroblasts. Structure-signalling relationships including iperoxo derivatives with either modified positively charged head group or altered tail suggest that 'superagonism' of iperoxo is mechanistically based on parallel activation of the receptor protein via two orthosteric interaction points.

CONCLUSION AND IMPLICATIONS

Supraphysiological agonist efficacy at muscarinic M2 ACh receptors is demonstrated for the first time. In addition, a possible underlying molecular mechanism of GPCR 'superagonism' is provided. We suggest that iperoxo-like orthosteric GPCR activation is a new avenue towards a novel class of receptor activators.

Decoding signaling and function of the orphan G protein-coupled receptor GPR17 with a small-molecule agonist

Replacement of the lost myelin sheath is a therapeutic goal for treating demyelinating diseases of the central nervous system (CNS), such as multiple sclerosis (MS). The G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptor (GPCR) GPR17, which is phylogenetically closely related to receptors of the "purinergic cluster," has emerged as a modulator of CNS myelination. However, whether GPR17-mediated signaling positively or negatively regulates this critical process is unresolved. We identified a small-molecule agonist, MDL29,951, that selectively activated GPR17 even in a complex environment of endogenous purinergic receptors in primary oligodendrocytes. MDL29,951-stimulated GPR17 engaged the entire set of intracellular adaptor proteins for GPCRs: G proteins of the Gα(i), Gα(s), and Gα(q) subfamily, as well as β-arrestins. This was visualized as alterations in the concentrations of cyclic adenosine monophosphate and inositol phosphate, increased Ca²⁺ flux, phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2), as well as multifeatured cell activation recorded with label-free dynamic mass redistribution and impedance biosensors. MDL29,951 inhibited the maturation of primary oligodendrocytes from heterozygous but not GPR17 knockout mice in culture, as well as in cerebellar slices from 4-day-old wild-type mice. Because GPCRs are attractive targets for therapeutic intervention, inhibiting GPR17 emerges as therapeutic strategy to relieve the oligodendrocyte maturation block and promote myelin repair in MS.

The allosteric vestibule of a seven transmembrane helical receptor controls G-protein coupling

Seven transmembrane helical receptors (7TMRs) modulate cell function via different types of G proteins, often in a ligand-specific manner. Class A 7TMRs harbour allosteric vestibules in the entrance of their ligand-binding cavities, which are in the focus of current drug discovery. However, their biological function remains enigmatic. Here we present a new strategy for probing and manipulating conformational transitions in the allosteric vestibule of label-free 7TMRs using the M₂ acetylcholine receptor as a paradigm. We designed dualsteric agonists as 'tailor-made' chemical probes to trigger graded receptor activation from the acetylcholine-binding site while simultaneously restricting spatial flexibility of the receptor's allosteric vestibule. Our findings reveal for the first time that a 7TMR's allosteric vestibule controls the extent of receptor movement to govern a hierarchical order of G-protein coupling. This is a new concept assigning a biological role to the allosteric vestibule for controlling fidelity of 7TMR signalling.

Class A seven transmembrane helical receptors harbour vestibules at the entrance to the ligand-binding domain. Here, Bock et al. use probes to monitor the conformation of the M2 muscarinic receptor and show that the vestibule alters the extent of receptor movement.

[Psammoma bodies in cytological vaginal smears in metastatic ovarian carcinoma]

The case of a 37-year old patient with ovarian cancer stage FIGO IV and vaginal metastasis is reported. The vaginal smear showed psammoma bodies, which are rarely found. The value of the diagnosis "psammoma bodies" is discussed, via a review of the literature.

[The value of colposcopy and portio biopsy in preventive examination]

133 patients attending the colposcopy-laser outpatient consultations were examined simultaneously by cytology, colposcopy and punch biopsy. A cone biopsy was taken 25 patients and one patient was hysterectomised later. A comparison between cytology and histology revealed 17.1% false negative smear results. Cytology and histology showed the same result in 84.6%. The highest percentage of high-grade dysplasia was found in colposcopy with signs of punctation and/or mosaicism. A similar diagnosis was achieved in 92.3% of cases comparing punch with cone biopsy. Simultaneous use of cytology, colposcopy and punch biopsy enables reliable diagnosis and follow-up of dysplastic lesions of the cervix. Besides, one can use punch biopsy as basic histology for local destructive manoeuvres such as laser vaporisation.

[Cancer register problems--modified reporting law model for the improvement of data protection]

The author suggests creating a "Reporting Law Model with Peripheral Part Anonymisation" that preserves the advantages of the reporting law model which are internationally recognised in respect of reliability of registration, on the one hand, while on the other hand the general and individual requirements of sufficient protection of sensitive data are also taken care of. This is achieved by separating the personal data from the factual data at the reporting office level. These data are transmitted separately to the registration offices and their confidential files. It is nevertheless possible to detect any double or multiple reporting and to perform fault finding in respect of personal data. It is also possible to add further data to any patient's case history. This cancer registration model can always cope with the required descriptive and analytical epidemiological tasks that are expected of it. It can be arranged to cover a wide area in a continuous manner without loss of time and without considerable expenditure. Documentation work to be performed by the reporting offices is minimised.

[Chlamydia trachomatis--studies on the reliability of its detection in Papanicolaou preparations]

In a matched group of 104 chlamydia culture-positive and 104 culture-negative women, the correlation between simultaneous cultures and cytological findings in the Papanicolaou smear was studied. Cellular changes in metaplastic cells that are described in the literature as being specific for Chlamydia trachomatis, were not associated with genital chlamydial infection. In particular the reported high sensitivity of intracytoplasmatic inclusion bodies could not be confirmed. Likewise, even severe inflammatory changes and a high concentration of lymphocytes were also no reliable diagnostic indicator. The authors conclude that the Papanicolaou smear is not useful as a routine screening method for genital chlamydial infection.

[Chlamydia trachomatis--cytologic findings in infections of the uterine cervix]

Cytologic, colposcopic, histologic and bacteriologic examination was performed in 229 patients because of previous abnormal cervical cytology. Chlamydia trachomatis was found in a significantly greater proportion as well in 70 women with spontaneous recurrence to normal (17.1%) as in 85 women with dysplasia (17.6%). In comparison, chlamydial infection is found in 4.1% of cytologically normal women. In the 2 to 22 months follow-up Chlamydia trachomatis was seen in 19.6% of 92 women with recurrence to normal cytologic pattern, however, in 10.8% of 65 patients with persistence or progression (p less than 0.025, t-test).

Amniotic fluid cells in the second trimester of pregnancy

The cell types of amniotic fluid in the second trimester of normal pregnancy are described and compared with the findings in the literature. Two hundred cell samples obtained by amniocentesis in pregnancies without known fetal neural tube or skin defects were studied. Anucleated and nucleated squamous epithelial cells of superficial and intermediate layers were found, as were macroforms of superficial cells. Parabasal cells were infrequent. Parabasallike cells were of amniotic origin. Other amniotic cell types, such as "balloon," or "goblet," cells, umbilical cord cells and hyperchromatic placental amniotic cells, were observed. Urothelial cells and nonepithelial cells, such as histiocytes and macrophages, were found. In several cases, "minicells" were seen; their different sites of origin are discussed.

[Problems of current diagnosis of neoplasms in women]

The value of early cancer detection in women is limited by the screening methods and their minor reliability in "mass-screening". The effect of detection programs is difficult to demonstrate. The interest in cancer detection is low, especially in elderly high risk patients. A more suitable application of screening tests with widespread indication of further methods together with exact demonstration could be the basis for better results in early cancer detection programs in women.

[Results of cancer screening in women (author's transl)]

The results of cancer screening in women were evaluated from 1,1 million investigations during the third quarter of 1971 to the second quarter of 1974. Positive cytological results of the uterine cervix were found in 0,39% on first investigation and in 0,38% on repeat investigations. Positive results in the breast amounted only to a quarter (0,1%) of the frequency of positive cytological results despite the fact that breast cancer occurs more frequently than cervical carcinoma. Only 0,03% positive findings were obtained by digital rectal palpation. The low incidence of the diseases sought for and the partly low sensitivity of the screening methods are responsible for the small numbers of positive findings in early detection investigations and are an indication of the effort involved. Participation of the population in investigations for early detection of cancer is unsatisfactory especially in older age groups with an increased risk.

[Are more girls than boys born in breech presentation compared with head presentation?]

In breech presentations a little more girls are born than boys, among head presentations there is a slight excess of boys. Among the factors favoring pelvic presentation birth weight has, according to present investigations, a decisive influence on the different sex relationship in the two presentations. Boys are little more common than girls in head presentation in the higher weight groups, in breech presentation in the upper and lower weight groups, while girls predominate in the middle weight groups. The absolute size of the middle weight groups in breech presentation causes the small excess of girls. A possible link with the slightly higher mortality of boys during the first year and its higher incidence in very high and very low weight groups are discussed as well as the dependence of the production of breech presentation on weight and mobility of the fetus.

[The diagnosis of corpus carcinoma (Differentialdiagnostic importance of history- and clinical criteria in post-menopausal hemorrhage) (author's transl)]

Among 1554 patients with post-memopausal hemorrhage over 7 years one half were due to benign causes, the other in almost equal parts to carcinoma of the fundus or cervix. Ca of the fundus is more likely when post-menopausal bleeding occurs at a relatively old age, a late menopause and a long interval between menopause and post-menopausal bleeding. Nulliparae more often have Ca of the corpus than in the cervix or have benign changes. The trias known for the corpus Ca: adiposity, diabetes and hypertension is confirmed. An enlargement or softening of the uterus and myomatous changes also indicate Ca. Anatomical and clinical criteria permit not only a detailed assessment of post-menopausal bleeding but also a definition of cases at risk before bleeding occurs and give an indication for detailed investigations.

[The timing of tubal ligation (Author's transl)]

In spite of medical or mixed medical and social indications, the sterilization by tubal ligation is frequently not carried out or done very late as in sterilization combined with a therapeutic abortion. This is borne out by the review of case histories and consultations of patients who had a sterilization operation other than post-partum, multiparous patients who had no sterilization, multiparous patients who had sterilization post-partum and patients who had an application for therapeutic abortion rejected and patients who had a therapeutic abortion with concomitant sterilization. The medical indications, medical social indications, the duration of the disease, the desire for child bearing, the social conditions and the family conditions were of such nature that in 29-80 percent of the cases under review sterilization could have been carried out at an earlier time. The relatively high incidence of women who presented with indications for sterilization but whose sterilization was delayed shows that more active individual counseling regarding sterilization by the attending physician is desirable. If necessary the physician should raise the question of sterilization and discuss the problem with the patient. This type of counseling would insure that the patient can make an informed decision and would minimize the psychological side effects and after-effects of sterilization.