mGlu5 positive allosteric modulation normalizes synaptic plasticity defects and motor phenotypes in a mouse model of Rett syndrome.

Rett syndrome (RS) is a neurodevelopmental disorder that shares many symptomatic and pathological commonalities with idiopathic autism. Alterations in protein synthesis-dependent synaptic plasticity (PSDSP) are a hallmark of a number of syndromic forms of autism; in the present work, we explore the consequences of disruption and rescue of PSDSP in a mouse model of RS. We report that expression of a key regulator of synaptic protein synthesis, the metabotropic glutamate receptor 5 (mGlu5) protein, is significantly reduced in both the brains of RS model mice and in the motor cortex of human RS autopsy samples. Furthermore, we demonstrate that reduced mGlu5 expression correlates with attenuated DHPG-induced long-term depression in the hippocampus of RS model mice, and that administration of a novel mGlu5 positive allosteric modulator (PAM), termed VU0462807, can rescue synaptic plasticity defects. Additionally, treatment of Mecp2-deficient mice with VU0462807 improves motor performance (open-field behavior and gait dynamics), corrects repetitive clasping behavior, as well as normalizes cued fear-conditioning defects. Importantly, due to the rationale drug discovery approach used in its development, our novel mGlu5 PAM improves RS phenotypes and synaptic plasticity defects without evoking the overt adverse effects commonly associated with potentiation of mGlu5 signaling (i.e. seizures), or affecting cardiorespiratory defects in RS model mice. These findings provide strong support for the continued development of mGlu5 PAMs as potential therapeutic agents for use in RS, and, more broadly, for utility in idiopathic autism.

Discovery and characterization of N-(1,3-dialkyl-1H-indazol-6-yl)-1H-pyrazolo[4,3-b]pyridin-3-amine scaffold as mGlu4 positive allosteric modulators that mitigate CYP1A2 induction liability.

Previous reports from our laboratory disclosed the structure and activity of a novel 1H-pyrazolo[4,3-b]pyridine-3-amine scaffold (VU8506) which showed excellent potency, selectivity and in vivo efficacy in preclinical rodent models of Parkinson's disease. Unfortunately, this compound suffered from significant CYP1A2 induction as measured through upstream AhR activation (125-fold) and thus was precluded from further advancement in chronic studies. Herein, we report a new scaffold developed recently which was systematically studied in order to mitigate the CYP1A2 liabilities presented in the earlier scaffolds. We have identified a novel structure that maintains the potency and selectivity of other mGlu4 PAMs, leading to 9i (hmGlu4 EC50 = 43 nM; AhR activation = 2.3-fold).

Selective actions of novel allosteric modulators reveal functional heteromers of metabotropic glutamate receptors in the CNS.

Metabotropic glutamate (mGlu) receptors play important roles in regulating CNS function and are known to function as obligatory dimers. Although recent studies have suggested heterodimeric assembly of mGlu receptors in vitro, the demonstration that distinct mGlu receptor proteins can form heterodimers or hetero-complexes with other mGlu subunits in native tissues, such as neurons, has not been shown. Using biochemical and pharmacological approaches, we demonstrate here that mGlu2 and mGlu4 form a hetero-complex in native rat and mouse tissues which exhibits a distinct pharmacological profile. These data greatly extend our current understanding of mGlu receptor interaction and function and provide compelling evidence that mGlu receptors can function as heteromers in intact brain circuits.

Synthesis and SAR of a novel metabotropic glutamate receptor 4 (mGlu4) antagonist: unexpected 'molecular switch' from a closely related mGlu4 positive allosteric modulator.

Herein we report the discovery and SAR of a novel antagonist of metabotropic glutamate receptor 4 (mGlu(4)). The antagonist was discovered via a molecular switch from a closely related mGlu(4) positive allosteric modulator (PAM). This antagonist (VU0448383) displays an IC(50) value of 8.2±0.4 µM and inhibits an EC(80) glutamate response by 63.1±6.6%.

mGlu7 potentiation rescues cognitive, social, and respiratory phenotypes in a mouse model of Rett syndrome.

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the methyl-CpG binding protein 2 (MECP2) gene. The cognitive impairments seen in mouse models of RTT correlate with deficits in long-term potentiation (LTP) at Schaffer collateral (SC)-CA1 synapses in the hippocampus. Metabotropic glutamate receptor 7 (mGlu7) is the predominant mGlu receptor expressed presynaptically at SC-CA1 synapses in adult mice, and its activation on GABAergic interneurons is necessary for induction of LTP. We demonstrate that pathogenic mutations in MECP2 reduce mGlu7 protein expression in brain tissue from RTT patients and in MECP2-deficient mouse models. In rodents, this reduction impairs mGlu7-mediated control of synaptic transmission. We show that positive allosteric modulation of mGlu7 activity restores LTP and improves contextual fear learning, novel object recognition, and social memory. Furthermore, mGlu7 positive allosteric modulation decreases apneas in Mecp2+/- mice, suggesting that mGlu7 may be a potential therapeutic target for multiple aspects of the RTT phenotype.

Identification of positive allosteric modulators VU0155094 (ML397) and VU0422288 (ML396) reveals new insights into the biology of metabotropic glutamate receptor 7.

Metabotropic glutamate receptor 7 (mGlu7) is a member of the group III mGlu receptors (mGlus), encompassed by mGlu4, mGlu6, mGlu7, and mGlu8. mGlu7 is highly expressed in the presynaptic active zones of both excitatory and inhibitory synapses, and activation of the receptor regulates the release of both glutamate and GABA. mGlu7 is thought to be a relevant therapeutic target for a number of neurological and psychiatric disorders, and polymorphisms in the GRM7 gene have been linked to autism, depression, ADHD, and schizophrenia. Here we report two new pan-group III mGlu positive allosteric modulators, VU0155094 and VU0422288, which show differential activity at the various group III mGlus. Additionally, both compounds show probe dependence when assessed in the presence of distinct orthosteric agonists. By pairing studies of these nonselective compounds with a synapse in the hippocampus that expresses only mGlu7, we have validated activity of these compounds in a native tissue setting. These studies provide proof-of-concept evidence that mGlu7 activity can be modulated by positive allosteric modulation, paving the way for future therapeutics development.

Functional selectivity induced by mGlu4 receptor positive allosteric modulation and concomitant activation of Gq coupled receptors.

Metabotropic glutamate receptors (mGlus) are a group of Family C Seven Transmembrane Spanning Receptors (7TMRs) that play important roles in modulating signaling transduction, particularly within the central nervous system. mGlu(4) belongs to a subfamily of mGlus that is predominantly coupled to G(i/o) G proteins. We now report that the ubiquitous autacoid and neuromodulator, histamine, induces substantial glutamate-activated calcium mobilization in mGlu(4)-expressing cells, an effect which is observed in the absence of co-expressed chimeric G proteins. This strong induction of calcium signaling downstream of glutamate activation of mGlu(4) depends upon the presence of H(1) histamine receptors. Interestingly, the potentiating effect of histamine activation does not extend to other mGlu(4)-mediated signaling events downstream of G(i/o) G proteins, such as cAMP inhibition, suggesting that the presence of G(q) coupled receptors such as H(1) may bias normal mGlu(4)-mediated G(i/o) signaling events. When the activity induced by small molecule positive allosteric modulators of mGlu(4) is assessed, the potentiated signaling of mGlu(4) is further biased by histamine toward calcium-dependent pathways. These results suggest that G(i/o)-coupled mGlus may induce substantial, and potentially unexpected, calcium-mediated signaling events if stimulation occurs concomitantly with activation of G(q) receptors. Additionally, our results suggest that signaling induced by small molecule positive allosteric modulators may be substantially biased when G(q) receptors are co-activated. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Solution-phase parallel synthesis and SAR of homopiperazinyl analogs as positive allosteric modulators of mGlu4.

Using a functional high-throughput screening (HTS) and subsequent solution-phase parallel synthesis approach, we have discovered a novel series of positive allosteric modulators for mGlu4, a G-protein coupled receptor. This series is comprised of a homopiperazine central core. The solution-phase parallel synthesis and SAR of analogs derived from this series will be presented. This series of positive allosteric modulators of mGlu4 provide critical research tools to further probe the mGlu4-mediated effects in Parkinson's disease.

Discovery, synthesis, and structure-activity relationship development of a series of N-(4-acetamido)phenylpicolinamides as positive allosteric modulators of metabotropic glutamate receptor 4 (mGlu(4)) with CNS exposure in rats.

Herein we report the discovery, synthesis, and evaluation of a series of N-(4-acetamido)-phenylpicolinamides as positive allosteric modulators of mGlu(4). Compounds from the series show submicromolar potency at both human and rat mGlu(4). In addition, pharmacokinetic studies utilizing subcutaneous dosing demonstrated good brain exposure in rats.

Discovery, synthesis, and structure-activity relationship development of a series of N-4-(2,5-dioxopyrrolidin-1-yl)phenylpicolinamides (VU0400195, ML182): characterization of a novel positive allosteric modulator of the metabotropic glutamate receptor 4 (mGlu(4)) with oral efficacy in an antiparkinsonian animal model.

There is an increasing amount of literature data showing the positive effects on preclinical antiparkinsonian rodent models with selective positive allosteric modulators of metabotropic glutamate receptor 4 (mGlu(4)). However, most of the data generated utilize compounds that have not been optimized for druglike properties, and as a consequence, they exhibit poor pharmacokinetic properties and thus do not cross the blood-brain barrier. Herein, we report on a series of N-4-(2,5-dioxopyrrolidin-1-yl)phenylpicolinamides with improved PK properties with excellent potency and selectivity as well as improved brain exposure in rodents. Finally, ML182 was shown to be orally active in the haloperidol induced catalepsy model, a well-established antiparkinsonian model.

Synthesis and evaluation of a series of heterobiarylamides that are centrally penetrant metabotropic glutamate receptor 4 (mGluR4) positive allosteric modulators (PAMs).

We report the synthesis and evaluation of a series of heterobiaryl amides as positive allosteric modulators of mGluR4. Compounds 9b and 9c showed submicromolar potency at both human and rat mGluR4. In addition, both 9b and 9c were shown to be centrally penetrant in rats using nontoxic vehicles, a major advance for the mGluR4 field.

3'-Untranslated region of the type 2 bradykinin receptor is a potent regulator of gene expression.

Regulation of the constitutively expressed type 2 bradykinin (B2) receptor, which mediates the principal actions of bradykinin, occurs at multiple levels. The goal of the current study was to determine whether the human B2 3'-untranslated region (UTR) has effects on gene expression, with particular focus on the variable number of tandem repeats (B2-VNTR) polymorphic portion of the 3'-UTR and its flanking AU-rich elements (AREs). When inserted downstream of the luciferase coding region of the pGL3-Promoter vector, the B2-VNTR reduced reporter gene activity by 85% compared with pGL3-Promoter alone (promoter control; P < 0.001), an effect that was not appreciably affected by mutation of the flanking AREs. The negative regulatory effects of the B2-VNTR region were position and orientation dependent and strongly positively correlated with the number of tandem repeats in the B2-VNTR region (r = 0.85, P < 0.001). With respect to mechanism, quantitative RT-PCR revealed that the B2-VNTR mRNA level was 32% of that of promoter control (P = 0.008), whereas the number of polyadenylated transcripts was 4% (P = 0.02). In contrast, the mRNA half-life of the B2-VNTR was increased (B2-VNTR: 14.9 vs. promoter control: 12.2 h, P = 0.009). Transient transfection of human kidney-derived tsA201 cells with the B2-VNTR construct increased transcription of the native B2 receptor mRNA by 43% (P < 0.05), supporting an endogenous B2 receptor-regulatory capacity of the B2-VNTR. In conclusion, these results identify novel pretranslational effects of the B2-VNTR region to act as a potent negative regulator of heterologous gene expression and support the notion that the bradykinin B2 3'-UTR may impact endogenous receptor regulation.

Síndrome diarreico agudo (SDA) en niños atendidos en un consultorio del Servicio de Salud Metropolitano Norte 1999-2000 / Acute diarrhea syndrome in children attended at an outpatient care clinic of the Metropolitan Health Service (North) 1999-2000

En un consultorio del Servicio de Salud Metropolitano Norte, se realizó seguimiento, durante 12 meses, a 249 niños consultantes por síndrome diarreico agudo en 1999. Se calculan tasas de morbilidad por grupos de edad; se describen los casos por edad, mes de ocurrencia, consultas y duración de episodios. Se encontró que 37,8 por ciento de los niños eran menores de 2 años, 31,6 por ciento tenían entre 2 y 5 años. La incidencia fue 10,7 por ciento en menores de dos años; 3,3 por ciento en preescolares; 2,1 por ciento entre 6 y 9 años y 1,1 por ciento entre 10 y 14 años. El promedio de episodios fue de 1,59 por niño; la distribución anual fue heterogénea: 28,1 por ciento en meses cálidos; 40,4 por ciento entre junio y septiembre; 4 por ciento presentó deshidratación y sólo uno necesitó hospitalización. El promedio de consultas fue 1,45 por episodio y 2,3 por niño. Se solicitó exámenes al 53,9 por ciento de los casos, resultando positivo el 31 por ciento y los agentes etiológicos más frecuentes fueron: blastocystos, giardias y oxiuros. Conclusión: el riesgo de enfermar es 5 veces mayor en lactantes; los casos no revistieron gravedad; el SDA también se presentó en meses fríos.

Different arrangement of human papillomavirus E2 binding sites distinguishes cutaneous types from those associated with mucosal lesions

High-risk-type human papillomavirus DNA sequences are found in a high percentage of carcinomas from the uterine-cervix, with the viral E1-E2 gene region usually disrupted and the E6 and E7 oncoproteins consistently expressed. The E2 protein is known to repress early transcription from genital HPV promoters having a proximal E2 binding site (2BS) close to the TATA box. On the contrary, the E2 protein activates cutaneous early promotes, the E2 protein activates cutaneous early promoters having a longer distance between these sites. Using an in vivo approach we analyzed the regulation, by the BPV-1 E2 protein, of a natural HPV-18 promoter where proximal E2BS were placed at variable positions relative to the TATA box, and of heterologous promoters where E2BS was placed upstream of any other known DNA-binding elements. Our results confirm that the E2 protein represses or activates HPV early gene transcription depending on the distance between the TATA box and the proximal E2BS