Correlation between brain/plasma ratios and efficacy in neuropathic pain models of selective metabotropic glutamate receptor 1 antagonists

N-Alkylpyrido[1',2':1,5]pyrazolo-[4,3-d]pyrimidin-4-amines: A new series of negative allosteric modulators of mGlu1/5 with CNS exposure in rodents

Selective negative allosteric modulators (NAMs) of each of the group I metabotropic glutamate receptors (mGlu1 and mGlu5) have been well characterized in the literature and offer potential as therapeutics in several disorders of the central nervous system (CNS). Still, compounds that are potent mGlu1/5 NAMs with selectivity versus the other six members of the mGlu family as well as the balance of properties required for use in vivo are lacking. A medicinal chemistry effort centered on the identification of a lead series with the potential of delivering such compounds is described in this Letter. Specifically, a new class of pyrido[1',2':1,5]pyrazolo[4,3-d]pyrimidin-4-amines was designed as a novel isosteric replacement for 4-aminoquinazolines, and compounds from within this chemotype exhibited dual NAM activity at both group I mGlus. One compound, VU0467558 (29), demonstrated near equipotent activity at both receptors, selectivity versus other mGlus, a favorable ancillary pharmacology profile, and CNS exposure in rodents.

Octahydropyrrolo[3,4-c]pyrrole negative allosteric modulators of mGlu1

Development of SAR in an octahydropyrrolo[3,4-c]pyrrole series of negative allosteric modulators of mGlu1 using a functional cell-based assay is described in this Letter. The octahydropyrrolo[3,4-c]pyrrole scaffold was chosen as an isosteric replacement for the piperazine ring found in the initial hit compound. Characterization of selected compounds in protein binding assays was used to identify the most promising analogs, which were then profiled in P450 inhibition assays in order to further assess the potential for drug-likeness within this series of compounds.

N-Acyl-N'-arylpiperazines as negative allosteric modulators of mGlu1: identification of VU0469650, a potent and selective tool compound with CNS exposure in rats

Development of SAR in an N-acyl-N'-arylpiperazine series of negative allosteric modulators of mGlu1 using a functional cell-based assay is described in this Letter. Characterization of selected compounds in protein binding assays was used to aid in selecting VU0469650 for further profiling in ancillary pharmacology assays and pharmacokinetic studies. VU0469650 demonstrated an excellent selectivity profile and good exposure in both plasma and brain samples following intraperitoneal dosing in rats.

Oral administration of a small molecule targeted to block proNGF binding to p75 promotes myelin sparing and functional recovery after spinal cord injury

The lack of effective therapies for spinal cord injury points to the need for identifying novel targets for therapeutic intervention. Here we report that a small molecule, LM11A-31, developed to block proNGF-p75 interaction and p75-mediated cell death crosses the blood-brain barrier efficiently when delivered orally. Administered starting 4 h postinjury, LM11A-31 promotes functional recovery without causing any toxicity or increased pain in a mouse model of spinal contusion injury. In both weight-bearing open-field tests and nonweight-bearing swim tests, LM11A-31 was effective in improving motor function and coordination. Such functional improvement correlated with a >50% increase in the number of surviving oligodendrocytes and myelinated axons. We also demonstrate that LM11A-31 indeed inhibits proNGF-p75 interaction in vivo, thereby curtailing the JNK3-mediated apoptotic cascade. These results thus highlight p75 as a novel therapeutic target for an orally delivered treatment for spinal cord injury.

Synthesis and SAR development of novel mGluR1 antagonists for the treatment of chronic pain

High throughput screening identified the pyridothienopyrimidinone 1 as a ligand for the metabotropic glutamate receptor 1 (mGluR1=10 nM). Compound 1 has an excellent in vivo profile; however, it displays unfavorable pharmacokinetic issues and metabolic stability. Therefore, using 1 as a template, novel analogues (10i) were prepared. These analogues displayed improved oral exposure and activity in the Spinal Nerve Ligation (SNL) pain model.

Fused tricyclic mGluR1 antagonists for the treatment of neuropathic pain

A series of fused tricyclic mGluR1 antagonists containing a pyridone ring were synthesized. In vitro, these antagonists were potent against both human and rat isozymes, as well as selective for inhibiting mGluR1 over mGluR5. When dosed orally, several examples were active in vivo in a rat SNL test.

A medicinal chemistry perspective on structure-based drug design and development

The application of X-ray crystallography and molecular modeling can provide valuable insight into the optimization of the molecular interactions of a drug-protein complex to achieve potency and selectivity of a drug candidate. For the successful application of SBDD in a drug development program, the impact of these structural modifications required to improve potency and selectivity must be considered in the context of balancing of a multitude of drug properties and other considerations that include solubility, bioavailability, metabolism, distribution, toxicology, chemical stability, and intellectual property space. The utility of structure-based design from the medicinal chemist's perspective is described in this chapter.

Recent advances in the medicinal chemistry of the metabotropic glutamate receptor 1 (mGlu₁)

This Review summarizes the medicinal chemistry found in publications on both orthosteric and allosteric modulators of the metabotropic glutamate receptor 1 (mGlu(1)) from 2005 to the present. The time period covered by the scope of this current review has been particularly rich in mGlu(1)-related publications with numbers quadrupling when compared to the preceding five year period of 2000-2005. Publications in the field peaked in 2007 with over 35 articles appearing in the peer reviewed literature in the course of that year. Given that glutamate is one of the primary excitatory neurotransmitters in the mammalian central nervous system (CNS), it is unsurprising that it acts upon several receptors that are considered to be of potential therapeutic interest for many indications. Orthosteric and allosteric modulation of the receptor is possible, with a logical extrapolation to the chemotypes used for each strategy. The last five years of publications have yielded many mGlu(1) selective antagonist chemotypyes, most of which have shown efficacy in pain in vivo models. However, the primary impact of these compounds has been to highlight the mechanistic safety risks of mGlu(1) antagonism, independent of chemotype. As a review in medicinal chemistry, the primary focus of this paper will be on the design and, to a lesser degree, synthetic strategies for the delivery of subtype selective, CNS penetrant, druglike compounds through a "medchem" program, targeting modulators of the mGlu(1) receptor.

Function of Plectranthus barbatus herbal tea as neuronal acetylcholinesterase inhibitor

This study aims to determine the function of Plectranthus barbatus (Lamiaceae) herbal tea as inhibitor of the brain acetylcholinesterase (AChE) activity. To accomplish this objective the herbal tea as well as its main component, rosmarinic acid were administered to laboratory animals (rats) and the effect on the brain AChE activity was evaluated. The study of the herbal tea metabolites in the plasma and also in the brain was undertaken. The herbal water extract was administered intragastrically and also intraperitoneally. When the plant extract was intragastrically administered, vestigial amounts of metabolites from P. barbatus extract compounds were present in rat plasma, but none were found in brain, although inhibition of brain acetylcholinesterase activity was detected. However, when P. barbatus extract was administered intraperitoneally, all its compounds were found in plasma, and rosmarinic acid was found in brain. The highest concentrations of compounds/metabolites were found 30 min after administration. An inhibition of 29.0 ± 2.3% and 24.9 ± 3.7% in brain acetylcholinesterase activity was observed 30 and 60 min after intraperitoneal administration, respectively. These values were higher than those expected, taking into account the quantity of rosmarinic acid detected in the brain, which suggests that other active extract compounds or metabolites may be present in non-detectable amounts. These results prove that the administration of P. barbatus aqueous extract can reach the brain and act as AChE inhibitor.

The effect of plasma protein binding on in vivo efficacy: misconceptions in drug discovery

Data from in vitro plasma protein binding experiments that determine the fraction of protein-bound drug are frequently used in drug discovery to guide structure design and to prioritize compounds for in vivo studies. However, we consider that these practices are usually misleading, because in vivo efficacy is determined by the free (unbound) drug concentration surrounding the therapeutic target, not by the free drug fraction. These practices yield no enhancement of the in vivo free drug concentration. So, decisions based on free drug fraction could result in the wrong compounds being advanced through drug discovery programmes. This Perspective provides guidance on the application of plasma protein binding information in drug discovery.