Alan Wheeldon

Behavioral and Neurochemical Alterations in Mice Deficient in Anaplastic Lymphoma Kinase Suggest Therapeutic Potential for Psychiatric Indications

The receptor tyrosine kinase product of the anaplastic lymphoma kinase (ALK) gene has been implicated in oncogenesis as a product of several chromosomal translocations, although its endogeneous role in the hematopoietic and neural systems has remained poorly understood. We describe that the generation of animals homozygous for a deletion of the ALK tyrosine kinase domain leads to alterations in adult brain function. Evaluation of adult ALK homozygotes (HOs) revealed an age-dependent increase in basal hippocampal progenitor proliferation and alterations in behavioral tests consistent with a role for this receptor in the adult brain. ALK HO animals displayed an increased struggle time in the tail suspension test and the Porsolt swim test and enhanced performance in a novel object-recognition test. Neurochemical analysis demonstrates an increase in basal dopaminergic signalling selectively within the frontal cortex. Altogether, these results suggest that ALK functions in the adult brain to regulate the function of the frontal cortex and hippocampus and identifies ALK as a new target for psychiatric indications, such as schizophrenia and depression, with an underlying deregulated monoaminergic signalling.

A rapid method for the quantification of mouse hippocampal neurogenesis in vivo by flow cytometry. Validation with conventional and enhanced immunohistochemical methods.

Neural stem cells reside in the subventricular zone and the dentate gyrus of the hippocampus in adult mammalian brain. In the hippocampus, a number of factors are reported to modulate the rate of neural progenitor proliferation in the hippocampus, such as exercise, corticosteroids, and many pharmacological agents including several classes of antidepressants. It is currently unclear whether this increased proliferation is physiologically relevant, but it provides a potentially useful biomarker to assess novel antidepressant compounds. Changes in neurogenesis are typically quantified by administration of bromodeoxyuridine (BrdU) in vivo, and subsequent quantification of labelled nuclei. A robust and rapid means of quantifying BrdU labelling in adult hippocampus in vivo would allow higher throughput screening of potential antidepressant compounds. In this study we describe a FACS-based method for quantification of BrdU labelled cells in fixed cell suspensions from BrdU-treated adult mouse hippocampus. A variety of experimental conditions known to modulate proliferation were tested, including administration of corticosterone and the antidepressants imipramine and fluoxetine. The robust changes compared to control groups observed in these models were similar to previously reported studies, thus offering a more rapid and streamlined means to quantify effects of compounds on hippocampal proliferation.

UDP-glucose modulates gastric function through P2Y14 receptor-dependent and -independent mechanisms

P2Y receptors have been reported to modulate gastrointestinal functions. The newest family member is the nucleotide-sugar receptor P2Y14. P2ry14 mRNA was detected throughout the rat gut, with the highest level being in the forestomach. We investigated the role of the receptor in stomach motility using cognate agonists and knockout (KO) mice. In rat isolated forestomach, 100 microM UDP-glucose and 100 muM UDP-galactose both increased the baseline muscle tension (BMT) by 6.2+/-0.6 and 1.6+/-0.6 mN (P<0.05, n=3-4), respectively, and the amplitude of contractions during electrical field stimulation (EFS) by 3.7+/-1.7 and 4.3+/-2.5 mN (P<0.05, n=3-4), respectively. In forestomach from wild-type (WT) mice, 100 microM UDP-glucose increased the BMT by 1.0+/-0.1 mN (P<0.05, n=6) but this effect was lost in the KO mice (change of -0.1+/-0.1 mN, n=6). The 100 microM UDP-glucose also increased the contraction amplitude during EFS in this tissue from the WT animals (0.9+/-0.4 mN, P < 0.05, n=6) but not from the KO mice (0.0+/-0.2 mN, n=6). In vivo, UDP-glucose at 2,000 mg/kg ip reduced gastric emptying in rats by 49.7% (P<0.05, n=4-6) and in WT and KO mice by 56.1 and 66.2%, respectively (P<0.05, n=7-10) vs. saline-treated control animals. There was no significant difference in gastric emptying between WT and KO animals receiving either saline or d-glucose. These results demonstrate a novel function of the P2Y14 receptor associated with contractility in the rodent stomach that does not lead to altered gastric emptying after receptor deletion and an ability of UDP-glucose to delay gastric emptying without involving the P2Y14 receptor.

Fused bicyclic pyrrolizinones as new scaffolds for human NK1 antagonists.

Previous work on human NK(1) antagonists in which the core of the structure is a substituted pyrrolidine has been disclosed. These compounds showed good binding affinity and functional IP activity, however, many did not exhibit the necessary brain penetration for good in vivo activity. The discovery and preparation of a novel 5,5-fused pyrrolidine core is presented in this paper. This scaffold maintains the excellent binding affinity and functional IP activity of the previously reported compounds, but also exhibits excellent brain penetration as observed in a gerbil foot-tapping assay. The determination of the core structural stereochemistry, which eventually led to the final synthesis of a single active diastereomer, is described.

Potent, Brain-Penetrant, Hydroisoindoline-Based Human Neurokinin-1 Receptor Antagonists

3-[(3aR,4R,5S,7aS)-5-{(1R)-1-[3,5-bis(trifluoromethyl)phenyl]ethoxy}-4-(4-fluorophenyl)octahydro-2H-isoindol-2-yl]cyclopent-2-en-1-one (17) is a high affinity, brain-penetrant, hydroisoindoline-based neurokinin-1 (NK(1)) receptor antagonist with a long central duration of action in preclinical species and a minimal drug-drug interaction profile. Positron emission tomography (PET) studies in rhesus showed that this compound provides 90% NK(1) receptor blockade in rhesus brain at a plasma level of 67 nM, which is about 10-fold more potent than aprepitant, an NK(1) antagonist marketed for the prevention of chemotherapy-induced and postoperative nausea and vomiting (CINV and PONV). The synthesis of this enantiomerically pure compound containing five stereocenters includes a Diels-Alder condensation, one chiral separation of the cyclohexanol intermediate, an ether formation using a trichloroacetimidate intermediate, and bis-alkylation to form the cyclic amine.

Fused tricyclic pyrrolizinones that exhibit pseudo-irreversible blockade of the NK1 receptor.

Previously, we had disclosed a novel class of hNK(1) antagonists based on the 5,5-fused pyrrolidine core. These compounds displayed subnanomolar hNK(1) affinity along with good efficacy in a gerbil foot-tapping (GFT) model, but unfortunately they had low to moderate functional antagonist (IP-1) activity. To elaborate on the SAR of this class of hNK(1) compounds and to improve functional activity, we have designed and synthesized a new class of hNK(1) antagonist with a third fused ring. Compared to the 5,5-fused pyrrolidine class, these 5,5,5-fused tricyclic hNK(1) antagonists maintain subnanomolar hNK(1) binding affinity with highly improved functional IP-1 activity (<10% SP remaining). A fused tricyclic methyl, hydroxyl geminally substituted pyrrolizinone (compound 20) had excellent functional IP (<2% SP remaining), hNK(1) binding affinity, off-target selectivity, pharmacokinetic profile and in vivo activity. Complete inhibition of agonist activity was observed at both 0 and 24h in the gerbil foot-tapping model with an ID(50) of 0.02 mpk at both 0 and 24h, respectively.

Substituted fused bicyclic pyrrolizinones as potent, orally bioavailable hNK1 antagonists.

Previous work on human NK(1) (hNK(1)) antagonists in which the core of the structure is a 5,5-fused pyrrolizinone has been disclosed. The structural-activity-relationship studies on simple alpha- and beta-substituted compounds of this series provided several potent and bioavailable hNK(1) antagonists that displayed excellent brain penetration as observed by their good efficacy in the gerbil foot-tapping (GFT) model assay. Several of these compounds exhibited 100% inhibition of the foot-tapping response at 0.1 and 24h with ID(50)s of less than 1 mpk. One particular alpha-substituted compound (2b) had an excellent pharmacokinetic profile across preclinical species with reasonable in vivo functional activity and minimal ancillary activity.

Tetrahydroindolizinone NK1 antagonists.

A new class of potent NK(1) receptor antagonists with a tetrahydroindolizinone core has been identified. This series of compounds demonstrated improved functional activities as compared to previously identified 5,5-fused pyrrolidine lead structures. SAR at the 7-position of the tetrahydroindolizinone core is discussed in detail. A number of compounds displayed high NK(1) receptor occupancy at both 1 h and 24 h in a gerbil foot tapping model. Compound 40 has high NK(1) binding affinity, good selectivity for other NK receptors and promising in vivo properties. It also has clean P(450) inhibition and hPXR induction profiles.