Charles W. Locuson

Role for the M1 Muscarinic Acetylcholine Receptor in Top-Down Cognitive Processing Using a Touchscreen Visual Discrimination Task in Mice.

The M1 muscarinic acetylcholine receptor (mAChR) subtype has been implicated in the underlying mechanisms of learning and memory and represents an important potential pharmacotherapeutic target for the cognitive impairments observed in neuropsychiatric disorders such as schizophrenia. Patients with schizophrenia show impairments in top-down processing involving conflict between sensory-driven and goal-oriented processes that can be modeled in preclinical studies using touchscreen-based cognition tasks. The present studies used a touchscreen visual pairwise discrimination task in which mice discriminated between a less salient and a more salient stimulus to assess the influence of the M1 mAChR on top-down processing. M1 mAChR knockout (M1 KO) mice showed a slower rate of learning, evidenced by slower increases in accuracy over 12 consecutive days, and required more days to acquire (achieve 80% accuracy) this discrimination task compared to wild-type mice. In addition, the M1 positive allosteric modulator BQCA enhanced the rate of learning this discrimination in wild-type, but not in M1 KO, mice when BQCA was administered daily prior to testing over 12 consecutive days. Importantly, in discriminations between stimuli of equal salience, M1 KO mice did not show impaired acquisition and BQCA did not affect the rate of learning or acquisition in wild-type mice. These studies are the first to demonstrate performance deficits in M1 KO mice using touchscreen cognitive assessments and enhanced rate of learning and acquisition in wild-type mice through M1 mAChR potentiation when the touchscreen discrimination task involves top-down processing. Taken together, these findings provide further support for M1 potentiation as a potential treatment for the cognitive symptoms associated with schizophrenia.

Substituted indoles as selective protease activated receptor 4 (PAR-4) antagonists: Discovery and SAR of ML354

Herein we report the discovery and SAR of an indole-based protease activated receptor-4 (PAR-4) antagonist scaffold derived from a similarity search of the Vanderbilt HTS collection, leading to MLPCN probe ML354 (VU0099704). Using a novel PAC-1 fluorescent αIIbβ3 activation assay this probe molecule antagonist was found to have an IC50 of 140nM for PAR-4 with 71-fold selectivity versus PAR-1 (PAR-1IC50=10μM).

Progress towards small molecule menin-mixed lineage leukemia (MLL) interaction inhibitors with in vivo utility

A series of substituted hydroxymethyl piperidine small molecule inhibitors of the protein-protein interaction between menin and mixed lineage leukemia 1 (MLL1) are described. Initial members of the series showed good inhibitory disruption of the menin-MLL1 interaction but demonstrated poor physicochemical and DMPK properties. Utilizing a structure-guided and iterative optimization approach key substituents were optimized leading to inhibitors with cell-based activity, improved in vitro DMPK parameters, and improved half-lives in rodent PK studies leading to MLPCN probe ML399. Ancillary off-target activity remains a parameter for further optimization.

Discovery and Characterization of ML398, a Potent and Selective Antagonist of the D4 Receptor with in Vivo Activity.

Herein, we report the structure-activity relationship of a chiral morpholine-based scaffold, which led to the identification of a potent and selective dopamine 4 (D4) receptor antagonist. The 4-chlorobenzyl moiety was identified, and the compound was designated an MLPCN probe molecule, ML398. ML398 is potent against the D4 receptor with IC50 = 130 nM and K i = 36 nM and shows no activity against the other dopamine receptors tested (>20 μM against D1, D2S, D2L, D3, and D5). Further in vivo studies showed that ML398 reversed cocaine-induced hyperlocomotion at 10 mg/kg.

Synthesis and structure-activity relationships of a series of 4-methoxy-3-(piperidin-4-yl)oxy benzamides as novel inhibitors of the presynaptic choline transporter.

The synthesis and SAR of 4-methoxy-3-(piperidin-4-yl) benzamides identified after a high-throughput screen of the MLPCN library is reported. SAR was explored around the 3-piperidine substituent as well as the amide functionality of the reported compounds. Starting from the initial lead compounds, 1-7, iterative medicinal chemistry efforts led to the identification of ML352 (10m). ML352 represents a potent and selective inhibitor of CHT based on a drug-like scaffold.

A Screen of Approved Drugs Identifies the Androgen Receptor Antagonist Flutamide and Its Pharmacologically Active Metabolite 2-Hydroxy-Flutamide as Heterotropic Activators of Cytochrome P450 3A In Vitro and In Vivo

Once thought to be an artifact of microsomal systems, atypical kinetics with cytochrome P450 (CYP) enzymes have been extensively investigated in vitro and found to be substrate and species dependent. Building upon increasing reports of heterotropic CYP activation and inhibition in clinical settings, we screened a compound library of clinically approved drugs and various probe compounds to identify the frequency of heterotropism observed with different drug classes and the associated CYP enzymes thereof (1A2, 2C9, 2D6, and 3A4/5). Results of this screen revealed that the prescribed androgen receptor antagonist flutamide activated the intrinsic midazolam hydroxylase activity of CYP3A in human hepatic microsomes (66%), rat and human hepatocytes (36 and 160%, respectively), and in vivo in male Sprague-Dawley rats (>2-fold, combined area under the curve of primary rat in vivo midazolam metabolites). In addition, a screen of the pharmacologically active metabolite 2-hydroxy-flutamide revealed that this principle metabolite increased CYP3A metabolism of midazolam in human microsomes (30%) and hepatocytes (110%). Importantly, both flutamide and 2-hydroxy-flutamide demonstrated a pronounced increase in the CYP3A-mediated metabolism of commonly paired medications, nifedipine (antihypertensive) and amiodarone (antiarrhythmic), in multispecies hepatocytes (100% over baseline). These data serve to highlight the importance of an appropriate substrate and in vitro system selection in the pharmacokinetic modeling of atypical enzyme kinetics. In addition, the results of our investigation have illuminated a previously undiscovered class of heterotropic CYP3A activators and have demonstrated the importance of selecting commonly paired therapeutics in the in vitro and in vivo modeling of projected clinical outcomes.

Discovery and Optimization of Potent and CNS Penetrant M5-Preferring Positive Allosteric Modulators Derived from a Novel, Chiral N-(Indanyl)piperidine Amide Scaffold

The pharmacology of the M5 muscarinic acetylcholine receptor (mAChR) is the least understood of the five mAChR subtypes due to a historic lack of selective small molecule tools. To address this shortcoming, we have continued the optimization effort around the prototypical M5 positive allosteric modulator (PAM) ML380 and have discovered and optimized a new series of M5 PAMs based on a chiral N-(indanyl)piperidine amide core with robust SAR, human and rat M5 PAM EC50 values <100 nM and rat brain/plasma Kp values of ∼0.40. Interestingly, unlike M1 and M4 PAMs with unprecedented mAChR subtype selectivity, this series of M5 PAMs displayed varying degrees of PAM activity at the other two natively Gq-coupled mAChRs, M1 and M3, yet were inactive at M2 and M4.