Paul E. Harrington

Calcium sensing receptor activators: calcimimetics.

The calcium sensing receptor (CaR) is a G protein-coupled receptor (GPCR) that plays a fundamental role in serum calcium homeostasis. The CaR is expressed on the chief cells of the parathyroid gland and is responsible for controlling the secretion of parathyroid hormone (PTH). PTH acts on several organs including the bone, kidney, and intestine to tightly regulate the concentration of serum calcium. Substances other than calcium that activate the CaR are referred to as calcimimetics. Calcimimetics that bind to the CaR as agonists are referred to as type I. Type II calcimimetics bind to a site that is distinct from the physiological ligand and function as positive allosteric modulators of the CaR. Type II calcimimetics amplify the sensitivity of the CaR to serum calcium and are thus able to lower the concentration of serum PTH. Calcimimetics are being pursued as therapeutics for the treatment of disorders that are characterized by elevated levels of PTH such as primary and secondary hyperparathyroidism (primary HPT and secondary HPT). In this review, we provide an overview of key results in the discovery of cinacalcet HCl (Sensipar in the US, Mimpara in Europe). In addition, other recently disclosed type II calcimimetics are discussed.

Discovery of clinical candidate 1-(4-(3-(4-(1H-benzo[d]imidazole-2-carbonyl)phenoxy)pyrazin-2-yl)piperidin-1-yl)ethanone (AMG 579), a potent, selective, and efficacious inhibitor of phosphodiesterase 10A (PDE10A).

We report the identification of a PDE10A clinical candidate by optimizing potency and in vivo efficacy of promising keto-benzimidazole leads 1 and 2. Significant increase in biochemical potency was observed when the saturated rings on morpholine 1 and N-acetyl piperazine 2 were changed by a single atom to tetrahydropyran 3 and N-acetyl piperidine 5. A second single atom modification from pyrazines 3 and 5 to pyridines 4 and 6 improved the inhibitory activity of 4 but not 6. In the in vivo LC-MS/MS target occupancy (TO) study at 10 mg/kg, 3, 5, and 6 achieved 86-91% occupancy of PDE10A in the brain. Furthermore, both CNS TO and efficacy in PCP-LMA behavioral model were observed in a dose dependent manner. With superior in vivo TO, in vivo efficacy and in vivo PK profiles in multiple preclinical species, compound 5 (AMG 579) was advanced as our PDE10A clinical candidate.

Facile synthesis of substituted 5-amino- and 3-amino-1,2,4-thiadiazoles from a common precursor.

A novel approach to the synthesis of substituted 5-amino- and 3-amino-1,2,4-thiadiazoles beginning from a common precursor has been achieved. Derivatization by palladium-catalyzed Suzuki-Miyaura coupling enables the rapid preparation of analogs around this pharmaceutically relevant core. FMO calculations rationalize the observed chemoselectivity for coupling at chlorine.

The discovery of an orally efficacious positive allosteric modulator of the calcium sensing receptor containing a dibenzylamine core

The discovery of a series of novel and orally efficacious type II calcimimetics, developed from the lead compound 1, is described herein. Compound 22 suppressed plasma PTH levels relative to vehicle when dosed orally in a rat pharmacodynamic model.

Discovery and Optimization of Substituted 1-(1-Phenyl-1H-pyrazol-3-yl)methanamines as Potent and Efficacious Type II Calcimimetics

Our efforts to discover potent, orally bioavailable type II calcimimetic agents for the treatment of secondary hyperparathyroidism focused on the development of ring constrained analogues of the known calcimimetic R-568. The structure-activity relationships of various substituted heterocycles and their effects on the human calcium-sensing receptor are discussed. Pyrazole 15 was shown to be efficacious in a rat in vivo pharmacodynamic model.

Quinolinone-based agonists of S1P1: Use of a N-scan SAR strategy to optimize in vitro and in vivo activity

We reveal how a N-scan SAR strategy (systematic substitution of each CH group with a N atom) was employed for quinolinone-based S1P(1) agonist 5 to modulate physicochemical properties and optimize in vitro and in vivo activity. The diaza-analog 17 displays improved potency (hS1P(1) RI; 17: EC(50)=0.020 μM, 120% efficacy; 5: EC(50)=0.070 μM, 110% efficacy) and selectivity (hS1P(3) Ca(2+) flux; 17: EC(50) >25 μM; 5: EC(50)=1.5 μM, 92% efficacy), as well as enhanced pharmacokinetics (17: CL=0.15 L/h/kg, V(dss)=5.1L/kg, T(1/2)=24h, %F=110; 5: CL=0.93L/h/kg, V(dss)=11L/kg, T(1/2)=15 h, %F=60) and pharmacodynamics (17: 1.0mg/kg po, 24h PLC POC=-67%; 5: 3mg/kg po, 24h PLC POC=-51%) in rat.

Metabolism-guided discovery of a potent and orally bioavailable urea-based calcimimetic for the treatment of secondary hyperparathyroidism.

A series of urea based calcimimetics was optimized for potency and oral bioavailability. Crucial to this process was overcoming the poor pharmacokinetic properties of lead thiazole 1. Metabolism-guided modifications, characterized by the use of metabolite identification (ID) and measurement of time dependent inhibition (TDI) of CYP3A4, were essential to finding a compound suitable for oral dosing. Calcimimetic 18 exhibited excellent in vivo potency in a 5/6 nephrectomized rat model and cross-species pharmacokinetics.

Isoform-selective thiazolo[5,4-b]pyridine S1P1 agonists possessing acyclic amino carboxylate head-groups.

Replacement of the azetidine carboxylate of an S1P(1) agonist development candidate, AMG 369, with a range of acyclic head-groups led to the identification of a novel, S1P(3)-sparing S1P(1) agonist, (-)-2-amino-4-(3-fluoro-4-(5-(1-phenylcyclopropyl)thiazolo[5,4-b]pyridin-2-yl)phenyl)-2-methylbutanoic acid (8c), which possessed good in vivo efficacy and pharmacokinetic properties. A 0.3mg/kg oral dose of 8c produced a statistically significant reduction in blood lymphocyte counts 24h post-dosing in female Lewis rats.

Abstract 711: Small molecule compounds that target cell division cycle 7 (Cdc7) kinase inhibit cell proliferation and tumor growth.

Cdc7 is an essential, serine/threonine protein kinase that activates the initiation of DNA synthesis at replication origins. Cdc7 also promotes cell cycle checkpoint activation in response to replication stress. As a key regulator of S phase entry and progression, Cdc7 kinase is a potential target for cancer therapy, with a distinct mechanism of action from known drugs that inhibit DNA replication. Following a high throughput screen for inhibitors of Cdc7 kinase activity, we investigated structure-activity relationships of azole-based compounds and optimized the compounds for potency and pharmacokinetic properties. Here we present the characterization of one of these compounds as a potent, selective, bioavailable Cdc7 kinase inhibitor. In cells, Cdc7 inhibition decreases MCM2 phosphorylation and DNA synthesis, causes DNA damage, and slows S phase progression. Cdc7 inhibition also induces chromosome missegregation leading to cell lethality in vitro and tumor growth inhibition in vivo. Cdc7 inhibition provides a new approach to target cancers, either as a single agent or in combination with chemotherapy. Citation Format: Julie Bailis, Li Fang, Jessica Orf, Scott Heller, Tammy Bush, Matthew Bourbeau, Sonia Escobar, Michael Frohn, Paul Harrington, Faye Hsieh, Alexander Pickrell, Kelvin Sham, Aaron Siegmund, Helming Tan, Leeanne Zalameda, John Allen, Dineli Wickramasinghe. Small molecule compounds that target cell division cycle 7 (Cdc7) kinase inhibit cell proliferation and tumor growth. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 711. doi:10.1158/1538-7445.AM2013-711