In vitro pharmacological profile of PHA-022121, a small molecule bradykinin B2 receptor antagonist in clinical development.

PHA-022121 is a novel small molecule bradykinin B2 receptor antagonist, in clinical development for the treatment and prevention of hereditary angioedema attacks. The present study describes the in vitro pharmacological characteristics of PHA-022121 and its active metabolite, PHA-022484 (M2-D). In mammalian cell lines, PHA-022121 and PHA-022484 show high affinity for the recombinant human bradykinin B2 receptor with Ki values of 0.47 and 0.70 nM, respectively, and potent antagonism of the human bradykinin B2 receptor with Kb values of 0.15 and 0.26 nM, respectively (calcium mobilization assay). Antagonist potency at the recombinant cynomolgus monkey bradykinin B2 receptor is similarly high (Kb values of 1.42 and 1.12 nM for PHA-022121 and PHA-022484, respectively), however, potency at rat, mouse, rabbit and dog bradykinin B2 receptors is at least 100-fold lower than the potency at the human receptor for both compounds. In the human umbilical vein contractility assay, both PHA-022121 and PHA-022484 show a potent, surmountable and reversible B2 antagonist activity with pA2 values of 0.35 and 0.47 nM, respectively. The in vitro off-target profile of PHA-022121 and PHA-022484 demonstrates a high degree of selectivity over a wide range of molecular targets, including the bradykinin B1 receptor. It is concluded that PHA-022121 is a novel, low-molecular weight, competitive antagonist of the human bradykinin B2 receptor with high affinity, high antagonist potency, and high selectivity. It is about 20-fold more potent than icatibant at the human bradykinin B2 receptor as assessed using recombinant or endogenously expressed receptors.

In Vitro Pharmacological Profile of a New Small Molecule Bradykinin B2 Receptor Antagonist.

We here report the discovery and early characterization of Compound 3, a representative of a novel class of small molecule bradykinin (BK) B2 receptor antagonists, and its superior profile to the prior art B2 receptor antagonists Compound 1 and Compound 2. Compound 3, Compound 2, and Compound 1 are highly potent antagonists of the human recombinant B2 receptor (Kb values 0.24, 0.95, and 1.24 nM, respectively, calcium mobilization assay). Compound 3 is more potent than the prior art compounds and icatibant in this assay (Kb icatibant 2.81 nM). The compounds also potently inhibit BK-induced contraction of endogenous B2 receptors in a human isolated umbilical vein bioassay. The potencies of Compound 3, Compound 2, Compound 1, and icatibant are (pA2 values) 9.67, 9.02, 8.58, and 8.06 (i.e. 0.21, 0.95, 2.63, and 8.71 nM), respectively. Compound 3 and Compound 2 were further characterized. They inhibit BK-induced c-Fos signaling and internalization of recombinant human B2 receptors in HEK293 cells, and do not antagonize the venous effects mediated by other G protein-coupled receptors in the umbilical vein model, including the bradykinin B1 receptor. Antagonist potency of Compound 3 at cloned cynomolgus monkey, dog, rat, and mouse B2 receptors revealed species selectivity, with a high antagonist potency for human and monkey B2 receptors, but several hundred-fold lower potency for the other B2 receptors. The in vitro off-target profile of Compound 3 demonstrates a high degree of selectivity over a wide range of molecular targets, including the bradykinin B1 receptor. Compound 3 showed a lower intrinsic clearance in the microsomal stability assay than the prior art compounds. With an efflux ratio of 1.0 in the Caco-2 permeability assay Compound 3 is predicted to be not a substrate of efflux pumps. In conclusion, we discovered a novel chemical class of highly selective and very potent B2 receptor antagonists, as exemplified by Compound 3. The compound showed excellent absorption in the Caco-2 assay, predictive of good oral bioavailability, and favourable metabolic stability in liver microsomes. Compound 3 has provided a significant stepping stone towards the discovery of the orally bioavailable B2 antagonist PHA-022121, currently in phase 1 clinical development.

Natural products in parallel chemistry--novel 5-lipoxygenase inhibitors from BIOS-based libraries starting from alpha-santonin.

Recently, we developed a concept known as biology-oriented synthesis (BIOS), which targets the design and synthesis of small- to medium-sized compound libraries on the basis of genuine natural product templates to provide screening compounds with high biological relevance. We herein describe the parallel solution phase synthesis of two BIOS-based libraries starting from alpha-santonin (1). Modification of the sesquiterpene lactone 1 by introduction of a thiazole moiety followed by a Lewis-acid-mediated lactone opening yielded a first library of natural product analogues. An acid-mediated dienone-phenol rearrangement of 1 and a subsequent etherification/amidation sequence led to a second natural product-based library. After application of a fingerprint-based virtual screening on these compounds, the biological screening of 23 selected library members against 5-lipoxygenase resulted in the discovery of four potent novel inhibitors of this enzyme.

Identification of inhibitors for mycobacterial protein tyrosine phosphatase B (MptpB) by biology-oriented synthesis (BIOS).

Protein phosphatases have recently emerged as important targets for research in chemical biology and medicinal chemistry, and new classes of phosphatase inhibitors are in high demand. BIOS (biology-oriented synthesis) employs the criteria of relevance to nature and biological prevalidation for the design and synthesis of compound collections. In an application of the BIOS principle, an efficient solid-phase synthesis of highly substituted indolo[2,3-a]quinolizidines by using a vinylogous Mannich-Michael reaction in combination with phosgene- or acid-mediated ring closure was developed. Screening of this library for phosphatase inhibitors yielded a new inhibitor class for the Mycobacterium tuberculosis phosphatase MptpB.

Natural products in combinatorial chemistry: an andrographolide-based library.

The generation of a natural-product-based library starting from andrographolide is described. Utilizing andrographolide itself in parallel solution-phase synthesis leads to a 360-membered library. The initial transformation of the starting material via ozonolysis is followed by the conversion into a suitable template by introduction of a thiazole moiety. Subsequent decoration at two points of diversity yields the desired natural product derivatives. The selection of actually synthesized compounds is based on a virtually generated library and the assessment of its members with respect to physicochemical parameters, thus ensuring pharmacological relevance of the compounds.