Drugs in Clinical Pipeline: PF-4693627 | Microsomal Prostaglandin E2 Synthase-1 (mPGES-1) Inhibitor | Treatment for Inflammation

PF-4693627 [1-(5-chloro-6-(4-chlorophenyl)benzo[d]oxazol-2-yl)-N-((1S,3S)-3-(hydroxymethyl)cyclohexyl)piperidine-4-carboxamide] is a small molecule, orally bioavailable and selective inhibitor of microsomal prostaglandin E₂ synthase-1 (mPGES-1). Inhibition of mPGES-1, the terminal enzyme in the arachidonic acid/COX pathway to regulate the production of pro-inflammatory prostaglandin PGE₂, is considered an attractive new therapeutic target for safe and effective anti-inflammatory drugs [1, 2].

PF-4693627 : 2D and 3D Structure

Chemically, PF-4693627 is a member of benzoxazole family and displayed good anti-inflammatory activity in various test models. Moreover, the selectivity of PF-4693627 was profiled against several relevant human targets in the following assays: (a) HWB/1483 for selectivity against TXAS, PGDS, 5-LOX, 15-LOX and 12-LOX; (b) Human fetal fibroblasts for selectivity against COX-2. The data show that PF-4693627 is selective for microsomal prostaglandin E₂ synthase-1 (mPGES-1) against relevant human enzymes. PF-4693627 was also submitted to a broad panel screen (CEREP) and no significant findings were observed.


Microsomal Prostaglandin E Synthase-1 (mPGES-1) as Anti-inflammatory Target:

Microsomal prostaglandin E synthase-1 (mPGES-1) belongs to the membrane-associated proteins involved in eicosanoid and glutathione metabolism (MAPEG) super family. It is the terminal enzyme in the metabolism of arachidonic acid (AA) via the cyclooxygenase (COX) pathway (particularly COX-2), responsible for the conversion of prostaglandin H₂ (PGH₂) to a more stable product prostaglandin E₂ (PGE₂). As PGE₂ is a key mediator of pain and inflammation, the enhanced mPGES-1 expression is associated with many pathological conditions in humans; including rheumatoid arthritis (RA), osteoarthritis (OA), inflammatory bowel disease (IBD), cancer etc [1 - 3].

The biosynthesis of PGE₂ begins with the cleavage of arachidonic acid (AA) from membrane phospholipids by phospholipase A₂, followed by the conversion of AA to PGH₂ by cyclooxygenase (COX), and finally to the production of PGE₂ by PGE synthase (PGES). Three forms of PGES have been reported: cytosolic PGES (cPGES), microsomal PGES-1 (mPGES-1), and microsomal PGES-2 (mPGES-2). Both cPGES and mPGES-2 are constitutively expressed in a variety of tissues, while mPGES-1 is up-regulated under inflammatory conditions.

For patients with inflammatory pain caused by osteoarthritis (OA) and rheumatoid arthritis (RA), the first line of treatment is nonsteroidal anti-inflammatory drugs (NSAIDs) and COX-2 inhibitors (COXIBs). The COXIBs are superior to NSAIDs due to their lower incidence of GI side effects, but they are no more effective in symptom remission than NSAIDs and safety issues have surfaced, including renal toxicity and increased cardiovascular risk. A selective inhibitor of mPGES-1 would be expected to inhibit PGE₂ production induced by inflammation while sparing constitutive PGE₂, prostacyclin (PGI₂), and thromboxane production. This selectivity should differentiate mPGES-1 inhibitors from NSAIDS and COX-2 inhibitors in the treatment of inflammation and arthritis.

Mechanism of Action in PF-4693627:

PF-4693627 is an orally available and highly selective microsomal prostaglandin E₂ synthase-1 (mPGES-1) inhibitor. PF-4693627 is also species selective, as it only inhibits human mPGES-1 (IC₅₀ = 0.003 µM). PF-4693627 inhibits PGE₂ synthesis in a human whole blood assay without interfering with PGD₂, thromboxane or leukotriene synthesis. It was shown to inhibit PGE₂ synthesis in vivo in the guinea pig air pouch model of acute inflammation [1, 2].

Dosages and Approvals:

PF-4693627 (Tradename: -) is discovered and being developed at Pfizer. It is first microsomal prostaglandin E₂ synthase-1 (mPGES-1) inhibitor selected as a clinical candidate for the treatment of inflammation caused by rheumatoid arthritis (RA) and osteoarthritis (OA).

Reported Activities for PF-4693627:

PF-4693627 was identified as a very potent inhibitor of microsomal prostaglandin E2 synthase-1 (mPGES-1; IC₅₀ = 3 nM) with comparable potency in a fetal fibroblast cell assay (mPGES-1 IC₅₀ = 6 nM). Moreover, the compound showed good activity in human whole blood (HWB) cell-based assay (IC₅₀ = 109 nM).

The selectivity of PF-4693627 was profiled against several relevant human targets in the following assays: (a) HWB/1483 for selectivity against TXAS, PGDS, 5-LOX, 15-LOX and 12-LOX (IC₅₀ greater than 50 uM); (b) Human fetal fibroblasts for selectivity against COX-2 (IC₅₀ greater than 10 uM).

IC₅₀ (Inhibition of mPGES-1 activity) = 3 nM

IC₅₀ (Inhibition of mPGES-1 activity in HWB cells) = 109 nM

IC₅₀ (Inhibition of mPGES-1 activity in fetal fibroblast cells) = 6 nM

IC₅₀ (Inhibition of mPGES-1 activity in HWB-1483 cells) = 180 nM

Summary

Common name: PF-4693627; PF4693627; PF 4693627

Trademarks: -

Molecular Formula: C26H29Cl2N3O3

CAS Registry Number: 1312815-93-2

CAS Name: 1-(5-chloro-6-(4-chlorophenyl)benzo[d]oxazol-2-yl)-N-((1S,3S)-3-(hydroxymethyl)cyclohexyl)piperidine-4-carboxamide

Molecular Weight: 502.43

SMILES:OC[C@H]1CCC[C@H](NC(C(CC2)CCN2C3=NC4=CC(Cl)=C(C5=CC=C(Cl)C=C5)C=C4O3)=O)C1

InChI Key: CPDNPVKDQXLYHO-JXFKEZNVSA-N

InChI: InChI=1S/C26H29Cl2N3O3/c27-19-6-4-17(5-7-19)21-13-24-23(14-22(21)28)30-26(34-24)31-10-8-18(9-11-31)25(33)29-20-3-1-2-16(12-20)15-32/h4-7,13-14,16,18,20,32H,1-3,8-12,15H2,(H,29,33)/t16-,20-/m0/s1

Mechanism of Action: Microsomal Prostaglandin E2 Synthase-1 (mPGES-1) Inhibitor

Activity: Treatment for Inflammation; Anti-inflammation Agents

Status: Preclinical

Chemical Class: Small molecules; Chlorine containing; Amides; Piperidine containing; Chlorobenzenes; Benzoxazole derivatives

Originator: Pfizer

PF-4693627 Synthesis

WO2011077313A1: The patent reports synthesis of PF-4693627 and all the intermediates involved. Also see Ref 1 and 2.

Synthesis of PF-4693627

Identifications:

1H NMR (Estimated) for PF-4693627

Experimental: ¹H NMR (400 MHz, METHANOL-c₄) δ 1 .16 - 1 .29 (m, 1 H), 1 .38 - 1.48 (m, 1 H), 1.55 - 1.62 (m, 4 H), 1 .64 - 1.73 (m, 2 H), 1.75 - 1.92 (m, 5 H), 2.50 - 2.63 (m, 1 H), 3.16 - 3.27 (m, 2 H), 3.44 (d, J = 6.83 Hz, 2 H), 3.96 - 4.03 (m, 1 H), 4.26 - 4.35 (m, 2 H), 7.32 (s, 1 H), 7.35 (s, 1 H), 7.38 - 7.46 (m, 4 H).

Sideeffects: Nothing reported.

Others:

1. Discovery of PF-4693627: PF-9184 [N-(3’, 4’-dichlorobiphenyl-4-yl)-4-hydroxy-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide] is the first mPGES-1 selective inhibitor generated at Pfizer. Chemically, PF-9184 bears an oxicam template and has an IC₅₀ of 0.016 µM for mPGES-1. Its selectivity however, was only tested against recombinant COX enzymes. It was mainly used to characterize the impact of mPGES-1 inhibition on the prostanoid profile in cultures of synovial fibroblasts from RA patients, in which it causes a shunt of PGH₂ to the prostacylin pathway in a short incubation assay, but a reduction in both PGE₂ and 6-keto PGF1α in a long incubation assay. An inhibition of prostacyclin synthase can thus be ruled out, but it remains unclear whether PF-9184 has an inhibitory potential on the other prostanoid synthases. PF-9184 has poor aqueous solubility and attempts to improve this property unequivocally led to loss of potency. PF-9184 is inactive on rat mPGES-1 [4, 5].

Early Inhibitors of mPGES-1

Screening of the Pfizer compound collection identified compound 1 as a modest inhibitor of human mPGES-1, with an IC₅₀ = 1.2 uM. Short listing of other, related benzoxazoles through similarity and substructure searching of the Pfizer collection led to the discovery of compound 2, which has increased potency (IC₅₀ = 0.85 uM) and selectivity for mPGES-1 (PGE₂) over COX-2 (PGF2 α) in an IL-1 stimulated fetal fibroblast cell assay (PGE₂ IC₅₀ = 1.01 uM; PGF2α IC₅₀ greater than 100 uM). Compound 2 offers several positive attributes, including low molecular weight and clogP, which allow significant changes to the structure without destroying its drug-like character. Compound 2 is stable to human liver microsomes and is predicted by the Pampa assay to have high permeability; a drawback is that it displays high protein binding (99.5%), which negatively impacts its efficacy in whole blood assays. Compound 3 displays mPGES-1 inhibition of 0.018 uM and selectivity over COX-2 in the human fetal fibroblast cell assay. It inhibits PGE2 production in the LPS/human whole blood assay with an IC₅₀ of nearly 7 uM, with the discrepancy between enzymatic and whole blood assays due to the high protein binding of the molecule.  It is predicted to show poor permeability and is highly metabolized in rat and human microsomes with a very short half-life in both species. However, the results were better in a dog PK study, possibly due to differences in plasma protein binding across species [1, 2].

References:

1. Nugent, R. A.; et. al. Novel benzoxazole inhibitors of mPGES-1. Bioorg Med Chem Lett 2013, 23(3), 907 - 911. (FMO)

2. Arhancet, G. B.; et. al. Discovery and SAR of PF-4693627, a potent, selective and orally bioavailable mPGES-1 inhibitor for the potential treatment of inflammation. Bioorg Med Chem Lett  2013, 23(4), 1114 - 1119. (FMO)

3. Koeberle, A.; et. al. Design and Development of Microsomal Prostaglandin E2 Synthase-1 Inhibitors: Challenges and Future Directions. J Med Chem 2016, 59(13), 5970 - 5986. (FMO)

4. Mbalaviele, G.; et. al. Distinction of microsomal prostaglandin E synthase-1 (mPGES-1) inhibition from cyclooxygenase-2 inhibition in cells using a novel, selective mPGES-1 inhibitor. Biochem Pharmacol 2010, 79(10), 1445 - 1454. (FMO)

5. Wang, J.; et. al. Selective inducible microsomal prostaglandin E(2) synthase-1 (mPGES-1) inhibitors derived from an oxicam template. Bioorg Med Chem Lett 2010, 20(5), 1604 - 1609. (FMO)

6. Springer, J. R.; et. al. Piperidinecarboxamides as mpges - 1 inhibitors. WO2011077313A1

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