pubs.acs.org/acsmedchemlett
Discovery of an Oral Potent Selective Inhibitor of Hematopoietic Prostaglandin D Synthase (HPGDS)
Chris P. Carron,† John I. Trujillo,† Kirk L. Olson,† Wei Huang,† Bruce C. Hamper,† Tom Dice,† Bradley E. Neal,† Matthew J. Pelc,† Jacqueline E. Day,† Douglas C. Rohrer,† James R. Kiefer,† Joseph B. Moon,† Barbara A. Schweitzer,† Tanisha D. Blake,† Steve R. Turner,† Rhonda Woerndle,† Brenda L. Case,† Christine P. Bono,† Vickie M. Dilworth,† Christie L. Funckes-Shippy,† Becky L. Hood,† Gina M. Jerome,† Christine M. Kornmeier,† Melissa R. Radabaugh,† Melanie L. Williams,† Michael S. Davies,† Craig D. Wegner,† Dean J. Welsch,† William M. Abraham,‡ Chad J. Warren,† Martin E. Dowty,† Fengmei Hua,† Anup Zutshi,† Jerry Z. Yang,† and Atli Thorarensen*,† †
Pfizer Global Research and Development, 700 Chesterfield Parkway West, Chesterfield, Missouri 63017, and ‡Department of Research, Mount Sinai Medical Center, 4300 Alton Road, Miami Beach, Florida 33140 . ABSTRACT Hematopoietic prostaglandin D synthase (HPGDS) is primarly expressed in mast cells, antigen-presenting cells, and Th-2 cells. HPGDS converts PGH2 into PGD2, a mediator thought to play a pivotal role in airway allergy and inflammatory processes. In this letter, we report the discovery of an orally potent and selective inhibitor of HPGDS that reduces the antigen-induced response in allergic sheep. KEYWORDS Hematopoietic prostaglandin D synthase (HPGDS), PGH2, PGD2, airway allergy, inflammatory processes, cyclooxygenase (COX)
A
in inflamed nasal mucosa and is associated with the induction of chemotactic migration and/or activation of Th-2, eosinophils, and basophils.7-9 Collectively, these data support a role for PGD2 in inflammatory diseases of the upper airways and suggest that blockade of PGD2 action at either or both receptors might be beneficial for the treatment of nasal allergies and other PGD2-mediated inflammatory conditions. This has created significant interest in both DP-1 and CRTH2 as targets, and several publications have appeared describing inhibitor design.10,11 PGD2 is synthesized from arachidonic acid via the oxidation by cyclooxygenase PGH2 (COX) and isomerization of PGH2 to PGD2 by prostaglandin D synthase (PGDS). Hematopoietic PGDS (HPGDS) is responsible for the synthesis of PGD2 by mast cells and Th-2 cells, whereas a lipocalin type PGDS (LPGDS) catalyzes the production of PGD2 in the central nervous system, male genital organs, and heart.12 The production of PGD2 by HPGDS is thought to play a pivotal role in airway allergic and inflammatory processes and induces vasodilatation, bronchoconstriction, pulmonary eosinophil and lymphocyte infiltration, and cytokine release in asthmatics.12 Inhibition of HPGDS may be therapeutically beneficial in the treatment of allergic disease and may be more effective than blocking either DP-1 or CRTH2 alone.13
sthma is a chronic inflammatory disorder of the airways that causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing in susceptible individuals.1,2 Prostaglandin D2 (PGD2), a mediator of allergy and inflammation, is produced by mast cells and Th-2 cells in a variety of human tissues. PGD2 is the most abundant de novo cyclooxygenase-derived mediator produced following IgE-mediated degranulation of mast cells.3 The mast cell, following allergen-provoked degranulation, is believed to be the major source of PGD2 found in the nasal exudates of patients with allergic rhinitis. PGD2 levels increase dramatically in bronchoalveolar lavage fluid following allergen challenge, and the observation that patients with asthma exhibit bronchoconstriction upon inhalation of PGD2 underscores the pathologic consequences of high levels of PGD2 in the lung.4 Treatment with PGD2 produces significant nasal congestion and fluid secretion in man and dogs, and PGD2 is 10 times more potent than histamine and 100 times more potent than bradykinin in producing nasal blockage in humans, demonstrating a role for PGD2 in allergic rhinitis.5,6 Mast cell-derived PGD2 exerts its effect by activating two distinct G-protein-coupled receptors (GPCRs): the DP-1 receptor, a member of the prostanoid receptor subfamily, and the recently discovered chemoattractant receptor-homologous molecule expressed on T-helper 2 cells (CRTH2 receptor). The DP-1 receptor is localized on the nasal vasculature and in mucin-secreting cells and is associated with tissue swelling and a concomitant increase in nasal airway resistance, while the CRTH2 receptor is expressed on a subset of infiltrating T cells
r 2010 American Chemical Society
Received Date: December 21, 2009 Accepted Date: January 22, 2010 Published on Web Date: February 02, 2010
59
DOI: 10.1021/ml900025z |ACS Med. Chem. Lett. 2010, 1, 59–63
pubs.acs.org/acsmedchemlett
Table 1. Heterocyclic Variation of the Body
Figure 1. Examples of literature inhibitors.
Figure 2. Advanced lead as an inhibitor of HPGDS.
HPGDS and LPGDS are genetically distinct synthases that have presumably arisen as a consequence of convergent evolution. These isoenzymes are named according to their differential requirement for GSH as a cofactor. The GSH-independent PGD2 synthase is a member of the lipocalin superfamily, while the GSH-dependent synthase is the only vertebrate member of the class Sigma family of glutathione S-transferases (GSTs) identified to date.14,15 HPGDS is a cytosolic homodimer of 26 kDa subunits, and several crystal structures have been published.16,17 Those structures reveal a well-defined active site, enabling a structure-based design of inhibitors. There have been several reports of potent enzyme inhibitors18-20 of HPGDS along with HQL-79 as an in vivo efficacious inhibitor21 (Figure 1). In this letter, we will describe our effort to identify an orally active inhibitor of HPGDS.22 A subset screen was performed on the Pfizer compound collection based on structural diversity. This resulted in numerous leads for further manipulation. Our lead generation group at the Research and Technology Center completed a triage and lead validation identifying the thiazole 1 as an advanced lead for further optimization (Figure 2). Thiazole 1 is a potent inhibitor of HPGDS enzyme (IC50, 10 nM) and cell (IC50, 300-1300 nM). In addition, the compound had a very acceptable pharmacokinetic (PK) profile (Cl, 14 mL/min/kg; T1/2, 2 h; and BA, 20%). In analysis of this compound, we identified several parameters that required optimization, most importantly, the poor cell activity of the compound. In addition, we desired a scaffold with improved novelty as judged by substructure searching in Scifinder. The thiazole could easily be divided into three major areas for exploration utilizing high-throughput chemistry: the head, the body, and the tail. Our initial effort was focused on the body, and a series of heterocycles were explored that could retain a similar hydrogen-bonding network as 1 with a conserved water molecule in the active site.23 Those compounds were easily prepared from available acids by an amide coupling reaction with 2; selective examples are
r 2010 American Chemical Society
illustrated in Table 1. Most of those building blocks were commercially available with a few exceptions, which were available in our in-house chemical storeroom. This initial iteration provided a wealth of information regarding the shape and the nature of the heteroatom equal to the nitrogen in the thiazole. Only heterocycles with a N location similar to the thiazole such as the potent compounds 5 and 6 were found to be active. The location of the nitrogen in relationship to the trajectory of the tail was found to be just as important, as 7 illustrated. The activity of 4 (27 nM), which lacks a central ring nitrogen atom, was therefore very surprising and confounded the structure-activity relationship interpretation until isothermal calorimetry illustrated that entropy was the major driving force for affinity.24 The series represented by scaffolds such as 5 and 6 were subsequently evaluated further by several cycles of high-throughput synthesis focused on the tail variation. This was done to address one of our major objectives, improved cell activity (Figure 3). It was clear that we consistently could prepare potent inhibitors of HPGDS, but only a handful of compounds illustrated potency in our cell assay. A key observation was made that certain substructures in the tail had a higher probability for good cell activity. The most noticeable fragments were benzylamines and 4-aminopiperdines. A focused effort in preparing analogues of 5 and 6 containing a tail with the 4-aminopiperdine substructure was therefore undertaken. Those compounds were designed utilizing a range of both structural and physical properties (MW,
Discovery of an Oral Potent Selective Inhibitor of Hematopoietic Prostaglandin D Synthase (HPGDS)
Chris P. Carron,† John I. Trujillo,† Kirk L. Olson,† Wei Huang,† Bruce C. Hamper,† Tom Dice,† Bradley E. Neal,† Matthew J. Pelc,† Jacqueline E. Day,† Douglas C. Rohrer,† James R. Kiefer,† Joseph B. Moon,† Barbara A. Schweitzer,† Tanisha D. Blake,† Steve R. Turner,† Rhonda Woerndle,† Brenda L. Case,† Christine P. Bono,† Vickie M. Dilworth,† Christie L. Funckes-Shippy,† Becky L. Hood,† Gina M. Jerome,† Christine M. Kornmeier,† Melissa R. Radabaugh,† Melanie L. Williams,† Michael S. Davies,† Craig D. Wegner,† Dean J. Welsch,† William M. Abraham,‡ Chad J. Warren,† Martin E. Dowty,† Fengmei Hua,† Anup Zutshi,† Jerry Z. Yang,† and Atli Thorarensen*,† †
Pfizer Global Research and Development, 700 Chesterfield Parkway West, Chesterfield, Missouri 63017, and ‡Department of Research, Mount Sinai Medical Center, 4300 Alton Road, Miami Beach, Florida 33140 . ABSTRACT Hematopoietic prostaglandin D synthase (HPGDS) is primarly expressed in mast cells, antigen-presenting cells, and Th-2 cells. HPGDS converts PGH2 into PGD2, a mediator thought to play a pivotal role in airway allergy and inflammatory processes. In this letter, we report the discovery of an orally potent and selective inhibitor of HPGDS that reduces the antigen-induced response in allergic sheep. KEYWORDS Hematopoietic prostaglandin D synthase (HPGDS), PGH2, PGD2, airway allergy, inflammatory processes, cyclooxygenase (COX)
A
in inflamed nasal mucosa and is associated with the induction of chemotactic migration and/or activation of Th-2, eosinophils, and basophils.7-9 Collectively, these data support a role for PGD2 in inflammatory diseases of the upper airways and suggest that blockade of PGD2 action at either or both receptors might be beneficial for the treatment of nasal allergies and other PGD2-mediated inflammatory conditions. This has created significant interest in both DP-1 and CRTH2 as targets, and several publications have appeared describing inhibitor design.10,11 PGD2 is synthesized from arachidonic acid via the oxidation by cyclooxygenase PGH2 (COX) and isomerization of PGH2 to PGD2 by prostaglandin D synthase (PGDS). Hematopoietic PGDS (HPGDS) is responsible for the synthesis of PGD2 by mast cells and Th-2 cells, whereas a lipocalin type PGDS (LPGDS) catalyzes the production of PGD2 in the central nervous system, male genital organs, and heart.12 The production of PGD2 by HPGDS is thought to play a pivotal role in airway allergic and inflammatory processes and induces vasodilatation, bronchoconstriction, pulmonary eosinophil and lymphocyte infiltration, and cytokine release in asthmatics.12 Inhibition of HPGDS may be therapeutically beneficial in the treatment of allergic disease and may be more effective than blocking either DP-1 or CRTH2 alone.13
sthma is a chronic inflammatory disorder of the airways that causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing in susceptible individuals.1,2 Prostaglandin D2 (PGD2), a mediator of allergy and inflammation, is produced by mast cells and Th-2 cells in a variety of human tissues. PGD2 is the most abundant de novo cyclooxygenase-derived mediator produced following IgE-mediated degranulation of mast cells.3 The mast cell, following allergen-provoked degranulation, is believed to be the major source of PGD2 found in the nasal exudates of patients with allergic rhinitis. PGD2 levels increase dramatically in bronchoalveolar lavage fluid following allergen challenge, and the observation that patients with asthma exhibit bronchoconstriction upon inhalation of PGD2 underscores the pathologic consequences of high levels of PGD2 in the lung.4 Treatment with PGD2 produces significant nasal congestion and fluid secretion in man and dogs, and PGD2 is 10 times more potent than histamine and 100 times more potent than bradykinin in producing nasal blockage in humans, demonstrating a role for PGD2 in allergic rhinitis.5,6 Mast cell-derived PGD2 exerts its effect by activating two distinct G-protein-coupled receptors (GPCRs): the DP-1 receptor, a member of the prostanoid receptor subfamily, and the recently discovered chemoattractant receptor-homologous molecule expressed on T-helper 2 cells (CRTH2 receptor). The DP-1 receptor is localized on the nasal vasculature and in mucin-secreting cells and is associated with tissue swelling and a concomitant increase in nasal airway resistance, while the CRTH2 receptor is expressed on a subset of infiltrating T cells
r 2010 American Chemical Society
Received Date: December 21, 2009 Accepted Date: January 22, 2010 Published on Web Date: February 02, 2010
59
DOI: 10.1021/ml900025z |ACS Med. Chem. Lett. 2010, 1, 59–63
pubs.acs.org/acsmedchemlett
Table 1. Heterocyclic Variation of the Body
Figure 1. Examples of literature inhibitors.
Figure 2. Advanced lead as an inhibitor of HPGDS.
HPGDS and LPGDS are genetically distinct synthases that have presumably arisen as a consequence of convergent evolution. These isoenzymes are named according to their differential requirement for GSH as a cofactor. The GSH-independent PGD2 synthase is a member of the lipocalin superfamily, while the GSH-dependent synthase is the only vertebrate member of the class Sigma family of glutathione S-transferases (GSTs) identified to date.14,15 HPGDS is a cytosolic homodimer of 26 kDa subunits, and several crystal structures have been published.16,17 Those structures reveal a well-defined active site, enabling a structure-based design of inhibitors. There have been several reports of potent enzyme inhibitors18-20 of HPGDS along with HQL-79 as an in vivo efficacious inhibitor21 (Figure 1). In this letter, we will describe our effort to identify an orally active inhibitor of HPGDS.22 A subset screen was performed on the Pfizer compound collection based on structural diversity. This resulted in numerous leads for further manipulation. Our lead generation group at the Research and Technology Center completed a triage and lead validation identifying the thiazole 1 as an advanced lead for further optimization (Figure 2). Thiazole 1 is a potent inhibitor of HPGDS enzyme (IC50, 10 nM) and cell (IC50, 300-1300 nM). In addition, the compound had a very acceptable pharmacokinetic (PK) profile (Cl, 14 mL/min/kg; T1/2, 2 h; and BA, 20%). In analysis of this compound, we identified several parameters that required optimization, most importantly, the poor cell activity of the compound. In addition, we desired a scaffold with improved novelty as judged by substructure searching in Scifinder. The thiazole could easily be divided into three major areas for exploration utilizing high-throughput chemistry: the head, the body, and the tail. Our initial effort was focused on the body, and a series of heterocycles were explored that could retain a similar hydrogen-bonding network as 1 with a conserved water molecule in the active site.23 Those compounds were easily prepared from available acids by an amide coupling reaction with 2; selective examples are
r 2010 American Chemical Society
illustrated in Table 1. Most of those building blocks were commercially available with a few exceptions, which were available in our in-house chemical storeroom. This initial iteration provided a wealth of information regarding the shape and the nature of the heteroatom equal to the nitrogen in the thiazole. Only heterocycles with a N location similar to the thiazole such as the potent compounds 5 and 6 were found to be active. The location of the nitrogen in relationship to the trajectory of the tail was found to be just as important, as 7 illustrated. The activity of 4 (27 nM), which lacks a central ring nitrogen atom, was therefore very surprising and confounded the structure-activity relationship interpretation until isothermal calorimetry illustrated that entropy was the major driving force for affinity.24 The series represented by scaffolds such as 5 and 6 were subsequently evaluated further by several cycles of high-throughput synthesis focused on the tail variation. This was done to address one of our major objectives, improved cell activity (Figure 3). It was clear that we consistently could prepare potent inhibitors of HPGDS, but only a handful of compounds illustrated potency in our cell assay. A key observation was made that certain substructures in the tail had a higher probability for good cell activity. The most noticeable fragments were benzylamines and 4-aminopiperdines. A focused effort in preparing analogues of 5 and 6 containing a tail with the 4-aminopiperdine substructure was therefore undertaken. Those compounds were designed utilizing a range of both structural and physical properties (MW,
