Prostaglandin D2: Therapeutic Indications World Allergy Organisation Cancun 2011

1. Prostaglandin D2: Therapeutic IndicationsWorld Allergy OrganisationCancun 2011 Andy Wardlaw

2. Disclosures • Research grants from Glaxo Smith Kline (GSK), AstraZeneca and Pfizer • Honorariums for advisory boards from GSK and Cephalon

3. Environmental Trigger Allergen Infection Smoking Eos BRONCHIAL INFLAMMATION Neuts Uncontrolled Falls in FEV1 (Severe Exacerbations) Airway Damage (fixed airflow obstruction Bronchiectasis) Variable Airflow Obstruction & AHR (Asthma Like) Increased cough reflex (cough) Airway inflammation leads to several patho-physiological outcomes

4. The A to E of Airway diseasePavord ID and Wardlaw AJ Clin Exp Allergy 2010;40:62-67 • AAirway hyperresponsiveness • Rapid variations in airflow obstruction • B Bronchitis • Eosinophilic:neutrophilic:both • C Cough • D Damage • Bronchiectasis • fixed airflow obstruction • emphysema • E Extrapulmonary factors • Psychological and lifestyle issues including adherence • Obesity and obstructive sleep apnoea • Dysfunctional breathing: • Treatment side effects and co-morbidities

5. Methacholine PC20 (mg/ml) Sputum Eosinophil Count (%) Eosinophilic Airway Inflammation and Variable Airflow Obstruction (AHR) are Largely Independent Uncontrolled, Treatment Unresponsive Falls in FEV1 Variable Airflow Obstruction/AHR Asthma Symptoms Severe Exacerbations Eosinophilic Inflammation Smooth Muscle Dysfunction

6. PGD2 • Prostaglandin is produced (outside the brain), mainly by mast cells by the combined action of cyclooxygenase enzymes and prostaglandin D2 synthase • 50ng per 106 mast cells • Not produced in significant amounts by basophils • Released as part of the early but not the late response to allergen challenge

7. Synthetic pathway for PGD2 Roy Pettipher et al Nature Reviews Drug Discovery 6, 313-325 (April 2007)

8. PGD2 • Some evidence synthesis is increased in clinical asthma although concentrations in sputum and BAL are variable with inconsistent difference between asthma and healthy subjects. • Inhalation causes bronchoconstriction and vasodilation. • Injection into the skin causes recruitment of neutrophils and to a lesser extent eosinophils.

9. No increase in PGD2 in sputum from patients with asthma Mediator concentrations ng/ml sputum *p<0.05, ANOVA Brightling et al Am J Respir Crit Care Med 2000; 162: 878-882

10. Antagonism and over-expression of PGD2 • PGD2 is primarily synthesised by COX1 and PGE2 by COX2. Non-specific COX inhibitors will inhibit both so cancelling each other out • Dahem K et al CEA 2011 • PGD2 synthase transgenic mouse had increased production of PGD2 and increased Th2 inflammation in the mouse model of asthma • Fujitana et al J Immunol 2002

11. PGD2 Receptors • Three receptors: • DP1 receptor expressed on airway smooth muscle, vascular tissue, dendritic cells and T cells. • DP2; Chemoattractant receptor homologous molecule expressed on Th2 cells (CRTh2). Expressed on Th2 cells (also Th1 in mice), basophils and eosinophils • TP: Thromboxane A2 receptor expressed on airway smooth muscle • PGD2 metabolites bind to CRTh2 but not DP1

12. DP1 receptor • Primary function appears to be vasodilation but may also mediate bronchodilation • In vitro down-regulates Th1 and dendritic cell function possibly leading to increased Th2 responses. • DP1 gene deleted mouse had reduced inflammation and AHR in the mouse model of asthma as did mice and sheep treated with a DP1 antagonist. (Shichijo et al CEA 2009) • However DP1agonist was anti-inflammatory in allergic responses in skin in mouse and in the mouse model of asthma by modulating dendritic cell and Treg function. (Hammad et al J Exp Med 2007)

13. Clinical efficacy of a DP1 antagonist laropiprant(Phillip G et al JACI 2009:124:942-8) • Rhinitis: • 767 patients with seasonal allergic rhinitis treated with laropiprant for two weeks: no difference in nasal symptom score from placebo • Asthma: • 100 patients with asthma randomised to laropiprant or placebo for three weeks: no difference in asthma symptoms or FEV1

14. TP receptor • Receptor for a stable metabolite of PGD2 (9alpha11betaPGF2),as well as thromboxane A2 • Mediates bronchoconstrictor activities of PGD2 • A selective antagonist of the TP receptor, GR32191 blocked PGD2 induced bronchoconstriction and had a modest effect on the early response to allergen challenge, but no effect on exercise induced asthma or clinical disease after three weeks of treatment

15. CRTh2 receptor • Identified in 2001 as a receptor for PGD2 expressed on eosinophils, Th2 cells (hence its name) and basophils where it mediates activation and migration • Hirai et al J Exp Med 2001:193:255 • Gene deletion showed increased eosinophil accumulation in the mouse model of asthma with short term exposure but decreased eosinophil infiltration with chronic exposure • Chevalier et al J Immunol: 2005:175:2056. Kagawa et al Int Arch All Imm 2011:155suppl • Gene deletion inhibits allergic skin inflammation in mice • He et al JACI:2010:126:784. Satoh et al J Immunol 2006:177:2621

16. CRTh2 expression on T cells in asthma Mutalithas K et al Clin Exp Immunol 2010:161:34-40

17. CRTh2 is preferentially expressed on Th2 cells Asthma Healthy

18. CCR3, CCR4, CRTh2 and CCR8 are preferentially expressed on Th2 cells but only a minority of Th2 cells express these receptors IL-4 IFNg

19. % of BAL T cells expressing CRTH2

20. PGD2 concentrations in BAL

21. Antagonists of CRTh2 in clinical development • It has been relatively easy to make potent and effective CRTh2 antagonists and there are several in early phase clinical trials which appear safe and well tolerated • Some are based on NSAID’s as indomethacin was found to be a selective antagonist and some based on the structure of angiotensin receptor antagonists. • Ramatroban used for allergic rhinitis in Japan is a potent TP antagonist with moderate antagonism for CRTh2, but there is little literature on clinical efficacy

22. Trial of a CRTh2 inhibitor (OC000459) in moderate steroid naïve asthmaBarnes et al CEA 2012 epub • Double blind placebo controlled with parallel group design carried out in Russia • Moderate asthma but not taking inhaled corticosteroids • One month treatment • Change in FEV1 was primary outcome • Modest improvement which was significant in the per protocol, but not the full analysis population

23. Study design

24. OC000459 Phase II Asthma Study Effect on FEV1 (Per Protocol Population) Start double blind treatment End double blind treatment End Placebo washout Start double blind treatment End double blind treatment End Placebo washout % Change in FEV1 vs. Baseline Change in FEV1 (ml) vs. Baseline Placebo (n=50) vs. OC000459 (n=55) OC000459 Clinic FEV1 9.2% greater than baseline at end of randomised treatment period; Treatment difference OC000459-Placebo = 7.4%; p-value = 0.037 OC000459 Clinic FEV1 214mL greater than baseline at end of randomised treatment period; Treatment difference OC000459-Placebo = 184mL Clinically relevant improvement in FEV1

25. Effect of OC000459 on sputum eosinophilia in 28 day asthma study

26. Conclusions • PGD2 is a major mast cell derived mediator with several activities relevant to allergic disease • Three receptors, DP1(vasodilation and immune modulation), TP (bronchoconstriction) and CRTh2 (immune modulation, cell recruitment) • Mouse models for a role for DP1 and CRTh2 are conflicting and not particularly compelling for an important role of DP1 and CRTh2 in asthma • Human studies of antagonists of TP and DP1 have been negative • Single study in humans of CRTh2 antagonist in moderate asthma demonstrated modest effect at best, but several antagonists in early phase development

27. Acknowledgements Das Mutalithas C Guillen Caroline Day C Brightling ID Pavord F Symon Asthma UK GSK