Phosphodiesterase 4 inhibitors for the treatment of inflammation associated with respiratory disease

• Main Author: Cooper, Nicola
• Other Authors: Chowdhry, Babur ; Spencer, John
• Published: University of Greenwich 2010
• Subjects: 500; RC Internal medicine
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526136

This submission for a PhD, by publication, which is based upon a series of original research studies published between 1998 and 2002 focuses on the selection of novel phosphodiesterase 4 (PDE4) inhibitors for the treatment of inflammation associated with respiratory diseases such as asthma and chronic obstructive pulmonary disease. A number of issues, relevant at the time, have been considered including: a) in vitro methods predictive of in vivo therapeutic index of anti-inflammatory efficacy over emetic side effects, b) in vivo methods for confirming therapeutic index and c) early confirmation of functional activity in a human system. In addition to 10 peer-reviewed articles, a poster presented at the American Thoracic Society (ATS) conference in 1999 and a review article published in Trends in Pharmacological Sciences (publication 1) in 1997 are also included. In the initial work (publication 2) to investigate if it was possible to correlate in vitro activity with in vivo efficacy for PDE4 inhibitors structurally diverse compounds were tested in a series of experimental systems. The compounds tested were SB 207499, LAS 31025, CDP 840, rolipram and RP 73401. The in vitro experiments consisted of PDE4 enzyme activity (guinea pig and human inflammatory cells) and rolipram binding activity, RBA (rat brain). The in vivo model used was the guinea pig skin model of eosinophil recruitment, which involves systemic 111In-eosinophil recruitment to guinea pig skin induced by a range of inflammatory mediators [i.e. PCA, PAF and zymosan activated plasma (ZAP)]. Previous studies with PDE4 inhibitors had not examined the correlation between in vitro and in vivo activities in this way. RP73401 was the most potent PDE4 enzyme inhibitor (guinea pig macrophage) followed by SB 207499>CDP 840> rolipram>LAS 31025. Rolipram binding activity did not follow the same ranking, though RP73401 was again the most potent followed by rolipram>SB 207499>CDP 840>LAS31025. Attenuation of eosinophil recruitment was consistently observed regardless of inflammogen with the following rank order of potency: RP 73401= rolipram>LAS 31025>SB 207499>CDP 840. In this model no correlation was found between the in vitro activities and in vivo efficacy. A cell based in vitro assay, LPS induced TNF release from human PBMCs was also included in this publication. All of the PDE4 inhibitors tested were efficacious in this assay with a potency order of: RP 73401>SB 207499 = rolipram = CDP 840>LAS 31025. In publications 3-7, in vitro and in vivo data are presented on a large number of compounds from a diverse range of chemical classes. In all cases the in vitro focus pertains to the ratio of PDE4 enzyme activity to rolipram binding activity (PDE4:RBA) as a method of selecting compounds with an improved therapeutic index of anti-inflammatory efficacy over emetic side effects. In these publications emesis data were included together with efficacy data in order to determine if in vitro predictions of therapeutic index were of relevance in vivo. The drug classes examined were xanthines, aryl sulphonamides, quinolones, 7-methoxybenzofuran-4-carboxamides, and 7-methoxyfuro[2,3-c]pyridine-4-carboxamides. The lead molecules selected in each publication had improved PDE4:RBA ratios which translated into an improved therapeutic window in vivo. These generated lead molecules (compound numbers from publication); corresponding PDE4:RBA ratios, skin eosinophilia efficacious dose and ferret non-emetic doses are as follows: publication 3, xanthine (3c), 4.1, 5 mg/kg, 10 mg/kg; publication 4, aryl sulphonamide (20), <0.6, 5 mg/kg, 10 mg/kg; publication 5, quinolone (7g), <0.7, 10 mg/kg, 20 mg/kg; publication 6, 7-methoxybenzofuran-4-carboxamides (3a), 0.37, 0.5 mg/kg, 10 mg/kg and publication 7, 7-methoxyfuro[2,3-c]pyridine-4-carboxamides (8a), 0.16, 10 mg/kg (lung eosinophilia), not evaluated in the ferret. The objective of the method for the selection of novel PDE4 inhibitors for the treatment of inflammation associated with respiratory diseases was to nominate compounds into drug development. The molecules had to successfully exhibit all of the criteria set in the screening cascade to be considered safe and efficacious enough to be tested in clinical trials. Publication 8 and the ATS poster refer to the first development compound nominated for clinical development, D 4418. This compound demonstrated efficacy in the guinea pig lung model of airway function, eosinophil infiltration and bronchial hyperreactivity at 10 mg/kg, p.o. and did not evoke emesis in the ferret at 100 mg/kg. In a Phase I clinical trial when dosed between 5 and 200 mg, D 4418 had a good pharmacokinetic profile and only mild side effects of headache, dizziness and nausea but no vomiting. No further clinical development was carried out with this molecule. Publications 9, 10 and 11 refer to the discovery, synthesis and pharmacology of a second development candidate, SCH 351591. This compound was more potent than D 4418 both in vitro and in vivo and had a wider therapeutic index for efficacy over side effects. SCH 351591 demonstrated efficacy in the guinea pig lung model of airway function, eosinophil infiltration and bronchial hyperreactivity at 0.3 mg/kg, p.o. and did not evoke emesis in the ferret at 5 mg/kg showing it to have a promising preclinical profile for the treatment of respiratory inflammation. Due to the final submitted publication being dated as 2002 two sections are included at the end of this thesis to cover further work carried out on SCH 351591 and in the PDE4 area from 2002 to date.