228P Queen Elizabeth II Conference Centre London
Pharmacology 2014

 

 

QAW039, a slowly dissociating CRTh2 antagonist with potential for improved clinical efficacy

David Sykes1,2, Michelle Bradley1, Darren Riddy1, Liz Willard1, Ellen Powell-Herlaar1, Simon Watson1, Carsten Bauer1, Dave Sandham1, Gerald Dubois1, Steven Charlton1,2. 1Novartis, Horsham, UK, 2Nottingham University, Nottingham, UK

PGD2 is the major prostanoid released by activated mast cells and is an important proinflammatory mediator in allergic asthma acting through the CRTh2 receptor. QAW039 is an oral, selective, competitive and reversible CRTh2 antagonist currently in clinical development for treatment of asthma. This study describes the detailed investigation of the receptor binding kinetics of QAW039 and compares it to several other known CRTh2 antagonists.

[3H3]-QAW039 was used to label the CRTh2 receptor expressed in CHO-membranes. Competition kinetic experiments were carried out at 37oC in the presence of unlabelled CRTh2 receptor antagonists using methodology previously described (1). PGD2 stimulated [35S]-GTPγS binding was carried out essentially as described by Sykes et al. (2), using an antagonist preincubation period of 120min and PGD2 concentrations ranging from 0.0005 to 30μM. The ability of compounds to inhibit the whole blood shape change (WBSC) response to PGD2 was monitored using FACSCalibur flow cytometry as described by Sandham et al. (3).

The dissociation rate constant for QAW039 was significantly lower than all other clinically relevant CRTh2 antagonists tested including QAV680, OC459 and AZD1981, see Table 1. QAW039 was the most potent compound tested in the WBSC assay, being active at sub nM concentrations. In the [35S]-GTPγS binding assay all CRTh2 antagonists tested produced concentration-dependant rightward shift of the PDG2 agonist effect curve. However in contrast to the other CRTh2 antagonists tested QAW039 markedly reduced the maximal effect of PDG2 following a 15min stimulation period.

Compound Kinetically derived parameters WBSC IC50 (nM)
k on (M-1min-1) k off (min-1) Dissociation t1/2 (min) Kinetic pK d
QAW039 6.27 ± 0.93 x107 0.061 ± 0.006 12.04 ± 1.32 8.99 ± 0.06 0.55 ± 0.14
QAV680 4.80 ± 2.14 x107 0.66 ± 0.18 1.29 ± 0.38 7.82 ± 0.06 42.8 ± 15.5
OC459 9.50 ± 5.14 x108 1.83 ± 0.32 0.41 ± 0.09 8.61 ± 0.17 422.5±155.9
AZD1981 1.60 ± 0.36 x108 0.77 ± 0.23 1.26 ± 0.56 8.58 ± 0.03 13.1 ± 4.0

Table 1. Kinetic parameters and WBSC IC50 values. Data are mean ± standard error means (n ≥ 3) using significance tested using one factor ANOVA (P < 0.0001) and Tukey’s multiple comparison test.

The slower off-rate of QAW039 from the CRTh2 receptor potentially affords it an improved efficacy as it is able to insurmountably block the CRTh2 receptor even in the face of high local concentrations of PDG2.

References:

1. Sykes et al., (2009). Mol Pharm. 76, 543-551.

2. Sykes et al., (2014). Br J Pharm. Feb 12. doi: 10.1111/bph.12620.

3. Sandham et al., (2014). Bioorg Med Chem. 21, 6582-91.