Novel p38 MAPK inhibitor ML3403 has potent anti-inflammatory activity in airway smooth muscle

SB203580 is the prototypical p38 MAPK inhibitor; however it cannot be used clinically due to liver toxicity. We developed a structural analogue of SB203580 - ML3403 - with equal in vitro and ex vivo p38alpha MAPK inhibition as SB203580, but with reduced activity towards liver cytochrome P450 enzymes. In addition, we developed a selective p38alpha MAPK inhibitor - CP41. The aim of this study is to compare the anti-inflammatory activity of ML3403 and CP41, with SB203580. We compare and contrast the ability of the p38 MAPK inhibitors to repress tumour necrosis factor alpha (TNFalpha)-induced interleukin 6 (IL-6) and interleukin 8 (IL-8) mRNA expression and protein secretion from airway smooth muscle cells. We also examined and compared the binding affinities of ML3403 and SB203580 to the active and inactive p38alpha MAPK. We demonstrate that ML3403 binds to both active and inactive p38 MAPK with high affinity and that it inhibits p38 MAPK-mediated airway smooth muscle synthetic function to an equivalent degree with SB203580. CP41 was not able to reduce IL-6 and IL-8 secretion in airway smooth muscle cells; a function of its higher IC(50) against p38alpha MAPK when compared to SB203580 and ML3403. We show that p38 MAPK-mediated pro-inflammatory pathways in airway smooth muscle cells can be inhibited by ML3403. The anti-inflammatory activity is equivalent to the prototypical p38 MAPK inhibitor SB203580. Our results implicate a future pharmacotherapeutic strategy towards reducing inflammation in asthma and airway remodelling.