Toward an in vivo Proof of Concept

Compounds 10a, 12a, and 12b represent promising combinations of good target affinity, high cell permeability, and acceptable CYP3A4 induction profile. We also found no hints for CYP inhibition or hERG charmel interactions and the compounds were clean in AMES and MNT testing. A broad study of 10a and 12a on the commercial CEREP profile [45] of a diverse set of 100 ion-channels, enzymes, and receptors revealed no hits above 70% inhibition at a concentration of 10 pM. 

Eor a further differentiation between the compounds 10a, 12a, and 12b, we initiated pharmacokinetic studies in rat and the results are presented in Table 23.2 Cmax AUC values of 10a in the plasma are considerably higher compared to 12a and 12b. In addition, the overall tissue distribution profile is similar in all three compounds with the highest tissue exposure in the targeted organ heart observed with 10a. 

As discussed earlier, CatA is strongly involved in urinary bradykinin metabolism in rat and humans. Therefore, elevated bradykinin levels after CatA inhibition should result in increased diuresis. Based on these considerations, the group of Majima investigated effects on urinary kinin levels, natriuresis, and diuresis after administration of the CatA inhibitor ebelactone B to rats [48,49]. Using a sophisticated experimental protocol with cannulated ureters in anesthetized animals. 

With such an in vivo proof of concept established, we profiled several of the CatA inhibitors in advanced models of cardiovascular diseases. These studies indicated a significant impact of CatA inhibition on several disease parameters including cardiac hypertrophy [2], Based on the outcome of these studies and its promising ADME and safety profile, one of our CatA inhibitors has now been progressed into phase I clinical trials. 

The observed effects in cardiovascular disease modek can be rationalized by a local increase of bradyldnin and a local decrease of Ang II levek in affected tissues, but more detailed investigations on the biological and pharmacological mechanism have to be carried out. The absence of enzyme expression in the vasculature and the acidic pH optimum of proteolytic enzyme activity might be beneficial in terms of a clinical safety profile for CatA inhibitors. However, the most obvious challenge right now will be the clinical validation of thk novel target in humans by the demonstration of safety and efficacy. 

---