LY 3000328 (Cathepsin S inhibitor) is a potent, highly selective Cathepsin S (Cat S) inhibitor (IC50s: 7.7 and 1.67 nM for hCat S and mCat S).

LY3000328 shows low in vitro CYP450 inhibition (<15% at 10 μM for CYP3A4, CYP2D6, and CYP2C9); low in vitro metabolism in mouse, rat, dog, and human liver microsomes (<20% after 30 min incubation at 4 μM); and good permeability (MDCK A-B>4%) [1]. LY3000328 is a potent and specific inhibitor of cathepsin S (CatS). The inhibition of CatS activity in plasma would be 50% of maximal when LY3000328 plasma concentration is approximately 60 ng/mL [2].

The efficacies of LY3000328 is studied in a mouse model of abdominal aortic aneurysm (AAA). In this model, inflammation is induced using CaCl2 applied to the ablumenal surface. It is shown that the features of the disease state in this model resemble those of human AAA. LY3000328 (1, 3, 10, 30 mg/kg) exhibits a dose-responsive aortic diameter reduction. At the lowest dose of 1 mg/kg of LY3000328, the aortic diameter is reduced by 58%, then 83% at 3 mg/kg, and 87% at 10 mg/kg. The exposure (AUC) for both compounds increased in a dose-dependent manner, suggesting that the drug disposition properties of LY3000328 are favorable [1].