DPP8/9-IN-2 (Compound 21) is an inhibitor targeting DPP8 and DPP9 with IC50 values of 0.22 nM and 3 nM, and Ki values of 2.9 nM and 6 nM, respectively. It exhibits certain cardiac toxicity, with IC50 values against the hERG potassium channel, Nav1.5 sodium channel, and Cav1.2 calcium channel of 0.7 µM, 29.0 µM, and 27.7 µM. DPP8/9-IN-2 is applicable for research into diseases such as cancer.