Figure 2.

In vitro activity of FAP-activated prodrugs. A) Hydrolysis of FAP-activated prodrugs in tissue culture media supplemented with 10% FBS but not in its absence. Non-FAP cleavable prodrug analogs are stable in FBS-supplemented media. B) Effect of FAP prodrugs on the growth of the MCF-7 human breast cancer cell line in vitro. Mean absorbance was calculated from a single experiment with seven replicates/concentration and reported with 95% confidence intervals (CI). C) Comparison of FAP enzymatic activity in the plasma/serum from multiple species based upon the rate of hydrolysis of a FAP-selective fluorescent substrate (MCa-ASGPAGPA-Dnp, 20 μM). The mouse had as much as 10-fold greater FAP activity in the plasma than did the human. The FAP-selective dipeptide boronic acid inhibitor, AcGbP, was used at a concentration of 200 μM. Error bars represent 95% CI. IC₅₀ = half maximal inhibitory concentration; FBS = fetal bovine serum; CI = confidence interval; FAP = fibroblast activation protein α; RFU = relative fluorescence units.