Evaluation of the tumor targeting of a FAPα-based doxorubicin prodrug

Fibroblast activation protein-a (FAP alpha) is a tumor-associated antigen uniquely expressed by reactive stromal fibroblasts in the majority of human epithelial tumors. FAP alpha also possesses both post-prolyl peptidase and endopeptidase activities. Consequently, FAP alpha is increasingly considered as a potential pan-tumor target for designing tumor-targeted prodrugs. We previously conjugated Doxorubicin (Dox) with a FAP alpha-specific dipeptide (Z-Gly-Pro) to develop a FAP alpha-targeting prodrug of Dox (FTPD). The aim of current work was to validate the tumor targeting of this targeted-delivery strategy. The results demonstrated that FTPD could effectually release Dox upon the hydrolysis of FAP alpha as well as the incubation with tumor homogenate of FAP alpha-positive tumor (4T1 tumor), while it was highly stable in mouse plasma and a variety of tissue homogenates including heart, liver, and so on. And the FAP alpha-cleaved FTPD exhibited significantly higher cytotoxicity against 4T1 cells in vitro than the uncatalyzed prodrug. Additionally, FTPD produced similar antitumor efficacy in 4T1 tumor-bearing mice to free Dox without obvious cardiotoxic effect. Moreover, subsequent study indicated that the accumulation of FTPD reduced significantly in the heart compared to free Dox. These findings suggest that such FAP alpha-based prodrug strategy is promising to achieve targeted delivery of antitumor agents.