Abrogation of fibroblast activation protein enzymatic activity attenuates tumor growth

Abstract

Tumor-associated fibroblasts are functionally and phenotypically distinct from normal fibroblasts that are not in the tumor microenvironment. Fibroblast activation protein is a 95 kDa cell surface glycoprotein expressed by tumor stromal fibroblasts, and has been shown to have dipeptidyl peptidase and collagenase activity. Site-directed mutagenesis at the catalytic site of fibroblast activation protein, Ser 624 ! ! ! ! Ala 624 , resulted in an f f f100,000-fold loss of fibroblast activation protein dipeptidyl peptidase (DPP) activity. HEK293 cells transfected with wild-type fibroblast activation protein, enzymatic mutant (S624A) fibroblast activation protein, or vector alone, were inoculated subcutaneously into immunodeficient mouse to assess the contribution of fibroblast activation protein enzymatic activity to tumor growth. Overexpression of wild-type fibroblast activation protein showed growth potentiation and enhanced tumorigenicity compared with both fibroblast activation protein S624A and vector-transfected HEK293 xenografts. HEK293 cells transfected with fibroblast activation protein S624A showed tumor growth rates and tumorigenicity potential similar only to vector-transfected HEK293. In vivo assessment of fibroblast activation protein DPP activity of these tumors showed enhanced enzymatic activity of wild-type fibroblast activation protein, with only baseline levels of fibroblast activation protein DPP activity in either fibroblast activation protein S624A or vector-only xenografts. These results indicate that the enzymatic activity of fibroblast activation protein is necessary for fibroblast activation protein -driven tumor growth in the HEK293 xenograft model system. This establishes the proof-of-principle that the enzymatic activity of fibroblast activation protein plays an important role in the promotion of tumor growth, and provides an attractive target for therapeutics designed to alter fibroblast activation protein -induced tumor growth by targeting its enzymatic activity.

Fibroblast heterogeneity in the cancer wound

“…For instance, urokinase-type plasminogen activator (uPA) activates the serine protease Plasmin and has thereby been shown to increase proliferation, migration, and invasion (Danø et al, 2005;Noskova et al, 2009). Finally, the CAF marker FAP is a membrane-bound glycoprotein with both collagenase and dipeptidyl peptidase (DPP) activities that are important for degrading the ECM (Scanlan et al, 1994) and stimulating tumor growth (Cheng et al, 2005).…”

Selective inhibitors of fibroblast activation protein (FAP) with a xanthine scaffold

“…12 Inhibition of FAP in mouse cancer models has been shown to attenuate tumor growth. 13,14 Furthermore, several studies are currently ongoing that investigate the effect of FAP-inhibition in other diseases characterised by FAP expression. Most of the previously reported FAP inhibitors have a dipeptide-derived architecture and bind covalently to the catalytic serine of the enzyme via an electrophilic warhead.…”

Bioluminescent Probe for Monitoring Endogenous Fibroblast Activation Protein-Alpha

“…Fibroblast activation protein-α (FAP, FAPα), a member of dipeptidyl peptidase (DPP) family, pocesses the enzymatic activity of both dipeptidyl peptidase and endopeptidase . FAP has been reported to overexpress in more than 90% of epithelial cancers and affect the proliferation as well as invasion of tumors. , Hence, it is accepted as a biomarker of tumor stromal fibroblasts and potential drug target. What’s more, some diseases linked with activated stroma, such as fibrosis diseases and wound healing, also promote the expression of FAP. , Therefore, it is related to tissue remodeling as well.…”