Effect of short hairpin RNA targeting of fibroblast activation protein on tumor growth and angiogenesis in a 4T1 murine breast cancer model.

e13538 Background: Fibroblast activation protein(FAP) is an increased abnormal signal protein in the TME and has both dipeptidyl peptidase and endopeptidase activity. FAP has been recognized to influence cancer growth and invasion, through its non- enzyme function or proteolytic activities in concert with other moleculars such as CD26, uPAR, β1-integrin, and MMP-1. Since FAP is over expression in epithelial cancers and absent from normal adult tissues, it has long been suggested to be a target of antitumor therapy. Methods: 21 BALB/C female mice implanted with 4T1 breast cancer were enrolled and randomly divided into three groups (n=7 per group) .The experiment group(E-group) was administered with shRNA targeting of FAP every 48 hours in 2 weeks by local administration, and the two control groups with HK or 5%GS. Tumor volumes and weights were monitored. Expression of FAP was detected by RT-PCR and immunohistochemistry staining. Collagen fiber, microvessel density and cell apoptosis were investigated. Results: The expression of FAP was reduced about 50% by shRNA targeting of FAP; the tumor volume and weight of the E-group showed significant reduction of 40% compared with the controls (p=0.001). Knockdown of FAP increased accumulation of disorganized collagen fibers; the MVD in control groups was about 4 times at least compared to the E-group (p<0.001) and apoptosis cells markedly increased 3 fold (p=0.0015). Conclusions: Knockdown of FAP by shRNA interference mediated inhibition of breast cancer growth, amelioration of the tumor microenvironment including increased accumulation of disorganized collagen, suppressed angiogenesis, and promotion of apoptosis. FAP contributes to the formation of TME and is a stimulative factor of breast cancer growth. Target of FAP may be a potential supplemental therapeutic method for breast cancer.