Diagnostic and Therapeutic Implications of Sortilin Expressed on the Surface of Bladder Carcinoma Cells

BACKGROUND & OBJECTIVE: Cell surface expression of sortilin in different types of cancer signifies it as a therapeutic target for cancer therapy. The aim of this study was to detect sortilin expression in bladder cancer cells using an anti-sortilin monoclonal antibody (mAb) to evaluate sortilin as a target for developing diagnostic and therapeutic agents against bladder carcinoma. METHODS: The protein expression of sortilin in bladder cancer tissues and cell lines (5637 and EJ138) was investigated by immunohistochemistry (IHC), immune-cytochemistry (ICC), and flow cytometry. Furthermore, the capability of anti-sortilin mAb in apoptosis induction in bladder cancer cells was evaluated. RESULTS: A high expression level was observed in bladder carcinoma tissues (P≤0.001) and cell lines, using IHC and ICC, respectively. Flow cytometry results showed cell surface expression of 27.5±3% (P≤0.01), 74.4±7.8% (P≤0.001), and 4.2±0.4% of sortilin in EJ138, 5637, and HFFF cells, respectively. In EJ138 anti-sortilin mAb induced apoptosis in 25.2±11.5% (P≤0.05) (early) and 4.5±1.1% (P>0.05) (late) after 6 h incubation, while for 12 h, the values of 11.6±3.8% (P>0.05) and 20.7±4.4% (P≤0.05) were achieved. In 5637 cells, 6 h incubation resulted in 10.2±0.3% (P>0.05) and 6.6±1.4% (P>0.05) apoptosis induction, while these values were 12.1±0.8% (P>0.05) and 27.4±4.5% (P≤0.01) after 12 h. The HFFF cells did not show significant apoptosis. CONCLUSION: The overexpression of sortilin in bladder tumor cells and its potential in inducing apoptosis via directed targeting with the specific monoclonal antibody may represent this protein as a potential candidate of targeted therapy in bladder carcinoma.