TCS 401 is a selective inhibitor of protein tyrosine phosphatase 1B (PTP1B). In Vitro: TCS-401 (0.5, 1, 2 μM) significantly increases the proliferation of RPE cells. TCS-401 significantly increases the expression of cyclin A and cyclin D1 at the concentrations of 1 and 2 μM in a concentration-dependent manner. TCS-401 at concentrations of 0.5, 1, and 2 μM significantly increases phosphorylation of Erk and Akt compared to the control group. The activation of Erk and Akt by TCS-401 is blocked by pretreatment with PD98059 and LY294002, respectively. CS-401 treatment activates the MEK/Erk and PI3K/Akt signaling pathways and induces proliferation, differentiation, and migration in RPE cells^[1]. CS-401 dose dependently inhibits the RPTC-Sup-induced reduction of fibronectin and α-SMA. At 1 μM, TCS-401 reverses the levels of fibronectin and α-SMA about onefold and at a dose of 2 μM, TCS-401 brings back fibronectin and α-SMA expression to near normal levels^[2].