AT-1002 reversibly increases the paracellular transport of molecules across the epithelial barrier. AT-1002 can undergo Cys-Cys dimerization [1]. Undifferentiated Caco-2 cells are treated with AT-1002 (0 to 5 mg/mL, 3 or 24 hours) and viability is assessed by measuring cellular ATP content. Treatment with AT-1002 for up to 3 h does not affect cell viability at any concentration. In particular, the viability of Caco-2 cells is not affected by 5 mg/mL AT-1002. AT-1002 reduces cell viability after 24 h at concentrations of 2.5 mg/mL and higher. However, the cells remain viable after 24 h if the cells are washed after exposure to AT-1002 for 3 h [2].