GSTP1 and cholangiocarcinoma: human cholangiocarcinoma cells: GSTP1-1 antisense transfection decreases intracellular GSTP1-1 levels and increases sensitivity to adriamycin, cisplatin, melphalan, and 4-hydroxyperoxycyclophosphamide; C16C2, a GSTP1-1-specific inhibitor, also reduces resistance