tokens: Two human breast cancer cell lines , MDA - MB - 468 and BT - 20 , were transiently transfected with a pool of four siRNA oligonucleotides directed against the MUC1 mRNA ( 468 . siMUC1 and BT . siMUC1 ) , or a control oligonucleotide directed against luciferase ( 468 . siLuc and BT . siLuc ) .