*2.1. Cell Lines*

Two PCa cell lines (DU145 and C4-2) and DTX-resistant DU145 cells (DU145-DR) and DTX-resistant C4-2 cells (C4-2-DR) were kindly provided by Dr. Masaki Shiota (Kyushu University, Fukuoka, Japan). The DU145 cell lines were maintained in MEM (Nissui Pharmaceutical Co. Ltd., Tokyo, Japan), and the C4-2 cells were maintained in RPMI 1640 (Nissui Pharmaceutical Co. Ltd.) containing 10% fetal bovine serum (BioWhittaker, Walkersville, MD, USA), 2 mM L-glutamine, 50 U/mL penicillin, and 50 g/mL streptomycin in a humidified atmosphere of 5% CO2 at 37 ◦C. DTX cell lines were cultured under DTX at a dose of 2 ng/mL for DU145-DR and 5 ng/mL for C4-2-DR.

### *2.2. DTX and CW069 Treatment*

DTX was obtained from Sanofi-Aventis and handled according to the manufacturer's recommendations [18]. CW069 was obtained from Funakoshi (Tokyo, Japan). Twenty-four hours after transfection of siRNAs for KIFC1 or negative control, these cells were exposed to DTX for 48 hr. Cell viability was measured by an MTT assay. An MTT assay was performed 48 h after DTX or CW069 treatment. Drug sensitivity curves and IC50 values were calculated using GraphPad Prism 4.0 software (GraphPad Software) [17].
