**5. Conclusions**

In our studies of drug repositioning, we demonstrate that PFD may serve as a novel therapeutic drug that induces G1 cell cycle arrest in human PCa cells independently of androgen sensitivity.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2077-0383/8/1/44/s1, Figure S1: Effects of pirfenidone (PFD) treatment on the expression of cell cycle-related proteins in human prostate cancer cells. E9, F10, and AIDL cells were plated in 100-mm dishes and treated with PFD for 2 days. Cell lysates (50 μg) were separated by electrophoresis using a 12.5% SDS–polyacrylamide gel. After separation, the proteins in the gel were transferred to a polyvinylidene difluoride membrane by electroblotting. p21 and CDK2 protein levels were determined by Western blot analysis using specific antibodies. Equal loading of the samples was confirmed by measuring β-actin protein levels.

**Author Contributions:** conceptualization, M.W. and Y.S.; investigation, T.S., M.K., K.I. (Kazuhiro Iguchi) and H.K.; writing—original draft preparation, K.I. (Kenichiro Ishii); writing—review and editing, Y.H. and K.A.

**Funding:** This research was funded by Ministry of Education for Science and Culture of Japan, gran<sup>t</sup> number 23791751 to Kenichiro Ishii.

**Acknowledgments:** We would like to thank Yumi Yoshikawa and Izumi Matsuoka for their technical support.

**Conflicts of Interest:** The authors declare no conflict of interest.
