**Loss of Fibroblast-Dependent Androgen Receptor Activation in Prostate Cancer Cells Is Involved in the Mechanism of Acquired Resistance to Castration**

**Kenichiro Ishii 1,2,\*, Izumi Matsuoka 1, Takeshi Sasaki 1, Kohei Nishikawa 1, Hideki Kanda 1, Hiroshi Imai 3, Yoshifumi Hirokawa 2, Kazuhiro Iguchi 4, Kiminobu Arima 1 and Yoshiki Sugimura 1**


Received: 16 August 2019; Accepted: 2 September 2019; Published: 3 September 2019

**Abstract:** Loss of androgen receptor (AR) dependency in prostate cancer (PCa) cells is associated with progression to castration-resistant prostate cancer (CRPC). The tumor stroma is enriched in fibroblasts that secrete AR-activating factors. To investigate the roles of fibroblasts in AR activation under androgen deprivation, we used three sublines of androgen-sensitive LNCaP cells (E9 and F10 cells: low androgen sensitivity; and AIDL cells: androgen insensitivity) and original fibroblasts derived from patients with PCa. We performed in vivo experiments using three sublines of LNCaP cells and original fibroblasts to form homotypic tumors. The volume of tumors derived from E9 cells plus fibroblasts was reduced following androgen deprivation therapy (ADT), whereas that of F10 or AIDL cells plus fibroblasts was increased even after ADT. In tumors derived from E9 cells plus fibroblasts, serum prostate-specific antigen (PSA) decreased rapidly after ADT, but was still detectable. In contrast, serum PSA was increased even in F10 cells inoculated alone. In indirect cocultures with fibroblasts, PSA production was increased in E9 cells. Epidermal growth factor treatment stimulated Akt and p44/42 mitogen-activated protein kinase phosphorylation in E9 cells. Notably, AR splice variant 7 was detected in F10 cells. Overall, we found that fibroblast-secreted AR-activating factors modulated AR signaling in E9 cells after ADT and loss of fibroblast-dependent AR activation in F10 cells may be responsible for CRPC progression.

**Keywords:** prostate cancer; androgen deprivation therapy; androgen sensitivity; androgen receptor dependency; fibroblast-dependent androgen receptor activation
