Although prostate cancer (CaP) is the most frequently diagnosed malignant tumor in American men, the mechanisms underlying the development and progression of CaP remain largely unknown. Recent studies have shown that downregulation of miR-124 occurs in several types of human cancer, suggesting a tumor suppressive function of miR-124. Until now, however, it has been unclear whether miR-124 is associated with CaP. In the present study, we completed a series of experiments to understand the functional role of miR-124 in CaP. We detected the expression level of miR-124 in clinical CaP tissues, evaluated the influence of miR-124 on the growth of CaP cells, and investigated the mechanism underlying the dysregulation of miR-124. We found that i) miR-124 directly targets the androgen receptor (AR) and subsequently induces a upregulation of p53; ii) miR-124 is significantly down-regulated in malignant prostatic cells compared to that in benign cells and DNA methylation causes the reduced expression of miR-124; and iii) miR-124 can inhibit the growth of CaP cells in vitro and in vivo. Data from this study revealed that loss of miR-124 expression is a common event in CaP, which may contribute to pathogenesis of CaP. Our studies also suggest that miR-124 is a potential tumor suppressive gene in CaP, and restoration of miR-124 expression may represent a novel strategy for CaP therapy.

Btk and Etk/BMX are Tec-family non-receptor tyrosine kinases. Btk has previously been reported to be expressed primarily in B cells and has an important role in immune responses and B-cell malignancies. Etk has been shown previously to provide a strong survival and metastasis signal in human prostate cancer cells, and to confer androgen independence and drug resistance. While the role of Etk in prostate carcinogenesis is well established, the functions of Btk in prostate cancer have never been investigated, likely due to the perception that Btk is a hematopoietic, but not epithelial, kinase. Herein, we found that Btk is overexpressed in prostate cancer tissues and prostate cancer cells. The level of Btk in prostate cancer tissues correlates with cancer grades. Knockdown of Btk expression selectively inhibits the growth of prostate cancer cells, but not that of the normal prostate epithelial cells, which express very little Btk. Dual inhibition of Btk and Etk has an additive inhibitory effect on prostate cancer cell growth. To explore Btk and Etk as targets for prostate cancer, we developed a small molecule dual inhibitor of Btk and Etk, CTN06. Treatment of PC3 and other prostate cancer cells, but not immortalized prostate epithelial cells with CTN06 resulted in effective cell killing, accompanied by the attenuation of Btk/Etk signals. The killing effect of CTN06 is more potent than that of commonly used inhibitors against Src, Raf/VEGFR and EGFR. CTN06 induces apoptosis as well as autophagy in human prostate cancer cells, and is a chemo-sensitizer for docetaxel (DTX), a standard of care for metastatic prostate cancer patients. CTN06 also impeded the migration of human prostate cancer cells based on a ‘wound healing' assay. The anti-cancer effect of CTN06 was further validated in vivo in a PC3 xenograft mouse model.