Inhibition Of STAT3 Signaling Targets Both Tumor-initiating And Differentiated Cell Populations In Prostate Cancer

Objective:Despite of tremendous research efforts to profile prostate cancer, the genetic alterations and biological processes that correlate with disease progression remain partially elusive. In this research, we study the effect of STAT3 signaling pathway on both tumor-initiating and differentiated cell populations in prostate cancer.Methods:14 human primary prostate tumors and adjacent non-tumor tissues were obtained at the time of surgical resection or by biopsy from May 2012 to January 2014. Western blotting and ELISA were used to detect protein expression. We used Stattic, a STAT3 small molecular inhibitor on PC3M-1E8 cells. Cell cycle alteration and apoptosis were detected by flow cytometry. Distribution of pSTAT3 in nucleus is evaluated by cell immunofluorescence and confocal microscopy. Soft agar colony-forming assays were used to evaluate tumor cell proliferation. ALDH activity was detected by ALDEFLUOR assay. ALDHhigh subpopulations were sorted by FACS. STAT3 shRNA lentivirus was constructed to infect PC3M-1E8 cells. Animal models, cell-line xenograft and PDTX model were used to assess the tumorigenic ability.Results:We show that the STAT3 small molecule inhibitor Stattic caused S-phase accumulation at low-dose levels and led to massive cell apoptosis at a relatively high-dose level in prostate cancer cells. Prostate cancer cell line and primary human prostate cancer cells contained high aldehyde dehydrogenase activity (ALDHhigh) cell subpopulations with stem cell-like characteristics, which expressed higher levels of the active phosphorylated form of STAT3 (pSTAT3) than that of non-ALDHhigh cell subpopulations. Stattic could significantly decrease the population of ALDHhigh prostate cancer cells even at low-dose levels. IL-6 can convert non-ALDHhigh cells to ALDHhigh cells in prostate cancer cell line as well as from cells derived from human primary prostate tumors, the conversion induced by IL-6 was abrogated upon STAT3 knockdown or in the presence of STAT3 inhibitor. STAT3 knockdown significantly impaired the ability of prostate cancer cells to initiate the development of prostate adenocarcinoma. Moreover, blockade of STAT3 signaling pathway was significantly effective in eradicating the tumor-initiating and bulk tumor cancer cell populations in both prostate cancer cell-line xenograft model and patient-derived tumor xenograft (PDTX) models.Conclusion:This data suggests that targeting both tumor initiating and differentiated cell populations by STAT3 inhibition is predicted to have greater efficacy for prostate cancer treatment.