MECHANISMS OF CANCER-BONE MICROENVIRONMENTAL INTERACTIONS IN PROSTATE CANCER

Prostate Cancer (PCa) patients’ mortality is mainly attributed to complications caused by metastasis of the tumor cells to organs critical for survival, such as bone. We hypothesized that prostate cancer cell-bone interactions would promote paracrine signaling. A panel of prostate cancer cell lines were co-cultured with Hydroxyapatite (HA; inorganic component of bone) of different densities. Conditioned media (CM) was collected and analyzed for calcium levels and effect on paracrine signaling, cell migration and viability in vitro and in vivo. Our results showed that calcium levels were elevated in CM from cancer cell-bone co-cultures, compared to media or cancer cells alone, and this could be antagonized by EGTA, a calcium chelator, or knockdown of Snail protein. We also observed increased STAT3 phosphorylation and paracrine cell proliferation and migration in LNCaP cells incubated with CM from various cell lines; this phosphorylation and cell migration could be antagonized by Snail knockdown or various inhibitors including EGTA, STAT3 inhibitor (WP1066) or Cathepsin L inhibitor (Z-FY-CHO). In vivo, higher HA bone density increased tumorigenicity and migration of tumor cells to HA implant. Finally, nuclear Snail and Cathepsin L was more highly expressed in cancer compared to normal patient tissue. Our study shows that cancer-bone microenvironment interactions mediated by Snail leads to calcium-STAT3 signaling, which may present an area for therapeutic targeting of metastatic prostate cancer.