Circulating prostate cancer cells have differential resistance to fluid shear stress-induced cell death.

Circulating tumor cells (CTCs) are exposed to fluid shear stress (FSS) of greater than 1000 dyn/cm2 (100 Pa) in circulation. Normally, CTCs that are exposed to FSS of this magnitude die. However, some CTCs develop resistance to this FSS, allowing them to colonize distant organs. We explored how prostate CTCs can resist cell death in response to forces of this magnitude. The DU145, PC3 and LNCaP human prostate cancer cell lines were used to represent cells of different metastatic origins. The cell lines were briefly treated with an average FSS of 3950 dyn/cm2 (395 Pa) using a 30 G needle and a syringe pump. DU145 cells had no change in cell viability, PC3 cells had some cell death and LNCaP cells exhibited significant cell death. These cell death responses correlated with increased cell membrane damage, less efficient membrane repair and increased stiffness. Additionally, FSS treatment prevented the LNCaP FSS-sensitive cell line from forming a growing tumor in vivo This suggests that these properties play a role in FSS resistance and could represent potential targets for disrupting blood-borne metastasis.

Cancer associated fibroblasts confer shear resistance to circulating tumor cells during prostate cancer metastatic progression.

Previous studies have demonstrated that CTCs do not travel in the bloodstream alone, but rather are accompanied by clusters of stromal cells such as cancer associated fibroblasts (CAFs). Our laboratory has confirmed the presence of CAFs in the peripheral blood of prostate cancer (PC) patients. The observation that CAFs disseminate with CTCs prompts the examination of the role of CAFs in CTC survival under physiological shear stress during the dissemination process using a clinically relevant, three-dimensional (3D) co-culture model. In this study, we found that "reactive CAFs" induce shear resistance to prostate tumor cells via intercellular contact and soluble derived factors. In addition, these reactive CAFs conserve the proliferative capability of tumor cells in the presence of high magnitude fluid shear stress (FSS). This reactive CAF phenotype emerges from normal fibroblasts (NF), which take on the CAF phenotype when co-cultured with tumor cells. The reactive CAFs showed higher expression of α-smooth muscle actin (α-SMA) and fibroblast activation protein (FAP) compared to differentiated CAFs, when co-cultured with PC cells at the same experimental conditions. Together, we found that the activation mechanism of NF to CAF comprises different stages that progress from a reactive to quiescent cellular state in which these two states are differentiated by the fluctuation of intensity in CAF markers. Here we determined that a reactive state of CAFs proved to be important for supporting tumor cell survival and proliferation. These findings suggest the use of CAFs as a marker for cancer progression and a potential target for novel cancer therapeutics to treat metastatic disease.