Inadequate tissue mineralization promotes cancer cell attachment.

Bone metastases are a frequent complication in prostate cancer, and several studies have shown that vitamin D deficiency promotes bone metastases. However, while many studies focus on vitamin D's role in cell metabolism, the effect of chronically low vitamin D levels on bone tissue, i.e. insufficient mineralization of the tissue, has largely been ignored. To investigate, whether poor tissue mineralization promotes cancer cell attachment, we used a fluorescence based adhesion assay and single cell force spectroscopy to quantify the adhesion of two prostate cancer cell lines to well-mineralized and demineralized dentin, serving as biomimetic bone model system. Adhesion rates of bone metastases-derived PC3 cells increased significantly on demineralized dentin. Additionally, on mineralized dentin, PC3 cells adhered mainly via membrane anchored surface receptors, while on demineralized dentin, they adhered via cytoskeleton-anchored transmembrane receptors, pointing to an interaction via exposed collagen fibrils. The adhesion rate of lymph node derived LNCaP cells on the other hand is significantly lower than that of PC3 and not predominately mediated by cytoskeleton-linked receptors. This indicates that poor tissue mineralization facilitates the adhesion of invasive cancer cells by the exposure of collagen and emphasizes the disease modifying effect of sufficient vitamin D for cancer patients.

Probing the interaction forces of prostate cancer cells with collagen I and bone marrow derived stem cells on the single cell level.

Adhesion of metastasizing prostate carcinoma cells was quantified for two carcinoma model cell lines LNCaP (lymph node-specific) and PC3 (bone marrow-specific). By time-lapse microscopy and force spectroscopy we found PC3 cells to preferentially adhere to bone marrow-derived mesenchymal stem cells (SCP1 cell line). Using atomic force microscopy (AFM) based force spectroscopy, the mechanical pattern of the adhesion to SCP1 cells was characterized for both prostate cancer cell lines and compared to a substrate consisting of pure collagen type I. PC3 cells dissipated more energy (27.6 aJ) during the forced de-adhesion AFM experiments and showed significantly more adhesive and stronger bonds compared to LNCaP cells (20.1 aJ). The characteristic signatures of the detachment force traces revealed that, in contrast to the LNCaP cells, PC3 cells seem to utilize their filopodia in addition to establish adhesive bonds. Taken together, our study clearly demonstrates that PC3 cells have a superior adhesive affinity to bone marrow mesenchymal stem cells, compared to LNCaP. Semi-quantitative PCR on both prostate carcinoma cell lines revealed the expression of two Col-I binding integrin receptors, α1ß1 and α2ß1 in PC3 cells, suggesting their possible involvement in the specific interaction to the substrates. Further understanding of the exact mechanisms behind this phenomenon might lead to optimized therapeutic applications targeting the metastatic behavior of certain prostate cancer cells towards bone tissue.