In vivo bone metastases, osteoclastogenic ability, and phenotypic characterization of human cancer cells

Mouse bone marrow cells cultured with human breast cancer MCF-7 cell-conditioned media showed osteoclastogenesis with an increment of bone resorption, although conditioned media from an adriamycin-selected MCF-7 clone (MCF-7(ADR)) had no effect. Consistently, MCF-7 cells induced 5-fold more in vivo experimental osteolytic bone metastases, with no soft tissue lesions, compared to MCF-7(ADR) cells. Paracrine factors stimulating (interleukin (IL)-6, IL-1beta, tumor necrosis factor-alpha (TNF-alpha)) or inhibiting (IL-12, IL-18, granulocyte macrophage-colony stimulating factor (GM-CSF)) osteoclastogenesis were significantly increased in MCF-7(ADR) relative to MCF-7 cells, suggesting that the inhibitory cytokines could selectively overwhelm the effects of the stimulatory ones. Treatment of osteoblast primary Cultures with MCF-7-conditioned medium induced a selective upregulation of IL-6 expression, suggesting an indirect stimulation of osteoclastogenesis via the osteoblasts. MCF-7 and MCF-7(ADR) showed no difference in proliferation rate. However, a higher ability to migrate and invade gelatin and matrigel was observed in MCF-7(ADR). Enhanced invasiveness might result from increased metalloproteinase (MMP) activity and cytoskeleton rearrangement. MCF-7(ADR) cells expressed higher levels of c-Src, focal adhesion kinase (FAK), and protein tyrosine kinase 2 (PYK2) involved in cell adhesion and motility. MCF-7 and MCF-7(ADR) expressed high and faint levels of functional estrogen receptor alpha (ERalpha), respectively. MCF-7(ADR) also showed significantly higher levels of the protein kinase C (PKC) alpha and beta(2) and a selective activation of PKCepsilon compared to MCF-7, where the most abundant isoforms were beta(1) and delta. Heat shock protein 27 (Hsp27) was more abundant in MCF-7 cells, but failed to translocate to the nucleus in response to heat shock. In conclusion, we have demonstrated that despite the fact that MCF-7(ADR) cells showed a more invasive phenotype relative to MCF-7, they have low potential to induce osteolytic bone lesions and stimulate osteoclastogenesis and osteoclast activity. Therefore, we believe that reduced aggressiveness of breast carcinomas could correlate with a greater osteolytic activity featuring their bone metastases. (C) 2004 Elsevier Inc. All rights reserved.