Sequential treatment with doxorubicin and zoledronic acid has no additive effects in an aggressive model of established bone metastases

Aim: Bisphosphonates are used as an adjuvant treatment in breast cancer bone metastasis patients, often simultaneously with chemotherapeutic agents. Interestingly, their sequential combination has been reported to have synergistic anti-tumor effects on bone metastases in preclinical models. We studied the effects of doxorubicin (DOX) and zoledronic acid (ZOL) and their combination on established bone metastases in the MDA-MB-231(SA)GFP bone metastasis model.Methods: Tumor burden and osteolytic bone lesions were quantitated by fluorescence imaging and radiography, respectively. The mice were randomized in four groups receiving vehicle, DOX, ZOL or both DOX and ZOL in a sequential combination on day 14. Serum marker of osteoclast number was followed weekly, and blood ionized calcium was measured at sacrifice. Bone and tumor area, apoptosis and proliferation of tumor cells were analyzed from histological sections.Results: ZOL prevented hypercalcemia and osteolytic lesion progression, whereas DOX induced apoptosis in the MDA-MB-231(SA)GFP cells. However, neither of the treatments alone nor in sequential combination were able to reduce tumor burden in bone. Furthermore, no additive effects on tumor cell apoptosis were observed in the combination group.Conclusion: No additive effects in combination of DOX and ZOL were observed in this aggressive model of breast cancer bone metastasis

Heparin-like Polysaccharides Reduce Osteolytic Bone Destruction and Tumor Growth in a Mouse Model of Breast Cancer Bone Metastasis

TGF-β regulates several steps in cancer metastasis, including the establishment of bone metastatic lesions. TGF-β is released from bone during osteoclastic bone resorption and it stimulates breast cancer cells to produce osteolytic factors such as interleukin 11 (IL-11). We conducted a cell-based siRNA screen and identified heparan sulfate 6-O-sulfotransferase 2 (HS6ST2) as a critical gene for TGF-β–induced IL-11 production in highly bone metastatic MDA-MB-231(SA) breast cancer cells. HS6ST2 attaches sulfate groups to glucosamine residues in heparan sulfate glycosaminoglycans. We subsequently showed how heparin and a high-molecular-weight Escherichia coli K5-derived heparin-like polysaccharide (K5-NSOS) inhibited TGF-β–induced IL-11 production in MDA-MB-231(SA) cells. In addition, K5-NSOS inhibited bone resorption activity of human osteoclasts in vitro. We evaluated the therapeutic potential of K5-NSOS and fragmin in a mouse model of breast cancer bone metastasis. MDA-MB-231(SA) cells were inoculated into the left cardiac ventricle of athymic nude mice which were treated with fragmin, K5-NSOS, or vehicle once a day for four weeks. Both heparin-like glycosaminoglycans inhibited weight reduction, decreased osteolytic lesion area, and reduced tumor burden in bone. In conclusion, our data imply novel mechanisms involved in TGF-β induction and support the critical role of heparan sulfate glycosaminoglycans in cancer metastasis as well as indicate that K5-NSOS is a potential antimetastatic and antiresorptive agent for cancer therapy. This study illustrates the potential to translate in vitro siRNA screening results toward in vivo therapeutic concepts