Doxorubicin-Mediated Bone Loss in Breast Cancer Bone Metastases Is Driven by an Interplay between Oxidative Stress and Induction of TGFβ

Breast cancer patients, who are already at increased risk of developing bone metastases and osteolytic bone damage, are often treated with doxorubicin. Unfortunately, doxorubicin has been reported to induce damage to bone. Moreover, we have previously reported that doxorubicin treatment increases circulating levels of TGFβ in murine pre-clinical models. TGFβ has been implicated in promoting osteolytic bone damage, a consequence of increased osteoclast-mediated resorption and suppression of osteoblast differentiation. Therefore, we hypothesized that in a preclinical breast cancer bone metastasis model, administration of doxorubicin would accelerate bone loss in a TGFβ-mediated manner. Administration of doxorubicin to 4T1 tumor-bearing mice produced an eightfold increase in osteolytic lesion areas compared untreated tumor-bearing mice (P = 0.002) and an almost 50% decrease in trabecular bone volume expressed in BV/TV (P = 0.0005), both of which were rescued by anti-TGFβ antibody (1D11). Doxorubicin, which is a known inducer of oxidative stress, decreased osteoblast survival and differentiation, which was rescued by N-acetyl cysteine (NAC). Furthermore, doxorubicin treatment decreased Cu-ZnSOD (SOD1) expression and enzyme activity in vitro, and treatment with anti-TGFβ antibody was able to rescue both. In conclusion, a combination therapy using doxorubicin and anti-TGFβ antibody might be beneficial for preventing therapy-related bone loss in cancer patients.