P38 regulates the Wnt inhibitor Dickkopf-1 in breast cancer.

Dickkopf-1 (DKK-1) is an inhibitor of canonical Wnt signalling and has been associated with the progression of osteolytic bone metastases by impairing osteoblast activity. In addition, there is growing evidence supporting a direct anti-tumour effect of DKK-1. The p38 mitogen-activated protein kinase (MAPK) regulates intracellular responses that have been linked to cell cycle, apoptosis and tumorigenesis. P38 inhibitors are currently under clinical evaluation for the treatment of malignancies. However, the influence of p38 on DKK-1 in breast cancer remains elusive. In this work, we show that p38 inhibition using SB202190 or LY2228820 potently suppressed DKK-1 expression by MDA-231 and MCF-7 breast cancer cell lines as well melanoma derived MDA-435 cells. Vice versa, activation of p38 signalling by anisomycin induced DKK-1 expression. Immunohistochemical analysis of DKK-1 expression in 97 breast cancer samples revealed that high expression of p38 was associated with a higher expression of DKK-1 compared to tumours with low p38 expression. In conclusion, these results support a role of p38 in the regulation of DKK-1 in osteolytic tumours and warrant further research on the potential of p38 inhibition for the treatment of malignant bone disease.

Regulation of VEGF by mevalonate pathway inhibition in breast cancer.

Aminobisphosphonates are used for the treatment of benign and malignant bone disorders. As inhibitors of the mevalonate pathway they exert direct anti-tumor effects in vitro and in preclinical models of bone metastases. Bisphosphonates are thought to have an anti-angiogenic activity as decreased levels of VEGF have been reported in some, although not all patients, following treatment with bisphosphonates. Direct effects of bisphosphonates on tumor derived VEGF have not been examined in detail. We therefore investigated VEGF expression in breast cancer cell lines following mevalonate pathway inhibition. Treatment of cell lines with increasing doses of zoledronic acid and atorvastatin resulted in increased levels of VEGF production. Similar results were seen with the geranylgeranyltransferase I inhibitor GGTI-298. The induction of VEGF was reversed by the supplementation of geranylgeranyl pyrophosphate but not by farnesyl pyrophosphate indicating that this effect is mediated by inhibited geranylgeranylation. Previous reports have reported decreased VEGF levels in patients following BP treatment in vivo. We assessed VEGF levels in patients with non-metastatic breast cancer following repeated treatment with zoledronic acid. In contrast to our in vitro findings, VEGF serum levels decreased in all patients after 6-9 months of treatment (by an average of 41%) as assessed in a small pilot trial. These results indicate that tissues other than breast tumors contribute to the serum pool of circulating VEGF and may be responsible for the observed VEGF decreases. The increases of VEGF in the cancer cells may provide a rationale for the combined treatment with VEGF inhibitors.