Peroxisome proliferator-activated receptor-γ ligands for the treatment of breast cancer

Pioglitazone and rosiglitazone are thiazolidinediones used for the treatment of Type 2 diabetes mellitus. They modulate glucose and fat metabolism, mainly by binding to the nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR)-γ. PPAR-γ signalling is involved in a number of other disease conditions including cancer. In breast cancer cells, PPAR-γ ligands inhibit proliferation and induce apoptosis both in vitro and in vivo. PPAR-γ ligands also inhibit tumour angiogenesis and invasion. The only published clinical trial using a PPAR-γ ligand in patients with metastatic breast cancer failed to show any clinical benefits. The mechanism of action of the thiazolidinediones in breast cancer cells is not fully understood but involves interactions with other nuclear hormone receptors, transcriptional co-activators and repressors as well as PPAR-γ-independent effects. A better understanding of these mechanisms will be needed before PPAR-γ ligands may be useful in the treatment of breast cancer patients.