Background: The majority of women who die from breast cancer have oestrogen receptor positive (ER+) tumours. Thus, there is a need to identify alternative safe and effective therapies for ER+ breast cancers. Previously, we published that a gut derived-peptide, des-acyl ghrelin (DAG), hypothesized to act at a yet unidentified GPCR, inhibits aromatase in breast adipose stromal cells. However, little is known of the effect of DAG on breast cancer cell growth in vitro and in vivo.
Hypothesis: DAG will inhibit the growth of ER+ breast cancer.
Aims: To determine the effects of DAG on breast tumour growth in vitro and in vivo, and evaluate its mechanism of action.
Methods: Effects of DAG on cell cycle and apoptosis were examined in ER+ breast and mouse mammary cancer cell lines (MCF7, ZR75, J110) using flow cytometry. Effects of DAG on breast cancer cell proliferation was examined by quantifying EdU incorporation in vitro and in vivo. In vitro studies were performed using 3D cultures, whereas the effect of DAG in vivo was examined in xenografted balb/c nude mice and a syngeneic model of breast cancer (FVB/J110). The effect of DAG on second messenger systems (cAMP, Ca2+) was and involvement of Gαi was confirmed using pertussis toxin.
Results: DAG (10-1000pM) inhibits the oestrogen-stimulated proliferation of MCF7, ZR75 and J110 cells in vitro through inducing G1-phase arrest and apoptosis. DAG (50-200μg/kg) also significantly inhibits ER+ tumour growth in mice compared to vehicle control. DAG has no effect on Ca2+, but inhibits the forskolin-stimulated formation of cAMP, suggesting that it is acting via Gαi-coupled GPCR. Gαi inhibitor, pertussis toxin (20-200ng/ml) prevents DAG suppression of cell proliferation.
Conclusions: Our findings provide evidence for a novel mechanism of action of DAG and suggest that it may be useful for the treatment of ER+ breast cancer.