Cyclooxygenase-2 inhibition: effects on tumour growth, cell cycling and lymphangiogenesis in a xenograft model of breast cancer

Cyclooxygenase-2 (COX-2) is associated with poor-prognosis breast cancer. We used a nude mouse xenograft model to determine the effects of COX-2 inhibition in breast cancer. Oestrogen receptor (ER)-positive MCF7/HER2-18 and ER- negative MDAMB231 breast cancer cell lines were injected into nude mice and allowed to form tumours. Mice then received either chow containing Celecoxib (a COX-2 inhibitor) or control and tumour growth measured. Tumour proliferation, apoptosis, COX- 2, lymphangiogenesis and angiogenesis were assessed by immunohistochemistry (IHC), Western blotting or Q- PCR. Celecoxib inhibited median tumour growth in MCF7/HER2-18 (58.7%, P = 0.029) and MDAMB231 (46.3%, P = 0.0002) cell lines compared to control. Cyclooxygenase- 2 expression decreased following Celecoxib treatment (MCF7/HER2-18 median control 65.3% vs treated 22.5%, P = 0.0001). Celecoxib increased apoptosis in MCF7/ HER2- 18 tumours (TUNEL 0.52% control vs 0.73% treated, P 0.0004) via inactivation of AKT (median pAKT(ser473) 57.3% control vs 35.5% treated, P = 0.0001-confirmed at Western blotting). Q- PCR demonstrated decreased podoplanin RNA (lymphangiogenesis marker) in the MCF7/HER2-18 median 2.9 copies treated vs 66.6 control (P = 0.05) and MDAMB231-treated groups-median 160.7 copies vs 0.05 control copies (P =0.015), confirmed at IHC. Cyclooxygenase-2 is associated with high levels of activated AKT(ser473) and lymphangiogenesis in breast cancer. Cyclooxygenase-2 inhibition decreases tumour growth, and may potentially decrease recurrence, by inactivating AKT and decreasing lymphangiogenesis.