Inhibition von mTOR reduziert Tumorwachstum und Angiogenese des Magenkarzinoms in einem experimentellen Modell

Abstract

In the PI3K/Akt signaling pathway, »mammalian target of rapamycin« (mTOR) is a central mediator for transcription and translation of different target genes. Interestingly, the transcription factor »hypoxia inducible factor-1a« (HIF-1α) which is involved in tumor progression and metastases, is regulated by mTOR. We hypothesized that blockade of mTOR with rapamycin (RAPA) would significantly inhibit HIF-1α expression in human gastric cancer cells in vitro and impair angiogenesis and tumor growth in vivo. Effects of RAPA (10 ng/ml) on nuclear HIF-1α expression in human gastric cancer cells (TMK-1) were investigated by chemical hypoxia with desferroxamine (DFX 100 µM) and subsequently Western blot analyses. Cytotoxic effects of RAPA on TMK-1 cells were assessed by MTT assays under the same conditions. Effects of mTOR inhibition on cancer cell migration and invasion were tested in in vitro assays using modified Boyden chambers. Modulation of angiogenesis in vivo by RAPA treatment (1.5 mg/kg/day) (or vehicle) was first investigated in the dorsal skinfold chamber (DSFC) model in athymic nude mice (n = 6/group). Effects of RAPA on tumor growth were subsequently investigated in a subcutaneous tumor model. Tumor diameters were measured every second day and volumes calculated. mTOR blockade led to a 70% reduction in HIF-1α expression in vitro. MTT assays revealed modest cytotoxic effects of RAPA. In contrast, cell migration and invasion were significantly inhibited (P < 0.05). In vivo, in the DSFC model, RAPA treatment significantly reduced angiogenesis and microvessel density (P < 0.05), compared to controls. In addition, in the SQ model, RAPA led to significant reduction of tumor volumes (P < 0.05) and tumor weights (P < 0.05). In conclusion, mTOR inhibition with rapamycin could be a promising approach to augment antineoplastic/antiangiogentic therapy regimes for the treatment of gastric cancer.