In vitro and in vivo anti-tumor efficacy of krill oil against bladder cancer: Involvement of tumor-associated angiogenic vasculature

Krill oil (KO) obtained from Euphausia superba is nutrient-rich and has a positive effect on human health. Here, we explored the efficacy of KO in inhibiting tumor progression and tumor vascularization. KO (100-300 mu g/mL) repressed the proliferation of bladder tumor cell lines MBT-2 and T24. Treatment of cells with KO raised cell cycle arrest at G0/G1-phase via modulation of positive regulators and negative regulators in bladder cancer cells. KO treatment regulated phosphorylation of proteins involved in PI3K/AKT and MAPK signaling pathways, including ERK, JNK, and p38 MAPK. Additionally, KO hampered the invasion and migration of both cell lines via reduction of MMP-9 expression levels by disrupting transcriptional binding of Sp-1, AP-1, and NF-kappa B motifs. Moreover, in animal studies, KO (150-300 mg/kg) significantly decreased tumor growth in xenograft mice bearing T24 tumor cells. No significant toxic effects were observed in acute toxicity tests, including biological analysis and H&E staining. The reduced level of CD31 expression in KO-treated tumor tissues prompted us to investigate the effect of KO on tumor angiogenesis. KO (5-40 mu g/mL) treatment impeded VEGF-induced capillary tube formation and proliferation by inhibiting VEGFR2-modulated eNOS/AKT/ERK1/2 signaling axis in HUVECs. Treatment of HUVECs with KO inhibited VEGF-stimulated migration and invasion by reducing MMP-2 expression level. VEGF-driven sprouting capacity of neo-microvessels was suppressed in the presence of KO (20-40 mu g/mL), as determined via an ex vivo aortic ring assay. Our results indicated that KO can regulate both tumor growth and tumor-associated angiogenesis via a novel mechanism. Thus, KO may be a promising antitumor candidate, potentially useful to prevent or treat bladder cancer.