Investigation of the effectiveness of oleuropein in a three-dimensional in vitro hepatocellular tumor sphere model

Abstract

Objectives: This study was conducted to examine the dose-related effects over time of oleuropein on the proliferation and area of tumor spheroids in hepatocellular carcinoma cells. Materials and methods: We examined the possible effects of 100 to 500 mu M dose concentrations of oleuropein on HepG2 cell proliferation using a real-time cell analyzer. A 3-dimensional hepatocellular carcinoma tumor spheroid model was established by seeding HepG2 cells at a density of 160 cells/well in custom 96-well microplates with low attachment surfaces and culturing for 3 days. Tumor spheres were treated with increasing oleuropein doses for 72 hours, and images were captured every 24 hours. The dose-dependent effects of oleuropein on tumor sphere size were analyzed by measuring the area of tumor spheres with ImageJ software. We conducted oleuropein viability and cytotoxicity analyses using calcein acetoxymethyl ester-based and propidium iodide-based staining in the tumor model. Results: Oleuropein inhibited cell proliferation; as the dose concentration of oleuropein increased, so did its capacity to inhibit cell proliferation (P < .001). The size of untreated tumor spheres increased at 72 hours (P < .001). However, treatment with 100 to 500 mu M oleuropein reduced tumor size by 63.56% to 88.06% compared with untreated cells at the end of 72 hours (P < .001). With increasing concentrations, oleuropein inhibited the viability of tumor spheres, eliminating necrotic death caused by tumor hypoxia. Conclusions: Overall, oleuropein reduced the size of tumors by inhibiting tumor proliferation and viability. In this context, oleuropein could be a candidate molecule for further extensive studies to reduce hepatocellular carcinoma tumors to meet Milan criteria for liver transplant.