Evaluation of Combined Treatment With Atorvastatin and SREBP2 Inhibitors Against Colorectal Cancer Cells Under Two-dimensional and Three-dimensional Culture Models

Background/Aim: Statins, inhibitors of 3-hydroxy-3-methylglutaryl–coenzyme A reductase, have been reported to exert anti-cancer effects. Recently, sterol regulatory element-binding protein 2 (SREBP2) has been shown to be involved in statin resistance in cancer cells. Inhibiting SREBP2 enhances the anti-cancer effects of statins in several cancer cell lines. Three-dimensional (3D) cultured cells are known to exhibit different drug sensitivities compared to two-dimensional (2D) cultured cells. In this study, we evaluated the cytotoxicity induced by combined treatment with atorvastatin and SREBP2 inhibitors in 2D and 3D cultured colorectal cancer (CRC) cells.

Materials and Methods: 25-Hydroxycholesterol and δ-tocotrienol were used as SREBP2 inhibitors. The viability of 2D and 3D cultured cells was measured using the MTT assay and the CellTiter-Glo^® 3D Cell Viability Assay. Gene expression levels were analyzed by qRT-PCR. Protein levels were determined by western blotting.

Results: 3D cultured cells exhibited lower statin sensitivity compared to 2D cultured cells. The expression levels of SREBP2 and its target genes differed between 2D and 3D cultured cells. In 2D cultured cells, SREBP2 inhibitors blocked atorvastatin-induced SREBP2 activation and enhanced the cytotoxicity of atorvastatin. However, in 3D cultured cells, SREBP2 inhibitors failed to enhance atorvastatin-induced cytotoxicity, although they successfully suppressed atorvastatin-induced SREBP2 activation.

Conclusion: The efficacy of a combined statin and SREBP2 inhibitors strategy differs substantially between 2D and 3D cultured CRC cells. 3D cultured cells may possess an SREBP2-independent mechanism of statin resistance that differs from that of 2D cultured cells.