Probing Drug Delivery and Mechanisms of Action in 3D Spheroid Cells by Quantitative Analysis
Human tumor cells in a 3-dimensional (3D) spheroid can reflect the characteristics of solid tumors by forming cell-cell interactions and microenvironments. This makes 3D cell culture useful for preclinical stability and drug efficacy tests. In this study, the drug delivery and action mechanisms in SK-N-SH neuroblastoma cells cultured in 3D spheroids were quantitatively compared to those in 2D monolayers using confocal microscopy imaging and inductively coupled plasma-mass spectrometry. In the 3D spheroids, cisplatin only accessed the surface, accumulating in the cells on the spheroid exterior. As a result, enhanced cellular amount of cisplatin was required to obtain similar cytotoxicity in the 3D spheroid cells as that in 2D monolayers. Mechanisms of reduced drug efficacy by dimethyl sulfoxide (DMSO) in the 3D spheroid cells compared to those in 2D monolayer cells were further investigated. DMSO reduced the drug cytotoxicity by forming stable DMSO-substituted compounds that inhibited cellular uptake of cisplatin and DNA-Pt adduct formation. The quantitative analysis used in this study is promising for understanding drug delivery and drug action mechanisms in cells under various microenvironments.