Integrative <i>In Situ</i> Photodynamic Therapy-Induced Cell Death Measurement of 3D-Bioprinted MCF-7 Tumor Spheroids.

The development of new <i>in vitro</i> models that closely mimic the tumor microenvironment (TME) to evaluate the efficacy of anticancer drugs has received great attention. In this study, a three-dimensional (3D) bioprinted Michigan Cancer Foundation-7 (MCF-7) cancer spheroid-embedded hydrogel model was suggested for integrative <i>in situ</i> determination of the half-maximal inhibitory concentration (IC₅₀) values of photosensitizers (PSs). The MCF-7 cell-laden alginate/gelatin hydrogel was printed for the fabrication of tumor spheroids. The hydrogel was used to mimic the extracellular matrix (ECM) surrounding the cancer cells in the TME. The fluorescence intensities corresponding to photodynamic therapy (PDT)-induced death of tumor spheroids probed by the laser showed a random distribution in the hydrogel, regardless of the focus of the laser and the vertical-axis direction in which the laser was passed. These results enabled integrative <i>in situ</i> measurement of all tumor spheroids probed by the laser without needing to separate the tumor spheroids in the hydrogel and measure them individually. When compared with two-dimensional (2D) monolayer cultures, very large IC₅₀ values of the PSs, chlorin e6 (Ce6) and sulfonated tetraphenyl porphyrin (sTPP), were achieved in MCF-7 spheroid-embedded hydrogels mainly due to the drug resistance of the tumor spheroids. Additionally, the heterogenic PDT response of single MCF-7 cancer cells in a single tumor spheroid was observed through 3D imaging of irregular apoptosis in a single spheroid since single tumor spheroids showed a heterogenic PDT response. Furthermore, the laser-power-dependent IC₅₀ values of PSs were obtained using the MCF-7 spheroid-embedded hydrogel model.