Generating Large Numbers of Pancreatic Microtumors on Alginate-Gelatin Hydrogels for Quantitative Imaging of Tumor Growth and Photodynamic Therapy Optimization.

The emerging use of 3D culture models of cancer has provided novel insights into the therapeutic mechanisms of photodynamic therapy on a mesoscopic scale. Especially microscale tumors grown on scaffolds of extracellular matrix can provide statistically robust data on the effects of photosensitizers and photodynamic therapy by leveraging high-throughput imaging-based assays. Although highly informative, the use of such 3D cultures can be impractical due to the high costs and inter-batch variability of the extracellular matrix scaffolds that are necessary to establish such cultures. In this study, we therefore provide a protocol to generate inexpensive and defined hydrogels composed of sodium alginate and gelatin that can be used for culturing 3D microtumors in a manner that is compatible with state-of-the-art imaging assays. Our results reveal that the alginate-gelatin hydrogels can perform similarly to a commercially available ECM scaffold in terms of facilitating microtumor growth. We then applied these microtumor models to quantify the uptake and dark toxicity of benzoporphyrin derivative encapsulated in liposomes with either an anionic or a cationic surface charge. The results indicate that cationic liposomes achieve the highest level of uptake in the microtumors, yet also exert minor toxicity. Moreover, we reveal that there is typically a significant positive correlation between microtumor size and liposome uptake. In conclusion, alginate-based hydrogels are inexpensive and effective scaffolds for 3D culture models of cancer, with versatile applications in research toward photodynamic therapy.