Tumor spheroids and organoids as preclinical model systems

Abstract

The generation of three-dimensional (3D) cancer models is a novel and fascinating development in the study of personalized medicine and tumor-specific drug delivery. In addition to the classical two-dimensional (2D) adherent cell culture models, 3D spheroid and organoid cancer models that mimic the microenvironment of cancer tissue are emerging as an important preclinical model system. 3D cancer models form, similar to cancer, multiple cell-cell and cell-extracellular matrix interactions and activate different cellular cascades/pathways, like proliferation, quiescence, senescence, and necrotic or apoptotic cell death. Further, it is possible to analyze genetic variations and mutations, the microenvironment of cell-cell interactions, and the uptake of therapeutics and nanoparticles in nanomedicine. Important is also the analysis of cancer stem cells (CSCs), which could play key roles in resistance to therapy and cancer recurrence. Tumor spheroids can be generated from one tumor-derived cell line or from co-culture of two or more cell lines. Tumor organoids can be derived from tumors or may be generated from CSCs that differentiate into multiple facets of cancerous tissue. Similarly, tumorspheres can be generated from a single CSC. By transplanting spheroids and organoids into immune-deficient mice, patient-derived xenografts can serve as a preclinical model to test therapeutics in vivo. Although the handling and analysis of 3D tumor spheroids and organoids is more complex, it will provide insights into various cancer processes that cannot be provided by 2D culture. Here a short overview of 3D tumor systems as preclinical models is provided.

Keywords: Cancer organoids; patient-dervied xenograft; three-dimensional cancer model; tumor model systems.

Figure 1

Prostate cancer spheroid treated with the anti-tumor therapeutic androgen receptor antagonist Enzalutamide, which reduces growth. Spheroids from the castration-resistant human prostate cancer cell line C4-2 were generated. After 3 days, spheroids were further cultured for 14 days treated with the second-generation androgen receptor antagonist Enzalutamide or solvent control. Spheroid volume was reduced by antagonist treatment. Spheroid slices were generated and stained for the senescence marker senescence-associated beta-galactosidase and with hematoxylin for nuclear staining. Scale bar: 200 µm.

Figure 2

Schematic view of 3D cancer models. Tumor spheroids and tumorspheres can be generated from cancer cell lines. Tumorspheres are embedded in a matrix resembling extracellular matrix which in combination with specific culture media will enrich for stemness in tumorspheres. Tumor organoids preserve patient-specific phenotypic and genetic characteristics and fill the experimental gap between cancer cell lines and animal models in an ex vivo system. Preclinical patient-derived xenograft models are preferably used for anti-cancer treatment in vivo.