High attrition of new oncology drug candidates in clinical trials is partially caused by the poor predictive capacity of artificial monolayer cell culture assays early in drug discovery. Monolayer assays do not take the natural three-dimensional (3D) microenvironment of cells into account. As a result, false positive compounds often enter clinical trials, leading to high dropout rates and a waste of time and money. Over the past 2 decades, tissue engineers and cell biologists have developed a broad range of 3D in vitro culturing tools that better represent in vivo cell biology. These tools preserve the 3D architecture of cells and can be used to predict toxicity of and resistance against antitumor agents. Recent progress in tissue engineering further improves 3D models by taking into account the tumor microenvironment, which is important for metastatic progression and vascularization. However, the widespread implementation of 3D cell cultures into cell-based research programs has been limited by various factors, including their cost and reproducibility. In addition, different 3D cell culture techniques often produce spheroids of different size and shape, which can strongly influence drug efficacy and toxicity. Hence, it is imperative to morphometrically characterize multicellular spheroids to avoid generalizations among different spheroid types. Standardized 3D culturing procedures could further reduce data variability and enhance biological relevance. Here, we critically evaluate the benefits and challenges inherent to growing cells in 3D, along with an overview of the techniques used to form spheroids. This is done with a specific focus on antitumor drug screening.

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