Critical role of three-dimensional tumorsphere size on experimental outcome.

Three-dimensional in vitro spheroids are a reliable model to study tumor biology and drug toxicity. However, inconsistencies exist in terms of seeding cell density that governs spheroid size and shape, influencing the experimental outcome. We investigated the effect of varying cell densities using glioblastoma cells on tumorsphere formation and their responsiveness to drug treatment. Our results demonstrated that in comparison with spheroids formed with lower cell density, spheroids formed with higher cell density were not only larger in size but also had a larger necrotic core surrounded by a higher number of quiescent cells and were irresponsive to drug treatment. Our study highlights the importance of predetermination of cell density to obtain desired/appropriate spheroid size to produce consistent and reliable data on drug toxicity studies in tumor cells.