Combination drug therapy of glioblastoma: lessons from 3D in vitro models and the roadmap for future research

Combination drug therapy addresses the auxiliary cancer pathways of the tumor progression unaffected by the standard adjuvant treatments such as radio- and chemotherapy. It is a particularly attractive strategy to improve the treatment outcomes and the quality of life in patients with the deadliest brain cancer, glioblastoma (GB). Testing of combination drug treatment protocols requires reliable, efficient, and biologically accurate preclinical testbeds applicable before the transition to clinical trials. The 3D in vitro models of GB are a promising platform for pharmacological research. However, there is notable methodological uncertainty and a highly scattered data landscape regarding drug testing in 3D in vitro models of GB. In particular, it is not completely clear how to mimic clinically relevant dozing and schedule of the main chemotherapy drug for GB, temozolomide (TMZ) in 3D in vitro GB models. Here, the authors carefully explore the available literature on the application of TMZ in 3D in vitro models of GB, both as a sole agent and in combination with other medications. The joint analysis of the tumor modeling approaches, the employed assays, and the obtained treatment responses provided in this review may be used as a roadmap for future research in combination treatments of GB.