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Abstract
Drug combinations have been proposed to combat drug resistance, but putative treatments are challenged by low bench-to-bed translational efficiency. To explore the effect of cell culture format and readout methods on identification of synergistic drug combinations in vitro, we studied response to 21 clinically relevant drug combinations in standard planar (2D) layouts and physiologically more relevant spheroid (3D) cultures of HCT-116, HT-29 and SW-620 cells. By assessing changes in viability, confluency and spheroid size, we were able to identify readout- and culture format-independent synergies, as well as synergies specific to either culture format or readout method. In particular, we found that spheroids, compared to 2D cultures, were generally both more sensitive and showed greater synergistic response to combinations involving a MEK inhibitor. These results further shed light on the importance of including more complex culture models in order to increase the efficiency of drug discovery pipelines.
Highlights
Colorectal cancer (CRC) is the third most common neoplastic malignancy w orldwide[1], and improvements in standard treatments have increased the survival rates over the past 20 y ears[2], far from all patients benefit from currently available therapies
Drugs were selected based on approval for clinical use in CRC or other cancer types (5-FU, oxaliplatin, olaparib, palbociclib), and on their ability to target pathways frequently dysregulated in cancer (MAPK/ERK pathway, PI3K/AKT/ mTOR pathway and TGF-beta pathway)
Five out of six MEK inhibitor combinations were among the most synergistically effective combinations in 3D, whereas only two of these combinations were among the five most synergistic and effective combinations in 2D (Fig. 4c). These results indicate that whereas in 2D cultures high sensitivity towards MEK inhibition alone most likely accounts for the strong reduction in viability observed upon treatment with MEK inhibitor combinations, the viability reduction in 3D cultures is a synergistic effect that can to a larger extent be ascribed to both drugs in the pairwise combinations involving the MEK inhibitor
Summary
Colorectal cancer (CRC) is the third most common neoplastic malignancy w orldwide[1], and improvements in standard treatments have increased the survival rates over the past 20 y ears[2], far from all patients benefit from currently available therapies. In the study ALMANAC of the National Cancer Institute (NCI), where a large number of pairwise combinations of FDA-approved cancer drugs were screened in vitro, several novel pairs of synergistic drug combinations were identified, whereof roughly a third were shown to be efficient and synergistic in vivo[5]. Monitoring the effect of drugs considering non-proliferating cells may be of great significance in order to increase the bench-to-bed translational efficiency Overall, these considerations are some, among many others, that may partly explain why drugs with documented efficiency in 2D cultures often do not show the same effect in more complex cellular contexts and in vivo. These findings highlight the importance of more advanced screening platforms, encompassing different phenotypic readouts and more so, 3D culture models, for identification of synergistic drug combinations
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