Exposure time versus cytotoxicity for anticancer agents

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Time is a critical factor in drug action. The duration of inhibition of the target or residence time of the drug molecule on the target often guides drug scheduling.


The effects of time on the concentration-dependent cytotoxicity of approved and investigational agents [300 compounds] were examined in the NCI60 cell line panel in 2D at 2, 3, 7 and in 3D 11 days.


There was a moderate positive linear relationship between data from the 2-day NCI60 screen and the 3-, 7- and 11-day and a strong positive linear relationship between 3-, 7- and 11-day luminescence screen IC50s by Pearson correlation analysis. Cell growth inhibition by agents selective for a specific cell cycle phase plateaued when susceptible cells were growth inhibited or killed. As time increased the depth of cell growth inhibition increased without change in the IC50. DNA interactive agents had decreasing IC50s with increasing exposure time. Epigenetic agents required longer exposure times; several were only cytotoxic after 11 days’ exposure. For HDAC inhibitors, time had little or no effect on concentration response. There were potency differences amongst the three BET bromodomain inhibitors tested, and an exposure duration effect. The PARP inhibitors, rucaparib, niraparib, and veliparib reached IC50s < 10 μM in some cell lines after 11 days.


The results suggest that variations in compound exposure time may reflect either mechanism of action or compound chemical half-life. The activity of slow-acting compounds may optimally be assessed in spheroid models that can be monitored over prolonged incubation times.

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This project was funded in whole or in part with federal funds from the National Cancer Institute, National Institutes of Health, under contract HHSN261200800001E. The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. This research was supported [in part] by the Developmental Therapeutics Program in the Division of Cancer Treatment and Diagnosis of the National Cancer Institute.

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Supplemental Figure 1. Median concentrations (micromolar, blue) and mean log IC50 concentrations (micromolar, red) for the NCI60 cell line panel after compound exposure for 2 days, 3 days, 7 days or 11 days for methotrexate, raltitrexed, doxorubicin, topotecan, belinostat, panobinostat, romidepsin and selinexor. Supplemental Figure 2A. Mean log IC50 concentrations for the NCI60 cell line panel after compound exposure for 2 days, 3 days, 7 days or 11 days for the EGFR inhibitor erlotinib (blue), the FAK inhibitor TAE-226, the MPS-1 inhibitor BAY-1217389 and for the Akt inhibitor MK-2206. 2B. Mean log IC50 concentrations for the NCI60 cell line panel after compound exposure for 2 days, 3 days, 7 days or 11 days for the BET bromodomain inhibitors MK8628, BET-BAY-002 and GSK-525762. 2C. Mean log IC50 concentrations for the NCI60 cell line panel after compound exposure for 2 days, 3 days, 7 days or 11 days for the IAP inhibitors birinapant and LCL-161. Supplemental Figure 3A. Concentration response curves in three representative NCI60 panel cell lines after compound exposure for 2 days (blue), 3 days (red), 7 days (yellow) or 11 days (green) for the cell surface transmembrane receptor tyrosine kinase inhibitors sorafenib, erlotinib, crizotinib and nintedanib. B. Concentration response curves in three representative NCI60 panel cell lines after compound exposure for 2 days (blue), 3 days (red), 7 days (yellow) or 11 days (green) for selected intracellular kinases: FAK inhibitors TAE-226, MPS-1 inhibitor BAY-1217389, and Akt inhibitor MK-2206 (PPTX 2132 kb)

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Evans, D.M., Fang, J., Silvers, T. et al. Exposure time versus cytotoxicity for anticancer agents. Cancer Chemother Pharmacol 84, 359–371 (2019). https://doi.org/10.1007/s00280-019-03863-w

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  • CxT
  • NCI60
  • Concentration times time
  • Epigenetic agents