Exposure time versus cytotoxicity for anticancer agents

David M. Evans¹, Jianwen Fang³, Thomas Silvers¹, Rene Delosh¹, Julie Laudeman¹, Chad Ogle¹, Russell Reinhart¹, Michael Selby¹, Lori Bowles¹, John Connelly¹, Erik Harris¹, Julia Krushkal³, Larry Rubinstein³, James H. Doroshow², Beverly A. Teicher^2,4

¹Molecular Pharmacology Group, Leidos Biomedical Research, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland, 21702; ²Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute, Rockville, Maryland 20852; ³Biometric Research Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute, Rockville, Maryland 20852 

⁴Corresponding author: Beverly A. Teicher, PhD, Chief, Molecular Pharmacology Branch, National Cancer Institute, 9609 Medical Center Drive, Bethesda, MD 20892. Phone: 240-276-5972; FAX: 240-276-7895; Email: Beverly.Teicher@nih.gov

 

Abstract

Purpose: 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.

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

Results: 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 killing by agents selective for a specific cell cycle phase plateaued when susceptible cells were killed. As time increased the depth of cell-kill 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 mM in some cell lines after 11 days.

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

 

Supplementary materials:

2-day IC₅₀, etc.

3-day IC₅₀, etc.

7-day IC₅₀, etc.

11-day IC₅₀, etc.