Abstract B136: Application of a mathematical model to understand the cell cycle progression effects of MEK1/2 kinase inhibition using the investigational small-molecule allosteric inhibitor TAK-733.
Authors: Blair Derek , Mettetal Jay , Collins Sabrina , Zarycki Jodi , Vincent Patrick , Ecsedy Jeffrey , Chakravarty Arijit 
Published: June 2012

Abstract
In order to more precisely understand the effects of MEK1/2 inhibition on cell cycle progression, cellular imaging and biochemical assays were coupled with mathematical modeling.
The MEK/ERK signaling cascade modulates multiple outcomes relevant to cancer therapy including cell growth, proliferation, differentiation and apoptosis. Moreover, MEK/ERK signaling regulates transitions between the G1, S and G2 cell cycle phases, and mediates the response to DNA damage induced by a wide variety of DNA damaging agents. Inhibition of the MEK/ERK pathway represents a promising approach for the treatment of cancer. A number of small-molecule inhibitors are currently in clinical trials, including TAK-733, a novel, investigational, selective, non ATP competitive, allosteric inhibitor of MAP kinase-ERK kinase (MEK) activity.
MEK inhibition is often described to invoke a complete arrest at the G1-S cell cycle transition leading to a rapid cessation of cell growth. In order to assess this, the kinetics of cell cycle progression using continuous quantitative techniques in several different cell types was examined. Time-lapse microscopy studies and confluence analyses using an IncuCyte system demonstrated that cells treated with TAK-733 continue to divide over a period of five days, albeit at a slower rate than the DMSO treated cells. These observations were corroborated with flow cytometry using CFSE, a fluorescent cytoplasmic dye whose rate of decay is a measure of the cell division rate, and with immunofluorescence microscopy using the G2/M marker cyclin B. This continued cell cycling in the presence of TAK-733 was demonstrated to occur with abnormal cell cycle progression times and abnormal DNA content profiles, suggesting altered rates of passage through S and G2/M phase.
A mathematical model was constructed to quantitatively describe how MEK inhibition is affecting the passage of the cell population through the cell cycle. When the model is fitted to the experimentally observed data, it inferred the rate of entrance and exit from each phase of the cell cycle under both control and treatment conditions. The model simultaneously captured both the observed accumulation in G0/G1 as well as the observed progression through the cell cycle during treatment. Interestingly, it was able to explain both of these results without invoking a complete G1 arrest. Instead it showed that the rate of exit from G1 is reduced upon inhibition. These findings were supported by time-lapse microscopy observations which were not used in fitting the model.
This reassessment of the canonical view of cell-cycle progression defects following MEK1/2 inhibition by means of the mathematical modeling approach described here may provide key differentiation opportunities in the rational development of TAK-733 and other MEK1/2 inhibitors.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B136.