Biomarker Discovery for Cancer Sensitivity to CDK8 Inhibitors

Abstract

BackgroundA novel piperazinylpyrimidine compound, Q12, was synthesized and tested for its potential to selectively inhibit the growth of certain tumor cell lines within the NCI‐60 cell line panel. Q12 is an ATP competitive inhibitor of cyclin dependent kinase 8 (CDK 8). We studied Q12 in the context of sensitive cell lines MDA‐MB‐468 (GI50 0.06 μM) and HCT‐116 (GI50 0.27 μM) and a non‐sensitive cell line COLO 205 (GI50 30 μM). The MDA‐MD‐468 cell line represents triple negative breast cancer, a difficult type of cancer to treat because of lacking HER2, estrogen and progesterone receptors. HCT‐116 and COLO 205 are human colon cancer cell lines, which harbor β‐catenin and APC mutations respectively. We hypothesized that Q12 is a promising molecule that can be used to probe biomarker discovery for CDK8 inhibitor sensitive tumor types.Material and MethodsIn vitro studies were performed by using of MDA‐MB‐468 breast cancer cell line, HCT‐116 and COLO 205 colon cancer cell lines. GI50 was measured and apoptosis assay was performed. The growth inhibitory effect of Q12 was assessed by Muse Cell Viability Kit. To evaluate the effects of Q12 on β‐catenin and STATs, Western Blotting were used.ResultsThe cell viability essay shows Q12 potently inhibited the growth and viability of MDA‐MB‐468 cells and HCT‐116 cells, but COLO 205 cell line was resistant. Western blotting shows the reduction of STAT1 phosphorylation, a robust indicator of CDK8 target engagement, in all three cell lines upon Q12 treatment. Western blotting also showed a reduction in β‐catenin in both HCT‐116 and COLO 205 cells, but unchanged in MDA‐MB‐468 cell line, upon treatment with Q12.ConclusionOur data shows that active β‐catenin is not necessarily a driver of colon tumor cell proliferation and viability nor is it a marker for CDK8 inhibitor sensitivity. Both HCT‐116 and COLO205 cells harbor mutations that stabilize β‐catenin (β‐catenin and APC respectively), and both experience reductions in β‐catenin upon treatment with CDK8, but have vastly different proliferation and viability responses. The MDA‐MD‐468 cell line is very sensitive to Q12, but does not experience a reduction in β‐catenin. What is interesting to note is that both HCT‐116 and MDA‐MB‐468 harbor mutations related to RB1 (CDKN2A and RB1 respectively). Disparate E2F1 transcriptional activity may hold the key to discovery of a biomarker of CDK8 inhibitor sensitivity.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.