Abstract 3097: CDKs inhibitor: potential monotherapy for treatment of triple-negative breast cancer
Authors: Rajput Sandeep , Guo Zhanfang , Ma Cynthia 
Published: August 2015

Background: Limitless replicative potential is one of the hallmarks of cancer which occur due to dysregulated cell cycle. Cyclin dependent kinases (CDKs) are major regulators of mammalian cell cycle, which are often hyperactivated in cancer. Therefore, inhibition of cyclin dependent kinases represents an attractive therapeutic approach in cancer therapy. Dinaciclib is a CDK1, CDK2, CDK5 and CDK9 inhibitor, currently being tested in clinical trials in patients with advanced malignancies. The goal of this project was to determine the efficacy and the mechanisms of action of Dinaciclib in triple negative breast cancer (TNBC) by using patient derived xenografts (PDXs).The study results will provide more insights in identification of predictive biomarkers that are important for its clinical development.

Methods: The efficacy of Dinaciclib was determined in 3 TNBC PDXs and 3 established TNBC cell lines by in vitro cytotoxic assays and calculating the IC50. Colony formation assay was also performed in 3 dimensional matrigel matrixes to confirm in vitro cytotoxic assay results. Cell cycle analysis was done using PI staining to determine the percentage of cells in G2/M phase after Dinaciclib treatment. Apoptosis analysis was done by Annexin V and PI double staining using FACS. Effect of CDK1, CDK2, and CDK9 on cell proliferation and Dinaciclib efficacy was determined by knocking down these proteins using CRISPER-CAS plasmid. Efficacy of Dinaciclib on tumor growth inhibition was also determined in vivo by implanting PDX cell lines in nude mice.

Results: All the PDXs and established breast cancer cell lines tested were sensitive to Dinaciclib as demonstrated by IC50 value ranging from 1 to 20nM. Dinaciclib effectively inhibited the colony formation in 3D culture in all the PDXs and established breast cancer cell lines at 10nM dose. Dinaciclib significantly caused cell cycle arrest at G2/M phase after 24 hours of treatment. It also caused apoptosis induction after 24 hours of treatment. Dinaciclib reduced the CyclinB1, phospho-CDK1, Survivin and MYC protein levels after 24 hour of treatment as analyzed by western blotting. Knockdown of CDK1 and CDK2 inhibited cell proliferation by 30% and 50% in MDA-MB-231 cells in vitro. Dinaciclib significantly inhibited PDX tumor growth in vivo.

Conclusions: These data suggest that Dinaciclib is effective in inhibiting triple negative breast cancer growth in vitro and in vivo. Dinaciclib induced both cell cycle arrests at G2/M phase and apoptosis in breast cancer cells. Dinaciclib targets multiple proteins like CDK1, CDK2, CyclinB1 and cMYC, which can be further validated as predictive biomarkers. Dinaciclib can be used as a potential monotherapy for TNBC patients in clinics.

Citation Format: Sandeep Rajput, Zhanfang Guo, Cynthia Ma. CDKs inhibitor: potential monotherapy for treatment of triple-negative breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3097. doi:10.1158/1538-7445.AM2015-3097