Evaluation of novel CDK-inhibitors in combination with apoptosis-modulating agents for the treatment of colorectal cancer

Abstract

Background: Colorectal cancer (CRC) still remains one of the deadliest malignancies in the world for both men and women. The development of resistance to cytotoxic and targeted therapies remains the primary reason for treatment failures. A novel therapeutic approach is urgently needed. The discovery of Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) in the end of the 1990s was a bright spot for colorectal cancer management. However, a universal hallmark of most of cancers is the intrinsic or acquired resistance to apoptotic signals. Cyclin-dependent kinase 9 (CDK9) plays the most crucial role in regulating cell cycle progression, transcription elongation and mRNA processing in almost all tissues. In this work, we first investigated the role of CDK9 in colorectal cancer tissues. Methods: Immunohistochemical analysis of CDK9 expression in tumor and normal tissues of colorectal cancer revealed an overexpression of CDK9 in tumor tissues. In addition, high CDK9 expression significantly shortened survival, especially in well-differentiated tumors. Moreover, the combinational therapeutic potential of selective CDK9 inhibition with TRAIL on colorectal cancer cells was evaluated by analysis of cell viability, long-term survival, colony formation and induction of apoptosis and characterized by flow cytometry and western blotting. Results: Pharmacologically, CDK9 inhibition by Dinaciclib drastically reduced cell viability at different time points in colorectal cancer cells. Additionally, non-sensitive colorectal cancer cells could be strongly sensitized to TRAIL-induced cell death by the combination and potently suppressed long-term survival and colony formation. Mechanistic analysis revealed that CDK9 inhibition induced apoptosis and Sub G1 phase arrest by downregulation of antiapoptotic proteins Mcl-1, cFLIP and IAPs and upregulation of DR5. Conclusion: In summary, we identified CDK9 inhibition in combination with TRAIL is a novel and promising therapeutic approach for colorectal cancer.