Synergistic apoptotic effects in cancer cells by the combination of CLK and Bcl-2 family inhibitors

• DOI: 10.1371/journal.pone.0240718
• Publication Date: 2020-10-16T17:33:07Z
• Authors: Aiko Murai; Shunsuke Ebara; Satoshi Sasaki; Tomohiro Ohashi; Tohru Miyazaki; Toshiyuki Nomura; Shinsuke Araki
• Keywords: G2 Phase; 0301 basic medicine; Proteasome Endopeptidase Complex; Science; CASP8 and FADD-Like Apoptosis Regulating Protein; Antineoplastic Agents; Apoptosis; Mechanistic Target of Rapamycin Complex 2; Protein Serine-Threonine Kinases; 03 medical and health sciences; Cell Line, Tumor; RNA Precursors; Humans; Protein Kinase Inhibitors; Cell Proliferation; Q; R; Drug Synergism; Cell Cycle Checkpoints; Protein-Tyrosine Kinases; 3. Good health; Alternative Splicing; Proto-Oncogene Proteins c-bcl-2; Medicine; Myeloid Cell Leukemia Sequence 1 Protein; Research Article

Emerging evidence indicates that alternative splicing plays a critical role in cancer progression through abnormal expression or mutation of splicing factors. Small-molecule splicing modulators have recently attracted considerable attention as a novel class of cancer therapeutics. CDC-like kinases (CLKs) are central to exon recognition in mRNA splicing and CLK inhibitors exhibit anti-tumour activities. Most importantly, molecular mechanism-based combination strategies for cancer therapy must be considered. However, it remains unclear whether CLK inhibitors modulate expression and splicing of apoptosis-related genes, and whether CLK inhibitors enhance cytotoxicity in combination with apoptosis inducers. Here we report an appropriate mechanism-based drug combination approach. Unexpectedly, we found that the CLK inhibitor T3 rapidly induced apoptosis in A2780 cells and G2/M cell cycle arrest in HCT116 cells. Regardless of the different phenotypes of the two cancer cell types, T3 decreased the levels of anti-apoptotic proteins (cIAP1, cIAP2, XIAP, cFLIP and Mcl-1) for a short period of exposure and altered the splicing of the anti-apoptotic MCL1L and CFLAR isoform in A2780 and HCT116 cells. In contrast, other members of the Bcl-2 family (i.e., Bcl-xL and Bcl-2) were resistant to T3-induced expression and splicing modulation. T3 and a Bcl-xL/Bcl-2 inhibitor synergistically induced apoptosis. Taken together, the use of a CLK inhibitor is a novel therapeutic approach to sensitise cancer cells to Bcl-xL/Bcl-2 inhibitors.