MLCK Inhibition is Synthetically Lethal to MYC-Overexpressing Cancer Cells

Abstract

The dysregulation of MYC is widely implicated in human cancers and is considered an 'undruggable' target to date. Here, we conducted a CRISPR-based loss-of-function screen, focusing on kinases, the majority of which are recognized as 'druggable' targets, to identify genes essential for MYChigh but not MYClow cells. An isogenic pair of nonmalignant cells, with or without ectopic MYC expression, was used in the screening. Our screen uncovers new MYC synthetic lethal (MYC-SL) interactions and identifies the majority of MYC-SL genes previously described. In particular, the screen reveals Myosin Light-Chain Kinase (MLCK) as the most potent MYC-SL interaction. Inhibition of MLCK induced selective cell death in a MYC-dependent manner, significantly suppressing tumor growth in MYC-dependent xenografts, as well as in the ApcMin/+ mouse model of colon cancer and the MYC-transgenic hepatocellular carcinoma (HCC) model, without apparent toxicity. This selective cell death is primarily attributed to specific DNA damage and subsequent p53-mediated apoptosis. Mechanistically, the activation of MYC leads to the nuclear accumulation of F-actin and myosin II, a critical substrate of MLCK. This interaction facilitates the repair of replication stress, thereby promoting cell survival. Inhibiting MLCK suppresses myosin II activity, causing unresolved replication stress, leading to DNA damage, and activating the p53-mediated apoptosis pathway. These results propose a therapeutic strategy for eliminating tumor cells that overexpress MYC while sparing normal cells.

Note:
Funding Information: This work is supported by the National Science Foundation of China (82373160, 81972632, 82322073, 82173846), Oriental Scholars of Shanghai Universities (TP2022081), Jiangxi Province Thousand Talents Program (jxsq2023102168), Shanghai Rising-Star Program (22QA1409100), 2021 Shanghai Science and Technology Innovation Action Plan (21S11902800). Three-year Action Plan for Shanghai TCM Development and Inheritance Program [ZY(2021-2023)-0401], Innovation Team and Talents Cultivation Program of National Administration of Traditional Chinese Medicine (ZYYCXTD-D-202004), and the CAMS Innovation Fund for Medical Sciences (CIFMS) (2023-I2M-3-009).

Declaration of Interests: The authors declare no potential conflicts of interest.

Ethics Approval Statement: All animal experimentation procedures were conducted per the guidelines and regulations set forth by the institutional animal care and use committee of the Shanghai University of Traditional Chinese Medicine, with their approval.

Keywords: MYC, MLCK, Synthetic lethality