Pushing ploidy to its limit as a new therapeutic strategy for hepatocellular carcinoma

Abstract

Aneuploidy, arises from mitotic defects, is a common feature of cancer cells, including HCC. The unbalanced karyotype is a marker of cells harbouring gene amplifications or deletions to optimize gene dosages for malignant transformation. Paradoxically, cancer cells cannot survive with too extensive aneuploidies, thus the cell cycle process must be controlled. PLK4 (centrosome regulator) and TTK (SAC regulator) are overexpressed in HCC and other cancers, implying their importance in cancer development. CFI-400945 and CFI-402257 are two newly developed small molecule inhibitors targeting PLK4 and TTK, respectively. Using HCC as the model, we discovered that inhibitors targeting these two proteins efficiently suppressed HCC proliferation by disrupting cell cycle, inducing DNA damage and severe aneuploidy. Specifically, inhibiting PLK4 caused endoreplication and inhibiting TTK abolished SAC functioning. The inhibitors treated-HCC cells entered senescence and secreted senescence associated secretory phenotype (SASP) to the tumor microenvironment as chemokines to attract immune cells. The SASP was elicited by cytosolic DNA via DDX41-STING-IRF3/7-NFκ-β axis as a consequence of chromosome missegregation-mediated micronuclei formation, accumulation of cytosolic DNA, and DNA damage. Therapeutically, CFI-400945 and CFI-402257 effectively suppressed growth of HCC tumors and increased immune infiltration through the STING pathway. We observed that combination treatment of these inhibitors with immune checkpoint inhibitors including currently available anti-PD1/PDL1 mAbs for HCC patients could extend survival. Further, we explored the CFI-400945 sensitivity by CRISPR library screening and identified CDCA8 as the gene conferring resistance. More experiments are needed to clarify the mechanism of actions. To conclude, cancer cells rely on certain cell cycle regulators (e.g. PLK4 and TTK) to maintain the dysregulated cell cycle. Our study unprecedentedly revealed targeting ploidy and inducing cytosolic DNA as the vulnerability of cancer cells, suggesting the development of new cell cycle inhibitors as cancer therapeutics.