Threonine Tyrosine Kinase Inhibition Eliminates Lung Cancers by Augmenting Apoptosis and Polyploidy

The spindle assembly checkpoint (SAC) maintains genomic integrity. A key component is threonine tyrosine kinase (TTK, also known as Mps1). TTK antagonism is hypothesized to cause genomic instability and cell death. Interrogating The Cancer Genome Atlas (TCGA) revealed high TTK expression in lung adenocarcinomas and squamous cell cancers versus the normal lung (P < 0.001). This correlated with an unfavorable prognosis in examined lung adenocarcinoma cases (P = 0.007). TTK expression profiles in lung tumors were independently assessed by RNA in situ hybridization (RNA-ISH). CFI-402257 is a highly selective TTK inhibitor. Its potent antineoplastic effects are reported here against a panel of well-characterized murine and human lung cancer cell lines. Significant anti-tumorigenic activity followed independent treatments of athymic mice bearing human lung cancer xenografts (6.5 mg/kg, P < 0.05; 8.5 mg/kg, P < 0.01) and immunocompetent mice with syngeneic lung cancers (P < 0.001). CFI-402257 antineoplastic mechanisms were explored. CFI-402257 triggered aneuploidy and apoptotic death of lung cancer cells without changing centrosome number. Reverse phase protein arrays (RPPAs) of vehicle versus CFI-402257-treated lung cancers were examined using more than 300 critical growth-regulatory proteins. RPPA bioinformatic analyses discovered CFI-402257 enhanced mitogen-activated protein kinases signaling, implicating MAPK antagonism in augmenting TTK inhibitory effects. This was independently confirmed using genetic and pharmacologic repression of MAPK that promoted CFI-402257 anticancer actions. TTK antagonism exerted marked antineoplastic effects against lung cancers and MAPK inhibition cooperated. Future work should determine if CFI-402257 treatment alone or with a MAPK inhibitor is active in the lung cancer clinic. Copyright ©2019, American Association for Cancer Research.

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