CK1α-targeting inhibits primary and metastatic colorectal cancer in vitro, ex vivo, in cell-line-derived and patient-derived tumor xenograft mice models

BACKGROUND: Colorectal cancer (CRC) remains a leading cause of cancer-related deaths globally. Despite improved understanding of its initiation and progression, and advances in diagnostic or therapeutic strategies, the treatment of metastatic CRC remains a clinical challenge, necessitating identification of novel efficacious therapeutics with little/no toxicity to non-tumor colorectal cells. The present study investigated the effect of Epiblastin A, an adenosine triphosphate (ATP)-mediated competitive inhibitor of casein kinase 1α (CK1α) on the viability, proliferation, and oncogenicity of CRC cells. METHODS: Comparative evaluation of the effect of Epiblastin A on CK1α in fetal human normal colonic mucosa (FHC) and CRC (HCT116, HT29, DLD1) cell lines, using western blot, immunohistochemical staining, real-time polymerase chain reaction (RT-PCR), and sulforhodamine B (SRB) cytotoxicity assays. Primary culture cells, patient-derived xenograft (PDX), and tumor xenograft mice CRC models were also employed. Kaplan-Meier plots were used for survival analysis of our CRC cohort. RESULTS: CRC cells aberrantly express CK1α at mRNA and protein levels. This overexpression of CK1α is strongly associated with worse 5-year overall survival (OS) in patients with CRC. Epiblastin A inhibits CK1α and compared to its apparent non-effect on FHC cells regardless of concentration, it elicits significant dose-dependent inhibition of the viability of HT29, HCT116, and DLD1 cells with a 48 h IC(50) of 6.8, 5.0, and 3.2 μM, respectively. The expression of CK1α in CRC primary cultures and PDX samples, significantly correlated with Ki-67 expression, and both were attenuated by Epiblastin A. We also observed that the effect of 5 mg/kg Epiblastin A on tumor volume, and body weight in the CRC PDX mice models, was similar to that of 5 mg/kg Cetuximab over the time-course of our in vivo study. In DLD1-derived tumor xenograft mice, Epiblastin A with very mild effect on mice body weight, suppressed tumor volume and tumor weight in a CK1α-dependent manner (P=0.024). CONCLUSIONS: Our results demonstrate the efficacy of Epiblastin A in CRC and its potential as a putative small-molecule inhibitor of CK1α and Ki-67 signaling, which are relevant in the CRC initiation, progression and prognosis.