Phosphoproteomics guides low dose drug combination of cisplatin and silmitasertib against concurrent chemoradiation resistant cervical cancer

Cisplatin-based concurrent chemoradiotherapy (CCRT) is the standard treatment for cervical patients with locally advanced disease. Despite the improved survival rates and prognosis observed in patients undergoing CCRT, over 30-40% do not achieve complete response and are at risk of locoregional recurrence. Targeting crucial molecules that confer resistance may improve the clinical outcomes of the treatment resistant patient cohort. Herein, we employed a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based phosphoproteomic approach to identify the altered phosphophorylation events, activated kinases and dysregulated pathways involved in treatment resistance. We quantified 2531 unique phosphopeptides mapping to 1099 proteins of which 74 proteins were differentially phosphorylated between the cohorts. Pathway analysis revealed dysregulation of the DNA repair pathway and the proteins involved in DNA repair in the non-responder cohort. Additionally, we identified kinase signature associated with CCRT resistance. Kinases such as CSNK2A1, PRKDC, PLK-1, NEK2, ATM and CDK1 are predicted to be activated in non-responders. In particular, we showed that CSNK2A1 is involved in oncogenesis of cervical cancer and pharmacological inhibition led to reduced cell proliferation, migration and colony formation. Moreover, the combination of the CSNK2A1 inhibitor, silmitasertib with cisplatin demonstrated synergism (combination index < 1) and yielded a beneficial reduction in dosage. The dose reduced combination potentially reduced the proliferative, migratory and colony formation ability <i>in vitro</i>. Our findings highlight the potential of phosphoproteomics to identify clinically significant targets and pathways implicated in CCRT resistance. Our study also indicates that combination therapy could serve as an effective treatment strategy to improve the efficacy of patients undergoing CCRT.