NVP-BSK805, An Inhibitor of JAK2 Kinase, Significantly Enhances the Radiosensitivity of Esophageal Squamous Cell Carcinoma In Vitro and In Vivo

Abstract

Esophageal squamous cell carcinoma (ESCC) is a prevalent cancer with high morbidity and mortality in the world. Radiotherapy is one major curative treatment modality for ESCC patients. Our study aimed to find out small-molecular kinase inhibitors that could significantly enhance the sensitivity of radiotherapy in ESCC. Through high-content screening, 93 kinase inhibitors were tested for their radiosensitizing effect on esophageal cancer cells. The radiosensitizing effect of kinase inhibitors was investigated in vitro by clonogenic survival assay, detection of DNA double-strand breaks (DSBs) and by flow cytometry analysis on cell apoptosis. By establishment of xenograft tumor models in BALB/c nude mice, the radiosensitizing effect of kinase inhibitors was investigated in vivo. Our study found that NVP-BSK805, an inhibitor of JAK2 kinase, can significantly radiosensitize ESCC cells by enhancing DSBs and inhibiting DNA damage repair, resulting in decreased clonogenic survival and increased tumor growth inhibitory effect. Mechanism studies discovered that radiation promoted the activation and expression of JAK2 kinase, leading to the development of radioresistance in ESCC cells. JAK2 kinase was highly expressed in tumor tissues of ESCC patients, while rarely expressed in normal esophageal epithelial tissues. Survival analysis revealed JAK2 kinase as a prognostic factor of ESCC patients treated with chmoradiotherapy. Bio-informatics analysis showed that JAK2 kinase regulated those genes that were enriched in DNA recombination and repair pathways. POLQ, one DNA polymerase, was a downstream effector of JAK2 kinase to mediate radioresistance. By whole-exome sequencing (WES) analysis, radiation-induced SNV (single nucleotide variants) in JAK2 kinase was found to be closely associated with the relapse of ESCC patients after radiotherapy. The analysis of RNA sequencing (RNA-seq) showed that IL-1 up-regulated by radiation may be involved in cytokine receptors-mediated JAK2 activation. Our study discovered that NVP-BSK805 could significantly enhance the sensitivity of radiotherapy by inhibiting the expression and activation of JAK2 kinase in ESCC.