Preclinical evaluation of JQ1 in esophageal squamous cell carcinoma: growth and migration suppression with BRD4-associated DNA damage and apoptotic signaling.

BACKGROUND: Esophageal squamous cell carcinoma (ESCC) is an aggressive malignancy with limited therapeutic options. Bromodomain-containing protein 4 (BRD4), a BET family epigenetic reader, regulates oncogenic transcription and may represent a pharmacological vulnerability in ESCC. This study evaluated the pharmacological effects of the BET inhibitor JQ1 in ESCC models, with particular attention to cell migration under non-cytotoxic conditions and BRD4-associated stress signaling. METHODS: The effects of JQ1 were examined in ESCC cell lines and in a KYSE150 subcutaneous xenograft model established in BALB/c nude mice. Cell viability was assessed by CCK-8 assays at 24, 48, and 72 h. Wound healing and Transwell assays were performed using cell-line-specific low concentrations of JQ1 that did not significantly reduce cell viability during the 24 h assay period, as confirmed by parallel viability controls. Cell-cycle distribution and apoptosis were analyzed by flow cytometry. Western blotting, immunofluorescence staining, qRT-PCR, and alkaline comet assay were used to assess BRD4-related signaling, apoptosis-associated proteins, γ-H2AX accumulation, and DNA strand breaks. RESULTS: JQ1 reduced ESCC cell viability and clonogenic growth, induced G1-phase accumulation, and promoted apoptosis-associated changes. Under non-cytotoxic conditions, JQ1 reduced wound closure and Transwell migration in KYSE150, KYSE450, and ECA109 cells. Molecular analyses showed that JQ1 treatment was accompanied by decreased BRD4 expression, suppression of c-Myc/Cyclin D1-related signaling, increased p53 and Bax expression, reduced Bcl-2 expression, and elevated levels of cleaved PARP1 and cleaved Caspase-3. JQ1 also increased γ-H2AX accumulation and DNA strand breaks. In vivo, JQ1 suppressed KYSE150 xenograft growth and reduced Ki67 expression, while body weight monitoring and routine H&E staining did not reveal obvious toxicity under the current experimental conditions. CONCLUSION: JQ1 exhibited anti-proliferative, pro-apoptotic, and anti-migratory effects in preclinical ESCC models. These effects were accompanied by BRD4-related signaling changes, DNA damage-associated responses, and apoptosis-related molecular alterations. The findings support further investigation of BET/BRD4-associated pharmacological strategies in ESCC, while target-specific validation and expanded in vivo mechanistic and safety studies remain warranted.