The design, synthesis and cellular imaging of a tumor-anchored, potent and cell-permeable BRD4-targeted fluorescent ligands

[Display omitted] •A set of BRD4 inhibitor-fluorescence conjugates with diversal structures was reported.•Conjugate 6 was cell-permeable and low cytotoxic.•Conjugate 6 showed specific BRD4 engagement in the cellular content.•Conjugate 6 exerted tumor-target imaging with pronounced fluorescent signal. Bromodomain 4 (BRD4) proteins play an important role in histone post-translational modifications and facilitate several important physiological and pathological processes, including cancers. The inhibition of BRD4 by small molecule inhibitors shows promise as a therapeutic strategy for cancer treatment. However, their clinical applications were limited, which is largely hampered by off-target effects-induced toxicity. We herein report the design, synthesis, and cellular imaging of a set of tumor-anchored and BRD4-targeted fluorescent ligands by introducing selective and potent BRD4 inhibitor into different fluorophores via variable linkers. One of the fluorescent conjugates (compound 6) was demonstrated to be cell-permeable and low cytotoxic, preferentially accumulated in cancer cells, and display pronounced fluorescent signal. More importantly, 6 was identified to show specific BRD4 engagement in the cellular content. Collectively, this study provides a pathway for developing labeled BRD4 ligands and highlights that compound 6 may represent a valuable tool for explorative learning and target delivery study of BRD4.