Design, synthesis and biological evaluation of novel plumbagin derivatives as potent antitumor agents with STAT3 inhibition

Based on the structure of signal transducer and activator of transcription 3 (STAT3), a series of 1,4-naphthoquinones derived from plumbagin (PL) with STAT3 inhibition potential were designed, synthesized, and biologically evaluated in vitro against several human cancer cell lines (MDA-MB-231, HepG2 and A549 cells) and three normal cells. The structure-activity relationship (SAR) and molecular docking result showed that the presence of hydroxyl group at C-5 of PL might interact with STAT3 in the form of hydrogen bonds, which is conducive to the binding of this kind structures with STAT3. Among the target compounds, 7a displayed the most potent inhibition against cancer cells and weaker cytotoxicity on normal cells than PL. The western bolting analysis showed that 7a could suppress the phosphorylation of STAT3 as well as the downstream genes instead of affecting its upstream tyrosine kinases (Src and JAK2) levels and p-STAT1 expression. Furthermore, molecular docking indicated that 7a bound to STAT3 more tightly than PL, and it could significantly induce the apoptosis of cancer cells in vitro. All these results may provide reference for the discovery of effective STAT3 inhibitors.