Discovery of hydrazone derivatives as novel STAT3 antagonists against pancreatic and colorectal cancers.

Signal transducer and activator of transcription 3 (STAT3) has been an anti-cancer protein target for three decades due to its over-activation in various cancers; however, direct STAT3 inhibitors have not reached the market. In this study, a series of novel hydrazone derivatives were designed, synthesized, and characterized. The most promising compound P42 was found to selectively target the STAT3 SH2 domain over the DNA-binding domain, as suggested by the results from fluorescence polarization assays. The GI50 values after 72 h of P42 treatment were determined to be 0.85-5 μM in STAT3-overexpressing pancreatic and colorectal cancer cell lines harboring KRAS mutations (MIA PaCa-2, DLD-1 and HCT 116). Western blot analyses showed that P42 significantly inhibited phosphorylated STAT3 levels without affecting total STAT3 and its upstream kinases JAK2 and SRC. P42 demonstrated significant autophagy-associated cell death rather than apoptosis or necrosis in flow cytometry analyses, with increases in LC3II/I ratios and decreases in p62 levels. Cancer stemness potential was significantly abrogated with P42 as shown in colony formation assay and decreases in epithelial-mesenchymal transition/stemness markers SNAIL and ZEB1 levels. Molecular docking further supported a plausible binding mode within the STAT3 SH2 domain for P42, and SwissADME prediction suggested its favorable drug-likeness properties. Taken together, P42 warrants future anti-cancer drug development.