Design, synthesis, and evaluation of anti-solid-tumor activity of niclosamide-based STAT3/HDAC dual-target inhibitors

Inspired by reports that HDAC blockade can trigger compensatory activation of the LIFR-JAK1-STAT3 axis in solid tumors, we designed and synthesized a series of niclosamide-based STAT3/HDAC dual-target inhibitor candidates by incorporating a SAHA-derived hydroxamate zinc-binding group into the pleiotropic, STAT3-modulating niclosamide scaffold. Biological evaluation identified NS06 as the best-balanced analogue, with IC₅₀ values of 1.49 and 1.41 μM against MDA-MB-231 and HCT116 cells, respectively. Mechanistic studies showed that NS06 bound STAT3 in vitro (SPR, K_D = 5.82 μM), suppressed STAT3 phosphorylation, and inhibited HDAC1, HDAC3, and HDAC6 with IC₅₀ values of 129.1, 451.2, and 230.4 nM, respectively, while showing limited inhibition of HDAC4 and HDAC11 in the primary screen. NS06 also increased histone H3 acetylation, induced apoptosis, and inhibited migration and colony formation. In addition, NS06 retained antiproliferative activity in a 3D tumor spheroid model and showed improved Caco-2 permeability together with moderate liver microsomal stability (t_1/2 ≈ 48.6 min in rat liver microsomes). Docking and 100-ns molecular dynamics simulations further supported chemically plausible binding modes in the HDAC1 catalytic pocket and the STAT3 SH2 domain. Overall, these findings support niclosamide as a tractable scaffold for mechanism-driven STAT3/HDAC dual-target inhibitor design and identify NS06 as a promising lead for further optimization against solid tumors.