Discovery of 4-[2.2]paracyclophanylthiazole derivatives as topoisomerase ll/malic enzyme 1 inhibitors modulating autophagy/apoptosis pathways in breast cancer therapy

Two series of [2.2]paracyclophanylthiazoles 5a–h and 7a–e were rationally designed, synthesized, and screened for anticancer activity against breast cancer cell lines representing both luminal (MCF-7) and aggressive (MDA-MB-231) subtypes, as well as safety profiling by a normal epithelial breast cell line MCF-10A. Of these, thiazolidinone derivatives 7a , 7d , and 7e possessed outstanding dual antiproliferative potency against MCF-7 (IC₅₀ = 3.1 ± 0.17, 3.76 ± 0.08, 1.19 ± 0.07 μM) and MDA-MB-231 (IC₅₀ = 1.04 ± 0.07, 1.08 ± 0.05, 2.50 ± 0.12 μM), significantly better than doxorubicin (IC₅₀ = 6.87 ± 0.18 μM and 4.16 ± 0.13 μM, respectively). Thiosemicarbazide derivative 3d also showed impressive cytotoxic potency against MCF-7 cells (IC₅₀ = 4.74 ± 0.14 μM). All four compounds were also safe for normal MCF-10A cells. Mechanistic studies revealed that most active derivatives engaged both autophagy and apoptosis pathways by modulating Beclin-1, Bax, Bcl-2, and caspase-9 with compound 7a validated by LC3-II and cleaved PARP assays. In addition, compounds 7a and 7e exhibited robust topo II inhibitory activity, whereas 7a and 7d efficiently disabled ME-1 function, both of which exhibited better IC₅₀ values than doxorubicin. Such biological results were also reinforced by molecular docking studies, which confirmed desirable binding of active candidates by topo II and ME-1 active sites, along with reasonable scoring energies and accepted physiochemical properties. Overall, these studies recognize paracyclophanyl-thiazolidinone hybrid 7a as a potential dual topo II/ME-1 inhibitor of clinical interest for treating triple-negative breast cancer (TNBC).