Scorpion-Inspired 1,3,4-Oxadiazole-Based GSK-3β-Targeting Agents: Design, Synthesis, and Biological Evaluation

Glycogen synthase kinase-3β (GSK-3β) is a promising therapeutic target for anticancer drug development because it is involved in cell proliferation, apoptosis, and tumor progression. However, developing structurally distinct GSK-3β-directed anticancer scaffolds with favorable cancer-cell selectivity remains challenging. In this study, 10 scorpion-inspired 2-(phenacylthio)-1,3,4-oxadiazole derivatives (ODS1-10) were synthesized in 65–97% yields and evaluated for their anticancer potential. Among the synthesized compounds, ODS-7 showed the highest activity against MDA-MB-231 cells (IC50 = 32.7 μM), whereas ODS-5 was the most active derivative against SH-SY5Y cells (IC50 = 21.2 μM). Structure–activity relationship analysis indicated that the electronic properties and substitution pattern of the aryl moieties substantially influenced antiproliferative activity. ODS-5 and ODS-7 showed preferential activity toward cancer cells, with ODS-5 exhibiting a selectivity index of 2.80 against non-cancerous HaCaT keratinocytes. Both compounds significantly reduced SH-SY5Y clonogenic capacity and disrupted three-dimensional spheroid integrity. Immunofluorescence analysis revealed reduced GSK-3β-associated fluorescence intensity in treated SH-SY5Y cells, while RT-qPCR demonstrated upregulation of BAX and CASP3 and downregulation of BCL2, supporting the involvement of apoptosis in the observed cytotoxic response. Molecular docking also showed favorable predicted binding energies for ODS-5 (−8.67 kcal/mol) and ODS-7 (−8.44 kcal/mol) within the GSK-3β binding site, comparable to the co-crystallized ligand 3HT (−8.37 kcal/mol). Overall, ODS-5 and ODS-7 represent promising preliminary lead structures within the 2-(phenacylthio)-1,3,4-oxadiazole series, providing a rational SAR basis for further medicinal chemistry optimization and direct evaluation of GSK-3β target engagement.