Thiazole- and 1,3,4-Thiadiazole-Based Hybrids: Synthesis and In Vitro Cytotoxicity Against Human Cancer Cell Lines

Problems such as high toxicity, low selectivity, and drug resistance encountered in cancer treatment increase the need for more effective and safe anticancer agents. In this study, the anticancer effects of new compounds consisting of thiazole and 1,3,4-thiadiazole derivatives were investigated. Compound 6e, which showed the strongest cytotoxic effect, was evaluated in detail in human bladder (HTB-9) and lung (A549) cancer cells. According to the WST-1 test results, the IC₅₀ value of compound 6e was determined as 38.9 μM for HTB-9 cells and 82.86 μM for A549 cells. As a result of Annexin V-FITC/PI double staining and flow cytometry analysis, it was determined that compound 6e application significantly increased the apoptotic cell rates in both HTB-9 and A549 cells. It was observed that it significantly induced early apoptosis in HTB-9 cells and late apoptosis in A549 cells (p < 0.0001). Caspase-3/7 activity was significantly increased in HTB-9 cells after compound 6e application compared to the control group and similarly increased in A549 cells (p < 0.0001). In cell cycle analyses, compound 6e caused cell cycle arrest in the G2/M phase in HTB-9 and A549 cells. In the wound healing test, the migration speed in HTB-9 and A549 cells treated with compound 6e after 24 h was significantly decreased (p < 0.0001). Molecular docking revealed strong binding to caspase-3 (PDB ID: 1NMQ, score: -8.2 kcal/mol), identifying key interactions that mechanistically support its pro-apoptotic effects. In addition, the low cytotoxicity of compound 6e in healthy BEAS-2B cells suggests that it has a selective anticancer effect.