In an attempt to develop potent antitumor agents, new 1,3,4-thiadiazole derivatives were synthesized and evaluated for their cytotoxic effects on multiple human cancer cell lines, including the K562 chronic myelogenous leukemia cell line that expresses the Bcr-Abl tyrosine kinase. N-(5-Nitrothiazol-2-yl)-2-((5-((4-(trifluoromethyl)phenyl)amino)-1,3,4-thiadiazol-2-yl)thio)acetamide (2) inhibited the Abl protein kinase with an IC₅₀ value of 7.4 µM and showed selective activity against the Bcr-Abl positive K562 cell line. Furthermore, a Bcr-Abl-compound 2 molecular modelling simulation highlighted the anchoring role of the nitrothiazole moiety in bonding and hydrophobic interaction with the key amino acid residues. These results provide promising starting points for further development of novel kinase inhibitors.

Epidermal growth factor receptor (EGFR) and cyclooxygenase-2 (COX-2) are crucial targetable enzymes in cancer management. Therefore, herein, new 2-[(5-((1H-indol-3-yl)methyl)-1,3,4-oxadiazol-2-yl)thio]-N-(thiazol/benzothiazol-2-yl)acetamides (2a–i) were designed and synthesized as EGFR and COX-2 inhibitors. The cytotoxic effects of compounds 2a–i on HCT116 human colorectal carcinoma, A549 human lung adenocarcinoma, and A375 human melanoma cell lines were determined using MTT assay. 2-[(5-((1H-Indol-3-yl)methyl)-1,3,4-oxadiazol-2-yl)thio]-N-(6-ethoxybenzothiazol-2-yl)acetamide (2e) exhibited the most significant anticancer activity against HCT116, A549, and A375 cell lines with IC₅₀ values of 6.43 ± 0.72 μM, 9.62 ± 1.14 μM, and 8.07 ± 1.36 μM, respectively, when compared with erlotinib (IC₅₀ = 17.86 ± 3.22 μM, 19.41 ± 2.38 μM, and 23.81 ± 4.17 μM, respectively). Further mechanistic assays demonstrated that compound 2e enhanced apoptosis (28.35%) in HCT116 cells more significantly than erlotinib (7.42%) and caused notable EGFR inhibition with an IC₅₀ value of 2.80 ± 0.52 μM when compared with erlotinib (IC₅₀ = 0.04 ± 0.01 μM). However, compound 2e did not cause any significant COX-2 inhibition, indicating that this compound showed COX-independent anticancer activity. The molecular docking study of compound 2e emphasized that the benzothiazole ring of this compound occupied the allosteric pocket in the EGFR active site. In conclusion, compound 2e is a promising EGFR inhibitor that warrants further clinical investigations.

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