Camphor-Based Thiosemicarbazone Analogues Induced G2 Cell Cycle Arrest and Apoptosis via Reactive Oxygen Species (ROS)-Mediated Mitochondrial Pathway in Human Breast Cancer Cells

22 novel camphor-based thiosemicarbazone derivatives were synthesized using camphor-based thiosemicarbazone as material and their structures were determined by H-1 NMR, C-13 NMR and HRMS. The crystal structure of 2-(3-(pyridin-4-ylmethylene)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)hydrazinecarbothioamide (3n) was determined by single crystal X-ray diffraction. The derivatives were screened in vitro for anticancer activities against human breast cancer cell line (MDA-MB-231), human lung adenocarcinoma cell line (A549), human multiple myeloma cell line (RPMI-8226) and toxicity against a normal human cell line (GES-1) by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS). It was found that majority of the tested analogs showed moderate to significant antitumor activity against selected cancer cell lines. Noticeably, 2-(3-(anthracen-9-ylmethylene)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)hydrazinecarbothioamide (3s) exhibited selective anti-tumor activities against MDA-MB-231 cells (IC50=3.90 +/- 0.04 mu mol.L-1) and low toxicity to GES-1 cells (IC50>50 mu mol.L-1). In the process of exploring the underlying mechanism of 3s, it was found that compound 3s could cause G2 phase arrest and apoptosis in MDA-MB-231 cells by overproduction of intracellular reactive oxygen species and collapse of mitochondrial membrane potential. The measured results were confirmed by western blot assay.