Evaluation and SAR analysis of the cytotoxicity of tanshinones in colon cancer cells.

Aim: This study was designed to evaluate the anti-cancer actions of tanshinone I and tanshinone IIA, and six derivatives of tanshinone IIA on normal and cancerous colon cells. Structure activity relationship (SAR) analysis was conducted to delineate the significance of the structural modifications of tanshinones for improved anti-cancer action.

Method: Tanshinone derivatives were designed and synthesized according to the literature. The cytotoxicity of different compounds on colon cancer cells was determined by the MTT assay. Apoptotic activity of the tanshinones was measured by flow cytometry (FCM).

Results: Tanshinone I and tanshinone IIA both exhibited significant cytotoxicity on colon cancer cells. They are more effective in p53(+/+) colon cancer cell line. It was also noted that the anti-cancer activity of tanshinone I was more potent and selective. Two of the derivatives of tanshinone IIA (N1 and N2) also exhibited cytotoxicity on colon cancer cells.

Conclusion: The anti-colon cancer activity of tanshinone I was more potent and selective than tanshinone IIA, and is p53 dependent. The derivatives obtained by structural modifications of tanshinone IIA exhibited lower cytotoxicity on both normal and colon cancer cells. From steric and electronic characteristics point of view, it was concluded that structural modifications of ring A and furan or dihydrofuran ring D on the basic structure of tanshinones influences the activity. An increase of the delocalization of the A and B rings could enhance the cytotoxicity of such compounds, while a non-planar and small sized D ring region would provide improved anti-cancer activity.