Synthesis of novel S-linked dihydroartemisinin derivatives and evaluation of their anticancer activity.

We report herein the synthesis and anticancer activity of a set of novel S-linked artemisinins bearing an aliphatic/aromatic/heterocyclic nucleus as a substituent on the sulfur. The compounds were prepared from artemisinin via its lactol-form by an acid-catalyzed condensation of the desired thiol with the lactol. Both the C-10-α- and β-configured thiol ethers were synthesized with a view to making them available for the anticancer activity evaluation using a variety of cell lines. The results show that many of the synthetic derivatives studied possessed good potential as anticancer agents. In order to draw more information on the origin of the anticancer activity, one of the compounds (9a), that showed a broad-spectrum activity in terms of reducing the viability of most of the cell lines studied, in particular proven to be most effective against Prostate (PC-3) cells, was studied in detail to find the underlying mechanism of its action by MTT assay, immunoblotting, flow cytometry and microscopy. Pretreatment of the PC-3 cells with N-acetyl cysteine affected the efficacy of 9a, suggesting the role of reactive oxygen species in reducing their viability. Cell cycle analysis showed increase in G1 phase that was indicative of G1 cell cycle arrest. Wound healing assay revealed anti-migratory effect of 9a Quantitative PCR and western blot analysis showed changes in the gene expression of PCNA, E2F1, Pin1, cyclinD1, phospho-c-jun, c-Myc, eIF4E and other genes involved in proliferation and maintaining the transformed phenotype of prostate cancer cells. Here we report the anti-proliferative property of 9a with a vital and potent target(s) in prostate cancer cells with one of such targets being Pin1 belonging to the parvulin family of PPIases. The results suggest that 9a could be a promising agent in combating prostate cancer.