13,14-bis(cis-3,5-dimethyl-1-piperazinyl)-β-elemene, a novel β-elemene derivative, shows potent antitumor activities via inhibition of mTOR in human breast cancer cells

Elemene has been approved for the treatment of advanced cancer in China, however, it inhibits cell growth only at high concentrations and is an essential oil with poor water solubility and stability. The discovery of new β-elemene derivatives is of increasing interest. We recently reported that the compound 13,14-bis(cis-3,5-dimethyl-1-piperazinyl)-β-elemene (IIi), a novel β-elemene derivative with a cis-2,6-dimethylpiperazine substitution, is a potent agent for inhibiting the proliferation of SGC-7901 and HeLa cells. In the present study, we further verified that IIi is cytotoxic to a wide spectrum of human cancer cells in culture, including those of breast, ovarian, lung, gastric, hepatocellular and colon cancer, as well as leukemia cell lines, with an average IC(50) of 3.44 μmol/l. Notably, IIi showed significant cytotoxicity in two multidrug-resistant (MDR) cell lines, with an average resistance factor (RF) of 1.66. Moreover, in mice with S-180 sarcoma xenografts, the intraperitoneal administration of IIi inhibited tumor growth. The immunoblotting study showed that treatment with IIi decreases phosphorylated p70S6K1 and 4EBP1 levels in the human breast cancer MCF-7 and MDA-MB-468 cells. In the MCF-7 cells, IIi also significantly increased the expression of cleaved LC3. This indicated that IIi inhibits mTOR activity and induces autophagy. The mTOR inhibitory function and the potent antitumor activity, taken together with the appreciable anti-multidrug resistance action, shows IIi to be a novel potential antitumor agent, which merits further research and development.