A series of novel betulin-28-hydrazone derivatives (7a-7o) were synthesized. All compounds were evaluated for their in vitro cytotoxicities in four human carcinoma cells (HepG2, MCF-7, HCT-116 and A549). Among them, compound 7l displayed the most potent cytotoxicity with an IC50 (concentration of the tested compound that inhibits 50% of cell growth) value of 7.37 ± 0.38 μM against MCF-7 cells. The preliminary cellular mechanism studies indicated that compound 7l could induce MCF-7 cells apoptosis. The above findings indicated that compound 7l may be used as a lead compound for antitumor agents with improved efficacy.

Two new series of betulin derivatives with semicarbazone (7a–g) or thiosemicarbazone (8a–g) groups at the C-28 position were synthesized. All compounds were evaluated for their in vitro cytotoxicities in human hepatocellular carcinoma cells (HepG2), human breast carcinoma cells (MCF-7), human lung carcinoma cells (A549), human colorectal cells (HCT-116) and normal human gastric epithelial cells (GES-1). Among these compounds, 8f displayed the most potent cytotoxicity with an IC50 value of 5.86 ± 0.61 μM against MCF-7 cells. Furthermore, the preliminary mechanism studies in MCF-7 cells showed that compound 8f could trigger the intracellular mitochondrial-mediated apoptosis pathway by losing MMP level, which was related with the upregulation of Bax, P53 and cytochrome c expression; the downregulation of Bcl-2 expression; activation of the expression levels of caspase-3, caspase-9, cleaved caspase-3 and cleaved caspase-9; and an increase in the amounts of intracellular reactive oxygen species. These results indicated that compound 8f may be used as a valuable skeleton structure for developing novel antitumor agents.

A series of novel betulin derivatives containing hydrazide-hydrazone moieties were synthesized. All compounds were evaluated for their cytotoxicity against four human carcinoma cell lines (HepG2, A549, MCF-7 and HCT-116) and a normal human gastric epithelial cell line (GES-1). Among them, compound 6i was the most potent against HepG2 and MCF-7 cell lines, with IC50 values of 9.27 and 8.87 μM, respectively. The results suggest that the incorporation of a hydrazide-hydrazone side chain at the C-28 position of betulin is beneficial for compounds to display significant cytotoxicity. Compound 6i may be used as a promising skeleton for antitumor agents with improved efficacy.

Ergosterol peroxide (EP) has been extensively studied for its antitumor activities. However, its further development has been restricted due to its limited intracellular accumulation and poor aqueous solubility. In this study, a novel triphenylphosphonium cation (TPP+) moiety was coupled to ergosterol peroxide to precisely target it at tumor cell mitochondria. The synthesized Mito-EP derivatives Mito-EP-3a-3d displayed stronger cytotoxicity than the EP parent and exhibited selectively cytotoxic effects between cancer cells and normal gastric epithelial (GES-1) cells. The most potent compound, Mito-EP-3b, was 9.7-fold more efficacious than ergosterol peroxide in the MCF-7 (breast cancer) cell line and showed good selectivity (SI = IC50GES-1/IC50MCF-7 = 4.04, IC50: concentrations to inhibit 50% of cell growth). Furthermore, Mito-EP-3b was able to decrease the mitochondrial membrane potential and induced reactive oxygen species production, accompanied by activating the expression of cytochrome c and Bax, while Bcl-2 expression was suppressed. The molecular mechanism may refer to the mitochondrial apoptotic pathway. Overall, the above results incentivize the further study of Mito-EP-3b derivatives as potent anticancer agents.

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