Synthesis of novel lipophilic N-substituted norcantharimide derivatives and evaluation of their anticancer activities

Abstract

This research attempted to study the effect of lipophilicity on the anticancer activity of N-substituted norcantharimide derivatives. Twenty-three compounds were synthesized and their cytotoxicities against five human cancer cell lines studied. The lipophilicity of each derivative was altered by its substituent, an alkyl, alkyloxy, terpenyl or terpenyloxy group at the N-position of norcantharimide. Further, among all synthesized derivatives studied, the compounds N-farnesyloxy-7-oxabicyclo[2.2.1]heptane-2,3-dicarboximide (9), and N-farnesyl-7-oxabicyclo[2.2.1]heptane-2,3-dicarboximide (18), have shown the highest cytotoxicity, anti-proliferative and apoptotic effect against human liver carcinoma HepG2 cell lines, yet displayed no significant cytotoxic effect on normal murine embryonic liver BNL CL.2 cells. Their overall performance led us to believe that these two compounds might be potential candidates for anticancer drugs development.

Figure 1

Chemical structures of cantharidin (1), norcantharidin (2) and norcantharimide (15).

Scheme 1

Synthesis of norcantharidin (2) and compounds 5–12.

Scheme 2

Synthesis of compounds 14–27.

Figure 2

(Top) Cell morphological observations of nuclear change of human hepatoma HepG2 cell lines after 48 h exposure (untreated), with 40 μM norcantharidin (2), compounds 9 and 18. (Bottom) Cells were stained with Hoechst 33258 and examined using a Nikon (Tokyo, Japan) fluorescence microscope. (Magnification, 400×).

Figure 3

Induction of cells arrest by norcantharidin (2), compounds 9 and 18. Effects of different concentrations of norcantharidin (2), compounds 9 and 18 on cell-cycle progression of HepG2 cells. HepG2 cells were untreated or treated with 10–60 μM norcantharidin (2), compounds 9 and 18 for 48 h. After treatment, cells were fixed and stained with PI, and the cell cycle distribution was examined by flow cytometer.

Figure 4

Flow cytometry analysis of HepG2 cells treated with different concentrations of norcantharidin (2), compounds 9 and 18 for 48 h. Treated cells were examined for apoptotic cells using Annexin V-FITC apoptosis detection kit. Annexin V-positive/PI-negative cells were in early stages of apoptosis and double-positive cells were in late stages of apoptosis, whereas annexin V-negative/PI-positive cells were necrotic.