Synthesis of Cucurbitacin B Derivatives as Potential Anti-Hepatocellular Carcinoma Agents

Abstract

Cucurbitacin B shows potent activity against tumor cells, but its high toxicity limits its application in the clinic. A series of cucurbitacin B derivatives was synthesized and evaluated for their anti-hepatocellular carcinoma (HCC) activities against the HepG-2 cell line. These compounds were also tested for their toxicity against the L-O2 normal cell line. The compound with the most potential, 10b, exhibited potent activity against the HepG-2 cell line with an IC₅₀ value of 0.63 μM. Moreover, compound 10b showed the highest TI value (4.71), which is a 14.7-fold improvement compared to its parent compound cucurbitacin B. A preliminary molecular mechanism study of 10b indicated that 10b could inhibit P-STAT3 to induce the activation of mitochondrial apoptotic pathways. An in vivo acute toxicity study indicated that the compound 10b has preferable safety and tolerability compared with cucurbitacin B. These findings indicate that compound 10b might be considered as a lead compound for exploring effective anti-HCC drugs.

Keywords: Anti-hepatocellular carcinoma; Cucurbitacin B; Derivative; Synthesis; Toxicity.

Figure 1

The chemical structures of cucurbitacin B (1), cucurbitacin D, cucurbitacin E, and cucurbitacin I.

Scheme 1

The synthesis of compounds 3a–3q and 4. Reagents and conditions: a) TBSCl, imidazole, DCM, 43%; b) R¹COOH, EDCI, TEA, DMAP, DCM; c) TBAF/AcOH, THF, 47–86% yield in two steps; d) Cinnamic acid, EDCI, TEA, DMAP, DCM, 90%.

Scheme 2

The synthesis of compounds 9a–9c, 10a–10o, and 11. Reagents and conditions: a) Corresponding diol, 2N NaOH, THF; b) Corresponding alcohol amine, 2N NaOH, THF; c) 6a–6o, succinic anhydride, DMAP, DCM; d) EDCI, TEA, DMAP, DCM; e) TBAF, AcOH, THF, 61–82% yield in two steps; f) succinic anhydride, DMAP, DCM; g) 7a–7c, TFA, DCM; h) HATU, DIPEA, DMF; i) TBAF, AcOH, THF, 44–73% yield in three steps; j) TBAF, AcOH, THF, 79%.

Figure 2

(A) The representative images and the statistical results of flow cytometry after treatment with compound 10b at 0, 1, and 2 µM in a cell apoptosis assay. ** p < 0.01. (B) The level of STAT3, P-STAT3, Bax, Bim, Bcl-2, and caspase 3 after treatment with compound 10b at different concentrations by a Western blot assay.

Figure 3

(A) The percentage of death in mice after the administration of cucurbitacin B and compound 10b. (B) The body weight change after the administration of compound 10b by intravenous injection.