In vitro and in vivo anti-tumour activities of echinoside A and ds-echinoside A from Pearsonothuria graeffei

Background: Echinoside A (EA) and ds-echinoside A (DSEA) are triterpene glycosides isolated from the sea cucumber Pearsonothuria graeffei. DSEA, the desulfurisation product of EA, has the following structure: β-D-xylopyranosyl-holost-8(9),11(12)-diene-3β,17α-diol. In the present study, we examined the anti-tumour activities-in particular, the structure-activity relationships-of EA and DSEA in vitro and in vivo.

Results: Both EA and DSEA exhibited an inhibitory effect on cell proliferation, along with apoptosis-inducing activity, in HepG2 cells. Moreover, they significantly arrested the cell cycle in the G₀/G₁ phase. A reverse transcriptase-polymerase chain reaction assay revealed that EA and DSEA significantly increased the expression of the cell-cycle-related genes, namely, p16, p21 and c-Myc, and decreased that of cyclin D₁. Western blotting analysis demonstrated that they down-regulated the expression of Bcl-2, and enhanced mitochondria cytochrome c release, Caspase-3 activation, and poly(adenosine diphosphate ribose) polymerase, cleavage. Nuclear factor kappa B (NF-κB) expression was significantly decreased by DSEA, but was unaffected by EA. EA and DSEA (2.5 mg kg⁻¹) treatment of mice bearing H22 hepatocarcinoma tumours reduced the tumour weight by 49.8% and 55.0%, respectively.

Conclusion: EA and DSEA exhibit marked anti-cancer activity in HepG2 cells, by blocking cell-cycle progression and inducing Apoptosis through the mitochondrial pathway. DSEA-induced Apoptosis was more potent than EA-induced Apoptosis. Furthermore, the two triterpene glycosides derived from P. graeffei may induce Apoptosis of HepG2 cells in an NF-κB-dependent or NF-κB-independent manner, depending on their structure.