Composition of Triterpene Glycosides of the Far Eastern Sea Cucumber Cucumaria conicospermium Levin et Stepanov; Structure Elucidation of Five Minor Conicospermiumosides A3-1, A3-2, A3-3, A7-1, and A7-2; Cytotoxicity of the Glycosides Against Human Breast Cancer Cell Lines; Structure–Activity Relationships

Abstract

Five new non-holostane di- and trisulfated triterpene pentaosides, conicospermiumosides A3-1 (1), A3-2 (2), A3-3 (3), A7-1 (4), and A7-2 (5) were isolated from the Far Eastern sea cucumber Cucumaria conicospermium Levin et Stepanov (Cucumariidae, Dendrochirotida). Twelve known glycosides found earlier in other Cucumaria species were also obtained and identified. The structures of new compounds were established on the basis of extensive analysis of the 1D and 2D NMR spectra, as well as by the HR-ESI-MS data. The aglycones of 1–5 differed by side chains structures. Additionally, conicospermiumoside A7-1 (4) had a 9(11)-double bond in the aglycone, while the remaining glycosides contained a 7(8)-intranuclear double bond. Eight types of carbohydrate chains known earlier from the glycosides of the sea cucumbers of the Cucumaria genus were found as part of the glycosides of C. conicospermium. The set of sugar chains of the glycosides from C. conicospermium was similar to that from C. okhotensis. The raw biogenetic series of aglycones, leading to the formation of hexa-nor-lanostane derivatives in the process of biosynthesis and a sort of functionally-structural division that was realized due to separation of biosynthetic pathways of holostane and lanostane derivatives, can be traced when the structures of the glycosides isolated from C. conicospermium are compared. The cytotoxic action against three human breast cancer cell lines (MCF-7, T-47D, MDA-MB-231), and non-tumor MCF-10A and hemolytic activity of compounds 1–5, as well as seven known glycosides were tested. Conicospermiumosides A3-3 (3) and A7-1 (4), having a 22-oxo-23(24)-en fragment, were strongly hemolytic despite lacking a lactone in their aglycones. Moreover, both compounds demonstrated a promising suppressing action against triple negative breast cancer cells. The cells of the MDA-MB-231 line were most sensitive to the cytotoxic action of the glycosides, while the MCF-7 cell line was most sustainable. Six glycosides were selected for further study of some aspects of anticancer action against MDA-MB-231. The selective action of the compounds 4 and 8 on the MDA-MB-231 cells without significant toxicity against the MCF-10A cells was noticeable. More importantly, the selectivity of the compounds was changed over time and maximal selectivity to cancer cells was demonstrated by glycoside 1 at 48 h of exposition. The glycosides 1, 3 and the desulfated derivative 7a strongly inhibited colony formation and growth of the TNBC cells until the process stops completely. Okhotoside B1 (8), DS-okhotoside A1-1 (7a), and conicospermiumoside A3-3 (3) showed a potent cell migration-inhibiting capacity. Quantitative structure–activity relationships (QSARs) calculated on the basis of a correlational analysis of the physicochemical properties and structural features of the glycosides and their cytotoxic activity against different cell lines showed some structural features influenced differently, sometimes even in opposite ways, on the activity of glycosides toward diverse cells (erythrocytes, MCF-10A, and TNBC MDA-MB-231 cells). This observation indicated that glycosides obviously target different membrane components, such as lipids of erythrocytes and some receptors on the surface of mammary normal or tumor cells.