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Present study investigated the possible role of P-glycoprotein in the intracellular exposure of active substance (robinin) of natural medicine Flaroninum™ and effect of robinin on the cellular accumulation of mitoxantrone in either BCRP-overexpressing and BCRP-negative cells.Robinin -kaempferol-3-O--D-robinoside-7-O-α-L-rhamnopyranoside, has been obtained from over ground parts of Astragalus falcatus Lam., growing in Georgia. The compound possesses hypoazotemic and diuretic activities and is proposed for the complex therapy of kidney diseases. Pgp-overexpressing and P-gp-negative human breast cancer cells (MCF7) were used to examine the absorption character of kaempferol and robinin with or without of verapamil (P-gp inhibitor).Flavonoids concentrations were determined by LC/MS/MS. Robinin transport was P-gp-dependent and verapamil significantly increased the extent of uptake of robinin in cells, which is attributed in part to P-gp-inhibition by verapamil. When comparing the intracellular accumulation of aglycone with kaempferol-3-O--D-robinoside-7-O-α-L-rhamnopyranoside, we found that kaempferol uptake was greater than robinin. Since some glycosylated forms of flavonoids have been demonstrated to significantly suppress breast cancer resistance protein (BCRP/ABCG2), we hypothesized that kaempferol-3-O--D-robinoside-7-O-α-L-rhamnopyranoside may act as a BCRP-inhibitor. Mitoxantrone accumulation studies were performed in BCRP-overexpressing and BCRP-negative MCF7 cells using flow cytometric analysis. Robinin (5 and 50 M) had no significant impacts on the BCRP-mediated mitoxantrone transport; on the contrary, the aglycone kaempferol produced increased accumulation of mitoxantrone. From these results, we suggest that the active component of natural hypoazotemic medicine Flaroninum™, robinin, may be a substrate of P-gp and its efflux outside of the cells mediated P-gp may contribute to its decreased intracellular concentration.

Structures of isolated compounds were established on the basis of their physical, chemical and physical-chemical properties, by studying of products of chemical transformation and by spectral (1 H and 13 C NMR, HSQC, HMBC, COSY, DEPT, mass-spectroscopy) data. The new individual compounds displayed interesting biological effect to be promising from medical application standpoint.

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