Diterpenes from Euphorbia mellifera Ait – Search for multidrug resistance modulators in cancer cells

MDR is known to be the major cause of chemotherapy failure. The primary mechanism of multidrug resistance is the overexpression of P-glycoprotein (Pgp), a transport membrane protein which acts as an ATP dependent efflux pump, thereby reducing the intracellular accumulation of anticancer drugs [1]. Despite the decades of efforts, the discovery of a potent, specific, clinically useful MDR inhibitor is yet to be achieved. Euphorbia species (Euphorbiaceae) have been found to synthesize compounds with in vitro Pgp mediated MDR inhibiting activity [2].

The EtOAc soluble part (44g) of the methanol extract of the air-dried aerial parts of Euphorbia mellifera was fractionated by column chromatography and purified by TLC and HPLC to yield five macrocyclic diterpenes with the jathrophane skeleton. Their structures were established on the basis of spectroscopic methods, including 2D NMR experiments (COSY, HMQC, HMBC and NOESY). The reversal of Pgp mediated MDR was evaluated by flow cytometric determination of intracellular accumulation of rhodamine 123 in L5178 Y mouse T-lymphoma cells transfected with pHa MDR1/A, using verapamil as the positive control. All the isolated diterpenes were shown to enhance drug retention (FAR values: 36.1–90.1at 40µg/mL) in the cells by inhibiting the efflux-pump activity, mediated by P-glycoprotein.

Acknowledgements: This work was partially supported by FCT (Fundação para a Ciência e a Tecnologia).

References: 1. Teodori, E. et al. (2007) Current Drug Targets 7:893–909.

2. Duarte, N. et al. (2007) Bioorg. Med. Chem. 15:546–554.