Reversal of ABCG2/BCRP-Mediated Multidrug Resistance by 5,3',5'-Trihydroxy-3,6,7,4'-Tetramethoxyflavone Isolated from the Australian Desert Plant Eremophila galeata Chinnock.

Malene J Petersen,Bevan Buirchell,Dan Staerk,Kenneth T Kongstad,Michael Gajhede,Xamuel L Lund,Susan J Semple,Jan Stenvang,Henrik Franzyk

doi:10.3390/biom11101534

Abstract

Multidrug resistance (MDR) is a major challenge in cancer treatment, and the breast cancer resistance protein (BCRP) is an important target in the search for new MDR-reversing drugs. With the aim of discovering new potential BCRP inhibitors, the crude extract of leaves of Eremophila galeata, a plant endemic to Australia, was investigated for inhibitory activity of parental (HT29par) as well as BCRP-overexpressing HT29 colon cancer cells resistant to the chemotherapeutic SN-38 (i.e., HT29SN38 cells). This identified a fraction, eluted with 40% acetonitrile on a solid-phase extraction column, which showed weak growth-inhibitory activity on HT29SN38 cells when administered alone, but exhibited concentration-dependent growth inhibition when administered in combination with SN-38. The major constituent in this fraction was isolated and found to be 5,3′,5′-trihydroxy-3,6,7,4′-tetramethoxyflavone (2), which at a concentration of 25 μg/mL potentiated the growth-inhibitory activity of SN-38 to a degree comparable to that of the known BCRP inhibitor Ko143 at 1 μM. A dye accumulation experiment suggested that 2 inhibits BCRP, and docking studies showed that 2 binds to the same BCRP site as SN-38. These results indicate that 2 acts synergistically with SN-38, with 2 being a BCRP efflux pump inhibitor while SN-38 inhibits topoisomerase-1.

Highlights

Multidrug resistance (MDR) remains a major challenge in the treatment of patients suffering from different types of cancer
The assay was performed with a parental HT29 colon cancer cell line (HT29par ) and a HT29 colon cancer cell line made resistant to SN-38 (HT29SN38 ), of which the latter has previously been shown to be upregulated in the ABCG2 gene and to be overexpressing ABCG2/breast cancer resistance protein (BCRP) [22]
We have shown that solid phase extraction (SPE) fractions of a crude extract of E. galeata were able to increase the effect of SN-38 on HT29SN38 cells, and for the fraction eluted with

Summary

Introduction

Multidrug resistance (MDR) remains a major challenge in the treatment of patients suffering from different types of cancer. MDR is defined as resistance of cancer cells to structurally unrelated classes of chemotherapeutic drugs, and can manifest itself through various mechanisms. Reported mechanisms that appear to contribute to cancer MDR comprise, among others, the induction of apoptosis, hypoxia, autophagy, drug efflux, epigenetic regulation, and DNA damage/repair [1]. MDR can either be acquired during treatment or be pre-existing at the time of diagnosis, and it is a major cause of treatment failure in cancer patients [2], raising the need for drugs capable of reversing the resistance. Plasma membrane-bound transporters are highly involved in the uptake and/or efflux of chemotherapeutic drugs, and efflux pumps are very often associated with the development of MDR [3]. ABC transporters known to contribute to MDR

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