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Interaction of crown ethers with the ABCG2 transporter and their implication for multidrug resistance reversal

Abstract

Overexpression of ABC transporters, such as ABCB1 and ABCG2, plays an important role in mediating multidrug resistance (MDR) in cancer. This feature is also attributed to a subpopulation of cancer stem cells (CSCs), having enhanced tumourigenic potential. ABCG2 is specifically associated with the CSC phenotype, making it a valuable target for eliminating aggressive and resistant cells. Several natural and synthetic ionophores have been discovered as CSC-selective drugs that may also have MDR-reversing ability, whereas their interaction with ABCG2 has not yet been explored. We previously reported the biological activities, including ABCB1 inhibition, of a group of adamantane-substituted diaza-18-crown-6 (DAC) compounds that possess ionophore capabilities. In this study, we investigated the mechanism of ABCG2-inhibitory activity of DAC compounds and the natural ionophores salinomycin, monensin and nigericin. We used a series of functional assays, including real-time microscopic analysis of ABCG2-mediated fluorescent substrate transport in cells, and docking studies to provide comparative aspects for the transporter–compound interactions and their role in restoring chemosensitivity. We found that natural ionophores did not inhibit ABCG2, suggesting that their CSC selectivity is likely mediated by other mechanisms. In contrast, DACs with amide linkage in the side arms demonstrated noteworthy ABCG2-inhibitory activity, with DAC-3Amide proving to be the most potent. This compound induced conformational changes of the transporter and likely binds to both Cavity 1 and the NBD–TMD interface. DAC-3Amide reversed ABCG2-mediated MDR in model cells, without affecting ABCG2 expression or localization. These results pave the way for the development of new crown ether compounds with improved ABCG2-inhibitory properties.

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All data generated or analysed during this study are included in this published article (and its supplementary information files).

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Acknowledgements

This work was financed by Croatian Science Foundation project number IP-2013-5660 (“MultiCaST”) to MK. The work was also supported by the FP7-REGPOT-2012-2013-1 project, grant agreement number 316289–InnoMol. MM received a financial support from the Ruđer Bošković Institute for a short-term secondment to the ELKH Research Centre for Natural Sciences, Budapest. We sincerely thank Lucija Horvat for wonderful assistance with confocal microscopy, Dr Marijana Popović Hadžija and Lucija Lulić for invaluable experimental help. TŠ is thankful to Prof. K. Majerski for her support and introduction to the field of crown ethers.

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Correspondence to Marijeta Kralj.

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Mioč, M., Telbisz, Á., Radman, K. et al. Interaction of crown ethers with the ABCG2 transporter and their implication for multidrug resistance reversal. Histochem Cell Biol (2022). https://doi.org/10.1007/s00418-022-02106-z

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  • DOI: https://doi.org/10.1007/s00418-022-02106-z

Keywords

  • ATP-binding cassette (ABC) transporters
  • ABCG2
  • Crown ethers
  • Ionophores
  • Multidrug resistance
  • In vitro functional studies