Therapeutic potential of flavonoid pigments: transport mechanisms in Dictyostelium discoideum

How Multidrug and Toxin Efflux (MATE) transporter proteins affect therapeutics should be considered in preclinical research and when utilising model microbes such as the amoeba Dictyostelium discoideum as a biomedical model microbe. We are investigating whether MATE transporters could help or hinder the efficacy of novel flavonoid therapies because MATEs transport flavonoid pigments within plant cells whereas equivalent proteins in bacteria are known to efflux antibiotics and precipitate antibiotic resistance. Many flavonoids, kaempferol amongst them, inhibit the growth of cancer cell lines: indeed, in our assays, kaempferol decreased Dictyostelium cell division. Our collaborators showed the flavonoid naringenin decreased growth but not development of Dictyostelium, but did not affect a pkd-null Dictyostelium (lacking polycystin-2, a divalent cation channel, mutations in which are linked with type 2 autosomal dominant polycystic kidney disease) and, notably, reduced cyst formation in mammalian kidney model cell lines. How these compounds are transported in the amoeba is not known. We identified two MATE genes in Dictyostelium. We have found that the genes are expressed at different levels and life-cycle stages, suggesting distinct, not redundant, functions. Assays of mate and pkd-transcription in flavonoid- and toxin-treated Dictyostelium cells, in vegetative and aggregation-competent cells, also revealed differential regulation of each transporter in each life stage and, in combination with cell viability assays, indicate the response to flavonoids is not due to toxicity. Using fluorescence and LCMS assays with a range of flavonoids and chemical inhibitors, we have found that there are varying rates of uptake of different flavonoid subclasses, suggestive of differential and specific transport as seen in plants. We are currently using dyes in co-localisation experiments to determine their subcellular sites of accumulation.