Objectives: T-2307, a novel arylamidine, exhibits potent broad-spectrum activities against pathogenic fungi, particularly Candida albicans. We previously reported that T-2307 uptake was mainly mediated by a saturable high-affinity carrier at the MIC for C. albicans. Since we hypothesized that the potent anticandidal activity arose from accumulation via the high-affinity carrier, we characterized the specificity and kinetic features of the carrier.
Methods: The MICs of T-2307 for C. albicans strains were evaluated in the presence and absence of potential competitive substrates. The cells were exposed to [(14)C]T-2307, [(14)C]spermine or [(14)C]spermidine in the presence of unlabelled T-2307, pentamidine, propamidine, or competitive substrates if necessary, and the radioactivity in the cells was measured. C. albicans gene deletion was performed using a one-step PCR-based technique.
Results: Coapplication with exogenous spermine or spermidine decreased the antifungal activity and uptake of T-2307 in C. albicans strains. T-2307 competitively inhibited spermine and spermidine uptake with inhibition constants similar to its Km for the high-affinity carrier. The comparison of MICs and kinetic values between T-2307 and other diamidine compounds suggested that the different antifungal properties could be partially attributable to the variations in their affinity with the carrier. Studies of gene deletion mutants revealed that T-2307 was transported into C. albicans by a high-affinity spermine and spermidine carrier regulated by Agp2.
Conclusions: Uptake of T-2307 via the high-affinity spermine and spermidine carrier regulated by Agp2 could contribute to its potent antifungal activity. Further investigation is required to identify the high-affinity carrier for potential targeting with novel therapies.
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