Vu Kiem, Blumwald Eduardo, Gelli Angie
Department of Pharmacology, School of Medicine, Genome and Biomedical Sciences Facility, University of California, Davis, Davis, CA, United States.
Department of Plant Sciences, University of California, Davis, Davis, CA, United States.
Front Microbiol. 2021 May 5;12:673035. doi: 10.3389/fmicb.2021.673035. eCollection 2021.
One path toward identifying effective and easily accessible antifungals is to repurpose commonly used drugs. Amiloride, a widely used diuretic, inhibits different isoforms of Na/H exchangers, Na channels, and Na/Ca exchangers. Here, we found that amiloride had poor antifungal activity against isolates of prompting the examination of the amiloride analog, HMA [5-(,-hexamethylene)amiloride]. HMA possesses strong activity against Na/H exchangers (NHEs) and little K-associated toxicity since HMA has only minimal inhibitory effects toward epithelial sodium channels (ENaC), the diuretic and antikaliuretic target of amiloride. Although HMA produced a robust dose-dependent growth inhibition of several fungal isolates, susceptibility assays revealed modest MICs against isolates of . A checkerboard dilution strategy resulted in fractional inhibitory concentrations (FIC) < 0.5, suggesting that HMA displays synergy with several antifungal azole drugs including posaconazole, voriconazole, and ketoconazole. Itraconazole and ravuconazole showed moderate synergy with HMA across all tested fungal isolates. In combination with HMA, ravuconazole had MICs of 0.004-0.008 μg/ml, a ∼16-fold reduction compared to MICs of ravuconazole when used alone and significantly more effective than the overall MIC (0.25 μg/ml) reported for ravuconazole against 541 clinical isolates of . In combination with azole drugs, MICs of HMA ranged from 3.2 μM (1 μg/ml) to 26 μM (16 μg/ml), HMA was not cytotoxic at concentrations ≤ 8 μg/ml, but MICs were above the reported HMA K of 0.013-2.4 μM for various Na/H exchangers. Our results suggest that HMA has limited potential as a monotherapy and may have additional targets in fungal/yeast cells since strains lacking NHEs remained sensitive to HMA. We determined that the hydrophobic substituent at the 5-amino group of HMA is likely responsible for the observed antifungal activity and synergy with several azoles since derivatives with bulky polar substitutions showed no activity against , indicating that other 5-substituted HMA derivatives could possess stronger antifungal activity. Moreover, substitution of other positions around the pyrazine core of HMA has not been investigated but could reveal new leads for antifungal drug development.
确定有效且易于获取的抗真菌药物的一条途径是重新利用常用药物。氨氯吡咪是一种广泛使用的利尿剂，可抑制钠/氢交换体、钠通道和钠/钙交换体的不同亚型。在此，我们发现氨氯吡咪对……的分离株抗真菌活性较差，这促使我们对氨氯吡咪类似物HMA [5-(,-六亚甲基)氨氯吡咪] 进行研究。HMA对钠/氢交换体（NHEs）具有强大活性，且几乎没有与钾相关的毒性，因为HMA对上皮钠通道（ENaC）的抑制作用极小，而ENaC是氨氯吡咪的利尿和抗利尿靶点。尽管HMA对几种真菌分离株产生了强大的剂量依赖性生长抑制作用，但药敏试验显示其对……分离株的最低抑菌浓度（MIC）适中。棋盘稀释策略导致部分抑菌浓度（FIC）< 0.5，这表明HMA与几种抗真菌唑类药物（包括泊沙康唑、伏立康唑和酮康唑）具有协同作用。在所有测试的真菌分离株中，伊曲康唑和雷夫康唑与HMA表现出中等程度的协同作用。与HMA联合使用时，雷夫康唑的MIC为0.004 - 0.008 μg/ml，与单独使用雷夫康唑时的MIC相比降低了约16倍，且比雷夫康唑针对541株……临床分离株报告的总体MIC（0.25 μg/ml）显著更有效。与唑类药物联合使用时，HMA的MIC范围为3.2 μM（1 μg/ml）至26 μM（16 μg/ml），HMA在浓度≤8 μg/ml时无细胞毒性，但MIC高于报道的针对各种钠/氢交换体的HMA K值0.013 - 2.4 μM。我们的结果表明，HMA作为单一疗法的潜力有限，并且在真菌/酵母细胞中可能有其他靶点，因为缺乏NHEs的菌株对HMA仍敏感。我们确定HMA 5-氨基处的疏水取代基可能是观察到的抗真菌活性以及与几种唑类药物协同作用的原因，因为具有大体积极性取代的衍生物对……无活性，这表明其他5-取代的HMA衍生物可能具有更强的抗真菌活性。此外，尚未研究HMA吡嗪核心周围其他位置的取代情况，但这可能会揭示抗真菌药物开发的新线索。
