Triazole antifungals function as ergosterol biosynthesis inhibitors and are frontline therapy for invasive fungal infections, such as invasive aspergillosis. The primary mechanism of action of triazoles is through the specific inhibition of a cytochrome P450 14-α-sterol demethylase enzyme, Cyp51A/B, resulting in depletion of cellular ergosterol. Here, we uncover a clinically relevant secondary mechanism of action for triazoles within the ergosterol biosynthesis pathway. We provide evidence that triazole-mediated inhibition of Cyp51A/B activity generates sterol intermediate perturbations that are likely decoded by the sterol sensing functions of HMG-CoA reductase and Insulin-Induced Gene orthologs as increased pathway activity. This, in turn, results in negative feedback regulation of HMG-CoA reductase, the rate-limiting step of sterol biosynthesis. We also provide evidence that HMG-CoA reductase sterol sensing domain mutations previously identified as generating resistance in clinical isolates of Aspergillus fumigatus partially disrupt this triazole-induced feedback. Therefore, our data point to a secondary mechanism of action for the triazoles: induction of HMG-CoA reductase negative feedback for downregulation of ergosterol biosynthesis pathway activity. Abrogation of this feedback through acquired mutations in the HMG-CoA reductase sterol sensing domain diminishes triazole antifungal activity against fungal pathogens and underpins HMG-CoA reductase-mediated resistance.

三唑类抗真菌药作为麦角甾醇生物合成抑制剂，是侵袭性真菌感染（例如侵袭性曲霉菌病）的一线治疗方法。三唑类药物的主要作用机制是通过特异性抑制细胞色素 P450 14-α-甾醇脱甲基酶 Cyp51A/B，导致细胞麦角甾醇消耗。在这里，我们揭示了三唑类在麦角甾醇生物合成途径中临床相关的二级作用机制。我们提供的证据表明，三唑介导的 Cyp51A/B 活性抑制会产生甾醇中间扰动，这些扰动很可能通过 HMG-CoA 还原酶和胰岛素诱导基因直向同源物的甾醇传感功能解码为途径活性增加。这反过来又导致 HMG-CoA 还原酶（甾醇生物合成的限速步骤）的负反馈调节。我们还提供了证据，证明之前确定的 HMG-CoA 还原酶甾醇感应结构域突变会在烟曲霉临床分离株中产生抗性，部分破坏了这种三唑诱导的反馈。因此，我们的数据指出了三唑类的次要作用机制：诱导 HMG-CoA 还原酶负反馈，从而下调麦角甾醇生物合成途径活性。通过 HMG-CoA 还原酶甾醇感应结构域的获得性突变消除这种反馈会降低三唑针对真菌病原体的抗真菌活性，并增强 HMG-CoA 还原酶介导的耐药性。