Estrogen Receptor Antagonists Are Anti-Cryptococcal Agents That Directly Bind EF Hand Proteins and Synergize with Fluconazole In Vivo

Butts, A. and Koselny, K. and Chabrier-Rosello, Y. and Semighini, C. P. and Brown, J. C. S. and Wang, X. and Annadurai, S. and DiDone, L. and Tabroff, J. and Childers, W. E. and Abou-Gharbia, M. and Wellington, M. and Cardenas, M. E. and Madhani, H. D. and Heitman, J. and Krysan, D. J. (2014) Estrogen Receptor Antagonists Are Anti-Cryptococcal Agents That Directly Bind EF Hand Proteins and Synergize with Fluconazole In Vivo. mBio, 5 (1). e00765-13. ISSN 2150-7511

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Cryptococcosis is an infectious disease of global significance for which new therapies are needed. Repurposing previously developed drugs for new indications can expedite the translation of new therapies from bench to beside. Here, we characterized the anti-cryptococcal activity and antifungal mechanism of estrogen receptor antagonists related to the breast cancer drugs tamoxifen and toremifene. Tamoxifen and toremifene are fungicidal and synergize with fluconazole and amphotericin B in vitro. In a mouse model of disseminated cryptococcosis, tamoxifen at concentrations achievable in humans combines with fluconazole to decrease brain burden by ~1 log10. In addition, these drugs inhibit the growth of Cryptococcus neoformans within macrophages, a niche not accessible by current antifungal drugs. Toremifene and tamoxifen directly bind to the essential EF hand protein calmodulin, as determined by thermal shift assays with purified C. neoformans calmodulin (Cam1), prevent Cam1 from binding to its well-characterized substrate calcineurin (Cna1), and block Cna1 activation. In whole cells, toremifene and tamoxifen block the calcineurin-dependent nuclear localization of the transcription factor Crz1. A large-scale chemical genetic screen with a library of C. neoformans deletion mutants identified a second EF hand-containing protein, which we have named calmodulin-like protein 1 (CNAG_05655), as a potential target, and further analysis showed that toremifene directly binds Cml1 and modulates its ability to bind and activate Cna1. Importantly, tamoxifen analogs (idoxifene and methylene-idoxifene) with increased calmodulin antagonism display improved anti-cryptococcal activity, indicating that calmodulin inhibition can be used to guide a systematic optimization of the anti-cryptococcal activity of the triphenylethylene scaffold.

Item Type: Article
Subjects: Pharmaceutical Sciences
Divisions: College of Pharmacy > Pharmaceutical Sciences
Depositing User: Dr Sivakumar Annadurai
Date Deposited: 15 May 2017 14:15
Last Modified: 15 May 2017 14:15

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