Puupehenone, a marine sponge-derived sesquiterpene quinone, potentiates the antifungal drug Caspofungin by disrupting Hsp90 activity and the cell wall integrity pathway

Authors: TRIPATHI, SIDDHARTH - University Of Mississippi; FENG, QIN - University Of Mississippi; LIU, LI - Boston University; LEVIN, DAVID - Boston University; ROY, KULDEEP - University Of Mississippi; DOERKSEN, ROBERT - University Of Mississippi; Baerson, Scott; SHI, XIAOMIN - Baylor College Of Medicine; PAN, XUEWEN - Baylor College Of Medicine; XU, WEN-HUI - University Of Mississippi; LI, XING-CONG - University Of Mississippi; CLARK, ALICE - University Of Mississippi; AGARWAL, AMEETA - University Of Mississippi

Submitted to: mSphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2019
Publication Date: 1/8/2020
Citation: Tripathi, S.K., Feng, Q., Liu, L., Levin, D.E., Roy, K.K., Doerksen, R.J., Baerson, S.R., Shi, X., Pan, X., Xu, W., Li, X., Clark, A.M., Agarwal, A.K. 2020. Puupehenone, a marine sponge-derived sesquiterpene quinone, potentiates the antifungal drug Caspofungin by disrupting Hsp90 activity and the cell wall integrity pathway. mSphere. 5(1):e00818-19. https://doi.org/10.1128/mSphere.00818-19.
DOI: https://doi.org/10.1128/mSphere.00818-19

Interpretive Summary: Caspofungin is a potent and safe drug that is used to treat fungal infections. It inhibits the biosynthesis of cell walls in fungal species, and because human cells lack a cell wall, this drug has fewer toxic side effects. However, due to its extensive use, caspofungin has become less effective against certain fungal species because these organisms have developed resistance to the drug. In these organisms, a specialized pathway called the cell wall integrity pathway (CWI) is highly induced, which helps the organisms to overcome the inhibitory effect of caspofungin. In this work, a marine-derived natural product named puupehenone (PUUP) was found to work as a ‘potentiator’ of caspofungin, causing caspofungin to become effective against the resistant fungal organisms. PUUP was found to prevent the induction of the CWI pathway. Specifically, PUUP interacts with a complex of two proteins, Hsp90 and Cdc37, and prevents them from binding to each other. The binding of these proteins is important for CWI pathway function, and by inhibiting the CWI pathway in this manner, PUUP improves the effectiveness of drugs such as caspofungin.

Technical Abstract: The cell wall-targeting echinocandin antifungals, although potent and well-tolerated, are inadequate in treating fungal infections due to their narrow spectrum of activity and their propensity to induce pathogen resistance. A promising strategy to overcome these drawbacks is to combine echinocandins with a molecule that improves their activity and also disrupts drug adaptation pathways. In this study, we show that puupehenone (PUUP), a marine sponge-derived sesquiterpene quinone potentiates the echinocandin drug, caspofungin (CAS) in CAS-resistant fungal pathogens. We have conducted Ribonucleic Acid Sequencing (RNA-Seq) analysis, followed by genetic and molecular studies, to elucidate PUUP’s CAS-potentiating mechanism. We found that the combination of CAS and PUUP blocked the induction of CAS-responding genes required for the adaptation to cell wall stress through the cell wall integrity (CWI) pathway. Further analysis showed that PUUP inhibited the activation of Slt2 (Mpk1), the terminal mitogen-activated protein (MAP) kinase in this pathway. We also found that PUUP induced heat shock response genes and inhibited the activity of heat shock protein 90 (Hsp90). Molecular docking studies predicted that PUUP occupies a binding site on Hsp90 required for the interaction between Hsp90 and its co-chaperone Cdc37. Thus, we show that PUUP potentiates CAS activity by a previously undescribed mechanism which involves disruption of Hsp90 activity and the CWI pathway. Given the requirement of the Hsp90-Cdc37 complex in Slt2 activation, we suggest that inhibitors of this complex would disrupt the CWI pathway and synergize with echinocandins. Therefore, the identification of PUUP’s CAS-potentiating mechanism has important implications in the development of new antifungal combination therapies.