Change in Expression of Genes Involved in the G-Protein Signaling Pathway (GP-SP) is Associated with Voriconazole-Resistance (VCZ-R) in Aspergillus Species

Background: Invasive infections due to Aspergillus species continue to be associated with a significant morbidity in immuno-compromised patients. Despite the availability of several azoles [isavuconazole (ISZ), posaconazole (POS), voriconazole (VCZ) and itraconazole (ITZ)], mortality remains high. Studies from various cancer and transplant centers around the world have reported the emergence of azole-resistance in clinical and environmental isolates of Aspergillus fumigatus and Aspergillus flavus. The major mechanism of high-level azole- resistance in Aspergillus species reported so far is mutation and/or overexpression of target site namely cyp51A, that encodes lanosterol demethylase of the fungal cell wall. However, some azole-resistant isolates have not exhibited either of these mechanisms, suggesting other novel non-cyp51 related mechanisms of triazole- resistance.

Aim: To evaluate the possible role of G-protein signaling pathway genes in VCZ-R in Aspergillus species.

Materials and Methods: CLSI based susceptibility, and cyp51 gene-specific PCR experiments were performed on wild type and specific mutant strains of Aspergillus species to analyse the phenotypic alterations and changes in triazole-susceptibility pattern in Aspergillus species.

Results: Voriconazole inhibits conidiation in A. flavus, possibly through its effect on several genes involved in the GP-SP. Mutations or changes in expression of these genes contribute to VCZ-R in A. flavus. Loss of conidiation and pigmentation with switch to pure vegetative growth, exclusively by hyphal elongation, is associated with VCZ-R in A. flavus.

Conclusion: Our results suggest that VCZ inhibits conidiation by targeting one of the critical genes in the G-protein pathway and specific alterations in these genes likely lead to loss of conidiation and VCZ-R in A. flavus. Cross resistance to other triazoles including POS and ISZ need to be tested as well. Based on our data we propose to continue our studies on G-protein pathway genes involved in antifungal drug resistance in Aspergillus species. This pathway needs to be further explored not only for its possible contribution to VCZ-R but also to delineate its role in pathogenesis and also as a potential antifungal drug target.