Objectives: Invasive aspergillosis is a devastating disease in immunocompromised patients. It mostly affects patients with hematological malignancies, especially those with severe and prolonged neutropenia, but is also encountered in solid organ transplant recipients. Immunosuppressive agents are used as anti-rejection drugs in organ transplant patients, but besides their immunosuppressive activity, these drugs also possess intrinsic antifungal activity. The aim of the present study was to assess the in vitro interaction of the broad-spectrum azole isavuconazole with the calcineurin inhibitors (e.g. tacrolimus or cyclosporin A) or the mTOR pathway inhibitor (e.g. sirolimus) against the most important Aspergillus species responsible for human disease.
Methods: A panel of 30 Aspergillus isolates belonging to 5 species responsible for human invasive aspergillosis was used for the experiments (10 Aspergillus fumigatus, 5 Aspergillus flavus, 5 Aspergillus terreus, 5 Aspergillus nidulans, and 5 Aspergillus niger). Combinations of isavuconazole with cyclosporine A, tacrolimus or sirolimus were tested by a broth microdilution checkerboard technique based on the EUCAST reference methodology. Plates were read spectrophotometrically, and 90% of inhibition was used as an endpoint for both, the drugs alone and in combination. Results were interpreted with the fractional inhibitory concentration index (FICI). Drug interactions were defined as synergistic (FICI≤0.5), indifferent (FICI>0.5≤4) or antagonistic (FICI>4).
Results: Isavuconazole MICs ranged from 0.25 to 16 µg/ml. When tested alone, immunosuppressive drugs showed poor activity with MICs < 16 µg/ml for only 2, and 3 isolates for tacrolimus and cyclosporin A, respectively. Combinations of isavuconazole with tacrolimus, cyclosporine A or sirolimus were synergistic for 53, 20, and 10% of the tested isolates, respectively. There were some differences between species (Table). Antagonism was never seen.
Conclusion: Calcineurin is a key enzyme in the calcium-dependent signal transduction pathways of eukaryotes. Antifungal drug resistance and virulence of several pathogenic fungi, including Aspergillus species, is regulated by this pathway. Results of the present study showed synergistic interactions between isavuconazole and tacrolimus and underline the role of the calcineurin pathway as a target for the development of new antifungal drugs.
Full conference title:
- TIMM (2019)