In Vitro Interactions between Tacrolimus and Azoles against Candida albicans Determined by Different Methods

Abstract

Combination therapy could be of use for the treatment of fungal infections, especially those caused by drug-resistant fungi. However, the methods and approaches used for data generation and result interpretation need further optimizing. The fractional inhibitory concentration index (FICI) is the most commonly used method, but it has several drawbacks in characterizing antifungal drug interaction. Alternatively, some new methods can be used such as the ⌬E model (difference between the predicted and measured fungal growth percentages) and the response surface approach, which uses the concentration-effect relationship over the whole concentration range instead of just the MIC. In the present study, in vitro interactions between tacrolimus (FK506) and three azoles-fluconazole (FLC), itraconazole (ITR), and voriconazole (VRC)-against Candida albicans were evaluated by the checkerboard microdilution method and time-killing test. The intensity of the interactions was determined by visual reading and the spectrophotometric method in a checkerboard assay, and the nature of the interactions was assessed by nonparametric models of FICI and ⌬E. Colony counting and colorimetric viable detection methods (2,3-bis {2-methoxy-4-nitro-5-[(sulfenylamino) carbonyl]-2H-tetrazolium hydroxide} [XTT] reduction test)were used for evaluating the combination antifungal effects over time. Synergistic and indifferent effects were found for the combination of FK506 and azoles against azole-sensitive strains, while strong synergy was found against azole-resistant strains analyzed by FICI. The ⌬E model gave more consistent results with FICI. The positive interactions were also confirmed by the time-killing test. Our findings suggest a potential role for combination therapy with calcineurin pathway inhibitors and azoles to augment activity against resistant C. albicans.

Components of the Calcium-Calcineurin Signaling Pathway in Fungal Cells and Their Potential as Antifungal Targets

“…Therefore, the authors screened approximately 800 methanol extracts from natural resources for compounds that could restore the growth inhibition of ubiquitin deletion mutant strains following high-temperature treatment and found that some diterpenoid compounds inhibited calcineurin, while their specific antifungal activities and mechanisms require further research. The calcineurin inhibitors FK506 and CsA not only showed antifungal effects when used alone, their combination with antifungal drugs like fluconazole, posaconazole, and itraconazole has also been proposed to treat calcineurin-mediated azole resistance due to their synergistic antifungal effects (115)(116)(117)(118).…”

Mechanism of Action of Tetrandrine, a Natural Inhibitor of <i>Candida albicans</i> Drug Efflux Pumps

“…15 24) Drugs such as tacrolimus 22) and cyclosporine 18,19) can reverse CDR-mediated C. albicans FLC and ketoconazole resistance in vitro by inhibiting Cdr1p and Cdr2p, but because these drugs have signiˆcant cardio-and nephrotoxicity, their clinical applicability is low. Tetrandrine (TET) is a low-toxicity drug extracted from the plant Stephania tetrandra S. Moore (or Fenfangji) of the Menispermaceae family.…”

ABC Transporter Cdr1p Contributes More than Cdr2p Does to Fluconazole Efflux in Fluconazole-Resistant Candida albicans Clinical Isolates

“…Known chemosensitizers include drugs already in therapeutic use for other conditions. FK506, for example, used in cancer chemotherapy as an immunosuppressant, may act both directly (since overexpression of Cdr1p significantly reduces susceptibility to FK506) (30,42) and indirectly (by effects on the calcineurin pathway) (2,12,46,47,49) to reverse resistance to FLC in fungi. Ibuprofen is a potent anti-inflammatory and analgesic drug, which at low concentrations inhibits azole efflux from C. albicans, and has been proposed for combination treatment of fungal infections with FLC (36).…”