IN VITRO INTERACTION BETWEEN ANTIFUNGAL DRUGS AND PHYTOLACCA TETRAMERA FRUIT?S EXTRACTS

BUTASSI, E.; SVETAZ, L.; RAIMONDI, M.; ZACCHINO, S.

Simposio; VIII Simpósio Ibero-americano de Plantas Medicinais e III Simpósio Ibero-americano de Investigação em Cancer.; 2016

Universidade do Vale do Itajaí

Introduction: Combination of an antifungal drug with a plant extract has emerged as an approach to achieve an antifungal effect with lower quantities of the drug, also lowering its toxic side effects. Phytolacca tetramera H. (Phytolaccaceae) fruits? extracts (PhyE) have previously shown antifungal activity against Candida spp.1 and its major antifungal component phytolaccoside B has shown to act by thickening the fungal cell-wall.2 Since the wall is absent in mammalian cells, this target represents an ideal mode of action of antifungal agents. Objectives: To prepare combinations of PhyE (quantified in their marker compounds) with an azole [posaconazole (Pos)] or a polyene [amphotericin B (AmB)] that attack two different fungal targets, the membrane (Pos and AmB) and the fungal cell-wall (PhyE) and to evaluate their interactions. Material and Methods: The Minimum Inhibitory Concentration (MIC) of each the PhyE and the antifungal drug was obtained with the microbroth dilution assay (M-27A3) of Clinical and Laboratory Standards Institute against Candida albicans and C. glabrata. To evaluate the interactions, the checkerboard method was used and the Fractional Inhibitory Concentration Index (FICI) was calculated. Interpretation: synergism: FICI ≤ 0.5; indifference, >0.50 - 4; and; antagonism:  4. Dose Reduction Index (DRI) was also calculated. Results and Discussion: PhyE potentiated the activity of AmB by decreasing 32-fold the MIC of AmB (0.5 to 0.015 µg/mL) and showed only additivism (FICI=0.53). In turn, PhyE potentiated 32 to 64?fold the MIC of Pos, also showing a clear synergistic effect with FICIs as low as 0.19. Conclusions: Combinations of PhyE with AmB or Pos, showed high DRIs. Also Pos interacted synergistically with all PhyE. Since each partner has a different mode of action, these results open the avenue to develop a new bi-targeted antifungal drug, with the possibility of adding the safe cell-wall target to the already known fungal cell membrane target.