CHARACTERIZATION OF ECHINOCARDIN-RESISTANT MUTANTS OF CANDIDA-ALBICANS - GENETIC, BIOCHEMICAL, AND VIRULENCE STUDIES

The pneumocandins are potent antifungal agents of the echinocandin cla ss which are under development for use as broad-spectrum antimycotic t herapy, One important consideration for and ne-cu therapeutic class fo r treating serious fungal infections is the potential for drug resista nce development, Hn this study we have isolated and characterized four independent spontaneous Candida albicans mutants resistant to the pot ent semisynthetic pneumocandin L-733,560. These mutants have many of t he properties of FKS1/ETG1 echinocandin-resistant mutants of Saccharom yces cerevisiae, including (i) cross-resistance to other 1,3-beta-D-gl ucan synthase inhibitors, such as papulacandin and echinocandins, but no change in sensitivity to other antifungal agents; (ii) in vitro glu can synthase activity that is more resistant to pneumocandins than the wild-type parent enzyme; and (iii) semidominant drug resistance in sp heroplast fusion strains. The mutants were compared with C. albicans e chinocandin-resistant mutants isolated by mutagenesis by L. Beckford a nd D. Kerridge (mutant M-2) (abstr. PS3.11, in Proceedings of the XI C ongress of the International Society for Human and Animal Mycology, Mo ntreal, Canada, 1992) and by A. Cassone, R. E. Mason, and D. Kerridge (mutant CA-2) (Sabouraudia 19:97-110, 1981). All of the strains had re sistant enzyme activity in vitro. M-2 grew poorly and had low levels o f enzyme activity, In contrast, CA-2 and the spontaneous mutants grew as well as the parents and had normal levels of glucan synthase activi ty. These results suggest that these resistant mutants may have altera tions is glucan synthase. Ca-2 was unable to form germ tubes, an abili ty retained by the spontaneous mutants, Tile virulence of the spontane ous mutants was unimpaired in a mouse model of disseminated candidiasi s, while M-2 and CA-2 were 2 orders of magnitude less virulent than th eir parent strains. Significantly, mice challenged with the spontaneou s mutant CAI4R1 responded therapeutically to lower levels of L-733,560 than would be predicted by the increase in in vitro susceptibility.