In Vitro and In Vivo Evaluation of APX001A/APX001 and Other Gwt1 Inhibitors against Cryptococcus

Cryptococcal meningitis (CM), caused primarily by Cryptococcus neoformans, is uniformly fatal if not treated. Treatment options are limited, especially in resource-poor geographical regions, and mortality rates remain high despite current therapies. Here we evaluated the in vitro and in vivo activity of several compounds, including APX001A and its prodrug, APX001, currently in clinical development for the treatment of invasive fungal infections. These compounds target the conserved Gwt1 enzyme that is required for the localization of glycosylphosphatidylinositol (GPI)-anchored cell wall mannoproteins in fungi. The Gwt1 inhibitors had low MIC values, ranging from 0.004 μg/ml to 0.5 μg/ml, against both C. neoformans and C. gattii. APX001A and APX2020 demonstrated in vitro synergy with fluconazole (fractional inhibitory concentration index, 0.37 for both). In a CM model, APX001 and fluconazole each alone reduced the fungal burden in brain tissue (0.78 and 1.04 log(10) CFU/g, respectively), whereas the combination resulted in a reduction of 3.52 log(10) CFU/g brain tissue. Efficacy, as measured by a reduction in the brain and lung tissue fungal burden, was also observed for another Gwt1 inhibitor prodrug, APX2096, where dose-dependent reductions in the fungal burden ranged from 5.91 to 1.79 log(10) CFU/g lung tissue and from 7.00 and 0.92 log(10) CFU/g brain tissue, representing the nearly complete or complete sterilization of lung and brain tissue at the higher doses. These data support the further clinical evaluation of this new class of antifungal agents for the treatment of CM.