Efficacy of APX2039 in a Rabbit Model of Cryptococcal Meningitis

Cryptococcal Meningitis (CM) is uniformly fatal if not treated, and treatment options are limited. We previously reported on the activity of APX2096, the prodrug of the novel Gwt1 inhibitor APX2039, in a mouse model of CM. Here, we investigated the efficacy of APX2039 in mouse and rabbit models of CM. In the mouse model, the controls had a mean lung fungal burden of 5.95 log₁₀ CFU/g, whereas those in the fluconazole-, amphotericin B-, and APX2039-treated mice were 3.56, 4.59, and 1.50 log₁₀ CFU/g, respectively. In the brain, the control mean fungal burden was 7.97 log₁₀ CFU/g, while the burdens were 4.64, 7.16, and 1.44 log₁₀ CFU/g for treatment with fluconazole, amphotericin B, and APX2039, respectively. In the rabbit model of CM, the oral administration of APX2039 at 50 mg/kg of body weight twice a day (BID) resulted in a rapid decrease in the cerebrospinal fluid (CSF) fungal burden, and the burden was below the limit of detection by day 10 postinfection. The effective fungicidal activity (EFA) was -0.66 log₁₀ CFU/mL/day, decreasing from an average of 4.75 log₁₀ CFU/mL to 0 CFU/mL, over 8 days of therapy, comparing favorably with good clinical outcomes in humans associated with reductions of the CSF fungal burden of -0.4 log₁₀ CFU/mL/day, and, remarkably, 2-fold the EFA of amphotericin B deoxycholate in this model (-0.33 log₁₀ CFU/mL/day). A total drug exposure of the area under the concentration-time curve from 0 to 24 h (AUC_0-24) of 25 to 50 mg · h/L of APX2039 resulted in near-maximal antifungal activity. These data support the further preclinical and clinical evaluation of APX2039 as a new oral fungicidal monotherapy for the treatment of CM. IMPORTANCE Cryptococcal meningitis (CM) is a fungal disease with significant global morbidity and mortality. The gepix Gwt1 inhibitors are a new class of antifungal drugs. Here, we demonstrated the efficacy of APX2039, the second member of the gepix class, in rabbit and mouse models of cryptococcal meningitis. We also analyzed the drug levels in the blood and cerebrospinal fluid in the highly predictive rabbit model and built a mathematical model to describe the behavior of the drug with respect to the elimination of the fungal pathogen. We demonstrated that the oral administration of APX2039 resulted in a rapid decrease in the CSF fungal burden, with an effective fungicidal activity of -0.66 log₁₀ CFU/mL/day, comparing favorably with good clinical outcomes in humans associated with reductions of -0.4 log₁₀ CFU/mL/day. The drug APX2039 had good penetration of the central nervous system and is an excellent candidate for future clinical testing in humans for the treatment of CM.