Safety and pharmacokinetics of antifungal agent VT-1598 and its primary metabolite, VT-11134, in healthy adult subjects: phase 1, first-in-human, randomized, double-blind, placebo-controlled study of single-ascending oral doses of VT-1598.

VT-1598 is a novel fungal CYP51 inhibitor and 1-tetrazole-based antifungal drug candidate with improved selectivity minimizing off-target binding to and inhibition of human CYP450 enzymes. Data are presented from this first clinical study in the evaluation of the safety and pharmacokinetic (PK) of single ascending doses of 40, 80, 160, 320, and 640 mg VT-1598, comprising a 160 mg cohort in both fasting and fed states. Eight healthy adults per dose were randomized to receive either oral VT-1598 or placebo (3:1). Over the dose range, exposures were with relatively high variation. The maximum plasma concentrations (Cmax) for VT-1598 were 31.00-279.4 ng/ml and for its primary metabolite, VT-11134, were 27.80-108.8 ng/ml. The plasma area under the concentration-time curve to the last measurable concentration (AUC0-last) for VT-1598 were 116.1-4507 ng*h/ml, and for VT-11134 were 1140-7156 ng*h/ml. The dose proportionality was inconclusive based on the results of the power model. The peak concentration time (Tmax) was 4-5 h for VT-1598 and for VT-11134. Half-life was 103-126 h for VT-11134. After food intake, Cmax of VT-1598 increased by 44% (geometric mean ratio (GMR), 1.44; 90%CI [0.691, 2.19]) and AUC0-last by 126% (GMR, 2.26; 90%CI [1.09, 3.44]), while exposure of VT-11134 was decreased 23% for Cmax (GMR, 0.77; 90%CI [0.239, 1.31]) and unchanged for AUC0-last (GMR, 1.02; 90%CI [0.701, 1.33]). Neither VT-1598 nor VT-11134 were detected in urine. No serious adverse events (AEs) or AEs leading to early termination were observed. The safety and PK profiles of VT-1598 support its further clinical development.

VT-1598 is a tetrazole antifungal with improved selectivity and demonstrated a high survival rate when murine infected with invasive aspergillosis, coccidiodomycosis, cryptococcosis, and candidiasis. We report a first-in-human study to evaluate safety and pharmacokinetics after an oral dose of VT-1598.

Recent advances and future perspectives in the pharmacological treatment of Candida auris infections.

INTRODUCTION: Candida auris is responsible for hospital outbreaks worldwide. Some C. auris isolates may show concomitant resistance to azoles, echinocandins, and polyenes, thereby possibly leaving clinicians with few therapeutic options. AREAS COVERED: Antifungal agents both in early and in late phases of clinical development showing anti-C. auris activity. EXPERT OPINION: The research on antifungal agents active against C. auris has made important steps forward in recent years: (i) the development of drugs with novel mechanisms of action, such as ibrexafungerp and fosmanogepix, could provide a valid option against C. auris strains resistant to one or more older antifungals, including pan-resistant strains; (ii) rezafungin could allow once weekly administration of an active drug in the case of echinocandin-susceptible isolates, providing an effective outpatient treatment, while at the same time relieving selective pressure on novel classes; (iii) the development of oral formulations could allow step-down therapy and/or early discharge, or even to avoid hospitalization in mild or noninvasive diseases; (iv) according to available data, these novel agents show a good safety profile and a low potential for drug-drug interactions.

The novel fungal CYP51 inhibitor VT-1598 displays classic dose-dependent antifungal activity in murine models of invasive aspergillosis.

Aspergillus spp. infections remain a global concern, with ∼30% attributable mortality of invasive aspergillosis (IA). VT-1598 is a novel fungal CYP51 inhibitor designed for exquisite selectivity versus human CYP enzymes to achieve a maximal therapeutic index and therefore maximal antifungal efficacy. Previously, its broad-spectrum in vitro antifungal activity was reported. We report here the pharmacokinetics (PK) and pharmacodynamics (PD) of VT-1598 in neutropenic mouse models of IA. The plasma area-under-the-curve (AUC) of VT-1598 increased nearly linearly between 5 and 40 mg/kg after 5 days of QD administration (155 and 1033 µg*h/ml, respectively), with a further increase with 40 mg/kg BID dosing (1354 µg*h/ml). When A. fumigatus isolates with in vitro susceptibilities of 0.25 and 1.0 µg/ml were used in a disseminated IA model, VT-1598 treatment produced no decrease in kidney fungal burden at QD 10 mg/kg, intermediate decreases at QD 20 mg/kg and maximum or near maximum decreases at 40 mg/kg QD and BID. The PK/PD relationships of AUCfree/MIC for 1-log killing for the two strains were 5.1 and 1.6 h, respectively, similar to values reported for approved CYP51 inhibitors. In a survival study where animals were observed for 12 days after the last treatment, survival was 100% at the doses tested (20 and 40 mg/kg QD), and fungal burden remained suppressed even though drug wash-out was complete. Similar dose-dependent reductions in lung fungal burden were observed in a pulmonary model of IA. These data strongly support further exploration of VT-1598 for the treatment of this lethal mold infection.

The Fungal Cyp51-Specific Inhibitor VT-1598 Demonstrates In Vitro and In Vivo Activity against Candida auris.

Candida auris is an emerging pathogen associated with significant mortality and often multidrug resistance. VT-1598, a tetrazole-based fungal CYP51-specific inhibitor, was evaluated in vitro and in vivo against C. auris Susceptibility testing was performed against 100 clinical isolates of C. auris by broth microdilution. Neutropenic mice were infected intravenously with C. auris, and treatment began 24 h postinoculation with a vehicle control, oral VT-1598 (5, 15, and 50 mg/kg of body weight once daily), oral fluconazole (20 mg/kg once daily), or intraperitoneal caspofungin (10 mg/kg once daily), which continued for 7 days. Fungal burden was assessed in the kidneys and brains on day 8 in the fungal burden arm and on the days the mice succumbed to infection or on day 21 in the survival arm. VT-1598 plasma trough concentrations were also assessed on day 8. VT-1598 demonstrated in vitro activity against C. auris, with a mode MIC of 0.25 µg/ml and MICs ranging from 0.03 to 8 µg/ml. Treatment with VT-1598 resulted in significant and dose-dependent improvements in survival (median survival, 15 and >21 days for VT-1598 at 15 and 50 mg/kg, respectively) and reductions in kidney and brain fungal burden (reductions of 1.88 to 3.61 log10 CFU/g) compared to the control (5 days). The reductions in fungal burden correlated with plasma trough concentrations. Treatment with caspofungin, but not fluconazole, also resulted in significant improvements in survival and reductions in fungal burden compared to those with the control. These results suggest that VT-1598 may be a future option for the treatment of invasive infections caused by C. auris.

The Novel Fungal Cyp51 Inhibitor VT-1598 Is Efficacious in Experimental Models of Central Nervous System Coccidioidomycosis Caused by Coccidioides posadasii and Coccidioides immitis.

Coccidioidal meningitis can cause significant morbidity, and lifelong antifungal therapy is often required. VT-1598 is a fungus-specific Cyp51 inhibitor that has potent in vitro activity against Coccidioides species. We evaluated the in vivo efficacy of VT-1598 in murine models of central nervous system coccidioidomycosis caused by C. posadasii and C. immitis Infection was introduced via intracranial inoculation, and therapy began 48 h postinoculation. Oral treatments consisted of vehicle control, VT-1598, and positive controls of fluconazole in the C. immitis study and VT-1161 in the C. posadasii study. Treatment continued for 7 and 14 days in the fungal-burden and survival studies, respectively. Fungal burden was assessed in brain tissue collected 24 to 48 h posttreatment in the fungal-burden studies, on the days the mice succumbed to infection, or at prespecified endpoints in the survival studies. VT-1598 plasma concentrations were also measured in the C. posadasii study. VT-1598 resulted in significant improvements in survival in mice infected with either species. In addition, the fungal burden was significantly reduced in the fungal-burden studies. Plasma concentrations 48 h after dosing stopped remained above the VT-1598 MIC against the C. posadasii isolate, although levels were undetectable in the survival study after a 4-week washout. Whereas fungal burden remained suppressed after a 2-week washout in the C. immitis model, a higher fungal burden was observed in the survival arm of the C. posadasii model. This in vivo efficacy supports human studies to establish the utility of VT-1598 for the treatment of coccidioidomycosis.

Crystal Structure of the New Investigational Drug Candidate VT-1598 in Complex with Aspergillus fumigatus Sterol 14α-Demethylase Provides Insights into Its Broad-Spectrum Antifungal Activity.

Within the past few decades, the incidence and complexity of human fungal infections have increased, and therefore, the need for safer and more efficient, broad-spectrum antifungal agents is high. In the study described here, we characterized the new tetrazole-based drug candidate VT-1598 as an inhibitor of sterol 14α-demethylase (CYP51B) from the filamentous fungus Aspergillus fumigatus VT-1598 displayed a high affinity of binding to the enzyme in solution (dissociation constant, 13 ± 1 nM) and in the reconstituted enzymatic reaction was revealed to have an inhibitory potency stronger than the potencies of all other simultaneously tested antifungal drugs, including fluconazole, voriconazole, ketoconazole, and posaconazole. The X-ray structure of the VT-1598/A. fumigatus CYP51 complex was determined and depicts the distinctive binding mode of the inhibitor in the enzyme active site, suggesting the molecular basis of the improved drug potency and broad-spectrum antifungal activity. These data show the formation of an optimized hydrogen bond between the phenoxymethyl oxygen of VT-1598 and the imidazole ring nitrogen of His374, the CYP51 residue that is highly conserved across fungal pathogens and fungus specific. Comparative structural analysis of A. fumigatus CYP51/voriconazole and Candida albicans CYP51/VT-1161 complexes supports the role of H bonding in fungal CYP51/inhibitor complexes and emphasizes the importance of an optimal distance between this interaction and the inhibitor-heme iron interaction. Cellular experiments using two A. fumigatus strains (strains 32820 and 1022) displayed a direct correlation between the effects of the drugs on CYP51B activity and fungal growth inhibition, indicating the noteworthy anti-A. fumigatus potency of VT-1598 and confirming its promise as a broad-spectrum antifungal agent.