Evidence brief: Synergistic antifungal activity of antiretrovirals with amphotericin B against Aspergillus species

Abstract

Aspergillosis is a life-threatening fungal infection that primarily affects the lungs of immunocompromised individuals, including those living with human immunodeficiency virus (HIV), and is associated with mortality rates exceeding 50%. The infection is predominantly caused by Aspergillus fumigatus, a pathogen that has become increasingly difficult to treat due to the emergence of azole-resistant strains. Although azoles have traditionally served as first-line antifungals, the rise in resistance has necessitated broader use of amphotericin B (AmB), a polyene agent whose clinical utility is limited by its considerable toxicity. To address this therapeutic challenge, we screened a library of 618 antiviral compounds to identify agents that could synergize with AmB and enhance its antifungal efficacy. An initial screen identified 18 compounds that enhanced the antifungal activity of AmB. From this hit set, we prioritized the two FDA-approved HIV drugs, cobicistat and elvitegravir, as promising lead candidates. When combined with AmB, both compounds exhibited potent synergistic activity against A. fumigatus and other clinically relevant Aspergillus species, with FICI values <0.5 in over 90% of isolates tested. To further evaluate the breadth of this synergy, the assay was extended to include A. brasiliensis, A. flavus, A. niger, and A. terreus. Synergistic interactions were observed in three of the four species tested, while the combination displayed indifference against A. flavus. In time-kill assays, both combinations demonstrated sustained fungistatic effects over 48 hours and significantly impaired hyphal development as early as 16 hours, indicating early disruption of fungal growth. Additionally, both cobicistat and elvitegravir significantly enhanced the antibiofilm activity of AmB, reducing biofilm biomass by over 60% when combined with sub-inhibitory AmB concentrations. These combinations also disrupted mature biofilms, achieving up to 80% eradication, a substantial improvement over AmB alone. These findings highlight the potential of these drug combinations as promising treatment options for aspergillosis, leveraging already approved therapies.

Introduction

Fungi are ubiquitous, ecologically diverse organisms that inhabit virtually every environmental niche [1]. While most coexist harmlessly with humans as commensals or environmental saprophytes, a subset has evolved to act as opportunistic pathogens, particularly in individuals with weakened immune defenses [2,3]. Globally, pathogenic fungi are responsible for a substantial and growing burden of disease, with invasive fungal infections estimated to affect more than 6.5 million people annually [3,4]. These infections account for over 1.6 million deaths each year, a toll comparable to tuberculosis and more than triple the mortality caused by malaria [5]. In U.S. hospitals, fungal pathogens rank among the leading causes of healthcare-associated infections, surpassed only by staphylococci and enterococci [3].

Among these fungal pathogens, Aspergillus species, particularly A. fumigatus, are major contributors to morbidity and mortality in immunocompromised and critically ill patients [6]. A. fumigatus is the principal etiologic agent of invasive aspergillosis (IA), a rapidly progressive and often fatal infection whose incidence has risen alongside the expanding population of immunosuppressed individuals [7]. High-risk groups include patients in intensive care units (ICUs), individuals with chronic obstructive pulmonary disease (COPD), those recovering from surgery, people living with HIV, and recipients of immunosuppressive therapies such as tumor necrosis factor-alpha (TNF-α) inhibitors [8]. In these vulnerable populations, mortality rates for IA have been reported to range from 40% to as high as 90% [7].