Host Defense Peptide-Mimetic Polymer Enables Self-Delivery and Synergistic Enhancement of Antifungal Drugs

Today, we share an important study led by Professor Runhui Liu's team at East China University of Science and Technology, published in Nature Biotechnology. This research addresses the global challenge of limited efficacy in treating systemic fungal infections (especially meningitis) caused by inconsistent in vivodistribution of synergistic antifungal drugs. The team developed a host defense peptide-mimetic self-assembling micelle delivery system. This strategy involves a bifunctional polymer possessing both antifungal activity and self-assembly carrier capability, which efficiently encapsulates amphotericin B (AmB). This enables spatiotemporally consistent co-delivery of both drugs to the infection site. The system significantly reduces AmB toxicity, broadens its therapeutic window, and demonstrates efficacy superior to the clinical gold-standard therapy (AmBisome combined with 5-fluorocytosine) in mouse models of systemic candidiasis and cryptococcal meningitis. It offers a novel solution for tackling drug-resistant fungal infections.

Fig. 1 | The current clinical strategy and this strategy in treating fungal infections.

01 Research Background

According to World Health Organization statistics, bacterial and fungal infections cause nearly ten million deaths annually. Systemic fungal infections, particularly fungal meningitis, are especially difficult to treat due to limited available drugs, significant drug side effects, and the presence of the blood-brain barrier. Combination therapy is a common strategy to enhance efficacy and overcome drug resistance; for example, the clinical gold standard for treating fungal meningitis is liposomal amphotericin B (AmBisome) combined with 5-fluorocytosine (5FC). However, these two drugs have vastly different in vivodistribution and pharmacokinetics, preventing maintenance of the optimal synergistic ratio at the infection site. This makes it difficult to achieve synergistic effects in vivo, and mortality rates remain high. Nano-delivery carriers (e.g., liposomes) can co-load multiple drugs, but the drug-loading ratio is difficult to precisely control due to differences in the physicochemical properties of the drugs. Therefore, developing a novel delivery platform that ensures consistent spatiotemporal distribution of synergistic drugs in vivois an urgent need to improve antifungal efficacy and save lives.

02 Innovative Highlights

Development of a Bifunctional Polymer with Combined Antifungal and Self-Assembly Properties

The research team designed and synthesized a series of poly(2-oxazoline) block copolymers (PGlyx-b-PNapy). The PGly block provides a positive charge, mimicking the membrane-targeting action of host defense peptides. The PNap block provides hydrophobicity, driving self-assembly and encapsulating the hydrophobic drug AmB. The optimal polymer, PGly6-b-PNap14, not only self-assembles into micelles approximately 70 nm in size but also exhibits potent antimicrobial activity against drug-resistant Candida(MIC = 13μg mL^-1) with very low mammalian cell cytotoxicity.

Utilizing the Bifunctional Polymer for Precise Co-delivery of Synergistic Drugs

The core of this strategy lies in the polymer micelle itself acting as an antifungal component, which can synergize with the encapsulated AmB. Since both are "bundled" within the same nanoparticle, their in vivopharmacokinetic behavior is highly consistent, ensuring release at the optimal synergistic ratio at the infection site. This overcomes the bottleneck of inconsistent distribution inherent in traditional combination therapy.

Elucidating Multiple Mechanisms of Micelle-Enhanced AmB Efficacy

The study found that the micelles not only reduce the acute toxicity of AmB through slow release but also, due to their positive charge, can selectively target and accumulate on negatively charged fungal surfaces. More importantly, the micelles can perturb the fungal cell wall, facilitating penetration of both the disassembled polymer units and AmB through the cell wall to reach the cell membrane, where they exert synergistic killing. This significantly enhances AmB's potency.

Demonstrating Exceptional Therapeutic Potential in Severe Disease Models 

The study validated the efficacy of AmBmicelles in systemic Candidainfection and the highly challenging cryptococcal meningitis model (including a delayed treatment model). Their performance far exceeded the existing gold-standard regimen. Particularly in the meningitis model, AmBmicelles achieved a 100% survival rate and completely cleared fungal burden from multiple organs, including the brain, showcasing significant clinical translation potential.

03 Results and Discussion

3.1 Synthesis, Self-Assembly, and Synergistic Effect Verification of the Bifunctional Polymer

The study successfully synthesized a series of PGlyx-b-PNapy block copolymers, with controlled structure confirmed by gel permeation chromatography and NMR. The optimal polymer, PGly6-b-PNap14, self-assembled into uniform micelles (~70 nm). Checkerboard assays demonstrated that both the polymer and its formed micelles exhibited strong synergy with AmB in vitroagainst various fungi (e.g., Candida albicans, Cryptococcus neoformans) (FICI = 0.19-0.5) (Fig. 2).

Fig. 2 | Synthesis, characterization and biological activity study of polymers and polymer micelles.

3.2 Multidimensional Explanation of the Synergistic Mechanism

Fluorescence microscopy, membrane potential, and membrane permeability experiments confirmed that the micelles rapidly aggregate on fungal surfaces and cause cell membrane depolarization. Transmission electron microscopy images clearly showed that combined use of micelles and AmB leads to fungal cell membrane rupture. Further studies indicated that the micelles perturb the fungal cell wall and promote AmB entry into the fungal cells, thereby exerting synergistic killing.

3.3 Fungal Pathogen Targeting and Preparation of AmBmicelles

In co-culture systems of fungi and mammalian cells, fluorescently labeled micelles selectively bound to fungal cells, whereas the control AmBisome was primarily taken up by mammalian cells. This targeting is attributed to the higher negative charge on fungal cell surfaces. AmBmicelles were successfully prepared using a nanoprecipitation method, achieving a drug loading capacity of 9.5%. They enabled slow release of AmB and significantly improved AmB's water solubility and stability.

3.4 In VivoSafety, Pharmacokinetics, and Therapeutic Window Broadening

Acute toxicity tests showed that the maximum tolerated dose (MTD) of AmBmicelles was six times that of free AmB (6 mg kg⁻¹ vs. 1 mg kg⁻¹), with no impact on indicators like liver and kidney function, demonstrating excellent safety. Pharmacokinetic studies revealed that the elimination half-lives of the micelles and AmB in key organs were similar, achieving spatiotemporally consistent delivery. In the systemic candidiasis model, AmBmicelles significantly broadened AmB's therapeutic window from 0.65-0.75 mg kg^-1 to 0.1-4 mg kg^-1.

3.5 Outstanding Efficacy in Severe Infection Models

In the systemic candidiasis model, the AmBmicelles treatment group (0.5 mg kg⁻¹ AmB) achieved a survival rate as high as 86%, significantly superior to the group receiving a simple mixture of AmB and micelles (29%). It also reduced fungal burden in multiple organs by up to 4.5 log10 units. In the most groundbreaking cryptococcal meningitis model, AmBmicelles (1 mg kg⁻¹ AmB) achieved a 100% survival rate, whereas the gold-standard AmBisome+5FC group experienced 100% mortality. Even in the severe delayed-treatment model (treatment initiated 3 days post-infection), AmBmicelles still achieved 100% survival and cleared brain fungal burden, far outperforming all control groups

04 Conclusion and Future Perspectives

This study successfully developed a self-assembling micelle co-delivery system based on host defense peptide-mimetic polymers, effectively addressing the core challenge of inconsistent in vivodistribution in combination antifungal therapy. By endowing the drug carrier itself with therapeutic function, this strategy achieves synergistic enhancement through an integrated therapeutic and diagnostic ("theranostic") approach and significantly reduces drug toxicity.

The profound significance of this work lies in providing a universal strategic concept applicable to other infectious diseases or cancer treatments requiring combination therapy where pharmacokinetic mismatch is an issue. The groundbreaking efficacy demonstrated by AmBmicelles in severe disease models lays a solid foundation for clinical translation. Future work could focus on: 1) Scaling up production and quality control of this polymer platform; 2) Exploring its application in other life-threatening fungal infections (e.g., aspergillosis); 3) Advancing it towards clinical trials to validate its safety and efficacy in humans. In summary, this research represents a significant breakthrough not only in the antifungal field but also provides a novel paradigm for the design of nanomedicine delivery and combination therapy strategies.

Original Article： 

Liu L, Zhou M, Xiao X, Cong Z, Wu Y, Xie J, Zhang Q, Zhang J, Jiang W, Liu R. Effective combinatorial antifungal therapy using a host defense peptide mimic that self-assembles into delivery micelles. Nat Biotechnol. 2026 Jan 2.