Targeted Drug Delivery Systems for Eliminating Intracellular Bacteria

Maltodextrin-derived nanoparticles resensitize intracellular dormant Staphylococcus aureus to rifampicin

Intracellular bacteria are recognized as a crucial factor in the persistence and recurrence of infections. The efficacy of current antibiotic treatments faces substantial challenges due to the dormant state formation of intracellular bacteria. In this study, we devised a strategy aimed at reverting intracellular dormant bacteria to a metabolically active state, thereby increasing their vulnerability to antibiotics. We found that oligosaccharides, especially maltodextrin (MD), can be absorbed by dormant S. aureus, leading to their revival and restoration of sensitivity to rifampicin (Rif). We then synthesized a reactive oxygen species (ROS)-responsive MD-prodrug by covalently binding MD with 4-(hydroxymethyl) phenylboronic acid pinacol ester (MD-PBAP) and prepared a ROS-responsive nanoparticles (MDNP) using a nanoprecipitation and self-assembly method. Once internalized by host cells, MDNP was degraded to MD, reactivating dormant S. aureus, and enhancing their susceptibility to Rif. More importantly, MDNP treatment restored the sensitivity of intracellular persistent S. aureus to Rif in both a reservoir transfer model and whole-body infection model. Additionally, MDNP have demonstrated excellent biocompatibility in both in vitro and in vivo settings. These results offer a promising therapeutic avenue for managing persistent intracellular bacterial infections by reviving and resensitizing intracellular dormant bacteria to conventional antibiotics.

Combining functionalities-nanoarchitectonics for combatting bacterial infection

New antimicrobial and anti-inflammatory therapeutics are needed because of antibiotic resistance development and resulting complications such as inflammation, ultimately leading to septic shock. The antimicrobial effects of various nanoparticles (NPs) are currently attracting intensive research interest. Although various NPs display potent antimicrobial effects against strains resistant to conventional antibiotics, the therapeutic use of such materials is restricted by poor selectivity between bacteria and human cells, leading to adverse side effects. As a result, increasing research efforts during the last few years have focused on targeting NPs against bacteria and other components in the infection micro-environment. Examples of approaches explored include peptide-, protein- and nucleic acid-based NP coatings for bacterial membrane recognition, as well as NP conjugation with enzyme substrates or other moieties that respond to bacterial or other enzymes present in the infection micro-environment. In general, this study aims to add to the literature on the antimicrobial effects of nanomaterials by discussing surface modification strategies for targeting bacterial membranes and membrane components, as well as how such surface modifications can improve the antimicrobial effects of nanomaterials and simultaneously decrease toxicity towards human cells and tissues. In doing so, the biological effects observed are related throughout to the physico-chemical modes of action underlying such effects.

Near Infrared-Triggered Nitric Oxide-Release Nanovesicles with Mild-Photothermal Antibacterial and Immunomodulation for Healing MRSA-Infected Diabetic Wounds

Bacterial infection-induced excessive inflammation is a major obstacle in diabetic wound healing. Nitric oxide (NO) exhibits significant antibacterial activity but is extremely deficient in diabetes. Hence, a near-infrared (NIR)-triggered NO release system is constructed through codelivery of polyarginine (PArg) and gold nanorods (Au) in an NIR-activatable methylene blue (MB) polypeptide-assembled nanovesicle (Au/PEL-PBA-MB/PArg). Upon NIR irradiation, the quenched MB in the nanovesicles is photoactivated to generate more reactive oxygen species (ROS) to oxidize PArg and release NO in an on-demand controlled manner. With the specific bacterial capture of phenylboronic acid (PBA), NO elevated membrane permeability and boosted bacterial vulnerability in the photothermal therapy (PTT) of the Au nanorods, which is displayed by superior mild PTT antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) at temperatures < 49.7 °C in vitro. Moreover, in vivo, the antibacterial nanovesicles greatly suppressed the burst of MRSA-induced excessive inflammation, NO relayed immunomodulated macrophage polarization from M1 to M2, and the excessive inflammatory phase is successfully transferred to the repair phase. In cooperation with angiogenesis by NO, tissue regeneration is accelerated in MRSA-infected diabetic wounds. Therefore, nanoplatform has considerable potential for accelerating the healing of infected diabetic wounds.

Cascade-targeting polymeric particles eliminate intracellular C. neoformans in fungal infection therapy

C. neoformans, a life-threatening invasive fungal pathogen, can hijack the pulmonary macrophages as 'Trojan horse', leading to cryptococcal meningitis and recurrence. Combatting these elusive fungi has posed a long-standing challenge. Here, we report an inhaled cascade-targeting drug delivery platform that can sequentially target host cells and intracellular fungi. The delivery system involves encapsulating amphotericin B (AMB) into polymeric particles decorated with AMB, creating a unique surface pattern, denoted as APP@AMB. The surface topology of APP@AMB guides the efficient macrophages internalization and intracellular drugs accumulation. Following endocytosis, the surface-functionalized AMB specifically targets intracellular fungi by binding to ergosterol in the fungal membrane, as demonstrated through co-localization studies using confocal microscopy. Through on-site AMB delivery, APP@AMB displays superior efficacy in eliminating C. neoformans in the lungs and brain compared to free AMB following inhalation in infected mice. Additionally, APP@AMB significantly alleviates the nephrotoxicity associated with free AMB inhalation therapy. Thus, this biocompatible delivery system enabling host cells and intracellular fungi targeting in a cascade manner, provides a new avenue for the therapy of fungal infection.

Reactive oxygen species driven prodrug-based nanoscale carriers for transformative therapies

Reactive oxygen species (ROS) drive processes in various pathological conditions serving as an attractive target for therapeutic strategies. This review highlights the development and use of ROS-dependent prodrug-based nanoscale carriers that has transformed many biomedical applications. Incorporating prodrugs into nanoscale carriers not only improves their stability and solubility but also enables site-specific drug delivery ultimately enhancing the therapeutic effectiveness of the nanoscale carriers. We critically examine recent advances in ROS-responsive nanoparticulate platforms, encompassing liposomes, polymeric nanoparticles, and inorganic nanocarriers. These platforms facilitate precise control over drug release upon encountering elevated ROS levels at disease sites, thereby minimizing off-target effects and maximizing therapeutic efficiency. Furthermore, we investigate the potential of combination therapies in which ROS-activated prodrugs are combined with other therapeutic agents and underscore their synergistic potential for treating multifaceted diseases. This comprehensive review highlights the immense potential of ROS-dependent prodrug-based nanoparticulate systems in revolutionizing biomedical applications; such nanoparticulate systems can facilitate selective and controlled drug delivery, reduce toxicity, and improve therapeutic outcomes for ROS-associated diseases.

Rifampicin-Loaded Polyelectrolyte Complex Eliminates Intracellular Bacteria through Thiol-Mediated Cellular Uptake and Oxidative Stress Enhancement

The poor accumulation of antibiotics in the cytoplasm leads to the poor eradication of intracellular bacteria. Herein, a polyelectrolyte complex (PECs@Rif) allowing direct cytosolic delivery of rifampicin (Rif) was developed for the treatment of intracellular infections by complexation of poly(α-lipoic acid) (pLA) and oligosaccharide (COS) in water and loading Rif. Due to the thiol-mediated cellular uptake, PECs@Rif delivered 3.9 times higher Rif into the cytoplasm than that of the free Rif during 8 h of incubation. After entering cells, PECs@Rif released Rif by dissociating pLA into dihydrolipoic acid (DHLA) in the presence of intracellular thioredoxin reductase (TrxR). Notably, DHLA could reduce endogenous Fe(III) to Fe(II) and provide a catalyst for the Fenton reaction to produce a large amount of reactive oxygen species (ROS), which would assist Rif in eradicating intracellular bacteria. In vitro assay showed that PECs@Rif reduced almost 2.8 orders of magnitude of intracellular bacteria, much higher than 0.7 orders of magnitude of free Rif. The bacteremia-bearing mouse models showed that PECs@Rif reduced bacterial levels in the liver, spleen, and kidney by 2.2, 3.7, and 2.3 orders of magnitude, respectively, much higher than free Rif in corresponding tissues. The direct cytosolic delivery in a thiol-mediated manner and enhanced oxidative stress proposed a feasible strategy for treating intracellular bacteria infection.

Strategies for the eradication of intracellular bacterial pathogens

Intracellular pathogens affect a significant portion of world population and cause millions of deaths each year. They can invade host cells and survive inside them and are extremely resistant to immune systems and antibiotics. Current treatments have limitations, and therefore, new effective therapies are needed to combat this ongoing health challenge. Active research efforts have been made to develop many new strategies to eradicate these intracellular pathogens. In this review, we focus on the intracellular bacterial pathogens and first introduce several representative intracellular bacteria and the diseases they cause. We then discuss the challenges in eradicating these bacteria and summarize the current therapeutics for intracellular bacteria. Finally, recent advances in intracellular bacteria eradication are highlighted.

A macrophage cell membrane-coated cascade-targeting photothermal nanosystem for combating intracellular bacterial infections

Current antibacterial interventions encounter formidable challenges when confronting intracellular bacteria, attributable to their clustering within phagocytes, particularly macrophages, evading host immunity and resisting antibiotics. Herein, we have developed an intelligent cell membrane-based nanosystem, denoted as MM@DAu NPs, which seamlessly integrates cascade-targeting capabilities with controllable antibacterial functions for the precise elimination of intracellular bacteria. MM@DAu NPs feature a core comprising D-alanine-functionalized gold nanoparticles (DAu NPs) enveloped by a macrophage cell membrane (MM) coating. Upon administration, MM@DAu NPs harness the intrinsic homologous targeting ability of their macrophage membrane to infiltrate bacteria-infected macrophages. Upon internalization within these host cells, exposed DAu NPs from MM@DAu NPs selectively bind to intracellular bacteria through the bacteria-targeting agent, D-alanine present on DAu NPs. This intricate process establishes a cascade mechanism that efficiently targets intracellular bacteria. Upon exposure to near-infrared irradiation, the accumulated DAu NPs surrounding intracellular bacteria induce local hyperthermia, enabling precise clearance of intracellular bacteria. Further validation in animal models infected with the typical intracellular bacteria, Staphylococcus aureus, substantiates the exceptional cascade-targeting efficacy and photothermal antibacterial potential of MM@DAu NPs in vivo. Therefore, this integrated cell membrane-based cascade-targeting photothermal nanosystem offers a promising approach for conquering persistent intracellular infections without drug resistance risks. STATEMENT OF SIGNIFICANCE: Intracellular bacterial infections lead to treatment failures and relapses because intracellular bacteria could cluster within phagocytes, especially macrophages, evading the host immune system and resisting antibiotics. Herein, we have developed an intelligent cell membrane-based nanosystem MM@DAu NPs, which is designed to precisely eliminate intracellular bacteria through a controllable cascade-targeting photothermal antibacterial approach. MM@DAu NPs combine D-alanine-functionalized gold nanoparticles with a macrophage cell membrane coating. Upon administration, MM@DAu NPs harness the homologous targeting ability of macrophage membrane to infiltrate bacteria-infected macrophages. Upon internalization, exposed DAu NPs from MM@DAu NPs selectively bind to intracellular bacteria through the bacteria-targeting agent, enabling precise clearance of intracellular bacteria through local hyperthermia. This integrated cell membrane-based cascade-targeting photothermal nanosystem offers a promising avenue for conquering persistent intracellular infections without drug resistance risks.

Drug delivery systems for enhanced tumour treatment by eliminating intra-tumoral bacteria

Cancer remains one of the serious threats to human health. The relationship between bacteria and various tumours has been widely reported in recent years, and studies on intra-tumoral bacteria have become important as intra-tumoral bacteria directly affect the tumorigenesis, progression, immunity and metastatic processes. Therefore, eliminating these commensal intra-tumoral bacteria while treating tumour is expected to be a potential strategy to further enhance the clinical outcome of tumour therapy. Drug delivery systems (DDSs) are widely used to deliver antibiotics and chemotherapeutic drugs for antibacterial and anticancer applications, respectively. Thus, this review firstly provides a comprehensive summary of the association between intra-tumoral bacteria and a host of tumours, followed by a description of advanced DDSs for improving the therapeutic efficacy of cancer treatment through the elimination of intra-tumoral bacteria. It is hoped that this review will provide guidelines for the therapeutic and "synergistic antimicrobial and antitumour" drug delivery strategy.

Advance Progress in Assembly Mechanisms of Carrier-Free Nanodrugs for Cancer Treatment

Nanocarriers have been widely studied and applied in the field of cancer treatment. However, conventional nanocarriers still suffer from complicated preparation processes, low drug loading, and potential toxicity of carriers themselves. To tackle the hindrance, carrier-free nanodrugs with biological activity have received increasing attention in cancer therapy. Extensive efforts have been made to exploit new self-assembly methods and mechanisms to expand the scope of carrier-free nanodrugs with enhanced therapeutic performance. In this review, we summarize the advanced progress and applications of carrier-free nanodrugs based on different types of assembly mechanisms and strategies, which involved noncovalent interactions, a combination of covalent bonds and noncovalent interactions, and metal ions-coordinated self-assembly. These carrier-free nanodrugs are introduced in detail according to their assembly and antitumor applications. Finally, the prospects and existing challenges of carrier-free nanodrugs in future development and clinical application are discussed. We hope that this comprehensive review will provide new insights into the rational design of more effective carrier-free nanodrug systems and advancing clinical cancer and other diseases (e.g., bacterial infections) infection treatment.