Draft:Macrophage Membrane-Coated Nanovesicles for Drug Delivery

Introduction to Macrophage Membrane-Coated Nanovesicles
Macrophage membrane-coated nanovesicles are a drug delivery system where a targeted drug is embedded in a nanovesicle created using reconstructed macrophage membranes to promote biocompatibility and enhance immune response. The use of macrophage membrane-coated nanovesicles represents a creative approach to enhance the specificity, efficacy, and safety of drug delivery [21]. By leveraging the unique properties of macrophage membranes, such as their ability to target specific tissues or diseases, our research contributes to the development of more precise and personalized therapeutic interventions.

The primary limitation of most treatment therapeutics is their inability to deliver therapeutics directly to the target site. Nanoparticle drug delivery systems are the most promising therapeutic that has overcome this limitation by controlling the delivery to the inflamed site or tumor. Cell-membrane nanoparticles acquire specific biological attributes, such as prolonged circulation, targeted recognition, increased accumulation at disease sites, and deep penetration into tumors [21]. This strategy has involved various types of cells including macrophage membranes.

Macrophages play a vital role in the immune system, they are primarily responsible for protecting the body by fighting infection, aiding in tissue repair, and defending against pathogens. Macrophage membranes feature self-recognition mechanisms that can avoid phagocytosis and their ligands from the membrane have the ability to bind to receptors directly at the disease site.

In the innate immune system, when infected, the immune cells including macrophages use their pattern recognition receptors (PRRs) to recognize pathogens. These PRRs include toll-like receptors, RIG-I-like receptors, and NOD-like receptors and they have the ability to recognize the pathogen-associated molecular patterns (PAMPs) that are only on the surface of pathogens. Macrophage membrane-coated nanoparticles, specifically, can detect and react to both pathogens and immune signals. They have the ability to live several months in the body and they have high immune compatibility, active targeting ability, and long circulation. Macrophages are one of the most predominant cells that respond to pathogens in the immune system. In response to tissue damage or infection, cytokines orchestrate the recruitment of monocytes, which subsequently mature into macrophages. They are highly specialized so they are able to actually mediate homeostasis in all organs [21]. During the initial phases of inflammation, macrophages contribute significantly by releasing cytokines and chemokines. These signaling molecules then facilitate the recruitment of other immune cells to the sites of inflammation, initiating the adaptive response of the immune system.

The process of synthesizing specifically these macrophage membrane-coated nanoparticles consists of three steps: the extraction of the macrophage cell membrane, the fabrication of the core, and the encapsulation of the core with the extracted membrane to form membrane-coated nanoparticles.

The extraction and isolation of macrophage membranes are important because when the membrane is extracted the intracellular components like biomacromolecules, vesicles, and nuclei need to be removed while maintaining the whole functional surface protein of membranes. These proteins have the ability to transport molecules in or out of the cells. The isolation of the cell membrane needs to be carried out carefully in order to prevent and reduce the denaturation of membrane proteins. Proteins on the cell membrane are important for biomimetic therapy because they can provide bioinspired nanoparticles with targeting ability and immune escape capacity.

The selection of the inner core depends on the application because the core is the effective load that is delivered to the targeted tissue. There are both organic and inorganic inner cores that have both advantages and disadvantages. Organic particles, like polymeric and lipid nanoparticles, offer simplicity in design, high biocompatibility, and efficient drug loading, but face challenges such as high costs, poor stability in vivo, and difficulty in size control. In contrast, inorganic cores like silica, gold, and iron oxide nanoparticles, among others, provide advantages such as controllable size, stability, and unique properties for therapeutic and imaging purposes. However, they may suffer from low biodegradability and high toxicity in vivo, limiting their clinical applications [21].

Finally, to create the membrane-coated nanoparticles there are four methods: incubation, membrane extrusion, sonication, and electroporation. Incubation is beneficial in maintaining the stability of the membrane proteins. The extrusion method is very effective and stable but cannot be translated into large-scale manufacturing. Sonication, although popular, the parameters needs further optimization to improve its efficiency and minimize protein denaturation and drug leakage [21]. Electroporation is beneficial in maintaining the integrity of the cell membranes and reducing the loss of surface proteins.

Despite the long process, macrophage membrane-coated nanovesicles have proven to be a very successful and promising approach to drug delivery, utilizing the unique properties of macrophage membranes to enhance biocompatibility and immune response. These nanovesicles offer improved specificity, efficacy, and safety compared to traditional therapeutics. By harnessing the targeting abilities of macrophage membranes, research further contributes to the development of personalized therapeutic interventions.

Biomimetic Approaches in Drug Delivery
In the dynamic landscape of drug delivery, biomimetic approaches have emerged as a promising strategy to overcome many challenges associated with traditional systems. This section serves as a gateway to understanding the innovative realm of biomimetic drug delivery by exploring various strategies employed in mimicking biological structures and processes for enhanced therapeutic outcomes.

Researchers have harnessed a diverse array of biomaterials and biological components to construct drug carriers that closely mimic the behavior and functionality of natural biological entities. One such strategy involves the development of cell membrane-coated nanoparticles, where synthetic nanoparticles are enveloped with membranes derived from cells such as macrophages [17]. This biomimetic platform leverages the unique properties of cell membranes to enhance drug delivery efficacy, targeting specificity, and biocompatibility. The fabrication and characterization of these membrane-coated nanoparticles involve intricate processes, including the isolation of macrophage membranes and their subsequent camouflage onto synthetic nanoparticles [17]. Such biomimetic nanocarriers, exemplified by macrophage membrane-coated nanovesicles, have shown remarkable stability and biocompatibility, making them promising candidates for targeted drug delivery [17].

The membrane-coating process ensures that the resulting nanoparticles inherit key surface markers and functionalities from the source cells, facilitating interactions with biological targets and evading immune recognition. This biomimetic approach not only enhances the circulation time of nanoparticles in the bloodstream but also enables specific targeting of diseased tissues, such as atherosclerotic plaques. Furthermore, the biomimetic nature of these nanoparticles confers reduced immunogenicity and improved biocompatibility, minimizing adverse effects associated with traditional drug delivery systems.

Additionally, liposomes inspired by cellular vesicles have been engineered to encapsulate and deliver therapeutic agents, offering another avenue for biomimetic drug delivery [1]. These liposomal formulations, designed to mimic the structure and function of natural cellular vesicles, exhibit improved pharmacokinetics and biodistribution profiles compared to conventional liposomes [1]. By leveraging the intrinsic properties of lipid bilayers and membrane proteins, biomimetic liposomes can enhance drug stability, promote cellular uptake, and modulate drug release kinetics, leading to enhanced therapeutic efficacy [1].

By delving into the intricacies of biomimetic drug delivery, we gain insight into the ingenious ways researchers draw inspiration from nature to design innovative drug carriers. This section not only highlights the diversity and versatility of biomimetic approaches but also underscores their significance in addressing the limitations of conventional drug delivery systems. Ultimately, it sets the stage for a focused exploration of one such biomimetic approach – macrophage membrane-coated nanovesicles – which holds promise for revolutionizing targeted drug delivery in biomedical applications.

Macrophage Membrane-Coated Nanovesicles in Cancer Therapy
Macrophage membrane-coated nanovesicles in cancer therapy is a relatively new application that can be characterized as an immunotherapy where nanovesicles loaded with anti-cancer medication are coated in macrophage membranes to promote tumor regression and cancer treatment. In recent years, the utilization of immunotherapy in cancer therapy has grown significantly. Unlike more traditional treatment methods, immuno-oncology aims to activate the body's innate and adaptive immune system and allow it to target and destroy cancer cells. Compared to other treatments such as chemotherapy and radiotherapy, this new generation of cancer treatment shows promising results due to its higher specificity and significantly lower toxicity.

Specifically regarding macrophage membrane-coated nanovesicles, this method appeals to the innate immune system and has many advantages related to biocompatibility and tumor targeting. One of the primary advantages of coating nanovesicles in macrophage membranes is that the immune system recognizes these vesicles as one of its own [6]. This allows the cancer treatment to evade the immunological foreign body response which extends the amount of time that the nanovesicles can stay in circulation [6].

The easy integration into the body allows the cancer-treating nanovesicles to then target tumors using surface proteins on the macrophage membrane. Specific surface proteins that are located on macrophages and aid in cancer therapy include toll-like receptors and interleukin-1 (IL-1) receptors [7]. These proteins help identify cancer cell endothelium which increases targeting specificity. Furthermore, tumor-associated macrophages (TAMs) express 𝛼4 integrins on their cell membranes which can bind to vascular cell adhesion molecules (VCAM-1s) located in cancer cells [7]. This binding has a high affinity and enhances the macrophage's ability to target tumors. An example of the importance of this interaction in cancer therapy can be found when tailoring macrophage membranes to target glioblastoma cells. Due to the attraction of 𝛼4 integrins and MAC-1 proteins on macrophage membranes to VCAM-1 and ICAM-1 receptors on brain endothelial cells, macrophage-coated nanoparticles can break down the blood-brain barrier’s tight junctions in order to travel into the brain and treat glioblastoma [6]. One concern with the utilization of macrophages for cancer therapy is that the high affinity between TAMs and cancerous tumors can facilitate the survival of cancer cells and their ability to metastasize due to macrophages' ability to secrete tumor-promoting factors [7]. However, when coating anti-cancer nanovesicles in macrophage membranes, it is possible to harness the targeting ability of macrophages to access tumor cells and deliver drugs that prompt cancer regression without activating the tumor promotion factors that macrophages also possess.

Recent studies have demonstrated promising results when targeting various types of cancers. One specific cancer treatment that has been studied includes coating PLGA nanoparticles loaded with the anti-cancer drug, doxorubicin, with a macrophage membrane and targeting breast cancer cells that have metastasized into the lungs [5]. Results from the study indicate that the presence of macrophage coating enhances biocompatibility and target specificity of metastasized breast cancer cells, while also maintaining an efficient drug release profile and low cytotoxicity levels [5]. Another study looked at the ability of M1 macrophage membrane coated liposomes loaded with doxorubicin and tyrosine phosphatase inhibitor 1 (TPI-1) to target and treat osteosarcoma [20]. M1 macrophages are pro-inflammatory and have specific tumor-targeting phagocytic properties, making them an ideal candidate for anti-cancer immunotherapy techniques [20]. Based on the results from this experiment, the macrophage coated drug delivery system displayed the ability to target tumor cells and effectively reduce tumor volume [20].

Applications in Inflammatory Disease Treatment
Macrophage membrane-coated nanovesicles possess an inherent ability to target inflamed tissues due to their surface receptors and adhesion molecules derived from the macrophage membrane [17]. The receptors recognize chemokine signals, often a molecular signal associated with inflammation, and the nanovesicles selectively accumulate at the inflamed site. Macrophage membrane-coated nanovesicles' immunomodulatory properties allow them to actively modulate immune responses within inflamed tissues. They interact with T cells, B cells, and dendritic cells through membrane-bound signaling molecules and surface receptors [13]. This interaction can influence immune cell activation, polarization, and cytokine production, leading to the attenuation of excessive inflammation and the promotion of tissue repair processes. The encapsulation of drugs or therapeutic agents within macrophage membrane-coated nanovesicles protects them from degradation and enhances their stability in circulation.

In osteoarthritis, these nanovesicles have shown potential in targeting inflammation in synoviocytes and macrophages, thereby promoting cartilage repair and reducing inflammation in the affected joints. Moreover, in rheumatoid arthritis, macrophage membrane-coated nanovesicles have been utilized to target activated inflammatory cells and alleviate the inflammatory microenvironment within the synovium [7]. Strategies such as inducing M1-to-M2 macrophage repolarization, phototherapy-induced cell death in inflammatory cells, and silencing pro-inflammatory cytokines have demonstrated promising results in mitigating rheumatoid arthritis symptoms. Additionally, in gouty arthritis, these nanovesicles have been explored for enzyme-thermo-immunotherapy, aiming to simultaneously reduce urate levels and inflammation in affected joints.

Advancements and Future Directions


Drug delivery systems using nanoparticles (NDDSs) hold the potential for effectively transporting medications. Macrophage-derived vesicles (MVs), such as reconstructed membranes, and vesicles derived from cell membranes, membrane vesicles possess chemotactic migration ability and high biocompatibility [8]. Recently, cell membrane camouflage emerged as a novel therapeutic approach, utilizing natural cell properties to address challenges [3]. Wrapping synthetic nanoparticles with macrophage membranes shields them from being engulfed and eliminated by immune cells, a process called phagocytosis. This protection helps the nanoparticles stay in the body longer for targeted drug delivery.

The advancements in macrophage membrane-coated nanovesicles indicate a transformative era in medicine, offering promising avenues for targeted drug delivery with precision and efficacy. These innovative nanovesicles mimic the natural properties of macrophage membranes indicating its potential to revolutionize therapeutic interventions across various medical domains. Their ability to evade immune detection, navigate biological barriers, and selectively target diseased tissues holds significance for enhancing treatment outcomes while minimizing adverse effects.

Macrophage-coated nanoparticles are widely applied for delivering imaging agents, drugs, and more in cancer therapy and diagnosis. The capture of circulating tumor cells (CTCs) is facilitated by the macrophage cell membrane (MCM)-coated nanosystems, which mimic natural interactions between macrophages and CTCs, allowing them to be captured from the bloodstream. Imaging agents loaded into the nanoparticles' core enable visualization of CTCs or other cancer-related biomarkers. The MCM coating actively binds to tumor cells, enhancing tumor penetration and facilitating the delivery of imaging agents to the tumor site. Through these steps, MCM-coated nanosystems effectively capture CTCs, deliver imaging agents to tumor cells, and improve tumor imaging for diagnostic and monitoring purposes.

Additionally, they've been utilized for treating non-cancer diseases like inflammatory vascular disorders [10]. Macrophage-based drug delivery systems (MDDSs) hold promise for treating cancers, including metastatic breast cancer, either alone or in combination with other therapies. They capitalize on the tumor's inflammatory environment, offering targeted treatment while minimizing adverse effects associated with traditional chemotherapy. Cancer imaging relies on MRI contrast agents, but their lack of targeting and quick elimination results in increased doses and more side effects. The use of MVDDSs promises more accurate diagnosis and monitoring [8].

Macrophage membrane-coated nanovesicles, designed with inflammatory homing ability, may effectively sequester cytokines and chemokines to combat inflammation. These nanovesicles hold potential for arthritis treatment, targeting inflamed sites [7]. Photothermal therapy (PTT) utilizing macrophage cell membrane (MCM)-coated nanosystems involves several steps. Firstly, the nanoparticles' core contains a photothermal agent capable of absorbing light in the near-infrared range. Upon exposure to near-infrared light, this agent converts the light energy into heat. Subsequently, the generated heat induces hyperthermia, effectively damaging cancer cells and leading to their death. By absorbing near-infrared light and converting it into heat, MCM-coated nanosystems enable PTT, providing a selective and targeted approach to destroying cancer cells while minimizing harm to healthy tissue. This heat effectively kills cancer cells by inducing hyperthermia [10].

Limitations
Looking ahead, the future of this field holds great promise as researchers continue to explore novel applications and refine existing methodologies. However, persistent challenges such as coating nanoparticles, scalability, stability, and regulatory hurdles necessitate concerted efforts for continued progress. Various techniques coat nanoparticles (NPs) [10] with cell membranes for biomedical applications. These techniques include physical extrusion or coextrusion, sonication, electrostatic interaction, electroporation, and in situ production. Physical extrusion or coextrusion disrupts cell membrane structure, enabling its reconstruction around the NP core, but faces scalability issues, time constraints, and potential disruptions to cell membrane integrity. Sonication induces cell membrane reconstruction around the NP core but yields varying NP sizes, requiring optimization of ultrasonic parameters. Electrostatic interaction relies on attractions between charged NP cores and vesicles but may result in incomplete membrane coating. Electroporation involves applying an electric field to open pores on cell membranes but is unsuitable for larger nanomaterials. In situ production entails incubating living cells with NPs but exhibits reduced fusion efficiency.

Nonetheless, these challenges also present opportunities for innovation, driving the development of novel formulations, delivery routes, and therapeutic combinations. By addressing these challenges and leveraging emerging technologies, the field of macrophage membrane-coated nanovesicles is poised to catalyze groundbreaking advancements in drug delivery, ultimately transforming the landscape of modern medicine.