With the development of nanomaterials, the application of nanocarriers has become increasingly common in medical research, especially in the fields of drug delivery and gene delivery. Organic and inorganic nanoparticles, such as liposomes, polymer micelles, polymer nanoparticles, gold nanoparticles, and silica nanoparticles, are widely used in medical research and clinical trials. However, their susceptibility to immune system recognition and clearance, as well as poor biocompatibility and biodegradability, limit the practicality of synthetic nanomaterials. Using cell membranes to camouflage nanoparticles is a novel drug delivery strategy. These biomimetic nanoparticles inherit specific biological activities from their source cells (such as red blood cells, immune cells, tumor cells, and platelets), enabling them to evade immune system recognition, prolong their circulation time in the body, and even achieve targeting through specific cell membrane proteins. This makes them a promising delivery strategy.
Preparation Methods for Cell Membrane Biomimetic Nanodrugs
The preparation methods for cell membrane biomimetic nanodrugs mainly include top-down and microfluidic electroporation. The top-down approach is commonly used for the preparation of cell membrane biomimetic nanodrugs, mainly involving two steps: cell membrane extraction and fusion of the membrane with the nanocarrier. Among them, blood cells such as red blood cells, white blood cells, and platelets are isolated from whole blood; immune cells such as neutrophils, macrophages, and natural killer (NK) cells are primarily obtained from bone marrow; tumor cells are obtained through passage culturing of corresponding cells; and stem cells are generally acquired from animal tissues. After collecting purified cells, the cells undergo hypotonic treatment or repeated freeze-thaw cycles, and then the cellular contents are removed by high-speed centrifugation to obtain cell membrane fragments. Cell membrane-derived vesicles are prepared using porous polycarbonate membranes through extrusion, and further, these cell membrane-derived vesicles are co-extruded with nanocarriers to obtain membrane biomimetic core-shell nanodrugs. While the co-extrusion method is a simple and effective technique, it is not suitable for large-scale production, which poses a significant obstacle to the clinical application of cell membrane therapeutic technologies.
At the current stage, some researchers utilize ultrasonic methods to prepare membrane biomimetic nanodrugs. The ultrasonic method primarily involves co-incubating membrane vesicles with nanocarriers under ultrasound conditions, enabling the membrane vesicles to encapsulate the inner core nanocarriers. During this process, factors such as ultrasound frequency, duration, and intensity have significant impacts on parameters like the uniformity of the biomimetic nanodrug's appearance and drug loading capacity. However, the biomimetic nanodrugs prepared by ultrasonic methods often exhibit uneven distribution, and local high temperatures may lead to denaturation of membrane proteins.
With the development of microfluidic technology, the electroporation technique based on microfluidic chips has attracted much attention due to its ability to achieve highly reproducible and high-throughput preparation of membrane biomimetic nanodrugs. The microfluidic chip system consists of five parts: sample inlets, a Y-shaped merging channel, an S-shaped mixing channel, an electroporation zone, and sample outlets. After membrane vesicles and nanocarriers enter the system through the sample inlets, they merge in the Y-shaped channel and mix in the S-shaped channel. Then, under the effect of electrical pulses in the electroporation zone, the membrane vesicles encapsulate the nanocarrier cores. By fine-tuning parameters such as pulse voltage, duration, and flow rate, nanoparticles with good encapsulation and high stability can be obtained. However, the cost of this device is relatively higher compared to co-extrusion and ultrasonic methods.
Membrane Biomimetic Nanodrug Characterization
After the preparation of membrane biomimetic nanodrugs, it is necessary to characterize their physicochemical properties to achieve the best preparation results. By detecting changes in basic parameters such as particle size, potential, and morphology before and after membrane modification of the nanodrugs, the preparation process can be adjusted accordingly to improve the yield of membrane biomimetic nanodrugs. Additionally, the biological functions of the membrane-modified nanodrugs need to be tested, including the retention of specific proteins and markers, as well as the safety, drug release, and therapeutic effects of the nanodrugs.
Transmission Electron Microscopy (TEM) is a common instrument for detecting the morphology and membrane encapsulation efficiency of nanodrugs, with a resolution of 0.1 to 0.2 nm. After negative staining with phosphomolybdic acid or uranyl acetate, membrane biomimetic nanodrugs can exhibit typical bilayer nanoparticle images, allowing analysis of their particle size and calculation of the ratio of membrane-encapsulated nanodrugs in the sample.
Dynamic Light Scattering (DLS) technology, as a basic method for detecting nanoparticle size distribution and Zeta potential, can evaluate changes in particle size and Zeta potential after cell membrane modification. The membrane encapsulation effect can also be verified by detecting residual carbohydrates from the cell membrane, such as glycoproteins and sialic acid.
Finally, characterization techniques such as SDS-PAGE gel electrophoresis, Western blotting, Enzyme-Linked Immunosorbent Assay (ELISA), and immunofluorescence can be used to detect the biological functions and membrane surface protein markers of membrane-encapsulated nanodrugs. Due to differences in the source of biological membranes, membrane modification principles, nanocarrier functions, and loaded drugs, the aforementioned characterization methods should be designed specifically for each system to verify the structure and performance of the nano-drug delivery system.
The advantages of cell membrane biomimetic modified nanoparticles in tumor therapy:
1.Excellent immune evasion ability
One of the primary objectives in nanomedicine is to achieve prolonged circulation of therapeutic nanocarriers in the body. While nanoparticles can deliver drugs through passive targeting mechanisms such as the enhanced permeability and retention (EPR) effect and active targeting, they are prone to being recognized and eliminated by the immune system as a foreign substance. Subsequently, polyethylene glycol (PEG) was used as a material to reduce the clearance of nanoparticles. However, studies have found that after multiple injections of PEG-modified nanoparticles, the body produces anti-PEG antibodies, which paradoxically promote the clearance of nanoparticles.
Cell membrane biomimetic nanoparticles represent a novel biomimetic approach that involves coating the surface of nanoparticles with cell membranes. The membrane structure, proteins, and saccharides originating from the cells are preserved on the surface of the nanoparticles, thus endowing them with the relevant surface properties and biological functions of natural cell membranes. For instance, using red blood cell (RBC) membranes to coat poly(lactic-co-glycolic acid) (PLGA) nanoparticles loaded with rapamycin (RAPA) leverages the inherent self-recognition function of cell membranes to enable the nanoparticles to evade clearance by the immune system and achieve on-demand drug release targeting vascular lesions. Nanoparticles coated with macrophage membranes can reduce the clearance of nanoparticles by immune cells, extending their circulatory lifespan. Additionally, nanoporous silicon particles coated with leukocyte membranes have also achieved immune evasion and targeted therapy using the inherent biological functions of leukocyte membranes. In summary, cell membrane biomimetic nanoparticles leverage the natural functions of cell membranes to enhance the biocompatibility and immune evasion capabilities of nanoparticles, significantly extending their circulatory time.
2.Excellent Drug Loading Capacity
Nanoparticles serve as excellent drug delivery carriers, capable of loading various therapeutic or imaging agents through the combination of multiple functional units with soluble macromolecules or the self-assembly of copolymers. The direct binding of drug molecules to the polymer backbone allows for precise drug loading and enhanced kinetic control over drug release. To this end, researchers have designed various nano-carriers, such as polymer carriers, liposome nanoparticles, lyotropic liquid crystals, metal nano-carriers, and fibrous spinnings, all of which possess remarkable drug loading and controlled release capabilities.
Cell membrane biomimetic nanoparticles form a core-shell structure by coating the cell membrane on the surface of the nanoparticles, which does not affect the drug loading capacity of the nanoparticles while providing better protection for the drug. By loading the photosensitizer TCPP into nanoparticles modified with biomimetic natural killer cells (NK), it was found through photodynamic therapy (PDT) for the treatment of primary tumors that the drug encapsulation efficiency and drug loading rate of NK-nanoparticles were comparable to those of non-membrane-modified nanoparticles, while TCPP leakage was significantly reduced. This indicates that NK-nanoparticles possess good drug loading and protection capabilities. The excellent drug loading and protection abilities of cell membrane biomimetic nanoparticles can improve drug utilization and the therapeutic effect of single-dose medication in tumor treatment.
3.Excellent Tumor Targeting Capability
Studies have found that utilizing the tumor homing properties of immune cells can endow cell membrane biomimetic nanoparticles with tumor targeting capabilities, thus demonstrating a positive impact on tumor-targeted chemotherapy. Additionally, leveraging the natural homotypic or heterotypic adhesion properties of cells, cell membrane biomimetic nanoparticles with targeting functions can be designed and constructed. For example, cancer cells can exhibit excellent self-recognition and internalization of nanoparticles coated with their homologous cancer cell membranes, enabling specific targeting of tumors. Furthermore, stem cell membrane biomimetic modified nanoparticles also demonstrate good tumor targeting ability. For instance, iron oxide magnetic nanoparticles coated with a hybrid membrane of platelets (PLT) and cancer stem cells can actively target tumors, enhancing the inhibitory effect on tumor growth. Due to their excellent targeting properties, cell membrane biomimetic modified drug delivery systems have become common nano-drug systems in tumor treatment research.
4.Capability to Cross the Blood-Brain Barrier
Endothelial cells in the brain's blood vessels are interconnected through various tight junction proteins and interact with pericytes and astrocytes within the brain, forming a special barrier system known as the blood-brain barrier (BBB). The BBB strictly restricts the entry of various substances into the central nervous system, such as inflammatory factors, neurotoxic substances, and immune cells from the blood. This characteristic poses a challenge in the treatment of brain tumors.
Cell membrane biomimetic nanoparticles are a drug delivery platform designed primarily through nanotechnology that can cross various physiological barriers, including the BBB, allowing drugs to reach brain tumor sites smoothly, enhancing drug accumulation in brain tumors, and further improving the therapeutic effect of brain tumor treatment. For example, studies have shown that paclitaxel (PTX) cationic liposomes (CL) coated with neutrophil (NEs) membranes can penetrate the blood-brain barrier and inhibit postoperative recurrence of gliomas. When PTX-CL/NEs, PTX-CL, and PTX were administered via tail vein injection to glioma-bearing mice after surgery, and the PTX delivered to the brain was quantified, it was found that the accumulation of PTX in the brain was significantly higher in the PTX-CL/NEs group than in the PTX and PTX-CL groups. This confirms the superiority of PTX-CL/NEs mediated by postoperative inflammatory responses in targeting brain tumors through the BBB.
References:
[1] Shi Wen, Hu Fangfang, Yin Tieying, et al. Research Progress in Tumor Therapy Using Cell Membrane Biomimetic Modified Nanoparticles [J]. Progress in Biochemistry and Biophysics, 2022, 49(03): 525-539.
[2] Gong Jiaqi, Zhao Jianing, Wang Yanhong, et al. Research Progress in Cell Membrane Biomimetic Drug Delivery Systems for Tumor Therapy [J]. Herald of Medicine, 2022, 41(12): 1810-1815.
About the Author
Xiaomichong, a pharmaceutical quality researcher, has been committed to pharmaceutical quality research and drug analysis method validation for a long time. Currently employed by a large domestic pharmaceutical research and development company, she is engaged in drug inspection and analysis as well as method validation.
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