Although passive targeting offers significant advantages in tumour treatment, not all therapeutic doses can effectively reach the target tissues, and some drugs may leak into normal tissues. The significance of the EPR effect in tumour-targeted NP drug treatment has been a subject of controversy for many years (Shi et al., 2020). Notably, research has revealed that nearly all NPs (approximately 97%) are transported to tumour sites via active transport rather than the EPR effect (de Lazaro and Mooney, 2020; Sindhwani et al., 2020). Consequently, active targeting has been increasingly used to enhance drug delivery, thereby improving the precision and safety of targeting.

Compared with passive brain targeting drug delivery, active brain targeting drug delivery exhibits greater selectivity. This is exemplified by adsorption-mediated transcytosis (involving electrostatic interactions between cations and anions) and receptor-mediated transcytosis (involving the binding of ligands to specific receptors). Furthermore, active brain targeting drug delivery demonstrates a stronger affinity, as observed in cell and virus-mediated transcytosis. Active brain targeting drug delivery can efficiently transport NP drugs to the intended site, leading to enhanced therapeutic effects and reduced local cytotoxicity (Kang et al., 2018). Overall, these advantages establish active brain targeting drug delivery as a reliable strategy (Figure 2).

Similar to the physiological structure of the cell membrane, the Lip is composed of a water nucleus surrounded by a lipid bilayer and exhibits good biocompatibility, biodegradability, low toxicity, and hydrophilic and lipophilic properties (Nakhaei et al., 2021; Lombardo and Kiselev, 2022). Consequently, they are among the most common carriers for passive targeting delivery of drugs. However, a key challenge faced by Lips is their physical and chemical instability, which can lead to adverse reactions and uncertainty regarding their efficacy (Nakhaei et al., 2021). Importantly, the stability of Lips can be effectively improved through polyethylene glycol (PEG)ylation (Najlah et al., 2019). For instance, Ghaferi et al. prepared PEGylated Lip (PEG-Lip) NP loaded with doxorubicin (DOX) and carboplatin (CB), which demonstrated superior therapeutic effects, safety, extended survival times, and enhanced drug loading compared with Lip-DOX/CB and DOX + CB (Ghaferi et al., 2022). Waghule et al. formulated and investigated PEGylated lipid nanocarriers loaded with temozolomide (TMZ), referred to as PEG-Lip-TMZ. In comparison with free TMZ, both Lip-TMZ and PEG-Lip-TMZ exhibited increased cytotoxicity, with enhancements of 1.7-fold and 1.6-fold, respectively. Moreover, PEGylated NPs provided a longer blood circulation time, with a 1.25-fold increase compared to that of Lip-TMZ (Waghule et al., 2023b). Cationic CPPs demonstrate superior cell membrane penetration capabilities (Zhou et al., 2022), so they can traverse the BBB through electrostatic interactions with negatively charged proteins on the cell membrane, making them the most commonly used (Zhou et al., 2022). For instance, R8 (comprising eight arginine residues, RRRRRRRR) is one of the most common traditional CPPs (Tian and Zhou, 2021). In order to improve the targeting, Liu et al. demonstrated that an RGD reverse sequence dGR was conjugated to R8 (R8-dGR), which could bind to both integrin αvβ3 and neuropilin-1 receptors. When applied to Lips to load paclitaxel (PTX-R8-dGR-Lip), this modification effectively targeted gliomas and improved penetration (Liu et al., 2016). The TfR has been reported to be expressed on both the BBB and tumour cells (Ramalho et al., 2022b). Importantly, TfR may be overexpressed in tumour cells up to 100 times more than in normal cells, as tumour cells require a large amount of iron for rapid proliferation (Choudhury et al., 2018). Therefore, Tf can be used to treat gliomas via specific receptor binding. Wang et al. developed R8 and Tf co-modified DOX-loaded liposomes (Tf-LPs), aiming to efficiently target glioma and overcome the BBB (Wang et al., 2019). Their team discovered that glioma cells effectively took up Tf-LPs. Compared to free DOX and LPs, Tf-LPs exhibited potent and low-toxicity anti-tumour effects. Therefore, Tf-LPs may be worth further study.

Although PEGylation can improve the stability of Lips, it is still necessary to address the low loading of Lip NPs (owing to lipid bilayer thickness limitations) and high cost of mass production (De Leo et al., 2022; Lombardo and Kiselev, 2022). Furthermore, the EPR effect observed in animal models may not directly apply to humans (Zi et al., 2022). Thus, additional verification is required to determine whether the use of Lip or PEG-Lip provides clinical benefits to patients. Notably, numerous clinical trials have demonstrated the viability of this carrier delivery method, and further details are discussed in the subsequent clinical trial section. Additionally, the targeting of Lips can be enhanced through conjugating ligands and/or peptides. Overall, Lips, particularly PEG-Lips, are a promising option.

CS is a naturally occurring amino acid polysaccharide known for its biocompatibility, biodegradability, low toxicity, and cost-effectiveness (Eslahi et al., 2021; Narmani and Jafari, 2021). Its cationic properties contribute to its water solubility and bioadhesion, enabling excellent binding affinity with negatively charged brain endothelial cells (BECs) (Mikusova and Mikus, 2021). Alswailem et al. developed microRNA-219 (miR-219) loaded CS NPs (CNPs), that inhibited tumour growth by regulating gene expression in GBM (Alswailem et al., 2022). This study demonstrated that the cationic properties of CS not only facilitate BBB penetration but also form complexes with anionic miR-219, enhancing its stability. Moreover, the CNPs loaded with miR-219 exhibited specificity for GBM cells, satisfying the drug targeting and safety requirements (Alswailem et al., 2022). Nasab et al. utilised CS-modified mesoporous silica to load curcumin, thereby creating Cur@CS-MCM-41. This modification reduced the potential toxicity of unmodified MCM-41 to cell membranes. In vitro experiments revealed that CS-MCM-41 not only enabled sustained release and increased the solubility of curcumin but also enhanced its bioavailability and toxic effects on GBM cells (Ahmadi Nasab et al., 2018). Moreover, primary amino group of CS exhibits sensitive stimuli-responsive characteristics, such as pH and temperature responsiveness, ensuring targeted drug delivery at specific times and doses (Budiarso et al., 2023). Turabee et al. developed a thermosensitive hydrogel drug delivery system using Pluronic F127 (PF127) and N,N,N-trimethyl CS (TMC) to load docetaxel, known as PF127-TMC/DTX. The addition of TMC increased the number of pores in the gel network, leading to enhanced drug release. PF127-TMC/DTX exhibited sustained drug release over 30 days and demonstrated greater growth inhibition of GBM cells than free DTX and PF127/DTX (Turabee et al., 2019). Thus, CS-based NPs are promising drug delivery systems for glioma treatment.

These studies underscore the exceptional potential of CS in diverse drug delivery applications owing to its advantageous properties. However, ongoing research is focused on enhancing the properties of CS further (Mikusova and Mikus, 2021). For example, CS exhibits poor water solubility and limited endosome escape ability, necessitating structural modifications (Zhang E. et al., 2019). Additionally, blood compatibility of CS is not promising and carries the risk of thrombosis (Sachdeva et al., 2023). Moreover, although CS has demonstrated low or non-toxicity in animal experiments, further studies are required to confirm its toxicity in humans (Zhang E. et al., 2019).

Ferrin is found universally across all living organisms and is composed of heavy chain ferrin (HFN) and light chain ferrin (LFN). It serves as an endogenous protein responsible for transporting and storing iron, thereby regulating the dynamic balance of Fe(II) and Fe(III) in the human body (Zhang B. et al., 2021). Additionally, ferrin has the advantages of uniform size, low immunogenicity, good biocompatibility, pH-responsive drug release capability, and self-assembly to form nanocage structures (Xia et al., 2024).

Similar to transferrin, ferrin can bind to TfR1 on endothelial and tumour cells. Liu et al. developed endogenous human ferritin heavy chain nanocages (HFn) for the specific delivery of PTX to the target by binding to TfR1. Satisfactory targeting effects were observed, which promoted PTX accumulation in the brain. HFn-PTX exhibited potent anti-GBM effects and outperformed free PTX. Importantly, no competitive inhibition was observed between HFn and endogenous Tf (Liu et al., 2020). However, the preparation conditions for HFn are challenging, and the process of NP formation in the cavity is sensitive to the reaction conditions (Zhang J. et al., 2021). Therefore, its potential for widespread application is limited.

Graphene oxide (GO) is a derivative of graphene, with a large number of oxygencontaining functional groups on its surface. Owing to its favourable physicochemical properties including good biocompatibility, large specific surface area conducive to biomolecule modification, high drug loading capacity, and relatively low toxicity, it has attracted the attention of researchers in the field of drug delivery (Wang B. et al., 2022). Wang et al. designed Fe3O4/GO NPs for the delivery of 5-fluorouracil (5-FU), utilising electrostatic interactions to coat GO onto the surface of hollow Fe3O4. Fe3O4/GO-5-FU reportedly shows no cytotoxicity within the concentration range of 2.5–40 μg/mL and exhibits controlled release capabilities; therefore, it may represent a promising potential anticancer drug (Wang et al., 2017). Interestingly, Lf is an iron-binding glycoprotein with a cation, and has proven to be non-toxic (Sabra and Agwa, 2020). Belonging to the Tf family of glycoproteins, Lf can bind to both LfR and TfR (Agwa and Sabra, 2021). Furthermore, LfR, akin to TfR, is widely expressed on the surface of brain endothelial cells (Agwa and Sabra, 2021). Moreover, Lf carries a positive charge, enabling dual-targeting of the tumour site through adsorption and receptor transcytosis, effectively enhancing the therapeutic effect (Elzoghby et al., 2020). Therefore, in order to further improve the therapeutic effect, Song et al. loaded the targeting ligand LF and superparamagnetic Fe3O4 NPs onto the surface of GO to form Lf@GO@Fe3O4 nanocomposite. In comparison to free DOX and DOX@GO@Fe3O4, Lf@GO@Fe3O4@DOX exhibited a higher inhibitory effect on tumour cell proliferation. Additionally, Lf@GO@Fe3O4@DOX demonstrated superior drug sustained release capability, possibly owing to the chemical interaction between DOX and Lf through hydrogen bonding (Song et al., 2017). Folic acid, a water-soluble vitamin B, plays a crucial role in cell proliferation and DNA synthesis (Ebrahimnejad et al., 2022). Tumour cells have folate receptors on their surface, enabling them to recognize and bind to folic acid; utilising this characteristic, surface modification of NPs with folic acid can facilitate their recognition and uptake by tumour cells. Interestingly, this approach has been proven feasible in studies targeting hepatocellular carcinomas, and breast and lung cancers (Hanafy et al., 2023a; Hanafy et al., 2023b; Ghazy and Hanafy, 2024). Therefore, this method may be a novel strategy to enhance the efficiency of glioma treatment. Wang et al. developed folate-modified graphene oxide (GO-FA) for the delivery of TMZ (GO-FA-TMZ). Their study found that GO-FA-TMZ exhibits controlled release of TMZ and pH-dependence. Moreover, in vitro experiments demonstrated significant inhibition of glioma cell growth by GO-FA-TMZ (Wang et al., 2020).

The application of GO as a nanocarrier for drug delivery is still in the early stages of research and has certain limitations. For instance, the distribution of GO in gliomas is not yet clear, and the safety of modified GO in vivo requires further confirmation. Additionally, the technology for drug release control is still developing (Wang B. et al., 2022). However, continuous exploration suggests that GO holds potential for applications in NDDS.

SiO2 (Silica) is one of the most abundant inorganic compounds in the world and has garnered widespread attention. Silica NPs (SiNPs) with uniform pore size, ease of surface modification, good biocompatibility, and stability have also been favoured by researchers (Huang et al., 2022). SiNPs can induce cellular damage in GBM, with a specific mechanism involving exposure of SiNPs leading to oxidative stress, subsequent mitochondrial dysfunction, and activation of inflammatory responses, ultimately causing cell death through apoptotic pathways (Kusaczuk et al., 2018). This suggests that SiNPs may represent a new therapeutic strategy; however, the specific distribution and safety of siNPs in vivo must be considered. SiNPs exposure can induce pathological features associated with Alzheimer’s disease, such as Aβ deposition and excessive tau protein phosphorylation, which could lead to irreversible harm to patients (Yang X. et al., 2014). Therefore, most of the current research has focused on targeting tumour tissues. Janjua et al. synthesised ultrasmall particles with large pore silica NPs (USLP) and conjugated them with Lf to load doxorubicin. In vitro experiments demonstrated that, compared to DOX alone and USLP-DOX, USLP-DOX-Lf enhanced the ability to cross the BBB and improved the anti-tumour therapeutic effect (Janjua et al., 2021a).

To optimise the rational application of SiNPs, it is essential to understand the methods of synthesising SiNPs and explore strategies for enhancing their targeting specificity while minimising their impact on normal tissues. These considerations are crucial for advancing future developments in this field.

NGs are among the most widely used NPs for drug delivery, particularly for temporal control. Notably, NG combines the advantages of hydrogels and NPs, including high biocompatibility, excellent drug-loading capacity, and responsiveness to environmental stimuli (Zhang H. et al., 2016). Therefore, NGs are ideal drug carriers.

Zhang et al. developed an Lf/phenylboronic acid (PBA)-functionalized hyaluronic acid NGs, referred to as Lf-DOX/PBNG, to deliver DOX for the targeted treatment of GBM. In vitro transport across the BBB model revealed that compared to DOX/NG and DOX/PBNG, Lf-DOX/PBNG exhibited stronger cytotoxicity, higher cell uptake efficiency, and enhanced brain permeability, leading to an improved area under the curve and biosafety of DOX (Zhang M. et al., 2021). Another study developed a biomimetic NG loaded with TMZ and the photosensitizer indocyanine green (ICG), which was surface-modified with a red blood cell membrane (ARNGs@TMZ/ICG) (Zhang et al., 2022). Under light exposure, ICG generates reactive oxygen species (ROS), leading to the degradation of ARNGs@TMZ/ICG and the release of drugs, thereby achieving therapeutic effects. These results indicate that this biomimetic NG can prolong the half-life of the drug, enhance its tumour-targeting effects, and consequently extend median survival.

NGs also have limitations, such as immunogenicity and colloidal instability. Therefore, continuous optimisation is necessary for clinical applications.

Leukocytes play a crucial role in the body’s defence response. There are various types of leukocytes, including neutrophils (NEs), eosinophils, basophils, monocytes, and lymphocytes, depending on their form, function, and source. The first three cells are collectively referred to as granulocytes (Stock and Hoffman, 2000; Angelillo-Scherrer, 2012; Kameritsch and Renkawitz, 2020). Our main focus was on NEs, which comprise more than half of the leukocytes in the blood (Friedmann-Morvinski and Hambardzumyan, 2023). During inflammation or tumour formation, chemokines recruit NEs, which then bind to chemokine receptors and subsequently to endothelial cells, allowing them to adhere. This process facilitates the migration of NEs through the spaces between endothelial cells to reach the sites of inflammation or tumours (Wang H. et al., 2021). For instance, GBM can produce IL-8 and attract NEs to tumour sites (Wang G. et al., 2022). Additionally, creating an inflammatory microenvironment through strategies such as surgery, radiation, and photothermal therapy can enhance chemokine recruitment, thereby improving the targeting ability of NEs (Wang H. et al., 2021). In summary, these findings highlighted the potential of NE-mediated NP drug delivery.

Xue et al. used NEs to transport cationic Lips (CL) containing PTX (PTX-CL/NEs). Subsequently, the PTX-CL/NEs effectively penetrated the BBB and inhibited the growth of GBM cells. Although this approach did not completely eradicate GBM in mice after surgery, it reduced or delayed glioma recurrence, thereby improving the survival rates. GBM recurrence may have been owing to the development of resistance to PTX or the presence of escaped tumour cells (Xue et al., 2017). Li et al. developed a nanosensitizer delivered by NEs, consisting of a core composed of ZnGa2O4:Cr3+ (ZGO) with the ability to emit persistent luminescence, and a shell composed of hollow sono-sensitive TiO2, which could enhance the production of ROS under insonation to control drug release. The anti-PD-1 antibody and PTX-loaded Lip (ALP) were encapsulated to form ZGO@TiO2@ALP. The results demonstrated that the ZGO@TiO2@ALP-NEs exhibited the strongest penetration ability, with the drug concentration targeting tumour cells reaching 35.6% (compared with 3.6% for PTX and 5.2% for ZGO@TiO2@ALP). This is attributed to the ability of ZGO@TiO2@ALP to induce local inflammation in the tumour environment and attract a large number of NEs. Furthermore, this method increased the survival rate of mice by 40% and significantly improved the therapeutic efficacy (Li Y. et al., 2021). Additionally, exosomes secreted by NEs can serve as an integral component of NEs, exhibiting strong inflammatory chemotaxis and the ability to traverse the BBB for the treatment of brain diseases, such as glioma (Wang H. et al., 2021). Wang et al. developed a system for GBM treatment using NE-derived exosomes (NEs-Exos) loaded with DOX. Experimental results showed that NEs-Exos effectively inhibited glioma growth in mice and prolonged their survival following intravenous injection. NEs-Exos also exhibit the same chemotaxis as NEs under inflammatory stimulation and successfully cross the BBB for tumour targeting (Wang J. et al., 2021).

The use of NEs as carriers is a novel concept; however, there are concerns regarding the potential for chronic inflammation following the injection of a large quantity of NEs (Hosseinalizadeh et al., 2022). Moreover, the extraction and purification of NEs from patients is invasive and may not be suitable for all patients requiring treatment (Hosseinalizadeh et al., 2022). Notably, the inflammatory tumour microenvironment has been implicated in the progression of low-grade to highly malignant GBM (Basheer et al., 2021). Therefore, a more rational and systematic design is required to address safety and feasibility concerns.

AAV is a non-enveloped, single-stranded DNA virus with a 4.7 kb genome enclosed in an icosahedral capsid (Issa et al., 2023). It contains two flanked inverted terminal repeats and two genes encoded by the genome: the rep gene responsible for DNA replication and packaging, and the cap gene coding for the capsid protein (Sabatino et al., 2022). Interestingly, AAV has been detected in various organisms but has not been associated with any disease (Issa et al., 2023; Li et al., 2023), suggesting its non-pathogenic nature. Consequently, AAV has gained popularity among researchers, with three AAV-based gene therapy drugs approved by the FDA in 2022 (Blair, 2022; Keam, 2022; Heo, 2023). Currently, there are 13 known serotypes of AAV (AAV1 to AAV13), with AAV2, 5, 8, and 9 being the most prevalent in clinical studies (Young, 2023). Furthermore, different AAVs demonstrate distinct tissue tropisms (Pupo et al., 2022), allowing the selection of brain targeting AAVs as carriers to enhance delivery efficiency.

AAVs have been used to treat gliomas for many years. Initially, owing to the presence of the BBB, therapy primarily involved local injections, which resulted in reduced local tumour growth (Zhong et al., 2017). The BBB-crossing function of AAV9 was discovered in 2009, leading to the adoption of systemic injections for the treatment of glioma (Foust et al., 2009). This noninvasive approach has shown broad efficacy in inhibiting glioma growth at various brain locations (Silva-Pinheiro et al., 2020), offering advantages over local injections. Similarly, AAVrh.8 and AAVrh.10 have also been found to exhibit BBB-crossing effects (Yang B. et al., 2014). In 2016, Crommentuijn et al. employed AAV9 as a carrier to deliver sTRAIL to treat gliomas via systemic injection for the first time (Crommentuijn et al., 2016). These findings confirmed that sTRAIL alone could not penetrate the BBB. However, when loaded onto AAV9, it successfully crossed the BBB, targeted GBM in the brain, slowed tumour growth, and significantly improved survival (Crommentuijn et al., 2016). Another study demonstrated that systemic injection of AAV9-IFN-β was more effective in inducing regression of multifocal GBM compared to local injection (GuhaSarkar et al., 2016).

However, systemic injection of AAV-based therapies presents numerous challenges; the foremost among these is the immune response (Weber, 2021). However, the presence of AAV antibodies in the human body severely limits the effectiveness of AAV gene therapy. Additionally, the capacity to cross the BBB and the transduction efficiency are significant concerns. Although AAV9 exhibits good BBB-crossing ability and transduction efficiency, it is not the most potent. Studies have indicated that AAV9 variants, such as AAV-PHP.B, AAV-PHP.eB, and AAV.CPP.16, possess stronger BBB crossing ability and transduction efficiency than those of AAV9 (Deverman et al., 2016; Chan et al., 2017; Yao et al., 2022). Furthermore, the broad transduction effect of AAV lacks specificity, making it prone to failure in achieving optimal therapeutic doses at the target and causing high toxicity to peripheral cells. Therefore, reducing the immune response, enhancing the BBB-crossing ability, and improving transduction specificity are crucial areas for future research.