Glioblastoma (GBM) is the most common primary malignant tumor of the central nervous system, with a median survival of less than one year documented forthe approximately 100,000 patients diagnosed with high-grade or malignant GBM every year [1,2]. The high invasiveness of GBM and the structural limitations of the blood–brain barrier (BBB) lead to poor prognoses for surgical resection, radiotherapy, and chemotherapy [[3], [4], [5]]. Researchers are precisely engineering nanoplatforms to carry different cargoes, such as drugs, antibodies, and gene fragments, to address the challenges associated with GBM treatment [[6], [7], [8], [9]]. Engineered nanoplatforms usually have improved GBM homing properties, which could reduce the side effects of conventional chemotherapeutic drugs. Unfortunately, single-functional nanoplatforms (with a single drug to treat GBM) have difficulty achieving ideal effects. Thus, multifunctional nanoplatforms have received attention in the development of nanomedicine. Photothermal therapy (PTT) usually synergizes with chemotherapy and surgery to enhance efficacy in treating tumors [10,11]. Therefore, researchers are interested in using a proper nanomaterial as a photothermal agent and building drug-loaded nanoplatforms for treatment of GBM [12].

With the ability to adsorb polycyclic aromatic hydrocarbons, strong photoabsorption in the near-infrared region (NIR), and photothermal conversion efficiency, graphdiyne (GDY) is recognized as a promising nanoplatform to overcome malignant tumors [[13], [14], [15], [16]]. Resembling a two-dimensional structure such as graphene, GDY has a huge specific surface area and certain folds and pore structures that indicate outstanding drug loading capacity [17]. However, inadequate tissue targeting and high cargo selection largely limit the applications of GDY. The polycyclic aromatic hydrocarbon-rich chemotherapeutic drug doxorubicin was once employed as a cargo and tracer to load on GDY, and it significantly inhibited tumor growth [15,18]. To date, investigators have designed GDY nanosheets with tumor-targeting functions by coating iRGD peptide-modified erythrocyte membranes or peptide polymers on graphdiyne oxide (GDYO) and have obtained enhanced antitumor activity [19,20]. Considering the biosecurity and photothermal conversion efficiency of GDY [15,21], we asked whether the combination of a drug and PTT, based on GDY-engineered GBM-targeting nanoplatforms, could effectively inhibit GBM growth.

Inducing tumor cell death is an attractive strategy to inhibit tumor growth. Ferroptosis is a new type of cell death characterized by the iron-dependent overproduction of reactive oxygen species (ROS) [22,23]. Increasing evidence has revealed that GBM cells are susceptible to ferroptosis [[24], [25], [26]], indicating that ferroptosis is a promising target for treating GBM. Glutathione peroxidase 4 (GPX4) is a vital regulator of ferroptosis since it has the capacity to resist lipid peroxidation and ROS accumulation [27,28]. Inhibition of GPX4 expression has been shown to effectively induce ferroptosis in GBM cells [[29], [30], [31]]. Interestingly, FIN56 was identified as a specific inhibitor of GPX4 since it could alternatively promote the lysosomal degradation of GPX4 [32,33]. Most importantly, FIN56 possesses a polycyclic aromatic hydrocarbon structure [33,34], suggesting that GDY could load FIN56.

Drug-loaded nanoplatforms combined with PTT have great potential in the treatment of malignant tumors. The elevated temperature at the tumor site leads to cell death and further catalyzes the Fenton reaction, which is considered necessary in ferroptosis [35,36]. Hence, a FIN56-loaded GDY nanosheet undergoing PTT may have a combination of effects on ferroptosis in GBM cells. However, based on the limitations of the BBB, detailed engineering is required to realize the photothermal properties of GDY in GBM lesions. Therefore, researchers have developed a series of brain-targeting peptide strategies that enable nanoplatforms to penetrate the BBB and the blood-tumor barrier (BTB) [37,38]. These approaches have also enabled several nanoplatforms with photothermal properties to achieve GBM targeting and therapeutic functions [39,40]. Since the overexpression of low-density lipoprotein receptor-associated protein-1 (LRP1) was observed in GBM, the tumor neovascular system, the BBB, and the BTB, Lu et al. miniaturized receptor-associated protein (RAP), an LRP1 ligand, to a short peptide RAP12 (EAKIEKHNHYQK), which contains essential lysine at positions 253 and 256 and exhibits high binding affinity for LRP1 [[41], [42], [43]]. These features of RAP12 provide the RAP12-modified nanoplatform with the capacity to penetrate the BBB and BTB. Therefore, it is reasonable to assume that a RAP12-modified GDY nanoplatform is highly likely to target GBM and exhibit phototherapeutic-chemotherapeutic effects in situ.

In this study, we constructed a nanotherapeutic platform termed GDY-FIN56-RAP (GFR), which incorporated a precise drug delivery system, the photothermal characteristics of GDY, and the ferroptosis susceptibility of GBM cells. Our data revealed that FIN56 was released from GFR in a pH-responsive manner and that GFR considerably promoted ferroptosis by decreasing GPX4 expression in GBM cells. In addition, GDY experienced heat under 808 nm irradiation, which directly destroyed cells by heat and ROS and further facilitated FIN56 emission from GFR. Notably, the GFR nanoplatforms achieved noticeable GBM accumulation in vivo, inhibited tumor growth, and prolonged lifespan in an orthotopic xenograft mouse model of GBM, and these phenomena were further enhanced by 808 nm irradiation. Hence, combining GFR with PTT may be a potential strategy against GBM.