The concept of BNCT originated in the 1950s, with early efforts focusing on inorganic boron compounds (32). Critical milestones in its development include the synthesis of sulfhydryl-containing boron hydrides by Soloway et al (33) at Massachusetts General Hospital in the 1960s, which led to the identification of sodium borocaptate (BSH) as the first clinically viable boron carrier through thiol-mediated tumor targeting (34). Subsequently, in the 1980s, Hatanaka and Nakagawa (35) conducted pioneering clinical trials in Japan that established the application of BSH for treating brain tumors. Additionally, boronophenylalanine (BPA) emerged later, initially for cutaneous melanomas, expanding the applicability of BNCT (36).

Parallel to these advances in pharmacology, a significant evolution in technology occurred. Historically, BNCT relied exclusively on nuclear reactors for neutron generation, imposing significant limitations on clinical accessibility due to facility complexity and regulatory constraints. The paradigm shifted post-2015 with the maturation of accelerator-based neutron sources (37), which enabled hospital-based deployment, exemplified by Japan's 2020 regulatory approval of BNCT for recurrent head and neck cancer. This technological evolution underscores the emergence of BNCT as a precision radiotherapy modality, providing the foundation for its expanded clinical investigation.

Capitalizing on these technical and pharmacological advancements, BNCT demonstrates significant potential for invasive and recurrent malignancies (such as GBM and head and neck squamous cell carcinoma) by exploiting molecular disparities between tumor and normal tissues (Table I) (38-40). To date, >14 registered clinical trials (ClinicalTrials.gov and ChiCTR.org.cn) across multiple cancer types have been validating the broadening therapeutic scope of BNCT. A key element in modern BNCT is the use of BPA, an amino acid analog internalized by cancer cells via specific transport pathways, most notably LAT1 (36). To visualize and quantify its uptake, ¹⁸F-labeled BPA (¹⁸F-FBPA) has been developed as a potent positron emission tomography (PET) tracer. The high tumor-to-normal tissue uptake ratio of ¹⁸F-FBPA allows for non-invasive assessment of boron biodistribution, which is crucial for patient selection, treatment planning and verifying the efficacy of boron delivery (34,41). Despite these advances, clinical data reveal a persistent challenge: Achieving sufficiently high and tumor-selective boron concentrations to maximize the therapeutic effect.

To address this limitation, LAT1 has become a central molecular target for enhancing BNCT. As shown in Fig. 1, LAT1 is upregulated in metabolically active tumors (such as GBM and squamous cell carcinoma) and facilitates BPA uptake by mimicking essential amino acid transport (17). The expression of LAT1 positively correlates with intracellular ¹⁰B accumulation, which is critical for BNCT efficacy (42). Although LAT1 upregulation often indicates a poor prognosis (43), it enhances BNCT sensitivity by enabling higher boron delivery and increased cytotoxicity after neutron irradiation (31). Once boron compounds have selectively accumulated in tumor cells, patients undergo thermal neutron irradiation, which triggers the neutron capture reaction. This reaction produces ⁴He and ⁷Li that cause localized and substantial damage to cancer cells (44).

Current and future research is intensely focused on refining this targeted approach. Key strategies include elucidating the molecular biology of LAT1 and developing novel boron compounds with improved tumor specificity and delivery efficiency (11,36,45,46). These efforts, combined with ongoing improvements in neutron source technology and computational treatment planning, aim to optimize the therapeutic index of BNCT. By systematically addressing its current challenges, these advancements are poised to establish BNCT as a more effective and widely applicable treatment modality for a broad spectrum of intractable cancer types.

LAT1, also known as SLC7A5, is a member of the heterodimeric amino acid transporter family. Structurally, it forms a complex with two distinct subunits: A light chain (LAT1) and a heavy chain (4F2hc). The LAT1 subunit is directly responsible for translocating amino acids across the cell membrane. However, it requires a functional partnership with the 4F2hc heavy chain, which is essential for stabilizing the LAT1 subunit and ensuring its correct localization to the plasma membrane (50). This partnership is maintained through extensive interactions at the extracellular, intramembrane and intracellular interfaces. A crucial covalent disulfide bond between Cys164 on LAT1 and Cys210 on 4F2hc links the two subunits (Fig. 2). The stability of this complex is further enhanced by non-covalent polar interactions at the extracellular interface, such as those between Thr163 and Glu303 of LAT1 and Lys533 and Arg535 of 4F2hc. Additionally, the transmembrane helix of 4F2hc stabilizes the complex via hydrophobic interactions with transmembrane helix (TM) 4 of LAT1 and contributes to membrane localization through an intracellular lipid-binding pocket involving residues such as Arg183 (48,51). The functional significance of this intricate structural arrangement is underscored by experimental evidence. Purified LAT1 alone exhibits no transport activity, whereas the recombinant LAT1-4F2hc complex is fully functional. Consistent with this, deletion of the extracellular domain of 4F2hc abrogates >90% of transport activity (48). Therefore, the precise and multi-faceted interaction between LAT1 and 4F2hc is indispensable for the structural integrity, stability and overall transport function of the complex (52,53).

The transport process is dictated by the specific structure of the LAT1 subunit, which is composed of 12 transmembrane helices arranged in a characteristic LeuT fold (49). These helices and specific amino acids play a critical role in substrate recognition and binding, enabling efficient substrate translocation across the membrane through dynamic conformational changes (48,52,54). The substrate binding pocket of LAT1, formed by the Gly255 side chain, accommodates amino acids with larger side chains, thereby conferring the substrate selectivity of LAT1 (49,55). This selectivity allows it to preferentially bind amino acids with specific side chain sizes and shapes. Critical residues, such as Trp405 and Tyr259, stabilize substrates within the transporter through hydrogen bonding and electrostatic interactions (48,56). Mutations in these residues significantly impair the transport efficiency of LAT1 (48,52,57).

LAT1 undergoes dynamic conformational changes during substrate translocation, alternating between outward-facing and inward-facing states (48,52,54). In its outward-facing conformation, LAT1 binds substrates such as histidine at the binding site, triggering a transition to the inward-facing state. This conformational change facilitates the extracellular transport of substrates such as glutamine. LAT1 exhibits different affinities for different amino acid substrates, including isoleucine, during this bidirectional transport process (58).

The unique structural features of LAT1 allow it to recognize neutral amino acids with branched or aromatic side chains. The α-amino and α-carboxyl functional groups are key determinants for substrate recognition (59). LAT1 has a strong binding affinity for its substrates, with a K_m value between 15 and 50 µM (56). In addition, the charge of the carbonyl oxygen near the amino group (ranging from -0.55 to -0.56) influences substrate recognition. The introduction of lipophilic and aromatic groups enhances LAT1-mediated drug transport. Factors such as pK_a, log P, polar surface area and hydrogen bond donor groups further influence LAT1-mediated transport (58).

As aforementioned, LAT1, a sodium-independent transmembrane protein, plays multiple significant roles in organisms. The specialized structural configuration and transport mechanism of LAT1 allows for selective and efficient amino acid transport across cell membranes (60,61). LAT1 mainly facilitates the uptake of large neutral amino acids such as leucine, phenylalanine, tyrosine and methionine, which are fundamental for protein synthesis, cell growth and energy metabolism (11,62,63). Notably, the critical role of LAT1 in regulating essential cellular processes extends to pathological contexts, particularly in the development and progression of cancer.

In oncogenesis, LAT1 extends beyond nutrient transport, serving as a critical modulator of pro-tumorigenic signaling pathways. As depicted in Fig. 2, LAT1 positively regulates mTORC1 and β1-integrin pathways, directly accelerating tumor proliferation and metastatic dissemination (16). The upregulation of LAT1 in tumor cells ensures a continuous supply of nutrients, facilitating faster growth. Meanwhile, LAT1 forms a functional heterodimer with 4F2hc (CD98hc), activating focal adhesion kinase (FAK)/SRC cascades essential for cancer survival (58). In the tumor microenvironment, LAT1 displays notable adaptability, operating efficiently under fluctuating ionic conditions and independent of sodium gradients. This adaptability allows LAT1 to maintain amino acid transport and metabolic support for tumor cells even in stressful environments (16,64). Moreover, in malignant cells, LAT1 upregulation creates a feed-forward loop. Beyond its role in oncogenesis, LAT1 is also indispensable for central nervous system homeostasis. LAT1 transports essential amino acids across the blood-brain barrier, supporting neurotransmitter synthesis and overall neuronal health. Disruptions in LAT1 activity have been associated with several neurological disorders, making it a promising therapeutic target for diseases of the nervous system (61).

In summary, LAT1, a vital amino acid transporter, is highly expressed in numerous types of cancer cells, supporting rapid proliferation and survival under challenging conditions. The unique functional properties of LAT1 make it a compelling target for novel therapeutic strategies, including its application in targeted cancer therapies such as BNCT.

BPA, a key boron carrier in BNCT, is predominantly transported into tumor cells via the L-type amino acid transport system, particularly LAT1. The recognition of substrates by LAT1 occurs within a sterically defined binding pocket. For canonical substrates such as L-phenylalanine and L-tyrosine, the α-carboxyl and α-amino groups interact with the backbones of TM1 and TM6, respectively. Concurrently, the aromatic side chain is oriented toward Gly255 and stabilized by van der Waals forces (55,65). This specific binding mechanism also accounts for the transporter's recognition of structural analogs, such as BPA. In melanoma cells, BPA uptake occurs through mechanisms similar to L-tyrosine transport (66), involving both amino acid carrier-mediated uptake and passive intracellular accumulation due to its lipophilicity. L-tyrosine is primarily transported by the L system but also via the ASC (alanine, serine and cysteine) transport system (66). Preloading with L-tyrosine increases BPA uptake by altering intracellular amino acid gradients; however, co-incubation leads to competitive inhibition, reducing BPA uptake by ~50% (66). In gliosarcoma cells, BPA uptake is specifically mediated by the L system rather than the A system and is modulated by amino acid concentrations across the cell membrane. Pre-accumulation of L-tyrosine or BCH induces a trans-stimulation effect, enhancing BPA influx through exchange mechanisms, whereas simultaneous incubation results in competitive inhibition (15). BPA efflux is also an exchange-based process, with its rate influenced by the presence of amino acids and L/A system substrates in the extracellular medium. For instance, in C6 glioma cells, preloading with L-DOPA significantly enhances BPA uptake (up to five-fold), likely through activation of membrane-bound LAT transporters. This effect is selectively observed in tumor tissues in vivo, suggesting the potential clinical benefit of amino acid preloading strategies in BNCT (67).

Moreover, ¹⁸F-FBPA, a radiolabeled BPA derivative, has been identified as a selective substrate for LAT1 and LAT4, confirming the predominant role of the L system in its tumor-specific accumulation (68). In other tumor cell lines, including human hepatocellular carcinoma (HuH-7), human colorectal adenocarcinoma (CaCo-2) and mouse melanoma (B16-F1) cell lines, preloading with L-BPA, L-tyrosine or L-DOPA has been shown to significantly enhance ¹⁸F-FBPA uptake (69). These findings reinforce the therapeutic potential of modulating extracellular amino acid levels and administration timing to optimize LAT1-mediated drug delivery in cancer treatment.

The specificity of LAT1 for boron compounds, such as BPA, boronotyrosine and fluoroboronotyrosine (12,14), is driven by their structural similarity to natural substrates such as tyrosine, allowing competitive binding and selective uptake in LAT1-upregulated tumor cells (49,70). This uptake is further optimized by designing boron compounds that mimic amino acid substrates or modifying side chains to enhance LAT1 affinity (12,71). For example, compounds such as 4(benzo[d] thiazol-2-yl)phenylboronic acid, which exhibit high brain permeability, or ¹⁸F-FBPA, which predicts ¹⁰B concentrations in tumors, demonstrate the potential for enhancing tumor targeting and boron delivery. These innovations aim to maximize LAT1-mediated delivery and improve therapeutic outcomes (72).

The development of boron carriers, such as BPA, has been pivotal in BNCT but faces challenges, such as its low boron content and suboptimal pharmacokinetics (68). The core objective of the next-generation boron drugs is to address the shortcomings of existing boron drugs (including BPA and BSH), such as insufficient targeting, low boron content and toxic side effects, through precise targeting, efficient delivery and multi-functional integration, thereby promoting the clinical application of BNCT in more tumor types (36,71). Additionally, nanotechnology-based delivery systems, such as polyboronate ester micelles, are being explored to enhance pharmacokinetics and tumor selectivity while minimizing systemic toxicity (21,73).

LAT1 is a critical protein in oncology, serving as both a marker of aggressive disease and a key mediator for therapeutic intervention. LAT1 is upregulated in a wide variety of malignancies, including brain, head and neck, lung, breast and pancreatic cancer (18,47,74), where its presence is strongly correlated with increased tumor proliferation, angiogenesis and poor prognosis (42,49,75). Crucially for BNCT, LAT1 is the primary transporter for boron-containing agents such as BPA. Since LAT1 is expressed in ~70% of viable tumor cells, its expression level is a key determinant of how much boron can be delivered to the cancer, directly influencing the potential efficacy of the therapy (17). While high LAT1 expression is necessary for BNCT, its inconsistent and heterogeneous expression within and across tumors presents a major therapeutic obstacle (Table II) (76,77). This variation leads to the uneven microdistribution of BPA, where regions with high LAT1 levels respond favorably, while regions with low LAT1 levels are undertreated, creating pockets of resistant cells (17,78). This heterogeneity is a direct cause of treatment failure and recurrence. For example, in a study of patients with recurrent head and neck cancer, non-homogeneous BPA uptake contributed to frequent local recurrence despite a high initial response rate (12/17 patients) (79). Similarly, in high-grade glioma, uneven BPA delivery resulted in inconsistent tumor regression and, in some cases, led to cerebrospinal fluid dissemination post-BNCT, particularly in highly heterogeneous small-cell GBM (80). The correlation between LAT1 expression and tumor grade can also be inconsistent; while it rises with malignancy in glioma (77), prostate (81) and neuroendocrine (82) tumors, no clear link has been established for biliary tract, ovarian or lung cancer (47).

This clinically significant heterogeneity is not random but is driven by complex molecular signals within the tumor microenvironment (TME). Key regulatory factors include: i) Hypoxia: The hypoxic TME regulates LAT1 via hypoxia-inducible factors (HIFs) (62). While HIFs can upregulate LAT1 to facilitate nutrient uptake in deprived conditions (47,76), some factors such as HIF-1α can also reduce its expression, limiting the effectiveness of BNCT in certain tumor zones (83). ii) Oncogenic pathways: Several major cancer-driving pathways directly control LAT1 expression. Signaling through c-Myc (84,85) and mTOR (64), as well as pathways associated with cancer stem cell markers such as CD133 (86), can significantly alter LAT1 levels, contributing to the mixed expression patterns observed in tumors.

Overcoming LAT1 heterogeneity is paramount for improving BNCT outcomes. A multi-pronged approach is required, focusing on assessment, modulation and further research. Advanced imaging techniques capable of mapping LAT1 expression across the entire tumor are urgently needed to optimize treatment planning. Furthermore, future clinical trials must incorporate larger patient samples and stratification by LAT1 expression to definitively correlate expression with survival and tumor control rates (17). Additionally, strategies aimed at upregulating LAT1 expression could sensitize resistant tumor regions to BNCT. This includes pharmacological interventions or gene therapies, such as using the CD133 promoter to drive LAT1 upregulation specifically in cancer stem cells, thereby enhancing boron uptake in this critical population (86). Targeting the regulatory pathways (such as mTOR and c-Myc) may also offer a route to normalize LAT1 expression. Continued research should also focus on developing next-generation, LAT1-targeted boron compounds with improved uptake and retention, alongside exploring novel gene regulation mechanisms to ensure more uniform and effective boron delivery across diverse tumor types.

LC-MS provides distinct analytical advantages for characterizing metabolites in LAT1-expressing tumors. Unlike elemental detection techniques (such as inductively coupled plasma atomic emission spectroscopy), LC-MS enables the simultaneous quantification of parent compounds and their biotransformation products in biological matrices, offering critical insights into metabolic stability (89,90). Critically, LC-MS uniquely resolves species-specific biodistribution patterns. In a preclinical study, LC-MS was used to assess the metabolic stability of agents such as ¹⁸F-FIMP and its biodistribution in tumor-bearing models (91), demonstrating the utility of LC-MS in LAT1-mediated tumor targeting. This molecular specificity makes LC-MS indispensable for mapping the metabolic fates of boron carriers and identifying LAT1-dependent biomarkers predictive of BNCT response.

NMR spectroscopy is crucial for studying the structure and behavior of boron compounds used in BNCT, such as L-p-B and its complexes (92,93). NMR helps researchers understand the structural configurations of these compounds in solution, aiding in the optimization of therapeutic efficacy. Beyond structural analysis, NMR methods, such as non-destructive ¹⁰B NMR, allow the quantification of boron species such as ¹⁰B-BPA, facilitating the monitoring of BPA concentrations in the blood (94). This real-time tracking is essential for evaluating selective tumor uptake and minimizing off-target effects. NMR also provides reliable methods for monitoring the chemical stability of boron complexes, ensuring their efficacy and safety. Understanding how LAT1 influences the intracellular distribution of boron compounds could lead to more targeted BNCT strategies, improving outcomes in LAT1-expressing tumors.

The integration of LC-MS and NMR in metabolomic studies offers a powerful approach for advancing the understanding of LAT1 in BNCT (95). Specifically, LC-MS enables precise quantification of metabolites and metabolic pathway tracing, whereas NMR provides structural and dynamic insights into boron compound behavior. The combination of these techniques, along with metabolic flux analysis and stable isotope tracing, could unveil how LAT1 affects boron compound metabolism and tumor-specific metabolic signatures (96).

Building on this technical synergy, multi-omics integration further expands mechanistic insights through a three-tiered causal inference framework (97): i) Genomic input: Transcriptomic profiling (such as RNA-sequencing) and somatic mutation data may identify cohorts with aberrant LAT1 regulation; ii) metabolomic correlations: LC-MS/NMR-derived metabolic profiles (such as amino acid pool imbalances) can be mapped to genomic subgroups using multivariate regression; and iii) functional validation: Machine learning can help prioritize candidate metabolic vulnerabilities for experimental validation via CRISPR-interference or pharmacologic inhibition (98). Collectively, this pipeline can establish mechanistic links between the LAT1 genomic status and metabolic rewiring.

By leveraging these multi-omics approaches, researchers can develop comprehensive systems biology models of LAT1-targeted BNCT and uncover regulatory mechanisms governing boron uptake. Ultimately, these advances will enable more effective BNCT strategies, overcoming resistance and improving patient outcomes.

An ideal boron carrier for targeted cancer therapy should exhibit sustained high tumor accumulation, minimal normal tissue accumulation, rapid metabolism, excellent biocompatibility, non-toxicity, thermal and chemical stability and uniform tumor distribution (71). The ability of LAT1 to selectively transport boron compounds such as BPA into tumor cells positions it as a critical target for BNCT (12,46,99).

Structural research has expanded the scope of LAT1-targeted therapeutic strategies by providing insights into its binding affinity and interactions with boron compounds. Modifications of the amino acids within the binding pocket of LAT1 can increase its affinity for boron compounds, thereby optimizing therapeutic efficacy (100,101). In addition, identifying regions where LAT1 interacts with regulatory proteins, as well as its mechanism of action, provides new avenues for modulating LAT1 activity and improving the selectivity of cancer therapy (56,57). Advances in computational modeling have deepened the understanding of LAT1 dynamics and ligand interactions, revealing how ligands influence drug and nutrient delivery via LAT1. These insights are enabling the characterization and optimization of ligands through advanced techniques such as structure-based drug design and high-throughput screening, expanding the potential of LAT1 as a transporter for a wide range of therapeutic agents (56,102).

The ability of BPA to carry only a single boron atom also limits its overall efficiency in BNCT (11). To overcome this limitation, researchers are developing novel boron compounds with higher boron atom content to increase boron delivery to tumor cells. For example, polyboronate compounds and boron-rich nanomaterials are being explored as next-generation agents to maximize therapeutic efficacy (71). These advancements aim to improve the boron loading capacity while maintaining high selectivity and stability in vivo. Continued innovation in boron compound design, supported by computational modeling and experimental validation, is essential to overcome these challenges and unlock the full potential of LAT1-targeted BNCT.

The widespread expression of LAT1 in both cancerous and non-cancerous tissues raises concerns about potential off-target effects, including the inadvertent uptake of boron compounds in healthy tissues, which may result in collateral damage during neutron irradiation (16,17,103).

Clinical data have clearly documented specific adverse events associated with BNCT across different tumor types. In head and neck cancer trials, the most common acute toxicities are low-grade oral mucositis, radiation dermatitis and alopecia, with rare severe events such as grade 4 laryngeal edema and carotid hemorrhage (79,104). For high-grade gliomas and meningiomas, adverse events are primarily characterized by brain edema (48.1% of cases) (105), radiation necrosis (13.6% of cases) (3) and transient hyperamylasemia (81.5% of cases) (105). Additionally, 18% of patients with glioma treated in Finland experienced grade 3 seizures (78), and 2 out of 17 patients with head and neck cancer developed cranial neuropathy (79). The causes of these adverse events are supported by clinical observations. Radiation-induced tissue damage is a key factor; for instance, transient hyperamylasemia is attributed to salivary gland irradiation (105), while brain edema and radiation necrosis result from normal brain tissue exposure to neutrons, exacerbated by prior radiotherapy (3,10). Cumulative treatment effects also play a role, as patients with multiple prior radiotherapy courses or short intervals (such as 5 months) between prior radiation and BNCT face higher risks of severe toxicities such as carotid hemorrhage (104). Furthermore, tumor and treatment characteristics, such as larger target volumes and proximity to critical structures (including the carotid artery and cranial nerves), increase the likelihood of adverse events (3,79). Minimizing these off-target effects is crucial for optimizing BNCT efficacy.

The strategies to enhance the selectivity of LAT1 span several key areas. Gene therapy can selectively increase LAT1 expression in tumors. Oncogenic drivers such as c-Myc and HIF-2α can upregulate LAT1, helping tumors meet their metabolic demands (84,85). Studies have shown that increasing LAT1 expression in GBM cells enhances BNCT efficacy by promoting boron uptake (31,86). Epigenetic changes in tumor cells can also upregulate LAT1, facilitating greater boron uptake. Targeting these epigenetic regulators with agents such as DNA methyltransferase inhibitors or histone deacetylase inhibitors can selectively increase LAT1 expression, improving BNCT outcomes (101,106). Combining epigenetic therapies with BNCT may address LAT1 expression variability and resistance challenges. The TME also plays an important role in regulating LAT1 expression. Tumor-specific conditions such as hypoxia and nutrient deprivation upregulate LAT1 through HIF-2α, enabling cancer cells to maintain metabolic activity. Therapeutic strategies that induce local hypoxia or mimic nutrient-deprived environments can selectively increase LAT1 expression in cancer cells, enhancing boron uptake while minimizing off-target effects (86,102,107).

LAT1 inhibitors offer another avenue for reducing off-target effects and improving therapeutic specificity in BNCT. For example, the LAT1-specific inhibitor JPH203 has been shown to block the mTORC1 pathway and reduce the survival and proliferation of medulloblastoma cell lines (108). An in vitro study has shown that 30 µM JPH203 inhibits LAT1-mediated uptake of BPA derivatives by 40-95% in cell models, with stronger effects on LAT1-specific carriers such as D-4-BPA (109). In the context of BNCT, JPH203 could be strategically used to block LAT1 activity in normal cells, thereby reducing unnecessary boron uptake and sparing healthy tissues from collateral damage during neutron irradiation. In summary, these strategies aim to optimize LAT1 expression and function, enhancing BNCT efficacy while reducing off-target effects and improving patient outcomes.

A major challenge with LAT1-targeted therapies is the potential for resistance mechanisms that could limit their efficacy (110). For instance, in estrogen receptor-positive breast cancer cells, LAT1-mediated leucine uptake enhances mTORC1 signaling, contributing to the resistance to endocrine therapies and chemotherapy (111,112). Tumor cells can also adapt to targeted therapies by altering LAT1 expression or function through genetic mutations, epigenetic modifications (107,110,113) or by activating alternative amino acid transporters to compensate (114,115). These adaptations complicate the use of LAT1 as a sole target for BNCT and require innovative approaches to overcome resistance.

To address these challenges, combination therapies targeting multiple pathways hold great potential. For example, combining LAT1-targeted BNCT with immunotherapy, radiation therapy or other targeted therapies could have synergistic effects and improve treatment efficacy. Specifically, integrating BNCT with immunotherapy may enhance the ability of the immune system to eliminate residual tumor cells after neutron irradiation. A recent study has shown that boron-rich polymer microspheres used in BNCT can block the programmed death-ligand 1 immune checkpoint, activating the host immune system (21). Additionally, BNCT-induced tumor cell death can release tumor antigens into the microenvironment, potentially enhancing the effects of immune checkpoint inhibitors (116,117). This dual mechanism may be particularly effective in overcoming tumor resistance to LAT1-targeted therapies.

Furthermore, combining LAT1-targeted BNCT with traditional chemotherapeutic agents or molecularly targeted therapies offers promising opportunities. For example, BPA has been combined with the monoclonal antibody cetuximab, which blocks epidermal growth factor receptor signaling, to enhance the efficacy of BNCT. This approach disrupts key signaling pathways and improves tumor cell sensitivity to BNCT (118). Targeted inhibitors of key pathways, such as mTOR inhibitors, could further sensitize tumor cells to BNCT by increasing their dependence on LAT1 for nutrient uptake (82,119). By targeting the mTOR pathway, these inhibitors reduce tumor cell proliferation and metabolic flexibility, thereby increasing the efficacy of LAT1-mediated boron compound delivery. Notably, certain chemotherapeutic agents that induce cellular stress may upregulate LAT1 expression as a compensatory mechanism (111,112,120). This could potentially increase boron uptake in tumor cells, thereby enhancing the efficacy of BNCT. Future research should explore this avenue to identify chemotherapeutic agents that synergize with LAT1-targeted BNCT by exploiting this adaptive response.

LAT1 is aberrantly upregulated in a wide range of tumors, but the underlying regulatory mechanisms remain incompletely understood. Future research should focus on elucidating the molecular pathways that control LAT1 expression, including the role of transcription factors such as c-Myc and HIF-2α (107), and epigenetic modifications such as DNA methylation and histone acetylation (101,106). These studies will identify critical factors that influence LAT1 regulation and provide a theoretical basis for the development of targeted intervention strategies to either upregulate LAT1 for improved boron compound delivery or downregulate it to minimize off-target effects.

Furthermore, the function of LAT1 does not operate in isolation, but can be influenced by its interactions with other transporter proteins (11,121), which can significantly affect the intracellular uptake and distribution of boron compounds. Future investigations into the interaction networks of LAT1, including its relationships with other transporters, will provide insight into how these networks affect the efficiency of boron-containing compound transport. Protein interaction screening techniques such as yeast two-hybridization (122), co-immunoprecipitation (123) and high-throughput mass spectrometry (124) could be used to identify LAT1-interacting proteins and elucidate the molecular mechanisms underlying amino acid and nutrient uptake in tumor cells. These findings may shed light on new therapeutic strategies to enhance LAT1-mediated delivery in BNCT.

For example, advances in the design of boron compounds, such as fluorinated and α-methylated 3-borono-L-phenylalanine derivatives, have shown promise. These derivatives show improved water solubility, higher LAT1 selectivity and reduced boron accumulation in non-target tissues (125). Understanding the molecular interactions between LAT1 and boron-containing compounds may guide the design of next-generation boron carriers that optimize LAT1 activity and selectivity. This integration of regulatory and transport dynamics could lead to more efficient and targeted BNCT therapies.

The advancement of BNCT is critically dependent on the development of boron-containing compounds that possess low toxicity, high stability and the ability to accumulate selectively within tumor cells. Consequently, future research prioritizes the rational design of agents that can exploit tumor-specific biological features. A primary strategy involves targeting membrane proteins that are upregulated in cancer cells. LAT1, which is upregulated on the surface of tumor cells, is a promising therapeutic target. For example, drug design based on the structure-function properties of LAT1 has led to the identification and screening of selective, high-affinity boron-containing compounds (20,126). This targeting principle extends to other transporters, such as the glucose transporter, for which glucose-BSH compounds have been developed as a potential strategy against pancreatic cancer (127). More sophisticated approaches leverage multiple features of the tumor simultaneously. For instance, taking advantage of the unique features of the tumor microenvironment such as hypoxia and acidity, researchers developed the dual-target drug B139, which targets LAT1 and nitroreductase (128). In vitro, B139 shows high uptake in hypoxic tumor regions, with a boron content 70-fold that of BPA. In vivo, it remains in tumor cells for a long time, maintaining an effective therapeutic concentration, with a tumor-to-blood boron ratio of >3 and low cytotoxicity. Moreover, it may assist in developing prodrug systems for selective boron release in such environments (74,129,130).

Another powerful strategy for improving boron delivery is the application of nanotechnology. Nanoparticles, including polymer-based, liposomal or inorganic materials, have demonstrated the ability to improve the pharmacokinetic properties of boron compounds and achieve synergistic effects with BNCT. These nanocarriers protect boron compounds from rapid clearance in vivo, increase their stability and improve permeability in tumor tissues (117,131,132). The selective accumulation of these nanomedicines is largely driven by the enhanced permeability and retention effect, a phenomenon unique to the abnormal vasculature and poor lymphatic drainage of tumors. This passive targeting mechanism allows for prolonged drug retention at the tumor site, which maximizes therapeutic efficacy while minimizing off-target toxicity to healthy tissues (133).

An example of this approach is the development of surface-modified nanoparticles, such as a carboranylphosphatidylcholine based liposome for combinational BNCT and chemotherapy (24). These nanoparticles prolong the blood circulation time and tumor accumulation, allowing the selective delivery of high concentrations of ¹⁰B to the tumor microenvironment. Another innovative strategy involves metal nanoparticles that possess photothermal properties that can be activated by external stimuli. These nanoparticles are often used in tumor photothermal therapy (PTT) due to their high photothermal conversion efficiency, adding a complementary mechanism for tumor cell destruction. Recent breakthroughs include the development of boronophenylalanine-containing polydopamine nanoparticles, which combine BNCT with PTT to synergistically enhance tumor cell killing. These nanoparticles target upregulated LAT1 in melanoma using BPA, while their photothermal properties induce localized heating upon external stimulation, resulting in tumor cell death (73). Similarly, compounds with a higher boron content, such as ¹⁰B₄C-PG, have demonstrated significant therapeutic potential in BNCT through pharmacokinetic studies (134).

Future research should also address the challenges of metabolic stability and the biodistribution of boron compounds. Chemical modifications and structural optimization could improve in vivo stability while reducing accumulation in normal tissues, thereby minimizing toxicity. In addition, understanding the metabolic pathways of boron compounds and developing strategies to control their metabolism through molecular design will be critical to improving therapeutic outcomes. Through these approaches, the development of next-generation boron compounds tailored to LAT1-targeted BNCT may transform this therapeutic modality into a more effective and precise cancer treatment.

LAT1 expression is heterogeneous across different tumor types, and even within the same type of cancer. This variability is crucial to understanding its role in tumor biology and optimizing BNCT. A key challenge for BNCT is overcoming LAT1 heterogeneity, as it affects boron uptake and the overall effectiveness of the therapy. One approach is to develop dual-targeted therapies, which combine LAT1-targeted BNCT with other treatments to address multiple pathways involved in tumor progression. For instance, the glucose-binding boron compound G-BSH targets pancreatic cancer types with low LAT1 expression and enhances therapeutic efficacy when combined with BPA (127). Combining LAT1-targeted BNCT with immunotherapy may offer synergistic effects, improving treatment efficacy and reducing resistance. For example, engineered polyboronate ester micelles synthesized for BNCT can be paired with immune checkpoint inhibitors to activate the immune system and enhance tumor cell killing (21).

Non-invasive imaging and biomarkers are essential for personalizing BNCT treatments. LAT1-specific PET tracers, such as ¹⁸F-FBPA, can help assess LAT1 levels in tumors before treatment, ensuring improved patient stratification (41,68). Integrating high-throughput sequencing, proteomics and metabolomics will help identify factors that influence LAT1 function and improve treatment planning. These technologies can also reveal biomarkers associated with LAT1 activity, helping to predict patient responses and further tailor BNCT strategies.