In cancer, BCAAs metabolism is rewired to drive anabolic growth. Tumors frequently upregulate BCAT1, enhancing the conversion of BCAAs to BCKAs in the cytosol (Qian et al., 2023). Concurrently, BCKDH activity is often suppressed through dysregulation of its regulatory enzymes-typically via enhanced BCKDK activity or loss of PPM1K function-leading to marked accumulation of BCKAs (Lu et al., 2024; Du et al., 2018). These metabolites function as biosynthetic precursors for protein and lipid synthesis, directly facilitating biomass accumulation in proliferating cells. This metabolic shift is frequently accompanied by aberrant overexpression of transporters such as LAT1 and SLC25A44, thereby supplying ample substrate to fuel BCAT-driven metabolic flux (Schroeder et al., 2024; Yoneshiro et al., 2019).

Notably, accumulated BCKAs contribute to sustained activation of the mechanistic target of rapamycin complex 1 (mTORC1), further stimulating cell growth and establishing a feed-forward loop that reinforces metabolic reprogramming and malignant progression (Di Malta and Ballabio, 2018). Thus, tumor cells divert BCAAs catabolism from energy generation toward biosynthesis and oncogenic signaling, unveiling this pathway as a key metabolic vulnerability in cancer.

The reliance of various cancers on BCAAs metabolism can be stratified into three distinct archetypes, providing a clarifying framework that moves beyond a simple listing.

Reprogramming of BCAAs metabolism operates as a central signaling hub. This hub dynamically coordinates tumor growth, immune evasion, and therapy resistance through a network of interlocking feedback loops (Figure 4). Initiation of this circuit commonly stems from tumor-intrinsic metabolic rewiring, typified by upregulation of BCAT1 and/or suppression of the BCKDH complex. This diversion of BCAAs from oxidative catabolism toward biosynthetic pathways serves a dual role: it supplies precursors for macromolecule synthesis (e.g., branched-chain α-keto acids for protein and lipid production) and generates metabolite-derived oncogenic signals. A pivotal consequence of elevated BCAT1 activity is the depletion of cytosolic α-ketoglutarate (α-KG). This reduction impairs the function of α-KG-dependent dioxygenases, such as the TET family of DNA demethylases, leading to epigenetic dysregulation (e.g., DNA hypermethylation) and stabilization of hypoxia-inducible factors (HIFs). Consequently, a pro-growth transcriptional program becomes entrenched (Hattori et al., 2017; Meurs and Nagrath, 2022; Raffel et al., 2017). In parallel, accumulating BCKAs and leucine provide sustained activation of mTORC1, establishing a feed-forward loop that further induces the expression of BCAAs transporters like LAT1, thereby amplifying substrate uptake and reinforcing the metabolic shift (Di Malta and Ballabio, 2018; Mayers et al., 2016).

The altered metabolic state of the cancer cell extends its influence to remodel the tumor microenvironment (TME). Nutrient competition and the release of specific metabolites, including BCKAs, enact context-dependent immunomodulatory effects. These changes can potentiate the immunosuppressive activity of regulatory T cells (Tregs) and drive the polarization of tumor-associated macrophages toward a pro-tumorigenic M2 phenotype. Simultaneously, they contribute to a metabolically restrictive niche that compromises the effector functions of CD8⁺ T cells and natural killer (NK) cells (Ikeda et al., 2017; Zhang et al., 2024; Zhang et al., 2023). Collectively, these actions reshape the TME into an immunosuppressive ecosystem conducive to immune escape.

This integrated metabolic network also constitutes a direct engine of therapy resistance. The very enzymes that propel tumor growth and immune suppression simultaneously confer resilience against therapeutic agents. For example, BCAT1 has been shown to mediate resistance to conventional chemotherapeutics like cisplatin and to targeted agents such as EGFR tyrosine kinase inhibitors, achieved through adaptive signaling and epigenetic modifications (Zhang et al., 2024; Sjögren, 2021). Correspondingly, activation of BCKDK promotes tumor progression via mTORC1 and MAPK signaling pathways and has been linked to radioresistance by enhancing DNA damage repair mechanisms. This connection implicates BCAAs metabolism in treatment failure across diverse therapeutic modalities (Bo et al., 2025; Wang Y. et al., 2021; Liu et al., 2025).

These processes are not linear but are interconnected through reinforcing feedback loops. The hypoxic and acidic conditions of the TME, frequently a product of rapid tumor expansion, can themselves induce BCAT1 expression via HIF signaling (Meurs and Nagrath, 2022). The subsequent BCAT1-mediated depletion of α-KG then further stabilizes HIFs, creating a vicious cycle that perpetuates both metabolic and epigenetic reprogramming. In a similar vein, therapeutic pressure can select for cell populations with upregulated BCAAs pathway enzymes or directly induce their expression, thereby driving acquired resistance.

In summary, BCAAs metabolic reprogramming not as a peripheral supportive feature, but as a core orchestrator of malignant progression. It functions as a self-amplifying network that synergistically augments tumor cell fitness, dismantles anti-tumor immunity, and subverts therapeutic efficacy. Disruption of this network-via targeted enzyme inhibition, dietary modulation, or combination strategies informed by specific tumor dependency archetypes-represents a promising multidimensional therapeutic approach. Such strategies aim to simultaneously intercept multiple hallmark capabilities of cancer. Future research and clinical translation must rigorously account for the interconnected nature of this pathway to design effective and context-specific interventions.

BCAT1 and BCAT2 constitute a spatially compartmentalized regulatory circuit that fundamentally dictates BCAAs metabolic fate. Their distinct subcellular localization-cytosolic versus mitochondrial-establishes a metabolic bifurcation point (Figure 5) (Ananieva and Wilkinson, 2018). BCAT1 primarily channels BCAAs toward anabolic and signaling outputs: its transamination reaction depletes α-ketoglutarate (α-KG), influencing epigenetics and hypoxia responses, while elevating leucine to directly activate mTORC1. The resultant branched-chain α-keto acids (BCKAs) may accumulate or be secreted, acting as paracrine signals (Wegermann et al., 2018). In contrast, BCAT2 commits BCKAs to oxidative catabolism in the mitochondria, thereby controlling their clearance rate and preventing aberrant accumulation that can lead to sustained, low-grade mTORC1 activation (Sjögren, 2021). This dynamic interplay between the two enzymes regulates the balance between cytosolic α-KG availability, BCKA pools, and downstream anabolic signaling. Functionally, BCAT1 often drives pro-inflammatory immune modulation and confers resistance to chemotherapy and targeted therapies (Mayers et al., 2016; Zhang et al., 2024; Zheng et al., 2016). Conversely, BCAT2 frequently supports an immunosuppressive tumor microenvironment and its modulation can synergize with specific agents to induce metabolic stress (Cai et al., 2023; Wang K. et al., 2021). Thus, the BCAT1/BCAT2 axis acts as a metabolic rheostat, where the relative activity of each enzyme determines whether BCAAs fuel growth signals or are catabolized for homeostasis-a balance frequently disrupted in cancer to support progression and therapy resistance.

Branched-chain amino acid transaminase 1 (BCAT1) is frequently overexpressed across multiple cancer types (Table 1), where it has been functionally linked to enhanced tumor proliferation, therapy resistance, and immune evasion. In gastric cancer, elevated BCAT1 activates PI3K/AKT/mTOR pathway, drives tumor proliferation, invasion, and angiogenesis, correlating with unfavorable clinical outcomes (Shu et al., 2021; Xu et al., 2018). Similarly, in oral carcinomas, BCAT1 promotes cell proliferation and migration through activation of the PI3K/Akt signaling axis (Yuan et al., 2025). Within triple-negative breast cancer models, BCAT1 appears indispensable for sustaining tumor growth; its inhibition induces apoptosis via suppression of the SHOC2–RAS–ERK pathway induce apoptosis, highlighting a potential therapeutic vulnerability (Huang et al., 2025). Consistent with these findings, BCAT1 expression is markedly higher in breast tumor tissues compared to adjacent normal tissue, where it supports tumor cell proliferation by promoting mitochondrial biogenesis through an mTOR-dependent mechanism (Thewes et al., 2017). Further evidence indicates that in chronic myeloid leukemia (CML), BCAT1 catalyzes the conversion of branched-chain α-keto acids (BCKAs) to BCAAs, leading to mTOR pathway activation independent of AKT signaling and thereby accelerating disease progression (Hattori et al., 2017). Experimental inhibition of BCAT1 with gabapentin significantly curbs proliferation in human colorectal cancer cells (Jedi et al., 2018). In glioblastoma, knockdown of BCAT1 compromises oxidative phosphorylation (OXPHOS), mTORC1 activity, and nucleotide synthesis. Supplementation with α-ketoglutarate synergistically potentiates these impairments, leading to tumor cell death (Zhang et al., 2022; Meurs and Nagrath, 2022). Under hypoxic conditions, hypoxia-inducible factor (HIF) regulates BCAAs metabolic reprogramming via BCAT1, and gabapentin treatment substantially impairs colony-forming capacity in glioma cell lines (Zhang et al., 2021). It should be noted, however, that BCAT1 is not universally overexpressed; in certain non-small cell lung cancer (NSCLC) subtypes, its expression remains relatively low, and inhibition exerts no significant effect on tumor growth (Mayers et al., 2016).

Beyond promoting tumor progression, BCAT1 also mediates resistance to chemotherapy. In hepatocellular carcinoma (HCC), it confers resistance to cisplatin (Zheng et al., 2016) while in lung adenocarcinoma, BCAT1 drives resistance to EGFR tyrosine kinase inhibitors (TKI) through epigenetic modulation of glycolytic pathways (Zhang et al., 2024). A parallel role is observed in CML, where BCAT1 enhances TKI resistance (Jiang et al., 2025). Collectively, these observations position BCAT1-driven metabolic reprogramming as a recurrent mechanism underlying acquired therapy resistance in diverse malignancies.

BCAT2, another key enzyme in BCAAs metabolism, is essential for the development and progression of various cancers (Table 2). BCAT2 enhances cellular BCAAs uptake, maintains metabolic homeostasis, and supports mitochondrial respiration. Notably, in mouse models of pancreatic cancer, exogenous BCAAs promote ductal organoid growth, whereas supplementation with BCKAs and nucleobases reverses the antitumor effects of BCAT2 inhibition (Li et al., 2020). In PDAC patient specimens and murine models, BCAT2 is consistently upregulated; its targeted knockdown in pancreatic tissue effectively suppresses the formation of pancreatic intraepithelial neoplasia (Lei et al., 2020). Post-translational regulation of BCAT2 involves acetylation at lysine 44 (K44), which promotes degradation via the ubiquitin-proteasome system, thereby attenuating BCAAs catabolism and restraining pancreatic cancer cell growth (Lei et al., 2020). In melanoma, BCAT2 fosters lipogenesis by depleting acetyl-CoA and inhibiting histone acetylation at promoter regions of lipogenic enzymes such as fatty acid synthase and ATP-citrate lyase (Tian et al., 2023a). In colorectal cancer, loss of BCAT2 leads to sustained mTORC1 activation and accelerates tumor progression (Kang et al., 2024). In prostate cancer, BCAT2 interacts with poly(C)-binding protein 1 through leucine 239, suppressing autophagy-dependent apoptosis and ferroptosis via the PI3K/AKT pathway (Mei et al., 2025). Furthermore, BCAT2 contributes to an immunosuppressive tumor microenvironment by downregulating pro-inflammatory chemokines and limiting cytotoxic lymphocyte infiltration, which in turn drives resistance to anti-PD-1/PD-L1 therapies (Cai et al., 2023). In HCC, BCAT2 modulates ferroptosis and exhibits synergistic antitumor activity when combined with sorafenib and sulfasalazine (Wang K. et al., 2021).

In summary, BCAT1 upregulation is observed in a wide spectrum of cancers-including gastric, oral, nasopharyngeal, breast, gliomas, certain NSCLC subtypes, and AML-where it promotes progression through PI3K/Akt, SHOC2–RAS–ERK, and mTOR signaling pathways. BCAT2, by contrast, has been implicated in NSCLC, PDAC, melanoma, HCC, and prostate cancer, where it accelerates tumorigenesis via mechanisms such as K44 acetylation-mediated degradation, ferroptosis regulation, and activation of mTORC1 and PI3K/AKT signaling. Although both enzymes generally exert pro-tumor effects, their roles can diverge depending on context. In AML, co-upregulation of BCAT1 and BCAT2 triggers BCAAs metabolic reprogramming and fuels disease progression. Interestingly, in colorectal cancer, the two enzymes appear to function antagonistically: BCAT1 inhibition impairs proliferation, whereas BCAT2 loss activates mTORC1 and accelerates disease, suggesting tissue-specific regulatory networks that remain to be fully elucidated. The differential involvement of BCAT1 and BCAT2 in therapy resistance further highlights their clinical relevance. While BCAT1 confers resistance to cisplatin in HCC and to TKIs in lung adenocarcinoma and CML, BCAT2 synergizes with sorafenib and sulfasalazine in HCC. These contrasting profiles imply that tailored therapeutic strategies-combining specific chemotherapy agents with selective inhibition or modulation of BCAT1 or BCAT2-could offer novel avenues for overcoming treatment resistance, particularly in malignancies such as HCC.

BCAAs play a dual and context-dependent role in tumor progression by modulating T cell function. On one hand, BCAAs-particularly leucine-are essential for immune regulation through metabolic reprogramming and can contribute to antitumor responses, though their precise mechanisms remain incompletely elucidated (Zhou et al., 2025). On the other hand, BCAAs depletion may compromise T cell effector functions, dampening the anti-tumor immune response (Xia et al., 2021). Specific ablation of Slc3a2 in Foxp3⁺ Tregs impairs their in vivo expansion by disrupting isoleucine-dependent mTORC1 activation and cellular metabolism; conversely, enhanced BCAA metabolism sustains Treg survival and immunosuppressive function to promote tumor immune evasion (Ikeda et al., 2017). BCAAs accumulation enhances CD8⁺ T cell antitumor immunity by reprogramming glucose metabolism. This mechanism strengthens CD8⁺ T cell effector function, improving responses in lung cancer (Yao et al., 2023). Correspondingly, high BCAAs levels inhibit breast cancer progression and metastasis, likely through boosting CD8⁺ T cell activity (Chi et al., 2022). SLC3A2 and SLC7A5 serve as primary transporters for essential amino acids (O'Sullivan et al., 2019). Within activated T cells, SLC3A2 promotes T cell expansion, whereas SLC7A5 is involved in T cell differentiation, mTORC1 signaling activation, and c-Myc expression (Ikeda et al., 2017; Nachef et al., 2021; Kanai, 2022). Notably, inhibition of SLC7A5 compromises the capacity of T cells to eliminate tumor cells. Following T cell receptor activation, human CD4⁺ T cells upregulate both BCAT1 and SLC7A5, thereby enhancing leucine influx and catabolism-a process particularly critical for T helper 17 (Th17) cell responses (Najumudeen et al., 2021).

Branched-chain amino acids (BCAAs) are implicated in the metabolism and genetics of macrophages. BCAAs significantly suppress nitric oxide production in macrophages, with leucine exhibiting the most pronounced inhibitory effect. Additionally, BCAAs exert a protective role by mitigating hydrogen peroxide-induced DNA damage in macrophages (Lee et al., 2017). BCAAs metabolism also regulates macrophage polarization. In the pancreatic tumor microenvironment, infiltration of M2-type macrophages is markedly elevated which promotes pancreatic tumor growth and is associated with poor disease prognosis (Zhang et al., 2023). BCAT1 collaborates with bone marrow stromal antigen 2 (BST2) and the tyrosine kinase MERTK to facilitate cancer progression by regulating the type 2 polarization of tumor-associated macrophages, offering a potential therapeutic target for pancreatic cancer (Peng et al., 2023). Furthermore, BCAAs accumulation may promote M2-type macrophages, which support tumor growth and immunosuppression, while suppressing M1-type macrophages that possess anti-tumor functions.

In acute myeloid leukemia (AML), elevated expression of SLC7A5 enables natural killer (NK) cells to sustain a proliferative and activated state even under arginine-depleted conditions, promoting apoptosis of AML cells (Stavrou et al., 2023). Beyond leukemic contexts, increased levels of Branched-chain amino acids (BCAAs) enhance NK cell function, thereby restraining breast cancer progression and metastasis (Chi et al., 2022). Conversely, in cytokine-activated NK cells, pharmacological inhibition of SLC7A5 lowers c-Myc protein abundance and suppresses mTORC1 signaling, which unexpectedly amplifies their antitumor efficacy (Loftus et al., 2018). Together, these observations highlight the context-dependent role of SLC7A5 and BCAAs metabolism in shaping NK cell activity, offering potential therapeutic avenues for modulating antitumor immunity.

BCAAs metabolism orchestrates a context-dependent immunomodulatory network that differentially regulates the function of major immune cell populations. In T cells, BCAAs exhibit a dual role: while required for maintaining CD8⁺ T cell effector capacity and antitumor immunity, they concurrently reinforce the immunosuppressive activity of regulatory T cells (Tregs), thereby facilitating immune escape. In macrophages, BCAAs-driven metabolic reprogramming promotes polarization toward a pro-tumor M2 phenotype while suppressing the antitumor functions associated with M1 macrophages. With respect to NK cells, although BCAAs availability generally supports cytotoxic function, pharmacological inhibition of the BCAAs transporter SLC7A5 has been observed to unexpectedly enhance antitumor efficacy, revealing a targetable metabolic checkpoint in these cells. Central to this regulatory network, SLC7A5 integrates extracellular BCAAs levels with intracellular metabolic and signaling rewiring across immune cell types, positioning it as a promising therapeutic target for reprogramming antitumor immunity.

BCAT1, which is highly expressed in neuronal tissues and contributes to glutamate synthesis can be inhibited by several compound classes N-Arylcarbonylarylsulfonylhydrazides function as BCAT1 inhibitors and have been explored as neuroprotective agents in neurodegenerative contexts. Their mechanism extends to the preservation of mitochondrial function, achieved by mitigating oleic acid–induced ROS generation and membrane potential loss, thereby reducing autophagic flux and suppressing associated airway inflammation and remodeling (Hu et al., 2006). Thiazolones represent another class of BCAT1 inhibitors primarily investigated for preventing neuronal loss, though their potential application in cancer therapy remains to be elucidated (Li et al., 2004). Among compounds evaluated in oncology, 4-methyl-5-oxohexanoic acid (MOHA) has been identified as a BCAT1 inhibitor with antitumor activity. In MDA-MB-231 breast cancer cells, MOHA downregulates surface CD147 expression, attenuates immune reactivity, and inhibits proliferation. It also suppresses the growth of other cancer lines, including MCF-7, MDA-MB-435, and HT-29, while reducing levels of matrix metalloproteinase-2 (MMP2) (Papatthanassiu, 2012). The widely used neuroactive agent gabapentin-along with its analogs-acts as a selective, competitive inhibitor of BCAT1 and has been proposed for the treatment of glioblastoma and astrocytoma (Kukkar et al., 2013; Chen et al., 2022; Radlwimmer et al., 2013). Interestingly, however, studies in HCT116 colorectal cancer cells revealed that gabapentin-mediated growth suppression occurs independently of BCAAs transamination, pointing to an off-target effect possibly involving mitochondrial BCKA catabolism (Grankvist et al., 2018). This suggests that gabapentin may exert context-dependent antitumor effects through both BCAT1-dependent and -independent pathways. Beyond conventional small molecules, several other agents modulate BCAT1 activity in cancer settings. Bufalin, a broad-spectrum anticancer compound known to regulate PI3K/Akt, Wnt/β-catenin, and NF-κB signaling, has recently been shown to bind directly to BCAT1, thereby sensitizing pancreatic cancer cells to gemcitabine and 5-fluorouracil (Zhang W. et al., 2025). The GABA-derived molecule WQQ-345, featuring a unique bridged bicyclic scaffold, exhibits in vitro and in vivo activity against TKI-resistant lung cancer cells with high BCAT1 expression (Luo et al., 2025). Epigenetic regulation also plays a role: low circulating levels of miR-320a in patients with growth hormone–secreting pituitary neuroendocrine tumors correlate with BCAT1 upregulation, and restoration of this microRNA suppresses tumor progression via BCAT1 targeting (Zhao et al., 2024). Furthermore, curcumin induces apoptosis in cytarabine-resistant AML cells partly through downregulation of BCAT1 and inhibition of mTOR signaling (Tseng et al., 2021). The AT1R antagonist candesartan dose-dependently inhibits both wild-type and mutant BCAT1 (E61A), impairs migration and Ras Homolog Gene Family, Member C (RhoC) activity in esophageal and gastric cancer cells, and suppresses peritoneal metastasis in a RhoC-dependent manner (Qian et al., 2023).

Inhibition of BCAT2 has been pursued using structurally diverse compounds. Fused imidazoles containing cis-1,3-cycloalkanedi-amine scaffolds-such as benzimidazoles, pyridinoimidazoles, and pyrimidinoimidazoles-effectively reduce BCAT2 levels in engineered A549 cells (Deng et al., 2015). Through screening of DNA-encoded libraries encompassing 14 billion compounds, Deng et al. identified biphenyl-tetrahydropyrrole (12-15e) as a potent BCAT2 inhibitor active after DNA cleavage (Deng et al., 2015). Another orally available agent, dihydropyrazolopyrimidine with benzylamine (13–61), elevates plasma BCAAs concentrations in a dose-dependent manner via BCAT2 inhibition. Additional BCAT2-directed molecules include thiophenopyrimidine carboxamides, which show micromolar inhibition, detectable cellular activity, and favorable solubility. The clinically used angiotensin receptor blocker telmisartan concentration-dependently suppresses BCAT2 enzymatic activity in biochemical and cellular assays and may promote lipid metabolism through BCAT2-mediated PPAR activation, suggesting potential utility in metabolic disorders (Zhang et al., 2025b). Finally, Ray and colleagues designed a series of pyrazoline derivatives, among which compounds 16-4a, 16-4e, and 16-4f demonstrated effective binding to the BCAT2 active site in molecular docking studies (Ray et al., 2023). Together, these findings underscore the pharmacologic tractability of BCAAs catabolic enzymes and highlight a growing repertoire of chemical tools and drug candidates for potentially modulating BCAT1 and BCAT2 in cancer and related pathologies.

Branched-chain α-ketoacid dehydrogenase kinase (BCKDK) plays a multifaceted role in tumorigenesis, notably through phosphorylation of MEK to activate the RAS/RAF/MEK/ERK signaling axis, thereby promoting cellular proliferation (Xue et al., 2017). Given its central regulatory function, BCKDK has emerged as a compelling therapeutic target in oncology. Pharmacological inhibition of BCKDK, achieved via small-molecule allosteric modulators such as 3,6-dichloro-1-benzothiophene-2-carboxylic acid (BT2) and (S)-α-chlorophenylpropionate, disrupts its activity by inducing conformational shifts within the N-terminal domain helix (Tso et al., 2014). This structural alteration triggers the dissociation of BCKDK from the BCKDH complex and facilitates its subsequent degradation, ultimately suppressing tumor growth (Du et al., 2022; East et al., 2021). Comparative analyses indicate that BT2 possesses superior inhibitory potency and metabolic stability relative to (S)-α-chlorophenylpropionate, alongside an ability to enhance BCKDH activity in primary hepatocytes (East et al., 2021).

The therapeutic potential of BCKDK inhibition has been validated across diverse malignancies. In triple-negative breast cancer models, intervention targeting BCKDK lowers branched-chain ketoacid levels, remodels BCAAs metabolic flux, and concurrently upregulates Sestrin2 while suppressing mTORC1 signaling-a combination that attenuates proliferation and induces apoptotic cell death. Synergy with doxorubicin has further been documented (Biswas et al., 2021). Similarly, in ovarian cancer and non-small cell lung cancer, BCKDK expression correlates with disease progression, and its genetic or pharmacological inhibition curbs cancer cell proliferation, migration, and cell cycle progression (Li H. et al., 2022; Bagheri et al., 2022). Continuous optimization of inhibitory strategies is underway. Leveraging virtual screening and structural biology, novel allosteric compounds including PPHN and POAB have been identified, demonstrating potent BCKDK inhibition coupled with marked anti-proliferative and pro-apoptotic activities both in vitro and in vivo (Li C. et al., 2024). One particularly optimized derivative, PF-07328948, was developed through strategic modification of the BT2 core via 3-aryl substitution, capitalizing on a cryptic binding pocket. This agent effectively degrades BCKDK in situ, markedly reduces circulating BCAAs and BCKA concentrations, exhibits favorable pharmacokinetics, and improves both metabolic parameters and cardiac function endpoints in rodent models of heart failure (Filipski et al., 2025).

Beyond its metabolic roles, BCKDK participates in DNA damage response pathways, including homologous recombination repair. Co-administration of BCKDK inhibitors such as GSK180736A with DNA-damaging chemotherapeutics can therefore overcome treatment resistance in breast cancer models (Liu et al., 2025). In parallel, fragment-based screening employing NMR and computational methods has identified tetrazole-containing scaffolds that bind BCKDK at multiple sites. Subsequent structure-based virtual screening revealed that certain angiotensin receptor blocker antihypertensives and related compounds also act as potent BCKDK inhibitors, suggesting a novel therapeutic avenue that merges BCKDK inhibition with cardiovascular management in conditions like heart failure (Liu et al., 2023). Reports of bioactive bicyclic carboxyamide inhibitors further underscore the expanding chemical space for targeting this kinase (Liang et al., 2024). Collectively, these advances highlight BCKDK and associated pathways-including the USP1/BCAT2 axis-as precision oncology targets with translational promise across several disease contexts.

It should be noted, however, that current inhibitors present certain pharmacological challenges. BT2, for instance, acts as a lipophilic weak acid capable of mitochondrial uncoupling, which may lead to off-target effects. Its high affinity for plasma albumin also potently reduces systemic tryptophan levels, a phenomenon that warrants consideration in therapeutic development.

Building upon prior mechanistic insights, the translational targeting of branched-chain amino acid (BCAAs) metabolism-especially through inhibition of BCAT1, BCAT2, and BCKDK-reveals considerable therapeutic potential alongside substantial complexity.

Concerning inhibitor development, although multiple chemical scaffolds have been explored-from gabapentin and its analogs against BCAT1 to allosteric modulators such as BT2 for BCKDK-most remain in preclinical or early discovery stages (Kukkar et al., 2013; Tso et al., 2014; Li C. et al., 2024). Exceptions include repurposed clinically approved agents like the AT1R antagonist candesartan and the neuroactive drug gabapentin, which exhibit direct BCAT1 inhibitory activity in cancer models and may allow accelerated clinical evaluation (Qian et al., 2023; Kukkar et al., 2013). Nevertheless, a dedicated, clinical-grade inhibitor designed specifically for oncology applications has not yet been developed, underscoring a persistent disconnect between target validation and drug discovery.

A central translational concern involves potential effects on normal tissues. BCAAS metabolism is integral to physiological homeostasis, particularly in the brain and skeletal muscle. BCAT1, for example, supports glutamate synthesis in neuronal tissue, raising the possibility of neurotoxicity with systemic inhibition (Dimou et al., 2022). Likewise, BCAT2 plays a key role in nitrogen and energy balance in muscle. Consequently, establishing a therapeutic window will likely require tumor-selective delivery approaches-such as nanoparticle conjugates or protease-activated prodrugs-or the identification of isoform- or context-selective inhibitors that preserve essential physiological functions.

Several key challenges hinder clinical translation. First, metabolic plasticity within tumors and a dynamic tumor microenvironment may enable compensatory pathways or alternative nutrient acquisition, leading to inherent or adaptive resistance. Second, the absence of validated predictive biomarkers represents a major obstacle to identifying patients whose tumors display genuine dependence on BCAAs pathways. Putative biomarkers, including BCAT1 promoter methylation, circulating levels of branched-chain ketoacids (BCKAs), or specific transcriptional signatures, require rigorous clinical validation (Wegermann et al., 2018; Zou et al., 2019). Third, achieving favorable pharmacokinetics and target selectivity with current lead compounds, while limiting on-target toxicity in normal tissues, remains a demanding pharmacological challenge.

Pharmacological modulation may also provoke unintended off-target or compensatory responses. For instance, gabapentin’s anti-proliferative effects in certain settings appear independent of BCAT1 inhibition and may involve off-target mitochondrial actions (Grankvist et al., 2018). The BCKDK inhibitor BT2, though effective, functions as a lipophilic weak acid capable of mitochondrial uncoupling-a property that could influence both its efficacy and adverse effect profile (East et al., 2021). Moreover, systemic BCAT2 inhibition would be expected to increase circulating BCAAs, which might inadvertently support tumor growth in contexts where BCAAs uptake is not limiting, or induce unanticipated systemic metabolic alterations.

In summary, while BCAAs-catabolizing enzymes remain attractive therapeutic targets, their successful incorporation into oncology demands a multifaceted approach. This includes the rational design of next-generation inhibitors with improved selectivity, the parallel development of reliable companion diagnostics, and the proactive addressing of metabolic adaptation through rationally designed combination regimens. Navigating these translational subtleties will be critical to transforming the compelling preclinical data on BCAAs metabolism into precise and clinically viable cancer therapies.