Abstract: Bemcentinib (also known as BGB324 or R428) is a first-in-class, highly selective, orally bioavailable small-molecule inhibitor targeting the AXL receptor tyrosine kinase. Originally developed for oncology, bemcentinib has demonstrated significant potential in overcoming therapeutic resistance and immune evasion driven by epithelial-mesenchymal transition (EMT) in various malignancies, including non-small cell lung cancer (NSCLC) and acute myeloid leukemia (AML). By blocking the AXL/GAS6 signaling axis, bemcentinib remodels the tumor microenvironment, enhances the efficacy of immune checkpoint inhibitors, and restores sensitivity to targeted therapies. Furthermore, recent research has expanded its therapeutic scope into infectious diseases, particularly COVID-19, where AXL and EMT play critical roles in viral pathophysiology and lung injury. This review synthesizes the pharmacological activity, molecular mechanisms, limitations, and future perspectives of bemcentinib based on current literature.
1. Introduction
Bemcentinib (R428, BGB324) is a highly selective, orally bioavailable small-molecule inhibitor of AXL, a receptor tyrosine kinase belonging to the TAM (TYRO3, AXL, MER) family [1]. AXL is frequently overexpressed in multiple cancers and is a key driver of tumor progression, metastasis, and epithelial-mesenchymal plasticity (EMP) [1][2]. The activation of AXL promotes epithelial-mesenchymal transition (EMT), a process that not only facilitates cancer dissemination but also contributes significantly to resistance against chemotherapy, radiotherapy, and targeted therapies such as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) [2].
Beyond its established role in oncology, the therapeutic application of bemcentinib is being actively explored in the context of infectious diseases, most notably COVID-19. Recent clinical and preclinical findings highlight the role of kinase inhibitors in COVID-19 management, as Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) induces EMT, which significantly contributes to the pathophysiology and lung damage associated with the disease [1]. By targeting AXL, bemcentinib offers a dual therapeutic approach: combating oncogenic signaling in treatment-resistant cancers and modulating viral-induced cellular plasticity in severe infectious diseases.
2. Pharmacological Activity
Bemcentinib exhibits broad pharmacological activity across multiple disease models, primarily characterized by its ability to reverse EMT and modulate immune responses.
Oncology: In NSCLC, AXL blockade by bemcentinib restores sensitivity to EGFR inhibitors (such as osimertinib and gefitinib) by preventing compensatory survival signaling [1][2]. It also demonstrates profound immunomodulatory effects. Bemcentinib remodels the tumor microenvironment (TME) by enhancing the activation of CD103+ dendritic cells, increasing CD8+ T-cell proliferation, and reducing the presence of immunosuppressive regulatory T cells (Tregs) and myeloid-derived suppressor cells [1][2]. In clinical trials, bemcentinib combined with pembrolizumab (an anti-PD-1 antibody) achieved a 26% overall response rate in advanced NSCLC patients, with durable benefits particularly in AXL-positive tumors [2]. It has also shown efficacy in acute myeloid leukemia (AML), melanoma, pancreatic cancer, and glioblastoma [1]. The FDA has granted bemcentinib Fast Track designation for patients with STK11-mutant metastatic NSCLC, a subgroup notoriously unresponsive to standard therapies [1][2].
Infectious Diseases (COVID-19): The pharmacological scope of bemcentinib extends to viral infections. Kinase inhibitors are increasingly recognized for their role in COVID-19 management. SARS-CoV-2 infection induces EMT, which exacerbates lung pathophysiology and fibrosis. By inhibiting AXL, bemcentinib attenuates these EMT-driven processes, presenting a novel pharmacological intervention for mitigating severe COVID-19 symptoms and related fibrotic complications [1].
Pharmacokinetics: Bemcentinib is administered orally once daily. It possesses favorable pharmacokinetics characterized by rapid absorption, high bioavailability, and hepatic metabolism primarily via the CYP3A4 enzyme. Steady-state plasma concentrations are achieved within days, ensuring sustained AXL inhibition [1].
3. Molecular Mechanism of Action
Bemcentinib functions by selectively binding to the ATP-binding pocket of the AXL receptor tyrosine kinase. This binding blocks the autophosphorylation of the receptor, thereby preventing its activation by its primary ligand, Growth Arrest-Specific 6 (GAS6) [1]. The inhibition of the GAS6/AXL axis disrupts several critical downstream signaling cascades, including the PI3K/AKT, MAPK/ERK, NF-κB, and STAT3 pathways, which are responsible for driving cell proliferation, survival, migration, and immune evasion [1][2].
At the cellular level, bemcentinib exerts its effects through multiple mechanisms:
- EMT Reversal: Unlike TGF-β-driven EMT, AXL promotes EMT through sustained PI3K/AKT and NF-κB signaling. Bemcentinib attenuates this signaling, reversing the mesenchymal phenotype back to an epithelial state, which reduces metastatic potential and restores drug sensitivity [1].
- Immune Modulation: Bemcentinib downregulates PD-L1 expression on tumor cells via PI3K/Akt pathway inhibition. It also reverses chemotherapy-induced immunosuppression by restoring antigen presentation and reducing neutrophil infiltration [2].
- DNA Damage Induction: In TP53-deficient NSCLC cells, bemcentinib induces DNA damage and replication stress. It enhances cytotoxicity when combined with ATR inhibitors by increasing RPA32 hyperphosphorylation and triggering mitotic catastrophe [2].
4. Structure-Activity Relationship (SAR)
Bemcentinib is a rationally designed small-molecule kinase inhibitor. Its structure-activity relationship is defined by its high selectivity for the AXL kinase over other receptor tyrosine kinases. The molecule is structurally optimized to competitively and selectively occupy the ATP-binding pocket of the AXL intracellular kinase domain [1]. By fitting precisely into this pocket, bemcentinib prevents the binding of adenosine triphosphate (ATP), which is an absolute requirement for the autophosphorylation of the receptor's tyrosine residues. This targeted structural engagement ensures potent inhibition of AXL-mediated downstream signaling while maintaining a manageable safety profile compared to multi-targeted kinase inhibitors [1].
5. Current Limitations
Despite its therapeutic promise, the clinical application of bemcentinib faces several limitations:
- Adverse Events and Toxicity: While generally manageable, bemcentinib is associated with toxicities such as fatigue, nausea, diarrhea, anemia, and thrombocytopenia. Mild to moderate transaminase (ALT/AST) elevations are common, and rare but severe events include hepatotoxicity, pneumonitis, QTc prolongation, and medication-related osteonecrosis of the jaw (MRONJ) [1][2]. Combination with immune checkpoint inhibitors can also lead to overlapping immune-related adverse events [1].
- Acquired Resistance: Tumor cells can develop resistance to bemcentinib through compensatory signaling via parallel receptor tyrosine kinases (such as c-MET, EGFR, HER3, or FGFR1) or through secondary mutations within the AXL kinase domain itself [1][2].
- Drug-Drug Interactions: Because bemcentinib is heavily metabolized by the hepatic enzyme CYP3A4, its co-administration with CYP3A4 inducers or inhibitors requires strict monitoring to prevent altered drug plasma concentrations [1].
6. Future Perspectives
The future development of bemcentinib relies on rational combination strategies and precision medicine approaches. To overcome compensatory resistance mechanisms, ongoing clinical trials are evaluating bemcentinib in combination with other targeted agents, such as MEK inhibitors, EGFR TKIs, and ATR inhibitors [1][2]. Furthermore, its ability to convert "immune-cold" tumors into "immune-hot" environments makes it a prime candidate for combination with immune checkpoint blockade (e.g., pembrolizumab), particularly in PD-L1-low or STK11-mutant populations [2].
Advancing biomarker-driven patient selection is critical. Future trials must utilize predictive biomarkers—such as AXL expression levels (via immunohistochemistry), circulating GAS6 levels, EMT gene signatures, and circulating tumor DNA (ctDNA)—to identify patients most likely to benefit from AXL inhibition [1][2].
Finally, the role of bemcentinib outside of oncology warrants further investigation. Its capacity to inhibit EMT and modulate immune responses positions it as a potential therapeutic agent for fibrotic diseases and severe viral infections, including COVID-19, where EMT-driven tissue remodeling contributes to disease severity [1].
