Abstract: Non-small cell lung cancer (NSCLC) remains a major clinical challenge due to the frequent emergence of resistance to traditional chemotherapy, targeted therapies, and immune checkpoint inhibitors. The mesenchymal-epithelial transition/plasticity (MET/EMP) axis and the AXL receptor tyrosine kinase have been identified as critical drivers of tumor progression, epithelial-mesenchymal transition (EMT), and therapeutic resistance. Bemcentinib (R428 or BGB324) is a first-in-class, highly selective, orally bioavailable small-molecule inhibitor of AXL. This review synthesizes current literature on bemcentinib in the context of NSCLC, highlighting its pharmacological activity, molecular mechanism of action, and its synergistic potential when combined with epidermal growth factor receptor (EGFR) inhibitors and immune checkpoint blockade. Furthermore, we discuss the current limitations of bemcentinib, including toxicity and acquired resistance, and outline future perspectives focusing on biomarker-driven personalized treatment strategies to optimize clinical outcomes in advanced NSCLC.
1. Introduction
Lung cancer is a leading cause of cancer-related morbidity and mortality worldwide, with non-small cell lung cancer (NSCLC) accounting for approximately 85% of all cases [2]. While advancements in targeted therapies (such as EGFR tyrosine kinase inhibitors) and immune checkpoint inhibitors (ICIs) have revolutionized the treatment landscape for NSCLC, primary and acquired resistance mechanisms continue to limit long-term patient survival [2]. A major contributor to this resistance is epithelial-mesenchymal plasticity (EMP), a dynamic process encompassing the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET), which facilitates tumor dissemination, metastasis, and immune evasion [1].
The AXL receptor tyrosine kinase, a member of the TAM (TYRO3, AXL, MER) family, is frequently overexpressed in NSCLC and is a central mediator of EMT, tumor survival, and adaptive resistance to both targeted therapies and immunotherapies [1][2]. Bemcentinib (also known as BGB324 or R428) has emerged as a highly selective, orally bioavailable small-molecule inhibitor targeting AXL [1]. By interfering with AXL signaling, bemcentinib represents a promising therapeutic strategy to counteract drug resistance, modulate the tumor microenvironment (TME), and enhance the efficacy of existing NSCLC treatments [1][2].
2. Pharmacological Activity
Bemcentinib has demonstrated potent antitumor activity in preclinical NSCLC models and early-phase clinical trials, both as a monotherapy and in combination regimens [1]. Preclinically, bemcentinib reverses resistance to EGFR-TKIs (such as osimertinib and erlotinib) by suppressing EMT, down-regulating DNA repair genes, and inducing G2/M cell cycle arrest and apoptosis [2]. In TP53-deficient NSCLC cells, bemcentinib induces DNA damage and replication stress, which significantly enhances cytotoxicity when combined with ATR inhibitors [2].
Beyond direct tumor cytotoxicity, bemcentinib exhibits profound immunomodulatory pharmacological activity. It reprograms the immunosuppressive TME by enhancing dendritic cell activity, increasing CD8+ T-cell proliferation, and reducing the presence of regulatory T cells and immunosuppressive myeloid cells [1][2]. Furthermore, AXL blockade by bemcentinib reduces PD-L1 expression on tumor cells, creating a strong biological rationale for its combination with anti-PD-1/PD-L1 therapies [2].
Clinically, bemcentinib has shown favorable tolerability and preliminary efficacy. In a phase I trial combining bemcentinib with docetaxel in previously treated advanced NSCLC, patients achieved a 35% partial response rate and a 47% stable disease rate [2]. The phase II BGBC008 trial evaluating bemcentinib in combination with pembrolizumab reported a 26% overall response rate with durable benefits lasting over 12 months in AXL-positive tumors [2]. Notably, bemcentinib has been granted FDA Fast Track designation for patients with STK11-mutant metastatic NSCLC, a subgroup notoriously unresponsive to standard therapies [1][2].
3. Molecular Mechanism of Action
Bemcentinib functions as a first-in-class, highly selective inhibitor of the AXL receptor tyrosine kinase [1]. At the molecular level, bemcentinib selectively binds to the ATP-binding pocket of the AXL kinase domain [1]. This binding competitively blocks the autophosphorylation of the receptor that is normally induced upon binding of its endogenous ligand, growth arrest-specific 6 (GAS6) [1][2].
The inhibition of AXL autophosphorylation subsequently prevents the activation of critical downstream oncogenic signaling cascades, including the PI3K/AKT/mTOR, MAPK/ERK, and NF-κB pathways [1][2]. By shutting down these pathways, bemcentinib effectively halts tumor cell proliferation, invasion, and metastasis [1]. Additionally, the suppression of sustained PI3K/AKT and NF-κB signaling promotes the reversal of EMT (facilitating MET), thereby reducing mesenchymal traits that drive therapy resistance and immune evasion [1].
4. Structure-Activity Relationship (SAR)
While exhaustive chemical structure-activity relationship (SAR) details are limited in the provided literature, the pharmacological design of bemcentinib (R428) is centered on its ability to act as an ATP-competitive inhibitor. The compound is structurally optimized to selectively occupy the ATP-binding pocket of the AXL receptor tyrosine kinase [1]. This specific binding interaction is responsible for its high selectivity for AXL over other kinases, which minimizes off-target effects while maintaining potent inhibition of AXL autophosphorylation [1]. Furthermore, the molecular structure of bemcentinib confers favorable pharmacokinetic properties, including rapid absorption, high oral bioavailability, and steady-state plasma concentrations that ensure sustained AXL inhibition [1].
5. Current Limitations
Despite its therapeutic promise, the clinical application of bemcentinib faces several limitations regarding toxicity, resistance, and biomarker validation. The safety profile of bemcentinib is generally manageable, but it presents specific adverse events. Common toxicities include fatigue, nausea, diarrhea, anemia, thrombocytopenia, QTc prolongation, and mild transaminase (ALT/AST) elevations [1]. More severe, though less frequent, toxicities include hepatotoxicity, pneumonitis, and neutropenia; the latter required prophylactic G-CSF management when bemcentinib was combined with docetaxel [1][2]. Furthermore, combining bemcentinib with immune checkpoint inhibitors can exacerbate inflammatory responses and lead to immune-related adverse events (irAEs), necessitating proactive monitoring [1][2].
Acquired resistance to bemcentinib also remains a significant hurdle. Tumors can develop compensatory survival signaling through parallel receptor tyrosine kinase pathways (such as c-MET or HER3) or acquire mutations within the AXL kinase domain, which limit the long-term efficacy of the drug [1][2].
Finally, patient selection is complicated by the dual predictive role of AXL expression. While high tumor AXL expression correlates with improved disease control in certain first-line ICI cohorts, it is also linked to immunosuppressive phenotypes and poor overall survival in chemotherapy-pretreated patients [2]. Discrepancies between tumor-cell AXL and immune-cell AXL expression make the standardization of predictive biomarkers challenging [2].
6. Future Perspectives
The future development of bemcentinib in NSCLC relies heavily on refining rational combination strategies and advancing precision oncology approaches. To overcome adaptive resistance and maximize the therapeutic window, ongoing clinical trials are actively exploring the integration of bemcentinib with EGFR-TKIs, traditional chemotherapies, and PD-1/PD-L1 inhibitors [1][2]. Combinations with other pathway modulators, such as TGF-β inhibitors, are also suggested to counteract microenvironment-driven resistance [2].
A critical future direction is the implementation of biomarker-driven patient selection. Utilizing tumor AXL expression levels, PD-L1 status, and specific genetic profiles—most notably STK11/LKB1 mutations—will be essential to identify the populations most likely to benefit from AXL inhibition [2]. Additionally, the use of liquid biopsies to dynamically monitor circulating tumor DNA (ctDNA), circulating GAS6 levels, and mesenchymal gene signatures will allow clinicians to track EMP dynamics, optimize dosing, and detect emerging resistance mechanisms in real-time [1][2]. Ultimately, integrating these molecular profiling techniques with bemcentinib-based regimens holds the potential to significantly improve personalized care and survival outcomes for patients with advanced NSCLC [2].
