What are the preclinical assets being developed for c-Met?

Overview of c-Met
c-Met, also known as the hepatocyte growth factor receptor (HGFR), is a receptor tyrosine kinase that has been extensively studied in the context of cancer biology for its multifunctional roles in tumor initiation, progression, and metastasis. Preclinical research over the past two decades has revealed that aberrant c-Met signaling—whether caused by overexpression, gene amplification, mutations, or ligand‐dependent autocrine mechanisms—can drive cellular processes such as proliferation, migration, invasion, survival, and angiogenesis. These findings have positioned c-Met as a significant oncogenic driver in a wide spectrum of malignancies, including non‐small cell lung cancer, gastric cancer, renal cell carcinoma, and others.

Role in Cancer Biology
At its core, the c-Met receptor operates by binding to its only known ligand, hepatocyte growth factor (HGF). This binding event prompts receptor dimerization and autophosphorylation of critical tyrosine residues (e.g., Y1234/Y1235 and Y1349/Y1356), which in turn initiate a complex intracellular signaling cascade. Such pathways include the PI3K-AKT, RAS-RAF-MAPK, and STAT cascades that strongly contribute to malignant phenotypes such as increased proliferation and enhanced migratory capacity. Notably, preclinical models have demonstrated that c-Met signaling not only promotes tumor cell growth but also plays a pivotal role in epithelial–mesenchymal transition (EMT), drug resistance, and even in the maintenance of cancer stem cell (CSC) populations. This biochemical versatility highlights the ability of c‐Met to regulate multiple aspects of tumor biology concurrently.

Importance as a Therapeutic Target
The inherent role of c-Met in oncogenesis has led to heightened interest in exploiting this receptor as a therapeutic target. In numerous preclinical studies, inhibiting c-Met activity has resulted in marked tumor growth suppression and, in some instances, complete regression of xenograft tumors. Inhibition strategies focus on disrupting the receptor’s activation—from blocking HGF binding, preventing receptor dimerization, to inhibiting the downstream catalytic activity. Given that dysregulated c-Met signaling is associated with poor clinical outcomes and resistance to standard therapies, there is a strong rationale for developing targeted agents that modulate this pathway. Consequently, the pipeline of c-Met therapeutic agents includes both small molecule inhibitors and biologic assets, each designed to address various molecular aberrations within the pathway.

Current Preclinical Assets
The current portfolio of preclinical assets targeting c-Met can broadly be divided into two categories: small molecules and biologics. Each of these is being developed to improve specificity, efficacy, and delivery while minimizing off-target toxicities. Preclinical studies using in vitro assays, cell-based models, and in vivo xenograft studies have provided strong evidence supporting the potential of these assets.

Small Molecules
Small molecule inhibitors form a well‐established segment of preclinical assets targeting c-Met. These compounds generally function by competing with ATP for binding to the kinase domain of c-Met, thereby inhibiting its catalytic activity. Detailed structure–activity relationships have been exploited to optimize these molecules, with the aim of achieving high potency and selectivity. For example, novel chemotypes incorporating triazolopyrazine or pyridoxazine scaffolds have been synthesized and optimized, leading to agents such as KRC-00715, which in preclinical studies demonstrated potent inhibition of c-Met activity with exclusive selectivity in kinase panel assays. Other assets such as MK-8033 have also been under investigation; although clinical results indicated limited clinical activity, the insights gathered in these first-in-human studies have helped fine-tune further small molecule design for enhanced target engagement.

Several patents have reported novel nitrogen-containing heterocyclic compounds as c-Met inhibitors, highlighting an emphasis on structure optimization and improved metabolic stability. Moreover, another patent describes analogous compounds with carefully designed substituents that increase selectivity against c-Met mutant forms while reducing off-target interactions. In addition to traditional ATP-competitive inhibitors, efforts are underway to develop allosteric inhibitors that can modulate c-Met conformation without competing with ATP, potentially leading to a distinct resistance profile. These small molecules are often tested via in vitro kinase assays, detailed cellular phosphorylation studies, and eventually in xenograft models to assess tumor inhibition and safety profiles in animal subjects. Such compounds are typically characterized by endpoints such as maximum tolerated dose (MTD), progression-free survival (PFS) in murine models, and pharmacokinetic/pharmacodynamic (PK/PD) relationships. The overall goal is to yield a compound that is not only potent in inhibiting c-Met but also amenable to combination strategies that can overcome the tumor heterogeneity and resistance seen in clinical settings.

Biologics
Biologic approaches to targeting c-Met have attracted significant preclinical interest, particularly owing to their potential for high specificity and novel mechanisms of action. This category includes monoclonal antibodies, bispecific antibodies, antibody-drug conjugates (ADCs), and even cell-based therapies such as chimeric antigen receptor (CAR)-T cells targeting c-Met.

Monoclonal antibodies (mAbs) directed against c-Met have been designed with the aim of either blocking the receptor’s interaction with HGF or inducing receptor internalization and subsequent degradation. Unlike small molecule inhibitors that primarily compete at the ATP-binding site, these mAbs can engage the extracellular domain of c-Met and prevent ligand-induced dimerization. In preclinical studies, several mAbs demonstrated favorable outcomes; for example, certain antibodies with epitopes in the cysteine-rich or β-propeller regions have been found to promote receptor internalization and degradation, essentially reducing the receptor surface expression on tumor cells. This approach has been further refined to produce non-agonistic antibodies that avoid receptor activation, a common pitfall encountered with bivalent antibody formats.

Bispecific antibodies represent another innovative biologic asset. These dual-targeting agents are designed to engage both c-Met and immune effector cells, such as by simultaneously binding to CD3 on T cells. One such bispecific antibody (e.g., BS001) not only inhibits HGF/c-Met signaling by blocking the interaction but also recruits T-cells to mediate cytotoxicity against tumor cells. This dual mechanism has shown promising activity in preclinical models, with bispecific antibodies demonstrating tumor growth inhibition in xenograft models when administered alone or in combination with other immunotherapies.

CAR-T cell therapy directed at c-Met is also a notable preclinical asset. c-Met-specific CAR-T cells are engineered to express a chimeric antigen receptor that recognizes the extracellular domain of c-Met. Preclinical evidence shows that these CAR-T cells exhibit robust proliferation, cytokine secretion (including IL-2, IFN-γ, and TNF-α), and potent cytotoxicity against c-Met–expressing tumor cells in both in vitro coculture assays and in vivo xenograft models. This cell-based immunotherapy leverages the power of the adaptive immune system to target tumors with high c-Met expression, thereby offering a potential option for tumors that have developed resistance to conventional small molecule therapies.

Additionally, antibody-drug conjugates (ADCs) targeting c-Met have been developed, where a monoclonal antibody is conjugated to a cytotoxic payload. The ADC binds to c-Met on the tumor cell surface, is internalized, and releases the cytotoxic drug intracellularly, leading to cell death even in cells with lower c-Met expression. These ADCs are engineered to have an optimal drug-to-antibody ratio (DAR) to ensure maximum potency while avoiding rapid clearance and off-target toxicity. This approach adds another dimension to the biologics portfolio, combining precise targeting with the delivery of potent chemotherapeutics.

Research and Development Strategies
The development of preclinical assets for targeting c-Met has been guided by a comprehensive set of strategies aimed at understanding the molecular mechanisms of c-Met activation, resistance, and cross-talk with other signaling pathways. These strategies integrate structure-based drug design, advanced animal models, and innovative assay technologies to optimize both small molecules and biologics.

Mechanisms of Action
A central strategy in the preclinical development of c-Met inhibitors is the detailed elucidation of their mechanisms of action. Small molecule inhibitors typically function by binding to the kinase domain of c-Met, thereby preventing ATP binding and subsequent receptor autophosphorylation. These compounds are subjected to meticulous structure–activity relationship studies to improve potency and selectivity. For instance, novel analogs are designed to accommodate the conformational flexibility of the c-Met kinase domain, thereby targeting both wild-type and mutant forms of the receptor. Some agents have been engineered to function as allosteric inhibitors, offering a unique approach to modulate receptor function without blockade of the ATP pocket. This design potentially overcomes some forms of drug resistance, which arise from mutations in the active site.

On the biologics side, monoclonal antibodies and bispecific antibodies operate by binding to distinct epitopes on the extracellular domain of c-Met. This binding may either block ligand (HGF) binding directly, sterically hinder the receptor dimerization, or induce receptor internalization. Some antibodies are specifically optimized to avoid agonistic activity—a critical feature given that receptor cross-linking can inadvertently activate c-Met signaling. CAR-T cells and ADCs also have their own mechanisms; CAR-T cells mediate cytotoxicity via a complex interaction with tumor antigens and can be engineered to enhance cytokine production and T-cell persistence, while ADCs deliver cytotoxic payloads intracellularly to induce programmed cell death. Each of these modalities is designed after deep molecular characterization of the c-Met receptor structure and its interaction with ligands and inhibitors, ensuring that the asset disrupts the oncogenic signaling cascade at multiple levels.

Preclinical Models and Studies
Preclinical development for c-Met targeting assets relies heavily on robust in vitro and in vivo models that recapitulate human cancer biology. In vitro kinase assays, along with cellular phosphorylation studies, are used to quantify the inhibition of c-Met activity by small molecules. These assays often involve using cancer cell lines selected for high c-Met expression or genetic amplification, enabling the study of drug response dynamics under controlled conditions. Techniques such as Western blot analysis, immunoprecipitation, and high-throughput screening assays provide quantitative measures of receptor phosphorylation, downstream signaling inhibition, and subsequent cellular responses like cell cycle arrest or apoptosis.

For in vivo studies, xenograft models in immunocompromised mice are commonly employed to evaluate the antitumor efficacy of both small molecules and biologics. These models allow researchers to observe the impact of c-Met inhibition on tumor growth, metastasis, and overall survival. For example, agents such as KRC-00715 have been evaluated in Hs746T xenograft models, where significant tumor size reduction was observed, accompanied by modulation of downstream signaling pathways such as Akt and Erk. Additionally, cell-based assays using three-dimensional culture systems and spheroid models are emerging as important tools to assess the penetration, distribution, and efficacy of ADCs and bispecific antibodies.

Moreover, advanced imaging techniques have been incorporated into preclinical studies to monitor the pharmacokinetics and biodistribution of c-Met inhibitors. PET probes based on small molecules, antibodies, or peptides have been utilized to quantify c-Met expression and activation states in vivo, providing a dynamic readout of drug activity and receptor occupancy. These preclinical studies are critical to validate the therapeutic potential of the assets and fine-tune dosage, formulation, and combination strategies before progressing to clinical trials.

Challenges and Future Directions
While significant progress has been made in developing preclinical assets for c-Met targeting, several challenges remain along with promising future opportunities to enhance therapeutic efficacy and overcome resistance.

Developmental Challenges
One of the primary challenges in the development of c-Met inhibitors is the issue of tumor heterogeneity. Tumors are increasingly recognized to possess a heterogeneous expression pattern of c-Met, which can complicate targeted therapy since not all cells within a tumor may rely equally on c-Met signaling. Moreover, the development of acquired resistance is a significant concern. Resistance mechanisms may involve secondary mutations in the c-Met kinase domain, bypass signaling through alternative growth factor receptors, or compensation by downstream signaling pathways. In the biologics arena, a major hurdle lies in avoiding undesired receptor activation. For example, bivalent antibodies sometimes display agonistic activity, which can paradoxically stimulate rather than inhibit c-Met signaling. Therefore, engineering non-agonistic antibodies that can effectively trigger receptor internalization and degradation without activating downstream pathways has been a considerable technical challenge.

Another key challenge is balancing the drug’s pharmacokinetics and pharmacodynamics while minimizing off-target toxicity. With small molecule inhibitors, issues such as rapid clearance or metabolic instability can reduce effective tumor exposure. Similarly, ADCs must maintain an optimal drug-to-antibody ratio (DAR) to avoid destabilization of the antibody structure and off-target effects that can damage normal tissues expressing basal levels of c-Met. Additionally, since normal cells (particularly those of mesenchymal origin) express c-Met and rely on its physiological functions for tissue regeneration and repair, careful dosing and selective targeting are imperative to avoid impairing normal tissue function.

Future Research Opportunities
Despite these challenges, the preclinical landscape for c-Met–targeting assets provides ample opportunities for future research. One important area is the identification and validation of predictive biomarkers that can aid in patient selection. Preclinical studies are actively incorporating molecular markers, such as MET amplification, phosphorylation status, and gene mutation profiles, to stratify patients who might benefit from specific c-Met inhibitors. The development of companion diagnostic tools, including imaging probes and liquid biopsies, could further refine patient selection and treatment monitoring.

Another promising approach involves combining c-Met targeting agents with other therapeutic modalities. For example, combining small molecule inhibitors or biologics with immune checkpoint inhibitors or other targeted therapies may yield synergistic effects. Preclinical studies have begun evaluating combination strategies in xenograft models, where dual blockade of c-Met and parallel pathways (such as EGFR or VEGFR) has shown improved antitumor efficacy. In addition, CAR-T cells and bispecific antibodies targeting c-Met may demonstrate enhanced activity when combined with pharmacologic modulators that sensitize tumors to immune-mediated killing.

Further research is also merited in the area of drug delivery and formulation. Nanotechnology and novel drug conjugation techniques could improve the bioavailability and tumor-specific delivery of c-Met inhibitors. For instance, the encapsulation of small molecule inhibitors in nanoparticles or liposomes might improve their pharmacokinetic profiles and reduce off-target toxicities. Additionally, the design of multispecific molecules that can target c-Met along with key co-receptors or downstream effectors holds promise to overcome compensatory resistance mechanisms.

Finally, next-generation preclinical models, such as patient-derived xenografts (PDX) and organoid cultures, are increasingly being integrated into the drug development pipeline. These models can more accurately recapitulate human tumor heterogeneity and microenvironment, providing a robust platform for evaluating the efficacy of novel c-Met inhibitors and for understanding the molecular underpinnings of drug resistance. The continuous exploration of these advanced models is expected to lead to improved translation of preclinical findings into clinical benefits.

Conclusion
In summary, the preclinical assets being developed for targeting c-Met encompass a wide array of innovative approaches that span both small molecule inhibitors and biologic therapies. Small molecules, designed to inhibit the c-Met kinase domain via ATP-competitive or allosteric mechanisms, are undergoing extensive optimization in structure–activity relationship studies to enhance their potency, selectivity, and metabolic stability. Biologic assets, including monoclonal antibodies, bispecific antibodies, ADCs, and CAR-T cells, provide alternative strategies aimed at blocking ligand-receptor interactions, inducing receptor internalization, and engaging the immune system to target c-Met–expressing tumors.

Research and development strategies in this field integrate detailed mechanistic studies with robust preclinical models—ranging from in vitro kinase assays and cell-based phosphorylation studies to in vivo xenograft and PDX models—to evaluate efficacy, toxicology, and pharmacokinetic/pharmacodynamic relationships. Despite significant progress, substantial challenges remain, including tumor heterogeneity, the emergence of resistance mechanisms, off-target toxicities, and the need for predictive biomarkers to properly select patients who will benefit most from c-Met–targeted therapies.

Looking forward, future research opportunities include the development of combination regimens that pair c-Met inhibitors with immunotherapies or agents targeting complementary pathways, as well as innovations in drug delivery systems (such as nanoparticle formulations) to further improve therapeutic index and efficacy. The integration of advanced imaging techniques and next-generation models such as organoids and PDXs will likely enhance our understanding of c-Met dynamics and facilitate the translation of preclinical assets into successful clinical therapies.

In conclusion, the preclinical assets targeting c-Met represent a diverse and innovative armamentarium aimed at disrupting a key oncogenic driver in multiple cancers. Through a multi-pronged approach that includes the optimization of small molecule inhibitors and the design of sophisticated biologics, researchers have laid a robust foundation for the eventual clinical application of these agents. Continued investment in understanding c-Met biology, combined with the integration of advanced preclinical models and biomarker-driven patient selection strategies, is expected to propel the development of effective c-Met–targeted therapies that overcome current limitations and improve patient outcomes.