Application of bispecific antibodies in tumor therapy
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Application of bispecific antibodies in tumor therapy
Application of bispecific antibodies in tumor therapy. Application of bispecific antibodies targeting two tumor-associated antigens in tumor therapy.
More than 30 years ago, the FDA approved the world’s first monoclonal antibody drug (OKT3) for marketing. Since then, the development of therapeutic antibody drugs has kicked off. Currently, more than 70 therapeutic antibody drugs have been approved for marketing worldwide, and more than 550 antibody drugs are in the clinical development stage. This indicates that therapeutic antibody drugs have grown into one of the fastest growing types in the pharmaceutical market.
In recent years, among the large family of antibody drugs, bispecific antibodies (BsAbs) have sprung up, and they have received extensive attention in the application of tumor therapy. Compared with traditional monoclonal antibodies, bispecific antibodies have the following potential advantages: by targeting two different tumor-associated antigens at the same time (not requiring strict tumor specificity), in theory, BsAb can improve the drug targeting tumor. Specificity, reduce toxic side effects to normal tissues.
Since cancer is a very complex multi-factor disease, targeting two targets at the same time can regulate two tumor-related signal pathways, thereby avoiding tumor resistance to a certain extent. In addition, BsAb can also mediate many biological functions that cannot be achieved by combining two monospecific antibodies, such as redirecting a certain type of immune cells to target tumor cells, extending the half-life and crossing the blood-brain barrier.
In the 1960s, Nisonoff and others combined antigen-binding fragments (Fab) derived from two kinds of rabbit-derived polyclonal antibody sera through a gentle reoxidation method, thus creating the world’s first simultaneous binding Two kinds of antigen capable antibodies, namely bispecific antibodies (BsAb).
While people were expecting that it could become the next generation of therapeutic antibody drugs, BsAb did not succeed because of clinical failure and production and purification problems. In the past two decades, the development of BsAb has been greatly promoted due to the protein engineering and the improvement of production and purification technology brought about by the advancement of biotechnology. In the face of increasingly complex BsAbs, our process has the ability to meet its specific structure, function, and physical and chemical properties. In oncology, two BsAbs have been approved for clinical treatment.
One is Catumaxomab. It is a BsAb that targets both CD3 and EpCAM (Epithelial Cell Adhesion Molecule). It was approved by the European Medicines Agency (EMA) in 2009 for the treatment of malignant ascites but was delisted in 2017 for commercial reasons. The other is Blinatumomab (Blinatumomab).
The antibody targets both CD3 and CD19 and was approved by the FDA in 2014 for the treatment of acute lymphoblastic leukemia (ALL) in Philadelphia chromosome-negative B cells. The approval of these two BsAbs for listing has further aroused strong attention from pharmaceutical and biotech companies and stimulated investment in this field.
Compared with other types of BsAbs, especially BsAbs that play a cell bridging function, BsAbs that simultaneously target two tumor-associated antigens (TAAs) have received very limited attention and discussion. Therefore, this article will summarize the research status of this type of BsAb, and discuss various factors that need to be paid attention to when developing this type of antibody, so as to provide references for future research.
Configuration of bispecific antibodies
According to different constant regions, antibodies can be divided into five categories: IgG, IgM, IgA, IgD and IgE. The basic structure of IgG antibody is composed of two pairs of heavy chain-light chain polypeptide chains. Among them, the heavy chain and the light chain are combined by interchain disulfide bonds and non-covalent bonds. The structure of the entire IgG antibody is similar to the “Y” type, with a total molecular weight of approximately 150KDa.
An antibody molecule can also be divided into two parts according to different functions: antigen-binding fragment (Fab) and fragment crystallizable (Fc) region (Figure 1a). The Fc region of the antibody is located at the tail of the antibody and can bind to the neonatal receptor to extend the half-life of the antibody. In addition, the Fc region can also mediate a series of secondary immune responses to kill target cells, for example, antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and complement-dependent cytotoxicity ( CDC).
Traditional antibodies usually consist of two identical heavy-light chain complexes, and are symmetrical and monospecific. BsAb has two different antigen binding sites. Therefore, the configuration of BsAb is more diverse and complex than traditional antibodies.
Due to advances in protein and genetic engineering technology, scientists have now invented more than 100 different BsAb configurations, about a quarter of which have been converted into commercial platforms for the production of BsAb. According to whether it contains the Fc region, we can roughly divide the different BsAb configurations into two categories, namely, BsAbs containing Fc region and BsAbs lacking Fc region.
figure 1
BsAb configuration containing Fc region
The configurations of BsAbs containing Fc region mainly include Duobody, FIT-Ig, 2:2 CrossMab, mAb-Trap, etc. (Figure 1b). The presence of Fc allows them to bind to neonatal Fc receptors (FcRn), thereby obtaining a longer half-life. In addition, according to the different mechanisms of action of different antibodies, the Fc region can also be designed to mediate different secondary immune responses to meet its needs (Table 1). On the other hand, in order to solve the mismatch problem in the production and purification of BsAb, BsAb containing Fc region needs to be engineered, which may lead to changes in the physical and chemical, biological properties and even affinity of the antibody. Therefore, an additional series of analysis and detection are required. Come for quality control.
BsAb configuration lacking Fc region
BsAb without Fc is composed of single chain variable region fragment (scFv) and heavy chain variable region fragment (VHH) or two different antibody Fabs, such as BiTE, DART, TandAb, Bi-VHH, etc. (Figure 1c ). Because of the lack of the Fc region, this type of BsAb usually has a smaller molecular weight, which has a relatively high yield and better tissue penetration, lower immunogenicity, and avoids the problem of heavy chain mismatches. However, this feature also brings some disadvantages, such as short half-life in vivo, poor stability, and easier formation of aggregates (Table 1).
Table 1: Comparison of BsAbs with/without Fc region
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CMC (Chemical Manufacturing and Control): chemical composition production and control
BsAb targeting two TAAs
As of April 2020, at least 123 types of BsAbs are undergoing tumor-related clinical research (including the already marketed catumaxomab and Bonatumumab). Among the 123 types of BsAb, most of them can be classified as bispecific immune cell engagers (BICE) (82/123). BICE can simultaneously target a receptor expressed on the surface of immune cells and a receptor on the surface of tumor cells, thereby redirecting immune cells to the surrounding tumor cells. Given that this type of antibody has received widespread attention and discussion, this article will summarize and discuss another type of BsAb: BsAb that targets two TAAs.
Compared with traditional antibodies, the application of BsAb to target two TAAs at the same time may have the following advantages: increase the specificity of the drug to target tumors; simultaneously regulate two tumor-related signaling pathways; improve drug delivery efficiency (Figure 2). Although BsAbs targeting the two TAAs account for only a small percentage (9/123) of BsAbs undergoing tumor-related clinical research, and they involve very limited targets, this also means their huge growth potential ( Table 2).
figure 2
Increase the specificity of drugs targeting tumors
Many tumor-targeted monospecific antibodies not only kill tumor cells, but also cause serious on-target toxicity in healthy tissues. For example, a monoclonal antibody targeting CD47 can block the “don’t eat me” signal expressed on tumor cells. Tumor cells usually express this signal to escape macrophage-mediated phagocytosis, but the signal also exists on red blood cells, platelets and some healthy cells.
Because anti-CD47 monoclonal antibody can cause severe anemia and thrombocytopenia, Celgene terminated the phase I clinical study of CC-90002 (an antibody targeting CD47) (NCT02641002). In order to solve this problem, one arm of BsAb is designed to specifically target tumor cells, and the other arm is a fragment that targets CD47 with optimized affinity to improve the tumor specificity of CD47 antibody.
For example, TG-1801 (also known as NI-1701) is a 1:1 IgG1 BsAb that targets CD19 (a biomarker widely expressed on normal B cell and B cell leukemia) and CD47. TG-1801 has a relatively low affinity CD47 binding fragment and a high affinity CD19 binding fragment. Therefore, TG-1801 may be able to overcome the limitations of the CD47 monospecific antibody by using the tumor specificity of CD19 to allow the antibody to only block the “don’t eat me” signal expressed on B cells.
Similarly, IMM0306, a BsAb targeting CD20 and CD47 developed by ImmuneOnco, not only achieved significant anti-tumor effects in preclinical studies, but also did not show binding to human red blood cells in various tumor models. In addition to hematological malignancies, there are also some BsAbs that increase their blocking/activation specificity in solid tumors in a similar manner, such as IBI322 and RO6874813 (RO7386).
In the treatment of B-cell-derived leukemia, it is acceptable to kill healthy B-cells to a certain extent (such as CD19 targeted therapy). However, in the treatment of solid tumors, the situation is different. IBI322 is a BsAb targeting CD47 and PDL-1 developed by Cinda Biopharmaceuticals. The data shows that the antibody will preferentially accumulate in PDL-1 positive solid tumor tissues in vivo, thereby reducing the side effects caused by blocking the CD47 signaling pathway of healthy cells.
In another example, RO6874813 is a 2:2 CrossMab that can tightly bind fibroblast activating protein (FAP) expressed on tumor stroma and bind death receptor 5 (DR5) with low affinity. Tumor necrosis factor receptor (TNFR) superfamily member DR5 is usually expressed on tumor cells, and its activation can induce apoptosis.
Targeting FAP can enrich RO6874813 on tumor-associated fibroblasts rather than healthy cells, increase its local concentration around DR5, and induce DR5 clusters to activate, thereby inducing tumor cell apoptosis.
In fact, no tumor-specific antigens in the strict sense have been found to be used as antibody targets. Although targeting two TAAs at the same time will increase the specificity of the antibody to tumor cells, this alone is not enough. To solve this problem, Mazor et al. prepared a number of different BsAbs that target EGFR and HER2.
The difference between them is that they have different affinity for targeting EGFR. In the end, one of the BsAbs is more likely to bind to EGFR and HER2 double-positive cells and rarely binds to EGFR single-positive cells. This study proves that we may need to further optimize the affinity of BsAbs targeting two TAAs to achieve better tumor specificity.
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MCLA-128 PB4188 |
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(NCT03321981) |
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(NCT02370160) |
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(NCT03797391) |
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(NCT02609776 and NCT04077463) |
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(NCT03804996) |
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(NCT04338659 and NCT04328831) |
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(NCT03526835) |
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(CTR20192612) |
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(NCT02558140) |
Simultaneously block two tumor-related signaling pathways
Cancer is a highly complex multifactorial disease involving the interaction of multiple pathogenic proteins and signaling pathways. The complex molecular network constructed by the interaction between different signaling pathways may lead to tumor resistance and immune escape. Due to the heterogeneity of tumors, tumor resistance often occurs in tumor patients who relapse after receiving single-molecule targeted therapy.
Epidermal growth factor receptor (EGFR) is the first receptor tyrosine kinase discovered. It plays an important role in regulating cell proliferation, survival and differentiation. Overexpression of EGFR is associated with many epithelial malignancies, such as non-small cell lung cancer, ovarian cancer, colon cancer, and prostate cancer.
In the past two decades, tyrosine kinase inhibitors (TKIs) such as gefitinib and erlotinib have achieved great success in clinical applications by targeting the EGFR signaling pathway, but they are also facing resistance to tumors Sexual issues. For example, patients with non-small cell lung cancer (NSCLC) who respond to a generation of TKI drugs will usually relapse and develop resistance within a year or less.
Although the second/third-generation TKIs can temporarily solve the problem of resistance to the first-generation TKIs, they will eventually be caused by new EGFR mutations, making patients insensitive to the second/third-generation TKIs treatment. Another important cause of tumor resistance to TKIs is the activation of other receptor tyrosine receptor kinase (RTK) pathways. For example, scientists have found that tumors can compensate for the EGFR signaling pathway inhibited by TKIs by activating the hepatocyte growth factor/mesenchymal transition factor (HGF/MET) pathway.
Based on this, two companies, Johnson & Johnson and Anmai Bio, have respectively developed a BsAb targeting EGFR and c-Met (JNJ-61186372, Johnson & Johnson; EMB01, Anmai Bio) is currently undergoing clinical research. JNJ-61186372 is a humanized BsAb targeting EGFR and c-Met prepared by Fab exchange technology (controlled Fab-arm exchange, cFAE), which can simultaneously block ligand-induced phosphorylation of EGFR and c-MET.
Its Fc region has been engineered to reduce fucosylation so that it can initiate a stronger ADCC reaction. In addition, JNJ-61186372 directly reduces the expression of EGFR and c-Met protein on the tumor surface, avoiding the root cause of drug resistance due to new mutations in EGFR or c-MET.
In a phase I clinical study (NCT02609776), 108 patients with advanced NSCLC received the antibody treatment and showed good safety and anti-tumor effects, including EGFR exon 20 insertion and EGFR C797S mutation , Met amplification and patients who are resistant to third-generation TKI ossitinib.
Based on these data, the FDA has granted JNJ-61186372 Breakthrough Drug Designation (BTD) for the treatment of metastatic NSCLC patients who have progressed after platinum-containing chemotherapy and have insertion mutations in EGFR exon 20.
In another example, BsAb Zenocutuzumab (also known as MCLA-128, PB4188), which targets HER2 and HER3, is undergoing clinical trials to treat patients with solid tumors with neuregulin-1 (NRG1) fusion mutations.
NRG1 is a member of the EGF family, which can bind to HER3 and induce HER2 and HER3 to form a heterodimeric complex. Studies have found that many patients with HER2-driven tumors develop resistance after receiving HER2 targeted therapy because of the occurrence of NRG1 fusion mutations that activate the HER3 pathway. NRG1 fusion mutation may be used as a potential marker to select patients most likely to respond to Zenocutuzumab.
NRG1 fusion occurs in about 3% of NSCLC and about 1.5% of pancreatic cancer patients, and the incidence in other cancer patients is less than 1%. In addition, NRG1 fusion often occurs in KRAS wild-type pancreatic ductal adenocarcinoma, which provides a new potential therapeutic target for patients who do not respond to KRAS inhibitors.
Due to its high affinity for HER2, Zenocutuzumab can be anchored to HER2 protein, preventing the formation of HER2/3 heterodimers and the binding of NRG1 fusion protein to HER3, thereby inhibiting tumor cell proliferation.
Improve drug delivery efficiency
Antibody-drug conjugate (ADC) therapy takes advantage of the targeting of antibodies and the cytotoxicity of carrier drugs, and couples the two. Once the ADC drug binds to the antigen expressed by the target cell, it will be endocytosed by receptor-mediated endocytosis and release the cytotoxic drug in the cell.
In the case that strict tumor-specific targets have not been found and some targets cannot be well endocytosed, BsAb may be a better drug carrier than monospecific antibodies.
For example, a large number of clinical data and the approval of trastuzumab antibody-drug conjugates for the treatment of metastatic breast cancer have proved that HER2 is an effective ADC drug target.
However, the endocytosis of ADC drugs targeting HER2 usually depends on the aggregation and cross-linking of HER2 protein, and monomeric HER2 cannot well mediate endocytosis. In order to improve the endocytosis efficiency of ADC drugs targeting HER2, scientists have developed a BsAbADC drug targeting CD63 and HER2.
CD63, also known as Lysosomal Associated Membrane Protein 3 (LAMP3), is a member of the four transmembrane protein superfamily that can shuttle between cell membranes and cells, and is overexpressed in pancreatic cancer, gastric cancer and melanoma. This BsAb targeting HER2 and CD63 mediates a strong endocytosis reaction, enriching lysosomes in HER2-positive tumors and releasing cytotoxicity.
Targeted therapies for CD19 and CD22 have been successful in the treatment of B-cell lymphoma and hairy cell leukemia (HCL), respectively. However, for CD19-targeted therapy, some leukemia cells lose CD19 and express CD22, so they can escape CD19-targeted therapy-mediated killing.
For CD22 targeted therapy, the number of patients with HCL is very limited and cannot benefit more leukemia patients. To solve these problems, scientists have developed OXS-1550 (also known as DT2219ARL), a BsAb that targets CD19 and CD22 and carries diphtheria toxin. The antibody is currently undergoing clinical phase I studies for the treatment of relapsed/refractory B-cell lymphoma.
In summary, BsAb-based ADC drugs can increase the tumor characteristics of the drug, enhance endocytosis or overcome the escape mechanism of tumor cells. Therefore, ADC drugs based on BsAb have great potential to become the next generation ADC drugs.
Challenges in developing BsAb targeting two TAAs
There is sufficient scientific evidence to support the use of BsAb in the treatment of multifactorial diseases, such as cancer. Compared with monospecific antibodies, BsAb has its unique advantages, but there are also some problems that need to be solved in the development. Based on this, although the monoclonal antibody supervision and evaluation system has been very mature, the FDA published the BsAb development guidelines in April 2019.
This guideline highlights the special precautions for BsAb development, including unique mechanism of action, CMC, non-clinical pharmacology and clinical research. The development of specific BsAb drugs usually requires strong scientific evidence as support, including but not limited to:
Full knowledge of the two targets of the antibody;
The scientific principle behind targeting these two targets (mechanism of action, MOA); the rationality of the dose;
And a better risk-benefit ratio than monospecific antibody drugs and existing therapies.
Although diversified antibody configurations and engineering modifications make BsAb meet its original MOA and clinical applications, it may also lead to:
(1) Unexpected changes in BsAb properties, such as immunogenicity, antigen specificity, affinity and half-life or
(2) Issues related to production, including output, process-related impurities and stability. Each different BsAb may have its unique development and process factors to consider.
But in the end, all BsAb products need to meet the relevant requirements of standard monoclonal antibodies, which poses a severe challenge to the CMC of BsAb.
In addition, when BsAb is undergoing clinical research, in addition to comparing it with existing standard therapies or placebos, in some cases, the FDA may require that BsAb be compared with monospecific antibodies with the same target on the market. In order to evaluate its risk-benefit ratio. According to the BsAb guidelines issued by the FDA, there are several key factors that need to be carefully considered when developing targeting two TAAs, including:
- (1) Selection of target;
- (2) The affinity and biological function of each antigen-binding arm of BsAb;
- (3) Configuration selection.
Target selection
The target selection basically determines the MOA of the BsAb, and a reasonable target selection is the most important step in developing a successful BsAb. The ideal BsAb should be able to mediate new biological functions that cannot be achieved through the combined use of two monospecific antibodies. Basic biological research has revealed the important role of c-Met in NSCLC patients resistant to EGFR TKI, which not only strongly supports the development and design of JNJ-61186372 (BsAb targeting EGFR × c-MET), It also provides evidence support for patient screening.
Finally, JNJ-61186372 showed a good anti-tumor effect in NSCLC patients resistant to EGFR TKI. Interestingly, duligotuzumab (also known as MEHD7945A), a BsAb that targets EGFR and HER3, did not achieve a better performance in a phase II clinical trial for the treatment of metastatic colorectal cancer and head and neck squamous cell carcinoma. Cetuximab (cetuximab, a monoclonal antibody targeting EGFR) has better efficacy.
The RNA or protein expression level of HER3 in tumor biopsy also has no correlation with the response rate of patients to duligotuzumab. Therefore, the researchers concluded that HER3 does not play a key role in patients with metastatic colorectal cancer and head and neck squamous cell carcinoma who are not using EGFR inhibitors.
However, there are other researchers who hold different views on this. They believe that the reason why this study did not get the expected results was mainly due to the improper selection of subjects (the patients were not screened according to the criteria for resistance to cetuximab). Similarly, before duligotuzumab, a phase III study (NCT02134015) using patritumab (HER3 inhibitor) in combination with erlotinib (EGFR inhibitor) in the treatment of NSCLC patients also failed.
Therefore, the scientificity and rationality of choosing EGFR and HER3 as BsAb targets are debatable. So far, BsAbs targeting the two TAAs only involve very limited targets, and they are mainly ErbB family proteins. Therefore, there is an urgent need to develop BsAbs targeting new target combinations to cope with unmet clinical needs.
The affinity and biological function of each antigen-binding arm of BsAb
The affinity and biological activity of BsAb targeting each target will have a significant impact on the final clinical outcome. Before JNJ-61186372 of Johnson & Johnson, Eli Lilly also developed BsAb (LY3164530) targeting EGFR and c-Met. However, the study was terminated due to its side effects and lack of predictive biomarkers and did not enter the Phase II clinical trial.
LY3164530 is a combination of c-MET-targeting IgG4 antibody (emibetuzumab, LY2875358) and EGFR-targeting scFv (cetuximab) fused to the N-terminus of each heavy chain. Because Eli Lilly used two existing antibodies (cetuximab and emibetuzumab) to construct LY3164530, the affinity and activity of each independent arm in LY3164530 have been fixed, so the BsAb cannot regulate the blocking effect of EGFR and c-MET. Strong or weak, it is impossible to optimize the affinity of the antibody for each antigen according to actual needs.
In clinical trials, the researchers found that LY3164530 showed obvious toxicity, and the toxicity was related to its strong EGFR inhibition but not to c-MET inhibition. These data means that improving the affinity and biological function of each antigen-binding arm of LY3164530 may improve its overall toxicity to patients.
In contrast, JNJ-61186372 was selected from the EGFR×c-MET BsAb pool based on functional activity. Similarly, zenocutuzumab is also selected from an antibody pool containing 545 BsAbs.
In addition, sometimes a BsAb is composed of two parent antibodies, and the combined BsAb can exhibit completely opposite biological properties to its two parent antibodies. For example, there is a DVD-Ig (dual-variable-domain immunoglobulin) BsAb that targets HER2, which is composed of two HER2 antagonist antibodies (trastuzumab and pertuzumab), but This BsAb finally proved to be a HER2 agonist antibody.
Therefore, to determine the biological function of a BsAb, the affinity and biological activity of the BsAb should be tested after the BsAb is constructed, and cannot be inferred from the function of its parent antibody.
Configuration selection
The configuration of BsAb can greatly affect its final physical and chemical properties and biological functions. At present, researchers have invented more than 100 different BsAb configurations to solve various scientific or technical problems. There has never been a universal BsAb configuration suitable for all application scenarios.
The configuration suitable for the specific application scenario required by it is the best BsAb configuration. Appropriate configuration design can enhance the anti-tumor effect of BsAb and/or reduce its side effects. Currently, BsAbs targeting two TAAs usually use human IgG1 backbones. This is mainly because it can give BsAb a longer half-life and induce a strong secondary immune response.
Many studies have shown that the slight difference in the amino acid sequence of CH2 and CH3 domains and the glycosylation distribution of the Fc region have a great impact on the thermal stability, pharmacokinetic properties and FcγR-mediated secondary immune response of antibodies. FcγRIII expressed on human macrophages, monocytes, neutrophils, plasma cells, and NK cells can bind more tightly to antibodies with low glycosylation, thereby more effectively inducing ADCC effects.
For example, MCLA-128 uses GlymaxX® technology (ProBiogen) to reduce fucosylation and enhance the ADCC effect of MCLA-128, while retaining its ability to bind to FcRn. JNJ-61186372 is produced by a special CHO cell line, which cannot be modified by protein fucosylation, thus enhancing the ADCC effect of the antibody.
In addition to the difference in the Fc region of an antibody, the direction of the variable region and the flexibility of the hinge region also affect the function of IgG antibodies. According to reports by Kapelskia et al., the hinge regions of human IgG subclasses show different flexibility (IgG1>IgG4>IgG2, where IgG1 is the most flexible) and affects the ability of BsAb to redirect T cells.
In another example, researchers used the DVD-Ig platform to use the same parent antibody as raw materials to prepare eight anti-HER2 bi-epitope BsAbs with different variable region directions or different hinge region lengths. Surprisingly, the four BsAbs with the same variable region orientation showed strong agonist activity, while the other four BsAbs with the opposite orientation behaved as HER2 antagonists.
Further experiments have shown that the BsAbs with the four variable regions in the same direction can specifically prevent the formation of EGFR/HER2 and HER2/HER3 heterodimers, so that more HER2 homodimers are formed in the body, leading to HER2 signaling Activation of the pathway. Unlike the factors that affect the activity of T cell bridging BsAbs that have been fully studied and summarized, we still know little about how these factors affect the activity of BsAbs targeting two TAAs.
Because different TAAs have different epitope topologies, geometric structures and distributions on the tumor surface, factors such as IgG subclass, variable domain orientation and hinge length have yet to be further affected on the activity of BsAbs targeting two TAAs. the study.
Compared with the traditional monovalent BsAb (1:1, that is, there is only one binding site for each antigen), there are more and more multivalent BsAb configurations, and they show obvious advantages under certain circumstances. Cibisatamab (RG7802), a 2:1 BsAb targeting CEA and CD3.
The antibody is optimized to have two CEA binding arms, each of which has a low affinity, but when added together, the entire antibody has a high affinity (note the difference between avidity and affinity here). This design increases the specificity of the BsAb to tumor cells with high CEA expression and reduces the killing of healthy cells with low CEA expression.
Studies have shown that this design can make Cibisatamab more inclined to bind to cells that express more than 10,000 CEA molecules on the cell surface, which is most likely to be tumor cells. When developing BsAbs targeting two TAAs, the potency of each TAA should be considered based on the actual situation and specific properties of the target.
For example RO7386, a 2:2 BsAb that targets FAP and DR5. It uses a bivalent FAP binding arm with high affinity to ensure the tumor specificity of the antibody, and a bivalent low affinity DR5 binding arm to promote DR5 clustering and kill tumor cells. Interestingly, for both BsAbs targeting EGFR and c-MET, JNJ-61186372 uses a 1:1 configuration, while EMB01 uses a 2:2 configuration.
Some early data support the use of a 1:1 design because binding c-MET in a bivalent form always induces its formation as a dimer, leading to its activation rather than inhibition. However, in preclinical studies, EMB01 can bind to c-MET bivalently, and the c-MET pathway has not been activated in the absence of HGF.
In addition, the developers of EMB01 claimed that they showed better and lasting anti-tumor effects than JNJ-61186372 in the NCI-H1975-HGF CDX model (JNJ-61186372 was also tested in a similar model). They believe that this difference in efficacy may be due to antigen clusters caused by the binding of tetravalent antibodies (2+2), which leads to more effective endocytosis and degradation of the tumor surface EGFR protein.
In addition to the most commonly used IgG configuration, the IgM backbone can also be used for BsAb development. The IgM configuration of BsAb can provide more antigen binding sites than IgG configuration. For example, IgM-2323 is a bispecific IgM antibody targeting CD20 and CD3 developed by IGM Biosciences. It is currently in Phase I clinical treatment for B-cell non-Hodgkin’s lymphoma (NHL) and other B-cell malignancies ( NCT04082936).
Compared with BsAbs of other configurations, IGM-2323 has up to 10 binding sites targeting CD20 and 1 binding site for CD3. Because IGM-2323 has 10 binding sites that target CD20, the researchers speculate that it has a very high affinity for CD20-expressing cancer cells, and can bind and kill those CD20 that can escape from conventional anti-CD20 treatments. The expression is very low. Cancer cells.
Summary and outlook
Unlike therapeutic monospecific antibodies that have been widely and effectively used in the field of cancer treatment, BsAb is still in the exploratory stage. Due to its unique design and structure, compared with monospecific antibodies, BsAb has incomparable advantages, but it also faces huge challenges in quality control and production.
One of the difficulties in developing BsAb is that for different designs and concepts, we all need to analyze them according to specific conditions. The permutation and combination of different configurations and targets make each BsAb unique, so that we cannot draw inferences and conclusions from the experience of other BsAb development.
For the treatment of multifactorial diseases such as cancer, therapies based on monospecific antibodies have always had the risk of tumor resistance and escape. Therefore, theoretically, BsAb-based therapy may be a better solution. The clinical data to date also supports this view, but it is far from enough.
In this review, we have summarized three key factors that need attention in the development and design of BsAbs targeting two TAAs: the choice of BsAb targets, the affinity/affinity for the two antigens, and functional activity. We believe that BsAb has great potential to become one of the most effective tumor treatment methods in the future. We firmly believe that BsAb-based therapies may innovate existing cancer treatment programs in the future, and this will be an important step on our way to fight cancer.
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