Recombinant Mouse Antibody (3F8 antibody) is capable of binding to GD2 ganglioside, expressed in Chinese Hamster Ovary cells (CHO). It is a murine IgG3 with a moderate affinity for GD2.
What is GD2?
In 1935, researchers first discovered a new substance, ganglioside, in the Ganglionzellen cells of the gray matter of the brain. There are many kinds of gangliosides. So far, more than 70 kinds of gangliosides have been isolated and identified. Gangliosides are a group of sphingolipids containing sialic acid. They are composed of hydrophobic ceramide and hydrophilic oligosaccharide chains containing sialic acid. They are widely distributed in the cell membranes of vertebrate tissues, and the nervous system is the most abundant one. According to the number of sialic acids, it can be divided into monosialic ganglioside (GM), disialic ganglioside (GD) and trisialic ganglioside (GT). Each ganglioside can also be divided into several subgroups according to the number of glycosyl groups, such as GD1, GD2, GD3, etc. Ganglioside GD2 is an important component of the cell membrane of nervous system. It plays an important role in regulating the proteins in the cell membrane. In addition, ganglioside GD2 mediates melanoma cell adhesion and can be used as a target for clinical immunotherapy of neuroblastoma.
Biosynthesis and structure of GD2
Sugar chains are not only structural substances in vivo, but also play an important role in signal transduction between cells and cells. Abnormal expression of glycosylation is usually a marker of the transformation of cancer cells. Glycosyl antigens of some tumors are considered to be closely related to proliferation, invasion, angiogenesis and metastasis of cancer cells. Ganglioside is a glycolipid containing sugar chain. It is mainly synthesized in the endoplasmic reticulum and Golgi body. First, in the endoplasmic reticulum, serine and fatty acid coenzyme A (CoA) synthesize mother nucleus ceramide. Then, ganglioside is processed by a series of glycosyltransferases step by step in the Golgi body to form various forms of gangliosides. Ganglioside GD2, a B-series ganglioside, contains two sialic acid units and plays an important role in cell adhesion and recognition related signal transduction. Gangliosides are the main components of glycolipid-rich microstructural domains, which can bind to sphingomyelin, cholesterol, glycosylphosphatidylinositol anchoring protein and tyrosine receptor kinase.
Anti-GD2 antibody therapy
Figure1. Action mechanism of anti-GD2 antibody
Based on the in-depth study of the structure and function of ganglioside GD2, it is recognized that anti-GD2 antibody therapy may have a therapeutic effect on neuroblastoma. However, in order to play an anti-tumor role, anti-GD2 antibodies are confronted with two great challenges: 1) Usually high-affinity antibodies rely on Fc receptor-mediated action to kill cancer cells, but the immune response to sugar chains is usually lack of T cell intervention, so the antibodies produced by anti-GD2 antigens are mostly low-affinity IgM antibodies, while the high molecular weight of IgM is well known. It is often more difficult to invade tumor cells, so the anti-tumor effect is not ideal. 2) The presence of blood-brain barrier prevents intravenous injection of anti-GD2 antibodies into the central nervous system, and may cause adverse reactions to peripheral nerve cells and melanogenesis cells with low GD2 expression. Over the past 30 years, anti-GD2 antibody therapy represented by the Dinutuximab monoclonal antibody has been developing steadily, which has brought the treatment of high-risk neuroblastoma into a new stage.
- 3F8 is the first anti-GD2 antibody to be used for the treatment of neuroblastoma in clinical trials. It is a mouse-derived IgG3 antibody with a maximum affinity of 5 nmol/L to GD2. Pre-clinical studies have shown that 3F8 can kill neuroblastoma in a dose-dependent manner by effectively binding with lymphocytes, granulocytes and Fc gamma receptors, further through complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC).
- ME36.1 is another mouse-derived IgG3 antibody which is still in the early stage of research. Its affinity to GD2 is lower than 3F8 and 77 nmol/L, but it not only binds to GD2, but also has partial affinity to GD3. Pre-clinical studies have shown that the IgG2a subtype variant of ME36.1 not only has no decrease in antigen affinity, but also has certain antitumor activity.
- The most striking mouse-derived IgG3 antibody is14.18, and its affinity to GD2 is between 3F8 and ME36.1, which is 19 nmol/L. Subsequently, according to the amino acid skeleton of 14.18, mouse-derived IgG2a antibody, human-mouse chimeric antibody (ch14.18 antibody) and humanized antibody (hu14.18) are further developed, among which ch14.18 is Dinutuximab monoclonal antibody.
Strategies to improve the effectiveness of anti-GD2 antibody
Although anti-GD2 antibody represented by ch14.18 has achieved some success, there are still some challenges in its efficacy and safety. Like other anti-GD2 drugs, there are three strategies to improve the efficacy of anti-GD2 antibodies: 1) coupling with radioactive reagents, toxins and cytokines to enhance the lethality of anti-GD2 antibodies; 2) forming bispecific antibodies with anti-immune cell antibodies, or specific modification of T cells to enhance the tumor immunity of T cells; 3) using single-chain antibodies as nuclei. Through a series of functional improvements, the heart can improve the activity of antibodies and enhance their invasiveness to tumors at the same time.
- Coupled antibodies
Previous studies have shown that anti-GD2 antibody combined with cytokine IL-2 and GM-CSF has a certain therapeutic effect on cancer. Therefore, scientists couple cytokines with anti-GD2 antibodies for cancer treatment. In addition to coupling cytokines, some bacterial or plant-derived protein immunotoxins have also been attempted to couple with anti-GD2 antibodies to enhance the anti-GD2 antibody’s tumor killing activity.
- Nanoparticle coupled antibody
Nanoparticles are usually 3-200 nm-sized particles composed of polymers, liposomes and viruses. They have the ability to carry large payloads for the treatment of cancer diseases. Liposomes are the most widely used nanoparticles in anti-GD2 antibody drugs. The greatest advantage of drug liposome nanoparticles is that they can through the capillary space of tumor tissue, the infiltration of drugs is effectively improved, while the normal tissue is more closely linked, which limits the entry of drugs, thus further improving the targeting of drugs.
- T-cell enhanced antibodies
Activating T cells in human body is the most effective treatment for cancer. Therefore, in recent years, CTLA-4, PD-1 and other immunological checkpoint inhibitors have achieved remarkable results in the treatment of melanoma and other diseases. However, the immunogenicity of most tumors in human body is not strong, so the therapeutic effect of these immuno-checkpoint inhibitors is not obvious. Fortunately, neuroblastoma is more sensitive to antibody-mediated killing effects. Therefore, T cell-related immunotherapy can be widely used in the treatment of neuroblastoma.
Generally speaking, the introduction of Dinutuximab monoclonal antibody is only the beginning of clinical application of anti-GD2 therapy, and there are still many challenges in the treatment of high-risk neuroblastoma. On the one hand, the relationship between GD2 and neuroblastoma remains to be further studied, and the regulatory mechanism of the interaction between GD2 and glycosyltransferase is still unknown. On the other hand, the current course of Dinutuximab monoclonal antibody immunotherapy is relatively complex, and its side effects and adverse reactions cannot be ignored. Therefore, the structure and function of anti-GD2 antibody should be optimized to further improve the safety and efficacy of anti-GD2 therapy. It is believed that with more advanced treatment technologies such as CAR-T coming into clinical practice, anti-GD2 therapy will make greater progress in the treatment of high-risk neuroblastoma.