Bioconjugation involves the attachment of one molecule to another molecule, often through a covalent bond, to produce a complex of two molecules linked together. The development of novel studies on particular targeted derivatized proteins, DNA, RNA, and carbohydrates frequently makes use of bioconjugation technology, such as ligand discovery, disease diagnosis, and efficient screening, and is a research field with broad prospects. At present, it mainly includes the development of mild, specific targeted derivatized proteins, DNA, RNA and carbohydrates and other antibody protein conjugates. New conjugates are usually used for ligand discovery and disease diagnosis.

Bioconjugation Chemistry

At the nexus of chemistry, biology, and materials science, bioconjugate chemistry is a multidisciplinary discipline that studies how biomolecules bind covalently to a wide range of other molecules or surfaces. The exact and deliberate coupling of physiologically active molecules, such as proteins, enzymes, antibodies, peptides, or nucleic acids, to other molecules, such as tiny molecules, synthetic polymers, nanoparticles, dyes, or surfaces, is the fundamental process of bioconjugate chemistry. The resulting bioconjugates exhibit unique properties and functionality not possessed by the individual components, allowing researchers to tailor specific properties for a variety of biomedical and biotechnological applications.

In its most basic terms, bioconjugation simply involves the attachment of one molecule to another, usually via a covalent bond, to create a complex consisting of two molecules linked together. In most cases, at least one of the molecules is of biological origin or is a fragment or derivative of a biomolecule. In some cases, the conjugates formed are completely synthetic, but their use is targeted for biological or life science applications. When forming such bioconjugates, the method can produce complexes with approximately equal proportions of each component, or conjugates that are intentionally designed to have more of one component than the other. The final form of the bioconjugate depends on the desired application as well as the components and methods used to couple them together. With an understanding of the basic concepts of bioconjugation, the process can be accomplished without difficulty and can even be controlled by appropriate selection of reagents, reactions, and conditions.

Bioconjugation Methods

One of the key aspects of bioconjugation chemistry is the development of robust and efficient methods to link biomolecules to other molecules while maintaining their biological activity and structural integrity. Various chemical strategies have been developed to achieve site-specific conjugation, including the use of reactive functional groups, click chemistry, enzymatic conjugation, and genetic engineering techniques.

• Reactive Functional Groups

Reactive functional groups, such as primary amines, thiols, carboxylic acids, and aldehydes, are commonly used in bioconjugation reactions. These functional groups can react selectively with complementary chemical handles, such as maleimides, NHS esters, azides, and aldehydes, to form stable covalent bonds. By carefully selecting reactive groups and conjugation chemistry, researchers can control the binding site and minimize nonspecific interactions, resulting in highly specific and well-defined bioconjugates.

• Click Chemistry

Click chemistry is a powerful tool in bioconjugation chemistry due to its high efficiency, high selectivity, and bioorthogonality. Reactions such as copper-catalyzed azide-alkyne cycloaddition (CuAAC) and strain-promoted azide-alkyne cycloaddition (SPAAC) enable rapid and selective bioconjugation under mild conditions without affecting the stability and activity of biomolecules. Click chemistry methods have been widely used in the development of bioorthogonal labeling techniques, bioimaging probes, and drug delivery systems.

• Enzymatic Conjugation

Enzymatic conjugation methods provide another general approach for bioconjugation, taking advantage of the high specificity and efficiency of enzymes in catalyzing specific chemical reactions. For example, transglutaminase can promote the formation of amide bonds between lysine and glutamine residues in proteins, thereby achieving site-specific protein labeling and modification. Enzymatic bioconjugation strategies are particularly suitable for conjugating complex biomolecules with high selectivity and precision.

• Genetic Engineering

Genetic engineering technology provides an effective way to introduce specific chemical handles into biomolecules through recombinant DNA technology. By incorporating unnatural amino acids or peptide tags with reactive groups into target proteins or antibodies, researchers can precisely control the binding sites and optimize the bioconjugation process. Genetic engineering approaches have revolutionized the field of bioconjugation, enabling the development of novel bioconjugates with enhanced properties and functionalities.

Antibody Conjugation

Antibody conjugation is a process that chemically links antibodies to other molecules, such as fluorescent dyes, enzymes, drugs, or nanoparticles. The process is commonly used in various fields such as medicine, research, and diagnostics to target specific cells or molecules for various purposes. Antibody conjugation can enhance these molecules' functionality, sensitivity, and specificity, making them useful instruments for immunology, biotechnology, and medical applications. Antibody conjugation is a multi-step process that necessitates careful consideration of both the target conjugation and the properties of the antibody. Choosing the right technique to fuse the antibody to the chosen molecule is one of the most important steps in the antibody conjugation process. Antibody conjugation can be accomplished using a number of popular techniques, each with pros and cons. These techniques include site-specific conjugation, indirect conjugation, and direct conjugation. The type of molecule to be conjugated, the intended use, and the characteristics of the antibody all influence the conjugation process selection. Considerations for conjugation methods include stability of the conjugated product, binding effectiveness, and possible implications on specificity and function of the antibody. To guarantee consistent outcomes in large-scale applications, researchers must also assess the conjugation method's scalability and repeatability.

Drug Conjugation

Drug conjugation is a process of chemically linking a drug molecule to another molecule (called a ligand or conjugate) to enhance its properties or for targeted delivery. This strategy is used to improve the pharmacokinetic and pharmacodynamic profiles of a drug, making it more effective and reducing potential side effects. Drug conjugates can target specific cells or tissues, increase drug solubility, prolong drug circulation time, or optimize drug distribution in the body. Currently, there are several types of drug conjugates, each with unique properties and applications.

• Antibody Drug Conjugate

Antibody-Drug Conjugates (ADCs) are a new type of biological drug that is conjugated by a monoclonal antibody and a small molecule drug (ADCs Cytotoxin) with potent cytotoxicity through a bioactive linker (ADCs Linker). ADCs specifically target cancer cells through monoclonal antibodies, and then kill cancer cells with the conjugated small molecule drug. Therefore, ADCs have the characteristics of high specificity and targeting of monoclonal antibody drugs, as well as the high efficiency of small molecule drugs in eliminating cancer cells. They can synergistically exert the advantages of antibody drugs and chemical drugs, and can reduce damage to biological systems. At present, there are 244 ADC drugs in clinical trials worldwide, of which 15 have been approved for marketing, 2 are applying for marketing, 16 are in clinical phase III, and most of the rest are in early clinical stages.

• Peptide Drug Conjugate

Peptide-drug conjugates (PDCs) are an emerging targeted therapy in which peptide molecules are linked to drugs to improve their cell permeability, stability or targeting ability. PDCs are mainly composed of three parts: peptides, linkers, and cytotoxic payloads. Peptides can be designed to specifically bind to cell surface receptors or penetrate cell membranes, thereby enhancing the delivery of drugs to their intended targets. Compared with non-targeted anticancer drugs, PDCs can significantly prolong blood circulation time, increase maximum tolerated doses, enhance tumor accumulation, and improve anticancer biological activity. Because normal cells lack targeting receptors and cannot bind to tumor-targeting peptides, compounds will be enriched in receptor-positive tumor cells, which can reduce the dosage and reduce toxic side effects. In addition, PDCs can also rely on the properties of peptides to improve the solubility, permeability, and selectivity of drugs.

• Nucleic Acid Drug Conjugate

Nucleic acid-drug conjugates combine drug molecules with nucleic acids (such as DNA or RNA) to achieve targeted delivery of drugs to specific cells or tissues. By taking advantage of the inherent targeting properties of nucleic acids, these conjugates can improve the efficacy and safety of drugs for treating diseases such as cancer or genetic diseases. For example, aptamer-drug conjugates (ApDCs) are composed of nucleic acid aptamers, linkers, and small molecule drugs, which replace the targeting effect of antibodies in traditional ADCs with nucleic acid aptamers. Nucleic acid aptamers, also known as chemical antibodies, are single-stranded DNA/RNA composed of 15-60 bases that can specifically bind to target substances.

• Lipid Drug Conjugate

Lipid-drug conjugates use lipid molecules as carriers to enhance drug delivery and stability. Lipids can increase the solubility of poorly water-soluble drugs, promote cellular absorption of drugs, or protect drugs from degradation in the body. Lipid-drug conjugates are typically used in formulations for oral, intravenous, or topical administration.

• Small Molecule Drug Conjugate

Small molecule-drug conjugates (SMDC) are usually composed of targeting molecules, linkers and effector molecules (cytotoxic, E3 ligase, etc.). The most direct difference between SMDC and ADC is the targeting molecule. ADC uses biological antibodies as drug targeting, while SMDC adopts small molecule orientation. In the preparation of ADC, the ratio of payload to antibody is usually uncertain. The use of site-specific conjugation technology can achieve a relatively accurate drug-antibody ratio (DAR), while the small molecule targeting ligand and payload of SMDC usually have accurate values. Cytotoxic molecules are the core part of SMDC and are crucial to achieving clinical therapeutic value. Cytotoxic molecules must first have strong enough toxicity. Usually, compound molecules with extremely high toxicity but cannot be used alone as drugs are selected; secondly, cytotoxic molecules must have sufficient water solubility and remain relatively stable in the blood circulation; thirdly, there needs to be a modifiable site that can introduce functional groups to connect with the targeting ligand. However, the requirements for this part of SMDC are similar to those for ADC, so vinblastine, paclitaxel, mitomycin C, epothilone, microtubule inhibitors, and irinotecan metabolite SN-38 are also used as cytotoxic molecules.

Cytotoxic Agents

BOC Sciences offers a comprehensive range of cytotoxic reagents for drug conjugation. These cytotoxic drugs are potent compounds that inhibit cell proliferation and induce cell death, making them key components in the development of targeted cancer therapies. Our broad range of cytotoxic agents includes chemotherapeutic drugs such as doxorubicin, methotrexate, and paclitaxel, which have demonstrated potent anticancer activity against various types of cancer. Each cytotoxic drug undergoes rigorous quality control measures to guarantee purity, potency, and stability for research and development purposes.