The treatment of malignant tumors is now mostly a comprehensive treatment combining surgery, radiotherapy and chemotherapy. As we all know, it is difficult to completely remove tumor tissues by surgery, and radiotherapy lacks specificity in killing tumor tissues, and at the same time, it damages normal tissues and has strong toxic side effects. For many years, people have been seeking drugs and methods with specific killing effects on tumors.
With the development of molecular biology, immunology, bioengineering theory and technology, targeted therapy of tumor has become a hot direction of research. Targeted tumor therapy is to combine cytotoxic substances such as radionuclides, chemotherapeutic drugs and toxins with carriers by using highly specific tumor-friendly substances as carriers, so as to limit the therapeutic drugs to the tumor site as much as possible without affecting normal cells, thus improving the efficacy and reducing the toxic side effects.
After more than 20 years of development, the research on targeted therapy for tumors has made breakthrough progress and shown bright development prospects. The current situation of targeted therapy for tumors at home and abroad is now reviewed.
I. Targeted therapy of tumor with single anti-drug
The basic requirement of targeted therapy is that the drug has high concentration in the tumor site, can stay for a long time and has strong killing activity to the tumor target cells. Since monoclonal antibodies are highly specific to their corresponding antigens, monoclonal antibodies that bind specifically to specific molecular targets can be prepared. Since 1975, when kohler and milstein founded the monoclonal antibody preparation technology, the development and application of monoclonal antibodies have greatly contributed to the development of targeted drugs.
Most of the currently developed antitumor targeted drugs belong to monoclonal antibodies or immunocouples with monoclonal antibodies as carriers. Immunocouples are composed of monoclonal antibodies and warheads, and there are three types of warheads available: radionuclides, drugs and toxins.
Since the first targeted tumor therapy, rituximab, was launched in 1997, eight have entered clinical use, and more are under development and research than can be counted. Rituxia is a human-mouse chimeric antibody targeting the B-cell CD20 molecule that has shown efficacy against non-Hodgkin’s lymphoma and was the first monoclonal antibody approved by the FDA for the treatment of malignancies. herception is a monoclonal antibody against the protein encoding the her2/neu oncogene and has been clinically studied to be effective against Herception is an anti-her2/neu oncogene encoding protein that has been clinically studied to be effective in breast cancer, with more significant efficacy in combination with chemotherapy agents.
Mylotary is a coupling of an anti-CD33 monoclonal antibody with calicheamicin that is approved for relapsed myeloid leukemia. Imatinib mesylate is an inhibitor against the specific protein lorine kinase, which inhibits tumor cell growth and proliferation and promotes apoptosis by inhibiting the binding of ATP to lorine kinase, and is currently used clinically in gastrointestinal mesenchymal tumors and chronic myeloid leukemia.
Epidermal growth factor receptor EGFR is highly expressed in human squamous carcinoma, breast cancer and glioma, and the coupling of anti-EGFR monoclonal antibody and vincristine derivative has been reported to show good anti-cancer effect in nude mice in vivo, and the human-mouse chimeric anti-EGFR antibody has entered clinical research. VEGF, a vascular endothelial growth factor, has an important role in angiogenesis, and neutralizing antibodies against VEGF have been reported to have broad-spectrum antitumor effects and significant efficacy against human cancer tumors transplanted in nude mice.
Studies have shown that monoclonal antibodies are well targeted in vivo, binding specifically to the surface of target cells, entering the cells through a receptor-mediated internalization process, and displaying selective killing effects on tumor cells. However, the results of preliminary clinical studies were unsatisfactory, and monoclonal anti-targeting drugs did not achieve outstanding efficacy.
Comprehensive analysis shows that the main reasons for this may be the following.
1, most monoclonal antibodies are mouse-derived monoclonal antibodies, which will cause human to produce anti-mouse antibodies, which will not only neutralize the targeting antibodies, but also cause allergic reactions in humans.
2. The affinity and specificity of the antibody itself are problematic.
3. The amount of drug reaching the tumor is insufficient. The delivery of monoclonal antibodies in the body is affected by many factors. Monoclonal antibodies are heterogeneous proteins that are taken up by the reticuloendothelial system and a considerable amount accumulates in the liver, spleen and bone marrow. The pressure inside the tumor is high, the molecular mass of monoclonal antibody coupling is large, and the penetration ability is low. 4. The heterogeneity of tumor autoantigen expression and the modulation of antigen are factors that affect the success of targeted therapy.
In order to solve the obstacles of the problem of applying monoclonal targeted therapeutic drugs, current research is more focused on the following aspects.
①Humanization of antibodies, mainly through genetic engineering technology to prepare chimeric antibodies or modified antibodies. Studies have shown that the HAMA response rate of chimeric antibodies is low.
②Searching for new molecular targets, identifying and using molecular targets related to cancer is the key to developing monoclonal antibodies, specific oncogene expression proteins, growth factor receptors can be used as molecular targets for monoclonal antibodies.
③Miniaturization of coupling molecules.
The development of highly effective monoclonal anti-drugs requires highly effective “warhead” substances, which can kill tumor cells by reaching the target site with only a small amount, and some drugs with strong tumor-killing effects have been discovered in recent years; for example, the anti-tumor antibiotic Calicheamicin C1027 provides a warhead substance for the development of highly effective monoclonal anti-drugs. The anti-tumor antibiotic Calicheamicin C1027 provides the warhead material for the development of highly effective monoclonal antibody drugs.
Targeted therapy with antibody as carrier
By using the method of antigen-antibody specific binding, anti-tumor drugs or toxins are combined with antibodies, so that the antibodies can bring them to the antigen site of tumor to play a role.
1.Radioimmunotherapy RIT (radioimmunotherapy RIT) applying mAb with high energy radioactive material connection system for drug delivery is an encouraging branch in malignant tumor treatment, because mAb can also be said to be the selective distribution feature of radioisotope in tumor tissue. It enables tumor tissues to receive high doses of radiation with minimal damage to normal tissues. It has been reported in the literature that peanut agglutinin has a special affinity for GC-916 in nude mice with I131-labeled peanut agglutinin for GC-916 targeted therapy study in nude mice with human gastric cancer.
131I-PNA has obvious tumor suppression effect with 73.2% tumor suppression rate, while recent studies mostly use 90Y (yttrium) to connect.
2.Immunocouples therapy
Couples made from anti-human tumor monoclonal antibodies and drugs have inhibitory effects on the growth of corresponding human tumors transplanted in nude mice, and the couples generally have higher efficacy or show lower toxicity compared to the corresponding free drugs. Anticancer drugs that have been coupled with monoclonal antibodies and observed in nude mice include adriamycin, roxithromycin, boanamycin, mitomycin, methotrexate, azelaic acid phenylpropionate, azelaic acid phenylpropionate, cisplatin, and vincristine derivatives.
The tumor models used include lung cancer, liver cancer, gastric cancer, colon cancer, breast cancer, ovarian cancer, glioma, melanoma, leukemia, lymphoma, etc. Studies have shown that the coupling of chemotherapeutic drugs and monoclonal antibodies show high efficacy in animal hormonal models.
3.Antibody-mediated enzymatic prodrug therapy, antibody directed enzyme catalyzed precursor drug therapy (ADEPT) and dual selection specificity with antigen and antibody, enzyme and substrate for precursor drug research of anticancer drugs, that is, by locating an enzyme at the tumor target first, thus making no The active (non-toxic) precursor drug is transformed into a drug with killing activity only at the tumor site, concentrating its efficacy at the tumor site.
ADEPT integrates today’s molecular biology enzyme engineering and rational design of drugs, and opens up a new direction of targeted anti-cancer drug research. This mechanism has been successful in anti-cancer drugs such as fluorouracil, nitrogen mustard, antibiotics, vincristine and platinum, and there are more than a dozen enzymes used in this field of research.
Magnetic drug-targeted therapy for tumors
Magnetic drug targeting therapy is a kind of targeted therapy, which makes the magnetically responsive drugs gather at the target site with the help of magnetic field to increase the concentration of the target site and reduce the toxic side effects of the drugs on normal tissues.
The development of magnetic drugs has gone through several stages. At the earliest in the 70s and early 80s, magnetic protein microspheres were mostly used as carriers, with a diameter of 1 um, which is a denatured albumin complex wrapped with magnetic particles (Fe304 10-20 nm) and drugs, with high drug carrying rate, good targeting, simple synthesis and easy preservation.
However, a large number of experiments later proved that it could cause thrombosis-like vascular embolism and even lead to the death of experimental animals, and then it was gradually eliminated or improved. 80s came 90s later, immunomagnetic liposomes became an emerging drug carrier. Liposomes are synthetic biofilms that can reduce drug toxicity, protect encapsulated drugs, and have better natural targeting and permeability as carriers of drugs.
Magnetic sensitive liposomes are mostly used in magnetically oriented therapy, which can help drug particles locate more effectively at the targeting site and further enhance their targeting specificity after binding antibodies. ), which are easily engulfed by the RES system and passively targeted to the liver and spleen, are difficult to achieve targeted drug delivery to other tissues;
Nowadays, carboxymethyl dextran magnetic milli-particles (CMD MNP) are mostly used instead of dextran milli-particles as carriers, which change the properties of the carrier surface and make it have certain negative electrical properties, which can be better applied to active targeting therapy. Experiments have proved that this drug carrier has good guiding property and promising application.
IV. Liposome targeted drug delivery
Liposome (Liposome) is a spherical lipid bilayer with a diameter of 50~1000nm and flexible phospholipid membrane components, which can be made into various types with different sizes as an effective carrier of bioactive substances. Neutral drugs can be stably bound in liposomes by adjusting the pH value of liposomes or adding reversed-phase ions to form molecular complexes with drugs.
1.Conventional liposomes Liposomes only consist of natural phospholipids, which are easily adsorbed on the surface of blood conditioners (complement, immunoglobulin) after entering the bloodstream, prompting monocytes to phagocytose and remove them, and these lipids are short in blood circulation and do not easily reach the tumor area, so their application is limited.
2.Long circulating liposomes Long circulating liposomes are the phospholipids of ordinary liposomes mixed with large molecules such as polyethylene glycol to hinder the adsorption of conditioner. The surface of polyethylene glycol liposomes can form an encircling water layer to effectively reduce the adsorption of conditioner on its surface and reduce the phagocytosis of liposomes by mononuclear phagocytosis system, so that the circulation time of liposomes in the blood is significantly prolonged. 5 mg DXR/kg was administered intravenously to 26 rectal cancer BALb/c tumor-bearing mice;
The concentration in their blood was significantly increased after 24 hours compared with the intravenous injection of normal adriamycin and normal adriamycin liposomes. The long-circulating liposomes reduced the phagocytosis of adriamycin by the liver and reticuloendothelial system, and their aggregation at the tumor site was 3.4 and 9.4 times higher than that of normal adriamycin liposomes and normal adriamycin alone.
3.Immunoliposomes Antibodies specific for tumor-preserving cell surface antigens are bound to the surface of liposomes to make immunoliposomes, so that they can reach the tumor site and be released. This is a hot spot in liposome research, and it has been reported that the antibody Fab’ fragment of anti-human CEA is combined with liposomes to form immunoliposomes, and good targeting has been achieved in the in vivo experiments of caustic mice. effect.
4. Heat-sensitive liposomes For a certain phospholipid at a certain temperature, the phospholipid can undergo a transfer from colloidal phase to liquid crystal phase, and the state of the liposome membrane changes at the phase change temperature, and the permeability increases and the amount of drug released is the largest. DXR-PEG-TSL(SUV)] has a long circulation time in the body;
When heated at the lesion site can release the drug selectively at the tumor site, after 3 hours of intravenous injection of this liposome to tumor-bearing BALb/c mice, the tumor was locally heated and there was a high concentration of adriamycin locally in the tumor tissue, suggesting that the drug was mainly released in the interstitium of the lesion tissue and had an inhibitory effect on tumor growth and prolonged the survival time of the mice.
V. Virus-mediated targeted tumor therapy
The cytopathic effect is the basis of viral pathogenesis. If this effect is selective, i.e., the virus only kills cells that are harmful to human body, such as tumor cells, but not normal cells, then this effect can be the basis of viral therapy. The current anti-cancer virus is a selective attack on tumor cells by taking advantage of the difference between tumor cells and normal cells.
For example, compared with normal cells, tumor cells have significantly increased growth and proliferation ability, and this growth phenotype is based on the inactivation of oncogenes and/or over-activation of oncogenes at the genetic level. The tumor cells were lysed and died due to the massive multiplication of the virus.
In contrast, in cells with normal P53 function, virus multiplication was low and virulence was minimal. The viral genome has been modified to confine the proliferation of the virus to the tumor cells, thus lysing the tumor cells with little effect on normal cells, and this virus is called tumor lysing virus.
For example, Reovirus is a tumor lysis virus designed based on the proto-oncogene ras, cells carrying activated ras gene are sensitive to Reovirus, even cells with inactivated Ras gene become sensitive to Reovirus after introducing activated Ras gene, thus Reovirus may become a promising anti-cancer drug. HSV-1) has also been recently modified to attack cancer cells.
Gene Targeted Therapy for Tumors
Gene targeting therapy for tumors is a new medical field that integrates multiple disciplines and technologies, and many new technological approaches have emerged in recent years. Gene targeting is an important research direction, targeting in three meanings: first, transfer targeting, introducing therapeutic genes into target cells as much as possible through targeting technology; second, targeting of gene transcription, controlling gene transcription in target cells by using tumor tissue-specific overexpression of gene regulatory elements; third, targeting of gene expression in time and level, applying artificial synthetic regulatory system to manipulate gene expression.
In recent years, research on targeting of gene therapy has been attempted mainly from the above three aspects, and great progress has been made.
There are three main aspects of targeting studies on gene transfer.
(1) receptor-ligand or antigen-antibody-mediated targeted gene transfer, where many cells specifically express or overexpress a certain receptor or antigen on their surface. If the target gene or the vector carrying the target gene is linked to the corresponding ligand or antibody, the specificity of the ligand-receptor or antigen-antibody interaction can be exploited. Then the target gene can be specifically transferred into the target cell.
(2) Virus-mediated targeted gene transfer takes advantage of the specific affinity of certain viruses for certain tissues in the human body, and transforms these viruses into vectors to specifically introduce the target gene into the target cell. For example, by taking advantage of the natural neurophilic nature of herpes viruses, they can be transformed into gene carriers for the treatment of neurological disorders.
(3) Targeted gene transfer mediated by anaerobic bacteria, solid tumors have a hypoxic metabolic zone, and anaerobic bacteria have the characteristics of tending to hypoxic metabolism, and thus have good targeting to tumor cells, which can be used as carriers for tumor gene therapy, and the current research mainly focuses on non-pathogenic anaerobic bacteria such as Bifidobacterium, Lactobacillus and Escherichia coli. Meanwhile, the feasibility of pathogenic oxygenic bacteria such as wild-type Salmonella typhimurium as a targeting gene vector has also been investigated.
Targeting studies of gene expression are mainly done by using tissue-specific gene promoters to restrict the target gene to be expressed only in the target cells. The most applied ones are the methemoglobin gene promoter, carcinoembryonic antigen gene promoter, tyrosine gene promoter for melanoma and prostate-specific antigen gene promoter.
Gene therapy for certain diseases also requires that the target genes be expressed at a certain time and at a certain level, and thus the timing and expression level of the genes targeted for the treatment of these diseases should be precisely regulated, mostly by using oral non-toxic small molecule drugs at present. Such as tetracycline, ecdysone, Ru486, etc. to control a genetically engineered modified transcription factor by which the expression of the target gene is regulated.
After taking these small molecule drugs, the expression of the target gene can reach a high level in a short period of time, and the timing and dose given by the small molecule drugs can be used to regulate the target gene expression time and expression level.
VII. Problems and Prospects
Targeted therapy of tumors has made great progress, and there are many different ways to target tumors, but no matter which method is used, there are more or less defects. Achieving targeted drug delivery of macromolecular carriers requires not only its specific affinity to the target site, but also suitable pharmacokinetic properties at the intra-Hugh organ, cellular and subcellular levels, and targeted therapy is influenced by many factors, including tumor vascularity, carrier Targeted therapy is affected by many factors, including tumor vasculature, vector specificity, tumor size, drug dose, and whether the body produces antibodies against the vector, etc. The research and development of large molecule vectors depends largely on the progress of related fields.
For example, biochemistry, immunology, cellular and molecular biology, pharmacokinetics and pharmacology, targeted therapy will also be developed with further research in basic science, and it is expected to obtain new targeted introduction and treatment systems that are safe, harmless, highly targeted and easy to administer through multidisciplinary intersection.