Overview of Therapeutic Genes and Their Role in Cancer Therapy

A therapeutic gene is a gene that can repair or replace an abnormal or missing gene, thereby improving the function of cells or enhancing the immune system's attack on cancer cells. In cancer therapy, therapeutic genes serve multiple roles. For example, through gene transfer technology, normal or modified genes are introduced into cancer cells or normal cells to make them produce beneficial proteins, such as antibodies, enzymes, inhibitors, etc. Through gene editing technology, such as CRISPR/Cas9, certain genes in cancer cells or immune cells are knocked out or repaired, thereby affecting their growth, differentiation, apoptosis, immune escape, etc. Through gene silencing techniques, such as RNA interference, the expression of certain genes in cancer cells or normal cells can be reduced, thereby inhibiting the proliferation, invasion, and metastasis of cancer cells. Therapeutic genes are a cutting-edge and innovative approach in cancer treatment, but they are still in the stage of research and development (R&D) and clinical trials, and some challenges and limitations need to be overcome, such as safety, efficacy, drug resistance, cost, and so on.

HSV-Thymidine Kinase

HSV-Thymidine Kinase (HSV-TK) is an enzyme encoded by herpes simplex virus and can catalyze the phosphorylation of antiviral drugs such as ganciclovir or acyclovir, converting it to the toxic triphosphate form, which inhibits DNA synthesis and leads to cell death. HSV-TK can be used as a suicide gene, introduced into cancer cells by gene transfer, and then specific killing of cancer cells can be achieved by administering prodrugs such as guanosine or acyclovir. This method has a certain bystander effect—cancer cells transfected with the HSV-TK gene can deliver toxic triphosphate drugs to surrounding untransfected cancer cells through gap junctions or lysosome release, thereby expanding the treatment effect. In addition, the HSV-TK/guanosine system can also induce cancer cells to produce tumor-specific cytotoxic T cells, thereby enhancing the body's immune response. At present, the HSV-TK/guanosine system has been clinically tested in a variety of solid tumors and blood tumors, showing certain safety and efficacy. At the same time, there are also some new strategies exploring how to improve the therapeutic efficiency of the HSV-TK/guanosine system, such as using substances that stimulate HSV-TK activity, improving gene transfer vectors and methods, and combining other gene therapies, radiotherapy, and chemotherapy.

Expression pattern of thymidine kinase 1 in the human cell cycle. Figure 1 Expression pattern of thymidine kinase 1 in the human cell cycle. (Aufderklamm, 2012)

Cytosine Deaminase

Cytosine Deaminase (CD) is an enzyme that can catalyze the deamination of cytosine to uracil. It exists in bacteria, fungi and plants, but it is missing in humans and other mammals. As a suicide gene, CD can be introduced into cancer cells by gene transfer, and then the specific killing of cancer cells can be achieved by administering the prodrug 5-fluorocytosine (5-FC). CD is able to convert 5-FC to toxic 5-fluorouridine (5-FU), which is further processed intracellularly into metabolites that lead to DNA fragmentation and apoptosis. This approach also has a bystander effect, in that cancer cells transfected with the CD gene can deliver 5-FU to surrounding non-transfected cancer cells, amplifying the therapeutic effect. At present, the CD/5-FC system has been clinically tested in a variety of solid tumors and blood tumors, showing certain safety and efficacy. At the same time, there are also some new strategies exploring how to improve the therapeutic efficiency of the CD/5-FC system, such as using oncolytic virus vectors, combining other suicide genes or immune stimulating genes, and combining other chemotherapy drugs.

Cytochrome P450 2B1

Cytochrome P450 2B1 (CYP2B1) is an enzyme belonging to the cytochrome P450 superfamily, which exists in the liver and other tissues of mammals and can catalyze the oxidative metabolism of a variety of endogenous and exogenous substrates, including drugs, hormones, lipids and carcinogens. As a suicide gene, CYP2B1 can be introduced into cancer cells by gene transfer, and then specific killing of cancer cells can be achieved by administering prodrugs such as cyclophosphamide or ifosfamide. CYP2B1 converts these prodrugs into the toxic phosphoramide mustard, an alkylating agent that generates DNA crosslinks and DNA breaks, leading to cell death. This approach also has a bystander effect, in that cancer cells transfected with the CYP2B1 gene can deliver the phosphoramide mustard to surrounding untransfected cancer cells, amplifying the therapeutic effect. At present, the CYP2B1/cyclophosphamide or ifosfamide system has been clinically tested in a variety of solid tumors, showing certain safety and efficacy. At the same time, there are also some new strategies to explore how to improve the therapeutic efficiency of CYP2B1/prodrug system, such as using directed evolution to improve the catalytic activity and selectivity of CYP2B1, combining with other suicide genes or immune stimulating genes, combining with other chemotherapy drugs.

Suicide Genes

Suicide genes are a class of genes that can lead to cell suicide. Through the process of programmed cell death, cells undergo irreversible damage to structure and function and are eventually eliminated. Suicide genes can be used as a cancer treatment strategy. It is introduced into cancer cells by gene transfer, and then the specific killing of cancer cells can be achieved by administering non-toxic or low-toxic prodrugs. Suicide genes usually encode an enzyme capable of converting prodrugs into toxic metabolites, such as thymidine kinase, cytosine deaminase, and cytochrome P450 of viral or bacterial origin. This method has a bystander effect, that is, cancer cells transfected with suicide genes can deliver toxic metabolites to surrounding non-transfected cancer cells, thereby amplifying the therapeutic effect. At present, suicide gene therapy has been clinically tested in a variety of cancers, showing certain safety and efficacy. At the same time, some new strategies are exploring how to improve the efficiency of suicide gene therapy, such as using ultrasound-targeted microbubble destruction (UTMD) to enhance gene transfer efficiency or combining other gene therapies or radiotherapy and chemotherapy.

Gene Therapy-Directed Apoptosis and Cell Control

Gene therapy-directed apoptosis and cell control is a strategy that uses gene therapy to induce cancer cell apoptosis or control the proliferation and differentiation of cancer cells to achieve the purpose of inhibiting tumor growth and metastasis. This strategy can be achieved in a variety of ways, such as by transfecting suicide genes, activating endogenous apoptotic signaling pathways, inhibiting the expression of anti-apoptotic genes or proteins, and repairing or enhancing the functions of cell cycle regulatory genes or proteins. Gene therapy-directed apoptosis and cell control require the use of appropriate gene carriers and delivery systems to ensure efficient gene transfer and expression while avoiding immune reactions and toxic side effects. At present, Gene therapy-directed apoptosis and cell control have been clinically tested in various cancers, showing certain safety and efficacy. At the same time, there are also some new strategies exploring how to improve the treatment efficiency of gene therapy-directed apoptosis and cell control, such as using CRISPR/Cas9 technology for precise gene editing, combining other gene therapies, or radiotherapy and chemotherapy.

Cytokine Genes

Cytokine genes are a class of genes encoding cytokines, which are soluble proteins that mediate intercellular communication and can regulate processes such as immune response, inflammatory response, cell proliferation, and differentiation. Cytokine genes can be used as a cancer treatment strategy, which can be introduced into cancer cells or immune cells through gene transfer, and then the killing of cancer cells or the activation of immune cells can be achieved by administering cytokines or their receptor ligands. Cytokine genes usually encode a cytokine with anti-tumor activity, such as interferons, interleukins, tumor necrosis factors, etc. This method has multiple functions such as enhancing the body's immunity, inducing apoptosis of cancer cells, and inhibiting angiogenesis. Currently, cytokine gene therapy has been clinically tested in various cancers, showing certain safety and efficacy. At the same time, there are also some new strategies to explore how to improve the efficiency of cytokine gene therapy, such as using targeted microbubbles to enhance gene transfer efficiency, combining other gene therapies, or radiotherapy and chemotherapy.

Costimulatory Genes

Costimulatory genes are a class of genes encoding costimulatory molecules. Costimulatory molecules are surface proteins that mediate the activation and proliferation of T cells. They can bind to ligands on antigen-presenting cells (APCs) and provide a second signal, thereby enhancing T cells. Cellular response to antigen. Costimulatory genes can be used as a strategy for cancer treatment. It can be introduced into cancer cells or immune cells through gene transfer, and then through the administration of co-stimulatory molecules or their ligands, the killing of cancer cells or the activation of immune cells can be achieved. Costimulatory genes usually encode a costimulatory molecule with anti-tumor activity, such as CD28, CD40, OX40, and 4-1BB. This method has multiple functions such as enhancing the body's immunity, inducing the apoptosis of cancer cells, and inhibiting immune tolerance. At present, costimulatory gene therapy has been carried out in clinical trials in a variety of cancers, showing certain safety and efficacy. At the same time, there are also some novel strategies exploring how to improve the efficiency of costimulatory gene therapy, such as using biomimetic nanoparticles to deliver mRNA, combining other gene therapies or immune checkpoint blockade.

Tumor-Associated Antigen Genes

Tumor-associated antigen genes are a class of genes encoding tumor-associated antigens (TAAs). Tumor-associated antigens are tumor-specific or overexpressed molecules that can be recognized by the immune system and can be used as targets for immunotherapy. The relationship between tumor-associated antigen genes and cancer therapy is mainly mediated by the immune system. Tumor-associated antigens can be captured by APCs and processed into peptides, then bound to major histocompatibility complex (MHC) molecules, and presented to T cell receptors (TCR) on the surface of APCs, thereby activating T cells killing of tumor cells. According to the type of MHC molecules, T cells can be divided into CD8+ T cells and CD4+ T cells. The former mainly recognize endogenous antigens presented by MHC class I molecules, and the latter mainly recognize exogenous antigens presented by MHC class II molecules. Different types of tumor-associated antigen genes can produce different antigenic peptides through different pathways, and affect the response intensity and specificity of T cells.

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For research use only. Not intended for any clinical use.