An Overview: Genetic Tumor Markers for Early Detection and Current Gene Therapy Strategies

Abstract

Genomic instability is considered a fundamental factor involved in any neoplastic disease. Consequently, the genetically unstable cells contribute to intratumoral genetic heterogeneity and phenotypic diversity of cancer. These genetic alterations can be detected by several diagnostic techniques of molecular biology and the detection of alteration in genomic integrity may serve as reliable genetic molecular markers for the early detection of cancer or cancer-related abnormal changes in the body cells. These genetic molecular markers can detect cancer earlier than any other method of cancer diagnosis, once a tumor is diagnosed, then replacement or therapeutic manipulation of these cancer-related abnormal genetic changes can be possible, which leads toward effective and target-specific cancer treatment and in many cases, personalized treatment of cancer could be performed without the adverse effects of chemotherapy and radiotherapy. In this review, we describe how these genetic molecular markers can be detected and the possible ways for the application of this gene diagnosis for gene therapy that can attack cancerous cells, directly or indirectly, which lead to overall improved management and quality of life for a cancer patient.

Keywords: DNA vaccine therapy; Gene therapy; cytokine therapy; immune cell therapy; tumor suppressor gene therapy.

Figure 1.

Demonstrate the release of CfDNA into the blood circulation by normal cells and cells involved in the pathogenic processes including cell death. The human bloodstream contains cell-free DNA, cell-free RNA, and proteins that can be used as biomarkers for various diseases.

Figure 2.

Diagrammatic representation of cfDNA concentration as a biomarker. The concentration is found higher in cancer patients than in healthy individuals due to the presence of necrosis or apoptosis in the body cells. Other causes of higher cfDNA concentration should be excluded, such as pregnancy, transplant, and intense physical activity.

Figure 3.

Promoter methylation and gene silence. Promoter methylation (CH₃ group addition on CpG islands) sometimes called hypermethylation, is an important factor in carcinogenesis when it can prevent the proper expression (functions) of a tumor suppressor gene.

Figure 4.

In a broad sense, gene therapy involves restoring or manipulating the altered genes found in the diseased cells, as detected by the gene test or gene diagnosis. In the molecular gene therapy approach, a gene can be constructed and inserted in a mammalian expression plasmid and then infused into the body to replace the function of a damaged or mutated gene, such as wild type TP53 gene or any other tumor suppressor gene (TSG). A plasmid can also be used to deliver the antigenic sequence of a tumor antigen (DNA Vaccine) which produces the peptide to present on the cell surface with a major histocompatibility complex (MHC) molecule to activate the cellular immunity against the tumor. Cytokines are another option that can be constructed in the plasmid to encode and modulate the immune system cells. Immuno-cellular gene therapy is an approach that modulates the immune system to work against cancerous cells; both humoral and cellular arms can be manipulated. Anti-tumor immune cells such as NK, NKT, and DC can be activated and educated against the tumor in vivo by plasmid-based cytokines or DNA vaccines, these anti-tumor cells can also be taken out of the body, expanded in vitro, educated by tumor peptide culture method or by transfection method and then re-infused into the body.

Figure 5.

Basic components of a plasmid. A plasmid is constructed to have a gene of interest (expression of which is required), origin of replication (at which replication is initiated), multiple cloning sites (restriction sites for DNA insertion), antibiotic resistance gene (to select the transformed bacteria), and a promoter (transcription of an inserted gene).