In 1975, EA Carswell and LJ Old et al found that after injection of lipopolysaccharide in mice vaccinated with BCG, a substance in the serum of mice that caused hemorrhagic necrosis in animal tumor tissue was produced. This substance has killing effects to most of the cells, so they named it tumour necrosis factor (TNF). TNF is the most potent cytokine found to date. Since 1984, European and American countries have begun to apply TNF genetic engineering products to cancer clinical treatment, and achieved sensational results, but eventually forced to terminate due to serious side effects. Since the end of the 1990s, with the deepening of basic research and the development of genetic engineering technology, scientists have developed some highly efficient and low-toxic TNF allosteric bodies, thus re-establishing the important position of TNF in anti-tumor research and treatment.

1) An introduction to TNF

TNF is a glycoprotein that exists in two forms: TNF-a and TNF-b. TNF-a is produced by monocytes and macrophages, which can cause hemorrhagic necrosis of tumor tissue, while lipopolysaccharide (LPS) is a strong stimulator. TNF-b is a lymphokine, also known as lymphotoxin (LT). Antigen or mitogen can stimulate T lymphocytes to secrete TNF-b, which has tumor killing and immune regulation. The human TNF-a gene is 2.76 kb in length and consists of 4 exons and 3 introns, which are located on chromosome 6. The human TNF-a precursor consists of 233 amino acids and contains a signal peptide of 76 amino acid residues. After excision of the signal peptide, 157 amino acids of mature non-glycosylated TNF-a are formed. The genetically engineered TNF-a has better biological activity and anti-tumor effect.

2) TNF and NF-κB signaling pathway

TNF-a and TNF-b have similar molecular structures and exert similar biological effects. The extracellular factor TNF-α acts as a trimeric form of signal transduction and binds to TNF receptor (TNFR) to cause receptor multimerization. This multimerization causes TNF receptors and TRADD molecules in the cytoplasm to interact with each other. TRADD recruits the corresponding protein to mediate two transduction pathways: one is the induction of NF-κB activation by TRAF2 and RIP molecules, and is involved in anti-apoptosis; the other is the apoptosis caused by FADD molecules. TNFR induces apoptosis only when protein synthesis is blocked. In this article we will focus on the NF-κB signaling pathway activated by TNF.

NF-kB (nuclear factor-kappa B) is a transcription factor found in the nuclear extract of B lymphocytes in 1986. It binds specifically to the enhancer B sequence GGGACTTTCC of the immunoglobulin kappa light chain gene and promotes κ. Light chain gene expression. It is a member of the Rel family of eukaryotic transcription factors and is widely found in various mammalian cells. To date, five NF-kB/Rel family members have been found in mammalian cells, which are RelA (ie, p65), RelB, C-Rel, p50/NF-kB1 (ie, p50/RelA) and p52/NF. -kB2. These members all have a Rel homology domain (RHD) of approximately 300 amino acids. This highly conserved domain mediates the formation of a homologous or heterodimer of the Rel protein, which is also a region of specific binding of NF-kB to the DNA sequence of the target gene. The activation process of NF-kB in cells is finely regulated.

Normally, NF-kB in the cytoplasm is inactivated and binds to the inhibitory protein of NF-kB to form a trimer complex. When TNF-a signaling, inflammatory factors, and external stimuli such as LPS and ultraviolet rays are present, cytokines bind to TNF receptors on the surface of cell membranes, and TNF receptors multimerize and interact with TRADD molecules in the cytoplasm. TRADD recruits TRAF (TNFR-associated factor) and kinase RIP (receptor interacting protein), and signals are transmitted by RIP to IKK (IkB kinase). IKK plays a very important role in the NF-κB signaling pathway, and although it is different in the upstream signal path, it eventually aggregates into IKK.

3) NF-κB signaling pathway and cancer
NF-kB has obvious functions of inhibiting apoptosis, and is closely related to multiple processes such as tumor occurrence, growth and metastasis. Mutations in the NF-kB family of genes are often found in human tumors, especially in the lymphatic system. The first clue to the association of the NF-kB family with cancer is the discovery of the c-Rel gene, a homologous gene in the cell of the avian retroviral oncogene v-Rel. The virus causes malignant transformation of various hematopoietic cells in chickens, causing lymphoma. Since the downstream genes of NF-kB include CyclinD1 and c-Myc, sustained activation of NF-kB stimulates cell growth, leading to uncontrolled cell proliferation. NF-kB is abnormally expressed in many cancer cells, such as NF-kB2 expression in 75% of breast cancer samples is many times higher than adjacent normal tissues. The migration and infiltration of tumor cells into surrounding tissues is a prerequisite for tumor spread and metastasis. NF-kB has a significant effect on tumor metastasis, which can promote the expression of tumor metastasis-associated genes ICAM-1, VCAM-1, MMP-9. NF-kB also induces the expression of vascular endothelial growth factor VEGF and promotes angiogenesis. In addition, NF-kB can also promote tumor growth by regulating the expression of genes such as COX2.

NF-kB is closely related to cancer therapy. IFN-a, IFN-b, TNF-a, IL-2, G-CSF, GM-CSF and EPO are several cytokines that have been approved for clinical tumor therapy to date, of which the first six growth factors have been confirmed to be related to NF-κB signaling pathway. At present, scientist at home and abroad view NF-kB as the main target, using antioxidants to inhibit NF-kB activity and designing small interfering RNA (siRNA) against p65 and p50 to inhibit NF-kB synthesis, which is a therapeutic strategy for cancer treatment in animals.

Different degrees of efficacy have been achieved in experiments and cell cultures, but there is still a large distance from clinical applications. Because TNF-a has a good anti-tumor effect and a variety of immune regulation functions, many countries have carried out clinical research on the treatment of cancer with TNF. Animal experiments and clinical experiments have shown that TNF-a has obvious inhibitory effects on certain tumors, but because of the inability to distinguish between cancer cells and normal cells, the side effects are greater after using TNF-a, which is an obstacle to the large-scale clinical application.

Author's Bio: 

BOC Sciences is one of the fastest growing chemical companies whose quality products (such as inhibitors, APIs, metabolites, impurities) and services (such as biosynthesis, carbohydrate synthesis) are widely recognized across the nation. To offer the public some scientific insights concerning cancer, scientists at this company have compiled a series of articles regarding various pathways, including IL-1 Receptor Signaling Pathway, PI3K/Akt Signaling Pathway, Insulin Signaling Pathway, Notch Signaling Pathway, VEGF Signaling Pathway, Gamma Secretase Signalling Pathway, p38 Signaling Pathway, HIF Signaling Pathway, NOD-like Receptor Signaling Pathway, NF-κB Signaling Pathway, and more.