Metastasis Inhibiting Peptides

Peptides inhibit metastasis-associated cancer cell adhesion.

Metastasis is a deadly aspect of cancer resulting from interconnected steps, including cell proliferation, developing new blood vessels (angiogenesis), cell adhesion, migration, and invasion of surrounding tissues. During metastasis, tumor cells spread from the primary focus to invade other cells and tissue leading to mortality. Cancerous, latent cells can lodge in the bone marrow and organs distant from the primary tumor seeding new metastatic growth later.

Cancer starts after a single tissue cell is genetically damaged. Progressive damage caused by mutations produces cells that proliferate in an uncontrolled manner. The spread of cancer from one organ or cell tissue to another is known as "metastasis." Some cancer cells can penetrate the walls of lymphatic or blood vessels allowing these cells to circulate through the bloodstream to other sites and tissues in the body. These cells are known as circulating tumor cells.

Intravascular cancer is cancer that occurs within a blood vessel or blood vascular system. Intravascular cancer cell adhesion plays a significant role in the metastatic process. The lectin galectin-3 is involved in carbohydrate-mediated metastatic cell adhesion via interaction with the tumor-specific Thomsen-Friedrich glycoantigen (TF or TFAg). The Thomsen–Friedenreich antigen (Gal-GalNAc) represents a tumor-associated molecule.

Mereiter et al., in 2018, observed a highly significant association between the expression status of the Thomsen-Friedenreich (TF) antigen and microsatellite instability in gastric cancer, identifying the first single marker for MSI in gastric cancer. In colorectal cancer, microsatellite instability (MSI) caused by deficient DNA mismatch repair (dMMR) is associated with several clinical and histopathological features.

In 2021, Leão et al. reported the results of a study that correlated the expression of the TF antigen in colorectal cancer with microsatellite instability. The study results indicated that the TF antigen is not a predictor of MSI in colorectal cancer, contrary to what has been described in gastric cancer with MSI. However, the study’s results revealed that patients harboring MSI-high tumors that express the TF antigen have significantly better survival than TF-negative cases.

The Thomsen-Friedenreich antigen, Galβ1-3GalNAcα1-O-Ser/Thr (Figure 1 ans 2), is the core one (1) structure of O-linked mucin-type glycans found in tumor-associated glycosylation. This antigen occurs in about 90% of human cancer cells and is a potential ligand for the human endogenous galectins.

In 2005, Zou et al. reported that galectin-3 plays a significant role in metastasis. Galectin-3 is a member of the galectin family of soluble animal lectins. This lectin mediates carbohydrate-mediated metastatic cell adhesion between carcinoma cells and the endothelium and between carcinoma cells. The tumor-specific Thomsen–Friedenreich glycoantigen is involved in cell-specific interactions.

Isolation of galectin-3-binding peptides

Zou et al. selected Galectin-3-specific peptides by screening a random 15 amino acid and a cysteine-constrained library displayed on coat protein VIII. After the fourth round of selection, the output phage yield from both libraries was ∼100-fold higher than the first round, indicating enrichment of galectin-3-binding phage clones in the eluted phage population. The study identified short synthetic peptides bound to the carbohydrate recognition domain of galectin-3 using a combinatorial phage display technology. The peptides inhibited the interaction between galectin-3 and its sugar ligand TFAg, interfering with metastasis-associated carcinoma cell adhesionG3-A9 and G3-C12 were the predominant output clones ( Table I ).

Table I.  Results of combinatorial peptide selections against galectin 3.Deduced peptide sequences, percent occurrence of phage clones and affinity of peptides (Zou et al.). 

Note: The percentage of individual clones is reported that were represented in the populations of 80 f88-15 and 60 f88-Cys6 libraries selected. 

Reference

Khan N, Mukhtar H. Cancer and metastasis: prevention and treatment by green tea. Cancer Metastasis Rev. 2010;29(3):435-445. [PMC]

Leão B, Wen X, Duarte HO, et al. Expression of Thomsen-Friedenreich Antigen in Colorectal Cancer and Association with Microsatellite Instability. Int J Mol Sci. 2021;22(3):1340. [PMC]

Mereiter S, Polom K, Williams C, et al. The Thomsen-Friedenreich Antigen: A Highly Sensitive and Specific Predictor of Microsatellite Instability in Gastric Cancer. J Clin Med. 2018;7(9):256. [PMC]

Pinho, S., Reis, C. Glycosylation in cancer: mechanisms and clinical implications. Nat Rev Cancer 15, 540–555 (2015). [NRC]

Jun Zou, Vladislav V. Glinsky, Linda A. Landon, Leslie Matthews, Susan L. Deutscher, Peptides specific to the galectin-3 carbohydrate recognition domain inhibit metastasis-associated cancer cell adhesion, Carcinogenesis, Volume 26, Issue 2, February 2005, Pages 309–318. [Article]

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