Chapter 32 invasion and metastasis

general oncology from devita presentation

1. DR. MANIN CHAUDHARY DNB MEDICAL ONCOLOGY 1 ST YEAR 23-05-2017 INVASION AND METASTASIS

2. The process by which tumor cells from a primary site invade and migrate to other parts of body is called metastasis. The spread of cells throughout the body results in physical obstruction, competition with normal cells for nutrients and oxygen, and invasion and interference with organ function.

3. As the bloodstream is the predominant means of long distance transport, organs in close proximity “en route” are likely to be main sites of metastasis for a particular primary tumor. “Seed and soil” theory: Cancer cells = seeds Optimal environment = soil Pre-metastatic niche: as a result of factors released by the primary tumor, a site of future metastasis is altered in preparation for the arrival of tumor cells.

4. The invasion-metastasis cascade 1. Localized invasion 2. Intravasation 3. Transport 4. Extravasation 5. Formation of micrometastasis 6. Colonization

5. The Invasion – Metastasis Cascade

6. 1. Localized invasion In order for cells of primary tumor to invade into their local environment, cells must break free from the normal molecular constraints that link adjacent cells to each other (cell adhesion molecules, E- cadherin , catenin ). The best characterized alteration involves loss of E- cadherin by the carcinoma cells .

7. E- cadherin It is an important epithelial cell-to-cell adhesion molecule, forming adherens junctions between adjacent epithelial cells . Increased expression of E- cadherin is associated with prevention of invasion and metastasis, whereas decreased expression is known to potentiate it. The E- cadherin is encoded by the gene CDH1.

8. Matrix metalloproteinases (MMPs) Invasion of tumor cells into the surrounding tissue requires the action of specific proteases that degrade a path through the ECM and stroma. The most important effectors are matrix metalloproteinases (MMPs). In some tumors, invading carcinoma cells make their own proteases, while in others, bulk of these proteases are secreted by macrophages, mast cells and fibroblasts in the tumor stroma.

9. Collaboration of MT1-MMP and MMP-2 in carcinoma

10. The epithelial- mesenchymal transition (EMT) It is a prominent means by which neoplastic epithelial cells can acquire the ability to invade, resist apoptosis and disseminate. It involves the conversion of a sheet of closely connected epithelial cells into highly mobile mesenchymal cells. Common in early embryogenesis and in wound healing, reactivated in cancer cells.

11. Other modes of invasion Amoeboid invasion: Cancer cells show morphologic plasticity enabling them to slither though existing interstices in ECM rather than clearing a path for themselves Collective invasion: Group of cancer cells advancing in masses into adjacent tissues eg . Squamous cell carcinoma

12. 2. Intravasation It is the entry of tumor cell into a blood or lymphatic vessel. It requires several steps: Tumor cells must attach to the stromal face of the vessel Degrade the basement membrane using MMPs Pass between the endothelial cells ( transendothelial migration) into the bloodstream Influenced by the structural properties of the blood vessel : New blood vessels stimulated by tumor; leaky and tortuous allowing easy access.

13. The process of intravasation is assisted by tumor-associated macrophages which guide tumor cells to the vessels. This process involves the CSF-1 receptor on macrophages and EGF receptor on tumor cells. The tumor cells produce CSF-1 and macrophages associate with blood vessels to form EGF leading to chemotaxis -mediated co-migration.

14. 3. Transport Once the cancer cells have intravasated into the lumen of a blood or lympatic vessel, they may travel with blood or lymph to other areas of the body. However, cancer cells require anchorage to solid substrates for survival; without such attachment, the migrating cells may die of anoikis . The blood represents an actively hostile environment for metastatizing cancer cells.

15. Hydrodynamic shear forces in the circulation, may tear the wandering cancer cells apart. The survival of cancer cells in circulation is greatly enhanced if they can attract a group of blood platelets, called emboli, to escort them through the circulation. The large size of tumor cells (20-30 µm) relative to the diameter of capillaries (about 8 µm) suggests that a large fraction of tumor cells get trapped in the first capillary beds that they encounter (first pass organ).

16. 4. Extravasation It is the escape of a tumor cell from a blood vessel or lymphatic vessel, and penetration into surrounding tissue. The steps involved are similar to intravasation, but in reverse : Attachment to endothelial side of blood vessel (E- selectin ) Pass through endothelial cells and basement membrane Migrate into surrounding stroma

17. Lodging and extravasation of circulating tumor cells

18. 5. Formation of micrometastasis Once the metastasizing cancer cells arrive within the tissue parenchyma, they form small clumps or minute colonies of disseminated cancer cells, called micrometastasis. These micrometastases may lack certain hallmark capabilities necessary for vigorous growth, such as ability to activate angiogenesis. Moreover, nutrient starvation can induce intense autophagy that causes cancer cells to shrink and adopt a state of reversible dormancy.

19. Such cells can resume active growth and proliferation when permitted by changes in tissue microenvironment such as increased availability of nutrients, or inflammation due to infection or wound healing. Other mechanisms of micrometastatic dormancy involve antigrowth signals of normal tissue ECM and tumor-suppressing actions of immune system.

20. 6. Colonization It is the growth of micrometastasis into macroscopic tumors. It is the most difficult step of all, as the foreign tissue environment do the provide the newly arrived cancer cells the growth and survival factors, that the primary tumor provided them. Without this physiological support, the metastasizing cells may die rapidly, or survive for extended periods as micrometastasis that can only be detected microscopically, and rarely increase beyond this size.

21. The probability of an individual cancer cell successfully completing all the steps of the invasion-metastasis cascade is very low. This low rate of success in forming metastases is called metastatic insufficiency. The earlier steps of this cascade are executed quite efficiently, while the last step involving colonization succeeds only rarely, therefore it is the rate limiting step of the process.

22. Primary tumors and their metastatic tropisms

23. Having developed a tissue-specific colonizing ability, the cells in the metastatic colonies may proceed to disseminate further, not only to new sites in the body, but also back to the primary tumors : self-seeding process . The supportive stroma of the primary tumor provides a hospitable site for reseeding and colonization by circulating cancer cells.

24. Metastasis suppressor genes A new class of genes called metastasis suppressor genes have been identified. They are defined by their ability to inhibit overt metastasis without affecting the growth of primary tumor. Loss of function of the gene increases the metastatic propensity of a cancer cell.

25. NM23 was the first metastasis suppressor gene to be identified, now 23 such genes have been identified. MKK4 ( mitogen activated protein kinase 4) is another important gene. Both promote dormancy of micrometastatic colonies, and prevent overt metastasis.

26. Strategies for treatment using metastasis suppressors genes Drug development strategies that reactivate metastasis suppressor genes are being developed. The promoter of NM23 gene is regulated by glucocorticoid response pathway. Medroxy progesterone acetate (MPA), a progesterone and glucocorticoid agonist was shown to induce expression of the NM23 promoter .

27. Metalloproteinase inhibitors (MPI) Several trials were conducted regarding the potential development of MPIs as a cancer treatment drug, but were unsuccessful due to low efficacy and several side effects. No MPIs have received approval for cancer treatment so far. Targeting membrane-bound metalloproteinases by selective therapeutic antibodies is a more recent strategy for development of next generation of metalloproteinase inhibitors.

28. Targeting several steps of metastasis at once Recently, sets of genes or “ genes signatures ” that are associated with primary tumor growth and risk of metastasis have been identified. Functions of 4 genes of a lung metastasis gene signature in human cancer cells were analyzed (the EFGR ligand epiregulin , COX2, MMP1 and MMP2). These 4 genes mediate the processes of tumor growth, angiogenesis, migration, intravasation and extravasation.

29. When all 4 genes were inactivated, tumor growth and lung metastasis were inhibited. A combination of existing drugs was able to target the protein products of 4 genes and demonstrated inhibition of growth and metastasis ( Cetuximab : an EGFR antibody; Celecoxib : a COX inhibitor; and GM6001: A MMP inhibitor). These results hold great potential for the future and are being developed.

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