1. Activating Invasion and Metastasis
Nov 28, 2017

2. Hallmarks of Cancer, 2011

3. Metastasis

4. Extravasation
The exit of a tumor cell from a blood or lymphatic vessel
Steps are opposite of Intravasation
Attachment to the endothelial side of the blood vessel
Pass through the endothelial cells and basement membrane
Migrate into the surrounding stroma
The mechanisms differ because of the cell approaches the endothelium from opposite sides

5. Extravasation
Supports the “Seed and Soil” theory

6. Extravasation
Upon binding to E-selectin, Signaling between the tumor cell and endothelial cell is bidirectional
In endothelial cells , E-selectin induces tyrosine phosphorylation and modifies the cell’s shape
In tumor cells, Stress-activated protein kinase-2 (SAPK2/p38), a MAPK isoform in induced, important for transendothelial migration
Other molecules on tumor cells include CD44 and MUC1

7. Extravasation Transendothelial migration
-VEGF has been implicated from in vitro studies
Migration
-Proteases are important
-MMP9

8. Metastatic Colonization
Sites of Metastasis is influenced by:
Location of Extravasation
Ability of tumor cells to adapt to the new environment
Metastatic Colonization is the establishment of a progressively growing tumor at a distant site
To Grow or Not to Grow???

9. Metastatic Colonization
“Not to Grow”
Tumor cells which have reached a secondary site but have not grown are called disseminated tumor cells
-Can occur early during carcinogenesis
Micrometastases
-Remain dormant for years
-Maintain a balance between proliferation and apoptosis
-Angiogenesis is not initiated
-Molecular factors induce quiescence (stable blood vessels)
-Need to undergo a mesenchymal-to-epithelial transition (a reversal of EMT)

10. Pre-Metastatic Niche and Exosomes
“To Grow”
Tumor-specific factors are released from the primary tumor facilitate changes to the microenvironment of a distant and future site of colonization before tumor cells arrive

11. Exosomes
Small vesicles (30-100nm) that carry protein and nucleic acids
Characteristics:
-Important for intercellular communication
-Carry DNA, RNA, and protein
Horizontal transfer - Exosome transfer can educate and change the behavior of the receiving cells

12. Exosomes Experiments:
Mice treated with concentrated tumor exosomes, there was an increase in the number of metastases
Reduced exosome production via RNA interference, caused a decrease in the number of metastases
Pancreatic exosomes promote liver metastases
-Pancreatic exosomes fuse with Kupffer cells in the liver
-Kupffer cells upregulate TFG-β
-Results in expression of fibronectin in liver stellate cells
-Fibronectin recruits bone-marrow-derived cells
-Pre-metastatic niche ready to accept pancreatic tumor cells

13. Evidence for Horizontal Transfer
-Potential recipient cells would express GFP if it received the CRE-recombinase
-When exposed to CRE-containing exosomes, the cells
fluoresced green

14. Exosome Composition

16. Metastasis Suppressor Genes
-Expressed in low levels in metastatic cells
-Inhibit overt metastasis without affecting the growth of the primary tumor
-Regulation of Growth of metastatic cells at secondary sites
-Maintain these cells as noon-proliferating dormant cells
-Therefore, Loss of function, promotes metastasis

17. Metastasis Suppressor Genes
-23 metastasis suppressor genes identified
-NM23
-a nucleoside disphosphate kinase and a histidine kinase
-MKK4 (mitogen-activated protein kinase-kinase 4)
-induces apoptosis in response to a stressful environment
miRNAs
-miR-335 and miR-126
-Promote dormancy of micrometastatic colonies

18. Exosomes Video