invasion and metastasis

metastasis definition

process by which tumour cells disseminate to distant sites to establish discontinuous secondary tumours

how is metastasis different to invasion

creating a distant, secondary tumour

invasion metastasis cascade

1. Breakaway from the primary tumor and breach the underlying basement membrane

2. Migrate through the surrounding stroma

3. Enter the blood flow by crossing the endothelial cell layer

4. In order to travel through the blood/lymph vessel the have to survive in this “strange” environment

5. extravasate into distant tissue

6. establish a new colony of cells - colonisation

requirement for invasion metastasis cascade

• cell migration

• ability to invade and remodel the ECM

• intravasation

• dissemination through the circulation

• extravasation

• survival in inappropriate tissue contexts

acquisition of local invasiveness

• Reduced cell-cell adhesion

  • Down-regulation of E-cadherin

• Proteolytic degradation of the basement membrane

  • Invadopodia are specialized subcellular structures which perform this role

• Acquisition of a motile phenotype

• Adhesion to the stromal ECM

• Cytoskeletal reorganisation

• Propulsive force

  • actomyosin contraction and actin

  • polymerisation

• Proteolytic degradation of the stromal ECM

  • prominent role for matrix metalloproteinases

How are motility and invasiveness acquired?

• induction of oncogenes such as ras

• stimulation of TNF alpha and HGF - induce JNK, NF-kB, Erk cascades

• HGF activation leads to activation of cmet, tyrosine kinase receptor, ras → migratory machinery

• pro migratory growth factors released by cancer cells or fibroblasts, immune cells

• spindle morphology - mobility

• EMT

which cadherin is lost through EMT

E

invadopodia

• like drills

• actin rich protrusions with metalloproteases

• allow degradation of laminin and collagen, degrading BM

which receptor is upregulated for invasion

• alpha v beta 6 fibronectin receptor

injections of RGD

• interfere with integrin binding to ECM

• effective in mice but not in humans

cell migration through actin cytoskeletal reorganisation

• actin polymerisation at front and myosin contraction at the rear end of the cell

• extension of front of cell creates new attachments, focal contacts contain integrins

lamellipodia

• lamellipodia - actin based, at the leading edge

filopodia

thin protrusions which help the cell to explore the surroundings of the cell, allowing polarisation, detecting stiffness and gradients

Rho GTPases 3 families

• Rac

• Rho

• Cdc42

Regulation of GTPase activity

• GEFs promote binding to GTP leading to activation

• GAPS stimulate hydrolysis of GDP leading to deactivation

• Rho GDI binding leads to inactivation

rho induction of lamellipodia and focal contacts

• leads to reorganisation of actin cytoskeleton leading to lamellipodia

cdc42 induction of filopodia

• cdc42 activation leads to reorganisation of the actin cytoskeleton to form filopodia

• cells use the filopodia to detect chemical changes and direct migration

• vinculin distribution changes but still coinicdes with organised actin at filopodia

rho and stress fibres

when rho is activated the cells form stress fibres which act as cables to retract the cell and after lamellipodia formation create net movement

Proteases role in invasiveness

• matrix metallopases are the most important

• also include serine proteinases, cysteine cathepsins etc

which matrix is more tightly organised than collagen I

basal membranes

alternatives to mesencyhmal invasion

1. amoeboid

   1. high contractility Rho-ROCK, squeezes through without breakdown of ECM

2. collective cell invasion

   1. brute force, cells retain many of the cell-cell adhesions, so no lack of e cadherin

   2. may be reason why integrin inhibitors dont always work

survival of metastases in circulation

• intravasation degrades blood vessel membrane

• tumour cells need to resist apoptosis

• vast majority perish

• can get stuck in first capillary bed

why are micrometastases hard to treat

• tend to be resilient and hard to find, cannot focus radiation

• many are not clinically significant

• mostly become dormant and form micrometastases due to hypoxia and angiogenic switch

• can create residual disease after main tumour is treated

What determines sites of metastases

• pattern of blood flow - passive

• tissue ‘tropism’ - selection

• homing signals - active

mechanism of circulation examples for metastasis

eg colon and liver

• blood from intestines pass through the liver before entering the venous system

• hepatic portal circulatory system before liver

eg breast cancer to lymph nodes to main circulation and then from heart to lungs

seed and soil hypothesis

• only certain tissues will have similar trophic signals

• chemokines drive a homing response - trigger chemostatic and invasive responses

• metastatic cells create a niche to establish a tumour

what is the pre metatsatic niche?

• inflammation

• immune supression

• angiogenesis

• ECM remodelling

antimetastatic compounds

• trigger measurable responses where treatment is initiated prior to the formation of primary tumours or metastases

• display efficacy in preventative models to impair metastasis only after formation of small micrometastases

dastinib MPA

inhibit the metastatic outgrowth of already disseminated tumour cells in intervention assays

what have no effect on metastases

• MMP inhibitors - lack of specificity

ras leads to which acquired capabilities

• apoptosis

• evasion

• mitogenic independence

• angiogenesis

• metastasis invasion

breast cancer invasion and feedback loop

• breast cancer invasiveness can be stimulated through IL-6

• secretion of IL-4 by breast cancer cells can trigger cathespin protease activity, increasing the carcinoma cell invasiveness

• shows bi directional interactions between tumour cells and nearby stroma

• carcinoma cells stimulate formation of inflamed stroma, and the stroma enhances the malignant traits of the carcinoma cells

  • self amplifying pos feedback loop

vimentin

intermediate filament protein of the cytoskeleton of mesenchymal cells such as fibroblasts

TGF Beta role

• leads to progressive loss of epithelial morphology

• reduction in epithelial markers - cytokeratins and e cadherins

• induction of EMT

signals which induce EMT programs?

• TGF beta

• cytokines

• stiff extracellular matrix

• absence of epithelial neighbours

• collagen type I

Interactions between macrophage and carcinoma cell

• carcinoma cell produces CSF-1 which binds to receptor on macrophage

• stimulates macrophage to release EGF which binds to EGF receptor on carcinoma cell

What leads to proteolytic degradation of E cadherin?

cathepsin B protease