Molecular mechanisms of tumor growth and spreading

Question 1

Tumor growth – cell proliferation and cell death

Answer 1

Tumor-forming cells can be:
Proliferating cells => proliferative pool (S phase) Non-proliferating cells => non-proliferative pool Differentiation
Cell death
G0 phase cells
Tumor growth depends on both cell proliferation and cell death rate!

Question 2

Cell proliferation

Answer 2

• Proliferating cells:
  • Active cell cycle
  • S phase (DNA replication) cell detection:
• Ki-67 proliferation marker: immunhistochemical detection =>a factor influencing tumor prognosis
  • PCNA protein

Question 3

Role of PCNA protein in DNA replication

Answer 3

• PCNA = Proliferating Cell Nuclear Antigen

* Increasing the activity of DNA polimerase δ

Question 4

The prerequisites of tumor growth

Answer 4

• Hypoxia
  • HIF-1 (Hypoxia-induced Factor-1) transcription factors  HIF-1 signaling
• Vascularisation: angiogenesis!

Question 5

Therapeutic significance of HIF-1 signaling

Answer 5

• Tumor => goal: inhibiting HIF-1 signaling => decreased angiogenesis, less adapted cells to hypoxia => slower growth
• Ischaemia =>goal: stimulating HIF-1 signaling => increased angiogenesis, better adaptation to hypoxia
- Main therapeutical targets of HIF-1 signaling:
• Proline hydroxylases
• Binding of HIF-1α to its coactivators
• HIF-1α gene expression (gene therapy)

Question 6

Vascularisation of tumors

Answer 6

The main ways of tumor vascularisation: 
• (Neo)angiogenesis 
• Vasculogenesis: from bone marrow progenitor cells 
• Co-option = vessel incorporation 
• Vascular mimicry

-Factors influencing tumor vascularisation:
• The vascularisation of the original tissue
• The angiogenic cytokine profile of the tumor: e.g. VEGF, PDGF, TGFβ, leptin…
• Hypoxia =>HIF-1 signaling => cytokine production
• Genetic/epigenetic pattern

Question 7

Inhibition of VEGF signaling: antiangiogenic chemotherapy

Answer 7

2 main drug types:
• VEGF inhibitors (antibodies!): e.g. bevacizumab
• Tyrosine kinase inhibitors (TKIs): e.g. sorafenib

Question 8

The main steps of tumor spreading

Answer 8

1. Local invasion
2. Intravasation
3. Lymphatic/haematogen spreading
4. Adhesion to vessel walls
5. Extravasation
6. Local invasion
7. Metastasis

Question 9

Local invasion – the role of integrins

Answer 9

• Changes in EC matrix (ECM) recognition – receptor over-expression: integrins, laminin receptors => transformed to oncogenes!
• Integrin activation => several pathways are activated => stimulating local invasion & metastasis formation:
• E-cadherin repression=>detachment of tumor cells
• Cytoskeleton rearrangement =>cell migration
• Stimulating cell adhesion (to pericytes and endothel cells)

Question 10

Local invasion – the role of E-cadherin

Answer 10

• Tumor suppressor, metastasis suppressor
• Binding tumor cells to each others
• EGF, IGF, TGFβ, integrins => E-cadherin repression  tumor cells are detached => local invasion

Question 11

Local invasion – degradation of ECM

Answer 11

• ECM degradation: LOX and ECM proteases!
  • LOX = Lysine oxidase=> collagen: more cross linkages are formed
  • ECM proteases:
• Matrixmetalloproteases (MMP)
• Cystein proteases (e.g. catepsins)
• Serine proteases
  • Decreased activity of protease inhibitors
  • Autocrine and paracrine factors => cell migration

Question 12

Metastasis formation

Answer 12

•Lymphatic spreading => metastasis in lymph nodes (sentinel lymph node!): easy intravasation, but immune factors in the lymph!
- Lymph angiogenesis
- Via normal lymph vessels
•Haematogenic spreading => metastasis in further organs

Question 13

Steps of haematogenic metastasis formation

Answer 13

Local invasion=> intravasation:
• Endothel contraction =>increased permeability
*VEGF=> endothel contraction
* Lipoxygenase => eicosanoid synthesis(12-HETE)  endothel contraction
• Enzymatic cleavage of basal membrane

Spreading with the blood stream:
• Resistance to altered conditions – anti-apoptotic mutations may facilitate spreading (Bcl, Bax)
• Integrins => micro-aggregates with thrombocytes  protective role
Adhesion
Extravasation => local invasion, (micro-)metastasis

Question 14

Formation of bone metastases

Answer 14

• Primary tumor: producing bone-specific matrix proteins => bone is a perfect location for tumor cells:
* Osteopontin
* Osteonectin
* BMP = bone morphogenic protein
• Osteolytic and osteoblastic metastasis types
• Parathormone-related protein (PTHrP) production =>osteoblast activation and differentiation to osteoclasts => osteolytic processes

Question 15

Molecular diagnostics

Answer 15

• Molecular diagnostics: genetic profile, mutations, alterations on the gene expression level  aimed therapy => new opportunities!