Advanced Cancer Biology Exam - Colloquia 4

Why are mice suitable as model organisms in cancer research? Name four advantages of using mice as model organisms in cancer research.

- They have a complex interplay between cancer cells and host cells in the tumor environment. - Mice are easy to genetically manipulate. They are also easy to manipulate with cancer cells and make them grow tumors. - Mice and human are very similar. They have very homologous genomes. - They are small and cost-effetive - Easy to handle - Their generation time is short

Describe and explain the invasion‐metastasis cascade in steps

1. Invasion = Breachment of the basement membrane that leads to a local invasion of the tissue. 2. Intravasation = The tumor cells enter the blood vessels or lymphatic vessels where they can be transported. 3. Extravasation = The tumor cells exit the blood vessels or lymphatic vessels. 4. Micrometastasis = The formation of a small metastatic mass where the cell has colonized new tissue yet the number of cells are still too small to be detected in a screening. 5. Colonozation = When the cell settles and starts growing and expanding in the new tissue into macroscopic metastases.

What are the key cellular changes that occur during the EMT?

1. Loss of cytokeratin expression (and E-cadherin expression) 2. Loss of intracellular adhesion and polarity (E- to N-cadherin) 3. Loss of attatchment dependancy for survival (anoikis) 4. Gain of invasiveness 5. Gain of motility 6. Gene expression changes 7. Change of cellular shape into more fibroblast like

Subcutaneous transplantation

A transplantation of cancer cells of tumor tissue under the skin

At which step in the invasion‐metastasis cascade are cancer cells thought to undergo MET?

At the extravasation state. They need to be able to create anchorage to other cells and not be as motile as the mesynchymal cell types.

At which sites does prostate cancer typically form metastatic colonies?

Bones

At which sites does breast cancer typically form metastatic colonies?

Brain, liver, bones and lungs

List three disadvantages of using radiotherapy to treat cancer.

Cardiac toxicity => cannot be used all over the body Gastrointestinal damage Hair loss Secondary malignancies

2 examples of immunohistochemical analyses to see EMT at the invasive edges of the carcinomas

Chromogenic IHC Fluorescent IHC Both uses antibodies to mark specific molecules.

Explain briefly what is meant by the oxygen fixation hypothesis.

DNA damage induced by ionizing free radicals can be made permanent and irreparable if oxygen is available.

Two proteins whose expression is typically increased during EMT and two proteins whose expression is repressed.

E-cadherin and cytokeratin is repressed as they are epithelial markers Fibronektin and vimentin are increased as they are mesynchymal markers

List three advantages of using radiotherapy to treat cancer.

Effective Relatively low cost Directly on the disease tissue - spares more of the normal healthy tissue

Allograft (syngenic) model

In the allograft model, mouse cancer cells or tissues are transplanted into the host mouse, which is derived from the same strain the the harvest mouse.

Xenograft model

In the xenograft model, human cancer cells or tissues are transplanted into an immunocompromised mouse.

Advantage of the xenograft model

It can be used to study human tumors and their initiation and metastases in mice. It also allows to study the effect of drugs on the cancer and cancer therapy in general

At which sites does colon cancer typically form metastatic colonies?

Liver

What is a meant by a dormant micrometastasis?

Metastatic tumor cells that have spread as micrometastasis into distant organs for many years, without forming macrometastases. It is latent metastatic tumor cells

Why is secretion of proteases required for invasion (i.e. what is the role of proteases in the invasion process)?

Proteases like MMP-2 and MMP-9 are secreted either from stromal cells near cancer cells or from the cancer cells themselves to remodel the extracellular matrix (ECM). This removes hindrances and allows the cells to move around.

Implication of synthetic lethality on cancer therapy

Synthetic lethality can be used to kill cancer cells. Cancer cells with mutations in 1 of the genes in a synthetic lethal pair will die if the wt gene is also inhibited. In that way the whole pathway is inhibited - that could ex. in DNA repair and the cancer cell will die.

What is synthetic lethality?

Synthetic lethality is when inactivation of one of 2 genes involved in the same pathway (ex. DNA repair) does not affect cell survival. In the case where both genes/ both synthetic lethal partners were inactivated it would kill the cell.

2 examples of signaling molecules that are secreted by cells in the tumor stroma and then bind to receptors in the cancer cells located in the edges of the carcinoma to promote their EMT program

TGF-b Wnt's TNF-a EGF IGF-1

Advantage of the allograft model

The host immune system is not compromised. It is more representative of the real life situation in the tumor microenvironment.

Limitation of the xenograft model

The mouse has to be immunodeficient and immunocompromised. All aspects of the affect of the immune system on the cancer progression can not be taken into account.

Limitation of the allograft model

The mouse tumor tissue may not fully represent or resemble the complexity of human tumors.

Define the term metastasis

The spread and growth of cancer cells to sites distant from the primary tumor.

Why are only a small fraction of the circulating tumor cells successful in forming metastatic colonies. What could be the possible reasons for this?

There are many obstacles for a circulating tumor cell. It must overcome the innate immune system, oxidative stress and the shear forces from the blood flow. They can overcome this by attatching to platelets in the blood.

What might be the reason the cancer cells undergo MET at the extravasation state?

To be able to colonize and form a new mass/tumor in the secondary tissue

Orthotopic transplantation

Transplantation into the same tissue as the human cancer. Ex. brain cancer cells that are transplanted into the brain of the mouse.

Intravenous transplantation

Transplantation through the veins and directly into the blood stream

What does the term "circulating tumor cell" describe?

Tumor cells that have intravasated and is now in circulation. They are on their way to settle in distant organs and create sites of metastasis. It is a tumor cell that has left the primary tumor and is now circulating.

Explain briefly what tumor hypoxia is.

Tumor hypoxia is the reduction of sufficient oxygen available for a region of the tumor. The further away the cancer cells are from the supply the more hypoxic is the environment.

How can you study the role of EMT‐inducing transcription factors in the formation of metastases by using mouse models?

Use knockout mice for these TFs and inject tumor cell orthotopically and see if it metastasizes Use an siRNA against EMT TFs and injection of tumor cells and measure the tumor sizes and metastases with and without EMT TFs.

EMT is controlled by a small number of transcription factors. Name two such EMT‐inducing transcription factors.

ZEB1 and ZEB2 Snail Slug Twist