Cancer cell, horrifying but intriguing

Magdalena CHECHLIŃSKAMagdalena CHECHLIŃSKADepartment of Immunology

Maria Skłodowska-Curie Memorial Cancer Centre and Institute of Oncology

Warszawa

CellsYour body is made up of approx.

1013-1014 cells that can only be seen under a microscope. These cells are grouped together to make up the tissues and organs of our bodies. 

Cells are basically similar. They all have a centre called a nucleus. Inside the nucleus are the genes.

Genes are really bits of code. The information they carry can be switched on or off. The genes control the cell. They decide when it will reproduce, what it does and even when it will die.

Body tissues• Body tissues grow by

increasing the number of cells that make them up.  The cells reproduce themselves exactly. 

• But once we are grown up, most cells  mature, become specialised for their particular job in the body and lose the ability to reproduce.

• There are always immature cells around (called stem cells) to replace cells that are damaged or killed.

• Some cells carry on reproducing.  These include sperm cells, hair cells, cells in the gut and cells that make blood in the bone marrow.

How do the cells know when to stop

growing?

Normal growth and healing is very orderly and precise.  The cells send chemical messages to each other.  The messages come from the genes inside the cells. 

How do new cells end up in the right place?

The cells have a natural ability to stick together in the right place.  Scientists call this cell adhesion.

If the cell does find itself in a place where its surface molecules are different from its neighbours, it will die.

How cells reproduce

• Cells double up very precisely so that the new cells are exactly the same as the old ones.  Each cell makes copies of all its genes.  Then it splits into two with one set of genes in each new cell. 

• This is called mitosis

Can cells carry on doubling for ever?

No they can't!

It seems human cells are pre-programmed

to reproduce up to 50 or 60 times maximum. 

Then they will become senescent

and eventually die. 

40 population doublings = 1 cell gives rise to 1012 cells

What cancer is

Cancer is a disease caused by normal cells changing so that they grow in an uncontrolled way.  The uncontrolled growth causes a lump called a tumour to form. 

There are over 200 different types of cancer because there are over 200 different types of body cells.  For example, cells that make up the lungs can cause a lung cancer.  There are different cells in the lungs, so these may cause different types of lung cancer. 

How cancer starts - MUTATIONS

One cell (?) that has lost a number of vital control systems due to mutations.  Mutation means a gene has been damaged or lost. 

One gene 'codes' for one protein.

Mutation too much protein is made

a protein is not made at all.

the properties of a protein are changed

3 types of genes that are important in making a cell cancerous:» Genes that encourage the cell to multiply » Genes that stop the cell multiplying » Genes that repair the other damaged genes

How cancer starts

Oncogenes Some genes encourage cells to multiply (proliferate). If these genes become abnormal, they tell the cell to multiply all the time. 

Tumour suppressor genes (anti-oncogenes) Some genes specifically to stop the cell multiplying - they act as the brake to the oncogene's accelerator. 

If one of these 'tumour suppressor genes' becomes damaged and stops working, then the cell may carry on and on multiplying and it becomes immortal, which is one of the properties of a cancer cell.  p53 normally stops cells with other damaged genes from reproducing and encourages them to commit suicide (apoptosis).  p53 is damaged or missing in most human cancers.

Genes that repair other damaged genes These genes normally repair any damage to the DNA that the cell's genes are made of.  If these genes are damaged, then other mutations are not repaired and the cell can reproduce the mutations in its daughter cells.  These genes have been found to be damaged in some human cancers, including bowel cancer.

How cancer starts

How do mutations happen? By chance when a cell is reproducing.  It is not easy for a normal cell to turn into a cancer cell.  There have to be about half a dozen different mutations before this happens.  Cells often self destruct if they carry a mutation.  Or they might be recognised by the immune system as abnormal and killed.  This means most pre-cancerous cells die before they can cause disease.  Only a few can turn into a cancer. 

•It can take a long time before enough mutations happen for a cell to become cancerous.  This is why many cancers are more common in older people.  There has been more time to be exposed to carcinogens.  And more time for accidents when cells reproduce.

How cancer starts

Genetic make up• There have to be a number of genetic mutations within a cell before it

becomes cancerous.  Sometimes we are born with one of these mutations already.  This does not mean we will get cancer.  But with one mutation from the outset, it makes it more likely statistically that we will ( 'genetic predisposition‘).

Examples: the BRCA1 and BRCA2 breast cancer genes.  Women who carry one of these faulty genes have a higher chance of developing breast cancer than women who do not.

BUT: Most women with breast cancer do not have a mutated BRCA1 or BRCA 2 gene.  Less than 5% of all breast cancer is due to these genes.  So most breast cancer is not caused by a high risk inherited gene fault.

How cancer starts

Genetic make up• There have to be a number of genetic mutations within a cell before it

becomes cancerous.Sometimes we are born with one of these mutations already. This does not mean we will get cancer. But with one mutation from the outset, it makes it more likely statistically that we will ( 'genetic predisposition‘).

Examples: the BRCA1 and BRCA2 breast cancer genes. Women who carry one of these faulty genes have a higher chance of developing breast cancer than women who do not.

BUT: Most women with breast cancer do not have a mutated BRCA1 or BRCA 2 gene. Less than 5% of all breast cancer is due to these genes. So most breast cancer is not caused by a high risk inherited genefault.

How cancer starts

Genetic make up• There have to be a number of genetic mutations within a cell before it

becomes cancerous.Sometimes we are born with one of these mutations already. This does not mean we will get cancer. But with one mutation from the outset, it makes it more likely statistically that we will ( 'genetic predisposition‘).

Examples: the BRCA1 and BRCA2 breast cancer genes. Women who carry one of these faulty genes have a higher chance of developing breast cancer than women who do not.

BUT: Most women with breast cancer do not have a mutated BRCA1 or BRCA 2 gene. Less than 5% of all breast cancer is due to these genes. So most breast cancer is not caused by a high risk inherited genefault.

Progression of epithelial cancer (carcinoma)

Thiery, 2002

Normal cells

• Reproduce themselves exactly (FIDELITY)

• Stop reproducing at the right time (CONTACT INHIBITION)

• Stick together in the right place

• Self destruct if they are damaged (APOPTOSIS)

• Become specialised or 'mature‘ (DIFFERENTIATION)

Cancer cells

• Carry on reproducing  • Don't obey signals from

other neighbouring cells  • Don't stick together   • Don't become

specialised, but stay immature  

• Don't die if they move to another part of the body

Cancer cell – acquired capabilities

Hanahan, 2000

Self-sufficiency in growth signals

• Synthesis of growth factors

• Expression of growth factor receptors

• Receptor structure changes resulting in signal transmission in spite of the lack of a growth factor

Intracellular signals

Membrane

Kassis, 2001

Normal cells:• Tightly packed• Autocrine interactions -

blocked

Dysplasia• Cells do not stick together

• Autocrine activation and further detachment of cells

EGFR

Tumour

Kunz-Schugart, 2002

ECM

„successful neoplastic cells are those able

to engage other cells to promote their

growth ”. Skobe i Fusenig

Tumour microenvironment influence

cancer cell growth

HaCaT (immortalised human keratinocytes)

Tranfected with H-ras oncogene

Benign cells Malignant cells

Increased growth potential

Malignant transformation

INCREASED POTENTIAL TO PRODUCE DISTANT METASTASES

in v i v o

i n v i t r o

No malignant transformation,

Reduced malignant

tumour development

potential

dośw.Mueller i wsp. 2001

Wounding stimulates the growth of primary and secondary tumours. (Experimental models of human cancers)

Hofer, 1999

TGFRII- mice, selectively on fibroblasts,

excessive fibroblasts in prostate, followed by

prostate cancer.

Conclusion: defective stromal fibroblasts

stimulate epithelial tumour growth due to the

lack of TGFinhibitory activity

Bhowmick i wsp., Science, 2004

Inhibits:● nomal melanocytes, ● melanoma cells – early stages czerniaka

● lung and liver epithelial cells

Insensitivity to anti-growth signals

stimulates:● advanced melanoma cells

Does not inhibit cell lines in vitro:

● lung cancer

● liver cancer

IL-6

Apoptosis = programmed cell death = = gene-directed cellular self-destruction

Cells are programmed to die at a particular point.This cell suicide mechanism enables metazoans (multicellular

organisms) to control cell number.

„Apoptosis” is of greek origin, meaning "falling off or dropping off", in analogy to leaves falling off trees. This analogy emphasizes that the death of living matter is an integral and necessary part of the life cycle of organisms.

Apoptosis

Functions of apoptosis– Development – Homeostasis:

• Immune cell regulation • Cell damage or infection • Response to stress or DNA damage

• In the human body 100.000 cells are produced every second by mitosis and a similar number die by apoptosis, i.e. 50 to 70 billion cells die each day due to apoptosis in the average human adult. In a year, this amounts to the proliferation and subsequent destruction of a mass of cells equal to an individual's body weight.

Evading apoptosis :example: TNF – pro- and anti-apoptotic

Apoptosis

• Cell damage or infection • Response to stress or DNA damage

DNA damage Damage response

p53

Repair

Arrest

Apoptosis

Evading apoptosis – ineffective effectors

IL-10

TGF-

mTNF

sTNF

TNFR

FasL

Fas

Fas

FasL

Cytotoxic/effector cellTumour cell

IL-6

No apoptosis Apoptosis

Limitless proliferative potential – cancer cells are immortal

Avoiding the progressive erosion of chromosomes (all cancer cells) by telomerase expression (85-90%) and other mechanism.

What telomeres are

• Telomeres are extensions of the linear, double-stranded DNA molecules of which chromosomes are composed, and are found at each end of both of the chromosomal strands.

• Telomeres are essential for chromosome stability

• Telomeres shorten with each cell division each round of DNA replication leaves 50-200 bp DNA unreplicated

Telomeres, normal

metaphase

Telomere shortening as a mitotic counter

Telomere lenghtSperm, eggs 20 kilobasesFoetal cells ~15 kilobasesAdult cells ~10 kilobasesSenescent cells ~5 kilobases

Each round of DNA replication leaves 50-200 base pairs DNA unreplicated

Cells with telomeres that are 10-12 kb in length (average) divide 50-60 times

Telomere maintenance is evident in all types of malignant cells.

The main mechanism: upregulation of telomerase (85-90% of malignant cells).

Telomerase is an enzyme, which is able to extend telomeres.

Progression of epithelial cancer (carcinoma)

Thiery, 2002

Cancer cells stimulate angiogenesis, i.e. new vessels’ development

Angiogenesis – the growth of new blood vessels

< 100m from capillaries

Pro-and anti-angiogenic factorsThere are at least:

• 20 angiogenic growth factors• 30 known natural angiogenesis inhibitors found in the body.

Tumours present „proangiogenic” profile,

i.e the balance between angiogenic inducers and inhibitors

is disturbed in favour of the inducers.

Proangiogenic factors

• Hypoxia

• VEGF increased expression: breast, ovarian, pancreatic,prostate cancer

High serum levels correlate with adverse prognosis.

Progression of epithelial cancer (carcinoma)

Thiery, 2002

Cancer cells invade and colonise other sites

• Adhesion to extracellular matrix components and basement membrane

• Basement membrane degradation

• Extracellular matrix modification and degradation

• Active migration in extracellular matrix

• Penetration thorough: blood vessel walls, lymphatic vessel walls, body cavities walls

• Implantation, survival and growth at distant sites

Carcinoma cells in primary mammary tumour move along ECM fibres

Scale bar 25m

Intravasation in primary mammary tumour

Condeelis and Segal, 2003

Adhesion molecules

• Growth factors released in tumour microenvironment induce changes of adhesion molecules on:

• Cancer cells

• Fibroblasts

• Endothelial cells

Proteases - enzymes

• Released not only by cancer cells but also by other cells in the microenvoronment

• Role: extracellular matrix degradation

• Activation and release of matrix-associated growth factors

• Protease activity correlates with the ability to form distant metstases.

• Protease inhibitors inhibit cell migration

Active migration

Distant metastases

Organ-specific pattern of metastasis

Site 10% 10-30% 30-50% 50-70% 70%

Breast Kidney, skin, brain

Adrenal Liver, bone, lung

Lymph nodes

Bladder Brain, skin Kidney, bone Adrenal, lung

Cervix Brain, skin Kidney, bone Adrenal, lung

Colorectum Skin Brain, kidney, lung

Bone, adrenal, liver

Lymph nodes

Kidney Skin, bone Brain, kidney Liver Lung

Lung Lung Kidney, distant nodes

Adrenal, brain Bone Liver, local lymph nodes

Melanoma Kidney Adrenal, brain, bone, skin

Lung. Liver nodes

Ovary Brain, skin, kidney

Bone, adrenal Lung, liver nodes

Prostate Brain, skin Kidney, adrenal, liver, lung

Bone, nodes

„What is that decides which organs shall suffer in a case of disseminated cancer?” (S. Paget, The Lancet, 1889)

• „When a plant goes to seed, its seeds are carried in all directions, but they can only live and grow if they fall in congenial soil.”

• Cancer cell dissemination – an ineffective process

• New microenvironment may be favourable to cancer cells, e.g. in the bone marrow breast cancer cells are stimulated by IGF 1, prostate cancer cells - by TGF; in the liver, colorectal cancer cells have an increased ability to grow due to TGF presence.

Molecules determining cancer dissemination

• Constitutively expressed in the metastasis development site

• Promote cancer cell adhesion to endothelium and migration in and out the vessels

• Induce invasion into the new, favourable environment

• Cells colonising new sites must express the receptors relevant to the growth factors present in the secondary sites.

Cancer cells express patterns of chemokine receptors that match chemokines specifically expressed in organs

to which they commonly metastasise.

Muller, 2001

Immunosuppression

• Impairment of immune reponse, local and systemic

FasLImmunosupresja

Mutation rate: 2.2 x 10-9 per base pair per year X 3 billion (3x109) chemical base

pairs that make up human DNA X 5% of genome encoding X 1014 cells in the

average human = 3.3 x 1013 mutations per person per year.

Still, cancer arises in only 1 in 3 lifetimes.

The rarity of cancer highlights the efficacy of potent anti-tumorigenic

mechanisms presiding over somatic cells. Cancers prevail only when these

mechanisms have failed.

We perceive only the rare surviving clones that beat all the odds and appear as

clinical disease. We see only successes of cancer cells, not the failures.

The relative rarity of the cancer cell

Cancer progression and clinical appearance

Liotta, 2001

„Biology and Cancer Research have developed together.

Invariably, at each stage, the characteristics of the

cancer cell have been ascribed to some defect in

whatever branch of biology happens at the time to be

fashionable and exciting ” John Cairns