Oncopathophysiology Tornóci László Semmelweis University Institute of Pathophysiology.

Oncopathophysiology

Tornóci László

Semmelweis University

Institute of Pathophysiology

A few risk factors of malignant tumors

• smoking

• diet

• viruses

• hormones

• irradiation

• environmental pollution

Malignant tumors are monoclonal

Virtually all malignant tumors are of monoclonal origin.

All descendants of a single cell are called a clone in cellular biology. Members of a clone are genetically identical in theory.

First proof: CML G6PD, Fialkow

Consequences of clonality #1

0

20

1 2

tim e [ce ll cy c le s]:

n u m b er o f ce lls :

1

21

2

22

8

3 n

23 2 n

Exponential cell growth

Consequences of clonality #2Exponential cell growth

0

1 g

1 k g

tu m o rm ass

n u m b ero f c e lls

m a lig n an ttran sfo rm

a tio nd iag n is

o s

(lo g sca le )

tim e

p a tien t

d ie s

2 0

3 0

4 0

1 0

1 0

3

1 0

6

1 0

1 2

1 0

9

Heterogeneity

The mutation rate of malignant tumors is higher than that of the healthy tissues. The original clone will give rise to subclones because of this (heterogeneity).

Why do some cancers appear to ‘accelerate’?Why are the therapeutical results better:

• with cases that have been diagnosed early?• after the first use of a chemotherapeutical drug, than after

subsequent uses?

The malignant transformation

The malignant transformation is not a single step, but it is believed to be a result of 5-10 subsequent somatic mutations (accumulating in the same cell). This is the so called multi-step theory.

This is why:• tumors are seen more frequently with age• there are inherited malignant tumor

syndromes(e.g. Li-Fraumeni sy: p53 mutation)

Development of colon cc.

CGAP: Cancer Genome Anatomy Project

Genes affected by the malignant transformation

proto-oncogenes

tumor suppressor genesgenes correcting DNAgenes controlling apoptosis

Mechanisms of the genetical changes

• point mutation(eg. ras proto-oncogene)

• gene amplification(eg. ERBB2 in breast cancer, resistance to

drugs)

• chromosomal aberrations (eg. reciprocal translocation, Ph

chromosome)

• epigenetic mechanisms

The Philadelphia chromosome

The Philadelphia chromosome

ABL (9q34.1) Abelson leukemia proto-oncogeneBCR (22q11) breakpoint cluster region

Genes affected by the reciprocal translocation:

The result is a new, abnormal, fusion gene on chromosome 9, which is translated into a protein that has tyrosine kinase enzyme activity. This is specifically inhibited by the drug called Gleevec. Very good results have been achieved in CML and some other malignancies using this novel drug.

Epigenetic mechanisms

A gene control mechanism which is not coded in the DNA sequence. Such is eg. parental imprinting (gene expression depending on the parent’s sex).

The mechanism of imprinting is selective methylation of genes. (Methylated genes are not expressed.) Most malignant tumors seem to have less methylated genes, than healthy cells.

A few important tumor suppressor genes

• p53, p21, Rb

• HNPCC

• BRCA1, BRCA2

Function of p53 gene

D N Ad am ag e

a rre s t in G 1

D N A rep a ir o r

ap o p to s is

U V irrad ia tio n - irrad ia tio n

ch em ica ls

p 5 3 g en eex p re ss io n

p 5 3 p ro te ino lig o m eriza tio n

p 5 3 o lig o m ers b in d to sp ec ifics ite s o f D N A , ac tin g a s

tran sc rip tio n a l a c tiv a to rs

Function of p53

WAF1: wild type p53-activated fragment 1

Cip1: cdk-interacting protein 1

sdi1: senescent cell derived inhibitor 1

cdk: cyclin dependent kinasecyc: cyclin

a rre s t in G 1

p 5 3

p 5 3o lig o m er

p 2 1

p 2 1

cd k cy c

g en es

p ro te in s

WA F 1 /C ip 1 /sd i1

Function of the Rb gene

Cell cycle continues in the presence of phosphorylated (inactive) pRb; however, if pRb is not phosphorylated, then the cell cycle stops because of binding the transcription factors

C D K 4 /6

C y c lin Dp R b

p o l IU B F

E 2 F

rR N A

m R N Ap o l II

p h o sp h o ry la tio n sy n th es istran sc rip tio n , tran sla tio no f R N A p o ly m erase g en es

R N A p o ly m erasesfree (ac tiv e )

tran sc rip tio n fac to rse .g . U B F, E 2 F

p h o sp h o ry la ted p R b

HNPCC

HNPCC: Hereditary nonpolyposis colon cancer

• Incidence cca. 1:200• It is present in 15% of colon cancers• Risk of developing colon, ovarian, uterine and kidney

tumors• It is analogous with MutS/MutL gene of yeast

BRCA1

• Incidence cca. 1:200

• In a family with breast cancer cases a BRCA1 positive woman has an 85% lifetime chance to develop breast or ovarian cancer

• Prophylactic bilateral mastectomy is advised

Problems with genetic tests

• What to do if the test is positive?• A negative result cannot ensure that the

person tested will not get cancer.• The most important privacy issue of the

future: how our tissues will be handled? (Our genetic code is our own secret: the employer, the insurance company must not learn it!)

Therapeutical approaches

• surgery• chemotherapy• irradiation

• gene therapy• inhibition of angiogenesis• immunotherapy

Classic methods New methods

Examples of using gene therapy to treat malignant tumors

• reintroduce the normal copy of an inactivated tumor suppressor gene (would need 100% efficacy)

• introduce genes coding for antigenes, cytokines to enhance the immune response

• Introduce a gene causing toxicity (thymidine kinase gene + gancyclovir treatment)

• artificial viruses (cytopathogenic adenovirus, that can infect only cells deficient of p53)

Angiogenesis #1

• Tumors can grow to a maximum size of 1 mm without their own blood supply (in situ carcinoma)

• Tumors spend a significant amount of time in the „in situ” stage, before they become angiogenetic, this is when they start growing

• Metastasis is angiogenesis dependent (it is both needed for leaving the primary tumor and for the growth of the metastasis)

Angiogenesis #2

• VEGF (vascular endothelial growth factor)

• FGFs (fibroblast growth factors)

• angiopoietins

• thrombospondin-1 (induced by p53)

• angiostatin• endostatin

Endogenous promoters Endogenous inhibitors

Several tumors produce materials stimulating or inhibiting angiogenesis. The primary tumor can inhibit the growth of metastases or the growth of other tumors.

Inhibition of angiogenesis

Methods/drugs: • endogenous inhibitors• gene therapy• drugs (eg. thalidomid=Contergan)

Even leukemias were proved to be angiogenesis dependent! (Increased microvascularization is seen in the bone marrow.)

Vascular endothelial cells are said genetically stable, so resistance is not likely to develop against the inhibitors of angiogenesis.

Targeted inhibition of angiogenesis using nanoparticles

nanoparticles

integrins

target-recognizingmolecules

tumor endothelium

ag-inhibiting gene