Carcinogenesis Flashcards
What is cancer?
Cancer is the general name for a group of diseases characterized by uncontrolled cellular growth
- Neoplasia: the growth of new tissue
- Neoplasm/tumor: an abnormal growth of tissue forming a mass
- Transformation: process of converting a normal cell into a cell having attributes of a cancer cell
Normal vs transformed cells
Transformed cells have attributes of cancer cells
NORMAL CELLS
- cell proliferation: controlled
- number of cell divisions: limited, 50 cell cycles (Hayflick limit), mortal
- contact inhibition: yes, monolayer culture
- dependent on growth factors: yes
- tumor formation: no
TRANSFORMED CELL
- cell proliferation: uncontrolled
- number of cell divisions: unlimited (immortal)
- contact inhibition: no, multilayer culture
- dependent on growth factors: no
- tumor formation: yes, tumorigenic in laboratory animals
Immprtalization: process whereby a cell normally having limited replicative potential acquires the ability to multiply indefinitely
Major classifications of malignant tumors
- Epithelial tissue: carcinoma (squamous epithelial carcinoma, adenocarcinoma)
- non-epithelial tissue: Sarcoma (connective and supporting tissue -> e.g. fibrosarcoma, liposarcoma), Leukemia, lymphoma (hematopoietic), neuroectodermal tumors (e.g. glioma, neuroblastoma)
- other tumors (do not fit to the major classification): melanoma, small-cell lung carcinoma
Carcinomas are responsible for more than 80 % of the cancer-related deaths in the Western countries.
Tumor dignity: Benign or malignant
Benign tumors
* Local growth without invading adjacent tissues
* Often harmless to their hosts
* In some cases, complications through
(1) “Mass effect”
- obstruct passage ways
- press on nerves
- disrupt the function of vital organs etc.
(2) Hormone overproduction
- e.g. thyroid adenoma
physical & mental symptoms (depression, apathy, weight loss,
weakness, heart arrhythmia, etc.)
(3) Malignant transformation
(colorectal adenoma (polyp) -> adenocarcinoma
Malignant tumors
* Infiltration of nearby tissues
* Production of metastases
* Metastases are responsible for more than 90% of deaths
- hepatic metastasis -> liver failure
- pulmonary metastasis-> lung failure etc.
Other complications, e.g.:
* Obstruction of the colon, bile duct, etc.
*Cancer cachexia (loss of weight, atrophy of muscle and fatty tissue, etc.)
Staging of cancer
Obligatory parameters
* TNM staging system (Tumor, Nodes, Metastases)
- Description of the size of the primary tumor and the extension of spreading (tissue infiltration)
- Involvement of lymph nodes
- Spreading to distant organs (metastasis)
- Grading
- Determination of cell anaplasia (loss of differentiation) in tumor tissue
in comparison to the normal tissue - Degree of tumor aggressiveness
- Variability in size, shape and staining of cells and their nuclei
- Nucleus (↑) to cytoplasm (↓) ratio - Mitotic activity (↑)
- Atypical mitoses (↑)
Other parameters
* Measurement of serum tumor markers (LDH, alpha-fetoprotein, PSA)
* Completeness of the operation (resection-boundaries free of cancer cells or not)
Aims: help to plan treatment and give an indication of prognosis
Risk factors
Factors that increase the probability to develop cancer
Risk factors (increased probability for a disease)
-> parental inheritance (predisposition) (5-10%)
-> environmental factors (90-95%) <-> genetic constitution (genotype)
The percentage contribution of genetic factors and environmental factors toward cancer risk.
Environmental risk factors
(1) Lifestyle
- nutrition (20-40%), tobacco use (25-30%), alcohol (3%), obesity, physical activity, etc.
(2) Naturally occurring exposures - ultraviolet light, radon gas
- infectious agents, predominantly viruses (5%) (e.g. HCV, EBV, HPV)
(3) Medical treatment
- chemotherapy, radiation, and immune system-suppressing
drugs used after organ transplants, etc.
(4) Air pollution (2%)
- car exhaust gases, industrial emission
(5) Workplace exposures (4-8%*)
Carcinoma in situ (CIS)
- locally limited primary tumor
- intact basement membrane
- no invasion/infiltration into adjacent tissue
Cervical cancer as example for tumor progression
Hyperplasia (CIN 1)
* Thickened epithelium
* Basal cells with increased mitosis rate (purple cells)
* Shift of the nucleus (↑) - cytoplasm (↓) ratio
Dysplasia (CIN 2)
* Mitoses now also in the intermediate layer
* Morphological changes visible
Carcinoma in situ (CIN 3)
* All cell layers contain immature, polymorphic, proliferating cells
Cervical carcinoma
* Infiltration/Invasion (Basal membrane is broken through)
* Metastasis
Clonal expansion and selection
Normal cells:
1st mutation in one cell
➢Proliferative and/or survival advandage
Pre-cancerous:
Progeny of the mutant cell dominate over cells lacking this mutation
➢1st clonal expansion
2nd mutation results in a double mutated cell ➢Greater proliferative
and/or survival advantage
Carcinoma:
Progeny of the double mutated cell dominate over single mutated cells
➢2nd clonal expansion
… and so forth
Clonal expansion of tumors
monoclonal tumors:
* Only one cell becomes cancerous
* All of the cells in the tumor are descendants of that cell
polygonal tumors:
* Individual cells become cancerous
* The tumor represents the descendants of these original cells
X-inactivation pattern
early embryo -> X-inactivation -> adult tissue
Marker to measure the clonality of tumor cell populations:
* Inactivated X chromosome in human female cells
X-inactivation
* Early embryogenesis (during formation of the blastocyst)
* Random X-inactivation in each cell (m, maternal; p, paternal)
* Causing
- transcriptional silencing of almost all of the genes (~900)
- condensation of this chromosome (Barr body)
* Descendants of a cell: inactivation of the same X chromosome
* Formation of cell patches (clones) in the adult female body
Mp: inactive paternal X
mP: inactive maternal X
The Barr body is visible in the interphase nuclei, where it remains condensed & associated with the nuclear membrane
X-linked G6PD
- X-linked marker: glucose-6-phosphate dehydrogenase (G6PD)
- some human females are heterozygous for G6PD (mosaic)
- the two allelic forms of G6PD show different heat sensitivity
Enzyme-histochemistry of heated tissue from a heterozygous female (section of intestine)
Dark spots: heat-resistant isoform, active enzyme
Light grey spot: heat-sensitive isoform, inactive enzyme
-> Normal tissue contains both type A and B of G6PD
-> tumours contain either type A and B of the G6PD, never both
- The two allelic isoforms of G6PD differ in their gel electrophoretic mobility
-> the tumor cells originate from a single cell (monoclonal)
Monoclonality in multiple myelomas
Healthy person
* Immunoglobulins (Ig) migrate as heterogeneous collection (smear), they are polyclonal
Multiple myeloma patient
(malignant plasma cells secreting Igs)
* The heterogeneous population of Ig molecules is replaced by a single antibody species (M-spike)
* Myeloma cells secret the same form of Igs, because they are monoclonal (monoclonal gammopathy)
-> Most – if not all – human cancers appear to be monoclonal
Intra-tumor heterogeneity
During tumor progression, cells in the tumor mass become heterogeneous
monoclonal tumor cell -> tumor progression -> heterogenous cell population
Intra-tumor heterogeneity:
1. genetic level (different mutations, epigenetic changes, chromosomal instability)
2. morphological level (e.g. cell size, nucleus size, marker proteins)
3. functional level (proliferation rate, tumorigenic potential)
Intra-tumor heterogeneity in high-grade non-small-cell lung cancer.
- Numbers of chromosomes fluctuate strongly from cell to cell (chromosomes 11 and 17)
- presence of polyploid nuclei in some cells
- different cell size
Hierarchical organization of regenerative tissues
Tissue stem cell
* Self-renewing
* Long-lived
* High potency*
* Low division rate
* Asymmetric division
* Very rare
Progenitors
*“transient amplifying cells”
* No self-renewal
* High division rate
* Limited number of division
* Limited potency
* Symmetric division
Specialized cells
* No division
* Terminal differentiated
* Limited lifespan
Potency describes a stem cell’s ability to differentiate into other cell types. The more cell types a cell can differentiate into, the greater its potency.
Multipotent: Able to form multiple mature cell types that constitute an entire tissue or tissues, e.g. haematopoietic stem cells.
Oligopolen: Able to form two or more mature cell types within a tissue, e.g. lymphoid stem cells.
Unipotent: Forms a single mature cell type, e.g. spermatogonia can only form sperm cell.
Stem cell microenvironment
Stem cell niche
is a specialized microenvironment that protects stem cells and regulates their behavior
Supporting stem cell viability
* minimizing the accumulation of genetic damage (shielded from toxic agents)
Regulating self-renewal and differentiation
* communication between stem cells and niche cells through direct or indirect interactions
Examples:
C. elegans germline stem cell niche
- One cell, the mesenchymal distal tip cell, provides a niche for germline stem cells
Mammalian (mouse model)
- Intestinal Paneth cells & myofibroblasts provide essential stem cell niche signals
Influence of the stem cell niche
The stem cell niche can act on a stem cell by various machanisms
- Direct contact: direct contact between the stem cell and the niche cells
- soluble factors: releasing of soluble factors by the niche
- intermediare cell: intermediate cells “communicate” between the niche and the stem cell
Identification of tumor-initiating cells by FACS
Identification of potential surface protein markers/antigens
1) Markers which were found in somatic stem cells
2) Markers which were found to be related to tumorigenesis, progression, metastasis and recurrence in malignant tumors
Isolation of cancer cells from fresh human biopsy samples -> Optimize dissociation to preserve cell viability and marker integrity -> staining with fluorophore- conjugated antibodies against surface protein markers -> cell sorting by FACS (large cell pool and small cell pool) -> in vivo Xenotransplantation (immunocompromised mice)
Assessment of tumorigenicity: in vitro 3D culture assay -> tumors arose from the injected minority cells are also composed of the minority and majority cell population!
Cancer stem cell characteristics
Fraction with a small number of cells
- behave like stem cells
- self-renewal
- unlimited proliferative potential
- production of a large number of progeny -> which are in different state of differentiation (different surface markers) and with
limited proliferative potential
Therapeutic challenge of cancer stem cells
Target Cancer Stem Cells (CSCs) to Prevent Subsequent Relapse
Radio- and chemotherapy resistance due to „Stemness“ induction:
* Drug export: elevated expression and high activity of ABC transporters
* ROS decrease: High ALDH activity
* High survival: Anti-apoptotic molecules, high telomerase activity, DNA damage
* Quiescence
The tumor microenvironment
- Cancer is a disease of extraordinary complexity at all levels: genetic, histological, pathological, prognostic, therapeutic…
- Reductionist view: Cancer is a disease of cells and the phenotype of cancer cells can be understood by examining genes and proteins within them.
- New model: Neoplastic cells are in continuous communication with their non- neoplastic neighbor cells within the tumor mass.
Six hallmarks of (malignant) cancer -> Hanahan and Weinberg (2000)
- Self-suffiency in growth signals
- Insensitivity to anti-growth signals
- evading apoptosis
- limitless replicative potential
- sustained angiogenesis
- tissue invasion and metastasis
- The hallmarks of cancer are thought to be necessarily acquired during the multistep pathogenesis pathways leading to most forms of human cancer
- Certain forms of cancer may be less dependent on one hallmark or another
- The order of hallmarks can be variable across the spectrum of cancer types
- A capability may only be acquired through the collaboration of two or more distinct genetic changes
- A particular genetic lesion may confer several capabilities simultaneously (e.g. p53)
Hallmarks of Cancer: The next generation
Emerging hallmarks:
- deregulating cellular energetics
- avoiding immune destruction
Two enabling characteristics crucial to the acquisition of the six hallmark capabilities:
- genome instability and mutation
- tumor-promoting inflammation
