301 Cancer Flashcards
Epigenetics: what are stable or dynamic changes?
Stable: pass on to next generations
Dynamic: response to environmental stimuli
What are epigenetics?
Pattern of inheritance in which gene/chromosome is modified temporarily that changes gene expression & function/regulation of DNA, protein or RNA molecules without changing primary sequences
What happens in chromosome inactivation?
Allow only one X chromosome to remain active and inactivate the rest of them (forming Barr body from inactive ones)
This is why phenotypes associated with X are less severe than Y
What are Barr bodies?
Condensed inactive X chromosomes found in nuclei of female mammals: 1 of 2 C chromosomes randomly inactivated in dosage compensation so 1 Barr body visible in cell nucleus
What is dosage compensation?
Process by which organisms equalise expression of genes between members of different biological sexes
Number of Barr bodies:
Normal female
Normal male
Turner syndrome (female)
Triple X syndrome (female)
Klinefelter syndrome (male)
XX 1
XY 0
X0 0
XXX 2
XXY 1
What is genomic imprinting?
Expression of gene depends on parent sex
Marking of alleles can be changed between generations
What is DNA methylation?
Chemical marking process important in genomic imprinting
Methyl (CH3) group added to cytosine in DNA regions needed for gene regulation & expression
Where does DNA methylation take place and what does it result in?
Sperm (chromosome X0) or oocyte (not both)
Gene expression inhibition (silences genes)
What are classical genetic controlled by?
Promoters, enhancers or proteins binding sites that are present or absent in DNA sequences
What is the difference between genetic & epigenetic regulation?
E: do not involve change to DNA sequence or mutations to sequence
Implies modification of DNA & proteins, without changing DNA sequence
Regulation at level above genetic mechanism regulation
What is model organism in epigenetics?
Different advantage & all important for learning about processes & mechanisms involved in epigenetic regulation
Saccharomyces cerevisiae (budding yeast) has helped what?
Elucidate chromosome structure & telomere silencing (regulates gene transcription near telomeres - prevents premature aging & aging-related diseases)
Protozoan Tetrahymena thermophilia is used for what?
Study of RNAipathway that functions gene silencing
What is a classic genetic model used for epigenetic research?
Drosophila melanogaster
What is a plant model with considerable epigenetic mechanisms like mammals
Arabidopsis thaliana
When are mice used in epigenetic research?
Embryology
What are biological applications of epigenetics?
Control expression of embryonic development genes
Erasure & re-establishment of DNA methylation
Genetic imprinting
X-chromosome inactivation
Stem cell development
Somatic cell differentiation
Production of differentiated cells from adult stem cells & specific cell types
What is found to correlate with cancer?
DNA methylation biomarkers
Cancer tumour suppressor genes show hypermethylation but also hypomethylation are expressed in other cancers
What is not involved in epigenetic alterations to genome?
Change in nucleotide sequence
Managing and controlling alterations plays role in cancer prevention and treatment
Examples of epigenetic mechanisms applied in different cancer types
Silencing tumour suppressor
Activation of oncogenes
Histone modifications
Epigenetic therapy: tumour suppressor genes
Decrease of tumour growth
Induction of apoptosis
Suppression of invasion & metastasis
Epigenetic therapy:
Stem cell genes
miRNAs regulating stem cell genes in CICs
Decrease of self-renewal or survival of CICs
Differentiation of CICs
Epigenetic therapy:
Tumour suppressor genes
Drug response genes
Resensitisation to chemotherapy
FDA approved epigenetic chemotherapy
Azacitidine (Vidaza)
Decitabine (Dacogen)
Vorinostat (Zolinza)
Romidepsin (Istodax)
Epigenetic therapy: Azacitidine (Vidaza)
Make genes fight cancerous cells when given at low doses, shows effectiveness against certain lung cancers
Epigenetic therapy: Azacitidine (Vidaza)
Make genes fight cancerous cells when given at low doses, shows effectiveness against certain lung cancers
Epigenetic therapy: decitabine (Dacogen)
Treats myelodysplasia (affects blood cell production in bone marrow) and leukaemia
Epigenetic therapy: Vorinostat (Zolinza)
Treats immune system cancer (cutaneous T-cell lymphoma)
Epigenetic therapy: romidepsin (Istodax)
Epigenetic injection therapy (like Vorinostat and romidepsin)
Treats peripheral T-cell lymphoma in patients who have received 1+ prior treatment
Epigenetic therapy: romidepsin (Istodax)
Epigenetic injection therapy (like Vorinostat and romidepsin)
Treats peripheral T-cell lymphoma in patients who have received 1+ prior treatment
What is carcinogenesis?
Molecular process where cancer develops
External, lifestyle and environmental factors in carcinogenesis
Ex: chemicals, viruses, diet & radiation
Env: chemicals (air pollutants, asbestos)
Life: diet, smoke, alcohol, direct sun exposure
What is cancer development?
Multi-stage process involving damage to genetic material of cells (DNA)
Damage of genes that regulate normal cell growth and division
What are carcinogens?
Agents causing cancer
Classified as genotoxic or nongenotoxic (epigenetic)
What are genotoxins?
Cause irreversible genetic damage (mutations) by binding to DNA
Examples of genotoxins
Chemical agents like N-methyl-N-nitrosourea or non-chemical agents UV light
Why can viruses act as carcinogens?
Interact with DNA (HBV and liver and HPV and cervix)
Stages of carcinogenesis
- Initiation
- Promotion
- Transformation
- Progression
Stages of carcinogenesis: initiation
Involve random change in genetic makeup of cell
>1 agent acts together as carcinogens
Carcinogen interacts with DNA causing damage at gene location that regulates cell growth
If cell repair systems do not occur, cell may turn cancerous
What is the 1st stage in neoplastic development?
Initiation stage of carcinogenesis
Stages of carcinogenesis: progression
Malignant conversion stage
Irreversible
Changes in structure of genome, increased growth rate
Invasiveness
Metastatic capability
Biochemical changes & neoplastic cells born
Expansion of tumour cells
Genetic material of tumour is more fragile and go through additional mechanisms
Stages of carcinogenesis: promotion
Initial cell damage rarely results in cancer due to cell mechanisms to repair damaged DNA
Reversible and revocable if stimulus stops
Promoted not always carcinogen but enhances carcinogenicity
Continually controlled through environmental alterations
Cigarette smoke, bile acids & chemical pollutants involved in promotion
When does cancer occur?
When tumour suppressor genes inactivated and oncogenes are activated
What are tumour suppressor genes associated with?
Healthy cell activities like cell growth, cell differentiation & apoptosis
What do tumour suppressor genes produce?
Proteins that inhibit cell reproduction during inappropriate growth times (control cell division during repair times)
What are proto-oncogenes?
Altered version of normal genes, regulate cell growth and survival
What activate proto-oncogenes?
Mutations
Mechanism of oncogene action
Cell surface receptors
Intercellular signal transduction pathways
DNA-binding nuclear protein (transcription factor)
Cell cycle proteins (cyclins & cyclin-dependent protein kinases)
Inhibitors of apoptosis
What do oncogenes trigger?
Signal transduction (cascade of biochemical signals)
These signals control genes that regulate cell growth and division
What is important for cancer to occur?
Activation of oncogenes and inactivation of tumour suppressor genes
What tumour suppressor genes are associated with cell growth and differentiation?
P53 and DCC
What are the most common mutations seen in humans?
Mutations that inactivate tumour suppressor gene p53
Colon carcinogenesis
- Mutations of APC: sometimes inherited, leads to dysplasia or polyp formations on mucous membrane surface
- DCC: subsequent mutations lead to late adenoma and then carcinoma
- Changes in p53 genes: progressive changes seen in colonic epithelium as polyps remain dormant for years
- DNA microsatellite instability (MSI): hyper mutable phenotype caused by loss of DNA repair activity
p53 mutations lead to what?
Over expression of oncogenes and deletion of anti-oncogenes and DNA repair gene
What does APC stand for?
Adenomatous polyposis coli
What does DCC mean?
Deletion in colon cancer gene
What are the tumour markers for:
Lung cancer
Liver cancer
Prostate cancer
Testicular cancer
Breast cancer
Stomach cancer
Colon cancer
Pancreatic cancer
Ovarian cancer
CA125, CEA
AFP
PSA
AFP, HCG
CA125, CEA, HER2
CEA
CEA
CA125, CEA
CA125, CEA
What are tumour markers and can be detected where?
Substances produced by cells (normal or cancer) of body in response to cancer or benign conditions
Blood, urine, stool, tumour tissue and other body fluid samples
Benefits of tumour markers in cancer care
Used in highly sensitive and specific screening tests for early detection
Elevated levels suggest but do not diagnose
Combine with other tests for diagnosis
Used to manage some types of cancer
Helps doctors know stage & suitable therapy
Determines whether tumour responds to treatment
Limitations of tumour markers in cancer care
Tumour markers may increase in non-cancerous conditions
Not all patients have elevated tumour markers
Tumour markers not identified for all types of cancer
Alpha-fetoprotein (AFP):
Cancer types
Tissue analysed
How used?
Liver, germ cell tumours
Blood
Diagnose liver cancer and follow treatment response, assess stage, prognosis and response to treatment to germ cell tumours
Beta-2-microglobulin (B2M):
Cancer types
Tissue analysed
How used?
Multiple myeloma, chronic lymphocytic leukaemia and some lymphomas
Urine or blood
Assess stage, prognosis and treatment response
Mitomycin and fluorouracil are categorised under which groups and what are the major S/Es of these cytotoxic agents?
M: antineoplastic antibiotic, works by cross-linking DNA, inhibiting DNA synthesis
Bone marrow suppression, renal toxicity, interstitial pneumonitis and risk of extravasation leading to severe tissue damage
5FU: antimetabolite, inhibits thymidylate synthase, disrupting DNA synthesis
Myelosuppression, GI toxicity (mucositis and diarrhoea), hand-foot syndrome and potential cardiotoxicity
What is extravasation and which cytotoxic agents can cause extravasation?
Accidental leakage of vesicant or irritant drug into surrounding tissue during IV admin., vesicants are agents that cause tissue damage & necrosis
Mitomycin and other vesicants (anthracyclines - doxorubicin) high risk of causing tissue damage, 5FU less vesicant but can cause irritation
What are the symptoms of extravasation?
Pain, sudden pain or stinging, swelling or oedema, redness, blisters or sores at injection site
Slowed flow, infusion pump may alarm, absence of blood return
Treatment for patients with rectal cancer with extravasation from adjuvant IV push chemotherapy
Immediately stop infusion, leave needle in place and aspirate
Specific to mitomycin - use cold compress reducing local inflammation, administer topical dimethyl sulfoxide (DMSO)
Pain relief with analgesics, monitor for necrosis or tissue damage signs
What is irinotecan and what does it do?
Semisynthetic derivatives plant alkaloid, inhibit topoisomerase I
Creates single-strand breaks in DNA during replication, preventing DNA re-ligating so double-strand breaks and cell death