Lecture 14: Mouse Models of Cancer Flashcards
What are different mouse tumour models?
Transplanted cancer models:
1. syngenic transplanted (mouse to mouse)
2. xenotransplanted (human to mouse)
Induced cancer models
1. virus induced
2. chemically induced
3. genetically induced (transgenic mouse)
What is the syngenic transplant model?
- originating mouse develops tumour (spontaneous or induced)
- Cells from tumour cultured in vitro producing cell line
- Tumour cells transplanted into same strain of mice
- Tumour evolved only once but can be propagated infinetly
What are the implantation sites of syngenic transplantation mouse models
- subcutaneous (under the skin)
- Orthotopic (impantation of tumour cells into same organ/tissue)
- Ectopic (different organ/tissue site than original site)
- intravenous (blood stream)
What is an example of syngenic transplantation
B16 Melanoma model
Original tumour: spontaneous melanoma on C57BL/6 mouse
Subcutaneous injection into same inbred strain
Produces primary tumour in skin and metastasis in lungs
What are the pros and cons of the syngenic model
+ quick
+ cheap
+ consistent genetics
+ intact immune system
- steep growth of tumour
- different repsonses in different strains
- site of metastasis is dependent on implant site
- orthotopic tumour retain stromal characteristic more than subcutaneous
What is the xenograft transplant model?
Taking cancer from one species and transplanting it into another
E.g., Human cancer, produce cell line, implant to mouse
What happens with immune compromised mice?
Prevention of tumour cells being rejected
Nude mice: no T-cells
NOD/SCID mice: no T or B cells
NOD/SCID/GAMMA mice: no T, B, or NK cells
What is PDX in xenograft transplant models?
PDX (Patient-Derived Xenographs)
Transplanting freshly resecuted tumour fragments into immune compromised mice
Can be grown, and re-implanted into additional animals to analyse:
1. Tumour growth
2. Evolution
3. Response to therapy
What are the pros and cons of xenograft transplantation?
+ Quick
+ Cheap
+ Reproducability of cultured cells
+ Patient material
+ expandability
- No intact immune system
- cross-species interactions
What are virus-induced mouse models?
Tumour induce by viral infection.
Very few models:
1. PyV - polyomavirus (mouse) causes tumours in
immunocompromised (or v young) mice
2. MLV - murine leukaemia virus. Causes T-cell lymphoma
erythroleukemia, in immunocompromised or young mice
3. MMTV - mouse mammary tumour virus. Causes breast cancer
What is an example of virus-induced mouse model?
MMTV
1930s: J. J. Bittner demonstrated that a milk-bourne agent caused mammary tumours in female mice and suggested this agent might be a virus.
Route: through milk or inherited
Integration into genome of breast epithelial cells. Insertional mutagenesis, deregulating proto-oncogenes:
1. Wnt1
2. GFG3
What are the pros and cons of virus-induced models
+ Historical: oncogene discovery
- viruses can infect other cell types
- difficult to control the amount of virus, thus tumour induction
- often immune compromised mice required
What are chemically induced mouse models
“use chemical to induce cancer”
How are chemically-induced models used
- experimental cancer research
- Carcinogen bioassay (testing chemicals for carcinogenic activity)
Why might chemicals be combined with genetically engineered mice for cancer models
To study the interaction between genotype and environment in cancer development
How are chemically-induced mouse models used?
Experimental research
1. chemicals don’t cause cancer at site of exposure (but at distal
sites)
2. Chemicals bound to DNA (implicating DNA as relevant target)
3. Some chemicals require metabolic activity to become carcinogens
4. DNA mutation - mechanism of action
What is an example of chemically induced mouse models?
2 stage skin carcinogenesis model:
1. berenblum and Shubik (1947)
2. carcinogenesis occurs through at least two distinct steps
Initiation step (DMBA)
DNA damage
irreversibile
Promotion step (TPA)
growth stimulus
reversible process
What are the pros and cons of chemically induced mouse models
+ can study all stages of cancer progression (initiation, promotion, progression)
+ less invasive
+ large number of tumours generated
+ Robust model
- unpredictable (timing, number and location of lesions)
- Long latency periods
- Difficult to model subtle environmental conditions (diet)
What are genetically induced models?
Transgenic mouse: Genetically engineered mouse models (GEMMs)
Oncogenes over-expressed (transgene) e.g., c-myc, ras
Tumour suppressor genes silenced (KO) e.g., Rb, p53
Transgenic mouse developed only once
Mouse line is then permanent
Same type of tumour develops again
What i an example of genetically induced models?
MMTV-neu breast cancer model
MMTV (mouse mammary tumour virus promoter) drives expression of an oncogene in mammary epithelium
Neu (ErbB2) is an oncogene
Large amounts of neu oncogene (ErbB2) produced specifically in mammary gland epithelium
FIrst genetically indcuced cancer model (1984)
What i an example of genetically induced models?
RIP-TAg pancreatic cancer model
Rat insulin promoter (RIP) drives expression of an ocgene in pancreatic cells
SV40 T-antigen gene (Tag) is an oncogene
Large amounts of the SV40 oncogene produced specifically in pancreas
What are pros and cons of genetically induced models?
+intact immune system
+tumours in situ
+precise modification of genes (TSGs and oncogenes)
+Tissue specific analysis of gene functin
+Robust system (mouse develop tumours in same place and time)
- loss of tumour variability
- Rapid tumour growth in some models
-non standard sites for metastasis - time consuming
-expensive
How are transgenic mouse generated
- Micro-injection of DNA constructs into male pronucleus of fertilised
mouse oocytes
a. Promoter: cell/tissue specific, Time specific (under TET or DOX
control)
b. DNA construct: Gene of interest, endonuclease (CRISPR)
targeted mutations
(Potential problems, intergration into critical gene, silence region, or multiple copies intergrated)
- Gene targeted transgene approach
a. generally to study loss of function or gene KO
b. Genetic manipulation of embryonic stem cells
c. E.g., introduction mutated gene of interest
d. Use marker genes (e.g., neo)
e. Homologous recombination results in introduction of gene
What if a gene knock out is lethal
Can use:
1. inducible promoters
2. Tissue specific promoters
3. Use cre-lox system
