Cancer Model Organisms Flashcards
Need animal models b/c
- can’t go from cell culture to human might kill human imediatley
- animal models allow us to do preclinical testing of diagnostic, preventative, and treatment approaches
- allow us to understand gene fx in context of whole organism
- understand dx etiology and pathogenesis by accurate recapitulation in model animal
Classification of animal models
- spontaneous models
- induced dx models
- Negative dx models
- Orphan dx models
spontaneous dx modeles
conditions occur naturally (not too many of these)
induced dx models
conditions are experimentally induced (can induce these with good specificity)
negative dx models
conditions never occur in particular species as compared to other species (some species just won’t get certain caners)
orphan dx models
conditions never occur in humans (like neoplasia on a mouse tail)
Animal models of cancer spontaneous causes
- chemical
- viral
- irradiation-induced
- hormonal
- transpolantaiton-based
- genetic
induced models
have more of these available to us know b/c CRISPR/ cas9
Advantages of modeling caner I mouse
- mouse biology well characterized
- genetic homology btwn mice and other mammals like humans is high
- commonly used for pharmacological, toxicological, carcinogenic testing
- genetic tools well estabilished (genome sequenced, many strains inbred/ knockout/ transgenic mice available)
- short lived species
- fast expansion mouse colony possible
- relavitly inexpesinve
Main approaches for cancer modeling
- Patient derived xenograph
2. Genetically engineered mouse
genetically engineered mouse
put in genetically engineered embryonic stem cells in make tumor bearing genetically engineered mouse can do GEM derived allograph and can transplant tumors to diff types of mice (immunocompetent mice so can test things involving immune response like drug treatment and metastasis)
Patient derived xenograph
- Xenograph models require immunocompromised host**
- isolate cancer cells and inject into immunocompromised mouse or can isolate genes with mutations to put into immuniocompromised mouse
- may inject along with humanized stroma to make microenviorment in mouse more like human microenvionrment (“patient in mouse transplantation model”)
- absence of immune response makes many drugs that work in xenogrpahs fail in clinical trails
- this is good for studying early stages of carcinogenesis and this is well suitable for studies of cancer propagating cells
cancer stem cell targeting
cancer stem cells have ability to propagate and these typically are hardest to kill and if they stay will lead to cancer recurrence; trying to make specific drugs against cancer propagating cells
Guides for validation of animal models of cancer
- Common molecular mechanisms
- Pathology mimics patient cancer
- Neoplastic progression includes metastasis recapitulates patient cancer
- Therapeutic and host immune response resemble pateint
- Involvement of specific organ or cell linage resembles patient
- can be difficult to get all of these in one model system but it is good guidline
Common molecular mechanisms
ideally model of cancer should have similar molecular mechanisms to those that have been studied genomically
Target pathays in molecular circuitry of cancer
p53 and Rb
- both TSGs
- defects in these pathways in over 80% human cancers
- both play critical roles in cell cycle differentiation and apoptosis
- p53 and Rb gene replacement is clinically beneficial
- trying to develop diff drugs to work on the but they were tested on xenograph animal systems so not getting great results
Mouse heterozygous for Rb
they end up with pituitary tumor instead of eye tumor
- great model for studying carcinogenesis bc can make many sections of pitiuatory glands
- loss of reaming WT copy Rb is initiating/ early event in carcinogenesis in these mice
- takes time for enough mutations to form to get tumors (progression tumors from early to late stages requires significant time)
synergistic mutations
need combination of mutations ie synergiestic mutations to -> tumor and in some cases metastasis
(in Rb heterozygous mice synergistic mutations = p27, p21, p53, and Arf)
p53 and Rb heterozygous mice
shorter lived than if just knockout one of the two b/c accelerates cancer formation
adenovirus-mediated Rb gene therapy
arrests tumor growth (make injection of adenovirus expressing Rb gene and inject into tumor and see tumor growth arrest and start to resorb)
importance of Rb heterozygous mouse model
- shows loss of reamingn WT Rb copy is initating/ early event in carcinogenesis in these mice
- indicates other genes cooperate in tumor supression
- suggests Rb gene replacement = clinically beneficial
- shows not all mouse tumors similar to humans (pititiary, thyroid, parathyroid, and adrenal gland tumors instead of retinoblastoma)
Brca1 gene heterozygous mice
die while in humans get breast and ovarian cancer
Why do mice w/ hereditary targeted gene mutations have different dxs than humans
- negative model (diff genetic mechanisms in mice and humans, not v often)
- mice die early from something else and human tumor doesn’t have time to develop; need more selective cell type-specific models
- conventional (transgenic and targeted mutant) mice = hereditary cause for caner while in humans most cancer inducing mutations in somatic cells in adult life; need mouse models with better controlled time of mutagenesis to get sporadic cancers instead of familial in mice (human cancer almost entirely sporadic)
systems for conditional regulation of gene expression
- Cre-LoxP system
- Tamoxifen-mediated regulation
- Tet-mediated gene activation or inactivation
Cre-LoxP system
LoxP is locus of crossing over in bacteriophage; Are protein cleaves these sites and can cleave them in mammalian cells
Using Cre-LoxP system
scientists made LoxP sites via homologs recembination in vertebrates which lets you use recombinase to cut part of gene; using this system can regulate gene fx in temporal, spatial, and cell type-specific manner
conditional alleles p53 and Rb
- can use Cre-LoxP system to flank exons and climate these genes
Modeling ovarian cancer
look for genetic makeup of these cancers; in ovarian cancer have p53 mutations in 96% and Rb alterations inf 67%
- remove mouse ovary and bursa and inject adenovirus with recombinase in bulsa mouse have specific inactive genes with recombine to mimic ovarian cancer; successfully get model that reproduces human epithelial ovarian cancer via inactivation of p53 and Rb
modeling small cell lung carcinoma in mice
use nasal delivery of Cre-LoxP mediated genes to inactivate p53 and Rb and mice will develop lung tumors v similar to humans
Modeling mammary carcinoma by cell type specific gene activation
spontaneous mouse mammary carcinomas have little stroll component but if initiated by p53 inactivation via Cre recombinase get mammary carcinomas w/ pronounced desmoplastic rxns like you would see in humans (incidiating more accurate mouse model for humans to test on)
Modeling tumor progression including metastasis in mice
- spontaneous mouse tumors rarely progress to malignancy and metastasis but if we inactivate genes w/ Cre can make more accurate models (mammary gland tumors w./ inactivated p53 in mice metastasize to lung and liver in both humans and mice)
Companion animal use in cancer research
companion animals have some types of cancer that is simular to humans
Canine: non-Hodgkin lymphoma, Osteosarcoma, over expression neu/erbB2 gene and mutations p53 gene in mammary carcinomas, spontaneous canine prostate carcinoma
Feline- NonHodlkin lymphoma related to FLV might be similar to human with HIV
Dog breeds lympjhomas
some breeds more prone to B cell lymphomas some T cell this offers great way to study gene patterns of different lymphomas
Advantages to studying companion animal cancers
- Share common environment with people
- Relative size of tumor to mass of subject more similar to that of humans
- Spontaneous tumors more similar to humans than those of lab animals
- Tumor specific immune responses more similar to humans
- Larger size companion animals means easier sample collection (urine, serum, cerebrospinal fluid)
- Sx and imagine approaches easier to adapt for humans in future
- Clinical trials on animals more acceptable to general public than those on ppl
Challenges in modeling cancer in companion animals
- Genetic tools still less developed
- Large scale experiments more expensive than those in rats/mice
- Collection epidemiological data much less well established as compared to humans
- Some cancers dissimilar to humans
General challenges in animal modeling
- Model improvement
- Study settings
- Physiological difference between species
Model improvement
- more precise spatial and temporal control genetic alterations in tissues
- Patient relevance of stroma, immune system, and therapeutic targets in caner models
- Recapitution of tumor heterogeneity found in patient caners
study setting
- dx progression and clinically relevant endpoints in preclinical study
- integration of pathologic, genomic, bioinformatic, molecular, and immunological analysis
- Evaluating effects of lifestyle on therapeuticc outcomes
physiological differences between species
ok to look at one health but need to know differenced between species
