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New to mouse work

In Vivo experiments have become increasingly important in publication of small molecule or tumor driver studies. These experiments are technical, and can be costly to initiate. At the PRR, we strive to make this barrier easier to cross. We maintain breeding colonies for several strains of mice, have the surgical expertise to transplant tumor cells or chunks, and can identify and process tissue upon necropsy.

Tumor type and growth site
When initiating an in vivo tumor experiment, the first important factor to consider are the tumor cells and growth location best suited for your needs.

There are several models for tumor growth available, including PDX, cell lines, and transgenic mice, each with advantages and disadvantages.

Cell Type Definition Advantages Disadvantages
PDX Patient derived xenografts
are transplanted directly
from human patients into
mice. Thought to be the
model which provides the
closest genetic representation
to human cancer
Genetically similar to
human patients, growth
time of 2-3 months,
several successful examples
of preclinical experiments
working in clinical trials
Must be grown in a
mouse with a compromised
immune system, thus
immune and tumor cell
interactions are lost, limited
material and tumor types
Cell Lines Derived from either human or
mouse tumors, these are grown
in culture dishes and are a
versatile tool for knockdown
and in vitro assays
Easy to maintain and
manipulate, tumor growth
in 1-2 months, many models
and tumor types available
Many cell lines have altered
genetic mutations from years
out of the host and being grown
on plastic
Genetically
engineered
models
One or several genes are mutated
in the DNA of mice, creating a
new strain that develops cancer
spontaneously; this system works
best for studying genes involved
in cancer development and
progression
Known genetic alterations,
no surgery required for tumor
growth, intact immune system,
several tumor models established
Difficult to produce, do not fully
represent the genetic complexity
of human tumors, do not reliably
predict success of treatments in
human patients
If you have been working with a cell line in the lab, it may be best to transplant that cell line subcutaneously. A subcutaneous injection is done just under the skin, usually in the shoulder or hip area of the mouse. The benefits of a subcutaneous injection are ease of transplant, limited mouse recovery time, ready blood supply, and accessibility to measure tumor growth with calipers. With these benefits, a subcutaneous injection is commonly used for tumor studies.

Alternatively, you may want the tumor to grow within its normal microenvironment, within the organ of origin. This is called an orthotopic growth model. Common sites are the mammary gland, tibia, and colon. These surgeries are more complex, and usually require bioluminescent imaging to monitor the growth of the tumor, however, these models are thought to better simulate the tumor microenvironment and progression occurring in humans.

Investigational drug studies
For an investigational drug study, the proper dose and route are important considerations. Optimization must occur to find a suitable solvent, and often, a maximum tolerable dose study will be performed. This study uses increasing concentrations of the compound to find a dose that is lethal to 10% of the mice. When that concentration is found, one tenth of that concentration is used for daily dosing.

In addition, there are several routes available for dosing. These most commonly include intra peritoneal (within the organ cavity), oral gavage (via the stomach, and intravenous (into the bloodstream). Depending on the stage of molecule discovery, intra peritoneal or intravenous routes may be more preferable, as the drug does not have to cross the membrane of the gut. Pharmacokinetic studies can determine the best route and the time it takes the molecule to metabolize in the body.

Tissues collected upon necropsy
Mice need to be sacrificed when the tumor size reaches two centimeters or when the mice are in pain or distress. The tissue types you need after sacrifice will be study dependent, but usually include tissue for histology, RNA/DNA, and chunks for potential re-transplant. In addition, you may want metastatic organs or blood to find circulating tumor cells or immune cells.