Animal, or in vivo, tests are the next logical step in the progression from in vitro (such as RT-PCR and gene sequencing) and in situ assays (such as IHC and cell viability tests) to human clinical trials. Experiments involving the manipulation of certain key genes or the effects of certain drugs in different grades of prostate cancer may show promise in cells growing in a Petri dish, but may yield very different results within the complexity of a living organism. Therefore, animal testing is an inevitable step in the scientific discovery process. Mice are used because they are small, easy to handle, prolific, inexpensive to maintain, and 90% of genes associated with disease are identical in the human and the mouse, supporting the use of mice as model organisms.

Xenografts: A xenograft is tissue (e.g. prostate cancer) from one organism (e.g. humans) that is transplanted into a different organism (e.g. a mouse). To facilitate transfer, we typically use immunocompromised mice: either born without a thymus (nude) or with SCID (severe combined immunodeficiency). This prevents the host (i.e. mouse) immune system from attacking the foreign tissue. We can then grow human tumors in mice and thereby test the efficacy (and side effects) of promising drugs or the effects of certain genetic mutations in the cancer in a living organism over time.

A plot of tumor (xenograft) size over time under different treatment conditions. Notice the high average tumor growth in group A, the untreated mice, relative to the drug-treated mice.

Knockouts: These are new to the PCC lab. They are mice bred to be missing a key gene or gene(s), the knock out gene.