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Why is so much cancer research done in mice?

 

Lab Mouse

 

This is a common question when it comes to cancer research. And mice aren't the only organisms besides humans used to understand cancer.

As it turns out, not all research can be ethically or feasibly (humans are complicated) done in humans. One type of experiment considered unethical in humans is the testing of newly created drugs. In these and other cases, scientists have a few options: computer models, lab-grown cells, and model organisms.

Genetics researchers Stanley Fields and Mark Johnston explain, “[M]odel organisms are non-human species that are extensively studied in order to understand a range of biological phenomena, with the hope that data and theories generated through use of the model will be applicable to other organisms, particularly those that are in some way more complex than the original model.”

Model organisms are simpler than humans, but have many of the same key chemical or physiological processes. This is what allows model organisms to be useful in understanding how human biology works.

Model organisms are meant to represent organisms other than themselves. They typically use a simplified form of the process researchers are trying to study. Fields and Johnston say, “These organisms are not being studied because they are interesting in their own right (though they may well be) but primarily because of the value they can have for investigating processes in a manner that will be generalizable beyond the specific model organism itself”.

The main model organisms in use today are E. coli, baker’s yeast, fruit flies, nematodes, flatworms, and mice. Guinea pigs were historically used to study anatomy and bacterial infections but are less common today. The zebrafish, heavily studied at Huntsman Cancer Institute, is gaining popularity as a model organism because—as a baby—its body is nearly transparent, allowing researchers to see its organs without performing surgery on the fish. 

Zebrafish

 The question a researcher works on decides what model organism should be used. Some are very useful for genetics research and cancer research.

Chimpanzees and humans have very similar genes. In fact, there are only about 50 genes present in humans which are not present in chimps. Comparing the genes of chimps and humans can help identify the function of those genes. For example, chimpanzees do not get AIDS or malaria. Researchers could work to understand if some of those 50 genes are involved in those diseases.

Mice and humans also have pretty similar genes, along with anatomy and physiology. Mice have the added benefit of being small, easy to care for, and breed quickly. Scientists can manipulate almost any mouse gene—to create disease like Huntington’s disease, Alzheimer’s disease, and some forms of cancer. This means they are very commonly used in cancer research.

Other organisms like roundworms and yeast are useful for studying things like cell division and genetics.

According to Fields and Johnston, “Almost everything we know about the fundamental properties of living cells—how they grow and divide, how they express their genetic information, and how they use and store energy—has come from the study of model organisms.”

They continue, “Model organisms offer the best hope for coming to grips with the breadth of genetic diversity and the depth of its consequences. Most often variance among individuals of a species is due to small differences in multiple genes, and it is with model organisms that we will first learn how to analyze and understand complex quantitative traits. Such an understanding will provide the principles and procedures for predicting disease susceptibilities in humans and tailoring optimal methods for prevention and treatment.”

The researchers say model organisms have also been “the proving ground” for new technology, like manipulating genes. In fact, University of Utah and HCI researcher Mario Capecchi won a Nobel Prize for inventing one such technique.

Some model organisms are animals, and experimentation on animals can be a controversial subject. For this reason, animal subjects research is strictly regulated and must be approved by regulatory agencies before it can begin—much like human subjects research. When applying for approval to do research in animals, researchers must:

  • Prove the study has potential to benefit human health
  • Prove that they will minimize pain and distress in the animals
  • Have procedures in place for sick animals to be euthanized in a timely and humane manner by a professional
  • Show that alternatives to research using animals as subjects will not work
  • Choose low-order animals (cold-blooded animals, bacteria, invertebrates, etc.) over higher-order animals (primates and other mammals) wherever possible
  • Use the absolute minimum number of animal subjects necessary to achieve meaningful results
  • Avoid unnecessary replication of experiments already done in animals
  • Design the experiment to minimize pain and suffering for animal subjects by being as painless and efficient as possible
  • Perform any procedures on animal subjects (like surgical procedures) under sedation, analgesia, or anesthesia
  • House, feed, and provide nonmedical care for animal subjects under the direction of a veterinarian or other animal professional

These are the regulations put in place by federal law. Individual states and research institutions may put even stricter rules into place.

 


Sources

Ankeny, R. A., & Leonelli, S. (2011). What Is So Special About Model Organisms? Studies in History and Philosophy of Science: Part A,42(2), 313-323. Retrieved from https://ore.exeter.ac.uk/repository/bitstream/handle/10036/3660/Studies_MO_paper_FINAL.pdf?sequence=6fckLR

Biology Animation Library - Model Organisms. (n.d.). Retrieved from https://www.dnalc.org/resources/animations/model_organisms.html

M. (n.d.). Brachydanio rerio[Photograph]. Wikimedia Commons. Retrieved from https://commons.wikimedia.org/wiki/File:Brachydanio_rerio.jpg. (Originally photographed 2005, August 22)

Fields, S., & Johnston, M. (2005). CELL BIOLOGY: Whither Model Organism Research? Science,307(5717), 1885-1886. doi:10.1126/science.1108872

R. (n.d.). Lab mouse mg 3263[Photograph]. Wikimedia Commons. Retrieved from https://commons.wikimedia.org/wiki/File:Lab_mouse_mg_3263.jpg. (Originally photographed 2008, July 4)

Model Center :: DNA Learning Center. (n.d.). Retrieved from https://www.dnalc.org/view/548-Model-Center.html 

Model Organisms :: DNA Learning Center. (n.d.). Retrieved from https://www.dnalc.org/view/555-Model-Organisms.html 

PHS Policy on Humane Care and Use of Laboratory Animals. (2015). Retrieved from https://olaw.nih.gov/policies-laws/phs-policy.htm 

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