In Vitro Oncology Versus In Vivo Models
As previously discussed, there is great value in using in vivo models such as genetically modified mice and xenograft models for oncology research. However as stated in the latin term in vivo, both require using a live animal. Conversely, in vitro models are all carried out in a test tube instead of a mouse, thus reducing cost and circumventing any ethical issues. We weigh up the benefits and downsides of in vitro oncology research.
In vitro oncology models rely on techniques such as cell line development, cell viability assays, and high throughput screening. These methods are much easier to perform than in vivo models as these types of tests are performed routinely by many researchers. Additionally, tumor cells cultured in vitro can be manipulated to express desired traits. For example, PxE6, an extended life-span epithelial cell line from prostate cancer biopsies, was developed to be “similar to those of early prostate cancer cells and retain expression of many prostate-associated antigens.”1 In vitro oncology testing also can “assess the safety and possible mechanisms of future anticancer substances”2 without needing to use animals.
The ethics of using animals is a long-standing debate within the scientific community. In vitro oncology models avoid the issue, and used intelligently, can greatly facilitate the eventual shift into in vivo testing. Testing first in vitro usually minimizes the number of animals required and the risk to each animal; if studies are carefully planned and tumors characterized well, then in vivo studies have a greater chance of success.
In vivo models test in a live environment that takes into account “receptors, hormones, bioavailability, enzymatic influence, blood supply, age of tested cells, [and] severity of disease”.2 In vitro oncology cannot provide valuable information about anticancer therapies or tumor development in animals because the test tube does not adequately imitate the human condition. Cancer cell lines also run the risk of contamination, which can ruin the validity of data and waste time and money if the problem is not caught early on.
Drug discovery has begun trying to unite the principles of in vitro oncology testing with in vivo testing in the form of screening. New models use “mixture-based combinatorial libraries directly… to carry out successful preliminary studies in which tens to hundreds of thousands of compounds would be screened directly in translational in vivo assays.”3 Novel methods that can apply the best of both worlds could prove to be difference maker for drug discovery in the future.
- Maitland N et al. In Vitro Models to Study Cellular Differentiation and Function in Human Prostate Cancers. Radiation Research. http://www.rrjournal.org/doi/abs/10.1667/0033-7587%282001%29155%5B0133%3AIVMTSC%5D2.0.CO%3B2?journalCode=rare
- Wesserling M, Drewa T. Will In Vitro Tests Replace Animal Models in Experimental Oncology? J Tissue Sci Eng. http://www.ahc.umn.edu/rar/ethics.html
- Carroll F, Houghten R. From rapid In Vitro screening to rapid In Vivo screening in the dur gdiscovery process. Neuropsychopharmacology. http://www.nature.com/npp/journal/v34/n1/full/npp2008160a.html