Evolution Of The Rat Model

Jack Crawford on September 30, 2022

Rats have been favored for drug development studies because the metabolism and pharmacokinetic properties of drugs in rats are most similar to humans. Rats are also preferable for xenograft studies because they allow for tumor volumes 10-fold higher than in mice, they are easier to surgically manipulate, and they can accommodate multiple blood samplings to assess the pharmacokinetic properties of a drug. To successfully generate cancer xenografts from humans in rats, the animal must be immunodeficient to prevent rejection of the xenograft by the animal’s immune system.

The first generation of immunodeficient rats is the nude rat. Nude rats are characterized as being devoid of T-cells, but still retaining functional B- and NK-cells. The nude rat accepts human xenografts, but studies have shown that nude rats have increased incidences of tumor regression likely related to age-dependent changes in immunocompetence 1-2.

The answer to some of these deficiencies was the development of severe combined immunodeficiency (SCID) rats. SCID rats are Prkdc deficient which means the rat has no B- or T-cells. SCID rats demonstrate severe immunodeficiencies without the “leaky” phenotype that is observed in SCID mice – where detectable levels of Ig are generated by a few clones of functional B-cells3. SCID rats also demonstrate growth retardation and exhibit premature senescence. SCID rats host xenografts successfully, but only survive for around a year if kept under very strict pathogen-free conditions.

In order to overcome the limitations of the SCID rat, Hera Biolabs developed the Sprague-Dawley Rag2 null (SDR) rat. SDR rats are generated on a Sprague-Dawley background – an albino, outbred lab rat that is preferred for metabolism and toxicity studies. Sprague-Dawley rats are also preferred for their calm demeanor, ease of handling, and larger size than Wistar rats. The SDR rat is null for the Rag2 gene which results in a lack of B-cells and a severely reduced T-cell population4. These rats are highly permissible to xenografts and xenografts demonstrate greater uniformity in growth profiles. SDR rats have also been shown to successfully host large, rapidly developing xenografts of human cancer cell lines (e.g. H358, VCaP) that are difficult or impossible to generate in NSG mouse models. The SDR rat maintains a population of NK-cells which makes this model unlikely to accept xenografts of all tumor types.

The researchers at Hera Biolabs noted that a limitation of the SDR model is the large population of NK-cells that is maintained. To overcome this limitation, an evolution on the SDR rat has been developed at Hera biolabs that contains an additional Il2gamma null, known as the OncoRat®-SRG™. The OncoRat is completely depleted of B-cells, T-cells, and NK-cells. The OncoRat boasts an engraftment take rate of 90%+ using non-small cell lung cancer (NSCLC) patient derived xenograft model establishment as the example.

Hera - Blog - Evolution of the rat model - Figure 1

References

  1. Colston, M. J.; Fieldsteel, A. H.; Dawson, P. J., Growth and regression of human tumor cell lines in congenitally athymic (rnu/rnu) rats. Journal of the National Cancer Institute 1981, 66 (5), 843-8.
  2. Maruo, K.; Ueyama, Y.; Kuwahara, Y.; Hioki, K.; Saito, M.; Nomura, T.; Tamaoki, N., Human tumour xenografts in athymic rats and their age dependence. British Journal of Cancer 1982, 45 (5), 786-789.
  3. Mashimo, T.; Takizawa, A.; Kobayashi, J.; Kunihiro, Y.; Yoshimi, K.; Ishida, S.; Tanabe, K.; Yanagi, A.; Tachibana, A.; Hirose, J.; Yomoda, J.-i.; Morimoto, S.; Kuramoto, T.; Voigt, B.; Watanabe, T.; Hiai, H.; Tateno, C.; Komatsu, K.; Serikawa, T., Generation and Characterization of Severe Combined Immunodeficiency Rats. Cell Reports 2012, 2 (3), 685-694.
  4. Noto, F. K.; Adjan Steffey, V.; Tong, M.; Ravichandran, K.; Zhang, W.; Arey, A.; McClain, C. B.; Ostertag, E.; Mazhar, S.; Sangodkar, J.; Difeo, A.; Crawford, J.; Narla, G.; Jamling, T. Y., Sprague Dawley Rag2 null rats created from engineered spermatogonial stem cells are immunodeficient and permissive to human xenografts. Mol Cancer Ther 2018.

Syngeneic Orthotopic Brain Cancer Xenografts In Rats

Hera Admin on June 13, 2022

C6, 9L, and F98 are the three of the most used rat glioma models in research. In their recent review article, Sahu et al. describe the origin, genomics, and use of these three models in research1. To this day, gliomas remain incredibly hard to treat and patients commonly have very low survival rates. Orthotopic rat brain cancer models are central to generating better clinical interventions. Leveraging our expertise in genetically engineered cell-lines, rat surgeries, and in vivo bioluminescent imaging capabilities, Hera BioLabs is expanding our orthotopic brain offerings in rats.

Some of the advantages of rat versus mouse brain tumor models are as follows:

  • A larger brain allows more precise stereotactic implantation and a longer time until tumor endpoint
  • The larger tumor size creates better in vivo imaging
  • Therapeutic agents can be given intracerebrally (i.c.) with greater ease
  • More literature and research exist on rat brain tumors compared to their mouse counterparts

Hera BioLabs’s SRG Rat™

We offer another significant advantage – a highly immunocompromised rat model, the SRG. Lack of a complete immune system can counteract the inability to generate orthotopic data as two of these most widely used glioma models, C6 and 9L are highly immunogenic in many rat strains. If an intact immune system is not required, the SRG rat facilitates studies using immunogenic cell lines.

The C6 cell line is the most used rodent brain tumor model and expresses genes resembling those reported in human gliomas. Several of these genes are responsible for stimulation of the Ras pathway. C6 is widely used to evaluate therapeutic efficacy in vitro, yet it is immunogenic even in its host Wistar rat and currently has no host it can be successfully propagated in.

9L is the second most commonly used rat brain tumor model. 9L is a gliosarcoma derived from Fischer rats and develops rapidly growing tumors when implanted i.c. This cell line is primarily used to study drug transport in the brain and tumor blood barriers, drug resistance, modeling brainstem tumors, and MRI, PET, and PK studies. Similar to C6, 9L can provoke a strong antitumorigenic immune response.

F98 glioma is the third most common rat brain tumor model. Genes that are overexpressed in F98 include Ras, PDGFβ, cyclin D1/D2, EGFR, and Rb. This model simulates human GBMs closer than other cell lines due to its high invasiveness and weak immunogenicity, making it an ideal candidate for studying efficacy of therapeutic agents. F98 also has several gene-modified versions including F98-EGFR, F98npEGFRvlll, and a luciferase expressing line which allows for in-vivo imaging.

 

Hera BioLabs - Blog - Hera BioLabs Is Expanding Our Orthotopic Brain Offerings In Rats-Table 1 Image

Table 1: Comparison of C6, 9L, and F98 significant molecular markers.

 

Hera BioLabs - Blog - Hera BioLabs Is Expanding Our Orthotopic Brain Offerings In Rats-Figure 1 Image

Figure 1: Histopathological view of the C6, 9L, and F98 rat brain tumors. A. C6 glioma is composed of pleomorphic cells ranging from round to oblong nuclei with a mild herring pattern of growth and focal invasion of contiguous normal brain. B. 9L gliosarcoma is composed of spindle-shaped cells with a sarcomatoid appearance. A whorled pattern of growth is seen, with little invasion of contiguous normal brain. C. F98 glioma is composed of a mixed population of spindle-shaped cells with fusiform nuclei, a frequent whorled pattern of growth is seen with a smaller subpopulation of polygonal cells with round to oval nuclei. Extensive invasion of the contiguous brain occurs with islands of tumor cells and a central area of necrosis.

 

Work With Hera BioLabs

Reach out to us to learn more about using our SRG Rat for your research.

References

  1.  Sahu, U., Barth, R. F., Otani, Y., McCormack, R. & Kaur, B. Rat and Mouse Brain Tumor Models for Experimental Neuro-Oncology Research. J Neuropathol Exp Neurol 81, 312-329, doi:10.1093/jnen/nlac021 (2022).