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.

The OncoRat® Is The Ideal Host For Patient-Derived Xenografts Of Ovarian Cancer Cells

Jack Crawford on December 11, 2018

Ovarian cancer is the most lethal gynecological cancer in the United States. Advances in cytotoxic, platinum-based chemotherapeutics combined with tumor resection surgery allows approximately 80% of these patients to achieve remission. Unfortunately, the vast majority have a tumor recurrence within 12-24 months and relapsed ovarian cancer is recognized as being universally incurable1-2.

Large genomic analyses of ovarian tumors, using databases including The Cancer Genome Atlas (TCGA), have revealed that ovarian tumors are highly heterogeneous. Specifically, no over-represented, targetable oncogenic mutations were revealed. Thus, alternative strategies must be employed to identify targetable driver pathways and sources of drug resistance in ovarian tumors1.

Ovarian tumors have a high degree of cell-population heterogeneity and also contain populations of cancer stem cells (CSCs) that contribute to growth and drug resistance in these cancers. It has been demonstrated that exposure of ovarian cancer cells to chemotherapeutics induces a gene expression program increasing cell-stemness, including the expression of CSC marker. For this reason, it is incredibly important that ovarian tumor models mimic the disease physiology in the patient as much as possible.

To leverage and study the natural heterogeneity of ovarian tumors, the DiFeo lab, lead by Dr. Analisa DiFeo, took resected high-grade serous ovarian cancer (HGSOC) tissue from a patient and established a patient-derived xenograft in a murine host – designated OV81. The importance of OV81 is that HGSOC tumors make up around 70% of the ovarian tumors diagnosed. Additionally, OV81 is cisplatin-naïve, so the tumor landscape is unchanged by chemotherapeutic treatment and the tissue taken is the best representation of the patient’s tumor.

From this patient-derived xenograft, the DiFeo lab isolated a cell line for in vitro study, designated OV81.2. OV81.2 cells have been used to identify some of the mechanisms of chemo-induced stemness, the mechanisms of drug resistance development, and metabolic changes that are unique to chemo-resistant ovarian cancer cells1-3. Having OV81.2 cells derived from a chemo-naïve ovarian tumor is paramount to identifying the mechanisms that define drug resistance.

Further examination of drug resistance development will require study replication and expansion into an in vivo xenograft model. OV81.2 cells were implanted into the OncoRat® and NSG mice. After three weeks of growth, the tumor xenografts in the OncoRat had grown to volumes nearly ten-fold higher than the NSG mouse. This demonstrates that the OncoRat is the ideal xenograft host for OV81.2 cells for further preclinical study of this important cell line.

Hera - Blog - The OncoRat® is the ideal host for patient-derived xenografts of ovarian cancer cells - Figure 1

References

  1. Wiechert, A.; Saygin, C.; Thiagarajan, P. S.; Rao, V. S.; Hale, J. S.; Gupta, N.; Hitomi, M.; Nagaraj, A. B.; DiFeo, A.; Lathia, J. D.; Reizes, O., Cisplatin induces stemness in ovarian cancer. Oncotarget 2016, 7 (21), 30511-30522.
  2. Hudson, C. D.; Savadelis, A.; Nagaraj, A. B.; Joseph, P.; Avril, S.; DiFeo, A.; Avril, N., Altered glutamine metabolism in platinum resistant ovarian cancer. Oncotarget 2016, 7 (27), 41637-41649.
  3. Nagaraj, A. B.; Joseph, P.; Kovalenko, O.; Singh, S.; Armstrong, A.; Redline, R.; Resnick, K.; Zanotti, K.; Waggoner, S.; DiFeo, A., Critical role of Wnt/β-catenin signaling in driving epithelial ovarian cancer platinum resistance. Oncotarget 2015, 6 (27), 23720-23734.