Abstract 5898: The consomic xenograft model identifies genetic changes in the tumor microenvironment that alter the growth and metastasis of head and neck cancers
Authors: Straza Michael W. , Rymaszewski Amy , Nickel Kwangok P. , Frei Anne , Chatterjee Anirban , Schlaak Rachel , Joshi Amit , Flister Michael , Kimple Randy J. , Bergom Carmen 
Published: July 2017

Abstract
Background: The tumor microenvironment (TME) is known to impact tumor growth, metastatic potential, and treatment response. Nearly all studies of head and neck cancer (HNC) have focused on somatic mutations in the malignant cells. We hypothesized that genetic determinants limited to the microenvironment would influence HNC growth and metastatic potential.
Approach: To demonstrate the impact of genetic differences in the TME on HNC cell line in vivo growth we utilized a novel tool, the consomic xenograft model (CXM). A consomic rat has an entire chromosome substituted into the isogenic background of another inbred strain by selective breeding. Use of immunodeficient (IL2Rγ-/-) consomic rats allows one to study the influence of stromal genetics on tumor biology without the confounding effect of differences in the immune system through the orthotopic implantation of cancer cells into different consomic rat strains. In this system, any differences in tumor growth or metastases are due to differences in the TME rather than cancer cells or immune response. We utilized SS and SS.BN3 consomic rat strains, previously shown to affect the growth of breast tumors, to study the effects of the TME on HNC tumor growth using two well-characterized HPV negative HNC cell lines, SCC-6 (base of tongue derived) and SCC-22b (derived from a hypopharyngeal cancer that had metastasized to lymph nodes). Both cell lines were modified to stably express luciferase. HNC cells were inoculated into the tongue of SS and SS.BN3 animals and tumor growth was monitored by biophotonic imaging after luciferin injection.
Results: A significant difference in the tumor growth was seen between rat strains for both cell lines, with the SS.BN3 rats exhibiting less tumor growth and metastasis. Median luciferase activity from baseline increased by 4.1-fold vs. 1.1 fold in SCC-6 tumors in SS vs SS.BN3 rats, respectively (p&lt;0.03). SCC-22B tumors demonstrated a significant difference in tumor size as well, with median luciferase activity from baseline 12.7 vs 4.4 fold on day 26, for SS vs SS.BN3, respectively (p&lt;0.05). A significant differences in lung metastases was also seen between strains. Lung metastases were seen in 88% of SS and 0% of SS.BN3 rats (n=6 per group) inoculated with SCC-6 (p&lt;0.02) and in 75% of SS and 30% of SS.BN3 rats (n=10 per group) inoculated with SCC-22b (p&lt;0.08). Despite a non-statistically significant difference in the number of SCC-22b inoculated animals with lung metastases, there was a significantly higher metastatic burden as measured by luciferase signal, with the median signal 6.8 fold higher in SS as compared to SS.BN3 (p&lt;0.03).
Conclusions: The use of the CXM model demonstrates an important role for the TME in the growth and metastatic spread of HNC cell lines. This model allows for future congenic mapping to identify the causative genetic variants in the TME mediating the HNC changes in tumor growth and metastasis.
Citation Format: Michael W. Straza, Amy Rymaszewski, Kwangok P. Nickel, Anne Frei, Anirban Chatterjee, Rachel Schlaak, Amit Joshi, Michael Flister, Randy J. Kimple, Carmen Bergom. The consomic xenograft model identifies genetic changes in the tumor microenvironment that alter the growth and metastasis of head and neck cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5898. doi:10.1158/1538-7445.AM2017-5898