Abstract 3865: Regional and temporal variations in gene expression and vasculature during retinoblastoma tumorigenesis and its impact on ocular treatment
Authors: Murray Timothy , Pina Yolanda , Decatur Christina , Shah Nikesh , Houston Samuel , Cavalcante Ludimila 
Published: June 2012

Abstract
Purpose: The aims of this study were to evaluate the hypothesis that LHBETATAG retinoblastoma tumors exhibit regional and temporal variations in gene expression and vascular development in retinoblastoma.
Methods: To evaluate intratumoral gene expression, LHBETATAG mice aged 12, 16, and 20 weeks were euthanized (n=9). Specimens were taken from 5 tumor areas (apex, anterior lateral, center, base, and posterior lateral). Samples were hybridized with an Affymetrix GeneChip Mouse Gene ST 1.0 arrays. To examine the spatial distribution of new and mature blood vessels, immunohistochemical analyses were conducted on enucleated human (n=10) and LHBETATAG retinal tumors from 16-week-old mice (n=11).
Results: There were significant temporal differences in gene expression for LHBETATAG retinoblastoma tumors (p&lt;10-8). Genes were identified with a greater than 2.5-fold difference in expression across the three time points with variation in expression depending on region. At p&lt;0.01 and log2 fold change &gt; 2.5 there were significant changes in gene expression for 190 genes apically, 84 genes anterolaterally, 126 genes posteriorly, 56 genes centrally, and 134 genes at the base. Differentially expressed genes were analyzed with significant involvement in angiogenesis (p&lt;10-40, 4 pathways), hypoxia (p&lt;10-7, 140 pathways), and cellular metabolism (p&lt;10-8). Additionally, there were significant spatial changes in the distribution of blood vessels in human and LHBETATAG retinal tumors (p&lt;0.01), which correlated with the gene expression related to angiogenesis. The density of new blood vessels was higher in the periphery of the tumor than in the center (p=0.021) in human retinoblastoma tumors. This finding was mostly attributed to the distribution of large-caliber vessels (i.e., new blood vessels were higher in the periphery for large [p=0.050]- and medium [p=0.032]-caliber vessels; and mature vessels were higher in the center for large-caliber vessels [p=0.032]). In this small series, vessel maturation did not correlate with risk for metastasis. Similar results were observed in LHBETATAG retinal tumors. The percentage of large-caliber new blood vessels was higher in the periphery than in the center (p=0.038).
Conclusions: There are significant temporal and regional variations in the gene expression and vasculature of retinoblastoma. Differentially expressed genes overlap with angiogenesis, hypoxia, and cellular metabolism. There is a heterogeneous vessel population in advanced retinoblastoma disease. These findings provide further understanding of the mechanisms involved in tumor progression, and emphasize that tumor biopsies cannot be used for prognostication secondary to tumor regionalization. Finally, optimally-timed adjuvant therapies that target critical components of identified pathways may potentially enhance retinoblastoma tumor control.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3865. doi:10.1158/1538-7445.AM2011-3865