Appendiceal Adenocarcinoma PDX Models Have Improved Growth in an Orthotopic Tumor Environment

Abstract

Appendiceal Adenocarcinoma (AA) is a rare cancer that commonly metastasizes to the peritoneal cavity. Few preclinical models of AA exist. Patient-derived xenograft (PDX) models maintain molecular and histologic features of human tumors along with intratumoral heterogeneity. We hypothesized that orthotopic engraftment in the peritoneal cavity would more faithfully recapitulate the tumor microenvironment in AA. Three AA PDX tumor models were implanted into the peritoneal cavity and flank of female NSG mice to compare tumor growth in the peritoneum and subcutis. These mice are genetically modified to lack mature B cells, T cells, and Natural Killer Cells, allowing for the tumors to grow. Tumor growth rates were calculated and normalized. H&E and Immunohistochemical (IHC) staining were performed. Ki-67 staining was used to evaluate cell proliferation. Serial sections were stained with human marker KU80, human GI epithelial marker CDX2, and stromal marker vimentin. Slides were scanned with an Aperio AT2 whole slide digital scanner. Images were deconvoluted and merged using HALO v3.6 to evaluate human tumor cells and human stroma in PDX tumors. Two out of three of the tumor models evaluated showed a faster growth rate in the peritoneal cavity with increased Ki-67 proliferation rate and cellularity after engraftment. CDX2 and KU80 co-localized indicating that human AA cells persisted in both environments; however, the stroma was murine in both tumors. Our results showed that AA PDX tumors implanted in the peritoneum have a faster growth rate, increased cell proliferation, and increased cellularity compared to tumors grown subcutaneously in two out of three models evaluated. Also, PDX tumor cells persist in both environments but differences in the microenvironments murine stroma may impact tumor growth. This study supports our hypothesis that the peritoneal cavity is a preferred microenvironment for AA to engraft, grow, and metastasize.