Development of a specialized zebrafish xenotransplantation database and establishment of ALU-based tumor DNA quantification method in zebrafish: focus on models of overexpression and microenvironment

Abstract

Successful xenotransplantation of human cancer cells into zebrafish host marked a new era in cancer research enabling high throughput in vivo screens. Zebrafish xenotransplantation literature continues to rapidly accumulate, and this necessitates the development of an interactive database for accommodating the collective data for fined-tune search, visualization and statistical representation purposes. Herein, I have introduced an interactive database, ZenoFishDb v1.1 (https://konulab.shinyapps.io/zenofishdb), housing manually curated details on molecularly-modified cell transplantations, PDXs, stem cell and cancer stem cell transplantation studies as well as transplantation studies bearing modified host details. The database projects collected data in a table format via various attributes and provides graphical representation of the curated details as well as statistical analyses yielding information on incorporated numbers and frequencies of selected attributes; hence can be used for reviews and designing new experiments. Zebrafish PDX studies are separately conceptualized and displayed through ZenoFishDb v1.1. Development of the ZenoFishDb v1.1 leads to a better understanding of tumor analysis methods such as assessment of proliferation and/or tumor growth in xenotransplantation studies and further marks the need for development of novel methods for precise quantification of tumor size. In the light of these findings, I have helped establish a novel qRT-PCRbased proliferation assessment method for xenografts in zebrafish, adapted from previous mouse xenotransplantation studies. Herein, the use and precision of ALU repeat-based quantification of transplanted liver cancer cells in genotyped zebrafish ache mutants and wildtype siblings was shown exemplifying microenvironment as an important factor for tumor growth. I further demonstrated the power of ALU repeatbased quantification in Mineralocorticoid Receptor (MR) overexpressing breast cancer cells (MCF7) injected to the transparent casper zebrafish as a case study. First, I demonstrated that MR expression and signaling was important in breast cancer biology and prognosis based on in silico TCGA and custom RNA sequencing as well as other in vitro and ex vivo assays. I further showed that results obtained from ALU repeatbased quantification of tumor growth in MR-overexpressing MCF7 cells paralleled fluorescent image-based intensity measurements while the former being relatively less time-consuming and more high-throughput. In this study, accurate quantification of MR overexpression in xenografts was also successfully performed by a cDNA-specific primer pair; and the rate of tumor growth based on image analysis, did not correlate with the amount of MR DNA in casper fish xenografts. However, MCF7 cells overexpressing MR exhibited lower cell viability in vitro although some of these effects were due to empty vector (EV) integration. Accordingly, tumor size in xenografts of naïve, EV- and MR-transfected MCF7 cells injected into pigmented AB larvae were quantified for ALU-repeats yet no significant difference was observed due to high within-group variability in vivo. Future studies are needed to assess the role of varying the volume and placement of injected cells along with the amount of MR gene transfected on tumor growth in vivo.