Improving zebrafish embryo xenotransplantation conditions by increasing incubation temperature and establishing a proliferation index with ZFtool

Background: Zebrafish (Danio rerio) is a model organism that has emerged as a tool for cancer research, cancer being the second most common cause of death after cardiovascular disease for humans in the developed world. Zebrafish is a useful model for xenotransplantation of human cancer cells and toxicity studies of different chemotherapeutic compounds in vivo. Compared to the murine model, the zebrafish model is faster, can be screened using high-throughput methods and has a lower maintenance cost, making it possible and affordable to create personalized therapies. While several methods for cell proliferation determination based on image acquisition and quantification have been developed, some drawbacks still remain. In the xenotransplantation technique, quantification of cellular proliferation in vivo is critical to standardize the process for future preclinical applications of the model. Methods: This study improved the conditions of the xenotransplantation technique - quantification of cellular proliferation in vivo was performed through image processing with our ZFtool software and optimization of temperature in order to standardize the process for a future preclinical applications. ZFtool was developed to establish a base threshold that eliminates embryo auto-fluorescence and measures the area of marked cells (GFP) and the intensity of those cells to define a proliferation index'. Results: The analysis of tumor cell proliferation at different temperatures (34 degrees C and 36 degrees C) in comparison to in vitro cell proliferation provides of a better proliferation rate, achieved as expected at 36 degrees, a maintenance temperature not demonstrated up to now. The mortality of the embryos remained between 5% and 15%. 5-Fluorouracil was tested for 2 days, dissolved in the incubation medium, in order to quantify the reduction of the tumor mass injected. In almost all of the embryos incubated at 36 degrees C and incubated with 5-Fluorouracil, there was a significant tumor cell reduction compared with the control group. This was not the case at 34 degrees C. Conclusions: Our results demonstrate that the proliferation of the injected cells is better at 36 degrees C and that this temperature is the most suitable for testing chemotherapeutic drugs like the 5-Fluorouracil.