Xenotransplantation of solid tumours in zebrafish embryos: towards personalised medicine

Cancer is a major public health problem worldwide; in many countries it ranks as the second leading cause of death. Due to the high intra- and inter- individual cancer variability, the best therapeutic option for individual patients is difficult to predict. During the last decade animal avatars and co-clinical trials are being developed to personalise the cancer therapy, and zebrafish has recently been proposed for implementing avatar models. In this study, patient-derived xenograft in zebrafish embryos (zPDX) has been developed from fresh human tumor fragments taken from surgical specimens. Experimental data confirms that the cells of the tissue implanted could engraft in the host, survive, spread and migrate, maintaining the primary tumor phenotypic traits based on histology. The aim was to obtain a model to test the response of the patient's tumor to different chemotherapy regimens, with an assessment in less than one week. Due to the lack of a general criterion for the human-fish chemotherapy dose conversion, we carried out a toxicity study by testing 10 different chemotherapy regimens used in cancer treatment. Safety data were matched with the efficacy study carried out in zebrafish embryos xenografted with HCT 116 and MIA PaCa-2 cancer cell lines. We found a general criterion for dose equivalence that was validated in a co-clinical trial (XenoZ, NCT03668418) of hepato-biliary-pancreatic cancer and gastro-intestinal cancer patients. In the XenoZ study, patients were treated with standard chemotherapeutic regimens as determined by the oncologist, while the avatars were treated with different traditional chemotherapeutic regimens to test chemosensitivity. In order to analyze the effects of the treatments on zPDX tumors and to investigate if there is a patient specific response to the treatments we adopted a linear mixed effect model. The model showed that treatments could reduce the size of the tumor xenograft, hindering the tumor cell growth, as opposed to the absence of chemotherapy. Moreover, comparing the treatment effects between each zPDX group and the zPDX population mean, a statistically significant reduction in tumor size was observed with different chemotherapy schemes both in pancreatic and colorectal cancer, documenting a treatment efficacy to impair the tumor growth after the xenograft in zebrafish embryos. In conclusion, our experimental data have shown that zebrafish avatars offer a promising solution to perform patient drug efficacy assay.