Background & Aims Pediatric liver cancer is a rare but serious disease whose incidence is rising, and for which the therapeutic options are limited. Development of more targeted, less toxic therapies is hindered by the lack of an experimental animal model that captures the heterogeneity and metastatic capability of these tumors. Methods Here we established an orthotopic engraftment technique to model a series of patient-derived tumor xenograft (PDTX) from pediatric liver cancers of all major histologic subtypes: hepatoblastoma, hepatocellular cancer and hepatocellular malignant neoplasm. We utilized standard (immuno) staining methods for histological characterization, RNA sequencing for gene expression profiling and genome sequencing for identification of druggable targets. We also adapted stem cell culturing techniques to derive two new pediatric cancer cell lines from the xenografted mice. Results The patient-derived tumor xenografts recapitulated the histologic, genetic, and biological characteristics—including the metastatic behavior—of the corresponding primary tumors. Furthermore, the gene expression profiles of the two new liver cancer cell lines closely resemble those of the primary tumors. Targeted therapy of PDTX from an aggressive hepatocellular malignant neoplasm with the MEK1 inhibitor trametinib and pan-class I PI3 kinase inhibitor NVP-BKM120 resulted in significant growth inhibition, thus confirming this PDTX model as a valuable tool to study tumor biology and patient-specific therapeutic responses. Conclusions The novel metastatic xenograft model and the isogenic xenograft-derived cell lines described in this study provide reliable tools for developing mutation- and patient-specific therapies for pediatric liver cancer. Lay summary Pediatric liver cancer is a rare but serious disease and no experimental animalmodel currently captures the complexity and metastatic capability of these tumors. We have established a novel animal model using human tumor tissue that recapitulates the genetic and biological characteristics of this cancer. We demonstrate that our patient-derived animal model, as well as two new cell lines, are useful tools for experimental therapies.

A new therapeutic field is emerging as obstacles are overcome to the clinical applications of mRNA drugs. The immunogenicity of mRNA has been reduced by the use of modified nucleosides and ultra‐purification. The stability and translatability of mRNA is increased by attention to optimizing codon use, the translational ramp, the 3′ and 5′UTRs, and by adding nuclease‐resistant secondary structure. The delivery of mRNA depends upon the application, but advances in targeted nanoparticle delivery vehicles, electro‐ or mechanoporation, microneedles and scaffolds have increased the delivery of therapeutic mRNA to the desired tissue. Because mRNA is non‐integrating, it is safer for human use than DNA‐based gene therapies. Cell therapies, including stem cell therapies for regenerative medicine, may be enhanced by mRNA‐based strategies. For example, in immunodeficient mice bearing a human B cell lymphoma, chimeric antigen receptor T (CART) cell therapy against the tumor was improved by treating the CART cells with human telomerase mRNA (hTERT mRNA). Treatment with hTERT mRNA increased telomere length of CART cells; reduced senescence of the cells with expansion; increased therapeutic cell product; and increased the anti‐tumor effect in vivo. Similarly, the ability of mesenchymal stem cells (MSCs) to induce angiogenesis in ischemic tissue was enhanced by increasing MSC telomerase activity and telomere length. Induced pluripotent stem cells (iPSCs) can be generated using mRNA encoding the Yamanaka factors, avoiding the viral integration of DNA encoding these factors. The lack of integration and its potential off‐target effects may be beneficial for iPSC‐derived cells for regenerative applications. Furthermore, mRNA encoding lineage‐determination factors can facilitate directed differentiation of these iPSCs to the therapeutic cells of choice. Alternatively, mRNA encoding the differentiation factors of choice can be administered directly to the tissue in scaffolds or nanocarriers to enhance endogenous cellular regenerative processes. Because mRNA constructs encoding any protein of interest can be generated rapidly in a cGMP fashion, and because many effective delivery vehicles are also now cGMP capable, mRNA therapeutics is a fast, flexible, and disruptive technology that has great promise in the field of regenerative medicine and cell therapy.