Zebrafish as a Model for the Study of Solid Malignancies

Biological and therapeutic insights from animal modeling of fusion-driven pediatric soft tissue sarcomas

Survival for children with cancer has primarily improved over the past decades due to refinements in surgery, radiation and chemotherapy. Although these general therapies are sometimes curative, the cancer often recurs, resulting in poor outcomes for patients. Fusion-driven pediatric soft tissue sarcomas are genetically defined by chromosomal translocations that create a chimeric oncogene. This distinctive, almost 'monogenic', genetic feature supports the generation of animal models to study the respective diseases in vivo. This Review focuses on a subset of fusion-driven pediatric soft tissue sarcomas that have transgenic animal tumor models, which includes fusion-positive and infantile rhabdomyosarcoma, synovial sarcoma, undifferentiated small round cell sarcoma, alveolar soft part sarcoma and clear cell sarcoma. Studies using the animal models of these sarcomas have highlighted that pediatric cancers require a specific cellular state or developmental stage to drive tumorigenesis, as the fusion oncogenes cause different outcomes depending on their lineage and timing of expression. Therefore, understanding these context-specific activities could identify targetable activities and mechanisms critical for tumorigenesis. Broadly, these cancers show dependencies on chromatin regulators to support oncogenic gene expression and co-opting of developmental pathways. Comparative analyses across lineages and tumor models will further provide biological and therapeutic insights to improve outcomes for these children.

Methods to Study Liver Disease Using Zebrafish Larvae

Liver disease affects millions of people worldwide, and the high morbidity and mortality is attributed in part to the paucity of treatment options. In many cases, liver injury self-resolves due to the remarkable regenerative capacity of the liver, but in cases when regeneration cannot compensate for the injury, inflammation and fibrosis occur, creating a setting for the emergence of liver cancer. Whole animal models are crucial for deciphering the basic biological underpinnings of liver biology and pathology and, importantly, for developing and testing new treatments for liver disease before it progresses to a terminal state. The cellular components and functions of the zebrafish liver are highly similar to mammals, and zebrafish develop many diseases that are observed in humans, including toxicant-induced liver injury, fatty liver, fibrosis, and cancer. Therefore, the widespread use of zebrafish larvae for studying the mechanisms of these pathologies and for developing potential treatments necessitates the optimization of experimental approaches to assess liver disease in this model. Here, we describe protocols using staining methods, imaging, and gene expression analysis to assess liver injury, fibrosis, and preneoplastic changes in the liver of larval zebrafish.

VGLL2-NCOA2 leverages developmental programs for pediatric sarcomagenesis

Clinical sequencing efforts are rapidly identifying sarcoma gene fusions that lack functional validation. An example is the fusion of transcriptional coactivators, VGLL2-NCOA2, found in infantile rhabdomyosarcoma. To delineate VGLL2-NCOA2 tumorigenic mechanisms and identify therapeutic vulnerabilities, we implement a cross-species comparative oncology approach with zebrafish, mouse allograft, and patient samples. We find that VGLL2-NCOA2 is sufficient to generate mesenchymal tumors that display features of immature skeletal muscle and recapitulate the human disease. A subset of VGLL2-NCOA2 zebrafish tumors transcriptionally cluster with embryonic somitogenesis and identify VGLL2-NCOA2 developmental programs, including a RAS family GTPase, ARF6. In VGLL2-NCOA2 zebrafish, mouse, and patient tumors, ARF6 is highly expressed. ARF6 knockout suppresses VGLL2-NCOA2 oncogenic activity in cell culture, and, more broadly, ARF6 is overexpressed in adult and pediatric sarcomas. Our data indicate that VGLL2-NCOA2 is an oncogene that leverages developmental programs for tumorigenesis and that reactivation or persistence of ARF6 could represent a therapeutic opportunity.

Mitochondrial targeted drug delivery combined with manganese catalyzed Fenton reaction for the treatment of breast cancer

In previous studies, we found that triphenylphosphine-modified doxorubicin (TPP-DOX) can effectively kill drug-resistant tumor cells, but its effect on sensitive tumor cells is weakened. In this research, with albumin from Bovine Serum (BSA) as a carrier, TPP-DOX@MnBSA (TD@MB) nanoparticles were prepared by co-loading TPP-DOX and manganese which can realize the combination of chemotherapy and chemodynamic therapy (CDT). The uniform and stable nano-spherical nanoparticle can promote drug uptake, achieve mitochondrial-targeted drug delivery, increase intracellular reactive oxygen species (ROS) and catalyze the production of highly toxic oxidative hydroxyl radicals (OH·), further inhibiting the growth of both sensitive and drug-resistant MCF-7 cells. Besides, TD@MB can down-regulate the stemness-related proteins and the metastasis-related proteins, potentially decreasing the tumor stemness and metastasis. In vivo experiment indicated that TD@MB was able to exert desired antitumor effect, good tumor targeting and biocompatibility.

Dysregulated heparan sulfate proteoglycan metabolism promotes Ewing sarcoma tumor growth

The Ewing sarcoma family of tumors is a group of malignant small round blue cell tumors (SRBCTs) that affects children, adolescents, and young adults. The tumors are characterized by reciprocal chromosomal translocations that generate chimeric fusion oncogenes, the most common of which is EWSR1-FLI1. Survival is extremely poor for patients with metastatic or relapsed disease, and no molecularly-targeted therapy for this disease currently exists. The absence of a reliable genetic animal model of Ewing sarcoma has impaired investigation of tumor cell/microenvironmental interactions in vivo. We have developed a new genetic model of Ewing sarcoma based on Cre-inducible expression of human EWSR1-FLI1 in wild type zebrafish, which causes rapid onset of SRBCTs at high penetrance. The tumors express canonical EWSR1-FLI1 target genes and stain for known Ewing sarcoma markers including CD99. Growth of tumors is associated with activation of the MAPK/ERK pathway, which we link to dysregulated extracellular matrix metabolism in general and heparan sulfate catabolism in particular. Targeting heparan sulfate proteoglycans with the specific heparan sulfate antagonist Surfen reduces ERK1/2 signaling and decreases tumorigenicity of Ewing sarcoma cells in vitro and in vivo. These results highlight the important role of the extracellular matrix in Ewing sarcoma tumor growth and the potential of agents targeting proteoglycan metabolism as novel therapies for this disease.

Silibinin Induces G2/M Cell Cycle Arrest by Activating Drp1-Dependent Mitochondrial Fission in Cervical Cancer

Cervical cancer is the fourth leading cancer type and the second most common gynecological malignancy among women worldwide. Silibinin (SB), a chief bioactive natural polyphenolic flavonoid of Silybum marianum L., has been used clinically for its hepatocyte protective effects. It also has anticancer effects via the induction of apoptosis and cell cycle arrest. However, the effects of SB on cervical cancer cells through mitochondrial fission have not been studied. Here, we showed that SB markedly suppressed cervical cell proliferation by inducing G2/M cell cycle arrest via the activation of dynamin-related protein 1 (Drp1), which in turn mediated the mitochondrial fission dysfunction both in vitro and in vivo. SB decreased the ATP content, mitochondrial membrane potential, and mtDNA copy number, as well as reduced the reactive oxygen species levels in cervical cells. Furthermore, SB induced excessive mitochondrial fragmentation and reduced tubule formation. Further study showed that knockdown of Drp1 abolished the SB-induced G2/M cell cycle arrest in cervical cancer cells by inhibiting the mitochondrial fission pathway. More importantly, SB inhibited Hela cell growth in vivo model. In conclusion, we are the first to demonstrate that SB induces cervical cancer cell G2/M cell cycle arrest by activating Drp1-dependent mitochondrial fission dysfunction. This study suggests the strategy of inducing Drp1-dependent mitochondrial fission for cervical cancer prevention and treatment.

PAX3-FOXO1 transgenic zebrafish models identify HES3 as a mediator of rhabdomyosarcoma tumorigenesis

Alveolar rhabdomyosarcoma is a pediatric soft-tissue sarcoma caused by PAX3/7-FOXO1 fusion oncogenes and is characterized by impaired skeletal muscle development. We developed human PAX3-FOXO1 -driven zebrafish models of tumorigenesis and found that PAX3-FOXO1 exhibits discrete cell lineage susceptibility and transformation. Tumors developed by 1.6–19 months and were primitive neuroectodermal tumors or rhabdomyosarcoma. We applied this PAX3-FOXO1 transgenic zebrafish model to study how PAX3-FOXO1 leverages early developmental pathways for oncogenesis and found that her3 is a unique target. Ectopic expression of the her3 human ortholog, HES3, inhibits myogenesis in zebrafish and mammalian cells, recapitulating the arrested muscle development characteristic of rhabdomyosarcoma. In patients, HES3 is overexpressed in fusion-positive versus fusion-negative tumors. Finally, HES3 overexpression is associated with reduced survival in patients in the context of the fusion. Our novel zebrafish rhabdomyosarcoma model identifies a new PAX3-FOXO1 target, her3/HES3, that contributes to impaired myogenic differentiation and has prognostic significance in human disease.

One of the most common cancers in children and adolescents is rhabdomyosarcoma, a cancer of soft tissue such as muscle, tendon or cartilage. The fusion of DNA on two different chromosomes causes the most aggressive form of rhabdomyosarcoma. The fused DNA produces an abnormal protein called PAX3-FOXO1. During normal muscle development, a subset of rapidly growing cells eventually slow down and form mature, working muscle cells. It is still unclear how exactly rhabdomyosarcoma develops, but it is thought that PAX3-FOXO1 stops muscle cells from maturing and the cells that grow out of control result in a tumor. Learning how PAX3-FOXO1 hijacks normal muscle development could lead to new treatments for rhabdomyosarcoma.

One treatment approach is to slow the growth of a tumor and force the cells to mature. Then, young patients might avoid chemotherapy or radiation treatments and their side effects. Efforts to improve treatment for this type of cancer face several obstacles. Currently, only one vertebrate animal model of the disease is available to test drugs, and it is still not known how PAX3-FOXO1 causes healthy cells to become cancerous. It is also hard to turn off PAX3-FOXO1 itself, so scientists must find additional proteins that collaborate with it to target with drugs.

Now, Kendall et al. show that genetically engineered zebrafish with human PAX3-FOXO1 develop rhabdomyosarcoma-like tumors. Experiments on these zebrafish showed that the protein turns on a gene called her3. Humans have a similar gene called HES3. In zebrafish or mouse cells, human HES3 interferes with muscle-cell maturation and allows cells that acquire PAX3-FOXO1 to persist during development instead of dying. It also increases the cell growth and cancerous behavior in human tumor cells. Kendall et al. further looked at HES3 levels in tumors collected from patients with rhabdomyosarcoma and found that having higher levels of HES3 increased the risk of death from the cancer.

Human rhabdomyosarcoma tumors with high HES3 levels were also more likely to have certain cell-growth and cell-differentiation related proteins. Drugs that turn off or modify the activity of these proteins already exist. Testing these drugs that target processes such as cell growth in the zebrafish with rhabdomyosarcoma-like tumors may help scientists determine if they reduce tumor growth. If they do, additional trials could determine if they would help patients with rhabdomyosarcoma.