Refined high-content imaging-based phenotypic drug screening in zebrafish xenografts

Zebrafish xenotransplantation models are increasingly applied for phenotypic drug screening to identify small compounds for precision oncology. Larval zebrafish xenografts offer the opportunity to perform drug screens at high-throughput in a complex in vivo environment. However, the full potential of the larval zebrafish xenograft model has not yet been realized and several steps of the drug screening workflow still await automation to increase throughput. Here, we present a robust workflow for drug screening in zebrafish xenografts using high-content imaging. We established embedding methods for high-content imaging of xenografts in 96-well format over consecutive days. In addition, we provide strategies for automated imaging and analysis of zebrafish xenografts including automated tumor cell detection and tumor size analysis over time. We also compared commonly used injection sites and cell labeling dyes and show specific site requirements for tumor cells from different entities. We demonstrate that our setup allows us to investigate proliferation and response to small compounds in several zebrafish xenografts ranging from pediatric sarcomas and neuroblastoma to glioblastoma and leukemia. This fast and cost-efficient assay enables the quantification of anti-tumor efficacy of small compounds in large cohorts of a vertebrate model system in vivo. Our assay may aid in prioritizing compounds or compound combinations for further preclinical and clinical investigations.

High-content drug screening in zebrafish xenografts reveals high efficacy of dual MCL-1/BCL-XL inhibition against Ewing sarcoma

Ewing sarcoma is a pediatric bone and soft tissue cancer with an urgent need for new therapies to improve disease outcome. To identify effective drugs, phenotypic drug screening has proven to be a powerful method, but achievable throughput in mouse xenografts, the preclinical Ewing sarcoma standard model, is limited. Here, we explored the use of xenografts in zebrafish for high-throughput drug screening to discover new combination therapies for Ewing sarcoma. We subjected xenografts in zebrafish larvae to high-content imaging and subsequent automated tumor size analysis to screen single agents and compound combinations. We identified three drug combinations effective against Ewing sarcoma cells: Irinotecan combined with either an MCL-1 or an BCL-XL inhibitor and in particular dual inhibition of the anti-apoptotic proteins MCL-1 and BCL-XL, which efficiently eradicated tumor cells in zebrafish xenografts. We confirmed enhanced efficacy of dual MCL-1/BCL-XL inhibition compared to single agents in a mouse PDX model. In conclusion, high-content screening of small compounds on Ewing sarcoma zebrafish xenografts identified dual MCL-1/BCL-XL targeting as a specific vulnerability and promising therapeutic strategy for Ewing sarcoma, which warrants further investigation towards clinical application.

Abstract 6245: 3D-models of pediatric bone sarcomas for personalized therapeutic screening

Osteosarcoma (OS) and Ewing sarcoma (ES) are the most common bone cancers in children. They are rare cancers and thus difficult to study due to scarcity of patient material, large genomic instability and a wide histological heterogeneity (in OS) or a lack of satisfactory transgenic animal model and availability of preclinical tests (in ES). There is a dire need for new models and novel therapeutic approaches. Although patient-derived xenografts (PDXs) may recapitulate human tumor biology and predict drug response, propagating PDXs in mice limits its use as a drug-testing platform.

We have established and standardized ES and OS spheroid culture and developed a semi-automated drug-screening platform in tumor spheroids. We established several robust techniques for spheroid formation, with clear pathophysiological gradients, but without central necroses at the onset of drug treatment. We performed RNA-seq comparing spheroid transcription profiles to 2D culture and observed dramatic changes in overall expression patterns. We observed upregulation of genes shown to correlate with poor prognosis in OS patients. We saw upregulation of processes associated with regulation of cell migration, negative regulation of proliferation and modulation of the extracellular matrix (ECM). In addition to ES spheroid models, we created bioprinted 3D-models of ES cell lines and of cells obtained from ES PDXs, using extrusion bioprinting techniques (where cells are encapsulated within the cross-linked polymers, thus allowing homogeneous distribution and high cell density). PDX-derived cells were kept in liquid culture and as 3D-bioprinted constructs, while their transcription profiles were compared with the initial PDX. The mevalonate pathway was the most overrepresented in all ES 3D-models, consistent with predominant upregulation of this metabolic pathway integral to tumor growth and progression. After 15 days in 3D-bioprinted culture, we observed pronounced upregulation of genes involved in ECM signaling, suggesting that the construct promoted in vivo-like tumor-ECM interactions, without further promoting main proliferation and cell survival pathways, which was observed in liquid culture. Furthermore, we showed potential for combinatorial treatment with statins and confirmed feasibility of drug testing in patient-derived 3D models.

Finally, as our spheroid models showed upregulation of many processes involved in metastasis (genes associated with invasion, migration, angiogenesis and hypoxia), we focused on lung as the most common site of metastasis in ES and OS patients. We are thus establishing mixed airway organoid/tumoroid cultures, to investigate further the lung metastatic niche, with a goal to provide proof of concept for patient-specific 3D-models of lung metastatic tumors to guide personalized drug selection for patients with advanced disease.

Citation Format: Branka Radic Sarikas, Mathias Ilg, Marica Markovic, Caterina Sturtzel, Eva Scheuringer, Justine Zulini, Martin Metzelder, Florian Halbritter, Martin Distel, Didier Surdez, Olivier Delattre, Aleksandr Ovsianikov, Heinrich Kovar. 3D-models of pediatric bone sarcomas for personalized therapeutic screening [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6245.