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Tumor Profiler Consortium author list

Table ST5: Table of the 15 most informative proteins upregulated in MEK inhibitor-resistant cell culture (ranked by log2 fold-change).

S13: Immunohistochemical analysis of CyTof biomarker panel.

S16: scRNA-sequencing analysis of xenograft tumors M130227

Clinical management of melanomas with NRAS mutations is challenging. Targeting MAPK signaling is only beneficial to a small subset of patients due to resistance that arises through genetic, transcriptional, and metabolic adaptation. Identification of targetable vulnerabilities in NRAS-mutated melanoma could help improve patient treatment. Here, we used multiomics analyses to reveal that NRAS-mutated melanoma cells adopt a mesenchymal phenotype with a quiescent metabolic program to resist cellular stress induced by MEK inhibition. The metabolic alterations elevated baseline reactive oxygen species (ROS) levels, leading these cells to become highly sensitive to ROS induction. In vivo xenograft experiments and single-cell RNA sequencing demonstrated that intratumor heterogeneity necessitates the combination of a ROS inducer and a MEK inhibitor to inhibit both tumor growth and metastasis. Ex vivo pharmacoscopy of 62 human metastatic melanomas confirmed that MEK inhibitor–resistant tumors significantly benefited from the combination therapy. Finally, oxidative stress response and translational suppression corresponded with ROS-inducer sensitivity in 486 cancer cell lines, independent of cancer type. These findings link transcriptional plasticity to a metabolic phenotype that can be inhibited by ROS inducers in melanoma and other cancers.Significance:Metabolic reprogramming in drug-resistant NRAS-mutated melanoma cells confers sensitivity to ROS induction, which suppresses tumor growth and metastasis in combination with MAPK pathway inhibitors.

Neutrophils are evolutionarily conserved innate defense cells implicated in diverse pathological processes. Zebrafish models have contributed substantially to our understanding of neutrophil functions, but similarities to human neutrophil maturation have not been characterized limiting applicability to study human disease.We generated transgenic zebrafish strains to distinguish neutrophil maturation gradesin vivoand established a high-resolution transcriptional profile of neutrophil maturation. We linked gene expression at each stage to characteristic transcription factors, including C/ebpβ, important for late neutrophil maturation. Cross-species comparison of zebrafish, mouse, and human confirmed high molecular similarity in immature stages and discriminated zebrafish-specific from pan-species gene signatures. Applying pan-species neutrophil maturation signatures in RNA-seq data from neuroblastoma patients revealed an association of metastatic tumor cell infiltration in the bone marrow with an increase in mature neutrophils.Our detailed neutrophil maturation atlas provides a valuable resource for studying neutrophil function at different stages across species in health and disease.Graphical abstract

Early childhood tumours are thought to arise from transformed embryonic cells, which often carry large copy number variants (CNVs). However, it remains unclear how CNVs contribute to embryonic tumourigenesis due to a lack of suitable models. Here we employ human embryonic stem cell (hESC) differentiation to assess the effects of chromosome 17q/1q gains, which are prevalent in the embryonal tumour neuroblastoma (NB). We show that CNVs impair the specification of hESC-derived trunk neural crest (NC) cells and their sympathoadrenal derivatives, the putative cells-of-origin of NB. Overexpression ofMYCN, whose amplification co-occurs with CNVs in NB, exacerbates the differentiation block, and enables tumourigenic cell proliferation. We find links between disrupted cell statesin vitroand tumour cells and connect these states with stepwise disruption of developmental transcription factor networks. Together, our results chart a possible route to NB and provide a mechanistic framework for the CNV-driven initiation of embryonal tumours.

Pleural mesothelioma (PM) is characterized by rapid growth, local invasion and limited therapeutic options. The multifunctional oncoprotein Y-box-binding protein-1 (YB-1) is frequently overexpressed in cancer and its inhibition reduces aggressive behavior in multiple tumor types. Here, we investigated the effects of YB-1 on target gene regulation and PM cell behavior. Whereas siRNA-mediated YB-1 knockdown reduced cell motility, YB-1 overexpression resulted in scattering, increased migration and intravasation in vitro. Furthermore, YB-1 stimulated PM cell spreading in zebrafish. Combined knockdown and inducible overexpression of YB-1 allowed bidirectional control and rescue of cell migration, the pattern of which was closely followed by the mRNA and protein levels of EGFR and the protein level of Snail, whereas the mRNA levels of MMP1, EPHA5 and PARK2 showed partial regulation by YB-1. Finally, we identified Snail as a critical regulator of YB-1-mediated cell motility in PM. This study provides insights into the mechanism underlying the aggressive nature of PM and highlights the important role of YB-1 in this cancer. In this context, we found that YB-1 closely regulates EGFR and Snail, and, moreover, that YB-1-induced cell migration depends on Snail.

Metabolic reprogramming is an emerging hallmark of resistance to cancer therapy but may generate vulnerabilities that can be targeted with small molecules. Multi-omics analysis revealed that NRAS-mutated melanoma cells with a mesenchymal transcriptional profile adopt a quiescent metabolic program to resist cellular stress response induced by MEK-inhibitor resistance. However, as a result of elevated baseline ROS levels, these cells become highly sensitive to ROS induction.In vivoxenograft experiments and single-cell RNA sequencing demonstrated that intra-tumor heterogeneity requires the combination of a ROS-inducer and a MEK-inhibitor to target both tumor growth and metastasis. Byex vivopharmacoscopy of 62 human metastatic melanomas, we found that MEK-inhibitor resistant tumors significantly benefitted from the combination therapy.Finally, we profiled 486 cancer cell lines and revealed that oxidative stress responses and translational suppression are biomarkers of ROS-inducer sensitivity, independent of cancer indication. These findings link transcriptional plasticity to a metabolic phenotype that can be inhibited by ROS-inducers in melanoma and other cancers.Statement of SignificanceTargeted-therapy resistance in cancer arises from genetic selection and both transcriptional and metabolic adaptation. We show that metabolic reprogramming sensitizes resistant cells to ROS-induction in combination with pathway inhibitors. Predictive biomarkers of metabolic sensitivity to ROS-inducing agents were identified in many cancer entities, highlighting the generalizability of this treatment approach.Graphical summary

Ewing sarcoma is the second most prevalent paediatric malignant bone tumour. In most cases, it is driven by the fusion oncoprotein EWS::FLI1, which acts as an aberrant transcription factor and dysregulates gene expression. EWS::FLI1 and a large number of downstream dysregulated proteins are Hsp90 client proteins, making Hsp90 an attractive target for the treatment of Ewing sarcoma. In this article, we report a new structural class of allosteric Hsp90 C-terminal domain (CTD) inhibitors based on the virtual screening hit TVS24, which showed antiproliferative activity in the SK-N-MC Ewing sarcoma cell line with an IC$_{50}$ value of 15.9 ± 0.7 µM. The optimised compounds showed enhanced anticancer activity in the SK-N-MC cell line. Exposure of Ewing sarcoma cells to the most potent analogue 11c resulted in depletion of critical Hsp90 client proteins involved in cancer pathways such as EWS::FLI1, CDK4, RAF-1 and IGF1R, without inducing a heat shock response. The results of this study highlight Hsp90 CTD inhibitors as promising new agents for the treatment of Ewing sarcoma.

Multiphoton microscopy (MPM) including two-photon excited fluorescence (TPEF), second harmonic generation (SHG), coherent anti-Stokes Raman scattering (CARS) is an important tool in biology and medicine to explore the dynamics of cells and to investigate tissue structure in living systems and biopsies. However, MPM still suffers from limited applicability due to the integration of highly sophisticated lasers. In this paper, we introduce our triple-modal multicolor MPM platform employing a single direct diode-pumped femtosecond Kerr-lens-mode-locked Ti:sapphire oscillator and acquire simultaneously intrinsic co-registered multicolor TPEF, TPEF, SHG and CARS signals in the backward direction. The complexity and by that the footprint as well the cost of the laser are considerably reduced by the direct diode-pumping scheme. In combination with an Yb fiber amplifier such a laser is suited for biomedical applications allowing for detailed morphologic and molecular spectroscopic in vivo investigation. The optimized emission wavelengths of our Ti:sapphire laser and Yb fiber amplifier provide simultaneous excitation at 805 nm, 1050 nm and 911 nm for multicontrast information from exogenous and endogenous fluorophores. We perform in vivo imaging of C. elegans and visualize metabolic changes in zebrafish larvae to investigate the tumor microenvironment with spectral focusing CARS and multicolor TPEF of green fluorescent protein.

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-X

We introduce a new approach to reduce uncorrelated background signals from fluorescence imaging data, using real-time subtraction of background light. This approach takes advantage of the short fluorescence lifetime of most popular fluorescent activity reporters, and the low duty-cycle of ultrafast lasers. By synchronizing excitation and recording, laser-induced multiphoton fluorescence can be discriminated from background light levels with each laser pulse. We demonstrate the ability of our method to – in real-time – remove image artifacts that in a conventional imaging setup lead to clipping of the signal. In other words, our method enables imaging under conditions that in a conventional setup would yield corrupted data from which no accurate information can be extracted. This is advantageous in experimental setups requiring additional light sources for applications such as optogenetic stimulation.

Models that more accurately reflect Ewing sarcoma (ES) will enable the prioritization of novel targeted agents from bench to clinic. To date, development of an ES mouse model have been unsuccessful1 and engraftment of human ES in mice is variable2. Coupled with a moral obligation to minimize the use of mammals, we have established and characterized models using patient-derived ES cultures in vitro and in larval zebrafish. The transcriptomes of ES cell lines and patient-derived ES cultures3 were analyzed and compared using total RNAseq followed by DESeq2 and Gene Set Enrichment analysis. Cells in 2D, as 3D spheroids, in combination with cells of the tumor microenvironment and in larval zebrafish (Danio rerio) were characterized. Six cell lines clustered independently from patient-derived ES cultures (n=20), reflecting differential expression of 15,709 RNAs (p10μM, p0.05), although there was heterogeneity in spheroid weight (range 205-3639ng, p 1Minas et al. 2017.Oncotarget,8(21):34141-34163.2Nanni et al. 2019.Sci Rep,9(1):12174 3Roundhill et al. 2021.Cell Oncol,44(5):1065-1085. Citation Format: Elizabeth A. Roundhill, Elton J. Vasconcelos, David R. Westhead, Sarah Grissenberger, Martin Distel, Susan A. Burchill. Developing human Ewing sarcoma in vitro models to prioritise new treatments. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4683.

Early childhood malignancies are driven by sparse genetic aberrations in oncogenes that often co-occur with large copy number variants (CNVs). The combination of these mutations is thought to transform developmentally pliant embryonic cells to initiate tumorigenesis. However, the mechanistic interactions between CNVs, oncogenes, and differentiation have not been systematically studied due to several obstacles: (i) CNVs cannot be engineered efficiently yet; (ii) transient embryonic progenitors are absent in full-grown tumors; and (iii) inter-species differences in lineage specification limit the applicability of animal models. To overcome these challenges, we used isogenic human embryonic stem cell (hESC) lines carrying gains of chromosome 17q/1q, which are prevalent in the embryonal tumor neuroblastoma (NB). We differentiated these cells toward trunk neural crest (NC) and their sympathoadrenal derivatives, the putative cells-of-origin of NB, and performed single-cell RNA sequencing and cell-biological assays at key differentiation stages. We found that CNVs impaired the specification of sympathoadrenal cell types and instead potentiated early Schwann-cell-precursor-like phenotypes. Additional overexpression of the oncogene MYCN (which is frequently amplified together with CNVs in high-risk NB tumors) exacerbated these differentiation defects, enabled tumourigenic cell proliferation, and generated cell states in vitro that transcriptionally resembled NB tumor cells. Finally, using epigenome analysis, we connected these states to a stepwise disruption of gene-regulatory networks centered on developmental transcription factors. Together, our results chart a mechanistic route to NB tumorigenesis and provide a general framework for the CNV-driven initiation of embryonal tumors, in which CNVs ‘prime’ embryonic cells for oncogenic transformation. The tumor-like cells in our model may serve as proxies to experimentally test therapeutic interventions during tumorigenesis. Citation Format: Ingrid M. Saldana-Guerrero, Luis F. Montano-Gutierrez, Christoph Hafemeister, Dylan Stavish, Lisa E. Shaw, Irfete S. Fetahu, Andrea Wenninger-Weinzierl, Caterina Sturtzel, Celine Souilhol, Sophia Tarelli, Mohamed R. Shoeb, Marie Bernkopf, Polyxeni Bozatzi, Maria Guarini, Eva Bozsaky, Michelle C. Buri, Eva M. Putz, Peter W. Andrews, Ivana Barbaric, Helen E. Bryant, Martin Distel, Sabine Taschner-Mandl, Matthias Farlik, Anestis Tsakiridis, Florian Halbritter. A stem cell model dissects detrimental effects of neuroblastoma-linked chromosomal aberrations on cell differentiation during neural crest development. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3542.

Engineered chimeric antigen receptor T cells (CAR T cells) have emerged as a promising immunotherapy for cancer and have proven to be effective for B cell malignancies. Currently, great efforts are undertaken to expand the application of CAR T cells to other cancer entities, to increase the efficacy of CAR T cell-mediated killing of cancer cells and to reduce possible side effects of CAR T cell therapy. This creates a need for preclinical models to test the many emerging novel CAR designs. Traditionally, mouse xenograft models are applied to investigate the efficacy of CAR T cells in vivo. Here, we describe a complementing xenograft protocol for testing CAR T cells against human leukemia cells in zebrafish embryos. The embryonic zebrafish xenograft promises to be a fast and cost-efficient model and particularly offers live imaging opportunities of CAR T cell distribution and killing of cancer cells in vivo.

The zebrafish is a valuable vertebrate animal model in pre-clinical cancer research. A Jones matrix optical coherence tomography (JM-OCT) prototype operating at 1310 nm and an intensity-based spectral-domain OCT setup at 840 nm were utilized to investigate adult wildtype and a tumor-developing zebrafish model. Various anatomical features were characterized based on their inherent scattering and polarization signature. A motorized translation stage in combination with the JM-OCT prototype enabled large field-of-view imaging to investigate adult zebrafish in a non-destructive way. The diseased animals exhibited tumor-related abnormalities in the brain and near the eye region. The scatter intensity, the attenuation coefficients and local polarization parameters such as the birefringence and the degree of polarization uniformity were analyzed to quantify differences in tumor versus control regions. The proof-of-concept study in a limited number of animals revealed a significant decrease in birefringence in tumors found in the brain and near the eye compared to control regions. The presented work showed the potential of OCT and JM-OCT as non-destructive, high-resolution, and real-time imaging modalities for pre-clinical research based on zebrafish.

Here we demonstrate a long-depth-of-focus imaging method using polarization sensitive optical coherence tomography (PS-OCT). This method involves a combination of Fresnel-diffraction-model-based phase sensitive computational refocusing and Jones-matrix based PS-OCT (JM-OCT). JM-OCT measures four complex OCT images corresponding to four polarization channels. These OCT images are computationally refocused as preserving the mutual phase consistency. This method is validated using a static phantom, postmortem zebrafish, and ex vivo porcine muscle samples. All the samples demonstrated successful computationally-refocused birefringence and degree-of-polarization-uniformity (DOPU) images. We found that defocusing induces polarization artifacts, i.e., incorrectly high birefringence values and low DOPU values, which are substantially mitigated by computational refocusing.

Tumor models allowing for the in vivo investigation of molecular mechanisms driving tumor progression and metastasis are important to develop novel strategies for cancer treatment. Unfortunately, for Ewing sarcoma no adequate genetic animal models are currently available. Mouse xenograft models are the state of the art to model Ewing sarcoma in vivo. Here, we describe an alternative Ewing sarcoma xenograft model in embryonic and larval zebrafish. This xenograft model offers live imaging and easy compound testing opportunities hereby complementing mouse xenograft models. In this chapter, we provide a detailed protocol how to xenograft Ewing sarcoma cells (shSK-E17T) into 2-day-old zebrafish and how xenografted zebrafish can be imaged and analyzed over consecutive days to study tumor proliferation.

The tumor microenvironment significantly contributes to tumor initiation, progression, neo-angiogenesis, and metastasis, and a better understanding of the role of the different cellular players would facilitate the development of novel therapeutic strategies for cancer treatment. Towards this goal, intravital imaging is a powerful method to unravel interaction partners of tumor cells. Among vertebrate model organisms, zebrafish is uniquely suited for in vivo imaging studies. In recent years zebrafish has also become a valuable model in cancer research. In this chapter, we will summarize, how zebrafish has been used to characterize cells of the tumor microenvironment. We will cover both genetically engineered cancer models and xenograft models in zebrafish. The majority of work has been done on the role of innate immune cells and their role during tumor initiation and metastasis, but we will also cover studies focusing on adipocytes, fibroblasts, and endothelial cells. Taken together, we will highlight the versatile use of the zebrafish model for in vivo tumor microenvironment studies.

Ewing sarcoma is a pediatric bone and soft tissue cancer for which new therapies to improve disease outcome and to reduce adverse effects of current standard treatments are urgently needed. To identify new and effective drugs, phenotypic drug screening has proven to be a powerful method and a cancer model ideally suited for this approach is the larval zebrafish xenograft system. Complementing mouse xenografts, zebrafish offer high-througput screening possibilities in an intact complex vertebrate organism. Here, we generated Ewing sarcoma xenografts in zebrafish larvae and established a workflow for automated imaging of xenografts, tumor cell recognition within transplanted zebrafish and quantitative tumor size analysis over consecutive days by high-content imaging. The increased throughput of our in vivo screening setup allowed us to identify combination therapies effective against Ewing sarcoma cells. Especially, combined inhibition of MCL-1 and BCL-XL, two anti-apoptotic proteins, was highly efficient at eradicating tumor cells in our zebrafish xenograft assays with two Ewing sarcoma cell lines and with patient-derived cells. Transcriptional analysis across Ewing sarcoma cell lines and tumors revealed that MCL-1 and BCL2L1, coding for BCL-XL, are the most abundantly expressed anti-apoptotic genes, suggesting that combined MCL-1/BCL-XL inhibition might be a broadly applicable strategy for Ewing sarcoma treatment.

The formation of new blood vessel networks occurs via angiogenesis during development, tissue repair, and disease. Angiogenesis is regulated by intracellular endothelial signalling pathways, induced downstream of vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs). A major challenge in understanding angiogenesis is interpreting how signalling events occur dynamically within endothelial cell populations during sprouting, proliferation, and migration. Extracellular signal-regulated kinase (Erk) is a central downstream effector of Vegf-signalling and reports the signalling that drives angiogenesis. We generated a vascular Erk biosensor transgenic line in zebrafish using a kinase translocation reporter that allows live-imaging of Erk-signalling dynamics. We demonstrate the utility of this line to live-image Erk activity during physiologically relevant angiogenic events. Further, we reveal dynamic and sequential endothelial cell Erk-signalling events following blood vessel wounding. Initial signalling is dependent upon Ca2+ in the earliest responding endothelial cells, but is independent of Vegfr-signalling and local inflammation. The sustained regenerative response, however, involves a Vegfr-dependent mechanism that initiates concomitantly with the wound inflammatory response. This work reveals a highly dynamic sequence of signalling events in regenerative angiogenesis and validates a new resource for the study of vascular Erk-signalling in real-time.

Photoswitchable reagents to modulate microtubule stability and dynamics are an exciting tool approach towards micron- and millisecond-scale control over endogenous cytoskeleton-dependent processes. When these reagents are globally administered yet locally photoactivated in 2D cell culture, they can exert precise biological control that would have great potential forin vivotranslation across a variety of research fields and for all eukaryotes. However, photopharmacology’s reliance on the azobenzene photoswitch scaffold has been accompanied by a failure to translate this temporally- and cellularly-resolved control to 3D models or toin vivoapplications in multi-organ animals, which we attribute substantially to the metabolic liabilities of azobenzenes.Here, we optimised the potency and solubility of metabolically stable, druglike colchicinoid microtubule inhibitors based instead on the styrylbenzothiazole (SBT) photoswitch scaffold, that are non-responsive to the major fluorescent protein imaging channels and so enable multiplexed imaging studies. We applied these reagents to 3D systems (organoids, tissue explants) and classic model organisms (zebrafish, clawed frog) with one- and two-protein imaging experiments. We successfully used systemic treatment plus spatiotemporally-localised illuminationsin vivoto photocontrol microtubule dynamics, network architecture, and microtubule-dependent processes in these systems with cellular precision and second-level resolution. These nanomolar,in vivo-capable photoswitchable reagents can prove a game-changer for high-precision cytoskeleton research in cargo transport, cell motility, cell division and development. More broadly, their straightforward design can also inspire the development of similarly capable optical reagents for a range of protein targets, so bringing generalin vivophotopharmacology one step closer to productive realisation.

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.

Selective targeting of DNA by means of fluorescent labeling has become a mainstay in the life sciences. While genetic engineering serves as a powerful technique and allows the visualization of nucleic acid by using DNA‐targeting fluorescent fusion proteins in a cell‐type‐ and subcellular‐specific manner, it relies on the introduction of foreign genes. On the other hand, DNA‐binding small fluorescent molecules can be used without genetic engineering, but they are not spatially restricted. Herein, we report a photocaged version of the DNA dye Hoechst33342 (pcHoechst), which can be uncaged by using UV to blue light for the selective staining of chromosomal DNA in subnuclear regions of live cells. Expanding its application to a vertebrate model organism, we demonstrate uncaging in epithelial cells and short‐term cell tracking in vivo in zebrafish. We envision pcHoechst as a valuable tool for targeting and interrogating DNA with precise spatiotemporal resolution in living cells and wild‐type organisms., Precision without genetic engineering: pcHoechst allows light‐triggered DNA staining by photochemical uncaging. As such, it can be used to visualize and track nuclei with cellular resolution, which is demonstrated in live cells and in vivo. This chemical tool does not rely on genetic engineering and can ultimately be used to target and track DNA in subnuclear regions with high resolution.

The tumor microenvironment significantly contributes to tumor initiation, progression, neo-angiogenesis, and metastasis, and a better understanding of the role of the different cellular players would facilitate the development of novel therapeutic strategies for cancer treatment. Towards this goal, intravital imaging is a powerful method to unravel interaction partners of tumor cells. Among vertebrate model organisms, zebrafish is uniquely suited for in vivo imaging studies. In recent years zebrafish has also become a valuable model in cancer research. In this chapter, we will summarize, how zebrafish has been used to characterize cells of the tumor microenvironment. We will cover both genetically engineered cancer models and xenograft models in zebrafish. The majority of work has been done on the role of innate immune cells and their role during tumor initiation and metastasis, but we will also cover studies focusing on adipocytes, fibroblasts, and endothelial cells. Taken together, we will highlight the versatile use of the zebrafish model for in vivo tumor microenvironment studies.