Name: Author Spotlight: Advancing Cancer Therapeutics Using Tumor Xenotransplantation in Zebrafish
Uploaded: 2024-07-12T12:40:00
Description: In vivo studies of tumor behavior are a staple of cancer research; however, the use of mice presents significant challenges in cost and time. Here, we ...

This work was supported by NIH grants R37AI110985 and P30CA006927, an appropriation from the Commonwealth of Pennsylvania, the Leukemia and Lymphoma Society, and the Bishop Fund. This study was also supported by the core facilities at Fox Chase, including Cell Culture, Flow Cytometry, and Laboratory Animal facility.&#160;We thank Dr. Jennifer Rhodes for maintaining the zebrafish and microinjection facility at FCCC.

Zebrafish maintenance, feeding, and husbandry occurred under standard aquaculture conditions at 28.5 &#176;C, as described31. All zebrafish-related experiments were done at this temperature; however, following xenotransplantation, the animals were cultured at 34 &#176;C for the duration of the experiment, in accordance with procedures approved by the Institutional Animal Care and Use Committee (IACUC).
1. Breeding (3 days before injection)
<ol>
	<li>P...

Utilizing Larval Zebrafish for Efficient In Vivo Tumor Studies

<ol>
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Zebrafish xenotransplantation has emerged as a rapid, robust, and cost-effective alternative to mouse studies12. Though several approaches to zebrafish xenotransplantation have been reported, our adaptation has resulted in significant improvements. In addition to standardizing parameters around the procedure, these improvements specifically focus on accelerating the rate at which tumor injections can be performed, thus enabling an increase in the number of animals per study arm and using tumor lab...

Analysis of the behavior of tumors in response to genetic alteration or drug treatment in vivo is an essential element of cancer research1,2,3,4. Such studies most often involve the use of immunocompromised mouse (Mus musculus) models5; however, xenotransplantation studies in mice are limited in many respects, including limited capacity, extended duration, significant expense, and the requirement for sophisticated imaging equipment to monitor the progression of internal tumors6,7. By contrast, the zebrafish model (Danio rerio) enables greater capacity, shorter duration, lower expense, and, due to their transparency, simple monitoring of disease progression8,9.
Zebrafish is a well-developed vertebrate model system with ex-utero development and high fecundity, with individual females producing more than 100 embryos10. Moreover, zebrafish embryos are transparent, enabling easy visualization of developmental processes using fluorescence-related techniques such as reporters. Finally, the conservation of critical developmental processes makes them an ideal model for many types of studies, including the behavior of transplanted malignant cells11,12. Wild-type zebrafish embryos develop melanocytes, which render them optically opaque by 2 weeks of age, but this has been overcome by the generation of casper embryos (roya9; mitfaw2), which remain transparent throughout life13. Because of their optical properties, casper zebrafish are ideal recipients of transplanted tumor cells14,15,16. Xenotransplantation of tumor cells into zebrafish has gained importance in the past 2 decades17,18,19,20,21. Zebrafish embryos have innate immunity; however, they lack adaptive immunity during their larval stage, rendering them functionally immunocompromised, which enables them to serve as effective hosts for transplanted tumor xenografts22.
Protocols have been developed for tumor engraftment in zebrafish embryos as well as adults that have considered a number of different variables23,24,25,26,27. These have explored numerous sites of tumor deposition in zebrafish, including injections in yolk, peri-vitelline space, and heart and at different developmental stages16,28. The ambient temperature of aquaculture for zebrafish xenografts is also important as zebrafish rearing typically occurs at 28 &#176;C, while mammalian cells grow at 37 &#176;C. Consequently, a compromise temperature must be employed that is tolerated by the fish yet supports tumor growth, and 34 &#176;C appears to achieve both goals29. Analysis of the behavior and progression of tumors following xenotransplantation is another major area of focus, and this involves the use of a variety of imaging modalities as well as survival analysis30. One of the major advantages of the zebrafish model is the availability of large numbers of study animals to provide immense statistical power to in vivo studies of tumor behavior; however, previous approaches have severely limited this potential because of the requirement of tedious mounting procedures for injections.
Here, we address this limitation through the development of a simple, rapid method with which to stage embryos that enables high throughput and monitoring of injection quality using the transparent casper zebrafish line. This entails the injection of xenografts into the yolk sac of the casper zebrafish embryos at 2 days post fertilization (dpf). We observe the survival of embryos following xenotransplantation as part of tumor behavior analysis. We further show the assessment of disease burden after xenotransplantation by making single cell suspensions and analyzing by flow cytometry (Figure 1).

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1-phenyl 2-thiourea (PTU)</td>
			<td>Sigma</td>
			<td>P7629</td>
			<td></td>
		</tr>
		<tr>
			<td>70 micron cell strainer</td>
			<td>Corning&#160;</td>
			<td>CLS431751-50EA</td>
			<td></td>
		</tr>
		<tr>
			<td>90 mm Petri dish</td>
			<td>Thermo Fisher Scientific</td>
			<td>S43565</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Apex bioresearch</td>
			<td>20-102GP</td>
			<td></td>
		</tr>
		<tr>
			<td>APC APC anti-mouse CD45.2 Antibody</td>
			<td>Biolegend</td>
			<td>109814</td>
			<td></td>
		</tr>
		<tr>
			<td>BD FACSymphony A5 Cell Analyzer</td>
			<td>BD Biosciences</td>
			<td>BD FACSymphony A5</td>
			<td></td>
		</tr>
		<tr>
			<td>calibration capillaries</td>
			<td>Sigma&#160;</td>
			<td>P1424-1PAK</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell tracker CM-dil dye</td>
			<td>Invitrogen</td>
			<td>C7001</td>
			<td></td>
		</tr>
		<tr>
			<td>Collageanse IV</td>
			<td>Gibco</td>
			<td>17104019</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont forceps number 55</td>
			<td>Fine science tools</td>
			<td>11255-20</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Corning&#160;</td>
			<td>35-015-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescence microscope</td>
			<td>Nikon</td>
			<td>model SMZ1500</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass capillaries (Borosilicate)</td>
			<td>World precision instruments</td>
			<td>1B100-4</td>
			<td></td>
		</tr>
		<tr>
			<td>HBSS</td>
			<td>Corning&#160;</td>
			<td>21-023-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Helix NP Blue</td>
			<td>Biolegend</td>
			<td>425305</td>
			<td></td>
		</tr>
		<tr>
			<td>Instant Ocean Sea Salt</td>
			<td>Instant ocean</td>
			<td>SS15-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Light microscope</td>
			<td>Nikon</td>
			<td>model SMZ1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Methylene blue</td>
			<td>Sigma</td>
			<td>M9140-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Microloader (long tips for laoding cells)</td>
			<td>eppendorf</td>
			<td>930001007</td>
			<td></td>
		</tr>
		<tr>
			<td>P1000 micropipette puller</td>
			<td>Sutter instruments</td>
			<td>model P-97</td>
			<td></td>
		</tr>
		<tr>
			<td>PM 1000 cell microinjector</td>
			<td>MicroData Instruments, Inc. (MDI)</td>
			<td>PM1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Tricaine methanesulphate (Ethyl 3- aminobenzoate methanesulphate)</td>
			<td>Sigma</td>
			<td>E10521-10G</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin-EDTA (0.5%), no phenol red</td>
			<td>Gibco</td>
			<td>15400054</td>
			<td></td>
		</tr>
		<tr>
			<td>Zebrafish adult irradiated diet (dry feed)</td>
			<td>Zeigler</td>
			<td>388763</td>
			<td></td>
		</tr>
	</tbody>
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a simple, rapid, and effective method for tumor xenotransplantation analysis in transparent zebrafish embryos

In vivo studies of tumor behavior are a staple of cancer research; however, the use of mice presents significant challenges in cost and time. Here, we present larval zebrafish as a transplant model that has numerous advantages over murine models, including ease of handling, low expense, and short experimental duration. Moreover, the absence of an adaptive immune system during larval stages obviates the need to generate and use immunodeficient strains. While established protocols for xenotransplantation in zebrafish embryos exist, we present here an improved method involving embryo staging for faster transfer, survival analysis, and the use of flow cytometry to assess disease burden. Embryos are staged to facilitate rapid cell injection into the yolk of the larvae and cell marking to monitor the consistency of the injected cell bolus. After injection, embryo survival analysis is assessed up to 7 days post injection (dpi). Finally, disease burden is also assessed by marking transferred cells with a fluorescent protein and analysis by flow cytometry. Flow cytometry is enabled by a standardized method of preparing cell suspensions from zebrafish embryos, which could also be used in establishing the primary culture of zebrafish cells. In summary, the procedure described here allows a more rapid assessment of the behavior of tumor cells in vivo with larger numbers of animals per study arm and in a more cost-effective manner.

Author Spotlight: Advancing Cancer Therapeutics Using Tumor Xenotransplantation in Zebrafish

A Simple, Rapid, and Effective Method for Tumor Xenotransplantation Analysis in Transparent Zebrafish Embryos

Xenotransplantation 
A comprehensive view of the entire experiment and analysis is depicted in Figure 1, spanning from embryo production to the assessment of disease progression by both survival and disease burden analysis by flow cytometry. This approach brings several improvements that enhance the reproducibility and scalability of xenotransplantation, as well as adding a new way to assess disease burden. The success of these experiments is highly dependent upon the h...

We describe a protocol for xenotransplantation into the yolk of transparent zebrafish embryos that is optimized by a simple, rapid staging method. Post-injection analyses include survival and assessing the disease burden of xenotransplanted cells by flow cytometry.

In vivo studies of tumor behavior are a staple of cancer research; however, the use of mice presents significant challenges in cost and time. Here, we ...