The Chorioallantoic Membrane of the Chick Embryo to Assess Tumor Formation and Metastasis

Establishment of patient-derived 3D in vitro models of sarcomas: literature review and guidelines on behalf of the FORTRESS working group

Sarcomas are a large family of rare and heterogeneous mesenchymal tumors, which respond poorly to available systemic treatments. Translation of preclinical findings into clinical applications has been slow, limiting improvements in patients' outcomes and ultimately highlighting the need for a better understanding of sarcoma biology to develop more effective, subtype-specific therapies. To this end, reliable preclinical models are crucial, but the development of 3D in vitro sarcoma models has been lagging behind that of epithelial cancers. This is primarily due to the rarity and heterogeneity of sarcomas, and lack of widespread knowledge regarding the optimal growth conditions of these in vitro models. In this review, we provide an overview of currently available sarcoma tumoroid models, together with guidelines and suggestions for model development and characterization, on behalf of the FORTRESS (Forum For Translational Research in Sarcomas) international research working group on 3D sarcoma models.

Accumulation of Small-Size, Highly Dispersive Mesoporous Silica Nanoparticles in a Tumor in Both Chorioallantoic Membrane and Mouse Models

(1) Background: The chorioallantoic membrane (CAM) model has the potential to contribute to the development of personalized medicine based on individual cancer patients. We previously established the CAM model using patient-derived CIC-DUX4 sarcoma cells. We also used the CAM model for characterization and a comparison with the mouse model by examining the tumor accumulation of small-size, highly dispersive mesoporous silica nanoparticles (MSNs). (2) Method: In this study, we transplanted a variety of cancer cell lines, including patient-derived osteosarcoma (OS) and extraskeletal osteosarcoma (ESOS) cells. Patient-derived OS, ESOS and other cell lines were transplanted onto CAMs. The proliferation of cancer cells within CAM tumors was confirmed using H&E staining. For the comparison of the CAM and mouse models, rhodamine B-labeled MSNs were administered intravenously to CAMs and to xenograft mice. Tumor accumulation was evaluated by examining fluorescence and by confocal microscopy. The biodistribution of MSNs was examined by measuring the Si content by ICP. (3) Results: H&E staining demonstrated the proliferation of cancer cells of OS, ESOS and others on CAMs. While growth patterns and morphologies varied among different cancer types, H&E staining confirmed the establishment of tumors. As for the tumor accumulation, both the CAM and mouse models showed that MSNs were selectively accumulated in the tumors in both the CAM and mouse models. (4) Conclusions: We have expanded the range of CAM models by using a variety of cancer cells, including patient-derived cell lines. We also report that the small-size, highly dispersive MSNs exhibit excellent tumor accumulation in both the CAM and mouse models. These results point to the usefulness of the CAM model for patient-derived cancer cells as well as for evaluating drug carriers for tumor targeting.

Chick Chorioallantoic Membrane as an in vivo Model for the Study of Angiogenesis and Lymphangiogenesis

BACKGROUND

The high incidence of vascular and lymphatic metastasis is closely associated with poor prognosis and mortality in cancer. Finding effective inhibitors to prevent pathological angiogenesis and lymphangiogenesis relies on appropriate in vivo models. The chick embryo chorioallantoic membrane (CAM) is formed by the fusion of the chorion and allantois during embryonic development.

SUMMARY

In this context, we primarily summarize the changes in vascular and lymphatic vessel formation in tumors under the action of drugs using this model, providing a preclinical model basis for effective tumor inhibitors.

KEY MESSAGES

Due to natural immunological defects, chick embryos accept various tissue and species transplants without immune response. The CAM model has been widely used in studying angiogenesis, antiangiogenesis, tumor growth, tumor metastasis, and drug efficacy. This review describes the use of CAM assays as a valuable method for testing the in vivo effects of drugs on vascular and lymphatic vessel formation before further investigating the effects of drugs on tumor vessels and lymphatic vessels in animal models.

BACKGROUND

The high incidence of vascular and lymphatic metastasis is closely associated with poor prognosis and mortality in cancer. Finding effective inhibitors to prevent pathological angiogenesis and lymphangiogenesis relies on appropriate in vivo models. The chick embryo chorioallantoic membrane (CAM) is formed by the fusion of the chorion and allantois during embryonic development.

SUMMARY

In this context, we primarily summarize the changes in vascular and lymphatic vessel formation in tumors under the action of drugs using this model, providing a preclinical model basis for effective tumor inhibitors.

KEY MESSAGES

Due to natural immunological defects, chick embryos accept various tissue and species transplants without immune response. The CAM model has been widely used in studying angiogenesis, antiangiogenesis, tumor growth, tumor metastasis, and drug efficacy. This review describes the use of CAM assays as a valuable method for testing the in vivo effects of drugs on vascular and lymphatic vessel formation before further investigating the effects of drugs on tumor vessels and lymphatic vessels in animal models.

The chicken chorioallantoic membrane as a low-cost, high-throughput model for cancer imaging

Mouse models are invaluable tools for radiotracer development and validation. They are, however, expensive, low throughput, and are constrained by animal welfare considerations. Here, we assessed the chicken chorioallantoic membrane (CAM) as an alternative to mice for preclinical cancer imaging studies. NCI-H460 FLuc cells grown in Matrigel on the CAM formed vascularized tumors of reproducible size without compromising embryo viability. By designing a simple method for vessel cannulation it was possible to perform dynamic PET imaging in ovo, producing high tumor-to-background signal for both 18F-2-fluoro-2-deoxy-D-glucose (18F-FDG) and (4S)-4-(3-18F-fluoropropyl)-L-glutamate (18F-FSPG). The pattern of 18F-FDG tumor uptake were similar in ovo and in vivo, although tumor-associated radioactivity was higher in the CAM-grown tumors over the 60 min imaging time course. Additionally, 18F-FSPG provided an early marker of both treatment response to external beam radiotherapy and target inhibition in ovo. Overall, the CAM provided a low-cost alternative to tumor xenograft mouse models which may broaden access to PET and SPECT imaging and have utility across multiple applications.

Technical Implications of the Chicken Embryo Chorioallantoic Membrane Assay to Elucidate Neuroblastoma Biology

The chorioallantoic membrane (CAM) can be used as a valuable research tool to examine tumors. The CAM can be used to investigate processes such as migration, invasion, and angiogenesis and to assess novel antitumor drugs. The CAM can be used to establish tumors in a straightforward, rapid, and cost-effective manner via xenotransplantation of cells or tumor tissues with reproducible results; furthermore, the use of the CAM adheres to the three "R" principle, i.e., replace, reduce, and refine. To achieve successful tumor establishment and survival, several technical aspects should be taken into consideration. The complexity and heterogeneity of diseases including neuroblastoma and cancers in general and their impact on human health highlight the importance of preclinical models that help us describe tumor-specific biological processes. These models will not only help in understanding tumor biology, but also allow clinicians to explore therapeutic alternatives that will improve current treatment strategies. In this review, we summarize the technical characteristics as well as the main findings regarding the use of this model to study neuroblastoma for angiogenesis, metastasis, drug sensitivity, and drug resistance.

Differential Angiogenic Induction Impacts Nasal Polyp Tissue Growth

In chronic rhinosinusitis with nasal polyps, inflammatory edema drives tissue remodeling favoring anomalous growth of the nasal mucosa, but a proangiogenic contribution of nasal polyp in support of tissue growth is still controversial. The chorioallantoic membrane of chicken embryo model was employed to address the potentiality of nasal tissue fragments to modulate angiogenesis. Fifty-seven fertilized eggs were implanted with polyp or healthy nasal mucosa tissue or were kept as non-implanted controls. The embryos' size, length, and development stage, and chorioallantoic membrane vasculature morphology were evaluated after 48 h. Quantitative computer vision techniques applied to digital chorioallantoic membrane images automatically calculated the branching index as the ratio between the areas of the convex polygon surrounding the vascular tree and the vessels' area. Ethics approval and consent to participate: the study was approved by the Human Research Ethics Committee of the Federal University of São Paulo (CAAE number: 80763117.1.0000.5505) and by the Animal Research Ethics Committee of University of São Paulo (nº CEUA 602-2019). Mucosal, but not polyp tissue implants, hampered embryo development and induced underdeveloped chorioallantoic membranes with anastomosed, interrupted, and regressive vessels. Vessels' areas and branching indexes were higher among the chorioallantoic membranes with polyp implants and controls than among those with healthy mucosa implants. Nasal polyp presents differential angiogenic induction that impacts tissue growth.

Curcumin, thymoquinone, and 3, 3′-diindolylmethane combinations attenuate lung and liver cancers progression

Cancer can develop due to abnormal cell proliferation in any body’s cells, so there are over a hundred different types of cancer, each with its distinct behavior and response to treatment. Therefore, many studies have been conducted to slow cancer progression and find effective and safe therapies. Nutraceuticals have great attention for their anticancer potential. Therefore, the current study was conducted to investigate the anticancer effects of curcumin (Cur), thymoquinone (TQ), and 3, 3′-diindolylmethane (DIM) combinations on lung (A549) and liver (HepG2) cancer cell lines’ progression. Results showed that triple (Cur + TQ + DIM) and double (Cur + TQ, Cur + DIM, and TQ + DIM) combinations of Cur, TQ, and DIM significantly increased apoptosis with elevation of caspase-3 protein levels. Also, these combinations exhibited significantly decreased cell proliferation, migration, colony formation activities, phosphatidylinositol 3-kinase (PI3K), and protein kinase B (AKT) protein levels with S phase reduction. Triple and double combinations of Cur, TQ, and DIM hindered tumor weight and angiogenesis of A549 and HepG2 implants in the chorioallantoic membrane model. Interestingly, Cur, TQ, and DIM combinations are considered promising for suppressing cancer progression via inhibiting tumor angiogenesis. Further preclinical and clinical investigations are warranted.

Tumor Accumulation of PIP-Based KRAS Inhibitor KR12 Evaluated by the Use of a Simple, Versatile Chicken Egg Tumor Model

Simple Summary

One of the goals of nanoplatform-based cancer therapy is to achieve tumor accumulation of anticancer agents. We have focused on PIP-based KRAS inhibitor KR12 (pyrrole–imidazole polyamide indole-seco–CBI conjugate), which has been reported to exhibit tumor growth inhibition in a xenograft mouse model. To evaluate the tumor accumulation property of KR12, we have synthesized a fluorescently labeled KR12 derivative (KR12-TAMRA) and employed a chicken egg tumor assay, a simple and versatile assay to examine tumor accumulation. Our results show that KR12-TAMRA accumulates specifically in the tumor when injected into a fertilized chicken egg transplanted with human cancer cells. We also demonstrate nuclear accumulation of KR12-TAMRA. Finally, inhibition of tumor growth in the chorioallantoic membrane (CAM) assay is shown. These results uncover a number of attractive features of PIP-based KR12 for cancer therapy.

Abstract

Background: The KRAS inhibitor KR12, based on pyrrole-imidazole polyamide (PIP), has been developed and shown to exhibit efficacy in mouse experiments. Because some PIP species exhibit tumor accumulation capability, we decided to evaluate whether the PIP portion of KR12 exhibits tumor accumulation. We employed the CAM assay that provides a simple method for tumor accumulation evaluation. Methods: KR12 PIP was synthesized and conjugated to TAMRA to produce a fluorescently labeled reagent (KR12-TAMRA). This reagent was injected into a fertilized chicken egg that has been transplanted with human cancer cells. Distribution of the red fluorescence was examined by cutting out tumor as well as various organs from the embryo. Results: The red fluorescence of KR12-TAMRA was found to overlap with the green fluorescence of the tumor formed with GFP-expressing cancer cells. We also observed nuclear localization of KR12-TAMRA. Treatment of KR12 that contained the alkylating agent CBI in the tumor-bearing chicken egg resulted in tumor growth inhibition. Conclusions: KR12 contains a PIP that has two key features: tumor accumulation and nuclear localization. KR12 conjugated with CBI exhibits inhibition of tumor growth in the CAM model.

The CAM Model for CIC-DUX4 Sarcoma and Its Potential Use for Precision Medicine

(1) Background: CIC-DUX4 sarcoma is a rare mesenchymal small round cell tumor which belongs to rare cancers that occupy a significant percentage of cancer cases as a whole, despite each being rare. Importantly, each rare cancer type has different features, and thus there is a need to develop a model that mimics the features of each of these cancers. We evaluated the idea that the chicken chorioallantoic membrane assay (CAM), a convenient and versatile animal model, can be established for the CIC-DUX4 sarcoma. (2) Methods: Patient-derived cell lines of CIC-DUX4 were applied. These cells were transplanted onto the CAM membrane and tumor formation was examined by H&E staining, immunohistochemistry and Western blotting. The CAM tumor was transferred onto a fresh CAM and was also used to form organoids. Retention of the fusion gene was examined. (3) Results: H&E staining as well as molecular characterization demonstrated the formation of the CIC-DUX4 tumor on the CAM membrane. Expression of cyclin D2 and ETV4 was identified. The CAM tumor was transferred to a fresh CAM to form the second-generation CAM tumor. In addition, we were successful in forming tumor organoids using the CAM tumor. Retention of the fusion gene CIC-DUX4 in the CAM, second-generation CAM, and in the CAM-derived organoids was confirmed by RT-PCR. (4) Conclusions: The CAM assay provides a promising model for CIC-DUX4 sarcoma.

TBC1D9: An Important Modulator of Tumorigenesis in Breast Cancer

Triple-negative breast cancer (TNBC) is a major concern among the different subtypes of breast cancer (BC) due to the lack of effective treatment. In a previous study by our group aimed at understanding the difference between TNBC and non-TNBC tumors, we identified the gene TBC1 domain family member 9 (TBC1D9), the expression of which was lower in TNBC as compared to non-TNBC tumors. In the present study, analysis of TBC1D9 expression in TNBC (n = 58) and non-TNBC (n = 25) patient tumor samples validated that TBC1D9 expression can differentiate TNBC (low) from non-TNBC (high) samples and that expression of TBC1D9 was inversely correlated with grade and proliferative index. Moreover, we found that downregulation of the TBC1D9 gene decreases the proliferation marginally in non-TNBC and was associated with increased migratory and tumorigenic potential in both TNBC and luminal BC cell lines. This increase was mediated by the upregulation of ARL8A, ARL8B, PLK1, HIF1α, STAT3, and SPP1 expression in TBC1D9 knockdown cells. Our results suggest that TBC1D9 expression might limit tumor aggressiveness and that it has a differential expression in TNBC vs. non-TNBC tumors.

Construction of Boronophenylalanine-Loaded Biodegradable Periodic Mesoporous Organosilica Nanoparticles for BNCT Cancer Therapy

Biodegradable periodic mesoporous organosilica (BPMO) has recently emerged as a promising type of mesoporous silica-based nanoparticle for biomedical applications. Like mesoporous silica nanoparticles (MSN), BPMO possesses a large surface area where various compounds can be attached. In this work, we attached boronophenylalanine (¹⁰BPA) to the surface and explored the potential of this nanomaterial for delivering boron-10 for use in boron neutron capture therapy (BNCT). This cancer therapy is based on the principle that the exposure of boron-10 to thermal neutron results in the release of α-particles that kill cancer cells. To attach ¹⁰BPA, the surface of BPMO was modified with diol groups which facilitated the efficient binding of ¹⁰BPA, yielding ¹⁰BPA-loaded BPMO (¹⁰BPA-BPMO). Surface modification with phosphonate was also carried out to increase the dispersibility of the nanoparticles. To investigate this nanomaterial’s potential for BNCT, we first used human cancer cells and found that ¹⁰BPA-BPMO nanoparticles were efficiently taken up into the cancer cells and were localized in perinuclear regions. We then used a chicken egg tumor model, a versatile and convenient tumor model used to characterize nanomaterials. After observing significant tumor accumulation, ¹⁰BPA-BPMO injected chicken eggs were evaluated by irradiating with neutron beams. Dramatic inhibition of the tumor growth was observed. These results suggest the potential of ¹⁰BPA-BPMO as a novel boron agent for BNCT.

Prognostic significance of phosphoglycerate dehydrogenase in breast cancer

PURPOSE

Breast cancer is the most common type of cancer affecting women worldwide. Phosphoglycerate dehydrogenase (PHGDH) is an oxidoreductase in the serine biosynthesis pathway. Although it has been reported to affect growth of various tumors, its role in breast cancer is largely unknown. This study aimed to analyze the expression of PHGDH in breast cancer tissue samples and to determine if PHGDH regulates breast cancer cell proliferation.

METHODS

Tissue microarrays consisting of 305 cases of breast invasive ductal carcinoma were used for immunohistochemical evaluation of PHGDH expression. The role of PHGDH in breast cancer was investigated in vitro by knocking down its expression and determining the effect on cell proliferation and cell cycling, and in ovo by using a chorioallantoic membrane (CAM) assay.

RESULTS

Immunohistochemical examination showed that PHGDH is mainly localized in the cytoplasm of breast cancer cells and significantly associated with higher cancer grade, larger tumor size, increased PCNA expression, and lymph node positivity. Analysis of the GOBO dataset of 737 patients demonstrated that increased PHGDH expression was associated with poorer overall survival. Knockdown of PHGDH expression in breast cancer cells in vitro resulted in a decrease in cell proliferation, reduction in cells entering the S phase of the cell cycle, and downregulation of various cell cycle regulatory genes. The volume of breast tumor in an in ovo CAM assay was found to be smaller when PHGDH was silenced.

CONCLUSION

The findings suggest that PHGDH has a regulatory role in breast cancer cell proliferation and may be a potential prognostic marker and therapeutic target in breast cancer.

Laser speckle contrast analysis (LASCA) technology for the semiquantitative measurement of angiogenesis in in-ovo-tumor-model

BACKGROUND

The process of angiogenesis is a key element for tumor growth and proliferation and therefore one of the determining factors for aggressiveness and malignancy. A better understanding of the underlying processes of tumor induced angiogenesis is crucial for superior cancer treatment. Furthermore, the PeriCam perfusion speckle imager (PSI) system high resolution (HR) model by PERIMED presents a noninvasive method for semi-quantitative measurement of blood perfusion, based on laser speckle contrast analysis (LASCA). Aim of the present study was to utilize the chick chorioallantoic membrane (CAM) model as an in-ovo-tumor-model which enables rapid neovascularization of tumors while allowing real-time observation of the microcirculation via LASCA.

METHODS

Fertilized chicken eggs were grafted with embryonal/alveolar rhabdomyosarcoma cells or primary sarcoma tumors. The blood perfusion was measured before and after tumor growth using LASCA. The procedure is accelerated and simplified through the integrated PIMSoft software which provides real-time graphs and color-coded images during the measurement.

RESULTS

Sarcoma cells and primary sarcoma tumors exhibited satisfactory growth processes on the CAM. LASCA visualized microcirculation accurately and enabled an extensive investigation of the angiogenic potential of sarcoma cells on the CAM. We were able to show that sarcoma cells and primary sarcoma tumors induced larger quantities of neovasculature on the CAM than the controls.

CONCLUSIONS

The utilization of LASCA for the investigation of tumor angiogenesis within the CAM model appears to be a highly beneficial, cost-efficient and easily practicable procedure. The proposed model can be used as a drug-screening model for individualized cancer therapy, especially with regards to anti-angiogenic agents.

Successful growth of fresh retinoblastoma cells in chorioallantoic membrane

The authors developed a retinoblastoma model using fresh harvested cells from an enucleated eye that were transplanted in chick embryos (chorioallantoic membrane model). The transplanted embryos were treated with escalating doses of Melphalan. This exploratory model was developed with the goal of testing drug sensitivity. Our findings suggest this tumor model could be employed to personalize treatment for patients with retinoblastoma, especially those with bilateral and more refractory disease.

Metabolic Signatures of Tumor Responses to Doxorubicin Elucidated by Metabolic Profiling in Ovo

BACKGROUND

Dysregulated cancer metabolism is associated with acquired resistance to chemotherapeutic treatment and contributes to the activation of cancer survival mechanisms. However, which metabolic pathways are activated following treatment often remains elusive. The combination of chicken embryo tumor models (in ovo) with metabolomics phenotyping could offer a robust platform for drug testing. Here, we assess the potential of this approach in the treatment of an in ovo triple negative breast cancer with doxorubicin.

METHODS

MB-MDA-231 cells were grafted in ovo. The resulting tumors were then treated with doxorubicin or dimethyl sulfoxide (DMSO) for six days. Tumors were collected and analyzed using a global untargeted metabolomics and comprehensive lipidomics.

RESULTS

We observed a significant suppression of tumor growth in the doxorubicin treated group. The metabolic profiles of doxorubicin and DMSO-treated tumors were clearly separated in a principle component analysis. Inhibition of glycolysis, nucleotide synthesis, and glycerophospholipid metabolism appear to be triggered by doxorubicin treatment, which could explain the observed suppressed tumor growth. In addition, metabolic cancer survival mechanisms could be supported by an acceleration of antioxidative pathways.

CONCLUSIONS

Metabolomics in combination with in ovo tumor models provide a robust platform for drug testing to reveal tumor specific treatment targets such as the antioxidative tumor capacity.

Recent excitements in the study of the CAM assay

Chick chorioallantoic membrane (CAM) assay provides a convenient and versatile model for the study of tumor formation, angiogenesis and metastasis. While the assay has been used for more than 100 years, the CAM assay has recently received renewed interest. One of the recent interests comes from the development of Precision Medicine in cancer therapy. The idea is to develop treatments that are tailor-made for each individual patient. For this to happen, patient-derived tumor models are critical and the CAM assay can make significant contribution. The other development concerns various applications of the CAM assay. Using this assay, various reagents have been identified. This includes sensitizers for radiation therapy and photodynamic therapy. We also discuss boron neutron capture therapy (BNCT) that is based on the splitting of boron-10 upon exposure to neutron beam. Recently, various boron-10 reagents have been developed and they can be examined for their efficacy for BNCT therapy using the CAM assay.

CDK inhibitors reduce cell proliferation and reverse hypoxia-induced metastasis of neuroblastoma tumours in a chick embryo model

Neuroblastoma is a paediatric cancer with a poor prognosis. This is in part due to widespread metastasis at time of presentation, which is refractory to current treatment modalities. New therapeutic agents that can control not only tumour growth but also metastasis are urgently needed. The differentiation therapy, retinoic acid, is currently used in clinic, leading to terminal differentiation of neuroblastoma cells thus reducing tumour growth in the primary tumour as well as at metastatic sites. However, retinoic acid only works in a subset of patients. We investigated the potential of CDK inhibitors, Palbociclib and RO-3306, on neuroblastoma cell differentiation, tumour progression and metastasis by utilising a 3R compliant cost effective preclinical chick embryo model. In both SK-N-AS and BE(2)C cell lines, when engrafted on the chorioallantoic membrane of chick embryos, we observed a reduction of tumour cell proliferation as well as a reduction in hypoxia preconditioning-driven metastasis by 60%. In addition, the expression of a panel of genes with known roles in metastasis, which increased upon hypoxia-preconditioning, was largely reduced by a CDK1 inhibitor. These results provide a promising alternative to currently existing therapies and might aid the development of new treatment protocols for retinoic acid-resistant patients.

Patient Derived Chicken Egg Tumor Model (PDcE Model): Current Status and Critical Issues

Chorioallantoic membrane assay (CAM assay) using fertilized chicken eggs has been used for the study of tumor formation, angiogenesis and metastasis. Recently, there is growing realization that this system provides a valuable assay for a patient-derived tumor model. Several reports establish that tumor samples from cancer patients can be used to reproduce tumor in the chicken egg. High transplantation efficiency has been achieved. In this review, we discuss examples of transplanting patient tumors. We then discuss critical issues that need to be addressed to pursue this line of experiments. The patient-derived chicken egg model (PDcE model) has an advantage over other models in its rapid tumor formation. This raises the possibility that the PDcE model is valuable for identifying optimum drug for each individual patient.

Magnetic Resonance Imaging for Characterization of a Chick Embryo Model of Cancer Cell Metastases

Metastasis is the most common cause of death for patients with cancer. To fully understand the steps involved in metastatic dissemination, in vivo models are required, of which murine ones are the most common. Therefore, preclinical imaging methods such as magnetic resonance imaging (MRI) have mainly been developed for small mammals and their potential to monitor cancer growth and metastasis in nonmammalian models is not fully harnessed. We have here used MRI to measure primary neuroblastoma tumor size and metastasis in a chick embryo model. We compared its sensitivity and accuracy to end-point fluorescence detection upon dissection. Human neuroblastoma cells labeled with green fluorescent protein (GFP) and micron-sized iron particles were implanted on the extraembryonic chorioallantoic membrane of the chick at E7. T₂ RARE, T₂-weighted fast low angle shot (FLASH) as well as time-of-flight MR angiography imaging were applied at E14. Micron-sized iron particle labeling of neuroblastoma cells allowed in ovo observation of the primary tumor and tumor volume measurement noninvasively. Moreover, T₂ weighted and FLASH imaging permitted the detection of small metastatic deposits in the chick embryo, thereby reinforcing the potential of this convenient, 3R compliant, in vivo model for cancer research.

Effects of hypoxic preconditioning on neuroblastoma tumour oxygenation and metabolic signature in a chick embryo model

Hypoxia episodes and areas in tumours have been associated with metastatic dissemination and poor prognosis. Given the link between tumour tissue oxygen levels and cellular metabolic activity, we hypothesised that the metabolic profile between metastatic and non-metastatic tumours would reveal potential new biomarkers and signalling cues. We have used a previously established chick embryo model for neuroblastoma growth and metastasis, where the metastatic phenotype can be controlled by neuroblastoma cell hypoxic preconditioning (3 days at 1% O₂). We measured, with fibre-optic oxygen sensors, the effects of the hypoxic preconditioning on the tumour oxygenation, within tumours formed by SK-N-AS cells on the chorioallantoic membrane (CAM) of chick embryos. We found that the difference between the metastatic and non-metastatic intratumoural oxygen levels was small (0.35% O₂), with a mean below 1.5% O₂ for most tumours. The metabolomic profiling, using NMR spectroscopy, of neuroblastoma cells cultured in normoxia or hypoxia for 3 days, and of the tumours formed by these cells showed that the effects of hypoxia in vitro did not compare with in vivo tumours. One notable difference was the high levels of the glycolytic end-products triggered by hypoxia in vitro, but not by hypoxia preconditioning in tumours, likely due to the very high basal levels of these metabolites in tumours compared with cells. In conclusion, we have identified high levels of ketones (3-hydroxybutyrate), lactate and phosphocholine in hypoxic preconditioned tumours, all known to fuel tumour growth, and we herein point to the poor relevance of in vitro metabolomic experiments for cancer research.

Chick chorioallantoic membrane assay as an in vivo model to study the effect of nanoparticle-based anticancer drugs in ovarian cancer

New therapy development is critically needed for ovarian cancer. We used the chicken egg CAM assay to evaluate efficacy of anticancer drug delivery using recently developed biodegradable PMO (periodic mesoporous organosilica) nanoparticles. Human ovarian cancer cells were transplanted onto the CAM membrane of fertilized eggs, resulting in rapid tumor formation. The tumor closely resembles cancer patient tumor and contains extracellular matrix as well as stromal cells and extensive vasculature. PMO nanoparticles loaded with doxorubicin were injected intravenously into the chicken egg resulting in elimination of the tumor. No significant damage to various organs in the chicken embryo occurred. In contrast, injection of free doxorubicin caused widespread organ damage, even when less amount was administered. The lack of toxic effect of nanoparticle loaded doxorubicin was associated with specific delivery of doxorubicin to the tumor. Furthermore, we observed excellent tumor accumulation of the nanoparticles. Lastly, a tumor could be established in the egg using tumor samples from ovarian cancer patients and that our nanoparticles were effective in eliminating the tumor. These results point to the remarkable efficacy of our nanoparticle based drug delivery system and suggests the value of the chicken egg tumor model for testing novel therapies for ovarian cancer.

Optimising the chick chorioallantoic membrane xenograft model of neuroblastoma for drug delivery

BACKGROUND

Neuroblastoma is a paediatric cancer that despite multimodal therapy still has a poor outcome for many patients with high risk tumours. Retinoic acid (RA) promotes differentiation of some neuroblastoma tumours and cell lines, and is successfully used clinically, supporting the view that differentiation therapy is a promising strategy for treatment of neuroblastoma. To improve treatment of a wider range of tumour types, development and testing of novel differentiation agents is essential. New pre-clinical models are therefore required to test therapies in a rapid cost effective way in order to identify the most useful agents.

METHODS

As a proof of principle, differentiation upon ATRA treatment of two MYCN-amplified neuroblastoma cell lines, IMR32 and BE2C, was measured both in cell cultures and in tumours formed on the chick chorioallantoic membrane (CAM). Differentiation was assessed by 1) change in cell morphology, 2) reduction in cell proliferation using Ki67 staining and 3) changes in differentiation markers (STMN4 and ROBO2) and stem cell marker (KLF4). Results were compared to MLN8237, a classical Aurora Kinase A inhibitor. For the in vivo experiments, cells were implanted on the CAM at embryonic day 7 (E7), ATRA treatment was between E11 and E13 and tumours were analysed at E14.

RESULTS

Treatment of IMR32 and BE2C cells in vitro with 10 μM ATRA resulted in a change in cell morphology, a 65% decrease in cell proliferation, upregulation of STMN4 and ROBO2 and downregulation of KLF4. ATRA proved more effective than MLN8237 in these assays. In vivo, 100 μM ATRA repetitive treatment at E11, E12 and E13 promoted a change in expression of differentiation markers and reduced proliferation by 43% (p < 0.05). 40 μM ATRA treatment at E11 and E13 reduced proliferation by 37% (p < 0.05) and also changed cell morphology within the tumour.

CONCLUSION

Differentiation of neuroblastoma tumours formed on the chick CAM can be analysed by changes in cell morphology, proliferation and gene expression. The well-described effects of ATRA on neuroblastoma differentiation were recapitulated within 3 days in the chick embryo model, which therefore offers a rapid, cost effective model compliant with the 3Rs to select promising drugs for further preclinical analysis.