Metastatic and nonmetastatic models of retinoblastoma

The predictive capacity of in vitro preclinical models to evaluate drugs for the treatment of retinoblastoma

Retinoblastoma is a rare childhood cancer of the eye. Of the small number of drugs are used to treat retinoblastoma, all have been repurposed from drugs developed for other conditions. In order to find drugs or drug combinations better suited to the improved treatment of retinoblastoma, reliable predictive models are required, which facilitate the challenging transition from in vitro studies to clinical trials. In this review, the research performed to date on the development of 2D and 3D in vitro models for retinoblastoma is presented. Most of this research was undertaken with a view to better biological understanding of retinoblastoma, and we discuss the potential for these models to be applied to drug screening. Future research directions for streamlined drug discovery are considered and evaluated, and many promising avenues identified.

Review: New horizons in retinoblastoma treatment: an updated review article

Retinoblastoma (Rb) is a rare childhood intraocular malignancy with an incidence rate of approximately 9000 children per year worldwide. The management of Rb is inherently complex and depends on several factors. The orders of priorities in the treatment of Rb are saving life, globe salvage and vision salvage. Rarity and the young age at diagnosis impede conducting randomized clinical trials (RCTs) for new therapeutic options, and therefore pre-RCTs studies are needed. This review provides an overview of advances in Rb treatment options, focusing on the emergence of new small molecules to treat Rb. Articles related to the management and treatments of Rb were searched in different databases. Several studies and animal models discussing recent advances in the treatment of Rb were included to have a better grasp of the biological mechanisms of Rb. Over the years, the principles of management and treatment of Rb have changed significantly. Innovations in targeted therapies and molecular biology have led to improved patient and ocular survival. However, there is still a need for further evaluation of the long-term effects of these new treatments.

SP2509, a Selective Inhibitor of LSD1, Suppresses Retinoblastoma Growth by Downregulating β-catenin Signaling

Purpose

To study the role of lysine-specific demethylase 1 (LSD1) in retinoblastoma (RB) growth and to determine whether the LSD1 inhibitor SP2509 can inhibit RB progression.

Methods

We detected the levels of LSD1 in 12 RB tissue samples, two RB cell lines (Y79 and Weri-RB1), and a retinal pigment epithelium cell line (ARPE-19). Overexpression or knockdown of LSD1 was performed to examine the role of LSD1 in RB cancer cell survival. In vitro and in vivo experiments were conducted to detect the antitumor effect of SP2509, and the antitumor mechanism of SP2509 was examined by RNA sequencing and Western blot.

Results

LSD1 is overexpressed in RB tissues and cells and increases RB cancer cell viability and colony formation ability. The LSD1 inhibitor SP2509 inhibits RB cell proliferation in vitro and in vivo. Treatment with SP2509 increases the levels of dimethylated histone 3 lysine 4 (H3K4me2) and inhibits the expression of β-catenin signaling pathway–related proteins in RB cells.

Conclusions

We demonstrated that LSD1 is overexpressed in RB cells and promotes RB cell survival. The LSD1 inhibitor SP2509 exerted strong growth inhibition in vitro and in vivo, which was at least partially mediated by suppression of the β-catenin pathway.

AN IN VIVO STUDY OF INTRAVITREAL RANIBIZUMAB FOLLOWING SUBRETINAL INOCULATION OF RB CELLS IN RABBITS EYES

AIM

This study aimed to determine the effects of a single intravitreal ranibizumab injection in rabbits induced with retinoblastoma (RB).

MATERIAL AND METHODS

RB was induced in six New Zealand white rabbits by subretinal injection of a cultured WERI-RBb-1 cell line into the right eye. After six weeks, Group A (n = 3) was given intravitreal ranibizumab injection (0.3mg in 0.03ml) and Group B (n = 3) was the control. Baseline and serial clinical examinations were performed on days 1, 3, 6, 12, 15, 18 and 21. The right eyes were enucleated for both groups on day 21 for histopathological examination.

RESULTS

The rabbits in both groups developed intraocular lesions which was detectable clinically at one-week post-tumor inoculation. The tumor grew slowly without spontaneous regression. After the animals in Group A were given an intravitreal ranibizumab injection, regression of the tumor was detected clinically, while the tumor in Group B continued to grow slowly. Histopathological findings confirmed the presence of a tumor that closely resembled features of poorly differentiated human RB cells. At the end of 21 days, the size of the tumor was larger in Group B in comparison to Group A. However, the treated group also developed a focal area of retinal hyperplasia. There was no significant side effect of ranibizumab injection except temporary high intraocular pressure immediately post-injection, which was relieved after paracentesis.

CONCLUSIONS

Intravitreal ranibizumab is a potential treatment for RB. It is an effective therapy with a tolerable safety profile in this animal experimental study.

Biodistribution of Cy5-labeled Thiolated and Methylated Chitosan-Carboxymethyl Dextran Nanoparticles in an Animal Model of Retinoblastoma

Purpose

The use of more potent medicine for local chemotherapy of retinoblastoma in order to minimize local and systemic adverse effects is essential. The main goal of this investigation was to assess the biodistribution of thiolated and methylated chitosan-carboxymethyl dextran nanoparticles (CMD-TCs-NPs and CMD-TMC-NPs) following intravitreal (IVT) injection into rat eyes with retinoblastoma.

Methods

An ionic gelation method was used to fabricate Cy5-labelled CMD-TCs-NPs and CMD-TMC-NPs. The NPs were characterized. Cellular internalization of Cy5-labelled NPs was investigated using confocal microscopy and the absorption of labeled NPs was quantified by flow cytometry in human retinoblastoma (Y79) cells. In addition, the Cy5-labeled distribution of nanoparticles in the posterior segment of the eye was histologically imaged by confocal microscopy after IVT injection of NPs into the eyes of rats with retinoblastoma.

Results

CMD-TCs-NPs and CMD-TMC-NPs showed a mean diameter of 34 ± 3.78 nm and 42 ± 4.23 nm and zeta potential of +11 ± 2.27 mV and +29 ± 4.31mV, respectively. The in vivo study of intraocular biodistribution of Cy5-labeled CMD-TCs-NPs and CMD-TMC-NPs revealed that there is more affinity of CMD-TCs-NPs to the retina and retinoblastoma tumor after IVT administration while methylated chitosan nanoparticles are immobilized in the vitreous and are not able to reach the retina even after 24 hr.

Conclusion

The ionic gelation technique was efficient in synthesizing a biocompatible polymeric nanosystem for drug delivery into the posterior segment of the eye. The current study demonstrated increased ocular bioavailability of CMD-TCs-NPs relative to CMD-TMC-NPs in retinoblastoma induced rat eyes.

Natural History of Untreated Retinoblastoma

Treatment abandonment is a leading cause of death in children with retinoblastoma worldwide. We studied children who abandoned treatment upfront at diagnosis to delineate the natural history of untreated retinoblastoma. Studied were children who received no treatment, diagnosed between 2007 and 2017 at 29 Chinese centers. Data were retrospectively collected from medical chart reviews and interviews with each patient's family. During the study period, 44 children received no treatment after diagnosis of retinoblastoma. Clinical or radiologic evidence of orbital extension was available for 25 children, and radiologic evidence of systemic metastasis was available for 12 children. Median times from diagnosis of intraocular tumor to orbital disease was 13.7 months, orbital disease to metastasis was 2.6 months, and metastasis to death was 2.0 months. Children with brain metastasis had shorter survival than those with metastasis to other sites (median 1.0 vs. 3.1 months; p = 0.015). Overall, 36% of patients died within 12 months of diagnosis, 77% within 24 months, 95% within 36 months and 100% within 48 months. While multiple factors influence refusal of treatment, insights into the natural history of retinoblastoma derived from real-world evidence can inform clinicians and parents that retinoblastoma is life-threatening and encourage urgent treatment at diagnosis.

Efficacy of topotecan nanoparticles for intravitreal chemotherapy of retinoblastoma

Retinoblastoma (Rb) is the most common intraocular malignancy in children that accounts for approximately 4% of all pediatric malignancies. Since chemotherapy is a widely practiced treatment for Rb, there is a growing interest in developing new and effective drugs to overcome systemic and local side effects of chemotherapy to improve the quality of life and increase the chances of survival. This study sought to fabricate thiolated chitosan nanoparticles containing topotecan (TPH-TCs-NPs) with a view of enhancing drug loading and release control. This research was also designed to assess the ability of TPH-TCs-NPs to improve cell association, increase treatment efficacy in retinoblastoma cells and xenograft-rat-model of retinoblastoma, and overcome current topotecan hydrochloride (TPH) intravitreal administration challenges, including stability loss and poor cellular uptake. Modified ionic gelation method was optimized to fabricate TPH-TCs-NPs and TPH-TMC-NPs (N-trimethyl chitosan nanoparticles containing TPH). We characterized the NPs and quantified topotecan loading and release against a free TPH standard. The efficacy of TPH-NPs was quantified in human retinoblastoma cells (Y79) by XTT and flow cytometry measurement. In addition, Y79 cells were injected intravitreally in both eyes of immunodeficient wistar albino rats to create a xenograft-rat-model to compare the antitumor effectiveness of TPH-NPs and TPH by intravitreal administration. TPH-NPs complexation was confirmed by EDX, FTIR, and DSC techniques. TPH-TCs-NPs and TPH-TMC-NPs had high encapsulation efficiency (85.23 ± 2 and 73.34 ± 2% respectively). TPH-TCs-NPs showed a mean diameter, polidispersity index, and zeta potential of 25±2 nm, 0.21 ± 0.03 and +12 ± 2 mV, respectively. As a function of dose, TCs and TMC NPs were more efficacious than free topotecan (IC50s 53.17 and 85.88 nM, relative to 138.30 nM respectively, P = 0.012). Kruskal-Wallis test showed a statistically significant difference between the groups. Additionally, a significant difference between the tumor control and TPH-TCs-NPs treated group in xenograft-rat-model ( Range of P-value: 0.026 to 0.035) was shown by Bonferroni post hoc test. The current investigation demonstrated enhanced efficacy and association of TPH-TCs-NPs relative to free TPH in retinoblastoma cells and tumor in vitro and in vivo.

Adhesion G protein-coupled receptor, ELTD1, is a potential therapeutic target for retinoblastoma migration and invasion

BACKGROUND

Prognosis for pediatric metastatic Retinoblastoma (Rb) is poor and current therapies are limited by high systemic toxicity rates and insufficient therapeutic efficacy for metastatic Rb. Tumor dissemination to the brain is promoted by the heterogeneous adhesive and invasive properties of Rb cells within the tumor. In this study we evaluate, for the first time, the expression, and roles of the ELTD1 and GPR125 adhesion G protein-coupled receptors (GPCRs) in Rb cell migration, viability and invasion.

METHODS

We characterized the RNA expression of adhesion-GPCRs in 64 Rb tumors compared to 11 fetal retinas using the database from the Childhood Solid Tumor Network from St Jude Children's Research Hospital. The role of ELTD1 and GPR125 in Rb were investigated ex vivo by microarray analysis, in vitro by cell viability, Western blot and migration assays, in addition to imaging of the subcellular localization of the GPCRs. To elucidate their role in vivo we utilized siRNA technology in an established Rb orthotopic xenograft murine model.

RESULTS

Our investigation demonstrates, for the first time, that ELTD1 but not GPR125, is significantly increased in Rb tumors compared to fetal retinas. We utilized established the Rb cell lines Y79 and Weri-Rb-1, which represent an aggressive, metastatic, and non-metastatic phenotype, respectively, for the in vitro analyses. The studies demonstrated that ELTD1 is enriched in Weri-Rb-1 cells, while GPR125 is enriched in Y79 cells. The measured differences extended to their subcellular localization as ELTD1 labeling displayed punctate clusters in cell-to-cell adhesion sites of Weri-Rb-1 cells, while GPR125 displayed a polarized distribution in Y79 cells. Lastly, we demonstrated the lack of both adhesion receptors does not affect Rb cell viability, yet inhibition of ELTD1 decreases Y79 cell migration in vitro and invasion in vivo.

CONCLUSION

Taken together, our data suggest that ELTD1, is a potential target to prevent extraocular Rb. The results within establish ELTD1 as a potential therapeutic target for metastatic Rb.

JQ1, a selective inhibitor of BRD4, suppresses retinoblastoma cell growth by inducing cell cycle arrest and apoptosis

Retinoblastoma (RB) is the most common intraocular cancer in children, and chemotherapy has been the first-line treatment. However, due to the side effects of chemotherapy drugs, novel treatments must be developed. JQ1, a selective inhibitor of BRD4, suppresses cell growth in several cancers in which BRD4 is overexpressed. In the present study, BRD4 was overexpressed in retinoblastoma, and JQ1 effectively inhibited RB cell proliferation and colony formation by inducing cell cycle arrest and promoting apoptosis. Furthermore, the Myc-P21-CDK2 and Myc-cyclinD3/CDK6 pathways were activated in RB cells treated with JQ1, and an animal experiment suggested that JQ1 significantly inhibited tumour growth in vivo. In conclusion, JQ1 may be a potential drug treatment for retinoblastoma.

Characteristics of Myelogram in Patients with Extraocular Metastatic Retinoblastoma and Morphological Analysis of Tumor Cells in Bone Marrow and Cerebrospinal Fluid

BACKGROUND

Retinoblastoma (RB) is a common intraocular malignant tumor in infants and young children. However, reports on the morphological descriptions of RB tumor cells from native and foreign scholars are rare.

OBJECTIVES

To investigate the myelogram characteristics of RB with extraocular tumor extension and the morphological characteristics of tumor cells in the bone marrow and cerebrospinal fluid.

METHODS

For the period from May 2011 to February 2015, we analyzed clinical data on 18 patients in our hospital diagnosed as having metastatic RB in the extraocular and other distant regions associated with clear bone marrow metastasis. The morphology of tumor cells in the bone marrow and cerebrospinal fluid was retrospectively analyzed after staining with Wright-Giemsa stain. A summary of the cytological characteristics was also presented.

RESULTS

RB tumor cells in the bone marrow and cerebrospinal fluid not only appeared as aggregated clumps, but were distributed in a scattered manner. The tumor cells may present different characteristic morphologies in different cases, with different tumor cell smears from the same tumor mass even showing different features. According to the degree of tumor metastasis, changes in myelogram were significantly different.

CONCLUSION

The tumor cells of RB patients show unique morphological characteristics in the bone marrow and cerebrospinal fluid. Therefore, correct identification of the cells is of great value in the diagnosis, staging, and prognosis of RB.

Clinical, Genomic, and Pharmacological Study of MYCN-Amplified RB1 Wild-Type Metastatic Retinoblastoma

An uncommon subgroup of unilateral retinoblastomas with highly aggressive histological features, lacking aberrations in RB1 gene with high-level amplification of MYCN (MCYNamplRB1+/+) has only been described as intra-ocular cases treated with initial enucleation. Here, we present a comprehensive clinical, genomic, and pharmacological analysis of two cases of MCYNamplRB1+/+ with orbital and cervical lymph node involvement, but no central nervous system spread, rapidly progressing to fatal disease due to chemoresistance. Both patients showed in common MYCN high amplification and chromosome 16q and 17p loss. A somatic mutation in TP53, in homozygosis by LOH, and high chromosomal instability leading to aneuploidy was identified in the primary ocular tumor and sites of dissemination of one patient. High-throughput pharmacological screening was performed in a primary cell line derived from the lymph node dissemination of one case. This cell line showed resistance to broad spectrum chemotherapy consistent with the patient's poor response but sensitivity to the synergistic effects of panobinostat-bortezomib and carboplatin-panobinostat associations. From these cells we established a cell line derived xenograft model that closely recapitulated the tumor dissemination pattern of the patient and served to evaluate whether triple chemotherapy significantly prolonged survival of the animals. We report novel genomic alterations in two cases of metastatic MCYNamplRB1+/+ that may be associated with chemotherapy resistance and in vitro/in vivo models that serve as basis for tailoring therapy in these cases.

Clinicohistopathological implications of MMP/VEGF expression in retinoblastoma: a combined meta-analysis and bioinformatics analysis

BACKGROUND

No in-depth systematic evidence is available for assessing retinoblastoma malignancy and eligibility for subsequent treatment.

METHODS

The Cochrane Library, EMBASE, PubMed, Web of Science, and China Biology Medicine databases were searched, and 16 studies comprising 718 retinoblastoma patients were included. Pooled odds ratios (ORs) and summary correlation coefficients (r) with 95% confidence intervals (CIs) in random-effects, fixed-effects or quality-effects models were calculated using Review Manager 5.3 and MetaXL. GO functional annotation and KEGG pathway analysis were performed using the GO and STRING databases.

RESULTS

We observed significant associations between high levels of MMP-1 (OR, 4.21; 95% CI 1.86-9.54), MMP-2 (OR, 11.18; 95% CI 4.26-29.30), MMP-9 (OR, 10.41, 95% CI 4.26-25.47), and VEGF (OR, 8.09; 95% CI 4.03-16.20) with tumor invasion; high levels of MMP-1 (OR, 3.58; 95% CI 1.48-8.71), MMP-2 (OR, 2.96; 95% CI 1.32-6.64), MMP-9 (OR, 5.49; 95% CI 3.55-8.48) and VEGF (OR, 5.30; 95% CI 2.93-9.60) with poor differentiation; and overexpression of MMP-9 (OR, 5.17; 95% CI 2.85-9.38) with advanced clinical stages. Moreover, MMP-9 and VEGF expression were positively correlated (r, 0.61; 95% CI 0.38-0.77). Multiple GO terms were enriched associated with MMP-1, MMP-2, MMP-9 and VEGF, and they are closely associated with pathways, proteoglycans and microRNAs related to cancer.

CONCLUSIONS

MMP-1, MMP-2, MMP-9 and VEGF play important roles in the development and progression of retinoblastoma. High levels of MMP-1, MMP-2, MMP-9 and VEGF are credible implications for increased malignancy, thus the need for more aggressive treatments.

Pentoxifylline Enhances the Apoptotic Effect of Carboplatin in Y79 Retinoblastoma Cells

BACKGROUND/AIM

Retinoblastoma (RB) is the most common primary intraocular malignancy. Carboplatin (CPt) is a DNA damage-inducing agent that is widely used for the treatment of RB. Unfortunately, this drug also activates the transcription factor nuclear factor-kappa B (NF-ĸB), leading to promotion of tumor survival. Pentoxifylline (PTX) is a drug that inhibits the phosphorylation of I kappa B-alpha (IĸBα) in serines 32 and 36, and this disrupts NF-ĸB activity that promotes tumor survival. The goal of this study was to evaluate the effect of the PTX on the antitumor activity of CPt.

MATERIALS AND METHODS

Y79 RB cells were treated with CPt, PTX, or both. Cell viability, apoptosis, loss of mitochondrial membrane potential, the activity of caspase-9, -8, and -3, cytochrome c release, cell-cycle progression, p53, and phosphorylation of IĸBα, and pro- and anti-apoptotic genes were evaluated.

RESULTS

Both drugs significantly affected the viability of the Y79 RB cells in a time- and dose-dependent manner. The PTX+CPt combination exhibited the highest rate of apoptosis, a decrease in cell viability and significant caspase activation, as well as loss of mitochondrial membrane potential, release of cytochrome c, and increased p53 protein levels. Cells treated with PTX alone displayed decreased I kappa B-alpha phosphorylation, compared to the CPt treated group. In addition, the PTX+CPt combination treatment induced up-regulation of the proapoptotic genes Bax, Bad, Bak, and caspases- 3, -8, and -9, compared to the CPt and PTX individual treated groups.

CONCLUSION

PTX induces apoptosis per se and increases the CPt-induced apoptosis, augmenting its antitumor effectiveness.

Conservative management of retinoblastoma: Challenging orthodoxy without compromising the state of metastatic grace. "Alive, with good vision and no comorbidity"

Retinoblastoma is lethal by metastasis if left untreated, so the primary goal of therapy is to preserve life, with ocular survival, visual preservation and quality of life as secondary aims. Historically, enucleation was the first successful therapeutic approach to decrease mortality, followed over 100 years ago by the first eye salvage attempts with radiotherapy. This led to the empiric delineation of a window for conservative management subject to a "state of metastatic grace" never to be violated. Over the last two decades, conservative management of retinoblastoma witnessed an impressive acceleration of improvements, culminating in two major paradigm shifts in therapeutic strategy. Firstly, the introduction of systemic chemotherapy and focal treatments in the late 1990s enabled radiotherapy to be progressively abandoned. Around 10 years later, the advent of chemotherapy in situ, with the capitalization of new routes of targeted drug delivery, namely intra-arterial, intravitreal and now intracameral injections, allowed significant increase in eye preservation rate, definitive eradication of radiotherapy and reduction of systemic chemotherapy. Here we intend to review the relevant knowledge susceptible to improve the conservative management of retinoblastoma in compliance with the "state of metastatic grace", with particular attention to (i) reviewing how new imaging modalities impact the frontiers of conservative management, (ii) dissecting retinoblastoma genesis, growth patterns, and intraocular routes of tumor propagation, (iii) assessing major therapeutic changes and trends, (iv) proposing a classification of relapsing retinoblastoma, (v) examining treatable/preventable disease-related or treatment-induced complications, and (vi) appraising new therapeutic targets and concepts, as well as liquid biopsy potentiality.

LncRNA TP73-AS1 down-regulates miR-139-3p to promote retinoblastoma cell proliferation

Our study aimed to investigate the role of long non-coding RNAs (lncRNA) TP73-AS1 in retinoblastoma (Rb). In the present study, we found that TP73-AS1 was up-regulated, while miR-139–3p was down-regulated in Rb. TP73-AS1 and miR-139-3p were inversely correlated in Rb tissues. In cells of Rb cell lines, overexpression of miR-139-3p failed to affect TP73-AS1, while TP73-AS1 overexpression caused the down-regulated miR-139-3p. TP73-AS1 overexpression caused promoted proliferation of Rb cells but showed no significant effects on cell migration and invasion. miR-139-3p overexpression played an opposite role and attenuated the effects of TP73-AS1 overexpression. Therefore, lncRNA TP73-AS1 may down-regulate miR-139-3p to promote Rb cell proliferation.

Targeting the Platelet-Derived Growth Factor-beta Stimulatory Circuitry to Control Retinoblastoma Seeds

Purpose

Vitreous seeding remains the primary reason for treatment failure in eyes with retinoblastoma (Rb). Systemic and intra-arterial chemotherapy, each with its own inherent set of complications, have improved salvage rates for eyes with advanced disease, but the location and biology of vitreous seeds present a fundamental challenge in developing treatments with minimal toxicity and risk. The aim of this study was to target the platelet-derived growth factor (PDGF)- PDGF-receptor β (PDGFRβ) signaling pathway and investigate its role in the growth of Rb seeds, apoptotic activity, and invasive potential.

Methods

We performed ex vivo analyses on vitreous samples from Rb patients that underwent enucleation and from patient-derived xenografts. These samples were evaluated by quantitative PCR, immunohistochemistry, and ELISA. The effects of disruption of the PDGF-PDGFRβ signaling pathway, both by pharmacologic and genomic knockdown approaches, were evaluated in vitro by cell proliferation and apoptotic assays, quantitative PCR analyses, Western blotting, flow cytometry, and imaging flow cytometry. A three-dimensional cell culture system was generated for in-depth study of Rb seeds.

Results

Our results demonstrated that PDGFRβ signaling is active in the vitreous of Rb patients and patient-derived xenografts, sustaining growth and survival in an AKT-, MDM2-, and NF-κB-dependent manner. The novel three-dimensional cell culture system mimics Rb seeds, as the in vitro generated spheroids have similar morphologic features to Rb seeds and mimicked their natural physiology.

Conclusions

Targeting the PDGFRβ pathway in vitro reduces Rb cell growth, survival, and invasiveness and could augment current therapies. This represents a novel signaling pathway for potential targeted therapy to further improve ocular survival in advanced Rb.

Heterogeneity in retinoblastoma: a tale of molecules and models

Retinoblastoma, an intraocular pediatric cancer, develops in the embryonic retina following biallelic loss of RB1. However, there is a wide range of genetic and epigenetic changes that can affect RB1 resulting in different clinical outcomes. In addition, other transformations, such as MYCN amplification, generate particularly aggressive tumors, which may or may not be RB1 independent. Recognizing the cellular characteristics required for tumor development, by identifying the elusive cell-of-origin for retinoblastoma, would help us understand the development of these tumors. In this review we summarize the heterogeneity reported in retinoblastoma on a molecular, cellular and tissue level. We also discuss the challenging heterogeneity in current retinoblastoma models and suggest future platforms that could contribute to improved understanding of tumor initiation, progression and metastasis in retinoblastoma, which may ultimately lead to more patient-specific treatments.

Inhibition of MMP-2 and MMP-9 decreases cellular migration, and angiogenesis in in vitro models of retinoblastoma

Background

Retinoblastoma (Rb) is the most common primary intraocular tumor in children. Local treatment of the intraocular disease is usually effective if diagnosed early; however advanced Rb can metastasize through routes that involve invasion of the choroid, sclera and optic nerve or more broadly via the ocular vasculature. Metastatic Rb patients have very high mortality rates. While current therapy for Rb is directed toward blocking tumor cell division and tumor growth, there are no specific treatments targeted to block Rb metastasis. Two such targets are matrix metalloproteinases-2 and -9 (MMP-2, −9), which degrade extracellular matrix as a prerequisite for cellular invasion and have been shown to be involved in other types of cancer metastasis. Cancer Clinical Trials with an anti-MMP-9 therapeutic antibody were recently initiated, prompting us to investigate the role of MMP-2, −9 in Rb metastasis.

Methods

We compare MMP-2, −9 activity in two well-studied Rb cell lines: Y79, which exhibits high metastatic potential and Weri-1, which has low metastatic potential. The effects of inhibitors of MMP-2 (ARP100) and MMP-9 (AG-L-66085) on migration, angiogenesis, and production of immunomodulatory cytokines were determined in both cell lines using qPCR, and ELISA. Cellular migration and potential for invasion were evaluated by the classic wound-healing assay and a Boyden Chamber assay.

Results

Our results showed that both inhibitors had differential effects on the two cell lines, significantly reducing migration in the metastatic Y79 cell line and greatly affecting the viability of Weri-1 cells. The MMP-9 inhibitor (MMP9I) AG-L-66085, diminished the Y79 angiogenic response. In Weri-1 cells, VEGF was significantly reduced and cell viability was decreased by both MMP-2 and MMP-9 inhibitors. Furthermore, inhibition of MMP-2 significantly reduced secretion of TGF-β1 in both Rb models.

Conclusions

Collectively, our data indicates MMP-2 and MMP-9 drive metastatic pathways, including migration, viability and secretion of angiogenic factors in Rb cells. These two subtypes of matrix metalloproteinases represent new potential candidates for targeted anti-metastatic therapy for Rb.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3418-y) contains supplementary material, which is available to authorized users.

Establishment of a novel retinoblastoma (Rb) nude mouse model by intravitreal injection of human Rb Y79 cells - comparison of in vivo analysis versus histological follow up

Retinoblastoma (Rb) is the most frequent primary intraocular tumour in children and, if left untreated, can cause death. Preclinical animal models that mimic molecular, genetic, and cellular features of cancers are essential for studying cancer and searching for promising diagnosis and treatment modalities. There are several models described for Rb, but none of them fully meet our requirements. The aim of this study was to create a novel xenograft-nude mouse-model with broad application possibilities, which closely resembles the clinical observations of Rb patients and which could be used to investigate the development and spread of the tumour by using scanning laser ophthalmoscopy/optical coherence tomography (SLO/OCT) as well as histology methods. We injected human retinoblastoma Y79 cells intravitreally in both eyes of immune-deficient nude mice. The incidences of retinoblastoma as well as growth velocity were analysed 3, 6, 9 and 12 weeks after cell injection in vivo by SLO/OCT as well as ex vivo by electron microscopy (EM) and hematoxylin/eosin (HE) staining. Moreover, internal organs were histologically screened for potentially occurring metastases. Three weeks post-injection, animals developed a retinoblastoma, and after five weeks tumour growth resulted in swelling of the eyes in individual animals, showing a similar phenotype to that of untreated Rb patients at advanced stages of tumour-development. After 12 weeks, 67.5% of all analysed eyes (29 of 42) contained a retinoblastoma. At early stages of Rb development, the SLO/OCT analysis correlated with the histology results. If the tumours were too large, only histological investigations were feasible. The ultrastructural characteristics of the xenograft-tumours were very similar to those described for patient's tumours. In one mouse, brain metastases were observed. Our retinoblastoma mouse model closely resembles the human disease. SLO/OCT can be used for the detection of Rb at early stages of development and could be used for monitoring the success of future therapies.

Summary: We present a novel retinoblastoma nude xenograft mouse model which closely resembles the human disease and allows broad application possibilities and a comparison of in vivo and histological analysis.

Efficacy and safety of aflibercept in in vitro and in vivo models of retinoblastoma

Background

To evaluate the inhibitory effects of aflibercept on the growth and subretinal invasion of retinoblastoma.

Methods

Xenotransplantation and orthotopic mouse models were created by injecting Y-79 cells subcutaneously and intravitreally, respectively. After induction of retinoblastoma, animals were intraperitoneally injected with aflibercept (25 mg/kg body weight) or saline twice a week for 3 weeks. Tumor size was measured weekly and compared between the two groups. At 4 weeks, animals were sacrificed and an immunohistochemical examination was conducted to compare the microvascular density and degree of apoptosis between groups. In addition, the degree of choroidal invasion was also analyzed in the orthotopic xenotransplantation model. A co-culture system of Y-79 or WERI-Rb-1 cells and human umbilical vein endothelial cells (HUVECs) was used for in vitro experiments, and the anti-angiogenic effect of aflibercept was evaluated by analyzing cell numbers.

Results

In the Y-79 xenotransplantation model, aflibercept treatment significantly inhibited tumor growth at 4 weeks versus baseline compared with saline-injected mice (188.53 ± 118.53 mm³ vs. 747.87 ± 118.83 mm³, respectively, P < 0.001). Tumors isolated from aflibercept-treated mice contained fewer blood vessels (8.59 % ± 7.60 % vs. 14.91 % ± 4.53 %, respectively, P < 0.05) and an increased number of apoptotic cells (15.10 ± 9.13 vs. 4.44 ± 2.24, respectively, P < 0.05). In the orthotopic model, the degree of subretinal invasion of tumor cells was significantly reduced after aflibercept treatment (0.07 ± 0.06 vs. 0.15 ± 0.10, P < 0.05). And addition of aflibercept to co-cultures of HUVECs and Y-79, WERI-Rb-1 cells significantly reduced HUVEC proliferation.

Conclusions

Aflibercept reduced retinoblastoma angiogenesis in association with a significant reduction in tumor growth and invasion. These findings suggest that aflibercept could be used in an adjuvant role together with systemic chemotherapy to reduce tumor size and angiogenesis in retinoblastoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0451-7) contains supplementary material, which is available to authorized users.

Nucleolin-aptamer therapy in retinoblastoma: molecular changes and mass spectrometry-based imaging

Retinoblastoma (RB) is an intraocular childhood tumor which, if left untreated, leads to blindness and mortality. Nucleolin (NCL) protein which is differentially expressed on the tumor cell surface, binds ligands and regulates carcinogenesis and angiogenesis. We found that NCL is over expressed in RB tumor tissues and cell lines compared to normal retina. We studied the effect of nucleolin-aptamer (NCL-APT) to reduce proliferation in RB tumor cells. Aptamer treatment on the RB cell lines (Y79 and WERI-Rb1) led to significant inhibition of cell proliferation. Locked nucleic acid (LNA) modified NCL-APT administered subcutaneously (s.c.) near tumor or intraperitoneally (i.p.) in Y79 xenografted nude mice resulted in 26 and 65% of tumor growth inhibition, respectively. Downregulation of inhibitor of apoptosis proteins, tumor miRNA-18a, altered serum cytokines, and serum miRNA-18a levels were observed upon NCL-APT treatment. Desorption electrospray ionization mass spectrometry (DESI MS)-based imaging of cell lines and tumor tissues revealed changes in phosphatidylcholines levels upon treatment. Thus, our study provides proof of concept illustrating NCL-APT-based targeted therapeutic strategy and use of DESI MS-based lipid imaging in monitoring therapeutic responses in RB.

Preclinical platform of retinoblastoma xenografts recapitulating human disease and molecular markers of dissemination

Translational research in retinoblastoma - a pediatric tumor that originates during the development of the retina - would be improved by the creation of new patient-derived models. Using tumor samples from enucleated eyes we established a new battery of preclinical models that grow in vitro in serum-free medium and in vivo in immunodeficient mice. To examine whether the new xenografts recapitulate human disease and disseminate from the retina to the central nervous system, we evaluated their histology and the presence of molecular markers of dissemination that are used in the clinical setting to detect extraocular metastases. We evaluated GD2 synthase and CRX as such markers and generated a Taqman real-time quantitative PCR method to measure CRX mRNA for rapid, sensitive and specific quantification of local and metastatic tumor burden. This approach was able to detect 1 human retinoblastoma cell in 100.000 mouse brain cells. Our research adds novel preclinical tools for the discovery of new retinoblastoma treatments for clinical translation.

Lentivirus-Mediated Knockdown of Astrocyte Elevated Gene-1 Inhibits Growth and Induces Apoptosis through MAPK Pathways in Human Retinoblastoma Cells

Purpose

To explore expression and function of astrocyte elevated gene-1 (AEG-1) in human retinoblastoma (RB).

Methods

The expression of AEG-1 in histological sections of human RBs and in RB cell lines was examined using immunohistochemical staining and RT-PCR and Western blotting respectively. We knocked down AEG-1 gene levels by AEG-1-siRNA lentivirus transfection of human RB cell lines SO-RB50 and Y79, and using an MTT assay, we assessed the role of AEG-1 on RB cell proliferation. The biological significance of lentivirus transfection induced AEG-1 down-regulation was examined by assessing the apoptosis rate in the transfected RB cells by Annexin V-APC staining and flow cytometry. We additionally measured the expression of Bcl-2, Bax, cleaved-caspase-3 and caspase-3, and the phosphorylation and non-phosphorylation alternation of MAPKs.

Results

AEG-1 expression was detected to be strongly positive in the histological slides of 35 out of 54 (65%) patients with RB. AEG-1 expression increased significantly (P<0.05) with tumor stage. In the RB cell lines SO-RB50, Y79 and WERI-RB1 as compared with retinal pigment epithelium cells, expression of AEG-1 mRNA and AEG-1 protein was significantly higher. In AEG-1-siRNA lentivirus transfected cell cultures as compared with negative control lentivirus transfected cell cultures, levels of AEG-1 mRNA and of AEG-1 protein (P<0.05) and cell growth rates (P<0.01) were significantly lower, and apoptosis rate (P<0.001), Bax/Bcl-2 ratio and cleaved-caspase-3 protein level were significantly increased. The P-ERK/ERK ratio was significantly decreased in the AEG-1-siRNA lentivirus transfected cell lines.

Conclusions

Expression of AEG-1 was associated with RB, in histological slides of patients and in cell culture experiments. Lentivirus transfection induced knockdown of AEG-1 had a tumor suppressive effect, potentially by tumor cell apoptosis induction through inhibition of ERK.

Novel miRNA-31 and miRNA-200a-Mediated Regulation of Retinoblastoma Proliferation

Retinoblastoma is the most common intraocular tumor in children. Current management includes broad-based treatments such as chemotherapy, enucleation, laser therapy, or cryotherapy. However, therapies that target specific pathways important for retinoblastoma progression could provide valuable alternatives for treatment. MicroRNAs are short, noncoding RNA transcripts that can regulate the expression of target genes, and their aberrant expression often facilitates disease. The identification of post-transcriptional events that occur after the initiating genetic lesions could further define the rapidly aggressive growth displayed by retinoblastoma tumors. In this study, we used two phenotypically different retinoblastoma cell lines to elucidate the roles of miRNA-31 and miRNA-200a in tumor proliferation. Our approach confirmed that miRNAs-31 and -200a expression is significantly reduced in human retinoblastomas. Moreover, overexpression of these two miRNAs restricts the expansion of a highly proliferative cell line (Y79), but does not restrict the growth rate of a less aggressive cell line (Weri1). Gene expression profiling of miRNA-31 and/or miRNA-200a-overexpressing cells identified differentially expressed mRNAs associated with the divergent response of the two cell lines. This work has the potential to enhance the development of targeted therapeutic approaches for retinoblastoma and improve the efficacy of treatment.

Invasiveness and metastasis of retinoblastoma in an orthotopic zebrafish tumor model

Retinoblastoma is a highly invasive malignant tumor that often invades the brain and metastasizes to distal organs through the blood stream. Invasiveness and metastasis of retinoblastoma can occur at the early stage of tumor development. However, an optimal preclinical model to study retinoblastoma invasiveness and metastasis in relation to drug treatment has not been developed. Here, we developed an orthotopic zebrafish model in which retinoblastoma invasion and metastasis can be monitored at a single cell level. We took the advantages of immune privilege and transparent nature of developing zebrafish embryos. Intravitreal implantation of color-coded retinoblastoma cells allowed us to kinetically monitor tumor cell invasion and metastasis. Further, interactions between retinoblastoma cells and surrounding microvasculatures were studied using a transgenic zebrafish that exhibited green fluorescent signals in blood vessels. We discovered that tumor cells invaded neighboring tissues and blood stream when primary tumors were at the microscopic sizes. These findings demonstrate that retinoblastoma metastasis occurs at the early stage and antiangiogenic drugs such as Vegf morpholino and sunitinib could potentially interfere with tumor invasiveness and metastasis. Thus, this orthotopic retinoblastoma model offers a new and unique opportunity to study the early events of tumor invasion, metastasis and drug responses.

Establishment of an Orthotopic Xenograft Mice Model of Retinoblastoma Suitable for Preclinical Testing

Retinoblastoma is a rare cancer that occurs during childhood. The goal of current and future therapeutic strategies is to conserve the eye and visual function without using external beam radiotherapy, which is known to increase the risk of secondary cancers in genetically predisposed patients. Multimodality therapy (usually intravenous but also intra-arterial and intravitreal chemotherapy, transpupillary thermotherapy, cryotherapy, or brachytherapy) has recently improved the eye salvage rate in retinoblastoma and has led to a decreased need for external beam radiotherapy. However, the treatment of advanced intraocular retinoblastoma remains a real challenge, especially in cases of vitreous and subretinal seeding. There is a need for alternative and less toxic therapies as well as for better ways to administer the drugs. Animal models are an integral part of preclinical research in the field of oncology. This paper describes the different xenograft rodent models published in the literature so far. We will also describe a new orthotopic xenografted retinoblastoma model in immunodeficient mice, which is suitable for preclinical assays. The xenograft model was established from tumor tissue obtained directly from surgical samples and closely mimics human retinoblastoma.

Blocking the maturation of OncomiRNAs using pri-miRNA-17∼92 aptamer in retinoblastoma

The miR-17∼92. or oncomiR-1, cluster encodes oncogenic microRNAs (miRNAs), and it also promotes retinoblastoma (RB) tumor formation. Antagomir and miRNA mimics based approaches are widely tried against oncogenic and tumor suppressive miRNAs. Other methods for targeting cancer related miRNAs are still under development. In the current study, we focused on the pri-miRNA-17∼92 aptamer (pri-apt), which can potentially replace the mix of five antagomirs by one aptamer that function to abrogate the maturation of miR-17, miR-18a, and miR-19b (P<0.05) for targeting RB. We used RB cell lines WERI-Rb1 and Y79 as an in vitro model. Cellular changes upon transfecting the pri-apt led to S-phase arrest in WERI-Rb1 cells and onset of apoptosis in both Y79 and WERI-Rb1 cell lines. There was increased cytotoxicity as measured by lactate dehydrogenase activity in pri-apt treated Y79 cells (P<0.05), and significant inhibition of cell proliferation was observed in both of the cell lines. Thus we showed the antiproliferative property of pri-apt in RB cell lines, which can be readily modified by developing appropriate vectors for the delivery of the aptamer specifically to cancer cells.

EpCAM knockdown alters microRNA expression in retinoblastoma--functional implication of EpCAM regulated miRNA in tumor progression

The co-ordinated regulation of oncogenes along with miRNAs play crucial role in carcinogenesis. In retinoblastoma (RB), several miRNAs are known to be differentially expressed. Epithelial cell adhesion molecule (EpCAM) gene is involved in many epithelial cancers including, retinoblastoma (RB) tumorigenesis. EpCAM silencing effectively reduces the oncogenic miR-17-92 cluster. In order to investigate whether EpCAM has wider effect as an inducer or silencer of miRNAs, we performed a global microRNA expression profile in EpCAM siRNA knockdown Y79 cells. MicroRNA profiling in EpCAM silenced Y79 cells showed seventy-three significantly up regulated and thirty-six down regulated miRNAs. A subset of these miRNAs was also validated in tumors. Functional studies on Y79 and WERI-Rb-1 cells transfected with antagomirs against two miRNAs of miR-181c and miR-130b showed striking changes in tumor cell properties in RB cells. Treatment with anti-miR-181c and miR-130b showed significant decrease in cell viability and cell invasion. Increase in caspase-3 level was noticed in antagomir transfected cell lines indicating the induction of apoptosis. Possible genes altered by EpCAM influenced microRNAs were predicted by bioinformatic tools. Many of these belong to pathways implicated in cancer. The study shows significant influence of EpCAM on global microRNA expression. EpCAM regulated miR-181c and miR-130b may play significant roles in RB progression. EpCAM based targeted therapies may reduce carcinogenesis through several miRNAs and target genes.

MicroRNA-21 Down-regulates Rb1 Expression by Targeting PDCD4 in Retinoblastoma

Retinoblastoma (RB) is a children's ocular cancer caused by mutated retinoblastoma 1 (Rb1) gene on both alleles. Rb1 and other related genes could be regulated by microRNAs (miRNA) via complementarily pairing with their target sites. MicroRNA-21 (miR-21) possesses the oncogenic potential to target several tumor suppressor genes, including PDCD4, and regulates tumor progression and metastasis. However, the mechanism of how miR-21 regulates PDCD4 is poorly understood in RB. We investigated the expression of miRNAs in RB cell lines and identified that miR-21 is one of the most deregulated miRNAs in RB. Using qRT-PCR, we verified the expression level of several miRNAs identified by independent microarray assays, and analyzed miRNA expression patterns in three RB cell lines, including Weri-Rb1, Y79 and RB355. We found that miR-19b, -21, -26a, -195 and -222 were highly expressed in all three cell lines, suggesting their potential role in RB tumorigenesis. Using the TargetScan program, we identified a list of potential target genes of these miRNAs, of which PDCD4 is one the targets of miR-21. In this study, we focused on the regulatory mechanism of miR-21 on PDCD4 in RB. We demonstrated an inverse correlation between miR-21 and PDCD4 expression in Weri-Rb1 and Y79 cells. These data suggest that miR-21 down-regulates Rb1 by targeting PDCD4 tumor suppressor. Therefore, miR-21 could serve as a therapeutic target for retinoblastoma.

Animal models in retinoblastoma research

Advances in animal models of retinoblastoma have accelerated research in this field, aiding in understanding tumor progression and assessing therapeutic modalities. The distinct pattern of mutations and specific location of this unique intraocular tumor have paved the way for two types of models- those based on genetic mutations, and xenograft models. Retinoblastoma gene knockouts with an additional loss of p107, p130, p53 and using promoters of Nestin, Chx10, and Pax6 genes show histological phenotypic changes close to the human form of retinoblastoma. Conditional knockout in specific layers of the developing retina has thrown light on the origin of this tumor. The use of xenograft models has overcome the obstacle of time delay in the presentation of symptoms, which remains a crucial drawback of genetic models. With the advances in molecular and imaging technologies, the current research aims to develop models that mimic all the features of retinoblastoma inclusive of its initiation, progression and metastasis. The combination of genetic and xenograft models in retinoblastoma research has and will help to pave way for better understanding of retinoblastoma tumor biology and also in designing and testing effective diagnostic and treatment modalities.

The effect of imatinib mesylate on the proliferation, invasive ability, and radiosensitivity of retinoblastoma cell lines

PURPOSE

Our aim was to evaluate the potential effect of imatinib mesylate (IM), a small molecule that specifically inhibits the tyrosine quinase receptors, on the proliferation and invasive abilities of two human retinoblastoma (Rb) cell lines. Furthermore, the ability of IM to radiosensitize Rb cells was evaluated. The potential targets of IM (C-kit, PDGRF-α and -β, and c-Abl) were also investigated in these cell lines.

METHODS

Two human Rb cell lines (WERI-RB-1 and Y79) were cultured under normal growth conditions. An MTT-based proliferation assay and a Matrigel invasion assay were performed with and without exposure to 10 μM of IM. The cells were also irradiated with graded dosages of 0, 2, 4, 6, 8, and 10 Gy with and without IM and their proliferations rates were analyzed. Western blot and immunocytochemical analysis of cytospins were performed to evaluate the expression of C-kit, PDGRF-α and -β, and c-Abl.

RESULTS

When IM was added to both cell lines a statistically significant (P<0.05) reduction in proliferation and invasive ability were observed. Exposure to IM also significantly increased the radiosensitivity of both Rb cell lines. The c-Abl expression was strongly positive, PDGRF-α and -β expression were also positive but the C-kit expression was negative in both cell lines.

CONCLUSIONS

These results indicate that Gleevec may be useful as an adjuvant treatment in Rb patients, specially those considered for radiation therapy.

Molecular deregulation induced by silencing of the high mobility group protein A2 gene in retinoblastoma cells

AIM

To explore the molecular mechanisms deregulated by high mobility group protein A2 (HMGA2) gene silencing in retinoblastoma (RB) cells.

METHODS

Synthetic anti-HMGA2 short interfering RNA (siRNA) was used to silence the HMGA2 gene in cultured Y79 RB cells that were subjected to whole genome microarray analysis. The expression of differentially regulated key genes was confirmed with quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) in post-silenced RB cell lines (Y79 and WERI Rb1). These deregulated genes were compared for their constitutive expression in primary RB tumors (n=10). Zymographic determination of matrix metalloproteinase (MMP) activity was performed in RB cells. A cell cycle assay and a proliferation assay were performed in post-transfected RB cells.

RESULTS

HMGA2 gene silencing in cultured RB cells results in reduced cell proliferation and transition in the G1/S phase. The whole genome microarray analysis of HMGA2 silenced Y79 cells revealed overall upregulation of 1,132 genes (≥ 1.0 fold) and downregulation of 1,562 genes (≤ -1.0 fold). Specific quantitative pathway analysis of the deregulated genes (using Biointerpreter) revealed 150 upregulated genes and 77 downregulated genes (≥ 1.0 fold) involved in vital pathways, namely, mitogen-activated protein kinase, Janus kinase/signal transducers and activators of transcription, Ras pathway, Ras-induced extracellular signal-regulated protein kinases 1 and 2, and tumor protein p53. The differential expression of genes obtained from microarray analysis (Homo sapiens ELK1, member of ETS oncogene family [ELK1], Homo sapiens cyclin-dependent kinase 6 [CDK6], Homo sapiens E2F transcription factor 4, p107/p130-binding [E2F4], Homo sapiens G-2 and S-phase expressed 1 [GTSE1], Damage-regulated autophagy modulator [DRAM], Homo sapiens cadherin 1, type 1,E-cadherin (epithelial) [CDH1], Homo sapiens snail homolog 1 (Drosophila) [SNAI1], Homo sapiens matrix metallopeptidase 2 [MMP2], and Homo sapiens matrix metallopeptidase 9 [MMP9]) was confirmed with quantitative reverse-transcriptase polymerase chain reaction in post-silenced RB cells. Zymographic analysis revealed that the increase in MMP mRNA expression in the post-silenced RB cells did not correlate with corresponding enzyme activity.

CONCLUSIONS

Our study revealed molecular regulatory changes induced by HMGA2 silencing in RB cancer cells, offering mechanistic insights into the anticancer potential. HMGA2 may be considered a promising candidate for gene silencing therapy in RB.

Embryonic retinal tumors in SV40 T-Ag transgenic mice contain CD133+ tumor-initiating cells

PURPOSE

Human retinoblastomas form during the proliferative phase of retina development and are caused by mutations that result in absent or functionally defective Rb protein. Similar tumors occur in mice only when multiple Rb gene family members are absent. We asked if retinal tumors can arise from an undifferentiated retinal cell. The tumor-initiating cells isolated from these tumors that formed in early embryonic murine retinas were characterized.

METHODS

Transgenic mice were created using a Pax6 promoter to target expression of SV40 large T-antigen (T-Ag) in the undifferentiated murine embryonic retina. T-Ag, which sequesters all Rb family proteins and p53, is expressed in the retina and lens by murine embryonic day 10 (E10) and tumors are observed by E12.5. A cell line that is adherent in serum-containing media and forms neurospheres in supplemented serum-free media was developed from retinal tumors isolated on postnatal day 7.

RESULTS

In all, 1.5% of attached cells form neurospheres when transferred to serum-free medium. All cultured cells express T-Ag, confirming that they derive from the original tumors; 0.5% of adherent cells express detectable levels of CD133. CD133+ FACS-sorted cells cultured in serum-free medium form 3-fold more neurospheres than do CD133- cells. Six of seven mice injected with CD133+ cells and one of seven mice injected with CD133- cells formed tumors during a 6-month period. Unlike primary adherent cells, primary and secondary tumors heterogeneously express markers of stem cells and differentiation similar to human retinoblastoma.

CONCLUSIONS

CD133+ tumor-initiating cells can originate from proliferating undifferentiated precursor cells.

Establishment and propagation of human retinoblastoma tumors in immune deficient mice

Culturing retinoblastoma tumor cells in defined stem cell media gives rise to primary tumorspheres that can be grown and maintained for only a limited time. These cultured tumorspheres may exhibit markedly different cellular phenotypes when compared to the original tumors. Demonstration that cultured cells have the capability of forming new tumors is important to ensure that cultured cells model the biology of the original tumor.

Here we present a protocol for propagating human retinoblastoma tumors in vivo using Rag2^-/- immune deficient mice. Cultured human retinoblastoma tumorspheres of low passage or cells obtained from freshly harvested human retinoblastoma tumors injected directly into the vitreous cavity of murine eyes form tumors within 2-4 weeks. These tumors can be harvested and either further passaged into murine eyes in vivo or grown as tumorspheres in vitro. Propagation has been successfully carried out for at least three passages thus establishing a continuing source of human retinoblastoma tissue for further experimentation.

Wesley S. Bond and Lalita Wadhwa are co-first authors.

Rabbit model of retinoblastoma

We created a rabbit model of retinoblastoma and confirmed the tumor clinically and histopathologically. Seventeen New Zealand rabbits were immunosuppressed with cyclosporin A at doses of 10–15 mg/kg. At day 3, the animals received a 30 μl subretinal injection of 1 × 10⁶ cultured WERI retinoblastoma cells. Digital fundus images were captured before euthanasia, and the eyes were submitted for histopathology. Retinoblastoma cells grew in all the inoculated eyes and established a tumor under the retina and/or in the vitreous. New blood vessels in the tumor were observed starting at week 5. Cuffs of viable tumor cells surrounded the blood vessels with regions of necrosis present at 70–80 μm from nutrient vessels. Occasional tumor seeds in the vitreous histologically exhibited central necrosis. This rabbit model demonstrated similar fundus appearance and pathologic features to human retinoblastoma and may be used as a model to test various routes of drug delivery for retinoblastoma.

Toxicogenomics of nanoparticulate delivery of etoposide: potential impact on nanotechnology in retinoblastoma therapy

To develop a suitable formulation with high entrapment efficiency, etoposide-loaded poly(lactide-co-glycolide) nanoparticles (NPs) were formulated by single emulsion-solvent evaporation method by changing different formulation parameters such as drug loading, choice of organic solvent and percentage of emulsifier polyvinyl alcohol. The NPs showed higher entrapment efficiency, ~86% (with 15% (w/w) drug loading). The physicochemical parameters revealed smooth topology with size range (240–320 nm), a negative zeta potential (~19 mV) and in vitro sustained-release activity (~60% drug release in 40 days). Greater anti-proliferative activity ~100 times was observed with NPs (IC₅₀ = 0.002 μg/ml) than that of native etoposide (IC₅₀ = 0.2 μg/ml) in retinoblastoma cell line (Y-79). These NPs demonstrated greater (G1/S) blocking and decreased mitochondrial membrane potential as measured by flow cytometry. There was upregulation of apoptotic gene activity in NPs than native etoposide, as revealed through microarray analysis. However, this is the first ever report demonstrating the intricate modulation of genetic network affected by NPs. Collectively, these results suggest that etoposide-loaded NPs could be potentially useful as a novel drug delivery system for retinoblastoma in the future.

Figure

Function and expression of ATP-binding cassette transporters in cultured human Y79 retinoblastoma cells

The aim of this study was to reveal the expression and function of P-glycoprotein and multidrug resistance-associated proteins (MRP), members of the ATP-binding cassette (ABC) superfamily of drug transporters, in cultured human Y79 retinoblastoma cells. ABC transporter mRNA expression was evaluated by conventional reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR analyses. Cellular accumulation of rhodamine 123 (P-glycoprotein substrate), calcein (MRP substrate), and doxorubicin (P-glycoprotein/MRP substrate) was analyzed by fluorometry. Conventional RT-PCR analysis showed the expression of multidrug resistance 1 (MDR1), MRP1, MRP2 and lung resistance-related protein (LRP) mRNAs. Real-time RT-PCR analysis revealed that the expression levels of the MDR1 and MRP2 genes in Y79 cells were much lower than those in human intestinal cell line Caco-2, while the expression level of MRP1 was higher than that in Caco-2 cells. The accumulation of rhodamine 123 was not enhanced by verapamil or reversin 205, inhibitors of P-glycoprotein, indicating no function of P-glycoprotein in Y79 cells. The accumulation of calcein was significantly increased by various MRP inhibitors including probenecid, indicating that MRP functions in Y79 cells. The accumulation of doxorubicin was increased in the presence of metabolic inhibitors (10 mM 2-deoxyglucose and 5 mM sodium azide). However, most MRP inhibitors such as probenecid and indomethacin did not affect doxorubicin accumulation, while cyclosporin A and taclorimus significantly increased doxorubicin accumulation. These results suggest that MRP, but not P-glycoprotein, functions in Y79 cells, and that the efflux of doxorubicin from Y79 cells may be due to an ATP-dependent transporter, which has not been identified yet.

Genome-wide changes accompanying the knockdown of Ep-CAM in retinoblastoma

PURPOSE

Previously we showed that epithelial cell adhesion molecule (Ep-CAM), a cell surface molecule, was highly expressed in primary retinoblastoma tumors. In the present study, we studied the genes regulated by Ep-CAM in a retinoblastoma Y79 cell line in vitro using a combination of short interference RNA and microarray technology.

METHODS

Flow cytometry, quantitative reverse transcriptase PCR (Q-RT-PCR), and immunohistochemistry were performed to confirm the Ep-CAM re-expression in the Y79 cells treated with 5'-azacytidine (AZC). Ep-CAM expression in AZC-treated Y79 cells was silenced using synthetic anti-Ep-CAM short interference RNA, and whole genome microarray was performed to determine the gene expression changes post Ep-CAM knockdown. Ep-CAM inhibition was confirmed by Q-RT-PCR, western blotting, and immunofluorescence.

RESULTS

Ep-CAM expression was significantly restored in Y79 cells on day 5 of AZC treatment. Ep-CAM inhibition significantly affected Y79 cell proliferation. We identified 465 upregulated genes (>or=1.0 fold) and 205 downregulated genes (<or=0.5 fold) in response to knockdown of Ep-CAM. These genes regulate several aspects of tumor function, including cell survival/proliferation, DNA replication/transcription, apoptosis, and angiogenesis. Quantitative pathway analysis using Biointerpreter further revealed that the most pronounced effect of Ep-CAM knockdown was deregulation of pathways that include mitogen-activated protein kinase (MAP) kinase and tumor protein 53 (P53) pathways. Real-time Q-RT-PCR confirmed microarray gene expression changes for selected genes.

CONCLUSIONS

Ep-CAM silencing significantly decreases Y79 cell proliferation and revealed a wide network of deregulated pathways in vitro. Future studies targeting Ep-CAM gene expression in vivo will help to delineate the mechanisms associated with Ep-CAM gene function in neoplastic transformation and define the potential for Ep-CAM-based molecular intervention in retinoblastoma patients.

Lithium chloride regulates the proliferation of stem-like cells in retinoblastoma cell lines: a potential role for the canonical Wnt signaling pathway

PURPOSE

Cancer stem cells are found in many tumor types and are believed to lead to regrowth of tumor mass due to their chemoresistance and self-renewal capacity. We previously demonstrated small subpopulations of cells in retinoblastoma tissue and cell lines that display cancer stem cell-like activities, including expression of stem cell markers, Hoechst dye exclusion, slow cycling, and self-renewal ability. Identifying factors regulating stem cell proliferation will be important for selectively targeting stem cells and controlling tumor growth. Wingless and Int1 (Wnt) signaling is an essential cellular communication pathway that regulates proliferation and differentiation of non-neoplastic stem/progenitor cells in the retina and other tissues, but its role in cancer stem cells in the retinal tumor retinoblastoma is unknown. In this study, we investigated whether the Wnt pathway activator lithium chloride (LiCl) regulates proliferation of retinoblastoma cancer stem-like cells.

METHODS

The number of stem-like cells in Weri and Y79 retinoblastoma cell line cultures was measured by 5-bromo-2-deoxyuridine (BrdU) pulse-chase, immunohistochemistry, and quantitative polymerase chain reaction (PCR) for stem cell marker genes. The cell lines were sorted into stem-like and non-stem-like populations by fluorescence-activated cell sorting (FACS), using an antibody against the stem cell marker ATP-binding cassette, subfamily G, member 2 (ABCG2). Activated Wnt signaling was measured in the sorted cells by western blotting and immunolocalization of the central mediator beta-catenin.

RESULTS

LiCl increased the number of stem-like cells, measured by BrdU retention and elevated expression of the stem cell marker genes Nanog, octamer transcription factor 3 and 4 (Oct3/4), Musashi 1 (Msi1), and ABCG2. Sorted ABCG2-positive stem-like cells had higher levels of beta-catenin than ABCG2-negative non-stem cells, suggesting elevated canonical Wnt signaling. Furthermore, stem cell marker gene expression increased after small interfering RNA (siRNA) knock-down of the Wnt inhibitor secreted frizzled-related protein 2 (SFRP2).

CONCLUSIONS

These results indicate that the cancer stem-like cell population in retinoblastoma is regulated by canonical Wnt/beta-catenin signaling, which identifies the Wnt pathway as a potential mechanism for the control of stem cell renewal and tumor formation in retinoblastoma tumors in vivo.

Changes in retinoblastoma cell adhesion associated with optic nerve invasion

In the 1970s, several human retinoblastoma cell lines were developed from cultures of primary tumors. As the human retinoblastoma cell lines were established in culture, growth properties and changes in cell adhesion were described. Those changes correlated with the ability of the human retinoblastoma cell lines to invade the optic nerve and metastasize in orthotopic xenograft studies. However, the mechanisms that underlie these changes were not determined. We used the recently developed knockout mouse models of retinoblastoma to begin to characterize the molecular, cellular, and genetic changes associated with retinoblastoma tumor progression and optic nerve invasion. Here we report the isolation and characterization of the first mouse retinoblastoma cell lines with targeted deletions of the Rb family. Our detailed analysis of these cells as they were propagated in culture from the primary tumor shows that changes in cadherin-mediated cell adhesion are associated with retinoblastoma invasion of the optic nerve prior to metastasis. In addition, the same changes in cadherin-mediated cell adhesion correlate with the invasive properties of the human retinoblastoma cell lines isolated decades ago, providing a molecular mechanism for these earlier observations. Most importantly, our studies are in agreement with genetic studies on human retinoblastomas, suggesting that changes in this pathway are involved in tumor progression.

AAV-mediated local delivery of interferon-beta for the treatment of retinoblastoma in preclinical models

Interferon-beta (IFN-beta) has been found to have anti-tumor properties against a variety of malignancies through different mechanisms. However, clinical trials involving systemic administration of IFN-beta have been hampered by secondary toxicity and the short half-life of IFN-beta in the circulation. In order to circumvent these limitations, we have developed an adeno-associated viral (AAV) vector gene-therapy approach to deliver IFN-beta to tumors. In this study, we tested the efficacy of AAV-mediated local delivery of IFN-beta for the treatment of retinoblastoma in preclinical models. Retinoblastoma is an ideal candidate for gene-therapy-based anti-cancer treatment because target cell transduction and, therefore, IFN-beta delivery can be contained within the ocular environment, thereby minimizing systemic toxicity. We report here that retinoblastoma cell lines exhibit pleiotropic responses to IFN-beta consistent with previous studies on a variety of tumor cell lines. Intravitreal injection of AAV-IFN-beta resulted in efficient retinal infection and sustained IFN-beta production in the eye with minimal systemic exposure. Vector spread outside of the eye was not detected. Using our orthotopic xenograft model of retinoblastoma, we found that intravitreal injection of AAV-IFN-beta had a potent anti-tumor effect in vivo. These data suggest that AAV-mediated delivery of IFN-beta may provide a complementary approach to systemic chemotherapy which is the standard of care for retinoblastoma around the world.

Basic fibroblast growth factor impact on retinoblastoma progression and survival

PURPOSE

Chemotherapy resistance is a problem in the treatment of advanced retinoblastoma (RB). Since basic fibroblast growth factor (bFGF) is a survival factor for neural precursor cells, bFGF was evaluated as a growth and chemoresistance factor in RB.

METHODS

bFGF expression was analyzed in the LH-betaTag transgenic mouse model of RB and human RB cell lines by immunofluorescence, RT-PCR, and Western blot. Proliferation and apoptosis (TUNEL) assays were performed.

RESULTS

bFGF levels significantly increased during tumorigenesis in transgenic RB, as a function of tumor status (P = 0.005). PCR and confocal microscopy confirmed that the human cell lines and primary tumors expressed bFGF. bFGF was localized to vascular and tumor cells and rarely to glial cells. Exogenous 18-kDa bFGF induced proliferation in two RB cell lines (WERI and Y79). Western blot analysis demonstrated 34-, 22-, and 18-kDa isoforms in transgenic RB and both cell lines. In TUNEL assays, chemoresistance to carboplatin-induced apoptosis was observed in the Y79 line, which expressed a higher ratio of high (34 kDa)- to low-molecular-weight bFGF isoforms, compared with the WERI line. Similar to other bFGF tumor studies, exogenous low-molecular-weight (18 kDa) bFGF (1 ng) significantly enhanced carboplatin-induced apoptosis in the more chemosensitive WERI, but not the chemoresistant Y79 line.

CONCLUSIONS

RB tumors produce significant amounts of bFGF, and the differential production and response to isoforms of bFGF may have implications for invasive tumor growth and chemoresistance.

Rescue of sight by gene therapy - closer than it may appear

This review will cover the state of the field in retinal degeneration and gene therapy with a focus on the great strides that have been made in retina gene therapy. Topics ranging from the development of animal models to clinical trials (for the treatment of Leber congenital amaurosis, age-related macular degeneration, and retinoblastoma) will be discussed. In addition, the results of gene therapy studies targeting the photoreceptors will be presented. Finally, strategies and progress in overcoming the challenges of photoreceptor-directed gene therapy will be presented.