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

Targeting GPC2 on Intraocular and CNS Metastatic Retinoblastomas with Local and Systemic Delivery of CAR T Cells

PURPOSE

Retinoblastoma is the most common intraocular malignancy in children. Although new chemotherapeutic approaches have improved ocular salvage rates, novel therapies are required for patients with refractory intraocular and metastatic disease. Chimeric antigen receptor (CAR) T cells targeting glypican-2 (GPC2) are a potential new therapeutic strategy.

EXPERIMENTAL DESIGN

GPC2 expression and its regulation by the E2F1 transcription factor were studied in retinoblastoma patient samples and cellular models. In vitro, we performed functional studies comparing GPC2 CAR T cells with different costimulatory domains (4-1BB and CD28). In vivo, the efficacy of local and systemic administration of GPC2 CAR T cells was evaluated in intraocular and leptomeningeal human retinoblastoma xenograft models.

RESULTS

Retinoblastoma tumors, but not healthy retinal tissues, expressed cell surface GPC2, and this tumor-specific expression was driven by E2F1. GPC2-directed CARs with 4-1BB costimulation (GPC2.BBz) were superior to CARs with CD28 stimulatory domains (GPC2.28z), efficiently inducing retinoblastoma cell cytotoxicity and enhancing T-cell proliferation and polyfunctionality. In vivo, GPC2.BBz CARs had enhanced persistence, which led to significant tumor regression compared with either control CD19 or GPC2.28z CARs. In intraocular models, GPC2.BBz CAR T cells efficiently trafficked to tumor-bearing eyes after intravitreal or systemic infusions, significantly prolonging ocular survival. In central nervous system (CNS) retinoblastoma models, intraventricular or systemically administered GPC2.BBz CAR T cells were activated in retinoblastoma-involved CNS tissues, resulting in robust tumor regression with substantially extended overall mouse survival.

CONCLUSIONS

GPC2-directed CAR T cells are effective against intraocular and CNS metastatic retinoblastomas.

Histone Deacetylases in Retinoblastoma

Retinoblastoma, a pediatric ocular malignancy, presents significant challenges in comprehending its molecular underpinnings and targeted therapeutic approaches. The dysregulated activity of histone deacetylases (HDACs) has been associated with retinoblastoma pathogenesis, influencing critical cellular processes like cell cycle regulation or retinal ganglion cell apoptosis. Through their deacetylase activity, HDACs exert control over key tumor suppressors and oncogenes, influencing the delicate equilibrium between proliferation and cell death. Furthermore, the interplay between HDACs and the retinoblastoma protein pathway, a pivotal aspect of retinoblastoma etiology, reveals a complex network of interactions influencing the tumor microenvironment. The examination of HDAC inhibitors, encompassing both established and novel compounds, offers insights into potential approaches to restore acetylation balance and impede retinoblastoma progression. Moreover, the identification of specific HDAC isoforms exhibiting varying expression in retinoblastoma provides avenues for personalized therapeutic strategies, allowing for interventions tailored to individual patient profiles. This review focuses on the intricate interrelationship between HDACs and retinoblastoma, shedding light on epigenetic mechanisms that control tumor development and progression. The exploration of HDAC-targeted therapies underscores the potential for innovative treatment modalities in the pursuit of more efficacious and personalized management strategies for this disease.

Translational screening platform to evaluate chemotherapy in combination with focal therapy for retinoblastoma

Retinoblastoma is the most common pediatric eye cancer. It is currently treated with a limited number of drugs, adapted from other pediatric cancer treatments. Drug toxicity and relapse of the disease warrant new therapeutic strategies for these young patients. In this study, we developed a robust tumoroid-based platform to test chemotherapeutic agents in combination with focal therapy (thermotherapy) - a treatment option widely used in clinical practice - in accordance with clinically relevant trial protocols. The model consists of matrix-embedded tumoroids that retain retinoblastoma features and respond to repeated chemotherapeutic drug exposure similarly to advanced clinical cases. Moreover, the screening platform includes a diode laser (810 nm, 0.3 W) to selectively heat the tumoroids, combined with an on-line system to monitor the intratumoral and surrounding temperatures. This allows the reproduction of the clinical settings of thermotherapy and combined chemothermotherapy treatments. When testing the two main drugs currently used in clinics to treat retinoblastoma in our model, we observed results similar to those clinically obtained, validating the utility of the model. This screening platform is the first system to accurately reproduce clinically relevant treatment methods and should lead to the identification of more efficient drugs to treat 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.

Emerging therapeutic targets for retinoblastoma

INTRODUCTION

Retinoblastoma (Rb) is an early childhood intraocular tumor of the retina and is managed by multimodal therapeutic approaches. Recent advanced targeted delivery of chemotherapeutic drugs to the eye has improved the possibility of globe salvage. However, enucleation is inevitable for advanced and recurrent Rb. The cumulative knowledge of identification of newer molecular biology tools, exosomal cargo, role of cancer stem cells (CSCs), and its microenvironment in the progression of the diseases warrants a relook at the traditional treatment protocol and explore the feasibility of targeted therapies.

AREAS COVERED

This review covers Rb pathobiology, novel molecular-targeted therapeutics, and strategies targeting Rb CSCs and provides an update on potential therapeutic targets such as second messengers and exosomal cargo.

EXPERT OPINION

The emergence of early diagnosis and multimodality treatment protocols have significantly improved the clinical outcome of children with advanced Rb; however, the problem of tumor recurrence has not yet been overcome. Improved understanding of the molecular pathways, identification, and characterization of CSCs opens up new targeted therapy approaches. The contemporary evidence from other fields shows promising evidence that combining conservative treatment modalities with targeting therapies specific for CSCs in clinical practice is essential for achieving high globe salvage rate in Rb patients.

Follow-up of intraocular retinoblastoma through the quantitative analysis of conserved nuclear DNA sequences in aqueous humor from patients

Fundoscopy is the standard method for diagnosis and follow-up of intraocular retinoblastoma, but it is sometimes insufficient to discern whether tumors are inactivated following treatments. In this work, we hypothesized that the amount of conserved nuclear DNA sequences in the cell-free DNA (cfDNA) fraction of the aqueous humor (AH) might complement fundoscopy for retinoblastoma follow-up. To address our hypothesis, we developed highly sensitive droplet digital polymerase chain reaction (ddPCR) methods to quantify highly conserved DNA sequences of nucleus-encoded genes (GAPDH and B4GALNT1) and of a mitochondrial gene, MT-ATP6. We obtained AH samples during intravitreal treatments. We analyzed 42 AH samples from 25 patients with intraocular retinoblastoma and 11 AH from controls (non-cancer patients). According to clinical criteria, we grouped patients as having progression-free or progressive retinoblastoma. cfDNA concentration in the AH was similar in both retinoblastoma groups. Copy counts for nucleus-derived sequences of GAPDH and B4GALNT1 were significantly higher in the AH from patients with progressive disease, compared to the AH from progression-free patients and control non-cancer patients. The presence of mitochondrial DNA in the AH explained that both retinoblastoma groups had similar cfDNA concentration in AH. The optimal cut-off point for discriminating between progressive and progression-free retinoblastomas was 108 GAPDH copies per reaction. Among patients having serial AH samples analyzed during their intravitreal chemotherapy, GAPDH copies were high and decreased below the cut-off point in those patients responding to chemotherapy. In contrast, one non-responder patient remained with values above the cut-off during follow-up, until enucleation. We conclude that the measurement of conserved nuclear gene sequences in AH allows follow-up of intraocular retinoblastoma during intravitreal treatment. The method is applicable to all patients and could be relevant for those in which fundoscopy evaluation is inconclusive.

Nanotechnology for Pediatric Retinoblastoma Therapy

Retinoblastoma is a rare, sometimes hereditary, pediatric cancer. In high-income countries this disease has a survival rate approaching 100%, while in low- and middle-income countries the prognosis is fatal for about 80% of cases. Depending on the stage of the disease, different therapeutic protocols are applied. In more advanced forms of the disease, surgical removal of the entire globe and its intraocular contents (enucleation) is, unfortunately, necessary, whereas in other cases, conventional chemotherapy is normally used. To overcome the side-effects and reduced efficacy of traditional chemotherapic drugs, nanodelivery systems that ensure a sustained drug release and manage to reach the target site have more recently been developed. This review takes into account the current use and advances of nanomedicine in the treatment of retinoblastoma and discusses nanoparticulate formulations that contain conventional drugs and natural products. In addition, future developments in retinoblastoma treatment are discussed.

Treatment of Retinoblastoma: What Is the Latest and What Is the Future

The management of retinoblastoma, the most common intraocular malignancy in children, has changed drastically over the last decade. Landmark developments in local drug delivery, namely, safer techniques for intravitreal chemotherapy injection and ophthalmic artery chemosurgery, have resulted in eye globe salvages that were not previously attainable using systemic chemotherapy or external beam irradiation. Novel drugs, oncolytic viruses, and immunotherapy are promising approaches in the treatment of intraocular retinoblastoma. Importantly, emerging studies of the pattern of tumor dissemination and local drug delivery may provide the first steps toward new treatments for metastatic disease. Here, we review recent advances in retinoblastoma treatment, especially with regard to local drug delivery, that have enabled successful conservative management of intraocular retinoblastoma. We also review emerging data from preclinical and clinical studies on innovative approaches that promise to lead to further improvement in outcomes, namely, the mechanisms and potential uses of new and repurposed drugs and non-chemotherapy treatments, and discuss future directions for therapeutic development.

SPARC-mediated long-term retention of nab-paclitaxel in pediatric sarcomas

Secreted protein acidic and rich in cysteine (SPARC) is a matricellular glycoprotein overexpressed by several cancers. Because SPARC shows high binding affinity to albumin, we reasoned that pediatric sarcoma xenografts expressing SPARC would show enhanced uptake and accumulation of nanoparticle albumin-bound (nab)-paclitaxel, a potent anticancer drug formulation. We first evaluated the expression of SPARC in patient-derived xenografts (PDXs) of Ewing sarcoma, rhabdomyosarcoma and osteosarcoma, finding variable SPARC gene expression that correlated well with SPARC protein measured by immunoblotting. We revealed that the activity of the fusion gene chimera EWSR1-FLI1, the genetic driver of Ewing sarcoma, leads to lower expression of the gene SPARC in these tumors, likely due to enriched acetylation marks of the histone H3 lysine 27 at regions including the SPARC promoter and potential enhancers. Then, we used SPARC-edited Ewing sarcoma cells (A673 line) to demonstrate that SPARC knocked down (KD) cells accumulated significantly less amount of nab-paclitaxel in vitro than SPARC wild type (WT) cells. In vivo, SPARC KD and SPARC WT subcutaneous xenografts in mice achieved similar maximum intratumoral concentrations of nab-paclitaxel, though drug clearance from SPARC WT tumors was significantly slower. We confirmed such SPARC-mediated long-term intratumoral accumulation of nab-paclitaxel in Ewing sarcoma PDX with high expression of SPARC, which accumulated significantly more nab-paclitaxel than SPARC-low PDX. SPARC-high PDX responded better to nab-paclitaxel than SPARC-low tumors, although these results should be taken cautiously, given that the PDXs were established from different patients that could have specific determinants predisposing response to paclitaxel. In addition, SPARC KD Ewing sarcoma xenografts responded better to soluble docetaxel and paclitaxel than to nab-paclitaxel, while SPARC WT ones showed similar response to soluble and albumin-carried drugs. Overall, our results show that pediatric sarcomas expressing SPARC accumulate nab-paclitaxel for longer periods of time, which could have clinical implications for chemotherapy efficacy.

A decision process for drug discovery in retinoblastoma

Intraocular retinoblastoma treatment has changed radically over the last decade, leading to a notable improvement in ocular survival. However, eyes that relapse remain difficult to treat, as few alternative active drugs are available. More challenging is the scenario of central nervous system (CNS) metastasis, in which almost no advancements have been made. Both clinical scenarios represent an urgent need for new drugs. Using an integrated multidisciplinary approach, we developed a decision process for prioritizing drug selection for local (intravitreal [IVi], intrathecal/intraventricular [IT/IVt]), systemic, or intra-arterial chemotherapy (IAC) treatment by means of high-throughput pharmacological screening of primary cells from two patients with intraocular tumor and CNS metastasis and a thorough database search to identify clinical and biopharmaceutical data. This process identified 169 compounds to be cytotoxic; only 8 are FDA-approved, lack serious toxicities and available for IVi administration. Four of these agents could also be delivered by IT/IVt. Twelve FDA-approved drugs were identified for systemic delivery as they are able to cross the blood-brain barrier and lack serious adverse events; four drugs are of oral usage and six compounds that lack vesicant or neurotoxicity could be delivered by IAC. We also identified promising compounds in preliminary phases of drug development including inhibitors of survivin, antiapoptotic Bcl-2 family proteins, methyltransferase, and kinesin proteins. This systematic approach may be applied more broadly to prioritize drugs to be repurposed or to identify novel hits for use in retinoblastoma treatment.

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.

Retinoblastoma: Etiology, Modeling, and Treatment

Retinoblastoma is a retinal cancer that is initiated in response to biallelic loss of RB1 in almost all cases, together with other genetic/epigenetic changes culminating in the development of cancer. RB1 deficiency makes the retinoblastoma cell-of-origin extremely susceptible to cancerous transformation, and the tumor cell-of-origin appears to depend on the developmental stage and species. These are important to establish reliable preclinical models to study the disease and develop therapies. Although retinoblastoma is the most curable pediatric cancer with a high survival rate, advanced tumors limit globe salvage and are often associated with high-risk histopathological features predictive of dissemination. The advent of chemotherapy has improved treatment outcomes, which is effective for globe preservation with new routes of targeted drug delivery. However, molecularly targeted therapeutics with more effectiveness and less toxicity are needed. Here, we review the current knowledge concerning retinoblastoma genesis with particular attention to the genomic and transcriptomic landscapes with correlations to clinicopathological characteristics, as well as the retinoblastoma cell-of-origin and current disease models. We further discuss current treatments, clinicopathological correlations, which assist in guiding treatment and may facilitate globe preservation, and finally we discuss targeted therapeutics for future treatments.

Proteomic Profiling of Retinoblastoma-Derived Exosomes Reveals Potential Biomarkers of Vitreous Seeding

Retinoblastoma (RB) is the most common tumor of the eye in early childhood. Although recent advances in conservative treatment have greatly improved the visual outcome, local tumor control remains difficult in the presence of massive vitreous seeding. Traditional biopsy has long been considered unsafe in RB, due to the risk of extraocular spread. Thus, the identification of new biomarkers is crucial to design safer diagnostic and more effective therapeutic approaches. Exosomes, membrane-derived nanovesicles that are secreted abundantly by aggressive tumor cells and that can be isolated from several biological fluids, represent an interesting alternative for the detection of tumor-associated biomarkers. In this study, we defined the protein signature of exosomes released by RB tumors (RBT) and vitreous seeding (RBVS) primary cell lines by high resolution mass spectrometry. A total of 5666 proteins were identified. Among these, 5223 and 3637 were expressed in exosomes RBT and one RBVS group, respectively. Gene enrichment analysis of exclusively and differentially expressed proteins and network analysis identified in RBVS exosomes upregulated proteins specifically related to invasion and metastasis, such as proteins involved in extracellular matrix (ECM) remodeling and interaction, resistance to anoikis and the metabolism/catabolism of glucose and amino acids.

Therapeutic targeting of the RB1 pathway in retinoblastoma with the oncolytic adenovirus VCN-01

Retinoblastoma is a pediatric solid tumor of the retina activated upon homozygous inactivation of the tumor suppressor RB1 VCN-01 is an oncolytic adenovirus designed to replicate selectively in tumor cells with high abundance of free E2F-1, a consequence of a dysfunctional RB1 pathway. Thus, we reasoned that VCN-01 could provide targeted therapeutic activity against even chemoresistant retinoblastoma. In vitro, VCN-01 effectively killed patient-derived retinoblastoma models. In mice, intravitreous administration of VCN-01 in retinoblastoma xenografts induced tumor necrosis, improved ocular survival compared with standard-of-care chemotherapy, and prevented micrometastatic dissemination into the brain. In juvenile immunocompetent rabbits, VCN-01 did not replicate in retinas, induced minor local side effects, and only leaked slightly and for a short time into the blood. Initial phase 1 data in patients showed the feasibility of the administration of intravitreous VCN-01 and resulted in antitumor activity in retinoblastoma vitreous seeds and evidence of viral replication markers in tumor cells. The treatment caused local vitreous inflammation but no systemic complications. Thus, oncolytic adenoviruses targeting RB1 might provide a tumor-selective and chemotherapy-independent treatment option for retinoblastoma.

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.

Tridimensional Retinoblastoma Cultures as Vitreous Seeds Models for Live-Cell Imaging of Chemotherapy Penetration

A preclinical model could aid in understanding retinoblastoma vitreous seeds behavior, drug penetration, and response to chemotherapy to optimize patient treatment. Our aim was to develop a tridimensional in vitro model of retinoblastoma vitreous seeds to assess chemotherapy penetration by means of live-cell imaging. Cell cultures from patients with retinoblastoma who underwent upfront enucleation were established and thoroughly characterized for authentication of human tumor origin. The correlation of the in vitro tridimensional structures resembling human spheres and dusts vitreous seeds was established. Confocal microscopy was used to quantify real-time fluorescence of topotecan as a measure of its penetration into different sizes of spheres. Cell viability was determined after chemotherapy penetration. The in vitro spheres and dusts models were able to recapitulate the morphology, phenotype, and genotype of patient vitreous seeds. The larger the size of the spheres, the longer the time required for the drug to fully penetrate into the core (p < 0.05). Importantly, topotecan penetration correlated with its cytotoxic activity. Therefore, the studied tridimensional cell model recapitulated several characteristics of vitreous seeds observed in patients with retinoblastoma and were successfully used to assess live-cell imaging of chemotherapy penetration for drug distribution studies.

Comprehensive characterization of RB1 mutant and MYCN amplified retinoblastoma cell lines

In retinoblastoma research tumor-derived cell lines remain an important model to investigate tumorigenesis and new therapy options, due to limited tumor material and lack of adequate animal models. A panel of 10 retinoblastoma cell lines was characterized with respect to mutation, methylation and expression of RB1 and MYCN. These established retinoblastoma cell lines represent the most frequent types of RB1 inactivation and together with the MYCN amplification status, three classes can be distinguished: RB1^mut/MYCN^nonA, RB1^mut/MYCN^A and RB1^wt/MYCN^A. MYCN amplification was identified in five cell lines, whereby two of them, RB522 and RB3823, harbor no aberration in RB1. Targeted sequencing of 160 genes often mutated in cancer identified only few variants in tumor-associated genes other than in RB1. None of these variants was recurrent. mRNA expression analyses of retinal markers, cell cycle regulators and members of the TP53 signaling pathway revealed a high variability between cell lines but no class-specific differences. The here presented thorough validation of retinoblastoma cell lines, including microsatellite analysis for cell line authentication, provides the basis for further in vitro studies on retinoblastoma.

ACVR1C/SMAD2 signaling promotes invasion and growth in retinoblastoma

Retinoblastoma is the most common intraocular cancer in children. While the primary tumor can often be treated by local or systemic chemotherapy, metastatic dissemination is generally resistant to therapy and remains a leading cause of pediatric cancer death in much of the world. In order to identify new therapeutic targets in aggressive tumors, we sequenced RNA transcripts in five snap frozen retinoblastomas which invaded the optic nerve and five which did not. A three-fold increase was noted in mRNA levels of ACVR1C/ALK7, a type I receptor of the TGF-β family, in invasive retinoblastomas, while downregulation of DACT2 and LEFTY2, negative modulators of the ACVR1C signaling, was observed in most invasive tumors. A two- to three-fold increase in ACVR1C mRNA was also found in invasive WERI Rb1 and Y79 cells as compared to non-invasive cells in vitro. Transcripts of ACVR1C receptor and its ligands (Nodal, Activin A/B, and GDF3) were expressed in six retinoblastoma lines, and evidence of downstream SMAD2 signaling was present in all these lines. Pharmacological inhibition of ACVR1C signaling using SB505124, or genetic downregulation of the receptor using shRNA potently suppressed invasion, growth, survival, and reduced the protein levels of the mesenchymal markers ZEB1 and Snail. The inhibitory effects on invasion, growth, and proliferation were recapitulated by knocking down SMAD2, but not SMAD3. Finally, in an orthotopic zebrafish model of retinoblastoma, a 55% decrease in tumor spread was noted (p=0.0026) when larvae were treated with 3 μM of SB505124, as compared to DMSO. Similarly, knockdown of ACVR1C in injected tumor cells using shRNA also resulted in a 54% reduction in tumor dissemination in the zebrafish eye as compared to scrambled shRNA control (p=0.0005). Our data support a role for the ACVR1C/SMAD2 pathway in promoting invasion and growth of retinoblastoma.

Assessment of retinoblastoma RNA reflux after intravitreal injection of melphalan

Background

Intravitreal injection of chemotherapy in retinoblastoma eyes with vitreous seeds may lead to a risk of extraocular tumour dissemination that has not been assessed so far.

Aims

To develop a sensitive and clinically feasible technique to assess for potential retinoblastoma cell reflux after intravitreal injection of melphalan.

Methods

Filter papers were cut in 6 mm diameter circles and sterilised before use. Eyes with retinoblastoma vitreous seeds (group D, International Classification) received weekly intravitreal melphalan injections (20 µg or 30 µg/dose) followed by cryotherapy as part of local treatment. Immediately after finishing the injection and cryotherapy, filter papers were placed on the injection site and on the cryoprobe tip to assess for the expression of the cone-rod homeobox gene (CRX) by real-time qPCR as a surrogate of retinoblastoma RNA. The assay was developed and validated to determine sensitivity, linearity, recovery, repeatability and reproducibility.

Results

The assay for quantitation of CRX expression was linear in the range of 1 to 1000 cells. The lowest limit of detection was one retinoblastoma cell and allowed to recover 100% of the cell load in external supplementation. A total of 14 eyes received 22 cycles of intravitreal melphalan and were evaluated for potential extraocular tumour cell dissemination using the developed technique. None of the cycles were positive for CRX in samples from the scar or from the cryoprobe tip.

Conclusions

A sensitive and simple method of tumour cell assessment has been developed that can be used in the clinics to assess for potential extraocular dissemination after intravitreal injections to assure its performance.

Targeted drug distribution in tumor extracellular fluid of GD2-expressing neuroblastoma patient-derived xenografts using SN-38-loaded nanoparticles conjugated to the monoclonal antibody 3F8

Neuroblastoma is a pediatric solid tumor with high expression of the tumor associated antigen disialoganglioside GD2. Despite initial response to induction therapy, nearly 50% of high-risk neuroblastomas recur because of chemoresistance. Here we encapsulated the topoisomerase-I inhibitor SN-38 in polymeric nanoparticles (NPs) surface-decorated with the anti-GD2 mouse mAb 3F8 at a mean density of seven antibody molecules per NP. The accumulation of drug-loaded NPs targeted with 3F8 versus with control antibody was monitored by microdialysis in patient-derived GD2-expressing neuroblastoma xenografts. We showed that the extent of tumor penetration by SN-38 was significantly higher in mice receiving the targeted nano-drug delivery system when compared to non-targeted system or free drug. This selective penetration of the tumor extracellular fluid translated into a strong anti-tumor effect prolonging survival of mice bearing GD2-high neuroblastomas in vivo.

Schedule-Dependent Antiangiogenic and Cytotoxic Effects of Chemotherapy on Vascular Endothelial and Retinoblastoma Cells

Current treatment of retinoblastoma involves using the maximum dose of chemotherapy that induces tumor control and is tolerated by patients. The impact of dose and schedule on the cytotoxicity of chemotherapy has not been studied. Our aim was to gain insight into the cytotoxic and antiangiogenic effect of the treatment scheme of chemotherapy used in retinoblastoma by means of different in vitro models and to evaluate potential effects on multi-drug resistance proteins. Two commercial and two patient-derived retinoblastoma cell types and two human vascular endothelial cell types were exposed to increasing concentrations of melphalan or topotecan in a conventional (single exposure) or metronomic (7-day continuous exposure) treatment scheme. The concentration of chemotherapy causing a 50% decrease in cell proliferation (IC50) was determined by MTT and induction of apoptosis was evaluated by flow cytometry. Expression of ABCB1, ABCG2 and ABCC1 after conventional or metronomic treatments was assessed by RT-qPCR. We also evaluated the in vivo response to conventional (0.6 mg/kg once a week for 2 weeks) and metronomic (5 days a week for 2 weeks) topotecan in a retinoblastoma xenograft model. Melphalan and topotecan were cytotoxic to both retinoblastoma and endothelial cells after conventional and metronomic treatments. A significant decrease in the IC50 (median, 13-fold; range: 3–23) was observed following metronomic chemotherapy treatment in retinoblastoma and endothelial cell types compared to conventional treatment (p<0.05). Metronomic topotecan or melphalan significantly inhibited in vitro tube formation in HUVEC and EPC compared to vehicle-treated cells (p<0.05). Both treatment schemes induced apoptosis and/or necrosis in all cell models. No significant difference was observed in the expression of ABCB1, ABCC1 or ABCG2 when comparing cells treated with melphalan or topotecan between treatment schedules at the IC50 or with control cells (p>0.05). In mice, continuous topotecan lead to significantly lower tumor volumes compared to conventional treatment after 14 days of treatment (p<0.05). Continuous exposure to melphalan or topotecan increased the chemosensitivity of retinoblastoma and endothelial cells to both chemotherapy agents with lower IC50 values compared to short-term treatment. These findings were validated in an in vivo model. None of the dosing modalities induced multidrug resistance mechanisms while apoptosis was the mechanism of cell death after both treatment schedules. Metronomic chemotherapy may be a valid option for retinoblastoma treatment allowing reductions of the daily dose.