Rb suppresses human cone-precursor-derived retinoblastoma tumours

Investigating druggable kinases for targeted therapy in retinoblastoma

Retinoblastoma (RB) is a childhood retinal neoplasm and commonly treated with cytotoxic chemotherapeutic agents. However, these therapeutic approaches often lead to diverse adverse effects. A precise molecular therapy will alleviate these side effects and offer better treatment outcomes. Over the years, kinases have become potential drug targets in cancer therapy. Hence, we aimed to investigate genetic alterations of putative kinase drug targets in RB. Targeted exome sequencing was performed on 35 RB tumors with paired blood samples using a gene panel consisting of 29 FDA-approved kinase genes. Single nucleotide variants were analyzed for pathogenicity using an in-house pipeline and copy number variations (CNVs) were detected by a depth of coverage and CNVPanelizer. The correlation between genetic changes and clinicopathological features was assessed using GraphPad Prism. Three somatic mutations, two in ERBB4 and one in EGFR were identified. Two of these mutations (ERBB4 c.C3836A & EGFR c.A1196T) were not reported earlier. CNV analysis revealed recurrent gains of ALK, MAP2K2, SRC, STK11, and FGFR3 as well as frequent losses of ATM, PI3KCA and ERBB4. Notably, nonresponsive tumors had a higher incidence of amplifications in clinically actionable genes such as ALK. Moreover, ALK gain and ATM loss were strongly correlated with optic nerve head invasion. In conclusion, our study revealed genetic alterations of druggable kinases in RB, providing preliminary insights for the exploration of kinase-targeted therapy in RB.

ALYREF/THOC4 expression and cell growth modulation in retinoblastoma

In this study, we tested the hypothesis that ALYREF/THOC4, a poor prognostic factor in different cancer types, has potential as a drug target and prognostic biomarker for retinoblastoma (RB). Immunostaining (IHC), Western blot, and RT-qPCR analyses detected overexpression of ALYREF in the RB cell lines Y79, RB143, WERI-RB1, and RB116. IHC analysis on RB tumor array showed that 11/14 of RB tumors were ALYREF+ to varying degrees, with eight tumors at maximum 3+ intensity. The IHC analysis also detected ALYREF+ cells in normal retina, mainly in the inner nuclear and ganglion cell layer, while some tumor-bearing human eyes were ALYREF+ in the optic nerve suggesting a role in optic invasion/tumor invasion. The expression of ALYREF within the tumor itself, in the optic nerve, as well as in adjacent "normal" retina, suggest that this pattern of expression may lead to ALYREF being a potentially useful prognostic indicator for RB, as it is for other tumors. siRNA knockdown of ALYREF resulted in a 40 % decrease in cell growth in both WERI-RB1 and Y79 cells (p<0.05) and this was associated with decreased expression of mRNAs for the cell proliferation markers Ki67 and PCNA (p<0.005). These results suggest a role for ALYREF in RB cell growth regulation and its potential as both a target and a biomarker for tumor growth inhibition by anti-cancer therapies.

Single cell transcriptomics reveals early photoreceptor states, cell-specific transcript isoforms, and cancer-predisposing features

Human cone photoreceptors differ from rods and serve as the retinoblastoma cell-of-origin. Here, we used deep full-length single-cell RNA-sequencing to distinguish post-mitotic cone and rod developmental states and cone-specific features that contribute to retinoblastomagenesis. The analyses revealed early post-mitotic cone- and rod-directed populations characterized by higher THRB or NRL regulon activities, an immature photoreceptor precursor population with concurrent cone and rod gene and regulon expression, and distinct early and late cone and rod maturation states distinguished by maturation-associated declines in RAX regulon activity. Unexpectedly, both L/M cone and rod precursors co-expressed NRL and THRB RNAs, yet they differentially expressed functionally antagonistic NRL isoforms and prematurely terminated THRB transcripts. Early L/M cone precursors exhibited successive expression of lncRNAs along with MYCN, which composed the seventh most L/M-cone-specific regulon, and SYK, which contributed to the early cone precursors' proliferative response to RB1 loss. These findings reveal previously unrecognized photoreceptor precursor states and a role for early cone-precursor-intrinsic SYK expression in retinoblastoma initiation.

Retinoblastoma - A comprehensive review, update and recent advances

Retinoblastoma is the most common pediatric ocular malignancy. It is triggered by a biallelic mutation in the RB1 gene or MYCN oncogene amplification. Retinoblastomas can be unilateral (60%-70%) or bilateral (30%-40%); bilateral tumors are always heritable and present at an earlier age as compared to unilateral ones (18-24 months vs. 36 months in India). High prevalence rates, delayed presentation, and inaccessibility to healthcare lead to worse outcomes in developing countries. The past few decades have seen a paradigm change in the treatment of retinoblastomas, shifting from enucleation and external beam radiotherapy to less aggressive modalities for eye salvage. Multimodality treatment is now the standard of care and includes intraarterial or intravenous chemotherapy along with focal consolidation therapies such as transpupillary thermotherapy, cryotherapy, and laser photocoagulation. Intravitreal and intracameral chemotherapy can help in controlling intraocular seeds. Advanced extraocular or metastatic tumors still have a poor prognosis. Genetic testing, counseling, and screening of at-risk family members must be incorporated as essential parts of management. A better understanding of the genetics and molecular basis of retinoblastoma has opened up the path for potential targeted therapy in the future. Novel recent advances such as liquid biopsy, prenatal diagnosis, prognostic biomarkers, tylectomy, and chemoplaque point to promising future directions.

FTO promotes the progression of retinoblastoma through YTHDF2-dependent N6-methyladenosine modification in E2F3

Early treatment of retinoblastoma (RB) has significantly improved clinical outcomes. N6-methyladenosine (m6A) methylation is crucial for cancer progression. Thus, we investigated the role of FTO-dependent demethylation in RB and its underlying mechanisms. The biological behavior of RB cells was analyzed using cell counting kit-8, colony formation analysis, transwell assay, flow cytometry, and western blot analysis. m6A modification was evaluated using methylated RNA immunoprecipitation and dual-luciferase reporter assays, and E2F3 stability was assessed using Actinomycin D. The roles of FTO and E2F3 were also elucidated in vivo. These results indicated that FTO was highly expressed in RB cells with low m6A levels. FTO knockdown inhibited RB cell growth, migration, invasion, and epithelial-mesenchymal transition and arrested the cell cycle at the G0/G1 phase. Mechanistically, FTO interference promoted m6A methylation of E2F3, which was recognized by YTHDF2, thereby reducing mRNA stability. E2F3 overexpression partially rescued the effects of FTO knockdown on biological behavior. Moreover, FTO knockdown reduced tumor weight, tumor volume, ki67 expression, and tumor cell infiltration by mediating E2F3. Taken together, FTO silencing inhibited the malignant processes of RB by suppressing E2F3 in an m6A-YTHD2-dependent manner. These findings suggest that FTO is a novel therapeutic target for RB.

Patterns in the tapestry of chromatin-bound RB

The retinoblastoma protein (RB)-mediated regulation of E2F is a component of a highly conserved cell cycle machine. However, RB's tumor suppressor activity, like RB's requirement in animal development, is tissue-specific, context-specific, and sometimes appears uncoupled from cell proliferation. Detailed new information about RB's genomic distribution provides a new perspective on the complexity of RB function, suggesting that some of its functional specificity results from context-specific RB association with chromatin. Here we summarize recent evidence showing that RB targets different types of chromatin regulatory elements at different cell cycle stages. RB controls traditional RB/E2F targets prior to S-phase, but, when cells proliferate, RB redistributes to cell type-specific chromatin loci. We discuss the broad implications of the new data for RB research.

Recent progress in retinoblastoma: Pathogenesis, presentation, diagnosis and management

Retinoblastoma, the primary ocular malignancy in pediatric patients, poses a substantial threat to mortality without prompt and effective management. The prognosis for survival and preservation of visual acuity hinges upon the disease severity at the time of initial diagnosis. Notably, retinoblastoma has played a crucial role in unraveling the genetic foundations of oncogenesis. The process of tumorigenesis commonly begins with the occurrence of biallelic mutation in the RB1 tumor suppressor gene, which is then followed by a cascade of genetic and epigenetic alterations that correspond to the clinical stage and pathological features of the tumor. The RB1 gene, recognized as a tumor suppressor, encodes the retinoblastoma protein, which plays a vital role in governing cellular replication through interactions with E2F transcription factors and chromatin remodeling proteins. The diagnosis and treatment of retinoblastoma necessitate consideration of numerous factors, including disease staging, germline mutation status, family psychosocial factors, and the resources available within the institution. This review has systematically compiled and categorized the latest developments in the diagnosis and treatment of retinoblastoma which enhanced the quality of care for this pediatric malignancy.

Classical and Innovative Evidence for Therapeutic Strategies in Retinal Dysfunctions

The human retina is a complex anatomical structure that has no regenerative capacity. The pathogenesis of most retinopathies can be attributed to inflammation, with the activation of the inflammasome protein platform, and to the impact of oxidative stress on the regulation of apoptosis and autophagy/mitophagy in retinal cells. In recent years, new therapeutic approaches to treat retinopathies have been investigated. Experimental data suggest that the secretome of mesenchymal cells could reduce oxidative stress, autophagy, and the apoptosis of retinal cells, and in turn, the secretome of the latter could induce changes in mesenchymal cells. Other studies have evidenced that noncoding (nc)RNAs might be new targets for retinopathy treatment and novel disease biomarkers since a correlation has been found between ncRNA levels and retinopathies. A new field to explore is the interaction observed between the ocular and intestinal microbiota; indeed, recent findings have shown that the alteration of gut microbiota seems to be linked to ocular diseases, suggesting a gut-eye axis. To explore new therapeutical strategies for retinopathies, it is important to use proper models that can mimic the complexity of the retina. In this context, retinal organoids represent a good model for the study of the pathophysiology of the retina.

Inhibition of high level E2F in a RB1 proficient MYCN overexpressing chicken retinoblastoma model normalizes neoplastic behaviour

PURPOSE

Retinoblastoma, a childhood cancer, is most frequently caused by bi-allelic inactivation of RB1 gene. However, other oncogenic mutations such as MYCN amplification can induce retinoblastoma with proficient RB1. Previously, we established RB1-proficient MYCN-overexpressing retinoblastoma models both in human organoids and chicken. Here, we investigate the regulatory events in MYCN-induced retinoblastoma carcinogenesis based on the model in chicken.

METHODS

MYCN transformed retinal cells in culture were obtained from in vivo MYCN electroporated chicken embryo retina. The expression profiles were analysed by RNA sequencing. Chemical treatments, qRT-PCR, flow cytometry, immunohisto- and immunocytochemistry and western blot were applied to study the properties and function of these cells.

RESULTS

The expression profile of MYCN-transformed retinal cells in culture showed cone photoreceptor progenitor signature and robustly increased levels of E2Fs. This expression profile was consistently observed in long-term culture. Chemical treatments confirmed RB1 proficiency in these cells. The cells were insensitive to p53 activation but inhibition of E2f efficiently induced cell cycle arrest followed by apoptosis.

CONCLUSION

In conclusion, with proficient RB1, MYCN-induced high level of E2F expression dysregulates the cell cycle and contributes to retinoblastoma carcinogenesis. The increased level of E2f renders the cells to adopt a similar mechanistic phenotype to a RB1-deficient tumour.

From diagnosis to therapy: The transformative role of lncRNAs in eye cancer management

The genomic era has brought about a transformative shift in our comprehension of cancer, unveiling the intricate molecular landscape underlying disease development. Eye cancers (ECs), encompassing diverse malignancies affecting ocular tissues, pose distinctive challenges in diagnosis and management. Long non-coding RNAs (lncRNAs), an emerging category of non-coding RNAs, are pivotal actors in the genomic intricacies of eye cancers. LncRNAs have garnered recognition for their multifaceted roles in gene expression regulation and influence on many cellular processes. Many studies support that the lncRNAs have a role in developing various cancers. Recent investigations have pinpointed specific lncRNAs associated with ECs, including retinoblastoma and uveal melanoma. These lncRNAs exert control over critical pathways governing tumor initiation, progression, and metastasis, endowing them with the ability to function as evaluation, predictive, and therapeutic indicators. The article aims to synthesize the existing information concerning the functions of lncRNAs in ECs, elucidating their regulatory mechanisms and clinical significance. By delving into the lncRNAs' expanding relevance in the modulation of oncogenic and tumor-suppressive networks, we gain a deeper understanding of the molecular complexities intrinsic to these diseases. In our exploration of the genomic intricacies of ECs, lncRNAs introduce a fresh perspective, providing an opportunity to function as clinical and therapeutic indicators, and they also have therapeutic benefits that show promise for advancing the treatment of ECs. This comprehensive review bridges the intricate relationship between lncRNAs and ECs within the context of the genomic era.

Investigation of PACAP38 and PAC1 Receptor Expression in Human Retinoblastoma and the Effect of PACAP38 Administration on Human Y-79 Retinoblastoma Cells

Retinoblastoma represents the most prevalent malignant neoplasm affecting the eyes in childhood. The clear-cut origin of retinoblastoma has not yet been determined; however, based on experiments, it has been suggested that RB1 loss in cone photoreceptors causes retinoblastoma. Pituitary adenylate-cyclase activating polypeptide (PACAP) is a pleiotropic neuropeptide which has been shown to be affected in certain tumorous transformations, such as breast, lung, kidney, pancreatic, colon, and endocrine cancers. This study aimed to investigate potential changes in both PACAP38 and PAC1 receptor (PAC1R) expression in human retinoblastoma and the effect of PACAP38 administration on the survival of a human retinoblastoma cell line (Y-79). We analyzed human enucleation specimens removed because of retinoblastoma for PACAP38 and PAC1R immunostaining and the effect of PACAP38 on the survival of the Y-79 cell line. We described for the first time that human retinoblastoma cells from patients showed only perinuclear, dot-like immunopositivity for both PACAP38 and PAC1R, irrespective of laterality, genetic background, or histopathological features. Nanomolar (100 nM and 500 nM) PACAP38 concentrations had no effect on the viability of Y-79 cells, while micromolar (2 µM and 6 µM) PACAP38 significantly decreased tumor cell viability. These findings, along with general observations from animal studies showing that PACAP38 has strong anti-apoptotic, anti-inflammatory, and antioxidant effects on ocular tissues, together suggest that PACAP38 and its analogs are promising candidates in retinoblastoma therapy.

Likelihood of germline mutation with solitary retinoblastoma based on tumour location at presentation

BACKGROUND/AIMS

To evaluate the likelihood of germline mutation in patients presenting with solitary retinoblastoma based on tumour location at first examination.

METHODS

Retrospective analysis of solitary unilateral retinoblastoma for likelihood of germline mutation (family history of retinoblastoma and/or genetic testing indicating germline RB1 mutation and/or development of additional new or bilateral tumours) based on tumur location at presentation (macular vs extramacular).

RESULTS

Of 480 consecutive patients with solitary retinoblastoma, 85 were in the macula (18%) and 395 were extramacular (82%). By comparison (macular vs extramacular tumours), macular tumours had smaller basal diameter (12.7 mm vs 18.9 mm, p<0.001) and smaller tumour thickness (6.1 mm vs 10.7 mm, p<0.001). Patients with macular tumours demonstrated greater likelihood for germline mutation (23% vs 12%, OR=2.18, p=0.011), specifically based on family history of retinoblastoma (13% vs 2%, OR=4.64, p=0.004), genetic testing showing germline RB1 mutation (27% vs 15%, OR=2.04 (95% CI 1.04 to 4.01), p=0.039), development of new tumours (13% vs 3%, OR=5.16 (95% CI 2.06 to 12.87), p=0.001) and/or development of bilateral disease (9% vs 2%, OR=4.98 (95% CI 1.70 to 14.65), p=0.004).

CONCLUSIONS

Among patients with solitary unilateral retinoblastoma, those presenting with macular tumour (compared with extramacular tumour) show 2.18 times greater likelihood for germline mutation and an even higher likelihood of development of subsequent tumours. Solitary macular retinoblastoma should raise an index of suspicion for likely germline mutation and multifocal disease.

Insights into the molecular roles of FOXR2 in the pathology of primary pediatric brain tumors

Forkhead box gene R2 (FOXR2) belongs to the family of FOX genes which codes for highly conserved transcription factors (TFs) with critical roles in biological processes ranging from development to organogenesis to metabolic and immune regulation to cellular homeostasis. A number of FOX genes are associated with cancer development and progression and poor prognosis. A growing body of evidence suggests that FOXR2 is an oncogene. Studies suggested important roles for FOXR2 in cancer cell growth, metastasis, and drug resistance. Recent studies showed that FOXR2 is overexpressed by a subset of newly identified entities of embryonal tumors. This review discusses the role(s) FOXR2 plays in the pathology of pediatric brain cancers and its potential as a therapeutic target.

The Use of rAAV2-RB1-Mediated Gene Therapy in Retinoblastoma

Purpose

Retinoblastoma (RB) is a life-threatening malignancy that arises from the retina and is activated upon homozygous inactivation of the tumor suppressor RB1. Gene therapy targeting RB1 is an effective strategy to treat RB. However, it is difficult to target the RB1 gene by site-specific repair, with up to 3366 gene mutation sites identified in RB1. Thus, it is necessary to construct a promising and efficacious gene therapeutic strategy for patients with RB.

Methods

To recover the function of the RB1 protein, we constructed a recombinant adeno-associated virus 2 (rAAV2) expressing RB1 that can restore RB1 function and significantly inhibit RB progression. To confirm the clinical feasibility of rAAV2-RB1, the RB1 protein was validated in vitro and in vivo after transfection. To further evaluate the clinical efficacy, RB patient-derived xenograft models were established and applied. The biosafety of rAAV2-RB1 was also validated in immunocompetent mice.

Results

rAAV2-RB1 was a rAAV2 expressing the RB1 protein, which was validated in vitro and in vivo. In vitro, rAAV2-RB1 was effectively expressed in patient-derived RB cells. In mice, intravitreal administration of rAAV2-RB1 in a population-based patient-derived xenograft trial induced limited tumor growth. Moreover, after transfection of rAAV2-RB1 in immunocompetent mice, rAAV2-RB1 did not replicate and was expressed in other important organs, except retinas, inducing minor local side effects.

Conclusions

Our study suggested a promising efficacy gene therapeutic strategy, which might provide a chemotherapy-independent treatment option for RB.

Associations between birth defects with neural crest cell origins and pediatric embryonal tumors

BACKGROUND

There are few assessments evaluating associations between birth defects with neural crest cell developmental origins (BDNCOs) and embryonal tumors, which are characterized by undifferentiated cells having a molecular profile similar to neural crest cells. The effect of BDNCOs on embryonal tumors was estimated to explore potential shared etiologic pathways and genetic origins.

METHODS

With the use of a multistate, registry-linkage cohort study, BDNCO-embryonal tumor associations were evaluated by generating hazard ratios (HRs) and 95% confidence intervals (CIs) with Cox regression models. BDNCOs consisted of ear, face, and neck defects, Hirschsprung disease, and a selection of congenital heart defects. Embryonal tumors included neuroblastoma, nephroblastoma, and hepatoblastoma. Potential HR modification (HRM) was investigated by infant sex, maternal race/ethnicity, maternal age, and maternal education.

RESULTS

The risk of embryonal tumors among those with BDNCOs was 0.09% (co-occurring n = 105) compared to 0.03% (95% CI, 0.03%-0.04%) among those without a birth defect. Children with BDNCOs were 4.2 times (95% CI, 3.5-5.1 times) as likely to be diagnosed with an embryonal tumor compared to children born without a birth defect. BDNCOs were strongly associated with hepatoblastoma (HR, 16.1; 95% CI, 11.3-22.9), and the HRs for neuroblastoma (3.1; 95% CI, 2.3-4.2) and nephroblastoma (2.9; 95% CI, 1.9-4.4) were elevated. There was no notable HRM by the aforementioned factors.

CONCLUSIONS

Children with BDNCOs are more likely to develop embryonal tumors compared to children without a birth defect. Disruptions of shared developmental pathways may contribute to both phenotypes, which could inform future genomic assessments and cancer surveillance strategies of these conditions.

Depleted hexokinase1 and lack of AMPKα activation favor OXPHOS-dependent energetics in retinoblastoma tumors

Lack of retinoblastoma (Rb) protein causes aggressive intraocular retinal tumors in children. Recently, Rb tumors have been shown to have a distinctly altered metabolic phenotype, such as reduced expression of glycolytic pathway proteins alongside altered pyruvate and fatty acid levels. In this study, we demonstrate that loss of hexokinase 1(HK1) in tumor cells rewires their metabolism allowing enhanced oxidative phosphorylation-dependent energy production. We show that rescuing HK1 or retinoblastoma protein 1 (RB1) in these Rb cells reduced cancer hallmarks such as proliferation, invasion, and spheroid formation and increased their sensitivity to chemotherapy drugs. Induction of HK1 was accompanied by a metabolic shift of the cells to glycolysis and a reduction in mitochondrial mass. Cytoplasmic HK1 bound Liver Kinase B1 and phosphorylated AMP-activated kinase-α (AMPKα Thr172), thereby reducing mitochondria-dependent energy production. We validated these findings in tumor samples from Rb patients compared to age-matched healthy retinae. HK1 or RB1 expression in Rb-/- cells led to a reduction in their respiratory capacity and glycolytic proton flux. HK1 overexpression reduced tumor burden in an intraocular tumor xenograft model. AMPKα activation by AICAR also enhanced the tumoricidal effects of the chemotherapeutic drug topotecan in vivo. Therefore, enhancing HK1 or AMPKα activity can reprogram cancer metabolism and sensitize Rb tumors to lower doses of existing treatments, a potential therapeutic modality for Rb.

Episodic live imaging of cone photoreceptor maturation in GNAT2-EGFP retinal organoids

Fluorescent reporter pluripotent stem cell-derived retinal organoids are powerful tools to investigate cell type-specific development and disease phenotypes. When combined with live imaging, they enable direct and repeated observation of cell behaviors within a developing retinal tissue. Here, we generated a human cone photoreceptor reporter line by CRISPR/Cas9 genome editing of WTC11-mTagRFPT-LMNB1 human induced pluripotent stem cells (iPSCs) by inserting enhanced green fluorescent protein (EGFP) coding sequences and a 2A self-cleaving peptide at the N-terminus of guanine nucleotide-binding protein subunit alpha transducin 2 (GNAT2). In retinal organoids generated from these iPSCs, the GNAT2-EGFP alleles robustly and exclusively labeled immature and mature cones. Episodic confocal live imaging of hydrogel immobilized retinal organoids allowed tracking of the morphological maturation of individual cones for >18 weeks and revealed inner segment accumulation of mitochondria and growth at 12.2 μm3 per day from day 126 to day 153. Immobilized GNAT2-EGFP cone reporter organoids provide a valuable tool for investigating human cone development and disease.

Retinal organoid and gene editing for basic and translational research

The rapid evolution of two technologies has greatly transformed the basic, translational, and clinical research in the mammalian retina. One is the retinal organoid (RO) technology. Various induction methods have been created or adapted to generate species-specific, disease-specific, and experimental-targeted retinal organoids (ROs). The process of generating ROs can highly mimic the in vivo retinal development, and consequently, the ROs resemble the retina in many aspects including the molecular and cellular profiles. The other technology is the gene editing, represented by the classical CRISPR-Cas9 editing and its derivatives such as prime editing, homology independent targeted integration (HITI), base editing and others. The combination of ROs and gene editing has opened up countless possibilities in the study of retinal development, pathogenesis, and therapeutics. We review recent advances in the ROs, gene editing methodologies, delivery vectors, and related topics that are particularly relevant to retinal studies.

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 apoptotic and anti-proliferative effect of Lysyl oxidase propeptide in Y79 human retinoblastoma cells

Purpose

Retinoblastoma (RB) caused by the mutation of the RB1 gene is one of the most common ocular malignancies in children The propeptide region of lysyl oxidase (LOX), the enzyme involved in the cross-linking of collagen and elastin, has been identified to be anti-tumorigenic in various cancers. However, this role of lysyl oxidase propeptide (LOX-PP) in RB is still elusive. This study aims to identify the anti-tumorigenic effect of LOX-PP in human Y79 RB cells.

Methods

LOX-PP was overexpressed in Y79 RB cells, and differential gene expression was assessed by microarray followed by pathway analysis using transcriptome analysis console (TAC) software. Additionally, cell proliferation was studied by PrestoBlue assay, and DNA content was evaluated by cell cycle and apoptosis assays. The pro-apoptotic and anti-proliferative mechanisms induced by the overexpression of/exogenously added LOX-PP was evaluated by western blotting and real-time PCR.

Results

The expression of the LOX-PP transcript was significantly decreased in Y79 RB cells compared to human retinal endothelial cells. Gene expression analysis in LOX-PP overexpressed Y79 RB cells showed deregulation of pathways involved in apoptosis, cell cycle, focal adhesion-PI3K-AKT signaling, and DNA repair mechanisms. Interestingly, LOX-PP overexpressed Y79 RB cells showed significantly increased apoptosis, decreased proliferation, and cell cycle arrest at S-phase with a concordant reduction of proliferative cell nuclear antigen and Cyclin D1 protein expressions. Moreover, pAKT (S473) was significantly downregulated in Y79 RB cells, which decreased NFκB leading to significantly reduced BCL2 expression.

Conclusions

Our results demonstrate the anti-tumorigenic effect of LOX-PP in Y79 RB cells by inducing apoptosis and decreasing proliferation. This effect was mediated by the downregulation of AKT signaling. These results suggest that LOX-PP can be explored as a therapeutic molecule in RB.

Genomic instability and eye diseases

Background

Genetic information is stored in the bases of double-stranded DNA. However, the integrity of DNA molecules is constantly threatened by various mutagenic agents, including pollutants, ultraviolet light (UV), and medications. To counteract these environmental damages, cells have established multiple mechanisms, such as producing molecules to identify and eliminate damaged DNA, as well as reconstruct the original DNA structures. Failure or insufficiency of these mechanisms can cause genetic instability. However, the role of genome stability in eye diseases is still under-researched, despite extensive study in cancer biology.

Main text

As the eye is directly exposed to the external environment, the genetic materials of ocular cells are constantly under threat. Some of the proteins essential for DNA damage repair, such as pRb, p53, and RAD21, are also key during the ocular disease development. In this review, we discuss five ocular diseases that are associated with genomic instability. Retinoblastoma and pterygium are linked to abnormal cell cycles. Fuchs' corneal endothelial dystrophy and age-related macular degeneration are related to the accumulation of DNA damage caused by oxidative damage and UV. The mutation of the subunit of the cohesin complex during eye development is linked to sclerocornea.

Conclusions

Failure of DNA damage detection or repair leads to increased genomic instability. Deciphering the role of genomic instability in ocular diseases can lead to the development of new treatments and strategies, such as protecting vulnerable cells from risk factors or intensifying damage to unwanted cells.

Retinal organoids provide unique insights into molecular signatures of inherited retinal disease throughout retinogenesis

The demand for induced pluripotent stem cells (iPSC)-derived retinal organoid and retinal pigment epithelium (RPE) models for the modelling of inherited retinopathies has increased significantly in the last decade. These models are comparable with foetal retinas up until the later stages of retinogenesis, expressing all of the key neuronal markers necessary for retinal function. These models have proven to be invaluable in the understanding of retinogenesis, particular in the context of patient-specific diseases. Inherited retinopathies are infamously described as clinically and phenotypically heterogeneous, such that developing gene/mutation-specific animal models in each instance of retinal disease is not financially or ethically feasible. Further to this, many animal models are insufficient in the study of disease pathogenesis due to anatomical differences and failure to recapitulate human disease phenotypes. In contrast, iPSC-derived retinal models provide a high throughput platform which is physiologically relevant for studying human health and disease. They also serve as a platform for drug screening, gene therapy approaches and in vitro toxicology of novel therapeutics in pre-clinical studies. One unique characteristic of stem cell-derived retinal models is the ability to mimic in vivo retinogenesis, providing unparalleled insights into the effects of pathogenic mutations in cells of the developing retina, in a highly accessible way. This review aims to give the reader an overview of iPSC-derived retinal organoids and/or RPE in the context of disease modelling of several inherited retinopathies including Retinitis Pigmentosa, Stargardt disease and Retinoblastoma. We describe the ability of each model to recapitulate in vivo disease phenotypes, validate previous findings from animal models and identify novel pathomechanisms that underpin individual IRDs.

Non-synonymous, synonymous, and non-coding nucleotide variants contribute to recurrently altered biological processes during retinoblastoma progression

Retinoblastomas form in response to biallelic RB1 mutations or MYCN amplification and progress to more aggressive and therapy-resistant phenotypes through accumulation of secondary genomic changes. Progression-related changes include recurrent somatic copy number alterations and typically non-recurrent nucleotide variants, including synonymous and non-coding variants, whose significance has been unclear. To determine if nucleotide variants recurrently affect specific biological processes, we identified altered genes and over-represented variant gene ontologies in 168 exome or whole-genome-sequenced retinoblastomas and 12 tumor-matched cell lines. In addition to RB1 mutations, MYCN amplification, and established retinoblastoma somatic copy number alterations, the analyses revealed enrichment of variant genes related to diverse biological processes including histone monoubiquitination, mRNA processing (P) body assembly, and mitotic sister chromatid segregation and cytokinesis. Importantly, non-coding and synonymous variants increased the enrichment significance of each over-represented biological process term. To assess the effects of such mutations, we examined the consequences of a 3' UTR variant of PCGF3 (a BCOR-binding component of Polycomb repressive complex I), dual 3' UTR variants of CDC14B (a regulator of sister chromatid segregation), and a synonymous variant of DYNC1H1 (a regulator of P-body assembly). One PCGF3 and one of two CDC14B 3' UTR variants impaired gene expression whereas a base-edited DYNC1H1 synonymous variant altered protease sensitivity and stability. Retinoblastoma cell lines retained only ~50% of variants detected in tumors and enriched for new variants affecting p53 signaling. These findings reveal potentially important differences in retinoblastoma cell lines and tumors and implicate synonymous and non-coding variants, along with non-synonymous variants, in retinoblastoma oncogenesis.

Lipid Metabolic Reprogramming in Embryonal Neoplasms with MYCN Amplification

Tumor cells reprogram their metabolism, including glucose, glutamine, nucleotide, lipid, and amino acids to meet their enhanced energy demands, redox balance, and requirement of biosynthetic substrates for uncontrolled cell proliferation. Altered lipid metabolism in cancer provides lipids for rapid membrane biogenesis, generates the energy required for unrestricted cell proliferation, and some of the lipids act as signaling pathway mediators. In this review, we focus on the role of lipid metabolism in embryonal neoplasms with MYCN dysregulation. We specifically review lipid metabolic reactions in neuroblastoma, retinoblastoma, medulloblastoma, Wilms tumor, and rhabdomyosarcoma and the possibility of targeting lipid metabolism. Additionally, the regulation of lipid metabolism by the MYCN oncogene is discussed.

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.

Episodic live imaging of cone photoreceptor maturation in GNAT2-EGFP retinal organoids

Fluorescent reporter pluripotent stem cell (PSC) derived retinal organoids are powerful tools to investigate cell type-specific development and disease phenotypes. When combined with live imaging, they enable direct and repeated observation of cell behaviors within a developing retinal tissue. Here, we generated a human cone photoreceptor reporter line by CRISPR/Cas9 genome editing of WTC11-mTagRFPT-LMNB1 human induced pluripotent stem cells (iPSCs) by inserting enhanced green fluorescent protein (EGFP) coding sequences and a 2A self-cleaving peptide at the N-terminus of Guanine Nucleotide-Binding Protein Subunit Alpha Transducin 2 (GNAT2). In retinal organoids generated from these iPSCs, the GNAT2-EGFP allele robustly and exclusively labeled both immature and mature cones starting at culture day 34. Episodic confocal live imaging of hydrogel immobilized retinal organoids allowed tracking of morphological maturation of individual cones for >18 weeks and revealed inner segment accumulation of mitochondria and growth at 12.2 cubic microns per day from day 126 to day 153. Immobilized GNAT2-EGFP cone reporter organoids provide a valuable tool for investigating human cone development and disease.

`Targeted pharmacologic inhibition of S-phase kinase-associated protein 2 (SKP2) mediated cell cycle regulation in lung and other RB-Related cancers: A brief review of current status and future prospects

Small cell lung cancer (SCLC) often exhibits Rb deficiency, TRβ and p130 deletion, and SKP2 amplification, suggesting TRβ inactivation and SKP2 activation. It is reported that SKP2 targeted therapy is effective in some cancers in vitro and in vivo, but it is not reported for the treatment of SCLC and retinoblastoma. SKP2 is the synthetic lethal gene in SCLC and retinoblastoma, so SKP2 can be used for targeted therapy in SCLC and retinoblastoma. RB1 knockout mice develop several kinds of tumors, but Rb1 and SKP2 double knockout mice are healthy, suggesting that SKP2 targeted therapy may have significant effects on Rb deficient cancers with less side effects, and if successful in SCLC and retinoblastoma in vitro and in animal model, such compounds may be promising for the clinical treatment of SCLC, retinoblastoma, and variety of Rb deficient cancers. Previously our studies showed that retinoblastomas exhibit retinal cone precursor properties and depend on cone-specific thyroid hormone receptor β2 (TRβ2) and SKP2 signaling. In this study, we sought to suppress SCLC and retinoblastoma cell growth by SKP2 inhibitors as a prelude to targeted therapy in vitro and in vivo. We knocked down TRβ2 and SKP2 or over-expressed p27 in SCLC and retinoblastoma cell lines to investigate SKP2 and p27 signaling alterations. The SCLC cell lines H209 as well as retinoblastoma cell lines Y79, WERI, and RB177 were treated with SKP2 inhibitor C1 at different concentrations, following which Western blotting, Immunostaining, and cell cycle kinetics studies were performed to study SKP2 and p27 expression ubiquitination, to determine impact on cell cycle regulation and growth inhibition. TRβ2 knockdown in Y79, RB177 and H209 caused SKP2 downregulation and degradation, p27 up-regulation, and S phase arrest, whereas, SKP2 knockdown or p27 over-expression caused p27 accumulation and G1-S phase arrest. In the cell lines Y79, WERI, RB177, and H209 treatment with C1 caused SKP2 ubiquitination and degradation, p27 de-ubiquitination and accumulation, and cell growth arrest. SKP2 inhibitor C1 significantly suppressed retinoblastoma as well as SCLC cell growth by SKP2 degradation and p27 accumulation. In vivo study also showed inhibition of tumor growth with C1 treatment. Potential limitations of the success of such a therapeutic approach and its translational application in human primary tumors, and alternative approaches to overcome such limitations are briefly discussed for the treatment of retinoblastoma, SCLC and other RB-related cancers.

Nitric oxide suppression by secreted frizzled-related protein 2 drives retinoblastoma

Retinoblastoma is a cancer of the infant retina primarily driven by loss of the Rb tumor suppressor gene, which is undruggable. Here, we report an autocrine signaling, mediated by secreted frizzled-related protein 2 (SFRP2), which suppresses nitric oxide and enables retinoblastoma growth. We show that coxsackievirus and adenovirus receptor (CXADR) is the cell-surface receptor for SFRP2 in retinoblastoma cells; that CXADR functions as a "dependence receptor," transmitting a growth-inhibitory signal in the absence of SFRP2; and that the balance between SFRP2 and CXADR determines nitric oxide production. Accordingly, high SFRP2 RNA expression correlates with high-risk histopathologic features in retinoblastoma. Targeting SFRP2 signaling by SFRP2-binding peptides or by a pharmacological inhibitor rapidly induces nitric oxide and profoundly inhibits retinoblastoma growth in orthotopic xenograft models. These results reveal a cytokine signaling pathway that regulates nitric oxide production and retinoblastoma cell proliferation and is amenable to therapeutic intervention.

Sunitinib efficacy with minimal toxicity in patient-derived retinoblastoma organoids

BACKGROUND

Recurrence of retinoblastoma (RB) following chemoreduction is common and is often managed with local (intra-arterial/intravitreal) chemotherapy. However, some tumors are resistant to even local administration of maximum feasible drug dosages, or effective tumor control and globe preservation may be achieved at the cost of vision loss due to drug-induced retinal toxicity. The aim of this study was to identify drugs with improved antitumor activity and more favorable retinal toxicity profiles via screening of potentially repurposable FDA-approved drugs in patient-derived tumor organoids.

METHODS

Genomic profiling of five RB organoids and the corresponding parental tissues was performed. RB organoids were screened with 133 FDA-approved drugs, and candidate drugs were selected based on cytotoxicity and potency. RNA sequencing was conducted to generate a drug signature from RB organoids, and the effects of drugs on cell cycle progression and proliferative tumor cone restriction were examined. Drug toxicity was assessed with human embryonic stem cell-derived normal retinal organoids. The efficacy/toxicity profiles of candidate drugs were compared with those of drugs in clinical use.

RESULTS

RB organoids maintained the genomic features of the parental tumors. Sunitinib was identified as highly cytotoxic against both classical RB1-deficient and novel MYCN-amplified RB organoids and inhibited proliferation while inducing differentiation in RB. Sunitinib was a more effective suppressor of proliferative tumor cones in RB organoids and had lower toxicity in normal retinal organoids than either melphalan or topotecan.

CONCLUSION

The efficacy and retinal toxicity profiles of sunitinib suggest that it could potentially be repurposed for local chemotherapy of RB.

Retinoblastoma: From genes to patient care

Retinoblastoma is the most common paediatric neoplasm of the retina, and one of the earliest model of cancer genetics since the identification of the master tumour suppressor gene RB1. Tumorigenesis has been shown to be driven by pathogenic variants of the RB1 locus, but also genomic and epigenomic alterations outside the locus. The increasing knowledge on this "mutational landscape" is used in current practice for precise genetic testing and counselling. Novel methods provide access to pre-therapeutic tumour DNA, by isolating cell-free DNA from aqueous humour or plasma. This is expected to facilitate assessment of the constitutional status of RB1, to provide an early risk stratification using molecular prognostic markers, to follow the response to the treatment in longitudinal studies, and to predict the response to targeted therapies. The aim of this review is to show how molecular genetics of retinoblastoma drives diagnosis, treatment, monitoring of the disease and surveillance of the patients and relatives. We first recap the current knowledge on retinoblastoma genetics and its use in every-day practice. We then focus on retinoblastoma subgrouping at the era of molecular biology, and the expected input of cell-free DNA in the field.

Retinal and optic nerve relapse in retinoblastoma secondary to epiretinal and epipapillary vitreous seeds implantation documented by optical coherence tomography

BACKGROUND

Retinal retinoblastoma growth phenotypes can be endophytic, exophytic, diffuse infiltrating or anterior diffuse. Herein, we describe a novel tumor growth pattern in two patients.

MATERIAL AND METHODS

Imaging with spectral-domain optical coherence tomography (SD-OCT).

RESULTS

Both cases were diagnosed with unilateral group D retinoblastoma treated with first-line or bridge intra-arterial chemotherapy (IAC). Case 1 had a new intravitreal/epiretinal relapse 3 months after brachytherapy and intravitreal chemotherapy. SD-OCT showed a disruption of the inner limiting membrane (INL) underneath a parapapillary epiretinal seed. The intravitreal/epiretinal disease completely regressed with intravitreal melphalan. Three months later, an isolated intraretinal growth was documented on SD-OCT at the site of previously INL disruption, which was treated by thermotherapy. He remained disease-free at 1-year follow-up with 0.6 visual acuity. Case 2 was seen 2 months after treatment interruption due to the COVID-19 pandemic. Fundus examination showed a massive intravitreal/epipapillary invasion completely obscuring the papilla. Salvage treatment of this seeing eye consisted of combined intra-arterial and intravitreal melphalan and topotecan injections. An infraclinical papillary regrowth 4 months later was treated with additional IAC. Six months later, enucleation was performed due to an infraclinical papillary relapse with suspicion of intralaminar invasion. Histopathology showed retrolaminar optic nerve invasion with tumor-free surgical section. The child received four cycles of adjuvant chemotherapy and remained disease-free at 1-year follow-up.

CONCLUSION

Epiretinal/epipapillary vitreous seeding can be the source of a secondary intraretinal/optic nerve head relapse. SD-OCT is instrumental to follow such cases. Enucleation remains the safest option if secondary optic nerve invasion is suspected.

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.

MDM2 inhibitors-mediated disruption of mitochondrial metabolism: A novel therapeutic strategy for retinoblastoma

MDM2 is the principal inhibitor of p53, and MDM2 inhibitors can disrupt the physical interaction between MDM2 and p53. The half-life of p53 is very short in normal cells and tissues, and an uncontrolled increase in p53 levels has potential harmful effects. It has been shown that p53 is frequently mutated in most cancers; however, p53 mutations are rare in retinoblastoma. Therefore, therapeutic strategies aimed at increasing the expression levels of wild-type p53 are attractive. In this minireview, we discuss the potential use of nutlin-3, the prototype small molecule inhibitor that disrupts the MDM2-p53 interaction, for the treatment of retinoblastoma. Although p53 has pleiotropic biological effects, the functions of p53 depend on its sub-cellular localization. In the nucleus, p53 induces the transcription of a vast array of genes, while in mitochondria, p53 regulates mitochondrial metabolism. This review also discusses the relative contribution of p53-mediated gene transcription and mitochondrial perturbation for retinoblastoma treatment.

Lack of Retinoblastoma Protein Shifts Tumor Metabolism from Glycolysis to OXPHOS and Allows the Use of Alternate Fuels

Mutations in the RB1 locus leading to a loss of functional Rb protein cause intraocular tumors, which uniquely affect children worldwide. These tumors demonstrate rapid proliferation, which has recently been shown to be associated with an altered metabolic signature. We found that retinoblastoma tumors and in-vitro models lack Hexokinase 1 (HK1) and exhibit elevated fatty acid oxidation. We show that ectopic expression of RB1 induces HK1 protein in Rb null cells, and both RB1 and HK1 can mediate a metabolic switch from OXPHOS to glycolysis with increased pyruvate levels, reduced ATP production and reduced mitochondrial mass. Further, cells lacking Rb or HK1 can flexibly utilize glutamine and fatty acids to enhance oxidative phosphorylation-dependent ATP generation, as revealed by metabolic and biochemical assays. Thus, loss of Rb and HK1 in retinoblastoma reprograms tumor metabolic circuits to enhance the glucose-independent TCA (tricarboxylic acid) cycle and the intermediate NAD+/NADH ratios, with a subsequent increase in fatty-acid derived L-carnitine to enhance mitochondrial OXPHOS for ATP production instead of glycolysis dependence. We also demonstrate that modulation of the Rb-regulated transcription factor E2F2 does not result in any of these metabolic perturbations. In conclusion, we demonstrate RB1 or HK1 as critical regulators of the cellular bioenergetic profile and identify the altered tumor metabolism as a potential therapeutic target for cancers lacking functional Rb protein.

Investigation of early neoplastic transformation and premalignant biology using genetically engineered organoid models

Organoid modeling is a powerful, robust and efficient technology faithfully preserving physiological and pathological characteristics of tissues of origin. Recently, substantial advances have been made in applying genetically engineered organoid models to study early tumorigenesis and premalignant biology. These efforts promise to identify novel avenues for early cancer detection, intervention and prevention. Here, we highlight significant advancements in the functional characterization of early genomic and epigenomic events during neoplastic evolution using organoid modeling, discuss the application of the lineage-tracing methodology in organoids to study cancer cells-of-origin, and review future opportunities for further development and improvement of organoid modeling of cancer precursors.

E2F1/CKS2/PTEN signaling axis regulates malignant phenotypes in pediatric retinoblastoma

Retinoblastoma (RB) is the most common pediatric intraocular malignancy and is a serious vision- and life-threatening disease. The biallelic mutation of the retinoblastoma gene RB1 is the initial event in the malignant transformation of RB, but the exact molecular mechanism is still unclear. E2F transcription factors can be activated by RB1 loss of function and lead to uncontrolled cell division. Among E2F family numbers, E2F1 has higher expression abundance than E2F2 and E2F3 in RB clinical samples. By integrating E2F1 ChIP-seq data, RNA-seq profiling from RB samples and RNA-seq profiling upon E2F1 knockdown, together with pathway analysis, literature searching and experimental validation, we identified Cyclin-dependent kinases regulatory subunit 2 (CKS2) as a novel regulator in regulating tumor-associated phenotypes in RB. CKS2 exhibited aberrantly higher expression in RB. Depletion of CKS2 in Y79 retinoblastoma cell line led to reduced cell proliferation, delayed DNA replication and decreased clonogenic growth. Downregulation of CKS2 also slowed tumor xenograft growth in nude mice. Importantly, reversed expression of CKS2 rescued cancer-associated phenotypes. Mechanistically, transcription factor E2F1 enhanced CKS2 expression through binding to its promoter and CKS2 regulated the cancer-associated PI3K-AKT pathway. This study discovered E2F1/CKS2/PTEN signaling axis regulates malignant phenotypes in pediatric retinoblastoma, and CKS2 may serve as a potential therapeutic target for this disease.

Genomic and Epigenomic Characterization of Tumor Organoid Models

Simple Summary

The patient-derived organoid (PDO) model is a versatile and dynamic tool for investigating individual genomic and epigenomic properties of cancer. PDOs preserve key (epi-)genomic features and maintain physiological and pathological characteristics, resembling patient tumor specimens. Coupled with the next-generation sequencing technology, PDOs can be used to accurately map (epi-)genomic alterations of “living” cancer specimens. Additionally, organoid modeling of matched normal and malignant tissues from the same patient serves as an adequate and valid platform to interrogate cancer-specific features. Because of these advantages, research on PDOs is rapidly growing for the investigation of genotype–phenotype association and precision oncology.

Abstract

Tumor organoid modeling has been recognized as a state-of-the-art system for in vitro research on cancer biology and precision oncology. Organoid culture technologies offer distinctive advantages, including faithful maintenance of physiological and pathological characteristics of human disease, self-organization into three-dimensional multicellular structures, and preservation of genomic and epigenomic landscapes of the originating tumor. These features effectively position organoid modeling between traditional cell line cultures in two dimensions and in vivo animal models as a valid, versatile, and robust system for cancer research. Here, we review recent advances in genomic and epigenomic characterization of tumor organoids and the novel findings obtained, highlight significant progressions achieved in organoid modeling of gene–drug interactions and genotype–phenotype associations, and offer perspectives on future opportunities for organoid modeling in basic and clinical cancer research.

RB1 loss triggers dependence on ESRRG in retinoblastoma

Retinoblastoma (Rb) is a deadly childhood eye cancer that is classically initiated by inactivation of the RB1 tumor suppressor. Clinical management continues to rely on nonspecific chemotherapeutic agents that are associated with treatment resistance and toxicity. Here, we analyzed 103 whole exomes, 20 whole transcriptomes, 5 single-cell transcriptomes, and 4 whole genomes from primary Rb tumors to identify previously unknown Rb dependencies. Several recurrent genomic aberrations implicate estrogen-related receptor gamma (ESRRG) in Rb pathogenesis. RB1 directly interacts with and inhibits ESRRG, and RB1 loss uncouples ESRRG from negative regulation. ESRRG regulates genes involved in retinogenesis and oxygen metabolism in Rb cells. ESRRG is preferentially expressed in hypoxic Rb cells in vivo. Depletion or inhibition of ESRRG causes marked Rb cell death, which is exacerbated in hypoxia. These findings reveal a previously unidentified dependency of Rb cells on ESRRG, and they implicate ESRRG as a potential therapeutic vulnerability in Rb.

Second hit impels oncogenesis of retinoblastoma in patient-induced pluripotent stem cell-derived retinal organoids: direct evidence for Knudson's theory

Retinoblastoma (Rb) is a type of malignant tumor due to abnormal retinogenesis with biallelic mutations of the RB1 gene. Its pathogenesis has been proposed as a "two-mutation hypothesis" by Knudson since 1971; however, there remain some debates on disease onset sufficiency of the biallelic RB1 mutations. To obtain straightforward evidence for this hypothesis, we investigated whether two-hit mutations of the RB1 gene drive tumorigenesis in patient-induced pluripotent stem cell (hiPSC)-derived human retinal organoids (hROs) and whether single allelic mutation hiPSC-derived hROs exhibit molecular and cellular defects. We generated hiPSCs with a heterozygous germline mutation (RB1^{m1/ wt} ) from a Rb patient. A second-allele RB1 gene mutation was knocked in to produce compound heterozygous mutations (RB1^m1/m2 ) in the hiPSCs. These two hiPSC lines were independently developed into hROs through a stepwise differentiation. The hiPSC-RB1^m1/m2 derived organoids demonstrated tumorigenesis in dishes, consistent with Rb profiles in spatiotemporal transcriptomes, in which developmentally photoreceptor fate-determining markers, CRX and OTX2, were highly expressed in hiPSC-RB1^m1/m2 derived hROs. Additionally, ARR3⁺ maturing cone precursors were co-labeled with proliferative markers Ki67 or PCNA, in agreement with the consensus that human Rb is originated from maturing cone precursors. Finally, we demonstrated that retinal cells of hROs with monoallelic RB1 mutation were abnormal in molecular aspects due to its haploinsufficiency. In conclusion, this study provides straightforward supporting evidence in a way of reverse genetics for "two-hit hypothesis" in the Rb tumorigenesis and opens new avenues for development of early intervention and treatment of Rb.

UBE2T/STAT3 Signaling Promotes the Proliferation and Tumorigenesis in Retinoblastoma

Purpose

The purpose of this paper was to investigate the expression and function of Ubiquitin-conjugating enzyme 2T (UBE2T), a human E2 ubiquitin-conjugating enzyme, in human retinoblastoma.

Methods

The expression of UBE2T in normal retina and retinoblastoma was analyzed using the Gene Expression Omnibus (GEO) databases, and its expression was immunohistochemically evaluated in 29 retinoblastoma sections and 5 normal retinas. Then CCK-8, flow cytometry, RNA-sequencing analysis, and in vivo assays were performed to explore the exact role of UBE2T in retinoblastoma.

Results

We found that retinoblastoma showed higher UBE2T expression than normal retina in GEO datasets and tissues. The immunoreactive score of UBE2T ≥4 was associated with group E in IIRC, T2-T4b in pTNM staging, poorly differentiated retinoblastoma, and high-risk histopathological factors. Knockdown of UBE2T reduced the cell viability, increased the apoptosis cells and G0/G1 cells, and inhibited subcutaneous tumor growth in vivo. Mechanistic studies showed that UBE2T knockdown induced down-regulation of phosphorylation of STAT3 and its downstream genes in vitro and in vivo. Rescue assays confirmed that STAT3 signaling pathway was involved in the effect of reduced cell viability, elevated apoptosis cells, and G0/G1 cells mediated by UBE2T knockdown.

Conclusions

Our data indicate that UBE2T significantly participates in the proliferation of retinoblastoma via the STAT3 signaling pathway, suggesting the potential of UBE2T as a therapeutic target for retinoblastoma treatment.

An immature, dedifferentiated, and lineage-deconstrained cone precursor origin of N-Myc-initiated retinoblastoma

Most retinoblastomas develop from maturing cone precursors in response to biallelic RB1 loss and are dependent on cone maturation-related signaling. Additionally, ∼2% lack RB1 mutations but have MYCN amplification (MYCN^A), N-Myc protein overexpression, and more rapid and invasive growth, yet the MYCN^A retinoblastoma cell of origin and basis for its responses to deregulated N-Myc are unknown. Here, using explanted cultured retinae, we show that ectopic N-Myc induces cell cycle entry in cells expressing markers of several retinal types yet induces continuous proliferation and tumorigenesis only in cone precursors. Unlike the response to RB1 loss, both immature cone arrestin-negative (ARR3^-) and maturing ARR3⁺ cone precursors proliferate, and maturing cone precursors rapidly dedifferentiate, losing ARR3 as well as L/M-opsin expression. N-Myc-overexpressing retinal cells also lose cell lineage constraints, occasionally coexpressing the cone-specific RXRγ with the rod-specific NRL or amacrine-specific AP2α and widely coexpressing RXRγ with the progenitor and Müller cell-specific SOX9 and retinal ganglion cell-specific BRN3 and GAP43. Mechanistically, N-Myc induced Cyclin D2 and CDK4 overexpression, pRB phosphorylation, and SOX9-dependent proliferation without a retinoma-like stage that characterizes pRB-deficient retinoblastoma, despite continuous p16^INK4A expression. Orthotopic xenografts of N-Myc-overexpressing retinal cells formed tumors with retinal cell marker expression similar to those in MYCN-transduced retinae and MYCN^A retinoblastomas in patients. These findings demonstrate the MYCN^A retinoblastoma origin from immature and lineage-deconstrained cone precursors, reveal their opportunistic use of an undifferentiated retinal progenitor cell feature, and illustrate that different cancer-initiating mutations cooperate with distinct developmental stage-specific cell signaling circuitries to drive retinoblastoma tumorigenesis.

Integrated Analysis of Cancer Tissue and Vitreous Humor from Retinoblastoma Eyes Reveals Unique Tumor-Specific Metabolic and Cellular Pathways in Advanced and Non-Advanced Tumors

Retinoblastoma (Rb) is a pediatric intraocular malignancy that is proposed to originate from maturing cone cell precursors in the developing retina. The molecular mechanisms underlying the biological and clinical behaviors are important to understand in order to improve the management of advanced-stage tumors. While the genetic causes of Rb are known, an integrated understanding of the gene expression and metabolic processes in tumors of human eyes is deficient. By integrating transcriptomic profiling from tumor tissues and metabolomics from tumorous eye vitreous humor samples (with healthy, age-matched pediatric retinae and vitreous samples as controls), we uncover unique functional associations between genes and metabolites. We found distinct gene expression patterns between clinically advanced and non-advanced Rb. Global metabolomic analysis of the vitreous humor of the same Rb eyes revealed distinctly altered metabolites, indicating how tumor metabolism has diverged from healthy pediatric retina. Several key enzymes that are related to cellular energy production, such as hexokinase 1, were found to be reduced in a manner corresponding to altered metabolites; notably, a reduction in pyruvate levels. Similarly, E2F2 was the most significantly elevated E2F family member in our cohort that is part of the cell cycle regulatory circuit. Ectopic expression of the wild-type RB1 gene in the Rb-null Y79 and WERI-Rb1 cells rescued hexokinase 1 expression, while E2F2 levels were repressed. In an additional set of Rb tumor samples and pediatric healthy controls, we further validated differences in the expression of HK1 and E2F2. Through an integrated omics analysis of the transcriptomics and metabolomics of Rb, we uncovered a significantly altered tumor-specific metabolic circuit that reduces its dependence on glycolytic pathways and is governed by Rb1 and HK1.

pRB-Depleted Pluripotent Stem Cell Retinal Organoids Recapitulate Cell State Transitions of Retinoblastoma Development and Suggest an Important Role for pRB in Retinal Cell Differentiation

Retinoblastoma (Rb) is a childhood cancer of the developing retina, accounting for up to 17% of all tumors in infancy. To gain insights into the transcriptional events of cell state transitions during Rb development, we established 2 disease models via retinal organoid differentiation of a pRB (retinoblastoma protein)-depleted human embryonic stem cell line (RB1-null hESCs) and a pRB patient-specific induced pluripotent (iPSC) line harboring a RB1 biallelic mutation (c.2082delC). Both models were characterized by pRB depletion and accumulation of retinal progenitor cells at the expense of amacrine, horizontal and retinal ganglion cells, which suggests an important role for pRB in differentiation of these cell lineages. Importantly, a significant increase in the fraction of proliferating cone precursors (RXRγ+Ki67+) was observed in both pRB-depleted organoid models, which were defined as Rb-like clusters by single-cell RNA-Seq analysis. The pRB-depleted retinal organoids displayed similar features to Rb tumors, including mitochondrial cristae aberrations and rosette-like structures, and were able to undergo cell growth in an anchorage-independent manner, indicative of cell transformation in vitro. In both models, the Rb cones expressed retinal ganglion and horizontal cell markers, a novel finding, which could help to better characterize these tumors with possible therapeutic implications. Application of Melphalan, Topotecan, and TW-37 led to a significant reduction in the fraction of Rb proliferating cone precursors, validating the suitability of these in vitro models for testing novel therapeutics for Rb.

Genome maintenance in retinoblastoma: Implications for therapeutic vulnerabilities (Review)

Retinoblastoma (RB) is a pediatric ocular malignancy that is initiated mostly by biallelic inactivation of the RB transcriptional corepressor 1 (RB1) tumor suppressor gene in the developing retina. Unlike the prevailing prediction based on multiple studies involving RB1 gene disruption in experimental models, human RB tumors have been demonstrated to possess a relatively stable genome, characterized by a low mutation rate and a few recurrent chromosomal alterations related to somatic copy number changes. This suggests that RB may harbor heightened genome maintenance mechanisms to counteract or compensate for the risk of massive genome instability, which can potentially be driven by the early RB1 loss as a tumor-initiating event. Although the genome maintenance mechanisms might have been evolved to promote RB cell survival by preventing lethal genomic defects, emerging evidence suggests that the dependency of RB cells on these mechanisms also exposes their unique vulnerability to chemotherapy, particularly when the genome maintenance machineries are tumor cell-specific. This review summarizes the genome maintenance mechanisms identified in RB, including findings on the roles of chromatin regulators in DNA damage response/repair and protein factors involved in maintaining chromosome stability and promoting survival in RB. In addition, advantages and challenges for exploiting these therapeutic vulnerabilities in RB are discussed.

RB1-Negative Retinal Organoids Display Proliferation of Cone Photoreceptors and Loss of Retinal Differentiation

Simple Summary

Retinoblastoma is a tumor of the eye’s retina, which is the very specialized tissue responsible for vision. In 98% of cases, the tumor is caused by inactivation of the RB1 gene. Due to lack of material and models, the understanding of RB1 mutations in tumor development is still unsatisfactory. We aimed to establish a human laboratory model for retinoblastoma. While differentiating stem cells with a mutation in RB1 into retina, we observed reduced differentiation potential but enhanced proliferation—general hallmarks of tumor development. The gene expression signature in the model resembled that of tumor material. This approach now enables research on retinoblastoma and probably therapy in the correct tissue, the human retina.

Abstract

Retinoblastoma is a tumor of the eye in children under the age of five caused by biallelic inactivation of the RB1 tumor suppressor gene in maturing retinal cells. Cancer models are essential for understanding tumor development and in preclinical research. Because of the complex organization of the human retina, such models were challenging to develop for retinoblastoma. Here, we present an organoid model based on differentiation of human embryonic stem cells into neural retina after inactivation of RB1 by CRISPR/Cas9 mutagenesis. Wildtype and RB1 heterozygous mutant retinal organoids were indistinguishable with respect to morphology, temporal development of retinal cell types and global mRNA expression. However, loss of pRB resulted in spatially disorganized organoids and aberrant differentiation, indicated by disintegration of organoids beyond day 130 of differentiation and depletion of most retinal cell types. Only cone photoreceptors were abundant and continued to proliferate, supporting these as candidate cells-of-origin for retinoblastoma. Transcriptome analysis of RB1 knockout organoids and primary retinoblastoma revealed gain of a retinoblastoma expression signature in the organoids, characterized by upregulation of RBL1 (p107), MDM2, DEK, SYK and HELLS. In addition, genes related to immune response and extracellular matrix were specifically upregulated in RB1-negative organoids. In vitro retinal organoids therefore display some features associated with retinoblastoma and, so far, represent the only valid human cancer model for the development of this disease.

P38 Mitogen-Activated Protein Kinase Protects Against Retinoblastoma Through Regulating USP22/SIRT1/SOST Axis

Retinoblastoma (RB) is the most common intraocular malignancy in children. It has been previously reported that p38 MAPK is related to the pathogenesis of RB. Here we aim at investigating how p38 MAPK affected RB progression through mediating USP22/SIRT1/SOST axis. In this study, Thirty-two cases of RB and normal retinal tissues were collected. The expression of p38 MAPK, phosphorylation of p38 MAPK (P-p38 MAPK), USP22, SIRT1 and SOST in clinical tissues and cells was measured using RT-qPCR, IHC assay or western blot analysis. Cell proliferation was detected by CCK-8. Apoptosis rate of cells was examined by flow cytometry. Cell migration was evaluated using scratch test. Cell invasion ability was examined by Transwell assay. Co-immunoprecipitation (CO-IP) was utilized to measure the deubiquitination of USP22 on SIRT1. In vivo, mice were respectively injected with plasmids and the tumor growth as well as the tumor weight were detected. Results showed that p38 MAPK, P-p38 MAPK and SOST were poorly expressed in RB tissues and cells whereas USP22 and SIRT1 were overly expressed. P-p38 MAPK inhibited the expression of USP22, and overexpression of USP22 eliminated the inhibitory roles of P-p38 MAPK on tumor growth, as well as cell proliferation, migration and invasion. USP22 stabilized and promoted the expression of SIRT1 through its deubiquitination function. Silencing the expression of SIRT1 contributed to boosted expression of SOST, thus suppressing the growth of tumor cells. Collectively, the phosphorylation of p38 MAPK regulates the SIRT1/SOST axis to protect against RB via silencing USP22. The findings present some cues for a further approach to RB.

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.

The roles of mouse double minute 2 (MDM2) oncoprotein in ocular diseases: A review

Mouse double minute 2 (MDM2), an E3 ubiquitin ligase and the primary negative regulator of the tumor suppressor p53, cooperates with its structural homolog MDM4/MDMX to control intracellular p53 level. In turn, overexpression of p53 upregulates and forms an autoregulatory feedback loop with MDM2. The MDM2-p53 axis plays a pivotal role in modulating cell cycle control and apoptosis. MDM2 itself is regulated by the PI3K-AKT and RB-E2F-ARF pathways. While amplification of the MDM2 gene or overexpression of MDM2 (due to MDM2 SNP T309G, for instance) is associated with various malignancies, numerous studies have shown that MDM2/p53 alterations may also play a part in the pathogenetic process of certain ocular disorders (Fig. 1). These include cancers (retinoblastoma, uveal melanoma), fibrocellular proliferative diseases (proliferative vitreoretinopathy, pterygium), neovascular diseases, degenerative diseases (cataract, primary open-angle glaucoma, age-related macular degeneration) and infectious/inflammatory diseases (trachoma, uveitis). In addition, MDM2 is implicated in retinogenesis and regeneration after optic nerve injury. Anti-MDM2 therapy has shown potential as a novel approach to treating these diseases. Despite major safety concerns, there are high expectations for the clinical value of reformative MDM2 inhibitors. This review summarizes important findings about the role of MDM2 in ocular pathologies and provides an overview of recent advances in treating these diseases with anti-MDM2 therapies.

SOX2 maintains the stemness of retinoblastoma stem-like cells through Hippo/YAP signaling pathway

PURPOSE

To explore the mechanisms underlying stemness maintenance of retinoblastoma (RB) stem cells (RSCs).

METHODS

The retinoblastoma stem-like cells (RSLCs) were isolated by single cell cloning in combination of examination of sphere-forming capacities. The stemness of the cells were characterized by the sphere-forming capacity and the expression levels of RSCs markers. Gene manipulation was performed by lentivirus system. Transcriptional regulation was identified by qRT-PCR, luciferase reporter, nuclear run-on and DNA pull-down assay. Spearman analysis was employed for correlation analysis of genes in tumor tissues of RB patients.

RESULTS

The isolated RSLCs exhibited enhanced sphere-forming capacity and constantly higher levels of CD44, ABCG2, SOX2 and PAX6, but not CD133. SOX2 positively regulated the stemness of RSLCs. SOX2 directly binds to the promoters of WWTR1 and YAP and transcriptionally activates WWTR1 and YAP. Knockdown of WWTR1 or YAP partially abolished the effect of SOX2 on the stemness of RSLCs.

CONCLUSIONS

SOX2, as a key deriver, maintains RB stemness by activating Hippo/YAP signaling. Inhibition of Hippo/YAP signaling would be an effective strategy for human RB caused by SOX2 upregulation.