Retinoblastoma epidemiology: does the evidence matter?

Molecular Biological Research on the Pathogenic Mechanism of Retinoblastoma

Retinoblastoma (RB) is the most common intraocular malignant tumor in children, primarily attributed to the bi-allelic loss of the RB1 gene in the developing retina. Despite significant progress in understanding the basic pathogenesis of RB, comprehensively unravelling the intricate network of genetics and epigenetics underlying RB tumorigenesis remains a major challenge. Conventional clinical treatment options are limited, and despite the continuous identification of genetic loci associated with cancer pathogenesis, the development of targeted therapies lags behind. This review focuses on the reported genomic and epigenomic alterations in retinoblastoma, summarizing potential therapeutic targets for RB and providing insights for research into targeted therapies.

MicroRNA-34b-5p inhibits proliferation, stemness, migration and invasion of retinoblastoma cells via Notch signaling

Retinoblastoma (RB) is one of the most common forms of childhood intraocular cancer. While the occurrence of RB is traditionally associated with dysregulation of the RB1 gene, efforts have been made to assess the role of several other pathways that may result in RB. The Notch signaling pathway has been identified as one of the sentinel pathways in retinal development and has been indicated to serve as a tumor suppressor. However, epigenetic modifications of the Notch signaling pathway, and their consequences on tumor establishment and progression, have received little attention. The present study attempted to elucidate the microRNA (miR)-mediated dysregulation of the Notch signaling pathway and its implications on tumor initiation. Upon recruitment of patients with RB (age, 4-25 months), the levels of miR-34b-5p were determined in tumor and adjacent healthy tissues. Simultaneously, the serum levels of miR-34b-5p were measured in tumor and healthy samples using reverse transcriptase-quantitative PCR (RT-qPCR). Binding of miR-34b-5p to Notch1 and Notch2 were confirmed bioinformatically. In vitro studies were performed in Y79 and Weri-Rb-1 RB cell lines. The cell lines were transfected with miR-34b-5p constructs and miR-34b-5p overexpression was confirmed using RT-qPCR. The impact of miR-34b-5p overexpression on cell growth and cancer stemness markers (Sox-2, Nanog, and CD133) was examined. The expression levels of Notch1 and Notch2 were evaluated in the presence of miR-34b-5p. The rescue of cell growth and cancer stemness phenotypes was evaluated by co-transfection of miR-34b-5p with Notch1 or Notch2. The results of the present study indicated that the expression levels of miR-34b-5p were reduced in patient tissues and serum samples compared with those in healthy tissues and samples. Notch1 and Notch2 expression level was negatively correlated with the expression level of miR-34b-5p. Overexpression of miR-34b-5p resulted in reduced cell proliferation, migration, invasion and cancer stemness compared with the control group. Further in vivo experiments confirmed the inhibitory effects of miR-34b-5p on RB cell proliferation. Upon co-transfection of miR-34b-5p with Notch1 or Notch2, these phenotypes were rescued with reversal of cell growth and tumor sphere formation. Collectively, the results indicated that miR-34b-5p functions as a tumor suppressor in RB via regulating the Notch signaling pathway. Therefore, miR-34b-5p may be explored for its utility as a therapeutic target in RB.

The long non-coding RNA ILF3-AS1 increases the proliferation and invasion of retinoblastoma through the miR-132-3p/SMAD2 axis

A great deal of evidence suggests that long non-coding RNAs (lncRNAs) function in the tumorigenesis of retinoblastoma (RB). However, the roles of lncRNA ILF3-AS1 in RB are still unclear. In the present study, our work revealed that the lncRNA ILF3-AS1 was increased in both RB tissues and cell lines. Repression of ILF3-AS1 suppressed both RB cell proliferation and invasion in vitro. ILF3-AS1 also promoted tumor growth in vivo. While exploring the mechanisms behind ILF3-AS1 in RB, we identified that ILF3-AS1 sponges with miR-132-3p that is expressed at low levels in RB tissues as well as attenuates RB progression. Furthermore, SMAD2 was confirmed to be a miR-132-3p target. Finally, we found that SMAD2 overexpression or miR-132-3p inhibitors recover the inhibitory effects of ILF3-AS1 suppression on RB progression. Collectively, these data indicate that ILF3-AS1 is involved in RB progression through the miR-132-3p/SMAD2 axis, providing a novel and promising biomarker that can be used for the treatment of RB.

Overexpression of Biglycan is Associated with Resistance to Rapamycin in Human WERI-Rb-1 Retinoblastoma Cells by Inducing the Activation of the Phosphatidylinositol 3-Kinases (PI3K)/Akt/Nuclear Factor kappa B (NF-κB) Signaling Pathway

Background

Biglycan (BGN) is an extracellular matrix (ECM) protein that regulates the growth of epithelial cells. The mammalian target of rapamycin (mTOR) inhibitor, rapamycin, is a treatment for advanced retinoblastoma. This study aimed to investigate the effects of expression of BGN on the response of human WERI-Rb-1 retinoblastoma cells to rapamycin and to investigate the associated signaling pathways.

Material/Methods

BGN gene expression was induced in human WERI-Rb-1 retinoblastoma cells, which were incubated with rapamycin at doses of 0, 5, 10, 20, 30, and 50 μg/ml. Cells were treated with the PI3K/Akt pathway inhibitor, LY294002. The MTT assay determined the rate of cell inhibition. Real-time polymerase chain reaction (RT-PCR) was performed to measure BGN gene expression using RT²-PCR. Western blot detected the protein levels of BGN, p-PI3K, p-Akt, nuclear NF-κB, and p65.

Results

Rapamycin impaired cell growth, induced cell apoptosis, and suppressed the expression levels of p-PI3K, p-Akt, nuclear NF-κB, and p65. Overexpression of the BGN gene restored growth potential and inhibited apoptosis and was associated with the activation of the PI3K/Akt-mediated NF-κB pathway. In cells that overexpressed BGN, inhibition of the PI3K/Akt pathway by LY294002 increased the sensitivity of human WERI-Rb-1 retinoblastoma cells to rapamycin.

Conclusions

Overexpression of BGN induced rapamycin resistance in WERI-Rb-1 retinoblastoma cells by activating PI3K/Akt/NF-κB signaling.

Secondary Craniofacial Sarcomas Following Retinoblastoma: A Systematic Review

OBJECTIVE

We conducted the largest systematic review of individual patient data to characterize secondary craniofacial sarcomas following retinoblastoma.

METHODS

We conducted a systemic search of the PubMed databases and compiled a comprehensive literature review. Student t tests were used to evaluate differences between variables. Kaplan-Meier analysis was used to estimate survival. Statistical significance was assessed using a log-rank test.

RESULTS

We analyzed 220 cases of secondary craniofacial sarcomas, including 112 osteosarcomas. The average age (±SD) of onset for retinoblastoma was 1.20 ± 2.77 years. External-beam radiotherapy was delivered in 207 patients (94.0%) and chemotherapy was delivered in 53 patients (24.0%) patients. The latency period between retinoblastoma diagnosis and the onset of secondary sarcomas was 12 years. Cranial extension was found in 66 patients (30.0%). The median overall survival was worse with cranial extension (P = 0.0073). In cranial extended patients, the median survival in patients who received chemotherapy was 41 months, whereas patients who did not receive chemotherapy had a median survival of 12 months (P = 0.0020).

CONCLUSIONS

The risk of incidence of secondary sarcomas in retinoblastoma patients warrants longer follow-up periods. Moreover, chemotherapy should be considered as a potential treatment option for secondary cranial sarcomas following retinoblastoma.

Maternal diet during pregnancy and unilateral retinoblastoma

PURPOSE

Previous studies have suggested a role for parental diet in childhood cancer prevention, but there are few studies of retinoblastoma. The aim of this study was to examine the relation between maternal diet and unilateral retinoblastoma.

METHODS

A case-control study of 163 unilateral RB cases and 136 controls ascertained information on maternal diet during pregnancy using a standardized food frequency questionnaire. Logistic regression was used to assess the relation between retinoblastoma and food groups and dietary patterns.

RESULTS

We observed a negative association between retinoblastoma and intake of fruit [odds ratio (OR) 0.38, 95 % confidence interval (CI) 0.14-1.02]. Positive associations were seen with intake of cured meats (OR 5.07, 95 % CI 1.63-15.70) and fried foods (OR 4.89, 95 % CI 1.72-13.89). A food pattern of high fruits and vegetables and low fried food and sweets was negatively associated with disease (OR 0.75, 95 % CI 0.61-0.92).

CONCLUSION

Our study provides preliminary evidence that mothers who consume diets higher in fruit and lower in fried foods and cured meats during pregnancy may reduce the risk of unilateral retinoblastoma in their offspring.

Differential expression of genes in retinoblastoma

Retinoblastoma is a pediatric eye tumor that serves as a paradigm for understanding the genetic basis of cancer. Mutations and/or epigenetic alterations inactivating both alleles of the retinoblastoma gene (RB) are associated with retinoblastoma. There are many other genes which express differentially in the preneoplastic retinal cells after RB loss, as cells progress to form tumors. These genetic changes and the pathways involved can provide valuable insight into the development and progression of this cancer. Conventional molecular and genetic methods for studying cancer are limited to the analysis of one locus at a time. A cluster of genes that are regulated together can be identified by DNA microarray, and the functional relationships can uncover new aspects of cancer biology. Meta analysis is an important tool for the identification and validation of differentially expressed genes to increase power in clinical and biological studies across different sets of data. Recently, meta analysis approaches have been applied to large collections of microarray datasets to investigate molecular commonalities of multiple cancer types not only to find the common molecular pathways in tumor development but also to compare the individual datasets to other cancer datasets to identify new sets of genes. The outcome of these analyses might accelerate the application of basic research findings into daily clinical practice through translational research and may have an impact on foreseeing the clinical outcome, predicting tumor response to specific therapy, identification of new prognostic biomarkers, discovering targets for the development of novel therapies and providing further insights. These and related research efforts reveal novel data that enhance our understanding of the biology of retinoblastoma. These observations may facilitate new therapeutic approaches to further decrease the morbidity and mortality associated with retinoblastoma and other more common forms of cancer.

Retinoblastoma and the genetic theory of cancer: an old paradigm trying to survive to the evidence

Retinoblastoma (Rb) is considered to represent the prototype of cancer linked to the sequential loss or inactivation of both alleles of a so-called “tumor suppressor gene”, the Rb1 gene. The pathogenetic mechanism behind this tumor was first hypothesized by Knudson in 1971 and further confirmed by others who identified the Rb1 gene whose loss or inactivation was claimed to be responsible for the disease. However, after about four decades of continuous research in the field of molecular biology, the evidence behind the role of the Rb1 gene in Rb appears to be seriously flawed in the light of epidemiological, biological, and clinical evidences. This editorial summarizes the inconsistencies on this subject. Nevertheless, the molecular biology establishment still adheres to the biased view of the genetic origin of Rb and other cancers, and hardly any alternative explanations are taken into account.

Recent advances in retinoblastoma genetic research

PURPOSE OF REVIEW

Retinoblastoma is a pediatric eye tumor that serves as a paradigm for understanding the genetic basis of cancer. This review will highlight recent advances in retinoblastoma genetic research and discuss how these new findings influence our knowledge of retinoblastoma tumorigenesis and management.

RECENT FINDINGS

Current data demonstrate that retinomas, benign retinal tumors found in some retinoblastoma patients, exhibit bi-allelic mutations in RB1, the retinoblastoma gene, and lack of expression of the retinoblastoma protein. Interestingly, retinomas demonstrate a low level of genomic instability that becomes progressively more severe in retinoblastoma tumors. Additionally, a subset of retinomas share genomic alterations with retinoblastoma. Collectively, these data suggest that retinomas represent true premalignant lesions and not regressed retinoblastoma tumors, as previously thought. Translational advances in retinoblastoma genetic research include development of an allele-specific assay that now enables the identification of mutational mosaicism, thereby increasing the rate of RB1 mutation detection in bilaterally affected patients to as high as 95%.

SUMMARY

These and related research efforts reveal novel data that enhance our understanding of the biology of retinoblastoma. These observations may facilitate new therapeutic approaches to further decrease the morbidity and mortality associated with retinoblastoma and other more common forms of cancer.