Nikia A. Laurie

Inactivation of the p53 pathway in retinoblastoma.

Most human tumours have genetic mutations in their Rb and p53 pathways, but retinoblastoma is thought to be an exception. Studies suggest that retinoblastomas, which initiate with mutations in the gene retinoblastoma 1 (RB1), bypass the p53 pathway because they arise from intrinsically death-resistant cells during retinal development. In contrast to this prevailing theory, here we show that the tumour surveillance pathway mediated by Arf, MDM2, MDMX and p53 is activated after loss of RB1 during retinogenesis. RB1-deficient retinoblasts undergo p53-mediated apoptosis and exit the cell cycle. Subsequently, amplification of the MDMX gene and increased expression of MDMX protein are strongly selected for during tumour progression as a mechanism to suppress the p53 response in RB1-deficient retinal cells. Our data provide evidence that the p53 pathway is inactivated in retinoblastoma and that this cancer does not originate from intrinsically death-resistant cells as previously thought. In addition, they support the idea that MDMX is a specific chemotherapeutic target for treating retinoblastoma.

Topotecan Combination Chemotherapy in Two New Rodent Models of Retinoblastoma

Chemotherapy combined with laser therapy and cryotherapy has improved the ocular salvage rate for children with bilateral retinoblastoma. However, children with late-stage disease often experience recurrence shortly after treatment. To improve the vision salvage rate in advanced bilateral retinoblastoma, we have developed and characterized two new rodent models of retinoblastoma for screening chemotherapeutic drug combinations. The first model is an orthotopic xenograft model in which green fluorescent protein– or luciferase-labeled human retinoblastoma cells are injected into the eyes of newborn rats. The second model uses a replication-incompetent retrovirus (LIA-EE1A) encoding the E1A oncogene. Clonal, focal tumors arise from mouse retinal progenitor cells when LIA-EE1A is injected into the eyes of newborn p53−/− mice. Using these two models combined with pharmacokinetic studies and cell culture experiments, we have tested the efficacy of topotecan combined with carboplatin and of topotecan combined with vincristine for the treatment of retinoblastoma. The combination of topotecan and carboplatin most effectively halted retinoblastoma progression in our rodent models and was superior to the current triple drug therapy using vincristine, carboplatin, and etoposide. Vincristine had the lowest LC50 in culture but did not reduce tumor growth in our preclinical retinoblastoma models. Taken together, these data suggest that topotecan may be a suitable replacement for etoposide in combination chemotherapy for the treatment of retinoblastoma.

Targeting MDM2 and MDMX in retinoblastoma.

Retinoblastoma is the third most common form of cancer in infants, and metastatic retinoblastoma is lethal in approximately 90% of cases. Early detection and aggressive therapy has resulted in a 95% probability of survival for retinoblastoma patients in the United States. However, the United States only represents 3-4% of the retinoblastoma cases worldwide. The majority of children diagnosed with retinoblastoma each year live in developing countries where the probability of survival is closer to 50%. This difference in survival rates reflects poor early detection rates and limited resources for the aggressive therapy necessary to treat retinoblastoma and manage the side effects associated with broad-spectrum systemic chemotherapy in young children. In order to have the most significant impact on retinoblastoma treatment in the United States and worldwide, current efforts have focused on local delivery of targeted chemotherapy. In this review, we summarize recent data showing that the p53 pathway is inactivated in 75% of retinoblastoma patients due to extra copies of the MDM2 and MDMX genes. A small molecule inhibitor of MDM2 called nutlin-3 can induce p53-mediated cell death in retinoblastoma cells. Subconjunctival delivery of nutlin-3 in preclinical models of retinoblastoma confirmed the efficacy of this approach in vivo. The advantage of local application of targeted chemotherapeutic agents such as nutlin-3 is that greater intraocular drug concentrations can be achieved without the side effects associated with systemic broad-spectrum chemotherapy. We propose that subconjunctival administration of targeted chemotherapy may be the best treatment option for children with retinoblastoma in the United States and throughout the developing world because it provides greater tumor response without the costs and complications associated with current treatment protocols.

Changes in retinoblastoma cell adhesion associated with optic nerve invasion

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

AAV-mediated Local Delivery of Interferon-β for the Treatment of Retinoblastoma in Preclinical Models

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

Differentially expressed miRNAs in retinoblastoma

MicroRNAs (miRNAs) are short non-coding RNA transcripts that have the ability to regulate the expression of target genes, and have been shown to influence the development of various tumors. The purpose of our study is to identify aberrantly expressed miRNAs in retinoblastoma for the discovery of potential therapeutic targets for this disease, and to gain a greater understanding of the mechanisms driving retinoblastoma progression. We report 41 differentially expressed miRNAs (p<0.05) in 12 retinoblastomas as compared to three normal human retinae. Of these miRNAs, many are newly identified as being differentially expressed in retinoblastoma. Further, we report the validations of five of the most downregulated miRNAs in primary human retinoblastomas (p<0.05), human retinoblastoma cell lines, and mouse retinoblastoma cell lines. This serves as the largest and most comprehensive retinoblastoma miRNA analysis to date with corresponding clinical and pathological characteristics. This is an essential step in the discovery of miRNAs associated with retinoblastoma progression, and in the identification of potential therapeutic targets for this disease.

MicroRNAs-449a and -449b exhibit tumor suppressive effects in retinoblastoma

Retinoblastoma is the most common pediatric cancer of the eye. Currently, the chemotherapeutic treatments for retinoblastoma are broad-based drugs such as vincristine, carboplatin, or etoposide. However, therapies targeted directly to aberrant signaling pathways may provide more effective therapy for this disease. The purpose of our study is to illustrate the relationship between the expressions of miRs-449a and -449b to retinoblastoma proliferation and apoptosis. We are the first to confirm an inhibitory effect of miR-449a and -449b in retinoblastoma by demonstrating significantly impaired proliferation and increased apoptosis of tumor cells when these miRNAs are overexpressed. This study suggests that these miRNAs could serve as viable therapeutic targets for retinoblastoma treatment.

Local angiotensin-converting enzyme inhibition blunts endothelin-1–induced increase in forearm vascular resistance

The physiologic role of endothelin‐1 is not well established; however, it may have a role in modulation of peripheral vascular tone complimentary to angiotensin II. In vitro and animal studies suggested an interrelationship between angiotensin II and endothelin‐1 vasoconstriction. We hypothesized that local vascular or systemic renin‐angiotensin II systems must be intact for endothelin‐1‐mediated vasoconstriction in humans.

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

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

Abstract 536: Elucidating the role of miRNA-31 in retinoblastoma

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Retinoblastoma is the most common pediatric ocular cancer. Although early detection of the disease may have a favorable outcome for the patient, retinoblastoma can aggressively develop and become fatal. Current treatment strategies include focal therapies, chemotherapy and in more severe cases, enucleation (removal of the eye) is necessary. This cancer may initiate from acquired or inherited mutations in the RB1 gene. As a result, the mutant retinal cell is conferred an unrestrained proliferative ability that is facilitated by multiple genetic events. Determining the mechanism(s) responsible for tumor growth, invasion, and metastasis may provide an alternative treatment strategy that may delay enucleation, prevent toxic side effects from chemotherapy, or even prevent metastatic spread altogether. Genetic factors that are highly involved in both carcinogenesis and homeostasis are often regulated by miRNAs. miRNAs are small, non-coding molecules that negatively regulate gene expression by mediating mRNA cleavage and/or disrupting protein synthesis. Our rationale for this study is that investigating aberrant miRNA regulation in retinoblastoma will enable us to identify key genetic factors that can be targeted therapeutically. Our miRNA array suggests that there is a significant number of miRNAs whose expression is significantly downregulated between retinoblastoma tumors and normal human retinae. From this data, we have identified candidate miRNAs, such as miRNA-31, that have been previously reported to have an important anti-metastatic role in different cancer types. We are currently investigating the role of these miRNAs in regulating retinoblastoma progression. These functional studies will allow us to determine how increasing miRNA expression in retinoblastoma models can disrupt important signaling pathways associated with retinoblastoma progression and invasion. Citation Format: Vanessa Montoya, Paul J. Bryar, Marilyn Mets, Joanna Weinstein, Nikia Laurie. Elucidating the role of miRNA-31 in retinoblastoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 536. doi:10.1158/1538-7445.AM2014-536