Effects of celecoxib in human retinoblastoma cell lines and in a transgenic murine model of retinoblastoma

Drug Repurposing for Retinoblastoma: Recent Advances

Retinoblastoma is the intraocular malignancy that occurs during early childhood. The current standard of care includes chemotherapy followed by focal consolidative therapies, and enucleation. Unfortunately, these are associated with many side and late effects. New drugs and/or drug combinations need to be developed for safe and effective treatment. This compelling need stimulated efforts to explore drug repurposing for retinoblastoma. While conventional drug development is a lengthy and expensive process, drug repurposing is a faster, alternate approach, where an existing drug, not meant for treating cancer, can be repurposed to treat retinoblastoma. The present article reviews various attempts to test drugs approved for different purposes such as calcium channels blockers, non-steroidal antiinflammatory drugs, cardenolides, antidiabetic, antibiotics and antimalarial for treating retinoblastoma. It also discusses other promising candidates that could be explored for repurposing for retinoblastoma.

Role of Cyclooxygenase-2 on Intermittent Hypoxia-Induced Lung Tumor Malignancy in a Mouse Model of Sleep Apnea

An adverse role for obstructive sleep apnea (OSA) in cancer epidemiology and outcomes has recently emerged from clinical and animal studies. In animals, intermittent hypoxia (IH) mimicking OSA promotes tumor malignancy both directly and via host immune alterations. We hypothesized that IH could potentiate cancer aggressiveness through activation of the cyclooxygenase-2 (COX-2) pathway and the concomitant increases in prostaglandin E2 (PGE₂). The contribution of the COX-2 in IH-induced enhanced tumor malignancy was assessed using celecoxib as a COX-2 specific inhibitor in a murine model of OSA bearing Lewis lung carcinoma (LLC1) tumors. Exposures to IH accelerated tumor progression with a tumor associated macrophages (TAMs) shift towards a pro-tumoral M2 phenotype. Treatment with celecoxib prevented IH-induced adverse tumor outcomes by inhibiting IH-induced M2 polarization of TAMs. Furthermore, TAMs isolated from IH-exposed mice treated with celecoxib reduced the proliferation of LLC1 naïve cells, while the opposite occurred with placebo-treated IH-exposed mice. Finally, in vitro IH exposures of murine macrophages and LLC1 cells showed that both cell types increased PGE₂ release in response to IH. These results suggest a crucial role for the COX-2 signaling pathway in the IH-exacerbated malignant processes, and designate macrophages and lung adenocarcinoma cells, as potential sources of PGE₂.

Targeting Survivin Enhances Chemosensitivity in Retinoblastoma Cells and Orthotopic Tumors

Treatments for retinoblastoma (Rb) vary depending on the size and location of the intraocular lesions and include chemotherapy and radiation therapy. We examined whether agents used to treat Rb induce a pro-survival phenotype associated with increased expression of survivin, a member of the inhibitor of apoptosis family of proteins. We document that exposure to carboplatin, topotecan or radiation resulted in elevated expression of survivin in two human Rb cell lines but not in normal retinal pigmented epithelial (RPE) cells. Cellular levels of survivin were attenuated in Rb cells exposed to an imidazolium-based survivin suppressant, Sepantronium bromide (YM155). Protein expression patterns of survivin in RPE cells were not altered following treatment protocols involving exposure to YM155. Including YM155 with chemotherapy or radiation increased levels of apoptosis in Rb cells but not in RPE cells. Intraocular luciferase expressing Rb tumors were generated from the Rb cell lines and used to evaluate the effects of carboplatin and YM155 on in-vivo survivin expression and tumor growth. Carboplatin induced expression of survivin while carboplatin combined with YM155 reduced survivin expression in tumor bearing eyes. The combination protocol was also most effective in reducing the rate of tumor regrowth. These results indicate that targeted inhibition of the anti-apoptotic protein survivin provides a therapeutic advantage for Rb cells and tumors treated with chemotherapy.

Transgenic Models in Retinoblastoma Research

Understanding the mechanism of retinoblastoma (Rb) tumor initiation, development, progression and metastasis in vivo mandates the use of animal models that mimic this intraocular tumor in its genetic, anatomic, histologic and ultrastructural features. An early setback for developing mouse Rb models was that Rb mutations did not cause tumorigenesis in murine retinas. Subsequently, the discovery that the p107 protein takes over the role of pRb in mice led to the development of several animal models that phenotypically and histologically resemble the human form. This paper summarizes the transgenic models that have been developed over the last three decades.

Nanoparticle-based topical ophthalmic formulations for sustained celecoxib release

Celecoxib-loaded NPs were prepared from biodegradable polymers such as poly-ε-caprolactone (PCL), poly(L-lactide) (PLA), and poly(D,L-lactide-co-glycolide) (PLGA) by spontaneous emulsification solvent diffusion method. Different concentrations of polymers, emulsifier, and cosurfactants were used for formulation optimization. Nanoparticles (NPs) were characterized regarding their particle size, PDI, zeta potential, shape, morphology, and drug content. Celecoxib-loaded NPs were incorporated into eye drops, in situ gelling system, and gel and characterized regarding their pH, viscosity, uniformity of drug content, in vitro release, and cytotoxicity. The results of optimized celecoxib-loaded PCL-, PLGA-, and PLA-NPs, respectively, are particle size 119 ± 4, 126.67 ± 7.08, and 135.33 ± 4.15 nm; zeta potential -22.43 ± 2.91, -25.46 ± 2.35, and -31.81 ± 2.54 mV; and encapsulation efficiency 93.44 ± 3.6%, 86.00 ± 1.67%, and 79.04 ± 2.6%. TEM analyses revealed that NPs have spherical shapes with dense core and distinct coat. Formulations possessed uniform drug content with pH and viscosity compatible with the eye. Formulations showed sustained release without any burst effect with the Higuchi non-fickian diffusion mechanism. Cytotoxicity studies revealed that all formulations are nontoxic. Our formulations provide a great deal of flexibility to formulation scientist whereby sizes and zeta potentials of our NPs can be tuned to suit the need using scalable and robust methodologies. These formulations can thus serve as a potential drug delivery system for both anterior and posterior eye diseases.

Cyclooxygenase-2 expression in the normal human eye and its expression pattern in selected eye tumours

PURPOSE

Cyclooxygenase-2 (COX-2) is an enzyme involved in neoplastic processes. The purpose of the present study is to investigate COX-2 expression in the normal human eye and the expression pattern in selected eye tumours involving COX-2 expressing cells.

METHODS

Immunohistochemical staining using antibodies against COX-2 was performed on paraffin sections of normal human eyes and selected eye tumours arising from cells expressing COX-2.

RESULTS

Cyclooxygenase-2 expression was found in various structures of the normal eye. Abundant expression was seen in the cornea, iris, ciliary body and retina. The COX-2 expression was less in tumours deriving from the ciliary epithelium and also in retinoblastoma.

CONCLUSION

Cyclooxygenase-2 is constitutively expressed in normal human eyes. The expression of COX-2 is much lower in selected eye tumours involving COX-2 expressing cells.

Cyclooxygenase-2 expression in retinoblastoma: an immunohistochemical analysis

PURPOSE

Increased level of cyclooxygenase-2 (COX-2) plays a significant role in the pathogenesis of cancers. High expression of COX-2 has been demonstrated in several cancer types including retinoblastoma. However, the in vivo study did not confirm the anti-proliferative effect of COX-2 inhibitor, celecoxib, on a murine transgenic retinoblastoma model. We, therefore, aim to investigate COX-2 expression in paraffin-embedded retinoblastoma specimens in a larger study group.

METHODS

We reviewed 55 retinoblastoma specimens obtained during 1995 to 2005. Clinical and histopathological data were recorded. Immunohistochemical evaluation of COX-2 expression was performed using a rabbit monoclonal antibody to human cyclooxygenase-2.

RESULTS

Forty-four of 55 specimens (80%) showed negative immunoreactivity for COX-2 expression. For the 11 specimens (20%, 95% CI = 11.6-32.4%) with positive COX-2, all immunostainings were less than 50% of tumor area. Demographic data and treatment details were available in 53 specimens. Enucleation was performed as a primary treatment in 43 specimens (81%). Other treatments, mainly systemic chemotherapy, were given prior to enucleation in 10 specimens (19%). There was no statistical difference in COX-2 expression between the specimens identified as primary and secondary enucleation (p = 0.66). Regarding the histopathological findings, there were no significant differences between COX-2 negative and COX-2 positive groups.

CONCLUSIONS

It appears that COX-2 is not overexpressed in our retinoblastoma specimens, which is different from previous studies. This conflicting data reduces the possibility of introducing Cox-2 inhibitors in the treatment of retinoblastoma.

Cdh11 acts as a tumor suppressor in a murine retinoblastoma model by facilitating tumor cell death

CDH11 gene copy number and expression are frequently lost in human retinoblastomas and in retinoblastomas arising in TAg-RB mice. To determine the effect of Cdh11 loss in tumorigenesis, we crossed Cdh11 null mice with TAg-RB mice. Loss of Cdh11 had no gross morphological effect on the developing retina of Cdh11 knockout mice, but led to larger retinal volumes in mice crossed with TAg-RB mice (p = 0.01). Mice null for Cdh11 presented with fewer TAg-positive cells at postnatal day 8 (PND8) (p = 0.01) and had fewer multifocal tumors at PND28 (p = 0.016), compared to mice with normal Cdh11 alleles. However, tumor growth was faster in Cdh11-null mice between PND8 and PND84 (p = 0.003). In tumors of Cdh11-null mice, cell death was decreased 5- to 10-fold (p<0.03 for all markers), while proliferation in vivo remained unaffected (p = 0.121). Activated caspase-3 was significantly decreased and β-catenin expression increased in Cdh11 knockdown experiments in vitro. These data suggest that Cdh11 displays tumor suppressor properties in vivo and in vitro in murine retinoblastoma through promotion of cell death.

Despite over two decades since loss of RB1 was implicated in initiating retinoblastoma, the unique tissue specificity of this process remains puzzling. Indeed, functional loss of both alleles of the RB1 tumor suppressor gene results in >40,000-fold increase in predisposition to retinal cancer during childhood, while one constitutional RB1 mutant allele confers a broader but much lower cancer predisposition later in life. We have proposed a specific signature of progressive genomic changes that leads to full tumor development. One of these changes is genomic loss of the CDH11 gene, suggesting that this gene normally suppresses the development of retinoblastoma. We present novel data indicating that Cdh11 functions as a tumor suppressor gene in retinoblastoma by facilitating cell death. Our insight into the sequence of events that contribute to retinoblastoma development is important for future therapies and fundamental understanding of cancer.

Lymphoblastic T-cell lymphoma in mice is unaffected by Celecoxib as single agent or in combination with cyclophosphamide

Celecoxib, an inhibitor of cyclooxygenase-2, is a promising novel antitumor agent with pleitropic mechanisms of action. Whereas this drug induces growth arrest and apoptosis of B-lymphoma cells, its effect against aggressive T-cell neoplasms remains to be studied. We therefore evaluated Celecoxib therapy of immunocompetent mice transplanted with lymphoblastic T-cell lymphomas. Oral Celecoxib in clinically relevant and non-toxic doses did not affect the degree of hypersplenism or the number of viable lymphoma cells. The clinical deterioration of Celecoxib-treated mice was not different from untreated controls. The impact of adding Celecoxib (60 mg/kg) to cyclophosphamide (200 mg/kg x 1, i.p.) was assessed but showed no benefit compared to cyclophosphamide alone. Thus, Celecoxib lacks effect against lymphoblastic T-cell lymphoma in mice.

Quantitative analysis of tumor size in a murine model of retinoblastoma

Murine models can provide valuable insight into mechanisms of tumorigenesis. Tumor size is often used to assess the impact of genetic insult or therapeutic treatment, usually using in vivo imaging of advanced tumors. We now describe a highly sensitive method to quantify tumor volume in a mouse model of retinoblastoma, from the earliest stages of tumor initiation to large, advanced tumors. This methodology combines immunohistochemistry, digital slide scanning and computer image analysis, and can be applied to quantitatively assess and characterize early tumor development in other models.

The expression of cyclooxygenase 2 in retinoblastoma: primary enucleated eyes and enucleation after conservative treatment

PURPOSE

To provide insight into the relationship between cyclooxygenase-2 (COX-2) expression and histopathologic features of retinoblastoma specimens treated either by primary or secondary enucleation.

DESIGN

Laboratory investigation.

METHODS

Twenty-five retinoblastoma specimens received between 1994 and 2003 were retrieved for this study from the Ocular Pathology Registry, Federal University of São Paulo, Brazil and the Henry C. Witelson Ocular Pathology Laboratory and Registry, McGill University, Montreal, Canada. The specimens retrieved were divided into two groups: Group I, enucleation was performed as a form of primary treatment (n = 15) and Group II, enucleation after failure of conservative treatment (n = 10). Patient information and formalin-fixed, paraffin-embedded specimens were obtained. New sections of these blocks were used for hematoxylin and eosin stain and for immunoassay using a monoclonal mouse anti-COX-2 antibody. Two independent ophthalmic pathologists reviewed all of the microslides.

RESULTS

Twenty-three specimens (92%) presented a high expression of COX-2 (15 in Group I; eight in Group II) and there was no statistical difference in COX-2 expression between the two groups (P = .07). However, all specimens expressed COX-2 to a different degree. The areas of tumor invasion were positive for COX-2 in 87.5% of the two groups.

CONCLUSION

Most retinoblastoma specimens revealed a high COX-2 expression. Future studies will be necessary to correlate the high expression of COX-2 in retinoblastoma and a possible applicability of anti-COX-2 medications in the treatment of these tumors.

Interaction of Nonsteroidal Anti-Inflammatory Drugs with Multidrug Resistance Protein (MRP) 2/ABCC2- and MRP4/ABCC4-Mediated Methotrexate Transport

Methotrexate (MTX) has been used in combination with nonsteroidal anti-inflammatory drugs (NSAIDs) in the treatment of inflammatory diseases as well as malignancies. Especially at high MTX dosages, severe adverse effects with this combination may occur, usually resulting from an impaired renal elimination. It has been shown that the mechanism of this interaction cannot be fully attributed to inhibition of basolateral MTX uptake in renal proximal tubules. Here, we studied the effect of various NSAIDs on MTX transport in membrane vesicles isolated from cells overexpressing the proximal tubular apical efflux transporters human multidrug resistance protein (MRP) 2/ABCC2 and MRP4/ABCC4. MTX was transported by MRP2 and MRP4 with Km values of 480 +/- 90 and 220 +/- 70 microM, respectively. The inhibitory potency of the NSAIDs was generally higher against MRP4- than MRP2-mediated MTX transport, with therapeutically relevant IC50 values, ranging from approximately 2 microM to 1.8 mM. Salicylate, piroxicam, ibuprofen, naproxen, sulindac, tolmetin, and etodolac inhibited MRP2- and MRP4-mediated MTX transport according to a one-site competition model. In some cases, more complex interaction patterns were observed. Inhibition of MRP4 by diclofenac and MRP2 by indomethacin and ketoprofen followed a two-site competition model. Phenylbutazone stimulated MRP2 and celecoxib MRP4 transport at low concentrations and inhibited both transporters at high concentration. Our data suggest that the inhibition by NSAIDs of renal MTX efflux via MRP2 and MRP4 is a potential new site and mechanism contributing to the overall interaction between these drugs.