RESUMO
PURPOSE: The purpose of this study is to analyze the dose response of the mammalian target of rapamycin (mTOR) inhibitor, rapamycin, on tumor burden and hypoxia, and study the treatment effect on vasculature in LH(BETA)T(AG) retinal tumors. METHODS: This study was approved by the Institutional Animal Care and Use Committee and follows Association for Research in Vision and Ophthalmology guidelines. Eighteen-week-old LH(BETA)T(AG) retinal tumor eyes (n = 30) were evaluated. Mice were divided into five groups and received periocular injections once weekly for two consecutive weeks of: a) 80% DMSO (dimethyl sulfoxide, vehicle control), b) 0.00333 mg/kg, c) 0.167 mg/kg, d) 3.33 mg/kg, and e) 6.67 mg/kg of rapamycin. Tumor sections were analyzed for hypoxia, tumor burden, and vasculature with immunohistochemistry techniques. RESULTS: Reduction in tumor burden and hypoxia was significantly different between rapamycin doses and control (P < 0.002). Eyes treated with rapamycin at 0.167, 3.33, and 6.67 mg/kg showed a significant decrease in tumor burden in comparison with the vehicle control group (P = 0.019, P = 0.001, P = 0.009, respectively) and the 0.00333 mg/kg dose response (P = 0.023, P = 0.001, P = 0.010, respectively). Eyes treated with rapamycin at 3.33 mg/kg showed a significant reduction in the amount of hypoxia in comparison with the lower concentration groups (0.00333 and 0.167 mg/kg) of rapamycin (P = 0.024 and P = 0.052, respectively). The number of mature vessels was significantly lower in the 3.33 mg/kg treated versus vehicle control (P = 0.015; equal variances assumed, t-test for equality of means). The number of neovessels was not significantly different between both groups (P = 0.092). CONCLUSION: Inhibition of mTOR was shown to reduce tumor burden, hypoxia, and vasculature in the LH(BETA)T(AG) retinoblastoma tumor model. Rapamycin may have a role in combination with chemotherapy or other adjuvant therapies to enhance retinoblastoma tumor control.
RESUMO
SU1498, a tyrosine kinase inhibitor of vascular endothelial growth factor receptor 2 (VEGFR-2), has activity against retinal neovascular diseases. To determine if this drug might have clinical utility against retinoblastoma, we evaluated the effects of SU1498, as well as the expression of VEGFR-2, in a transgenic animal model of retinoblastoma. Optical coherence tomography (OCT) was evaluated as a technology to measure retinal tumors in vivo, in response to treatment. Immunofluorescence analysis was performed to evaluate the distribution and expression of VEGFR-2 in enucleated eyes from LHbetaTag transgenic mice and controls at 4, 8, 12, and 16 weeks of age. VEGFR-2 and phosphorylated (p)VEGFR-2 levels were quantitated by Western blot. OCT was used to pair 10-week-old animals based on tumor volume (n=10), and these animals were treated with 6 periocular injections of SU1498 (50mg/kg, given twice weekly) or vehicle for 3 weeks. Tumor burden was determined by histology and in vivo imaging by OCT. VEGFR-2 and pVEGFR-2 expression levels were upregulated during tumorigenesis. However, SU1498 did not significantly reduce tumor burden compared to vehicle (p=0.29). OCT imaging of one matched pair demonstrated equivalent, linear tumor growth despite treatment with SU1498. Retinal tumors can be followed non-invasively and quantitatively measured with OCT. VEGFR-2 is strongly upregulated during tumorigenesis in transgenic retinoblastoma; however, SU1498 does not decrease tumor volume in transgenic murine RB at the studied dose and route of administration.
