Metastatic and nonmetastatic models of retinoblastoma

To generate animal models of retinoblastoma that closely resemble metastatic and nonmetastatic human disease for the purposes of examining tumor biology and developing alternate treatments, human retinoblastoma cell lines were injected into the vitreal cavities of immunodeficient mice. Two reproducible animal models with contrasting biological behaviors analogous to human retinoblastoma have been developed. The Y79 retinoblastoma model demonstrated specific tumor evolution similar to that seen in human invasive and metastatic disease. Y79 retinoblastoma cells formed intraocular tumors that were initially confined to the vitreal cavity. Tumors progressively invaded the retina, subretinal space, choroid, optic nerve head, and anterior chamber of the eye. Tumors progressed into the subarachnoid space and focally invaded the brain. Metastases were detected in the contralateral optic nerve. Large tumors developed extraocular extensions. The histology of the tumors showed a poorly differentiated pattern with high mitotic rate, foci of necrosis, and calcification. The WERI-Rb model more closely resembled nonmetastatic human retinoblastoma. WERI- Rb tumors were localized in the eye with only anterior choroidal invasion at late stages. To examine potential biological differences in vitro, the retinoblastoma cell lines were cocultured with adherent choroid cells or adherent glioma cells which represent the targets of invasive retinoblastoma in vivo. Consistent with the in vivo observations, Y79 cells but not WERI-Rb cells adhere specifically to both the choroidal and the glioma cell lines.

Suicide gene therapy for treatment of retinoblastoma in a murine model

Children presenting with large retinoblastomas are currently treated by enucleation. As most patients are young children, the long-term repercussions of such surgery are often devastating. Subsequent radiation or chemotherapy, although effective in managing residual tumor, greatly increase the probability of the development of second malignancies later in life. Smaller tumors can sometimes be managed with local cryo- or laser surgery, thus saving the eye. The hypothesis that gene therapy could be used to reduce the tumor size sufficiently to allow local control was tested using a murine model of retinoblastoma. Y79Rb human retinoblastoma cells can be killed in vitro when transduced with an adenoviral vector containing the herpes simplex thymidine kinase gene (AdV-TK) followed by treatment with the prodrug ganciclovir. Intravitreal injections of Y79Rb cells in immunodeficient mice produce an aggressive, metastatic murine model of retinoblastoma. When these murine retinoblastomas were transduced in vivo with AdV-TK and the animals treated with intraocular injections of ganciclovir, 70% showed a complete ablation of detectable tumor. Treated animals had a significant prolongation of progression-free survival as compared with untreated controls. Gene therapy effectively reduced the tumor burden in this murine model of retinoblastoma. Thus gene therapy, in conjunction with local surgical control, may provide an effective alternative to enucleation, systemic chemotherapy, or radiotherapy for treatment of large, nonmetastatic retinoblastomas in children.