Use of preclinical models to improve treatment of retinoblastoma

Abstract

Dyer and colleagues examine the most promising preclinical models that recapitulate the molecular, genetic, and cellular features of retinoblastoma.

Figure 1. p53 Prevents Invasive, Aggressive Retinoblastoma in Mice

Rb was conditionally inactivated in retinal progenitor cells by using the Chx10-Cre transgenic mouse line and the Rb^Lox allele. On a p107-deficient genetic background, these mice develop retinoblastoma with a penetrance of approximately 60%. However, the disease rarely progresses to invasive retinoblastoma with ocular hypertrophy, and the mice rarely become moribund. In contrast, mice lacking both copies of p53, Rb, and p107 (Chx10-Cre;Rb^Lox/−;p53^Lox/−;p107^−/−) in their retinal progenitor cells develop aggressive, invasive retinoblastoma. More importantly, penetrance is 100% as bilateral retinoblastoma with a short latency (100.3 ± 42.3 days), which is ideal for testing new chemotherapeutic drugs. Interestingly, mice with one copy of wild-type Rb also develop invasive, aggressive retinoblastoma, but with a longer latency than do Chx10-Cre;Rb^Lox/−;p53^Lox/−;p107^−/− mice. Preliminary studies indicated that these tumors have lost heterozygosity at the Rb locus; thus, Chx10-Cre;Rb^Lox/−;p53^Lox/−;p107^−/− mice are the only mouse model of retinoblastoma that recapitulates this feature of human retinoblastoma.

Figure 2. A Developmentally Appropriate Orthotopic Retinoblastoma Xenograft Model

(A) Injection of 1,000 cultured human retinoblastoma cells into the vitreal cavity of newborn rat eyes leads to retinoblastoma by two weeks of age. The rats do not require immunosuppression because they are immunonaive for the first 24 hours after birth. This is an ideal model for testing new drugs and for studying the retinoblastoma cancer stem cell properties. (B) Human retinoblastoma cells have been genetically engineered to express the luciferase reporter gene. A two-week-old rat that received an intravitreal injection of Y79-LUC cells at birth is shown. Y79-LUC cells are retinoblastoma cells that express the firefly luciferase gene under the control of a constitutive promoter (see [16]). At two weeks, the rat received an intraperitoneal injection of the luciferase substrate (luciferin). The fluorescence is directly proportional to the tumor volume and the number of cells in the tumor. By using the Xenogen imaging system, we can follow individual tumors as they grow and respond to chemotherapy.

Figure 3. The Eye Is a Transparent System That Permits Direct Visualization of Retinoblastoma

(A) Untreated retinoblastoma involving the macula of the left eye. The translucent cornea and lens allow detailed visualization. The tumor is an amelanotic, partially calcified mass that has broken through the overlying retina. Dilated arterioles infiltrate the tumor. (B) The same tumor after being treated with chemotherapy. The mass has completely calcified, and the caliber of the overlying retinal vessels has diminished. A focal area of atrophied retinal pigmented epithelium surrounds the lesion.