Retinoblastoma is a rare childhood
cancer of the retina that begins in utero and is diagnosed in the first years of life. The goals of
retinoblastoma treatment are ocular salvage, vision preservation, and reduction of short- and long-term side effects without risking mortality because of
tumor dissemination. To identify better chemotherapeutic combinations for the treatment of
retinoblastoma, several groups have developed genetic mouse models and orthotopic xenograft models of human
retinoblastoma for preclinical testing. Previous studies have implicated the
MDMX protein in the suppression of the p53 pathway in
retinoblastoma and shown that the MDM2/MDMX antagonist,
Nutlin-3a, can efficiently induce p53-mediated cell death in
retinoblastoma cell lines. However,
Nutlin-3a cannot be administered systemically to treat
retinoblastoma, because it has poor penetration across the blood-ocular barrier. Therefore, we developed an ocular formulation of
Nutlin-3a, Nutlin-3a(OC), and tested the pharmacokinetics and efficacy of this new formulation in genetic and human
retinoblastoma orthotopic xenograft models of
retinoblastoma. Here, we show that Nutlin-3a(OC) specifically and efficiently targets the p53 pathway and that the combination of Nutlin-3a(OC) with systemic
topotecan is a significantly better treatment for
retinoblastoma than currently used
chemotherapy in human orthotopic xenografts. Our studies provide a new standardized approach to evaluate and prioritize novel agents for incorporation into future clinical trials for
retinoblastoma.