N-(4-hydroxyphenyl) retinamide inhibits retinoblastoma growth through reactive oxygen species-mediated cell death

Retinoblastoma arises from a subset of developing retinal cells lacking the RB-1 gene product pRB, which have lost the ability to respond to apoptotic signals. A better understanding of retinoblastoma biological response to therapeutic agents with low toxicity could improve the development of novel approaches for treatment and prevention of the disease. Naturally occurring retinoids inhibit growth and induce differentiation of Y79 human retinoblastoma cells in vitro. The synthetic retinoid N-(4-hydroxyphenyl) retinamide (4HPR) has been shown to induce apoptosis and/or necrosis of tumor cells of neuroectodermal origin. We examined the sensitivity of Y79 retinoblastoma cells to 4HPR in vitro, and in a xenograft model of tumor growth in nude mice in vivo. 4HPR treatment in the range 2.5 to 10 muM induced a loss of Y79 cell viability, as determined by crystal violet, trypan blue exclusion, and long-term clonogenic assays, and impairment of mitochondrial function detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Reactive oxygen species were elevated in 4HPR-treated cells and antioxidants rescued cell viability, indicating that 4HPR-induced cell death was mediated by oxidative stress. 4HPR inhibited growth of Y79 xenografts in vivo in both chemoprevention and intervention settings. Tumor growth inhibition by 4HPR was also associated with significant inhibition of angiogenesis in vivo. These findings could have an important translational value for chemoprevention or early intervention in the treatment of retinoblastoma.