Evaluation of the in vitro and in vivo antitumor activity of histone deacetylase inhibitors for the therapy of retinoblastoma.

PURPOSE

To evaluate the potential utility of histone deacetylase inhibitors (HDACi) for treatment of retinoblastoma (RB).

EXPERIMENTAL DESIGN

Growth-inhibitory effects of HDACi [trichostatin A (TSA), suberoylanilide hydroxamic acid (SAHA), or MS-275] were assessed in human and transgenic murine RB cells. Effects of TSA and MS-275 were also assessed in combination with standard therapeutic agents for RB. Proapoptotic effects of MS-275 and TSA were evaluated by caspase-3/7 activity, Annexin V translocation, and/or Bim expression analyses. Effects of MS-275 on cell cycle distribution and reactive oxygen species levels were determined by flow cytometry. Retinal tissue morphology was evaluated in mice after local administration of MS-275. Analysis of retinal acetyl-histone levels was used to assess MS-275 delivery after systemic administration. Therapeutic effects of MS-275 were determined in transgenic mouse and rat ocular xenograft models of RB after i.p. injection of 20 mg/kg every other day for 21 or 13 days, respectively.

RESULTS

TSA, SAHA, and MS-275 dose dependently reduced RB cell survival. TSA and MS-275 showed additive growth-inhibitory effects in combination with carboplatin, etoposide, or vincristine. TSA and MS-275 increased caspase-3/7 activity. MS-275 increased Annexin V membrane translocation and induced G1 arrest. Cytotoxicity of MS-275 was dependent on increased reactive oxygen species levels and was reversed by antioxidant pretreatment. Intraocular administration of 1 microL of 10 micromol/L MS-275 did not alter ocular tissue morphology. Increased acetyl-histone levels confirmed MS-275 delivery to retinal tissue after systemic administration. MS-275 significantly reduced tumor burden in both mouse and rat models of RB.

CONCLUSIONS

HDACi should be considered for clinical trials in children with RB.