Antitumor effects of AR-42, a novel histone deacetylase inhibitor, in embryonal carcinoma.
232 Background: Histone deacetylase inhibitors (HDACIs) modulate gene expression and induce cellular differentiation, growth inhibition and apoptotic cell death by chromatin hyperacetylation. Developmental arrest of germ cell differentiation earlier in the life is responsible for the pathogenesis of germ cell tumors (GCT). With current treatment nearly 95% of patients with GCT can be cured. Yet, effective agents with less toxicity are desired. In addition, those with relapsed/refractory disease have a dismal prognosis, indicating a clear need for new, more effective agents. Here we assess the antitumor effects of AR-42, a novel HDACI in in vitro and in vivo models of embryonal carcinoma. Methods: In vitro effects of AR-42 and suberoylanilide hydroxamic acid (SAHA) were evaluated in NTERA-2, an embryonal carcinoma (EC) cell line derived from a human testicular cancer. Cell viability (MTS assay), apoptosis (caspase 3/7 activity and PARP cleavage), cell cycle analysis (flow cytometry) and HDAC inhibition (immunoblotting) were assessed. The in vivo efficacy of AR-42 was assessed in a NTERA-2 xenograft tumor model in male athymic nude mice. Mice were fed control diet and diet containing AR-42 at an average dose of 25 mg/kg/day. Tumor volumes and weights were used as in vivo endpoints. Results: Treatment of NTERA-2 cells with both agents at 0.1-10 μM concentrations showed a time- and dose-dependent reduction in cell viability. Both agents significantly induced apoptosis, cell cycle inhibition and hyperacetylation of histones H-3 and H-4 in a dose-dependent manner. In vitro studies showed that AR-42 was more potent than SAHA. In our rodent model, AR-42-containing diet resulted in a significant reduction in tumor volumes and weights (50% and 56%, respectively). The results for intratumoral changes of proliferation and apoptosis are pending. There were no significant toxicities associated with AR-42, except for testicular atrophy, known to be reversible. Conclusions: AR-42 appears to be a potent inhibitor of EC through different mechanisms, orally bioavailable and well tolerated in our rodent model. Our data indicates that AR- 42 may have clinical value in the treatment of GCT and requires further investigation in clinical trials. No significant financial relationships to disclose.