Valproate as a novel radiosensitizer in selective internal radiation therapy (SIRT) for unresectable hepatocellular carcinoma.

Abstract

314 Background: A large majority of Hepatocellular Carcinomas (HCC) present in locally advanced or metastatic stages; patients are usually poor candidates for surgical resection. Yttrium-90 Selective Internal Radiation Therapy (SIRT) is employed in both palliative and bridging therapy for unresectable HCCs. Histone Deacetylase Inhibitors (HDACi) are an emerging class of chemotherapeutics which exert their cytotoxicity through epigenetic modification. By maintaining DNA in an open conformation, it increases the surface area exposed for radiation damage- a postulated mechanism of its radiosensitizing effect. It is envisioned that HDACi will greatly augment therapeutic efficacy in brachytherapy. Here, the radiosensitizing effects of valproate, a known HDACi is investigated as potential adjunct with SIRT. Methods: 3 HCC cell lines were studied: HepG2, Hep3B and JNN4. They were first treated at various concentrations of valproate and cell viability was assessed. Next, a Caspase-3/7 assay was carried out to assess cell apoptosis. Westernblot analysis was performed on treated cells to elucidate histone acetylation status with Anti-Acetyl H3/H4 Antibodies. Finally, a clonogenic survival assay compared the effect of Yttrium-90, Lutetium-177, valproate and combination treatment on clonogenic proliferation. Results: Cell viability studies showed that valproate is cytotoxic to all HCC cell lines at concentrations from 10mM. Westernblot analysis demonstrated that valproate treatment maintained histone acetylation across all HCC cell lines validating it’s mechanism of action. Clonogenic Survival demonstrated a significant reduction of cell survival for all HCC cell lines treated with valproate and Isotope as compared to monotherapy. Conclusions: The use of HDACi such as valproate is not only novel in SIRT but showed great promise as an adjunct therapy. Experiments not only demonstrated its cytotoxicity, but also, reduction in clonogenic and proliferative ability of cancer cells. It can be postulated that the co-administration of valproate with SIRT will enhance therapeutic efficacy, allowing more aggressive and efficacious treatment of HCC.