Radiation protection and mitigation potential of phenylbutyrate: delivered via oral administration.

PURPOSE: Phenylbutyrate (PB), a histone deacetylase inhibitor (HDACi) has demonstrated radiation protection in both in vitro and in vivo models. Studies previously demonstrated that PB and other HDAC inhibitors could inhibit radiation lethality in vivo by subcutaneous (s.c) injection. The objective of this study was to test the ability of oral PB treatment to protect against or to mitigate acute gamma radiation-induced lethality in vivo. MATERIALS AND METHODS: Human osteoblasts cells were used to evaluate radiation survival when PB was delivered pre- or post-radiation. A 30-day radiation lethality study was used to assess the radioprotective (pre-radiation) and radiomitigative (post-radiation) capability of PB. Possible mechanisms evaluated were antioxidant activity effects, HDAC inhibition, DNA damage, and hematological recovery. RESULTS: Treatment of HOS cells with PB 50 µM either before or after radiation increased radiation resistance as assessed by clonogenic survival. Western blot studies showed that PB treatment acetylated histones in vivo and ameliorated the radiation-induced reduction in acetylated histone-4 (H4). Pre-radiation oral administration of PB (10 mg/kg) provided radioprotection against gamma radiation (7-11.5 Gy) with a dose reduction factor of 1.25 (p = 0.001). PB oral administration post-radiation provided moderate radiation mitigation against gamma radiation (7-11.5 Gy) and demonstrated a dose reduction factor of 1.18 (p = 0.05). PB pre-radiation and post-radiation treatment was associated with significant elevations in neutrophils and platelets and attenuation of DNA damage. CONCLUSIONS: These results indicate that oral PB has potential as a radiation protector and a radiation mitigator and that potential mechanisms of action include attenuation of DNA damage, antioxidant activity, and bone marrow protection.

Radioprotection by the histone deacetylase inhibitor phenylbutyrate.

The histone deacetylase inhibitor (HDAC), phenylbutyrate (PB), is a novel anti-tumor agent. Studies have demonstrated that HDAC inhibitors can suppress cutaneous radiation syndrome and stimulate hematopoiesis. The objective of this study was to test the ability of PB treatment to protect against acute gamma-radiation-induced lethality in the DBA/2 mouse model. A 30-day radiation lethality study was used to assess radioprotective capability of PB. Mechanisms were evaluated using western blots, flow cytometry, and the single-cell gel electrophoresis assay. Western blot studies showed that PB treatment acetylated histones in vivo. For radiation protection studies, prophylactic administration of PB (24 h preradiation; 1-50 mg/kg) provided radioprotection against gamma radiation (8-9.5 Gy) and PB demonstrated a DRF of 1.31 (P = 0.001; 95% confidence interval: 1.27, 1.36). When PB (10 mg/kg) was administered post-radiation (4 h), it also provided significant radioprotection at 8.0 Gy radiation (P = 0.022). PB treatment before radiation was associated with significant elevations in neutrophils and platelets following radiation. Results from single-cell gel electrophoresis of peripheral blood leukocytes demonstrated that PB treatment before radiation can attenuate DNA damage and inhibit radiation-induced apoptosis. These results indicate that an HDAC inhibitor like PB has potential as a radiation protector and that mechanisms of action include attenuation of DNA damage and inhibition of apoptosis.

Leukemic transformation of hematopoietic cells in mice internally exposed to depleted uranium.

Depleted uranium (DU) is a dense heavy metal used in military applications. During military conflicts, US military personnel have been wounded by DU shrapnel. The health effects of embedded DU are unknown. Published data from our laboratory demonstrated that DU exposure in vitro can transform immortalized human osteoblast cells (HOS) to the tumorigenic phenotype. Results from our laboratory have also shown that DU is genotoxic and mutagenic in cultured human cells. Internalized DU could be a carcinogenic risk and concurrent alpha particle and heavy metal toxic effects complicate this potential risk. Anecdotal reports have suggested that DU can cause leukemia. To better assess this risk, we have developed an in vivo leukemogenesis model. This model involves using murine hematopoietic cells (FDC-P1) that are dependent on stimulation by granulocyte-macrophage colony stimulating factor (GM-CSF) or interleukin 3 (IL-3) and injected into mice to produce myeloid leukemia. Although immortalized, these cells are not tumorigenic on subcutaneous inoculation in mice. Intravenous injection of FDC-P1 cells into DU-implanted DBA/2 mice was followed by the development of leukemias in 76% of all mice implanted with DU pellets. In contrast, only 12% of control mice developed leukemia. Karyotypic analysis confirmed that the leukemias originated from FDC-P1 cells. The growth properties of leukemic cells from bone marrow, spleen, and lymph node were assessed and indicate that the FDC-P1 cells had become transformed in vivo. The kidney, spleen, bone marrow, muscle, and urine showed significant elevations in tissue uranium levels prior to induction of leukemia. These results demonstrated that a DU altered in vivo environment may be involved in the pathogenesis of DU induced leukemia in an animal model.