Suberoylanilide Hydroxamic Acid as a Radiosensitizer through Modulation of RAD51 Protein and Inhibition of Homology-Directed Repair in Multiple Myeloma

Abstract

Histone deacetylase inhibitors (HDI) have shown promise as candidate radiosensitizers for many types of cancers. However, the mechanisms of action are not well understood, and whether they could sensitize multiple myeloma (MM) to radiation therapy is unclear. In this study, we show that suberoylanilide hydroxamic acid (SAHA) at low concentrations has minimal cytotoxic effects, yet can significantly increase radiosensitivity of MM cells. SAHA seems to block RAD51 protein response to ionizing radiation, consistent with an inhibitory effect on the formation of RAD51 focus in irradiated MM cells. These effects of SAHA on RAD51 focus are independent of cell-cycle distribution changes. Furthermore, we show that SAHA selectively inhibits the homology-directed repair (HDR) pathway. The results of this study suggest that SAHA, a recently approved HDI in clinical trials for malignancies, at lower concentrations may act as a radiosensitizer via disruption of the RAD51-dependent HDR pathway. Mol Cancer Res; 10(8); 1052-64. Ó2012 AACR.

Combined Effects of Suberoylanilide Hydroxamic Acid and Cisplatin on Radiation Sensitivity and Cancer Cell Invasion in Non–Small Cell Lung Cancer

“…On the other hand, our studies showed that exposure to SAHA reduced expression of Rad51, a key element involved in HDR pathway, and decreased HDR activity in irradiated cancer cells (14,16). These observations suggest that cisplatin and SAHA may act on distinct DNA damage repair pathways, both leading to the potential of enhancing cellular sensitivity to IR treatment.…”

“…U2OS reporter cell lines, which consist of the U2OS osteosarcoma cell line with integrated copies of the EJs-GFP, DR-GFP, and SSA-GFP reporters along with a unique I-SceI cleavage site, have been described previously (14,15), and were maintained in DMEM medium with 2 mmol/L L-Glutamine, 4.5 g/L glucose, and 10% FBS. Hamster lung fibroblast cell lines V79 (wild-type) and VC8 (defective in the BRCA2 gene), and Chinese hamster ovary (CHO) cell lines AA8 (wild-type) and V3 (defective in DNA-PKcs expression) were maintained in DMEM medium as described previously (14). All cell lines were tested as negative Mycoplasma contamination with Cell Culture Contamination Detection Kit (Thermo Fisher Scientific), and none of the cell lines was cultured longer than 6 months.…”

“…Immunofluorescence analyses for g-H2A.X were performed as previously reported (14). Images were acquired with LSM 510 confocal microscope (Zeiss) with Â40 objective and processed by Photoshop (Adobe).…”

“…Twenty-four hours later, cells were transfected with 0.8 mg pCBASce by using Lipofectamine 2000 transfection reagent (Life Technologies), and 1 mmol/L SAHA or 2 mmol/L cisplatin were added into culture medium 3 hours later after the initiation of the transfection. After exposure for 24 hours, cisplatin was removed from cell culture, and cells were maintained in fresh medium for cisplatin treatment or in SAHA-containing medium until analysis as described previously (14). GFP-positive cells were quantified by flow cytometric analysis.…”

Histone deacetylase inhibitors in the treatment for multiple myeloma

“…2). Most recently, Chen et al [33] reported that vorinostat blocks RAD51 protein response to ionizing radiation, thereby sensitizing MM cells to radiotherapy.…”