2-hexyl-4-pentynoic acid (HPTA), a novel radiosensitizer to breast cancer cells through increasing the instability of DNA repair proteins

Abstract

Background Breast cancer is one of the most common malignant tumors in the world which is the main cause of cancer death for women. Radiotherapy is the main treatment. Although some drugs have been found to enhance the effect of radiotherapy, there are also obvious deficiencies. Therefore, recent applied clinical research has been focusing on locating a suitable radiosensitizer to breast cancer radiotherapy. Methods MTT, clonogenic survival assays, comet assays, immunofluorescence and western blot analyses were used to detect the effect of VPA / HPTA on DNA damage induced by radiotherapy for breast cancer through a variety of cell models( MCF7, EUFA423, HCC1937, DMBA-induced rat breast cancer-derived primary culture cell and DMBA-induced transformed human normal breast cell line). At the same time, flow cytometry, immunofluorescence and western blot analyses were used to investigate the effect of VPA / HPTA on DNA damage repair induced by radiation. In vivo experiment, the effect of HPTA as radiosensitizer was investigated by DMBA-induced breast cancer in rats. Finally, the possible mechanism of HPTA acting on target protein was proved by cycloheximide chase experiment. Results In this study, a derivative of valproic acid (VPA), 2-hexyl-4-pentynoic acid (HPTA), was demonstrated for the first time that low concentration of HPTA (15 µM) has radiosensitizing properties to breast cancer cells by multiple working models of breast cancer cell lines (in vivo), equivalent to a high concentration of VPA (500 µM). Mechanistic investigations revealed that HPTA induced radiosensitivity through inhibiting the BRCA1-Rad51-mediated homologous recombination pathway. These results were further manifested in breast cancer animal model (in vitro). Most importantly, our study found that HPTA influenced the stability of BRCA1 and Rad51 proteins via shorting their half-life. Conclusions Our findings support the proposition HPTA as an alternate, safe and effective radiosensitizer to tumor cells. Targeting BRCA1-Rad51-mediated homologous recombination pathway through HPTA may be a rational strategy to improve the radiotherapeutic efficacy of breast cancer.