Radio-Sensitization by Piper longumine of Human Breast Adenoma MDA-MB-231 Cells in Vitro

Background: The current study investigated the effects of Piper longumine on radio-sensitization of humanbreast cancer MDA-MB-231 cells and underlying mechanisms. Materials and
Methods: Human breast cancerMDA-MB-231 cells were cultured in vitro and those in logarithmic growth phase were selected for experimentsdivided into four groups: control, X-ray exposed, Piper longumine, and Piper longumine combined with X-rays.Conogenic assays were performed to determine the radio-sensitizing effects. Cell survival curves were fitted bysingle-hit multi-target model and then the survival fraction (SF), average lethal dose (D0), quasi-threshold dose(Dq) and sensitive enhancement ratio (SER) were calculated. Cell apoptosis was analyzed by flow cytometry(FCM).Western blot assays were employed for expression of apoptosis-related proteins (Bc1-2 and Bax) aftertreatment with Piper longumine and/or X-ray radiation. The intracellular reactive oxygen species (ROS) levelwas detected by FCM with a DCFH-DA probe.
Results: The cloning formation capacity was decreased in thegroup of piperlongumine plus radiation, which displayed the values of SF2, D0, Dq significantly lower thanthose of radiation alone group and the sensitive enhancement ratio (SER) of D0 was1.22 and 1.29, respectively.The cell apoptosis rate was increased by the combination treatment of Piper longumine and radiation. Piperlongumine increased the radiation-induced intracellular levels of ROS. Compared with the control group andindividual group, the combination group demonstrated significantly decreased expression of Bcl-2 with increasedBax.
Conclusions: Piper longumine at a non-cytotoxic concentration can enhance the radio-sensitivity of MDAMB-231cells, which may be related to its regulation of apoptosis-related protein expression and the increase ofintracellular ROS level, thus increasing radiation-induced apoptosis.