P10. Radiosensitization of breast adenocarcinoma cells by a novel estrone analogue is dependent on reactive oxygen species signalling

• Published in: Physica medica 2016-09, Vol.32, p.164-164
• Main Authors: Verwey, M, Joubert, A.M, Meijer, W, Nolte, E.M, Lakier, R, Etsebeth, M, Helena, J, Theron, A.E
• Format: Article
• Language: English
• Subjects: Radiology
• ISSN: 1120-1797; 1724-191X
• DOI: 10.1016/j.ejmp.2016.07.077

Introduction and aim The novel antimitotic drug 2-ethyl-3- O -sulpamoyl-estra-1,3,5(10),15-tetraen-17-ol (ESE-15-ol) is an in silico -designed 17- β -estradiol analogue that induces apoptosis and disregulates autophagy in various neoplastic cell lines. The compound alters microtubule dynamics inducing both intrinsic and extrinsic death pathways. The hypothesis was formed that pre-exposure to the compound would sensitize breast adenocarcinoma (MDA-MB-231) cells to gamma radiation, in pathways dependent on reactive oxygen species (ROS) generation. Methods and materials The hypothesis was tested by inhibiting ROS formation with N -acetyl-cysteine (NAC). The half-maximal growth-inhibitory concentration ( IG 50 ) of ESE-15-ol after 24 h was determined with and without NAC via spectrophotometric quantification of crystal violet. MDA-MB-231 cells were presensitized with half the IG 50 concentrations prior to 6 Gy radiation. Morphological studies were done using polarized-optical transmitted light differential interference light microscopy and confocal microscopy using anti- α tubulin antibodies and Mitotracker® mitochondrial staining. Quantitative studies were completed using flow cytometry to detect apoptosis induction, loss of mitochondrial membrane potential and reactive oxygen species production, as well as to analyze cell cycle progression and mitochondrial signal transduction pathways. Results The IG 50 of ESE-15-ol was determined at a concentration of 0.18 μM after a 24-h exposure. Results obtained from the morphological studies indicated that incubation with NAC reduced apoptotic cell death despite microtubule depolarization after ESE-15-ol presensitization prior to gamma radiation. Flow cytometric quantification indicated a reduction in apoptosis, mitochondrial membrane depolarization, as well as in reactive oxygen species when samples were concurrently undergoing antioxidant treatment. Conclusion This in vitro study revealed that inhibition of reactive oxygen species signalling resulted in a decreased effectiveness of ESE-15-ol to presensitize MDA-MB-231 cells to gamma radiation. Thus the hypothesis was accepted. Further quantification of ROS on autophagy induction, as well as its role in the radiosensitization mechanisms, will be carried out in vitro and in vivo.