Abstract Background: We previously reported the identification of a novel nano-organic compound, EI236, an anti-cancer agent with intrinsic magnetic property. In addition to anti-cancer effect, its ferromagnetic property contributes to unique features.1) It can be attracted by a magnet. 2) It can be visualized by magnetic resonance imaging (MRI). Hereby, we have identified the key mechanism that contributes to magnetism by X-ray crystallographic analysis, and succeeded in generating a novel paclitaxel with intrinsic magnetism; this is a single paclitaxel compound, and is not a paclitaxel encapsulated in micelle with magnetic particles. Our aim is to examine its effect on triple negative-breast cancer (TNBC) cells. Material and Method: The magnetization of the magnetized paclitaxel was measured with a superconducting quantum interference device (SQUID) (Quantum Design MPMS7 system). Breast cancer cells, MDA-MB-453 (TNBC) and MCF7 (Non-TNBC), were obtained from RIKEN Bioresource center. Cell proliferation assay was performed using a commercially available kit, XTT Cell Proliferation Assay Kit. Apoptotic cells were stained with Annexin V, allophycocyanin conjugate and 7-amino-actinomycin D, and measured by fluorescence activated cell sorting (FACS), to evaluate early and late apoptosis. Cell cycle analysis was performed using The Cycletest™ Plus DNA Reagent Kit and assessed using FACS. Results: Plots of magnetization versus magnetic field revealed that the magnetized paclitaxel exhibits magnetic property in SQUID. Magnetized paclitaxel was easily attracted by a commercial bar magnet. Magnetized paclitaxel exhibits greater anti-cancer effect than original paclitaxel in TNBC and Non-TNBC cells in a dose-dependent manner. Magnetized paclitaxel induced apoptosis and G2/M arrest in cell cycle analysis in a dose-dependent manner, suggesting that magnetized paclitaxel retained the original anti-cancer property. In MRI T2 -weighted imaging, signal intensity was changed in a concentration-dependent manner with magnetized paclitaxel, but not with commercial available paclitaxel. Conclusion: These results suggested that various conventional anti-cancer drugs might be similarly magnetized, leading to novel drug development in future cancer chemotherapy. Citation Format: Masanari Umemura, Ayako Makino, Itaru Sato, Xianfeng Feng, Kayoko Oda, Makoto Ohtake, Satoshi Izuka, Maki Iwai, Kosuke Matsuo, Haruki Eguchi, Yoshihiro Ishikawa. A novel treatment for triple-negative breast cancer using intrinsic magnetized paclitaxel. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5399. doi:10.1158/1538-7445.AM2014-5399