A medicament for reducing radio-resistance of prostate cancer cells or treating prostate cancer and its use are provided, wherein the medicament comprises an effective amount of an active component and the active component is a nanoparticle of carrier-encapsulated cytolethal distending toxin subunit B (CdtB).一種降低前列腺癌細胞對放射線之抗性或治療前列腺癌之藥劑及其應用，其中該藥劑係包含一有效量之活性成分，且該活性成分係一經載體包覆之細胞致死腫脹毒素次單元B(cytolethal distending toxin subunit B，CdtB)蛋白之奈米粒子。
