ABSTRACT Radiation therapy is a potent element of standard cancer care, used in the treatment of over half of all cancer patients. While the clinical benefits of radiotherapy are well documented, the dose to adjacent and intermeshed normal organs and subsequent toxicity remains the biggest obstacle to continued escalation of radiation doses to tumors in order to obtain cancer cures with RT. Significant number of patients will develop locally persistent/recurrent tumors after radiotherapy. Therefore, radiosensitizing compounds, radiosensitizers, have been developed to enhance tumor killing effects without escalation of radiation doses. However, their clinical applications are limited due to invasive or insufficient tumor delivery and lack of specificity or systemic toxicity. The goal of this project is to develop a prodrug-based therapeutic strategy empowered by a nanotechnology pioneered by us —in cellulo nanoassembly—to amplify and enhance radiotherapeutic efficacy for treating prostate cancer. Unlike common nanoparticle-based delivery approach, this delivery strategy does not rely on the tumor enhanced permeability and retention effect. We propose to take advantage of the intrinsic heterogeneous response to radiation therapy by targeting this initial population of apoptotic cells for depositing radiosensitizers and enhancing radiotherapeutic effects. The project will develop and characterize the new prodrug radiosensitizers for targeting apoptosis (Aim 1); investigate the pharmacokinetics, toxicity and validate the in vivo treatment mechanism (Aim 2); and develop an image-guided treatment strategy, followed by a comprehensive evaluation of the therapeutic benefit in orthotopic prostate cancer mouse models (Aim 3).