One of the promises of nanoparticle (NP) carriers is the reformulation of promising therapeutics that have failed clinical development due to pharmacologic challenges. However, current nanomedicine research has been focused on the delivery of established and novel therapeutics. Here we demonstrate proof of the principle of using NPs to revive the clinical potential of abandoned compounds using wortmannin (Wtmn) as a model drug. Wtmn is a potent inhibitor of phosphatidylinositol 3′ kinase-related kinases but failed clinical translation due to drug-delivery challenges. We engineered a NP formulation of Wtmn and demonstrated that NP Wtmn has higher solubility and lower toxicity compared with Wtmn. To establish the clinical translation potential of NP Wtmn, we evaluated the therapeutic as a radiosensitizer in vitro and in vivo. NP Wtmn was found to be a potent radiosensitizer and was significantly more effective than the commonly used radiosensitizer cisplatin in vitro in three cancer cell lines. The mechanism of action of NP Wtmn radiosensitization was found to be through the inhibition of DNA-dependent protein kinase phosphorylation. Finally, NP Wtmn was shown to be an effective radiosensitizer in vivo using two murine xenograft models of cancer. Our results demonstrate that NP drug-delivery systems can promote the readoption of abandoned drugs such as Wtmn by overcoming drug-delivery challenges.nanotechnology | nanoparticle radiosensitizer N anoparticles (NPs) possess unique properties, such as preferential accumulation in tumors and reduced distribution in normal tissue, that make them ideally suited for the treatment of cancer. Consequently, there has been high interest in developing NP-based therapeutics for cancer treatment (1). Current research has been focused on developing NP formulations of widely used chemotherapeutics or newly discovered cancer agents, which are few in number (2). However, one of the promises and great potentials of NP drug-delivery carriers is the reformulation of abandoned cancer therapeutics that were initially promising but failed clinical development due to challenges in delivery. Although these challenges are difficult to overcome with traditional drugdelivery techniques, NP drug-delivery vehicles present an unprecedented opportunity. In this study, we aim to demonstrate proof of principle that NPs permit the reformulation of abandoned therapeutics into formulations appropriate for clinical use.We used wortmannin (Wtmn) as a model drug for our study. Wtmn is a furanosteroid metabolite of the fungi Penicillium funiculosum and Talaromyces (Penicillium) wortmannii (3). It is an inhibitor of phosphatidylinositol 3′ kinases (PI3Ks) and phosphatidylinositol 3′ kinase-related kinases (PIKKs) such as DNAdependent protein kinase (DNA-PK) (4). Although preclinical studies showed Wtmn was an extremely effective radiosensitizer, its clinical translation was limited by poor solubility, low stability, and high toxicity (3-8). Since its discovery more than four decades ago, many Wtmn analogs hav...