Background and Significance Over the last two decades, radiation dose enhancement by high atomic number elements such as iodine has been explored for cancer radiotherapy. As a small-molecule radiation dose enhancer (smRDE), iododeoxyuridine (IUdR) has been used due to its facile incorporation into cellular DNA. The subsequent external irradiation of high energy photons on the IUdR-containing target cells can trigger the secondary emission of photoelectric radiation (i.e. Auger/secondary electron emission or X-ray fluorescence). The resulting triggered emission from smRDE can cleave the nuclear DNA double strands that can induce the radio-sensitized cell death. In this smRDE-mediated radiotherapy, several advantages have been demonstrated. The triggered emission from smRDEs generally decays in several um which is a typical length scale of a cell so that the resulting cytotoxicity is highly dependent on the cellular location of smRDEs. Therefore, only those of smRDEs located inside the target cells can deliver high toxicity upon radiation but their off-target toxicity can be reduced out of the cells. Although such smRDEs can improve the radiotherapeutic efficacy with reduced side effects, safe and effective delivery of smRDE to target tissue remains one of the major drawbacks to clinical applications. As iodine-attached tumor-targeting antibodies were used to improve their biodistribution, their targeting and therapeutic efficacies were not satisfied due to the rapid dehalogenation mechanism in DNA as well as the heterogeneity and limited expression of target receptors on cancer cells. Furthermore, the prolonged treatments with high dosages of iodine compounds should be avoided due to their toxic side effects to the host organs. To overcome these limitations, we propose the development of a nano-encased RDE (nano-RDE) platform, based on functionalizable polymer-modified nanoparticles. NanoRDE platforms can demonstrate several advantages: First, the biodistribution of nanoRDE can be highly improved by the enhanced permeation and retention (EPR) effect in solid tumor tissue, that allows for the selective accumulation of nanoRDE at diseased sites (passive targeting). Second, high amount of nanoRDE can be readily internalized in target cells by endocytic pathway which is known as a completely different cellular internalization mechanism from that of small molecules. In addition, the subsequent acidic endosomal environments can be used as a trigger for the pH-sensitive release of additional chemotherapeutic agents. In conventional chemotherapy, the rapid developments of multidrug-resistant characteristics in cancer cells cause a critical problem in clinical cancer treatments. As such, it is obvious that a combinational therapy is highly favorable for the complete remission of cancers rather than a single-type treatment. To this end, anti-cancer drug-conjugated nanoRDE as a first example of multimodal delivery platform for both radio- and chemotherapy will be demonstrated in this project. Gold nanoparticles have been tested for improvement of both chemotherapy and radiotherapy . The TNFalpa-PEG-colloidal gold nanoparticle, CYT-6091 (Citimmune, Gaithersburg, MD), has been shown to selectively traffic to tumor tissue. This agent has been evaluated for its ability to selectively deliver TNFalpha to tumors in clinical trials. Gold nanoparticles are available in a broad range of sizes. In addition to its properties as a nano-carrier, colloidal gold, being a high-Z element, may also increase the radiation dose delivered specifically to the target cells. In this system, gold nanoparticles (AuNPs) are used as inorganic nanoRDEs for radiotherapy as well as a delivery platform for chemotherapeutic agents. Due to the K-edge of gold at 80.7 keV, X-ray radiation with the energy level of Au K-edge can trigger the secondary emission of photoelectric radiation from AuNPs. The resulting radiation can induce the degradation of target molecules by ionization and can interact with surrounding water molecules to produce reactive oxygen species that can damage the target molecules. As such, AuNP-sensitized degradations of plasmid DNA and human proteins upon X-ray radiation have been demonstrated in in vitro model systems. Additionally, when AuNP-containing tumor cells were irradiated, increased apoptotic cell death was detected due to the continuous stress on cytosolic organelles. Furthermore, enhanced in vivo efficacy of AuNPs upon radiotherapy was also observed in human cancer-bearing mouse models. However, these AuNPs have shown very poor pharmacokinetic results due in part to their limited surface functionality as a bare colloidal particle. Recently, AuNPs have been used in a wide range of biological applications due to their biocompatibility and well-known surface chemistry. Using the known reactions, AuNPs can be readily modified with thiol-end-capped polymers that can significantly alter the pharmacokinetics. This functional polymer can be prepared by highly controllable reversible addition-fragmentation chain-transfer (RAFT) radical polymerization which allows for copolymerization of a wide range of monomers. As the gold K-edge is at 80.7 keV and the enhancement is optimal in the photoelectric-dominated X-ray spectrum, irradiation conditions could be optimized by using monoenergetic X-rays. Finaly, gold can be easily activated with thermal neutrons to emit 411 keV gamma rays, which could provide a means for monitoring their biodistribution by SPECT. Hypothesis: Functionalized gold nanoparticles can be used for HER2-targeted delivery and triggered release of therapeutic agents, including radiosensitizers Research Aims 1. Development of HER2-targeted AuNP a) Characterization of biodistribution and pharmacokinetics of Au-NP b) Assessment of biodistribution of neutron-activated Au-NP in vivo by SPECT c) Testing the effect of combining AuNP with external irradiation in vitro and in vivo 2. Application of HER2-targeted AuNP for tumor-specific delivery of therapeutic agents a) Optimization of conditions required for triggered release of the molecules carried by Au NP b) In vitro and in vivo testing of the efficacy of Au-NP-delivered drugs as compared with current formulations. Accomplishments: 1. Methods for quantification of gold concentration in the tissue using neutron activation have been developed and presented on 2009 Annual Meetings of the American Nuclear Society and American Chemical Society 2. Methods for production of pegylated nanoparticles have been established and tested 3. X-ray-triggered release of fluorescent molecules from gold nanoparticles was tested and a poster presentation of the preliminary results received Best American Chemical Society (ACS) poster at the ACS Division of Colloid and Surface on the 2009 Annual Meetings of ACS. 4. Our theoretical work describing the requirements of nanoparticles to be used as photodynamic therapy-based radiosensitizers indicating that gold nanoparticles present an advantageous alternative to nano-scintillatots proposed by others has been published in Radiation Research.