The overall objective of the proposed research is to utilize a newly discovered, active transendothelial transport pathway, the caveolae pumping system, in order to provide an effective solution to the delivery and toxicity problem of Pt(II)-based chemotherapeutics in breast cancer. Systemic chemotherapy is one of the common forms of breast cancer treatments, however clinical efficacy of Pt(II) antitumor drugs is limited by the significant in vivo barriers inhibit delivery of these drugs into solid tumors, requiring the use of high doses, producing serious side effects and facilitating development of drug resistance. In order to address these problems and significantly improve treatment of breast cancer we propose two novel paradigms: 1) our newly discovered endothelial cell (EC) caveolae targeting system to sidestep passive delivery and dramatically enhance speed and efficiency of tumor penetration, and 2) to design and develop novel platinum(II) supramolecular coordination complexes (Pt(II)-SCCs), the nanoparticles (NPs) that have shown remarkable efficacy in tumor destruction in preclinical breast cancer models while being monodisperse, stable and well-characterized. Our main hypothesis is that immunoconjugates that fully utilize the advantages of caveolae-targeting antibodies will increase Pt(II)-SCCs delivery into tumors for enhanced efficacy and reduced toxicity, potentially resulting in a fundamentally new class of anticancer therapeutics. This hypothesis will be tested by the following specific aims: In Aim 1, we plan to design and synthesize Pt(II)-SCC immunoconjugates. In this Aim will also design, synthesize and characterize the chemical identity, purity and physicochemical properties of our Pt(II)-SCCs immunoconjugates. We will use caveolae-targeted antibody which we have shown can move the attached cargo from the blood across the EC barrier into solid tumor with unprecedented speed and specificity. In Aim 2 we will characterize in vivo delivery of Pt(II)-SCC immunoconjugates targeting the EC caveolae in tumors. We will perform dynamic monitoring of antibody-Pt(II)-SCC targeting in real time in live mice with intravital microscopy (IVM) using fluorescence emission of the assembled SCCs. In Aim 3 we will assess the therapeutic efficacy of the EC-targeting Pt(II)-SCC immunoconjugates. The efficacy of our targeted delivery system will be examined in IVM models using fluorescence microscopy and in non-IVM Her2/Neu tumor models with whole-body animal imaging. The long-term goal of this project is to translate our key basic discoveries into an innovative drug delivery platform in order to improve therapeutic efficacy and reduce toxicity in the breast cancer treatment.