(H) fluorescent photographs of LONp, antiCD33-LONp, LONp-PMI and antiCD33 -LONp-PMI measured in Milli-Q water and excited at 260nm. We characterized various forms of LONp nanoparticles, bare or loaded with PMI, anti-CD33 or both, using high-resolution transmission electron microscopy KP372-1 (TEM), dynamic light scattering and fluorescence spectroscopy techniques. real-time visualization of a series of apoptotic events in AML cells, proving a useful tool for possible disease tracking and treatment response monitoring. Our studies shed light on the development of antiCD33-LONp-PMI as a novel class of antitumor agents, which, if further validated, may help targeted molecular therapy of AML. Introduction Peptide inhibitors of intracellular protein-protein interactions (PPIs) involved in disease initiation and progression are increasingly recognized as potential leads for the development of new classes of therapeutics. Due to their relatively specific and often high-affinity mode of action against protein targets, peptide therapeutics can in theory work at low doses with a more favorable toxicity profile than that of small molecule drugs[2, 3]. This ideal scenario could certainly play out against the backdrop that small molecule inhibitors are in general ineffective against PPIs. In reality, however, the efficacy of peptide therapeutics is frequently limited by their poor proteolytic stability and inability to traverse the cell membrane [5, 6]. To alleviate these technical hurdles, various elaborate chemistries for peptide modification and delivery vehicles for peptide cargo have been developed, and significant progress has been made TSC1 in ways of improving the pharmacological properties of peptide therapeutics for clinical use [6C8]. Among the commonly used peptide delivery systems are lipids and biodegradable polymers fabricated often in the forms of liposome, micelle, and dendrimer. However, lipid-based delivery vehicles are rapidly removed by the liver and spleen; polymer-based ones, often highly positively charged, exhibit toxicity and non-specific cellular uptake. Such drawbacks necessarily impede the development of peptide therapeutics for widespread clinical applications. Conceptually novel and clinically viable delivery systems are therefore needed in order to advance peptide drug discovery and development. Toward this end, nanoparticle-mediated KP372-1 peptide drug delivery holds great promise in overcoming many limitations of lipid- and polymer-based delivery systems [13, 14]. Conjugation of peptide cargos to nanoparticles substantially improves peptide resistance to proteolysis, membrane permeability, and bioavailability [6, 15]. In fact, nanoparticle-based drug delivery systems are particularly attractive in the treatment of solid tumors as nanoparticles are capable of actively accumulating through leaky blood vessels in diseased tissues C a phenomenon known as the enhanced permeability and retention (EPR) effect [16, 17]. Importantly, when appropriate materials are used to construct nanoparticles, they can be endowed with a powerful imaging capability for both therapeutic and diagnostic applications [18, 19], yielding multi-functional theranostics that combine disease tracking, drug delivery and treatment response monitoring . Recent studies have demonstrated the superiority of lanthanide-doped nanoparticles (LDNp) as an imaging tool in biomedicine due to their excellent photoluminescence property and biocompatibility [15, 21]. LDNp loaded with appropriate therapeutic peptide cargos and disease-targeting molecules may be developed as a novel class of theranostics for clinical use [22C24]. In this work, we interrogated lanthanide oxyfluoride nanoparticles (LONp) as a drug delivery vehicle by conjugating a p53-activating dodecameric peptide termed PMI (TSFAEYWALLSP)  for potential treatment of acute myeloid leukemia (AML). Intracellular PMI kills AML cells by antagonizing MDM2 and/or MDMX C the two functional inhibitors of the tumor suppressor protein p53 [26C28]. To endow LONp-PMI with tumor targeting specificity, we also conjugated to the nanoparticle a monoclonal antibody against CD33, a receptor expressed at high levels on leukemic myeloid cells but not on normal hematopoietic pluripotent stem cells in the vast majority of AML patients [29, 30]. Our and data as well as mechanistic studies fully validate KP372-1 the design of antiCD33-LONp-PMI as a novel class of peptide-based antitumor agents with therapeutic potential in the treatment of AML. Results Preparation and physicochemical properties of antiCD33-LONp-PMI The strategy for the preparation of antiCD33-LONp-PMI is outlined in Fig. 1. Luminescent LONp nanoparticles.