Yong Deok Lee

Conjugated polymer nanoparticles for biomedical in vivo imaging

Conjugated polymer nanoparticles, produced by in situ colloidal Knoevenagel polymerization, show advantageous properties (bright emission, colloidal/chemical stability and mesoscopic size range) that allow the successful in vivo application to real-time sentinel lymph node mapping in a mouse model.

Dye/Peroxalate Aggregated Nanoparticles with Enhanced and Tunable Chemiluminescence for Biomedical Imaging of Hydrogen Peroxide

Hydrogen peroxide (H(2)O(2)) is an endogenous molecule that plays diverse physiological and pathological roles in living systems. Here we report multimolecule integrated nanoprobes with the enhanced chemiluminescence (CL) response to H(2)O(2) that is produced in cells and in vivo. This approach is based on the nanoscopic coaggregation of a dye exhibiting aggregation-enhanced fluorescence (AEF) with a H(2)O(2)-responsive peroxalate that can convert chemical reaction energy into electronic excitation. The coaggregated CL nanoparticles (FPOA NPs) with an average size of ~20 nm were formulated by aqueous self-assembly of a ternary mixture of a surfactant (Pluronic F-127) and concentrated hydrophobic dye/peroxalte payloads. Spectroscopic studies manifest that FPOA NPs as a reagent-concentrated nanoreactor possess the signal enhancement effect by AEF, as well as the optimized efficiencies for H(2)O(2) peroxalate reaction and subsequent intraparticle energy transfer to the dye aggregates, to yield greatly enhanced CL generation with a prolonged lifetime. It is shown that the enhanced CL signal thereby is capable of detecting intracellular H(2)O(2) overproduced during immune response. We also demonstrate that the densely integrated nature of FPOA NPs facilitates further intraparticle CL energy transfer to a low-energy dopant to red shift the spectrum toward the biologically more transparent optical window, which enables the high-sensitivity in vivo visualization of H(2)O(2) associated with early stage inflammation.

Self-assembled mirror DNA nanostructures for tumor-specific delivery of anticancer drugs.

Nanoparticle delivery systems have been extensively investigated for targeted delivery of anticancer drugs over the past decades. However, it is still a great challenge to overcome the drawbacks of conventional nanoparticle systems such as liposomes and micelles. Various novel nanomaterials consist of natural polymers are proposed to enhance the therapeutic efficacy of anticancer drugs. Among them, deoxyribonucleic acid (DNA) has received much attention as an emerging material for preparation of self-assembled nanostructures with precise control of size and shape for tailored uses. In this study, self-assembled mirror DNA tetrahedron nanostructures is developed for tumor-specific delivery of anticancer drugs. l-DNA, a mirror form of natural d-DNA, is utilized for resolving a poor serum stability of natural d-DNA. The mirror DNA nanostructures show identical thermodynamic properties to that of natural d-DNA, while possessing far enhanced serum stability. This unique characteristic results in a significant effect on the pharmacokinetics and biodistribution of DNA nanostructures. It is demonstrated that the mirror DNA nanostructures can deliver anticancer drugs selectively to tumors with enhanced cellular and tissue penetration. Furthermore, the mirror DNA nanostructures show greater anticancer effects as compared to that of conventional PEGylated liposomes. Our new approach provides an alternative strategy for tumor-specific delivery of anticancer drugs and highlights the promising potential of the mirror DNA nanostructures as a novel drug delivery platform.

Directed molecular assembly into a biocompatible photosensitizing nanocomplex for locoregional photodynamic therapy

Methylene blue (MB), a water-soluble cationic dye widely used in the clinic, is known to photosensitize the generation of cytotoxic singlet oxygen efficiently, and thus, has attracted interest as a potential drug for photodynamic therapy (PDT). However, its use for the in vivo PDT of cancer has been limited due to the inherently poor cell/tissue accumulation and low biological stability in the free molecular form. Here, we report a simple and biocompatible nanocomplex formulation of MB (NanoMB) that is useful for in vivo locoregional cancer treatment by PDT. NanoMB particles were constructed through the self-assembly of clinically usable molecules (MB, fatty acid and a clinically approved polymer surfactant) directed by the dual (electrostatic and hydrophobic) interactions between the ternary constituents. The nanocomplexed MB showed greatly enhanced cell internalization while keeping the photosensitization efficiency as high as free MB, leading to distinctive phototoxicity toward cancer cells. When administered to human breast cancer xenograft mice by peritumoral injection, NanoMB was capable of facile penetration into the tumor followed by cancer cell accumulation, as examined in vivo and histologically with the near-infrared fluorescence signal of MB. The quintuple PDT treatment by a combination of peritumorally injected NanoMB and selective laser irradiation suppressed the tumor volume efficaciously, demonstrating potential of NanoMB-based PDT as a biocompatible and safe method for adjuvant locoregional cancer treatment.

An activatable anticancer polymer–drug conjugate based on the self-immolative azobenzene motif

Triggered cellular uptake of a synthetic graft copolymer carrying an anticancer drug is achieved through self-immolation of the side-chain azobenzene groups. In this concept, the conjugate is initially chemically neutral and does not possess cell-penetrating function. However, upon cleavage of the azobenzene moieties, a cascade process is initiated that ultimately reveals an ammonium cation in the vicinity of the polymer backbone. Hence, self-immolation results in the transformation of the neutral polymer chain into a polycation. This structural transformation allows the conjugate to be taken up by the cancer cells through favorable electrostatic interactions with the negatively charged phospholipid components of the cell membrane. Once inside the cells, the polymer releases covalently attached doxorubicin in a pristine form through a low pH activated release mechanism. The significance of this approach lies in the sensitivity of the azobenzene group to hypoxic conditions and to the enzyme azoreductase that is secreted by the microbial flora of the human colon and suggests a pathway to targeted drug delivery applications under these conditions.

Nanoprobes for optical bioimaging

Imaging nanoprobes are a group of nano-sized contrast agents devised for providing improved contrast and spatial resolution for bioimaging. Among various imaging nanoprobes, optical nanoprobes capable of monitoring biological events or progresses in the cellular and molecular levels have been developed for early detection, accurate diagnosis, and personalized image-guided treatment of diseases. The optical activities of nanoprobes can be tuned on demand for specific applications by engineering their size, surface nature, morphology, and composition. In addition, by virtue of the nanostructure, nanoprobes have displayed favorable pharmacokinetic features and target specificity reflecting clinical demands. In this review, we focus on typical approaches and recent trends in development of nanoprobe-mediated optical imaging and their potential as a clinical diagnostic modality.

Size-engineered biocompatible polymeric nanophotosensitizer for locoregional photodynamic therapy of cancer

Current approaches in use of water-insoluble photosensitizers for photodynamic therapy (PDT) of cancer often demand a nano-delivery system. Here, we report a photosensitizer-loaded biocompatible nano-delivery formulation (PPaN-20) whose size was engineered to ca. 20nm to offer improved cell/tissue penetration and efficient generation of cytotoxic singlet oxygen. PPaN-20 was fabricated through the physical assembly of all biocompatible constituents: pyropheophorbide-a (PPa, water-insoluble photosensitizer), polycaprolactone (PCL, hydrophobic/biodegradable polymer), and Pluronic F-68 (clinically approved polymeric surfactant). Repeated microemulsification/evaporation method resulted in a fine colloidal dispersion of PPaN-20 in water, where the particulate PCL matrix containing well-dispersed PPa molecules inside was stabilized by the Pluronic corona. Compared to a control sample of large-sized nanoparticles (PPaN-200) prepared by a conventional solvent displacement method, PPaN-20 revealed optimal singlet oxygen generation and efficient cellular uptake by virtue of the suitably engineered size and constitution, leading to high in vitro phototoxicity against cancer cells. Upon administration to tumor-bearing mice by peritumoral route, PPaN-20 showed efficient tumor accumulation by the enhanced cell/tissue penetration evidenced by in vivo near-infrared fluorescence imaging. The in vivo PDT treatment with peritumorally administrated PPaN-20 showed significantly enhanced suppression of tumor growth compared to the control group, demonstrating great potential as a biocompatible photosensitizing agent for locoregional PDT treatment of cancer.

Fluorogenic nanoreactor assembly with boosted sensing kinetics for timely imaging of cellular hydrogen peroxide

The precise detection of endogenous H2O2 has been considered to be a useful tool for understanding cell physiology. Here, we have developed a nanoreactor co-incorporated with a H2O2-responsive fluorogenic molecule and a catalytic additive. The fast sensing kinetics allows us to visualize a subcellular response in real-time.

Real-time imaging of glioblastoma using bioluminescence in a U-87 MG xenograft model mouse

Glioblastoma multiforme (GBM), the most common malignant brain tumor, is characterized by aggressive proliferation and invasive potential. Xenograft animal models of GBM have critically contributed to evaluation of novel therapeutic agents, drug delivery system, and diagnostic tools. To mimic intrinsic behavior of GBM, orthotopic transplantation of cancer cells and continuous observation of cell growth should be conducted in animal study. Here, we generated xenograft model mouse of GBM in which U-87 MG human glioblastoma cells were intracranially implanted for live imaging. Introducing luciferase gene into U-87 MG cell line enabled real-time observation and quantification of tumor survival and propagation by detecting photon emission derived from luciferase. Our GBM model mouse has potentials to bring great advantages in pharmacological and mechanistic investigation on brain tumors.