Yucheng Wang

Functionalized Quantum Dots for Biosensing and Bioimaging and Concerns on Toxicity

Considerable efforts have been devoted to the development of novel functionalized nanomaterials for bio-oriented applications. With unique optical properties and molar scale production, colloidal photoluminescent quantum dots (QDs) have been properly functionalized with controlled interfaces as new class of optical probes with extensive use in biomedical research. In this review, we present a brief summary on the current research interests of using fine engineered QDs as a nanoplatform for biomedical sensing and imaging applications. In addition, recent concerns on the potential toxic effects of QDs are described as a general guidance for the development on QD formulations in future studies.

Preparation of quantum dot/drug nanoparticle formulations for traceable targeted delivery and therapy

Quantum dots (QDs) are luminescent nanocrystals with rich surface chemistry and unique optical properties that make them useful as probes or carriers for traceable targeted delivery and therapy applications. QDs can be functionalized to target specific cells or tissues by conjugating them with targeting ligands. Recent advancement in making biocompatible QD formulations has made these nanocrystals suitable for in vivo applications. This review provides an overview of the preparation of QDs and their use as probes or carriers for traceable, targeted therapy of diseases in vitro and in vivo. More specifically, recent advances in the integration of QDs with drug formulations for therapy and their potential toxicity in vitro and in vivo are highlighted. The current findings and challenges for optimizing QD/drug formulations with respect to optimal size and stability, short-term and long-term toxicity, and in vivo applications are described. Lastly, we attempt to predict key trends in QD/drug formulation development over the next few years and highlight areas of therapy where their use may provide breakthrough results in the near future.

Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models

The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive protocols are urgently needed to be developed and employed for fully assessing and understanding the origins of the toxicity arising from different QD formulations.

Aggregation-induced emission (AIE) dye loaded polymer nanoparticles for gene silencing in pancreatic cancer and their in vitro and in vivo biocompatibility evaluation

We have developed aggregation-induced emission (AIE) dye loaded polymer nanoparticles with deep-red emission for siRNA delivery to pancreatic cancer cells. Two US Food and Drug Administration (FDA) approved surfactant polymers, Pluronics F127 and PEGylated phospholipid, were used to prepare the dye-loaded nanoparticle formulations and they can be used as nanovectors for gene silencing of mutant K-ras in pancreatic cancer cells. The successful transfection of siRNA by the developed nanovectors was confirmed by the fluorescent imaging and quantified through flow cytometry. Quantitative real time polymerase chain reaction (PCR) indicates that the expression of the mutant K-ras oncogene from the MiaPaCa-2 pancreatic cancer cells has been successfully suppressed. More importantly, our in vivo toxicity study has revealed that both the nanoparticle formulations are highly biocompatible in BALC/c mice. Overall, our results suggest that the AIE dye-loaded polymer nanoparticle formulations developed here are suitable for gene delivery and have high potential applications in translational medicine research.

Biodegradable Nanocapsules as siRNA Carriers for Mutant K‐Ras Gene Silencing of Human Pancreatic Carcinoma Cells

The application of small interfering RNA (siRNA)-based RNA interference (RNAi) for cancer gene therapy has attracted great attention. Gene therapy is a promising strategy for cancer treatment because it is relatively non-invasive and has a higher therapeutic specificity than chemotherapy. However, without the use of safe and efficient carriers, siRNAs cannot effectively penetrate the cell membranes and RNAi is impeded. In this work, cationic poly(lactic acid) (CPLA)-based degradable nanocapsules (NCs) are utilized as novel carriers of siRNA for effective gene silencing of pancreatic cancer cells. These CPLA-NCs can readily form nanoplexes with K-Ras siRNA and over 90% transfection efficiency is achieved using the nanoplexes. Cell viability studies show that the nanoparticles are highly biocompatible and non-toxic, indicating that CPLA-NC is a promising potential candidate for gene therapy in a clinical setting.

Synthesis and Characterization of Mn:ZnSe/ZnS/ZnMnS Sandwiched QDs for Multimodal Imaging and Theranostic Applications

In this work, a facile aqueous synthesis method is optimized to produce Mn:ZnSe/ZnS/ZnMnS sandwiched quantum dots (SQDs). In this core-shell co-doped system, paramagnetic Mn(2+) ions are introduced as core and shell dopants to generate Mn phosphorescence and enhance the magnetic resonance imaging signal, respectively. T1 relaxivity of the nanoparticles can be improved and manipulated by raising the shell doping level. Steady state and time-resolved optical measurements suggest that, after high level shell doping, Mn phosphorescence of the core can be sustained by the sandwiched ZnS shell. Because the SQDs are free of toxic heavy metal compositions, excellent biocompatibility of the prepared nanocrystals is verified by in vitro MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. To explore the theranostic applications of SQDs, liposome-SQD assemblies are prepared and used for ex vivo optical and magnetic resonance imaging. In addition, these engineered SQDs as nanocarrier for gene delivery in therapy of Panc-1 cancer cells are employed. The therapeutic effects of the nanocrystals formulation are confirmed by gene expression analysis and cell viability assay.

Revisiting the principles of preparing aqueous quantum dots for biological applications: the effects of surface ligands on the physicochemical properties of quantum dots

Surface functionalization of quantum dots (QDs) is one of the most important aspects for the design and preparation of the desired QDs for specific biomedical applications. The surface ligands not only render the QDs water-dispersible, but also endow them with different functional groups for bioconjugation. More importantly, as the surface ligand layer on the QD surface is responsible for interacting with the biological environments, the type of surface ligand will greatly affect the response from the cells, such as the cellular uptake and cytotoxicity. In this paper, we investigate the effects of the surface ligand on the physicochemical properties of QDs and examine different QD formulations for possible biomedical applications. Seven types of QD formulations were prepared by anchoring the CdSe/CdS/ZnS QDs surface with either short-chain mercapto ligands (MPA, MSA, cysteine, AET) or PEG derivative ligands (mPEG-SH, CM-PEG-SH, NH2-PEG-SH). We then conducted a systematic study to evaluate the colloidal stability, photostability, cellular uptake and in vitro toxicity of the formulations. The colloidal stability was evaluated by the particle size change in water, acidic/neutral/alkaline buffer solutions and cell culture medium. Our results show that the carboxyl-terminated QDs have the best colloidal stability in water and alkaline solutions. PEG-capped QDs are more stable than short-chain ligand modified QDs in cell culture medium. For the photostability of different QD formulations under UV irradiation, we observed that the MPA-, MSA- and Cys-QDs had better photostability than that of the PEG modified QDs, whereas the AET-QD is the least stable one. Cellular uptake of QDs was evaluated using cell imaging and quantified by flow cytometry. The PEG chains and surface charge of QDs were found to play critical roles in the cellular uptake. Using RAW246.7 macrophage cells as the cellular uptake model, we discovered that the anionic QDs had a much higher uptake compared to the cationic QD formulations. In general, each set of prepared QD formulation with a specific type of surface ligand display certain strengths and limitations in different aspects of their physicochemical properties. Therefore, one should carefully consider and choose the type of QD formulation in the experiments thereby minimizing its impacts arising from their limitations.

Biodegradable nanoparticle-mediated K-ras down regulation for pancreatic cancer gene therapy

RNA interference (RNAi) targeting the K-ras oncogene mutation in pancreatic cancer mediated by small interfering RNA (siRNA) transfection is a very promising treatment. However, the rapid degradation and negative charge of naked siRNAs restrict their direct delivery into cells. In this contribution, we propose a safe and effective transmembrane transport nanocarrier formulation based on a newly developed biodegradable charged polyester-based vector (BCPV) for K-ras siRNA delivery into pancreatic cancer cells. Our results have shown that these biodegradable and biocompatible vectors are able to transfect siRNAs targeting mutant K-ras into MiaPaCa-2 cells with high transfection and knockdown efficiency. More importantly, the RNAi process initiated a cascade gene regulation of the downstream proteins of K-ras associated with cell proliferation, migration, invasion and apoptosis. We observed that after the mutant K-ras siRNA transfection, the growth, migration and invasion of the MiaPaCa-2 cells were significantly reduced; also, the apoptosis of the pancreatic cancer cells was promoted. Although in vivo testing data are limited, we propose that the BCPV based nanoparticle formulation could be a promising candidate as non-viral vectors for gene therapy in clinical settings.

Rational design of multimodal and multifunctional InP quantum dot nanoprobes for cancer: in vitro and in vivo applications

In this paper we report the development of multifunctional nanoprobes based on InP–ZnS quantum dots (QDs) for high contrast multimodal imaging and other applications for cancer in vitro and in vivo. These theranostic nanoprobes were synthesized by co-encapsulating InP–ZnS QDs and anticancer drug molecules within PEGylated phospholipid micelles covalently linked with DOTA-chelated Gd3+. Luminescent biocompatible InP–ZnS QDs and Gd3+ chelates can be used for fluorescence microscopy and magnetic resonance imaging (MRI), respectively. The nanoprobes showed both optical and MRI capabilities. The therapeutic effect of the theranostic nanoprobes was evaluated using cell viability assays and the toxic effect of the released anticancer drugs from the probes was confirmed on the cancer cells. For targeted delivery in vitro, the micelle-encapsulated QDs were conjugated with transferrin and anti-claudin-4 antibody, which target the transferrin- and claudin-4-receptors overexpressed in cancer cells, respectively. Employing in vivo optical imaging of mice bearing pancreatic cancer xenografts, we have demonstrated that systemically-delivered anti-claudin-4 conjugated QD nanoprobes can target and label the tumors with high contrast. These studies suggest that the developed theranostic InP–ZnS QD nanoprobes have the potential to be translated in clinical research for targeted multimodal diagnosis and therapy of cancer.

Optimizing the aqueous phase synthesis of CdTe quantum dots using mixed-ligands system and their applications for imaging of live cancer cells and tumors in vivo

Quantum dots (QDs) exhibit unique optical properties including size-tunable fluorescence, superior brightness, broad absorption and tiny emission bandwidth. These properties have made QDs promising candidates for bioimaging and biosensing applications. In this work, CdTe QDs were synthesized in aqueous phase using both mercaptopropionic acid (MPA) and Cysteine (Cys) as capping agents. Growth kinetics and optical properties of the resulted QDs were found to be dependent on both species and concentration of surfactant molecules. Considering the distinct nature and advantages of MPA and Cys, a mixed-ligands system was proposed as a potential approach to fabricate QDs with specific optical property and functions for in vitro and in vivo bioimaging applications.