[Show abstract][Hide abstract] ABSTRACT: pH is an important physiological parameter that plays a critical role in cellular and tissue homeostasis. Conventional small molecular pH sensors (e.g. fluorescein, Lysosensor) are limited by broad pH response and restricted fluorescent emissions. Previously, we reported the development of ultra-pH sensitive (UPS) nanoprobes with sharp pH response using fluorophores with small Stokes shifts (<40 nm). In this study, we expand the UPS design to a library of nanoprobes with operator-predetermined pH transitions and wide fluorescent emissions (400-820 nm). A copolymer strategy was employed to fine tune the hydrophobicity of the ionizable hydrophobic block, which led to desired transition pH based on standard curves. Interestingly, matching the hydrophobicity of the monomers was critical to achieve a sharp pH transition. To overcome the fluorophore limitations, we introduced copolymers conjugated with fluorescence quenchers (FQs). In the micelle state, the FQs effectively suppressed the emission of fluorophores regardless of their Stokes shifts, and further increased the fluorescence activation ratios. As a proof of concept, we generated a library of 10 nanoprobes each encoded with a unique fluorophore. The nanoprobes cover the entire physiologic range of pH (4-7.4) with 0.3 pH increments. Each nanoprobe maintained a sharp pH transition (on/off < 0.25 pH) and high fluorescence activation ratio (>50-fold between on and off states). The UPS library provides a useful toolkit to study pH regulation in many pathophysiological indications (e.g. cancer, lysosome catabolism) as well as establishing tumor-activatable systems for cancer imaging and drug delivery.
Journal of the American Chemical Society 07/2014; · 10.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Traditional micelle self-assembly is driven by the association of hydrophobic segments of amphiphilic molecules forming distinctive core-shell nanostructures in water. Here we report a surprising chaotropic-anion-induced micellization of cationic ammonium-containing block copolymers. The resulting micelle nanoparticle consists of a large number of ion pairs (≈60 000) in each hydrophobic core. Unlike chaotropic anions (e.g. ClO4 (-) ), kosmotropic anions (e.g. SO4 (2-) ) were not able to induce micelle formation. A positive cooperativity was observed during micellization, for which only a three-fold increase in ClO4 (-) concentration was necessary for micelle formation, similar to our previously reported ultra-pH-responsive behavior. This unique ion-pair-containing micelle provides a useful model system to study the complex interplay of noncovalent interactions (e.g. electrostatic, van der Waals, and hydrophobic forces) during micelle self-assembly.
Angewandte Chemie International Edition in English 06/2014; · 13.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: β-Lap prodrug micelle strategy improves the formulation properties of β-lap therapeutics. The resulting micelles yield apparent high β-lap solubility (>7 mg mL(-1) ), physical stability, and ability to reconstitute after lyophilization. In the presence of esterase, β-lap prodrugs are efficiently converted into parent drug (i.e., β-lap), resulting in NQO1-dependent lethality of NSCLC cells.
[Show abstract][Hide abstract] ABSTRACT: Objective: Folate receptor (FR) expression, while known to be elevated in many types of cancer and inflammatory cells, has not been well characterized in head and neck squamous cell carcinoma (HNSCC). We hypothesized that tumor infiltrating inflammatory cells expressing FR-β could allow fluorescent visualization of HNSCC tumors using folate conjugated dyes even when FR expression in cancer cells is low. Study Design: Retrospective review of clinical pathologic specimens and in vivo animal study. Methods: A tissue microarray (TMA) with tumor and tumor free tissue from 22 patients with HNSCC was stained with antibodies to FR-α and FR-β. We characterized FR-β(+) cells by examining CD45, CD68, CD206 and TGF-β expression. To investigate fluorescent imaging, mice with orthotopic tumor xenografts were imaged in vivo after intravenous injections of folate conjugated fluorescein isothiocyanate (folate-FITC) and were histologically evaluated ex vivo. Results: All tumor samples demonstrated significant FR-β staining and negligible FR-α staining. FR-β(+) cells found in tumors coexpressed CD68 and had increased expression of CD206 and TGF-β characteristic of tumor-associated macrophages. In the xenograft models, tumors showed strong in vivo fluorescence after folate-FITC injection in contrast to surrounding normal tissues. Histologic examination of the xenograft tissue similarly showed folate-FITC uptake in areas of inflammatory cellular infiltrate. Conclusion: While HNSCC tumor cells do not express FR, HNSCC tumors contain a significant population of FR-β expressing macrophages. Folate conjugated fluorescent dye is able to specifically target and label tumor xenografts to permit macroscopic fluorescence imaging due to FR-β expression on the infiltrating inflammatory cells.
[Show abstract][Hide abstract] ABSTRACT: Poly (ADP-ribose) polymerases (PARPs) are a family of related enzymes that share the ability to catalyze the transfer of ADP-ribose to target proteins. PARPs play an important role in various cellular processes, including modulation of chromatin structure, transcription, replication, recombination, and DNA repair. The role of PARP proteins in DNA repair is of particular interest, in view of the finding that certain tumors defective in homologous recombination mechanisms, may rely on PARP-mediated DNA repair for survival, and are sensitive to its inhibition. PARP inhibitors may also increase tumor sensitivity to DNA-damaging agents. Clinical trials of PARP inhibitors are investigating the utility of these approaches in cancer. The hyperactivation of PARP has also been shown to result in a specific programmed cell death pathway involving NAD+/ATP depletion, mu-calpain activation, loss of mitochondrial membrane potential, and the release of apoptosis inducing factor. Hyperactivation of the PARP pathway may be exploited to selectively kill cancer cells. Other PARP forms, including tankyrase 1 (PARP 5a), which plays an important role in enhancing telomere elongation by telomerase, have been found to be potential targets in cancer therapy. The PARP pathway and its inhibition thus offers a number of opportunities for therapeutic intervention in both cancer and other disease states.
[Show abstract][Hide abstract] ABSTRACT: Stimuli-responsive nanomaterials are increasingly important in a variety of applications such as biosensing, molecular imaging, drug delivery and tissue engineering. For cancer detection, a paramount challenge still exists in the search for methods that can illuminate tumours universally regardless of their genotypes and phenotypes. Here we capitalized on the acidic, angiogenic tumour microenvironment to achieve the detection of tumour tissues in a wide variety of mouse cancer models. This was accomplished using ultra pH-sensitive fluorescent nanoprobes that have tunable, exponential fluorescence activation on encountering subtle, physiologically relevant pH transitions. These nanoprobes were silent in the circulation, and then strongly activated (>300-fold) in response to the neovasculature or to the low extracellular pH in tumours. Thus, we have established non-toxic, fluorescent nanoreporters that can nonlinearly amplify tumour microenvironmental signals, permitting the identification of tumour tissue independently of histological type or driver mutation, and detection of acute treatment responses much more rapidly than conventional imaging approaches.
[Show abstract][Hide abstract] ABSTRACT: Improving patient outcome by personalized therapy involves a thorough understanding of an agent's mechanism of action. β-Lapachone (clinical forms, Arq501/Arq761) has been developed to exploit dramatic cancer-specific elevations in the phase II detoxifying enzyme, NAD(P)H:quinone oxidoreductase (NQO1). NQO1 is dramatically elevated in solid cancers, including primary and metastatic (e.g., triple-negative (ER-, PR-, Her2/Neu-)) breast cancers. To define cellular factors that influence the efficacy of β-lapachone using knowledge of its mechanism of action, we confirmed that NQO1 was required for lethality and mediated a futile redox cycle where ~120 moles of superoxide were formed per mole of β-lapachone in 5 min. β-Lapachone induced reactive oxygen species (ROS), stimulated DNA single strand break-dependent PARP1 hyperactivation, caused dramatic loss of essential nucleotides (NAD+/ATP) and elicited programmed necrosis in breast cancer cells. While PARP1 hyperactivation and NQO1 expression were major determinants of β-lapachone-induced lethality, alterations in catalase expression, including treatment with exogenous enzyme, caused marked cytoprotection. Thus, catalase is an important resistance factor, and highlights H2O2 as an obligate ROS for cell death from this agent. Exogenous superoxide dismutase (SOD) enhanced catalase-induced cytoprotection. β-Lapachone-induced cell death included AIF translocation from mitochondria to nuclei, TUNEL+ staining, atypical PARP1 cleavage, and GAPDH S-nitrosylation, which were abrogated by catalase. We predict that the ratio of NQO1:catalase activities in breast cancer versus associated normal tissue are likely to be the major determinants affecting the therapeutic window of β-lapachone and other NQO1 bioactivatable drugs.
Molecular Cancer Therapeutics 07/2013; · 5.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Imaging all the people: Using ionizable diblock copolymers a series of nanoprobes encoded with different (19) F reporters for specific pH transitions is prepared for use in MRI. The pH response of the nanoprobes is extremely sharp (ΔpHON/OFF ≈0.25 pH), and results from the disassembly of polymer micelles. A collection of three nanoprobes provides the proof of concept and allows for a qualitative measurement of environmental pH values.
Angewandte Chemie International Edition 06/2013; · 11.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this communication, we report that ionizable, tertiary amine-based block copolymers can be used as pH-responsive contrast agents for magnetic resonance imaging (MRI) through the chemical exchange saturation transfer (CEST) mechanism. The CEST signal is essentially "off" when the polymers form micelles near physiological pH but is activated to the "on" state when the micelles dissociate in an acidic environment.
Chemical Communications 06/2013; · 6.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here we demonstrate the use of multiple Si nanochannel (NC) or nanograting (NG) instead of the conventional single nanochannel or nanowire design in biosensors. The NG devices can significantly reduce device-to-device variation, and improve device performance, e.g. higher current, higher ON/OFF ratio, smaller subthreshold slope, lower threshold voltage Vt in buffer solution. NG devices also result in higher sensor stability in buffer and diluted human serum. We believe such improvements are due to reduced discrete dopant fluctuation in the Si nanowires and biochemical noise in the solution because of the multiple-channel design. The improved devices allow us to sense pH linearly with 3-aminopropyltriethoxysilane coated devices, and to selectively detect insulin with limit of detection down to 10fM in both buffer solution and diluted human serum without pre-purification.
[Show abstract][Hide abstract] ABSTRACT: Superparamagnetic iron oxide nanoparticles (SPION) are an important and versatile nano- platform with broad biological applications. Despite extensive studies, the biological and pharmacological activities of SPION have not been exploited in therapeutic applications. Recently, β-lapachone (β-lap), a novel anticancer drug, has shown considerable cancer specificity by selectively increasing reactive oxygen species (ROS) stress in cancer cells. In this study, we report that pH-responsive SPION-micelles can synergize with β-lap for improved cancer therapy. These SPION-micelles selectively release iron ions inside cancer cells, which interact with hydrogen peroxide (H(2)O(2)) generated from β-lap in a tumor-specific, NQO1-dependent manner. Through Fenton reactions, these iron ions escalate the ROS stress in β-lap-exposed cancer cells, thereby greatly enhancing the therapeutic index of β-lap. More specifically, a 10-fold increase in ROS stress was detected in β-lap-exposed cells pretreated with SPION-micelles over those treated with β-lap alone, which also correlates with significantly increased cell death. Catalase treatment of cells or administration of an iron chelator can block the therapeutic synergy. Our data suggest that incorporation of SPION-micelles with ROS-generating drugs can potentially improve drug efficacy during cancer treatment, thereby provides a synergistic strategy to integrate imaging and therapeutic functions in the development of theranostic nanomedicine.
[Show abstract][Hide abstract] ABSTRACT: Amide proton transfer (APT) imaging is one of the chemical exchange saturation transfer (CEST) imaging methods which images the exchange between protons of free tissue water and the amide groups (-NH) of endogenous mobile proteins and peptides. Previous work suggested the ability of APT imaging for characterization of the tumoral grade in the brain tumor. In this study, we tested the feasibility of in-vivo APT imaging of lung tumor and investigated whether the method could differentiate the tumoral types on orthotopic tumor xenografts from two malignant lung cancer cell lines. The results revealed that APT imaging is feasible to quantify lung tumors in the moving lung. The measured APT effect was higher in the tumor which exhibited more active proliferation than the other. The present study demonstrates that APT imaging has the potential to provide a characterization test to differentiate types or grade of lung cancer noninvasively, which may eventually reduce the need invasive needle biopsy or resection for lung cancer.
PLoS ONE 01/2013; 8(10):e77019. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Agents, such as β-lapachone, that target the redox enzyme, NAD(P)H:quinone oxidoreductase 1 (NQO1), to induce programmed necrosis in solid tumors have shown great promise, but more potent tumor-selective compounds are needed. Here, we report that deoxynyboquinone kills a wide spectrum of cancer cells in an NQO1-dependent manner with greater potency than β-lapachone. Deoxynyboquinone lethality relies on NQO1-dependent futile redox cycling that consumes oxygen and generates extensive reactive oxygen species (ROS). Elevated ROS levels cause extensive DNA lesions, PARP1 hyperactivation, and severe NAD+ /ATP depletion that stimulate Ca2+ -dependent programmed necrosis, unique to this new class of NQO1 "bioactivated" drugs. Short-term exposure of NQO1+ cells to deoxynyboquinone was sufficient to trigger cell death, although genetically matched NQO1- cells were unaffected. Moreover, siRNA-mediated NQO1 or PARP1 knockdown spared NQO1+ cells from short-term lethality. Pretreatment of cells with BAPTA-AM (a cytosolic Ca2+ chelator) or catalase (enzymatic H2O2 scavenger) was sufficient to rescue deoxynyboquinone-induced lethality, as noted with β-lapachone. Investigations in vivo showed equivalent antitumor efficacy of deoxynyboquinone to β-lapachone, but at a 6-fold greater potency. PARP1 hyperactivation and dramatic ATP loss were noted in the tumor, but not in the associated normal lung tissue. Our findings offer preclinical proof-of-concept for deoxynyboquinone as a potent chemotherapeutic agent for treatment of a wide spectrum of therapeutically challenging solid tumors, such as pancreatic and lung cancers.
Cancer Research 04/2012; 72(12):3038-47. · 9.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tunable, ultra-pH responsive fluorescent nanoparticles with multichromatic emissions are highly valuable in a variety of biological studies, such as endocytic trafficking, endosome/lysosome maturation, and pH regulation in subcellular organelles. Small differences (e.g., <1 pH unit) and yet finely regulated physiological pH inside different endocytic compartments present a huge challenge to the design of such a system. Herein, we report a general strategy to produce pH-tunable, highly activatable multicolored fluorescent nanoparticles using commonly available pH-insensitive dyes with emission wavelengths from green to near IR range. The primary driving force of fluorescence activation between the ON (unimer) and OFF (micelle) states is the pH-induced micellization. Among three possible photochemical mechanisms, homo Förster resonance energy transfer (homoFRET)-enhanced decay was found to be the most facile strategy to render ultra-pH response over the H-dimer and photoinduced electron transfer (PeT) mechanisms. Based on this insight, we selected several fluorophores with small Stoke shifts (<40 nm) and established a panel of multicolored nanoparticles with wide emission range (500-820 nm) and different pH transitions. Each nanoparticle maintained the sharp pH response (ON/OFF < 0.25 pH unit) with corresponding pH transition point at pH 5.2, 6.4, 6.9, and 7.2. Incubation of a mixture of multicolored nanoparticles with human H2009 lung cancer cells demonstrated sequential activation of the nanoparticles inside endocytic compartments directly correlating with their pH transitions. This multicolored, pH-tunable nanoplatform offers exciting opportunities for the study of many important cell physiological processes, such as pH regulation and endocytic trafficking of subcellular organelles.
Journal of the American Chemical Society 04/2012; 134(18):7803-11. · 10.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The endosomal barrier is a major bottleneck for the effective intracellular delivery of siRNA by nonviral nanocarriers. Here, we report a novel amphotericin B (AmB)-loaded, dual pH-responsive micelleplex platform for siRNA delivery. Micelles were self-assembled from poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diisopropylamino)ethyl methacrylate) (PDMA-b-PDPA) diblock copolymers. At pH 7.4, AmB was loaded into the hydrophobic PDPA core, and siRNA was complexed with a positively charged PDMA shell to form the micelleplexes. After cellular uptake, the PDMA-b-PDPA/siRNA micelleplexes dissociated in early endosomes to release AmB. Live cell imaging studies demonstrated that released AmB significantly increased the ability of siRNA to overcome the endosomal barrier. Transfection studies showed that AmB-loaded micelleplexes resulted in significant increase in luciferase (Luc) knockdown efficiency over the AmB-free control. The enhanced Luc knockdown efficiency was abolished by bafilomycin A1, a vacuolar ATPase inhibitor that inhibits the acidification of the endocytic organelles. These data support the central hypothesis that membrane poration by AmB and increased endosomal swelling and membrane tension by a "proton sponge" polymer provided a synergistic strategy to disrupt endosomes for improved intracellular delivery of siRNA.
[Show abstract][Hide abstract] ABSTRACT: Photodynamic therapy (PDT) is an emerging clinical modality for the treatment of a variety of diseases. Most photosensitizers are hydrophobic and poorly soluble in water. Many new nanoplatforms have been successfully established to improve the delivery efficiency of PS drugs. However, few reported studies have investigated how the carrier microenvironment may affect the photophysical properties of photosensitizer (PS) drugs and subsequently, their biological efficacy in killing malignant cells. In this study, we describe the modulation of type I and II photoactivation processes of the photosensitizer, 5,10,15,20-tetrakis(meso-hydroxyphenyl)porphyrin (mTHPP), by the micelle core environment. Electron-rich poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) micelles increased photoactivations from type II to type I mechanisms, which significantly increased the generation of O(2)(-) through the electron transfer pathway over (1)O(2) production through energy transfer process. The PDPA micelles led to enhanced phototoxicity over the electron-deficient poly(D,L-lactide) control in multiple cancer cell lines under argon-saturated conditions. These data suggest that micelle carriers may not only improve the bioavailability of photosensitizer drugs, but also modulate photophysical properties for improved PDT efficacy.
Journal of Controlled Release 08/2011; 156(3):276-80. · 7.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To characterize the properties of polymeric micelles containing different loading percentages of mTHPP, a photosensitizer for photodynamic therapy (PDT), with respect to fluorescence, singlet oxygen ((1)O(2)) yield, and in vitro cytotoxicity in head and neck cancer cells.
Polymer chemistry laboratory.
Absorption and emission spectroscopy was used to characterize the mTHPP-loaded micelles. The (1)O(2) yield was measured to determine the efficiency of reactive oxygen species (ROS) generation. In vitro studies were conducted using the HN5 cells and confirmed with H2009 cells to determine the photodynamic efficacy. DNA assay and confocal microscopy was used to measure intracellular fluorescence.
The mTHPP micelles demonstrated the highest fluorescence intensity at 0.5% loading. The (1)O(2) generation of the micelles in solution peaked at 2% loading. Phototoxicity and dark toxicity experiments in HN5 and H2009 cells demonstrated that the best therapeutic index was achieved with the 2% loaded micelles with 100% cell cytotoxicity at a micelle concentration of 10 µg/mL and less than 10% dark cytotoxicity. In comparison, 10% loaded micelles demonstrated 100% cell cytotoxicity at a concentration of 20 µg/mL under both light and dark conditions. Confocal microscopy demonstrated increasing intracellular fluorescence with higher loading.
The 2% mTHPP-loaded micelles generated greater (1)O(2), and 0.5% loading led to the most efficient generation of fluorescence in solution. Higher mTHPP loading density led to increased cellular fluorescence and dark cytotoxicity. Overall, 2% mTHPP-loaded micelles provided the optimal composition for photodynamic therapy with the largest therapeutic window.
Otolaryngology Head and Neck Surgery 07/2011; 145(4):612-7. · 1.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Low-doped silicon multi-nanowire field effect transistors with high ON/OFF ratio over 10(7) and a low subthreshold swing of 60-120 mV dec(-1) are fabricated using lithographic semiconductor processes. The use of multi-nanowires instead of a single nanowire as sensing elements has shown improved device uniformity and stability in buffer solutions. The device stability is further improved with surface silanization and biasing with a solution gate rather than a backgate. pH sensing with a linear response over a range of 2-9 is achieved using these devices. Selective detection of bovine serum albumin at concentrations as low as 0.1 femtomolar is demonstrated.
Lab on a Chip 06/2011; 11(11):1952-61. · 5.70 Impact Factor