Deju Ye

Bioorthogonal Cyclization-Mediated In Situ Self-Assembly of Small Molecule Probes for Imaging Caspase Activity in vivo

Directed self-assembly of small molecules in living systems could enable a myriad of applications in biology and medicine, and it has been widely used to synthesize supramolecules and nano/microstructures in solution and in living cells. However, controlling self-assembly of synthetic small molecules in living animals is challenging because of the complex and dynamic in vivo physiological environment. Here we employed an optimized first-order bioorthogonal cyclization reaction to control self-assembly of a fluorescent small molecule, and demonstrated its in vivo applicability by imaging of casapae-3/7 activity in human tumor xenograft mouse models of chemotherapy. The in situ assembled fluorescent nanoparticles have been successfully imaged in both apoptotic cells and tumor tissues using three-dimensional structured illumination microscopy. This strategy combines the advantages offered by small molecules with those of nanomaterials and should find widespread use for non-invasive imaging of enzyme activity in vivo.

Two-photon excitation nanoparticles for photodynamic therapy

Two-photon excitation (TPE) nanoparticle-based photosensitizers (PSs) that combine the advantages of TPE and nanotechnology have emerged as attractive therapeutic agents for near-infrared red (NIR) light excited photodynamic therapy (PDT) for cancer treatment. TPE PDT is characterized by nonlinear absorption of two relatively low-energy photons of NIR light with the resulting emission of high-energy visible light. This high-energy light can sensitize oxygen to produce cytotoxic reactive oxygen species (ROS) and singlet oxygen (1O2) which can kill cancer cells. The long-wavelength light used to excite TPE NPs allows for deeper tissue penetration to achieve efficient PDT of deep-seated tumors. Moreover, TPE nanoparticles normally have large two-photon absorption (TPA) cross-sections, which hold great potential as efficient two-photon donors in PDT. In this review, we will summarize the recent advances made in the development of TPE nanoparticles for cancer PDT. Five different TPE nanoparticles, including quantum dots (QDs), carbon nanomaterials, silica nanoparticles, gold nanomaterials, and polymer nanoparticles, are summarized in detail, and the existing challenges as well as the future perspectives are also discussed.

Controlling Intracellular Macrocyclization for the Imaging of Protease Activity

Macrocycles are an important class of molecules for their profound chemical and pharmacological properties derived from the preorganized ring structures. They are either isolated from microorganisms or prepared from acyclic precursors through chemical macrocyclization, such as ring-closing olefin metathesis. On the other hand, the control of macrocylization to synthesize macrocycles directly from acyclic precursors in living mammalian cells has been little explored. For example, a chemically stable, biologically inactive acyclic precursor (such as 1 in Figure 1) would enter cells and be converted into a macrocycle (such as 3). Specific cellular processes may be exploited to control the synthesis through regulation of the conversion of the chemically stable precursor into the reactive intermediate (2 in Figure 1) for subsequent macrocyclization. Because of the unique properties of macrocycles, the conversion from the acyclic into the cyclic form may lead to novel functions and applications for the probing of cellular biochemistry and biology. Herein, we describe an example of the control of macrocyclization in living cells to image local protease activity. The conceptual design in Figure 1 was demonstrated with an intramolecular macrocyclization system derived from a biocompatible condensation reaction between 2-cyanobenzothiazole (CBT) and free cysteine. We have previously shown that this bimolecular condensation reaction can lead to the formation of oligomers in vitro and in cells. For efficient macrocyclization in cells, intermolecular condensation of the acyclic precursors with intracellular endogenous free cysteine should be minimal. We hypothesized that if we used a CBT analogue with significantly reduced reactivity towards cysteine, the acyclic precursor would not react intermolecularly with free cysteine before activation by the target enzyme in cells, but only by an intramolecular cyclization after enzymemediated conversion into the reactive intermediate 2. To discover such CBT analogues, we screened a series of cyano-substituted aromatic compounds to determine their reaction rates with l-cysteine in phosphate-buffered saline (PBS) in an HPLC assay. A 13-fold decrease in the secondorder rate constant was observed for 4-methyl-2-thiazolecarbonitrile, and a more than 480-fold decrease for 2-cyano-6hydroxyquinoline (CHQ). The other three analogues gave no detectable condensation product on the HPLC column in 5 hours (see Table S1 in the Supporting Information). Aminothiol substrates were also screened for improved activity towards CBT; however, the second-order rate constant of all Figure 1. Proposed enzyme-controlled macrocyclization reaction in cells. A cell-permeable probe 1 enters cells and is converted by reduction and/or enzymatic processing into an intermediate 2, which quickly undergoes intramolecular cyclization to generate the macrocyclic product 3. The selfassembly of 3 leads to the formation of nanoparticles accumulated locally at or near the enzyme location in cells.

Caspase-responsive smart gadolinium-based contrast agent for magnetic resonance imaging of drug-induced apoptosis

Non-invasive detection of caspase-3/7 activity in vivo has provided invaluable predictive information regarding tumor therapeutic efficacy and anti-tumor drug selection. Although a number of caspase-3/7 targeted fluorescence and positron emission tomography (PET) imaging probes have been developed, there is still a lack of gadolinium (Gd)-based magnetic resonance imaging (MRI) probes that enable high spatial resolution detection of caspase-3/7 activity in vivo. Here we employ a self-assembly approach and develop a caspase-3/7 activatable Gd-based MRI probe for monitoring tumor apoptosis in mice. Upon reduction and caspase-3/7 activation, the caspase-sensitive nano-aggregation MR probe (C-SNAM: 1) undergoes biocompatible intramolecular cyclization and subsequent self-assembly into Gd-nanoparticles (GdNPs). This results in enhanced r1 relaxivity-19.0 (post-activation) vs. 10.2 mM-1 s-1 (pre-activation) at 1 T in solution-and prolonged accumulation in chemotherapy-induced apoptotic cells and tumors that express active caspase-3/7. We demonstrate that C-SNAM reports caspase-3/7 activity by generating a significantly brighter T1-weighted MR signal compared to non-treated tumors following intravenous administration of C-SNAM, providing great potential for high-resolution imaging of tumor apoptosis in vivo.

Gold-catalyzed one-pot cascade construction of highly functionalized pyrrolo[1,2-a]quinolin-1(2H)-ones.

An efficient protocol was developed for the synthesis of fused heterocyclic multiring compounds pyrrolo[1,2-a]quinolin-1(2H)-ones via a AuBr(3)/AgSbF(6)-catalyzed cascade transformation. Significantly, the strategy affords a straightforward and efficient approach to construction of tricyclic lactam molecular architectures in which two new C-C bonds and one new C-N bond are formed in a one-pot synthetic operation from simple starting materials. Moreover, a broad spectrum of substrates can participate in the process effectively to produce the desired products in good yields and with excellent regio- and chemoselectivities.

Microwave-assisted synthesis of quinazolinone derivatives by efficient and rapid iron-catalyzed cyclization in water

A green, rapid, and efficient method was developed for synthesizing quinazolinone derivatives from substituted 2-halobenzoic acids and amidines via microwave-assisted iron-catalyzed cyclization with or without ligand in water (methods A and B) or DMF (methods C and D). With these methods, moderate to high yields of the desired products can be obtained from even inactive substrates, such as guanidines. To the best of our knowledge, this is the first report on the synthesis of N-heterocyclic compounds by iron-catalyzed C–N coupling in aqueous media.

Regioselective Synthesis of 3-Benzazepinones and Unexpected 5-Bromo-3-benzazepinones

A regioselective hydroamidation of 2-(1-alkynyl)phenylacetamides with Au(PPh(3))Cl/AgSbF(6) as the catalyst proceeded by a 7-endo-dig pathway to afford 3-benzazepinones. This method accommodates a broad range of alkyl and aryl alkynyl substitutes in moderate to high yields (63-91%). Moreover, unexpectedly, we also discovered a gold-mediated transformation from 2-(1-alkynyl)phenylacetamides to 5-bromo-3-benzazepinones, and AuBr(3) was found to not only play an activation role but also act as a reactant in the reaction for the first time.

Gold-catalyzed intramolecular hydroamination of terminal alkynes in aqueous media: efficient and regioselective synthesis of indole-1-carboxamides

Using [Au(PPh3)]Cl/Ag2CO3-catalyzed 5-endo-digcyclization in water under microwave irradiation, we developed a fast and green route to prepare indole-1-carboxamides from N′-substituted N-(2-alkynylphenyl)ureas. The described method is tolerant to a variety of functional groups, including N′-aryl, alkyl, heterocyclic, various N-(substituted-2-ethynylphenyl) and N-(2-ethynylpyridin-3-yl)ureas and affords moderate to high yields of the desired products.

Novel thiophene derivatives as PTP1B inhibitors with selectivity and cellular activity

A series of novel thiophene derivatives was designed, synthesized and their activities as competitive inhibitors of protein tyrosine phosphatase (PTPs) 1B (PTP1B) inhibitors were evaluated. All the compounds showed inhibitory potencies, and 10 of these exhibited moderate inhibitory activities with IC(50) values less than 10 microM. The activity of the most potent compound P28 (IC(50)=2.1 microM) was 15 times higher than that of the hit compound P01. Further, four representative compounds (P19, P22, P28, and P31) demonstrated remarkably high selectivities against other PTPs (e.g., PTPalpha, LAR, CD45, and TCPTP); P19 exhibited greater than sixfold selectivity over highly homologous TCPTP. More importantly, these compounds are permeable to cell membranes. The treatment of CHO-K1 cells with P28 (10 microM) resulted in increased phosphorylation of AKT, which suggested extensive cellular activity of this compound. The novel chemical entities reported in this study could be used for overcoming the poor selectivity and low cellular activity of PTP1B inhibitors and might represent a starting point for development of therapeutic PTP inhibitors.

Cell-Permeable Iminocoumarine-Based Fluorescent Dyes for Mitochondria

A class of small molecule fluorophores, 2-iminocoumarin-3-carboxamide derivatives, has been developed by a rapid microwave-assisted process. These fluorescent probes are cell membrane permeable with low cytotoxicity and able to selectively stain organelles in living cells.