An Orthogonal Protection Strategy for Synthesizing Scaffold-Modifiable Dendrons and Their Application in Drug Delivery.

Dendrons have well-defined dendritic structures. However, it is a great challenge to preserve their high structural definition after multiple functionalization because the site-selective conjugation of different functional molecules is quite difficult. Scaffold-modifiable dendrons that have orthogonal reactive groups at the scaffold and periphery are ideal for achieving the site-specific bifunctionalization. In this paper, we present a new strategy for synthesizing scaffold-modifiable dendrons via orthogonal amino protection and a solid-phase synthesis method. This strategy renders the reactive sites at the scaffold and periphery of the dendrons a super selectivity, high reactivity, and wide applicability to various reaction types. The fourth-generation dendrons can be facilely synthesized within 2 days without structural defects as demonstrated by mass spectrometry. We conjugated doxorubicin (DOX) and phenylboronic acid (PBA) groups to the scaffold and periphery, respectively. Thanks to the PBA-enhanced lysosome escape, tumor targeting ability, and tumor permeability as well as the high drug loading content larger than 30%, the dendron-based prodrug exhibited extraordinary antitumor efficacy and could eradicate the tumors established in mice by multiple intravenous administration. This work provides a practical strategy for synthesizing scaffold-modifiable dendrons that can be a promising nanoplatform to achieve function integration in a precisely controlled manner.

Phenylboronic Acid Modification Augments the Lysosome Escape and Antitumor Efficacy of a Cylindrical Polymer Brush-Based Prodrug.

Timely lysosome escape is of paramount importance for endocytosed nanomedicines to avoid premature degradation under the acidic and hydrolytic conditions in lysosomes. Herein, we report an exciting finding that phenylboronic acid (PBA) modification can greatly facilitate the lysosome escape of cylindrical polymer brushes (CPBs). On the basis of our experimental results, we speculate that the mechanism is associated with the specific interactions of the PBA groups with lysosomal membrane proteins and hot shock proteins. The featured advantage of the PBA modification over the known lysosome escape strategies is that it does not cause significant adverse effects on the properties of the CPBs; on the contrary, it enhances remarkably their tumor accumulation and penetration. Furthermore, doxorubicin was conjugated to the PBA-modified CPBs with a drug loading content larger than 20%. This CPBs-based prodrug could eradicate the tumors established in mice by multiple intravenous administrations. This work provides a novel strategy for facilitating the lysosome escape of nanomaterials and demonstrates that PBA modification is an effective way to improve the overall properties of nanomedicines including the tumor therapeutic efficacy.

A Dendron-Based Fluorescence Turn-On Probe for Tumor Detection.

Specifically amplifying the emission signals of optical probes in tumors is an effective way to improve the tumor-imaging sensitivity and contrast. In this paper, the first case of dendron-based fluorescence turn-on probes mediated by a Förster resonance energy transfer (FRET) mechanism is reported. Dendrons up to the fourth generation with a hydrophilic oligo(ethylene glycol) scaffold are synthesized by a solid-phase synthesis strategy, and show precise and defect-free chemical structures. To construct the fluorescence turn-on probe, one Cy5.5 molecule is conjugated to the focal of a G3 dendron through a robust linkage and eight Black Hole Quencher 3 (BHQ-3) molecules are conjugated to its periphery through a PEG chain bearing a reductively cleavable disulfide linkage. By in vitro and in vivo experiments, it is demonstrated that the fluorescence of the dendron-based probe can be activated effectively and rapidly in the reductive environments of tumor cells and tissues, and the probe thus exhibits amplified tumor signals and weak normal tissue signals. Compared with the reported nanoscale turn-on probes, the dendron-based probe has several significant advantages, such as well-defined chemical structure, precisely controllable fluorophore/quencher conjugation sites and ratio, desirable chemical stability, and reproducible pharmacokinetic and pharmacological profiles, and is very promising in tumor detection.

Improving Quantum Yield of a NIR-II Dye by Phenylazo Group.

Understanding structure-fluorescence correlation is very helpful for the design of fluorescent probes. In this paper, a donor-acceptor-donor (D-A-D) type NIR-II fluorophore with benzobisthiadiazole as the acceptor and triphenyl amine as the donor, and its three derivatives bearing respectively amino, tert-butyloxycarbonyl amino and phenylazo groups in donor moieties, are synthesized. Their electronic structures and optical properties are investigated via theoretical and experimental studies. It is found that all the three types of substituents significantly influence its fluorescent properties and the phenylazo groups dramatically enhance its quantum yield (QY). To achieve biological applications and maintain high QY in aqueous environments, the phenylazo-containing fluorophore is encapsulated in polystyrene-co-poly(ethylene glycol) micelles. The obtained fluorescent micelles have a QY of ≈3.51% in 1000-1500 nm in aqueous medium that is among the highest of the organic NIR-II probes reported so far for biological imaging. The high QY enables the in vivo imaging of the micelle-administered mice to be conducted with high speed and quality. As an application example, ultrafast NIR-II imaging of intravenously injected mice is performed and used to determine their cardiac cycle and heart rate. The micelles also significantly accumulate in tumors after tail-vein injection and exhibit great application potentials in tumor detection.

Shape Effects of Cylindrical versus Spherical Unimolecular Polymer Nanomaterials on in Vitro and in Vivo Behaviors.

To date, how the shape of nanomaterials influences their biological properties is poorly understood, due to the insufficient controllability of current preparative methods, especially in the shape and size of nanomaterials. In this paper, we achieved the precise syntheses of nanoscale unimolecular cylindrical polymer brushes (CPBs) and spherical polymer nanoparticles (SPNPs) with the same volume and surface chemistry, which ensured that shape was essentially the only variable when their biological performance was compared. Accurate shape effects were obtained. Impressively, the CPBs had remarkable advantage in tissue penetration over the SPNPs. The CPBs also exhibited higher cellular uptake and rapider body clearance than the SPNPs, whereas the SPNPs had longer blood circulation time, rapider tumor vascular extravasation, and higher tumor accumulation than the CPBs. Additionally, this work also provided a controllable synthesis strategy for nanoscale unimolecular SPNPs by integrating 21 CPBs to a ß-cyclodextrin core, whose diameter in dry state could be up to 45 nm.

NIR-II Dye-Labeled Cylindrical Polymer Brushes for in Vivo Imaging.

Although many types of second near-infrared (NIR-II) dyes have been developed, the NIR-II dye bearing a single reactive group, which is indispensable for specifically labeling nanomaterials or biofunctional molecules, is still lacking. In this work, a donor-acceptor-donor type NIR-II dye named IR1032 bearing an amino group was synthesized and used to covalently label cylindrical polymer brushes. The labeled polymer brushes (named brushes1032) had densely grafted poly(ethylene glycol) (PEG) chains and exhibited a wormlike morphology. In aqueous medium, brushes1032 had an emission peak at 1032 nm and a quantum yield (QY) of ∼0.13% measured with IR 26 as a reference (QY = 0.05%). We demonstrated that the dense PEG chains in brushes1032 were greatly favorable for their QY by separating the fluorophores and shielding them from the interactions with water. After being injected intravenously into tumor-bearing mice, brushes1032 showed high tumor accumulation and provided high-resolution fluorescence imaging, exhibiting great application potentials in tumor detection.

Expression Profiles, Characterization and Function of HbTCTP in Rubber Tree (Hevea brasiliensis).

As a highly conserved protein, the translationally controlled tumor protein (TCTP) carries out vital roles in various life processes. In rubber tree, two TCTP genes, HbTCTP and HbTCTP1, were cloned, but only HbTCTP1 was studied in details. In this study, cis-acting regulatory elements, expression patterns, subcellular localization, interacting proteins, and antioxidant activity of HbTCTP were systematically analyzed. Besides the common cis-acting regulatory elements, HbTCTP promoter also harbored various known cis-elements that respond to hormone/stresses. Being consistent with the aforementioned results, HbTCTP was regulated by drought, low temperature, high salt, ethylene (ET), wounding, H2O2, and methyl jasmonate (MeJA) treatments. HbTCTP was expressed throughout different tissues and developmental stages of leaves. In addition, HbTCTP was associated with tapping panel dryness (TPD). HbTCTP was localized in the membrane, cytoplasm and the nucleus, and interacted with four proteins rubber elongation factor (REF), 17.5 kDa heat shock family protein, annexin, and REF-like stress related protein 1. Being similar to HbTCTP1, HbTCTP also indicated antioxidant activity in metal-catalyzed oxidation (MCO) system. Our results are useful for further understanding the molecular characterization and expression profiles of HbTCTP, but also lay a solid foundation for elucidating the function of HbTCTP in rubber tree.

Molecular cloning, expression profiles, and characterization of a novel polyphenol oxidase (PPO) gene in Hevea brasiliensis.

The polyphenol oxidase (PPO) is involved in undesirable browning in many plant foods. Although the PPOs have been studied by several researchers, the isolation and expression profiles of PPO gene were not reported in rubber tree. In this study, a new PPO gene, HbPPO, was isolated from Hevea brasiliensis. The sequence alignment showed that HbPPO indicated high identities to plant PPOs and belonged to dicot branch. The cis-acting regulatory elements related to stress/hormone responses were predicted in the promoter region of HbPPO. Real-time RT-PCR analyses showed that HbPPO expression varied widely depending on different tissues and developmental stages of leaves. Besides being associated with tapping panel dryness, the HbPPO transcripts were regulated by ethrel, wounding, H2O2, and methyl jasmonate treatments. Moreover, the correlation between latex coagulation rate and PPO activity was further confirmed in this study. Our results lay the foundation for further analyzing the function of HbPPO in rubber tree.