PEGylated Dendrimer-Doxorubicin Cojugates as pH-Sensitive Drug Delivery Systems: Synthesis and In Vitro Characterization.

To achieve liver-specific delivery of antitumor drug doxorubicin (DOX), PEGylated dendrimer-DOX conjugates were designed and synthesized, whereas DOX was conjugated to dendrimers via hydrazone bonds and the dendrimers were functionalized with galactose moieties. The release rates of DOX from the conjugates at pH 5.0 were much faster than those at pH 7.4 due to the pH-sensitive cleavage of the hydrazone bonds. The conjugates were shown to effectively kill HepG2 cells in vitro. Compared to other conjugates, the PEGylated dendrimer-DOX one with multiple galactose moieties (Dendrimer-DOX-PEG-Gal) demonstrated HepG2 cells specificity, higher efficacy and good biosafety due to the lower IC50 value and higher cellular uptake confirmed by in vitro cytotoxicity assays, confocal laser scanning microscopy and flow cytometric studies. These results suggest that Dendrimer-DOX-PEG-Gal is an efficient and biocompatible candidate for the specific delivery of antitumor drug to HepG2 cells and could be used as liver cancer specific drug delivery system.

PEGylated dendritic diaminocyclohexyl-platinum (II) conjugates as pH-responsive drug delivery vehicles with enhanced tumor accumulation and antitumor efficacy.

Environmentally responsive peptide dendrimers loaded with drugs are suitable candidates for cancer therapy. In this study, we report the preparation and characterization of mPEGylated peptide dendrimer-linked diaminocyclohexyl platinum (II) (dendrimer-DACHPt) conjugates as pH-responsive drug delivery vehicles for tumor suppression in mice. The DACHPt has a molecular structure, is and activity closely related to oxaliplatin and was linked to dendrimer via N,O-chelate coordination. The products were pH-responsive and released drug significantly faster in acidic environments (pH 5.0) than pH 7.4. Consequently, the conjugates suppressed tumor growth better than clinical oxaliplatin(®) without inducing toxicity in an SKOV-3 human ovarian cancer xenograft. Through the systemic delivery of conjugates, 25-fold higher tumor platinum uptake at 36 h post-injection was seen observed due to the enhanced permeability and retention (EPR) effect thereby remarkably enhancing the therapeutic indexes of this small-molecule drug. Thus, the mPEGylated peptide dendrimer-linked DACH-platinum conjugates are novel potential drug delivery systems with implications in future ovarian cancer therapy.

Peptide dendrimer-Doxorubicin conjugate-based nanoparticles as an enzyme-responsive drug delivery system for cancer therapy.

Peptide dendrimers have shown promise as an attractive platform for drug delivery. In this study, mPEGylated peptide dendrimer-doxorubicin (dendrimer-DOX) conjugate-based nanoparticle is prepared and characterized as an enzyme-responsive drug delivery vehicle. The drug DOX is conjugated to the periphery of dendrimer via an enzyme-responsive tetra-peptide linker Gly-Phe-Leu-Gly (GFLG). The dendrimer-DOX conjugate can self-assemble into nanoparticle, which is confirmed by dynamic light scattering, scanning electron microscopy, and transmission electron microscopy studies. At equal dose, mPEGylated dendrimer-DOX conjugate-based nanoparticle results in significantly high antitumor activity, and induces apoptosis on the 4T1 breast tumor model due to the evidences from tumor growth curves, an immunohistochemical analysis, and a histological assessment. The in vivo toxicity evaluation demonstrates that nanoparticle substantially avoids DOX-related toxicities and presents good biosafety without obvious side effects to normal organs of both tumor-bearing and healthy mice as measured by body weight shift, blood routine test, and a histological analysis. Thus, the mPEGylated peptide dendrimer-DOX conjugate-based nanoparticle may be a potential nanoscale drug delivery vehicle for the breast cancer therapy.

Dendronized heparin-doxorubicin conjugate based nanoparticle as pH-responsive drug delivery system for cancer therapy.

Heparin drug conjugates are currently investigated as excellent candidates for drug delivery vehicles. In this study, we report the preparation and characterization of dendronized heparin-doxorubicin (heparin-DOX) conjugate as pH-sensitive drug delivery vehicle by combination of the features of dendrimer and heparin. Dynamic light scattering (DLS) and transmission electron microscope (TEM) studies demonstrated the dendronized heparin-DOX conjugate self-assembled into compact nanoparticles with negatively charged surface. The nanoparticles with 9.0 wt% (weight percent) of doxorubicin (DOX) showed pH-sensitive property due to the faster drug release rate at pH 5.0 and slow release rate at pH 7.4 aqueous. The nanoparticles were shown to effectively kill cancer cells in vitro. Notablely, the nanoparticles resulted in strong antitumor activity, high antiangiogenesis effects and induced apoptosis on the 4T1 breast tumor model due to the evidences from mice weight shifts, tumor weights, tumor growth curves, immunohistochemical assessment and histological analysis. It's also noteworthy that dendronized heparin and its nanoparticle with drug demonstrated no significant toxicity to healthy organs of both tumor-bearing and healthy mice, which was confirmed by histological analysis compared with free drug DOX. The dendronized heparin-DOX conjugate based nanopatilce with high antitumor activity and low side effects may be therefore a potential nanoscale drug delivery vehicle for breast cancer therapy.

The potential of self-assembled, pH-responsive nanoparticles of mPEGylated peptide dendron-doxorubicin conjugates for cancer therapy.

Nanoparticles, such as dendritic polymers, are currently investigated as excellent candidates for drug delivery vehicles. In this study, we report the preparation and characterization of mPEGylated peptide dendron-doxorubicin (dendron-DOX) conjugate based vehicle carrying 14.0 wt% (weight percent) of doxorubicin (DOX). Dynamic light scattering (DLS), scanning electron microscope (SEM) and transmission electron microscope (TEM) studies demonstrated the dendron-DOX conjugate self-assembled into nanoscale particles with neutral charged surface. The globular morphology and compact nanoparticle with diameter around 80 nm were observed by SEM and TEM. The release rates of DOX from the nanoparticle at pH 5.0 were much faster than those at pH 7.4 due to the pH-sensitive cleavage of the hydrazone bonds. The nanoparticle was shown to effectively kill cancer cells in vitro. Importantly, the nanoparticle resulted in strong antitumor activity and induced apoptosis on the 4T1 breast tumor model. In vivo toxicity evaluation demonstrated that drug-free dendron and drug-loading nanoparticle provided good biosafety in healthy or tumor-bearing mice, because no significant systematic toxicity was revealed via histological analysis. The functionalized peptide dendron-DOX conjugate based nanoparticle may be therefore a potential candidate for drug delivery vehicle for cancer therapy.

Arginine functionalized peptide dendrimers as potential gene delivery vehicles.

The quest for highly efficient and safe gene delivery systems has become the key factor for successful application of gene therapy. Peptide dendrimers are currently investigated as excellent candidates for non-viral gene delivery vectors. In this study, we report the synthesis and characterization of arginine functionalized peptide dendrimer-based vectors ranging from 5th generation (G5A) to 6th generation (G6A) via click chemistry, and their use for gene transfection in vitro and in vivo. The dendrimers can condense plasmid DNA (pDNA) and protect pDNAs from nuclease digestion. Both atomic force microscopy (AFM) and dynamic light scattering (DLS) revealed that the sizes of dendrimer/DNA particles were within 180-250 nm range. In vitro studies showed that the functionalized peptide dendrimers provided serum independent and high transfection efficiency on all studied cells, as over 2 fold higher than that of branched polyetherimide (PEI) in the presence of serum. Dendrimer G5A with molecular weight of 17 kDa demonstrated 6-fold transfection activity than PEI in breast tumor models, as well as good biosafety proved by in vitro and in vivo toxicity evaluation. However, G6A with molecular weight of 46 kDa showed much higher cytotoxicity. The functionalized dendrimer G5A with optimal generation may be therefore a potential candidate for gene delivery vehicle.

Gadolinium-labeled peptide dendrimers with controlled structures as potential magnetic resonance imaging contrast agents.

Gadolinium (Gd(3+)) based dendrimers with precise and tunable nanoscopic sizes are excellent candidates as magnetic resonance imaging (MRI) contrast agents. Control of agents' sensitivity, biosafety and functionality is key to the successful applications. We report the synthesis of Gd(III)-based peptide dendrimers possessing highly controlled and precise structures, and their potential applications as MRI contrast agents. These agents have no obvious cytotoxicity as verified by in vitro studies. One of the dendrimer formulations with mPEG modification showed a 9-fold increase in T(1) relaxivity to 39.2 Gd(III) mM(-1) s(-1) comparing to Gd-DTPA. In vivo studies have shown that the mPEGylated Gd(III)-based dendrimer provided much higher signal intensity enhancement (SI) in mouse kidney, especially at 60 min post-injection, with 54.8% relatively enhanced SI. The accumulations of mPEGylated dendrimer in mouse liver and kidney were confirmed through measurement of gadolinium by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Meanwhile, mPEGylated dendrimer showed much higher Gd(III) concentration in blood with 38 µg Gd(III)/g blood at 1 h post-injection comparing to other dendrimer formulations. These findings provide an attractive alternative strategy to the design of multifunctional gadolinium-based dendrimers with controlled structures, and open up possibilities of using the Gd(III)-based peptide dendrimers as MRI probes.

Functional L-lysine dendritic macromolecules as liver-imaging probes.

Liver-imaging probes are prepared through the conjugation of Gd chelates and galactosyl moieties to peptide dendrimers. The dendritic probes possessing highly controlled structures and a single molecular weight have a two-fold increase in T(1) relaxivity to 9.1 x 10(3) (Gd M)(-1) s(-1) compared to Gd-DTPA. No obvious cytotoxicity of this multifunctional dendritic agent is discovered in vitro. The dendrimer bearing galactosyl moieties leads to a much-higher hepatocyte-cell uptake in vitro and provides good signal-intensity enhancement (35%) of mouse liver in vivo especially at 60 min after intravenous injection. In comparison, non-targeting Gd dendrimers provide only an 11% enhancement of imaging contrast at the same time point. Overall, the dendrimers bearing galactosyl moieties may be used as liver-imaging probes.