Jiahai Zhang

Comparison of generation 3 polyamidoamine dendrimer and generation 4 polypropylenimine dendrimer on drug loading, complex structure, release behavior, and cytotoxicity

Background Polyamidoamine (PAMAM) and polypropylenimine (PPI) dendrimers are the commercially available and most widely used dendrimers in pharmaceutical sciences and biomedical engineering. In the present study, the loading and release behaviors of generation 3 PAMAM and generation 4 PPI dendrimers with the same amount of surface amine groups (32 per dendrimer) were compared using phenylbutazone as a model drug. Methods The dendrimer-phenylbutazone complexes were characterized by 1H nuclear magnetic resonance and nuclear Overhauser effect techniques, and the cytotoxicity of each dendrimer was evaluated. Results Aqueous solubility results suggest that the generation 3 PAMAM dendrimer has a much higher loading ability towards phenylbutazone in comparison with the generation 4 PPI dendrimer at high phenylbutazone-dendrimer feeding ratios. Drug release was much slower from the generation 3 PAMAM matrix than from the generation 4 PPI dendrimer. In addition, the generation 3 PAMAM dendrimer is at least 50-fold less toxic than generation 4 PPI dendrimer on MCF-7 and A549 cell lines. Conclusion Although the nuclear Overhauser effect nuclear magnetic resonance results reveal that the generation 4 PPI dendrimer with a more hydrophobic interior encapsulates more phenylbutazone, the PPI dendrimer-phenylbutazone inclusion is not stable in aqueous solution, which poses a great challenge during drug development.

Host-guest chemistry of dendrimer-drug complexes. 6. Fully acetylated dendrimers as biocompatible drug vehicles using dexamethasone 21-phosphate as a model drug.

Fully acetylated poly(amidoamine) (PAMAM) dendrimer was proposed as a biocompatible drug vehicle using dexamethasone 21-phosphate (Dp21) as a model drug. NMR techniques including (1)H NMR and 2D NOE NMR were used to characterize the host-guest chemistry of acetylated dendrimer/Dp21 and cationic dendrimer/Dp21 complexes. The pH-dependent micellization, complexation, and inclusion behaviors of Dp21 were observed in the presence of acetylated and cationic PAMAM dendrimers. Acetylated dendrimer only encapsulates Dp21 at acidic conditions, while cationic dendrimer can host Dp21 at both acidic and neutral conditions. The orientation of Dp21 molecules in the dendrimer cavities depends on the quaternization degree of tertiary amine groups of dendrimer and the protonation ratio of phosphate group of Dp21. A distinctive pH-dependent release behavior of Dp21 from the acetylated and nonacetylated dendritic matrix was observed: Dp21 exhibits a much slower release rate from acetylated dendrimer at lower pH conditions and a much faster release rate from nonacetylated dendrimer with decreasing pH values. Cytotoxicity studies further confirmed the biocompatibility of acetylated dendrimers, which are much safer in the delivery of therapeutics for the treatment of various diseases than nonacetylated dendrimers. The dendrimer-drug binding and release mechanisms provide a new insight for the design and optimization of biocompatible dendrimer-based drug delivery systems.

High-Throughput Screening of Dendrimer-Binding Drugs

A convenient approach for the high-throughput screening of dendrimer-binding drugs by NMR techniques including saturation transfer difference (STD) NMR and Hadamard-encoded nuclear Overhauser effect measurements is presented. The screening results for insoluble drugs show that phenylbutazone and sulfamethoxazole prefer to localize in the interior pockets of dendrimer, while mycophenolic acid mostly binds on the dendrimer surface, and noncharged insoluble drugs like trimethoprim and primidone do not interact with dendrimers. In another path for soluble drugs, n-butanoic acid and dimethylformamide are screened as dendrimer-binding compounds from a screening pool containing eight soluble compounds by STD NMR. The screening of dendrimer-binding insoluble or soluble compounds can be finished within an hour.

Generation-dependent encapsulation/electrostatic attachment of phenobarbital molecules by poly(amidoamine) dendrimers: Evidence from 2D-NOESY investigations.

The interactions of phenobarbital with different generations of amine-terminated poly(amidoamine) (PAMAM) dendrimers were investigated by using two dimensional-nuclear Overhauser effect spectroscopic (2D-NOESY) investigations. The NOESY spectra clearly showed that there were cross-peaks from NOE interactions between the protons of phenobarbital and the protons in interior cavities of generation 5 or generation 6 PAMAM dendrimers but none of such cross-peaks was found in the case of generation 3 or generation 4 dendrimers. The NOESY analysis, together with aqueous solubility data, suggested that higher generation dendrimers are more capable of encapsulating phenobarbital molecules into the interior cavities than lower generation dendrimers, and that lower generation dendrimers are much easier for the electrostatic attachment of phenobarbital molecules than higher ones at a fixed mass concentration.

New Insights into Interactions between Dendrimers and Surfactants. 4. Fast-Exchange/Slow-Exchange Transitions in the Structure of Dendrimer−Surfactant Aggregates

The interactions between poly(amidoamine) (PAMAM) dendrimer and surfactant (sodium dodecyl sulfate, SDS) in aqueous solutions were investigated by a combination of (1)H NMR, diffusion measurements (PFG NMR), and NOE techniques. The diffusion studies suggested that different types of dendrimer-surfactant aggregates are formed by varying surfactant concentrations in the dendrimer solution. The (1)H NMR analysis proved that the presence of fast-exchange/slow-exchange transitions in the dendrimer-surfactant aggregates. The supramolecular structure of the aggregate was based on the hydrophobic interactions between the dendrimer scaffold and the surfactant aliphatic chain, as well as electrostatic/hydrogen-bond interactions between dendrimers and SDS monomers, bilayers, or globular micelles. In comparison with previous investigations, the present study provides a new insight into interactions between dendrimers and surfactants, which may be helpful for the design of dendrimer-based microreactors or nanovehicles.

Insights into the Interactions between Dendrimers and Multiple Surfactants: 5. Formation of Miscellaneous Mixed Micelles Revealed by a Combination of 1H NMR, Diffusion, and NOE Analysis

We studied the formation and growth of miscellaneous mixed micelles in dendrimer and surfactant mixtures. NMR techniques including (1)H NMR titration, diffusion (PGSE and DOSY) measurement, and NOE analysis were used to investigate the shape, size, interaction mode, spatial localization, and molecular orientation of the formed dendrimer/surfactant aggregates at different stages. The results suggest the formation of the following supramolecular aggregates when an equal molar concentration of sodium dodecylsulfate (SDS) and sodium deoxycholate (SDC) were added into a generation 4 (G4) cationic dendrimer: (1) the encapsulation of the two surfactants in the interior pockets of dendrimer at extremely low surfactant concentrations; (2) the binding of SDS on the surface of G4 dendrimer above the saturated encapsulation concentration; (3) the formation of globular SDS micelles and SDC dimer in the aqueous solution above the CMC of each surfactant; (4) the accumulation of SDS molecules on the surface of dendrimer in a bilayer fashion at high surfactant concentrations; (5) the interactions of dendrimer with the globular SDS micelles; and (6) the encapsulation of SDC monomers or dimers in the globular SDS micelles. The competitive binding/encapsulation of the two surfactants at different stages was evaluated. The results provide a new insight into the interactions of dendrimers with mixed surfactant systems.

Host–Guest Chemistry of Dendrimer–Drug Complexes: 7. Formation of Stable Inclusions between Acetylated Dendrimers and Drugs Bearing Multiple Charges

Drug molecules bearing multiple charges usually form precipitates with cationic dendrimers, which presents a challenge during the preparation of dendrimer inclusions for these drugs. In the present study, fully acetylated polyamidoamine (PAMAM) dendrimers were proposed as stable vehicles for drug molecules bearing two negative charges such as Congo red and indocyanine green. NMR techniques including (1)H NMR and (1)H-(1)H NOESY were used to characterize the host-guest chemistry of acetylated dendrimer and these guest molecules. The cationic PAMAM dendrimer was found to form a precipitate with Congo red and indocyanine green, but the acetylated one avoided the formation of cross-linking structures in aqueous solutions. NOESY studies revealed the encapsulation of Congo red and indocyanine green within the interior cavities of PAMAM dendrimers at mild acidic conditions and acetylated dendrimers show much stronger ability to encapsulate the guest molecules than cationic ones. Also, UV-vis-NIR studies suggest that acetylated dendrimers significantly improve the photostability of indocyanine green and prevent the formation of indocyanine green J-aggregates in aqueous solutions. The present study provides a new insight into dendrimer-based host-guest systems, especially for those guest molecules bearing multiple charges.

Stimuli Response of Cystamine-Core Dendrimer Revealed by Diffusion and NOE NMR Studies

Stimuli response behaviors of cystamine-core dendrimer in the presence of several reducing agents including vitamin C, sodium bisulfite, and DL-Dithiothreitol are described. A competitive redox cleavage and supramolecular aggregate formation model is proposed based on PFG NMR and (1)H NMR titration experiments. Furthermore, reduction-responsive release of guest molecules from interior pockets of the cystamine-core dendrimer is confirmed by NOE studies. The results suggest that cystamine-core dendrimer is a versatile scaffold or precursor in the design of reduction-sensitive polymeric nanocapsules for biomedical purposes.

Interactions between oppositely charged dendrimers

The interactions between cationic (G3, G4, and G5) and anionic (G4.5) poly(amidoamine) (PAMAM) dendrimers were investigated by isothermal titration calorimetry (ITC), photometric titration, nuclear magnetic resonance (NMR), and dynamic light scattering (DLS) studies. The results suggest that the formation of anionic–cationic dendrimer aggregates is an enthalpy-driven process. Ionic interactions occur between the cationic and anionic dendrimers, followed by the formation of supramolecular aggregates and precipitates. The phase separation of the resulting aggregate depends on dendrimer generation, surface charge density, anionic–cationic dendrimer molar ratio, and solution pH values. G5, with a relatively rigid structure, displayed a different binding behavior with G4.5 as compared to the G3 and G4 dendrimers with more flexible scaffolds. G4.5 and G5 with a molar ratio of 0.5 : 1 form the largest aggregates among the investigated G4.5–G5 molar ratios. G4.5 and G5 form aggregates in a size range of 300–3000 nm depending on the G4.5–G5 molar ratio. The G4.5–G5 supramolecular aggregates are not stable and will disassemble after several days of incubation. The results help us to understand the interactions between globular polyelectrodes as well as oppositely charged biomacromolecules.

Interactions between Dendrimers and Ionic Liquids Revealed by Pulsed Field Gradient and Nuclear Overhauser Effect NMR Studies

The host-guest interactions of cationic and anionic poly(amidoamine) (PAMAM) dendrimers with three ionic liquids including 1-butyl-3-methylimidazolium 2-(2-methoxyethoxy)ethyl sulfate ([BMIM][MDEGSO(4)]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]), and trihexyltetradecylphosphonium bis((trifluoromethyl)sulfonyl)imide ([THTDP][TFSI]) were investigated by several NMR techniques such as (1)H and (19)F NMR, pulsed field gradient (PFG) NMR, and 2D nuclear Overhauser enhancement spectroscopy (NOESY). Anionic PAMAM dendrimer interacts with the ionic liquids via ionic interactions. However, almost no interaction is observed between cationic PAMAM dendrimer and the ionic liquids without pH adjustment. Besides, no inclusion formation between the PAMAM dendrimers and the ionic liquids is observed on the basis of NOE NMR studies. The interactions between dendrimers and ionic liquids are very different from those between dendrimers and surfactants or amphiphilic drugs. The results obtained from PFG and NOE studies provide new insights into dendrimer-based host-guest systems.