Study of Reduction Process of Silver Ions on G4 PAMAM (Polyamidoamine) Dendrimers with Different Terminal Functional Groups: NH<sub>2</sub> and OH

Structural changes in lipid mesophases due to intercalation of dendritic polymer nanoparticles: Swollen lamellae, suppressed curvature, and augmented structural disorder

The applications of polyamidoamine (PAMAM) dendrimers have attracted much attention in biomedicine specially non-viral gene delivery because of thier unique characteristics including hyperbranching, multivalency, and well-defined uniform globular three-dimensional structures. In the current study, in order to enhance the transfection efficiency and reduce the cytotoxicity of PAMAMs, bromoalkylcarboxylates with different chain length (2-bromoacetic, 6-bromohexanoic, 10-bromodecanoic and 16-bromohexadecanoic acids) were covalently conjugated with 10% and 30% of primary amines of generation 4 and 5 (G4 and G5) of PAMAM dendrimers to increase the hydrophobicity of the carrier. At the next stage, the alkylcarboxylate-PAMAMs were pegylaed to further modify the PAMAM structures for biological applications. Obtained results demonstrated that the prepared PAMAM derivatives had particle size around 140 nm with net-positive surface charge. None of the prepared PAMAM-based non-viral vactors exhibited significant hemolytic activity and also cytotoxicity. Meanwhile decahexanoate-PAMAM G4 [G4(16C-10%)] and decanoate-PAMAM G4 conjugated to polyethylene glycol (PEG) (G4[(10C-30%)(10C-PEG)]) showed highest transfection efficiency in murine neuroblastoma (Neuro-2a) cell line, interestingly only the latter had improved transfection efficiency in mesenchymal stem cells (MSCs). This study proved the potential utility of alkylcarboxylate-grafted PAMAM dendrimers (G4 and G5) with or without PEG modification for efficient gene transfer into cancerous cells as well as MSCs.

Atomistic molecular dynamics simulations have been carried out to reveal the characteristic features of ethylenediamine (EDA) cored protonated (corresponding to neutral pH) poly amido amine (PAMAM) dendrimers of generation 3 (G3) and 4 (G4) that are functionalized with single strand DNAs (ssDNAs). The four ssDNA strands that are attached via an alkythiolate [–S(CH2)6–] linker molecule to the free amine groups on the surface of the PAMAM dendrimers are observed to undergo a rapid conformational change during the 25 ns long simulation period. From the RMSD values of ssDNAs, we find relative stability in the case of purine rich (having more adenine and guanine) ssDNA strands than pyrimidine rich (thymine and cytosine) ssDNA strands. The degree of wrapping of ssDNA strands on the dendrimer molecule was found to be influenced by the charge ratio of DNA and the dendrimer. As the G4 dendrimer contains relatively more positive charge than G3 dendrimer, we observe extensive wrapping of ssDNAs on the G4 dendrimer than G3 dendrimer. This might indicate that DNA functionalized G3 dendrimer is more suitable to construct higher order nanostructures. The linker molecule was also found to undergo drastic conformational change during the simulation. During nanosecond long simulation some portion of the linker molecule was found to be lying nearly flat on the surface of the dendrimer molecule. The ssDNA strands along with the linkers are seen to penetrate the surface of the dendrimer molecule and approach closer to the center of the dendrimer indicating the soft sphere nature of the dendrimer molecule. The effective radius of DNA-functionalized dendrimer nanoparticles was found to be independent of base composition of ssDNAs and was observed to be around 19.5 Å and 22.4 Å when we used G3 and G4 PAMAM dendrimers as the core of the nanoparticle respectively. The observed effective radius of DNA-functionalized dendrimer molecules apparently indicates the significant shrinkage in the structure that has taken place in dendrimer, linker and DNA strands. As a whole our results describe the characteristic features of DNA-functionalized dendrimer nanoparticles and can be used as strong inputs to design effectively the DNA–dendrimer nanoparticle self-assembly for their active biological applications.

Molecular association between biocompatible dendritic polymers, dendrigraft poly-l-lysines (DGLs), and an anionic fluorescent probe, 8-anilino-1-naphthalenesulfonate (ANS-), was studied at the polarized water|1,2-dichloroethane (DCE) interface. The fluorescence intensity of ANS measured in aqueous solution was enhanced by the coexistence of DGLs over a wide pH range (2 < pH < 10), where ANS and DGL exist as a monoanionic form and a polycation, respectively. The voltammetric responses indicated that the positively charged DGLs were adsorbed at the water|DCE interface, whereas ANS- was transferred across the interface accompanied by the adsorption process. The interfacial behavior of the DGL-ANS associates was analyzed by potential-modulated fluorescence (PMF) spectroscopy. The PMF results demonstrated that the ion association between DGLs and ANS at the water|DCE interface is strongly affected by the applied potential and the dendritic generation of DGL. By applying appropriate potentials, the ANS anion was dissociated from its ion associate with DGLs at the interface and transferred into the organic phase, whereas DGLs remained in the aqueous phase. The Gibbs free energy of ion association (Δ GD···ANS) was estimated for the second-fourth generation DGLs (DGL-G2-G4) and the G4 polyamidoamine (PAMAM) dendrimer as a control. The highest stability of the DGL-G4-ANS associate manifested itself through Δ GD···ANS: DGL-G4-ANS (>G4 PAMAM dendrimer-ANS) > DGL-G3-ANS > DGL-G2-ANS. The results elucidated the efficient anion-binding ability of higher generation DGLs and its potential dependence at the liquid|liquid interface.

Many oral care products incorporate an antibacterial compound to prevent the formation of dental plaque which predisposes teeth to dental caries or periodontal disease []. Triclosan (TCN) is a commonly used antiplaque agent in toothpastes []. Strategies to increase the delivery efficiency of antibacterials using formulation aids such as polyamidoamine (PAMAM) dendrimers are of interest.Solubilisation studies over the pH range 5-12 demonstrated an increase in the level of TCN solubilised with increasing dendrimer concentration (1 mM–5 mM). However, the dendrimer was unable to enhance TCN solubility at lower pH values and the solubilising effect observed was attributed to the ionization of TCN (pKa 8.14) resulting from dendrimer induced pH changes.End group modification of G3 PAMAM dendrimer with phenylalanine in order to promote solubility through π–π stacking between TCN and the amino acid has been carried out. Phenylalanine:G3 PAMAM conjugates of different ratios (32:1, 21:1, 16:1) were synthesized. The fully conjugated dendrimer (32:1) had poor aqueous solubility, whereas the 21:1 and 16:1 dendrimer conjugates were water soluble. The 21:1 conjugate was tested for its ability to solubilise TCN, however, again there was no increase over control buffer solutions of the same pH. An alternative approach under investigation is to directly conjugate TCN to PAMAM dendrimers via a hydrolysable linkage.

Activated and non-activated PAMAM dendrimers for gene delivery in vitro and in vivo

We previously synthesized a series of potent and selective A(3) adenosine receptor (AR) agonists (North-methanocarba nucleoside 5'-uronamides) containing dialkyne groups on extended adenine C2 substituents. We coupled the distal alkyne of a 2-octadiynyl nucleoside by Cu(I)-catalyzed "click" chemistry to azide-derivatized G4 (fourth-generation) PAMAM dendrimers to form triazoles. A(3)AR activation was preserved in these multivalent conjugates, which bound with apparent K(i) of 0.1-0.3 nM. They were substituted with nucleoside moieties, solely or in combination with water-solubilizing carboxylic acid groups derived from hexynoic acid. A comparison with various amide-linked dendrimers showed that triazole-linked conjugates displayed selectivity and enhanced A(3)AR affinity. We prepared a PAMAM dendrimer containing equiproportioned peripheral azido and amino groups for conjugation of multiple ligands. A bifunctional conjugate activated both A(3) and P2Y(14) receptors (via amide-linked uridine-5'-diphosphoglucuronic acid), with selectivity in comparison to other ARs and P2Y receptors. This is the first example of targeting two different GPCRs with the same dendrimer conjugate, which is intended for activation of heteromeric GPCR aggregates. Synergistic effects of activating multiple GPCRs with a single dendrimer conjugate might be useful in disease treatment.

Dendrimers have received more attention in all fields of research these days. In the present study, polyamidoamine (PAMAM) dendrimers were synthesized on the acrylic ultrafiltration membranes to minimize fouling as an important deficiency in the separation process. The antifouling activity of these dendrimers with different generations (G0‐3) was tested to restrict three macrolides (tylvalosin, tylosin, and tulathromycin) and two pleuromutilins (tiamulin and valnemulin) as veterinary antibiotic drugs with amine groups and positive charges at pH = 7 of the membrane surface. These compounds are risky for human consumption. Due to having several amine functional groups and branches, PAMAM dendrimers can be a great coating agent for antifouling. G3 PAMAM dendrimer‐coated membranes had the best performance (water flux: 130.7 L/m2·h, rejection of tulathromycin: 91.4%, flux recovery ratio: 86.3%). The function of this ultrafiltration process depended on pore size and also charge surface. A significant reduction for irreversible and reversible fouling was observed for this new ultrafiltration membrane (Fir: 14.5%, Fre: 21.9%). This observation was confirmed by the power law model. Three 5‐hour cycle ultrafiltration processes were carried out for veterinary antibiotic wastewater that showed 3.18% loss of initial water flux (for the third cycle), final cleaning efficiency of 96.82%, and tylvalosin rejection of 94.1%.

The present study compares the use of high generation G3 and low generation G0 Polyamidoamine (PAMAM) dendrimers as drug carriers of naproxen (NAP), a poorly water soluble drug. Naproxen was conjugated to G3 in different ratios and to G0 in a 1:1 ratio via a diethylene glycol linker. A lauroyl chain (L), a lipophilic permeability enhancer, was attached to G3 and G0 prodrugs. The G3 and G0 conjugates were more hydrophilic than naproxen as evaluated by the measurement of partitioning between 1-octanol and a phosphate buffer at pH 7.4 and pH 1.2. The unmodified surface PAMAM-NAP conjugates showed significant solubility enhancements of NAP at pH 1.2; however, with the number of NAP conjugated to G3, this was limited to 10 molecules. The lactate dehydrogenase (LDH) assay indicated that the G3 dendrimer conjugates had a concentration dependent toxicity towards Caco-2 cells. Attaching naproxen to the surface of the dendrimer increased the IC50 of the resulting prodrugs towards Caco-2 cells. The lauroyl G3 conjugates showed the highest toxicity amongst the PAMAM dendrimer conjugates investigated and were significantly more toxic than the lauroyl-G0-naproxen conjugates. The permeability of naproxen across monolayers of Caco-2 cells was significantly increased by its conjugation to either G3 or G0 PAMAM dendrimers. Lauroyl-G0 conjugates displayed considerably lower cytotoxicity than G3 conjugates and may be preferable for use as a drug carrier for low soluble drugs such as naproxen.

Evaluation of polyamidoamine (PAMAM) dendrimers as drug carriers of anti-bacterial drugs using sulfamethoxazole (SMZ) as a model drug

Transcorneal iontophoresis of dendrimers: PAMAM corneal penetration and dexamethasone delivery

Context: Polyamidoamine (PAMAM) dendrimers have attracted lots of interest as drug carriers. And little study about whether pluronic-attached PAMAM dendrimers could be potential drug delivery systems has been carried on.Objective: Pluronic F127 (PF127) attached PAMAM dendrimers were designed as novel drug carriers.Methods: Two conjugation ratios of PF127-attached PAMAM dendrimers were synthesized. 1H nuclear magnetic resonance (1H-NMR), Fourier transform infrared spectrum (FTIR), element analysis and ninhydrin assay were used to characterize the conjugates. Size, zeta potential and critical micelle concentrations (CMC) were also detected. And DOX was incorporated into the hydrophobic interior of the conjugates. Studies on their drug loading and drug release were carried on. Furthermore, hemolysis and cytotoxicity assay were used to evaluate the toxicity of the conjugates.Results and discussion: PF127 was successfully conjugated to the fifth generation PAMAM dendrimer at two molar ratios of 19% and 57% (PF127 to surface amine per PAMAM dendrimer molecular). The conjugates showed an increased size and a reduced zeta potential. And higher CMC values were obtained than pure PF127. Compared with unconjugated PAMAM dendrimer, PF127 conjugation significantly reduced the hemolytic toxicity and cytotoxicity of PAMAM dendrimer in vitro. The encapsulation results showed that the ability to encapsulate DOX by the conjugate of 19% conjugation ratio was better than that of 57% conjugation ratio. And the maximum is ∼12.87 DOX molecules per conjugate molecule. Moreover, the complexes showed a sustained release behavior compared to pure DOX.Conclusion: Findings from the in vitro study show that the PF127-attached PAMAM dendrimers may be potential carriers for drug delivery.

Permeability of surface-modified polyamidoamine (PAMAM) dendrimers across Caco-2 cell monolayers

Introduction: Nano radio-pharmaceutical therapy (NRPT) is a new method for solid tumor therapy. The treatment uses a radioactive form of radionuclide encapsulated in the poly amido amine dendrimers. The poly (amidoamine) (PAMAM) dendrimers have attracted attentions for cancer treatment by their characteristics of targeted drug carriers, delivery agents, and imaging agents in human systems. We have reported the preparation of dendrimer encapsulated ytterbium-175 radio- nanoparticles and its biodistribution in tumor bearing rats.175Yb (T1/2=4.2 days), decays to stable 175Lu with a β- emitter with 470 keV maximum energy (86.5%) and γ photons of 113 keV (1.9%), 282keV (3.1%) and 396 keV (6.5%) that are appropriate for imaging. This paper aims at comparing dosimetric assessments in human performed with Monte Carlo codes and MIRD based on the experimental results of biodistribution of dendrimer encapsulated ytterbium-175.Materials and Methods: All chemical materials including, Ytterbium (III) oxide (Yb2O3), PAMAMG5-NH2 dendrimer in 5% methanol solution and HNO3, Sodium boro- hydride (NaBH4) were purchased from Sigma Aldrich Chemical Co. USA and Merck, Germany. For biodistribution study 20 female Balb/c mice were purchased from Pasteur Institute of Iran. To estimate the absorbed dose by both methods, MCNP and MIRD, the cumulated activity in source organs were calculated by the percentage of injected dose in humans’ organs. The residence times (τ) in the source organs were obtained by integration of respective fit functions, on biokinetics curve, after accounting for the physical decay of the 175Yb. The dose calculation was done for a certain group of organs of human following the MIRD technique. To simulate the problem with MCNP, the ORNL phantom was used. The desired result for this study is absorbed doses of vital organs (liver, spleen, lung and kidney). Results: The maximum uptake of radio-compound are in the liver, lung and spleen. The biodistribution shows the characteristics of nanoparticles such as size and surface hydrophobicity that determine the amount of adsorbed radiopharmaceuticals in organs. The initial fast distribution of radiotracer is throughout liver, lung, and Bone, with slower accumulation in blood and spleen. The result of 2 methods (MIRD versus MCNPX) reveals that MIRD underestimate the absorbed dose for bladder, bone, lung, and ovaries while overestimate for liver, muscle and spleen. In this study the absorbed dose from 175Yb- PAMAM estimated by MCNPX for liver, lung, spleen, kidney and bone are 1.266, 8.081E-01, 8.347E-01, 3.979E-02 and 1.706E-02 mGy/MBq respectively Conclusion: Owing to the stability of PAMAM encapsulated Yb-175 and the size of nano- particle the concentrations are mostly in liver and lungs. State of- the-art dosimetry depends on the duration of the biokinetics of the radiopharmaceutical and a calculation of residence times including an analysis of the errors associated with the respective calculation that aimed in this study. The results showed that this nano-radiopharmaceutical has potential of application for liver and lung tumors.

Polyamidoamine (PAMAM) dendrimer is emerging as an effective nanocarrier for delivering anticancer drugs. Still, unmodified PAMAM dendrimer is hardly used in vivo because of unsatisfied drug release, high tendency of interfering with cellular membranes, and rapid clearance by reticuloendothelial system. In this study, low generation polyamidoamine (PAMAM) dendrimer G3.0 is developed and surface modified with methoxypolyethylene glycol (PAMAM G3.0-mPEG) to overcome its limitations. Specifically, PAMAM G3.0 conjugated with mPEG at different ratios are investigated to effectively eliminate its charge-associated toxicity, in which PAMAM G3.0-mPEG- 8 is chosen for oxaliplatin (OX) loading. Results reveal that OX-loaded PAMAM G3.0-mPEG-8 has desirable size, good entrapment efficiency, and sustained release with minimum drug leakage. In addition, Resazurin assay indicates that the toxicity of loaded OX is reduced as compared to free drug but still maintain substantially anticancer activity on HeLa cells, suggesting the potential application of PAMAM G3.0-mPEG-8 for OX delivery in cancer therapy.