Host-guest chemistry of dendrimer-drug complexes. 4. An in-depth look into the binding/encapsulation of guanosine monophosphate by dendrimers

Development of a quaternary ammonium poly (amidoamine) dendrimer-based drug carrier for the solubility enhancement and sustained release of furosemide

Furosemide (FRSD) is a loop diuretic that has been categorized as a class IV drug according to the Biopharmaceutics Classification System (BCS). It is used in the treatment of congestive heart failure and edema. Owing to low solubility and permeability, its oral bioavailability is very poor. In this study, two types of poly (amidoamine) dendrimer-based drug carriers (generation G2 and G3) were synthesized to increase the bioavailability of FRSD through solubility enhancement and sustained release. The developed dendrimers enhanced the solubility of FRSD 58- and 109-fold, respectively, compared with pure FRSD. In vitro studies demonstrated that the maximum time taken to release 95% of the drug from G2 and G3 was 420-510 min, respectively, whereas for pure FRSD the maximum time was only 90 min. Such a delayed release is strong evidence for sustained drug release. Cytotoxicity studies using Vero and HBL 100 cell lines through an MTT assay revealed increased cell viability, indicating reduced cytotoxicity and improved bioavailability. Therefore, the present dendrimer-based drug carriers are proven to be prominent, benign, biocompatible, and efficient for poorly soluble drugs, such as FRSD. Therefore, they could be convenient choices for real-time applications of drug delivery.

Physicochemical and in vitro cytotoxicity studies of inclusion complex between gemcitabine and cucurbit[7]uril host

Gemcitabine, a cytostatic drug from the pyrimidine antimetabolite group, exhibits limited storage stability and numerous side effects during therapy. One of the strategies to improve the effectiveness of therapy with such drugs is the use of supramolecular nano-containers, including dendrimers and macrocyclic compounds. The ability of gemcitabine to attach a proton in an aqueous environment necessitates the search for a carrier that is well-tolerated by an organism and capable of supramolecular binding of a ligand (drug) in a cationic form. In the current study a promising strategy was tested for using cucurbituril Q7 to bind gemcitabine cations for its efficient intracellular delivery on three selected cancer cell lines (MOLT4, THP-1 and U937). Based on physicochemical studies (equilibrium dialysis, UV and ¹H NMR titrations, DOSY ¹H NMR measurements, DSC calorimetry) and cytotoxicity tests on cells with a free and blocked hENT1 transporter, the conclusion was drawn about the binding and penetration of the cucurbituril-drug complex into cancer cells.

Formation of dendrimer-guest complexes as a strategy to increase the solubility of a phenazine N, N'-dioxide derivative with antitumor activity

Poly(amidoamine) and Poly(propylenimine) dendrimers with different generations and peripheral groups were studied as solubility enhancers and nanocarriers for 7-bromo-2-hydroxy-phenazine N⁵,N¹⁰-dioxide. This compound possesses potential antitumoral and anti-trypanosomal activity, but its low solubility in physiological media precludes its possible application as therapeutic drug. The amino terminated dendrimers association with the active compounds as observed trough NMR studies showed that electrostatic interactions are essential in the solubilization enhancement process. The obtaining of a stable and no cytotoxic formulation makes the drug-carried association a suitable strategy for the generation of a drug delivery system for phenazine derivatives.

Spectroscopic and calorimetric studies on the interaction between PAMAM G4-OH and 5-fluorouracil in aqueous solutions

The results of spectroscopic measurements (an increase in solubility, equilibrium dialysis, ¹H NMR titration) and calorimetric measurements (isothermal titration ITC) indicate spontaneous (ΔG<0) binding of 5-fluorouracil molecules by PAMAM G4-OH dendrimer with terminal hydroxyl groups in an aqueous solution. PAMAM G4-OH dendrimer bonds about n=8±1 molecules of the drug with an equilibrium constant of K=70±10. The process of saturating the dendrimer active sites by the drug molecules is exothermal (ΔH<0) and is accompanied by an advantageous change in entropy (ΔS>0). The parameters of binding 5-fluorouracil by PAMAM G4-OH dendrimer were compared with those of binding this drug by the macromolecules of PAMAM G3-OH and G5-OH.

Rapid Exchange Between Free and Bound States in RNA-Dendrimer Polyplexes: Implications on the Mechanism of Delivery and Release

A combination of solution NMR, dynamic light scattering (DLS), and fluorescence quenching assays were employed to obtain insights into the dynamics and structural features of a polyplex system consisting of HIV-1 transactivation response element (TAR) and PEGylated generation 5 poly(amidoamine) dendrimer (G5-PEG). NMR chemical shift mapping and (13)C spin relaxation based dynamics measurements depict the polyplex system as a highly dynamic assembly where the RNA, with its local structure and dynamics preserved, rapidly exchanges ( Collapse

Key Words

• therapeutic rna delivery
• pamam
• pegylation
• tar
• dls
• nmr spin relaxation

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MESH Headings

• Dendrimers/chemistry
• HIV-1/chemistry
• Magnetic Resonance Spectroscopy/methods
• Polyamines/chemistry
• Polyethylene Glycols/chemistry
• RNA/chemistry
• Response Elements/genetics
• Transfection/methods

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Grants

• R01 AI066975 NIAID NIH HHS
• P50 GM103297 NIGMS NIH HHS
• R01 AI087463-01 NIAID NIH HHS
• R01 EB005028 NIBIB NIH HHS
• R01EB005028 NIBIB NIH HHS
• R01 GM089846 NIGMS NIH HHS

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Affiliation(s)

Anisha Shakya Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
Casey A. Dougherty Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
Yi Xue Department of Biochemistry and Chemistry, Duke University Medical Center, Durham, NC 27710, USA
Hashim M. Al-Hashimi Department of Biochemistry and Chemistry, Duke University Medical Center, Durham, NC 27710, USA
Mark M. Banaszak Holl Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA

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Spectroscopic and calorimetric studies of formation of the supramolecular complexes of PAMAM G5-NH₂ and G5-OH dendrimers with 5-fluorouracil in aqueous solution

The results of spectroscopic measurements (increase in solubility, equilibrium dialysis, (1)H NMR titration) and calorimetric measurements (isothermal titration ITC) indicate exothermic (ΔH<0) and spontaneous (ΔG < 0) combination of an antitumor drug, 5-fluorouracil, by both cationic PAMAM G5-NH2 dendrimer and its hydroxyl analog PAMAM G5-OH in aqueous solutions at room temperature. PAMAM G5-NH2 dendrimer combines about 70 molecules of the drug with equilibrium constant K ≅ 300, which is accompanied by an increase in the system order (ΔS < 0). Hydroxyl dendrimer, PAMAM G5-OH, combines about 14 molecules of 5-fluorouracil with equilibrium constant K ≅ 100. This process is accompanied by an increase in the system disorder (ΔS > 0).

Evaluation of surface acetylated and internally quaternized poly(propylene imine) dendrimer as a biocompatible drug carrier for piroxicam as a model drug

Two types of new surface acetylated and internally quaternized poly(propylene imine) dendrimers QPPI-NHAc (G2)/(G3) were prepared, characterized and then demonstrated as potential and biocompatible drug carriers using piroxicam as a model drug.

Formation of complexes between PAMAM-NH2 G4 dendrimer and L-α-tryptophan and L-α-tyrosine in water

Interactions between electromagnetic radiation and the side substituents of aromatic amino acids are widely used in the biochemical studies on proteins and their interactions with ligand molecules. That is why the aim of our study was to characterize the formation of complexes between PAMAM-NH2 G4 dendrimer and L-α-tryptophan and L-α-tyrosine in water. The number of L-α-tryptophan and L-α-tyrosine molecules attached to the macromolecule of PAMAM-NH2 G4 dendrimer and the formation constants of the supramolecular complexes formed have been determined. The macromolecule of PAMAM-NH2 G4 can reversibly attach about 25 L-α-tryptophan molecules with equilibrium constant K equal to 130±30 and 24±6 L-α-tyrosine molecules. This characterization was deduced on the basis of the solubility measurements of the amino acids in aqueous dendrimer solutions, the (1)H NMR and 2D-NOESY measurements of the dendrimer solutions with the amino acids, the equilibrium dialysis and the circular dichroism measurements of the dendrimer aqueous solutions with L-α-tryptophan. Our date confirmed the interactions of L-α-tryptophan and L-α-tyrosine with the dendrimer in aqueous solution and indicated a reversible character of the formed complexes.

Improved tumor targetability of Tat-conjugated PAMAM dendrimers as a novel nanosized anti-tumor drug carrier

The generation 4-poly-amidoamine-dendrimers (PAMAM G4 dendrimer, P) was conjugated to Tat peptide (Tat, T), a cell-penetrating peptide, in search of an efficient anti-tumor drug delivery vehicle for cancer therapy. In this study, we synthesized BODIPY-labeled Tat-Conjugated PAMAM dendrimers (BPTs) as a novel nanosized anticancer drug carriers and systemically investigated their biodistribution and the tumor accumulation in Sarcoma 180-bearing mice. In addition, the uptake and the cytotoxicity to S180 cells of BPTs thereof were evaluated. The unmodified dendrimer (BP) showed a soon clearance from the blood stream and nonspecific accumulation in tumor. In contrast, the Tat-modified dendrimer, BPT(64) with appropriate particle size showed a better retention in blood and could be accumulated effectively in tumor tissue via the enhanced permeability and retention (EPR) effect. Moreover, BPTs with a high Tat modification rate was accumulated more effectively in tumor tissue. In vitro experiments, these BPTs displayed low cytotoxicity on S180 cells and high uptake to S180 cells. These findings indicate that the nanoparticulate system on the basis of Tat-conjugated PAMAM dendrimers is safer and effective in the concentration range (below 20 μg/ml) to be used as a carrier of anti-tumor drugs for tumor targeting by intravenous administration.

Dendrimers for drug delivery

Schematized types of interactions of dendrimers with drugs or biologically active substances.

Study of the complexation of oxacillin in 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers

The complexation of oxacillin to three generations of 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers was studied with NMR in CD3OD and CDCl3. The stochiometries, which were determined from Job plots, were found to be both solvent- and generation-dependent. The dissociation constants (K(d)) and Gibbs energies for complexation of oxacillin into the 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimer hosts were determined by (1)H NMR titrations and showed weaker binding of oxacillin upon increasing the size (generation) of the dendrimer.

Computationally efficient methodology for atomic-level characterization of dendrimer-drug complexes: a comparison of amine- and acetyl-terminated PAMAM

PAMAM dendrimers have been widely studied as a novel means for controlled drug delivery; however, computational study of dendrimer-drug complexation is made difficult by the conformational flexibility of dendrimers and the nonspecific nature of the dendrimer-drug interactions. Conventional protocols for studying drug binding have been designed primarily for protein substrates, and, therefore, there is a need to establish new protocols to deal with the unique aspects of dendrimers. In this work, we generate cavities in generation-5 polyamidoamine (PAMAM) dendrimers at selected distances from the center of mass of the dendrimer for the insertion of the model drug: dexamethasone 21-phosphate or Dp21. The complexes are then allowed to equilibrate with distance between centers of mass of the drug and dendrimers confined to selected ranges; the free energy of complexation is estimated by the MM-GBSA (MM, molecular mechanics; GB, generalized Born; SA, surface area) method. For both amine- and modified acetyl-terminated PAMAM at both low and neutral pH, the most favorable free energy of complexation is associated with Dp21 at distance of 15-20 Å from the center of mass of the dendrimer and that smaller or larger distances yield considerably weaker affinity. In agreement with experimental results, we find acetyl-terminated PAMAM at neutral pH to form the least stable complex with Dp21. The greatest affinity is seen in the case of acetyl-terminated PAMAM at low pH, which appears to be due a complex balance of different contributions, which cannot be attributed to electrostatics, van der Waals interactions, hydrogen bonds, or charge-charge interactions alone.

Theoretical and computational studies of dendrimers as delivery vectors

It is a great challenge for nanomedicine to develop novel dendrimers with maximum therapeutic potential and minimum side-effects for drug and gene delivery. As delivery vectors, dendrimers must overcome lots of barriers before delivering the bio-agents to the target in the cell. Extensive experimental investigations have been carried out to elucidate the physical and chemical properties of dendrimers and explore their behaviors when interacting with biomolecules, such as gene materials, proteins, and lipid membranes. As a supplement of the experimental techniques, it has been proved that computer simulations could facilitate the progress in understanding the delivery process of bioactive molecules. The structures of dendrimers in dilute solutions have been intensively investigated by monomer-resolved simulations, coarse-grained simulations, and atom-resolved simulations. Atomistic simulations have manifested that the hydrophobic interactions, hydrogen-bond interactions, and electrostatic attraction play critical roles in the formation of dendrimer-drug complexes. Multiscale simulations and statistical field theories have uncovered some physical mechanisms involved in the dendrimer-based gene delivery systems. This review will focus on the current status and perspective of theoretical and computational contributions in this field in recent years. (275 references).

Reducing cytotoxicity while improving anti-cancer drug loading capacity of polypropylenimine dendrimers by surface acetylation

Polypropylenimine (PPI) dendrimers have been widely used as effective delivery vehicles for drugs and nucleic acids during the past decade. However, biomedical applications of PPI dendrimers were limited because of their serious cytotoxicity and low drug loading capacity. In the present study, acetylated PPI dendrimers with different degrees of acetylation ranging from 14.2% to 94.3% were synthesized and used to encapsulate drugs, including methotrexate sodium, sodium deoxycholate and doxorubicin. Acetylated PPI dendrimers with a degree of acetylation >80% showed a significantly decreased cytotoxicity (>90% cell viability) on MCF-7 and A549 cells. The drug loading capacity of acetylated PPI dendrimers increased proportionally with the degree of acetylation on the dendrimer surface. In addition, 94.3% acetylated PPI dendrimers exhibited a pH-responsive release profile of anticancer drugs loaded within the nanoparticles. The cytotoxicities of methotrexate sodium and doxorubicin on MCF-7 and A549 cells were significantly reduced when they were complexed with acetylated PPI dendrimers with high degrees of acetylation (>80%), owing to sustained drug release from the dendrimers. The results suggest that surface acetylation can reduce the cytotoxicity and improve the anticancer drug loading capacity of cationic dendrimers, and that acetylated PPI dendrimers are promising vehicles for anticancer drugs in clinical trials.

Biogenic and synthetic polyamines bind cationic dendrimers

Biogenic polyamines are essential for cell growth and differentiation, while polyamine analogues exert antitumor activity in multiple experimental model systems, including breast and lung cancer. Dendrimers are widely used for drug delivery in vitro and in vivo. We report the bindings of biogenic polyamines, spermine (spm), and spermidine (spmd), and their synthetic analogues, 3,7,11,15-tetrazaheptadecane.4HCl (BE-333) and 3,7,11,15,19-pentazahenicosane.5HCl (BE-3333) to dendrimers of different compositions, mPEG-PAMAM (G3), mPEG-PAMAM (G4) and PAMAM (G4). FTIR and UV-visible spectroscopic methods as well as molecular modeling were used to analyze polyamine binding mode, the binding constant and the effects of polyamine complexation on dendrimer stability and conformation. Structural analysis showed that polyamines bound dendrimers through both hydrophobic and hydrophilic contacts with overall binding constants of K(spm-mPEG-G3) = 7.6 × 10(4) M(-1), K(spm-mPEG-PAMAM-G4) = 4.6 × 10(4) M(-1), K(spm-PAMAM-G4) = 6.6 × 10(4) M(-1), K(spmd-mPEG-G3) = 1.0 × 10(5) M(-1), K(spmd-mPEG-PAMAM-G4) = 5.5 × 10(4) M(-1), K(spmd-PAMAM-G4) = 9.2 × 10(4) M(-1), K(BE-333-mPEG-G3) = 4.2 × 10(4) M(-1), K(Be-333-mPEG-PAMAM-G4) = 3.2 × 10(4) M(-1), K(BE-333-PAMAM-G4) = 3.6 × 10(4) M(-1), K(BE-3333-mPEG-G3) = 2.2 × 10(4) M(-1), K(Be-3333-mPEG-PAMAM-G4) = 2.4 × 10(4) M(-1), K(BE-3333-PAMAM-G4) = 2.3 × 10(4) M(-1). Biogenic polyamines showed stronger affinity toward dendrimers than those of synthetic polyamines, while weaker interaction was observed as polyamine cationic charges increased. The free binding energies calculated from docking studies were: -3.2 (spermine), -3.5 (spermidine) and -3.03 (BE-3333) kcal/mol, with the following order of binding affinity: spermidine-PAMAM-G-4>spermine-PAMMAM-G4>BE-3333-PAMAM-G4 consistent with spectroscopic data. Our results suggest that dendrimers can act as carrier vehicles for delivering antitumor polyamine analogues to target tissues.

Dendrimers bind antioxidant polyphenols and cisplatin drug

Synthetic polymers of a specific shape and size play major role in drug delivery systems. Dendrimers are unique synthetic macromolecules of nanometer dimensions with a highly branched structure and globular shape with potential applications in gene and drug delivery. We examine the interaction of several dendrimers of different compositions mPEG-PAMAM (G3), mPEG-PAMAM (G4) and PAMAM (G4) with hydrophilic and hydrophobic drugs cisplatin, resveratrol, genistein and curcumin at physiological conditions. FTIR and UV-visible spectroscopic methods as well as molecular modeling were used to analyse drug binding mode, the binding constant and the effects of drug complexation on dendrimer stability and conformation. Structural analysis showed that cisplatin binds dendrimers in hydrophilic mode via Pt cation and polymer terminal NH(2) groups, while curcumin, genistein and resveratrol are located mainly in the cavities binding through both hydrophobic and hydrophilic contacts. The overall binding constants of durg-dendrimers are ranging from 10(2) M(-1) to 10(3) M(-1). The affinity of dendrimer binding was PAMAM-G4>mPEG-PAMAM-G4>mPEG-PAMAM-G3, while the order of drug-polymer stability was curcumin>cisplatin>genistein>resveratrol. Molecular modeling showed larger stability for genisten-PAMAM-G4 (ΔG = -4.75 kcal/mol) than curcumin-PAMAM-G4 ((ΔG = -4.53 kcal/mol) and resveratrol-PAMAM-G4 ((ΔG = -4.39 kcal/mol). Dendrimers might act as carriers to transport hydrophobic and hydrophilic drugs.

Design of biocompatible dendrimers for cancer diagnosis and therapy: current status and future perspectives

In the past decade, nanomedicine with its promise of improved therapy and diagnostics has revolutionized conventional health care and medical technology. Dendrimers and dendrimer-based therapeutics are outstanding candidates in this exciting field as more and more biological systems have benefited from these starburst molecules. Anticancer agents can be either encapsulated in or conjugated to dendrimer and be delivered to the tumour via enhanced permeability and retention (EPR) effect of the nanoparticle and/or with the help of a targeting moiety such as antibody, peptides, vitamins, and hormones. Imaging agents including MRI contrast agents, radionuclide probes, computed tomography contrast agents, and fluorescent dyes are combined with the multifunctional nanomedicine for targeted therapy with simultaneous cancer diagnosis. However, an important question reported with dendrimer-based therapeutics as well as other nanomedicines to date is the long-term viability and biocompatibility of the nanotherapeutics. This critical review focuses on the design of biocompatible dendrimers for cancer diagnosis and therapy. The biocompatibility aspects of dendrimers such as nanotoxicity, long-term circulation, and degradation are discussed. The construction of novel dendrimers with biocompatible components, and the surface modification of commercially available dendrimers by PEGylation, acetylation, glycosylation, and amino acid functionalization have been proposed as available strategies to solve the safety problem of dendrimer-based nanotherapeutics. Also, exciting opportunities and challenges on the development of dendrimer-based nanoplatforms for targeted cancer diagnosis and therapy are reviewed (404 references).