Capillary electrophoresis of polycationic poly(amidoamine) dendrimers

Cellular uptake of glucoheptoamidated poly(amidoamine) PAMAM G3 dendrimer with amide-conjugated biotin, a potential carrier of anticancer drugs

In search for soluble derivatives of PAMAM dendrimers as potential carriers for hydrophobic drugs, the conjugates of PAMAM G3 with biotin, further converted into glycodendrimer with d-glucoheptono-1,4-lactone, were prepared. Polyamidoamine dendrimer (PAMAM) of third generation, G3 was functionalized with four biotin equivalents covalently attached to terminal amine nitrogens via amide bond G3^4B. The remaining 28 amine groups were blocked by glucoheptoamide substituents (gh) to give G3^4B28gh or with one fluorescein equivalent (attached by reaction of G3^4B with fluorescein isothiocyanate, FITC) via thiourea bond as FITC followed by exhaustive glucoheptoamidation to get G3^4B27gh1F. As a control the G3 substituted totally with 32 glucoheptoamide residues, G3^gh and its fluorescein labeled analogue G3^31gh1F were synthesized. The glucoheptoamidation of PAMAM G0 dendrimer with glucoheptono-1,4-lactone was performed in order to fully characterize the ¹H NMR spectra of glucoheptoamidated PAMAM dendrimers and to control the derivatization of G3 with glucoheptono-1,4-lactone. Another two derivatives of G3, namely G3^4B28gh1F' and G3^32ghF', with ester bonded fluorescein were also obtained. Biological properties of obtained dendrimer conjugates were estimated in vitro with human cell lines: normal fibroblast (BJ) and two cancer glioblastoma (U-118 MG) and squamous carcinoma (SCC-15), including cytotoxicity by reduction of XTT and neutral red (NR) assays. Cellular uptake of dendrimer conjugates was evaluated with confocal microscopy. Obtained results confirmed, that biotinylated bioconjugates have always lower cytotoxicity and 3-4 times higher cellular uptake than non-biotinylated dendrimer conjugates in all cell lines. Comparison of various cell lines revealed different dose-dependent cell responses and the lower cytotoxicity of examined dendrimer conjugates for normal fibroblasts and squamous carcinoma, as compared with much higher cytotoxic effects seen in glioblastoma cell line. Synthetized multi-functional conjugate (G3^4B27gh1F) is a promising candidate as biocompatible vehicle for hydrophobic molecules used in anticancer therapy.

Charged dendrimers under the action of AC electric fields: breathing characteristics of molecular size, polarizations, and ion distributions

Langevin dynamics simulations are performed to study the response of charged dendrimers in alternating current electric fields in 3:1 salt solutions. Time evolutions of molecular size show breathing characteristics which take saw-tooth-like patterns in square-wave electric fields and undulated sine-function ones in sine-wave fields. Detailed study reveals how the dendrimer and condensed ions oscillate in the electric fields, which result in polarization of the molecule. To effect a significant deformation of the dendrimer, the applied field amplitude must be larger than some critical strength Ecrit and the field frequency smaller than a threshold fcrit. The response behavior is characterized by two relaxation times in square-wave fields, both of which decrease linearly with the strong field strength larger than Ecrit. In sine-wave fields, the molecular size exhibits interesting hysteretic behavior in plotting the curves with the field variation. A Maxwell-Wagner type polarization theory is derived and proved by simulations, which connects fcrit with the strength of the applied electric field.

Charged dendrimers in trivalent salt solutions under the action of DC electric fields

The structural properties and electrophoretic mobility of charged dendrimers in 3:1 electrolyte solutions subjected to direct current electric fields are studied using molecular dynamics simulations. The simulated dendrimer size is studied in zero fields and found to scale as R(g) ∼ N(0.29). The dendrimers exhibit shape distortions when the applied electric field is larger than some critical value, which scales with the number of dendrimer monomers as E(z,crit) ∼ N(0.39(6)). Families of curves, such as the curves of the square of radius of gyration, the asphericity, the degree of prolateness, and the electrophoretic mobility of dendrimers, are shown to collapse to single, master curves in electric fields through appropriate scaling. This reflects the fractal characteristics of these systems. The density profile of the surface monomers and salt cations reveals two pronounced combination effects between the polarization of dendrimer complexes and stripping-off of the condensed salt cations from the dendrimer surface.

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).

Quantitation of nanoparticles in serum matrix by capillary electrophoresis

Sensitive and fast analytical techniques are needed to determine the concentration of nanoparticles in biological samples (e.g., blood and tissues) for biodistribution and toxicity studies. This chapter describes a method for the use of capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) for the quantitation of fullerene nanoparticles in human serum matrix. Data on the fullerene-based nanoparticle carboxyfullerene (C3 fullerene) in human serum is presented as an example.

Tumour and dendrimers: a review on drug delivery aspects

Tumour is a morbid state, characterized by spontaneous outgrowth of an abnormal mass of cells. The evolution of tumours is random, disorganized, a condition of numerous mutations. The properties are biased and incompletely comprehended. It is a malignant or benign condition that encompasses its own rules of morphogenesis, an immortal state that elucidates different physiology. It is a pathological crisis that still haunts the minds of scientists, physicians and patients, a complete cure of which is still a dream to be realized. The unpredictable microenvironment of cancerous cells in all of its existing forms i.e. leukaemic cells, solid tumours and sarcomas is well documented. This phenomenon expressed by cancerous sites in the body poses various obstacles towards drug efficacy. Thus, it has become necessary to address briefly the issues relating to tumour physiology, its vasculature and angiogenesis. The information could provide insight towards the development of tumour-targeted drug delivery. The salient features regarding these have been discussed.

The role of ganglioside GM1 in cellular internalization mechanisms of poly(amidoamine) dendrimers

Generation 7 (G7) poly(amidoamine) (PAMAM) dendrimers with amine, acetamide, and carboxylate end groups were prepared to investigate polymer/cell membrane interactions in vitro. G7 PAMAM dendrimers were used in this study because higher-generation of dendrimers are more effective in permeabilization of cell plasma membranes and in the formation of nanoscale holes in supported lipid bilayers than smaller, lower-generation dendrimers. Dendrimer-based conjugates were characterized by (1)H NMR, UV/vis spectroscopy, GPC, HPLC, and CE. Positively charged amine-terminated G7 dendrimers (G7-NH(2)) were observed to internalize into KB, Rat2, and C6 cells at a 200 nM concentration. By way of contrast, neither negatively charged G7 carboxylate-terminated dendrimers (G7-COOH) nor neutral acetamide-terminated G7 dendrimers (G7-Ac) associated with the cell plasma membrane or internalized under similar conditions. A series of in vitro experiments employing endocytic markers cholera toxin subunit B (CTB), transferrin, and GM(1)-pyrene were performed to further investigate mechanisms of dendrimer internalization into cells. G7-NH(2) dendrimers colocalized with CTB; however, experiments with C6 cells indicated that internalization of G7-NH(2) was not ganglioside GM(1) dependent. The G7/CTB colocalization was thus ascribed to an artifact of direct interaction between the two species. The presence of GM(1) in the membrane also had no effect upon XTT assays of cell viability or lactate dehydrogenase (LDH) assays of membrane permeability.

Comprehensive profiling of the complex dendrimeric contrast agent Gadomer using a combined approach of CE, MS, and CE-MS

The complex dendrimeric contrast agent Gadomer has been comprehensively characterized using various mass spectrometric techniques in combination with capillary electrophoresis. The analytical challenges arising from the structure of this analyte, e.g., the presence of a complex isotopic pattern originating from multiple gadolinium chelates could be overcome using this combined approach. Results obtained from initial MALDI-TOF-MS measurements could subsequently be complemented and confirmed by CE-ESI-TOF-MS measurements. Furthermore, high resolution Fourier transform-ion cyclotron resonance-MS (FT-ICR-MS) as a stand alone technique and in combination with CE was performed to obtain mass spectra of high mass accuracy and resolution of various impurities and related dendrimers present in low concentrations in several Gadomer batches. The profile of related dendrimers and impurities of lower molecular weight present in Gadomer could be elucidated and variances in the pattern of related dendrimers present in batches obtained via different synthetic routes could be detected. The qualitative analysis of Gadomer using MS techniques in combination with CE provides the fundamental basis for a framework of analytical methodologies for the characterization of Gadomer. By designing such a framework of methodologies the challenges associated with the introduction of dendrimers into the clinical stage may be overcome and the reproducible quality and safety of these innovative products can be ensured.

Determination of binding constants of vasoactive intestinal peptide to poly(amidoamine) dendrimers designed for drug delivery using ACE

The purpose of the present paper was to study at physiological pH the affinity between vasoactive intestinal peptide (VIP) and four poly(amidoamine) dendrimers (PAMAMs) designed for drug delivery. Therefore, a fast and reproducible CE method was first developed to analyze the strongly basic peptide. To allow an accurate determination of binding constant (K) values, the ability to suppress peptide adsorption onto the silica capillary of nonpermanent coatings (poly(ethylene oxide) (PEO), low and medium relative molecular masses poly(diallyldimethylammonium chloride) (PDDA)) or poly(acrylamide) permanent coating (PAA) was evaluated. Very good intraday repeatability of VIP migration times and peak areas (0.1-0.6 and 2.9-4.9% RSD, respectively) was obtained using two of the investigated coatings (PEO and PDDA with medium molecular mass). ACE combined with these dynamic coatings was then employed to evaluate K between VIP and two amine-terminated PAMAM dendrimers of generation 2 and 5 (G2.NH2, G5.NH2) and two carboxyl-terminated PAMAM derivatives of generation 2 and 5 (G2.COOH, G5.COOH). Binding constant of (6.7 +/- 1.1) x 10(4)/M could be determined for the couple VIP/G5.NH2, while no affinity was evidenced between VIP and all other dendrimers investigated. These results suggest that G5.NH2 might be an interesting carrier for the delivery of VIP.

Analysis of fullerene-based nanomaterial in serum matrix by CE

With the increasing interest in using nanoparticles as vehicles for drug delivery and image contrast agents, there is a need to develop assays for their detection and quantitation in complex matrices to facilitate monitoring their biodistribution. In this study, we developed a CE approach for the analysis of two nanoparticles: carboxyfullerene (C3) and dendrofullerene (DF1) in both standard solutions and a serum matrix. These highly soluble, charged C(60) derivatives were characterized by CZE using either a bare or dynamically coated fused-silica capillaries. The resolution of both nanoparticles was slightly lower with the coated capillary; however, their migration times were faster. While separation of the DF1 nanoparticles using MEKC resulted in a greater number of observable peaks, the peak profile of C3 was basically unchanged regardless of whether SDS micelles were added to the running buffers or not. The MEKC and/or CZE assays were then used to quantitate the C3 and DF1 nanoparticles in spiked human serum samples. The quantitation of the nanoparticles was linear from 0-500 microg/mL with detection limits ranging from 0.5 to 6 microg/mL.

Influence of generation 2-5 of PAMAM dendrimer on the inhibition of Tat peptide/ TAR RNA binding in HIV-1 transcription

The special binding of Tat protein to TAR RNA leads to the transcription of HIV-1 virus. In this study, the influence of 2-5 generation of PAMAM dendrimers on the inhibition of Tat protein/TAR RNA binding has been investigated. The absorption of PAMAM dendrimers on TAR RNA, fixed on a gold substrate through an avidin-biotion connection, was carried out by using a quartz crystal microbalance. Experimental result shows a Langmuir-type isotherm could be used to describe this kind of binding, implying a specific and monolayer adsorption existed. The combination coefficient (K(D)(-1))s can be calculated according to Langmuir Equation, having the order of G3 > G4 > G5 >Tat > G2, indicating that PAMAM G3, G4 and G5 having the possibility to be the inhibitors of HIV-1 transcription. The migration time (T(migra)) of capillary electrophoretic technique has the same sequence as (K(D)(-1))s. These two parameters could be used as simple and quantitative criteria for the selection of possible drugs from numerous candidates for HIV therapy in vitro.

Use of poly(vinyl alcohol)-coated capillaries for separation of amino-terminated polyamidoamine dendrimers

Characterization of amino-terminated polyamidoamine dendrimers by CE suffers from a lack of resolution for higher generations and poor between-day reproducibility of retention times. Under optimal conditions of temperature, voltage, and sample amount, 0-5 generations of dendrimers could be resolved with a bare fused-silica capillary. However, reproducibility was poor due to potential interactions of the polycationic dendrimers with the uncoated quartz capillary wall. Use of a poly(vinyl alcohol)-coated capillary significantly decreased the migration times of the nanomolecules without compromising resolution. Dendrimer mixtures containing generations 0-5 are separated as discrete, nonoverlapping peaks in about 15 min. In addition, the between-day precision of retention times was dramatically improved without the need for internal standards or data normalization. Dendrimers of various generations and cores run on different days showed an RSD of retention times of less than 4%. The poly(vinyl alcohol) coating was very stable as shown by the excellent precision of migration times obtained on a capillary used for a month with more than 100 injections. Similar to PAGE, separation of polyamidoamine dendrimers on a bare fused-silica and poly(vinyl alcohol)-coated capillary showed an exponential relationship between migration times and calculated charge density of the nanomolecules.

Separation of poly(amidoamine) (PAMAM) dendrimer generations by dynamic coating capillary electrophoresis

The separation of compounds possessing amino groups (peptides, proteins, polyamino compounds) by capillary zone electrophoresis suffers from the interaction (sticking) of these solutes with the capillary wall. This sticking can result in the absence or incomplete separation of compounds or even in their retention in the capillary. Polyamidoamine (PAMAM) dendrimers are a class of spherical polymers with primary amino groups at the surface. These compounds can be separated reasonably well at acidic pH but not at neutral pH. A new method based on the dynamic coating of the capillary was developed for the separation of these compounds at pH 7.4. The method comprises separation in a fused-silica capillary (57 cm total length, 50 cm to the detector, ID 75 microm) and a background electrolyte consisting of a Tris-phosphate buffer (50 mmol/L, pH 7.4) and 0.05% (w/v) polyethyleneimine. This system is suitable for the separation of 7 generations of dendrimers (generations 0-6). The dynamic coating agent (polyethyleneimine) also improves the separation at acid pH.

Capillary electrophoresis for the characterization of the complex dendrimeric contrast agent Gadomer

A CE method for the characterization of the complex dendrimeric contrast agent Gadomer has been developed and validated. The method was capable of separating the target substance Gadomer 24 from related dendrimers containing amino or carboxyl functions and from impurities of lower molecular weight. The compounds were separated in a fused-silica capillary. The optimized BGE consisted of 15 mM sodium phosphate, pH 6.3, containing 0.5 mM hexadecyltrimethylammonium bromide. The assay was validated with regard to linearity, specificity, accuracy, LOD and LOQ as well as robustness according to the guidelines of the International Conference on Harmonization. The method allows the determination of the purity and stability of the drug substance Gadomer as well as its injectable formulation. On the basis of the present study, a strategy for the quality assurance and quality control of the complex dendrimeric drug candidate Gadomer may be devised. The method may therefore serve as a key component in a set of analytical methodologies designed to assure and control the reproducible quality and safety of this innovative product. To the best of our knowledge, this is the first work reporting a validated method for the characterization, impurity profiling, and stability testing of a dendrimeric agent designed for clinical use.

Electrophoretic mobility and molecular distribution studies of poly(amidoamine) dendrimers of defined charges

Generation 5 ethylenediamine (EDA)-cored poly(amidoamine) (PAMAM) dendrimers (E5, E denotes the EDA core and 5 the generation number) with different degrees of acetylation and carboxylation were synthesized and used as a model system to investigate the effect of charge and the influence of dendrimer surface modifications on electrophoretic mobility (EM) and molecular distribution. The surface-modified dendrimers were characterized by size-exclusion chromatography, 1H NMR, MALDI-TOF-MS, PAGE, and CE. The focus of our study was to determine how EM changes as a function of particle charge and molecular mass, and how the molecular distribution changes due to surface modifications. We demonstrate that partially modified dendrimers have much broader migration peaks than those of fully surface functionalized or unmodified E5 dendrimers due to variations in the substitution of individual dendrimer surfaces. EM decreased nonlinearly with increases in surface acetylation for both PAMAM acetamides and PAMAM succinamic acids, indicating a complex migration activity in CE separations that is not solely due to charge/mass ratio changes. These studies provide new insights into dendrimer properties under an electric field, as well as into the characterization of dendrimer-based materials being developed for medical applications.

Molecular heterogeneity analysis of poly(amidoamine) dendrimer-based mono- and multifunctional nanodevices by capillary electrophoresis

Poly(amidoamine) (PAMAM) dendrimer-based nanodevices are of recent interest in targeted cancer therapy. Characterization of mono- and multifunctional PAMAM-based nanodevices remains a great challenge because of their molecular complexity. In this work, various mono- and multifunctional nanodevices based on PAMAM G5 (generation 5) dendrimer were characterized by UV-Vis spectrometry, (1)H NMR, size exclusion chromatography (SEC), and capillary electrophoresis (CE). CE was extensively utilized to measure the molecular heterogeneity of these PAMAM-based nanodevices. G5-FA (FA denotes folic acid) conjugates (synthesized from amine-terminated G5.NH(2) dendrimer, approach 1) with acetamide and amine termini exhibit bimodal or multi-modal distributions. In contrast, G5-FA and bifunctional G5-FA-MTX (MTX denotes methotrexate) conjugates with hydroxyl termini display a single modal distribution. Multifunctional G5.Ac(n)-FI-FA, G5.Ac(n)-FA-OH-MTX, and G5.Ac(n)-FI-FA-OH-MTX (Ac denotes acetamide; FI denotes fluorescein) nanodevices (synthesized from partially acetylated G5 dendrimer, approach 2) exhibit a monodisperse distribution. It indicates that the molecular distribution of PAMAM conjugates largely depends on the homogeneity of starting materials, the synthetic approaches, and the final functionalization steps. Hydroxylation functionalization of dendrimers masks the dispersity of the final PAMAM nanodevices in both synthetic approaches. The applied CE analysis of mono- and multifunctional PAMAM-based nanodevices provides a powerful tool to evaluate the molecular heterogeneity of complex dendrimer conjugate nanodevices for targeted cancer therapeutics.

HPLC analysis of functionalized poly(amidoamine) dendrimers and the interaction between a folate-dendrimer conjugate and folate binding protein

Poly(amidoamine) (PAMAM) dendrimers of different generations with carboxyl, acetyl, and hydroxyl terminal groups and a folic acid (FA)-dendrimer conjugate were separated and analyzed using reverse-phase high performance liquid chromatography (HPLC). Analysis of both the individual PAMAM derivatives and the separation of mixed generations can be achieved using a linear gradient 0-50% acetonitrile (ACN) (balance water) within 40 min. We also show that PAMAMs with defined acetylation and carboxylation degrees can be analyzed using HPLC. Furthermore, a generation 5 dendrimer-FA conjugate (G5.75Ac-FA4; Ac denotes acetyl) was analyzed and its specific binding with a bovine folic acid binding protein (FBP) was monitored. The HPLC and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results indicate the formation of three complexes after the binding of G5.75Ac-FA4 with FBP. Dendrimers with FA moieties show much higher specific binding capability with FBP than those without FA moieties. Findings from this study indicate that HPLC is an effective technique not only for characterization and separation of functionalized PAMAM dendrimers and conjugates but also for investigation of the interaction between dendrimers and biomolecules.