Synergistic Antibacterial Effects of Amoxicillin and Gold Nanoparticles: A Therapeutic Option to Combat Antibiotic Resistance.

Compacted Au@16-mph-16/DNA-AMOX (NSi) nanosystems were prepared from amoxicillin (AMOX) and precursor Au@16-mph-16 gold nanoparticles (Ni) using a Deoxyribonucleic acid (DNA) biopolymer as a glue. The synthesized nanocarrier was tested on different bacterial strains of Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae to evaluate its effectiveness as an antibiotic as well as its internalization. Synthesis of the nanosystems required previous structural and thermodynamic studies using circular dichroism (CD) and UV-visible techniques to guarantee optimal complex formation and maximal DNA compaction, characteristics which facilitate the correct uptake of the nanocarrier. Two nanocomplexes with different compositions and structures, denoted NS1 and NS2, were prepared, the first involving external Au@16-mph-16 binding and the second partial intercalation. The Ni and NSi nanosystems obtained were characterized via transmission electron microscopy (TEM), zeta potential, and dynamic light scattering (DLS) techniques to measure their charge, aggregation state and hydrodynamic size, and to verify their presence inside the bacteria. From these studies, it was concluded that the zeta potential values for gold nanoparticles, NS1, and NS2 nanosystems were 67.8, -36.7, and -45.1 mV. Moreover, the particle size distribution of the Au@16-mph-16 gold nanoparticles and NS2 nanoformulation was found to be 2.6 nm and 69.0 nm, respectively. However, for NS1 nanoformulation, a bimodal size distribution of 44 nm (95.5%) and 205 nm (4.5%) was found. Minimal inhibitory concentration (MIC) values were determined for the bacteria studied using a microdilution plates assay. The effect on Escherichia coli bacteria was notable, with MIC values of 17 µM for both the NS1 and NS2 nanosystems. The Staphylococcus aureus chart shows a greater inhibition effect of NS2 and NP2 in non-diluted wells, and clearly reveals a great effect on Streptococcus pneumoniae, reaching MIC values of 0.53 µM in more diluted wells. These results are in good agreement with TEM internalization studies of bacteria that reveal significant internalization and damage in Streptococcus pneumoniae. In all the treatments carried out, the antibiotic capacity of gold nanosystems as enhancers of amoxicillin was demonstrated, causing both the precursors and the nanosystems to act very quickly, and thus favoring microbial death with a small amount of antibiotic. Therefore, these gold nanosystems may constitute an effective therapy to combat resistance to antibiotics, in addition to avoiding the secondary effects derived from the administration of high doses of antibiotics.

Gold Nanosystems Covered with Doxorubicin/DNA Complexes: A Therapeutic Target for Prostate and Liver Cancer.

Different gold nanosystems covered with DNA and doxorubicin (Doxo) were designed and synthesized for cancer therapy, starting from Au@16-Ph-16 cationic nanoparticles and DNA-Doxo complexes prepared under saturation conditions. For the preparation of stable, biocompatible, and small-sized compacted Au@16-Ph-16/DNA-Doxo nanotransporters, the conditions for the DNA-Doxo compaction process induced by gold nanoparticles were first explored using fluorescence spectroscopy, circular dichroism and atomic force microscopy techniques. The reverse process, which is fundamental for Doxo liberation at the site of action, was found to occur at higher CAu@16-Ph-16 concentrations using these techniques. Zeta potential, dynamic light scattering and UV-visible spectroscopy reveal that the prepared compacted nanosystems are stable, highly charged and of adequate size for the effective delivery of Doxo to the cell. This fact is verified by in vitro biocompatibility and internalization studies using two prostate cancer-derived cell lines (LNCaP and DU145) and one hepatocellular carcinoma-derived cell line (SNU-387), as well as a non-tumor prostate (PNT2) cell line and a non-hepatocarcinoma hepatoblastoma cell line (Hep-G2) model used as a control in liver cells. However, the most outstanding results of this work are derived from the use of the CI+NI combined treatments which present strong action in cancer-derived cell lines, while a protective effect is observed in non-tumor cell lines. Hence, novel therapeutic targets based on gold nanoparticles denote high selectivity compared to conventional treatment based on free Doxo at the same concentration. The results obtained show the viability of both the proposed methodology for internalization of compacted nanocomplexes inside the cell and the effectiveness of the possible treatment and minimization of side effects in prostate and liver cancer.

Use of Nanoparticles to Prevent Resistance to Antibiotics-Synthesis and Characterization of Gold Nanosystems Based on Tetracycline.

Antimicrobial resistance (AMR) is a serious public health problem worldwide which, according to the World Health Organization (WHO), requires research into new and more effective drugs. In this work, both gold nanoparticles covered with 16-3-16 cationic gemini surfactant (Au@16-3-16) and DNA/tetracycline (DNA/TC) intercalated complexes were prepared to effectively transport tetracycline (TC). Synthesis of the Au@16-3-16 precursor was carried out by using trihydrated gold, adding sodium borohydride as a reducing agent and the gemini surfactant 16-3-16 as stabilizing agent. Circular dichroism and atomic force microscopy techniques were then used to ascertain the optimal R range of the relationship between the concentrations of Au@16-3-16 and the DNA/TC complex (R = CAu@16-3-16/CDNA) that allow the obtainment of stable and compact nanosystems, these characteristics being fundamental for their use as antibiotic transporters. Stability studies over time were carried out for distinct selected Au@16-3-16 and Au@16-3-16/DNA-TC nanoformulations using the ultraviolet−visible spectrophotometry technique, checking their stability for at least one month. In addition, in order to know the charge and size distribution of the nanocomplexes, DLS and zeta potential measurements were performed in the solution. The results showed that the characterized nanosystems were highly charged, stable and of a reduced size (<100 nm) that allows them to cross bacterial membranes effectively (>1 µm). Once the different physicochemical characteristics of the gold nanosystems were measured, Au@16-3-16 and Au@16-3-16/DNA-TC were tested on Escherichia coli and Staphylococcus aureus to study their antibacterial properties and internalization capacity in microbes. Differences in the interaction of the precursors and the compacted nanosystems generated were observed in Gram-positive and Gram-negative bacteria, possibly due to membrane damage or electrostatic interaction with internalization by endocytosis. In the internalization experiments, depending on the treatment application time, the greatest bacterial destruction was observed for all nanoformulations explored at 18 h of incubation. Importantly, the results obtained demonstrate that both new nanosystems based on TC and Au@16-3-16 precursors have optimal antimicrobial properties and would be beneficial for use in patients, avoiding possible side effects.

Biocompatible DNA/5-Fluorouracil-Gemini Surfactant-Functionalized Gold Nanoparticles as Promising Vectors in Lung Cancer Therapy.

The design and preparation of novel nanocarriers to transport cancer drugs for chemotherapy purposes is an important line of research in the medical field. A new 5-fluorouracil (5-Fu) transporter was designed based on the use of two new biocompatible gold nanosystems: (i) a gold nanoparticle precursor, Au@16-Ph-16, stabilized with the positively charged gemini surfactant 16-Ph-16, and (ii) the compacted nanocomplexes formed by the precursor and DNA/5-Fu complexes, Au@16-Ph-16/DNA-5-Fu. The physicochemical properties of the obtained nanosystems were studied by using UV-visible spectroscopy, TEM, dynamic light scattering, and zeta potential techniques. Method tuning also requires the use of circular dichroism, atomic force microscopy, and fluorescence spectroscopy techniques for the prior selection of the optimal relative Au@16-Ph-16 and DNA concentrations (R = CAu@16-Ph-16/CDNA), biopolymer compaction/decompaction, and 5-Fu release from the DNA/5-Fu complex. TEM experiments revealed the effective internalization of the both precursor and Au@16-Ph-16/DNA-5-Fu-compacted nanosystems into the cells. Moreover, cytotoxicity assays and internalization experiments using TEM and confocal microscopy showed that the new strategy for 5-Fu administration enhanced efficacy, biocompatibility and selectivity against lung cancer cells. The differential uptake among different formulations is discussed in terms of the physicochemical properties of the nanosystems.

Reversible DNA compaction induced by partial intercalation of 16-Ph-16 gemini surfactants: evidence of triple helix formation.

The interaction between calf thymus DNA and the gemini surfactants N,N'-[α,ω-phenylenebis(methylene)bis [N,N'-dimethyl-N-(1-hexadecyl)]-ammonium dibromide], p-16-Ph-16 (α = 1, ω = 3) and m-16-Ph-16 (α = 1, ω = 2), has been investigated via circular dichroism, fluorescence and UV-vis spectroscopy, zeta potential, dynamic light scattering, and AFM microscopy. Measurements were carried out in aqueous media at different molar ratios, R = (C16-Ph-16)/CDNA and C16-Ph-16 always below the critical micellar concentration (CMC) of the surfactant. Under these conditions, DNA undergoes two reversible conformational changes, compaction and decompaction, due to interaction with the surfactant molecules at low and high molar ratios, respectively. The extent of such conformational changes is correlated with both the degree of surfactant partial intercalation, and the size and charge of the surfactant aggregates formed, in each case. Comparison of the results shows that the para-form of the surfactant intercalates into the DNA to a major extent; therefore, the compaction/decompaction processes are more effective. Among these, the structure of the resulting 16-Ph-16/DNA decompacted complex is worthy of note. For the first time it can be demonstrated that the partial intercalation of the 16-Ph-16 gemini surfactants induces the formation of triplex DNA-like structures at a high R ratio.

On the rearrangement of N-aryl-N-Boc-phosphoramidates to N-Boc-protected o-aminoarylphosphonates.

ABSTRACT: Various arylamines were converted in two steps to N-Boc-N-arylphosphoramidates. LiTMP and LDA induced directed ortho-metalation at temperatures from -78 to 0 °C. The ensuing [1,3]-migration of the phosphorus atom with its substituents from the nitrogen to the ortho-carbanionic carbon atom gave N-Boc-protected o-aminoarylphosphonates. The nature of the substituent of 3-substituted phenylphosphoramidates strongly influenced the regioselectivity of phosphonate formation. A crossover experiment with a deuterated phosphoramidate proved the intramolecular course of the rearrangement. Three representative N-Boc-o-aminoarylphosphonates were deprotected to access the corresponding o-aminoarylphosphonic acids.

Improving the understanding of DNA-propanediyl-1,3-bis(dodecyldimethylammonium) dibromide interaction using thermodynamic, structural and kinetic approaches.

A kinetic, thermodynamic and structural study of the interaction of the gemini surfactant propanediyl-1,3-bis(dimethyldodecylammonium dibromide) (12-3-12.2Br) with calf thymus DNA was carried out at several ionic strengths (NaCl) in aqueous solutions. A new 12-3-12(2+)-selective membrane was prepared in order to gain insight into the factors that control the binding of 12-3-12.2Br to DNA. We used ethidium bromide (EB) as a fluorescence probe to follow the kinetics of the interaction by using the stopped-flow fluorescence technique. The results can be explained in terms of a reaction mechanism involving two consecutive reversible (fast and slow) steps. The fast step was attributed to the union/separation of the surfactant with/from the DNA polynucleotide. Changes in the kinetic constants in the forward and backward directions were discussed in terms of the Brönsted-Pitzer equation and of the increase in hydrophobic interactions of the surfactant tails as a consequence of salting-out effects, respectively. The slow step corresponds to a conformational change of the surfactant-DNA complex to a more compacted form. The equilibrium constant, calculated from the forward and reverse rate constants of these steps, agrees with the results obtained from potentiometric titration using a 12-3-12-(2+) selective electrode.

Preparation of alpha-aminobenzylphosphonic acids with a stereogenic quaternary carbon atom via microscopically configurationally stable alpha-aminobenzyllithiums.

The enantiomers of 1-phenylethylamine were phosphorylated with diethyl chlorophosphate/Et(3)N and then Boc-protected (Boc=tert-butoxycarbonyl) at the nitrogen atom. These phosphoramidates were metalated by using sBuLi/N,N,N',N'-tetramethylethylenediamine (TMEDA) to give alpha-aminobenzyllithiums that isomerised to alpha-aminophosphonates in yields of up to 80 % with retention of the configuration at the carbon atom. The intermediate tertiary organolithiums were found to be microscopically configurationally stable from -78 to 0 degrees C in Et(2)O. The protected alpha-aminophosphonates were deblocked by using boiling 6 M HCl or preferably Me(3)SiBr/(allyl)SiMe(3). When the Boc group was replaced by the diethoxyphosphinyl group, the alpha-aminobenzyllithium intermediate partially enantiomerised even at -78 degrees C and rearranged to yield an alpha-aminophosphonate with 50 % ee (ee=enantiomeric excess). Similarly, N-Boc-protected phosphoramidates derived from racemates and/or enantiomers of 1-(1-naphthyl)ethyl-, 1-indanyl- and 1,2,3,4-tetrahydro-1-naphthylamine or 1-azidoindan- and 1-azido-1,2,3,4-tetrahydronaphthalene were converted to aminophosphonates in good yields. Deblocking gave alpha-aminophosphonic acids of excellent enantiomeric excess (97-99 %), as determined by means of HPLC on a chiral ion-exchange stationary phase based on quinine carbamate. When racemic Boc-protected diethyl phosphoramidate derived from 1,2,3,4-tetrahydro-1-naphthylamine was metalated with LiTMP/TMEDA (TMP=2,2,6,6-tetramethylpiperidine), 1-hydroxyethylphosphonamidates resulted. The configuration of the main isomer was determined by means of a single-crystal X-ray structure analysis.