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.

Aggregation and particle formation of tRNA by dendrimers.

Major attention has been focused on dendrimer-DNA complexes because of their applications in gene delivery systems. Dendrimers are also used to transport miRNA and siRNA in vitro. We examine the interaction of tRNA with several dendrimers of different compositions, mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) under physiological conditions using constant tRNA concentration and various dendrimer contents. FTIR, UV-visible, and CD spectroscopic methods as well as atomic force microscopy (AFM) were used to analyze the macromolecule binding mode, the binding constant, and the effects of dendrimer complexation on RNA stability, aggregation, particle formation, and conformation. Structural analysis showed that dendrimer-tRNA complexation occurred via RNA bases and the backbone phosphate group with both hydrophilic and hydrophobic contacts. The overall binding constants of K(mPEG-G3) = 7.6 (± 0.9) × 10(3) M(-1), K(mPEG-G4) = 1.5 (± 0.40) × 10(4) M(-1), and K(PAMAM-G4) = 5.3 (± 0.60) × 10(4) M(-1) show stronger polymer-RNA complexation by PAMAM-G4 than pegylated dendrimers. RNA remains in the A-family structure, whereas biopolymer aggregation and particle formation occurred at high polymer concentrations.