Degradable polymers (DPs) - “green materials” of the future, have an innumerable use in biomedicine, particularly in the fields of tissue engineering and drug delivery. Among these kind of materials naturally occurring polymers - proteins which constituted one of the most important “bricks of life” - α-amino acids (AAs) are highly suitable. A wide biomedical applicability of proteins is due to special properties such as a high affinity with tissues and releasing AAs upon biodegradation that means a nutritive potential for cells. Along with these positive characteristics proteins as biomedical materials they have some shortcomings, such as batch-to-batch variation, risk of disease transmission, and immune rejection. The last limitation is connected with the molecular architecture of proteins. Furthermore, the content of only peptide bonds in protein molecules significantly restricts their material properties. Artificial polymers with the composition of AAs are by far more promising as degradable biomaterials since they are free from the limitations of proteins retaining at the same time their positive features - a high tissue compatibility and nutritive potential. The present review deals with a brief description of different families of AA-based artificial polymers, such as poly(amino acid)s, pseudo-poly(amino acid)s, polydepsipeptides, and pseudo-proteins - relatively new and broad family of artificial AA-based DPs. Most of these polymers have a different macromolecular architecture than proteins and contain various types of chemical links along with NH-CO bonds that substantially expands properties of materials destined for sophisticated biomedical applications.

The success of gene therapy depends on safe and effective gene carriers. Despite being widely used, synthetic vectors based on poly(ethylenimine) (PEI), poly(l-lysine) (PLL), or poly(l-arginine) (poly-Arg) are not yet fully satisfactory. Thus, both improvement of established carriers and creation of new synthetic vectors are necessary. A series of biodegradable arginine-based ether-ester polycations was developed, which consists of three main classes: amides, urethanes, and ureas. Compared to that of PEI, PLL, and poly-Arg, much lower cytotoxicity was achieved for the new cationic arginine-based ether-ester polymers. Even at polycation concentrations up to 2 mg/mL, no significant negative effect on cell viability was observed upon exposure of several cell lines (murine mammary carcinoma, human cervical adenocarcinoma, murine melanoma, and mouse fibroblast) to the new polymers. Interaction with plasmid DNA yielded compact and stable complexes. The results demonstrate the potential of arginine-based ether-ester polycations as nonviral carriers for gene therapy applications.

Combinatorially synthesized materials, especially cationic polymers (CPs), with gene transfection function hold great promise in nanotechnology. However, the main limitations of the existing CPs [such as polyethylenimine (PEI), poly-L-arginine, or polyamidoaminebased dendrimers] as gene transfection agents are high cytotoxicity in the physiological environment. We have developed novel CPs composed of polyaminesendogeneous tetraamine spermine (Spm) and synthetically made triamine N-(2-aminoethyl)-1,3-propanediamine (Apd) for incorporating sec-amino groups and imparting PEI-like structure to the CP backbones. Naturally occurring building blocks such as amino acid arginine (R) was also used for incorporating guanidine-groups into the CPs. The cytotoxicity of resulting CPspolyureas (PUs) and polyamides such as polysuccinamides and R-attached polymalamides was evaluated using murine and human fibroblasts and carcinoma cell lines. The cell compatibility screening revealed that the CPs made of Apd are less cytotoxic compared to Spm-based analogues. From the novel polymer library, total of six polymers were further studied for oligonucleotide (pDNA) complexation and transfection abilities. Highly water-soluble CPs formed nano-sized polyplexes with pDNA at rather low CP/pDNA weight ratios and showed less cytotoxicity and higher transfection ability compared to widely used PEI as well as commercially available transfection agents. Furthermore, new CPs showed selective transfection activity toward certain cell lines (4T1, HeLa, NIH3T3, and CCD 27SK), which is important for their potential applications in gene therapy.

Synthetic cationic polymers are of interest as both nonviral vectors for intracellular gene delivery and antimicrobial agents. For both applications synthetic polymers containing guanidine groups are of special interest since such kind of organic compounds/polymers show a high transfection potential along with antibacterial activity. It is important that the delocalization of the positive charge of the cationic group in guanidine significantly decreases the toxicity compared to the ammonium functionality. One of the most convenient ways for incorporating guanidine groups is the synthesis of polymers composed of the amino acid arginine (Arg) via either application of Arg-based monomers or chemical modification of polymers with derivatives of Arg. It is also important to have biodegradable cationic polymers that will be cleared from the body after their function as transfection or antimicrobial agent is fulfilled. This chapter deals with a two-step/one-pot synthesis of a new biodegradable cationic polymer-poly(ethylene malamide) containing L-arginine methyl ester covalently attached to the macrochains in β-position of the malamide residue via the α-amino group. The goal cationic polymer was synthesized by in situ interaction of arginine methyl ester dihydrochloride with intermediary poly(ethylene epoxy succinimide) formed by polycondensation of di-p-nitrophenyl-trans-epoxy succinate with ethylenediamine. The cell compatibility study with Chinese hamster ovary (CHO) and insect Schneider 2 cells (S2) within the concentration range of 0.02-500 mg/mL revealed that the new polymer is not cytotoxic. It formed nanocomplexes with pDNA (120-180 nm in size) at low polymer/DNA weight ratios (WR = 5-10). A preliminarily transfection efficiency of the Arg-containing new cationic polymer was assessed using CHO, S2, H5, and Sf9 cells.

Many peptide ligands of nicotinic acetylcholine receptors (nAChRs) contain a large number of positively charged amino acid residues, a striking example being conotoxins RgIA and GeXIVA from marine mollusk venom, with an arginine content of .30%. To determine whether peptides built exclusively from arginine residues will interact with different nAChR subtypes or with their structural homologs such as the acetylcholinebinding protein and ligand-binding domain of the nAChR a9 subunit, we synthesized a series of R3, R6, R8, and R16 oligoarginines and investigated their activity by competition with radioiodinated a-bungarotoxin, two-electrode voltageclamp electrophysiology, and calcium imaging. R6 and longer peptides inhibited muscle-type nAChRs, a7 nAChRs, and a3b2 nAChRs in the micromolar range. The most efficient inhibition of ion currents was detected for muscle nAChR by R16 (IC 50 5 157 nM) and for the a9a10 subtype by R8 and R16 (IC 50 5 44 and 120 nM, respectively). Since the R8 affinity for other tested nAChRs was 100-fold lower, R8 appears to be a selective antagonist of a9a10 nAChR. For R8, the electrophysiological and competition experiments indicated the existence of two distinct binding sites on a9a10 nAChR. Since modified oligoarginines and other cationic molecules are widely used as cell-penetrating peptides, we studied several cationic polymers and demonstrated their nAChR inhibitory activity. SIGNIFICANT STATEMENT By using radioligand analysis, electrophysiology, and calcium imaging, we found that oligoarginine peptides are a new group of inhibitors for muscle nicotinic acetylcholine receptors (nAChRs) and some neuronal nAChRs, the most active being those with 16 and 8 Arg residues. Such compounds and other cationic polymers are cell-penetrating tools for drug delivery, and we also demonstrated the inhibition of nAChRs for several of the latter. Possible positive and negative consequences of such an action should be taken into account.