Poly(ethylene Oxide)-Modified Polyaspartamide–Ferrocene Conjugates

In continuation of earlier investigations of polymer–ferrocene conjugates for biomedical applications, this article deals with conjugates prepared by N-acylation of linear, amine-functionalized polyaspartamide carriers with 4-ferrocenylbutanoic acid. Acylation is brought about both by mediation of HBTU coupling agent and by the N-hydroxysuccinimide active ester method. The polymeric carriers contain oligo- or poly(ethylene oxide) side chains introduced here for enhancement of water solubility. The longer side chains, in addition, are to impart such biomedically important properties as increased resistance to uptake by the reticuloendothelial system and to protein binding, extended circulation life time, and lowered immunogenicity. The conjugates comprise from 10 to 25 mol% ferrocenylated subunits, corresponding to ca. 2–5% Fe by mass. Freshly prepared and isolated in the solid state, they dissolve smoothly in aqueous media, with upper concentration limits (>0.2g/ml) dictated solely by their viscosity behavior. The conjugates are of interest in biomedical applications.     

Water-Soluble Monoamineplatinum(II) Complexes Bound to Polyaspartamide Carriers by a Poly(ethylene Oxide) Spacer

In continuation of earlier work in this laboratory comprising the synthesis of water-soluble polyaspartamide-monoamineaquadichloroplatinum conjugates as potential antineoplastic agents, the presently described project is concerned with related conjugates in which the same type of monoamineplatinum complex unit is bound to polyaspartamide carriers via main chain-attached poly(ethylene oxide) (PEO) spacers introduced here in order to improve certain biomedical performance features. The conjugates are synthesized by aqueous-phase platination of amine terminals on the PEO side chains of the carriers, brought about by treatment with tetrachloroplatinate(II) anion under closely controlled conditions of time, temperature, and acidity, followed by dialysis. The target polymers, separated by freeze-drying, are completely water soluble upon isolation, yet undergo slow intermolecular interaction in the solid state with a gradual loss of solubility unless stored in (frozen) aqueous solution at –30°C.     

cis-Diaminedichloroplatinum(II) complexes reversibly bound to water-soluble polyaspartamide carriers for chemotherapeutic applications. II: Platinum coordination to ethylenediamine ligands attached to poly(ethylene oxide)-grafted carrier polymers

In continuation of previous investigations aiming at the development of macromolecular metal complexes for biomedical use, this communication describes poly(alkylene oxide)-grafted polymeric platinum complexes. The platinum-containing macromolecules are obtained from presynthesized polyaspartamide carriers bearing poly(ethylene/propylene oxide) side chains and hydroxyethyl side groups as hydrosolubilizing units in addition to ethylenediamine side group terminals for metal coordination. Platination is brought about by treatment of the carriers with tetrachloroplatinate(II) ion in aqueous solution at 25–60°C. pH 4–6. The polymeric products, purified by dialysis in aqueous solution, are isolated by freeze-drying in yields of 60–80%. Platinum contents are in the range of 4–15%. The metal is bound to the carrier through chelation with the ethylenediamine ligands, forming square-planarcis-dichloroethylenediamine-platinum(II) complex species as side-chain terminals. Initially, the product polymers dissolve smoothly in water. Although on room-temperature storage in the solid state they gradually turn insoluble as a consequence of intermolecular solid-state interaction, solubility is retained on low-temperature storage and in frozen aqueous solutions.Presented in part at the Fifth International Symposium on Macromolecule-Metal Complexes. September 29–October 3, 1993. Bremen, Germany. For Part I of this Series, see Ref. 1.     

Polymer–Ferrocene Conjugates Containing an Ester Function in the Connecting Links

Ferrocene, the parent of the metallocene family of organotransition metal compounds, has come to occupy a significant niche in cancer research. Developmental work in the authors' laboratory has been focused on the synthesis of antiproliferative ferrocene conjugates in which the bioactive ferrocene unit is covalently, yet bioreversibly bound (anchored) to water-soluble carrier polymers designed in accordance with requisite biomedical specifications. The anchoring link in most of these conjugates has been an aliphatic spacer containing the biofissionable amide group. In this communication the synthesis of a class of ferrocene conjugates is reported in which the ferrocene group is carrier-anchored through spacers containing an ester link, of interest here because of potentially different drug release behavior. The carriers are polyamides equipped with variously spaced hydroxyl side groups, to which the ferrocenylation agent, 4-ferrocenylbutanoic acid, is connected through esterification. The coupling reactions, mediated by carbodiimide agent and catalyzed by 4-(dimethylamino)pyridine, are carried out in DMF at temperatures not exceeding 65°C, and the water-soluble product polymers are isolated in yields of typically 70–85% by precipitation, aqueous dialysis, and freeze-drying. With the molar feed ratios chosen in these coupling experiments, the incorporation of ferrocene, assessed by ¹H NMR spectroscopy, corresponds to iron contents of roughly 2.5–5.5%, by mass. The conjugates will be included in a forthcoming bioactivity screening program.     

Hydrogels prepared from polysiloxane chains by end linking them with trifunctional silanes containing hydrophilic groups

A strongly hydrophobic polymer was converted into a hydrogel by introducing hydrophilic side chains of sufficient lengths and amounts to overcome the hydrophobicity but sufficiently well dispersed to avoid disadvantages such as loss of the transparency required in applications. Specifically, poly(dimethylsiloxane) (PDMS) hydrogels were successfully prepared by end linking a combination of long and short chains to give the bimodal distributions of network chain lengths that generally give unusually good mechanical properties. The end linkers were chosen using trialkoxylsilanes R′Si(OR)₃ having R′ side chains that are hydrophilic of variable lengths and of sufficient hydrophilicity to produce the desired hydrogels. The first trialkoxysilane was N-(triethoxysilylpropyl)-O-polyethylene oxide urethane (S1) with 4–6 units of ethylene glycol, and the second was [methyoxy(polyethyleneoxy)propyl]-trimethoxysilane (S2) with 6–9 units of ethylene glycol, and they were used to end link hydroxyl-terminated PDMS chains in standard room-temperature condensation reactions. It was possible to introduce the hydrophilic side chains into the hydrophobic networks without discernible phase separation. These linear side chains increase equilibrium water contents, from 0 to 11.2 wt% in the first series and from 0 to 29.8 wt% in the second. Longer hydrophilic chains clearly migrated to the surfaces of the resulting PDMS hydrogels to give reduction in static contact angles from 105° to 40° for the first series, and to 80° for the second. The longer hydrophilic chains were found to give larger decreases in the contact angles and larger equilibrium water contents. The mechanical properties demonstrated that Young's moduli of the hydrogels did not change upon introduction of the S1 hydrophilic cross linker, but did decrease from the presence of the S2. The tensile strength and elongation at break were relatively insensitive to the amounts of either of the hydrophilic groups.     

Anticoagulant Oligonucleotide–Peptide Conjugates: Identification of Thrombin Aptamer Conjugates with Improved Characteristics

Oligonucleotide–peptide conjugates (OPCs) are a promising class of biologically active compounds with proven potential for improving nucleic acid therapeutics. OPCs are commonly recognized as an efficient instrument to enhance the cellular delivery of therapeutic nucleic acids. In addition to this application field, OPCs have an as yet unexplored potential for the post-SELEX optimization of DNA aptamers. In this paper, we report the preparation of designer thrombin aptamer OPCs with peptide side chains anchored to a particular thymidine residue of the aptamer. The current conjugation strategy utilizes unmodified short peptides and support-bound protected oligonucleotides with activated carboxyl functionality at the T3 thymine nucleobase. The respective modification of the oligonucleotide strand was implemented using N3-derivatized thymidine phosphoramidite. Aptamer OPCs retained the G-quadruplex architecture of the parent DNA structure and showed minor to moderate stabilization. In a series of five OPCs, conjugates bearing T3–Ser–Phe–Asn (SFN) or T3–Tyr–Trp–Asn (YWN) side chains exhibited considerably improved anticoagulant characteristics. Molecular dynamics studies of the aptamer OPC complexes with thrombin revealed the roles of the amino acid nature and sequence in the peptide subunit in modulating the anticoagulant activity.     

Antiproliferative Activity of Polymer-Bound, Monoamine-Coordinated Platinum Complexes Against LNCaP Human Metastatic Prostate Adenocarcinoma Cells

The chemotherapeutic treatment of secondary, i.e., disseminated cancers, has until now remained an unsatisfactory modality. The LNCaP human metastatic prostate adenocarcinoma cell line lends itself as a useful tool to probe the efficaciousness of novel antineoplastic agents for the control of metastatic cell growth. In this paper we report on a series of cell culture tests assessing the antiproliferative activity of several water-soluble polymer–platinum conjugates in which the metal is tied (anchored) to various polymeric carriers through coordination by a single carrier-attached primary amine ligand. The conjugates are based on polyaspartamide carriers composed, within the backbone, of a majority fraction of subunits bearing water-solubilizing tertiary amine side-group functions and a minority fraction of subunits featuring side chain-terminating primary amino groups for metal binding. Two similarly structured conjugates in which the platinum center is coordinated by two amine ligands in cisoid orientation mimicking the structural skeleton of cisplatin are included in the study for comparison. In all structures cleavage of a side-chain segment is required for release of the monomeric bioactive platinum complex. The growth of LNCaP human metastatic prostate adenocarcinoma cells in RPMI 1640 medium in the presence and absence of the conjugates in a range of concentrations is assessed by a protein assay, and the IC₅₀ values, representing the drug concentrations required for 50% cell growth inhibition relative to untreated control, are determined. The results show both classes of conjugates, those comprising monoamine-coordinated platinum and those featuring cis-diamine-coordinated metal, to be well comparable in antiproliferative activity. A major program of synthesis and evaluation of polymer-bound monoamineplatinum complexes, prompted by these findings, is forthcoming in this laboratory.     

cis-Diaminedichloroplatinum(II) complexes reversibly bound to water-soluble polyaspartamide carriers for chemotherapeutic applications. II: Platinum coordination to ethylenediamine ligands attached to poly(ethylene oxide)-grafted carrier polymers

In continuation of previous investigations aiming at the development of macromolecular metal complexes for biomedical use, this communication describes poly(alkylene oxide)-grafted polymeric platinum complexes. The platinum-containing macromolecules are obtained from presynthesized polyaspartamide carriers bearing poly(ethylene/propylene oxide) side chains and hydroxyethyl side groups as hydrosolubilizing units in addition to ethylenediamine side group terminals for metal coordination. Platination is brought about by treatment of the carriers with tetrachloroplatinate(II) ion in aqueous solution at 25–60°C. pH 4–6. The polymeric products, purified by dialysis in aqueous solution, are isolated by freeze-drying in yields of 60–80%. Platinum contents are in the range of 4–15%. The metal is bound to the carrier through chelation with the ethylenediamine ligands, forming square-planarcis-dichloroethylenediamine-platinum(II) complex species as side-chain terminals. Initially, the product polymers dissolve smoothly in water. Although on room-temperature storage in the solid state they gradually turn insoluble as a consequence of intermolecular solid-state interaction, solubility is retained on low-temperature storage and in frozen aqueous solutions.     

Synthesis,Properties and Applications of Biodegradable Polymers Derived from Diols and Dicarboxylic Acids: From Polyesters to Poly(ester amide)s

Poly(alkylene dicarboxylate)s constitute a family of biodegradable polymers with increasing interest for both commodity and speciality applications. Most of these polymers can be prepared from biobased diols and dicarboxylic acids such as 1,4-butanediol, succinic acid and carbohydrates. This review provides a current status report concerning synthesis, biodegradation and applications of a series of polymers that cover a wide range of properties, namely, materials from elastomeric to rigid characteristics that are suitable for applications such as hydrogels, soft tissue engineering, drug delivery systems and liquid crystals. Finally, the incorporation of aromatic units and α-amino acids is considered since stiffness of molecular chains and intermolecular interactions can be drastically changed. In fact, poly(ester amide)s derived from naturally occurring amino acids offer great possibilities as biodegradable materials for biomedical applications which are also extensively discussed.     

Synthesis,characterization, and biomedical applications of core–shell-type stimuli-responsive nanogels – Nanogel composed of poly[2-(N,N-diethylamino)ethyl methacrylate] core and PEG tethered chains

We present a review of stimuli-responsive smart PEGylated nanogels and their biomedical applications. We describe the synthesis and characterization of stimuli-responsive PEGylated nanogels composed of a cross-linked poly[2-(N,N-diethylamino)ethyl methacrylate] (PDEAMA) core and PEG tethered chains that bear a carboxylic acid group as a platform moiety for the installation of bio-tags. In addition, PEGylated nanogels show unique properties and functions in synchronizing with the reversible volume phase transition of the PDEAMA core in response to various stimuli, such as pH, ionic strength and temperature. We list some of the biomedical applications of the nanogels, including endosomolytic agents for nonviral gene delivery, drug delivery carriers, nanoreactors, and skin-specific nanocatalysts for reactive oxygen species (ROS).