Keto-Functionalized Polymer Scaffolds As Versatile Precursors to Polymer Side Chain Conjugates.

A new methacrylate monomer with a reactive ketone side-chain, 2-(4-oxo-pentanoate) ethyl methacrylate (PAEMA), was synthesized and subsequently polymerized by reversible addition-fragmentation chain transfer (RAFT) polymerization to give a polymer with a narrow molecular weight distribution (PDI = 1.25). The polymer was chain extended with poly(ethylene glycol methyl ether acrylate) (PEGMA) to yield a block copolymer. Aminooxy containing small molecules and oligoethylene glycol were conjugated to the ketone functionality of the side chain in high yields. Cytotoxicity of the oxime-linked tetra(ethylene glycol) polymer to mouse fibroblast cells was investigated; the polymer was found to be non-cytotoxic up to 1 mg/mL. The ease with which this polymer is functionalized, suggests that it may be useful in forming tailored polymeric medicines.

Two-step synthesis of multivalent cancer-targeting constructs.

Selective targeting of constructs to pathological cells by conjugating one or more ligands for an overexpressed receptor has been proposed to enhance the delivery of therapeutics to and imaging of specific cells of interest. Previous work in our lab has demonstrated the efficacy of targeting glioblastoma cells with a multivalent, biomacromolecular construct targeted to the alpha(6)beta(1)-integrin. However, solid-phase synthesis of this construct was inefficient in terms of cost and number of steps. Here we show proof-of-concept of a two-step synthesis that can be used to create similar constructs targeted to glioblastoma cells. Specifically, a well-defined aldehyde side chain polymer was synthesized and oxime chemistry was employed to conjugate ligands specific for the alpha(6)beta(1)-integrin. These constructs were then tested in competitive binding, fluorescence binding, and toxicity assays, through which we demonstrate that constructs are multivalent, preferentially target glioblastoma cells, and are nontoxic. Rapid, potentially low-cost synthesis of targeting constructs will enable their use in the clinic and for personalized medicine.

Synthesis of a photo-caged aminooxy alkane thiol.

A photo-caged aminooxy alkane thiol synthesized in 7 steps and 15% overall yield was used to form a self-assembled monolayer (SAM). Photo-deprotection on the surface was confirmed by FT-IR spectroscopy and contact angle goniometry. Conjugation of a small molecule ketone, ethyl levulinate, further confirmed the presence of aminooxy groups on the surface.

Positioning multiple proteins at the nanoscale with electron beam cross-linked functional polymers.

Constructing multicomponent protein structures that match the complexity of those found in nature is essential for the next generation of medical materials. In this report, a versatile method for precisely arranging multicomponent protein nanopatterns in two-dimensional single-layer or three-dimensional multilayer formats using electron beam lithography is described. Eight-arm poly(ethylene glycol)s (PEGs) were modified at the chain ends with either biotin, maleimide, aminooxy, or nitrilotriacetic acid. Analysis by 1H NMR spectroscopy revealed that the reactions were efficient and that end-group conversions were 91-100%. The polymers were then cross-linked onto Si surfaces using electron beams to form micron-sized patterns of the functional groups. Proteins with biotin binding sites, a free cysteine, an N-terminal alpha-oxoamide, and a histidine tag, respectively, were then incubated with the substrate in aqueous solutions without the addition of any other reagents. By fluorescence microscopy experiments it was determined that proteins reacted site-specifically with the exposed functional groups to form micropatterns. Multicomponent nanoscale protein patterns were then fabricated. Different PEGs with orthogonal reactivities were sequentially patterned on the same chip. Simultaneous assembly of two different proteins from a mixture of the biomolecules formed the multicomponent two-dimensional patterns. Atomic force microscopy demonstrated that nanometer-sized polymer patterns were formed, and fluorescence microscopy demonstrated that side-by-side patterns of the different proteins were obtained. Moreover, multilayer PEG fabrication produced micron- and nanometer-sized patterns of one functional group on top of the other. Precise three-dimensional arrangements of different proteins were then realized.

Nanoscale growth factor patterns by immobilization on a heparin-mimicking polymer.

In this study, electrostatic interactions between sulfonate groups of an immobilized polymer and the heparin binding domains of growth factors important in cell signaling were exploited to nanopattern the proteins. Poly(sodium 4-styrenesulfonate-co-poly(ethylene glycol) methacrylate) (pSS-co-pPEGMA) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using ethyl S-thiobenzoyl-2-thiopropionate as a chain transfer agent and 2,2'-azoisobutyronitrile (AIBN) as the initiator. The resulting polymer (1) was characterized by 1H NMR, GPC, FT-IR, and UV-vis and had a number average molecular weight (Mn) of 24,000 and a polydispersity index (PDI) of 1.17. The dithioester end group of 1 was reduced to the thiol, and the polymer was subsequently immobilized on a gold substrate. Binding of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) to the polymer via the heparin binding domains was then confirmed by surface plasmon resonance (SPR). The interactions were stable at physiological salt concentrations. Polymer 1 was cross-linked onto silicon wafers using an electron beam writer forming micro- and nanopatterns. Resolutions of 100 nm and arbitrary nanoscale features such as concentric circles and contiguous squares and triangles were achieved. Fluorescence microscopy confirmed that bFGF and VEGF were subsequently immobilized to the polymer micro- and nanopatterns.

Reactive block copolymer scaffolds.

Block copolymers with sequences of differential reactivity were synthesized, and the step-wise and selective derivatization to form a new block copolymer was demonstrated.

Well-defined polymers with activated ester and protected aldehyde side chains for bio-functionalization.

Polymers with reactive side chains and narrow molecular weight distributions were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, and the potential to utilize these polymers to prepare drug carriers was demonstrated. p-Nitrophenyl methacrylate (NPMA) and diethoxypropyl methacrylate (DEPMA) were polymerized utilizing cumyl dithiobenzoate (CDB) as the chain transfer agent and azobisisobutyronitrile (AIBN) as the initiator to high conversions (> or = 86%). The resulting pNPMA and pDEPMA had narrow molecular weight distributions (polydispersity indices < 1.3). The ability to functionalize these polymers was confirmed. For pNPMA, up to 86% of the side chains were substituted with the amino acid, glycine methyl ester. The side chains of pDEPMA were hydrolyzed to aldehydes and reaction with O-benzylhydroxylamine and O-methylhydroxylamine to form stable oxime bond conjugates was demonstrated. The percent substitution depended on the feed ratios. Conjugation of an aminooxy-functionalized RGD peptide was also demonstrated.

One-step synthesis of low polydispersity, biotinylated poly(N-isopropylacrylamide) by ATRP.

Low polydispersity poly(N-isopropylacrylamide) with a biotin end-group was obtained in one step from a biotinylated initiator for atom transfer radical polymerization and interacted with streptavidin to generate the thermosensitive polymer-protein conjugate.

Phosphine-catalyzed synthesis of 6-substituted 2-pyrones: manifestation of E/Z-isomerism in the zwitterionic intermediate.

[reaction: see text] We report a one-step phosphine-catalyzed annulation between aldehydes and ethyl allenoate to form 6-substituted 2-pyrones. The mechanistic rationale for this reaction requires explicit discussion of the E/Z-isomerism of the zwitterionic intermediate formed by the addition of a phosphine to the allenoate. Sterically demanding trialkylphosphines facilitate the shift of equilibrium toward the E-isomeric zwitterion and lead to the formation of 6-substituted 2-pyrones. Various aromatic as well as aliphatic aldehydes undergo the transformation in moderate to excellent yield.

Post-antibiotic effect induced by an antibiotic combination: influence of altered susceptibility to individual components.

OBJECTIVES: The impact of altered susceptibility of an organism to the components of an antibiotic combination on post-antibiotic effect (PAE) was studied. METHODS: The baseline PAEs expressed by Pseudomonas aeruginosa ATCC 27853 were recorded following 1 h of exposure to piperacillin and gentamicin, alone and in combination. Similar PAE assessments were made after resistance to the individual antibiotics was induced over 0.5-2x of their respective MIC. RESULTS: Before any induction, the PAE produced by piperacillin alone was negligible and that by the combination was synergistic. After piperacillin resistance was induced, PAE exhibited by the beta-lactam remained negligible, and comparable PAEs were observed for gentamicin and the combination, suggesting an additive interaction with a dominant effect from gentamicin. When resistance was induced against gentamicin, progressively shorter PAE was expressed by the aminoglycoside alone and the combination at increasing levels of resistance. In addition, a measurable PAE was unexpectedly observed for piperacillin, whereas the interaction also became additive. CONCLUSIONS: In summary, the PAE expressed by the test combination was highly dependent on the status of gentamicin resistance. The resistance profile exhibited by the organism against individual antibiotics of the combination showed an impact on the type of interaction expressed.

Post-antibiotic effect induced by an antibiotic combination: influence of mode, sequence and interval of exposure.

OBJECTIVES: The effects of mode, sequence and interval of antibiotic exposure on the post-antibiotic effect (PAE) induced by rifampicin and tobramycin were studied using Escherichia coli ATCC 25922 as the test organism. METHODS: In triplicate, baseline PAEs were evaluated by exposing E. coli to rifampicin and tobramycin individually and simultaneously for 1 h. PAEs were further assessed in a second study, with the organism exposed first to rifampicin for 1 h, followed by a second 1 h tobramycin exposure, commencing at the beginning, middle and end of the PAE phase induced by rifampicin. The third study was similar to the above, but with the sequence of the two antibiotics reversed, i.e. tobramycin then rifampicin. RESULTS: The PAE produced by simultaneous exposure of the combination showed an apparent additive interaction (PAE: 5.0+/-0.3 h) when compared with the PAE of individual antibiotics (rifampicin alone: 3.0+/-0.1 h; tobramycin alone: 1.5+/-0.1 h). However, an antagonistic interaction was observed in the second study, with a more pronounced degree of antagonism at the beginning, dissipating towards the end of the previous rifampicin PAE (PAE at the beginning: 2.6+/-0.3 h; the middle: 1.5+/-0.2 h; and at the end: 1.7+/-0.3 h). By subtracting the residual contribution from the first rifampicin exposure, the net average PAEs attributed to the second tobramycin exposure actually increased, from -0.4 to 1.7 h from the beginning to the end of the rifampicin PAE. For the third study, an additive interaction was again observed when the organism was exposed to tobramycin first (PAE at the beginning: 4.7+/-0.4 h; the middle: 3.7+/-0.7 h; and at the end: 3.1+/-0.4 h). The timing of the second rifampicin exposure had no impact to the interaction; after correction, the net mean PAEs attributed to the second rifampicin exposure were maintained at 3.2, 3.2 and 3.1 h. CONCLUSIONS: The present data suggest that the expression of interaction type on PAE by an antibiotic combination was dependent on the mode, sequence and interval of exposure. The impact of these variables should not be overlooked when clinical dosing regimens are optimized.

Retention of 125I-labeled recombinant human bone morphogenetic protein-2 by biphasic calcium phosphate or a composite sponge in a rabbit posterolateral spine arthrodesis model.

The purpose of this study was to characterize the retention kinetics of recombinant human bone morphogenetic protein-2 (rhBMP-2) applied to two calcium-based delivery matrices. Biphasic calcium phosphate (BCP) and a composite containing BCP in an absorbable collagen sponge (BCP/ACS) were evaluated using a spinal fusion model in rabbits. rhBMP-2 labeled with radioactive iodine (125I) was used as a tracer to assess in vivo retention of rhBMP-2 in the presence of these materials (nine animals per material studied). Over a 36 day study period, animals were assessed for the following: percent administered dose retained at the implant site as measured by scintigraphic imaging (counting) with a gamma camera (all animals), radiography of the implant site (all animals), radioactivity in blood and plasma (all animals), and radioactivity in the urine and feces (three animals for each material). Radioactivity data were corrected for the decay of 125I and the attenuation between the implant in vivo and the gamma camera. Differences observed between the two materials for the area under the retention vs. time profile (AUC; 988%*day for BCP vs. 1070%*day for BCP/ACS, p = 0.57) and the mean residence time (MRT; 10.2 days for BCP vs. 7.6 days for BCP/ACS, p = 0.06) were not statistically significant. Initial retention/incorporation of rhBMP-2 was slightly higher for rhBMP-2/BCP/ACS than for rhBMP-2/BCP (96.8% vs. 86.0%, p < 0.05). Animals receiving rhBMP-2/BCP showed a longer terminal retention half-life (t1/2) than did those receiving rhBMP-2/BCP/ACS (7.5 vs. 4.5 days, p < 0.05). The urinary radioactivity recovery data supported the data obtained by scintigraphy. Over the 36 day collection period, essentially complete recovery of radioactivity (dose) in urine was observed for rhBMP-2/BCP and rhBMP-2/BCP/ACS and the majority of the radioactivity (approximately 95%) was soluble in trichloroacetic acid, suggesting extensive catabolism of rhBMP-2 before renal excretion. Fecal recovery of radioactivity was low, approximately 2-3%. In conclusion, rhBMP-2 was retained at the implant site when delivered with either BCP or BCP/ACS based on mean residence time and area under the retention curve vs. time profile. Use of these matrices resulted in detectable rhBMP-2 levels at the surgical site for over a week in contrast to data reported with several other matrices that lasted less time. Systemic catabolism and elimination of the rhBMP-2 was extensive and systemic presence of the protein was negligible.