Biomedical subjects

Hamidreza Ghandehari

Publications and source records attributed to Hamidreza Ghandehari.

At least 19 recordsLinked to original sources

PubMed2006

Transport of poly(amidoamine) dendrimers across Caco-2 cell monolayers: Influence of size, charge and fluorescent labeling.

PURPOSE: To investigate the transport of poly(amidoamine) (PAMAM) dendrimers with positive, neutral and negatively charged surface groups across Caco-2 cell monolayers. METHODS: Cationic PAMAM-NH2 (G2 and G4), neutral PAMAM-OH (G2), and anionic PAMAM-COOH (G1.5-G3.5) dendrimers were conjugated to fluorescein isothiocyanate (FITC). The permeability of fluorescently labeled PAMAM dendrimers was measured in the apical-to-basolateral direction. 14C-Mannitol permeability was measured in the presence of unlabeled and FITC labeled PAMAM dendrimers. Caco-2 cells were incubated with the dendrimers followed by mouse anti-occludin or rhodamine phalloidin, and visualized using confocal laser scanning microscopy to examine tight junction integrity. RESULTS: The overall rank order of PAMAM permeability was G3.5COOH > G2NH2 > G2.5COOH > G1.5COOH > G2OH. 14C-Mannitol permeability significantly increased in the presence of cationic and anionic PAMAM dendrimers with significantly greater permeability in the presence of labeled dendrimers compared to unlabeled. PAMAM dendrimers had a significant influence on tight junction proteins occludin and actin, which was microscopically evidenced by disruption in the occludin and rhodamine phalloidin staining patterns. CONCLUSIONS: These studies demonstrate that enhanced PAMAM permeability is in part due to opening of tight junctions, and that by appropriate engineering of PAMAM surface chemistry it is possible to increase polymer transepithelial transport for oral drug delivery applications.

Actins↗

PubMed2006

Polymeric conjugates of mono- and bi-cyclic alphaVbeta3 binding peptides for tumor targeting.

The alphaVbeta3 integrin plays important roles in tumor-induced angiogenesis and tumor metastasis and hence, many small molecule alphaVbeta3 ligands have been developed for cancer diagnosis and therapy. Although these show good alphaVbeta3 targeting, most have suboptimal pharmacokinetics and show rapid tumor washout. We studied the biodistribution and tumor targeting properties of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer based conjugates of mono-(RGDfK) and doubly cyclized (RGD4C) alphaVbeta3 binding peptides. Endothelial cell adhesion studies showed similar affinity of HPMA-RGD4C and HPMA-RGDfK conjugate for alphaVbeta3 integrins. Scintigraphic images of tumor bearing mice demonstrated that both conjugates showed tumor localization at 24 h post-injection and were retained at the tumor site until 192 h, whereas the efficient background clearance was observed over time. Necropsy organ counts showed that tumor accumulation of both HPMA-RGD4C and HPMA-RGDfK conjugates increased over time with peak accumulations at 4.9 +/- 0.9% and 5.0 +/- 1.2% ID/g, respectively. In contrast the background organ distribution rapidly cleared over time resulting in significant increases of tumor-to-background ratios. The radioactive dose as indicated by the area under curve (HPMA-RGD4C: 4825.3 microCi/g h and HPMA-RGDfK: 4424.9 microCi/g h) was highest for the tumor. The polymer conjugates of RGD4C or RGDfK provide a means to enhance tumor uptake, decrease background accumulation, and enable selective delivery of therapeutic or diagnostic agents to tumor sites.

Amino Acid Sequence↗

PubMed2006

Template synthesis of multifunctional nanotubes for controlled release.

In the past few decades, nanoscale materials have been widely used for controlled release applications. Importantly, many researches have focused on multifunctional nanoparticles for targeted delivery of bioactive and imaging agents as therapeutics and diagnostics. Recent advances in nanotechnology have made possible the design and development of tubular nanoscale particles called nanotubes. The tubular shape of such particles is highly attractive since it is possible to differentially functionalize the inner and outer surfaces to facilitate drug loading, biocompatibility and biorecognition. Novel synthetic strategies allow the fabrication of tubular structures with well-defined diameters and lengths. This can have important implications in biodistribution, subcellular trafficking and drug release. In this article the biomedical applications of nanotubes will be discussed with emphasis on the template synthesis of composite nanotubes containing silica and iron oxide that have potential use in drug delivery, magnetic resonance imaging (MRI), and chemical and biochemical separations.

Animals↗

PubMed2006

Polymer-peptide conjugates for angiogenesis targeted tumor radiotherapy.

INTRODUCTION: New methods of delivering radiotherapy to sites of occult or disseminated cancer are needed to control the disease and address the failure of conventional therapy. Because tumor cells rely on angiogenesis for survival, we assessed the effectiveness of beta-emitter radiotherapy delivered by polymer-peptide conjugates that target tumor neovasculature. This molecularly targeted radiation is intended to damage both the endothelial bed and surrounding neoplastic cells. METHODS: N-(2-Hydroxypropyl) methacrylamide (HPMA), a biocompatible and water-soluble copolymer, was derivatized to incorporate side chains for (99m)Tc and (90)Y chelation and was further conjugated to a alpha(V)beta(3) integrin-targeting peptide (RGD4C). The HPMA copolymer-RGD4C conjugate was characterized by its side-chain contents, in vitro endothelial cell adhesion assay and its biodistribution and antitumor effectiveness in a SCID mouse xenograft model of human prostate carcinoma. RESULTS: The conjugate contained about 16 RGD4C moieties per polymer backbone. Tumor accumulation significantly increased (P < .01) over time from 1.05 +/- 0.03 % injected dose (%ID)/g tissue at 1 h to 4.32 +/-0.32% at 72 h. The activity in major normal tissues significantly decreased (P < .05) during that period. At 21 days, the control tumors increased 442% in volume from baseline. In contrast, a 7% and a 63% decrease of tumor volume were observed for the 100- and 250-microCi (90)Y treatment groups, respectively. Histopathological examination revealed increased apoptosis in the treated tumors with no acute signs of radiation-induced toxicity to other organs. CONCLUSION: This copolymer-peptide conjugate targets tumor angiogenic vessels and delivers sufficient radiotherapy to arrest tumor growth.

Animals↗

PubMed2006

Nanocarriers for nuclear imaging and radiotherapy of cancer.

Several nanoscale carriers (nanoparticles, liposomes, water-soluble polymers, micelles and dendrimers) have been developed for targeted delivery of cancer diagnostic and therapeutic agents. These carriers can selectively target cancer sites and carry large payloads, thereby improving cancer detection and therapy effectiveness. Further, the combination of newer nuclear imaging techniques providing high sensitivity and spatial resolution such as dual modality imaging with positron emission tomography/computed tomography (PET/CT) and use of nanoscale devices to carry diagnostic and therapeutic radionuclides with high target specificity can enable more accurate detection, staging and therapy planning of cancer. The successful clinical applications of radiolabeled monoclonal antibodies for cancer detection and therapy bode well for the future of nanoscale carrier systems in clinical oncology. Several radiolabeled multifunctional nanocarriers have been effective in detecting and treating cancer in animal models. Nonetheless, further preclinical, clinical and long-term toxicity studies will be required to translate this technology to the care of patients with cancer. The objective of this review is to present a brief but comprehensive overview of the various nuclear imaging techniques and the use of nanocarriers to deliver radionuclides for the diagnosis and therapy of cancer.

Animals↗

PubMed2005

Transepithelial and endothelial transport of poly (amidoamine) dendrimers.

This article summarizes our efforts to evaluate the potential of poly (amidoamine) (PAMAM) dendrimers as carriers for oral drug delivery. Specifically, the permeability of a series of cationic PAMAM-NH2 (G0-G4) dendrimers across Caco-2 cell monolayers was evaluated as a function of dendrimer generation, concentration, and incubation time. The influence of dendrimer surface charge on the integrity, paracellular permeability, and viability of Caco-2 cell monolayers was monitored by measuring the transepithelial electrical resistance (TEER), 14C-mannitol permeability, and leakage of lactate dehydrogenase (LDH) enzyme, respectively. Microvascular extravasation of PAMAM-NH2 dendrimers in relation to their size, molecular weight, and molecular geometry is also discussed. Results of these studies show that transepithelial transport and microvascular extravasation of PAMAM dendrimers are dependent on their structural features including molecular size, molecular geometry, and surface chemistry. These results suggest that by optimizing the size and surface charge of PAMAM dendrimers, it is possible to develop oral delivery systems based on these carriers for targeted drug delivery.

Animals↗

PubMed2005

Targeting tumor angiogenic vasculature using polymer-RGD conjugates.

Sites of neovascular angiogenesis are important chemotherapy targets. In this study, the synthesis, characterization, in-vivo imaging and biodistribution of a technetium-99m labeled, water-soluble, N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer carrying doubly cyclized Arg-Gly-Asp motifs (HPMA copolymer-RGD4C conjugate) are reported. In vitro endothelial cell adhesion assays indicated that HPMA copolymer-RGD4C conjugates inhibited alphaVbeta3-mediated endothelial cell adhesion while HPMA copolymer Arg-Gly-Glu control conjugates (HPMA copolymer-RGE4C conjugate) and hydrolyzed HPMA copolymer precursor (HPMA copolymer) showed no activity. The scintigraphic images of prostate tumor bearing SCID mice obtained 24 h post-i.v. injection indicated greater tumor localization of HPMA copolymer-RGD4C conjugate than the control, HPMA copolymer-RGE4C conjugate. The 24-h necropsy radioactivity data showed that HPMA copolymer-RGD4C conjugate had significantly higher (p<0.001) tumor localization compared to HPMA copolymer-RGE4C conjugate and HPMA copolymer. Also, HPMA copolymer-RGD4C conjugates had sustained tumor retention over 72 h and reasonably efficient clearance from the background organs. These results suggest that specific tumor angiogenesis targeting is possible with HPMA copolymer-RGD4C conjugates. This construct provides a foundation that should support targeted delivery of radionuclides and drugs to solid tumors for diagnostic and therapeutic applications.

Animals↗

PubMed2005

Water-soluble polymers for targeted drug delivery to human squamous carcinoma of head and neck.

Human squamous cell carcinoma of the head and neck (SCCHN) is characterized by over expression of a tumor cell surface-specific receptor namely Hsp47/CBP2 that makes it a favorable candidate for targeted delivery of anticancer drugs. Several synthetic peptides have been identified as effective ligands for binding to CBP2. The purpose of this study is to investigate the potential of water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-doxorubicin (Dox) conjugates containing a Hsp47/CBP2 binding peptide sequence, namely WHYPWFQNWAMA for targeted delivery to SCCHN. An HPMA copolymer containing Dox and CBP2 targeting peptide conjugated via lysosomally degradable glycylphenylalanylleucylglycine (GFLG) spacer was synthesized by free radical precipitation copolymerization. A control polymer without targeting moiety was also synthesized. The conjugates were characterized for drug content, peptide content, molecular weight and molecular weight distribution. The uptake of polymeric conjugates by both drug resistant and drug sensitive SCCHN cells were determined in vitro by flow cytometry using FACS scan analysis. Cytotoxicity of the conjugates towards drug sensitive as well as multidrug resistant SCCHN cells were evaluated by a clonal survival assay and compared to free Dox. The cytotoxicity of the free peptide was similarly evaluated. The internalization and subcellular fate of the conjugates in drug sensitive SCCHN cells was monitored using confocal microscopy. The new targetable copolymer contained 0.16 mmole peptide/g polymer. Studies on drug sensitive SCCHN cells demonstrated lesser uptake of both targeted and non-targeted conjugates compared to free Dox suggesting a slower endocytic mechanism of uptake for the conjugates as opposed to rapid diffusion of free Dox. At higher Dox equivalent concentrations (>20 microM) the targeted conjugate showed significantly higher uptake (p < or = 0.028) than the non-targeted conjugate. The uptake of the targeted conjugate was inhibited in the presence of an anti Hsp47 antibody suggesting the involvement of active receptor mediated endocytosis in cell entry of the conjugate. Compared to free Dox, the targeted and non-targeted conjugates caused marginally lower inhibition (p < or = 0.01) of the drug sensitive SCCHN cells. In contrast, the same conjugates showed significantly higher uptake (p < or = 0.004) by drug resistant SCCHN cells and caused significantly higher inhibition (p < or = 0.02) of drug resistant SCCHN cells when compared to free Dox. Results suggest that the polymeric conjugates were able to overcome drug resistance. Confocal microscopy studies demonstrated the uptake of the polymeric conjugates, followed by internalization, intralysosomal localization and subsequent release of Dox. HPMA copolymer-Dox-peptide conjugates targeted to SCCHN cells were able to overcome drug resistance and increase efficacy in vitro. The results suggest that targetable polymeric conjugates have potential to improve systemic head and neck cancer chemotherapy by increasing tumor localization and reducing dose-limiting toxicity.

Antibiotics, Antineoplastic↗

PubMed2005

Targeting tumor angiogenesis: comparison of peptide and polymer-peptide conjugates.

UNLABELLED: Endothelial cells in tumor angiogenesis are highly accessible, genetically stable and present unique molecular markers for targeted therapy. Neoplasia is also characterized by enhanced vascular permeability and disordered lymphatics so that both active and passive targeting strategies may play a role in localizing angiogenesis-targeted agents. To investigate the relative importance of these targeting strategies, the tissue biodistribution of both endothelial-specific and nonspecific peptides and their macromolecular peptide-copolymer conjugates were studied in 2 xenograft models of prostate cancer. Tumor-to-normal tissue background ratios (T/B) of these constructs were compared to evaluate the effect of molecular size on blood clearance and nonspecific vascular permeability. METHODS: Water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers were synthesized with side chains terminated in a doubly cyclized Arg-Gly-Asp motif KACDCRGDCFCG (RGD4C: active peptide targeting the alpha(V)beta(3) integrin) and KACDCRGECFCG (RGE4C: nonactive peptide). The bioactivity of the polymer conjugates and free peptides was characterized in vitro by endothelial cell adhesion assay. The (99m)Tc(CO)(3)-labeled compounds were injected into SCID mice bearing DU145 or PC-3 prostate tumor xenografts for scintigraphic imaging and necropsy organ counting. RESULTS: HPMA copolymer-RGD4C conjugates showed similar inhibition of cell adhesion as free RGD4C attached to (99m)Tc(CO)(3) chelator N-omega-bis(2-pyridylmethyl)-L-lysine (RGD4C-DPK) and were significantly higher (P < 0.05) than RGE4C, HPMA copolymer-RGE4C, and a hydrolyzed HPMA copolymer precursor. Scintigraphic images obtained at 24 h showed specific tumor localization of HPMA copolymer-RGD4C and RGD4C compared with RGE4C conjugates in both prostate tumor models. Twenty-four-hour necropsy data in the DU145 model showed significantly higher (P < 0.001) tumor localization for HPMA copolymer-RGD4C (4.60 +/- 1.80%ID/g [percentage injected dose per gram tissue]) and RGD4C-DPK (3.37 +/- 0.32%ID/g) compared with HPMA copolymer-RGE4C (1.24 +/- 0.15%ID/g) and RGE4C-DPK (0.32 +/- 0.04%ID/g). Similar results were observed in the PC-3 model. Moreover, higher T/B for the polymer conjugates indicated reduced extravasation of the targeted polymeric conjugates in normal tissues. CONCLUSION: Specific molecular targeting of the alpha(v)beta(3) integrin and nonspecific vascular permeability are both significant in the relative tumor localization of polymeric conjugates of RGD4C. Extravascular leak in nonspecific organs appears to be a major factor in reducing the T/B for the peptide molecules.

Animals↗

PubMed2004

Genetically engineered polymers: status and prospects for controlled release.

Genetic engineering methodology has enabled the synthesis of protein-based polymers with precisely controlled structures. Protein-based polymers have well-defined molecular weights, monomer compositions, sequences and stereochemistries. The incorporation of tailor-made motifs at specified locations by recombinant techniques allows the formation of hydrogels, sensitivity to environmental stimuli, complexation with drugs and nucleic acids, biorecognition and biodegradation. Accordingly, a special interest has emerged for the use of protein-based polymers for controlled drug and gene delivery, tissue engineering and other biomedical applications. This article is a review of genetically engineered polymers, their physicochemical characteristics, synthetic strategies used to produce them and their biomedical applications with emphasis on controlled release.

Animals↗

PubMed2004

In vitro and in vivo evaluation of recombinant silk-elastinlike hydrogels for cancer gene therapy.

The objectives of this study were to evaluate: (i). the influences of hydrogel geometry, DNA molecular weight, and DNA conformation on DNA release from a silk-elastinlike protein polymer (SELP) hydrogel, (ii). the bioactivity and transfection efficiency of encapsulated DNA over time in vitro, (iii). the delivery and transfection of a reporter gene in a murine model of human breast cancer in vivo, and (iv). the in vitro release and bioactivity of adenovirus containing the green fluorescent protein (gfp) gene as a marker of gene transfer. Plasmid DNA was released from SELP hydrogels in a size-dependent manner, with the average effective diffusivity ranging from 1.70+/-0.52 x 10(-12) cm(2)/s for a larger plasmid (11 kbp) to 2.55+/-0.51 x 10(-10) cm(2)/s for a smaller plasmid (2.6 kbp). Plasmid conformation also influenced the rate of release, with the rank order linear>supercoiled>open-circular. DNA retained bioactivity in vitro, after encapsulation in a SELP hydrogel for up to 28 days. Delivery of pRL-CMV from a SELP hydrogel resulted in increased transfection in a murine model of human breast cancer by 1-3 orders of magnitude, as compared to naked DNA. The release of a bioactive adenoviral vector was related to the concentration of the polymer in the hydrogel. These studies indicate that genetically engineered SELP hydrogels have potential as matrices for controlled nonviral and viral gene delivery.

Amino Acid Sequence↗

PubMed2004

Targetable water-soluble polymer-drug conjugates for the treatment of visceral leishmaniasis.

The present work describes the synthesis, characterization, and biological evaluation of targetable N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-anti-leishmanial drug conjugates for the treatment of visceral leishmaniasis (VL). Conjugates of HPMA copolymer with NPC1161, an 8-aminoquinoline analog with anti-leishmanial activity, containing N-acetylmannosamine (ManN) in the side chains were synthesized and characterized. In vitro anti-leishmanial efficacy of the conjugates was determined in mouse peritoneal macrophages infected with Leishmania donovani amastigotes. The conjugates were tested against mammalian KB cells for cytotoxicity. The effect of ManN content on uptake was evaluated in RAW 264 murine macrophages. In vivo anti-leishmanial efficacy was evaluated at 1 mg/kg intravenous dose in BALB/c mice. HPMA copolymer-NPC1161 conjugates with 5 mole% or higher ManN content were significantly (p<0.0001) more active (ED50<15 microg/ml) than nontargeted conjugates (ED50>30 microg/ml). All conjugates were relatively nontoxic towards the mammalian cells. Significantly (p<0.003) higher uptake was observed for targeted conjugates compared to nontargeted conjugates. The targeted conjugates were significantly more effective in vivo (67-80% inhibition, p<0.0001) than nontargeted conjugate (47% inhibition). HPMA copolymers containing ManN in the side chains can potentially reduce the toxicity and increase efficacy of anti-leishmanial drugs for the treatment of VL.

Animals↗

PubMed2004

Technetium-99m-Labeled N-(2-hydroxypropyl) methacrylamide copolymers: synthesis, characterization, and in vivo biodistribution.

PURPOSE: To synthesize novel technetium-99m (99mTc)-labeled N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers and characterize the effect of charge and molecular weight on their biodistribution in SCID mice. METHODS: Electronegative and neutral 7-kDa, 21-kDa, and 70-kDa HPMA copolymers containing a 99mTc chelating comonomer, bearing N-omega-bis(2-pyridylmethyl)-L-lysine (DPK), were synthesized by free-radical precipitation copolymerization. The copolymers were labeled via 99mTc tricarbonyl chelation to DPK-bearing comonomer. They were characterized by side-chain content, molecular weight, molecular weight distribution, radiochemical purity, and labeling stability. Scintigraphic images were obtained during the first 90 min and at 24 h postintravenous injection in SCID mice. At 24 h, organ radioactivity was determined from necropsy tissue counting. RESULTS: 99mTc-labeled HPMA copolymers showed greater than 90% stability over a 24-h challenge with cysteine and histidine. Scintigraphic images and the necropsy data showed that the negatively charged copolymers were eliminated from the body significantly faster than the neutral copolymers in a size-dependent manner. CONCLUSIONS: To facilitate clinical scintigraphic imaging, stable chelation of 99mTc may be achieved by incorporation of a DPK-bearing comonomer into the HPMA backbone. Electronegative and neutral 99mTc-labeled HPMA copolymers of 7, 21, and 70 kDa show significant variation in organ biodistribution in SCID mice. 99mTc-labeled HPMA copolymers could be used as diagnostic agents and to study pharmacokinetics of delivery systems based on these copolymers.

Acrylamides↗

PubMed2002

Genetically engineered silk-elastinlike protein polymers for controlled drug delivery.

The silk-elastinlike class of genetically engineered protein polymers is composed of tandemly repeated silk-like (Gly-Ala-Gly-Ala-Gly-Ser) and elastin-like (Gly-Val-Gly-Val-Pro) amino acid blocks. The precision with which these polymers can be synthesized, as well as the ability to incorporate motifs that allow for gel-formation, stimuli-sensitivity, biodegradation, and biorecognition have stimulated interest in their use for controlled drug and gene delivery. This review will focus on the synthesis and characterization of silk-elastinlike polymers as related to controlled drug delivery. The design and biological synthesis of the copolymers, by recombinant DNA techniques, are reviewed. The characterization of the polymers is discussed. Finally, biocompatibility of the polymers and recent studies to determine their potential utility for controlled drug and gene delivery are reviewed.

Bacterial Proteins↗

PubMed2002

Solute diffusion in genetically engineered silk-elastinlike protein polymer hydrogels.

The partitioning and diffusion behavior of theophylline, vitamin B(12), and cytochrome c in physically crosslinked networks of a genetically engineered silk-elastinlike protein-based (SELP) copolymer with an amino acid sequence of [(GVGVP)(4)GKGVP(GVGVP)(3)(GAGAGS)(4)](12) was investigated. The effect of gelation kinetics on the equilibrium swelling ratio and normalized dimensions of loaded SELP hydrogel disks before and after release studies was also examined. Size dependent release behavior was quantified by diffusion studies with equilibrium loaded SELP hydrogels. Direct loading diffusion studies confirmed that hydrogels produced by direct incorporation of cytochrome c with the aqueous SELP solution did not significantly influence the release behavior compared to equilibrium loaded hydrogels. An overall increase in the equilibrium swelling ratio after the release studies was observed. Analysis of the hydrogel disk dimensions after the release studies revealed no expansion of the disk dimensions. The apparent increase in the equilibrium swelling ratio was most likely due to a decrease in the hydrogel crosslinking density following the removal of the polymer soluble fraction over the course of the release study.

Amino Acid Sequence↗

PubMed2002

Transepithelial transport of poly(amidoamine) dendrimers across Caco-2 cell monolayers.

The objective of this study was to investigate the influence of physiochemical parameters (such as size, molecular weight, molecular geometry, and number of surface amine groups) of poly (amidoamine) (PAMAM) dendrimers, on their permeability across Caco-2 cell monolayers. The permeability of a series of PAMAM dendrimers, generations 0-4 (G0-G4), was investigated across Caco-2 cell monolayers in both the apical to basolateral (AB) and basolateral to apical (BA) directions. The influence of PAMAM dendrimers on the integrity, paracellular permeability, and viability of Caco-2 cell monolayers was also monitored by measuring the transepithelial electrical resistance (TEER), mannitol permeability, and leakage of lactate dehydrogenase (LDH) enzyme, respectively. G0, G1 and G2 demonstrated similar AB permeabilities, which were moderate several fold higher than the AB permeability of higher generations. The AB and BA permeability of G0-G4 typically increased with the increase in donor concentration and incubation time. Permeability values are not reported at generations, concentrations or incubation times that the dendrimers were toxic to Caco-2 cells. TEER values decreased and mannitol permeability increased as a function of donor concentration, incubation time, and generation number. LDH results for G3 and G4 indicate that Caco-2 cell viability was reduced with increasing donor concentration, incubation time, and generation number. The appreciable permeability of G0-G2, coupled with their nontoxic effects on Caco-2 cells, suggest their potential as water-soluble polymeric drug carriers for controlled oral drug delivery.

Biocompatible Materials↗

PubMed2002

Genetic synthesis and characterization of pH- and temperature-sensitive silk-elastinlike protein block copolymers.

The purpose of this work was to synthesize and characterize a pH- and temperature-sensitive block copolymer containing repeating sequences from silk (Gly-Ala-Gly-Ala-Gly-Ser) and elastin (Gly-Val-Gly-Val-Pro) protein. The monomer contained one repeat of silk and eight repeat units of elastin, with the first valine in one of the elastin repeats being replaced by glutamic acid. The copolymer was synthesized using genetic engineering techniques. The sensitivity of the copolymer to pH and temperature was examined at various polymer concentrations and ionic strengths. Turbidity measurements were carried out over a temperature range of 20 to 100 degrees C at various pH, concentration, and ionic strength values. The introduction of an ionizable residue (glutamic acid) rendered the copolymer sensitive to changes in pH. The transition termperature (T(t)), the temperature at which the polymer became insoluble upon increase in temperature, was modulated by changing the pH. In general, the T(t) value, was found: (1) to increase with an increase in pH, (2) to decrease with increasing ionic strength, and (3) to decrease with increasing concentration. Results of these studies suggest that by strategic placement of charged amino acids in genetically engineered silk-elastinlike protein block copolymers it is possible to precisely control sensitivity to stimuli such as pH and temperature.

Amino Acid Sequence↗

PubMed2002

Swelling behavior of a genetically engineered silk-elastinlike protein polymer hydrogel.

The influence of environmental conditions such as pH, temperature, and ionic strength on the equilibrium swelling ratio of physically crosslinked networks of a genetically engineered silk-elastinlike protein-based copolymer (SELP) with an amino acid repeat sequence of [(GVGVP)4GKGVP(GVGVP)3(GAGAGS)4]12 was investigated. The effects of gelation cure time and initial polymer concentration on the equilibrium swelling ratio and soluble fraction of the hydrogels were also studied. It was found that the soluble fraction linearly correlated with the initial polymer concentration at higher gelation times. Soluble fraction results suggest that final hydrogel water content may be controlled by both initial polymer concentration and gelation time. Equilibrium swelling studies demonstrated that these hydrogels are relatively insensitive to environmental changes such as pH, temperature, and ionic strength. Over the concentration range studied, it was found that an increase in gelation time at 37 degrees C resulted in lower hydrogel weight equilibrium swelling ratios, which corresponds to less soluble polymer released post-gelation. Together, these results have implications for the controlled delivery of bioactive agents from silk-elastinlike hydrogels.

Amino Acid Sequence↗