Formulation and characterization of poly(propylacrylic acid)/poly(lactic-co-glycolic acid) blend microparticles for pH-dependent membrane disruption and cytosolic delivery.

Poly(lactic-co-glycolic acid) (PLGA) is widely used as a vehicle for delivery of pharmaceutically relevant payloads. PLGA is readily fabricated as a nano- or microparticle (MP) matrix to load both hydrophobic and hydrophilic small molecular drugs as well as biomacromolecules such as nucleic acids and proteins. However, targeting such payloads to the cell cytosol is often limited by MP entrapment and degradation within acidic endolysosomes. Poly(propylacrylic acid) (PPAA) is a polyelectrolyte polymer with the membrane disruptive capability triggered at low pH. PPAA has been previously formulated in various carrier configurations to enable cytosolic payload delivery, but requires sophisticated carrier design. Taking advantage of PPAA functionality, we have incorporated PPAA into PLGA MPs as a simple polymer mixture to enhance cytosolic delivery of PLGA-encapsulated payloads. Rhodamine loaded PLGA and PPAA/PLGA blend MPs were prepared by a modified nanoprecipitation method. Incorporation of PPAA into PLGA MPs had little to no effect on the size, shape, or loading efficiency, and evidenced no toxicity in Chinese hamster ovary epithelial cells. Notably, incorporation of PPAA into PLGA MPs enabled pH-dependent membrane disruption in a hemolysis assay, and a three-fold increased endosomal escape and cytosolic delivery in dendritic cells after 2 h of MP uptake. These results demonstrate that a simple PLGA/PPAA polymer blend is readily fabricated into composite MPs, enabling cytosolic delivery of an encapsulated payload. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1022-1033, 2018.

Poly(2-propylacrylic acid)/poly(lactic-co-glycolic acid) blend microparticles as a targeted antigen delivery system to direct either CD4+ or CD8+ T cell activation.

Poly(lactic-co-glycolic acid) (PLGA) based microparticles (MPs) are widely investigated for their ability to load a range of molecules with high efficiency, including antigenic proteins, and release them in a controlled manner. Micron-sized PLGA MPs are readily phagocytosed by antigen presenting cells, and localized to endosomes. Due to low pH and digestive enzymes, encapsulated protein cargo is largely degraded and processed in endosomes for MHC-II loading and presentation to CD4+ T cells, with very little antigen delivered into the cytosol, limiting MHC-I antigenic loading and presentation to CD8+ T cells. In this work, PLGA was blended with poly(2-propylacrylic acid) (PPAA), a membrane destabilizing polymer, in order to incorporate an endosomal escape strategy into PLGA MPs as an easily fabricated platform with diverse loading capabilities, as a means to enable antigen presentation to CD8+ T cells. Ovalbumin (OVA)-loaded MPs were fabricated using a water-in-oil double emulsion with a 0% (PLGA only), 3 and 10% PPAA composition. MPs were subsequently determined to have an average diameter of 1 µm, with high loading and a release profile characteristic of PLGA. Bone marrow derived dendritic cells (DCs) were then incubated with MPs in order to evaluate localization, processing, and presentation of ovalbumin. Endosomal escape of OVA was observed only in DC groups treated with PPAA/PLGA blends, which promoted high levels of activation of CD8+ OVA-specific OT-I T cells, compared to DCs treated with OVA-loaded PLGA MPs which were unable activate CD8+ T cells. In contrast, DCs treated with OVA-loaded PLGA MPs promoted OVA-specific OT-II CD4+ T cell activation, whereas PPAA incorporation into the MP blend did not permit CD4+ T cell activation. These studies demonstrate PLGA MP blends containing PPAA are able to provide an endosomal escape strategy for encapsulated protein antigen, enabling the targeted delivery of antigen for tunable presentation and activation of either CD4+ or CD8+ T cells.

Dynamic transcriptional response of Escherichia coli to inclusion body formation.

Escherichia coli is used intensively for recombinant protein production, but one key challenge with recombinant E. coli is the tendency of recombinant proteins to misfold and aggregate into insoluble inclusion bodies (IBs). IBs contain high concentrations of inactive recombinant protein that require recovery steps to salvage a functional recombinant protein. Currently, no universally effective method exists to prevent IB formation in recombinant E. coli. In this study, DNA microarrays were used to compare the E. coli gene expression response dynamics to soluble and insoluble recombinant protein production. As expected and previously reported, the classical heat-shock genes had increased expression due to IB formation, including protein folding chaperones and proteases. Gene expression levels for protein synthesis-related and energy-synthesis pathways were also increased. Many transmembrane transporter and corresponding catabolic pathways genes had decreased expression for substrates not present in the culture medium. Additionally, putative genes represented over one-third of the genes identified to have significant expression changes due to IB formation, indicating many important cellular responses to IB formation still need to be characterized. Interestingly, cells grown in 3% ethanol had significantly reduced gene expression responses due to IB formation. Taken together, these results indicate that IB formation is complex, stimulates the heat-shock response, increases protein and energy synthesis needs, and streamlines transport and catabolic processes, while ethanol diminished all of these responses.

The effects of protein solubility on the RNA Integrity Number (RIN) for recombinant Escherichia coli.

High quality, intact messenger RNA (mRNA) is required for DNA microarray and reverse transcriptase polymerase chain reaction analysis and is generally obtained from total RNA isolations. The most widely recognized measure of RNA integrity is the RNA Integrity Number (RIN) obtained from the Agilent Bioanalyzer, as it provides sizing, quantification, and quality control measures. This work describes comparisons of the RIN values obtained for recombinant E. coli. Uninduced recombinant E. coli cultures were examined, as well as induced cultures that produced either a soluble or insoluble recombinant protein. The uninduced cultures and the induced cultures producing soluble protein had higher RIN values than the induced cultures producing insoluble protein. These lower RIN values for E. coli producing the insoluble protein indicate that cellular degradation of the ribosomal RNA species is the likely cause of the lower RIN values. As the use of DNA microarrays and other gene expression tools increase in usage in the industrial recombinant protein production community, these results suggest the need for further studies to determine acceptable RIN ranges for gene expression analysis and effects of various culture conditions on RIN values for recombinant E. coli.

The relative brightness of PEG lipid-conjugated polymer nanoparticles as fluid-phase markers in live cells.

While conjugated polymer nanoparticles (CPNs) have been widely touted as ultra-bright labels for biological imaging, no direct comparative measurements of their intracellular brightness have been reported. Simple in vitro comparisons are not definitive since fluorophore brightness in vitro may not correspond with intracellular brightness. We have compared the fluorescence brightness of J774A.1 cells loaded with 24 nm methoxy-capped 2,000 M(r) polyethylene glycol lipid PFBT nanoparticles (PEG lipid-PFBT CPNs) to cells loaded with carboxy-functionalized quantum dots (Qdots) or a dextran-linked small molecule organic dye, Alexa Fluor 488 dextran (AF488-dex). Under conditions likely to be used for biological imaging or flow cytometry, these CPNs are 175× brighter than Qdots and 1,400× brighter than AF488-dex in cells. Evaluation of the minimum incubation concentration required for detection of nanoparticle fluorescence with a commercial flow cytometer indicated that the limit of detection for PEG lipid-PFBT CPNs was 19 pM (86 ppb), substantially lower than values obtained for Qdots (980 pM) or AF488-dex (11.2 nM). Investigation of the mechanism of cellular uptake of the three fluid-phase labels indicates that these particles are passively taken into macrophage cells via macropinocytosis without interaction with cell surface receptors, and ultimately localize in lysosomes. In addition, no cytotoxicity could be observed at any of the CPN concentrations tested. Together, these data suggest that these CPNs are appropriate and attractive candidates as fluid-phase markers with significantly greater fluorescence brightness than existing dyes or nanoparticles. We expect that these CPNs will find application in both imaging and flow cytometry.

Surface-enhanced raman scattering detection of pH with silica-encapsulated 4-mercaptobenzoic acid-functionalized silver nanoparticles.

Sensors based upon surface-enhanced Raman spectroscopy (SERS) are attractive because they have narrow, vibrationally specific spectral peaks that can be excited using red and near-infrared light which avoids photobleaching, penetrates tissue, and reduces autofluorescence. Several groups have fabricated pH nanosensors by functionalizing silver or gold nanoparticle surfaces with an acidic molecule and measuring the ratio of protonated to deprotonated Raman bands. However, a limitation of these sensors is that macromolecules in biological systems can adsorb onto the nanoparticle surface and interfere with measurements. To overcome this interference, we encapsulated pH SERS sensors in a 30 nm thick silica layer with small pores which prevented bovine serum albumin (BSA) molecules from interacting with the pH-indicating 4-mercaptobenzoic acid (4-MBA) on the silver surfaces but preserved the pH-sensitivity. Encapsulation also improved colloidal stability and sensor reliability. The noise level corresponded to less than 0.1 pH units from pH 3 to 6. The silica-encapsulated functionalized silver nanoparticles (Ag-MBA@SiO(2)) were taken up by J774A.1 macrophage cells and measured a decrease in local pH during endocytosis. This strategy could be extended for detecting other small molecules in situ.

Incorporating functionalized polyethylene glycol lipids into reprecipitated conjugated polymer nanoparticles for bioconjugation and targeted labeling of cells.

We report a simple and rapid method to prepare extremely bright, functionalized, stable, and biocompatible conjugated polymer nanoparticles incorporating functionalized polyethylene glycol (PEG) lipids by reprecipitation. These nanoparticles retain the fundamental spectroscopic properties of conjugated polymer nanoparticles prepared without PEG lipid, but demonstrate greater hydrophilicity and quantum yield compared to unmodified conjugated polymer nanoparticles. The sizes of these nanoparticles, as determined by TEM, were 21-26 nm. Notably, these nanoparticles were prepared with several PEG lipid functional end groups, including biotin and carboxy moieties that can be easily conjugated to biomolecules. We have demonstrated the availability of these end groups for functionalization using the interaction of biotin PEG lipid conjugated polymer nanoparticles with streptavidin. Biotinylated PEG lipid conjugated polymer nanoparticles bound streptavidin-linked magnetic beads, while carboxy and methoxy PEG lipid modified nanoparticles did not. Similarly, biotinylated PEG lipid conjugated polymer nanoparticles bound streptavidin-coated glass slides and could be visualized as diffraction-limited spots, while nanoparticles without PEG lipid or with non-biotin PEG lipid end groups were not bound. To demonstrate that nanoparticle functionalization could be used for targeted labelling of specific cellular proteins, biotinylated PEG lipid conjugated polymer nanoparticles were bound to biotinylated anti-CD16/32 antibodies on J774A.1 cell surface receptors, using streptavidin as a linker. This work represents the first demonstration of targeted delivery of conjugated polymer nanoparticles and demonstrates the utility of these new nanoparticles for fluorescence based imaging and sensing.

Mechanism of cellular uptake of highly fluorescent conjugated polymer nanoparticles.

Conjugated polymer nanoparticles are formed by precipitation of highly fluorescent conjugated polymers to form small nanoparticles with extremely bright fluorescence. We characterized cellular uptake and cytotoxicity of 18 ± 5 nm PFBT conjugated polymer nanoparticles in J774A.1 cells. Significant nanoparticle uptake was observed, indicating efficient nanoparticle entry into cells, even for short (1 h) incubations. The high fluorescence of these nanoparticles allows extremely low loading concentrations; PFBT nanoparticle fluorescence in cells could be detected with loading concentrations of 155 pM (270 ppb). Cellular uptake slows at low temperature, consistent with endocytic entry. Nanoparticles colocalize with Texas Red dextran and are trafficked to lysosomes, as demonstrated by the location of nanoparticle fluorescence in perinuclear organelles that also stain with an anti-LAMP-1 antibody. Inhibition of uptake by phosphoinositide 3-kinase inhibitors implicates macropinocytosis as the operative endocytic mechanism. No significant cytotoxic or inflammatory effects could be observed, making PFBT nanoparticles attractive probes for live cell imaging.

Nanoscale 3D tracking with conjugated polymer nanoparticles.

Small ( approximately 15 nm diameter), highly fluorescent conjugated polymer nanoparticles were evaluated for nanoscale 2D and 3D tracking applications. Nanoparticles composed of conjugated polymers possess high absorption cross sections, high radiative rates, and low or moderate aggregation quenching, resulting in extraordinarily high fluorescent brightness. The bright fluorescence ( approximately 200 000 photons detected per particle per 20 ms exposure) yields a theoretical particle tracking uncertainty of less than 1 nm. A lateral tracking uncertainty of 1-2 nm was determined from analysis of trajectories of fixed and freely diffusing particles. Axial (Z) position information for 3D particle tracking was obtained by defocused imaging. Nanoscale tracking of single particles in fixed cells was demonstrated, and a range of complex behaviors, possibly due to binding/unbinding dynamics, were observed.

Assembly, activation, and signaling by kinin-forming proteins on human vascular smooth muscle cells.

Cardiovascular disease is the number one cause of death in the United States. Vascular smooth muscle cells (VSMC) are an important constituent of the vessel wall that can bring about pathological changes leading to vascular disease. Depending on the environment, the function of VSMC can deviate profoundly from its normal contractile role. Despite advances in research, the underlying mechanisms that activate VSMC toward vascular disease are poorly understood. For the first time, we have observed that factor XII and high-molecular-weight kininogen, constituents of the blood plasma, can bind to VSMC in a Zn2+-dependent manner. In the presence of prekallikrein, this assembly of factor XII and high-molecular-weight kininogen on VSMC leads to the activation of prekallikrein to kallikrein with a rapid formation of bradykinin. The amount of bradykinin in the culture medium then decreases, presumably because of the presence of a kininase activity. p44/42 mitogen-activated protein kinase is rapidly phosphorylated in response to in situ-generated or in vitro-added bradykinin and is inhibited by bradykinin antagonist HOE-140. Binding of factor XII to VSMC also results in a concentration-dependent phosphorylation of p44/42 mitogen-activated protein kinase. This early mitogenic signal, which is also implicated in atherogenesis, may change the metabolic and proliferative activity of VSMC, which are key steps in the progression of atherosclerosis.

High molecular weight kininogen and factor XII binding to endothelial cells and astrocytes.

We have quantitated the binding of high molecular weight kininogen (HK) to human microvascular endothelial cells of lung and dermal origin as well as to astrocytes and compared the results with those reported for human umbilical vein endothelial cells (HUVEC). We also reassessed parameters of binding to HUVEC employing cells in suspension as well as cells attached to the culture plate and report similar numbers of sites varying from 6.96x10(5) to 7.71x10(5) per cell. The present study shows that HK binds with high specificity and affinity to microvascular endothelial cells (Kd = 1.86 to 4.5 nM) compared to HUVEC (Kd = 10.35 nM) but with lower affinity to astrocytes (Kd = 23.73 nM). Human cytokeratin 1, urokinase plasminogen activator receptor and gC1qR were found to be HK binding proteins present at the surface of microvascular endothelial cells and astrocytes analogous to that seen in HUVEC, as assessed by inhibition of binding with antibody to each protein. Lung microvascular endothelial cells had approximately half the number of HK binding sites as HUVEC while dermal micro vascular endothelial cells and astrocytes had only 8-10% of the sites/cell. The affinity of binding to the microvascular endothelial cells was greater than HUVEC, the affinity of binding to astrocytes was considerably less, nevertheless binding to each cell type involves gC1qR, cytokeratin 1 and u-PAR to varying degrees. We also demonstrate, for the first time, that factor XII binds to all of these cell types in a saturable and Zn(+2) dependent manner. Given that factor XII accelerates the interactions among cell surfaces and proteins of the contact activation cascade to generate bradykinin, binding of factor XII (and the prekallikrein-HK complex) may serve as a mechanism by which these proteins are concentrated locally to facilitate their interactions.

Quantitation of gene-specific DNA damage by competitive PCR.

A sensitive assay for quantitating DNA damage within individual genes would be a valuable tool for identifying the molecular mechanisms of disease and the sites of action of various carcinogens and anticancer drugs. This report describes a competitive PCR assay that was used to quantitate DNA damage induced by anticancer drugs within a 683-bp region of the c-myc gene in human CEM leukemia cells. Absolute quantitation of gene-specific DNA damage (attomoles or molecules of damaged DNA sequences) was achieved by coamplification of a homologous internal standard that has the same primer binding sites and PCR amplification efficiency as c-myc. The variability (standard error) associated with four separate determinations of the amount of c-myc sequence in 300 ng of DNA from untreated cells (6.80 +/- 0.05 SE amol) was less than 1% of the mean. The assay was capable of quantitating direct DNA damage that was induced by therapeutic concentrations of VM-26 and cisplatin prior to the onset of cellular apoptosis or necrosis. Both VM-26 (1-10 microM) and cisplatin (25-100 microM) induced a dose-dependent decrease in the amount of intact c-myc sequence. This assay should be readily adaptable to current real-time PCR protocols.