Monthly Archives: June 2015

Fluorescent PolyVivo PLGA-FPR648 used for tracking nanoparticles as part of oral insulin delivery

PolySciTech (www.polyscitech.com) provides a wide array of biodegradable polymers including fluorescently tagged PLGA. Recently, PolyVivo AV008 (PLGA-FPR648 conjugate) was used as part of research in the development of PLGA nanoparticles for oral insulin delivery. The particles were coated with a chitosan based shell to impart mucoadhesion to the particles for insulin delivery. Use of AV008 made the particles visible under microscopy so that their uptake in Caco-2 cells could be tracked more easily to determine nanoparticle fate. Read more: Sheng, Jianyong, Limei Han, Jing Qin, Ge Ru, Ruixiang Li, Lihong Wu, Dongqi Cui, Pei Yang, Yuwei He, and Jianxin Wang. “N-trimethyl Chitosan Chloride-Coated PLGA Nanoparticles Overcoming Multiple Barriers to Oral Insulin Absorption.” ACS Applied Materials & Interfaces (2015). http://pubs.acs.org/doi/abs/10.1021/acsami.5b03555

“Abstract: Although several strategies have been applied for oral insulin delivery to improve insulin bioavailability, little success has been achieved. To overcome multiple barriers to oral insulin absorption simultaneously, insulin-loaded N-trimethyl chitosan chloride (TMC)-coated polylactide-co-glycoside (PLGA) nanoparticles (Ins TMC-PLGA NPs) were formulated in our study. The Ins TMC-PLGA NPs were prepared using the double-emulsion solvent evaporation method and were characterized to determine their size (247.6±7.2 nm), zeta potential (45.2±4.6 mV), insulin-loading capacity (7.8±0.5%) and encapsulation efficiency (47.0±2.9%). The stability and insulin release of the nanoparticles in enzyme-containing simulated gastrointestinal fluids suggested that the TMC-PLGA NPs could partially protect insulin from enzymatic degradation. Compared with unmodified PLGA NPs, the positively charged TMC-PLGA NPs could improve the mucus penetration of insulin in mucus-secreting HT29-MTX cells, the cellular uptake of insulin via clathrin- or adsorption-mediated endocytosis in Caco-2 cells, and the permeation of insulin across a Caco-2 cell monolayer through tight junction opening. After oral administration in mice, the TMC-PLGA NPs moved more slowly through the gastrointestinal tract compared with unmodified PLGA NPs, indicating the mucoadhesive property of the nanoparticles after TMC coating. Additionally, in pharmacological studies in diabetic rats, orally administered Ins TMC-PLGA NPs produced a stronger hypoglycemic effect, with 2-fold higher relative pharmacological availability compared with unmodified NPs. In conclusion, oral insulin absorption is improved by TMC-PLGA NPs with the multiple absorption barriers overcome simultaneously. TMC-PLGA NPs may be a promising drug delivery system for oral administration of macromolecular therapeutics.”

Tumor spheroids for representative cancer therapy testing

One of the new product categories to come out of PolySciTech is 3DCellMaker (http://www.3dcellmaker.com/) which is a thermogelling media modifier that allows for easy and convenient growth of tumor spheroids. The importance of growing tumors in a spheroid pattern for chemotherapy testing has been described in a recent research paper. In traditional research methods, potential cancer therapies are tested on cancer cells grown as a flat-layer in the bottom of a petri dish or other container (2D cells). In the 2D growth pattern, practically every therapy tested works well against the cancer cells because all cells are exposed simultaneously to the drug and there is limited potential for drug-resistant properties to be observed. This does not match up with clinical pharmacology because, in the human body, cancer cells do not grow flat but rather into clumps/spheroids/tumors in which the outer layer of cells acts to create a unique environment for the inner cells. This growth pattern leads to a variety of drug-transport barriers and other changes which can make the tumor resistant to chemotherapeutic treatments. For this reason, in order to accurately assay treatment regimens, it is important to test the proposed therapy against a more realistic tumor spheroid rather than flat cells. Read more about tumor spheroids here: Giannattasio, Ariane, Sandra Weil, Stephan Kloess, Nariman Ansari, Ernst HK Stelzer, Adelheid Cerwenka, Alexander Steinle, Ulrike Koehl, and Joachim Koch. “Cytotoxicity and infiltration of human NK cells in in vivo-like tumor spheroids.” BMC cancer 15, no. 1 (2015): 351. http://www.biomedcentral.com/1471-2407/15/351/

“Abstract: Background: The complex cellular networks within tumors, the cytokine milieu, and tumor immune escape mechanisms affecting infiltration and anti-tumor activity of immune cells are of great interest to understand tumor formation and to decipher novel access points for cancer therapy. However, cellular in vitro assays, which rely on monolayer cultures of mammalian cell lines, neglect the three-dimensional architecture of a tumor, thus limiting their validity for the in vivo situation. Methods: Three-dimensional in vivo-like tumor spheroid were established from human cervical carcinoma cell lines as proof of concept to investigate infiltration and cytotoxicity of NK cells in a 96-well plate format, which is applicable for high-throughput screening. Tumor spheroids were monitored for NK cell infiltration and cytotoxicity by flow cytometry. Infiltrated NK cells, could be recovered by magnetic cell separation. Results: The tumor spheroids were stable over several days with minor alterations in phenotypic appearance. The tumor spheroids expressed high levels of cellular ligands for the natural killer (NK) group 2D receptor (NKG2D), mediating spheroid destruction by primary human NK cells. Interestingly, destruction of a three-dimensional tumor spheroid took much longer when compared to the parental monolayer cultures. Moreover, destruction of tumor spheroids was accompanied by infiltration of a fraction of NK cells, which could be recovered at high purity. Conclusion: Tumor spheroids represent a versatile in vivo-like model system to study cytotoxicity and infiltration of immune cells in high-throughput screening. This system might proof useful for the investigation of the modulatory potential of soluble factors and cells of the tumor microenvironment on immune cell activity as well as profiling of patient-/donor-derived immune cells to personalize cellular immunotherapy. Keywords: NK cell; tumor immune escape; tumor infiltration; tumor spheroid; 3D culture; innate immune system; NKG2D; ligand shedding”

Biodegradation rate trends with polyesters

A common question I receive about PolySciTech (www.polyscitech.com) polymers is biodegradation rate. The rate of degradation varies widely and depends on several factors including hydrophobicity, crystallinity, and steric hindrance. These factors are broken down and discussed on one of our technical help-pages here (www.lazypolymer.com). For our linear polyesters the general trend is the fastest degradation occurs with lowest molecular weight and highest glycolide content. The schematic shown here details the biodegradation trends and gives estimated degradation times for several of our products as they are organized on (https://akinainc.com/polyscitech/products/polyvivo/polyesters.php).

Image: http://4.bp.blogspot.com/-yNIHP7cUwvM/VYxFMia2yVI/AAAAAAAABpQ/KDY41tZe0Yw/s1600/Polyester%2Bdegradation%2Btrends.png

Increased efficacy of PEG-P(DL)La over PEG-PLLA for nanoparticle paclitaxel delivery to tumors

PolySciTech (www.polyscitech.com) division of Akina, Inc. provides a wide array of biodegradable block copolymers including mPEG-P(DL)La and mPEG-P(L)La. Recently a report from the University of Utah compared these two related polymers in terms of their efficacy for use as nanoparticle carriers of paclitaxel (PTX, a chemotherapeutic agent) to pancreatic tumors. For this they used PolyVivo AK09 from Polyscitech for the mPEG-P(DL)La test polymer. Poly(lactide) is commonly available in two forms. The ‘L’ and the ‘D’ are references to the chirality, or molecular arrangement, of the side methyl units of the poly-lactide chain relative to the main branch. For the enantiomerically pure poly-L-lactide, all the methyl units are aligned on the same side so the polymer chains tend to stack into crystalline forms. For the racemic poly-DL-lactide, the methyl units are randomly aligned and as such the polymer chains tend to be amorphously aggregated rather than crystalized to each other. This is a relatively minor difference in chemistry, but an interesting result from the recent research paper is that it does matter quite a bit in terms of drug delivery and, for this application, the amorphous P(DL)La form has advantages over the crystalline PLLA form. Read more: Gupta, Roohi, Jill Shea, Courtney Scafe, Anna Shurlygina, and Natalya Rapoport. “Polymeric Micelles and nanoemulsions as drug carriers: Therapeutic efficacy, toxicity, and drug resistance.” Journal of Controlled Release (2015). http://www.sciencedirect.com/science/article/pii/S0168365915006264

“Abstract: The manuscript reports the side-by-side comparison of therapeutic properties of polymeric micelles and nanoemulsions generated from micelles. The effect of the structure of a hydrophobic block of block copolymer on the therapeutic efficacy, tumor recurrence, and development of drug resistance was studied in pancreatic tumor bearing mice. Mice were treated with paclitaxel (PTX) loaded poly(ethylene oxide)-co-polylactide micelles or corresponding perfluorocarbon nanoemulsions. Two structures of the polylactide block differing in a physical state of micelle cores or corresponding nanodroplet shells were compared. Poly(ethylene oxide)-co-poly(D,L-lactide) (PEG-PDLA) formed micelles with elastic amorphous cores while poly(ethylene oxide)-co-poly(L-lactide) (PEG-PLLA) formed micelles with solid crystalline cores. Micelles and nanoemulsions stabilized with PEG-PDLA copolymer manifested higher therapeutic efficacy than those formed with PEG-PLLA copolymer studied earlier. Better performance of PEG-PDLA micelles and nanodroplets was attributed to the elastic physical state of micelle cores (or droplet shells) allowing adequate rate of drug release via drug diffusion and/or copolymer biodegradation. The biodegradation of PEG-PDLA stabilized nanoemulsions was monitored by the ultrasonography of nanodroplets injected directly into the tumor; the PEG-PDLA stabilized nanodroplets disappeared from the injection site within 48 hours. In contrast, nanodroplets stabilized with PEG-PLLA copolymer were preserved at the injection site for weeks and months indicating extremely slow biodegradation of solid PLLA blocks. Multiple injections of PTX-loaded PEG-PDLA micelles or nanoemulsions to pancreatic tumor bearing mice resulted in complete tumor resolution. Two of ten tumors treated with either PEG-PDLA micellar or nanoemulsion formulation recurred after the completion of treatment but proved sensitive to the second treatment cycle indicating that drug resistance has not been developed. This is in contrast to the treatment with PEG-PLLA micelles or nanoemulsions where all resolved tumors quickly recurred after the completion of treatment and proved resistant to the repeated treatment. The prevention of drug resistance in tumors treated with PEG-PDLA stabilized formulations was attributed to the presence and preventive effect of copolymer unimers that were in equilibrium with PEG-PDLA micelles. PEG-PDLA stabilized nanoemulsions manifested lower hematological toxicity than corresponding micelles suggesting higher drug retention in circulation. Summarizing, micelles with elastic cores appear preferable to those with solid cores as drug carriers. Micelles with elastic cores and corresponding nanoemulsions both manifest high therapeutic efficacy, with nanoemulsions exerting lower systemic toxicity than micelles. The presence of a small fraction of micelles with elastic cores in nanoemulsion formulations is desirable for prevention of the development of drug resistance. Keywords: Polymeric micelles; nanoemulsions; paclitaxel; tumor recurrence; drug resistance; hematological toxicity; poly(ethylene oxide)-co-poly(L-lactide); poly(ethylene oxide)-co-poly(D,L-lactide)”

Gupta, 2015 AK09 PTX delivery

AK100, A PLA-PEG-PLA thermogel with improved gelation at 37C

PolySciTech (www.polyscitech.com) provides a wide array of thermogelling polymers. One of these, AK100 P(DL)La-PEG-P(DL)La 1700-1500-1700 forms a very strong thermogel when dissolved as a 20% w/v solution in water as shown in the video.  For this video 1g of AK100 was dissolved at 5-10C in 5ml of water with shaking for 1-2 days and subsequently the solution was warmed to room temperature. At this temperature the polymer solution is very fluid like water. Afterwards it was placed in a 37 C incubator and equilibriated for 30 min to fully warm the solution. As can be seen, turning the vial upside down shows that a strong and stable gel is formed by this polymer.

mPEG-PDLLa from PolySciTech used for delivery of silver nanoparticles to kill antibiotic resistant bacteria

PolySciTech (www.polyscitech.com) provides a wide array of biodegradable block copolymers including mPEG-PDLLa. As bacteria mutate and evolve, traditional antibiotic therapies are becoming increasingly less effective due to bacterial resistance against such therapies.  Silver nanoparticles act as antibiotic agents which still retain effectiveness against antibiotic-resistant bacteria. However, silver suffer from poor aqueous solubility which hinders its capability to be administered. Recently, a study came out from Northeastern University where they utilized PolyVivo AK021 (mPEG-PDLLa 5000-50000) to create a polymersome which aided in delivery of silver nanoparticles and they used this system to effectively reduce the bacterial growth of antibiotic resistant E Coli. More effectively than conventional antibiotics thus showing the applicability of such a system for treatment. Read more:  Geilich, Benjamin M., Anne L. van de Ven, Gloria L. Singleton, Liuda J. Sepúlveda, Srinivas Sridhar, and Thomas J. Webster. “Silver nanoparticle-embedded polymersome nanocarriers for the treatment of antibiotic-resistant infections.” Nanoscale 7, no. 8 (2015): 3511-3519. http://pubs.rsc.org/en/content/articlehtml/2015/nr/c4nr05823b

“Abstract: The rapidly diminishing number of effective antibiotics that can be used to treat infectious diseases and associated complications in a physician’s arsenal is having a drastic impact on human health today. This study explored the development and optimization of a polymersome nanocarrier formed from a biodegradable diblock copolymer to overcome bacterial antibiotic resistance. Here, polymersomes were synthesized containing silver nanoparticles embedded in the hydrophobic compartment, and ampicillin in the hydrophilic compartment. Results showed for the first time that these silver nanoparticle-embedded polymersomes (AgPs) inhibited the growth of Escherichia coli transformed with a gene for ampicillin resistance (bla) in a dose-dependent fashion. Free ampicillin, AgPs without ampicillin, and ampicillin polymersomes without silver nanoparticles had no effect on bacterial growth. The relationship between the silver nanoparticles and ampicillin was determined to be synergistic and produced complete growth inhibition at a silver-to-ampicillin ratio of 1 : 0.64. In this manner, this study introduces a novel nanomaterial that can effectively treat problematic, antibiotic-resistant infections in an improved capacity which should be further examined for a wide range of medical applications.”

Geilich, 2015 silver nanoparticle mPEG-PLA

Polymer Molecular Weight: An Illustrative Story

PolySciTech (www.polyscitech.com) provides a wide variety of polymers. One of the most common questions I get is about polymer molecular weight. The problem with polymer molecular weight is that it is not truly a number but rather a distribution. As polymers are synthesized the individual chains grow and initiate at different rates and different times respectively. For this reason, polymers always exhibit a polydispersity often, but not always, in a roughly bell-curve shaped format. Due to the distribution of polymers and the historical difficulties in actually ‘measuring’ the molecular weight of polymers there are many different ‘numbers’ used to describe the molecular weight of a polymer set. These include number average (Mn), weight average (Mw), peak average (Mp), viscosity average (Mv), Mz, Mz+1, and many more. These numbers are used broadly in different fields to describe different polymer systems. A good way to initiate a fist-fight in a room full of polymer chemists is to simply ask which number represents the ‘true’ molecular weight of a polymer. This system is confusing and complex. There are very well written textbooks out there which clock in easily at hundreds of pages each full of mathematical equations and statistics that attempt to explain these various definitions of polymer molecular weight. When I train new employees at PolySciTech, I skip the books and tell the following story. For the purpose of this one, we will stick with the three most common molecular weight numbers which are weight average (Mw) number average (Mn) and peak average (Mp).

The story begins: “Once upon a time there was a census statistician tasked with defining the average weight of people living in a certain city. He had neither time nor resources to weigh every single person in the city, but wanted to get an estimate that he could report back as the average ‘weight’ of the city. He thought of the best way to do this and hit upon a simple plan. Letters were sent out at random informing a representatively large numbered group of people to report to a nearby truck weigh in station. The statistician watched as people lined up, young and old, heavy and thin, and considered how brilliant his plan was. That is until a van pulled up. The statistician blanched as the people got out of the van and he watched the tires pull away from the wheel-wells as they did so. They all had on bibs featuring a pig holding a knife and fork and indeed one of them was still gnawing away at a piece of pork-rib from their latest barbeque-fest. From sight, he estimated each one to weigh at least 150 to 200 kilos if not more and they all dutifully presented letters and hopped up on the scale. The statistician then began to feel faint as a school bus pulled up and he realized that he was not tasked with defining the weight of ‘adults’, but everyone in the city. The masses of squirrelly children, all with letters in hand, were ushered up onto the scale by their teachers and the statistician tried desperately to count them as they ran about and played with one another. At last, everyone was on and the truck-station weigh in scale was activated and the total mass of the group was recorded. The statistician sat down and counted the number of people on the scale and divided the mass total by the number of people to obtain the weight average of the people (this is polymer weight average “Mw”). He came up with 100 kilos! He frowned at this. There was no way the average was 100 kilos with all those little children on the scale and he cast a wary glance at the barbeque fans. Each of them was contributing an incredible amount of mass to the scale, but still only counted as one person. He shook his head realizing that he could not report this average to his boss since it was so badly skewed by a relatively small number of extra-heavy people. The statistician thought harder and had everyone in the group simply report their weight. He took the total ‘number’ at each weight and averaged them together (this is polymer number average “Mn”). However, to his shock, he came up with only 50 kilos! He cast a wary glance at the squirrelly children. Each one was maybe less than 30 kilos but they heavily outnumbered the barbeque fans so that when he averaged based on number the children now skewed the number too low. Finally the statistician took everyone out to a football field where they would have space. He laid out signs and lines across the field and labeled each lined section in 5 kilo increments and had each person stand in line behind the sign indicating their weight. He then climbed up high into the stadiums and looked down on the group from above. What he saw looked like a bell-curve. Although there were many children and some barbeque fans, both were outnumbered by the large group of people which were in between these two weight extremes. The statistician looked out and saw that the peak of the curve occurred around 70 kilos and so he marked this down as the peak average weight of the people (This is how we obtain peak average molecular weight Mp). Finally everyone was dismissed and the statistician reported back to his boss. His boss said “So what was the average weight of the city?” to which the statistician replied “Which number do you want?”

The moral of this story is that polymers are like people. There are going to be long chain polymers and short chain polymers mixed in with every batch. You must consider your method for measuring the polymers when you consider the ‘molecular weight’ of the polymer. In general, the number average Mn will always be low due to many small polymer chains and the weight average Mw will always be higher due to a handful of very long polymer chains.  On the COA’s provided with products, PolySciTech provides both of these numbers so that customers can see both the molecular weights as well as the distribution for all products.

PLGA nanoparticles in microgel for multistage drug delivery

PolySciTech (www.polyscitech.com) provides a wide array of PLGA polymers. Recently this type of polymer was used to generate a multi-stage drug delivery platform by incorporating the drug loaded PLGA nanoparticles inside of a PEG hydrogel. Read more: Hsu, Myat Noe, Rongcong Luo, Kerwin Zeming Kwek, Yong Chen Por, Yong Zhang, and Chia-Hung Chen. “Sustained release of hydrophobic drugs by the microfluidic assembly of multistage microgel/poly (lactic-co-glycolic acid) nanoparticle composites.” Biomicrofluidics 9, no. 5 (2015): 052601. http://scitation.aip.org/content/aip/journal/bmf/9/5/10.1063/1.4916230.

“Abstract: The poor solubility of many newly discovered drugs has resulted in numerous challenges for the time-controlled release of therapeutics. In this study, an advanced drug delivery platform to encapsulate and deliver hydrophobic drugs, consisting of poly (lactic-co-glycolic acid) (PLGA) nanoparticles incorporated within poly (ethylene glycol) (PEG) microgels, was developed. PLGA nanoparticles were used as the hydrophobic drug carrier, while the PEG matrix functioned to slow down the drug release. Encapsulation of the hydrophobic agents was characterized by fluorescence detection of the hydrophobic dye Nile Red within the microgels. In addition, the microcomposites prepared via the droplet-based microfluidic technology showed size tunability and a monodisperse size distribution, along with improved release kinetics of the loaded cargo compared with bare PLGA nanoparticles. This composite system has potential as a universal delivery platform for a variety of hydrophobic molecules.”

PEG-PLA used as delivery system for novel cancer-metabolism inhibition system

PolySciTech (www.polyscitech.com) provides a wide array of block copolymers including poly(ethylene glycol)-b-poly(lactide) which functions as a micelle that improves water solubility of poorly soluble medicines as well as circulation times of medicines allowing them to stay in the blood-stream longer without being removed by the kidneys. In order to survive, all cells (cancerous and healthy) have to metabolize glucose for energy. Recently, PEG-PLA was used to deliver siRNA based medicines that specifically target and reduce cancer cells capability to process glucose ‘starving’ the cancer cells leading to reduced growth and proliferation.  Read more: Xu, Cong-Fei, Yang Liu, Song Shen, Yan-Hua Zhu, and Jun Wang. “Targeting glucose uptake with siRNA-based nanomedicine for cancer therapy.” Biomaterials 51 (2015): 1-11. http://www.sciencedirect.com/science/article/pii/S014296121500085X

“Abstract: Targeting cancer metabolism is emerging as a successful strategy for cancer therapy. However, most of the marketed anti-metabolism drugs in cancer therapy do not distinguish normal cells from cancer cells, leading to severe side effects. In this study, we report an effective strategy for cancer therapy through targeting glucose transporter 3 (GLUT3) with siRNA-based nanomedicine to simultaneously inhibit the self-renewal of glioma stem cells and bulk glioma cells in a glucose restricted tumor micro-environment. We have demonstrated that cationic lipid-assisted poly(ethylene glycol)-b-poly(d,l-lactide) (PEG-PLA) nanoparticles can efficiently deliver siRNA into U87MG and U251 glioma stem cells and bulk glioma cells. Nanoparticles carrying specific siRNA targeting GLUT3 (NPsiGLUT3) were able to significantly reduce the expression of GLUT3 in glioma stem cells and bulk glioma cells, while GLUT3 knockdown results in obvious cell metabolism and proliferation inhibition, and further glioma stem cells percentage down-regulation. Moreover, systemic delivery of NPsiGLUT3, via intravenous injection, significantly inhibited tumor growth in a U87MG xenograft model, due to the reduced expression of GLUT3 and down-regulated stemness of glioma cells. Keywords: Nanomedicine; Cancer therapy; Glucose transporter 3; Glioma stem cells; siRNA delivery”

PLGA-PEG-PLGA/montmorillonite system used for delivery of aspirin

PolySciTech (www.polyscitech.com) provides a wide array of PLGA-PEG-PLGA block copolymers. Recently these types of polymers were used to generate a system of microparticles and this was used for asparin delivery. Read more: Liu, Hsin-Jiant, Hawn-Chung Chu, Li-Huei Lin, and Shu-Yuan Hsu. “Preparation and Drug Release of Aspirin-Loaded PLGA-PEG-PLGA/Montmorillonite Microparticles.” International Journal of Polymeric Materials and Polymeric Biomaterials 64, no. 1 (2015): 7-14. http://www.tandfonline.com/doi/abs/10.1080/00914037.2014.886238

“Abstract: A polymerization method was used to synthesize biodegradable poly(lactide-co-glycolide)/poly(ethyleneglycol)/poly(lactide-co-glycolide) (PLGA-PEG-PLGA) copolymers. These copolymers were then used to prepare microparticles for encapsulating drug (aspirin). The results of X-ray diffraction (XRD) analysis showed that the montmorillonite (MMT) can be converted into organic montmorillonite (o-MMT). Subsequently, the emulsion solvent evaporation method was used to separately prepare aspirin-loaded PLGA-PEG-PLGA and aspirin-loaded PLGA-PEG-PLGA/o-MMT microparticles. The results of scanning electron microscopy (SEM) showed that microparticle formation was related to the polyvinyl alcohol (PVA) concentration and the proportion of o-MMT. In addition, the ultraviolet-visible (UV-Vis) spectroscopy was conducted to determine the release rate of these microparticles.”