Protected Graft Copolymer Research Articles

Protected graft copolymer-formulated fibroblast growth factors mitigate the lethality of partial body irradiation injury.

We evaluated the mitigating effects of fibroblast growth factor 4 and 7 (FGF4 and FGF7, respectively) in comparison with long acting protected graft copolymer (PGC)-formulated FGF4 and 7 (PF4 and PF7, respectively) administered to C57BL/6J mice a day after exposure to LD50/30 (15.7 Gy) partial body irradiation (PBI) which targeted the gastrointestinal (GI) system. The PGC that we developed increased the bioavailability of FGF4 and FGF7 by 5- and 250-fold compared to without PGC, respectively, and also sustained a 24 hr presence in the blood after a single subcutaneous administration. The dose levels tested for mitigating effects on radiation injury were 3 mg/kg for the PF4 and PF7 and 1.5 mg each for their combination (PF4/7). Amifostine administered prior to PBI was used as a positive control. The PF4, PF7, or PF4/7 mitigated the radiation lethality in mice. The mitigating effect of PF4 and PF7 was similar to the positive control and PF7 was better than other mitigators tested. The plasma citrulline levels and hematology parameters were early markers of recovery and survival. GI permeability function appeared to be a late or full recovery indicator. The villus length and crypt number correlated with plasma citrulline level, indicating that it can act as a surrogate marker for these histology evaluations. The IL-18 concentrations in jejunum as early as day 4 and TPO levels in colon on day 10 following PBI showed statistically significant changes in irradiated versus non-irradiated mice which makes them potential biomarkers of radiation exposure. Other colon and jejunum cytokine levels are potentially useful but require larger numbers of samples than in the present study before their full utility can be realized.

Abstract 13284: A Novel Formulation of Vasoactive Intestinal Peptide Attenuates both Acute Hypoxic Pulmonary Vasoconstriction and the Development of Pulmonary Hypertension

Background: Vasoactive intestinal peptide (VIP) is an endogenous hormone that is known to relax vascular smooth muscle and has established anti-proliferative and immunomodulatory effects in the pulmonary circulation making it an attractive therapeutic target in pulmonary arterial hypertension (PAH). In the current study, a polymer-based nanocarrier (protected graft copolymer - PGC) formulation of VIP, which has been shown to increase the potency and duration of action of VIP, is used to show both acute vasodilatory effects and chronic therapeutic effects in experimental animal models of pulmonary hypertension. Methods: The isolated perfused mouse lung preparation is utilized to test acute hypoxic pulmonary vasoconstriction (HPV) in mice. Two animal models of pulmonary hypertension are used in preventative experiments, chronic hypoxic pulmonary hypertension in mice and monocrotaline-induced pulmonary hypertension in rats. Right ventricular systolic pressure and Fulton’s index (weight ratio of RV/[LV+Septum]) are used for measures of pulmonary hemodynamics and RV hypertrophy respectively. Results: PGC-VIP decreased resting pulmonary artery pressure and attenuated acute HPV elicited by 1% inhaled oxygen tension in a dose dependent manner from 0.1 μM to 1.0 μM. After four weeks of chronic hypoxia, both RVSP measurements and Fulton’s index were significantly decreased in mice receiving 100 mg/kg intraperitoneal PGC-VIP every other day compared to vehicle control. Higher doses were associated with mortality in the treatment group. MCT-PH rats receiving subcutaneous PGC-VIP at a dose of 250 mg/kg failed to show improvement in RVSP or Fulton’s index compared to vehicle control. Conclusion: This novel formulation of VIP demonstrates both acute and chronic vasodilatory effects in the pulmonary circulation. Treatment with PGC-VIP can attenuate the development of hypoxic pulmonary hypertension, yet significant mortality is seen at higher doses. Subcutaneous injection failed to attenuate the development of experimental PH in rats, possibly due to an ineffective dose or route of administration. Further studies are underway to identify the ideal dosing strategy necessary to attenuate and potentially reverse experimental PH in animal models.

Omeprazole and PGC-Formulated Heparin Binding Epidermal Growth Factor Normalizes Fasting Blood Glucose and Suppresses Insulitis in Multiple Low Dose Streptozotocin Diabetes Model

Our objective was to develop novel nanocarriers (protected graft copolymer, PGC) that improve the stability of heparin binding EGF (HBEGF) and gastrin and then to use PGC-formulated HBEGF (PGC-HBEGF) and Omeprazole (+/- PGC-gastrin) for normalizing fasting blood glucose (FBG) and improving islet function in diabetic mice. HBEGF, PGC-HBEGF, Omeprazole, Omeprazole + PGC-HBEGF, Omeprazole + PGC-gastrin + PGC-HBEGF and epidermal growth factor (EGF) + gastrin were tested in multiple low dose streptozotocin diabetic mice. Omeprazole + PGC-HBEGF normalized FBG and is better than EGF + gastrin at improving islet function and decreasing insulitis. Groups treated with Omeprazole, Omeprazole + PGC-HBEGF, or EGF + gastrin have significantly improved islet function versus saline control. All animals that received PGC-HBEGF had significantly reduced islet insulitis versus saline control. Non-FBG was lower for Omeprazole + PGC-gastrin + PGC-HBEGF but Omeprazole + PGC-HBEGF alone showed better FBG and glucose tolerance. Omeprazole + PGC-HBEGF provides a sustained exposure to both EGFRA and gastrin, improves islet function, and decreases insulitis in multiple low dose streptozotocin diabetic mice. Although HBEGF or EGF elevates non-FBG, it facilitates a reduction of insulitis and, in the presence of Omeprazole, provides normalization of FBG at the end of treatment. The study demonstrates Omeprazole and PGC-HBEGF is a viable treatment for diabetes.

Erratum to: Protected Graft Copolymer Excipient Leads to a Higher Acute Maximum Tolerated Dose and Extends Residence Time of Vasoactive Intestinal Peptide Significantly Better than Sterically Stabilized Micelles

Erratum to: Protected Graft Copolymer Excipient Leads to a Higher Acute Maximum Tolerated Dose and Extends Residence Time of Vasoactive Intestinal Peptide Significantly Better than Sterically Stabilized Micelles

Immune Rejection after Pancreatic Islet Cell Transplantation: In Vivo Dual Contrast-enhanced MR Imaging in a Mouse Model

To detect adoptively transferred immune attack in a mouse model of islet cell transplantation by using a long-circulating paramagnetic T1 contrast agent, a protected graft copolymer (PGC) that is covalently linked to gadolinium-diethylenetriaminepentaacetic acid with fluorescein isothiocyanate (Gd-DTPA-F), which accumulates in the sites of inflammation that are characterized by vascular disruption. All animal experiments were performed in compliance with institutional guidelines and approved by the subcommittee on research animal care. Six nonobese diabetic severe combined immunodeficiency mice received transplanted human islet cells under the kidney capsule and adoptively transferred 5 × 10(6) splenocytes from 6-week-old nonobese diabetic mice. These mice also served as control subjects for comparison of pre- and postadoptive transfer MR imaging results. Mice that received phosphate-buffered saline solution only were included as nonadoptive-transfer control subjects (n = 2). In vivo magnetic resonance (MR) imaging was performed before and 17 hours after intravenous injections of PGC-Gd-DTPA-F, followed by histologic examination. Statistical differences were analyzed by means of a paired Student t test and repeated two-way analysis of variance. MR imaging results showed significantly greater accumulation of PGC-Gd-DTPA-F in the graft area after immune attack initiated by adoptive transfer of splenocytes compared with that of the same area before the transfer (T1, 137.2 msec ± 39.3 and 239.5 msec ± 17.6, respectively; P < .001). These results were confirmed at histologic examination, which showed considerable leakage of the contrast agent into the islet cell interstitium. PGC-Gd-DTPA-F-enhanced MR imaging allows for the in vivo assessment of vascular damage of the graft T cell challenge.

Protected graft copolymer excipient leads to a higher acute maximum tolerated dose and extends residence time of vasoactive intestinal Peptide significantly better than sterically stabilized micelles.

To determine and compare pharmacokinetics and toxicity of two nanoformulations of Vasoactive Intestinal Peptide (VIP). VIP was formulated using a micellar (Sterically Stabilized Micelles, SSM) and a polymer-based (Protected Graft Copolymer, PGC) nanocarrier at various loading percentages. VIP binding to the nanocarriers, pharmacokinetics, blood pressure, blood chemistry, and acute maximum tolerated dose (MTD) of the formulations after injection into BALB/c mice were determined. Both formulations significantly extend in vivo residence time compared to unformulated VIP. Formulation toxicity is dependent on loading percentage, showing major differences between the two carrier types. Both formulations increase in vivo potency of unformulated VIP and show acute MTDs at least 140 times lower than unformulated VIP, but still at least 100 times higher than the anticipated highest human dose, 1-5μg/kg. These nanocarriers prevented a significant drop in arterial blood pressure compared to unformulated VIP. While both carriers enhance in vivo residence time compared to unformulated VIP and reduce the drop in blood pressure immediately after injection, PGC is the excipient of choice to extend residence time and improve the safety of potent therapeutic peptides such as VIP.

Abstract 3663: Characterization of Cerebrovascular Parameters using MRI in Endothelial Nitric Oxide Synthase Knockout Mice

Endothelial-derived nitric oxide (NO) is important for properly regulating vascular tone and maintaining blood pressure. Mice lacking endothelial NO synthase (eNOS), i.e. loss of endothelial NO production, have systemic hypertension and develop larger cerebral infarction upon cerebral ischemia. Given that constitutively produced NO is necessary for a normal endothelial function, we posit that cerebrovascular characters in eNOS KO mice brain may differ in structure and physiology. In this study, we aim to establish MRI-derived vascular parameters such as cerebral blood volume (CBV), water exchange index (WEI), and vessel size index (VSI) using two different MRI intravascular contrast agents (Gd-PGC (Protected graft copolymer bearing covalently linked Gd- DTPA residues) and SPION (superparamagnetic iron oxide nanoparticle)). We also investigated whether perivascular aquaporine (AQP) proteins, which play a central role in the pathophysiology of many diseases, are differently expressed in eNOS KO mice. Flip angle dependence of the MRI signal intensity on transvascular water exchange rate was used to quantify CBV and WEI before and after intravenous administration of Gd-PGC using wild type mice (C57BL/6, n=8) and eNOS KO mice (n=5). 2D T2 and T2* maps were also acquired before and after SPION administration for measurements of cerebral VSI. As results, eNOS KO mice have lower VSI than that that in wild type mice ( Fig. A ). The CBV of eNOS KO mice is not significantly different from that of wild type mice ( Fig. B ). Furthermore, baseline WEI significantly increased in the eNOS KO mice, indicating higher BBB water permeability. However, both AQP1 and AQP4 were less expressed in eNOS KO mice than those in wild type mice ( Fig. D ). These suggest that the loss of eNOS contribute to the decrease of the vessel diameter and increase of water permeability under a baseline physiological condition. However, expression of AQP proteins forming vascular water channels is not involved with the observed water exchange rate increase across the BBB in eNOS KO mice. The study warrants future investigations to elucidate the relationship between NO synthase and the BBB integrity and its involvement with ischemic damage.

Protected Graft Copolymer (PGC) in Imaging and Therapy: A Platform for the Delivery of Covalently and Non-Covalently Bound Drugs

Initially developed in 1992 as an MR imaging agent, the family of protected graft copolymers (PGC) is based on a conjugate of polylysine backbone to which methoxypoly(ethylene glycol) (MPEG) chains are covalently linked in a random fasion via N-ε-amino groups. While PGC is relatively simple in terms of its chemcial composition and structure, it has proved to be a versatile platform for in vivo drug delivery. The advantages of poly amino acid backbone grafting include multiple available linking sites for drug and adaptor molecules. The grafting of PEG chains to PGC does not compromise biodegradability and does not result in measurable toxicity or immunogenicity. In fact, the biocompatablility of PGC has resulted in its being one of the few 100% synthetic non-proteinaceous macromolecules that has suceeded in passing the initial safety phase of clinical trials. PGC is capable of long circulation times after injection into the blood stream and as such found use early on as a carrier system for delivery of paramagnetic imaging compounds for angiography. Other PGC types were later developed for use in nuclear medicine and optical imaging applications in vivo. Recent developments in PGC-based drug carrier formulations include the use of zinc as a bridge between the PGC carrier and zinc-binding proteins and re-engineering of the PGC carrier as a covalent amphiphile that is capabe of binding to hydrophobic residues of small proteins and peptides. At present, PGC-based formulations have been developed and tested in various disease models for: 1) MR imaging local blood circulation in stroke, cancer and diabetes; 2) MR and nuclear imaging of blood volume and vascular permeability in inflammation; 3) optical imaging of proteolytic activity in cancer and inflammation; 4) delivery of platinum(II) compounds for treating cancer; 5) delivery of small proteins and peptides for treating diabetes, obesity and myocardial infarction. This review summarizes the experience accumulated by various research groups that chose to use PGC as a drug delivery platform.

Protected Graft Copolymer (PGC) Basal Formulation of Insulin as Potentially Safer Alternative to Lantus® (Insulin-Glargine): A Streptozotocin-Induced, Diabetic Sprague Dawley Rats Study

To develop a long-acting formulation of native human insulin with a similar pharmacodynamics (PD) profile as the insulin analogue insulin glargine (Lantus®, Sanofi-Aventis) with the expectation of retaining native human insulin's superior safety profile as insulin glargine is able to activate the insulin-like growth factor 1 (IGF-1) receptor and is linked to a number of malignancies at a higher rate than regular human insulin. Development of protected graft copolymer (PGC) excipients that bind native human insulin non-covalently and testing blood glucose control obtained with these formulations in streptozotocin-induced diabetic Sprague Dawley rats compared to equally dosed insulin glargine. PGC-formulations of native human insulin are able to control blood glucose to the same extent and for the same amount of time after s.c. injection as the insulin analogue insulin glargine. No biochemical changes were made to the insulin that would change receptor binding and activation with their possible negative effects on the safety of the insulin. Formulation with the PGC excipient offers a viable alternative to biochemically changing insulin or other receptor binding peptides to improve PD properties.

Imaging the pancreatic vasculature in diabetes models

Vascular parameters, such as vascular volume, flow, and permeability, are important disease biomarkers for both type 1 and type 2 diabetes. Therefore, it is essential to develop approaches to monitor the changes in pancreatic microvasculature non-invasively. Here, we describe the application of the long-circulating, paramagnetic T1 contrast agent, protected Graft Copolymer bearing covalently linked gadolinium diethylenetriaminepentaacetic acid residues and labelled with fluorescein (PGC-GdDTPA-F) for the non-invasive semi-quantitative evaluation of vascular changes in diabetic models using magnetic resonance imaging. We observed a significantly higher accumulation of protected graft copolymer bearing covalently linked gadolinium diethylenetriaminepentaacetic acid residues and labelled with fluorescein in the pancreata of BBDR rats induced to develop diabetes, as compared to non-diabetic controls at 1 h post-injection. No differences were seen in the blood pool, kidney, or muscle, indicating that the effect is specific to the diabetic pancreas. Fluorescence microscopy revealed a marked increase in contrast agent availability in the pancreas with the development of the pathology. Similar changes were noted in the homozygous Leprdb mouse model of type 2 diabetes. This effect appeared to result both from the increase of vascular volume and permeability. High-molecular weight paramagnetic blood volume contrast agents are valuable for the in vivo definition of pancreatic microvasculature dynamics by magnetic resonance imaging. The increase in vascular volume and permeability, associated with diabetic inflammation, can be monitored non-invasively and semi-quantitatively by magnetic resonance imaging in diabetic BBDR rats. This imaging strategy represents a valuable research tool for better understanding of the pathologic process.

Extending Residence Time and Stability of Peptides by Protected Graft Copolymer (PGC) Excipient: GLP-1 Example

To determine whether a Protected Graft Copolymer (PGC) containing fatty acid can be used as a stabilizing excipient for GLP-1 and whether PGC/GLP-1 given once a week can be an effective treatment for diabetes. To create a PGC excipient, polylysine was grafted with methoxypolyethyleneglycol and fatty acid at the epsilon amino groups. We performed evaluation of the binding of excipient to GLP-1, the DPP IV sensitivity of GLP-1 formulated with PGC as the excipient, the in vitro bio-activity of excipient-formulated GLP-1, the in vivo pharmacokinetics of excipient-formulated GLP-1, and the efficacy of the excipient-formulated GLP-1 in diabetic rats. We showed reproducible synthesis of PGC excipient, high affinity binding of PGC to GLP-1, slowed protease degradation of excipient-formulated GLP-1, and that excipient-formulated GLP-1 induced calcium influx in INS cells. Excipient-formulated GLP-1 stays in the blood for at least 4days. When excipient-formulated GLP-1 was given subcutaneously once a week to diabetic ZDF rats, a significant reduction of HbA1c compared to control was observed. The reduction is similar to diabetic ZDF rats given exendin twice a day. PGC can be an ideal in vivo stabilizing excipient for biologically labile peptides.

PGC nanocarrier-formulated native GLP-1 prevents diabetes in NOD mice (42.3)

Abstract Formulation of peptides in a nanocarrier made up of protected-graft-copolymer (PGC) can greatly enhance pharmacokinetics and biodistribution of the peptides in vivo. Glucagon-like peptide 1 (GLP-1) is β-cell protective and decreases the severity symptoms of diabetes in Type 2 and streptozotocin models. We hypothesized that PGC-formulated GLP-1 can prevent Type 1 diabetes in NOD mice. 4-5 week old female NOD mice [n=25] were treated for eight weeks with 3mg/kg PGC-formulated GLP-1 administered s.c. either once or three times per week. After the treatment period, the mice were monitored for signs of diabetes until they reached 36 weeks of age. A group of NOD mice treated with anti-CD3 antibodies (0.5mg/kg i.p. once at treatment week 0 and once at treatment week 1) was used as a positive control for diabetes prevention. At 36 weeks of age, 48% of the mice treated with saline had developed diabetes. Anti-CD3 treatment prevented 50% of the diabetes cases in the mice with only 24% of the mice in this group having developed diabetes at 36 weeks of age. Once a week GLP-1 treatment (3mg/kg s.c.) was as effective in preventing diabetes as anti-CD3 treatment with only 28% of mice being diabetic at 36 weeks of age. Surprisingly, there was no difference between the three times per week GLP-1 treatment group (3mg/kg s.c.) and the saline control: 54.1% of the mice treated three times per week became diabetic, which was not statistically significantly different form the 48% diabetes incidence in the saline group.

Noninvasive Magnetic Resonance Imaging of Microvascular Changes in Type 1 Diabetes

The pathogenesis of type 1 diabetes involves autoimmune lymphocytic destruction of insulin-producing beta-cells and metabolic dysregulation. An early biomarker of pancreatic islet damage is islet microvascular dysfunction, and alterations in vascular volume, flow, and permeability have been reported in numerous models of type 1 diabetes. Consequently, the ability to noninvasively monitor the dynamics of the pancreatic microvasculature would aid in early diagnosis and permit the assessment, design, and optimization of individualized therapeutic intervention strategies. Here, we used the long circulating paramagnetic contrast agent, protected graft copolymer (PGC) covalently linked to gadolinium-diethylenetriaminepentaacetic acid residues (GdDTPAs) labeled with fluorescein isothiocyanate (PGC-GdDTPA-F), for the noninvasive semiquantitative evaluation of vascular changes in a streptozotocin (STZ)-induced mouse model of type 1 diabetes. Diabetic animals and nondiabetic controls were monitored by magnetic resonance imaging (MRI) after injection of PGC-GdDTPA-F. Our findings demonstrated a significantly greater accumulation of PGC-GdDTPA-F in the pancreata of diabetic animals compared with controls. MRI permitted the in vivo semiquantitative assessment and direct visualization of the differential distribution of PGC-GdDTPA-F in diabetic and control pancreata. Ex vivo histology revealed extensive distribution of PGC-GdDTPA-F within the vascular compartment of the pancreas, as well as considerable leakage of the probe into the islet interstitium. By contrast, in nondiabetic controls, PGC-GdDTPA-F was largely restricted to the pancreatic vasculature at the islet periphery. Based on these observations, we conclude that in the STZ model of type 1 diabetes, changes in vascular volume and permeability associated with early stages of the disease can be monitored noninvasively and semiquantitatively by MRI.

Detection of Early Antiangiogenic Effects in Human Colon Adenocarcinoma Xenografts:In vivoChanges of Tumor Blood Volume in Response to Experimental VEGFR Tyrosine Kinase Inhibitor

Antiangiogenesis is emerging as efficient strategy for targeting and potentially eliminating neoplastic tumor vessels. The main goal of this study was to establish whether absolute tumor blood volume (V(b)) change could be used as an early predictor of antiangiogenesis in ectopic and orthotopic colon carcinomas. To assess therapy-induced changes of V(b), we did comparative analysis of signal intensities in tumors and muscle using steady-state magnetic resonance imaging (MRI) assisted with an intravascular paramagnetic contrast agent [gadolinium-labeled protected graft copolymer (PGC-Gd)]. Athymic mice with implanted human MV522 tumors were treated with vascular endothelial growth factor type 2 receptor tyrosine kinase inhibitor (VEGFR2-TKI) that has been shown to inhibit VEGFR2 phosphorylation and tumor growth in vivo. Animals were imaged either after a single day or after a 1-week course of treatments. The measured V(b) in ectopic tumors was 2.5 +/- 1.5% of total tissue volume 1 week after the implantation (n = 8). Two doses of VEGFR2-TKI (25 mg/kg, p.o., b.i.d.) resulted in a decrease of V(b) to 1.3 +/- 0.3%. In orthotopic tumors, the measured V(b) was initially higher (11.9 +/- 2.0%); however, VEGFR2-TKI treatment also resulted in a statistically significant decrease of V(b). The absolute V(b) was not affected in the muscle as a result of treatments. MRI measurements were corroborated by using isotope and correlative histology experiments. Our results show that steady-state MRI is highly sensitive to early antiangiogenic effects caused by small molecule drugs.

Pan and sentinel lymph node visualization using a near-infrared fluorescent probe.

A number of different types of agents have been employed to aid in the visualization of lymph nodes, particularly the sentinel lymph node, and to decrease the tissue destruction associated with the diagnosis of nodal metastases. The current study was performed to see if a novel macromolecular near-infrared fluorescent (NIRF) probe could be used to visualize lymph nodes after intravenous administration (pan-node visualization) or subcutaneous administration (sentinel node visualization), and serve as method for guiding dissection with interventional radiologic and surgical procedures. Cy5.5-PGC, the near-infrared dye Cy5.5 coupled to a protected graft copolymer (PGC), was injected (i.v. or s.c.) into nude mice. Twenty-four hours later white light and NIRF images were obtained on (i) the live animal, (ii) a partially dissected animal, and (iii) tissue specimens. With Cy5.5-PGC administered intravenously, axillary nodes were visualized from outside a living mouse. With partial dissection, iliac and aortic nodes were visible as concentrated foci of high-intensity NIRF signals. With subcutaneous injection in the front extremity, axillary and brachial nodes draining the injection site were easily visualized. NIRF imaging provides a nonradioactive method of visualizing lymph nodes through layers of tissue that can be employed with intravenous or subcutaneous injection.

Pan and Sentinel Lymph Node Visualization Using a Near-Infrared Fluorescent Probe

A number of different types of agents have been employed to aid in the visualization of lymph nodes, particularly the sentinel lymph node, and to decrease the tissue destruction associated with the diagnosis of nodal metastases. The current study was performed to see if a novel macromolecular near-infrared fluorescent (NIRF) probe could be used to visualize lymph nodes after intravenous administration (pan-node visualization) or subcutaneous administration (sentinel node visualization), and serve as method for guiding dissection with interventional radiologic and surgical procedures. Cy5.5-PGC, the near-infrared dye Cy5.5 coupled to a protected graft copolymer (PGC), was injected (i.v. or s.c.) into nude mice. Twenty-four hours later white light and NIRF images were obtained on (i) the live animal, (ii) a partially dissected animal, and (iii) tissue specimens. With Cy5.5-PGC administered intravenously, axillary nodes were visualized from outside a living mouse. With partial dissection, iliac and aortic nodes were visible as concentrated foci of high-intensity NIRF signals. With subcutaneous injection in the front extremity, axillary and brachial nodes draining the injection site were easily visualized. NIRF imaging provides a nonradioactive method of visualizing lymph nodes through layers of tissue that can be employed with intravenous or subcutaneous injection.