James C. McRea

Biodegradable block copolymers for delivery of proteins and water-insoluble drugs

Release of several drugs from new ABA-type biodegradable thermal gels, ReGel, including proteins and conventional molecules, are presented. These are biodegradable, biocompatible polymers that demonstrate reverse thermal gelation properties. Organic solvents are not used in the synthesis, purification, or formulation of these polymers. The unique characteristics of ReGel hinge on the following two key properties: (1) ReGel is a water soluble, biodegradable polymer at temperatures below the gel transition temperature; (2) ReGel forms a water-insoluble gel once injected. This is consistent with a hydrophobically bonded gel state where all interactions are physical, with no covalent crosslinking. An increase in viscosity of approximately 4 orders of magnitude accompanies the sol--gel transition. The gel forms a controlled release drug depot with delivery times ranging from 1 to 6 weeks. ReGels inherent ability to solubilize (400 to >2000-fold) and stabilize poorly soluble and sensitive drugs, including proteins is a substantial benefit. The gel provided excellent control of the release of paclitaxel for approximately 50 days. Direct intratumoral injection of ReGel/paclitaxel (OncoGel) results in a slow clearance of paclitaxel from the injection site with minimal distribution into any organ. Efficacies equivalent to maximum tolerated systemic dosing were observed at OncoGel doses that were 10-fold lower. Data on protein release (pGH, G-CSF, insulin, rHbsAg) and polymer biocompatibility are discussed.

Self-regulating insulin delivery systems: III. In vivo studies☆

Abstract A biochemical approach for the development of a self-regulating insulin delivery system is based on the principle of competitive and complementary binding behavior of concanavalin A (Con A) with glucose and glycosylated insulin. The major objective of this system is to achieve delivery of a biologically active agent at appropriate levels in response to changing metabolic needs. Previously, we have synthesized several glycosylated insulin (G-insulin) derivatives which maintain biological activity. The G-insulin derivatives also demonstrate varying binding affinities to Con A when compared to glucose. In vitro characterization of the complementary and competitive binding behavior of the Con A-G-insulin complexes has shown that, when challenged with varying concentrations of glucose, corresponding levels of G-insulin are released. Furthermore, it has been shown that G-insulin exhibits enhanced stability against aggregation. For the in vivo studies, pancreatectomized mongrel dogs were used. Prior to the pancreatectomy, each animals glucose tolerance was measured by intravenous glucose tolerance test (IVGTT). After the pancreatectomy, animals were maintained by daily NPH insulin (subcutaneous) injection for one week. At the end of this period, NPH insulin was discontinued for 24 h, and identical IVGTT was performed to establish “diabetic controls” for each pancreatectomized dog. The implant used for delivery of the G-insulin (SAPM-insulin, succinylamidophenyl-α- d -mannopyranoside conjugated insulin in this case) consists of a regenerated cellulose membrane, approximately 5.7 cm in length and 1.8 cm in diameter. All components, SAPM-insulin—Con A complex, and the cellulose membrane, were sterilized prior to surgery. A 5 cm incision was made into the peritoneal cavity. The implant was inserted through the incision and was anchored to the abdominal wall by a simple ligature placed distal to one end of the implant. Peripheral glucose levels were monitored during the immediate 48 h post-op period. Then the IVGTT as described for the controls were performed on the implanted animals.

Self-reguiating isnssultn delivery systems II. In vitro studies

Abstract A design for a self-regulating insulin delivery system based on the competitive binding of glucose and glycosylated insulin to the lectin Concanavalin A is proposed. A different approach to diabetes therapy is the attempt to effect a permanent cure of the disease by supplementing the patients defective pancreas with a normally functioning transplant. However, pancreatic transplantation in humans is stilt in its early stage, and the major problems including rejection of the transplants still remain unsolved. In phase one of this investigation, described in a companion paper, eight glycosylated insulin derivatives were synthesized. In the experiments described here it was found that the glycosylated insulins all show biological activity; several are also more stable against aggregation than commercial insulin. Of various hydrogel membranes studied, porous poly (hydroxyethyl methacrylate) membranes showed optimum diffusvity for glucose and insulin ; p- HEMA was therefore selected as being most suitable for further investigation. The exchange release of two glycosylated insulin derivatives , p- (succinylamido)phenyl-α-D-mannopyranoside—insulin and p- (succinylamido)phenyl-α-D-glucopyranoside—insulin, through porous p- HEMA shows considerable promise for use in a self-regulating insulin delivery system .

Self Regulating Insulin Delivery System — A Chemical Approach

A design for a self regulating insulin delivery system via a chemical approach is proposed based on the competitive binding nature of blood glucose and glycosylated insulin to lectin. The glycosylated insulin bound lectin is encapsulated using biodegradable or nondegradable biomedical polymers. The polymer membranes control glucose influx and insulin efflux while subsequent insulin release depends upon the glucose concentration present, a natural biofeedback.

Reversal of anticoagulation without protamine using a heparin removal device after cardiopulmonary bypass

Protamine sulfate is routinely administered after cardiopulmonary bypass to reverse systemic heparinization, but may cause a severe hypotensive reaction in as many as 2% of patients. Research Medical, Inc., has developed an extracorporeal venovenous heparin removal device (HRD) for use in patients at high risk for a protamine reaction. Circulation through the HRD removes heparin by hollow fiber plasma separation and selective sorption of anionically charged heparin to a polycationically charged poly-L-lysine ligand coupled to a agarose substrate. The heparin depleted plasma then reenters the whole blood pathway and is returned to the patient through the double lumen catheter in the right atrium. To evaluate the HRD in a clinically relevant model, cardiopulmonary bypass was performed in pigs using RA-Ao cardiopulmonary bypass (120 min) with systemic heparinization (300 IU/kg), a nonpulsatile pump with a membrane oxygenator, and systemic hypothermia (28 degrees C). Group 1 (HEP n = 7) had no intervention to neutralize the heparin; Group 2 (HRD n = 7) used the HRD. After 19.7 +/- 4.2 min of circulation through the HRD, the activated clotting time had returned to baseline, whereas the pigs in the HEP group were still anticoagulated (activated clotting time = 396 +/- 152 sec; time to baseline was 124 +/- 9 min). There were no significant differences between groups with respect to hemodynamics, hematocrit levels, leukocyte profiles, or platelet counts, HRD is an effective heparin removal device in a pig model of cardiopulmonary bypass and awaits a phase I clinical trial in humans.

Heparin clearance profiles after systemic anticoagulation using a heparin removal device system

An extracorporeal heparin removal device system (HRDS) based on plasma separation and affinity adsorption has been developed to reduce the risks of protamine-related adverse reactions. The heparin clearance profile of the HRDS was characterized by the first-order exponential depletion. A mathematical model was established to predict the time to achieve 85% heparin removal for different body weights at 700 ml/min and 1400 ml/min extracorporeal HRDS blood flow. With an HRDS flow of 700 ml, 85% of total body heparin removal cannot be achieved within 30 min for subjects greater than 50 kg. With an HRDS flow of 1400 ml/min, 85% heparin removal can be achieved within 32 min for subjects larger than 90 kg. Such model predictions were validated in an adult swine (n = 10) model of 60-min, hypothermic (28°C) cardiopulmonary bypass (CPB). Animals were given 300 U/ kg intravenous heparin and 5000 U heparin in the circuit prime for initial heparinization, with subsequent heparin given to maintain activated clotting time above 450 sec. Immediately following CPB, plasma heparin concentration as determined by anti-factor Xa assays was 4.40 ± 1.08 U/ml in the 700 ml/min group and 4.78 ± 0.70 U/ml in the 1400 ml/min groups, respectively (p > 0.05). Target HRDS flow was 700 ml/min for animals below 75 kg and 1400 ml/min for animals above 75 kg. The mean body weight in the 1400 ml/min group (81.4 ± 3.7 kg) was significantly higher than that in the 700 ml/min group (67.2 ± 2.2 kg) (p < 0.05), with the actually achieved HRDS flow 658.5 ± 20.8 and 1437.4 ± 30.1 ml/min, respectively. During the HRDS run, plasma heparin concentration followed the predicted first-order exponential depletion (r2 = 0.97 for the 700 ml/min group and r2 = 0.99 for the 1400 ml/min group). In the 700 ml/min group, the time needed to achieve 85% heparin clearance was over 40 min, whereas in the 1400 ml/min group, this time was reduced to less than 30 min despite greater body weight. At 30 min on HRDS, the 700 ml/min group had 27.4 ± 3.7% heparin left in the plasma, whereas the 1400 ml/min group had only 12.6 ± 2.5% (p < 0.05). The authors conclude heparin clearance by the HRDS can be precisely predicted with the mathematical model of first-order exponential depletion. Increasing the HRDS flow can effectively reduce the time needed to achieve a targeted heparin removal.

Antithrombotic Agent Releasing Polymers

The use of pharmacologically active agents with antithrombotic effects combined with blood contacting polymers provides a novel approach towards the improvement of blood materials interactions. Antithrombotic agents can be physically combined in a polymer solution producing a monolithically dispersed delivery device. This monolithic system contains both dissolved and undissolved active agent and is capable of diffusional release of the active agent at the surface of the polymer. Through proper design, use of this technique provides optimal therapeutic levels of selected antithrombotic agents which can be delivered to a desired site of activity while minimizing unwanted systemic side effects.

Lack of CNS depression from large doses of trimethaphan in sheep.

It is not uncommon to observe prolonged CNS depression for several hours following controlled hypotension and halothane anesthesia for neurosurgery. The present study evaluates possible contribution of large doses of trimethaphan to CNS depression. Four adult sheep were placed on transapical left ventricular bypass (TALVB) withdrawing blood from the apex of the left ventricle through a roller pump, Pall Ultipor filter, and returning the blood to a carotid artery. In the awake and unanesthetized animals, 1 to 2 gm of trimethaphan were administered IV during each experiment while maintaining mean arterial pressure at 60 to 75 torr. Two sheep stood up and knelt down without obvious correlation with dose of trimethaphan administered at the time; two remained standing and continued eating during the trimethaphan infusion. Cardiovascular recovery from these large doses of trimethaphan was within 15 to 30 minutes after the conclusion of drug infusion. The data strongly suggest that large doses of trimethaphan have no significant CNS depression in the awake and unanesthetized sheep.