Hiroo Maeda

Development of a new drug delivery system for protein drugs using silicone (II)

In order to achieve a zero-order release of protein drugs, we have developed a new drug delivery system using silicone, which is named the covered-rod-type formulation. Preparation of the covered-rod-type formulation was conducted under mild conditions without heat treatment or the use of organic solvents. The covered-rod-type formulation released human serum albumin (HSA) or interferon (IFN) at a constant rate for 30-100 days in vitro without significant initial burst. When the IFN covered-rod-type formulation was implanted in nude mice, the serum IFN concentration was maintained at a constant level during the period of observation, i.e., 28 days. The covered-rod-type formulation enabled precise control of the release of the protein drugs and would be expected to increase the duration of the drug effect and to reduce the frequency of administration and side effects.

DISTRIBUTION OF NERVE GROWTH FACTOR IN CAT BRAINS FOLLOWING TOPICAL APPLICATION OF SOLUTION OR MINIPELLET

The distribution of nerve growth factor (NGF) was studied after topical application of NGF solution or NGF Minipellet into the caudate nucleus of cat brains. Each aliquot of NGF solution or a piece of NGF Minipellet contains 200 micrograms of mouse 2.5S beta-NGF. The concentrations of NGF in various areas of the brain were determined by enzyme-linked immunosolvent assay (ELISA). The tissue concentrations of NGF were very high at 6 h after injection of NGF solution (124.0 +/- 2.46 to 2144.0 +/- 16.03 ng g-1), but quickly decreased on day 1. The tissue concentrations of NGF were low at 6 h after implantation of NGF Minipellet, but were considerably increased on day 1 (11.22 +/- 3.36 to 72.04 +/- 20.45 ng g-1), and slowly decreased during the following 6 to 14 days. The present study demonstrates the temporal and spatial profiles of NGF distribution in the brain of middle-sized animals after topical application. Injection of NGF solution resulted in abrupt, but very transient, elevation of tissue NGF. Implantation of NGF Minipellet maintained the tissue NGF at biologically effective levels for 6 to 14 days.

Novel sustained release formulation using collagen as a carrier material. (1)-Dosage form design of interferon minipellet.

We have developed a novel sustained release formulation, minipellet, which is applicable to various kinds of biologically active proteins. In this study, dosage form design of interferon (IFN) minipellet was investigated. First, in order to select suitable carrier material, matrix type formulations were prepared with natural biodegradable polymers, human serum albumin (HSA), gelatin and atelocollagen, and the release profiles of IFN from these polymers were compared. IFN was released slowly from the sample made of atelocollagen but rapidly from the samples made of HSA and gelatin. The release of IFN from the atelocollagen films, prepared by drying the atelocollagen solution, varied with the atelocollagen concentration before drying. This suggested that IFN release was controlled by the density of atelocollagen matrix. So, in order to obtain the higher matrix density of atelocollagen, we newly designed a cylindical dosage formulation prepared by extrusion and air-drying of an atelocollagen solution with high concentration and named minipellet. IFN was constantly released from minipellet in vitro. Pharmacokinetic studies in mice showed that the serum IFN concentration was maintained for a long time with minipellet. To determin the optimal minipellet composition, IFN minipellets containing different amount of HSA were prepared and IFN release profile from them in dogs was evaluated, The IFN concentration increased gradually after the administration of IFN minipellet containing 30% (w/w) HSA, reached Cmax after 24h, and decreased gradually thereafter with a detectable level for 10 days. The IFN minipellet is expected to offer a significant advantage in IFN therapy because the attenuated peak IFN concentrations in serum may reduce the side effects and the sustained release may reduce the frequency of administration.

Profile of rhBMP-2 release from collagen minipellet and induction of ectopic bone formation

For a cylindrical controlled‐release formulation using collagen as a carrier, called the minipellet (MP), which contains rhBMP‐2, the relationship between the diameter of MPs and rhBMP‐2 release profiles was investigated, and its effect in inducing bone formation was evaluated. Samples with three different diameters were tested for each of the following formulations: MP without additives, MP with 10% (w/w) glutamic acid (Glu) and 20% (w/w) alanine (Ala), and MP with 20% (w/w) Glu and 20% (w/w) Ala. The results of the in vitro release test and the amount of rhBMP‐2 remaining in the MPs after subcutaneous implantation into mice were compared among different samples. It was found that the addition of Glu accelerated release of rhBMP‐2 effectively. Release was accelerated as the diameter of MP became smaller and the amount of Glu added increased. The amount of calcium formed in 3 weeks after subcutaneous implantation into mice was dose‐dependent. The amount of calcium formed per unit rhBMP‐2 dose tended to increase as the diameter of MP became smaller and the amount of Glu added became greater; calcification was thus associated with release rate. These results indicate that MPs with smaller diameters induce bone formation more efficiently. For use in the treatment of fracture, etc., MP is considered to be a suitable dosage form, which can be administered noninvasively.