Controlled release of interleukin-2 from biodegradable microspheres.

We have evaluated the use of biodegradable poly(DL-lactide-co-glycolide) microspheres for the controlled release of interleukin-2 (IL-2) and its modified forms: succinyl IL-2 (SIL-2) and polyethylene glycol-modified IL-2 (PEG IL-2). We show that a microsphere formulation can be prepared from PEG IL-2 using HSA as an excipient which, after an initial burst, releases 2-3% PEG IL-2 per day in a bioactive form continuously over a 20- to 30-day period.

Lyophilized formulations of recombinant tumor necrosis factor.

Recombinant tumor necrosis factor-alpha (TNF), an investigational biological response modifier, is a protein and is susceptible to particulate generation during handling in dilute aqueous solutions. TNF is prone to formation of nonreducible dimers and oligomers during formulation, lyophilization, and storage. The effect of various parameters, such as the pH, protein concentration, and nature of excipients present during lyophilization, on the formation of nonreducible dimers and oligomers was investigated. The results of these studies indicate that these parameters can significantly alter the rate of this reaction. Inclusion of an amorphous buffer and an appropriate amount of a crystallizing sugar (mannitol) combined with a suitable quantity of an amorphous protectant (dextran, sucrose, trehalose, or 2-hydroxypropyl-beta-cyclodextrin) was shown to reduce the formation of these dimeric and oligomeric species during lyophilization. Representative lyophilized formulations of TNF based on selected amorphous excipients were found to be fully bioactive and stable over 9 months.

The potential use of cyclodextrins in parenteral formulations.

The general use of cyclodextrins in drug formulations is reviewed. The ability of cyclodextrins to form reversible inclusion complexes with many drugs can eliminate various undesirable physicochemical properties. While beta-cyclodextrin is extremely useful in many of these applications, it is toxic when given parenterally, precluding its use in i.v. and other formulations. Chemically modified cyclodextrins such as 2-hydroxypropyl-beta-cyclodextrin are amorphous isomeric mixtures which are potent complexing agents and innocuous when administered i.e., either acutely or subchronically. The use of these modified cyclodextrins in parenteral formulations and to solubilize and stabilize various proteins and peptides is presented.

Use of 2-hydroxypropyl-beta-cyclodextrin as a solubilizing and stabilizing excipient for protein drugs.

A chemically modified, amorphous beta-cyclodextrin, namely, 2-hydroxypropyl-beta-cyclodextrin (HPCD), was examined as a solubilizing and stabilizing agent for protein drugs. The aqueous solubility of ovine growth hormone at pH 7.4 was increased through the use of HPCD. This effect was manifested by higher UV transparency at 600 nm. Interleukin-2 (IL-2) is rendered insoluble upon lyophilization in the absence of stabilizers. Use of aqueous HPCD provides a clear solution, as indicated by fluorometric light scattering, and inhibits aggregate formation, as shown by ultracentrifugation and Western blot analyses. In addition, there were no major conformational changes of IL-2 in HPCD formulation as indicated by fourth-derivative ultraviolet spectroscopy. Finally, IL-2 retained 100% of its biopotency when prepared in HPCD solutions. Aggregation of insulin was also suppressed by HPCD. These data, as well as the i.v. safety of HPCD and its well-characterized chemical composition, suggest that this starch derivative may be a potentially useful excipient for protein drugs intended for parenteral use.

Release of human serum albumin from poly(lactide-co-glycolide) microspheres.

Human serum albumin (HSA) was encapsulated in a 50:50 copolymer of DL-lactide/glycolide in the form of microspheres. These microspheres were used as a model formulation to study the feasibility of controlling the release of large proteins over a 20- to 30-day period. We show that HSA can be successfully incorporated into microspheres and released intact from these microspheres into various buffer systems at 37 degrees C. A continuous release of the protein could be achieved in physiological buffers at 37 degrees C over a 20- to 30-day period from microspheres with high protein loadings (11.6%). These results demonstrate the potential of poly(DL-lactide-co-glycolide) microspheres for continuous delivery of large proteins.

Development of a lyophilized formulation of interleukin-2.

Native human interleukin-2 (IL-2) comprises a group of glycoproteins of MW 13,000-17,500. Recombinant human IL-2 (rhIL-2) (Cetus) is derived from E. coli and is not glycosylated. We have evaluated several processes for manufacturing rhIL-2, based on different chaotropic agents for solubilization of insoluble protein pastes. Formulation work carried out with material purified by one of these processes is reported here. Our studies have indicated that the presence of a stabilizer in the form of an amorphous excipient, such as amino acids, a non-ionic surfactant (polysorbate 80), hydroxypropyl-beta-cyclodextrin or human serum albumin was essential for preservation of rhIL-2 during lyophilization. Each of these formulations exhibited its own unique problems. We have overcome these problems through a systematic formulation development program and have been successful in developing several lyophilized formulations of rhIL-2 with optimum properties and performance.