Chapter 16 C o n t r o l l e d I n t r a c r a n i a l Delivery of Antibodies in the R a t Samira Salehi-Had and W. Mark Saltzman
Downloaded by CORNELL UNIV on June 8, 2012 | http://pubs.acs.org Publication Date: August 19, 1994 | doi: 10.1021/bk-1994-0567.ch016
Departments of Chemical Engineering and Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21218
To provide long-term delivery of antibodies within the intracranial space, we have developed methods for the controlled release of antibodies from polymer matrices and microspheres. IgG concentrations in the rat brain were measured following injection of IgG in saline or implantation of a polymer matrix containing IgG. IgG (10 to 100,000 ng/g) was detected near the site of administration for 28 days following either injection or implantation. IgG was also detected at lower concentrations in other quadrants of the brain and in the plasma. In all cases, IgG concentrations were highest for animals treated by polymer implantation. Initial rates of elimination from the brain were similar for IgG administered by injection and implantation (half-life ~1 day). The advantage of polymer implantation over direct injection was observed most clearly in the 14 to 28 days following administration. Polymer treated animals continued to have high IgG concentrations, even at brain sites distant from the site of administration, while IgG concentrations in the brain of injection treated animals fell sharply. Nine thousand new cases of primary brain tumor are reported in the United States each year. Nearly one-half of these cases are malignant gliomas, which are frequently fatal; even with surgical resection and radiation therapy most patients die within two years of diagnosis. Chemotherapy for malignant brain tumors is problematic. Although agents with good activity against human brain tumors are available, tne blood-brain barrier limits the entry of most systemically delivered agents into the central nervous system (CNS). To bypass this barrier, improved methods for drug delivery to the CNS have been developed in tne last several years (2-4). In addition, novel antitumor strategies have been proposea including antisense-based vaccines (5), gene therapy (6), and immunotherapy with antibody-toxin conjugates (7, 8), growth factor-toxin
0097-6156/94/0567-0278$08.00/0 © 1994 American Chemical Society In Formulation and Delivery of Proteins and Peptides; Cleland, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
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SALEHI-HAD & SALTZMAN
Intracranial Delivery of Antibodies in Rats
conjugates (9), or activated lymphocytes (10,11). In these new approaches, the limitations of drug delivery to the C N S have become even more apparent, since macromolecules like immunoglobulins, cytokines, and gene therapy vectors must be delivered locally to the brain. Intracranial controlled release polymers provide sustained levels of active agents directly to a localized t>rain region. U s i n g animal models, the feasibility of this concept has been demonstrated for anticancer agents (12, 13), steroids (14), neurotransmitters and their agonists (15-1/), nerve rowth factor (18-20), and other macromolecules (21, 22). In addition, iodegradable polyanhydride matrices containing l,3-bis(2-chloroethyl)-lnitrosurea ( B C N U ; have been used to treat human patients w i t h recurrent lioblastoma multiforme (3, 23). Controlled drug delivery i n the C N S can e achieved w i t h a number of agents, but penetration into the tissue surrounding the implant is dependent on biological and physicochemical characteristics of the compound (24). Because of their increased retention i n the brain extracellular space, compounds that are water-soluble, high molecular weight, and slowly metabolized appear to be the best suited for direct intracranial delivery (22, 24). Antibodies and antibody proteolytic fragments (Fab or F(ab')2) bave all of the characteristics that are desirable for an intracranially delivered drug: they are water soluble (>100 m g / m L ) and large (50,000 to 1,000,000 daltons) molecules w i t h plasma half-lives of many clays (see (25) for a review of antibody pharmacokinetics). Different antibody classes (IgG, I g M , or IgA) or antibody proteolytic fragments can be employed, allowing selection of the most desirable elimination and tissue penetration characteristics. Importantly, antibody molecules can be conjugated w i t h toxins to provide intrinsic cytotoxicity {8,26,27). The specificity of antibody binding to brainspecific antigens can also be selected 17,28), changing the killing properties of the agent as w e l l as its ability to penetrate through brain tissue. M e t h o d s for generating "humanized" antibodies or antigen b i n d i n g proteins w i t h reduced immunogenicity i n humans have also been developed (29, 30). The kinetics of antibody delivery to brain tissue have been e x a m i n e d f o l l o w i n g i n t r a v e n o u s (31), i n t r a c a r o t i d ( 3 1 ) , intraventricular (32), and direct intracranial (33) injection, but antibody delivery from an intracranial controlled release polymer has never been studied. In previous reports, different formulations that provide a controlled release of biologically active antibodies have been described (34-38). Here, those studies were extended microspheres appropriate for use i n the brain. In addition, one particular antibody delivery system, poly(ethylene-co-vinyl acetate) (EVAc) matrices, was used to study the kinetics of antibody e l i m i n a t i o n f o l l o w i n g controlled release i n the rat brain.
Downloaded by CORNELL UNIV on June 8, 2012 | http://pubs.acs.org Publication Date: August 19, 1994 | doi: 10.1021/bk-1994-0567.ch016
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Methods and Materials E V A c polymer matrix preparation and characterization The procedure for the preparation of E V A c / a n t i b o d y matrices has been reported previously (37). Briefly, E V A c ( E L V A X 40W, Dupont, Wilmington, D E ) was washed extensively i n water and acetone prior to use. To produce matrices of E V A c and mouse IgG at 40% loading (mass percent IgG), l y o p h i l i z e d mouse IgG (Sigma Chemical Company, St. Louis, M O ) was sieved to
