99mTc-Interleukin-18-binding protein-Fc-interlukin-1 receptor antagonist

Excerpt

Interleukin-18 (IL-18) is a proinflammatory cytokine produced by macrophages, epithelial cells, and activated T cells (1, 2), and it plays an important role in inflammation and immune response (3, 4). IL-18 induces production of tumor necrosis factor and IL-1 in mononuclear cells. A variety of normal and malignant cells can produce and respond to IL-18 through its receptor (IL-18R). A soluble secreted IL-18 binding protein (IL-18bp) was found to bind to IL-18 with high affinity (dissociation constant (K_d) = 0.4 nM) and to neutralize the biological effects of IL-18 by blocking its interaction with IL-18R (5, 6). IL-18bp-Fc is a 40-kDa glycoprotein with an immunoglobulin (Ig) domain.

The interleukin-1 family of two proinflammatory cytokines, IL-1α and IL-1β, which bind to two IL-1 receptors (IL-1R1 and IL-1R2), and an IL-1R antagonist (IL-1ra), is mainly produced by activated macrophages and tissue macrophages (7). IL-1α and IL-1β are important mediators of the inflammatory response and hematopoiesis, and they are involved in a variety of cellular activities, including cell proliferation, differentiation, and apoptosis. IL-1 is involved in chronic inflammatory diseases and in neuropathological conditions (8, 9). The balancing action of IL-1 and IL-1ra plays an important role in the regulation of inflammation and immune responses (10). IL-1ra has been shown to be effective as an anti-inflammatory treatment in several chronic inflammatory diseases and stroke (11, 12). A human recombinant, non-glycosylated form of the human IL-1ra (rhIL-1ra, Anakinra) has been approved by the United States Food and Drug Administration for the treatment of rheumatoid arthritis (13).

IL-1 and IL-18 exhibit additive or synergistic effects in promoting pathophysiological processes observed in many inflammatory diseases (14). A dual domain IL-18bp-Fc-IL-1ra fusion protein was constructed by joining IL-18bp and IL-1ra cDNA to the Fc fragment of human IgG₁ cDNA in an expression plasmid (15). The amino-terminal segment binds to IL-18, and the carboxyl-terminal sequence binds to the IL-1R. Liu et al. (15) radiolabeled IL-18bp-Fc-IL-1ra with ^99mTc via 2-iminothiolane reduction to produce ^99mTc-IL-18bp-Fc-IL-1ra for use with single-photon emission computed tomography (SPECT) imaging of inflammation in mice.