Differences of biodistribution, pharmacokinetics, and tumor targeting between interleukins 2 and 15.
Interleukin-2 (IL-2) and interleukin-15 (IL-15) are T-cell tropic factors that share beta and gammac subunits of their receptors on T/NK-cells. Although these two cytokines share receptor components, the IL-15Ralpha molecule is expressed constitutively by various tissue cells, whereas the IL-2Ralpha expression is mostly restricted to activated mononuclear cells. Consequently, we postulated that the biodistribution of IL-15 might be different from that of IL-2 and that individual alpha chains play an important role in this respect. This study investigated the differences between IL-2 and IL-15 in pharmacokinetics, biodistribution, and their tumor-targeting abilities. It found that only IL-2 showed specific binding to a protein, alpha2-macroglobulin, which may be the reason that IL-2 displays longer blood clearance than IL-15. Upon injection of these cytokines into mice, we observed that IL-15 accumulated significantly more than IL-2 in kidney, spleen, and bone. These are all tissues that express IL-15 receptor alpha but not IL-2 receptor alpha. To evaluate the tumor-targeting ability of each cytokine, we used nude mice xenografted with three A431 tumors, parental and cells transfected with alpha subunit of the receptor for either IL-2 or IL-15. When examined using radioiodinated IL-2 or IL-15, each cytokine accumulated on the target cells, expressing its respective alpha chain, suggesting that the expression of the alpha chains is sufficient to define specific biodistribution of IL-2 and IL-15, although these cytokines share the beta and yc molecules of their receptors. IL-15 displayed better target-specific accumulation and more rapid clearance from the circulation than did IL-2, and thus it can be considered to be a novel and unique therapeutic agent.
Kobayashi
H
H
Department of Nuclear Medicine, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA.
Carrasquillo
J A
JA
Paik
C H
CH
Waldmann
T A
TA
Tagaya
Y
Y
D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000276:immunology / Q000378:metabolism*; D005260:Female; D006801:Humans; D019409:Interleukin-15 / Q000097:blood / Q000493:pharmacokinetics*; D007376:Interleukin-2 / Q000097:blood / Q000493:pharmacokinetics*; D007457:Iodine Radioisotopes; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D011994:Recombinant Proteins / Q000097:blood / Q000493:pharmacokinetics; D014018:Tissue Distribution; D014162:Transfection; D014183:Transplantation, Heterologous; D000511:alpha-Macroglobulins / Q000378:metabolism
D019409:Interleukin-15; D007376:Interleukin-2; D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D000511:alpha-Macroglobulins