title: Tumor targeting properties of monoclonal antibodies with different affinity for target antigen CD44V6 in nude mice bearing head-and-neck cancer xenografts.
abstract: The CD44 protein family consists of isoforms with tissue-specific expression, which are encoded by standard exons and up to 9 alternatively spliced variant exons (v2-v10) of the same gene. The murine MAbs U36 and BIWA-1, directed against overlapping epitopes within the v6 region of CD44, have previously been shown to efficiently target HNSCC. We herein report on the construction of 1 chimeric (BIWA-2) and 2 humanized (BIWA-4 and BIWA-8) derivatives of BIWA-1. Together with U36 and BIWA-1, these new antibodies were evaluated for affinity to the antigen in vitro as well as for biodistribution and efficacy in RIT using nude mice bearing the HNSCC xenograft line HNX-OE. As determined by surface plasmon resonance, the MAbs bound to CD44v6 with an up to 46-fold difference in affinity (K(d) ranging from 1.1 x 10(-8) to 2.4 x 10(-10) M) with the following ranking: mMAb U36 < hMAb BIWA-4 < hMAb BIWA-8 < mMAb BIWA-1 approximately cMAb BIWA-2. To evaluate their in vivo tumor-targeting properties, 2 MAbs with identical murine or human isotype were labeled with either (131)I or (125)I and administered simultaneously (50 microg/10 microCi each) as pairs showing a stepwise decrease in the difference in affinity: U36 vs. BIWA-1 (35.0-fold difference), BIWA-4 vs. BIWA-2 (14.0-fold) and BIWA-4 vs. BIWA-8 (4.0-fold). Biodistribution was assessed at 1, 2, 3 or 4 and 7 days after injection. Remarkably, for all 3 MAb pairs tested, the lower-affinity MAb showed a higher degree and specificity of tumor localization. The difference in tumor localization was more pronounced when the difference in affinity was larger. For example, 3 days after injection, the lower-affinity mMAb U36 showed a 50% higher tumor uptake than the higher-affinity mMAb BIWA-1, while blood levels and uptake in organs were similar. After labeling with (186)Re (300 or 400 microCi), the same MAb pairs showed RIT efficacy consistent with the biodistribution data: (186)Re-U36 was more effective than (186)Re-BIWA-1, (186)Re-BIWA-4 was slightly more effective than (186)Re-BIWA-2 and (186)Re-BIWA-4 and (186)Re-BIWA-8 demonstrated similar efficacy. Based on these data, we conclude that antibodies with markedly lower affinity to a given target antigen (e.g., U36, BIWA-4) may show superior tumor targeting in comparison with higher-affinity versions of these antibodies.
authors: Department of Otolaryngology/Head and Neck Surgery, Vrije Universiteit Medical Center, Amsterdam, the Netherlands.
authors: Iris
authors: I
authors: Verel
authors: Karl-Heinz
authors: KH
authors: Heider
authors: Miranda
authors: M
authors: Siegmund
authors: Elínborg
authors: E
authors: Ostermann
authors: Erik
authors: E
authors: Patzelt
authors: Marlies
authors: M
authors: Sproll
authors: Gordon B
authors: GB
authors: Snow
authors: Günther R
authors: GR
authors: Adolf
authors: Guus A M S
authors: GA
authors: van Dongen
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D000937:Antigen-Antibody Reactions; D004305:Dose-Response Relationship, Drug; D000939:Epitopes; D006023:Glycoproteins / Q000096:biosynthesis*; D006258:Head and Neck Neoplasms / Q000628:therapy*; D006801:Humans; D018960:Hyaluronan Receptors / Q000096:biosynthesis*; D007167:Immunotherapy / Q000379:methods*; D020128:Inhibitory Concentration 50; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000628:therapy*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011868:Radioisotopes; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012211:Rhenium; D020349:Surface Plasmon Resonance; D013997:Time Factors
chemical_list: D000911:Antibodies, Monoclonal; C112697:CD44v6 antigen; D000939:Epitopes; D006023:Glycoproteins; D018960:Hyaluronan Receptors; D011868:Radioisotopes; D011993:Recombinant Fusion Proteins; D012211:Rhenium