PT - JOURNAL ARTICLE AU - Huub J.J.M. Rennen AU - Cathelijne Frielink AU - Ernst Brandt AU - Sebastian A.J. Zaat AU - Otto C. Boerman AU - Wim J.G. Oyen AU - Frans H.M. Corstens TI - Relationship Between Neutrophil-Binding Affinity and Suitability for Infection Imaging: Comparison of <sup>99m</sup>Tc-Labeled NAP-2 (CXCL-7) and 3 C-Terminally Truncated Isoforms DP - 2004 Jul 01 TA - Journal of Nuclear Medicine PG - 1217--1223 VI - 45 IP - 7 4099 - http://jnm.snmjournals.org/content/45/7/1217.short 4100 - http://jnm.snmjournals.org/content/45/7/1217.full SO - J Nucl Med2004 Jul 01; 45 AB - The CXC chemokines are a family of closely related chemoattractant cytokines that bind to, attract, and activate neutrophils to variable degrees. In this study, the relationship between neutrophil-binding affinity and suitability for infection imaging was investigated in a selected group of CXC chemokines. Neutrophil–activating peptide-2 (NAP-2, 70 residues; also called CXCL7) binds with high affinity to the CXCR2 receptor on neutrophils. Recently, C-terminally truncated NAP-2-variants have been described that have enhanced neutrophil-binding affinity and neutrophil-stimulating capacity. Here, NAP-2 and its C-terminal shortened variants NAP-2(1–68), NAP-2(1–66), and NAP-2(1–63) were labeled with 99mTc via the hydrazinonicotinamide (HYNIC) chelator and their potential for imaging of infection was investigated in a rabbit model of infection. The CXC chemokine interleukin-8 (IL-8) was used for comparison. In addition, a series of 99mTc-labeled CXC chemokines were screened for their potential to image infection, including CTAP-III, GCP-2, ENA-78, PF-4, and IP-10. Methods: The receptor-binding affinity of HYNIC-conjugated NAP-2 and its analogs was compared in competitive binding assays on Jurkat cells transfected with the CXCR2 receptor gene. Biodistribution of labeled NAP-2 (analogs) and other CXC chemokines in rabbits with intramuscular Escherichia coli infections was determined both by γ-camera imaging and by counting dissected tissues at 6 h after injection. Results: The CXCR2-binding affinity of the HYNIC-conjugated NAP-2 analogs relative to NAP-2 was as follows: NAP-2(1–68), 2.5-fold; NAP-2(1–66), 10-fold; and NAP-2(1–63), 3-fold. In the rabbit model, uptake in the abscess (in percentage injected dose per gram ± SEM) was 0.084 ± 0.015 for NAP-2, 0.098 ± 0.010 for NAP-2(1–68), 0.189 ± 0.044 for NAP-2(1–66), and 0.114 ± 0.017 for NAP-2(1–63) at 6 h after injection. In comparison, higher uptake in the abscess was found for labeled IL-8, a modest uptake was found for GCP-2 and ENA-78, and a low uptake was found for CTAP-III, PF-4, and IP-10. Conclusion: This study showed a clear relationship between affinity to receptors on neutrophils and suitability for infection imaging. Of the NAP-2 variants, NAP-2(1–66) combined highest affinity to CXCR2 with the best characteristics for imaging. IL-8 binds to both CXCR1 and CXCR2 with high affinity and showed a superior imaging quality. The other CXC chemokines tested bind to neutrophils with lower affinity and were shown to be less suitable for infection imaging in this study.