Calix [6]arenes as building blocks for molecular receptors with rigid cavity

Dottorato di ricerca in scienze chimiche. 12. ciclo. A.a. 1996-99. Relatore A. Pochini. Coordinatore R. UngaroConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Evaluation of [Cu]Cu-DOTA and [Cu]Cu-CB-TE2A Chelates for Targeted Positron Emission Tomography with an αβ-Specific Peptide

Significant upregulation of the integrin α v β 6 has been described as a prognostic indicator in several cancers, making it an attractive target for tumor imaging. This study compares variants of a PEGylated α v β 6 -targeting peptide, bearing either an [>18F]fluorobenzoyl prosthetic group ([ 18 F]FBA-PEG-A20FMDV2) or different [ 64 Cu]copper chelators (DOTA-PEG-A20FMDV2, CB-TE2A-PEG-A20FMDV2). The compounds were evaluated in vitro by enzyme-linked immunosorbent assay (against the integrin α v β 6 and the closely related integrin α v β 6 ) and by cell labeling (α v β 6 -positive DX3puroβ6/α v β 6 -negative DX3puro) and in vivo using micro-positron emission tomography in a mouse model bearing paired DX3puroβ6/Dx3puro xenografts. In vitro, all three compounds showed excellent α v β 6 -specific binding (50% inhibitory concentration [IC 50 ](α v β 6 ) = 3 to g nmol/L; IC 50 (α v β 3 ) > 10 (μmol/L). In vivo, they displayed comparable, preferential uptake for the α v β 6 -expressmg xenograft over the α v β 6 -negative control (> 4:1 ratio at 4 hours postinjection). Whereas [ 64 Cu]Cu-DOTA-PEG-A20FMDV2 resulted in increased levels of radioactivity in the liver, [ 64 Cu]Cu-CB-TE2A-PEG-A20FMDV2 did not. Significantly, both 64 Cu-labeled tracers showed unexpectedly high and persistent levels of radioactivity in the kidneys (> 40% injected dose/g at 4 and 12 hours postinjection). The findings underscore the potential influence of the prosthetic group on targeted in vivo imaging of clinically relevant markers such as α v β 6 . Despite identical targeting peptide moiety and largely equal in vitro behavior, both 64 Cu-labeled tracers displayed inferior pharmacokinetics, making them in their present form less suitable candidates than the 18 F-labeled tracer for in vivo imaging of α v β

Comparison of Conjugation Strategies of Cross-Bridged Macrocyclic Chelators with Cetuximab for Copper-64 Radiolabeling and PET Imaging of EGFR in Colorectal Tumor-Bearing Mice

Epidermal growth-factor receptor (EGFR) is overexpressed in a wide variety of solid tumors and has served as a well-characterized target for cancer imaging and therapy. Cetuximab was the first mAb targeting EGFR approved by the FDA for the treatment of metastatic colorectal and head and neck cancers. Previous studies showed that ⁶⁴Cu (<i>T</i>_1/2 = 12.7 h; β⁺ (17.4%)) labeled DOTA–cetuximab showed promise for PET imaging of EGFR-positive tumors; however the <i>in vivo</i> stability of this compound has been questioned. In this study, two recently developed cross-bridged macrocyclic chelators (CB-TE1A1P and CB-TE1K1P) were conjugated to cetuximab using standard NHS coupling procedures and/or strain-promoted azide–alkyne cycloaddition (SPAAC) methodologies. The radiolabeling and <i>in vitro</i>/<i>vivo</i> evaluation of the resulting cetuximab conjugates were compared. Improved Cu-64 labeling efficiency and high specific activity (684 kBq/μg, decay corrected to the end of bombardment) were obtained with the CB-TE1K1P-PEG₄-click-cetuximab conjugate. Saturation binding assays indicated that the prepared cetuximab conjugates had comparable affinity (1.32–2.00 nM) in the HCT116 human colorectal tumor cell membranes. In the subsequent <i>in vivo</i> evaluation, ⁶⁴Cu-CB-TE1K1P-PEG₄-click-cetuximab demonstrated more rapid renal clearance with a higher tumor/nontumor ratio than other ⁶⁴Cu-labeled cetuximab conjugates, and it shows the greatest promise for imaging and therapy of EGFR-positive tumors