Beschreibung:
<jats:title>Abstract</jats:title><jats:sec>
<jats:title>Purpose</jats:title>
<jats:p>The clinical success non-invasive imaging of CXCR4 expression using [<jats:sup>68</jats:sup> Ga]Ga-PentixaFor-PET warrants an expansion of the targeting concept towards conventional scintigraphy/SPECT with their lower cost and general availability. To this aim, we developed and comparatively evaluated a series of <jats:sup>99m</jats:sup>Tc-labeled cyclic pentapeptides based on the PentixaFor scaffold.</jats:p>
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<jats:title>Methods</jats:title>
<jats:p>Six mas<jats:sub>3</jats:sub>-conjugated CPCR4 analogs with different 4-aminobenzoic acid (Abz)-D-Ala-D-Arg-aa<jats:sub>3</jats:sub> linkers (<jats:bold>L1–L6</jats:bold>) as well as the corresponding HYNIC- and N<jats:sub>4</jats:sub>-analogs of <jats:bold>L6-</jats:bold>CPCR4 were synthesized via standard SPPS. Competitive binding studies (IC<jats:sub>50</jats:sub> and IC<jats:sub>50</jats:sub>inv) were carried out using Jurkat T cell lymphoma cells and [<jats:sup>125</jats:sup>I]FC-131 as radioligand. Internalization kinetics were investigated using hCXCR4-overexpressing Chem-1 cells. Biodistribution studies and small animal SPECT/CT imaging (1 h p.i.) were carried out using Jurkat xenograft bearing CB17/SCID mice. Based on the preclinical results, [<jats:sup>99m</jats:sup>Tc]Tc-N<jats:sub>4</jats:sub>-<jats:bold>L6-</jats:bold>CPCR4 ([<jats:sup>99m</jats:sup>Tc]Tc-PentixaTec) was selected for an early translation to the human setting. Five patients with hematologic malignancies underwent [<jats:sup>99m</jats:sup>Tc]Tc-N<jats:sub>4</jats:sub>-<jats:bold>L6</jats:bold>-CPCR4 SPECT/planar imaging with individual dosimetry.</jats:p>
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<jats:title>Results</jats:title>
<jats:p>Of the six mas<jats:sub>3</jats:sub>-conjugated peptides, mas<jats:sub>3</jats:sub><jats:bold>-L6</jats:bold>-CPCR4 (mas<jats:sub>3</jats:sub>-dap-r-a-Abz-CPCR4) showed the highest CXCR4 affinity (IC<jats:sub>50</jats:sub> = 5.0 ± 1.3 nM). Conjugation with N<jats:sub>4</jats:sub> (N<jats:sub>4</jats:sub>-<jats:bold>L6</jats:bold>-CPCR4) further improved hCXCR4 affinity to 0.6 ± 0.1 nM. [<jats:sup>99m</jats:sup>Tc]Tc-N<jats:sub>4</jats:sub>-<jats:bold>L6-</jats:bold>CPCR4 also showed the most efficient internalization (97% of total cellular activity at 2 h) and the highest tumor accumulation (8.6 ± 1.3% iD/g, 1 h p.i.) of the compounds investigated. Therefore, [<jats:sup>99m</jats:sup>Tc]Tc-N<jats:sub>4</jats:sub>-<jats:bold>L6</jats:bold>-CPCR4 (termed [<jats:sup>99m</jats:sup>Tc]Tc-PentixaTec) was selected for first-in-human application. [<jats:sup>99m</jats:sup>Tc]Tc-PentixaTec was well tolerated, exhibits a favorable biodistribution and dosimetry profile (2.1–3.4 mSv per 500 MBq) and excellent tumor/background ratios in SPECT and planar imaging.</jats:p>
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<jats:title>Conclusion</jats:title>
<jats:p>The successive optimization of the amino acid composition of the linker structure and the N-terminal <jats:sup>99m</jats:sup>Tc-labeling strategies (mas<jats:sub>3</jats:sub> vs HYNIC vs N<jats:sub>4</jats:sub>) has provided [<jats:sup>99m</jats:sup>Tc]Tc-PentixaTec as a novel, highly promising CXCR4-targeted SPECT agent for clinical application. With its excellent CXCR4 affinity, efficient internalization, high uptake in CXCR4-expressing tissues, suitable clearance/biodistribution characteristics, and favorable human dosimetry, it holds great potential for further clinical use.</jats:p>
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<jats:title>Graphical abstract</jats:title>
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