Advancements in Pretargeted Imaging: Enhancing Tumor Contrast Through Bioorthogonal Chemistry

DZ-Lys-TCO paired with 68Ga-DOTA-H-Tz markedly improves tumor contrast and reduces off-target exposure in preclinical PET/NIRF models—sharpening lesion delineation while lowering systemic radionuclide burden through staged delivery of the targeting vector and radioligand.

Bioorthogonal pretargeting separates the tumor-targeting moiety from the radionuclide-bearing probe so each is administered at different times; this staging limits systemic radioactivity and concentrates signal at tumor sites. The net clinical advantage is a narrower window of background activity and a higher tumor-to-background ratio versus single-step labeling, because unbound radioligand can clear before image acquisition.

The investigators compared three DZ-TCO precursors and two 68Ga-labeled tetrazine probes across 24-, 48-, and 72-hour pretargeting intervals and quantified uptake and contrast metrics. DZ-Lys-TCO paired with 68Ga-DOTA-H-Tz at 48 hours produced the best balance of tumor uptake (peak ~3.24 ± 0.95 %ID/g) and tumor-to-muscle ratio (T/M ~8.30 ± 3.39), outperforming other tested combinations.

Biodistribution data showed rapid renal clearance with low off-target accumulation; peak tumor uptake reached approximately 3.53 ± 1.76 %ID/g (T/M 10.9 ± 0.3 at 30 min). Against the alternatives tested, DZ-Lys-TCO with 68Ga-DOTA-H-Tz delivered higher contrast and lower background exposure.

Higher tumor-to-muscle ratios should improve lesion conspicuity and may permit earlier or more confident detection on PET/NIRF scans. The 48-hour staging requires a two-visit workflow and precise timing for radioligand administration; because clearance is renal, patients with impaired kidney function may have higher residual background and require tailored planning. These preclinical data support early-phase human evaluation but do not establish safety, dosing, or efficacy in broad patient populations.