Two gallium-68-labeled peptides showed high tumor uptake and clear PET imaging in prostate cancer mouse models, supporting their use as diagnostic partners to radiation therapy versions.
16–17%IA/g tumor uptakeBoth peptide tracers concentrated heavily in prostate tumors while clearing rapidly from blood
What the researchers found
Two metabolically stable peptides targeting the gastrin-releasing peptide receptor (GRPR) — [68Ga]Ga-PKB2 and [68Ga]Ga-PKB3 — were successfully labeled with gallium-68 for PET imaging. Both showed high tumor uptake in prostate cancer xenografts (16 ± 3%IA/g and 17 ± 2%IA/g, respectively), fast blood clearance below 0.5%IA/g at 2 hours, and low nanomolar receptor affinity.
[68Ga]Ga-PKB3 showed significantly higher uptake in GRPR-expressing pancreas tissue and lower kidney uptake than PKB2, suggesting a potentially better safety profile. PET/CT images clearly delineated tumors, and both tracers are proposed as diagnostic counterparts to their lutetium-177-labeled therapy versions, forming a theranostic pair.
Why it matters
GRPR is overexpressed in several cancers including prostate, breast, and pancreatic cancer. Having matched diagnostic and therapeutic peptide pairs — one for imaging with PET, one for targeted radiation therapy — could let doctors first locate tumors precisely and then treat them with the same targeting molecule. This study advances the concept of peptide-based theranostics where the same receptor-binding peptide serves both diagnostic and therapeutic purposes.
The numbers in context
n=PC-3 xenograft mice · Tumor uptake: 16 ± 3%IA/g (PKB2), 17 ± 2%IA/g (PKB3) · IC50: low nanomolar · Radiochemical yield >99% · Radiochemical purity >97% · Blood clearance <0.5%IA/g at 2h
How the study worked
Researchers labeled two previously developed GRPR-targeting peptides (PKB2 with DOTAGA chelator, PKB3 with DOTA chelator) with gallium-68. They tested receptor affinity and cell uptake in PC-3 prostate cancer cells, then evaluated biodistribution and PET/CT imaging in mice bearing PC-3 tumor xenografts.
Who was studied
PC-3 prostate cancer xenograft mouse model
What this study cannot tell us
This is a preclinical animal study only — no human data exists yet. The mouse xenograft model may not perfectly reflect how these tracers behave in human tumors. Long-term toxicity and repeated dosing were not assessed. Translation to clinical use will require Phase I safety trials.
How to read the evidence
This is a preclinical animal study using mouse xenograft models. While results are promising, no human data has been generated yet, placing this at a preliminary evidence level.
When this study was published
Published in 2026, this is current research representing the latest developments in GRPR-targeted PET imaging peptides.
The bigger picture
Peptide-based theranostics — using the same targeting molecule for both imaging and therapy — is a rapidly growing approach in nuclear medicine. GRPR-targeting adds to the success seen with somatostatin receptor theranostics (like Lutathera). Developing matched gallium-68/lutetium-177 pairs could expand precision oncology to more cancer types.
Questions still open
- Will these tracers perform as well in human patients as they do in mouse models?
- Could PKB3's lower kidney uptake translate into fewer side effects during repeated therapeutic dosing?
- How do these GRPR-targeting tracers compare to existing bombesin-based imaging agents in clinical development?
Common questions
What is a theranostic peptide pair?
What is GRPR and why target it in cancer?
Read the original research
Exploring the theranostic potential of two metabolically stable GRPR-targeting peptides labelled with Ga-68 for PET imaging.
EJNMMI radiopharmacy and chemistry, 11(1)
Citation
Obeid, Karim; Bezverkhniaia, Ekaterina; Tolmachev, Vladimir; Orlova, Anna; Kanellopoulos, Panagiotis. (2026). Exploring the theranostic potential of two metabolically stable GRPR-targeting peptides labelled with Ga-68 for PET imaging.. EJNMMI radiopharmacy and chemistry, 11(1). https://doi.org/10.1186/s41181-026-00431-5