OPRK1 as a Radioligand Therapy Target
OPRK1, opioid receptor kappa 1, is a cell-surface protein (GPCR). In Human Protein Atlas immunohistochemistry, OPRK1 staining is highest in thyroid cancer (75% of samples positive), testicular cancer (58% of samples positive) and head and neck cancer (25% of samples positive). Published literature reports that OPRK1 internalizes after ligand binding, which helps retain a radionuclide inside tumor cells. Clinical status: Clinical-stage (up to phase 3, any modality).
Is OPRK1 a good radioligand therapy target?
Scored against the six criteria that decide whether a protein can become a radioligand therapy:
- ✅ Cell-surface accessibility: Localized to the cell surface, so a radioligand can reach it from circulation.
- ⚠️ Tumor expression: Medium IHC staining in thyroid cancer, 75% of samples positive.
- ✅ Internalization: Reported to internalize, which favors radionuclide retention.
- ✅ Clinical precedent: Clinical-stage (up to phase 3, any modality)
- ❔ Shedding: Not yet assessed.
- ❔ Normal-tissue dosimetry: Check kidney, liver, bone marrow and salivary expression in the Human Protein Atlas tissue atlas.
OPRK1 expression in cancer
Protein expression of OPRK1 across 20 cancer types from Human Protein Atlas immunohistochemistry. The score is a weighted staining intensity from 0 to 1; "% positive" is the share of patient samples with detectable staining.
| Cancer type | IHC score | Level | % positive |
|---|---|---|---|
| Thyroid Cancer | 0.25 | Medium | 75% |
| Testicular Cancer | 0.19 | Low | 58% |
| Head and Neck Cancer | 0.17 | Low | 25% |
| Skin Cancer | 0.11 | Low | 17% |
| Bladder Cancer | 0.08 | Low | 17% |
| Melanoma | 0.06 | Low | 17% |
| Lung Cancer | 0.06 | Low | 17% |
| Colorectal Cancer | 0.06 | Low | 8% |
| Ovarian Cancer | 0.03 | Low | 8% |
| Breast Cancer | 0.03 | Low | 8% |
| Gastric Cancer | 0.03 | Low | 8% |
Not detected by IHC in: lymphoma, kidney cancer, neuroendocrine tumors, cervical cancer, pancreatic cancer, prostate cancer, endometrial cancer, glioma, liver cancer.
Is OPRK1 internalized?
Yes. The abstract mentions C-terminal residues thought to be involved in receptor desensitization and internalization.
Sources: PMID 17060493. AI-extracted from abstracts, so verify before citing.
OPRK1 clinical trials
Clinical-stage (up to phase 3, any modality). Nuclens hasn't indexed trials for OPRK1 yet. Search ClinicalTrials.gov for OPRK1 trials.
OPRK1 normal tissue expression
Normal-tissue expression in dose-limiting organs (kidney, liver, bone marrow, salivary glands) drives radioligand dosimetry risk. Nuclens is re-validating its normal-tissue values, so they are not shown here yet. See OPRK1 in the Human Protein Atlas tissue atlas, and read how normal-tissue expression predicts radioligand dosimetry risk.
OPRK1 gene essentiality (DepMap)
CRISPR knockout effect across 1234 cancer cell lines: 0.07 (not essential). Radioligands kill by radiation, not by blocking the target, so essentiality matters less than for inhibitors. A non-essential target can still be an excellent radioligand target.
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Subcellular localization: UniProt via Open Targets (CC BY 4.0 / CC0). Tumor immunohistochemistry: Human Protein Atlas (CC BY-SA 4.0). Clinical trials: ClinicalTrials.gov (public domain). Gene essentiality: DepMap (CC BY 4.0). Internalization and shedding: AI-extracted from PubMed abstracts, so verify against the cited papers before relying on them. Nuclens is a first-pass triage layer, not a substitute for wet-lab validation or clinical dosimetry. Derived expression data on this page is shared under CC BY-SA 4.0.