κ-or

GR103545 is a selective agonist of the κ-opioid receptor, which is a radiotracer that can be used as in vivo imaging.

Ac-RYYRWK-NH2 is a highly effective and specific partial agonist for the nociceptin receptor (NOP). It demonstrates a remarkable affinity for rat cortical membranes ORL1, with [3H]Ac-RYYRWK-NH2 exhibiting a Kd value of 0.071 nM. However, it shows negligible affinity towards μ-, κ-, or δ-opioid receptors.

Dinalbuphine sebacate is a long-lasting prodrug of nalbuphine, acting as a moderate-efficacy partial agonist or antagonist of the μ-opioid receptor and as a high-efficacy partial agonist of the κ-opioid receptor.

UCK2 Inhibitor-3 is a non-competitive inhibitor of uridine-cytidine kinase 2 (UCK2), a pivotal enzyme in the pyrimidine salvage pathway, with an IC50 value of 16.6 μM. UCK2 can partially substitute for dihydroorotate dehydrogenase (DHODH) in infected or rapidly dividing cells, aiding uridine salvage. Additionally, UCK2 Inhibitor-3 inhibits DNA polymerase eta and kappa, with IC50 values of 56 μM and 16 μM, respectively.

Enadoline (Free Base) is a kappa-opioid receptor agonist; PD 129290 (CAM 570; CI 977) is the S,S(-)-enantiomer; PD 129289 (CAM 569) is the corresponding R,R(+)-enantiomer. In human studies, it produced visual distortions and feelings of dissociation, reminiscent of the effects of salvinorin A. It was studied as a potential analgesic, but abandoned because of the dose-limiting effects of dysphoria, which could be expected from a κ-opioid agonist. There was mention of its potential in treating comatose head injury or stroke victims, where that type of side effect would be immaterial.

Ontuxizumab (MORAb-004) is a potent IgG1 κ monoclonal antibody targeting endomelanic acid with anti-tumor effects. It specifically targets endothelin (TEM-1 or CD248) and is used for the treatment of metastatic melanoma.

Mitraciliatine, an alkaloid discovered in M. speciosa (Kratom in Thai), acts as a partial agonist for the μ-opioid receptor (MOR) and an agonist for the κ-opioid receptor (KOR), demonstrating selectivity for these receptors over the δ-opioid receptor (DOR) with EC50 values of 228, 218, and >1,000 nM respectively in mouse receptors through a GTPγS binding assay. When administered intracerebroventricularly (i.c.v.) at 100 nmol/animal, mitraciliatine increases latency to withdrawal in the warm water tail withdrawal assay in mice, an effect reversable by MOR knockout but unaffected by KOR knockout, distinguishing it from morphine by not causing hyperlocomotion or respiratory depression.

Renvistobart is a monoclonal antibody belonging to the immunoglobulin G1-κ class, targeting the human T cell immunoreceptor with Ig and ITIM domains (TIGIT, also known as VSIG9 or VSTM3) [1].