Table 1.

Affinity and agonist activity

ReceptorAgonist assayAntagonist assay
Ro27-4680 EC50(nm)Ro27-3225 EC50(nm)Ro27-4680
w/NDP-αMSH (20 nm) IC50 (nm)w/Ro27-3225 (250 nm) IC50 (nm)
MC1R42 (10.2)8 (1.1)No activityNo activity
MC3RNo activity675 (97.9)4989 (472.7)7329 (1433.3)1-a
MC4R16 pa (1.9) (partial agonist*)1 (0.3)13890 (3808)1-b4153 (479.8)1-c
MC5R340 (2.3)5779 (139.4)No activityNo activity
  • *The term “partial agonist” refers to the fact that, at very high concentrations, the selective antagonist (Ro27-4680) results in partial cAMP activation in MC4R-expressing cells. However, even at very high concentrations, the antagonist is incapable of producing 100% efficacy of NDP-αMSH. pa, Partial agonist.

  • F1-a Ro27-3225 concentration of 2.0 μm.

  • F1-b Partial antagonist of NDP-αMSH.

  • F1-c Partial antagonist of Ro27-3225.