Table 1. Agonistic Potencies of Xanthine Derivatives at GPR18 and GPR55 Determined in β-Arrestin Recruitment Assays.

^aCompounds were tested at a concentration of 10 μM. Effects were normalized to the signal induced by 10 μM THC (GPR18) or 1 μM LPI (GPR55).

^bEfficacy relative to the maximal effect of the standard agonist (GPR18, 30 μM THC; GPR55, 10 μM LPI) set at 100%.

^cPercent inhibition of agonist effect (GPR18, 10 μM THC; GPR55, 1 μM LPI) by test compound at 10 μM.

^dn.d., not determined.

^eLiterature value: EC₅₀ = 4.61 ± 0.50.²⁷