Table 2.

Biological activities of representative NPFF-derived peptidic probes.

Ligand	Sequence	Usage	In vitro activities	In vivo activities
NPFF (a.k.a. F8Fa, 1)	FLFQPQRF-NH2	Agonist	hNPFFR1 COS-7 or HEK cells Kd = 1.13 nM4 hNPFFR2 COS-7 or HEK cells Kd = 0.21 – 0.37 nM4, 81 Rat spinal cord Ki = 0.21 – 0.34 nM19, 77, 78, 81 hNPFFR2 EC50 = 3.16 nM81	Analgesia1, 10, 11, 36–38, 77, 78 Opioid abuse45, 49, 53 Amphetamine abuse55–57 Cocaine abuse58 Cardiovascular activities32, 59, 60, 62 Gastrointestinal mobility74
[Tyr1]NPFF (a.k.a. Y8Fa, 2)	YLFQPQRF-NH2	Agonist	Rat spinal cord Ki = 0.20 nM77	Pain77 Anorectic effect in fasted mice.82
1DMe (3)	[D-Tyr1,(NMe)Phe3] YLFQPQRF-NH2	Metabolically stable agonist	hNPFFR1 Ki = 2.0 – 7.9 nM4, 80 hNPFFR2 Ki = 3.2 nM4 rNPFFR1 Ki = 1.6 nM4 rNPFFR2 Ki = 2.0 nM4 Rat spinal cord Ki = 0.07 – 034 nM77, 78, 80, 81 hNPFFR2 EC50 = 2.69 nM81	Analgesia77 38, 40, 78, 80 Opioid abuse52 Gastrointestinal mobility75
Nic-1DMe (4)	[D-Tyr1,(NMe)Phe3,Nic-Pro5] YLFQPQRF-NH2	Metabolically stable agonist	Rat spinal cord Ki = 0.07 nM80 hNPFFR1 Ki = 1.30 nM80	Pain80
NPVF (5)	VPNLPQRF-NH2	NPFFR1 agonist	hNPFFR1 Ki = 0.59 nM23 hNPFFR2 Ki = 23 nM23	Cardiovascular activities62
dNPA (6)	[D-Asn1,(NMe)Ala3] NPAFLFQPQRF-NH2	NPFFR2 agonist	hNPFFR1 Ki = 2.9 nM23 hNPFFR2 Ki = 0.027 nM23	Cardiovascular activities62
FMRFamide (7)	FMRF-NH2	Agonist	Rat spinal cord Ki = 1.8 nM19 hNPFFR2 Ki = 6.6 nM81 hNPFFR2 EC50 = 517 nM81	Pain36 Feeding65 Gastrointestinal mobility74
PQRFamide (8)	PQRF-NH2	Agonist	hNPFFR1 Ki = 40 nM4 Rat spinal cord Ki = 15.5 nM81 hNPFFR2 Ki = 25 nM4 rNPFFR1 Ki = 25 nM4 rNPFFR2 Ki = 25 nM4 hNPFFR2 EC50 = 309 nM81	Cardiovascular activities61
PFR(Tic)amide (9)	[Tic-Arg3]PFR(Tic)-NH2 (Fig. 1)	NPFFR1 antagonist, NPFFR2 agonist	Rat NPFFR1 Ki = 101 nM56 Rat NPFFR1 IC50 = 0.1 nM56 hNPFFR2 EC50 = 2400 ± 400 nM83	Opioid abuse47 Cardiovascular activities61
daY8Ra (10)	[desamino-Tyr1]YFLFQPQR-NH2	Metabolically stable antagonist	Rat spinal cord Ki = 0.20 ± 0.04 nM50	Opioid addiction50
Dansyl-PQRNH2 (11)	[dns-Pro1]PQR-NH2 (Fig. 1)	CNS permeable antagonist	Rat spinal cord Ki = 13 μM84	Opioid addiction47, 84
RF9 (12)	See Fig. 1	Agonist/ Antagonist	hNPFFR1 Ki = 58 nM32 hNPFFR2 Ki = 75 nM32	Pain32 Opioid addiction32 Cardiovascular activities32
GJ14 (13)	See Fig. 1	Antagonist	hNPFFR1 EC50 = 21 nM72 hNPFFR1 EC50 = 387 nM72	Anxiety72