Cagriniltide: Mechanism of Action

Mechanism of Action

Cagriniltide functions as a non-selective dual agonist of both calcitonin receptors (CTR) and amylin receptors (AMY1R, AMY2R, AMY3R) — heterodimers of CTR with RAMPs 1, 2, or 3.[3][12]

Receptor Targets & Binding

Target	Interaction	Evidence
Calcitonin Receptor (CTR)	Non-selective agonist; class B1 GPCR; EC50 62 pM	Kruse et al. (2021); Cao et al. (2025) cryo-EM[3][9]
AMY1R (CTR+RAMP1)	Potent agonist; "bypass" conformation binding	RAMP1/3 KO abolishes weight-loss effects[8]
AMY3R (CTR+RAMP3)	Potent agonist; EC50 49 pM (hAMY3R)	Carvas et al. (2025): essential for efficacy[8][13]
CGRPR / AM1R / AM2R	No or very low activity — selective for amylin/calcitonin axis	Fletcher et al. (2021)[12]

Downstream Signaling

Pathway	Effect	Consequence
Gs / Adenylyl Cyclase / cAMP	Gs-protein activation → adenylyl cyclase → intracellular cAMP accumulation	Primary signaling cascade for satiety[9]
Neuronal cFos (AP/NTS/LPBN)	Induces cFos expression in area postrema, nucleus of solitary tract, lateral parabrachial nucleus	Satiety signaling; 57% fewer AP neurons in RAMP1/3 KO[8]
Gastric Emptying	Delays gastric emptying → prolonged postprandial fullness	Reduced caloric intake; may affect oral drug absorption
Glucagon Suppression	Suppresses postprandial glucagon from pancreatic α-cells	Improved glycemic control without hypoglycemia risk[6]

Unique Binding Characteristics

Property	Cagriniltide	Salmon Calcitonin
Receptor Conformation	"Bypass" (stabilized by ionic lock N14E–V17R)	"CT-like" conformation
Residence Time	3–6 minutes (rapid dissociation)	45–60 minutes (slow dissociation)
Desensitization	Prevents receptor downregulation → sustained weight loss	Causes receptor downregulation → weight regain

RAMP Dependence: Carvas et al. (2025) demonstrated that the weight-lowering and anorectic effects of cagriniltide are strictly dependent on AMY1R and AMY3R — knockout of RAMP1 and RAMP3 completely abolished drug efficacy, with 57% fewer neurons activated in the area postrema.[8]

Cryo-EM Structural Insights

Cao et al. (2025) and Gu et al. (2026) resolved the cagriniltide-bound calcitonin-receptor and amylin-receptor cryo-EM structures, revealing the distinct "bypass" binding conformation stabilized by the engineered N14E-V17R ionic lock. Unlike salmon calcitonin (which adopts a deep "CT-like" pose with prolonged residence time and progressive receptor desensitization), cagriniltide engages the receptor extracellular domain in a more shallow, dynamic geometry that produces full Gαs-coupled cAMP signaling but allows rapid dissociation. This kinetic difference appears to be the molecular basis for the durable weight-loss response observed across the REDEFINE program — the receptor remains responsive to repeat dosing rather than progressively downregulating.[9][10]

Hindbrain Satiety Circuitry

The principal central site of action is the area postrema (AP), a circumventricular organ outside the blood-brain barrier where AMY1R/AMY3R-expressing neurons project to the nucleus of the solitary tract (NTS) and the lateral parabrachial nucleus (LPBN). cFos mapping studies show robust neuronal activation across this AP→NTS→LPBN→hypothalamic axis after subcutaneous cagriniltide; RAMP1/3 knockout eliminates 57% of AP cFos induction and abolishes the anorectic response — establishing AMY1R/AMY3R (rather than the calcitonin receptor in isolation) as the primary therapeutic target.[8] Downstream effects include delayed gastric emptying (prolonged postprandial fullness), suppression of postprandial glucagon from pancreatic α-cells (improved glycemic control without hypoglycemia risk), and reduced caloric intake (-51% over 24 h in mouse food-intake studies at 30 nmol/kg).[6][13]

Synergy with GLP-1 Agonism

Cagriniltide's hindbrain AMYR/CTR target is non-overlapping with the GLP-1-receptor-driven satiety pathway engaged by semaglutide (NTS, ARC, PVN). Co-administration produces additive weight-loss effects exceeding either monotherapy — the molecular substrate for the +6.7-percentage-point CagriSema benefit (22.7% vs 15-16% semaglutide alone) observed in REDEFINE 1. This non-redundant satiety-pathway combination model is now driving exploration of cagriniltide pairings with next-generation incretin agonists.[5][14]