Octreotide is an octapeptide analog of somatostatin that binds to somatostatin receptors (SSTRs) with a higher affinity for the somatostatin subgroup 2 receptors, SST
2, SST
3, and SST
5 (K
is = 875, 0.57, 26.8, >1,000, and 6.8 nM for SST
1-5 receptors, respectively).
1 Within subgroup 2 SSTRs, it selectively binds to SST
2 over SST
3 and SST
5 receptors with IC
50 values of 0.02, 92.9, and 21.8 nM, respectively, for human receptors. Octreotide inhibits the secretion of growth hormone
in vitro in rat pituitary cells three-fold more potently than somatostatin and
in vivo in rhesus monkey (ID
50 = 0.38 μg/kg per hour).
2 It inhibits proliferation of VEGF-stimulated human umbilical endothelial cells (HUVECs) with an EC
50 value of approximately 1 μM.
3 It also inhibits growth of LCI-D20 human hepatocellular carcinoma cell tumors in a nude mouse xenograft model when administered at a dose of 50 μg/kg twice daily. Formulations containing octreotide have been used in the treatment of acromegaly to reduce growth hormone and IGF-1 levels.