Somatostatin analog · pituitary tumors
A lab-made ring-shaped peptide that mimics somatostatin, a natural hormone that switches off the release of other hormones. It treats two conditions caused by hormone-secreting pituitary tumors: Cushing's disease, where excess ACTH drives high cortisol, and acromegaly, where the tumor makes too much growth hormone. It comes as an injection under the skin and as a long-acting muscle depot.
Somatostatin acts through five receptor subtypes, SSTR1 to SSTR5, found in different tissues. Pasireotide has an unusually broad binding profile: it binds four of the five subtypes with high affinity, and binds SSTR5 most tightly1,2,3. That matters in Cushing's disease because the tumor cells that make ACTH, the pituitary hormone that drives cortisol production, often carry more SSTR5 than other subtypes; activating these receptors lowers ACTH and, in turn, cortisol1.
In acromegaly, it lowers growth hormone and IGF-1, the hormone growth hormone drives, which are the two measures used to judge control4,5. Blood sugar commonly rises during treatment, which is why glucose is monitored closely1,3.
In a 12-month phase 3 trial, 162 adults with Cushing's disease were randomized to two dose levels of the injection under the skin. Urine free cortisol fell by about half within two months, and 15% and 26% of the two groups reached a normal level at month 6 without needing a higher dose; clinical signs eased, but 118 of 162 patients had high-blood-sugar events and 74 started glucose-lowering medicine3. For acromegaly, a 12-month head-to-head trial in 358 patients not previously treated with drugs found biochemical control in 31% on long-acting pasireotide versus 19% on long-acting octreotide4.
In the PAOLA trial of 198 patients not controlled on octreotide or lanreotide, 15% to 20% reached control after switching to pasireotide, versus none who stayed on their prior drug; high blood sugar and diabetes were its most common adverse events5.
FDA-approved as Signifor (2012) for adults with Cushing's disease when pituitary surgery is not an option or has not cured it, and as Signifor LAR (2014) for acromegaly after an inadequate response to surgery or when surgery is not an option, with Cushing's disease added to that label later1,2.
Per the FDA labels, the most common effects are diarrhea, nausea, high blood sugar, gallstones, headache, abdominal pain, fatigue and diabetes. Warnings cover high blood sugar and new diabetes, which can be severe and can lead to ketoacidosis; cortisol falling too low; slow heart rate and QT prolongation; rises in liver tests; gallstone complications; deficiencies of other pituitary hormones; and fatty stools from poor fat absorption1,2.
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