Pasireotide (Signifor / Signifor LAR): Research Overview

Pasireotide is a cyclohexapeptide somatostatin analog engineered to bind with high affinity to four of the five human somatostatin receptor subtypes (SST1, SST2, SST3, and SST5). This multi-receptor binding profile distinguishes it fundamentally from first-generation analogs such as octreotide and lanreotide, which bind selectively to SST2 (and, to a lesser extent, SST5). The clinical rationale for pasireotide's design stems from the observation that corticotroph adenomas — the pituitary tumors that drive Cushing's disease — overexpress SST5 relative to SST2, meaning octreotide-class drugs are largely ineffective in this condition. Pasireotide was developed by Novartis and received FDA approval in December 2012 as Signifor (twice-daily subcutaneous injection) for adult patients with Cushing's disease for whom surgery is not an option or has not been curative. In December 2014, the FDA approved Signifor LAR (long-acting release, monthly intramuscular injection) for acromegaly patients who have responded inadequately to surgery. The clinical evidence is anchored by a landmark phase 3 trial published by Colao et al. in the New England Journal of Medicine in 2012.

What Is Pasireotide?

Pasireotide (formerly known as SOM230) is a synthetic cyclohexapeptide with a molecular weight of approximately 1047 Da (free base). It is structurally designed to overcome the limited receptor subtype coverage of octreotide, incorporating modifications that allow stable, high-affinity interactions with SST1, SST2, SST3, and SST5. Its affinity for SST5 is approximately 40-fold higher than that of octreotide, and its affinity for SST1 is approximately 30-fold higher. This differential binding profile is what enables suppression of ACTH secretion from SST5-expressing corticotroph adenomas in Cushing's disease. Pasireotide is administered subcutaneously (twice daily for Cushing's disease; Signifor formulation) or by intramuscular injection of a long-acting microsphere preparation (monthly for acromegaly; Signifor LAR).

Mechanism of Action

Pasireotide activates somatostatin receptors (SSTs), which are G-protein-coupled receptors coupled primarily to Gi proteins. SST activation inhibits adenylyl cyclase, reducing intracellular cAMP and thereby suppressing hormone secretion from neuroendocrine cells. In corticotroph adenoma cells, which overexpress SST5, pasireotide binding suppresses ACTH (adrenocorticotropic hormone) production and secretion. Reduced ACTH leads to decreased cortisol synthesis and secretion from the adrenal cortex, resulting in lower urinary free cortisol (UFC) levels — the primary biochemical efficacy endpoint in Cushing's disease. In somatotroph cells (growth hormone-secreting cells), SST receptor activation by pasireotide suppresses growth hormone (GH) secretion and, secondarily, reduces hepatic insulin-like growth factor 1 (IGF-1) production, the primary biochemical endpoint in acromegaly. Because pasireotide also engages SST5 more potently than octreotide, it can suppress GH in tumors where octreotide resistance has developed through SST2 downregulation.

A distinguishing adverse effect of pasireotide is hyperglycemia. Unlike octreotide, which causes mild glycemic effects through equal suppression of insulin and glucagon, pasireotide's potent SST5 engagement leads to disproportionate suppression of insulin secretion from pancreatic beta cells (which highly express SST5). This can cause clinically significant hyperglycemia requiring pharmacological management in a substantial proportion of patients.

What the Research Shows

The pivotal phase 3 trial for Cushing's disease was published by Colao et al. in the New England Journal of Medicine in 2012 (PMID 22397650). In this double-blind study, 162 adults with Cushing's disease (mean urinary free cortisol approximately 4–5 times the upper limit of normal) were randomized to receive pasireotide 600 mcg or 900 mcg subcutaneously twice daily. The primary endpoint was normalization of UFC at month 6 without dose escalation. At 6 months, UFC normalization was achieved in 26 of 82 patients (32%) in the 600 mcg group and 25 of 80 patients (31%) in the 900 mcg group. An additional proportion of patients showed meaningful reductions but did not fully normalize. Median UFC declined by approximately 50% from baseline in both groups by month 2 and remained stable thereafter. Reductions in clinical signs of hypercortisolism (blood pressure, body weight, waist circumference, serum cortisol, and quality of life measures) corroborated the biochemical findings [1].

For acromegaly, the PAOLA trial and related phase 3 studies evaluated Signifor LAR. In the PAOLA study, pasireotide LAR was compared with octreotide LAR or lanreotide in patients with inadequately controlled acromegaly. At 24 weeks, biochemical control (GH < 2.5 mU/L and normal IGF-1) was achieved in significantly more patients in the pasireotide LAR arm compared with first-generation somatostatin analogs, including patients who were previously considered partially or non-responsive to octreotide or lanreotide.

The most clinically significant adverse event observed across both trials was hyperglycemia. In the Colao NEJM 2012 trial, hyperglycemia-related adverse events occurred in 118 of 162 patients (73%), and glucose-lowering medication was initiated in 74 of 162 patients (46%). This hyperglycemic signal is substantially larger than that seen with octreotide and has defined clinical management guidelines around pasireotide: baseline glucose monitoring is mandatory, and proactive initiation of glucose-lowering therapy (typically with a glucagon-like peptide-1 agonist or DPP-4 inhibitor) is recommended once therapy begins [1].

Pharmacokinetics

For the twice-daily subcutaneous formulation (Signifor), pasireotide reaches peak plasma concentrations (Tmax) approximately 0.25–0.5 hours after injection. The terminal half-life is approximately 12 hours, consistent with twice-daily dosing. Pasireotide is approximately 88% bound to plasma proteins, primarily to lipoproteins and, to a lesser extent, albumin. It has a large volume of distribution (approximately 100 L). Pasireotide is predominantly eliminated unchanged in bile and feces; hepatic uptake is mediated by OATP transporters. Renal clearance is minimal. Hepatic impairment significantly increases pasireotide exposure, necessitating dose reduction. For the long-acting release formulation (Signifor LAR), the PLGA microsphere matrix slowly releases pasireotide over the injection interval, achieving sustained plasma concentrations with once-monthly dosing. Steady-state concentrations are reached after approximately 3 monthly injections.

Approved Indications and Clinical Dose Ranges

Not medical advice. These are ranges reported in research literature, not personalized recommendations. Consult your physician.

Pasireotide is FDA-approved under two formulations for two separate indications. For Cushing's disease in adult patients, the FDA label for Signifor specifies initiation at 0.6 mg or 0.9 mg subcutaneously twice daily. After 2 months, the response should be assessed; if UFC has not normalized but the drug is being tolerated, the dose may be increased. If UFC worsens or intolerable adverse events occur, the dose may be reduced by 0.3 mg twice daily. The maximum studied dose in the pivotal trial was 0.9 mg twice daily. For acromegaly in adults who have responded inadequately to surgery and/or radiotherapy, the Signifor LAR label specifies initiation at 40 mg intramuscularly every 28 days, with possible titration to 60 mg after 3 months in patients with inadequate biochemical control, or dose reduction to 20 mg in patients with adverse effects [2].

Storage and Handling

Signifor ampoules (subcutaneous formulation) should be stored at room temperature (15–30°C / 59–86°F), protected from light. They must not be frozen. Each ampoule is intended for single use only; any unused solution must be discarded. Signifor LAR (long-acting intramuscular formulation) should be stored in a refrigerator at 2–8°C (36–46°F). The kit should be removed from the refrigerator and allowed to equilibrate to room temperature for approximately 30 minutes before preparation. Once prepared, the suspension must be administered immediately; it cannot be stored after reconstitution. As with other PLGA-based long-acting formulations, the microsphere suspension must not be frozen, and the powder and diluent must not be mixed until immediately prior to injection.

What Pasireotide Is NOT

Pasireotide is not a first-line treatment for acromegaly or Cushing's disease. Surgery (transsphenoidal adenomectomy) remains the treatment of first choice for both conditions; pasireotide is indicated for patients in whom surgery has failed or is not an option. Pasireotide is not octreotide: the two drugs share a somatostatin analog class but have distinct receptor binding profiles, different approved indications, and different safety profiles — particularly regarding hyperglycemia. Pasireotide should not be used interchangeably with octreotide or lanreotide without specialist guidance. Pasireotide is not approved for any carcinoid syndrome indication (unlike octreotide). It is not used for non-neuroendocrine conditions and does not have a role in general endocrinology outside of the specific pituitary indications. It is not appropriate for patients with uncontrolled diabetes mellitus, and its use requires rigorous glucose monitoring and often proactive glucose-lowering co-therapy.

References

[1] Colao A, et al. A 12-Month Phase 3 Study of Pasireotide in Cushing's Disease. N Engl J Med. 2012;366(10):914–924. PMID 22397650.

[2] Signifor LAR (pasireotide for injectable suspension) Prescribing Information. Novartis. FDA Approval: 2014. Available at: https://www.accessdata.fda.gov/drugsatfda_docs/label/2024/209210s023lbl.pdf

[3] Pasireotide: a novel treatment for patients with acromegaly. PMC. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC4714742/

[4] Pasireotide — LiverTox, NCBI Bookshelf. Available at: https://www.ncbi.nlm.nih.gov/books/NBK548864/