Pasireotide
Hormonal / ClinicalAlso known as: Signifor, Signifor LAR, SOM230
Mechanism
A unique somatostatin-like drug that works on a broader range of somatostatin receptors than octreotide or lanreotide. It is the only somatostatin analog proven to treat Cushing's disease — a condition where the pituitary gland overproduces ACTH, leading to excess cortisol. Major side effect is high blood sugar, which occurs in the majority of patients.
Technical detail
Cyclohexapeptide somatostatin analog with pan-receptor binding profile: SSTR5 (IC50 ~0.2 nM, 39x higher than octreotide), SSTR2 (~1.0 nM), SSTR3 (~1.5 nM), SSTR1 (~9.3 nM). The SSTR5 selectivity is key for Cushing's disease — corticotroph adenomas overexpress SSTR5 relative to SSTR2. Suppresses ACTH secretion from pituitary corticotroph tumors via Gi-coupled inhibition of adenylyl cyclase and reduced POMC transcription. Also inhibits GH, IGF-1, and multiple GI hormones. Hyperglycemia (73% incidence) results from suppression of insulin and incretin secretion (SSTR5 expressed on pancreatic beta cells). Available as twice-daily SC injection (Signifor) and monthly IM depot (Signifor LAR). PASPORT trial confirmed efficacy in Cushing's.
Effects
**Endocrine — Somatostatin System (Tier 1 — Human Clinical):** Pasireotide is a multi-receptor somatostatin analog with high-affinity binding to SSTR1, SSTR2, SSTR3, and SSTR5 — a "pan-somatostatin receptor" profile. Its affinity for SSTR5 is 40-fold higher than octreotide, which is critical for Cushing disease where corticotroph adenomas predominantly express SSTR5. **Adrenal / HPA Axis (Tier 1 — Human Clinical):** In Cushing disease, pasireotide suppresses ACTH secretion from pituitary corticotroph adenomas via SSTR5. Phase III trials demonstrated normalization of urinary free cortisol (UFC) in 15–26% of patients, with meaningful UFC reduction in a larger proportion. This makes it the only pituitary-directed medical therapy for Cushing disease. **Endocrine — GH/IGF-1 (Tier 1 — Human Clinical):** Effective for acromegaly, particularly in patients who fail octreotide or lanreotide. The broader SSTR profile may capture tumors with heterogeneous SSTR expression. PAOLA trial showed pasireotide LAR was superior to octreotide LAR for biochemical control in acromegaly. **Metabolic — Hyperglycemia (Tier 1 — Human Clinical, MAJOR Safety Concern):** Pasireotide causes severe hyperglycemia in 40–70% of patients. This is dramatically worse than octreotide or lanreotide. The mechanism involves potent suppression of insulin secretion (SSTR5 on beta cells) AND suppression of incretin hormones (GLP-1, GIP) via SSTR5. Many patients require insulin therapy initiation or intensification. **Hepatobiliary (Tier 1 — Side Effect):** Gallstone risk similar to other somatostatin analogs (15–30%). Hepatic enzyme elevations (ALT, AST) reported more frequently than with octreotide. **Cardiac (Tier 1 — Safety Concern):** QT prolongation reported in clinical trials. ECG monitoring recommended, particularly in patients on other QT-prolonging medications.
Practitioner Guide
**APPROVED INDICATIONS:** • Cushing disease (when surgery fails or is not an option) — Signifor 0.6–0.9 mg SC BID. • Acromegaly (inadequate response to first-generation somatostatin analogs) — Signifor LAR 40–60 mg IM monthly. **DOSING:** • Cushing disease: Start 0.6 mg SC twice daily. May increase to 0.9 mg BID based on UFC response and tolerability. • Acromegaly: Signifor LAR 40 mg IM every 28 days. May increase to 60 mg monthly. • Dose reductions for hepatic impairment and if hyperglycemia is unmanageable. **MANAGING HYPERGLYCEMIA (Deep Clinical Pearls — THE Key Challenge):** • Pre-treatment assessment: Fasting glucose, HbA1c, and OGTT before starting. Establish baseline glycemic status. • Monitoring: Weekly fasting glucose for the first 2–3 months, then at least monthly. HbA1c every 3 months. • ANTICIPATE hyperglycemia — it is the rule, not the exception: - Previously normoglycemic patients: ~40% develop hyperglycemia requiring treatment. - Pre-diabetic patients: ~60–70% develop frank diabetes. - Known diabetics: Nearly all experience significant worsening. • Treatment approach: - Mild hyperglycemia (FG 126–200 mg/dL): Start metformin. If insufficient, add DPP-4 inhibitor or GLP-1 receptor agonist. GLP-1 RAs are particularly logical because pasireotide suppresses endogenous incretins — replacing incretin signaling may directly counter the mechanism. - Moderate hyperglycemia (FG 200–300 mg/dL): Start or intensify insulin therapy. Basal insulin + mealtime correction. - Severe hyperglycemia (FG >300 mg/dL or DKA risk): Consider dose reduction or discontinuation of pasireotide if glucose cannot be safely managed. • Clinical pearl: The hyperglycemia from pasireotide is NOT the same as typical type 2 diabetes. It is driven by insulin secretion suppression (not primarily insulin resistance), so medications targeting insulin secretion or replacement (insulin, sulfonylureas) or incretin pathways (GLP-1 RAs) are more effective than metformin alone. This is a crucial pharmacological distinction. • Clinical pearl: Some endocrinologists pre-emptively start metformin + a DPP-4 inhibitor BEFORE initiating pasireotide in patients with any glucose abnormality, rather than waiting for hyperglycemia to develop. **GALLSTONE PREVENTION:** • Same UDCA prophylaxis and monitoring as octreotide/lanreotide. **LAR INJECTION TECHNIQUE:** • Same deep IM gluteal injection as octreotide LAR. Use provided needle, do not substitute smaller gauge. **CARDIAC MONITORING:** • Baseline ECG before starting. Repeat ECG after dose stabilization and periodically. • Avoid co-administration with other QT-prolonging drugs when possible. If necessary, monitor with serial ECGs. • Correct hypokalemia and hypomagnesemia before starting pasireotide. **INTERACTION WITH GH PEPTIDE COMMUNITY:** • Pasireotide is NOT used in the GH peptide community and should not be. Its pan-SSTR profile and severe hyperglycemia make it wholly inappropriate for off-label GH suppression. • If patients using GH peptides present with acromegalic features, they need proper endocrine evaluation — pasireotide would only be indicated if a GH-secreting pituitary adenoma is diagnosed.
Research Summary
**Tier 1 (Human Clinical Evidence):** • Cushing disease: Phase III trial demonstrated UFC normalization in 15% (0.6 mg BID) to 26% (0.9 mg BID) at 6 months. While these rates seem modest, Cushing disease is notoriously difficult to treat medically, and pasireotide remains the only pituitary-targeted medical therapy. • Acromegaly (PAOLA trial, Lancet Diabetes Endocrinol): Pasireotide LAR 40–60 mg was superior to octreotide LAR 30 mg for biochemical control (GH <2.5 and normal IGF-1: 31.3% vs 19.2%). Published as a head-to-head superiority trial. • Hyperglycemia: Documented in every major trial. 40–73% incidence depending on population. Led to FDA-mandated REMS-like monitoring requirements. • Safety: QT prolongation, gallstones, hepatic enzyme elevations, and hyperglycemia are the major safety concerns. **Tier 2 (Strong Preclinical + Mechanistic):** • Pan-SSTR binding profile provides broader receptor coverage. SSTR5 predominance on corticotroph adenomas validates the Cushing disease indication. • The hyperglycemia mechanism (SSTR5-mediated insulin and incretin suppression) is well-characterized and explains why it is worse than SSTR2-selective analogs. **Tier 3 (Emerging / Theoretical):** • Investigation in other ACTH-secreting tumors (ectopic ACTH syndrome) is ongoing. • Combination with cabergoline or ketoconazole for Cushing disease is studied in refractory cases. • Whether the broader SSTR profile translates to anti-proliferative advantages in NETs vs octreotide/lanreotide is unclear.