Discovery and development of somatostatin agonists

Somatostatin and the "Small-For-Size" Liver

“Small-for-size” livers arising in the context of liver resection and transplantation are vulnerable to the effects of increased portal flow in the immediate postoperative period. Increased portal flow is an essential stimulus for liver regeneration. If the rise in flow and stimulus for regeneration are excessive; however, liver failure and patient death may result. Somatostatin is an endogenous peptide hormone that may be administered exogenously to not only reduce portal blood flow but also offer direct protection to different cells in the liver. In this review article, we describe key changes that transpire in the liver following a relative size reduction occurring in the context of resection and transplantation and the largely beneficial effects that peri-operative somatostatin therapy may help achieve in this setting.

Long-term safety of long-acting octreotide in patients with diabetic retinopathy: results of pooled data from 2 randomized, double-blind, placebo-controlled phase 3 studies

PURPOSE

Octreotide (OCT) has been successfully used for treatment of acromegaly and neuroendocrine tumors for more than 30 years. However, long-term safety of OCT has not been documented in placebo-controlled setting. This present analysis pooled safety data from two similarly-designed, randomized, and placebo-controlled studies to evaluate long-term safety of long-acting OCT (20, 30 mg); targeted post-hoc analyzes focused on cardiac, hepatic, and renal safety.

METHODS

Two studies (NCT00131144, NCT001308450) were conducted in patients with diabetic retinopathy (OCT20 = 191, OCT30 = 348, placebo = 347). In this analysis, patients were stratified based on baseline glomerular filtration rate. Hepatic, cardiac, and renal adverse events (AEs) were identified by standardized MedDRA queries.

RESULTS

Median duration of exposure was >3.5 years. Most common AEs reported with OCT were diarrhea, cholelithiasis, hypoglycemia, nasopharyngitis, and hypertension. Incidence of cardiac events (QT prolongation and arrhythmia) with OCT20 and OCT30 were comparable to placebo (OCT20, RR = 1.11 [95% CI, 0.61-2.03]; OCT30, RR = 1.09 [95% CI, 0.70-1.68]). For ECG findings, changes in QTcF were similar in treatment groups, and outliers did not exceed 480 ms. Incidence of cardiac ischemia was lower with OCT than placebo (OCT20 = 12.6%, OCT30 = 10.6%, placebo = 15.3%). Incidence of liver-related AEs was higher with OCT30 than placebo (RR = 2.04 [95% CI, 1.28-3.26]); incidences were comparable with OCT20 and placebo (RR = 1.50 [95% CI, 0.69-3.25]). Overall incidences of renal AEs were comparable between treatment groups (OCT20 = 5.8%; OCT30 = 6.3%; placebo = 7.2%). Drug-related SAEs were reported more frequently with OCT (OCT20 = 7.9%; OCT30 = 10.1%; placebo = 3.5%); predominantly gallbladder-related, GI-related, and hypoglycemia.

CONCLUSIONS

The results from these long-term placebo-controlled studies confirm the established safety profile of long-acting OCT, in particular low risk of cardiac, hepatic and renal toxicity in a high-risk population.

Clinical History of the Theranostic Radionuclide Approach to Neuroendocrine Tumors and Other Types of Cancer: Historical Review Based on an Interview of Eric P. Krenning by Rachel Levine

In nuclear medicine, the term theranostics describes the combination of therapy and diagnostic imaging. In practice, this concept dates back more than 50 years; however, among the most successful examples of theranostics are peptide receptor scintigraphy and peptide receptor radionuclide therapy of neuroendocrine tumors. The development of these modalities through the radiolabeling of somatostatin analogs with various radionuclides has led to a revolution in patient management and established a foundation for expansion of the theranostic principle into other oncology indications. This article provides a review of the evolution and development of the theranostic radionuclide approach to the management of neuroendocrine tumors, as described by the inventor of this technique, Eric P. Krenning, in an interview with Rachel Levine.

Intestinal absorption of octreotide using trimethyl chitosan chloride: studies in pigs

PURPOSE

To investigate the enhancing effect of trimethyl chitosan chloride (TMC) on the enteral absorption of octreotide and to delineate the required doses of both TMC and peptide in vivo in juvenile pigs.

METHODS

Six female pigs (body weight, 25 kg) were operated to induce a stoma at the beginning of their jejunum and to insert an in-dwelling fistula for intrajejunal (IJ) administration of the formulations. A silicone cannula was inserted at the jugular vein for blood sampling. One week after surgery the pigs received IJ octreotide solution administrations with or without TMC at pH 7.4 or chitosan HCl at pH 5.5. For determining bioavailability (F) values, the pigs also received an octreotide solution intravenously (IV). Blood samples were taken from the cannulated jugular vein and subsequently analyzed by radioimmunoassay.

RESULTS

Intrajejunal administration of 10 mg octreotide without any polymer (control solution) resulted in F values of 1.7 +/- 1.1% (mean +/- SE). Chitosan HCl 1.5% (w/v) at pH 5.5 led to a 3-fold increase in F compared to the control (non-polymer containing) formulations. Co-administration of octreotide with 5 and 10% (w/v) TMC at pH 7.4 resulted in 7.7- and 14.5-fold increase of octreotide absorption, respectively (F of 13.9 +/- 1.3% and 24.8 +/- 1.8%). IJ administration of 5 mg octreotide solutions resulted in low F values of 0.5 +/- 0.6%, whereas co-administration with 5% (w/v) TMC increased the intestinal octreotide bioavailability to 8.2 +/- 1.5%.

CONCLUSIONS

Cationic polymers of the chitosan type are able to enhance the intestinal absorption of the peptide drug octreotide in pigs. In this respect, TMC at neutral pH values of 7.4 appears to be more potent than chitosan HCl at a weak acidic pH of 5.5.

Somatostatin-induced control of cytosolic free calcium in pituitary tumour cells

1. In rat pituitary tumour cells (GC cells), spontaneous oscillations of the intracellular concentration of Ca2+ ([Ca2+]i) induce growth hormone (GH) secretion that is inhibited by octreotide, a somatostatin (SRIF) agonist which binds to SRIF subtype (sst) receptor 2. The effects of its functional activation on the control of [Ca2+]i were investigated using fluorimetric measurements of [Ca2+]i. 2. SRIF decreases the basal [Ca2+]i and the [Ca2+]i rise in response to forskolin (FSK) through the inhibition of L-type voltage-dependent Ca2+ channels. 3. Pretreatment with octreotide or with L-Tyr8++ Cyanamid 154806, a sst2 receptor antagonist, abolishes the SRIF-induced inhibition of [Ca2+]i. Octreotide is known to operate through agonist-induced desensitization, while the antagonist operates through receptor blockade. 4. sst1 and sst2 receptor-immunoreactivities (-IRs) are localized to cell membranes. sst2, but not sst1 receptor-IR, internalizes after cell exposure to octreotide. 5. SRIF-induced inhibition of basal [Ca2+]i or FSK-induced Ca2+ entry is blocked by pertussis toxin (PTX). 6. FSK-induced cyclic AMP accumulation is only partially decreased by SRIF or octreotide, indicating that sst2 receptors are coupled to intracellular pathways other than adenylyl cyclase (AC) inhibition. 7. In the presence of H-89, an inhibitor of cyclic AMP-dependent protein kinase (PKA), SRIF-induced inhibition of basal [Ca2+]i is still present, although reduced in amplitude. 8. SRIF inhibits [Ca2+]i by activating sst2 receptors. Inhibition of AC activity is only partly responsible for this effect, and other transduction pathways may be involved.