The somatostatin analogue somatoprim (also known as DG3173) causes greater growth hormone (GH) suppression than octreotide when applied to primary cell cultures of somatotroph adenomas, according to a German study.

Somatostatin analogues are considered safe for the treatment of acromegaly. The only long-term concern is their negative effect on glucose metabolism. A somatostatin analogue with high efficacy for GH suppression but little effect on insulin secretion would, therefore, be a valuable addition to the armamentarium of medical therapies for acromegaly.

“We were interested to explore the efficacy of the new multiligand somatostatin analogue somatoprim and hoped to observe an increased effect compared with the established agent octreotide,” recounts lead investigator Ursula Plöckinger from the Charité Hospital in Berlin. “In addition, we aimed to determine a possible pattern for predicting the GH-lowering effect of somatoprim.”

Using 27 primary cell cultures derived from somatotroph adenomas obtained after surgery, Plöckinger and her team quantitatively evaluated and directly compared the GH-suppressing effect of somatoprim and octreotide. Immunohistochemistry was used to evaluate possible prognostic markers: presence and distribution of somatostatin receptor (SSTR) subtypes; pattern of pituitary hormone expression in the tumor; and analysis of the morphological characteristics of the somatotroph adenomas.

Each somatostatin analogue has specific affinities to different SSTR subtypes. In contrast to octreotide, somatoprim has a high affinity for SSTR3, in addition to SSTR2 and SSTR5. All analyzed adenomas highly expressed SSTR3, the activation of which might have been responsible for the higher number of tumors responsive to somatoprim compared with octreotide.

Previous studies have shown a very low insulin-suppressing effect of somatoprim, which is an additional advantage of this drug over other somatostatin analogues, for example, SOM230 and octreotide. To further evaluate the potential of somatoprim as an effective drug in acromegaly, more clinical data are needed. “If clinical trials confirm the in vitro data, we feel that the drug may well become the treatment of choice for medical therapy in acromegaly owing to its high efficacy, potential for tumor shrinkage and its negligible effect on insulin secretion,” concludes Plöckinger.