Somatostatinergic ligands in dopamine-sensitive and -resistant prolactinomas

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Alessandra Fusco1, Ginette Gunz, Philippe Jaquet

  • 1Interactions Cellulaires Neuroendocrinnienes, UMR/CNRS 6544, Faculte de Medecine Nord, University of Aix-Marseilles II, Boulevard Pierre Dramard, 13015, Marseilles, France.

European Journal of Endocrinology
|April 23, 2008
PubMed
Abstract

Insights

Dopamine agonist (DA) resistance in prolactinoma patients is a challenge. While somatostatin receptor (SST) compounds were tested, they showed limited efficacy in suppressing prolactin (PRL) in resistant cases, indicating dopamine receptor 2 (D2DR) remains key.

Area of Science:

  • Endocrinology
  • Molecular Endocrinology
  • Tumor Biology

Background:

  • Prolactinomas are pituitary tumors often treated with dopamine agonists (DAs).
  • A subset of patients (10%) exhibit resistance to DA therapy, characterized by lack of prolactin (PRL) normalization and tumor shrinkage.
  • This resistance is often associated with a loss of dopamine receptor 2 (D2DR) expression.

Purpose of the Study:

  • To investigate the potential of somatostatin (SST) receptor ligands to overcome DA resistance in prolactinomas.
  • To compare the efficacy of different SST receptor subtypes (SSTR1, SSTR2, SSTR5) and novel compounds against DA-resistant prolactinomas.

Main Methods:

  • Primary prolactinoma cell cultures (10 cases: 6 DA-responders, 4 DA-resistant) were used.
  • The study assessed the effects of SSTR1, SSTR2, and SSTR5 ligands, a universal SST ligand (SOM230), and a chimeric SST-DA compound (BIM-23A760) on PRL secretion.
  • Receptor mRNA expression (D2DR, SSTR1, SSTR2, SSTR5) was quantified using real-time PCR.

Main Results:

  • Somatostatin receptor subtypes (SSTR1, SSTR2, SSTR5) were expressed in prolactinomas, but SSTR1 agonists showed no PRL suppression.
  • An SSTR5 agonist (BIM-23206) effectively inhibited PRL in DA-sensitive prolactinomas, similar to cabergoline.
  • In DA-resistant prolactinomas, BIM-23206 and SOM230 were ineffective; cabergoline and BIM-23A760 provided only partial PRL inhibition.

Conclusions:

  • Somatostatin receptor ligands show limited efficacy in suppressing prolactin secretion, particularly in DA-resistant prolactinomas.
  • Dopamine receptor 2 (D2DR) remains the primary therapeutic target for effective prolactinoma treatment.
  • Further research into novel therapeutic strategies targeting D2DR or alternative pathways is warranted.

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