Somatostatinergic ligands in dopamine-sensitive and -resistant prolactinomas.
OBJECTIVE
Ten percent of patients with prolactinoma fail to respond with normalization of prolactin (PRL) and tumor shrinkage under dopamine agonist (DA) therapy. The resistance to treatment is linked to a loss of dopamine receptor 2 (D2DR). Prolactinomas express somatostatin (SST) receptor subtypes, SSTR1, 2, and 5. The aim of this study was to determine whether different SST compounds could overcome the resistance to DA in prolactinomas.


METHODS
The efficacy of SSTR1, SSTR2, and SSTR5 ligands; the universal SST ligand, SOM230; and the chimeric SST-DA compound, BIM-23A760, was compared with cabergoline in suppressing PRL secretion from primary cultures of ten prolactinomas (six DA responders and four DA resistant). Receptor mRNAs were assessed by quantitative PCR.


RESULTS
The mean mRNA levels for D2DR, SSTR1, SSTR2, and SSTR5 were 92.3+/-47.3, 2.2+/-1.4, 1.1+/-0.7, and 1.6+/-0.6 copy/copy beta-glucuronidase (beta-Gus) respectively. The SSTR1 agonist, BIM-23926, did not suppress PRL in prolactinomas. In a DA-resistant prolactinoma, it did not inhibit [(3)H]thymidine incorporation. The SSTR5 compound, BIM-23206, produced a dose-dependent inhibition of PRL release similar to that of cabergoline in three DA-sensitive prolactinomas. BIM-23A760 produced a maximal PRL inhibition superimposable to that obtained with cabergoline with a lower EC(50) (0.5+/-0.1 vs 2.5+/-1.5 pmol/l). In DA-resistant prolactinomas, BIM-23206 and SOM230 were ineffective. Cabergoline and BIM-23A760 produced a partial inhibition of PRL secretion (19+/-6 and 21+/-3% respectively).


CONCLUSIONS
Although the SSTRs are expressed in prolactinomas, the somatostatinergic ligands analyzed do not appear to be highly effective in suppressing PRL. D2DR remains the primary target for effective treatment of prolactinomas.
Fusco
Alessandra
A
Interactions Cellulaires Neuroendocrinnienes, UMR/CNRS 6544, Faculte de Medecine Nord, University of Aix-Marseilles II, Boulevard Pierre Dramard, 13015, Marseilles, France.
Gunz
Ginette
G
Jaquet
Philippe
P
Dufour
Henry
H
Germanetti
Anne Laure
AL
Culler
Michael D
MD
Barlier
Anne
A
Saveanu
Alexandru
A
D000328:Adult; D000970:Antineoplastic Agents / Q000494:pharmacology; D000077465:Cabergoline; D004298:Dopamine / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004873:Ergolines / Q000494:pharmacology; D005260:Female; D049912:Growth Hormone-Secreting Pituitary Adenoma / Q000188:drug therapy* / Q000235:genetics / Q000503:physiopathology; D006801:Humans; D008024:Ligands; D008297:Male; D008875:Middle Aged; D010911:Pituitary Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000503:physiopathology; D015175:Prolactinoma / Q000188:drug therapy* / Q000235:genetics / Q000503:physiopathology; D012333:RNA, Messenger / Q000378:metabolism; D017448:Receptors, Dopamine D2 / Q000235:genetics; D017481:Receptors, Somatostatin / Q000819:agonists* / Q000235:genetics*; D013004:Somatostatin / Q000031:analogs & derivatives / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; C519494:BIM 23926; D004873:Ergolines; D008024:Ligands; D012333:RNA, Messenger; D017448:Receptors, Dopamine D2; D017481:Receptors, Somatostatin; C101130:somatostatin receptor type 1; D013004:Somatostatin; C094573:somatostatin receptor 5; C517782:pasireotide; C093733:somatostatin receptor 2; D000077465:Cabergoline; D004298:Dopamine