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Giselle F Taboada, Raul M Luque, Leonardo Vieira Neto, Evelyn de O Machado, Bruna C Sbaffi, Romeu C Domingues, Jorge B Marcondes, Leila M C Chimelli, Rosita Fontes, Paulo Niemeyer, Denise P de Carvalho, Rhonda D Kineman and Mônica R Gadelha

Objective

To determine whether the somatostatin receptor subtype (SSTR) expression profile correlates with hormonal and tumor volume responses to postsurgical octreotide long acting repeatable (OCT LAR) treatment.

Design and methods

Quantitative real-time RT-PCR was used to evaluate the absolute mRNA copy numbers for all five SSTR subtypes in 22 somatotropinomas. Response to OCT LAR was studied by hormone levels (GH and IGF-I) and tumor volume (sella turcica magnetic resonance imaging).

Results

SSTR5 was present at the highest level followed by SSTR2, SSTR3, SSTR1, and SSTR4 (2327 (1046–5555), 2098 (194–23 954), 97 (0–460), 14 (0–29 480), and 0 (0–652) copies respectively). Positive correlations were found between SSTR2 levels and the percentage decrease of GH and IGF-I after 3 (r=0.49, P<0.027 and r=0.49, P<0.029 respectively) and 6 (r=0.59, P<0.006 and r=0.58, P<0.008 respectively) months of OCT LAR. A negative correlation was found between SSTR5 mRNA levels and the percentage decrease of GH after 3 months of OCT LAR (r=−0.52, P=0.016, n=21). A higher SSTR2/SSTR5 ratio was observed among patients who obtained hormonal control with OCT LAR, when compared with those uncontrolled (2.4 (0.7–10) vs 0.3 (0.1–7.7), P=0.001). A ROC curve analysis showed a SSTR2/SSTR5 ratio of 1.3 as the best predictor of disease control, with a sensitivity of 88% and a specificity of 92% – area under curve, 0.9. A positive correlation was also found between SSTR2 mRNA levels and the percentage decrease in tumor volume after 6 months of OCT LAR (r=0.79, P=0.002, n=12).

Conclusions

Somatostatin receptor subtype 2 mRNA expression levels in somatotropinomas correlate positively with in vivo hormonal and tumor volume responses to OCT LAR.

Free access

Giselle F Taboada, Raul M Luque, Wildebranham Bastos, Renata F C Guimarães, Jorge B Marcondes, Leila M C Chimelli, Rosita Fontes, Paulo J P Mata, Paulo Niemeyer Filho, Denise P Carvalho, Rhonda D Kineman and Mônica R Gadelha

Objective: It is believed that the variable effectiveness of somatostatin analogs in post-surgical management of somatotropinomas and non-functioning pituitary adenomas (NFPA) may be due in part to variable expression of somatostatin receptor isoforms (SSTR1–5), within and between pituitary tumor types.

Design and methods: Quantitative real-time RT-PCR was used to compare absolute mRNA copy numbers for all five SSTR isoforms in 23 somatotropinomas and 19 NFPA.

Results: Somatostatin receptor subtype 5 mRNA was present at the highest level in somatotropinomas, followed by SSTR2>SSTR3≫SSTR1⋙SSTR4. In contrast, SSTR3 mRNA was present at the highest level in NFPA, followed by SSTR2, while SSTR1, SSTR4, and SSTR5 transcripts were only detectable in select tumors. Among somatotropinomas, a positive correlation was found between SSTR2 mRNA levels and the percent decrease of GH (%GH) after 3 and 6 months of therapy with octreotide long acting repeatable (LAR) (r=0.51 and r=0.66; P=0.05 and P=0.008). Also the percent decrease of IGF-I (%IGF-I) after 3 months of octreotide LAR was negatively correlated with SSTR5 and %IGF-I after 6 months of octreotide LAR was positively correlated with SSTR2.

Conclusions: The present report is a large series examining SSTR mRNA levels in somatotropinomas and NFPA. These initial findings suggest that detailed knowledge of the SSTR mRNA expression profile in somatotropinomas can help to predict the hormonal response to therapy with LAR. Also, it appears that SSTR3 in NFPA may be a potential target for SSTR3 preferential or universal ligands such as pasireotide.

Free access

Antonio J Martínez-Fuentes, Marcelo Molina, Rafael Vázquez-Martínez, Manuel D Gahete, Luis Jiménez-Reina, Jesús Moreno-Fernández, Pedro Benito-López, Ana Quintero, Andrés de la Riva, Carlos Diéguez, Alfonso Soto, Alfonso Leal-Cerro, Eugenia Resmini, Susan M Webb, Maria C Zatelli, Ettore C degli Uberti, María M Malagón, Raul M Luque and Justo P Castaño

Context

KISS1 was originally identified as a metastasis-suppressor gene able to inhibit tumor progression. KISS1 gene products, the kisspeptins, bind to a G-protein-coupled receptor (KISS1R, formerly GPR54), which is highly expressed in placenta, pituitary, and pancreas, whereas KISS1 mRNA is mainly expressed in placenta, hypothalamus, striatum, and pituitary.

Objective and design

KISS1/KISS1R pituitary expression profile, coupled to their anti-tumoral capacities, led us to hypothesize that this system may be involved in the biology of pituitary tumors. To explore this notion, expression levels of KISS1R and KISS1 were evaluated in normal and adenomatous pituitaries. Additionally, functionality of this system was assessed by treating dispersed pituitary adenoma cells in primary culture with kisspeptin-10 and evaluating intracellular calcium kinetics and apoptotic rate.

Results

Both KISS1 and KISS1R were expressed in normal pituitary, whereas this simultaneous expression was frequently lost in pituitary tumors, where diverse patterns of KISS1/KISS1R expression were observed that differed among distinct types of pituitary adenomas. Measurement of calcium kinetics revealed that kisspeptin-10 elicits a remarkable increase in [Ca2+]i in individual cells from four out of the five GH-producing adenomas studied, whereas cells derived from non-functioning pituitary adenomas (NFPA, n=45) did not respond. In contrast, kisspeptin-10 treatment increased the apoptotic rate in cells derived from both GH-producing and NFPA.

Conclusions

These results provide primary evidence that KISS1 and KISS1R expression can be differentially lost in pituitary tumor subtypes, where this system can exert functional, proapoptotic actions, and thereby offer novel insights to investigate the biology and therapeutic options to treat these tumors.