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SOM230, A New Somatostatin Analogue, Is Highly Effective in the Therapy of Growth Hormone/Prolactin-Secreting Pituitary Adenomas

Authors' Affiliations: ¹ Istituto di Endocrinologia ed Oncologia Sperimentale del CNR e/o Dipartimento di Biologia e Patologia Cellulare e Molecolare, ² Dipartimento di Endocrinologia ed Oncologia Molecolare e Clinica, and ³ Istituto di Patologia, Università di Napoli "Federico II"; ⁴ Istituto dei Tumori di Napoli Fondazione "G. Pascale"; ⁵ NOGEC (Naples Oncogenomic Center)-CEINGE Biotecnologie Avanzate & SEMM, European School of Molecular Medicine, Naples, Italy; ⁶ Novartis Institutes of Biomedical Research, Oncology, Basel, Switzerland; and ⁷ Department of Internal Medicine, Erasmus University, Rotterdam, the Netherlands

Requests for reprints: Alfredo Fusco, Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università di Napoli "Federico II," via Pansini, 5, 80131 Naples, Italy. Phone: 39-081-3737857; Fax: 39-081-3737808; E-mail: afusco{at}napoli.com.

Purpose: We have previously shown that transgenic mice ubiquitously overexpressing the HMGA2 gene develop growth hormone/prolactin-secreting pituitary adenomas. This animal model has been used to evaluate the therapeutic efficacy of SOM230, a somatostatin analogue with high affinity for the somatostatin receptor subtypes 1, 2, 3, and 5, on the growth of the pituitary adenomas.

Experimental Design: Four groups of 3- and 9-month-old HMGA2 transgenic mice were treated for 3 months with a continuous s.c. injection of two different dosages of SOM230 (5 or 50 µg/kg/h), one dose of octreotide, corresponding to that used in human therapy, and a placebo, respectively. The development of the tumor before and after therapy was monitored by magnetic resonance imaging of the pituitary region and evaluation of the serum prolactin levels.

Results: The highest dose of SOM230 induced a drastic regression of the tumor, whereas octreotide was not able to induce any significant tumor regression, although tumor progression was significantly slowed down. No significant differences were observed between the animals treated with the lowest dose of SOM230 and those receiving placebo.

Conclusions: These results clearly support the efficacy of the SOM230 treatment in human pituitary adenomas secreting prolactin based on the dramatic tumor shrinkage and fall in prolactin levels. This beneficial effect could be of crucial clinical usefulness in patients bearing tumors resistant to dopaminergic drugs.