Neurotensin receptors in human meningiomas

Meningiomas may be a component tumor of multiple endocrine neoplasia type 1

PURPOSE

Recently, an increased incidence of some nonendocrine tumors are reported in patients with multiple endocrine neoplasia type 1 (MEN 1). There are rare reports of meningiomas and other central nervous system tumors in these patients, but it is unknown if they are more frequent or if allelic loss of the MEN1 gene is important in their pathogenesis. The aim of this study was to address these two latter questions.

EXPERIMENTAL DESIGN

Results from a prospective study of 74 MEN 1 patients with suspected/proven pancreatic endocrine tumors (PETs) were analyzed, as well as molecular studies performed on a resected meningioma. All patients had serial brain imaging studies (computed tomography, magnetic resonance imaging, and octreoscanning since 1994) and yearly studies evaluating MEN 1 involvement with a mean follow-up of 7.2 years. Results were compared with 185 patients with sporadic Zollinger-Ellison syndrome.

RESULTS

Six patients (8%) had meningiomas. Meningiomas were single and found late in the MEN 1 course (mean age = 51 years). Magnetic resonance imaging/computed tomography were more sensitive than octreoscanning. Their diagnosis averaged 18 years after the onset of hyperparathyroidism, 10-15 years after pituitary disease or PETs. Meningiomas were 11 times more frequent in patients with PETs with MEN 1 than without MEN 1 (P = 0.017). No clinical, laboratory, or MEN 1 feature distinguished patients with meningiomas. Meningiomas were asymptomatic and 60% showed no growth. A resected meningioma showed loss of heterozygosity at 11q13 and 1p, including at p73 and ARHI/NOEY2 locus, but not at the neurofibromatosis 2 gene locus.

CONCLUSIONS

These results show meningiomas are not an infrequent occurrence in MEN 1, and loss of the function of the MEN1 gene product plays a role in their pathogenesis in these patients.

Peptide receptors as molecular targets for cancer diagnosis and therapy

During the past decade, proof of the principle that peptide receptors can be used successfully for in vivo targeting of human cancers has been provided. The molecular basis for targeting rests on the in vitro observation that peptide receptors can be expressed in large quantities in certain tumors. The clinical impact is at the diagnostic level: in vivo receptor scintigraphy uses radiolabeled peptides for the localization of tumors and their metastases. It is also at the therapeutic level: peptide receptor radiotherapy of tumors emerges as a serious treatment option. Peptides linked to cytotoxic agents are also considered for therapeutic applications. The use of nonradiolabeled, noncytotoxic peptide analogs for long-term antiproliferative treatment of tumors appears promising for only a few tumor types, whereas the symptomatic treatment of neuroendocrine tumors by somatostatin analogs is clearly successful. The present review summarizes and critically evaluates the in vitro data on peptide and peptide receptor expression in human cancers. These data are considered to be the molecular basis for peptide receptor targeting of tumors. The paradigmatic peptide somatostatin and its receptors are extensively reviewed in the light of in vivo targeting of neuroendocrine tumors. The role of the more recently described targeting peptides vasoactive intestinal peptide, gastrin-releasing peptide, and cholecystokinin/gastrin is discussed. Other emerging and promising peptides and their respective receptors, including neurotensin, substance P, and neuropeptide Y, are introduced. This information relates to established and potential clinical applications in oncology.

Neurotensin receptors in human neoplasms: high incidence in Ewing's sarcomas

Receptors for regulatory peptides, such as somatostatin or vasoactive intestinal peptide (VIP), expressed at high density by neoplastic cells, can be instrumental for tumor diagnosis and therapy. Little is known about the expression of neurotensin receptors in human tumors. In the present study, 464 human neoplasms of various types were investigated for their neurotensin receptor content by in vitro receptor autoradiography on tissue sections using 125I-[Tyr3]-neurotensin as radioligand. Neurotensin receptors were identified and localized in tumor cells of 11/17 Ewing's sarcomas, 21/40 meningiomas, 10/23 astrocytomas, 5/13 medulloblastomas, 7/24 medullary thyroid cancers and 2/8 small cell lung cancers. They were rarely found in non-small cell lung cancers and breast carcinomas; they were absent in prostate, ovarian, renal cell and hepatocellular carcinomas, neuroendocrine gut tumors, pituitary adenomas, schwannomas, neuroblastomas and lymphomas. When present, the receptors bound with nanomolar affinity neurotensin and acetyl-neurotensin-(8-13), with lower affinity neuromedin N, diethylenetriamine penta-acetic acidneurotensin-(8-13) and SR 48692, but not neurotensin-(1-11). They were all of the NT1 type, without high affinity for levocabastine. Further, in 2 receptor-positive Ewing's sarcomas, neurotensin mRNA was detected by in situ hybridization techniques. Since neurotensin is known to stimulate cell proliferation, the presence of neurotensin receptors in human neoplasia may be of biological relevance, possibly as an integrative part of an autocrine feedback mechanism of tumor growth stimulation.

Neurotensin is an autocrine trophic factor stimulated by androgen withdrawal in human prostate cancer

After therapeutic hormone deprivation, prostate cancer cells often develop androgen-insensitive growth through mechanisms thus far undefined. Neuropeptides have been previously implicated as growth factors in some prostate cancers. Here, we demonstrate that androgen-sensitive LNCaP human prostate cancer cells produce and secrete neurotensin following androgen withdrawal. We show that while LNCaP cells express the neurotensin receptor, only androgen-deprived cells exhibit a growth response to exogenous neurotensin. We further demonstrate that androgen-stimulated cells may be refractory to exogenous neurotensin due to androgen induction of a metalloprotease active toward neurotensin. Thus, prostate cancer cells deprived of androgen develop an alternative autocrine growth mechanism involving neurotensin.