Gastrin-Releasing Peptide Is a Growth Factor for Human Neuroblastomas

Neuroblastoma is the most common extracranial solid malignancy of childhood and has a death rate exceeding 50%, particularly in older children. 1 Neuroblastoma tumors are derived from neural crest precursors and are classified as ganglioneuromas (benign type), ganglioneuroblastomas (mixed type), or neuroblastomas (malignant type). 2,3 They occur at sites in the sympathetic nervous system distributed from the head and neck region to the pelvis. 4 Variations in tumor location and degree of histopathologic differentiation can result in a wide range of clinical and biologic characteristics; however, the two most important clinical prognostic variables are disease stage and the age of the patient at diagnosis. 5,6 Interestingly, the clinical behavior of neuroblastoma is varied and unpredictable and can range from spontaneous tumor regression, maturation from a malignant to a benign lesion, or progressive malignant change. 2,3 This unpredictable feature of neuroblastoma suggests that malignant transformation of cells may result, in part, from a failure to respond to normal signals regulating morphologic differentiation. Neuroblastomas are classified as amine precursor uptake decarboxylase tumors because they secrete peptides and other substances including vasoactive intestinal polypeptide and vasoactive metabolites such as catecholamines, serotonin, and acetylcholine. 7 These peptides may be involved in the regulation of tumor growth and differentiation. Further, the concentration of certain peptides (e.g., vanillylmandelic acid) has been correlated with the clinical behavior of neuroblastomas. Despite an ever-increasing ability to determine prognosis based on biologic features of neuroblastoma, such as N-myc amplification, 8 ploidy, 9 and deletion or loss of heterozygosity of chromosome 1p, 10 the cellular mechanisms involved in the growth regulation of this tumor remain unknown. Devising new therapeutic strategies for treating patients with high-risk neuroblastoma based on a better molecular understanding of neuroblastoma growth regulation remains a challenge. Gastrin-releasing peptide (GRP), the mammalian equivalent of bombesin, is a neuroendocrine peptide shown to have a growth stimulatory effect on various tissues. 11,12 Investigators in our laboratory have shown that GRP is a potent mitogen for normal intestinal mucosa 13 and pancreas. 14 In addition, we have demonstrated that GRP, binding to its G-protein coupled receptor (GRP-R), exerts a trophic effect on cancers of the lung, 14 pancreas, 15 stomach, 16 and colon. 17 We have also shown that bombesin exerts its mitogenic action in gastric cancer by functionally binding to GRP-R and activating the intracellular calcium [Ca2+] pathway. 18 Others have shown the trophic effects of GRP on breast 19 and prostate cancer cell lines. 20,21 Moreover, Cuttitta et al. 12 have shown that GRP is an autocrine growth factor for human small cell lung cancer. GRP mRNA expression has been identified in certain neuroblastomas;22 however, the expression of the GRP and the role of this peptide in neuroblastoma growth have not been elucidated. The purpose of our study was to define the potential mitogenic actions of GRP in human neuroblastomas. We examined paraffin-embedded archival samples of neuroblastomas of varying histopathology for expression of GRP and GRP-R by immunohistochemistry and correlated the expression of these proteins with clinical tumor behavior. In addition, we assessed human neuroblastoma cell lines for the presence of GRP-R mRNA, the effect of GRP on [Ca2+]i mobilization, the secretion of GRP, and the proliferative effects of GRP on these cell lines.