The Role of Peptides and their Receptors as Tumor Markers

Liquid biopsy to monitor melanoma patients

During the last six years, several innovative, systemic therapies for the treatment of metastatic malignant melanoma (MM) have emerged. Conventional chemotherapy has been superseded by novel first-line therapies, including systemic immunotherapies (anti-CTLA4 and anti-PD1; authorization of anti-PDL1 is anticipated) and therapies targeting specific mutations (BRAF, NRAS, and c-KIT). Thus, treating physicians are confronted with new challenges, such as stratifying patients for appropriate treatments and monitoring long-term responders for progression. Consequently, reliable methods for monitoring disease progression or treatment resistance are necessary. Localized and advanced cancers may generate circulating tumor cells and circulating tumor DNA (ctDNA) that can be detected and quantified from peripheral blood samples (liquid biopsy). For melanoma patients, liquid biopsy results may be useful as novel predictive biomarkers to guide therapeutic decisions, particularly in the context of mutation-based targeted therapies. The challenges of using liquid biopsy include strict criteria for the phenotypic nature of circulating MM cells or their fragments and the instability of ctDNA in blood. The limitations of liquid biopsy in routine diagnostic testing are discussed in this review.

The role of preclinical SPECT in oncological and neurological research in combination with either CT or MRI

Preclinical imaging with SPECT combined with CT or MRI is used more and more frequently and has proven to be very useful in translational research. In this article, an overview of current preclinical research applications and trends of SPECT combined with CT or MRI, mainly in tumour imaging and neuroscience imaging, is given and the advantages and disadvantages of the different approaches are described. Today SPECT and CT systems are often integrated into a single device (commonly called a SPECT/CT system), whereas at present combined SPECT and MRI is almost always carried out with separate systems and fiducial markers to combine the separately acquired images. While preclinical SPECT/CT is most widely applied in oncology research, SPECT combined with MRI (SPECT/MRI when integrated in one system) offers the potential for both neuroscience applications and oncological applications. Today CT and MRI are still mainly used to localize radiotracer binding and to improve SPECT quantification, although both CT and MRI have additional potential. Future technology developments may include fast sequential or simultaneous acquisition of (dynamic) multimodality data, spectroscopy, fMRI along with high-resolution anatomic MRI, advanced CT procedures, and combinations of more than two modalities such as combinations of SPECT, PET, MRI and CT all together. This will all strongly depend on new technologies. With further advances in biology and chemistry for imaging molecular targets and (patho)physiological processes in vivo, the introduction of new imaging procedures and promising new radiopharmaceuticals in clinical practice may be accelerated.

Serum levels of IGF-I and IGFBP-III and their relation with carcinoembryonic antigen and carbohydrate antigen 19-9 in cases of esophageal cancer

Tumour markers are used for diagnosis, staging, evaluation of response to treatment, prognosis and detection of recurrences in clinical oncology. In this study, we aim to investigate the levels of insulin-like growth factor (IGF)-I and IGF-binding protein (IGFBP)-III in cases with oesophageal carcinoma. We investigated their possible use as tumour markers and their relation to other tumour markers. Forty patients who were diagnosed as having oesophageal carcinoma by histopathological evaluation of endoscopic biopsies between January 2003 and July 2004 and 40 healthy people as the control group were included in the study. The serum levels of tumour markers including IGF-I, IGFBP-III, carcinoembryonic antigen (CEA) and carbohydrate antigen (CA) 19-9 were measured in both groups. Data were compared statistically, and the importance of IGF-I and IGFBP-III levels were investigated in cases with oesophageal carcinoma. IGF-I levels were significantly higher in patients with oesophageal carcinoma when compared with the control group (p < 0.05), whereas IGFBP-III levels were significantly lower (p < 0.05). The increase in CEA levels was not statistically significant when compared with the control group. The increase in CA 19-9 levels was statistically significant when compared with the control group (p < 0.05). No correlation was detected between levels of IGF-I and IGFBP-III and levels of CEA and CA 19-9. We suggest that the serum IGF-I level may be used as a tumour marker in oesophageal carcinoma. A low level of serum IGFBP-III is also significant in cases with oesophageal carcinoma. We believe that drugs which inhibit IGF-I function or which stimulate the function of IGFBP-III may open new horizons in extra-surgical modalities for the treatment of oesophageal cancer.

Optical imaging of metastatic tumors using a folate-targeted fluorescent probe

We describe the use of a tumor targeting ligand, the vitamin folic acid, to deliver an attached fluorescent probe to both primary and metastatic tumors overexpressing the folate receptor. Upon laser excitation, derived images of normal tissues generally show little or no fluorescence, whereas images of folate receptor-expressing tumors display bright fluorescence that can be easily distinguished from adjacent normal tissue. Furthermore, metastatic tumor loci of submillimeter size can also be visualized without the aid of image processing or enhancement. The sharp distinction between tumor and normal tissues provided by this technique could find application in the localization and resection of tumor tissue during surgery or in the enhanced endoscopic detection and staging of cancers.

Neuroendocrine tumor markers

Tumor markers used in the diagnosis and follow-up of patients with neuroendocrine tumors are in most instances not specific for a given tumor and circulate under normal conditions in the serum, making their use as an early diagnostic tool difficult (low sensitivity). By combining hormone measurements with tissue responsiveness, demonstrations of inappropriate secretions of PTH, insulin, and gastrin during hypercalcemia, hypoglycemia, and hyperacidity, respectively, become highly sensitive and specific diagnostic tests. The application of polyclonal antibodies in RIAs of hormones, such as ACTH, insulin, and gastrin, increase the diagnostic level of hormone measurements in patients with neuroendocrine tumors. Other markers, such as chromogranin A, neuron-specific enolase, and alpha-subunit, as well as peptide receptor visualization, are of increasing importance in the diagnosis and follow-up of neuroendocrine and non-neuroendocrine tumors.

Human adrenocortical NCI-H295 cells express VIP receptors. Steroidogenic effect of vasoactive intestinal peptide (VIP)

VIP receptors are frequently overexpressed by various endocrine tumors. In this study the expression of VIP receptors in the human adrenocortical carcinoma cell line NCI-H295 and their involvement in the regulation of steroidogenesis was investigated. NCI-H295 cells express VIP1 and VIP2 receptors as demonstrated by RT-PCR, whereas they do not express VIP itself. The receptors are functionally coupled to steroidogenesis since VIP (10(-9) M to 10(-6) M) exerted a dose-dependent stimulatory effect on the release of aldosterone, cortisol, and DHEA. VIP increased ACTH-stimulated releases of aldosterone and cortisol. The proliferation rate of NCI-H295 cells was not affected by VIP. These data show that NCI-H295 cells express both forms of the VIP receptor and that VIP is involved in an ACTH-independent regulation of steroidogenesis in the adrenal tumor cells.

Peptide receptors in gut endocrine tumours

A great number of gut endocrine tumours show high expression of receptors for neuropeptides, such as SRIF and VIP. The expression of ssts is essential for the control of hormonal hypersecretion and tumour growth by octapeptide somatostatin analogues. Five different sst subtypes, named sst1-5, have been cloned and characterized. The therapeutic efficacy of the octapeptide analogues is determined by the expression of sst2 (sst3) and sst5 on the tumour. In general, there is a predominant expression of sst1 and sst2 mRNA in gut endocrine tumours. In vivo sst scintigraphy, after injection of [111In]pentetreotide, provides a useful tool for the diagnostic work-up of patients with these tumours. This technique can be used for the localization of the primary tumour(s), for the determination of the extent of metastatic spread and for the selection of potential candidates for therapy with (radiolabelled) octapeptide analogues. Differentiated gut endocrine tumours also show a high expression of VIP-Rs. However, undifferentiated tumours show VIP-R expression to a smaller degree. In vivo scintigraphy with 123I-labelled VIP is a sensitive technique for the in vivo identification of gut endocrine tumours and their metastases. The functional role of the tumoral VIP-Rs is still unclear and at present there are no known therapeutic applications for VIP-R agonists or antagonists in humans.

Substance-P receptors in human primary neoplasms: tumoral and vascular localization

Primary human neoplasms were examined for the presence of substance-P receptors by receptor autoradiography with 125I-labelled Bolton-Hunter substance P. Substance-P receptors were localized and characterized in the neoplastic cells of 9/12 astrocytomas, 10/10 glioblastomas, 10/12 medullary thyroid carcinomas, 8/16 breast carcinomas and 4/5 ganglioneuroblastomas. Conversely, substance-P receptors were not or only rarely identified on non-small-cell carcinomas of the lung (1/16), neuroblastomas (0/8), adenocarcinomas of the colon (1/21) or the pancreas (1/9), or on malignant lymphomas (3/18). However, in the great majority of the investigated tumours, substance-P receptors were found on intra- and peritumoral blood vessels. All substance-P receptors detected had the pharmacological characteristics of the neurokinin-I receptor sub-type. In addition, the expression of somatostatin receptors was examined in all the neoplastic tissues mentioned above. Both substance-P and somatostatin receptors were present in astrocytomas and in ganglioneuroblastomas, whereas little or no receptor was found in pancreatic and non-small-cell lung carcinomas. The extent of somatostatin-receptor expression was inversely correlated to that of the substance-P receptors in glioblastomas, neuroblastomas and non-Hodgkin's lymphomas. The tumoral and vascular localization of substance-P receptors in tumours may have clinical implications. The use of radiolabelled substance P for in vivo scintigraphy may supplement the current set of diagnostic tools. Substance-P antagonists might be used in the treatment of tumours, as their binding to vascular receptors may decrease tumoral blood supply and drainage.

Multiple actions of somatostatin in neoplastic disease

The role played by the neuropeptide somatostatin, also known as somatotropin release inhibitory factor (SRIF), in human cancer is not well understood. Recent investigations involving somatostatin receptors in normal and neoplastic human tissues suggest that the action is complex and involves both direct and indirect mechanisms. In this article, Jean-Claude Reubi and Jean Laissue describe the variety of biological mechanisms involved in neoplasia that are associated with somatostatin, and illustrate the therapeutic potential and present limitations of somatostatin analogues.