Early diagnosis and targeted therapy are pivotal tools for the treatment success of neuroendocrine
tumors. The use of somatostatin analogs brought great benefits for NET patients, especially for inoperable
or metastasized gastroenteropancreatic tumors. However, this treatment modality cannot be applied
in all cases. Around one third of tumors do not overexpress somatostatin receptors, thus are not susceptibl
e for octreotide or similar SST analogs. Further G protein-coupled receptors (GPCR)
have to be investigated in neuroendocrine tumors for their use in alternative targeting approaches.
A novel DNA microarray was developed, for investigation of 368 genes, most of them GPCRs (357).
This array was designed to detect differential splice variants and expression levels in parallel. Pancreatic
neuroendocrine tumor samples and control pancreas tissue were hybridized on these DNA microarrays.
After applying splice detection and expression level analysis tools, several novel potential targets
where identified (for example GIPR, MC1R, FN1, TUBB3). These newly found receptors and extracellu
lar matrix proteins were validated with higher sample numbers, in both protein- (Westernblot,
immunohistochemistry) and mRNA-based (qPCR) assays.
For peptide G protein-coupled receptors, the two highly overexpressed genes MC1R and GIPR were
identified and validated. Gastric inhibitory polypeptide receptor (GIPR) has been shown to have similar
expression levels as somatostatin receptor 2 in pancreatic and ileal neuroendocrine tumors. The NET cell
lines H727 and KRJ-1 can be stimulated in functional cAMP production assays with the human
GIP1-42 peptide ligand. In direct comparison, MC1R is, on an absolute scale, less expressed than
GIPR but shows still a very high significant differentially expression towards healthy control tissues.
Neuroendocrine human cell lines LCC-18 and CM could be stimulated by applying both alphamelanocortin
but as well MC1R specific peptides and small molecules.
In a two rounds of peptide optimization, 43 novel ligands were designed. These have been analyzed
in cyclic adenosinmonophosphat production assays and in radioactive receptor-ligand binding studies with th
e human melanocortin 1, 3, 4 and 5 receptors. Here, several highly potent and very specific MC1R ligands
were designed which are composed of one C-terminal fatty acid and four amino acids. These novel compoun
ds will be evaluated for their potential use in diagnostic or therapeutic application
in the future.
د محمد محمود محمد عبد الفتاح | DR MOHAMMAD MAHMOUD MOHAMMAD ADEL FATAH | 9923