Gene transfer of somatostatin receptor type 2 by intratumoral injection inhibits established pancreatic carcinoma xenografts

AIM: To investigate the therapeutic effect of somatostatin receptor type 2 (SSTR2) gene transfection on pancreatic carcinoma xenografts in vivo in experimental cancers. METHODS: Human pancreatic cancer cell line Panc-1 was inoculated subcutaneously into the back of nude mice. When tumor nodules were grown as large as about 5 mmx5 mm days after inoculation, the mice were randomly divided into 3 groups (6 mice in each group). Group Ⅰ served as untreated control group. Group Ⅱ received an intratumoral injection of a combination of human cytomegalovirus promoter-6C (pCMV-6C) and lipofectamine 2000. Group Ⅲ received an intratumoral injection of a combination of pCMV-6C-SSTR2 and lipofectamine 2000. The rate of tumor growth was compared among these three groups. The expression of SSTR2 in these tumors was detected by immunohistochemistry and Western-blot. Apoptosis index (AI) in these tumors was examined by using TUNEL in situ. RESULTS: Intratumoral injection of a combination of pCMV-6C-SSTR2 and lipofectamine 2000 resulted in the expression of SSTR2 protein. The tumor size and weight in group Ⅲ (0.318±0.098 cm3, and 0.523±0.090 g, respectively) were significantly lower than those in group I (2.058±0.176 cms, and 1.412±0.146 g, respectively) and group Ⅱ (2.025±0.163 cm3, and 1.365±0.116 g, respectively) (P<0.05) The AI in group Ⅲ (1.47±0.13%) was significantly higher than that in groupⅠ(0.56±0.09%) and group Ⅱ (0.57±0.11%) (P<0.05). But there were no significant differences between groups Ⅰ and Ⅱ. CONCLUSION: Our data demonstrate that re-expression of SSTR2 gene has antitumor effects on experimental pancreatic cancer. Restoration of SSTR2 gene expression through gene transfer in vivo might be a potential gene therapy strategy for human pancreatic cancer.

Somatostatin receptor subtype 2-mediated scintigraphy and localization using ^(99m)Tc-HYNIC-Tyr^3-octreotide in human hepatocellular carcinoma-bearing nude mice

AIM: To investigate the uptake of 99mTc-HYNIC-Tyr3-octreotide (99mTc-HYNIC-TOC) in human hepatocellular carcinoma (HCC), which can provide the localizable diagnosis in hepatic carcinoma. METHODS: The expression of somatostatin receptor 2 (SSTR2) messenger RNA (mRNA) in human HCC cell line HepG2 was examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Uptake of 99mTc-HYNIC-TOC was evaluated in the human HCC implanted into BALB/c nude mice. ANMIS2000 nuclear medicine analysis system was used to calculate the ratio of 99mTc uptake between tumor tissue and vital organs. RESULTS: We demonstrated the expression of SSTR2 mRNA in human HCC cell line HepG2 by RT-PCR. The size of the RT-PCR products was 364 bp detected by sequence analysis of the human SSTR2 mRNA. Scintigraphy proved that 99mTc-HYNIC-TOC was uptaken in the tumor tissue, liver and kidney of the tumor-bearing mice. CONCLUSION: Based on expression of the SSTR2 mRNA in human HCC, 99mTc-HYNIC-TOC can markedly bind with and be uptaken by human HCC tissues as compared with normal liver tissue. The significant retention of radionudide in kidney and bladder is probably related to non-specific peptide uptake in the tubulus cells of kidney and possibly due to excretion by kidney. Our results show that localizable diagnosis and targeting radiotherapy with radionuclide-labeled somatostatin analog for HCC are of great value to be further studied.

Inhibition of Metastatic Progression of SSTR2 Gene Transfection Mediated by Adenovirus in Human Pancreatic Carcinoma Cells

The inhibition of metastatic progression of Somatostatin receptor type 2 （SSTR2） gene transfection mediated by adenovirus in human pancreatic carcinoma cells and the mechanisms involved in this effect were studied. The full-length human SSTR2 cDNA was introduced into the pancreatic cancer cell line BXPC-3 by adenovirus-mediated transfection. Stable expression of mRNAs and protein of SSTR2 was detected by RT-PCR and Western-blot. The Matrigel-coated Transwell was used to detect the migratory and invasive ability of SSTR2-expressing cells, Adv-GFP control cells and mock control cells. Furthermore, the expression of matrix metalloproteinase-2 （MMP-2） and tissue inhibitor of metalloproteinase-2 （TIMP-2） was detected by RT-PCR in these cells. The stable expression of SSTR2 was detected in BXPC-3 transfected by Adv-GFP-SSTR2. A dramatic decrease of BXPC-3 expressing sst2 cells migrating through a Matrigel-coated filter was observed, as compared with Adv-GFP control and mock control cells （P〈0. 01）. Moreover, the expression of MMP-2 mRNA was significantly reduced in the SSTR2-expressing cells and converse- ly the expression of TIMP-2 mRNA was significantly increased in the SSTR2-expressing cells when compared with the Adv-GFP control and mock control （P〈0. 01）. The expression of reintroduced human SSTR2 gene in BXPC-3 cells by Adv-GFP-SSTR2 had the anti-migratory and anti-invasive effects, and the mechanisms involved in this effect may be due to the down-regulated expression of MMP-2 and up-regulated expression of TIMP-2.

Novel gold nanoparticles targeting somatostatin receptor subtype two with near-infrared light for neuroendocrine tumour therapy

Neuroendocrine tumours(NETs)are rare cancers with positive somatostatin receptor 2(SSTR2)expression,and treatment strategies for NETs are not satisfactory.Nanomaterial-mediated therapy targeting SSTR2 in NETs is very promising.This study firstly combined mesoporous silica-coated gold nanorods(AuNRs@mSiO_(2))and targeting-SSTR2 dodecane tetraacetic acidtyrosine3-octreotate(DOTA-TATE)into AuNRs@mSiO_(2)@DOTA-TATE to investigate NETs inhibition under near-infrared light.AuNRs@mSiO_(2)@DOTA-TATE showed good photothermal conversion efficiency.In vitro,under light irradiation,the cell viability significantly decreased with increasing AuNR@mSiO_(2)@DOTA-TATE concentration;in two successfully established neuroendocrine tumour organoids with SSTR2 expression,AuNRs@mSiO_(2)@DOTA-TATE with light inhibited tumours significantly better than AuNRs@mSiO_(2) with light.In vivo,the SSTR2-targeting ability and biodistribution of AuNRs@mSiO_(2)@DOTA-TATE were confirmed with AuNRs@mSiO_(2)@64Cu-DOTA-TATE under micro-positron emission tomography/computed tomography(micro-PET/CT);in the AuNRs@mSiO_(2)@DOTA-TATE with laser group,the tumour surface temperature increased rapidly,with tumour volumes similar to those in the octreotide group and significantly lower than those in other groups.There was no significant difference in mice body weight between the AuNRs@mSiO_(2)@DOTA-TATE with laser group and other groups.No significant inflammatory lesions or cell necrosis was found in the main organs.In summary,we presented a feasible strategy to construct AuNRs@mSiO_(2)@DOTA-TATE with good photothermal conversion efficiency,targetingSSTR2 ability,significant antitumour effects,and good biocompatibility,warranting further explorations of AuNRs@mSiO_(2)@DOTA-TATE for NETs therapy applications.