Somatostatin receptor gene transfer induces bystander effects

Effect of octreotide on human pancreatic cancer cells after transfected with somatostatin receptor type 2 gene

AIM: To observe the effect of octreotide on apoptosis rate of human pancreatic cancer cells PC-3 after transfected with somatostatin receptor type 2 (SST2) gene.

METHODS: SST2 plasmid was transfected into PC-3 cells by liposome. Result of transfection was detected by immunocytochemical staining and Western blotting. Apoptosis rates of PC-3 cells under different dosages of octreotide were measured by MTT assay and flow cytometry (FCM).

RESULTS: Apoptosis rate caused by octreotide of transfected PC-3 cells was 7.56 ± 1.06% at the dosage of 0.20 μg/mL, 9.25 ± 1.73% at the dosage of 0.40 μg/mL and 14.18 ± 2.71% at the dosage of 0.80 μg/mL. Apoptosis rate caused by octreotide of non -transfected PC-3 cells was 5.76 ± 0.75% at the dosage of 0.20 μg/mL, 6.69 ± 0.80% at the dosage of 0.40 μg/mL and 7.26 ± 1.28% at the dosage of 0.80 μg/mL. Transfected PC-3 cells growth inhibition rate caused by octreotide was 9.36 ± 1.34% at the dosage of 0.20 μg/mL, 12.03 ± 1.44% at the dosage of 0.40 μg/mL and 20.23 ± 4.21% at the dosage of 0.80 μg/mL. Non-transfected PC -3 cells growth inhibition rate caused by octreotide was 6.44 ± 0.66% at the dosage of 0.20 μg/mL, 7.65 ± 0.88% at the dosage of 0.40 μg/mL and 9.29 ± 1.32% at the dosage of 0.80 μg/mL. We found that octreotide caused higher apoptosis rate and inhibition rate in transfected groups than in non-transfected groups (P < 0.05) at the tested dosages (0.20, 0.40 and 0.80 μg/mL).

CONCLUSION: Deficiency of SST2 was probably the major reason why octreotide had little effect on PC-3 cells. Transfecting SST2 gene could strengthen the ability of octreotide of killing PC-3 cells. It provided an experimental evidence for using both octreotide and transfection with SST2 gene on clinical treatment of pancreatic cancer.

Somatostatin receptor targeting for tumor imaging and therapy

Somatostatin receptors and their ligands constitute the prototype targeting system for contrast-enhanced detection and radiotherapy of cancer. Radiolabeled synthetic analogs of somatostatin have been successfully used in routine molecular imaging of primary gastroenteropancreatic neuroendocrine tumors and their metastases for more than 15 years. Likewise, analog conjugates for radiation therapy have been developed and have been under clinical trial for several years. The vast amount of knowledge accumulated by both basic and clinical science has made the somatostatin/somatostatin receptor system a popular model for new targeting strategies in imaging and therapy. Among those, the use of near-infrared fluorescent dye-peptide conjugates for the detection of tumors by endoscopy, mammography, or intraoperative imaging is one of the most promising. This article reviews recent developments in the field and discusses concepts for receptor-targeted molecular imaging and therapy.

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