Characterization of the Bystander Effect of Somatostatin Receptor sst2 AfterIn VivoGene Transfer into Human Pancreatic Cancer Cells

Abstract

Pancreatic cancer is one of the most aggressive and devastating human malignancies. The present study was conducted to determine whether in vivo sst2 gene transfer into human pancreatic tumors would impair tumor progression, and to characterize sst2 antitumoral bystander mechanisms. sst2 administration, using the synthetic vector PEI, strongly inhibited tumor progression of human pancreatic adenocarcinoma, in vivo. sst2 gene transfer induced intratumoral production of its ligand somatostatin. Disruption of this autocrine loop by RNA interference completely reversed sst2 antitumoral activity. Mice depleted of natural killer (NK) cells did not hamper sst2 tumor growth inhibition. However, microvessel density and vascular endothelial growth factor (VEGF) expression were markedly reduced in sst2-transfected tumors, whereas sst3 somatostatin receptor was upregulated. Depleting somatostatin by RNA interference completely abolished the sst2 inhibitory effect on VEGF expression and tumor angiogenesis, and sst2-induced sst3 expression in peripheral tumor vessels. We conclude that in vivo sst2 gene transfer elicited intratumoral somatostatin production and strongly impaired human pancreatic tumor growth. NK cells were not involved in this antitumoral bystander effect. VEGF and tumor vascularization were identified as novel targets for sst2-mediated antitumoral bystander effect. sst3 somatostatin receptor was upregulated in sst2-transfected tumors. Therefore, in vivo gene delivery of sst2 receptor to target the angiogenic process in pancreatic ductal adenocarcinoma might be a new therapeutic approach for treatment of pancreatic cancer in patients with unresectable disease.

Antitumor effects of somatostatin

“…Preclinical studies conducted in pancreatic adenocarcinoma animal models demonstrated that intratumoral sst2 gene transfer (using polyethylenimine synthetic vector) caused inhibition of intratumoral production of somatostatin that was critical for the sst2 antitumoral effect. As a consequence, primary tumor growth and angiogenesis were highly decreased and associated with a reduction in microvessel density, inhibition of intratumoral production of VEGF and up-regulation of anti-angiogenic sst3 receptor expression in peripheral tumor vessels (Vernejoul et al, 2002;Carrere et al, 2005). When co-injected with sst2 vector, small interfering RNA targeting somatostatin mRNA completely blocked somatostatin production in tumors and antagonized sst2-mediated antitumoral and antiangiogenic effects (Carrere et al;2005).…”

“…As a consequence, primary tumor growth and angiogenesis were highly decreased and associated with a reduction in microvessel density, inhibition of intratumoral production of VEGF and up-regulation of anti-angiogenic sst3 receptor expression in peripheral tumor vessels (Vernejoul et al, 2002;Carrere et al, 2005). When co-injected with sst2 vector, small interfering RNA targeting somatostatin mRNA completely blocked somatostatin production in tumors and antagonized sst2-mediated antitumoral and antiangiogenic effects (Carrere et al;2005). Based on the anti-tumor properties of sst2, we have proposed a phase I clinical trial aimed at rendering human pancreatic adenocarcinomas more sensitive to the cytotoxic action of the chemotherapeutic compound Gemcitabine (GEMZAR TM ).…”

Using lentiviral vectors for efficient pancreatic cancer gene therapy

“…[29][30][31] Other gene delivery systems, such as complexed DNA (PEI), adenovirus and SV40-derived vectors showed poor efficiencies or transient expression of the transgene, respectively. 8,9 Lentiviral vectors were developed to overcome these limitations. The lentiviral vector-mediated gene therapy has great promise in cancer treatment, because of its long-term expression and high efficiency in transducing dividing and nondividing cells, including the chemoresistant population located in the hypoxic cores of tumors.…”

“…In this study, lentiviral-based vectors surpass nonviral vectors (PEI), adenoviral or SV40-based vectors in their ability to transduce PC-derived cells. 8,9 Understanding the molecular basis of PC has provided a wide range of potential intracellular targets for gene therapy approaches. 36 Targeting PC by molecular abnormality remains elusive because of the accumulation of multiple genetic changes during its multistep carcinogenesis.…”

“…[4][5][6][7] We have experimented with nonviral vectors, adenoviral and SV40-based vectors, which showed gene delivery to PC cells, and provided evidence of therapeutic efficacy. [8][9][10][11] However, the current low transduction efficiency of the synthetic nonviral vector and the transient gene expression using both viral vectors present major disadvantages in the cost of clinical application. An alternative approach is the development of more competitive expression vectors for PC gene delivery.…”