title: let-7 MicroRNA transfer in pancreatic cancer-derived cells inhibits in vitro cell proliferation but fails to alter tumor progression.
abstract: Pancreatic ductal adenocarcinoma (PDAC) is still the fourth leading cause of cancer-related deaths in Western countries, with increasing incidence. Neither effective prognostic markers nor therapies exist for this cancer. MicroRNAs are potent inhibitors of protein translation, and aberrantly expressed in many cancers. Because let-7 microRNA targets the K-ras oncogene, we aimed to characterize let-7 expression and function in PDAC in vitro and in vivo. Let-7 expression was quantified by real-time RT-PCR from resected tumors and matching adjacent tissue, and in endoscopic ultrasound-guided fine needle aspiration material from patients with PDAC. Let-7 is detected by reverse transcription in situ PCR in a PDAC tissue microarray. PDAC-derived cells were transfected with plasmid-based synthetic microRNAs or by lentiviral transduction, in vitro and in vivo. Let-7 microRNA expression is strongly reduced in PDAC samples, as compared with adjacent tissue. Let-7 is present in normal acinar pancreatic cells, and lost in poorly differentiated cancer samples. In addition, let-7 expression was repressed in patients with PDAC not eligible for surgery. Restoring let-7 levels in cancer-derived cell lines strongly inhibits cell proliferation, K-ras expression, and mitogen-activated protein kinase activation, but fails to impede tumor growth progression after intratumoral gene transfer or after implantation of Capan-1 cells stably overexpressing let-7 microRNA. We describe here for the first time the extensive loss of expression of let-7 in PDAC. In addition, this study provides the initial steps for a microRNA replacement therapy for this cancer.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale Unité 858-12MR, Institut de Médecine Moléculaire de Rangueil, Département Cancers Epithéliaux, Angiogénèse et Signalisation, 31432 Toulouse Cedex 4, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Torrisani
authors.forename: Barbara
authors.initials: B
authors.lastname: Bournet
authors.forename: Maël Chalret
authors.initials: MC
authors.lastname: du Rieu
authors.forename: Michèle
authors.initials: M
authors.lastname: Bouisson
authors.forename: Anny
authors.initials: A
authors.lastname: Souque
authors.forename: Jean
authors.initials: J
authors.lastname: Escourrou
authors.forename: Louis
authors.initials: L
authors.lastname: Buscail
authors.forename: Pierre
authors.initials: P
authors.lastname: Cordelier