Suicide gene therapy of pancreatic cancer with cytosine deaminase: a promising in vitro tool.

Background: Gene therapy is a novel approach for pancreatic cancer (PC) treatment, and the insertion in the host genome of suicide genes seems somewhat promising. Among them cytosine deaminase (CD) is able to convert the 5-fluorocytosine (5-FC) into 5-fluorouracile (5-FU). Our aims were to ascertain in vitro whether CD or CD joint to 5-phosphoribosiltransferase (5PRT) gene transferred to a series of pancreatic cancer cell lines allows their killing by 5-FC treatment. Methods: Three pancreatic cancer cell lines (CAPAN-1, MIA PaCa 2, PANC-1) were chemically transfected with two plasmid vectors containing both a neo-selectable marker gene and a mammalian constitutive promoter (RSV) and CD (pRSV-CD) or CD 5PRT (pRSV-PRT) from Saccaromyces cerevisiae. Stable transfected cell lines were selected by G418 treatment. Each parental, pRSV-CD and pRSV-PRT transfected cell lines were treated with 5-FC at the dosages of 0, 0.1, 0.5, 1, 5 and 10mM for 1, 3, 6, 8, 10, 13 and 15 days. Results: pRSV-PRT/PANC-1 cell line growth was significantly inhibited at 0.5mM 5-FC just after 6 treatment days (F 18.3; p 0.001). The vector pRSV-CD conferred to PANC-1 cells a lesser sensitivity to 5-FC, which inhibited cell growth only after 8 treatment days at dosage of 5mM (F 33.4; p 0.001). MIA PaCa 2 cells transfected with both vectors become sensitive to 5-FC treatment at 5mM after 13 days (F 5.2; p 0.05). 5-FC at any dosage and for any time of treatment was uneffective on transduced CAPAN-1 cell growth. Conclusions: The suicide gene CD seems useful to confer 5-FC sensitivity to some pancreatic cancer cell lines. The co-transfection of CD and 5PRT enhances 5-FC sensitivity, possibly because the enzyme encoded by 5PRT may in part counteract the 5-FU degradation observable in some pancreatic cancer cells.