AN APOPTOSIS-INDUCING GENE-THERAPY FOR PANCREATIC-CANCER WITH A COMBINATION OF 55-KDA TUMOR-NECROSIS-FACTOR (TNF) RECEPTOR GENE TRANSFECTION AND MUTEIN TNF ADMINISTRATION

Intratumoral injection of recombinant human tumor necrosis factor (TNF ) for inoperable pancreatic cancer has shown some efficacy in suppress ing tumor growth or decreasing tumor markers. However, complete regres sion has not yet been achieved, possibly due to a lack of TNF receptor s on tumor cells or an abundance of intracellular resistance factors. Recently, two distinct types of TNF receptors, R55 and R75, were ident ified, which are responsible for signaling of cytotoxicity and of proi nflammation, respectively, In this study, a novel type of suicide gene therapy is proposed that is based on transfection of the R55 gene int o human pancreatic cancer cells (AsPC-1 and PANC-1) and subsequent adm inistration of TNF. The transfectants from both cell lines showed high er TNF susceptibility than their parental cells. In vivo tumor formati on of an AsPC-1 clone (clone 10) inoculated in nude mice was substanti ally suppressed by administration of TNF. For practical use of this st rategy, however, the adverse effects of TNF may become an obstacle. We previously produced mutein TNF 471, which had a higher affinity for R 55, superior antitumor activity, and fewer adverse effects. This mutei n TNF 471 manifested greater antitumor activity against clone 10, Beca use the R55 receptor is known to be involved in augmentation of cellul ar immunity by TNF, mutein TNF 471 is also expected to be highly poten t in this function. In fact, the mutein TNF 471 induced higher splenic natural killer cell activity in nude mice inoculated with clone 10 th an did native TNF. This property of augumenting cellular responses may be advantageous in the eradication of viable tumor cells left untrans fected in practical gene therapy regimens in which 100% transfection o f the R55 gene into tumors is not feasible. Thus, gene therapy combini ng transfection of the TNF-R55 gene with administration of mutein TNF 471 may provide a new modality for the treatment of pancreatic cancer.