A combinatorial approach for selectively inducing programmed cell death inhuman pancreatic cancer cells

Pancreatic cancer is an extremely aggressive neoplasm whose incidence equal s its death rate. Despite intensive analysis, the genetic changes that medi ate pancreatic cancer development and effective therapies for diminishing t he morbidity associated with this disease remain unresolved. Through subtra ction hybridization, we have identified a gene associated with induction of irreversible growth arrest, cancer reversion, and terminal differentiation in human melanoma cells, melanoma differentiation associated gene-7 (mda-7 ). Ectopic expression of mda-7 when using a recombinant adenovirus, Ad.mda- 7, results in growth suppression and apoptosis in a broad spectrum of human cancers with diverse genetic defects, without exerting deleterious effects in normal human epithelial or fibroblast cells. Despite the apparently ubi quitous antitumor effects of mda-7, pancreatic carcinoma cells are remarkab ly refractory to Ad.mda-7 induced growth suppression and apoptosis. In cont rast, the combination of Ad.mda-7 with antisense phosphorothioate oligonucl eotides, which target the K-ras oncogene (a gene that is mutated in 85 to 9 5% of pancreatic carcinomas), induces a dramatic suppression in growth and a decrease in cell viability by induction of apoptosis. In mutant K-ras pan creatic carcinoma cells, programmed cell death correlates with expression a nd an increase, respectively, in MDA-7 and BAX proteins and increases in th e ratio of BAX to BCL-2 proteins. Moreover, transfection of mutant K-ras pa ncreatic carcinoma cells with an antisense K-ras expression vector and infe ction with Ad.mda-7 inhibits colony formation in vitro and tumorigenesis in vivo in nude mice. These intriguing observations demonstrate that a combin atorial approach, consisting of a cancer-specific apoptosis-inducing gene a nd an oncogene inactivation strategy, may provide the foundation for develo ping an effective therapy for pancreatic cancer.