5-LIPOXYGENASE INHIBITORS REDUCE PANC-1 SURVIVAL - THE MODE OF CELL-DEATH AND SYNERGISM OF MK886 WITH GAMMA-LINOLENIC ACID

The 5-lipoxygenase inhibitors ETYA, SC41661A and MK 886 reduced the pr oliferation and viability of Panc-1 human pancreatic cancer cells. The extent of inhibition depended upon drug concentration and with contin ued culture, cells detached and stained with trypan blue. Although res ults from flow cytometry were those associated with programmed cell de ath, despite repeated attempts, no DNA laddering consistent with its l ater stages was detected and studies with the TUNEL assay were negativ e. Light and electron microscopy of cells cultured with SC41661A provi ded morphologic evidence of a population of ''dark'' cells and of an i ncompletely expressed type 1 programmed cell death including marginati on of chromatin at the nuclear membrane and by consolidation and degen eration of cytoplasmic organelles, along with extensive vacuolization. Cells cultured with MK886 exhibited compact ''dark'' cells and an unu sual cytoplasmic mode of cell death characterized by vacuolization and widely separated smooth infernal membranes without diagnostic nuclear changes. This is in marked contrast to the extensive type 1 PCD induc ed by 5-lipoxygenase inhibitors cultured with human U937 monoblastoid cells. On balance the response of Panc-1 cells to MK886 suggests expre ssion of a valiant type 2 (autophagic) cellular suicide, although some contribution from components of a ''cytoplasmic'' (type 3?) form of n on-necrotic cell death may also be considered. In a European clinical trial, gamma linolenic acid, a polyunsaturated fatty acid that generat es free radicals has been combined with 5-fluorouracil as chemotherapy for pancreatic cancer. Panc- 1 cell proliferation was insensitive to inhibition by several chemotherapeutic agents employed clinically, inc luding 5-fluorouracil, cisplatin or gemcitabine and only somewhat sens itive to GLA. When gamma linolenic acid was combined with MK886 the mo re effective of the two 5-lipoxygenase inhibitors, a synergistic reduc tion in Panc-1 cell number and viability occurred.