5-LIPOXYGENASE INHIBITORS REDUCE PC-3 CELL-PROLIFERATION AND INITIATENONNECROTIC CELL-DEATH

BACKGROUND. Products of the arachidonic acid-metabolizing enzyme, 5-li poxygenase, stimulate the growth of several cell types. Selective inhi bitors of the enzyme, including SC41661A and MK886, reduce PC-3 prosta te cell proliferation. With continued culture, cells die, but the mode of death, necrotic or nonnecrotic, has not been established. METHODS. Flow cytometry, laddering after agarose electrophoresis of DNA from i nhibitor-treated cells, and light and electron microscopy were employe d to examine the type of death in PC-3 prostate cells cultured with ei ther 5-lipoxygenase inhibitor. RESULTS. The inhibitors induced nonnecr otic, programmed cell death. SC41661A-treated cells exhibited ''foamy, '' vacuolated cytoplasm and mitochondria with disrupted cristae and li miting membranes, while some cells contained numerous polysomes and ex tended hyper trophic Golgi and secretory cisternal networks. A proport ion of the treated cells detached and the nuclei of these cells were c haracteristic of type 1 ''apoptotic'' programmed cell death. MK886, a 5-lipoxygenase- inhibitor with a different mechanism of action, induce d nonnecrotic changes largely confined to the cytoplasm, most consiste nt with type 2 ''autophagic'' programmed cell death. In preliminary st udies of mechanism, we demonstrated that PC-3 cells express mRNA for 5 -lipoxygenase and for 5-lipoxygenase-activating protein. The less acti ve inhibitor, SC45662 neither reduced proliferation nor induced DNA la ddering. The antioxidant, N-acetyl-1-cysteine but not butylated hydrox y toluene or alpha tocopherol, partially reduced the inhibition of pro liferation from SC41661A. CONCLUSIONS. SC41661A and MK886 inhibit PC-3 cell proliferation and induce a form of type 1 or type 2 programmed c ell death, respectively. PC-3 cells contain messenger RNA for 5-lipoxy genase and 5-lipoxygenase-activating proteins. Drug-induced changes in cluded altered redox potential, inferred from the increased survival d ue to the antioxidant and glutathione precursor, N-acetyl.-1-cysteine. PC-3 cells are an appropriate model for studying the mechanism respon sible for 5-lipoxygenase inhibitor-induced cellular suicide. (C) 1998 Wiley-Liss, Inc.