Differential cytostatic effects of NO donors and NO producing cells

A 3-h exposure to NO donors (spermine-NO, DETA-NO, or SNAP), or to NOS II-e xpressing cells (activated macrophages or EMT6 cells) reversibly inhibited DNA synthesis in K562 tumor cells. In GSA-depleted K562 cells, cytostasis r emained reversible when induced by DETA-NO or NOS II activity, but became i rreversible after exposure to spermine-NO or SNAP. Only SNAP and spermine-N O efficiently inhibited GAPDH, an enzyme with a critical thiol, in GSH-depl eted cells. Thus, the irreversible cytostasis induced in GSM-depleted cells by spermine-NO or SNAP can be tentatively attributed to S-nitrosating or o xidizing species derived from NO, However, these species did not contribute significantly to the early antiproliferative effects of macrophages. Ribon ucleotide reductase, a key enzyme in DNA synthesis, hits been shown to be i nhibited by NO. Supplementation of the medium with deoxyribonucleosides to bypass RNR inhibition restored DNA synthesis in target cells exposed to DET A-NO and NO-producing cells, but was inefficient for GSH-depleted cells pre viously submitted to spermine-NO or SNAP. These cells also exhibited a pers istent depletion of the dATP pool. In conclusion, GSH depletion reveals str iking qualitative differences in the nature of the toxic effectors released by various NO sources, questioning the significance of S-nitrosating or ox idizing nitrogen oxides in NOS II-dependent cytostasis. (C) 1999 Elsevier S cience Inc.