[Arg(6),D-Trp(7,9),N(me)Phe(8)]-substance P (6-11) activates JNK and induces apoptosis in small cell lung cancer cells via an oxidant-dependent mechanism

[Arg(6),D-Trp(7,9),N(me)Phe(8)]-substance P (6-11) (antagonist G) is a nove l class of anti-cancer agent that inhibits small-cell lung cancer (SCLC) ce ll growth in vitro and in vivo and is entering phase II clinical investigat ion for the treatment of SCLC, Although antagonist G blocks SCLC cell growt h (IC50 = 24.5 +/- 1.5 and 38.5 +/- 1.5 mu M for the H69 and H510 cell line s respectively), its exact mechanism of action is unclear. This study shows that antagonist G stimulates apoptosis as assessed by morphology (EC50 = 5 .9 +/- 0.1 and 15.2 +/- 2.7 mu M for the H69 and H510 cell lines respective ly) and stimulates c-jun-N-terminal kinase (JNK) activity in SCLC cells (EC 50 = 3.2 +/- 0.1 and 15.2 +/- 2.7 mu M). This activity is neuropeptide-inde pendent, but dependent on the generation of reactive oxygen species (ROS) a nd is inhibited by the free radical scavenger n-acetyl cysteine. Furthermor e, antagonist G itself induces inflammation (59% increase in oedema volume compared to control) and potentiates (by 35-40%) bradykinin-induced oedema formation in vivo. In view of these results we show that, as well as acting as a 'broad-spectrum' neuropeptide antagonist, antagonist G stimulates bas al G-protein activity in SCLC cell membranes (81 +/- 12% stimulation at 10 mu M), thereby displaying a unique ability to stimulate certain signal tran sduction pathways by activating G-proteins. This novel activity may be inst rumental for full anti-cancer activity in SCLC cells and may also account f or antagonist G activity in non-neuropeptide-dependent cancers.