Leukotriene C 4 is an essential 5-lipoxygenase intermediate in A23187-induced macrophage cytostatic activity against P815 tumor cells

Abstract

Resident peritoneal macrophages incubated with 3.5 × 10 −7 M Calcium ionophore A23187 in tumor cell growth medium (TGM) release large amounts of leukotriene (LT)E 4 and an unidentified 5-lipoxygenase product, whereas A23187-stimulated macrophages produce in serum free medium LTD 4, predominately. LTC 4 and 3H-LTC 4 incubated for 20 min at 37°C in serum containing TGM, convert into LTE 4 and 3H-LTE 4, respectively. Thus, LTC 4 released from A23187-stimulated macrophages is an intermediate in TGM which rapidly converts into LTE 4, probably because of the presence of gamma-glutamyl transpeptidase and cystenylglycinase in TGM. Macrophages express antitumor cytostatic activity towards P815 cells (49–53%) in a cocultured ratio (macrophage: tumor cell) 2:1 when stimulated with 3.5 × 10 −7 M A23187 in TGM. The 5-lipoxygenase inhibitor AA861 reverses the cytostatic activity by 42–58% and it inhibits also the formation of A23187-induced 5-lipoxygenase products from macrophages. Restoration of 38% macrophage- antitumor cytostatic activity by exogenous LTC 4 (10 −8 M) indicates that LTC 4 is an essential 5-lipoxygenase intermediate in the pathway of required signals underlying A23187-induced macrophage antitumor cytostatic activity. Macrophages not stimulated by A23187 do not express cytostatic activity in the presence of LTC 4. This implies that besides LTC 4, increased cytosolic [Ca 2+] is required for A23187 induction of macrophage cytostatic activity.