Alterations in eicosanoid levels during U937 bcl-xL tumour growth suppression and recovery in NU/NU mice in vivo—Involvement of phospholipase A2

Abstract We report the effects of two anti-cancer drugs, PBT-4, an experimental antagonist to the pro-inflammatory hepoxilins, and Gleevec (STI-571), an anti-leukaemic drug, on eicosanoid tumour levels in immunodeficient mice (NU/NU) xenografted with the leukaemic cell line, U937 bcl-x L . After the tumours had grown to 80–100 mm 3 volume, an 8-day treatment with the drugs was initiated and the animals were monitored for 28 days. On various days, tumours were removed for measurement of 24 omega-6 eicosanoids. The data show remarkable direct correlation between inhibition of tumour AA release and 12-LOX products (including 12-HETE and hepoxilins) during PBT or STI treatment with tumour growth suppression. These findings suggest that inhibition of AA release may represent a novel underlying mechanism of action of PBT-4 (and STI) in vivo in suppressing tumour growth. As the PBT wears off, AA and 12-LOX products rise rapidly (Day 18) leading to the observed tumour growth spurt.