Anti-angiogenic activity of macrolactin A and its succinyl derivative is mediated through inhibition of class I PI3K activity and its signaling

In the current study, macrolactin compounds,macrolactinA(MA) and 7-O-succinyl macrolactinA(SMA),were investigated for their anti-angiogenic activities andaction mechanism. MA and SMA inhibited in vitro andin vivo angiogenesis induced by three different classes of proangiogenicfactors, VEGF, IL-8, and TNF-a. SMA exhibitedstronger anti-angiogenic activity than MA, and such antiangiogenicactivity of SMA was consistently observed inMDA-MB-231 human breast cancer cell-inoculated CAMassay showing dose-dependent suppression of tumor growthand tumor-induced angiogenesis. In an in vitro PI3K competitiveactivity assay, SMA induced concentration-dependentinhibition of class I PI3K isoforms, p110a, p110b,p110d, and p110c. In addition, non-receptor tyrosine kinasec-Src, which is involved in the activation of PI3K heterodimer,was suppressed byMAand SMA.Correspondingly,MAand SMA significantly inhibited the stimulus-induced phosphorylationof Akt, mTOR, p70S6K, and ribosomal S6 inhuman umbilical vein endothelial cells (HUVECs). At thesame time, the stimulus-induced production of reactiveoxygen species (ROS) and activation of NF-jB were significantlysuppressed by MA and SMA. Moreover, the macrolactinssuppressed NF-jB-regulated HSP90 proteinexpression, which stabilizes phosphorylated Akt andNADPH oxidase. Suppression of NF-jB in macrolactintreatedHUVECs with concurrent inhibition of rS6 indicatesthat MAs effectively block angiogenesis through down-regulationof genes related to angiogenesis at both transcriptionaland translational levels. Taken together, the results demonstratethat anti-angiogenic effect ofMAandSMAis mediatedthrough inhibition of PI3K/Akt andNADPHoxidase-derivedROS/NF-jB signaling pathways. These results further indicatethat MA and SMA may be applicable for treatment ofvarious diseases associated with angiogenesis.