β-Caryophyllene oxide potentiates TNFα-induced apoptosis and inhibits invasion through down-modulation of NF-κB-regulated gene products

We have recently reported that beta-caryophyllene oxide (CPO) can induce apoptosis, suppress tumor growth, and inhibit metastasis through the suppression of signal transducer and activator of transcription 3, PI3K/AKT/mTOR/S6K1 signaling cascades and ROS-mediated MAPKs activation. In the present study, we found that CPO potentiated the apoptosis induced by tumor necrosis factor alpha (TNF alpha) and chemotherapeutic agents, suppressed TNF alpha-induced tumor cell invasion, all of which are known to require NF-kappa B activation. We found that TNF alpha stimulated the expression of gene products involved in anti-apoptosis (IAP1, IAP2, Bcl-2, Bcl-xL, and survivin), proliferation (COX-2, cyclin D1, and c-Myc), invasion (MMP 9 and ICAM-1), and angiogenesis (VEGF) and that CPO treatment suppressed their expression. Because these gene products are also regulated by proinflammatory transcription factor NF-kappa B, we postulated that CPO may mediate its effects by modulating the NF-kappa B pathway. We found that CPO blocked both inducible and constitutive NF-kappa B activation in a wide variety of tumor cells. CPO was also found to inhibit the TNF alpha-induced degradation of I kappa B alpha through the inhibition of activation of I kappa B alpha kinase and p65 nuclear translocation and phosphorylation. Interestingly, CPO failed to potentiate the apoptotic effect induced by TNF alpha in p65 (-/-) cells as compared to the wild-type. Thus, overall, our results indicate that the inhibition of NF-kappa B is one of major mechanisms by which CPO enhances TNF alpha-induced apoptosis and suppresses invasion.