Abstract #5506: Thymoquinone cause cell growth inhibition and induces apoptosis in primary effusion lymphoma cells via release of ROS

The mechanisms that regulate mitogenic and anti-apoptotic signals in primary effusion lymphoma (PEL) are not well known. In efforts to identify novel approaches to block the proliferation of PEL cells, we found that, thymoquinone (TQ), an active component of black seed, inhibit cell viability and induce apoptosis in several PEL cell lines in a dose dependent manner. Such effects of TQ appear to result from release of reactive oxygen species (ROS) leading to suppression of the constitutively active kinase AKT, and its effectors FOXO transcription factor and p-Bad. Our data demonstrate that TQ treatment of PEL cell lines causes de-phosphorylation of Bad protein leading to down regulation of the anti-apoptotic protein, Bcl-2 and subsequent increase of Bax protein that leads to an increase in the Bax/Bcl2 ratio. TQ treatment of PEL cells also causes conformational changes of Bax protein and subsequently translocation from cytosole to mitochondria causing loss of mitochondrial membrane potential with subsequent release of cytochrome c from the mitochondria. Interestingly, Bax conformational changes following TQ treatment can be blocked by pre-treatment of PEL cells with N-acetylcysteine, an inhibitor of ROS. Released cytochrome c into the cytosole activates caspases-9 and -3, followed by polyadenosin-5\#8217;-diphosphate-ribose polymerase (PARP) cleavage. In addition, pretreatment of PEL cells with either zVAD-fmk, a universal inhibitor of caspases and NAC prevents caspase-3 activation and abrogates cell death induced by TQ treatment of PEL cells strongly suggesting that TQ-induced apoptosis is ROS as well as caspase dependent. Finally, treatment of PEL cells with TQ down-regulates the expression of inhibitor of apoptosis proteins (IAP). Altogether, these data suggest a novel function for TQ, acting as a suppressor of AKT/PKB pathway in PEL cells, and raise the possibility that this agent may have a future therapeutic role in PEL and possibly other malignancies with constitutive activation of the AKT/PKB pathway.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 5506.