Koul et al. BMC Cancer 2010, 10:328 http://www.biomedcentral.com/1471-2407/10/328 R E S E A R C H A R T I C L E Open Access Bicyclic triterpenoid Iripallidal induces apoptosis and inhibits Akt/mTOR pathway in glioma cells Nitin Koul, Vivek Sharma, Deobrat Dixit, Sadashib Ghosh, Ellora Sen* Abstract Background: The highly resistant nature of glioblastoma multiforme (GBM) to chemotherapy prompted us to evaluate the efficacy of bicyclic triterpenoid Iripallidal against GBM in vitro. Methods: The effect of Iripallidal on proliferation and apoptosis in glioma cell lines was evaluated by MTS, colony formation and caspase-3 activity. The effect of iripallidal to regulate (i) Akt/mTOR and STAT3 signaling (ii) molecules associated with cell cycle and DNA damage was evaluated by Western blot analysis. The effect of Iripallidal on telomerase activity was also determined. Results: Iripallidal (i) induced apoptosis, (ii) inhibited Akt/mTOR and STAT3 signaling, (iii) altered molecules associated with cell cycle and DNA damage, (iv) inhibited telomerase activity and colony forming efficiency of glioma cells. In addition, Iripallidal displayed anti-proliferative activity against non-glioma cancer cell lines of diverse origin. Conclusion: The ability of Iripallidal to serve as a dual-inhibitor of Akt/mTOR and STAT3 signaling warrants further investigation into its role as a therapeutic strategy against GBM. Introduction Iripallidal [(-) (6R,10S,11S,18R,22S)-26-Hydroxy-22- a-methylcycloirid-16-enal NSC 631939]- a bicyclic triterpenoid isolated from Iris pallida belongs to the ter- penoid family as Paclitaxel. Paclitaxel is an effective che- motherapy for several types of neoplasms [1]. Iripallidal inhibited cell growth in a NCI 60 cell line screen [2] and induced cytotoxicity in human tumor cell lines [3]. Besides the fact that Iridals are ligands for phorbol ester receptors with modest selectivity for RasGRP3 [2], not much is known regarding its mechanism of action. Despite recent advances in understanding molecular mechanisms involved in GBM progression, the prognosis of the most malignant brain tumor continues to be dis- mal. Ras activation occurs in GBMs [4] and this high level of active Ras has been a target for glioma therapy. RasGRP3- is an exchange factor that catalyzes the forma- tion of the active GTP-bound form of Ras-like small GTPases [5]. Importantly, Ras activation stimulates its downstream effector Akt that plays a major role in glio- blastoma development as ~80% of GBM cases express * Correspondence: ellora@nbrc.ac.in National Brain Research Centre, Manesar, Haryana 122 050, India high Akt levels [6]. Akt activates mammalian target of rapamycin (mTOR), which is deregulated in glioblastoma [7]. mTOR phosphorylates p70 ribosomal S6 kinase (p70S6 kinase) that regulates translation of proteins involved in cellular proliferation and formation. More- over, blocking mTOR signaling reduces glioma cell pro- liferation [8]. Given the importance of Akt/mTOR signaling in glioma cell survival, significant efforts are being invested in identifying inhibitors that target this pathway [8-10]. In addition to aberrant PI3K/Akt signal- ing; heightened STAT3 activation plays a critical role in glioblastoma and STAT3 inhibitors have shown promise as therapeutics for GBM [11-13]. In addition to RasGRP3 Iripallidal also binds to PKCa [2] which is known to induce cells ectopically expressing hyperactive Ras to undergo apoptosis [14]. Not only is STAT3 essential for Ras transformation [15] but constitutively activated STAT3 is negatively regulated by PKC-activated tyrosine phosphatase(s) [16]. As Iridals interacts with PKCa and RasGRP3-molecules that regulate Akt and STAT3 signal- ing, and since inhibition of Akt/mTOR and STAT3 sig- naling are being targeted for GBM treatment we evaluated the effect of Iripallidal on glioma cell prolifera- tion and these signaling pathways. © 2010 Koul et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.