Abstract 4618: mTOR signaling complex can be targeted using Torin2 in colorectal cancer to induce efficient apoptosis
Authors: Ahmed Saeeda O. , Ahmed Maqbool , Siraj Abdul K. , Beg Shaham , Thangavel Saravanan , Al-Sanea Nasser , Al-Dayel Fouad , Hussain Azhar R. , Al-Kuraya Khawla S. 
Published: July 2016

Colorectal cancer (CRC) is the third most common cancer in the world and the 4th most common cause of cancer related death. Despite the considerable advances in awareness, diagnosis and modern therapeutic strategies, the incidence of CRC is increasing in the Middle Eastern population. In order to explore the molecular cause of increasing incidence of CRC in this region, we sought to evaluate the role of mammalian target of rapamycin (mTOR) survival pathway in CRC of this region. mTOR; a component of the phosphatidylinositol 3-kinase (PI3K) cell survival pathway, is known to play an important role in the regulation of many cellular activities leading to cell growth and proliferation through the formation of its two complexes mTORC1 and mTORC2. We therefore examined the expression of mTOR in 700 Saudi CRC cases by immunohistochemistry in a tissue microarray format and found that mTORC1 and mTORC2 were activated in 43.4% (294/677) and 46.2% (313/677) of cases respectively. mTORC1 activation was found to be significantly associated with Ki67 and mTORC2. In addition, mTORC2 activation was also found to be directly associated with their downstream target; p-AKT. In vitro, we found that treatment with a second generation mTOR inhibitor, Torin2 led to inhibition of cell viability and induction of apoptosis via inactivation of mTORC1 and mTORC2 in majority of CRC cell lines. Inactivation of mTORC1 and mTORC2 following Torin2 treatment also led to dephosphorylation of mTOR downstream targets; P70S6, 4E-BP1, AKT and BAD. Interestingly, one CRC cell line; HT29 that had over-activation of mTORC2 was found to be resistant to Torin2 treatment suggesting that increased activation of mTORC2 confers resistance to Torin2 treatment. As our clinical data demonstrated a significant association between mTORC2 over-expression and activation of AKT in clinical CRC samples, we synergistically targeted HT29 cells with combination of sub-optimal doses of PI3-kinase/AKT inhibitor; LY294002 in combination with Torin2. Our data showed that combination of Torin2 and LY294002 synergistically induced apoptosis in HT29 cells via inactivation of mTORC2 and AKT. These data highlight the utility of targeting mTOR signaling complex using second generation mTOR inhibitors such as Torin2 alone or in combination with other inhibitors such as LY294002 or chemotherapeutic agents to effectively treat these aggressive subgroups of CRC with over-activation of mTOR and AKT simultaneously.

Citation Format: Saeeda O. Ahmed, Maqbool Ahmed, Abdul K. Siraj, Shaham Beg, Saravanan Thangavel, Nasser Al-Sanea, Fouad Al-Dayel, Azhar R. Hussain, Khawla S. Al-Kuraya. mTOR signaling complex can be targeted using Torin2 in colorectal cancer to induce efficient apoptosis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4618.