Abstract 1874: Phosphatidylcholine synthesis as a potential therapeutic target in multiple myeloma.

Abstract

Abstract A metabolics screen with 8226 cells treated with AICAr showed that de novo pyrimidine synthesis was inhibited. AICAr -induced apoptosis in 5 different myeloma cell lines. This screen showed a significant decrease in CDP-choline, an intermediate of the Kennedy pathway involved in de novo synthesis of phosphatidylcholine (PC). Phosphatidylcholine is the most predominant phospholipid in mammalian ER membranes. The rate limiting step in this pathway is the conversion of phosphocholine and CTP to CDP-choline via the enzyme CTP:phosphocholine cytidylyltransferase (CCT). Although it is likely that the decrease in CDP-choline is a consequence of pyrimidine starvation, the fact that this pathway showed a significant decrease within 8 hours of AICAr treatment suggested to us that this pathway may have a high flux in 8226 cells and that phosphatidylcholine synthesis may be a relevant target in myeloma cells. Multiple myeloma (MM) cells may be particularly dependent on this biosynthetic reaction because of their high consistent level of ER stress and requirement to continuously replenish ER membranes. Indeed, CCT-null mice have a defect in differentiation of B lymphocytes to plasma cells and deficiencies in Ig synthesis. To test whether this pathway remains critical in survival of malignant MM cells, we exposed MM cell lines to an inhibitor shown to inhibit CCT activity, HexPC. HexPC induced apoptosis in all MM cell lines in a concentration- and time-dependent manner. The addition of lysophosphatidylcholine (LPC), presumably converted to PC independently of the Kennedy pathway, completely rescued MM cell apoptosis. Knocking down of CCT with shRNA in myeloma cell lines also resulted in apoptosis. Apoptosis of MM cells induced by HexPC was associated with induction of ER stress as shown by enhanced phosphorylation of IRE1 and eIF-2alpha. This ER stress was also prevented when LPC was added to HexPC although LPC could not prevent similar ER stress induced by bortezomib. These results underscore the importance of this phosphatidylcholine synthesis pathway in MM cells and provide new targets for future therapy. Citation Format: Carolyne Bardeleben, Alan Lichtenstein. Phosphatidylcholine synthesis as a potential therapeutic target in multiple myeloma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1874. doi:10.1158/1538-7445.AM2013-1874