Abstract 1637: The MEK/Erk pathway is required for PC3 cell survival following FdUMP[10] treatment

Abstract We have demonstrated that the novel polymeric fluoropyrimidine (FP) antitumor agent FdUMP[10] is efficacious towards prostate tumor (PC3) xenografts at well-tolerated doses while 5-fluorouracil (5FU) is not efficacious. FdUMP[10] treatment of PC3 cells results in complete inhibition of thymidylate synthase and S-phase arrest with generation of extensive DNA double-strand breaks as detected from γH2AX phosphorylation. S-phase arrest was confirmed by Western blots evaluating cyclin expression. In addition, we show that although cell-cycle arrested, FdUMP[10]-treated PC3 cells are not quiescent as indicated by extensive levels of DNA synthesis. The elevated DNA synthesis levels are likely indicative of futile repair. Although approximately 90% of cells are non-viable as assessed by a clonogenic assay, only about 30% of cells undergo apoptosis as assessed by Annexin V+ cells. The observation that FdUMP[10] treatment resulted in potent anti-tumor activity with minimal induction of apoptotic events lead us to assess to what extent activation of cell survival pathways inhibited cell death. The phosphoinositide 3-kinase PI3K/Akt and the mitogen-activated protein kinase kinase/extracellular signal-regulated protein kinases (MEK/ERK1/2) signal transduction pathways play critical roles in mammalian cell survival and have been shown to be activated in various cancers. Previous studies have shown that inhibition of PI3K/Akt or MEK/ERK1/2 can each enhance the effectiveness of cytotoxic chemotherapy. Our results show that FdUMP[10] treatment reduced phosphorylated Akt levels suggesting FdUMP[10] treatment inactivates the PI3K/Akt pro-survival pathway. However, inhibition of PI3K/Akt with LY294002 alone promoted a significant loss in the clonogenic capacity of PC3 cells independent of FdUMP[10] treatment while co-treatment did not provide an enhanced therapeutic effect. In contrast to these findings, inhibition of the MEK/ERK1/2 pathway with U0126 showed a significant decrease in viability only in combination with FdUMP[10] treatment. Here, we demonstrate that the potent effects of FdUMP[10]-induced cytotoxicity towards prostate cancer cells may be exacerbated by impairment of the MEK/ERK1/2 but not the PI3K/Akt cell survival pathway. Altogether, our studies suggest advanced prostate cancer may be amenable to treatment with FdUMP[10] in combination with inhibitors of MAPK signaling. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1637.