Abstract 1737: Carfilzomib transcriptionally regulates CIP2A/PP2A/p-Akt signaling and induces apoptosis in leukemia cells
Authors: Liu Chun-Yu , Tsai Wen-Chun , Hung Man-Hsin , Yu Yuan-Bin , Ko Po-Shen , Tzeng Cheng-Hwai , Shiau Chung-Wai , Chen Kuen-Feng 
Published: August 2015

Abstract
Background: Protein phosphatase 2A (PP2A) has been shown to be an important tumor suppressor protein and loss of PP2A function has been identified in several solid cancers and in leukemias. Recent studies have suggested strategies for enhancing PP2A activity as an anti-leukemic approach. Among the potential key players regulating PP2A, a new oncoprotein, called cancerous inhibitor of protein phosphatase 2A (CIP2A), is recently identified as a key factor in the development of malignancies in various human cells. Previously we studied novel drug mechanisms of bortezomib, a proteasome inhibitor, on acute leukemia cells. We discovered that CIP2A plays an indispensable role in mediating bortezomib-induced apoptosis in acute leukemia cells (Hematologica 2013), hepatocellular carcinoma cells (Oncogene 2010) and in breast cancer cells (Breast Cancer Research 2012). Importantly, this mechanism by bortezomib is independent to its proteasome inhibition. Carfilzomib, a more selective proteasome inhibitor than bortezomib, has shown efficacy in multiple myeloma and is being investigated in phase III clinical trials. In this study, we examined the effect of carfilzomib on CIP2A in leukemia cells.
Methods: Leukemia cell lines (HL-60, KG-1, THP-1, and K562) were used for in vitro studies. Apoptosis was examined by both flow cytometry and Western blot. Signal transduction pathways in cells were assessed by Western Blot. Quantitative RT-PCR was used for assessing gene transcription. In vivo efficacy of carfilzomib was tested in nude mice with subcutaneous leukemia xenografts.
Results: We found carfilzomib induced differential antiproliferative effects and apoptosis. HL-60, KG-1 and THP-1, but not K562 cells, were sensitive to carfilzomib-induced apoptosis. Similarly, carfilzomib-induced apoptosis may be dissociated with its proteasome inhibition. We found CIP2A mediated this apoptotic effect of carfilzomib in leukemia cells. Carfilzomib down-regulated CIP2A in association with p-Akt downregulation. Furthermore, carfilzomib increased PP2A activity and over-expression of CIP2A up-regulated p-Akt and suppressed carfilzomib-induced apoptosis. In addition, carfilzomib downregulated CIP2A mRNA but did not affect the degradation of CIP2A protein. Further dissecting the regulatory mechanism showed that carfilzomib may affect CIP2A transcription though transcriptional factors. Importantly, carfilzomib demonstrated anti-tumor activity in xenografted mice models.
Conclusions: CIP2A is a major determinant mediating carfilzomib-induced apoptosis in leukemia cells and may be a therapeutic target in leukemia. This study disclosed a novel drug mechanism of carfilzomib in leukemia cells. (Supported by Taiwan Clinical Oncology Research Foundation, MOST 103-2325-B-075-002, V103C-141; and TVGH-NTUH Joint Research Program VN103-08)
Citation Format: Chun-Yu Liu, Wen-Chun Tsai, Man-Hsin Hung, Yuan-Bin Yu, Po-Shen Ko, Cheng-Hwai Tzeng, Chung-Wai Shiau, Kuen-Feng Chen. Carfilzomib transcriptionally regulates CIP2A/PP2A/p-Akt signaling and induces apoptosis in leukemia cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1737. doi:10.1158/1538-7445.AM2015-1737