Oral Presentation 26th Lorne Cancer Conference 2014

A novel chemoresistance function for the lipid phosphatase INPP4B in Acute Myeloid Leukaemia (#20)

Sewa Rijal 1 , Nhu-Y N Nugyen 1 , Tse-Chieh Teh 1 , Natalie K Rynkiewicz 2 , Nik Cummings 1 , Lisa M Ooms 2 , Sharon Avery 3 , Julie Mcmanus 1 , Mark A Guthridge 1 , Catriona A Mclean 4 , Christina A Mitchell* 2 , Andrew H Wei* 1 3
  1. Australian Centre for Blood Diseases, Monash University, Melbourne, Victoria, Australia
  2. Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
  3. Department of Clinical Haematology, The Alfred Hospital, Melbourne, Victoria, Australia
  4. Department of Anatomical Pathology, The Alfred Hospital, Melbourne, Victoria, Australia

Growth factor activation of phosphoinositide 3-kinase (PI3K)/AKT orchestrate a diverse variety of critical physiological cell functions. Aberrant PI3K/AKT signaling is a hallmark of many solid tumours and hematopoietic malignancies, including acute myeloid leukaemia (AML). Negative regulation of PI3K activity is mediated by lipid phosphatases, categorized functionally as 3-, 4-, or 5-phosphoinositide phosphatases (PIPs). A constellation of clinical pathologies, including cancers, have been linked to abnormal expression of various PIPs. We therefore sought to identify the presence and consequences of pathological expression of 3-, 4-, or 5-PIPs in AML. A mass-spec based gene expression survey of PIPs in primary AML cases revealed unexpected overexpression of the inositol polyphosphate 4-phosphatase II (INPP4B), compared to normal bone marrow cells (p-value = 0.02). Overexpression (>20% blasts positive) of INPP4B protein as assessed by immunocytochemistry was detected in 16% of 120 primary AML bone marrow samples examined. INPP4B overexpression in AML patients was associated with striking chemoresistance, with only 33% of INPP4B-positive cases achieving remission with intensive chemotherapy. In contrast, the remission rate in INPP4B-low (5-20%) or -negative (<5%) AML subgroups, was 66% and 93%, respectively. Ectopic overexpression of INPP4B in MV4;11 and HEL AML cells conferred resistance to in vitro cell death from cytotoxic agents used to treat AML including cytarabine, daunorubicin and etoposide in cell survival and clonogenic assays. Furthermore, high INPP4B also conferred resistance to blast clearance of bone marrow blasts by cytarabine in vivo in human xenograft models of AML. INPP4B phosphatase function was found to be catalytically active in primary AML. Chemoresistance, however, was not reversed by expression of a phosphatase inactive mutant form of INPP4B suggesting phosphatase-independent function. In contrast, siRNA-mediated knockdown of INPP4B expression in KG1 and OCI-AML3 AML cells increased chemosensitivity to cytarabine. These findings support a novel phosphatase-independent function of INPP4B overexpression in mediating chemoresistance and reduced survival in AML.