Marina Konopleva

Aberrant Proliferative and Apoptotic Pathways in Acute Lymphoblastic Leukemia (ALL): Molecular Therapies to Overcome Chemo-Resistance

Adult acute lymphoblastic leukemia (ALL) is characterized by a high relapse rate, with the majority of patients developing chemo-resistance and ultimately dying of the disease with a 5-year survival rate of 40% (Faderl et al., 2010). Significant advances, however, have been made in cases carrying the acquired genetic alteration BCR-ABL (ALL-Ph+) targeted by tyrosine-kinase inhibitors (Ottmann & Pfeifer, 2009). Therefore, several studies have recently been carried out to look for additional, therapeutically exploitable, genetic lesions. Aberrant activation of signal transduction pathways (STP) implicated in proliferation and survival mechanisms are generally involved in leukemogenesis and drug resistance (Zhao et al., 2010). Genes in the PI3K/PTEN/AKT/mTOR, RAS/RAF/MEK/ERK, and Jak/STAT pathways are frequently mutated and their expression is often altered in hematopoietic malignancies, including ALL (McCubrey et al., 2011; Steelman et al. 2008). In addition, deregulation of survival mechanisms may confer chemo-resistance to leukemic cells, particularly involving alterations of the Bcl-2 signaling cascade, which may represent one of the most important, potentially druggable, pathways for therapeutic intervention in ALL. Starting from our studies on chemo-resistance in ALL, particularly on multidrug resistance (MDR1) expression and prognostic significance, in this chapter we will illustrate the major pathways aberrantly activated in ALL PI3K/PTEN/AKT/mTOR, RAF/RAS/MEK/ERK, and the Bcl-2 family of proteins with the ultimate goal of summarizing novel targets for

Development and validation of an RNAi screen for ABT-737 sensitizers

correspondence: John c reed Sanford-Burnham Medical research Institute, 10901 north Torrey Pines road, La Jolla, cA, USA Tel +1 858-646-3100 Fax +1 858-646-3194 Email reedoffice@sanfordburnham.org Abstract: The chemical compound ABT-737 is a nanomolar inhibitor of several antiapoptotic Bcl-2 family members with potential therapeutic efficacy for a variety of cancers. Herein, we describe the development of a complementation-based RNAi assay that can be used to identify mechanisms of ABT-737-resistance. HeLa cells, which were resistant to ABT-737, were optimized for reverse-transfection efficiency and tested for siRNA-mediated silencing. The developed assay utilized HeLa cell reverse-transfection with 10 nM siRNA, followed by 48 h incubation, ABT-737 or DMSO treatment for 24 h, and cell viability measurement using ATPlite (which measures ATP levels as an indicator of cell viability). As a validation, the kinase subset of the Ambion Silencer Human Druggable Genome siRNA Library V2, which consisted of 865 genes (three siRNA sequences per gene), was screened. Several assay-positive siRNAs were tested and confirmed to sensitize cells to ABT-737. Transfection of cells with siRNAs targeting Bcl-2 family member Mcl-1 also potently sensitized HeLa cells to ABT-737. The current assay thus represents a screen that can be utilized to identify ABT-737-sensitizing siRNAs and correspondingly, potential new targets for drug discovery.