dactolisib and Lymphoma

Stem cell leukemia/lymphoma syndrome (SCLL) is driven by constitutive activation of chimeric FGFR1 kinases generated by chromosome translocations. We have shown that FGFR inhibitors significantly suppress leukemia and lymphoma development in vivo, and cell viability in vitro. Since resistance to targeted therapies is a major reason for relapse, we developed FGFR1-overexpressing mouse and human cell lines that are resistant to the specific FGFR inhibitors AZD4547 and BGJ398, as well as non-specific inhibitors, such as ponatinib, TKI258 and E3810. Two mutually exclusive mechanisms for resistance were demonstrated; an activating V561M mutation in the FGFR1 kinase domain and mutational inactivation of PTEN resulting in increased PI3K/AKT activity. Ectopic expression of PTEN in the PTEN-mutant cells resensitizes them to FGFR inhibitors. Treatment of resistant cells with BGJ398, in combination with the BEZ235 PI3K inhibitor, shows an additive effect on growth in vitro and prolongs survival in xenograft models in vivo. These studies provide the first direct evidence for both the involvement of the FGFR1 V561M mutation and PTEN inactivation in the development of resistance in leukemias overexpressing chimeric FGFR1. These studies also provide a potential strategy to treat leukemias and lymphomas driven by FGFR1 activation that become resistant to FGFR1 inhibitors.

Topics: Animals; Benzamides; Cell Line, Tumor; Drug Resistance, Neoplasm; Gene Expression Regulation, Leukemic; Humans; Imidazoles; Leukemia; Lymphoma; Mice; Mutation; Neoplastic Stem Cells; Phenylurea Compounds; Phosphatidylinositol 3-Kinases; Piperazines; Protein Kinase Inhibitors; PTEN Phosphohydrolase; Pyrazoles; Pyrimidines; Quinolines; Receptor, Fibroblast Growth Factor, Type 1; Xenograft Model Antitumor Assays

Overexpression of anti-apoptotic BCL-2 family members is a hallmark of many lymphoid malignancies, including chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL) that can be targeted with small molecule inhibitors. ABT-199 is a rationally designed BCL-2 homology (BH)-3 mimetic that specifically binds to BCL-2, but not to MCL-1 and BCL-xL. Although the thrombocytopenia that occurs with navitoclax treatment has not been a problem with ABT-199, clinical trials in CLL could benefit by lowering the ABT-199 concentration through targeting other survival pathways. In this study, we investigated the mechanisms of resistance that develops to ABT-199 therapy by generating ABT-199-resistant (ABT199-R) cell lines via chronic exposure of NHL cell lines to ABT-199. Acquired resistance resulted in substantial AKT activation and upregulation of MCL-1 and BCL-xL levels that sequestered BIM. ABT199-R cells exhibited increased MCL-1 stability and failed to activate BAX in response to ABT-199. The ABT-199 acquired and inherent resistant cells were sensitized to treatment with ABT-199 by inhibitors of the PI3K, AKT, and mTOR pathways, NVP-BEZ235 and GS-1101. NVP-BEZ235, a dual inhibitor of p-AKT and mTOR, reduced MCL-1 levels causing BIM release from MCL-1 and BCL-xL, thus leading to cell death by BAX activation. The PI3Kδ inhibitor GS-1101 (idelalisib) downregulated MCL-1 and sensitized ABT199-R cells through AKT-mediated BAX activation. A genetic approach, through siRNA-mediated down-regulation of AKT, MCL-1, and BCL-xL, significantly decreased cell survival, demonstrating the importance of these cell survival factors for ABT-199 resistance. Our findings suggest a novel mechanism that modulates the expression and activity of pro-survival proteins to confer treatment resistance that could be exploited by a rational combination therapeutic regimen that could be effective for treating lymphoid malignancies.

Topics: Apoptosis Regulatory Proteins; Bcl-2-Like Protein 11; bcl-X Protein; Bridged Bicyclo Compounds, Heterocyclic; Cell Line, Tumor; Down-Regulation; Drug Resistance, Neoplasm; Gene Expression Regulation, Neoplastic; Humans; Imidazoles; Lymphoma; Membrane Proteins; Models, Biological; Myeloid Cell Leukemia Sequence 1 Protein; Phosphatidylinositol 3-Kinases; Phosphorylation; Protein Stability; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Purines; Quinazolinones; Quinolines; RNA, Messenger; Sulfonamides; TOR Serine-Threonine Kinases; Up-Regulation

The phosphoinositide 3-kinase (PI3K) pathway is known to play an active role in many malignancies. The role of PI3K inhibition in the treatment of lymphomas has not been fully delineated. We sought to identify a role for therapeutic PI3K inhibition across a range of B-cell lymphomas.. We selected three small molecule inhibitors to test in a panel of 60 cell lines that comprised diverse lymphoma types. We tested the selective PI3K inhibitor BKM120 and the dual PI3K/mTOR inhibitors BEZ235 and BGT226 in these cell lines. We applied gene expression profiling to better understand the molecular mechanisms associated with responsiveness to these drugs.. We found that higher expression of the PAK1 gene was significantly associated with resistance to all three PI3K inhibitors. Through RNA-interference-mediated knockdown of the PAK1 gene, we showed a dramatic increase in the sensitivity to PI3K inhibition. We further tested a small-molecule inhibitor of PAK1 and found significant synergy between PI3K and PAK1 inhibition.. Thus, we show that PI3K inhibition is broadly effective in lymphomas and PAK1 is a key modulator of resistance to PI3K inhibition.

Topics: Aminopyridines; Biomarkers, Tumor; Cell Proliferation; Drug Resistance, Neoplasm; Drug Synergism; Enzyme Inhibitors; Gene Expression Profiling; Humans; Imidazoles; Lymphoma; Morpholines; Oligonucleotide Array Sequence Analysis; p21-Activated Kinases; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Quinolines; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; RNA, Small Interfering; Small Molecule Libraries; TOR Serine-Threonine Kinases; Tumor Cells, Cultured