Selective Akt Inhibitors Synergize with Tyrosine Kinase Inhibitors and Effectively Override Stroma-Associated Cytoprotection of Mutant FLT3-Positive AML Cells

Department of Medical Oncology, Dana Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts, United States of America.
PLoS ONE (Impact Factor: 3.53). 02/2013; 8(2):e56473. DOI: 10.1371/journal.pone.0056473
Source: PubMed

ABSTRACT Tyrosine kinase inhibitor (TKI)-treated acute myeloid leukemia (AML) patients commonly show rapid and significant peripheral blood blast cell reduction, however a marginal decrease in bone marrow blasts. This suggests a protective environment and highlights the demand for a better understanding of stromal:leukemia cell communication. As a strategy to improve clinical efficacy, we searched for novel agents capable of potentiating the stroma-diminished effects of TKI treatment of mutant FLT3-expressing cells.
We designed a combinatorial high throughput drug screen using well-characterized kinase inhibitor-focused libraries to identify novel kinase inhibitors capable of overriding stromal-mediated resistance to TKIs, such as PKC412 and AC220. Standard liquid culture proliferation assays, cell cycle and apoptosis analysis, and immunoblotting were carried out with cell lines or primary AML to validate putative candidates from the screen and characterize the mechanism(s) underlying observed synergy.
Our study led to the observation of synergy between selective Akt inhibitors and FLT3 inhibitors against mutant FLT3-positive AML in either the absence or presence of stroma. Our findings are consistent with evidence that Akt activation is characteristic of mutant FLT3-transformed cells, as well as observed residual Akt activity following FLT3 inhibitor treatment. In conclusion, our study highlights the potential importance of Akt as a signaling factor in leukemia survival, and supports the use of the co-culture chemical screen to identify agents able to potentiate TKI anti-leukemia activity in a cytoprotective microenvironment.


Available from: James D Griffin, Apr 22, 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: Resistance to FLT3 inhibitors is a serious clinical issue in treating AML. AMG 925, a dual FLT3/CDK4 inhibitor, has been developed to overcome this resistance. It is hypothesized that the combined inhibition of FLT3 and CDK4 may reduce occurrence of the FLT3 resistance mutations and thereby prolong clinical responses. To test this hypothesis, we attempted to isolate AML cell clones resistant to AMG 925 or to FLT3 inhibitors. After a selection of over 8 months with AMG 925, we could only isolate partially-resistant clones. No new mutations in FLT3 were found, but a 2-3 fold increase in total FLT3 protein was detected and believed to contribute to the partial resistance. In contrast, selection with the FLT3-inhibitors sorafenib or AC220 (Quizartinib), led to a resistance and the appearance of a number of mutations in FLT3 kinase domains including the known hot spot sites D835 and F691. However, when AC220 was combined with CDK4-inhibitor PD0332991 (Palbociclib) at 0.1 μM or higher, no resistance mutations were obtained, indicating that the CDK4-inhibiting activity of AMG 925 contributed to the failure to develop drug resistance. AMG 925 was shown to potently inhibit the FLT3 inhibitor-resistant mutation D835Y/V. This feature of AMG 925 was also considered to contribute to the lack of resistance mutations to the compound. Together, our data suggest that AMG 925 has the potential to reduce resistance mutations in FLT3 and may prolong clinical responses. Copyright © 2014, American Association for Cancer Research.
    Molecular Cancer Therapeutics 12/2014; DOI:10.1158/1535-7163.MCT-14-0388 · 6.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Reversing multidrug resistance (MDR) has been an important goal for clinical and investigational oncologists. In the last few decades, significant effort has been made to search for inhibitors to reverse MDR by targeting ATP-binding cassette (ABC) transporters (Pgp, MRP) directly, but these efforts have achieved little clinical success. Protein kinases play important roles in many aspects of tumor cell growth and survival. Combinations of kinase inhibitors and chemotherapeutics have been observed to overcome cancer drug resistance in certain circumstances.
    BMC Cancer 09/2014; 14(1):681. DOI:10.1186/1471-2407-14-681 · 3.32 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Many patients with acute myeloid leukemia will eventually develop refractory or relapsed disease. In the absence of standard therapy for this population, there is currently an urgent unmet need for novel therapeutic agents. Targeted therapy with small molecule inhibitors represents a new therapeutic intervention that has been successful for the treatment of multiple tumors (e.g., gastrointestinal stromal tumors, chronic myelogenous leukemia). Hence, there has been great interest in generating selective small molecule inhibitors targeting critical pathways of proliferation and survival in acute myeloid leukemia. This review highlights a selective group of intriguing therapeutic agents and their presumed targets in both preclinical models and in early human clinical trials.
    Expert Review of Hematology 08/2014; 7(4):439-464. DOI:10.1586/17474086.2014.932687 · 2.14 Impact Factor