Improving nelarabine efficacy in T cell acute lymphoblastic leukemia by targeting aberrant PI3K/AKT/mTOR signaling pathway

J Hematol Oncol. 2016 Oct 24;9(1):114. doi: 10.1186/s13045-016-0344-4.

Abstract

Background: Although in recent years, the introduction of novel chemotherapy protocols has improved the outcome of T cell acute lymphoblastic leukemia (T-ALL) patients, refractory and/or relapsing disease remains a foremost concern. In this context, a major contribution was provided by the introduction of the nucleoside analog nelarabine, approved for salvage treatment of T-ALL patients with refractory/relapsed disease. However, nelarabine could induce a life-threatening, dose-dependent neurotoxicity. To improve nelarabine efficacy, we have analyzed its molecular targets, testing selective inhibitors of such targets in combination with nelarabine.

Methods: The effectiveness of nelarabine as single agent or in combination with PI3K, Bcl2, and MEK inhibitors was evaluated on human T-ALL cell lines and primary T-ALL refractory/relapsed lymphoblasts. The efficacy of signal modulators in terms of cytotoxicity, induction of apoptosis, and changes in gene and protein expression was assessed by flow cytometry, western blotting, and quantitative real-time PCR in T-ALL settings.

Results: Treatment with nelarabine as a single agent identified two groups of T-ALL cell lines, one sensitive and one resistant to the drug. Whereas sensitive T-ALL cells showed a significant increase of apoptosis and a strong down-modulation of PI3K signaling, resistant T-ALL cells showed a hyperactivation of AKT and MEK/ERK1/2 signaling pathways, not caused by differences in the expression of nelarabine transporters or metabolic activators. We then studied the combination of nelarabine with the PI3K inhibitors (both pan and dual γ/δ inhibitors), with the Bcl2 specific inhibitor ABT199, and with the MEK inhibitor trametinib on both T-ALL cell lines and patient samples at relapse, which displayed constitutive activation of PI3K signaling and resistance to nelarabine alone. The combination with the pan PI3K inhibitor ZSTK-474 was the most effective in inhibiting the growth of T-ALL cells and was synergistic in decreasing cell survival and inducing apoptosis in nelarabine-resistant T-ALL cells. The drug combination caused AKT dephosphorylation and a downregulation of Bcl2, while nelarabine alone induced an increase in p-AKT and Bcl2 signaling in the resistant T-ALL cells and relapsed patient samples.

Conclusions: These findings indicate that nelarabine in combination with PI3K inhibitors may be a promising therapeutic strategy for the treatment of T-ALL relapsed patients.

Keywords: Apoptosis; Combination therapy; Drug resistance; PI3K signaling.

MeSH terms

  • Antineoplastic Combined Chemotherapy Protocols / therapeutic use*
  • Antineoplastic Combined Chemotherapy Protocols / toxicity
  • Apoptosis / drug effects
  • Arabinonucleosides / therapeutic use
  • Arabinonucleosides / toxicity
  • Bridged Bicyclo Compounds, Heterocyclic / therapeutic use
  • Cell Survival / drug effects
  • Drug Synergism
  • Humans
  • Phosphoinositide-3 Kinase Inhibitors*
  • Precursor T-Cell Lymphoblastic Leukemia-Lymphoma / complications
  • Precursor T-Cell Lymphoblastic Leukemia-Lymphoma / drug therapy*
  • Proto-Oncogene Proteins c-akt
  • Pyridones / therapeutic use
  • Pyrimidinones / therapeutic use
  • Signal Transduction / drug effects*
  • Sulfonamides / therapeutic use
  • TOR Serine-Threonine Kinases / antagonists & inhibitors*
  • Triazines / therapeutic use
  • Tumor Cells, Cultured

Substances

  • Arabinonucleosides
  • Bridged Bicyclo Compounds, Heterocyclic
  • Phosphoinositide-3 Kinase Inhibitors
  • Pyridones
  • Pyrimidinones
  • Sulfonamides
  • Triazines
  • ZSTK474
  • trametinib
  • nelarabine
  • MTOR protein, human
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases
  • venetoclax