CDK4/CDK6 inhibition as a novel strategy to suppress the growth and survival of BCR-ABL1T315I+ clones in TKI-resistant CML

EBioMedicine. 2019 Dec:50:111-121. doi: 10.1016/j.ebiom.2019.11.004. Epub 2019 Nov 21.

Abstract

Purpose: Ponatinib is the only approved tyrosine kinase inhibitor (TKI) suppressing BCR-ABL1T315I-mutated cells in chronic myeloid leukemia (CML). However, due to side effects and resistance, BCR-ABL1T315I-mutated CML remains a clinical challenge. Hydroxyurea (HU) has been used for cytoreduction in CML for decades. We found that HU suppresses or even eliminates BCR-ABL1T315I+ sub-clones in heavily pretreated CML patients. Based on this observation, we investigated the effects of HU on TKI-resistant CML cells in vitro.

Methods: Viability, apoptosis and proliferation of drug-exposed primary CML cells and BCR-ABL1+ cell lines were examined by flow cytometry and 3H-thymidine-uptake. Expression of drug targets was analyzed by qPCR and Western blotting.

Findings: HU was more effective in inhibiting the proliferation of leukemic cells harboring BCR-ABL1T315I or T315I-including compound-mutations compared to cells expressing wildtype BCR-ABL1. Moreover, HU synergized with ponatinib and ABL001 in inducing growth inhibition in CML cells. Furthermore, HU blocked cell cycle progression in leukemic cells, which was accompanied by decreased expression of CDK4 and CDK6. Palbociclib, a more specific CDK4/CDK6-inhibitor, was also found to suppress proliferation in primary CML cells and to synergize with ponatinib in producing growth inhibition in BCR-ABL1T315I+ cells, suggesting that suppression of CDK4/CDK6 may be a promising concept to overcome BCR-ABL1T315I-associated TKI resistance.

Interpretation: HU and the CDK4/CDK6-blocker palbociclib inhibit growth of CML clones expressing BCR-ABL1T315I or complex T315I-including compound-mutations. Clinical studies are required to confirm single drug effects and the efficacy of `ponatinib+HU´ and ´ponatinib+palbociclib´ combinations in advanced CML.

Funding: This project was supported by the Austrian Science Funds (FWF) projects F4701-B20, F4704-B20 and P30625.

Keywords: BCR-ABL1 mutations; CDK4/CDK6 – Palbociclib; CML; Hydroxyurea; TKI resistance.

MeSH terms

  • Adult
  • Aged
  • Apoptosis / drug effects
  • Cell Cycle / drug effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cyclin-Dependent Kinase 4 / antagonists & inhibitors*
  • Cyclin-Dependent Kinase 6 / antagonists & inhibitors*
  • Dose-Response Relationship, Drug
  • Drug Resistance, Neoplasm / genetics*
  • Drug Synergism
  • Female
  • Fusion Proteins, bcr-abl / genetics*
  • Humans
  • Hydroxyurea / pharmacology
  • Hydroxyurea / therapeutic use
  • Imidazoles / pharmacology
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / genetics*
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / metabolism*
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / pathology
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / therapy
  • Male
  • Middle Aged
  • Mutation*
  • Protein Kinase Inhibitors / pharmacology*
  • Protein Kinase Inhibitors / therapeutic use
  • Pyridazines / pharmacology

Substances

  • BCR-ABL1 fusion protein, human
  • Imidazoles
  • Protein Kinase Inhibitors
  • Pyridazines
  • ponatinib
  • Fusion Proteins, bcr-abl
  • CDK4 protein, human
  • CDK6 protein, human
  • Cyclin-Dependent Kinase 4
  • Cyclin-Dependent Kinase 6
  • Hydroxyurea