title: Treatment with Ibrutinib Inhibits BTK- and VLA-4-Dependent Adhesion of Chronic Lymphocytic Leukemia Cells In Vivo.
abstract: OBJECTIVE
  Ibrutinib leads to a transient lymphocytosis in patients with chronic lymphocytic leukemia (CLL) that develops within hours of starting drug and is due to the efflux of cells from lymphoid tissues into the blood. We therefore sought to investigate the in vivo effect of ibrutinib on migration and adhesion of CLL cells.
  
  
  METHODS
  Patients received single-agent ibrutinib (420 mg daily) on an investigator-initiated phase II trial. Serial blood samples were collected pretreatment and during treatment for ex vivo functional assays.
  
  
  RESULTS
  Adhesion of CLL cells to fibronectin was rapidly (within hours) and almost completely inhibited (median reduction 98% on day 28, P < 0.001), while the effect on migration to chemokines was more moderate (median reduction 64%, P = 0.008) and less uniform. Although cell surface expression of key adhesion molecules such as CD49d, CD29, and CD44 were modestly reduced, this was only apparent after weeks of treatment. Stimulation of CLL cells from patients on ibrutinib with PMA, which activates PKC independent of BTK, restored the ability of the cells to adhere to fibronectin in a VLA-4-dependent manner. Finally, the addition of ibrutinib to CLL cells adhered to fibronectin in vitro caused the detachment of 17% of the cells, on average; consisten t with in vivo observations of an increasing lymphocytosis within 4 hours of starting ibrutinib.
  
  
  CONCLUSIONS
  Inhibition of BTK and VLA-4-dependent adhesion of CLL cells to stroma and stromal components provides a mechanistic explanation for the treatment-induced lymphocytosis and may reduce CD49d-dependent prosurvival signals in the tissue microenvironment.
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
authors.forename: Sarah E M
authors.initials: SE
authors.lastname: Herman
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
authors.forename: Rashida Z
authors.initials: RZ
authors.lastname: Mustafa
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland. Medical Research Scholars Program, NIH, Bethesda, Maryland.
authors.forename: Jade
authors.initials: J
authors.lastname: Jones
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
authors.forename: Deanna H
authors.initials: DH
authors.lastname: Wong
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Farooqui
authors.affiliation: Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland. wiestnea@nhlbi.nih.gov.
authors.forename: Adrian
authors.initials: A
authors.lastname: Wiestner
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000368:Aged; D002448:Cell Adhesion / Q000187:drug effects*; D005260:Female; D005353:Fibronectins / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D039041:Integrin alpha4beta1 / Q000037:antagonists & inhibitors*; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy* / Q000378:metabolism; D008218:Lymphocytosis / Q000378:metabolism; D008297:Male; D010880:Piperidines; D011493:Protein Kinase C / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000627:therapeutic use; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D011720:Pyrazoles / Q000627:therapeutic use*; D011743:Pyrimidines / Q000627:therapeutic use*
chemical_list: D005353:Fibronectins; D039041:Integrin alpha4beta1; D010880:Piperidines; D047428:Protein Kinase Inhibitors; D011720:Pyrazoles; D011743:Pyrimidines; C551803:ibrutinib; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; D011493:Protein Kinase C; D000225:Adenine