title: Targeted Axl Inhibition Primes Chronic Lymphocytic Leukemia B Cells to Apoptosis and Shows Synergistic/Additive Effects in Combination with BTK Inhibitors.
abstract: OBJECTIVE
  B-cell chronic lymphocytic leukemia (CLL) is an incurable disease despite aggressive therapeutic approaches. We previously found that Axl receptor tyrosine kinase (RTK) plays a critical role in CLL B-cell survival. Here, we explored the possibility of using a high-affinity Axl inhibitor as a single agent or in combination with Bruton's tyrosine kinase (BTK) inhibitors for future clinical trial to treat patients with CLL.
  
  
  METHODS
  Expression/activation status of other members of the TAM (e.g., Tyro3, Axl, and MER) family of RTKs in CLL B cells was evaluated. Cells were treated with a high-affinity orally bioavailable Axl inhibitor TP-0903 with or without the presence of CLL bone marrow stromal cells (BMSCs). Inhibitory effects of TP-0903 on the Axl signaling pathway were also evaluated in CLL B cells. Finally, cells were exposed to TP-0903 in combination with BTK inhibitors to determine any synergistic/additive effects of the combination.
  
  
  RESULTS
  CLL B cells overexpress Tyro3, but not MER. Of interest, Tyro3 remains as constitutively phosphorylated and forms a complex with Axl in CLL B cells. TP-0903 induces massive apoptosis in CLL B cells with LD50 values of nanomolar ranges. Importantly, CLL BMSCs could not protect the leukemic B cells from TP-0903-induced apoptosis. A marked reduction of the antiapoptotic proteins Mcl-1, Bcl-2, and XIAP and upregulation of the proapoptotic protein BIM in CLL B cells was detected as a result of Axl inhibition. Finally, combination of TP-0903 with BTK inhibitors augments CLL B-cell apoptosis.
  
  
  CONCLUSIONS
  Administration of TP-0903 either as a single agent or in combination with BTK inhibitors may be effective in treating patients with CLL.
authors: Division of Hematology, Mayo Clinic, Rochester, Minnesota.
authors: Sutapa
authors: S
authors: Sinha
authors: Division of Hematology, Mayo Clinic, Rochester, Minnesota.
authors: Justin
authors: J
authors: Boysen
authors: Division of Hematology, Mayo Clinic, Rochester, Minnesota.
authors: Michael
authors: M
authors: Nelson
authors: Division of Hematology, Mayo Clinic, Rochester, Minnesota.
authors: Charla
authors: C
authors: Secreto
authors: Tolero Pharmaceuticals, Inc., Lehi, Utah.
authors: Steven L
authors: SL
authors: Warner
authors: Tolero Pharmaceuticals, Inc., Lehi, Utah.
authors: David J
authors: DJ
authors: Bearss
authors: Division of Hematology, Mayo Clinic, Rochester, Minnesota.
authors: Connie
authors: C
authors: Lesnick
authors: Division of Hematology, Mayo Clinic, Rochester, Minnesota.
authors: Tait D
authors: TD
authors: Shanafelt
authors: Division of Hematology, Mayo Clinic, Rochester, Minnesota.
authors: Neil E
authors: NE
authors: Kay
authors: Division of Hematology, Mayo Clinic, Rochester, Minnesota. ghosh.asish@mayo.edu.
authors: Asish K
authors: AK
authors: Ghosh
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001402:B-Lymphocytes; D015153:Blotting, Western; D002478:Cells, Cultured; D018920:Coculture Techniques; D004357:Drug Synergism; D005434:Flow Cytometry; D006801:Humans; D047468:Immunoprecipitation; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000473:pathology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors*; D011743:Pyrimidines / Q000494:pharmacology*; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors*; D013449:Sulfonamides / Q000494:pharmacology*; D014162:Transfection; D000094963:Axl Receptor Tyrosine Kinase; D000096926:Benzenesulfonamides
chemical_list: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000970:Antineoplastic Agents; D047428:Protein Kinase Inhibitors; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D011743:Pyrimidines; D020794:Receptor Protein-Tyrosine Kinases; D013449:Sulfonamides; D000094963:Axl Receptor Tyrosine Kinase; C000606144:dubermatinib; D000096926:Benzenesulfonamides; C000625949:BTK protein, human; C000722289:AXL protein, human