Phosphatidylinositol 3-kinase-δ inhibitor CAL-101 shows promising preclinical activity in chronic lymphocytic leukemia by antagonizing intrinsic and extrinsic cellular survival signals

Blood. 2010 Sep 23;116(12):2078-88. doi: 10.1182/blood-2010-02-271171. Epub 2010 Jun 3.


Targeted therapy with imatinib in chronic myeloid leukemia (CML) prompted a new treatment paradigm. Unlike CML, chronic lymphocytic leukemia (CLL) lacks an aberrant fusion protein kinase but instead displays increased phosphatidylinositol 3-kinase (PI3K) activity. To date, PI3K inhibitor development has been limited because of the requirement of this pathway for many essential cellular functions. Identification of the hematopoietic-selective isoform PI3K-δ unlocks a new therapeutic potential for B-cell malignancies. Herein, we demonstrate that PI3K has increased enzymatic activity and that PI3K-δ is expressed in CLL cells. A PI3K-δ selective inhibitor CAL-101 promoted apoptosis in primary CLL cells ex vivo in a dose- and time-dependent fashion that was independent of common prognostic markers. CAL-101-mediated cytotoxicity was caspase dependent and was not diminished by coculture on stromal cells. In addition, CAL-101 abrogated protection from spontaneous apoptosis induced by B cell-activating factors CD40L, TNF-α, and fibronectin. In contrast to malignant cells, CAL-101 does not promote apoptosis in normal T cells or natural killer cells, nor does it diminish antibody-dependent cellular cytotoxicity. However, CAL-101 did decrease activated T-cell production of various inflammatory and antiapoptotic cytokines. Collectively, these studies provide rationale for the clinical development of CAL-101 as a first-in-class targeted therapy for CLL and related B-cell lymphoproliferative disorders.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents
  • Apoptosis / drug effects
  • B-Lymphocytes / enzymology
  • B-Lymphocytes / pathology
  • Cell Survival / drug effects*
  • Class I Phosphatidylinositol 3-Kinases
  • Enzyme Inhibitors / pharmacology
  • Enzyme Inhibitors / therapeutic use*
  • Humans
  • Leukemia, Lymphocytic, Chronic, B-Cell / drug therapy
  • Leukemia, Lymphocytic, Chronic, B-Cell / pathology
  • Phosphoinositide-3 Kinase Inhibitors*
  • Purines / pharmacology*
  • Quinazolinones / pharmacology*
  • Signal Transduction / drug effects*
  • Tumor Cells, Cultured


  • Antineoplastic Agents
  • Enzyme Inhibitors
  • Phosphoinositide-3 Kinase Inhibitors
  • Purines
  • Quinazolinones
  • Class I Phosphatidylinositol 3-Kinases
  • PIK3CD protein, human
  • idelalisib