title: Target of rapamycin signaling in leukemia and lymphoma.
abstract: Growth factors and many oncogenes activate the lipid kinase phosphoinositide 3-kinase (PI3K), initiating a signaling cascade that includes the protein kinases AKT and target of rapamycin (TOR). The PI3K/AKT/TOR signaling pathway is a significant contributor to disease in various human cancers, including hematologic malignancies. Here we discuss different strategies to inhibit TOR for the treatment of leukemia, lymphoma, and myeloma. The TOR enzyme exists in two complexes in cells, TORC1 and TORC2. The majority of preclinical and clinical efforts to target TOR have involved using rapamycin and its analogs (rapalogs), which suppress TORC1 only partially and do not acutely inhibit TORC2. A new class of small molecules targeting the ATP-binding site of the TOR kinase, termed active-site TOR inhibitors (asTORi), achieves greater inhibition of both TOR complexes, resulting in broader suppression of the PI3K/AKT/TOR signaling network. Preclinical evidence suggests that asTORi have greater efficacy than rapalogs in Philadelphia chromosome-positive acute lymphoblastic leukemia and in T-cell lymphoma. These agents also show greater tolerability in animal models relative to rapalogs or inhibitors of PI3K. These findings encourage broader evaluation of asTORi efficacy in acute myeloid leukemia, B-cell lymphoma, myeloma, and other blood cancers.
authors.affiliation: Division of Hematology/Oncology, Department of Medicine, University of California-Irvine, CA 92697, USA.
authors.forename: Collin
authors.initials: C
authors.lastname: Vu
authors.forename: David A
authors.initials: DA
authors.lastname: Fruman
mesh_terms: D000818:Animals; D006801:Humans; D007938:Leukemia / Q000188:drug therapy / Q000201:enzymology / Q000378:metabolism*; D008223:Lymphoma / Q000188:drug therapy / Q000201:enzymology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D019869:Phosphatidylinositol 3-Kinases; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors