The role of NOTCH1 signaling in T-ALL.

The identification of activating mutations in NOTCH1 in over 50% of T-cell acute lymphoblastic leukemias (T-ALL) has generated major interest in the elucidation of the mechanisms of transformation downstream of oncogenic NOTCH and in the targeting of the NOTCH signaling pathway in this disease. Small molecule gamma-secretase inhibitors (GSIs) block NOTCH1 signaling in T-ALL lymphoblasts, yet the clinical development of GSIs has been held back by the development of gastrointestinal toxicity and their weak antileukemic effects against human T-ALL. However, new therapeutic strategies aiming to optimize the use of anti-NOTCH1 therapies for T-ALL, including combination therapies with molecularly targeted drugs and glucocorticoids, have started to emerge as a result of improved understanding of the molecular mechanisms that mediate the effects of GSIs in leukemic cells and the intestinal epithelium. This review focuses on the molecular basis of NOTCH1-induced transformation, the mechanisms of action of oncogenic NOTCH1 and clinical significance of NOTCH1 mutations in T-ALL.