Inhibition of NOTCH Signaling by Gamma Secretase Inhibitor Engages the RB Pathway and Elicits Cell Cycle Exit in T-Cell Acute Lymphoblastic Leukemia Cells

Abstract

NOTCH signaling is deregulated in the majority of T-cell acute lymphoblastic leukemias (T-ALL) as a result of activating mutations in NOTCH1. Gamma secretase inhibitors (GSI) block proteolytic activation of NOTCH receptors and may provide a targeted therapy for T-ALL. We have investigated the mechanisms of GSI sensitivity across a panel of T-ALL cell lines, yielding an approach for patient stratification based on pathway activity and also providing a rational combination strategy for enhanced response to GSI. Whereas the NOTCH1 mutation status does not serve as a predictor of GSI sensitivity, a gene expression signature of NOTCH pathway activity does correlate with response, and may be useful in the selection of patients more likely to respond to GSI. Furthermore, inhibition of the NOTCH pathway activity signature correlates with the induction of the cyclin-dependent kinase inhibitors CDKN2D (p19 INK4d ) and CDKN1B (p27 Kip1), leading to derepression of RB and subsequent exit from the cell cycle. Consistent with this evidence of cell cycle exit, short-term exposure of GSI resulted in sustained molecular and phenotypic effects after withdrawal of the compound. Combination treatment with GSI and a small molecule inhibitor of CDK4 produced synergistic growth inhibition, providing evidence that GSI engagement of the CDK4/RB pathway is an important mechanism of GSI action and supports further investigation of this combination for improved efficacy in treating T-ALL.

Inhibition of γ-secretase activity synergistically enhances tumour necrosis factor-related apoptosis-inducing ligand induced apoptosis in T-cell acute lymphoblastic leukemia cells via upregulation of death receptor 5

“…This finding is in agreement with other studies demonstrating that exposure of cells expressing Notch to GSI does not necessary result in cell death (37). The present study demonstrates that TRAIL maintains GSI-induced downregulation of NCID whilst synergistically inducing apoptosis.…”

Gamma-secretase inhibitors target tumor-initiating cells in a mouse model of ERBB2 breast cancer

“…The effect of MRK-003 on sphere-and colony-formation by mammary epithelial cell and tumor cell populations To determine whether Notch pathway activity was required for the survival or self-renewal of tumorsphereand mammosphere-forming cells, we used MRK-003, an orally active inhibitor of g-secretase, which is required for the proteolytic processing of Notch receptors (Fan et al, 2006;Konishi et al, 2007;Lewis et al, 2007;Cullion et al, 2009;Rao et al, 2009). We performed quantitative sphere-and colony-forming assays, which can be used to approximate the frequency of mammary epithelial stem and progenitor cells in heterogeneous cell populations (Reynolds and Weiss, 1992;Dontu et al, 2003).…”

Notch1 in primary effusion lymphoma: a clinicopathological study

“…13 The expression of Notch1 in primary effusion lymphoma patients may also shed light on the potential therapeutic use of Notch1 inhibitors on primary effusion lymphoma patients. It has been recently shown that g-secretase inhibitor, which blocks the activation of Notch1, engages the retinoblastoma pathways and elicits cell cycle exit in T-cell acute lymphoblastic leukemia cell lines, 14 and inclusion of g-secretase inhibitor in the therapeutic regimen in T-cell acute lymphoblastic leukemia provides a better treatment outcome. 15 It is of equal interest to point out that one HHV-8-positive primary effusion lymphoma case (patient no.…”