n-(n-(3-5-difluorophenacetyl)alanyl)phenylglycine-tert-butyl-ester and Precursor-T-Cell-Lymphoblastic-Leukemia-Lymphoma

Notch signaling deregulation is linked to the onset of several tumors including T-cell acute lymphoblastic leukemia (T-ALL). Deregulated microRNA (miRNA) expression is also associated with several cancers, including leukemias. However, the transcriptional regulators of miRNAs, as well as the relationships between Notch signaling and miRNA deregulation, are poorly understood. To identify miRNAs regulated by Notch pathway, we performed microarray-based miRNA profiling of several Notch-expressing T-ALL models. Among seven miRNAs, consistently regulated by overexpressing or silencing Notch3, we focused our attention on miR-223, whose putative promoter analysis revealed a conserved RBPjk binding site, which was nested to an NF-kB consensus. Luciferase and chromatin immunoprecipitation assays on the promoter region of miR-223 show that both Notch and NF-kB are novel coregulatory signals of miR-223 expression, being able to activate cooperatively the transcriptional activity of miR-223 promoter. Notably, the Notch-mediated activation of miR-223 represses the tumor suppressor FBXW7 in T-ALL cell lines. Moreover, we observed the inverse correlation of miR-223 and FBXW7 expression in a panel of T-ALL patient-derived xenografts. Finally, we show that miR-223 inhibition prevents T-ALL resistance to γ-secretase inhibitor (GSI) treatment, suggesting that miR-223 could be involved in GSI sensitivity and its inhibition may be exploited in target therapy protocols.

Topics: Amyloid Precursor Protein Secretases; Animals; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Cluster Analysis; Dipeptides; Disease Models, Animal; Drug Resistance, Neoplasm; F-Box Proteins; F-Box-WD Repeat-Containing Protein 7; Gene Expression Profiling; Gene Expression Regulation, Leukemic; Gene Silencing; Humans; Mice, Transgenic; MicroRNAs; NF-kappa B; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Receptors, Notch; RNA Interference; Signal Transduction; Ubiquitin-Protein Ligases

Activating mutations in the NOTCH1 gene are found in over 50 % of T-ALL cases. Since Notch signaling contributes to the leukemia cell survival and growth, targeting Notch signaling using γ-secretase inhibitors (GSI) has been proposed as a molecularly targeted therapy for the treatment of T-ALL. However, not all T-ALL with NOTCH1 activating mutations respond to GSI treatment. We examined whether GSI could enhance the cytotoxic effect of anti-leukemic agents in the GSI-resistant T-ALL cells although GSI does not have anti-tumor effect as a single agent. GSI significantly increased cell death induced by Vincristine (VCR) but not other anti-leukemic drugs (Methotrexate, Asparaginase, and Cytarabine). The GSI effect in enhancing VCR efficacy was not the result of inhibition of Notch signaling. GSI augmented VCR-induced mitotic arrest, followed by apoptosis. GSI accelerated VCR-triggered loss of mitochondrial membrane potential and caspase-mediated apoptosis. Our finding suggests that GSI has other functions besides inhibiting Notch signaling in T-ALL and incorporating GSI into the conventional regimen containing VCR may offer therapeutic advantage by potentiating VCR treatment in leukemia patients.

Topics: Amyloid Precursor Protein Secretases; Antineoplastic Agents, Phytogenic; Apoptosis; Caspases; Cell Line, Tumor; Dipeptides; Drug Resistance; Drug Synergism; Humans; Membrane Potential, Mitochondrial; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Receptors, Notch; Vincristine