Daniel Herranz, PharmD, Ph.D., Assistant Professor in the Department of Pharmacology at the Robert Wood Johnson Medical School & Resident Member at Rutgers Cancer Institute of New Jersey speaks about the ASH 2021 Abstract 2221 Sirt1 Is a Novel Therapeutic Target in T-ALL.
Link to Abstract:
https://ash.confex.com/ash/2021/webprogram/Paper153950.html
T-cell Acute Lymphoblastic Leukemia (T-ALL) is leukemia that affects both children and adults. Despite this, 20 percent to 50 percent of individuals develop initial resistance or relapse after treatment and eventually succumb to their illness. Because more than 60% of T-ALL individuals have to activate mutations in the NOTCH1 gene, abnormal NOTCH1 signaling plays a key role in the disease’s development. In this regard, small-molecule -secretase inhibitors (GSIs) are being explored in clinical trials for the treatment of relapsed and refractory T-ALL. GSIs efficiently block NOTCH1 activation by inhibiting a crucial intramembrane proteolytic cleavage necessary for NOTCH1 signaling. However, limited and delayed therapeutic response to anti-NOTCH1 therapy in T-ALL has slowed their clinical development, highlighting the need to explore additional therapeutic targets and create more effective medications for the treatment of this disease. The relevance of NOTCH1-driven metabolic pathways in the response to anti-NOTCH1 treatments has previously been established (gamma-secretase inhibitors, GSIs). Furthermore, epigenetic plasticity has been postulated as a mediator of GSI resistance. As a result, we hypothesized that master regulators of NOTCH1-induced transformation could be central regulators that govern both the metabolic and epigenetic status of cells. Indeed, the SIRT1 histone deacetylase, a major epigenetic and metabolic regulator has been identified as a significant role in T-ALL by our findings. SIRT1 was shown to be significantly upregulated in T-ALL patients when gene expression profiling data were analyzed. When compared to the normal human thymus, SIRT1 protein levels are consistently elevated in T-ALL cells. Furthermore, we identified a distal enhancer of Sirt1 that is bound and controlled by NOTCH1, which may help explain the broad overexpression of Sirt1 reported in T-ALL patients, using a combination of GSI-washout assays, epigenetic profiling, and CRISPR/Cas9-induced experiments. Next, we created NOTCH1-driven primary T-ALLs from diverse Sirt1 genetic backgrounds to formally investigate the effects of Sirt1 on T-cell transformation. In this context, our findings show that Sirt1 genetic overexpression accelerates NOTCH1-induced T-ALL kinetics and enhances GSI resistance in T-ALL in vivo in a deacetylase-dependent way. T-ALL formation is delayed and disease penetrance is reduced when Sirt1 is lost in the germline. In T-ALL cell lines in vitro, pharmacological inhibition of SIRT1 with EX-527 has anti-leukemic and synergistic effects with NOTCH1 inhibition. Finally, genetic deletion of Sirt1 in primary isogenic Sirt1 conditional knockout leukemias results in significant and highly synergistic anti-leukemic effects in vivo when combined with GSI treatment. Acute deletion of Sirt1 causes hyperacetylation of Kat7 and Brd1, which are both members of a histone acetyltransferase complex, according to acetyl-proteomics investigations. Sirt1 deficiency causes worldwide epigenetic alterations, including lower levels of H4K12ac, a Kat7-target mark. Furthermore, gene expression profile analysis following Sirt1 deletion in leukemia in vivo revealed a wide range of transcriptional alterations. Gene-set enrichment analysis revealed that the transcriptional signature resulting from Sirt1 loss is highly correlated with that resulting from Kat7 loss, implying that Sirt1 loss causes Kat7 hyperacetylation, which makes it less active. Finally, our gene expression studies indicated a significant block in mTOR signaling, implying that when Sirt1 is lost, leukemia cells experience a metabolic crisis. Acute Sirt1 loss consistently causes significant global metabolic alterations in glycolysis, glutaminolysis, and TCA, as well as AMPK activation, culminating in cytotoxic consequences. Overall, our findings show that Sirt1 plays an oncogenic role in T-ALL development and progression, that Sirt1 helps to mediate resistance to anti-NOTCH1 therapies, that an unique Notch1-Sirt1-Kat7 link exists, and that Sirt1 represents a novel therapeutic target for T-ALL treatment.