Abstract 2436: The multi-faceted Integrator complex in Notch-driven esophageal cancer

Esophageal adenocarcinoma (EAC) is an aggressive type of cancer with a 5-year survival rate of less than 20%, which underscores the urgent need for new and effective targeted therapies. Treatment failures are often associated with activated Notch signaling and more than 70% of EAC cases possess aberrantly activated Notch. Recently, we identified the Integrator complex (INT), a multi-subunit assembly, as a new co-activator of Notch. In general transcription, INT is known to regulate RNAPII activity. Our previous study showed that INT is important in EAC. The INT complex initiates Notch-mediated transcription via RNAPII activation, and it is required for cell growth and proliferation in EAC. INT is also involved in cell cycle regulation and apoptosis. However, the functions of various INT subunits in EAC and their importance in Notch signaling remain unknown. Here, we investigate the importance of distinct INT subunits in Notch-mediated transcription as well as EAC tumor cell viability, growth and proliferation. Furthermore, we examine whether INT knockdown sensitizes EAC to the treatments with anti-cancer compounds.

We evaluated the depletion effects of several INT subunits in EAC using RNA interference and various assays. All gene knockdowns were confirmed by western blotting and/or RT-qPCR. When we examined the depletion effects of INT in Notch-driven EAC, we observed that the knockdown of some but not all of the INT subunits decreased the expression of Notch target genes as determined by RT-qPCR. This indicates the importance of these specific INT subunits in Notch signaling. We further evaluated the knockdown effects on cell viability, growth and proliferation utilizing a combination of flow cytometry, western blotting, CCK8 and colony formation assays. We observed a decrease in cell viability and inhibition of cell growth and proliferation in EAC cells with the knockdown of specific but not all INT complex subunits. These results indicate that only specific INT subunits are important in Notch-dependent EAC, and these INT subunits may provide a potential therapeutic axis. Furthermore, we determined that the knockdown of INT sensitized EAC cells to other drug treatments exhibiting synergistic effects.

In conclusion, EAC is an aggressive type of cancer with overactivated Notch and poor clinical outcomes. Here, we determined that several subunits of the INT complex may present a therapeutic opportunity in Notch-driven EAC as these subunits are important in Notch-mediated gene expression, EAC cell viability, and cell growth and proliferation.

Citation Format: Elena Shersher, Annamil Alvarez-Trotta, Mohini Lahiry, Giulia Diluvio, Ramin Shiekhattar, Anthony J. Capobianco. The multi-faceted Integrator complex in Notch-driven esophageal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2436.

A novel chemical attack on Notch-mediated transcription by targeting the NACK ATPase

Notch activation complex kinase (NACK) is a component of the Notch transcriptional machinery critical for the Notch-mediated tumorigenesis. However, the mechanism through which NACK regulates Notch-mediated transcription is not well understood. Here, we demonstrate that NACK binds and hydrolyzes ATP and that only ATP-bound NACK can bind to the Notch ternary complex (NTC). Considering this, we sought to identify inhibitors of this ATP-dependent function and, using computational pipelines, discovered the first small-molecule inhibitor of NACK, Z271-0326, that directly blocks the activity of Notch-mediated transcription and shows potent antineoplastic activity in PDX mouse models. In conclusion, we have discovered the first inhibitor that holds promise for the efficacious treatment of Notch-driven cancers by blocking the Notch activity downstream of the NTC.

AMP- activated protein kinase (AMPK) promotes breast cancer stemness and drug resistance

Breast cancer stem cells (BCSCs) are a major cause of therapy resistance and tumour progression. Currently, their regulation is not entirely understood. Previous work from our laboratory demonstrated a context-specific pro-tumorigenic role for AMP-activated protein kinase (AMPK) under anchorage-deprivation and mammosphere formation, which are hallmarks of BCSCs. Therefore, we investigated the role of AMPK in the maintenance of BCSC state/function. AMPK depletion reduces serial sphere formation in vitro and tumour initiation in vivo. Intriguingly, tumour-derived cell analysis using stem cell markers and functional assays revealed that AMPK is required for the maintenance of BCSC populations in vivo. AMPK promotes the expression of stemness genes such as NANOG, SOX2 and BMI1 through the transcriptional upregulation of TWIST via promoter acetylation. Further, AMPK-driven stemness plays a critical role in doxorubicin resistance. Significantly, AMPK activity increased after chemotherapy in patient-derived tumour samples alongside an increase in stemness markers. Importantly, AMPK depletion sensitises mouse tumours to doxorubicin treatment. Our work indicates that targeting of AMPK in conjunction with regular chemotherapy is likely to reduce the stem cell pool and improve chemosensitivity in breast cancers.

Summary: AMPK inhibition in conjunction with regular chemotherapy is likely to reduce the stem cell pool and improve chemosensitivity and therapeutic outcomes in breast cancers.

NACK and INTEGRATOR act coordinately to activate Notch-mediated transcription in tumorigenesis

BACKGROUND

Notch signaling drives many aspects of neoplastic phenotype. Here, we report that the Integrator complex (INT) is a new component of the Notch transcriptional supercomplex. Together with Notch Activation Complex Kinase (NACK), INT activates Notch1 target genes by driving RNA polymerase II (RNAPII)-dependent transcription, leading to tumorigenesis.

METHODS

Size exclusion chromatography and CBF-1/RBPJ/Suppressor of Hairless/Lag-1 (CSL)-DNA affinity fast protein liquid chromatography (FPLC) was used to purify Notch/CSL-dependent complexes for liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Chromatin immunoprecipitation (ChIP) and quantitative polymerase chain reaction (qPCR) were performed to investigate transcriptional regulation of Notch target genes. Transfection of Notch Ternary Complex components into HEK293T cells was used as a recapitulation assay to study Notch-mediated transcriptional mechanisms. Gene knockdown was achieved via RNA interference and the effects of protein depletion on esophageal adenocarcinoma (EAC) proliferation were determined via a colony formation assay and murine xenografts. Western blotting was used to examine expression of INT subunits in EAC cells and evaluate apoptotic proteins upon INT subunit 11 knockdown (INTS11 KD). Gene KD effects were further explored via flow cytometry.

RESULTS

We identified the INT complex as part of the Notch transcriptional supercomplex. INT, together with NACK, activates Notch-mediated transcription. While NACK is required for the recruitment of RNAPII to a Notch-dependent promoter, the INT complex is essential for RNAPII phosphorylated at serine 5 (RNAPII-S5P), leading to transcriptional activation. Furthermore, INT subunits are overexpressed in EAC cells and INTS11 KD results in G2/M cell cycle arrest, apoptosis, and cell growth arrest in EAC.

CONCLUSIONS

This study identifies the INT complex as a novel co-factor in Notch-mediated transcription that together with NACK activates Notch target genes and leads to cancer cell proliferation. Video abstract.

Pharmacological Disruption of the Notch1 Transcriptional Complex Inhibits Tumor Growth by Selectively Targeting Cancer Stem Cells

In many human cancers, deregulation of the Notch pathway has been shown to play a role in the initiation and maintenance of the neoplastic phenotype. Aberrant Notch activity also plays a central role in the maintenance and survival of cancer stem cells (CSC), which underlie metastasis and resistance to therapy. For these reasons, inhibition of Notch signaling has become an exceedingly attractive target for cancer therapeutic development. However, attempts to develop Notch pathway-specific drugs have largely failed in the clinic, in part due to intestinal toxicity. Here, we report the discovery of NADI-351, the first specific small-molecule inhibitor of Notch1 transcriptional complexes. NADI-351 selectively disrupted Notch1 transcription complexes and reduced Notch1 recruitment to target genes. NADI-351 demonstrated robust antitumor activity without inducing intestinal toxicity in mouse models, and CSCs were ablated by NADI-351 treatment. Our study demonstrates that NADI-351 is an orally available and potent inhibitor of Notch1-mediated transcription that inhibits tumor growth with low toxicity, providing a potential therapeutic approach for improved cancer treatment. SIGNIFICANCE: This study showcases the first Notch1-selective inhibitor that suppresses tumor growth with limited toxicity by selectively ablating cancer stem cells.