A Temporal PROTAC Cocktail-Mediated Sequential Degradation of AURKA Abrogates Acute Myeloid Leukemia Stem Cells

Research progress on the relationship between AURKA and tumorigenesis: the neglected nuclear function of AURKA

AURKA is a threonine or serine kinase that needs to be activated by TPX2, Bora and other factors. AURKA is located on chromosome 20 and is amplified or overexpressed in many human cancers, such as breast cancer. AURKA regulates some basic cellular processes, and this regulation is realized via the phosphorylation of downstream substrates. AURKA can function in either the cytoplasm or the nucleus. It can promote the transcription and expression of oncogenes together with other transcription factors in the nucleus, including FoxM1, C-Myc, and NF-κB. In addition, it also sustains carcinogenic signaling, such as N-Myc and Wnt signaling. This article will focus on the role of AURKA in the nucleus and its carcinogenic characteristics that are independent of its kinase activity to provide a theoretical explanation for mechanisms of resistance to kinase inhibitors and a reference for future research on targeted inhibitors.

The impact of E3 ligase choice on PROTAC effectiveness in protein kinase degradation

Proteolysis targeting chimera (PROTACs) provide a novel therapeutic approach that is revolutionizing drug discovery. The success of PROTACs largely depends on the combination of their three fragments: E3 ligase ligand, linker and protein of interest (POI)-targeting ligand. We summarize the pivotal significance of the precise combination of the E3 ligase ligand with the POI-recruiting warhead, which is crucial for the successful execution of cellular processes and achieving the desired outcomes. Therefore, the key to our selection was the use of at least two ligands recruiting two different ligases. This approach enables a direct comparison of the impacts of the specific ligases on target degradation.

Discovery of a Novel Orally Bioavailable FLT3-PROTAC Degrader for Efficient Treatment of Acute Myeloid Leukemia and Overcoming Resistance of FLT3 Inhibitors

Fms-like tyrosine receptor kinase 3 (FLT3) proteolysis-targeting chimeras (PROTACs) represent a promising approach to eliminate the resistance of FLT3 inhibitors. However, due to the poor druggability of PROTACs, the development of orally bioavailable FLT3-PROTACs faces great challenges. Herein, a novel orally bioavailable FLT3-ITD degrader A20 with excellent pharmacokinetic properties was discovered through reasonable design. A20 selectively inhibited the proliferation of FLT3-ITD mutant acute myeloid leukemia (AML) cells and potently induced FLT3-ITD degradation through the ubiquitin-proteasome system. Notably, oral administration of A20 resulted in complete tumor regression on subcutaneous AML xenograft models. Furthermore, on systemic AML xenograft models, A20 could completely eliminate the CD45+CD33+ human leukemic cells in murine and significantly prolonged the survival time of mice. Most importantly, A20 exerted significantly improved antiproliferative activity against drug-resistant AML cells compared to existing FLT3 inhibitors. These findings suggested that A20 could serve as a promising drug candidate for relapsed or refractory AML.

Cooperatively designed aptamer-PROTACs for spatioselective degradation of nucleocytoplasmic shuttling protein for enhanced combinational therapy

Nucleocytoplasmic shuttling proteins (NSPs) have emerged as a promising class of therapeutic targets for many diseases. However, most NSPs-based therapies largely rely on small-molecule inhibitors with limited efficacy and off-target effects. Inspired by proteolysis targeting chimera (PROTAC) technology, we report a new archetype of PROTAC (PS-ApTCs) by introducing a phosphorothioate-modified aptamer to a CRBN ligand, realizing tumor-targeting and spatioselective degradation of NSPs with improved efficacy. Using nucleolin as a model, we demonstrate that PS-ApTCs is capable of effectively degrading nucleolin in the target cell membrane and cytoplasm but not in the nucleus, through the disruption of nucleocytoplasmic shuttling. Moreover, PS-ApTCs exhibits superior antiproliferation, pro-apoptotic, and cell cycle arrest potencies. Importantly, we demonstrate that a combination of PS-ApTCs-mediated nucleolin degradation with aptamer-drug conjugate-based chemotherapy enables a synergistic effect on tumor inhibition. Collectively, PS-ApTCs could expand the PROTAC toolbox to more targets in subcellular localization and accelerate the discovery of new combinational therapeutic approaches.

Selective degradation of BRD4 suppresses lung cancer cell proliferation using GSH-responsive PROTAC precursors

BRD4,as a transcriptional and epigenetic regulator to mediate cellular functions, plays an important role in cancer development.Targeting BRD4 with conventional inhibitors in cancer therapy requires high doses, which often leads to off-target and adverse effects. BRD4-targeted proteolysis-targeting chimeras (PROTACs) can catalytically degrade BRD4 utilizing the endogenous proteasome system, and exhibit promising anti-tumor activity. However, most of the developed PROTACs are non-cancer specific and relatively toxic towards normal cells, limiting their practical applications in cancer treatment. By taking advantage of higher glutathione (GSH) levels in cancer cells than that in normal cells, we developed several GSH-responsive PROTAC precursors 1a-c via the attachment of a GSH-trigger unit on the hydroxyl group of the VHL (von Hippel-Lindau) ligand for the recruitment of E3 ligase. Among the precursors, 1a can be efficiently activated by the innately higher concentrations of GSH in lung cancer cells (A549 and H1299) to release active PROTAC 1, degrading intracellular BRD4 and resulting in cytotoxicity, which is confirmed by mechanistic investigation. On the other hand, 1a cannot be efficiently triggered in normal lung cells (WI38 and HULEC-5a) containing lower levels of GSH, therefore reducing the adverse effects on normal cells. This work provides an alternative proof of concept approach for developing stimuli-responsive PROTAC precursors, and affords a novel insight to improve the selectivity and minimize the adverse effects of current PROTACs, hence enhancing their clinical potential.

Chebulagic acid suppresses gastric cancer by inhibiting the AURKA/β-catenin/Wnt pathway

Gastric cancer (GC) is a prevalent malignant neoplasm that poses a serious threat to human health. Overexpression of Aurora A (AURKA) is frequently associated with the self-renewal and tumorigenicity of various cancers. Chebulagic acid (CA) has been examined as a potential tumor suppressor based on its ability against numerous tumor biological activities. However, the possible mechanisms of CA inhibition of the progression of GC by mediating the AURKA/β-catenin/Wnt signaling pathway have not been investigated. The present study investigated the level of AURKA expression in GC. We further examined the effect of CA on cell proliferation, migration, and apoptosis in the MKN1 and NUGC3 GC cell lines, and its efficacy in suppressing tumor growth was assessed in tumor bearing mice model. We demonstrated that AURKA was highly expressed in GC and associated with poor prognosis. We demonstrated that treatment with CA significantly inhibited the proliferation and migration of GC cells and induced apoptosis. Compared to the vehicle group, CA treatment severely diminished the volume and weight and the metastasis of tumors. CA also inhibited the expression of AURKA and the AURKA/β-catenin/Wnt signaling pathway in vitro and in vivo. Collectively, the present results demonstrated that high expression of AURKA may be an independent factor of poor prognosis in patients with GC, and CA significantly suppressed the tumor biological functions of GC and inhibited the AURKA/β-catenin/Wnt pathway.