Centrosomal Localization of RXRα Promotes PLK1 Activation and Mitotic Progression and Constitutes a Tumor Vulnerability

Dynamic heterogeneity towards drug resistance in AML cells is primarily driven by epigenomic mechanism unveiled by multi-omics analysis

INTRODUCTION

Acute myeloid leukemia (AML) is a hematologic malignancy characterized by aggressive proliferation and chemoresistance, leading to poor patient outcomes. Despite advances in chemotherapy, resistance mechanisms remain inadequately understood, particularly at the cellular and molecular level.

OBJECTIVES

This study aims to elucidate the cellular and molecular mechanisms underlying drug resistance in AML cells.

METHODS

A multi-omics approach was employed, integrating single-cell RNA sequencing (scRNA-seq), chromatin accessibility profiling (scATAC-seq), DNA methylation analysis, and whole-exome sequencing (WES). AML cell lines (KG-1a, Kasumi-1, and HL-60) were treated with standard chemotherapeutic agents, including cytarabine (Ara-C), daunorubicin (DNR), azacitidine (AZA), and decitabine (DEC). Additionally, we developed a novel multiplexed scRNA-seq strategy, NAMUL-seq, to enhance the efficiency and scalability of single-cell transcriptomic research.

RESULTS

We observed substantial cellular heterogeneity and dynamic transcriptomic trajectories in AML cells subjected to various treatments, uncovering a tendency for reprogramming towards a more stem-like state. Notably, Ara-C-resistant KG-1a cells predominantly originated from G2/M phase subpopulations, suggesting a resistance mechanism linked to specific cell cycle stages. Our findings further indicate that rapid Ara-C resistance is primarily driven by epigenomic changes, including alterations in DNA methylation, chromatin architecture, and transcription factor activity, whereas exonic mutations played a minimal role.

CONCLUSION

This study demonstrates that AML drug resistance is predominantly driven by epigenomic mechanisms rather than genetic mutations. This study provides a detailed cellular and molecular characterization of AML drug response and resistance, identifying potential therapeutic targets and laying the groundwork for future efforts to overcome chemoresistance.

Emerging Roles for Transcription Factors During Mitosis

The genome is dynamically reorganized, partitioned, and divided during mitosis. Despite their role in organizing interphase chromatin, transcription factors were largely believed to be mitotic spectators evicted from chromatin during mitosis, only able to reestablish their position on DNA upon entry into G1. However, a panoply of evidence now contradicts this early belief. Numerous transcription factors are now known to remain active during mitosis to achieve diverse purposes, including chromosome condensation, regulation of the centromere/kinetochore function, and control of centrosome homeostasis. Inactivation of transcription factors during mitosis results in chromosome segregation errors, key features of cancer. Moreover, active transcription and the production of centromere-derived transcripts during mitosis are also known to play key roles in maintaining chromosomal stability. Finally, many transcription factors are associated with chromosomal instability through poorly defined mechanisms. Herein, we will review the emerging roles of transcription factors and transcription during mitosis with a focus on their role in promoting the faithful segregation of sister chromatids.

Halogenated retinoid derivatives as dual RARα and RXRα modulators for treating acute promyelocytic leukemia cells

Acute promyelocytic leukemia (APL), a distinctive subtype of acute myeloid leukemia (AML), is characterized by the t(15; 17) translocation forming the PML-RARα fusion protein. Recent studies have revealed a crucial role of retinoid X receptor α (RXRα) in PML-RARα's tumorigenesis. This necessitates the development of dual RARα and RXRα targeting compounds for treating APL. Here, we developed a pair of brominated retinoid isomers, 5a and 5b, exhibiting RARα agonistic selectivity among the RAR subtypes and RXRα partial agonistic activities. In the treatment of APL cells, low doses (RARα activation range) of 5a and 5b degrade PML-RARα and strongly induce differentiation, while higher doses (RXRα activation range) induce G2/M arrest and apoptosis in both all-trans retinoic acid (ATRA)-sensitive and resistant cells. We replaced the bromine in 5a with chlorine or iodine to obtain compounds 7 or 8a. Interestingly, the chlorinated compound 7 tends to activate RXRα and induce G2/M arrest and apoptosis, while the iodinated compound 8a tends to activate RARα and induce differentiation. Together, our work underscores several advantages and characteristics of halogens in the rational design of RARα and RXRα ligands, offering three promising drug candidates for treating both ATRA-sensitive and resistant APL.

The regulatory role of mitotic catastrophe in hepatocellular carcinoma drug resistance mechanisms and its therapeutic potential

This review focuses on the role and underlying mechanisms of mitotic catastrophe (MC) in the regulation of drug resistance in hepatocellular carcinoma (HCC). HCC is one of the leading causes of cancer-related mortality worldwide, posing significant treatment challenges due to its high recurrence rates and drug resistance. Research suggests that MC, as a mechanism of cell death, plays a crucial role in enhancing the efficacy of HCC treatment by disrupting the replication and division mechanisms of tumor cells. The present review summarizes the molecular mechanisms of MC and its role in HCC drug resistance and explores the potential of combining MC with existing cancer therapies to improve treatment outcomes. Future research should focus on the in-depth elucidation of the molecular mechanisms of MC and its application in HCC therapy, providing new insights for the development of more effective treatments.

Implications of GPIIB-IIIA Integrin and Liver X Receptor in Platelet-Induced Compression of Ovarian Cancer Multi-Cellular Spheroids

Background: Platelets have been shown to promote ovarian cancer; however, the mechanism is poorly understood. Previously, we demonstrated that platelets reduce the size and increase the density of multi-cellular ovarian cancer spheroids in cell cultures. The objectives of this study were to determine if platelet inhibitors could counteract these effects, and to explore the mechanisms involved. Methods: FDA-approved platelet inhibitors were screened for their abilities to alter platelet effects on ovarian cancer spheroids. Mass spectrometry was used to identify proteins significantly altered in cancer cells upon exposure to platelets. The effects of platelets and/or liver x receptor agonists or antagonists on LXR activity were measured using ES-2 ovarian cancer cells transduced with an LXR-reporter vector. Results: Eptifibatide, a GPIIB-IIIA integrin inhibitor, and dipyridamole, an adenosine reuptake inhibitor, reduced and enhanced platelet effects on ovarian cancer spheroids, respectively. Proteomic studies identified the LXR/RXR and integrin pathways as mediators of platelet effects on ovarian cancer, and downstream effectors of eptifibatide. Conclusions: Integrin pathways and their downstream LXR/RXR effectors are implicated in how platelets alter ovarian cancer spheroid morphology. These results support studying eptifibatide and LXR/RXR agonists as candidate drugs for repurposing as therapeutic strategies to counteract platelet promotion of ovarian cancer.

Discovery of bipyridine amide derivatives targeting pRXRα-PLK1 interaction for anticancer therapy

Retinoid X receptor alpha (RXRα) is an important therapeutic target of cancer. Recently, small molecules (e.g.,XS-060 and its derivatives), which can significantly induce RXRα-dependent mitotic arrest by inhibiting pRXRα-PLK1 interaction, have been demonstrated as excellent anticancer agents. To further obtain novel RXR-targeted antimitotic agents with excellent bioactivity and drug-like properties, we herein synthesized two new series of bipyridine amide derivatives with XS-060 as the lead compound. In the reporter gene assay, most synthesized compounds showed antagonistic activity against RXRα. The most active compound, bipyridine amide B9 (BPA-B9), showed better activity than XS-060, with excellent RXRα-binding affinity (KD = 39.29 ± 1.12 nM) and anti-proliferative activity against MDA-MB-231 (IC50 = 16 nM, SI > 3). Besides, a docking study revealed a proper fitting of BPA-B9 into the coactivator binding site of RXRα, rationalizing its potent antagonistic effect on RXRα transactivation. Further, the mechanism studies revealed that the anticancer activity of BPA-B9 was dependent on its cellular RXRα-targeted mechanism, such as inhibiting pRXRα-PLK1 interaction and inducing RXRα-dependent mitotic arrest. Besides, BPA-B9 displayed better pharmacokinetics than the lead XS-060. Further, animal assays indicated BPA-B9 had significant anticancer efficacy in vivo with no considerable side effects. Together, our study reveals a novel RXRα ligand BPA-B9 targeting the pRXRα-PLK1 interaction, with great potential as a promising anticancer drug candidate for further development.

Unprecedented Monoterpenoid Polyprenylated Acylphloroglucinols with a Rare 6/6/5/4 Tetracyclic Core, Enhanced MCF-7 Cells' Sensitivity to Camptothecin by Inhibiting the DNA Damage Response

(±)-Hypersines A-C (1-3), the three pairs of enantiomerically pure monoterpenoid polyprenylated acylphloroglucinols with an unprecedented 6/6/5/4 fused ring system, were isolated from Hypericum elodeoides. Their structures, including absolute configurations, were elucidated by comprehensive spectroscopic data, single-crystal X-ray diffraction, and quantum chemical calculations. The plausible, biosynthetic pathway of 1-3 was proposed. Moreover, the bioactivity evaluation indicated that 1a might be a novel DNA damage response inhibitor, and could enhance MCF-7 cell sensitivity to the anticancer agent, camptothecin.

Protocol to identify centrosome-associated transcription factors during mitosis in mammalian cell lines

During eukaryotic cell mitosis, the nuclear envelope disintegrates and transcription factors are dissociated from condensed chromosomes. Here, we describe a protocol to study centrosomal translocation of nuclear receptor RXRα. We detail procedures for HeLa cell synchronization followed by immunofluorescence, in situ proximity ligation assay, and centrosome isolation. This protocol can be used to identify other transcription factors associated with the centrosome or other subcellular structures during mitotic progression.

For complete details on the use and execution of this protocol, please refer to Xie et al. (2020)

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Complementary approaches to study RXRα translocation to the centrosome during mitosis

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In situ PLA protocol to study centrosomal localization and action of RXRα

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Applicable for studying other transcription factors during mitosis

Moonlighting at the Centrosome: RXRα Turns to Plk1

One of the hardest working mitotic proteins, Polo-like kinase 1 (PLK1), functions at mitotic entry, cytokinesis, and many steps in between. In this issue, Xie et al. (2020) describe a centrosome-specific interaction between PLK1 and Retinoid X Receptor-α and they test selective inhibition of this interaction as an anti-mitotic cancer therapy.