Genetic enhancers of partial PLK1 inhibition reveal hypersensitivity to kinetochore perturbations

SKA1 promotes oncogenic properties in oral dysplasia and oral squamous cell carcinoma, and augments resistance to radiotherapy

Oral squamous cell carcinoma (OSCC) is a malignancy associated with high morbidity and mortality, yet treatment options are limited. In addition to genetic alterations, aberrant gene expression contributes to the pathology of malignant diseases. In the present study, we identified 629 genes consistently dysregulated between OSCC and normal oral mucosa across nine public gene expression datasets. Among them, mitosis-related genes were significantly enriched, including spindle and kinetochore-associated complex subunit 1 (SKA1), whose roles in OSCC had been studied only to a very limited extent. We show that SKA1 promoted proliferation and colony formation in 2D and 3D, shortened the duration of metaphase, and increased the migration of OSCC cell lines. In addition, high SKA1 expression enhanced radioresistance, a previously unknown effect of this gene, which was accompanied by a reduction of radiation-induced senescence. SKA1 was also upregulated in a subset of advanced oral premalignancies and promoted tumor-relevant properties in a corresponding cell line. Gene expression patterns evoked by SKA1 overexpression confirmed that this gene is able to advance properties required for both early and advanced stages of tumorigenesis. In summary, our data show that SKA1 contributes to malignant progression in OSCC and may be a useful marker of radioresistance in this disease.

Polo-like kinase inhibitors increase AAV production by halting cell cycle progression

Recombinant adeno-associated viruses (rAAVs) are commonly used in gene therapy for preclinical research and therapeutic applications. Despite the clinical efficacy of rAAVs, their manufacturing involves challenges in productivity and quality, leading to limited availability. In this study, we aimed to identify compounds that increase the capacity of cells to produce AAV9 with a high-throughput small-molecule screening strategy. With the Arrayed Targeted Library for AAV Screening platform, we screened a library of 3,300 small molecules and identified several targets, including cell cycle modulators, G protein-coupled receptor modulators, histone deacetylate inhibitors, Janus kinase inhibitors, and metabolic modulators. Most notably, we identified Polo-like kinase isoform 1 (PLK1) inhibitors as enhancers of adeno-associated virus (AAV) production. Inhibiting PLK1 with HMN-214 increased AAV production, which was largely consistent across HEK293 cell lines, vector payloads, and capsid serotypes. Using cell cycle and RNA-sequencing analysis, we showed that PLK1 inhibition halts cells in the G2/M phase and blocks their exit from the M to G1 phase. These findings support that inhibiting PLK1 may enhance AAV production and could be used to develop more cost-effective methods to manufacture AAV for gene therapies.

Mitochondrial signatures shape phenotype switching and apoptosis in response to PLK1 inhibitors

PLK1 inhibitors are emerging anticancer agents that are being tested as monotherapy and combination therapies for various cancers. Although PLK1 inhibition in experimental models has shown potent antitumor effects, translation to the clinic has been hampered by low antitumor activity and tumor relapse. Here, we report the identification of mitochondrial protein signatures that determine the sensitivity to approaches targeting PLK1 in human melanoma cell lines. In response to PLK1 inhibition or gene silencing, resistant cells adopt a pro-inflammatory and dedifferentiated phenotype, whereas sensitive cells undergo apoptosis. Mitochondrial DNA depletion and silencing of the ABCD1 transporter sensitize cells to PLK1 inhibition and attenuate the associated pro-inflammatory response. We also found that nonselective inhibitors of the p90 ribosomal S6 kinase (RSK) exert their antiproliferative and pro-inflammatory effects via PLK1 inhibition. Specific inhibition of RSK, on the other hand, is anti-inflammatory and promotes a program of antigen presentation. This study reveals the overlooked effects of PLK1 on phenotype switching and suggests that mitochondrial precision medicine can help improve the response to targeted therapies.

Chk2 sustains PLK1 activity in mitosis to ensure proper chromosome segregation

Polo-like kinase 1 (PLK1) protects against genome instability by ensuring timely and accurate mitotic cell division, and its activity is tightly regulated throughout the cell cycle. Although the pathways that initially activate PLK1 in G2 are well-characterized, the factors that directly regulate mitotic PLK1 remain poorly understood. Here, we identify that human PLK1 activity is sustained by the DNA damage response kinase Checkpoint kinase 2 (Chk2) in mitosis. Chk2 directly phosphorylates PLK1 T210, a residue on its T-loop whose phosphorylation is essential for full PLK1 kinase activity. Loss of Chk2-dependent PLK1 activity causes increased mitotic errors, including chromosome misalignment, chromosome missegregation, and cytokinetic defects. Moreover, Chk2 deficiency increases sensitivity to PLK1 inhibitors, suggesting that Chk2 status may be an informative biomarker for PLK1 inhibitor efficacy. This work demonstrates that Chk2 sustains mitotic PLK1 activity and protects genome stability through discrete functions in interphase DNA damage repair and mitotic chromosome segregation.

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.

Exploration of inhibitors targeting KIF18A with ploidy-specific lethality

Currently, various antimitotic inhibitors applied in tumor therapy. However, these inhibitors exhibit targeted toxicity to some extent. As a motor protein, kinesin family member 18A (KIF18A) is crucial to spindle formation and is associated with tumors exhibiting ploidy-specific characteristics such as chromosomal aneuploidy, whole-genome doubling (WGD), and chromosomal instability (CIN). Differing from traditional antimitotic targets, KIF18A exhibits tumor-specific selectivity. The functional loss or attenuation of KIF18A results in vulnerability of tumor cells with ploidy-specific characteristics, with lesser effects on diploid cells. Research on inhibitors targeting KIF18A with ploidy-specific lethality holds significant importance. This review provides a brief overview of the regulatory mechanisms of the ploidy-specific lethality target KIF18A and the research advancements in its inhibitors, aiming to facilitate the development of KIF18A inhibitors.

The two sides of chromosomal instability: drivers and brakes in cancer

Chromosomal instability (CIN) is a hallmark of cancer and is associated with tumor cell malignancy. CIN triggers a chain reaction in cells leading to chromosomal abnormalities, including deviations from the normal chromosome number or structural changes in chromosomes. CIN arises from errors in DNA replication and chromosome segregation during cell division, leading to the formation of cells with abnormal number and/or structure of chromosomes. Errors in DNA replication result from abnormal replication licensing as well as replication stress, such as double-strand breaks and stalled replication forks; meanwhile, errors in chromosome segregation stem from defects in chromosome segregation machinery, including centrosome amplification, erroneous microtubule-kinetochore attachments, spindle assembly checkpoint, or defective sister chromatids cohesion. In normal cells, CIN is deleterious and is associated with DNA damage, proteotoxic stress, metabolic alteration, cell cycle arrest, and senescence. Paradoxically, despite these negative consequences, CIN is one of the hallmarks of cancer found in over 90% of solid tumors and in blood cancers. Furthermore, CIN could endow tumors with enhanced adaptation capabilities due to increased intratumor heterogeneity, thereby facilitating adaptive resistance to therapies; however, excessive CIN could induce tumor cells death, leading to the "just-right" model for CIN in tumors. Elucidating the complex nature of CIN is crucial for understanding the dynamics of tumorigenesis and for developing effective anti-tumor treatments. This review provides an overview of causes and consequences of CIN, as well as the paradox of CIN, a phenomenon that continues to perplex researchers. Finally, this review explores the potential of CIN-based anti-tumor therapy.

Chk2 sustains PLK1 activity in mitosis to ensure proper chromosome segregation

Polo-like kinase 1 (PLK1) protects against genome instability by ensuring timely and accurate mitotic cell division. PLK1 activity is tightly regulated throughout the cell cycle. Although the pathways that initially activate PLK1 in G2 are well-characterized, the factors that directly regulate PLK1 in mitosis remain poorly understood. Here, we identify that human PLK1 activity is sustained by the DNA damage response kinase Checkpoint kinase 2 (Chk2) in mitosis. Chk2 directly phosphorylates PLK1 T210, a residue on its T-loop whose phosphorylation is essential for full PLK1 kinase activity. Loss of Chk2-dependent PLK1 activity causes increased mitotic errors, including chromosome misalignment, chromosome missegregation, and cytokinetic defects. Moreover, Chk2 deficiency increases sensitivity to PLK1 inhibitors, suggesting that Chk2 status may be an informative biomarker for PLK1 inhibitor efficacy. This work demonstrates that Chk2 sustains mitotic PLK1 activity and protects genome stability through discrete functions in interphase DNA damage repair and mitotic chromosome segregation.