Polo-like Kinase Research Articles

Polo-like Kinase 1 Inhibitors Demonstrate In Vitro and In Vivo Efficacy in Preclinical Models of Small Cell Lung Cancer

Polo-like Kinase 1 Inhibitors Demonstrate In Vitro and In Vivo Efficacy in Preclinical Models of Small Cell Lung Cancer

Abstract B015: PLK4 inhibition as a strategy to enhance non-small cell lung cancer radiosensitivity

Abstract Lung cancer is the leading cause of cancer-related mortality worldwide. Non-small cell lung cancer (NSCLC) is the most common subtype of lung cancer and comprises 85% of cases. Despite treatment advances, local control after curative-intent chemoradiation for NSCLC remains suboptimal. Polo-like kinase 4 (PLK4) is a serine-threonine kinase that plays a critical role in the regulation of centrosome duplication and cell cycle progression and is overexpressed in NSCLC, thus, making it a potential therapeutic target. CFI-400945 is an orally available PLK4 inhibitor currently undergoing clinical trial evaluation. As radiation causes cell death primarily by mitotic catastrophe, a process enhanced by alterations in centrosome amplification, we hypothesized that disruption of the mitotic machinery by inhibition of PLK4 would enhance the effects of radiation in NSCLC. PLK4 inhibition by CFI-400945 resulted in radiosensitization of NSCLC cell lines. In contrast, CFI-400945 had no effect on the radiosensitivity of normal lung fibroblasts. PLK4 inhibition did not affect cell-cycle phase distribution prior to radiation, but rather the combination of CFI-400945 and radiation resulted in increased G2/M cell cycle arrest, increased centrosome amplification, and a concomitant increase in cell death through mitotic catastrophe. Lastly, CFI-400945 treatment enhanced the radiation-induced tumor growth delay of NSCLC tumor xenografts. These data indicate that targeting PLK4 is a novel approach to enhance the radiation sensitivity of NSCLC in vitro and in vivo through potentiation of centrosome amplification and cell death through mitotic catastrophe. Citation Format: Irma G. Dominguez-Vigil, Kishore Banik, Marta John Baro, Joseph N. Contessa, Thomas J. Hayman. PLK4 inhibition as a strategy to enhance non-small cell lung cancer radiosensitivity. [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Targeted Therapies in Combination with Radiotherapy; 2025 Jan 26-29; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(2_Suppl):Abstract nr B015.

Abstract B024: CRISPR-Cas9 screening reveals a novel JAK1 dependent mechanism of radioresistance in head and neck squamous cell carcinoma

Abstract Head and Neck Squamous Cell Carcinoma (HNSCC) is the sixth most common cancer worldwide, and local failure of disease following treatment with radiation therapy remains a major challenge for improving patient outcomes. We therefore designed a CRISPR-Cas9 pooled genetic screen to identify signaling mechanisms that regulate HNSCC radiosensitivity. Using a kinome gRNA library (763 genes with 8 gRNAs each), Cal27 and Detroit562 cells were screened using fractionated exposure to ionizing radiation as a selection pressure. Deep sequencing results identified significant enrichment or depletion of gRNAs for DNA damage signaling (ATM and DNAPK) and NFKB signaling (IRAK4, IRAK1, IKKA, IKKB), pathways known to regulate cell survival after radiation. Surprisingly, the screen also identified significant depletion of Janus kinase signaling (JAK1 and TYK2) to be a cause of radiation resistance. Independent knockout (KO) of Janus Kinase 1 (JAK1) in both Cal27 and Detroit562 cells caused radioresistance in vitro and in vivo. JAK1 KO prolongs G2 cell cycle arrest in HNSCC after treatment with radiation or after thymidine synchronization. JAK1 KO cells also have enhanced Rad51 foci formation indicative of homologous recombination usage for DNA repair. Consistent with an enhanced mitotic arrest, JAK1 KO causes the appearance of cells with 4N and 8N DNA content after exposure to radiation as measured by flow cytometry with propidium iodide or following 5-ethynyl-2’deoxyuridine (EdU) labeling. HNSCC cells with JAK1 KO, or treated with the JAK1 specific inhibitor Abrocitinib, formed significantly fewer micronuclei after radiation treatment consistent with a reduction in mitotic errors. Consistent with these findings, live cell imaging demonstrated cells with JAK1 KO undergo fewer mitotic catastrophe events. Loss of JAK1 function did not alter CDK1, but delayed activation of Aurora Kinase A (AURKA) and Polo-like Kinase 1 (PLK1), identifying a cell cycle signaling pathway regulated by JAK1. Live cell imaging also showed a more than doubling of the time required from chromatin condensation to sister chromatid separation, suggesting an associated defect in kinetochore assembly. The effects of inhibiting Kif18a, a kinesin that regulates kinetochore tension, in combination with radiation was therefore tested. Kif18 inhibition significant radiosensitized JAK1 KO HNSCC in clonogenic survival and xenograft models. In summary we have elucidated a JAK1-dependent mechanism for the regulation of AURKA/PLK1 signaling, a protective G2 arrest, and radioresistance. Furthermore, we provide a mechanistic and targeted pharmacologic approach for overcoming therapeutic resistance and enhancing radiation therapy in HNSCC. Citation Format: Vanessa Kelley, Marta Baro, William Gasperi, Chatchai Phoomak, Hojin Lee, Joseph Contessa. CRISPR-Cas9 screening reveals a novel JAK1 dependent mechanism of radioresistance in head and neck squamous cell carcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Targeted Therapies in Combination with Radiotherapy; 2025 Jan 26-29; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(2_Suppl):Abstract nr B024.

Upregulation of phosphatase and tensin homolog deleted on chromosome ten inhibits lung cancer cell proliferation by suppressing the oncogene polo-like kinase 1 and inducing autophagy

Objective: Lung cancer is one of the main causes of cancer-related mortality globally, and it poses considerable therapeutic challenges. Polo-like kinase 1 (PLK1) exhibits upregulation in lung cancer, and PLK1 silencing promotes autophagy in lung cancer cells, which inhibits tumor progression. The phosphatase and tensin homolog deleted on chromosome ten (PTEN) acts as a tumor suppressor gene. This study aimed to investigate whether PTEN regulates autophagy and inhibits lung cancer-cell proliferation by suppressing PLK1. Material and Methods: In this study, we evaluated cell proliferation by silencing or overexpressing PLK1 and PTEN in A549 cells through 5-ethynyl-2'-deoxyuridine labeling and cloning experiments. The autophagy levels were detected through transmission electron microscopy, real-time quantitative polymerase chain reaction, and Western blot. Finally, the results of in vitro experiment were further verified using an in vivo xenograft tumor animal model. Results: The upregulation of PTEN suppressed PLK1 expression in lung cancer cells and reduced their proliferation rate. In addition, the overexpression of PTEN has been associated with the growth of lung cancer tumors. In parallel, the levels of autophagy of lung cancer cells rose in response to PTEN upregulation in vivo and in vitro. Conclusion: This study revealed that PTEN promotes the autophagy of lung cancer cells and inhibits cell proliferation and tumor growth by suppressing PLK1 expression. This finding provides a new strategy for lung cancer treatment by utilizing the autophagy-regulating effect of PTEN to inhibit lung cancer growth by targeting PLK1.

PLK3 weakens antioxidant defense and inhibits proliferation of porcine Leydig cells under oxidative stress

Aging is characterized by cellular degeneration and impaired physiological functions, leading to a decline in male sexual desire and reproductive capacity. Oxidative stress (OS) lead to testicular aging by impairing the male reproductive system, but the potential mechanisms remain unclear. In the present study, the functional status of testicular tissues from young and aged boars was compared, and the transcriptional responses of Leydig cells (LCs) to hydrogen peroxide (H2O2)-induced senescence were explored, revealing the role of OS in promoting aging of the male reproductive system. 601 differentially expressed genes (DEGs) associated with OS, cell cycle regulation, and intracellular processes were identified. These DEGs were significantly enriched in critical aging pathways, including the p53 signaling pathway, autophagy, and cellular senescence. Protein-protein interaction (PPI) network analysis unveiled 15 key genes related to cell cycle and DNA replication, with polo-like kinase 3 (PLK3) exhibiting increased expression under OS. In vitro, PLK3 knockdown significantly enhanced the viability and antioxidant capacity of LCs under OS. This study deepens our understanding of how LCs respond to OS and provides new therapeutic targets for enhancing cellular resistance to oxidative damage and promoting tissue health.

MYC and HSF1 Cooperate to Drive Sensitivity to Polo-like Kinase 1 Inhibitor Volasertib in High Grade Serous Ovarian Cancer.

Ovarian cancer is a deadly gynecological disease with frequent recurrence. Current treatments for patients include platinum-based therapy regimens with PARP inhibitors specific for HR-deficient high-grade serous ovarian cancers (HGSOCs). Despite initial effectiveness, patients inevitably develop disease progression as tumor cells acquire resistance. Toward the development of new therapeutic avenues, we describe a gene amplification involving both HSF1 and MYC, wherein these two genes are co-amplified in over 30% of HGSCO patients. We further found that HSF1 and MYC transcriptional activity was highly correlated in human HGSOC tumors and cell lines, suggesting they may cooperate in the disease. CUT&RUN for HSF1 and MYC revealed overlapping HSF1 and MYC binding throughout the genome. Moreover, binding peaks of both transcription factors in HGSOC cells were nearly identical, and a protein-protein interaction between HSF1 and MYC was detected, supporting molecular cooperation. Supporting a functional cooperation of these two transcription factors, growth of HGSOC cells with the co-amplification was dependent on both HSF1 and MYC. To identify a therapeutic target that could take advantage of this unique HSF1 and MYC dependency, polo-like kinase 1 (PLK1) was correlated with HSF1 and MYC in HGSOC specimens. Targeting PLK1 with volasertib revealed a greater than 200-fold increased potency in HSF1-MYC co-amplified HGSOC cells compared to those with wild-type HSF1 and MYC copy number. Although the success of volasertib and other PLK1 inhibitors in clinical trials has been modest, the current study suggests that targeting PLK1 in a precision medicine approach using HSF1-MYC co-amplification as a biomarker in HGSOC.

Polo-like kinase 2 ameliorates lipopolysaccharide-induced cardiac injury by blocking cardiomyocyte ferroptosis.

Polo-like kinase 2 (PLK2) is associated with cardiac fibrosis in patients with atrial fibrillation. However, the role of PLK2 in sepsis-induced cardiac injury has not been fully elucidated. We hypothesize that PLK2 may participate in the progression of sepsis-induced cardiac injury. We established a cardiac injury model in C57BL6 mice by injecting lipopolysaccharide (LPS). PLK2 was overexpressed in mice using an adeno-associated virus 9 vector. Cardiac function was evaluated using echocardiography 12 hours after the LPS injection. H9c2 cells were transfected with a PLK2 small interfering RNA. PLK2 was downregulated in the hearts of LPS-treated mice and LPS-stimulated H9c2 cardiomyocytes. Mice in the LPS group presented aggravated cardiac injury and a reduced survival rate with increased cardiac inflammatory responses and oxidative stress. Moreover, PLK2 relieved LPS-induced cardiac injury and increased the survival rate of the mice by weakening the inflammatory response and decreasing oxidative stress. Moreover, the LPS-induced increase in ferroptosis was inhibited by PLK2 overexpression.LPS caused an increase in inflammation and cell injury in H9c2 cardiomyocytes, and PLK2 silencing aggravated LPS-induced cell injury, inflammation, and oxidative stress. Furthermore, PLK2 overexpression increased the expression levels of the antiferroptotic proteins solute carrier family 7 member 11, glutathione peroxidase 4, and ferritin in heart tissue. PLK2 increased the nuclear NRF2 expression level. Moreover, the overexpression of PLK2 increased the phosphorylation of glycogen synthase kinase 3β and promoted the nuclear translocation of NRF2. NRF2 overexpression relieved cardiac injury in mice induced with LPS. However, NRF2 mitigated the deteriorating effects of PLK2 knockdown in the mouse heart. PLK2 ameliorated LPS-induced cardiac injury by blocking cardiomyocyte ferroptosis through NRF2 regulation.

AURKA/PLK1/CDC25C Axis as a Novel Therapeutic Target in INI1-Deficient Epithelioid Sarcoma.

Effective therapeutic strategies for epithelioid sarcoma (EpS), a high-grade soft tissue sarcoma characterized by loss of integrase interactor 1 (INI1), have not yet been developed. The present study therefore investigated the association between INI1 loss and upregulation of the aurora kinase A (AURKA)/polo-like kinase 1 (PLK1)/cell division cycle 25C (CDC25C) axis, as well as the therapeutic relevance of this axis in EpS. Notably, our findings showed that the reintroduction of INI1 in VA-ES-BJ cells significantly reduced proliferation, mitigated tumorigenicity, and negatively regulated the expression of AURKA and its downstream effectors, as well as the activation of PLK1 and CDC25C. These results suggest that INI1 deficiency enhanced EpS growth by upregulating the AURKA/PLK1/CDC25C axis. AURKA silencing using siRNAs inhibited VA-ES-BJ and Asra-EPS cell proliferation by inactivating PLK1 and CDC25C. Alisertib, a selective AURKA inhibitor, exerted markedly greater antiproliferative effects on EpS cells than on normal human dermal fibroblasts, and these effects were dependent on INI1 deficiency. Inhibition of AURKA activity by alisertib induced G2/M cell cycle arrest and apoptosis via the inactivation of AURKA downstream effectors in EpS cells. Alisertib also significantly decreased VA-ES-BJ xenograft tumor growth. Taken together, our findings revealed that INI1 loss in EpS cells enhances the expression of AURKA and its downstream effectors and persistently activates PLK1 and CDC25C mediated by AURKA, making the cells reliant on the AURKA/PLK1/CDC25C axis. Therefore, the AURKA/PLK1/CDC25C axis activated by INI1 deficiency could serve as a novel therapeutic target for this devastating disease.

ERK activation dynamics in maturing oocyte controls embryonic nuclear divisions in Caenorhabditis elegans.

ERK activity oscillates between sustained activation during oocyte formation and transient inactivation during oocyte maturation, fertilization, and early embryogenesis. Consequences of ectopic ERK activity upon oocyte maturation and in early embryogenesis are unknown. We show, in Caenorhabditis elegans, that ectopic ERK activity upon oocyte maturation (metaphase I oocytes) results in embryos with abnormalities in nuclear divisions leading to embryonic death. We uncover that ERK directly phosphorylates Polo-like kinase I (PLK-1), on Serine 404, to inhibit nuclear envelope breakdown (NEBD) in early embryogenesis. The RAS/ERK/PLK-1 pathway poisons zygotic NEBD and inhibits the merging of parental genomes, underlining the importance of turning off ERK prior to embryogenesis. Given the conserved nature of both ERK signaling to oocyte development and PLK1 to embryonic divisions, this work has implications for women undergoing invitro fertilization (IVF) where ectopic ERK activation during superovulation through hormonal stimulation may diminish oocyte quality and influence zygotic development.

Onvansertib and Navitoclax Combination as a New Therapeutic Option for Mucinous Ovarian Carcinoma.

Mucinous epithelial ovarian cancer (mEOC) is a rare subtype of epithelial ovarian cancer, characterized by poor responses to standard platinum-based chemotherapy. Polo-like kinase 1 (PLK1) is a key regulator of mitosis and cell cycle progression and its inhibition has been recently identified as a target in mEOC. In this study, we aimed to identify further therapeutic targets in mEOC using a CRISPR/Cas9 library targeting 3015 genes, with and without treatment with onvansertib, a PLK1 inhibitor. We identified twelve genes associated with cell survival (ZC2HC1C, RPA2, KIN17, TUBG1, SMC2, CDC26, CDC42, HOXA9, TAF10, SENP1, MRPS31, and COPS2) and three genes (JUND, CARD9, and BCL2L2) in synthetic lethality with onvansertib treatment. We validated that SENP1 downregulation is important for the growth of mEOC cells through esiRNA interference and the use of a pharmacological inhibitor Momordin Ic. The downregulation of CARD9 and BCL2L2 combined with subtoxic doses of onvansertib interfered with mEOC cell growth. Interestingly, the combination of navitoclax, an inhibitor of BcL2 family members including BCL2L2, was synergistic in all four of the mEOC cell lines tested and substantially induced cell death through apoptosis. These data support the use of a combination of navitoclax and onvansertib as a new therapeutic strategy for mEOC.

Isolation, cytotoxicity evaluation, and molecular docking of 3,4,3’-tri-O-methylflavellagic acid from Anogeissus leiocarpus (DC.) Guill. & Perr. root

Cancer kills about 10 million people every year. Medicinal plants remain a major source in the global search for anticancer drugs. In this study, 3,4,3’-tri-O-methylflavellagic acid (MFA) was isolated from the methanol root extract of Anogeissus leiocarpus. The structure was determined by 1D- and 2D-NMR data. The cytotoxic effects of MFA were evaluated against human breast (MCF-7), colorectal (Caco-2), and cervical (HeLa) cancer cell lines using the 3-[4,5-dimethylthiazole-2-yl] 3,5-diphenyltetrazolium bromide assay. A multi-protein target screening via molecular docking was conducted against ten cancer-related proteins, and ADMET properties were evaluated. MFA exhibited the most potent activity against Caco-2 (IC50: 46.75 ± 13.00 µM). Molecular docking analysis showed that MFA had a strong binding affinity for the colchicine-binding site of αβ-tubulin and polo-like kinase-1 (binding energies: −8.5 and −8.4 kcal/mol, respectively). MFA also satisfied the Lipinski’s Rule of Five. MFA could, therefore, potentially serve as a scaffold for developing new anticancer molecules.

The Role of Polo-Like Kinase 1 (PLK1) O-GlcNAcylation in Mitosis.

Polo-like kinase 1 (PLK1) is a crucial mitotic kinase that is implicated in various aspects of cell cycle. Many post-translational modifications have been identified on PLK1 to regulate its activation, stability, and localization. PLK1 has been shown previously to colocalize with the O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT), and OGT regulates PLK1 stability. In our recent work, we show that PLK1 is O-GlcNAcylated by click chemistry. Using stepped collisional energy/higher energy collision dissociation mass spectrometry, we mapped the PLK1 O-GlcNAc site to be T291. We further utilized fluorescent activated cell sorting and time-lapse microscopy to assess the mitotic defects of PLK1 O-GlcNAc mutants. In vivo studies in mouse xenograft demonstrated that it promoted uterine cancer tumorigenesis. In this chapter, we delineate the methodologies we used in studying PLK1 O-GlcNAcylation, including click chemistry, stepped collisional energy/higher energy collision dissociation mass spectrometry, fluorescent activated cell sorting, time-lapse microscopy, and mouse xenograft assays.

Time-Lapse Imaging to Analyze Cell Fate in Response to Antimitotics.

Time-lapse imaging is a powerful technique widely used in Cellular and Molecular Biology to capture and analyze the dynamic processes of living cells over specific time periods. Particularly, in the study of cell division, under normal conditions or after drug treatments, this methodology can provide essential data that is impossible to obtain from conventional cell-fixed-based assays. In the context of evaluating cell fate after antimitotic drug treatment, time-lapse imaging provides valuable insights into the mechanisms of action of these compounds. Antimitotic drugs belong to a class of anticancer compounds that interfere with mitosis by targeting microtubules or specific kinases and molecular motors involved in the mitotic apparatus. This chapter aims to highlight the significant advantage of using time-lapse microscopy to assess the effects of antimitotic drugs on cell behavior and fates. We describe the full protocol for time-lapse imaging, using the human lung adenocarcinoma A549 cell line as a model, after exposure to the antimitotic BI2536, a potent inhibitor of polo-like kinase 1 (PLK1). This description includes software for imaging acquisition and data analysis.

Knockdown of CNOT3, a subunit of the CCR4-NOT deadenylase complex, sensitizes A549 human non-small cell lung cancer cells to senescence-inducing stimuli.

Cellular senescence is an essentially irreversible cell cycle arrest associated with upregulated inflammatory responses that contribute to various pathological and physiological processes, including aging, cancer, and cancer prevention. However, the underlying mechanisms are not fully understood. Here, we show that the downregulation of CNOT3, a subunit of the CCR4-NOT complex that deadenylates mRNA poly(A) tails, promotes cellular senescence in subpopulation of A549 human non-small cell lung cancer cells. Previous work has shown that CNOT3 knockdown upregulates p21 (CDKN1A), a cyclin-dependent kinase inhibitor. Since p21 is one of the key regulators of cellular senescence, we hypothesized that CNOT3 downregulation might lead to cellular senescence. Indeed, CNOT3 knockdown upregulates several key cellular senescence hallmarks, including p53, senescence-associated β-galactosidase activity, and senescence-associated secretory phenotype in subpopulation of A549cell culture. The senescent cell hallmarks were more prominent in the culture after additional treatment with BI 2536, a polo-like kinase 1 inhibitor. These results suggest that CNOT3 downregulation followed by BI 2536 treatment upregulates the hallmarks of cellular senescence in A549cell culture.

Guanidyl-rich α-helical polypeptide enables efficient cytosolic pro-protein delivery and CRISPR-Cas9 genome editing.

Intracellular delivery of proteins has attracted significant interest in biological research and cancer treatment, yet it continues to face challenges due to the lack of effective delivery approaches. Herein, we developed an efficient strategy via cationic α-helical polypeptide-mediated anionic proprotein delivery. The protein was reversibly modified with adenosine triphosphate via dynamic covalent chemistry to prepare an anionic proprotein (A-protein) with abundant phosphate groups. A guanidyl-decorated α-helical polypeptide (LPP) was employed not only to encapsulate A-protein through electrostatic attraction and hydrogen bonding, forming stable nanocomplexes, but also to enhance cell membrane penetration due to its rigid α-helical conformation. Consequently, this strategy mediated the effective delivery of various proteins with different isoelectric points and molecular weights, including α-chymotrypsin, bovine serum albumin, ribonuclease A, cytochrome C, saporin, horseradish peroxidase, β-galactosidase, and anti-phospho-Akt, into cancer cells. More importantly, it enabled efficient delivery of CRISPR-Cas9 ribonucleoproteins to elicit robust polo-like kinase 1 genome editing for inhibiting cancer cell growth. This rationally designed protein delivery system may benefit the development of intracellular protein-based cancer therapy.

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

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

Polo-like Kinase 1 Expression as a Biomarker in Colorectal Cancer: A Retrospective Two-Center Study.

Background/Objectives: Early-onset colorectal cancer (EOCRC) is more frequently characterized by poorly differentiated, aggressive tumors, often diagnosed at advanced stages, and associated with worse prognoses. Despite these differences, current treatment guidelines do not distinguish between EOCRC and late-onset colorectal cancer (LOCRC). Elevated expression of polo-like kinase 1 (PLK-1) has been linked to advanced disease stages and poorer treatment outcomes, including resistance to both chemotherapy and radiotherapy. However, data on PLK-1 expression in EOCRC compared to LOCRC remain limited. Methods: Patients with sporadic CRC, aged >18 years, were included in this study. We categorized the patients into two groups: patients younger than 50 years, and those aged 50 years or older. Immunohistochemical staining was performed to assess PLK-1 expression. The aim of this study was to assess PLK-1 expression considering the age of the patients and its effects on overall survival (OS) and progression-free survival (PFS). Results: A total of 146 patients with metastatic colorectal cancer (mCRC) were included in this retrospective two-center study. Patients with low PLK-1 expression were older than patients with high PLK-1 expression (64 (49-71) years vs. 49 (42-67) years, p = 0.016). Multiple logistic regression confirmed that age is a significant predictor of PLK-1 expression, independent of the covariates (p = 0.036). The Kaplan-Meier analysis revealed no significant association between PLK-1 expression and PFS (p = 0.397) or OS (p = 0.448). Accordingly, Cox proportional hazards regression analysis showed no significant association between PLK-1 expression and OS (HR 1.20, 95% CI 0.73-1.96, p = 0.598) or PFS (HR 0.85, 95% CI 0.51-1.43, p = 0.611) when covariates were taken into account. Finally, no significant differences in PFS (p = 0.423) or OS (p = 0.104) were found between the age groups of interest. Conclusions: PLK-1 expression was not associated with survival or progression in EOCRC and LOCRC patients. Further research on these combinations is necessary, as well as the discovery of new potential targets for targeted therapy and the mechanisms of synergistic effects in tumors with PLK-1 overexpression.

PLK1 overexpression suppresses homologous recombination and confers cellular sensitivity to PARP inhibition

The overexpression of Polo-like kinase 1 (PLK1) is associated with poor clinical outcomes in various malignancies, making it an attractive target for anticancer therapies. Although recent studies suggest PLK1’s involvement in homologous recombination (HR), the impact of its overexpression on HR remains unclear. In this study, we investigated the effect of PLK1 overexpression on HR using bioinformatics and experimental approaches. Analyzing The Cancer Genome Atlas (TCGA) and Cancer Cell Line Encyclopedia (CCLE) datasets with the Homologous Recombination Deficiency (HRD) score, we found a positive correlation between PLK1 expression and HRD score, indicating that increased PLK1 expression suppresses HR. To validate these findings, we performed cell line-based experiments, demonstrating that PLK1 overexpression attenuates RAD51 focus formation and HR, as measured by ASHRA in T47D cells. Since HR-deficient cells are hypersensitive to PARP inhibitors, we further confirmed that PLK1 overexpression increases sensitivity to PARP inhibitors, both in CCLE dataset analysis and experiments using T47D cells. Additionally, we found that the effects of PLK1 overexpression on HR suppression and increased PARP inhibitor sensitivity were mitigated by either a PLK1 kinase inhibitor or the kinase-dead mutant [T210A]. This suggests that PLK1’s impact on HR and PARP inhibitor sensitivity is mediated through its kinase activity. Moreover, analysis of clinical ovarian cancer samples revealed that higher PLK1 expression correlates with increased sensitivity to PARP inhibitors. Our results suggest that PLK1 overexpression suppresses homologous recombination, leading to enhanced sensitivity to PARP inhibition, presenting a potential therapeutic strategy for targeting cancers with overexpression of PLK1.

PLK1 inhibition impairs erythroid differentiation

Polo-like kinase 1 (PLK1), a key regulator of the G2/M phase in mitosis, is frequently overexpressed in numerous tumors. Although PLK1 inhibitors have emerged as promising therapeutic agents for cancer, their use has been linked to significant anemia in a subset of patients, yet the underlying mechanisms remain poorly understood. In this study, we utilized an in vitro human umbilical cord blood-derived CD34+ cell-based erythroid differentiation system, alongside a murine model, to investigate the impact of PLK1 inhibitors on erythropoiesis. Our results indicate that PLK1 inhibitors, specifically GSK461364 and BI6727, significantly suppress the proliferation of erythroid cells, resulting in G2/M phase cell cycle arrest, increased apoptosis in erythroid cells, and the formation of abnormally nucleated late-stage erythroblasts. In vivo, administration of PLK1 inhibitors in mice induced severe anemia, as evidenced by a marked reduction in red blood cells and hemoglobin levels. More specifically, PLK1 inhibition impaired the differentiation and erythroid commitment of hematopoietic stem cells in the bone marrow, resulting in abnormal accumulation of BFU-E cells and reduced proliferation and differentiation of CFU-E, and a decrease in the number of terminal erythrocytes. Mechanistically, PLK1 inhibitors primarily induce apoptosis in erythroid cells by reducing Mitochondrial membrane potential and arresting the cell cycle at the G2/M phase. Overall, our findings underscore the critical role of PLK1 in erythropoiesis and shed light on the mechanisms underlying PLK1 inhibitor-induced anemia, providing essential guidance for developing strategies to prevent and manage anemia in clinical applications of PLK1-targeted therapies.

Internal feedback circuits among MEX-5, MEX-6, and PLK-1 maintain faithful patterning in the Caenorhabditis elegans embryo

Proteins become asymmetrically distributed in the one-cell Caenorhabditis elegans embryo thanks to reaction–diffusion mechanisms that are often entangled in complex feedback loops. Cortical polarity drives the enrichment of the RNA-binding proteins MEX-5 and MEX-6 in the anterior cytoplasm through concentration gradients. MEX-5 and MEX-6 promote the patterning of other cytoplasmic factors, including that of the anteriorly enriched mitotic polo-like kinase PLK-1, but also contribute to proper cortical polarity. The gradient of MEX-5 forms through a differential-diffusion mechanism. How MEX-6 establishes a gradient and how MEX-5 and MEX-6 regulate cortical polarity is not known. Here, we reveal that the two MEX proteins develop concentration asymmetries via similar mechanisms, but despite their strong sequence homology, they differ in terms of how their concentration gradients are regulated. We find that PLK-1 promotes the enrichment of MEX-5 and MEX-6 at the anterior through different circuits: PLK-1 influences the MEX-5 gradient indirectly by regulating cortical polarity while it modulates the formation of the gradient of MEX-6 through its physical interaction with the protein. We thus propose a model in which PLK-1 mediates protein circuitries between MEX-5, MEX-6, and cortical proteins to faithfully establish and maintain polarity.