Search Results (92)

Background/Objectives: Pancreatic ductal adenocarcinomas (PDACs) are lethal tumors exhibiting resistance to most cancer therapeutics, particularly DNA-damaging agents. The KRAS oncogene drives PDACs, and many of these tumors are addicted to it and its downstream effectors. One such effector is Rac1, a small GTPase involved in actin cytoskeleton remodeling and regulation of the DNA damage response. We previously showed that Rac1 inhibition blocks activation of ATM/Chk2 and ATR/Chk1 pathways in response to gamma rays, sensitizing PDAC cells to radiation. Methods: Western blot analyses were used to assess the impacts of Rac1 inhibition on the components of the ATR/Chk1 cascade. Results: Here, we show that Rac1 inhibition disrupts ATR/Chk1 signaling by promoting degradation of Claspin, a key component of the fork protection complex needed for the Ser345-phosphorylation of Chk1 by ATR. In PDACs and normal pancreatic ductal cells, Rac1 inhibition (via inhibitors or siRNA) decreased Claspin protein levels without affecting its mRNA, reflecting a >3-fold reduction in Claspin’s half-life. Claspin contains a phosphodegron recognized by SCF^βTrCP E3 ubiquitin ligase when phosphorylated at Ser30/Ser34, a process involving PLK1 kinase. In PDAC cells, Claspin degradation upon Rac1 inhibition required the proteasome and βTrCP1/2 proteins, and was blocked by the mutagenesis of Ser30/Ser34, but occurred independently of PLK1 activity. Although Rac1 inhibitors reduced Claspin in both normal and cancer cells, PDAC cells may be uniquely vulnerable due to elevated replication stress and greater reliance on ATR/Chk1. Accordingly, Claspin depletion sensitized PDAC cells but not normal cells to gamma rays, inducing apoptosis only in cancer cells. Conclusions: These findings identify Rac1 as a critical regulator of ATR/Chk1 signaling through stabilization of the fork protection protein Claspin. Rac1 inhibition promotes the βTrCP-dependent, proteasome-mediated degradation of Claspin via its phosphodegron, thereby impairing Chk1 activation in response to DNA damage. Full article

Background/Objectives. Breast cancer is the most frequently diagnosed cancer worldwide, with approximately 15% classified as Triple-Negative Breast Cancer (TNBC). TNBC is characterized by the absence of estrogen receptor (ER) and progesterone receptor (PR), and the lack of HER2 overexpression, limiting use of targeted therapies. Current TNBC treatment relies heavily on chemotherapy, most commonly taxanes including paclitaxel that stabilize microtubules, disrupt chromosome separation and induce apoptosis. TNBCs frequently develop chemoresistance after multiple treatment cycles, highlighting a critical unmet need for novel therapeutic strategies. This study addresses this challenge by targeting salt-inducible kinase 2 (SIK2), which is overexpressed in 85% of TNBCs compared to normal breast tissue. Methodes. In collaboration with Arrien Pharmaceuticals and Greenfire Biologics, we developed ARN-3261/GRN-300, a novel orally bioavailable SIK2 inhibitor and evaluated its ability to sensitize TNBC cells to paclitaxel in vitro and in vivo. Results. GRN-300 demonstrated strong synergy with paclitaxel in all eight TNBC cell lines tested, as indicated by favorable combination indices. In xenograft models, the combination therapy significantly enhanced tumor growth inhibition and prolonged survival compared to either agent alone. Mechanistic studies showed that GRN-300 disrupts the anaphase-promoting complex/cyclosome (APC/C) pathway by downregulating key mitotic regulators, including CDC27, CDK1, and PLK1, thereby potentiating G2/M cell cycle arrest and apoptosis. Conclusions. Together, these findings establish GRN-300 as a promising therapeutic agent that enhances paclitaxel efficacy through complementary disruption of mitotic regulatory pathways, providing strong preclinical rationale for clinical development in TNBC. Full article

Lung cancer remains the leading cause of cancer-related mortality worldwide and is characterized by high aggressiveness and therapeutic resistance, partly driven by mitotic dysregulation. Key mitotic regulators, including kinases such as PLK1, AURKA, AURKB, and MPS1 and kinesins such as CENPE and Eg5, are frequently overexpressed in NSCLC and SCLC, contributing to chromosomal instability, aneuploidy, and highly proliferative tumor phenotypes. Although multiple inhibitors targeting these proteins have been developed, their clinical efficacy as monotherapies has been limited. This is largely due to insufficient target dependency, adaptive resistance mechanisms, mitotic slippage, activation of compensatory pathways, and dose-limiting toxicity. This review integrates current knowledge on the physiological roles of major mitotic regulators, their dysregulation in lung tumorigenesis, and the biological and pharmacological barriers that underlie the limited success of antimitotic drugs. We further highlight preclinical and clinical evidence supporting rational combination strategies designed to enhance the antitumor activity of mitotic inhibitors while minimizing toxicity. Together, these insights underscore the need for refined therapeutic approaches that better exploit vulnerabilities in mitotic control to improve outcomes for patients with lung cancer. Full article

Triple-Negative Breast Cancer (TNBC) remains the most aggressive breast cancer subtype, characterized by profound heterogeneity and a lack of effective targeted therapies. Although cytotoxic chemotherapy is the standard of care, the rapid emergence of resistance driven by cancer stem cells (CSCs), metabolic plasticity, and the tumor microenvironment limits long-term survival. This review highlights the paradigm shift in TNBC treatment from 2021 to 2025, moving beyond broad cytotoxicity to precision medicine. We first examine the limitations of earlier targeted therapies, such as PI3K/AKT/mTOR inhibitors, which failed due to compensatory feedback loops and toxicity. We then discuss emerging synthetic lethality strategies targeting the G2/M checkpoint (WEE1, ATR) and mitotic kinases (PLK1, TTK) to exploit genomic instability in TP53-mutant tumors. Furthermore, we explore how novel modalities like PROTACs and Antibody–Drug Conjugates (ADCs) are unlocking the “undrugged kinome,” including targets like TNIK, PTK7, and PAK4, which were previously inaccessible. Finally, we propose that future success lies in combinatorial strategies integrating these next-generation kinase inhibitors with ADCs and immunotherapies to dismantle therapeutic resistance. Full article

Objective: Identifying biomarkers that predict metastatic potential or guide treatment selection is critical for improving breast cancer (BC) management. Previously, we established the Mitotic Network Activity Index (MNAI) as a prognostic marker in BC. Here, we bioinformatically and experimentally evaluated MNAI as a biomarker for metastasis risk and therapeutic response. Methods: We used Kaplan–Meier and Cox proportional hazard regression analyses to assess the association between MNAI and distant metastasis-free survival (DMFS) across 14 published BC datasets. A total of 16 publicly available clinical trial datasets, including the I-SPY trials, were used to evaluate the predictive value of MNAI for treatment response. Additionally, wound-healing and transmembrane assays were conducted to determine the effects of PLK1, CHEK1, and BUB1 inhibition on BC cell migration and invasion. Results: High MNAI levels were strongly associated with shorter DMFS. Multivariate analysis further confirmed MNAI as an independent risk factor for DMFS, beyond estrogen receptor status and PAM50-based molecular subtypes. Functionally, pharmacologic disruption of the mitotic network using PLK1, CHEK1, or BUB1 inhibitors significantly reduced cell migration and invasion in MDA-MB-231 and BT-549 BC cell lines. Moreover, BC cells with high MNAI increased sensitivity to microtubule-targeting agents such as docetaxel, paclitaxel, and ixabepilone but increased resistance to tamoxifen, AKT1/2 inhibitors, and mTOR inhibitors. Consistent with these findings, analysis of 16 clinical trial cohorts revealed that patients with high MNAI achieved higher pathological complete response rates to taxane-containing and ixabepilone-based therapies. Conclusions: Our findings demonstrate the MNAI as a clinically actionable biomarker that can refine risk stratification and guide the selection of targeted or chemotherapy regimens, advancing precision medicine in BC management. Full article

Polo-like kinase 1 (PLK1) is a serine/threonine kinase that orchestrates multiple critical events during mitosis, including centrosome maturation, spindle assembly, kinetochore–microtubule attachment, and cytokinesis. Dysregulation and overexpression of PLK1 are frequently observed in various cancers, correlating with increased proliferation, metastatic potential, and poor prognosis, which highlights its potential as a therapeutic target. Traditional small-molecule inhibitors have predominantly focused on the ATP-binding site of the N-terminal kinase domain, effectively inducing mitotic arrest and apoptosis in tumor cells; however, these compounds often suffer from limited selectivity and off-target toxicity. The C-terminal Polo-box domain (PBD), responsible for substrate recognition and subcellular localization, has emerged as an alternative and highly selective target for inhibitor design, enabling the disruption of protein–protein interactions critical for PLK1 function. Here, we present a comprehensive review demonstrating the potential inhibition of several compounds against PLK1. This work establishes a foundation for future preclinical development of small molecule-based therapeutics against PLK1-dependent malignancies. Full article

Polo-like kinase 1 (PLK1) is a serine/threonine protein kinase expressed in smooth muscle cells (SMCs), with emerging roles in regulating contraction. We hypothesize that PLK1 contributes to smooth muscle contractility in pudendal arteries (PA), small mesenteric arteries (SMA), and the corpus cavernosum (CC). Using male C57BL/6J mice, we assessed mRNA and protein expression of PLK1 in these tissues. In addition, the arteries and CC were mounted in myographs for isometric force measurement. We then investigated whether PLK1 regulates SMC contractility induced by phenylephrine (PE), U46619, and angiotensin II (Ang II) in arteries, and by PE, serotonin (5-HT), and electrical field stimulation (EFS; 1–16 Hz) in the CC, both in the presence and absence of the PLK1 inhibitor volasertib. PLK1 expression was confirmed in the SMA, PA, and CC by RT-qPCR or Western blotting. Notably, PLK1 inhibition significantly reduced Ang II-induced contraction in the PA and SMA and attenuated EFS-induced contraction at 2 and 4 Hz in the CC. In contrast, responses to PE, U46619, and 5-HT were unaffected by PLK1 inhibition. These results suggest that PLK1 selectively mediates contraction in response to Ang II and neurogenic stimuli. PLK1 may therefore represent a novel, stimulus-specific regulator of vascular and erectile smooth muscle contractility. Full article

Skin cancer remains a significant global health challenge, with rising incidence and associated mortality in late-stage and drug-resistant cases. This underscores a continuing need for more effective novel therapeutic options that can be utilized for efficient management of skin cancers. A promising approach involves exploiting novel targets, which are dysregulated in skin cancer, either alone or in combination with existing therapeutics. Among these, polo-like kinases (PLKs), a family of serine/threonine kinases, has emerged as promising candidates due to their essential role in cell cycle and maintaining genomic stability, key hallmarks of cancer. Within this family, polo-like kinase 4 (PLK4) stands out as a structurally distinct member and the master regulator of centriole duplication, ensuring this process occurs only once per cell division. Dysregulation of PLK4 can disrupt genomic integrity, contributing to tumorigenesis, thus making it a promising target for cancer management. Notably, PLK4 is frequently overexpressed in several cancers, including skin cancer, and its precise role in skin cancer is an area of current investigation. Further, several small-molecule PLK4 inhibitors such as centrinone, YLZ-F5, CFI-400945, and RP-1664 have demonstrated efficacy in targeting PLK4. Among these, CFI-400945 has advanced to clinical trials, where it has shown modest anti-cancer activity. In this review, we provide a comprehensive overview of the known functions of PLK4 in skin cancer. Additionally, we discuss potential mechanistic insights into PLK4′s involvement in skin cancer progression by extrapolating evidence from studies in other cancer types including colorectal cancer, thyroid cancer, lymphomas, leukemia, etc., while identifying gaps for future research. Full article

Background: Histiocytic sarcoma (HS) is a highly aggressive malignancy characterized by the excessive proliferation of histiocytes in dogs and humans. A subset of dog breeds, including the Bernese Mountain Dog (BMD), show a remarkably high prevalence of HS. Previous work by us and others has identified somatic driver mutations of HS in the PTPN11 and KRAS genes that activate the MAPK pathway in about 60% of canine HS. However, no somatic driver mutations have been identified in the remaining 40%. Objectives: Our goals are to study HS in BMDs to gain insight into the molecular pathogenesis of the disease, and identify rational approaches to therapy. Methods: Here, we report our whole transcriptome analysis of 18 well-characterized BMD HS tumor tissues, as well as three HS cell lines. Results: Our analysis reveals the significant upregulation of molecular pathways involving the FOXM1, AURKB, PLK1, and E2F genes, in HS as well as hemophagocytic HS, providing new information regarding pathways that may be targeted with inhibitors. In addition, we document the expression of multiple checkpoint genes, suggesting the option of treatment with small-molecule inhibitors together with checkpoint inhibitors. Further, we show that the transcriptomes of three canine HS cell lines mirror those of canine patient tumors, further highlighting their potential use in drug discovery and efficacy studies. Finally, we demonstrate, for the first time, that aurora kinase inhibitors are effective in curtailing the growth of HS cells in vitro and show synergism with MAPK inhibition. Conclusions: This study provides the most detailed analysis of the canine HS transcriptome to date, highlighting key pathways in its pathogenesis and suggesting new avenues for both single and combination treatment strategies, which may be pertinent to the treatment of human HS. Full article

Tetraploidy is a condition in which the entire set of chromosomes doubles, most often due to errors during cell division. Tetraploidy can lead to genomic instability and significant consequences, in particular metastasis and treatment failure in tumours, including radiotherapy. The development of new strategies to sensitise these cells to treatment is of great importance. In our study, we investigated the in vitro combination of chemical treatment with the kinase inhibitor SP600125 and irradiation on diploid versus metastatic tetraploid RKO colon cancer clones. We assessed mitochondrial transmembrane potential, cell cycle and subG1 population by flow cytometry and performed clonogenic assays to evaluate cell sensitivity. We found that the combination overcomes irradiation resistance in metastatic tetraploid clones. To identify the main pathway involved in cell sensitivity, we screened the Harvard Medical School KINOMEscan library and performed a gene ontology biological process analysis. We found that the major kinases inhibited by SP600125 were ANKK1, BIKE, IKKA, JNK1, MP2K3, MP2K4, MKNK2, MYLK, PLK4, RPS6KA4(Kin,Dom,1), MYLK4 and TTK, and the pathways involved in clone sensitivity were DNA damage repair, radiation resistance and apoptosis, through JNK pathway inhibition. Finally, our main finding was that combined treatment with SP600125 and radiotherapy reduced the resistance of metastatic tetraploid cells to treatment, essentially by inhibiting the JNK pathway. This result supports a promising anti-cancer strategy to overcome the resistance of tetraploid cancer cells to irradiation. Full article

Objective: To investigate the preclinical efficacy and identify predictive biomarkers of polo-like kinase 1 (PLK1) inhibitors in small cell lung cancer (SCLC) models. Methods: We tested the cytotoxicity of selective PLK1 inhibitors (rigosertib, volasertib, and onvansertib) in a panel of SCLC cell lines. We confirmed the therapeutic efficacy of subcutaneous xenografts of representative cell lines and in four patient-derived xenograft models generated from patients with platinum-sensitive and platinum-resistant SCLC. We employed an integrated analysis of genomic and transcriptomic sequencing data to identify potential biomarkers of the activity and mechanisms of resistance in laboratory-derived resistance models. Results: Volasertib, rigosertib, and onvansertib showed strong in vitro cytotoxicity at nanomolar concentrations in human SCLC cell lines. Rigosertib, volasertib, and onvansertib showed equivalent efficacy to that of standard care agents (irinotecan and cisplatin) in vivo with significant growth inhibition superior to cisplatin in PDX models of platinum-sensitive and platinum-resistant SCLC. There was an association between YAP1 expression and disruptive or inactivation TP53 gene mutations, with greater efficacy of PLK1 inhibitors. Comparison of lab-derived onvansertib-resistant H526 cells to parental cells revealed differential gene expression with upregulation of NAP1L3, CYP7B1, AKAP7, and FOXG1 and downregulation of RPS4Y1, KDM5D, USP9Y, and EIF1AY highlighting the potential mechanisms of resistance in the clinical setting. Conclusions: We established the efficacy of PLK1 inhibitors in vitro and in vivo using PDX models of platinum-sensitive and resistant relapsed SCLC. An ongoing phase II trial is currently testing the efficacy of onvansertib in patients with SCLC (NCT05450965). Full article

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. Full article

MLL-rearranged (MLLr) leukemia is characterized by a poor prognosis. Depending on the cell of origin, it differs in the aggressiveness and therapy response. For instance, in adults, volasertib blocking Polo-like kinase 1 (PLK-1) exhibited limited success. Otherwise, PLK-1 characterizes an infant MLLr signature, indicating potential sensitivity. By using our CRISPR/Cas9 MLLr model in CD34+ cells from human cord blood (huCB) and bone marrow (huBM) mimicking the infant and adult patient diseases, we were able to shed light on this phenomenon. The PLK-1 mRNA level was significantly increased in our huCB compared to the huBM model, which was underpinned by analyzing infant and adult MLLr leukemia patients. Importantly, the expression levels correlated with a functional response. Volasertib induced a significant dose-dependent decrease in proliferation and cell cycle arrest, most pronounced in the infant model. Mechanistically, upon volasertib treatment, we uncovered negative feedback only in the huBM model by compensatory upregulation of PLK-1 and related genes like AURKA involved in mitosis. Importantly, the poor response could be overcome by a combinatorial strategy with alisertib, an Aurora kinase A inhibitor. Our study emphasizes the importance of considering the cell of origin in therapeutic decision-making and provides the rationale for evaluating volasertib and alisertib in MLLr leukemia. Full article

Background/Objectives: Anoikis-related genes (ANRGs) are crucial in the invasion and metastasis of breast cancer (BC). The underlying role of ANRGs in the prognosis of breast cancer patients warrants further study. Methods: The anoikis-related prognostic signature (ANRS) was generated using a variety of machine learning methods, and the correlation between the ANRS and the tumor microenvironment (TME), drug sensitivity, and immunotherapy was investigated. Moreover, single-cell analysis and spatial transcriptome studies were conducted to investigate the expression of prognostic ANRGs across various cell types. Finally, the expression of ANRGs was verified by RT-PCR and Western blot analysis (WB), and the expression level of PLK1 in the blood was measured by the enzyme-linked immunosorbent assay (ELISA). Results: The ANRS, consisting of five ANRGs, was established. BC patients within the high-ANRS group exhibited poorer prognoses, characterized by elevated levels of immune suppression and stromal scores. The low-ANRS group had a better response to chemotherapy and immunotherapy. Single-cell analysis and spatial transcriptomics revealed variations in ANRGs across cells. The results of RT-PCR and WB were consistent with the differential expression analyses from databases. NU.1025 and imatinib were identified as potential inhibitors for SPIB and PLK1, respectively. Additionally, findings from ELISA demonstrated increased expression levels of PLK1 in the blood of BC patients. Conclusions: The ANRS can act as an independent prognostic indicator for BC patients, providing significant guidance for the implementation of chemotherapy and immunotherapy in these patients. Additionally, PLK1 has emerged as a potential blood-based diagnostic marker for breast cancer patients. Full article

Polo-like kinase 1 (PLK1) is a serine/threonine–protein kinase essential for regulating multiple stages of cell cycle progression in mammals. Aberrant regulation of PLK1 has been observed in numerous human cancers and is linked to poor prognoses. However, its role in the pathogenesis of colorectal cancer (CRC) in the Middle East remains unexplored. PLK1 overexpression was noted in 60.3% (693/1149) of CRC cases and was significantly associated with aggressive clinico-pathological parameters and p-ERK1/2 overexpression. Intriguingly, multivariate logistic regression analysis identified PLK1 as an independent predictor of lymph node metastasis. Our in vitro experiments demonstrated that CRC cells with high PLK1 levels were resistant to 5-Fu treatment, while those with low PLK1 expression were sensitive. To investigate PLK1′s role in chemoresistance, we used the specific inhibitor volasertib, which effectively reversed 5-Fu resistance. Interestingly, forced PLK1 expression activated the CRAF-MEK-ERK signaling cascade, while its inhibition suppressed this cascade. PLK1 knockdown reduced epithelial-to-mesenchymal transition (EMT) progression and stem cell-like traits in 5-Fu-resistant cells, implicating PLK1 in EMT induction and stemness in CRC. Moreover, silencing ERK1/2 significantly mitigated chemoresistance, EMT, and stemness properties in CRC cell lines that express PLK1. Furthermore, the knockdown of Zeb1 attenuated EMT and stemness, suggesting a possible link between EMT activation and the maintenance of stemness in CRC. Our findings underscore the pivotal role of PLK1 in mediating chemoresistance and suggest that PLK1 inhibition may represent a potential therapeutic strategy for the management of aggressive colorectal cancer subtypes. Full article