Polo-like Kinase Research Articles

A polo-like kinase 1 inhibitor enhances erastin sensitivity in head and neck squamous cell carcinoma cells in vitro

BackgroundPolo-like kinase 1 (PLK1) is a critical therapeutic target in the treatment of head and neck squamous cell carcinoma (HNSCC). The objective of this study was to investigate the therapeutic effect of the combination of BI 2536, a PLK1 inhibitor, and erastin, a ferroptosis inducer, in HNSCC.MethodsThe proliferation, invasion, and migration abilities of Tu177 and FaDu cells upon exposure to BI 2536 and erastin, used in combination or alone, were tested. Fe2+, glutathione (GSH), and malondialdehyde (MDA) detection kits were used to determine whether the addition of BI 2536 enhanced the accumulation of Fe2+ and MDA, along with the depletion of GSH. Quantitative real-time PCR, western blot analyses were performed to investigate whether BI 2536 further altered the mRNA and expression level of ferroptosis genes. Furthermore, si PLK1 was used to investigate whether targeting PLK1 gene promoted erastin-induced ferroptosis.ResultsThe combination of BI 2536 and erastin exerted a stronger cytotoxicity than treatment with a single agent. Compared with erastin treatment alone, the combination of BI 2536 and erastin lowered the ability of tumor cells to self-clone, invade, and migrate. BI 2536 enhanced the accumulation of Fe2+ and MDA, and the depletion of GSH. BI 2536 increased erastin-induced changes in ferroptosis-related gene mRNA and expression. Importantly, targeting PKL1 enhanced the anti-cancer effect of erastin.ConclusionBI 2536 enhanced the sensitivity of HNSCC cells to erastin, which provides a new perspective for cancer treatment.

Abstract 3482: Single-cell transcriptome analysis reveals that PLK4 signature genes are highly associated with cancer proliferation and hotspot mutations in non-small cell lung cancer (NSCLC)

Abstract Background: Polo-like kinase 4 (PLK4) is a member of the polo-like kinase family known for its precise regulation during the cell cycle and its key role in centriole duplication, which is essential for proper cell division. Dysregulation of PLK4 is associated with abnormal centriole number, genomic instability and cancer development. In our previous study, we proposed PLK4 as a potential therapeutic target and biomarker for LUAD patients with TP53 mutations by bulk RNA-seq analysis and confirmed its association with drug resistance. In this study, we analyzed the expression of PLK4 and its association with cell cycle at the cellular level by scRNA-seq in NSCLC data. Methods: In a previous study, we analyzed NSCLC data from The Cancer Genome Atlas (TCGA) database using the UCSC Xena data portal. In this study, we analyzed E-MTAB-6653 dataset from the single cell expression atlas(https://www.ebi.ac.uk/gxa/sc/home). Results: In the previous study, we demonstrated that PLK4 expression is higher in primary tumors compared to normal tissues in NSCLC. Higher PLK4 expression in patients is associated with an unfavorable prognosis. Using genes highly correlated with PLK4, we confirmed a significant association between PLK4 and TP53 mutation by statistical analysis. Using the Drug Gene Interaction database, we observed an association between the drug resistance-related genes PBK and BIRC5 with PLK4, and these genes were also correlated with TP53 mutation. In this study, we investigated the association between PLK4 and the cell cycle using single cell RNA-seq. First, we performed data pre-processing to selectively isolate NSCLC cells. Using a set of 87 PLK4 signature genes obtained from previous research, we stratified the samples into PLK4 high and low groups based on the expression of these genes. We then analyzed cell cycle related genes in both groups and observed a higher expression of G2/M phase related genes in the PLK4 high group compared to the PLK4 low group. We also examined the expression of PLK4 signature genes based on pathological differences and found higher expression in tumor tissue compared to normal tissue. There was also an increasing expression gradient from the tumor margin to the tumor core. Finally, using Gene Ontology analysis of both groups, we confirmed the upregulation of genes associated with transcription and translation, as indicated by the GO terms obtained. Conclusion: In a previous study, the association between PLK4 expression, TP53 mutation and drug resistance was identified by bulk RNA-seq. In the current study, we used single cell RNA-seq to verify the correlation between PLK4 and cell cycle in NSCLC. In addition, we observed that the expression of PLK4 signature genes increased towards the tumor core based on pathological differences. Citation Format: Youngtaek Kim, Joon Yeon Hwang, YoungJoon Park, Dong Kwon Kim, Kwangmin Na, Seul Lee, Sujeong Baek, Seong-san Kang, Seung Min Yang, Mi Hyun Kim, Heekyung Han, Chai Young Lee, Yu Jin Han, Min Hee Hong, Jii Bum Lee, Sun Min Lim, Kyoung-Ho Pyo, Byoung Chul Cho. Single-cell transcriptome analysis reveals that PLK4 signature genes are highly associated with cancer proliferation and hotspot mutations in non-small cell lung cancer (NSCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3482.

Abstract 594: ORIC-613, a potential first- and best-in-class, orally bioavailable, potent and selective PLK4 inhibitor with synthetic lethality in TRIM37 high cancer models

Abstract A synthetic lethal interaction between polo-like kinase 4 (PLK4) and elevated TRIM37 was discovered in breast cancer and neuroblastoma (Meitinger et al. 2020; Yeow et al. 2020). High TRIM37 renders cells dependent on PLK4, a kinase that controls centriole duplication. Amplification and copy number gains of the 17q23 amplicon, where TRIM37 resides, are common in breast cancer and neuroblastoma and associated with early relapse and poor prognosis, making PLK4 a promising new synthetic lethal target for these patients. The development candidate ORIC-613 is an orally bioavailable, potent and exquisitely selective small molecule inhibitor of PLK4, which is synthetic lethal in TRIM37 high cells. ORIC-613 is highly selective against the kinome, including against the closely related aurora and PLK families. ORIC-613 ADME/PK profile includes high cell permeability and low potential for drug-drug interactions based on CYP profiling. ORIC-613 blocked PLK4 trans-autophosphorylation of phosphodegrons, leading to stabilization of PLK4, thus directly demonstrating target engagement in cells. PLK4 protein stabilization correlated with cell viability for ORIC-613, providing a quantifiable pharmacodynamic (PD) association with antitumor activity. Cell viability assessment in cancer cell lines revealed that ORIC-613 showed greater potency in TRIM37 high versus TRIM37 low cell lines. Importantly, ORIC-613 induced significantly greater apoptosis in TRIM37 high versus low cancer cell lines as measured by caspase 3/7 assay. We confirmed that ORIC-613 activity is on-target using an engineered cell line system of PLK4 G95L, in which the leucine mutation maintains enzymatic function but blocks compound binding. In cell viability assays, ORIC-613 was potent in the parental cells and lost activity in G95L cells. Analysis of genomic data from tumors indicates that TRIM37 copy number amplification and gain is prevalent across numerous cancers. Oral dosing of ORIC-613 resulted in tumor growth inhibition and regressions in TRIM37 high xenograft breast tumors with no body weight loss. In summary, ORIC-613 is a potential first- and best-in-class development candidate, with exquisite selectivity for PLK4, which demonstrates synthetic lethality in TRIM37 high tumors and has the potential to benefit these patients. Citation Format: Kyle A. Edgar, Siobhan McRee, Gina Andretta, Chelsea Chen, Christophe Colas, Wei Fang, Wayne Kong, Jason Long, Fang Liu, Jared Moore, Aleskandr Pankov, Dan Shore, Joanne Tan, Robert Warne, Livia Ulicna, Rakesh Vekariya, Anneleen Daemen, F Romero, Melissa R. Junttila, Lori S. Friedman. ORIC-613, a potential first- and best-in-class, orally bioavailable, potent and selective PLK4 inhibitor with synthetic lethality in TRIM37 high cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 594.

Abstract 5726: The potential anti-cancer activity of dual TTK/PLK1 inhibitor, BAL0891, in bladder cancer

Abstract Background: BAL0891 is a novel dual inhibitor of threonine tyrosine kinase (TTK) and polo-like kinase 1 (PLK1) which affects mitotic spindle assembly checkpoint integrity resulting in aberrant mitotic progression of cancer cells. Since unlike other organs, bladder urothelium is highly regenerative in certain circumstances, there are high chances of cell cycle inhibitors to have anti-cancer activity over bladder cancer. In this study, we investigated the therapeutic potential of BAL0891 in bladder cancer compared to single TTK or PLK1 inhibitor and discovered the best therapeutic combination partner for BAL0891. Methods: We performed meta-analysis of the mRNA expression levels of bladder cancer using Gene Expression Profiling Interactive Analysis 2 (GEPIA2). Representative bladder cancer cell lines (253J, 253J-BV, J82, RT4, T24, J82, HT1197, and HT1376) were treated with the dual protein kinase inhibitors, BAL0891, in comparison with TTK inhibitor (BAY1217389) or PLK1 inhibitor (onvansertib). BAL0891 was combined with CDK4/6 inhibitor, another cell cycle inhibitor working at different point from BAL0891. Cell viability was assessed using CCK-8 assay during 72 hours after treatment. Expression levels of TTK and PLK1 were measured by immunoblotting. Cell cycle analysis and cell apoptosis detection were performed on T24 cell. Results: The mRNA expression levels of both TTK (16.7 times) and PLK1 (10.0 times) were significantly upregulated only in bladder cancers compared to normal bladder tissues (P<0.05). Compared to TTK or PLK1 inhibitor, BAL0891 was sensitive in 75% of bladder cancer cell lines (IC50 <0.1 uM) and significantly reduced proliferation of bladder cancer cell lines depending on the dosage. TTK and PLK1 expression levels of cancer cells were associated with the sensitivity to BAL0891. BAL0891 significantly induced necrosis and increased in polyploidy and G2/M arrest in T24 cell. The anti-cancer activity of BAL0891 was further enhanced in certain cell lines (RT4, and J82) by combination of CDK4/6 inhibitor. Conclusion: This is the first study to suggest the potent anti-cancer activity of BAL0891 in bladder cancer. BAL0891 effectively worked on bladder cancer by two tracks which not only induced G2/M arrest but also increased in polyploidy. Furthermore, BAL0891 in combination with CDK4/6 inhibitor promoted anti-cancer effects. Lastly, this study suggests the use of TTK and PLK1 as the predictive biomarker for BAL0891. These data support further investigation of BAL0891 for the treatment of bladder cancer patients. Citation Format: Jee Soo Park, Ji-eun Lee, Myung Eun Lee, Jongchan Kim, Won Sik Jang, Jae Jung Lee, Jun Seung Lee, Minkyung Kang, Won Sik Ham. The potential anti-cancer activity of dual TTK/PLK1 inhibitor, BAL0891, in bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5726.

Abstract 6014: PLK1-dependent phosphorylation of PRMT5 promotes DNA damage response in prostate cancer

Abstract Prostate cancer stands out as the most frequently diagnosed cancer in men and is projected to be the second leading cause of cancer-related deaths among men in the US. Consequently, there is an urgent need for studies focusing on innovative therapeutic approaches. DNA Damage Response (DDR) is critical for cell survival, as it promotes genomic stability and reduces the risk of inheriting damage. DDR also promotes cancer cells' survival, making it a therapeutic target in cancer. PRMT5, an enzyme in the methyltransferase family, is frequently activated and overexpressed in various cancers, including prostate cancer. Furthermore, research has revealed that PRMT5 has been implicated in DDR in prostate cancer, and the regulation of PRMT5-dependent DDR is influenced by its phosphorylation. Polo-like kinase 1 (PLK1) is a serine/threonine kinase also reportedly involved in DDR in prostate cancer. Our preliminary study found that PRMT5 is positively correlated with PLK1 in prostate cancer based on the TCGA database. Nonetheless, the mechanism through which PRMT5 is regulated needs to be clarified. Here, we found that PLK1 phosphorylates PRMT5 at the S470 site, and this specific phosphorylation is required for maintaining the enzymatic activity of PRMT5. Moreover, Plk1-associated phosphorylation of PRMT5 subsequently promotes DNA damage repair, indicated by the decreasing level of γH2AX after DNA double-strand breaks (DSB). Our RNA-seq analyses of prostate cancer cells with wild-type or mutant S470 sites indicate that Plk1-associated phosphorylation on the S470 site exerts an influence on DNA replication and DDR pathways. These findings shed light on a novel perspective regarding the roles of PLK1-mediated PRMT5 phosphorylation in DDR, offering potential therapeutic strategies in prostate cancer. Citation Format: Jia Peng, Yanquan Zhang, Jianlin Wang, Qianjin Li, Daheng He, Xinyi Wang, Xiongjian Rao, Meng Wu, Pingli Mo, Lei Wang, Sai Wu, Ruixin Wang, Jinghui Liu, Mansoureh Nouri, Izumi Tadahide, Xiaoqi Liu. PLK1-dependent phosphorylation of PRMT5 promotes DNA damage response in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6014.

Abstract 2102: Understanding the mechanism of action of rigosertib in recessive dystrophic epidermolysis bullosa-associated squamous cell carcinoma through single cellanalysis

Abstract The allosteric inhibitor rigosertib (an experimental therapeutic) was previously identified as an effective inducer of G2M arrest and apoptosis in squamous cell carcinoma (SCC) keratinocytes isolated from patients with the rare genetic disease recessive dystrophic epidermolysis bullosa (RDEB), both in vitro and in vivo. Early clinical trial data treating RDEB-associated SCC with rigosertib has shown remarkable efficacy in a sub-set of patients and understanding the mechanism of action of rigosertib in this lethal cancer would provide rationale for patient stratification. Multiple mechanisms of action were previously attributed to rigosertib, including polo-like kinase-1 (PLK1), PI3-kinase, activated RAS and microtubule polymerization inhibition. Our published data comparing PLK1 siRNA with PI3-Kinase inhibitors, MAPK inhibitors and microtubule disruption favored PLK1 as a mechanism of action without definitive conclusion. We therefore sought to determine the mechanism of action using transcriptomic profiling. Flow cytometry experiments identified three main categories of time to increase G2M in nine separate RDEB SCC keratinocyte populations in culture ranging from 1 to 6 hours after exposure to 1uM rigosertib. Bulk-RNA sequencing of representative populations from time to G2M groupings failed to identify consistent transcriptional change after exposure to rigosertib. However, single cell sequencing was able to identify increases in sub-populations of cells associated with G2M as well as transient emergence of unique populations that were specific to individual patient populations after exposure to rigosertib in culture. Of note a transient population of RDEB SCC keratinocytes only present after 1 hour of exposure to rigosertib was characterized by increased expression of the potassium regulator KCNRG which has previously been associated with apoptosis in chronic lymphocytic leukemia. Ongoing work is determining the role this gene may play in the mechanism of apoptosis induction in RDEB SCC keratinocytes after exposure to rigosertib. Citation Format: Andrew P. South, Suhao Han, Paolo Fortina. Understanding the mechanism of action of rigosertib in recessive dystrophic epidermolysis bullosa-associated squamous cell carcinoma through single cellanalysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2102.

Abstract 4658: Genome wide CRISPR/Cas9 library screening identifies aurora kinase A as a regulator of elraglusib sensitivity in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy with a dismal 5-year survival rate, highlighting the urgent need to improve drug response and overcome primary or acquired (secondary) resistance to conventional chemotherapy. Glycogen synthase kinase 3β (GSK-3β) is a target in PDAC and the GSK-3 inhibitor, elraglusib, has been shown to improve chemosensitivity of PDAC and survival in preclinical cancer models. In addition, data from phase II clinical trials in patients with previously untreated metastatic pancreatic cancer is demonstrating preliminary evidence of clinical benefit in patients receiving a combination of gemcitabine/nab-paclitaxel. While this early evidence is highly encouraging, the biological determinants of elraglusib response are unknown. Using genome wide CRISPR/Cas9 library screening, we identify aurora kinase A (AURKA), an oncogenic kinase with major roles in mitosis, as a critical regulator for elraglusib sensitivity. Elraglusib treatment activates AURKA by inducing a G2/M cell cycle arrest. We show that knocking out AURKA reduces the phosphorylation of polo like kinase 1 (PLK1), arresting cells in mitosis, and leading to mitotic catastrophe and significant apoptosis after elraglusib treatment. Strikingly, the AURKA inhibitor, alisertib, works synergistically with elraglusib to inhibit PDAC cell line growth and induce apoptosis. In summary, our results demonstrate that targeting AURKA is an effective approach to sensitize PDAC tumors to elraglusib. Citation Format: Li Ding, Easton Maeder, Cheng Zhang, Taylor Weiskittel, Daniel Schmitt, Andrew Mazar, Hu Li, Daniel Billadeau. Genome wide CRISPR/Cas9 library screening identifies aurora kinase A as a regulator of elraglusib sensitivity in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4658.

Abstract 945: In vivo anti-tumor activity of onvansertib, a PLK1 inhibitor, combined with gemcitabine or carboplatin in platinum- resistant ovarian carcinoma patient-derived xenograft models

Abstract Background: The standard treatment for high grade ovarian carcinoma (HGOC) is cytoreductive surgery followed by a platinum based therapy. Despite an initial high rate of complete remission, most of the patients relapse with a platinum resistant disease. Patients with resistant tumors have few options, including monotherapy with gemcitabine, and new effective therapeutic alternatives are needed. The Polo-like kinase 1 (PLK1) is a master regulator of mitosis and recent evidences suggest its role in interfering with several DNA repair mechanisms. We investigated the effect of onvansertib (ONVA), a highly selective ATP-competitor PLK1 inhibitor, in combination with carboplatin (CARBO) and gemcitabine (GEM) in platinum-resistant HGOC patient-derived xenografts (PDXs). Methods: The combination of ONVA with either CARBO or GEM was investigated in two platinum-resistant HGOC PDXs, one intrinsically resistant to platinum (MNHOC#315), the other made resistant after repeated in vivo treatments with cisplatin (MNHOC#266R). Tumors were subcutaneously (s.c.; MNHOC#315) or orthotopically (i.p.; MNHOC#266R) transplanted in nude mice, mice were treated for 4 weeks with vehicle, single agents or drug combinations and followed for tumor growth (s.c. model) and survival. Results: CARBO- and GEM-ONVA combinations were well tolerated, with a maximum body weight loss of 6.6%. Both combinations showed strong anti-tumor activities in the two tested models. In MNHOC#315 PDX, CARBO- and GEM-ONVA combinations caused a tumor stabilization that extended beyond the dosing period and resulted in a higher tumor growth inhibition as compared to vehicle and single agents treated mice. In i.p. MNHOC#266R PDX, single agents were inactive, while a statistically significant increase in survival was observed in CARBO/ONVA and in GEM/ONVA treated mice as compared to vehicle treated mice, with a 6.6- and 7-fold increase in mean survival time, respectively. Pharmacodynamic studies are ongoing to decipher the mechanisms underlying the synergic effects of both combinations. Conclusions: The combinations of ONVA with either CARBO or GEM showed potent anti-tumor activities in two platinum-resistant HGOC PDXs. Additional studies in other HGOC platinum-resistant models, both in vivo and in vitro, as well pharmacodynamic studies are ongoing to validate these results and to get insights in the mechanisms underlying their efficacy. Citation Format: Michela Chiappa, Federica Guffanti, Ilaria Mengoli, Maya Ridinger, Giovanna Damia. In vivo anti-tumor activity of onvansertib, a PLK1 inhibitor, combined with gemcitabine or carboplatin in platinum- resistant ovarian carcinoma patient-derived xenograft models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 945.

Abstract 706: Advancing radiotherapy strategies for high-risk rhabdomyosarcoma: Unveiling BCL-xL inhibition as a potent sensitizer to radiotherapy

Abstract Pediatric soft-tissue sarcomas are a group of solid tumors that account for about 7% of childhood cancer cases. Rhabdomyosarcoma (RMS), the most common subtype, further stratifies into PAX3 or PAX7 and FOXO1 fusion-negative (FN) or fusion-positive (FP) RMS. FP RMS is the higher risk subtype and is more aggressive, metastatic, and less responsive to treatment. Front-line treatments for RMS FP patients have had limited progress in the recent years and existing treatments such as radiotherapy lacks tumor cell selectivity, resulting in toxic side effects. To address this, we conducted a high-throughput drug screen to identify radiosensitizers to enhance efficacy of RMS radiotherapy. Using three patient-derived FP RMS tumoroids, we screened a comprehensive drug library with and without radiation, comprising 528 drugs at varying stages of pre-clinical and clinical trials. A validation screen of the top 29 drugs was conducted on a larger cohort of samples including eight patient-derived FP RMS tumoroids and three non-cancer models. The screening revealed that drugs targeting the anti-apoptotic protein B-cell lymphoma-extra-large (BCL-xL) exhibited both potent radiosensitization and cytotoxicity selectively for FP RMS. Notably, the sensitivity to BCL-xL inhibitors correlated with elevated BCL2L1 expression and PAX3 fusion status. Additionally, drugs targeting polo-like kinase 1 (PLK1) and other cell cycle-related genes exhibited robust radioprotective effects across both RMS and non-cancer models. Our findings propose the therapeutic potential of BCL-xL inhibition, either as a standalone treatment or in combination with radiotherapy. In parallel, we show the protective potential of PLK1 inhibition to mitigate radiation toxicity. In the long term, we aspire to integrate the identified radiosensitizing and radioprotecting compounds with existing treatment regiments for RMS, maximizing precision and efficacy in RMS radiotherapy. Citation Format: Sammy Se Whee Park, Nona Struyf, Tom Erkers, Sören Lehmann, Michael T. Meister, Jarno Drost, Frank C. Holstege, Nikolas Herold, Päivi Östling, Jakob Stenman, Olli Kallioniemi, Jan-Inge Henter, Brinton Seashore-Ludlow, Kasper Karlsson. Advancing radiotherapy strategies for high-risk rhabdomyosarcoma: Unveiling BCL-xL inhibition as a potent sensitizer to radiotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 706.

Abstract 5178: Guided by a predictive ex vivo test: Bringing the PLK1 inhibitor volasertib back into the clinic for venetoclax-HMA relapsed/refractory acute myeloid leukemia patients

Abstract INTRODUCTION: Volasertib, a polo-like kinase 1 (PLK1) inhibitor, has a roughly 30% CR/CRi response rate in de novo acute myeloid leukemia (AML) patients when combined with low-dose cytarabine. However, its development was halted due in part to toxicity in a Phase 3 study. We have built a flow cytometry-based, high-throughput predictive precision medicine platform to forecast clinical responses to various treatments. Here, we present our design plan for a Phase 2a clinical trial with volasertib in relapsed/refractory (R/R) AML using a modified protocol to reduce toxicity and the development of a companion diagnostic to predict responders in a follow-up Phase 2b study. METHODS: We will initiate an open-label clinical trial in AML with volasertib in venetoclax-hypomethylating agent (HMA) R/R patients while co-developing a companion diagnostic to selectively enroll predicted responders in a follow-up, Phase 2b, study. Primary and secondary objectives will focus on efficacy/safety of intravenous volasertib and ex vivo responses, respectively. To reduce the toxicity seen in the Phase 3 study, specific strategies like tailored dosing will be implemented. To develop the clinical trial assay, peripheral blood or bone marrow samples were collected from AML patients and treated ex vivo with volasertib for 3 days. Surviving blast cells were enumerated by flow cytometry. Using a dynamic separation model restricted to the 35% most sensitive samples, we estimated optimal blast cutoffs for volasertib sensitivity. RESULTS: In single-agent experiments with 41 primary AML samples (31 de novo, 9 R/R, 1 with disease status unclear), we observed dose-response profiles consistent with volasertib’s role as a cell cycle inhibitor. Irrespective of the disease status, median and mean EC50 values were about 10 nM (1st-3rd quartile from 7-12 nM). To identify an optimal concentration of volasertib for patient stratification, we compared the ex vivo resistant blast fractions at each concentration with the areas under the dose-response curves (AUCs), assuming that in our case, AUCs most accurately reflect clinical responses. At 31.6 and 100 nM, the Pearson correlation coefficients were highest (r > 0.8), suggesting that these are optimal stratifying doses. With these concentrations and corresponding blast cutoff values, 32-33% of the de novo and 25% of the R/R patients would have been predicted to be responders were they given volasertib, assuming a positive predictive value of 100%. CONCLUSION: Volasertib’s EC50 values clustered within a narrow range, suggesting that EC50 may not be a suitable metric to stratify patients into responders and nonresponders, in contrast to AUCs and residual blast fractions at 31.6 and 100 nM of volasertib, which displayed more heterogeneous distributions. Limitations include small sample sizes, especially for the R/R group. Citation Format: Markus Daniel Lacher, Glenn Michelson, Allen Ling, Wade Anderson, Jeaneille Vinas, Christine J. Gu, Chris Leonardi, Joseph Wagner, Gabriel N. Mannis. Guided by a predictive ex vivo test: Bringing the PLK1 inhibitor volasertib back into the clinic for venetoclax-HMA relapsed/refractory acute myeloid leukemia patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5178.

Abstract 1647: Plk4 phosphorylates the distal tip complex to promote centriole growth

Abstract The centrosome is the major microtubule-organizing center of the cell with a key role in forming the mitotic spindle. The centrosome consists of two core duplicating elements, the centrioles, surrounded by pericentriolar material, a cloud of proteins that nucleates microtubules. Centrioles are barrel-like structures composed of microtubule bundles and are essential to maintain centrosome number. Therefore, centriole duplication and growth are tightly regulated to ensure proper centrosome number throughout the cell cycle. Alterations in centrosome number lead to an abnormally shaped mitotic spindle that often mis-segregate chromosomes, thereby causing chromosomal instability, a hallmark of cancer. Defects in centriole growth, such as over-elongation, can increase centrosome numbers (known as ‘centriole amplification’, an overproduction of centrioles frequently observed in cancer cells). For example, over-elongation of the centriolar barrel can cause multiple ectopic daughter centrioles to assemble or simply fragment, producing multiple smaller (but functional) centrioles. Thus, understanding how centrioles grow and define length is a major question in the field. Centrioles elongate at their distal ends and, in Drosophila, elongation is regulated by a group of proteins, Cep97, CP110 and Klp10A. Elongation is negatively regulated by Cep97 and CP110 which cap centrioles at their distal end to maintain centriole length, by counteracting the microtubule depolymerizing kinesin, Klp10A. Recently, we identified a new centriole regulator, Cep104, that also localizes to the centriole distal tip. We discovered that Cep104 promotes centriole elongation through its microtubule-binding TOG domain. Additionally, Cep104 localization to the centriole distal ends is dependent on Cep97. Furthermore, Cep97, CP110, Cep104 and Klp10A form a complex and we have mapped their sites of interaction. Collectively, we refer to this as the Distal Tip Complex (DTC). Although the DTC is first recruited to new daughter centrioles during G1/S-phase, the majority of centriole elongation occurs during mitosis. Here, we explore the mechanisms that regulate the DTC to promote centriole growth during mitosis. We hypothesize that Polo-like kinase 4 (Plk4), the master regulator of centriole duplication, phosphorylates and inhibits the DTC to promote elongation of nascent centrioles. Notably, we found that centrioles are longer in cells overexpressing Plk4. Using tandem mass spectrometry, we identified multiple sites that Plk4 phosphorylates on each DTC protein. Analysis of DTC phosphomutants revealed that the phosphorylation state of Klp10A, Cep97 and CP110 affect centriole number. We are currently investigating how Plk4 phosphorylation regulates the activities of these conserved centriole length factors. Citation Format: Anastasia Amoiroglou, John M. Ryniawec, Daniel W. Buster, Gregory C. Rogers. Plk4 phosphorylates the distal tip complex to promote centriole growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1647.

Abstract 7205: PLK1 inhibition overcomes PARP inhibitor resistance in triple-negative breast cancer

Abstract Patients with aggressive breast cancer (BC) subtypes usually do not have favorable prognosis despite improvements in treatment modalities. These cancers remain a major cause of morbidity and mortality in women globally. This has fostered a major effort to discover actionable molecular targets to treat these patients. Polo-like Kinase (PLK1) is one of these molecular targets that are under comprehensive investigation for the treatment of such tumors. However, its role in the pathogenesis of BC from Middle Eastern ethnicity has not been explored. Therefore, we examined the expression of PLK1 protein in a large cohort of more than 1500 Middle Eastern ethnicity BC by immunohistochemistry. Correlation with clinico-pathological parameters and the prognosis was performed. PLK1 overexpression was observed in 27.4% of all BC and was significantly associated with aggressive clinico-pathological markers. The antitumor effect of PLK1 and PARP inhibitors either alone or in combination was tested in two BRCA mutated, and one BRCA proficient TNBC cell lines. We showed that combined inhibition significantly reduced cell survival and induced apoptosis in TNBC cell lines. Furthermore, our data suggest that PLK1 inhibition overcomes PARP inhibitor resistance in TNBC cell lines. These findings would pave the way to explore the future use of PLK1 inhibitors in the clinical setting of PARPi-resistant patients. Citation Format: Abdul K. Siraj, Pratheesh Kumar Poyil, Divya Padmaja, Sandeep Kumar Parvathareddy, Khadija Alobaisi, Rafia Begum, Osama Almalik, Fouad Al-Dayel, Khawla S. Al-Kuraya. PLK1 inhibition overcomes PARP inhibitor resistance in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7205.

Abstract 3266: Plk1 promotes Pdcd4 degradation to enhance enzalutamide resistance in prostate cancer

Abstract The androgen receptor (AR) signaling pathway plays critical role in the development of prostate cancer (PCa), including castration-resistant prostate cancer (CRPC). As a result, androgen signaling inhibitors (ASIs) like abiraterone and enzalutamide (ENZ) have emerged as the first-line treatment for CRPC. Nevertheless, the limited success of ASIs underscores the urgency of developing new approaches for managing CRPC patients who have become unresponsive to ASIs. Programmed cell death 4 (Pdcd4) is a tumor suppressor, which is frequently down-regulated during PCa progression. It has been shown that reduced Pdcd4 expression promotes both AR-dependent and AR-independent growth in PCa. In this study, we found that down-regulation of Pdcd4 led to acquisition of ENZ resistance in PCa. We also observed that down-regulation of Pdcd4 resulted in activation of mTORC2 activity. Additionally, knockdown of Rictor, a component of mTORC2 complex, enhanced sensitivity to ENZ treatment in PCa. These findings suggested that activation of mTORC2 due to Pdcd4 loss contributes to ASI resistance in PCa. To understand how Pdcd4 is down-regulated in the PCa, we identified that polo-like kinase (Plk1) phosphorylated Pdcd4 at Ser239. Phosphorylation of Pdcd4 by Plk1 led to ubiquitin-mediated proteasomal degradation of Pdcd4. Over-expression of the phosphomimic Pdcd4(S239D) in 22Rv1 cells promoted tumor cell growth in cultured cells and mice. Taken together, our data suggest that targeting Plk1/Pdcd4/mTORC2 signaling axis holds promise as a strategy to overcome ENZ resistance in PCa. Citation Format: Qing Wang, Qiongsi Zhang, Yanquan Zhang, Xiaoqi Liu, Hsin-Sheng Yang. Plk1 promotes Pdcd4 degradation to enhance enzalutamide resistance in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3266.

Abstract 1111: Poor radiation sensitivity and potential radiosensitizers for betel-nuts related head and neck squamous cell carcinoma in Taiwan

Abstract Background: Betel nut chewing might contribute to strong invasion & treatment refractoriness in HNSCC from Taiwan. Betel-nuts exposed HNSCC cell line, TW2.6, had high PDL1, defective p53 mutation, p16 loss, & BCL2 overexpression. In our studies, PI3K/AKT/mTOR inhibitors, anti-angiogenesis therapies, CDK4/6 inhibitors, DDR interventions, epigenetic modifications, and immunotherapy-containing regimens will be future combination options. The genomic signature of TW2.6 has been figured out in our study(AACR2020 & 2023), too, mainly with PIK3CA H1047R mutation, high TMB(8.42 muts/Mb)/MSS, VEGF-A amplification, p53/MYC/HRAS/DDR2/PDGFRbeta/EPHB1/ATM mutations, FAT1 loss, amplification of TERT/FGF10/CCND3/SOX9/IL-7R/SDHA/RICTOR/FLCN, CDK12/PTPRD loss of function, CDK8 mutation, & deletions of STK11/ARID1B/MITF/TNFAIP3 and molecularly-guided novel interventions will be designed. Purpose & Methods: Polo-like kinase 1 inhibitor(volasertib), gluconate(blocking citrate transport & glucose metabolism), IAP inhibitor(Debio1143), glutaminase 1 inhibitor(CB839) were tested on TW2.6 to evaluate synergistic effects with radiation. Results: TW2.6 was resistant to volasertib, gluconate, or radiation alone; but sensitive to Debio1143 and CB839. Volasertib significantly enhanced radiation. The flow cytometry revealed volasertib and radiation resulted in a significant G2/M arrest. Western blotting showed volasertib and radiation increased p-histone3, p-CDK1, & cyclin B levels and induced apoptosis. Gluconate, CB839, or Debio1143 each had significant synergistic effects with radiation. The radiosensitization efficacy would be volasertib>gluconate>CB839>Debio1143. Conclusions: In Taiwan, patients with R/M HNSCC progressing within 3 months after CCRT could be rescued by early ICIs. Recently, sequential CCRT followed by ICI or Debio-1143 with CCRT showed potential survival benefits. In our studies, novel agents such as PLK inhibitor, gluconate, and CB839 had even better radiosensitization compared with Debio1143. Sequential CCRT with novel agents followed by ICI will be the future trend, esp. in biology-aggressive betel-nuts related locally advanced HNSCC in Taiwan. Citation Format: Jo-Pai Chen, Jui-Ying Chang, Ruey-Long Hong. Poor radiation sensitivity and potential radiosensitizers for betel-nuts related head and neck squamous cell carcinoma in Taiwan [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1111.

Abstract 1406: Plk1 attenuates colon inflammation and tumorigenesis

Abstract Inflammation-associated colon cancer, linked with long-standing colon inflammation, is often seen in patients with inflammatory bowel diseases (IBD), such as Crohn’s disease and ulcerative colitis. Typically, these patients are diagnosed at a younger age compared to those with sporadic colon cancer. Despite some advancements, the detailed molecular mechanisms driving cancer development in IBD remain unclear. Polo-like kinase 1 (Plk1), a serine/threonine kinase and cell cycle regulator, is recognized as an oncogene in various cancers. Intriguingly, higher Plk1 expression correlates with better survival rates in colon cancer patients. Besides, Plk1 also elevates in IBD cases, suggesting its significant role in both colitis and colon cancer. Our study explores Plk1's role in IBD-associated colon cancer using the azoxymethane (AOM)/dextran sulfate sodium (DSS) mouse model, revealing Plk1's suppressive impact on both colitis and related colon cancer. Citation Format: Xinyi Wang, Dang he, Fengyi Mao, Yifan Kong, Chaohao Li, Sai Wu, Jia Peng, Chi Wang, Zhiguo Li, Xiaoqi Liu. Plk1 attenuates colon inflammation and tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1406.

Abstract 371: Hypoxia-induced centrosome loss as a driver of chromosomal instability in prostate cancer

Abstract PURPOSE: This study aims to identify a causal mechanism of centrosome loss previously observed in primary prostate cancer. Prostate cancer progression is accompanied by bursts of chromosomal instability (CIN), including chromosomal translocations, oncogene amplifications, and chromothripsis. While high CIN correlates with most metrics of aggressive disease, we lack a mechanistic understanding of how CIN originates in prostate cancer. Recently, we discovered that cells in primary prostate tumors lack centrosomes, cytoplasmic organelles that ensure the fidelity of chromosome segregation by organizing the shape of the mitotic spindle. Experimental elimination of centrosomes in immortalized, non-tumorigenic prostate cell lines was sufficient to generate extensive CIN, resulting in oncogenic transformation of these lines when sub-cutaneously injected into NSG mice. Because we identified centrosome loss as a potential driver of CIN, we sought to understand mechanisms that can trigger centrosome loss in the prostate. Although centrosome loss naturally occurs during the development of some tissues, for example centrosome elimination during oogenesis, the mechanisms that trigger loss are not known. Therefore, we first investigated microenvironmental changes in early prostate cancer as a potential cause. Hypoxia, pathologically low oxygen concentration, is common in the aging prostate due to loss of vasculature and is associated with poor prostate cancer prognosis and high CIN. Therefore, we hypothesized that hypoxic exposure induces centrosome loss in prostate cells. Indeed, we found that exposure to 1% oxygen concentrations leads to progressive centrosome loss in non-tumorigenic, immortalized prostate epithelial cell lines. Using immunofluorescence of centrosomes in cultured cells, we found that hypoxia-induced centrosome loss is independent of HIF transcription but requires activation of the confluence-dependent Hippo signaling pathway. Mechanistically, we found that centrosome disassembly begins with the removal of the pericentriolar material (PCM), the outer shell of the centrosome that nucleates microtubules. We were able to block centrosome disassembly by over-expressing a constitutively-active mutant of Polo-like Kinase 1, which normally strengthens the PCM during mitosis to promote centrosome maturation. Furthermore, centrosome loss was prevented by treatment with the Protein Phosphatase 2A (PP2A) inhibitor Okadaic Acid. Using RNAseq, we have identified potential PP2A regulatory subunits that are up-regulated in cells undergoing hypoxia-induced centrosome loss. Our model is that hypoxia induces dephosphorylation of the PCM, mechanically weakening the centrosome and leaving it vulnerable to disassembly. Together with previous findings, we conclude that hypoxia-induced centrosome disassembly is a plausible driver of CIN in early prostate cancer. Citation Format: John M. Ryniawec, Gregory C. Rogers, Anne E. Cress. Hypoxia-induced centrosome loss as a driver of chromosomal instability in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 371.

The prognostic values and immune characteristics of polo-like kinases (PLKs) family: A pan-cancer multi-omics analysis

BackgroundIn the realm of tumor-targeted therapeutics, Polo-like kinases (PLKs) are a significant group of protein kinases that were found recently as being related to tumors. However, the significance of PLKs in pan-cancer remains systematically studied. Methods and materialsWe integrated multi-omics data to comprehensively investigate the expression patterns of the PLK family across various cancer types. Subsequently, study examined the associations between tumor mutation burden (TMB), microsatellite instability (MSI), immune subtype classification, immune infiltration, tumor microenvironment scores, immune checkpoint gene expression, and the PLKs expression profiles within various tumor types. Furthermore, using our mRNA sequencing data (TRUCE01) and four bladder cancer (BLCA) cohorts (GSE111636, GSE176307, and IMvigor210), We examined the correlation between the expression level of PLK and immunotherapy effectiveness. Next, Gene set enrichment analysis (GSEA) was evaluated to find that potentially enriched PLK signaling pathways. Utilizing TIMER 2.0, we conducted an immune infiltration analysis underlying transcriptome expression, copy number variations (CNV), or somatic mutations of PLKs in BLCA. Finally, mRNA expression validation of PLK1/3/4 by real-time PCR within 10 paired BLCA tissues, protein expression verification through the Human Protein Atlas (HPA), and PLK4 in vitro cytological studies have been employed in BLCA. ResultsThe expression of most of the PLK family members exhibits variation between cancerous tissues and adjacent normal tissues across various cancer species. Furthermore, the expression of PLKs demonstrates a significant association with immunotyping, infiltration of immune cell, tumor mutational burden (TMB), microsatellite instability (MSI), immunological checkpoint gene activity and therapeutic effectiveness in pan-tumor tissues. Additional investigation into the correlation between the PLK family and BLCA has revealed that the expression of the PLK genes holds substantial significance in the biological processes of BLCA. Furthermore, a notable association has been observed between the copy number variation, variant status, and the degree of certain immunological cell infiltration. Of note, the expression validation and in vitro phenotypic experiments have demonstrated that PLK4 has a significant function in promoting the BLCA cell proliferation, migration, and invasion. ConclusionCollectively, based on various databases, our results highlight the involvement of PLK gene family in the formation of different types of tumors and identify PLK-related genes that may be used for therapy.

Therapeutic targeting nudix hydrolase 1 creates a MYC-driven metabolic vulnerability.

Tumor cells must rewire nucleotide synthesis to satisfy the demands of unbridled proliferation. Meanwhile, they exhibit augmented reactive oxygen species (ROS) production which paradoxically damages DNA and free deoxy-ribonucleoside triphosphates (dNTPs). How these metabolic processes are integrated to fuel tumorigenesis remains to be investigated. MYC family oncoproteins coordinate nucleotide synthesis and ROS generation to drive the development of numerous cancers. We herein perform a Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based functional screen targeting metabolic genes and identified nudix hydrolase 1 (NUDT1) as a MYC-driven dependency. Mechanistically, MYC orchestrates the balance of two metabolic pathways that act in parallel, the NADPH oxidase 4 (NOX4)-ROS pathway and the Polo like kinase 1 (PLK1)-NUDT1 nucleotide-sanitizing pathway. We describe LC-1-40 as a potent, on-target degrader that depletes NUDT1 in vivo. Administration of LC-1-40 elicits excessive nucleotide oxidation, cytotoxicity and therapeutic responses in patient-derived xenografts. Thus, pharmacological targeting of NUDT1 represents an actionable MYC-driven metabolic liability.

CRL4DCAF1 ubiquitin ligase regulates PLK4 protein levels to prevent premature centriole duplication.

Centrioles play important roles in the assembly of centrosomes and cilia. Centriole duplication occurs once per cell cycle and is dependent on polo-like kinase 4 (PLK4). To prevent centriole amplification, which is a hallmark of cancer, PLK4 protein levels need to be tightly regulated. Here, we show that the Cullin4A/B-DDB1-DCAF1, CRL4DCAF1, E3 ligase targets PLK4 for degradation in human cells. DCAF1 binds and ubiquitylates PLK4 in the G2 phase to prevent premature centriole duplication in mitosis. In contrast to the regulation of PLK4 by SCFβ-TrCP, the interaction between PLK4 and DCAF1 is independent of PLK4 kinase activity and mediated by polo-boxes 1 and 2 of PLK4, suggesting that DCAF1 promotes PLK4 ubiquitylation independently of β-TrCP. Thus, the SCFSlimb/β-TrCP pathway, targeting PLK4 for ubiquitylation based on its phosphorylation state and CRL4DCAF1, which ubiquitylates PLK4 by binding to the conserved PB1-PB2 domain, appear to be complementary ways to control PLK4 abundance to prevent centriole overduplication.

Polo-like Kinase 1 Inhibition in KRAS-Mutated Metastatic Colorectal Cancer.

Inhibition of Polo-like kinase 1 (Plk1) is a promising new target and therapeutic strategy in metastatic colorectal cancer, especially those with KRAS mutations. New data support further development of onvansertib, and highlights the role of circulating tumor DNA in phase I clinical trials. See related article by Ahn et al., p. 2039.