PLK1 inhibition enhances temozolomide efficacy in IDH1 mutant gliomas

Brain-targeted CRISPR/Cas9 nanomedicine for effective glioblastoma therapy

CRISPR/Cas9 gene-editing technology shows great potential for treating a variety of diseases, such as glioblastoma multiforme (GBM). However, CRISPR components suffer from inherent delivery challenges, such as poor in vivo stability of Cas9 protein and gRNA, low blood-brain barrier (BBB) permeability and non-specific tissue or cell targeting. These defects have limited the application of Cas9/gRNA ribonucleoprotein (RNP) complexes for GBM therapy. Here, we developed a brain-targeted CRISPR/Cas9 based nanomedicine by fabricating an angiopep-2 decorated, guanidinium and fluorine functionalized polymeric nanoparticle with loading Cas9/gRNA RNP for the treatment of GBM. The guanidinium and fluorine domains of our polymeric nanoparticles were both capable of interacting with Cas9/gRNA RNP to stabilize it in blood circulation, without impairing its activity. Moreover, by leveraging angiopep-2 peptide functionality, the RNP nanoparticles efficiently crossed the BBB and accumulated in brain tumors. In U87MG cells, we achieved approximately 32% gene knockout and 67% protein reduction in the targeted proto-oncogene polo-like kinase 1 (PLK1). This was sufficient to suppress tumor growth and significantly improved the median survival time of mice bearing orthotopic glioblastoma to 40 days, while inducing negligible side or off-target effects. These results suggest that the developed brain-targeted CRISPR/Cas9 based nanomedicine shows promise for effective human glioblastoma gene therapy.

PLK1 inhibition-based combination therapies for cancer management

Polo-like kinase I (PLK1), a cell cycle regulating kinase, has been shown to have oncogenic function in several cancers. Although PLK1 inhibitors, such as BI2536, BI6727 (volasertib) and NMS-1286937 (onvansertib) are generally well-tolerated with a favorable pharmacokinetic profile, clinical successes are limited due to partial responses in cancer patients, especially those in advanced stages. Recently, combination therapies targeting multiple pathways are being tested for cancer management. In this review, we first discuss structure and function of PLK1, role of PLK1 in cancers, PLK1 specific inhibitors, and advantages of using combination therapy versus monotherapy followed by a critical account on PLK1-based combination therapies in cancer treatments, especially highlighting recent advancements and challenges. PLK1 inhibitors in combination with chemotherapy drugs and targeted small molecules have shown superior effects against cancer both in vitro and in vivo. PLK1-based combination therapies have shown increased apoptosis, disrupted cell cycle, and potential to overcome resistance in cancer cells/tissues over monotherapies. Further, with successes in preclinical experiments, researchers are validating such approaches in clinical trials. Although PLK1-based combination therapies have achieved initial success in clinical studies, there are examples where they have failed to improve patient survival. Therefore, further research is needed to identify and validate novel biologically informed co-targets for PLK1-based combinatorial therapies. Employing a network-based analysis, we identified potential PLK1 co-targets that could be examined further. In addition, understanding the mechanisms of synergism between PLK1 inhibitors and other agents may lead to a better approach on which agents to pair with PLK1 inhibition for optimum cancer treatment.

Calcyphosine promotes the proliferation of glioma cells and serves as a potential therapeutic target

Calcyphosine (CAPS) was initially identified from the canine thyroid. It also exists in many types of tumor, but its expression and function in glioma remain unknown. Here we explored the clinical significance and the functional mechanisms of CAPS in glioma. We found that CAPS was highly expressed in glioma and high expression of CAPS was correlated with poor survival, in glioma patients and public databases. Cox regression analysis showed that CAPS was an independent prognostic factor for glioma patients. Knockdown of CAPS suppressed the proliferation, whereas overexpression of CAPS promoted the proliferation of glioma both in vitro and in vivo. CAPS regulated the G2/M phase transition of the cell cycle, but had no obvious effect on apoptosis. CAPS affected PLK1 phosphorylation through interaction with MYPT1. CAPS knockdown decreased p‐MYPT1 at S507 and p‐PLK1 at S210. Expression of MYPT1 S507 phosphomimic rescued PLK1 phosphorylation and the phenotype caused by CAPS knockdown. The PLK1 inhibitor volasertib enhanced the therapeutic effect of temozolomide in glioma. Our data suggest that CAPS promotes the proliferation of glioma by regulating the cell cycle and the PLK1 inhibitor volasertib might be a chemosensitizer of glioma. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

From Laboratory Studies to Clinical Trials: Temozolomide Use in IDH-Mutant Gliomas

In this review, we discuss the use of the alkylating agent temozolomide (TMZ) in the treatment of IDH-mutant gliomas. We describe the challenges associated with TMZ in clinical (drug resistance and tumor recurrence) and preclinical settings (variabilities associated with in vitro models) in treating IDH-mutant glioma. Lastly, we summarize the emerging therapeutic targets that can potentially be used in combination with TMZ.

Combined Delivery of Temozolomide and siPLK1 Using Targeted Nanoparticles to Enhance Temozolomide Sensitivity in Glioma

INTRODUCTION

Temozolomide (TMZ) is the first-line chemotherapeutic option to treat glioma; however, its efficacy and clinical application are limited by its drug resistance properties. Polo-like kinase 1 (PLK1)-targeted therapy causes G2/M arrest and increases the sensitivity of glioma to TMZ. Therefore, to limit TMZ resistance in glioma, an angiopep-2 (A2)-modified polymeric micelle (A2PEC) embedded with TMZ and a small interfering RNA (siRNA) targeting PLK1 (siPLK1) was developed (TMZ-A2PEC/siPLK).

MATERIALS AND METHODS

TMZ was encapsulated by A2-PEG-PEI-PCL (A2PEC) through the hydrophobic interaction, and siPLK1 was complexed with the TMZ-A2PEC through electrostatic interaction. Then, an angiopep-2 (A2) modified polymeric micelle (A2PEC) embedding TMZ and siRNA targeting polo-like kinase 1 (siPLK1) was developed (TMZ-A2PEC/siPLK).

RESULTS

In vitro experiments indicated that TMZ-A2PEC/siPLK effectively enhanced the cellular uptake of TMZ and siPLK1 and resulted in significant cell apoptosis and cytotoxicity of glioma cells. In vivo experiments showed that glioma growth was inhibited, and the survival time of the animals was prolonged remarkably after TMZ-A2PEC/siPLK1 was injected via their tail vein.

DISCUSSION

The results demonstrate that the combination of TMZ and siPLK1 in A2PEC could enhance the efficacy of TMZ in treating glioma.

IDH mutation in glioma: molecular mechanisms and potential therapeutic targets

Isocitrate dehydrogenase (IDH) enzymes catalyse the oxidative decarboxylation of isocitrate and therefore play key roles in the Krebs cycle and cellular homoeostasis. Major advances in cancer genetics over the past decade have revealed that the genes encoding IDHs are frequently mutated in a variety of human malignancies, including gliomas, acute myeloid leukaemia, cholangiocarcinoma, chondrosarcoma and thyroid carcinoma. A series of seminal studies further elucidated the biological impact of the IDH mutation and uncovered the potential role of IDH mutants in oncogenesis. Notably, the neomorphic activity of the IDH mutants establishes distinctive patterns in cancer metabolism, epigenetic shift and therapy resistance. Novel molecular targeting approaches have been developed to improve the efficacy of therapeutics against IDH-mutated cancers. Here we provide an overview of the latest findings in IDH-mutated human malignancies, with a focus on glioma, discussing unique biological signatures and proceedings in translational research.

Proneural and mesenchymal glioma stem cells display major differences in splicing and lncRNA profiles

Therapy resistance and recurrence in high-grade gliomas are driven by their populations of glioma stem cells (GSCs). Thus, detailed molecular characterization of GSCs is needed to develop more effective therapies. We conducted a study to identify differences in the splicing profile and expression of long non-coding RNAs in proneural and mesenchymal GSC cell lines. Genes related to cell cycle, DNA repair, cilium assembly, and splicing showed the most differences between GSC subgroups. We also identified genes distinctly associated with survival among patients of mesenchymal or proneural subgroups. We determined that multiple long non-coding RNAs with increased expression in mesenchymal GSCs are associated with poor survival of glioblastoma patients. In summary, our study established critical differences between proneural and mesenchymal GSCs in splicing profiles and expression of long non-coding RNA. These splicing isoforms and lncRNA signatures may contribute to the uniqueness of GSC subgroups, thus contributing to cancer phenotypes and explaining differences in therapeutic responses.

FOCAD loss impacts microtubule assembly, G2/M progression and patient survival in astrocytic gliomas

In search of novel genes associated with glioma pathogenesis, we have previously shown frequent deletions of the KIAA1797/FOCAD gene in malignant gliomas, and a tumor suppressor function of the encoded focadhesin impacting proliferation and migration of glioma cells in vitro and in vivo. Here, we examined an association of reduced FOCAD gene copy number with overall survival of patients with astrocytic gliomas, and addressed the molecular mechanisms that govern the suppressive effect of focadhesin on glioma growth. FOCAD loss was associated with inferior outcome in patients with isocitrate dehydrogenase 1 or 2 (IDH)-mutant astrocytic gliomas of WHO grades II-IV. Multivariate analysis considering age at diagnosis as well as IDH mutation, MGMT promoter methylation, and CDKN2A/B homozygous deletion status confirmed reduced FOCAD gene copy number as a prognostic factor for overall survival. Using a yeast two-hybrid screen and pull-down assays, tubulin beta-6 and other tubulin family members were identified as novel focadhesin-interacting partners. Tubulins and focadhesin co-localized to centrosomes where focadhesin was enriched in proximity to centrioles. Focadhesin was recruited to microtubules via its interaction partner SLAIN motif family member 2 and reduced microtubule assembly rates, possibly explaining the focadhesin-dependent decrease in cell migration. During the cell cycle, focadhesin levels peaked in G2/M phase and influenced time-dependent G2/M progression potentially via polo like kinase 1 phosphorylation, providing a possible explanation for focadhesin-dependent cell growth reduction. We conclude that FOCAD loss may promote biological aggressiveness and worsen clinical outcome of diffuse astrocytic gliomas by enhancing microtubule assembly and accelerating G2/M phase progression.

Origin recognition complex subunit 1 regulates cell growth and metastasis in glioma by altering activation of ERK and JNK signaling pathway

Origin recognition complex subunit 1(ORC1) is reported to be closely associated with the cell cycle. However, studies on the role of ORC1 in glioma remain undefined. The aim of the present study was to determine whether ORC1 affects cell migration, invasion, apoptosis, and proliferation and to explore the possible underlying mechanism. GEO database analysis indicated that ORC1 was significantly upregulated in glioma, while Gene set enrichment analysis (GSEA) analysis indicated that ORC1 primarily regulated the cell cycle and affects apoptotic signaling pathways. Analysis of protein-protein interaction (PPI) and gene ontology (GO) to further study the relevant mechanisms revealed that the function of the interaction between proteins and ORC1 was primarily concentrated in the regulation of cell cycle, and apoptosis played a critical role in the whole PPI network. Western blot assay and RT-PCR assay indicated that ORC1 was significantly upregulated in glioma tissues. Western blot assay and RT-PCR indicated that ORC1 was significantly upregulated in glioma cell lines. Cell migration, invasion, apoptosis, and proliferation were detected using Transwell and wound healing assays, flow cytometry, colony formation, and CCK8, respectively. Furthermore, OCR1 inhibition reduced invasion and migration, promoted cell apoptosis. In addition, OCR1 overexpression promoted cell proliferation and induced G2 phase arrest. Moreover, OCR1 downregulation suppressed activation of the ERK/JNK signaling pathway. The effects of ORC1 on biological processes were reversed by ERK and JNK inhibitors. These results indicate that ORC1 could be a novel prognostic marker of glioma via the activation of the ERK/JNK signaling pathway.

Deconvolution and network analysis of IDH-mutant lower grade glioma predict recurrence and indicate therapeutic targets

Aim: IDH-mutant lower grade glioma (LGG) has been proven to have a good prognosis. However, its high recurrence rate has become a major therapeutic difficulty. Materials & methods: We combined epigenomic deconvolution and a network analysis on The Cancer Genome Atlas IDH-mutant LGG data. Results: Cell type compositions between recurrent and primary gliomas are significantly different, and the key cell type that determines the prognosis and recurrence risk was identified. A scoring model consisting of four gene expression levels predicts the recurrence risk (area under the receiver operating characteristic curve = 0.84). Transcription factor PPAR-α explains the difference between recurrent and primary gliomas. A cell cycle-related module controls prognosis in recurrent tumors. Conclusion: Comprehensive deconvolution and network analysis predict the recurrence risk and reveal therapeutic targets for recurrent IDH-mutant LGG.

PLK1 Inhibition Targets Myc-Activated Malignant Glioma Cells Irrespective of Mismatch Repair Deficiency-Mediated Acquired Resistance to Temozolomide

Mismatch repair (MMR) deficiency through MSH6 inactivation has been identified in up to 30% of recurrent high-grade gliomas, and represents a key molecular mechanism underlying the acquired resistance to the alkylating agent temozolomide (TMZ). To develop a therapeutic strategy that could be effective in these TMZ-refractory gliomas, we first screened 13 DNA damage response modulators for their ability to suppress viability of MSH6-inactivated, TMZ-resistant glioma cells. We identified a PLK1 selective inhibitor, Volasertib, as the most potent in inhibiting proliferation of glioblastoma cells. PLK1 inhibition induced mitotic catastrophe, G2-M cell-cycle arrest, and DNA damage, leading to caspase-mediated apoptosis in glioblastoma cells. Importantly, therapeutic effects of PLK1 inhibitors were not influenced by MSH6 knockdown, indicating that their action is independent of MMR status of the cells. Systemic treatment with Volasertib potently inhibited tumor growth in an MMR-deficient, TMZ-resistant glioblastoma xenograft model. Further in vitro testing in established and patient-derived cell line panels revealed an association of PLK1 inhibitor efficacy with cellular Myc expression status. We found that cells with deregulated Myc are vulnerable to PLK1 inhibition, as Myc overexpression sensitizes, whereas its silencing desensitizes, glioblastoma cells to PLK1 inhibitors. This discovery is clinically relevant as glioma progression post-TMZ treatment is frequently accompanied by MYC genomic amplification and/or pathway activation. In conclusion, PLK inhibitor represents a novel therapeutic option for recurrent gliomas, including those TMZ-resistant from MMR deficiency. Genomic MYC alteration may serve as a biomarker for PLK inhibitor sensitivity, as Myc-driven tumors demonstrated pronounced responses.

PLK1 inhibitor facilitates the suppressing effect of temozolomide on human brain glioma stem cells

Glioblastoma is the most frequent and most aggressive brain tumour in adults. Temozolomide is an oral chemotherapy drug and one of the major components of chemotherapy regimens used as a treatment of some brain cancers. We examined the tolerance of stem cells isolated from glioma cell line U87 and U251 to temozolomide (TMZ) and explored the effect of PLK1 (Polo like kinase 1) protein expression on TMZ sensibility. In our results, the inhibitory effects of TMZ on glioma cells U87, U251 and its stem cells were confirmed to be dose dependent and time dependent. Compared with glioma cells, the glioma stem cells showed a greater degree of tolerance. As the concentration of TMZ increased, the expression of PLK1 protein increased in U87 cells, CD133+ U87 stem cells and CD133- U87 cells. The increase range of PLK1 protein was large in CD133+ U87 stem cells and small in CD133- U87 cells. TMZ treatment in cells with low PLK1 protein expression efficiently suppressed the cell proliferation and sphere formation, while G2/M arrest was strongly induced. What's more, TMZ and PLK1 inhibitor synergize to inhibit glioma growth in vivo. In conclusion, our results suggest that down-regulation of PLK1 protein enhanced the inhibition of TMZ on glioma stem cells, suggesting its clinical value to adverse TMZ resistance in glioma treatment.

Autophagy in glioma cells: An identity crisis with a clinical perspective

Over the last decade, autophagy has emerged as one of the critical cellular systems that control homeostasis. Besides management of normal homeostatic processes, autophagy can also be induced by tissue damage stress or by rapidly progressing tumors. During tumor progression, autophagy mediates a cellular reaction to the changes inside and outside of cells, which leads to tumor adaptation. Even though the regulation of autophagy seems universal and is a well-described process, its dysregulation and role in glioma progression remain an important topic of investigation. In this review, we summarize recent evidence of autophagy regulation in brain tumor tissues and possible interconnection between signaling pathways that govern cellular responses. This perspective may help to assess the qualitative differences and various outcomes in response to autophagy stimulation.