CDK8/19 inhibition induces premature G1/S transition and ATR-dependent cell death in prostate cancer cells

Cyclin-dependent kinases as mediators of aberrant transcription in prostate cancer

Transcriptional control of gene expression is fundamental to all cellular processes. Conversely, transcriptional dysregulation is a hallmark of cancer. While this hallmark is a key driver of all malignancy-related process, it also represents a vulnerability that can be exploited therapeutically. Prostate cancer is a prime example of this phenomenon: it is characterised by aberrant transcription and treated with drugs that influence transcriptional pathways. Indeed, the primary oncogenic driver and therapeutic target of prostate cancer, the androgen receptor (AR), is a transcription factor. Moreover, a plethora of other transcriptional regulators, including transcriptional cyclin-dependent kinases (CDK7, CDK8 and CDK9), MYC and Bromodomain-containing protein 4 (BRD4), play prominent roles in disease progression. In this review, we focus on the roles of transcriptional CDKs in prostate cancer growth, metastasis and therapy resistance and discuss their interplay with AR, MYC and BRD4. Additionally, we explore recent advances in the therapeutic targeting of transcriptional CDKs and propose how these strategies could be effectively harnessed for the treatment of prostate cancer.

Targeting Mediator Kinase Cyclin-Dependent Kinases 8/19 Potentiates Chemotherapeutic Responses, Reverses Tumor Growth, and Prolongs Survival from Ovarian Clear Cell Carcinoma

BACKGROUND/OBJECTIVE

Ovarian clear cell carcinomas (OCCCs) are a rare histological subtype of epithelial ovarian cancer characterized by resistance to platinum-based therapy. CDK8/19, a component of the regulatory CDK module associated with Mediator complex, has been implicated in transcriptional reprogramming and drug resistance in various solid tumors. Our study aimed to investigate the therapeutic potential of CDK8/19 kinase inhibition using selective inhibitors SNX631 and SNX631-6 in OCCC treatment, both as monotherapy and in combination with standard chemotherapeutics.

METHODS

CDK8 and Ki67 levels were evaluated via immunohistochemistry in benign, primary, and metastatic ovarian cancer tissues. The efficacy of SNX631 alone and in combination with cisplatin or paclitaxel was assessed in OCCC cell lines (ES-2, TOV-21-G, RMG-1). In vivo evaluation utilized xenograft models with subcutaneous and intraperitoneal delivery of the OCCC ES2 cells and oral delivery of SNX631-6, with the monitoring of tumor growth, metastatic spread, and survival.

RESULTS

CDK8 protein levels were elevated in OC tissues, particularly in OCCC primary and metastatic lesions compared to benign tissue. While CDK8/19 inhibition showed limited effects on in vitro cell proliferation, SNX631-6 demonstrated significant antitumor and anti-metastatic activity in vivo. Notably, SNX631-6 enhanced the efficacy of cisplatin, substantially inhibiting tumor growth and extending overall survival.

CONCLUSIONS

Therapeutically achievable doses of CDK8/19 inhibitors may provide clinical benefit for OCCC patients by inhibiting tumor growth and reversing platinum resistance, potentially addressing a critical treatment challenge in this rare ovarian cancer subtype.

CDK8/19 inhibition attenuates G1 arrest induced by BCR-ABL antagonists and accelerates death of chronic myelogenous leukemia cells

Imatinib mesylate (IM) and other BCR-ABL tyrosine kinase inhibitors (BCR-ABLi) are the mainstay of chronic myelogenous leukemia (CML) treatment. However, activation of circumventing signaling pathways and quiescence may limit BCR-ABLi efficacy. CDK8/19 Mediator kinases have been implicated in the emergence of non-genetic drug resistance. Dissecting the effects of pharmacological CDK8/19 inhibition on CML survival in response to BCR-ABLi, we found that a selective, non-toxic CDK8/19 inhibitor (CDK8/19i) Senexin B (SenB) and other CDK8/19i sensitized K562 cells to different BCR-ABLi via attenuation of cell cycle arrest. In particular, SenB prevented IM-induced upregulation of genes that negatively regulate cell cycle progression. SenB also antagonized IM-activated p27Kip1 elevation thereby diminishing the population of G1-arrested cells. After transient G1 arrest, cells treated with IM + SenB re-entered the S phase, where they were halted and underwent replicative stress. Consequently, the combination of IM and SenB intensified apoptotic cell death, measured by activation of caspase 9 and 3, subsequent cleavage of poly(ADPriboso)polymerase 1, positive Annexin V staining and increase of subG1 fraction. In contrast, IM-treated BCR-ABL-positive KU812 CML cells, which did not induce p27Kip1, readily died regardless of SenB treatment. Thus, CDK8/19i prevent the quiescence-mediated escape from BCR-ABLi-induced apoptosis, suggesting a strategy for avoiding the CML relapse.

Roles of CDK12 mutations in PCa development and treatment

Prostate cancer (PCa) is one of the most common cancers in men, and cyclin-dependent kinase 12 (CDK12) is emerging as a novel star player in the PCa tumorigenesis and progression to castration-resistant prostate cancer (CRPC). In PCa, CDK12 alterations are mostly loss-of-function mutations featuring intronic polyadenylation (IPA), focal tandem duplications (FTDs), and R-loops formation and transcription-replication conflicts (TRCs). The occurrence of IPA can result in homologous recombination deficiency (HRD) and androgen receptor (AR) variation. FTDs induce neoantigens and increase the expression of the AR, MYC, and other hotspot- associated genes. R-loops lead to TRCs and influence various cellular processes, including gene expression and genome stability. Due to the poor prognosis of CDK12-mutant PCa patients and the mediocre response to classic standard therapies, HRD and increased neoantigen levels have provided clinicians with new insights into alternative systematic treatments for this novel PCa phenotype. In this review, we summarize the roles of CDK12 mutations in PCa and discuss their clinical value, suggesting that CDK12 potentially represents a target for further research and the development of clinical strategies for PCa.

MED12 and CDK8/19 Modulate Androgen Receptor Activity and Enzalutamide Response in Prostate Cancer

Prostate cancer progression is driven by androgen receptor (AR) activity, which is a target for therapeutic approaches. Enzalutamide is an AR inhibitor that prolongs the survival of patients with advanced prostate cancer. However, resistance mechanisms arise and impair its efficacy. One of these mechanisms is the expression of AR-V7, a constitutively active AR splice variant. The Mediator complex is a multisubunit protein that modulates gene expression on a genome-wide scale. MED12 and cyclin-dependent kinase (CDK)8, or its paralog CDK19, are components of the kinase module that regulates the proliferation of prostate cancer cells. In this study, we investigated how MED12 and CDK8/19 influence cancer-driven processes in prostate cancer cell lines, focusing on AR activity and the enzalutamide response. We inhibited MED12 expression and CDK8/19 activity in LNCaP (AR+, enzalutamide-sensitive), 22Rv1 (AR-V7+, enzalutamide-resistant), and PC3 (AR-, enzalutamide-insensitive) cells. Both MED12 and CDK8/19 inhibition reduced cell proliferation in all cell lines, and MED12 inhibition reduced proliferation in the respective 3D spheroids. MED12 knockdown significantly inhibited c-Myc protein expression and signaling pathways. In 22Rv1 cells, it consistently inhibited the AR response, prostate-specific antigen (PSA) secretion, AR target genes, and AR-V7 expression. Combined with enzalutamide, MED12 inhibition additively decreased the AR activity in both LNCaP and 22Rv1 cells. CDK8/19 inhibition significantly decreased PSA secretion in LNCaP and 22Rv1 cells and, when combined with enzalutamide, additively reduced proliferation in 22Rv1 cells. Our study revealed that MED12 and CDK8/19 regulate AR activity and that their inhibition may modulate response to enzalutamide in prostate cancer.

Design and synthesis of 7-azaindole derivatives as potent CDK8 inhibitors for the treatment of acute myeloid leukemia

It is of great significance to design and synthesize novel structural inhibitors with good antitumor activity. In this study, based on rational design, a total of 42 7-azaindole derivatives as novel CDK8 inhibitors were designed and synthesized. All compounds were screened with antitumor activity and compound 6 (1-(3-((1H-pyrrolo[2,3-b]pyridin-5-yl)oxy)phenyl)-3-(m-tolyl)urea) exhibited the best activity, especially in acute myeloid leukemia (GI50 MV4-11 = 1.97 ± 1.24 μM). This compound also exhibited excellent inhibitory activity against CDK8 (IC50 = 51.3 ± 4.6 nM). Further mechanism studies shown that it could inhibit STAT5 phosphorylation and induce cell cycle arrest in the G1 phase, leading to apoptosis in acute myeloid leukemia cells. In addition, acute toxicity at a dose of 1000 mg kg-1 indicated the low toxicity of this compound.

Discovery of a Novel and Potent Cyclin-Dependent Kinase 8/19 (CDK8/19) Inhibitor for the Treatment of Cancer

The mediator kinases CDK8 and CDK19 control the dynamic transcription of selected genes in response to various signals and have been shown to be hijacked to sustain hyperproliferation by various solid and liquid tumors. CDK8/19 is emerging as a promising anticancer therapeutic target. Here, we report the discovery of compound 12, a novel small molecule CDK8/19 inhibitor. This molecule demonstrated not only decent enzymatic and cellular activities but also remarkable selectivity in CDK and kinome panels. Besides, compound 12 also displayed favorable ADME profiles including low CYP1A2 inhibition, acceptable clearance, and high oral bioavailability in multiple preclinical species. Robust in vivo PD and efficacy studies in mice models further demonstrated its potential use as mono- and combination therapy for the treatment of cancers.

Mediator kinase inhibition reverses castration resistance of advanced prostate cancer

Mediator kinases CDK19 and CDK8, pleiotropic regulators of transcriptional reprogramming, are differentially regulated by androgen signaling, but both kinases are upregulated in castration-resistant prostate cancer (CRPC). Genetic or pharmacological inhibition of CDK8 and CDK19 reverses the castration-resistant phenotype and restores the sensitivity of CRPC xenografts to androgen deprivation in vivo. Prolonged CDK8/19 inhibitor treatment combined with castration not only suppressed the growth of CRPC xenografts but also induced tumor regression and cures. Transcriptomic analysis revealed that Mediator kinase inhibition amplified and modulated the effects of castration on gene expression, disrupting CRPC adaptation to androgen deprivation. Mediator kinase inactivation in tumor cells also affected stromal gene expression, indicating that Mediator kinase activity in CRPC molded the tumor microenvironment. The combination of castration and Mediator kinase inhibition downregulated the MYC pathway, and Mediator kinase inhibition suppressed a MYC-driven CRPC tumor model even without castration. CDK8/19 inhibitors showed efficacy in patient-derived xenograft models of CRPC, and a gene signature of Mediator kinase activity correlated with tumor progression and overall survival in clinical samples of metastatic CRPC. These results indicate that Mediator kinases mediated androgen-independent in vivo growth of CRPC, supporting the development of CDK8/19 inhibitors for the treatment of this presently incurable disease.

Unveiling the impact of CDK8 on tumor progression: mechanisms and therapeutic strategies

CDK8 is an important member of the cyclin-dependent kinase family associated with transcription and acts as a key "molecular switch" in the Mediator complex. CDK8 regulates gene expression by phosphorylating transcription factors and can control the transcription process through Mediator complex. Previous studies confirmed that CDK8 is an important oncogenic factor, making it a potential tumor biomarker and a promising target for tumor therapy. However, CDK8 has also been confirmed to be a tumor suppressor, indicating that it not only promotes the development of tumors but may also be involved in tumor suppression. Therefore, the dual role of CDK8 in the process of tumor development is worth further exploration and summary. This comprehensive review delves into the intricate involvement of CDK8 in transcription-related processes, as well as its role in signaling pathways related to tumorigenesis, with a focus on its critical part in driving cancer progression.

CD24 induced cellular quiescence-like state and chemoresistance in ovarian cancer cells via miR-130a/301a-dependent CDK19 downregulation

Cancer stem-like cell (CSC) is thought to be responsible for ovarian cancer recurrence. CD24 serves as a CSC marker for ovarian cancer and regulates the expression of miRNAs, which are regulators of CSC phenotypes. Therefore, CD24-regulated miRNAs may play roles in manifesting the CSC phenotypes in ovarian cancer cells. Our miRNA transcriptome analysis showed that 94 miRNAs were up or down-regulated in a CD24-high clone from an ovarian cancer patient compared to a CD24-low one. The CD24-dependent expression trend of the top 7 upregulated miRNAs (miR-199a-3p, 34c, 199a-5p, 130a, 301a, 214, 34b*) was confirmed in other 8 clones (4 clones for each group). CD24 overexpression upregulated the expression of miR-199a-3p, 34c, 199a-5p, 130a, 301a, 214, and 34b* in TOV112D (CD24-low) cells compared to the control, while CD24 knockdown downregulated the expression of miR-199a-3p, 199a-5p, 130a, 301a, and 34b* in OV90 (CD24-high) cells. miR-130a and 301a targeted CDK19, which induced a cellular quiescence-like state (increased G0/G1 phase cell population, decreased cell proliferation, decreased colony formation, and decreased RNA synthesis) and resistance to platinum-based chemotherapeutic agents. CD24 regulated the expression of miR-130a and 301a via STAT4 and YY1 phosphorylation mediated by Src and FAK. miR-130a and 301a were positively correlated in expression with CD24 in ovarian cancer patient tissues and negatively correlated with CDK19. Our results showed that CD24 expression may induce a cellular quiescence-like state and resistance to platinum-based chemotherapeutic agents in ovarian cancer via miR-130a and 301a upregulation. CD24-miR-130a/301a-CDK19 signaling axis could be a prognostic marker for or a potential therapeutic target against ovarian cancer recurrence.

Key Proteins of Replication Stress Response and Cell Cycle Control as Cancer Therapy Targets

Replication stress (RS) is a characteristic state of cancer cells as they tend to exchange precision of replication for fast proliferation and increased genomic instability. To overcome the consequences of improper replication control, malignant cells frequently inactivate parts of their DNA damage response (DDR) pathways (the ATM-CHK2-p53 pathway), while relying on other pathways which help to maintain replication fork stability (ATR-CHK1). This creates a dependency on the remaining DDR pathways, vulnerability to further destabilization of replication and synthetic lethality of DDR inhibitors with common oncogenic alterations such as mutations of TP53, RB1, ATM, amplifications of MYC, CCNE1 and others. The response to RS is normally limited by coordination of cell cycle, transcription and replication. Inhibition of WEE1 and PKMYT1 kinases, which prevent unscheduled mitosis entry, leads to fragility of under-replicated sites. Recent evidence also shows that inhibition of Cyclin-dependent kinases (CDKs), such as CDK4/6, CDK2, CDK8/19 and CDK12/13 can contribute to RS through disruption of DNA repair and replication control. Here, we review the main causes of RS in cancers as well as main therapeutic targets-ATR, CHK1, PARP and their inhibitors.

Development of adaptive anoikis resistance promotes metastasis that can be overcome by CDK8/19 Mediator kinase inhibition

Anoikis resistance or evasion of cell death triggered by cell detachment into suspension is a hallmark of cancer that is concurrent with cell survival and metastasis. The effects of frequent matrix detachment encounters on the development of anoikis resistance in cancer remains poorly defined. Here we show using a panel of ovarian cancer models, that repeated exposure to suspension stress in vitro followed by attached recovery growth leads to the development of anoikis resistance paralleling in vivo development of anoikis resistance in ovarian cancer ascites. This resistance is concurrent with enhanced invasion, chemoresistance and the ability of anoikis adapted cells to metastasize to distant sites. Adapted anoikis resistant cells show a heightened dependency on oxidative phosphorylation and can also evade immune surveillance. We find that such acquired anoikis resistance is not genetic, as acquired resistance persists for a finite duration in the absence of suspension stress. Transcriptional reprogramming is however essential to this process, as acquisition of adaptive anoikis resistance in vitro and in vivo is exquisitely sensitive to inhibition of CDK8/19 Mediator kinase, a pleiotropic regulator of transcriptional reprogramming. Our data demonstrate that growth after recovery from repeated exposure to suspension stress is a direct contributor to metastasis and that inhibition of CDK8/19 Mediator kinase during such adaptation provides a therapeutic opportunity to prevent both local and distant metastasis in cancer.

Cyclin-dependent kinases: Masters of the eukaryotic universe

A family of structurally related cyclin-dependent protein kinases (CDKs) drives many aspects of eukaryotic cell function. Much of the literature in this area has considered individual members of this family to act primarily either as regulators of the cell cycle, the context in which CDKs were first discovered, or as regulators of transcription. Until recently, CDK7 was the only clear example of a CDK that functions in both processes. However, new data points to several "cell-cycle" CDKs having important roles in transcription and some "transcriptional" CDKs having cell cycle-related targets. For example, novel functions in transcription have been demonstrated for the archetypal cell cycle regulator CDK1. The increasing evidence of the overlap between these two CDK types suggests that they might play a critical role in coordinating the two processes. Here we review the canonical functions of cell-cycle and transcriptional CDKs, and provide an update on how these kinases collaborate to perform important cellular functions. We also provide a brief overview of how dysregulation of CDKs contributes to carcinogenesis, and possible treatment avenues. This article is categorized under: RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Processing > 3' End Processing RNA Processing > Splicing Regulation/Alternative Splicing.

CDK8 and CDK19: positive regulators of signal-induced transcription and negative regulators of Mediator complex proteins

We have conducted a detailed transcriptomic, proteomic and phosphoproteomic analysis of CDK8 and its paralog CDK19, alternative enzymatic components of the kinase module associated with transcriptional Mediator complex and implicated in development and diseases. This analysis was performed using genetic modifications of CDK8 and CDK19, selective CDK8/19 small molecule kinase inhibitors and a potent CDK8/19 PROTAC degrader. CDK8/19 inhibition in cells exposed to serum or to agonists of NFκB or protein kinase C (PKC) reduced the induction of signal-responsive genes, indicating a pleiotropic role of Mediator kinases in signal-induced transcriptional reprogramming. CDK8/19 inhibition under basal conditions initially downregulated a small group of genes, most of which were inducible by serum or PKC stimulation. Prolonged CDK8/19 inhibition or mutagenesis upregulated a larger gene set, along with a post-transcriptional increase in the proteins comprising the core Mediator complex and its kinase module. Regulation of both RNA and protein expression required CDK8/19 kinase activities but both enzymes protected their binding partner cyclin C from proteolytic degradation in a kinase-independent manner. Analysis of isogenic cell populations expressing CDK8, CDK19 or their kinase-inactive mutants revealed that CDK8 and CDK19 have the same qualitative effects on protein phosphorylation and gene expression at the RNA and protein levels, whereas differential effects of CDK8 versus CDK19 knockouts were attributable to quantitative differences in their expression and activity rather than different functions.

Discovery of a novel oral type Ⅰ CDK8 inhibitor against acute myeloid leukemia

CDK8 plays a key role in acute myeloid leukemia, colorectal cancer and other cancers. Here, a total of 54 compounds were designed and synthesized. Among them, the most potent one compound 43 (3-(1H-pyrrolo[2,3-b]pyridin-5-yl)benzamide), a novel CDK8 Ⅰ inhibitor, showed strong inhibitory activity against CDK8 (IC₅₀ = 51.9 nM), good kinase selectivity, good anti AML cell proliferation activity (molm-13 GC₅₀ = 1.57 ± 0.59 μM) and low toxicity in vivo (acute toxicity: 2000 mg/kg). Further mechanistic studies revealed that this compound could target CDK8 and then phosphorylate STAT-1 and STAT-5 thereby inhibiting of AML cell proliferation. In addition, compound 43 showed relatively good bioavailability (F = 28.00%) and could inhibit the growth of AML tumors in a dose-dependent manner in vivo. This study facilitates the further development of more potent CDK8 inhibitors for the treatment of the AML.

CDK8 and CDK19 act redundantly to control the CFTR pathway in the intestinal epithelium

CDK8 and CDK19 form a conserved cyclin-dependent kinase subfamily that interacts with the essential transcription complex, Mediator, and also phosphorylates the C-terminal domain of RNA polymerase II. Cells lacking either CDK8 or CDK19 are viable and have limited transcriptional alterations, but whether the two kinases redundantly control cell proliferation and differentiation is unknown. Here, we find in mice that CDK8 is dispensable for regulation of gene expression, normal intestinal homeostasis, and efficient tumourigenesis, and is largely redundant with CDK19 in the control of gene expression. Their combined deletion in intestinal organoids reduces long-term proliferative capacity but is not lethal and allows differentiation. However, double-mutant organoids show mucus accumulation and increased secretion by goblet cells, as well as downregulation of expression of the cystic fibrosis transmembrane conductance regulator (CFTR) and functionality of the CFTR pathway. Pharmacological inhibition of CDK8/19 kinase activity in organoids and in mice recapitulates several of these phenotypes. Thus, the Mediator kinases are not essential for cell proliferation and differentiation in an adult tissue, but they cooperate to regulate specific transcriptional programmes.

Discovery of the Novel 1H-Pyrrolo[2,3-b]pyridine Derivative as a Potent Type II CDK8 Inhibitor against Colorectal Cancer

Few targeted drugs were approved for treatment of colorectal cancer (CRC). Cyclin-dependent kinase 8 played a vital role in regulating transcription and was a key colorectal oncogene associated to colorectal cancer. Here, through de novo drug design and in depth structure-activity relationship analysis, title compound 22, (3-(3-(1H-pyrrolo[2,3-b]pyridin-5-yl)phenyl)-N-(4-methyl-3-(trifluoromethyl)phenyl)propenamide), was discovered as a potent type II CDK8 inhibitor, which exhibited potent kinase activity with an IC₅₀ value of 48.6 nM and could significantly inhibit tumor growth in xenografts of CRC in vivo. Further mechanism studies indicated that it could target CDK8 to indirectly inhibit β-catenin activity, which caused downregulation of the WNT/β-catenin signal and inducing cell cycle arrest in G2/M and S phases. More importantly, the title compound exhibited low toxicity with good bioavailability (F = 39.8%). These results could provide the reference for design of new type II CDK8 inhibitors against colorectal cancer.

Transcription associated cyclin-dependent kinases as therapeutic targets for prostate cancer

Transcriptional deregulation has emerged as a hallmark of several cancer types. In metastatic castration-resistant prostate cancer, a stage in which systemic androgen deprivation therapies fail to show clinical benefit, transcriptional addiction to the androgen receptor is maintained in most patients. This has led to increased efforts to find novel therapies that prevent oncogenic transactivation of the androgen receptor. In this context, a group of druggable protein kinases, known as transcription associated cyclin-dependent kinases (tCDKs), show great potential as therapeutic targets. Despite initial reservations about targeting tCDKs due to their ubiquitous and prerequisite nature, preclinical studies showed that selectively inhibiting such kinases could provide sufficient therapeutic window to exert antitumour effects in the absence of systemic toxicity. As a result, several highly specific inhibitors are currently being trialled in solid tumours, including prostate cancer. This article summarises the roles of tCDKs in regulating gene transcription and highlights rationales for their targeting in prostate cancer. It provides an overview of the most recent developments in this therapeutic area, including the most recent clinical advances, and discusses the utility of tCDK inhibitors in combination with established cancer agents.

Inhibition of Cyclin-Dependent Kinase 8/Cyclin-Dependent Kinase 19 Suppresses Its Pro-Oncogenic Effects in Prostate Cancer

Progression of prostate cancer (PCa) is characterized by metastasis and castration resistance after response to androgen deprivation. Therapeutic options are limited, causing high morbidity and lethality. Recent work reported pro-oncogenic implications of the Mediator subunits cyclin-dependent kinase (CDK) 8 and 19 for the progression of PCa. The current study explored the underlying molecular mechanisms of CDK8/CDK19 and tested effects of novel CDK8/CDK19 inhibitors. PC3, DU145, LNCaP, and androgen-independent LNCaP Abl were used for in vitro experiments. Two inhibitors and CDK19 overexpression were used to modify CDK8/CDK19 activity. MTT assay, propidium iodide staining, wound healing assay, Boyden chamber assay, and adhesion assay were used to investigate cell viability, cell cycle, migration, and adhesion, respectively. Peptide-kinase screen using the PamGene platform was conducted to identify phosphorylated targets. Combining CDK8/CDK19 inhibitors with anti-androgens led to synergistic antiproliferative effects and sensitized androgen-independent cells to bicalutamide. CDK8/CDK19 inhibition resulted in reduced migration and increased collagen I-dependent adhesion. Phosphorylation of multiple peptides linked to cancer progression was identified to be dependent on CDK8/CDK19. In summary, this study substantially supports recent findings on CDK8/CDK19 in PCa progression. These findings contribute to a better understanding of underlying pro-oncogenic effects, which is needed to develop CDK8/CDK19 as a therapeutic target in PCa.

Hotair promotes the migration and proliferation in ovarian cancer by miR-222-3p/CDK19 axis

Previous studies in our laboratory have reported that miR-222-3p was a tumor-suppressive miRNA in OC. This study aims to further understand the regulatory role of miR-222-3p in OC and provide a new mechanism for its prevention and treatment. We first found that miR-222-3p inhibited the migration and proliferation of OC cells. Then, we observed CDK19 was highly expressed in OC and inversely correlated with miR-222-3p. Besides, we observed that miR-222-3p directly binds to the 3′-UTR of CDK19 and inhibits CDK19 translation, thus inhibiting OC cell migration and proliferation in vitro and repressed tumor growth in vivo. We also observed the inhibitory effect of Hotair on miR-222-3p in OC. In addition, Hotair could promote the proliferation and migration of OC cells in vitro and facilitate the growth and metastasis of tumors in vivo. Moreover, Hotair was positively correlated with CDK19 expression. These results suggest Hotair indirectly up-regulates CDK19 through sponging miR-222-3p, which enhances the malignant behavior of OC. This provides a further understanding of the mechanism of the occurrence and development of OC.

Unravelling the Role of Kinases That Underpin Androgen Signalling in Prostate Cancer

The androgen receptor (AR) signalling pathway is the key driver in most prostate cancers (PCa), and is underpinned by several kinases both upstream and downstream of the AR. Many popular therapies for PCa that target the AR directly, however, have been circumvented by AR mutation, such as androgen receptor variants. Some upstream kinases promote AR signalling, including those which phosphorylate the AR and others that are AR-regulated, and androgen regulated kinase that can also form feed-forward activation circuits to promotes AR function. All of these kinases represent potentially druggable targets for PCa. There has generally been a divide in reviews reporting on pathways upstream of the AR and those reporting on AR-regulated genes despite the overlap that constitutes the promotion of AR signalling and PCa progression. In this review, we aim to elucidate which kinases—both upstream and AR-regulated—may be therapeutic targets and require future investigation and ongoing trials in developing kinase inhibitors for PCa.

CDK19 regulates the proliferation of hematopoietic stem cells and acute myeloid leukemia cells by suppressing p53-mediated transcription of p21

The cell cycle progression of hematopoietic stem cells (HSCs) and acute myeloid leukemia (AML) cells is precisely controlled by multiple regulatory factors. However, the underlying mechanisms are not fully understood. Here, we find that cyclin-dependent kinase 19 (CDK19), not its paralogue CDK8, is relatively enriched in mouse HSCs, and its expression is more significantly increased than CDK8 after proliferative stresses. Furthermore, SenexinB (a CDK8/19 inhibitor) treatment impairs the proliferation and self-renewal ability of HSCs. Moreover, overexpression of CDK19 promotes HSC function better than CDK8 overexpression. Using CDK19 knockout mice, we observe that CDK19^-/- HSCs exhibit similar phenotypes to those of cells treated with SenexinB. Interestingly, the p53 signaling pathway is significantly activated in HSCs lacking CDK19 expression. Further investigations show that CDK19 can interact with p53 to inhibit p53-mediated transcription of p21 in HSCs and treatment with a specific p53 inhibitor (PFTβ) partially rescues the defects of CDK19-null HSCs. Importantly, SenexinB treatment markedly inhibits the proliferation of AML cells. Collectively, our findings indicate that CDK19 is involved in regulating HSC and AML cell proliferation via the p53-p21 pathway, revealing a new mechanism underlying cell cycle regulation in normal and malignant hematopoietic cells.

Triple-negative breast cancer cells rely on kinase-independent functions of CDK8 to evade NK-cell-mediated tumor surveillance

Triple-negative breast cancer (TNBC) is an aggressive malignant disease that is responsible for approximately 15% of breast cancers. The standard of care relies on surgery and chemotherapy but the prognosis is poor and there is an urgent need for new therapeutic strategies. Recent in silico studies have revealed an inverse correlation between recurrence-free survival and the level of cyclin-dependent kinase 8 (CDK8) in breast cancer patients. CDK8 is known to have a role in natural killer (NK) cell cytotoxicity, but its function in TNBC progression and immune cell recognition or escape has not been investigated. We have used a murine model of orthotopic breast cancer to study the tumor-intrinsic role of CDK8 in TNBC. Knockdown of CDK8 in TNBC cells impairs tumor regrowth upon surgical removal and prevents metastasis. In the absence of CDK8, the epithelial-to-mesenchymal transition (EMT) is impaired and immune-mediated tumor-cell clearance is facilitated. CDK8 drives EMT in TNBC cells in a kinase-independent manner. In vivo experiments have confirmed that CDK8 is a crucial regulator of NK-cell-mediated immune evasion in TNBC. The studies also show that CDK8 is involved in regulating the checkpoint inhibitor programmed death-ligand 1 (PD-L1). The CDK8-PD-L1 axis is found in mouse and human TNBC cells, underlining the importance of CDK8-driven immune cell evasion in these highly aggressive breast cancer cells. Our data link CDK8 to PD-L1 expression and provide a rationale for investigating the possibility of CDK8-directed therapy for TNBC.

CDK19 as a diagnostic marker for high-grade prostatic intraepithelial neoplasia

High-grade prostatic intraepithelial neoplasia (HGPIN) is a facultative precursor lesion of prostate cancer (PCa). Multifocal HGPIN in needle biopsies in the absence of PCa indicates a higher risk of cancer detection in subsequent biopsies. Therefore, a reliable diagnosis of HGPIN is of high clinical relevance guiding the management of patients with cancer-negative biopsies. Detection of HGPIN is merely based on morphological features while biomarkers aiding in the diagnosis of HGPIN and its differentiation from benign glands and other glandular lesions are lacking yet. Here, we investigated the expression of CDK19 by immunohistochemistry on prostate needle biopsies of 140 patients who were all diagnosed with PCa using whole tissue sections, and compared CDK19 levels between HGPIN, PCa and adjacent benign glands. In addition, CDK19 was compared to AMACR expression in a subset of intraductal carcinomas (IDC) on radical prostatectomy (RP) specimens. HGPIN was present in 65.7% of biopsies and in 88% associated to adjacent PCa. CDK19 overexpression defined as moderate to high CDK19 expression visible at low magnification was found in 82.6% of HGPIN. In contrast, 89.3% of benign glands were CDK19-negative or demonstrated only low CDK19 expression highlighting a high sensitivity and specificity to accurately detect HGPIN based on CDK19 expression levels. CDK19 was overexpressed in 59% of PCa but did not correlate significantly with the expression of intermingled HGPIN. On RP, CDK19 and AMACR showed no significant difference in the detection rate of IDC. In summary, assessment of CDK19 facilitates accurate and simplified diagnosis of HGPIN with high sensitivity and specificity and aides the differentiation to non-neoplastic glandular alterations. Considering the high clinical significance of diagnosis HGPIN that still has a limited reproducibility among pathologists we suggest CDK19 as diagnostic biomarker for HGPIN.

MicroRNA-567 inhibits cell proliferation and induces cell apoptosis in A549 NSCLC cells by regulating cyclin-dependent kinase 8

MicroRNA-567 (miR-567) plays a decisive role in cancers whereas its role in non-small cell lung cancer (NSCLC) is still unexplored. This study was therefore planned to explore the regulatory function of miR-567 in A549 NSCLC cells and investigate its possible molecular mechanism that may help in NSCLC treatment. In the current study, miR-567 expression was examined by quantitative real time-polymerase chain reaction (qRT-PCR) in different NSCLC cell lines in addition to normal cell line. A549 NSCLC cells were transfected by miR-567 mimic, miR-567 inhibitor, and negative control siRNA. Cell proliferation was evaluated by MTT and 5-bromo-2'deoxyuridine assays. Cell cycle distribution and apoptosis were studied by flow cytometry. Bioinformatics analysis programs were used to expect the putative target of miR-567. The expression of cyclin-dependent kinase 8 (CDK8) gene at mRNA and protein levels were evaluated by using qRT-PCR and western blotting. Our results found that miR-567 expressions decreased in all the studied NSCLC cells as compared to the normal cell line. A549 cell proliferation was suppressed by miR-567 upregulation while cell apoptosis was promoted. Also, miR-567 upregulation induced cell cycle arrest at sub-G1 and S phases. CDK8 was expected as a target gene of miR-567. MiR-567 upregulation decreased CDK8 mRNA and protein expression while the downregulation of miR-567 increased CDK8 gene expression. These findings revealed that miR-567 may be a tumor suppressor in A549 NSCLC cells through regulating CDK8 gene expression and may serve as a novel therapeutic target for NSCLC treatment.

Evaluation of the Anticancer Activity of pH-Sensitive Polyketal Nanoparticles for Acute Myeloid Leukemia

Polyketals are a class of acid-responsive polymers that have been relatively less explored for drug delivery applications compared to polyesters. The degradation of these polymers is accelerated in an acidic medium and does not result in acidic byproducts. Their biocompatibility depends on the diol used for the synthesis. The present work aims to synthesize, characterize, and fabricate nanospheres of an aliphatic polyketal for delivery of the nucleotide analogue cytarabine toward the treatment of acute myeloid leukemia (AML). The internalization mechanism of the nanospheres was probed, and its implication on the nuclear localization and escape from the endo-lysosomal compartments were studied. The drug-loaded polyketal nanoparticles reduced the cell viability to a greater extent compared with the free drug. The effect of the drug-loaded polyketal nanoparticles on the differential gene expression of leukemic cells was investigated for the first time to understand their therapeutic implications. It was found that treatment with drug-loaded polyketal nanoparticles downregulated AML-specific genes involved in cell proliferation and recurrence compared to the free drug. The protein expression studies were performed for selected genes obtained from gene expression analysis. Biodistribution studies showed that the poly(cyclohexane-1,4-diyl acetone dimethylene ketal) (PCADK) nanoparticles exhibit prolonged circulation time. Overall, our results suggest that polyketal-based delivery of cytarabine represents a more effective alternative strategy for AML therapy.

Discovery of a potent, highly selective, and orally bioavailable inhibitor of CDK8 through a structure-based optimisation

CDK8 is deregulated in multiple types of human cancer and is viewed as a therapeutic target for the treatment of the disease. Accordingly, the search for small-molecule inhibitors of CDK8 is being intensified. Capitalising on our initial discovery of AU1-100, a potent CDK8 inhibitor yet with a limited degree of kinase selectivity, a structure-based optimisation was carried out, with a series of new multi-substituted pyridines rationally designed, chemically prepared and biologically evaluated. Such endeavour has culminated in the identification of 42, a more potent CDK8 inhibitor with superior kinomic selectivity and oral bioavailability. The mechanism underlying the anti-proliferative effect of 42 on MV4-11 cells was studied, revealing that the compound arrested the G1 cell cycle and triggered apoptosis. The low risk of hepato- and cardio-toxicity of 42 was estimated. These findings merit further investigation of 42 as a targeted cancer therapeutic.

Potent and orally bioavailable CDK8 inhibitors: Design, synthesis, structure-activity relationship analysis and biological evaluation

CDK8 regulates transcription either by phosphorylation of transcription factors or, as part of a four-subunit kinase module, through a reversible association of the kinase module with the Mediator complex, a highly conserved transcriptional coactivator. Deregulation of CDK8 has been found in various types of human cancer, while the role of CDK8 in supressing anti-cancer response of natural killer cells is being understood. Currently, CDK8-targeting cancer drugs are highly sought-after. Herein we detail the discovery of a series of novel pyridine-derived CDK8 inhibitors. Medicinal chemistry optimisation gave rise to 38 (AU1-100), a potent CDK8 inhibitor with oral bioavailability. The compound inhibited the proliferation of MV4-11 acute myeloid leukaemia cells with the kinase activity of cellular CDK8 dampened. No systemic toxicology was observed in the mice treated with 38. These results warrant further pre-clinical studies of 38 as an anti-cancer agent.

Angel or Devil ? - CDK8 as the new drug target

Cyclin-dependent kinase 8 (CDK8) plays an momentous role in transcription regulation by forming kinase module or transcription factor phosphorylation. A large number of evidences have identified CDK8 as an important factor in cancer occurrence and development. In addition, CDK8 also participates in the regulation of cancer cell stress response to radiotherapy and chemotherapy, assists tumor cell invasion, metastasis, and drug resistance. Therefore, CDK8 is regarded as a promising target for cancer therapy. Most studies in recent years supported the role of CDK8 as a carcinogen, however, under certain conditions, CDK8 exists as a tumor suppressor. The functional diversity of CDK8 and its exceptional role in different types of cancer have aroused great interest from scientists but even more controversy during the discovery of CDK8 inhibitors. In addition, CDK8 appears to be an effective target for inflammation diseases and immune system disorders. Therefore, we summarized the research results of CDK8, involving physiological/pathogenic mechanisms and the development status of compounds targeting CDK8, provide a reference for the feasibility evaluation of CDK8 as a therapeutic target, and guidance for researchers who are involved in this field for the first time.

Systemic Toxicity Reported for CDK8/19 Inhibitors CCT251921 and MSC2530818 Is Not Due to Target Inhibition

CDK8/19 kinases, which mediate transcriptional reprogramming, have become an active target for cancer drug discovery. Several small-molecule CDK8/19 inhibitors showed in vivo efficacy and two have entered clinical trials, with no significant toxicities reported. However, Clarke et al. (eLife 2016; 5; e20722) found severe systemic toxicity associated with two potent CDK8/19 inhibitors, Cmpd3 (CCT251921) and Cmpd4 (MSC2530818), and suggested that their toxicity was due to on-target effects. Here, we compared five CDK8/19 inhibitors: Cmpd3, Cmpd4, Senexin B, 16-didehydro-cortistatin A (dCA) and 15w, in different assays. Only Cmpd4 showed striking toxicity in developing zebrafish. In cell-based assays for CDK8 and CDK19 inhibition, Cmpd3, Cmpd4, dCA and 15w showed similar low-nanomolar potency and efficacy against CDK8 and CDK19, while Senexin B was less potent. Only dCA produced sustained inhibition of CDK8/19-dependent gene expression. While toxicity of different compounds did not correlate with their effects on CDK8 and CDK19, kinome profiling identified several off-target kinases for both Cmpd3 and Cmpd4, which could be responsible for their toxicity. Off-target activities could have been achieved in the study of Clarke et al. due to high in vivo doses of Cmpd3 and Cmpd4, chosen for the ability to inhibit STAT1 S727 phosphorylation in tumor xenografts. We show here that STAT1 S727 phosphorylation is induced by various cytokines and stress stimuli in CDK8/19-independent manner, indicating that it is not a reliable pharmacodynamic marker of CDK8/19 activity. These results illustrate the need for careful off-target analysis and dose selection in the development of CDK8/19 inhibitors.

A kinase-independent role for CDK8 in BCR-ABL1+ leukemia

Cyclin-dependent kinases (CDKs) are frequently deregulated in cancer and represent promising drug targets. We provide evidence that CDK8 has a key role in B-ALL. Loss of CDK8 in leukemia mouse models significantly enhances disease latency and prevents disease maintenance. Loss of CDK8 is associated with pronounced transcriptional changes, whereas inhibiting CDK8 kinase activity has minimal effects. Gene set enrichment analysis suggests that the mTOR signaling pathway is deregulated in CDK8-deficient cells and, accordingly, these cells are highly sensitive to mTOR inhibitors. Analysis of large cohorts of human ALL and AML patients reveals a significant correlation between the level of CDK8 and of mTOR pathway members. We have synthesized a small molecule YKL-06-101 that combines mTOR inhibition and degradation of CDK8, and induces cell death in human leukemic cells. We propose that simultaneous CDK8 degradation and mTOR inhibition might represent a potential therapeutic strategy for the treatment of ALL patients.

Cyclin-dependent kinases are deregulated in blood cancers. Here, the authors show that CDK8, independent of its kinase activity, regulates mTOR signalling for the maintenance of BCR-ABL1⁺ leukemia, and that the dual inhibition of CDK8 and mTOR signalling induces apoptosis in these cells.

Downregulation of miR‑138‑5p promotes non‑small cell lung cancer progression by regulating CDK8

Dysregulation of microRNAs (miRNAs) is frequently observed during cancer development. Aberrant expression of miRNA‑138‑5p (miR‑138‑5p) has been found in many types of cancer. However, the role and the mechanisms underlying miR‑138‑5p function in non‑small cell lung cancer (NSCLC) progression remain unknown. In the present study, miR‑138‑5p expression was identified to be decreased in tumor tissues compared with matched normal tissues from patients with NSCLC. In addition, low expression of miR‑138‑5p was detected in three NSCLC cell lines compared with a normal lung epithelium cell line. Moreover, CDK8 mRNA expression was increased in tumor tissues compared with matched normal tissues from patients with NSCLC, and an inverse association between miR‑138‑5p and CDK8 was observed. Furthermore, CDK8 was predicted to be a target of miR‑138‑5p. Dual luciferase assay confirmed that miR‑138‑5p could directly bind to the 3' untranslated region of CDK8 mRNA. In A549 cells, overexpression of miR‑138‑5p inhibited cell growth and significantly increased cell apoptosis rates and the number of cells in G0/G1 phase. Moreover, forced overexpression of CDK8 partially reversed miR‑138‑5p mimic‑induced cell growth arrest and alteration of cell apoptosis and cell cycle. In conclusion, the present results suggested that miR‑138‑5p may be a tumor suppressor in NSCLC cells and a promising therapeutic target for treating patients with NSCLC.

Identifying Cancers Impacted by CDK8/19

CDK8 and CDK19 Mediator kinases are transcriptional co-regulators implicated in several types of cancer. Small-molecule CDK8/19 inhibitors have recently entered or are entering clinical trials, starting with breast cancer and acute myeloid leukemia (AML). To identify other cancers where these novel drugs may provide benefit, we queried genomic and transcriptomic databases for potential impact of CDK8, CDK19, or their binding partner CCNC. sgRNA analysis of a panel of tumor cell lines showed that most tumor types represented in the panel, except for some central nervous system tumors, were not dependent on these genes. In contrast, analysis of clinical samples for alterations in these genes revealed a high frequency of gene amplification in two highly aggressive subtypes of prostate cancer and in some cancers of the GI tract, breast, bladder, and sarcomas. Analysis of survival correlations identified a group of cancers where CDK8 expression correlated with shorter survival (notably breast, prostate, cervical cancers, and esophageal adenocarcinoma). In some cancers (AML, melanoma, ovarian, and others), such correlations were limited to samples with a below-median tumor mutation burden. These results suggest that Mediator kinases are especially important in cancers that are driven primarily by transcriptional rather than mutational changes and warrant an investigation of their role in additional cancer types.

Increased mediator complex subunit CDK19 expression associates with aggressive prostate cancer

The Mediator complex is a transcriptional regulator interacting with transcription factors and RNA-polymerase-II. Recently, we identified its subunit CDK19 to be specifically expressed in prostate cancer (PCa) and to be functionally implicated in PCa aggressiveness. Aim of our study was to comprehensively characterize the protein expression of CDK19 and its paralog CDK8 in PCa. We performed immunohistochemistry (IHC) for CDK19/CDK8 on a large cohort including needle biopsies from 202 patients, 799 primary tumor foci of radical prostatectomy specimens from 415 patients, 120 locally advanced tumor foci obtained by palliative transurethral resection, 140 lymph node metastases, 67 distant metastases and 82 benigns. Primary tumors were stained for the proliferation marker Ki67, androgen receptor (AR) and ERG. For 376 patients, clinic-pathologic data were available. Primary endpoint was disease-recurrence-free survival (DFS). Nuclear CDK19 and CDK8 expression increases during progression showing the highest intensity in metastatic and castration-resistant tumors. High CDK19 expression on primary tumors correlates with DFS independently from Gleason grade and PSA. Five-year-DFS rates of patients with primary tumors expressing no, moderate and high CDK19 are 73.7, 56.9 and 30.4%, respectively. CDK19 correlates with Gleason grade, T-stage, Ki67 proliferation-index, nuclear AR expression and ERG-status. Therapeutic options for metastatic and castration-resistant PCa remain limited. In the current study, we confirmed an important role of the Mediator subunit CDK19 in advanced PCa supporting current developments to target CDK19 and its paralog CDK8. Furthermore, CDK19 protein expression has the potential to predict disease recurrence independently from established biomarkers thus contributing to individual management for PCa patients.

Molecular and in vivo Functions of the CDK8 and CDK19 Kinase Modules

CDK8 and its paralog, CDK19, collectively termed ‘Mediator Kinase,’ are cyclin-dependent kinases that have been implicated as key rheostats in cellular homeostasis and developmental programming. CDK8 and CDK19 are incorporated, in a mutually exclusive manner, as part of a 4-protein complex called the Mediator kinase module. This module reversibly associates with the Mediator, a 26 subunit protein complex that regulates RNA Polymerase II mediated gene expression. As part of this complex, the Mediator kinases have been implicated in diverse process such as developmental signaling, metabolic homeostasis and in innate immunity. In recent years, dysregulation of Mediator kinase module proteins, including CDK8/19, has been implicated in the development of different human diseases, and in particular cancer. This has led to intense efforts to understand how CDK8/19 regulate diverse biological outputs and develop Mediator kinase inhibitors that can be exploited therapeutically. Herein, we review both context and function of the Mediator kinases at a molecular, cellular and animal level. In so doing, we illuminate emerging concepts underpinning Mediator kinase biology and highlight certain aspects that remain unsolved.

CDK8 as a therapeutic target for cancers and recent developments in discovery of CDK8 inhibitors

Cyclin-dependent kinases 8 (CDK8) regulates transcriptional process via associating with the mediator complex or phosphorylating transcription factors (TF). Overexpression of CDK8 has been observed in various cancers. It mediates aberrant activation of Wnt/β-catenin signaling pathway, which is initially recognized and best studied in colorectal cancer (CRC). CDK8 acts as an oncogene and represents a potential target for developing novel CDK8 inhibitors in cancer therapeutics. However, other study has revealed its contrary role. The function of CDK8 is context dependent. Even so, a variety of potent and selective CDK8 inhibitors have been discovered after crystal structures were resolved in two states (active or inactive). In this review, we summarize co-crystal structures, biological mechanisms, dysregulation in cancers and recent progress in the field of CDK8 inhibitors, trying to offer an outlook of CDK8 inhibitors in cancer therapy in future.