CDK7/CDK9 mediates transcriptional activation to prime paraptosis in cancer cells.

BACKGROUND: Paraptosis is a programmed cell death characterized by cytoplasmic vacuolation, which has been explored as an alternative method for cancer treatment and is associated with cancer resistance. However, the mechanisms underlying the progression of paraptosis in cancer cells remain largely unknown. METHODS: Paraptosis-inducing agents, CPYPP, cyclosporin A, and curcumin, were utilized to investigate the underlying mechanism of paraptosis. Next-generation sequencing and liquid chromatography-mass spectrometry analysis revealed significant changes in gene and protein expressions. Pharmacological and genetic approaches were employed to elucidate the transcriptional events related to paraptosis. Xenograft mouse models were employed to evaluate the potential of paraptosis as an anti-cancer strategy. RESULTS: CPYPP, cyclosporin A, and curcumin induced cytoplasmic vacuolization and triggered paraptosis in cancer cells. The paraptotic program involved reactive oxygen species (ROS) provocation and the activation of proteostatic dynamics, leading to transcriptional activation associated with redox homeostasis and proteostasis. Both pharmacological and genetic approaches suggested that cyclin-dependent kinase (CDK) 7/9 drive paraptotic progression in a mutually-dependent manner with heat shock proteins (HSPs). Proteostatic stress, such as accumulated cysteine-thiols, HSPs, ubiquitin-proteasome system, endoplasmic reticulum stress, and unfolded protein response, as well as ROS provocation primarily within the nucleus, enforced CDK7/CDK9-Rpb1 (RNAPII subunit B1) activation by potentiating its interaction with HSPs and protein kinase R in a forward loop, amplifying transcriptional regulation and thereby exacerbating proteotoxicity leading to initiate paraptosis. The xenograft mouse models of MDA-MB-231 breast cancer and docetaxel-resistant OECM-1 head and neck cancer cells further confirmed the induction of paraptosis against tumor growth. CONCLUSIONS: We propose a novel regulatory paradigm in which the activation of CDK7/CDK9-Rpb1 by nuclear proteostatic stress mediates transcriptional regulation to prime cancer cell paraptosis.

Design, synthesis and evaluation of thieno[3,2-d]pyrimidine derivatives as novel potent CDK7 inhibitors.

The targeting of cyclin-dependent kinase 7 (CDK7) has become a highly desirable therapeutic approach in the field of oncology due to its dual role in regulating essential biological processes, encompassing cell cycle progression and transcriptional control. We have previously identified a highly selective thieno[3,2-d]pyrimidine-based CDK7 inhibitor with demonstrated efficacy and safety in animal model. In this study, we sought to optimize the thieno[3,2-d]pyrimidine core to discover a novel series of CDK7 inhibitors with improved potency and pharmacokinetic (PK) properties. Through extensive structure-activity relationship (SAR) studies, compound 20 has emerged as the lead candidate due to its potent inhibitory activity against CDK7 and remarkable efficacy on MDA-MB-453 cells, a representative triple negative breast cancer (TNBC) cell line. Furthermore, 20 has demonstrated favorable oral bioavailability and exhibited highly desirable pharmacokinetic (PK) properties, making it a promising lead candidate for further structural optimization.

Inhibition of cyclin-dependent kinase 7 mitigates doxorubicin cardiotoxicity and enhances anticancer efficacy.

AIMS: The anthracycline family of anticancer agents such as doxorubicin (DOX) can induce apoptotic death of cardiomyocytes and cause cardiotoxicity. We previously reported that DOX-induced apoptosis is accompanied by cardiomyocyte cell cycle re-entry. Cell cycle progression requires cyclin-dependent kinase 7 (CDK7)-mediated activation of downstream cell cycle CDKs. This study aims to determine whether CDK7 can be targeted for cardioprotection during anthracycline chemotherapy. METHODS AND RESULTS: DOX exposure induced CDK7 activation in mouse heart and isolated cardiomyocytes. Cardiac-specific ablation of Cdk7 attenuated DOX-induced cardiac dysfunction and fibrosis. Treatment with the covalent CDK7 inhibitor THZ1 also protected against DOX-induced cardiomyopathy and apoptosis. DOX treatment induced activation of the proapoptotic CDK2-FOXO1-Bim axis in a CDK7-dependent manner. In response to DOX, endogenous CDK7 directly bound and phosphorylated CDK2 at Thr160 in cardiomyocytes, leading to full CDK2 kinase activation. Importantly, inhibition of CDK7 further suppressed tumour growth when used in combination with DOX in an immunocompetent mouse model of breast cancer. CONCLUSION: Activation of CDK7 is necessary for DOX-induced cardiomyocyte apoptosis and cardiomyopathy. Our findings uncover a novel proapoptotic role for CDK7 in cardiomyocytes. Moreover, this study suggests that inhibition of CDK7 attenuates DOX-induced cardiotoxicity but augments the anticancer efficacy of DOX. Therefore, combined administration of CDK7 inhibitor and DOX may exhibit diminished cardiotoxicity but superior anticancer activity.

An Antiherpesviral Host-Directed Strategy Based on CDK7 Covalently Binding Drugs: Target-Selective, Picomolar-Dose, Cross-Virus Reactivity.

The repertoire of currently available antiviral drugs spans therapeutic applications against a number of important human pathogens distributed worldwide. These include cases of the pandemic severe acute respiratory coronavirus type 2 (SARS-CoV-2 or COVID-19), human immunodeficiency virus type 1 (HIV-1 or AIDS), and the pregnancy- and posttransplant-relevant human cytomegalovirus (HCMV). In almost all cases, approved therapies are based on direct-acting antivirals (DAAs), but their benefit, particularly in long-term applications, is often limited by the induction of viral drug resistance or side effects. These issues might be addressed by the additional use of host-directed antivirals (HDAs). As a strong input from long-term experiences with cancer therapies, host protein kinases may serve as HDA targets of mechanistically new antiviral drugs. The study demonstrates such a novel antiviral strategy by targeting the major virus-supportive host kinase CDK7. Importantly, this strategy focuses on highly selective, 3D structure-derived CDK7 inhibitors carrying a warhead moiety that mediates covalent target binding. In summary, the main experimental findings of this study are as follows: (1) the in vitro verification of CDK7 inhibition and selectivity that confirms the warhead covalent-binding principle (by CDK-specific kinase assays), (2) the highly pronounced antiviral efficacies of the hit compounds (in cultured cell-based infection models) with half-maximal effective concentrations that reach down to picomolar levels, (3) a particularly strong potency of compounds against strains and reporter-expressing recombinants of HCMV (using infection assays in primary human fibroblasts), (4) additional activity against further herpesviruses such as animal CMVs and VZV, (5) unique mechanistic properties that include an immediate block of HCMV replication directed early (determined by Western blot detection of viral marker proteins), (6) a substantial drug synergism in combination with MBV (measured by a Loewe additivity fixed-dose assay), and (7) a strong sensitivity of clinically relevant HCMV mutants carrying MBV or ganciclovir resistance markers. Combined, the data highlight the huge developmental potential of this host-directed antiviral targeting concept utilizing covalently binding CDK7 inhibitors.

A Phase I Dose-Escalation Study of LY3405105, a Covalent Inhibitor of Cyclin-Dependent Kinase 7, Administered to Patients With Advanced Solid Tumors.

BACKGROUND: This study aimed to evaluate the safety, pharmacokinetics (PKs), and preliminary activity of LY3405105, a covalent inhibitor of cyclin-dependent kinase 7 (CDK7), in patients with advanced solid tumors. MATERIALS AND METHODS: LY3405105 monotherapy was given once daily (QD; part A1) or thrice weekly (TIW; part A2) starting at 1 and 2 mg orally, respectively, and escalated per a Bayesian design in adult patients. The primary endpoint was safety, and secondary endpoints included PKs and antitumor activity. RESULTS: Fifty-four patients were enrolled: 43 in part A1 and 11 in part A2. Seven patients had dose-limiting toxicities, all in part A1 (45 mg: n = 3; 35 mg: n = 3; 25 mg: n = 1). Thirty-five patients (64.8%) reported at least one treatment-related adverse event (TRAE). TRAEs (≥10%) were diarrhea, nausea, fatigue, vomiting, abdominal pain, anemia, asthenia, and decreased platelet count. QD dosing showed sustained exposure with less peak-trough fluctuation compared to TIW dosing. Median time to maximum concentration was 1-2 hours and half-life was 15-19 hours. CDK7-target occupancy in skin and peripheral blood on day 15 was dose-dependent and reached near maximal occupancy of 75% at ≥15 mg QD. The maximum tolerated dose (MTD) was 20 mg QD. Twelve patients in part A1 (27.9%) and 5 patients in part A2 (45.5%) had a best overall response of stable disease. No complete response or partial response was observed. CONCLUSION: The MTD of LY3405105 monotherapy was 20 mg QD. The most common toxicities were gastrointestinal adverse events, myelosuppression, fatigue, and asthenia. Limited clinical activity was observed in this phase I trial, and there are no plans for further development. CLINICALTRIALS.GOV IDENTIFIER: NCT03770494.

The suppressive efficacy of THZ1 depends on KRAS mutation subtype and is associated with super-enhancer activity and the PI3K/AKT/mTOR signalling in pancreatic ductal adenocarcinoma: A hypothesis-generating study.

BACKGROUND: Inhibition of CDK7, a potent transcription regulator, may bring new hope for treating pancreatic ductal adenocarcinoma (PDAC), which is featured by large genetic heterogeneity and abundant KRAS mutations. This investigation aimed at exploring the discrepant efficacies of THZ1, a small-molecule covalent CDK7 inhibitor, on PDACs with different KRAS mutations and the underlying mechanisms. METHODS: Associations of CDK7 expression with survival by KRAS mutations were first assessed. Effects of THZ1 on PDAC by different KRAS mutations were then investigated in vitro and in vivo. Moreover, the effects of THZ1 on gene transcription and phosphorylation of RNA polymerase II (RNAPOLII) in different KRAS mutant PDACs were assessed, and the effect of THZ1 on super-enhancer activity was evaluated using chromatin immunoprecipitation sequencing. Lastly, the effects of THZ1 on the binding of H3K27ac to PIK3CA and on the PI3K/AKT/mTOR signalling were analysed. RESULTS: High CDK7 expression was significantly linked to worse survival within PDAC patients carrying KRAS-G12V mutation but not in those with KRAS-G12D mutation. The apoptosis-inducing effect of THZ1 was markedly stronger in KRAS-G12V PDAC than KRAS-G12D cancer. THZ1 significantly inhibited the growth of xenograft tumour with KRAS-G12V mutation, and the inhibition was markedly stronger than for KRAS-G12D tumour. In mini-cell-derived xenograft (CDX) models, THZ1 significantly suppressed KRAS-G12V PDAC but not KRAS-G12D cancer. THZ1 significantly suppressed the phosphorylation of RNAPOLII, and this effect was stronger in KRAS-G12V PDAC (especially at ser5). KRAS-G12V PDAC had more H3K27ac-binding super-enhancers, and the inhibition of THZ1 on super-enhancer activity was also stronger in KRAS-G12V PDAC. Furthermore, THZ1 significantly weakened the binding of H3K27ac to PIK3CA in KRAS-G12V PDAC. THZ1 significantly suppressed the PI3K/AKT/mTOR pathway and its downstream markers, and this effect was stronger in KRAS-G12V cells. CONCLUSIONS: In this hypothesis-generating study, THZ1 might selectively inhibit certain PDACs with KRAS-G12V mutation more potently compared with some other PDACs with KRAS-G12D mutation, which might be associated with its effect on super-enhancer activity and the PI3K/AKT/mTOR signalling. Our findings might offer novel key clues for the precise management of PDAC and important evidence for future targeted trial design. HIGHLIGHTS: THZ1 had a stronger effect on PDAC-bearing KRAS-G12V mutation than G12D mutation. Suppressive effect of THZ1 on phosphorylation of RNAPOLII was stronger in KRAS-G12V than KRAS-G12D PDAC. Inhibition of THZ1 on super-enhancer activity and H3K27ac binding to PIK3CA was stronger in KRAS-G12V PDAC. Suppressive effect of THZ1 on PI3K/AKT/mTOR pathway was stronger in KRAS-G12V PDAC.

N76-1, a novel CDK7 inhibitor, exhibits potent anti-cancer effects in triple negative breast cancer.

Emerging evidence suggests that genetically highly specific triple-negative breast cancer (TNBC) possesses a relatively uniform transcriptional program that is abnormally dependent on cyclin-dependent kinase 7 (CDK7). In this study, we obtained an inhibitor of CDK7, N76-1, by attaching the side chain of the covalent CDK7 inhibitor THZ1 to the core of the anaplastic lymphoma kinase inhibitor ceritinib. This study aimed to elucidate the role and underlying mechanism of N76-1 in TNBC and evaluate its potential value as an anti-TNBC drug. The results of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and colony formation assays showed that N76-1 inhibited the viability of TNBC cells. Kinase activity and cellular thermal shift assays showed that N76-1 directly targeted CDK7. Flow cytometry results revealed that N76-1 induced apoptosis and cell cycle arrest in the G2/M phase. N76-1 also effectively inhibited the migration of TNBC cells by high-content detection. The RNA-seq analysis showed that the transcription of genes, especially those related to transcriptional regulation and cell cycle, was suppressed after N76-1 treatment. Moreover, N76-1 markedly inhibited the growth of TNBC xenografts and phosphorylation of RNAPII in tumor tissues. In summary, N76-1 exerts potent anticancer effects in TNBC by inhibiting CDK7 and provides a new strategy and research basis for the development of new drugs for TNBC.

Targeting transcriptional kinase of CDK7 halts proliferation of multiple myeloma cells by modulating the function of canonical NF-kB pathway and cell cycle regulatory proteins.

Multiple myeloma (MM) is an incurable plasma cell neoplasm. Despite several effective frontline therapeutic regimens, including Bortezomib (BTZ), relapse is almost inevitable; therefore, better therapeutic modalities to improve the outcomes are needed. Cyclin-dependent kinases (CDKs) are an essential constituent of the cellular transcriptional machinery and tumors including MM are critically dependent on transcription to maintain their oncogenic state. In the present study, we explored the efficacy of THZ1, a covalent CDK7 inhibitor in MM treatment using Bortezomib resistant (H929BTZR) cells and zebrafish xenografts. THZ1 showed anti-myeloma activity in the models of MM but had no effect on healthy CD34+ cells. THZ1 suppresses phosphorylation of carboxy-terminal domain of RNA polymerase II and downregulates the transcription of BCL2 family of proteins both in H929BTZS and H929BTZR cells leading to G1/S arrest and apoptosis. THZ1 mediates inhibition of bone marrow stromal cells-induced proliferation and activation of NF-kB signaling. The data derived from zebrafish xenografts of MM demonstrate that THZ1 combined with BTZ synergistically reduces tumor growth in zebrafish embryos. Collectively, our results reveal that THZ1 alone as well as in combination with BTZ has effective anti-myeloma activity.

Disruption of CDK7 signaling leads to catastrophic chromosomal instability coupled with a loss of condensin-mediated chromatin compaction.

Chromatin organization is highly dynamic and modulates DNA replication, transcription, and chromosome segregation. Condensin is essential for chromosome assembly during mitosis and meiosis, as well as maintenance of chromosome structure during interphase. While it is well established that sustained condensin expression is necessary to ensure chromosome stability, the mechanisms that control its expression are not yet known. Herein, we report that disruption of cyclin-dependent kinase 7 (CDK7), the core catalytic subunit of CDK-activating kinase, leads to reduced transcription of several condensin subunits, including structural maintenance of chromosomes 2 (SMC2). Live and static microscopy revealed that inhibiting CDK7 signaling prolongs mitosis and induces chromatin bridge formation, DNA double-strand breaks, and abnormal nuclear features, all of which are indicative of mitotic catastrophe and chromosome instability. Affirming the importance of condensin regulation by CDK7, genetic suppression of the expression of SMC2, a core subunit of this complex, phenocopies CDK7 inhibition. Moreover, analysis of genome-wide chromatin conformation using Hi-C revealed that sustained activity of CDK7 is necessary to maintain chromatin sublooping, a function that is ascribed to condensin. Notably, the regulation of condensin subunit gene expression is independent of superenhancers. Together, these studies reveal a new role for CDK7 in sustaining chromatin configuration by ensuring the expression of condensin genes, including SMC2.

A patent review of cyclin-dependent kinase 7 (CDK7) inhibitors (2018-2022).

INTRODUCTION: Cyclin-dependent kinase 7 (CDK7) is a member of the CDK family of serine/threonine protein kinases and participates in the regulation of the cell cycle and mRNA transcription. CDK7 is emerging as a possible drug target in oncology and six exciting drug candidates have already undergone early evaluation in clinical trials. AREAS COVERED: This review examines CDK7 inhibitors as anticancer drugs reported in patents published in the online databases of the World Intellectual Property Organization and European Patent Office in the 2018-2022 period. This review provides an overview of available inhibitors, including their chemical structures, biochemical profile and stage of development. EXPERT OPINION: Small-molecule CDK7 inhibitors represent attractive pharmacological modalities for the treatment of various cancer types. Highly potent and selective inhibitors have been discovered and many of them show promising results in several preclinical cancer models. Developed compounds act on the kinase by various mechanisms, including traditional ATP competition, irreversible binding to tractable cysteine 312 outside the active site of CDK7, and induced protein degradation by proteolysis targeting chimeras. Ongoing preclinical research and clinical trials should reveal which strategy will provide the highest benefits.

Characterization of new highly selective pyrazolo[4,3-d]pyrimidine inhibitor of CDK7.

Targeting cyclin-dependent kinase 7 (CDK7) provides an interesting therapeutic option in cancer therapy because this kinase participates in regulating the cell cycle and transcription. Here, we describe a new trisubstituted pyrazolo[4,3-d]pyrimidine derivative, LGR6768, that inhibits CDK7 in the nanomolar range and displays favourable selectivity across the CDK family. We determined the structure of fully active CDK2/cyclin A2 in complex with LGR6768 at 2.6 Å resolution using X-ray crystallography, revealing conserved interactions within the active site. Structural analysis and comparison with LGR6768 docked to CDK7 provides an explanation of the observed biochemical selectivity, which is linked to a conformational difference in the biphenyl moiety. In cellular experiments, LGR6768 affected regulation of the cell cycle and transcription by inhibiting the phosphorylation of cell cycle CDKs and the carboxy-terminal domain of RNA polymerase II, respectively. LGR6768 limited the proliferation of several leukaemia cell lines, triggered significant changes in protein and mRNA levels related to CDK7 inhibition and induced apoptosis in dose- and time-dependent experiments. Our work supports previous findings and provides further information for the development of selective CDK7 inhibitors.

Castration-resistant prostate cancer cells are dependent on the high activity of CDK7.

PURPOSE: Prostate cancer (PC) is successfully treated with anti-androgens; however, a significant proportion of patients develop resistance against this therapy. Anti-androgen-resistant disease (castration-resistant prostate cancer; CRPC) is currently incurable. Cyclin-dependent kinase 7 (CDK7) is positioned to positively regulate both cell cycle and transcription, the two features critical for the rapid proliferation of the CRPC cells. Here, we assess if CDK7 is a viable target to halt the proliferation of CRPC cells. METHODS: We use recently developed clinically relevant compounds targeting CDK7 and multiple cell proliferation assays to probe the importance of this kinase for the proliferation of normal, androgen-dependent, and CRPC cells. PC patient data were used to evaluate expression of CDK7 at different disease-stages. Finally, comprehensive glycoproteome-profiling was performed to evaluate CDK7 inhibitor effects on androgen-dependent and CRPC cells. RESULTS: We show that CDK7 is overexpressed in PC patients with poor prognosis, and that CRPC cells are highly sensitive to compounds targeting CDK7. Inhibition of O-GlcNAc transferase sensitizes the CRPC, but not androgen-dependent PC cells, to CDK7 inhibitors. Glycoproteome-profiling revealed that CDK7 inhibition induces hyper-O-GlcNAcylation of the positive transcription elongation complex (pTEFB: CDK9 and CCNT1) in the CRPC cells. Accordingly, co-targeting of CDK7 and CDK9 synergistically blocks the proliferation of the CRPC cells but does not have anti-proliferative effects in the normal prostate cells. CONCLUSION: We show that CRPC cells, but not normal prostate cells, are addicted on the high activity of the key transcriptional kinases, CDK7 and CDK9.

Antileukemic activity of YPN-005, a CDK7 inhibitor, inducing apoptosis through c-MYC and FLT3 suppression in acute myeloid leukemia.

Acute myeloid leukemia (AML) is an aggressive blood cancer with a high rate of relapse associated with adverse survival outcomes, especially in elderly patients. An aberrant expression of cyclin dependent kinase 7 (CDK7) is associated with poor outcomes and CDK7 inhibition has showed antitumor activities in various cancers. We investigated the efficacy of YPN-005, a CDK7 inhibitor in AML cell lines, xenograft mouse model, and primary AML cells. YPN-005 effectively inhibited the proliferation of AML cells by inducing apoptosis and reducing phosphorylation of RNA polymerase II. The c-MYC expression decreased with treatment of YPN-005, and the effect of YPN-005 was negatively correlated with c-MYC expression. YPN-005 also showed antileukemic activities in primary AML cells, especially those harboring FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) mutation and in in vivo mouse model. Phosphorylated FLT3/Signal transducer and activator of transcription 5 (STAT5) was decreased and FLT3/STAT5 was downregulated with YPN-005 treatment. Our data suggest that YPN-005 has a role in treating AML by suppressing c-MYC and FLT3.

Carbon dots conjugated to SN38 for improved colorectal anticancer therapy.

Irinotecan (CTP-11) is one of the standard therapies for colorectal cancer (CRC). CTP-11 is enzymatically converted to the hydrophobic 7-ethyl-10-hydroxycamptothecin (SN38), a one hundred-fold more active metabolite. Conjugation of hydrophobic anticancer drugs to nanomaterials is a strategy to improve their solubility, efficacy, and selectivity. Carbon dots (CDs) have garnered interest for their small sizes (<10 â€‹nm), low toxicity, high water solubility, and bright fluorescence. This paper describes the use of CDs to improve drug vehiculation, stability, and chemotherapeutic efficiency of SN38 through a direct intracellular uptake in CRC. The covalent conjugation of SN38 to CDs via a carbamate bond provides a CD-SN38 hybrid material for slow, sustained, and pH-responsive drug release. CD-SN38 successfully penetrates the CRC cells with a release in the nucleus affecting first the cell cycle and then the cytoskeleton. Moreover, CD-SN38 leads to a deregulation of the extracellular matrix (ECM), one of the major components of the cancer niche considered a possible target therapy for reducing the cancer progression. This work shows the combined therapeutic and imaging potential of CD-based hybrid materials for the treatment of CRC. Future efforts for targeted therapy of chronic diseases characterized by altered ECM deposition, such as chronic kidney disease and chronic allograft nephropathy in kidney transplant patients are envisaged.

Cyclin-dependent kinase 7 contributes to myelin maintenance in the adult central nervous system and promotes myelin gene expression.

Mechanisms regulating oligodendrocyte differentiation, developmental myelination and myelin maintenance in adulthood are complex and still not completely described. Their understanding is crucial for the development of new protective or therapeutic strategies in demyelinating pathologies such as multiple sclerosis. In this perspective, we have investigated the role of Cyclin-dependent kinase 7 (Cdk7), a kinase involved in cell-cycle progression and transcription regulation, in the oligodendroglial lineage. We generated a conditional knock-out mouse model in which Cdk7 is invalidated in post-mitotic oligodendrocytes. At the end of developmental myelination, the number and diameter of myelinated axons, as well as the myelin structure, thickness and protein composition, were normal. However, in young adult and in aged mice, there was a higher number of small caliber myelinated axons associated with a decreased mean axonal diameter, myelin sheaths of large caliber axons were thinner, and the level of some major myelin-associated proteins was reduced. These defects were accompanied by the appearance of an abnormal clasping phenotype. We also used an in vitro oligodendroglial model and showed that Cdk7 pharmacological inhibition led to an altered myelination-associated morphological modification combined with a decreased expression of myelin-specific genes. Altogether, we identified novel functions for Cdk7 in CNS myelination.

Cyclin-dependent kinase 7/9 inhibitor SNS-032 induces apoptosis in diffuse large B-cell lymphoma cells.

Approximately 40% of patients with diffuse large B-cell lymphoma (DLBCL) are refractory or relapse to standard chemotherapy, and most of them are activated B cell-like DLBCLs (ABC-DLBCL) and germinal center B cell-like DLBCLs (GCB-DLBCL). SNS-032, a novel and selective CDK7/9 inhibitor, that the first phase clinical trials approved by US FDA for cancer treatment have been completed. In this study, we investigated the anti-tumor effect of SNS-032 in ABC- and GCB-DLBCL subtypes. We report that SNS-032 induced growth inhibition and cell apoptosis in both DLBCL cells in vitro, and inhibited the growth of both DLBCL xenografts in nude mice. Mechanistically, SNS-032 inhibited RNA polymerase II, which led to transcriptional-dependent suppression of NF-κB signaling pathway and its downstream targets involved in cell survival; SNS-032 also downregulates BCL-2 and c-MYC in both mRNA and protein levels. Significantly, these findings provide pre-clinical evidence for application of targeting the CDK7/9 in DLBCL.

Adipocyte-specific CDK7 ablation leads to progressive loss of adipose tissue and metabolic dysfunction.

Adipose tissue regulates whole-body energy homeostasis. Both lipodystrophy and obesity, the extreme and opposite aspects of adipose tissue dysfunction, result in metabolic disorders: insulin resistance and hepatic steatosis. Cyclin-dependent kinases (CDKs) have been reported to be involved in adipose tissue development and functions. Using adipose tissue-specific knockout mice, here we demonstrate that the deletion of CDK7 in adipose tissue results in progressive lipodystrophy, insulin resistance, impaired adipokine secretion and downregulation of fat-specific genes, which are aggravated on high-fat diet and during ageing. Our studies suggest that CDK7 is a key regulatory component of adipose tissue maintenance and systemic energy homeostasis.

Control of Expression of Key Cell Cycle Enzymes Drives Cell Line-Specific Functions of CDK7 in Human PDAC Cells.

Inhibition of the dual function cell cycle and transcription kinase CDK7 is known to affect the viability of cancer cells, but the mechanisms underlying cell line-specific growth control remain poorly understood. Here, we employed a previously developed, highly specific small molecule inhibitor that non-covalently blocks ATP binding to CDK7 (LDC4297) to study the mechanisms underlying cell line-specific growth using a panel of genetically heterogeneous human pancreatic tumor lines as model system. Although LDC4297 diminished both transcription rates and CDK T-loop phosphorylation in a comparable manner, some PDAC lines displayed significantly higher sensitivity than others. We focused our analyses on two well-responsive lines (Mia-Paca2 and Panc89) that, however, showed significant differences in their viability upon extended exposure to limiting LDC4297 concentrations. Biochemical and RNAseq analysis revealed striking differences in gene expression and cell cycle control. Especially the downregulation of a group of cell cycle control genes, among them CDK1/2 and CDC25A/C, correlated well to the observed viability differences in Panc89 versus Mia-Paca2 cells. A parallel downregulation of regulatory pathways supported the hypothesis of a feedforward programmatic effect of CDK7 inhibitors, eventually causing hypersensitivity of PDAC lines.

Pharmacological inhibition of CDK7 by THZ1 impairs tumor growth in p53-mutated HNSCC.

BACKGROUND: Cyclin-dependent kinase 7 (CDK7) has been critically linked to human cancer. However, the roles of CDK7 in head and neck squamous cell carcinoma (HNSCC) remain incompletely known. Here, we sought to dissect the functions of CDK7 underlying HNSCC tumorigenesis and explore whether pharmacological inhibition of CDK7 could induce anti-cancer effects. METHODS: CDK7 expression was measured in a panel of HNSCC cell lines with p53 mutation and 20 pairs of HNSCC samples and adjacent non-tumor tissues. Genetic targeting and pharmacological inhibition of CDK7 were conducted to dissect the biological roles of CDK7 in p53-mutated HNSCC cells. An HNSCC xenograft model was developed to determine the therapeutic effects of THZ1 in vivo. Potential genes and pathways responsible for therapeutic effects of THZ1 were identified by genome-wide RNA-sequencing and bioinformatics interrogations. RESULTS: CDK7 expression was significantly elevated in cancerous cells and samples as compared with their adjacent non-tumor counterparts. Impaired cell proliferation, migration, and invasion as well increased apoptosis were observed in cells upon CDK7 knockdown or THZ1 exposure. THZ1 administration potently inhibited tumor overgrowth in vivo. Mechanistically, hundreds of genes enriched in cell proliferation, apoptosis, and cancer-related categories were identified to be potentially mediated the therapeutic effects of THZ1 in HNSCC. CONCLUSION: Our findings reveal that CDK7 might serve as a novel putative pro-oncogenic gene underlying HNSCC tumorigenesis and therapeutic targeting of CDK7 might be a promising strategy for p53-mutated HNSCC.

TGF-ß/activin signaling promotes CDK7 inhibitor resistance in triple-negative breast cancer cells through upregulation of multidrug transporters.

Cyclin-dependent kinase 7 (CDK7) is a master regulatory kinase that drives cell cycle progression and stimulates expression of oncogenes in a myriad of cancers. Inhibitors of CDK7 (CDK7i) are currently in clinical trials; however, as with many cancer therapies, patients will most likely experience recurrent disease due to acquired resistance. Identifying targets underlying CDK7i resistance will facilitate prospective development of new therapies that can circumvent such resistance. Here we utilized triple-negative breast cancer as a model to discern mechanisms of resistance as it has been previously shown to be highly responsive to CDK7 inhibitors. After generating cell lines with acquired resistance, high-throughput RNA sequencing revealed significant upregulation of genes associated with efflux pumps and transforming growth factor-beta (TGF-ß) signaling pathways. Genetic silencing or pharmacological inhibition of ABCG2, an efflux pump associated with multidrug resistance, resensitized resistant cells to CDK7i, indicating a reliance on these transporters. Expression of activin A (INHBA), a member of the TGF-ß family of ligands, was also induced, whereas its intrinsic inhibitor, follistatin (FST), was repressed. In resistant cells, increased phosphorylation of SMAD3, a downstream mediator, confirmed an increase in activin signaling, and phosphorylated SMAD3 directly bound the ABCG2 promoter regulatory region. Finally, pharmacological inhibition of TGF-ß/activin receptors or genetic silencing of SMAD4, a transcriptional partner of SMAD3, reversed the upregulation of ABCG2 in resistant cells and phenocopied ABCG2 inhibition. This study reveals that inhibiting the TGF-ß/Activin-ABCG2 pathway is a potential avenue for preventing or overcoming resistance to CDK7 inhibitors.