CDK7 inhibitors as anticancer drugs

Targeting cell-cycle machinery in cancer

Abnormal activity of the core cell-cycle machinery is seen in essentially all tumor types and represents a driving force of tumorigenesis. Recent studies revealed that cell-cycle proteins regulate a wide range of cellular functions, in addition to promoting cell division. With the clinical success of CDK4/6 inhibitors, it is becoming increasingly clear that targeting individual cell-cycle components may represent an effective anti-cancer strategy. Here, we discuss the potential of inhibiting different cell-cycle proteins for cancer therapy.

Three targets in one complex: A molecular perspective of TFIIH in cancer therapy

The general transcription factor II H (TFIIH) plays an essential role in transcription and nucleotide excision DNA repair (NER). TFIIH is a complex 10 subunit containing molecular machine that harbors three enzymatic activities while the remaining subunits assume regulatory and/or structural functions. Intriguingly, the three enzymatic activities of the CDK7 kinase, the XPB translocase, and the XPD helicase exert different impacts on the overall activities of TFIIH. While the enzymatic function of the XPD helicase is exclusively required in NER, the CDK7 kinase is deeply involved in transcription, whereas XPB is essential to both processes. Recent structural and biochemical endeavors enabled unprecedented details towards the molecular basis of these different TFIIH functions and how the enzymatic activities are regulated within the entire complex. Due to its involvement in two fundamental processes, TFIIH has become increasingly important as a target in cancer therapy and two of the three enzymes have already been addressed successfully. Here we explore the possibilities of recent high resolution structures in the context of TFIIH druggability and shed light on the functional consequences of the different approaches towards TFIIH inhibition.

When Good Kinases Go Rogue: GSK3, p38 MAPK and CDKs as Therapeutic Targets for Alzheimer's and Huntington's Disease

Alzheimer's disease (AD) is a mostly sporadic brain disorder characterized by cognitive decline resulting from selective neurodegeneration in the hippocampus and cerebral cortex whereas Huntington's disease (HD) is a monogenic inherited disorder characterized by motor abnormalities and psychiatric disturbances resulting from selective neurodegeneration in the striatum. Although there have been numerous clinical trials for these diseases, they have been unsuccessful. Research conducted over the past three decades by a large number of laboratories has demonstrated that abnormal actions of common kinases play a key role in the pathogenesis of both AD and HD as well as several other neurodegenerative diseases. Prominent among these kinases are glycogen synthase kinase (GSK3), p38 mitogen-activated protein kinase (MAPK) and some of the cyclin-dependent kinases (CDKs). After a brief summary of the molecular and cell biology of AD and HD this review covers what is known about the role of these three groups of kinases in the brain and in the pathogenesis of the two neurodegenerative disorders. The potential of targeting GSK3, p38 MAPK and CDKS as effective therapeutics is also discussed as is a brief discussion on the utilization of recently developed drugs that simultaneously target two or all three of these groups of kinases. Multi-kinase inhibitors either by themselves or in combination with strategies currently being used such as immunotherapy or secretase inhibitors for AD and knockdown for HD could represent a more effective therapeutic approach for these fatal neurodegenerative diseases.

Targeting Mutated p53 Dependency in Triple-Negative Breast Cancer Cells Through CDK7 Inhibition

Background

Cyclin-dependent kinase 7 (CDK7) is crucial for cell cycle progression and gene expression transcriptional regulation, which are often not assessed in cancer developing process. CDK7 inhibitors have emerged as promising drugs for treating diverse cancers, including breast cancer. However, the mechanism behind its anticancer effect has not been well investigated. Here, the possible mechanism of CDK7 inhibitors for treating human triple-negative breast cancer (TNBC) has been studied.

Methods

The effects of CDK7 inhibitors on breast cancer cells have been identified by measuring cell viability (Cell Counting Kit-8) and cell proliferation and calculating colony formation. The short hairpin RNA and short interfering RNA were used for the construction of knockdown cells. To assess the expression of associated proteins, western blot was used.

Results

This study confirmed that, compared to hormone receptor-positive breast cancer cells, TNBC cells were more sensitive to THZ1, a novel CDK7 inhibitor. THZ1 treatment specifically downregulated mutated p53 in a dose- and time-dependent manner in TNBC cells with p53 mutation. Another CDK7 inhibitor, LDC4297, also potently interfered with the expression of mutated p53. Furthermore, endogenous CDK7 expression was positively correlated with the levels of mutated p53 in TNBC cells with p53 mutation. Downregulating mutated p53 expression significantly suppressed the proliferation of TNBC cells with p53 mutation.

Conclusion

Our findings demonstrated that targeting CDK7 was an effective approach for the treatment of TNBC with p53 mutation.

2.5 Å-resolution structure of human CDK-activating kinase bound to the clinical inhibitor ICEC0942

The human CDK-activating kinase (CAK), composed of CDK7, cyclin H, and MAT1, is involved in the control of transcription initiation and the cell cycle. Because of these activities, it has been identified as a promising target for cancer chemotherapy. A number of CDK7 inhibitors have entered clinical trials, among them ICEC0942 (also known as CT7001). Structural information can aid in improving the affinity and specificity of such drugs or drug candidates, reducing side effects in patients. Here, we have determined the structure of the human CAK in complex with ICEC0942 at 2.5 Å-resolution using cryogenic electron microscopy. Our structure reveals conformational differences of ICEC0942 compared with previous X-ray crystal structures of the CDK2-bound complex, and highlights the critical ability of cryogenic electron microscopy to resolve structures of drug-bound protein complexes without the need to crystalize the protein target.

Using biochemistry and biophysics to extinguish androgen receptor signaling in prostate cancer

Castration resistant prostate cancer (CRPC) continues to be androgen receptor (AR) driven. Inhibition of AR signaling in CRPC could be advanced using state-of-the-art biophysical and biochemical techniques. Structural characterization of AR and its complexes by cryo-electron microscopy would advance the development of N-terminal domain (NTD) and ligand-binding domain (LBD) antagonists. The structural basis of AR function is unlikely to be determined by any single structure due to the intrinsic disorder of its NTD, which not only interacts with coregulators but likely accounts for the constitutive activity of AR-splice variants (SV), which lack the LBD and emerge in CRPC. Using different AR constructs lacking the LBD, their effects on protein folding, DNA binding, and transcriptional activity could reveal how interdomain coupling explains the activity of AR-SVs. The AR also interacts with coregulators that promote chromatin looping. Elucidating the mechanisms involved can identify vulnerabilities to treat CRPC, which do not involve targeting the AR. Phosphorylation of the AR coactivator MED-1 by CDK7 is one mechanism that can be blocked by the use of CDK7 inhibitors. CRPC gains resistance to AR signaling inhibitors (ARSI). Drug resistance may involve AR-SVs, but their role requires their reliable quantification by SILAC-mass spectrometry during disease progression. ARSI drug resistance also occurs by intratumoral androgen biosynthesis catalyzed by AKR1C3 (type 5 17β-hydroxysteroid dehydrogenase), which is unique in that its acts as a coactivator of AR. Novel bifunctional inhibitors that competitively inhibit AKR1C3 and block its coactivator function could be developed using reverse-micelle NMR and fragment-based drug discovery.

G1 Cell Cycle Arrest and Extrinsic Apoptotic Mechanisms Underlying the Anti-Leukemic Activity of CDK7 Inhibitor BS-181

Simple Summary

Chemotherapy resistance in human T-cell acute lymphoblastic leukemia (T-ALL), an aggressive neoplasm, results in poor prognosis despite advances in treatment modalities. Toward the identification of an effective alternative, in the present study, we elucidated the mechanism underlying the antitumor activity of the CDK7 inhibitor BS-181 using malignant cells (Jurkat A3, U937, and HeLa) and normal human peripheral T cells. This is the first report to demonstrate that BS-181 antitumor activity is mainly caused by extrinsic apoptosis induction through cell-surface TRAIL/DR5 levels in human T-ALL Jurkat T cells. Moreover, combined treatment with recombinant TRAIL (rTRAIL) exerted synergistic effects on BS-181 cytotoxicity against malignant cells but not normal human peripheral T cells by augmenting both the extrinsic and intrinsic BCL-2-sensitive apoptosis pathways. Our findings suggest that the combination with rTRAIL may facilitate BS-181 antitumor activity against T-ALL cells while minimizing associated side effects, therefore potentially being applicable to clinical human T-ALL treatment.

Abstract

In vitro antitumor activity of the CDK7 inhibitor BS-181 against human T-ALL Jurkat cells was determined. Treatment of Jurkat clones (JT/Neo) with BS-181 caused cytotoxicity and several apoptotic events, including TRAIL/DR4/DR5 upregulation, c-FLIP down-regulation, BID cleavage, BAK activation, ΔΨ_m loss, caspase-8/9/3 activation, and PARP cleavage. However, the BCL-2-overexpressing Jurkat clone (JT/BCL-2) abrogated these apoptotic responses. CDK7 catalyzed the activating phosphorylation of CDK1 (Thr161) and CDK2 (Thr160), and CDK-directed retinoblastoma phosphorylation was attenuated in both BS-181-treated Jurkat clones, whereas only JT/BCL-2 cells exhibited G₁ cell cycle arrest. The G₁-blocker hydroxyurea augmented BS-181-induced apoptosis by enhancing TRAIL/DR4/DR5 upregulation and c-FLIP down-regulation. BS-181-induced FITC–annexin V-positive apoptotic cells were mostly in the sub-G₁ and G₁ phases. BS-181-induced cytotoxicity and mitochondrial apoptotic events (BAK activation/ΔΨ_m loss/caspase-9 activation) in Jurkat clones I2.1 (FADD-deficient) and I9.2 (caspase-8-deficient) were significantly lower than in A3 (wild-type). Exogenously added recombinant TRAIL (rTRAIL) markedly synergized BS-181-induced apoptosis in A3 cells but not in normal peripheral T cells. The cotreatment cytotoxicity was significantly reduced by the DR5-blocking antibody but not by the DR4-blocking antibody. These results demonstrated that the BS-181 anti-leukemic activity is attributed to extrinsic TRAIL/DR5-dependent apoptosis preferentially induced in G₁-arrested cells, and that BS-181 and rTRAIL in combination may hold promise for T-ALL treatment.

Super-enhancer in prostate cancer: transcriptional disorders and therapeutic targets

Abnormal activity of oncogenic and tumor-suppressor signaling pathways contributes to cancer and cancer risk in humans. Transcriptional dysregulation of these pathways is commonly associated with tumorigenesis and the development of cancer. Genetic and epigenetic alterations may mediate dysregulated transcriptional activity. One of the most important epigenetic alternations is the non-coding regulatory element, which includes both enhancers and super-enhancers (SEs). SEs, characterized as large clusters of enhancers with aberrant high levels of transcription factor binding, have been considered as key drivers of gene expression in controlling and maintaining cancer cell identity. In cancer cells, oncogenes acquire SEs and the cancer phenotype relies on these abnormal transcription programs driven by SEs, which leads to cancer cells often becoming addicted to the SEs-related transcription programs, including prostate cancer. Here, we summarize recent findings of SEs and SEs-related gene regulation in prostate cancer and review the potential pharmacological inhibitors in basic research and clinical trials.

Sauchinone: a prospective therapeutic agent-mediated EIF4EBP1 down-regulation suppresses proliferation, invasion and migration of lung adenocarcinoma cells

Lung adenocarcinoma (LUAD) is the top prevalent histological kind of lung cancer worldwide. Recent evidences have demonstrated that Sauchinone plays an anticancer role in tumor cell invasion and migration. Therefore, we performed this investigation to explain the potential role of Sauchinone in LUAD as well as the potential mechanism involved. Cell counting kit 8 (CCK-8) and transwell experiments were implemented to measure the proliferative, invasive and migratory abilities of LUAD cells. qRT-PCR and Western blot were performed to detect the transfection efficiency of si-EIF4EBP1s. Additionally, Western blot was also implemented to evaluate the effect of Sauchinone on EIF4EBP1 expression level as well as cell cycle-related proteins. Our findings showed that Sauchinone remarkably suppressed the proliferative ability of LUAD cells in a dose-dependent and time-dependent manner. EIF4EBP1 was a candidate target gene of Sauchinone. EIF4EBP1 expression was increased in LUAD tissues, and its high expression induced a poorer prognosis of LUAD patients. EIF4EBP1 expression was positively associated with cell cycle in LUAD. Sauchinone treatment attenuated EIF4EBP1 expression and cell cycle-related protein levels. Knockdown of EIF4EBP1 repressed the proliferation, invasion and migration of LUAD cells; furthermore, Sauchinone stimulation enforced its inhibitory effect. Meanwhile, the treatment of Sauchinone intensified the arrest of cell cycle induced by EIF4EBP1 knockdown. To sum up, our discovery indicated that Sauchinone exerts an anticancer role through down-regulating EIF4EBP1 and mediating cell cycle in LUAD.