Cyclin-dependent kinases as therapeutic targets in melanoma

Shining Light on Protein Kinase Biomarkers with Fluorescent Peptide Biosensors

Protein kinases (PKs) are established gameplayers in biological signalling pathways, and a large body of evidence points to their dysregulation in diseases, in particular cancer, where rewiring of PK networks occurs frequently. Fluorescent biosensors constitute attractive tools for probing biomolecules and monitoring dynamic processes in complex samples. A wide variety of genetically encoded and synthetic biosensors have been tailored to report on PK activities over the last decade, enabling interrogation of their function and insight into their behaviour in physiopathological settings. These optical tools can further be used to highlight enzymatic alterations associated with the disease, thereby providing precious functional information which cannot be obtained through conventional genetic, transcriptomic or proteomic approaches. This review focuses on fluorescent peptide biosensors, recent developments and strategies that make them attractive tools to profile PK activities for biomedical and diagnostic purposes, as well as insights into the challenges and opportunities brought by this unique toolbox of chemical probes.

Converged DNA Damage Response Renders Human Hepatocellular Carcinoma Sensitive to CDK7 Inhibition

Simple Summary

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer. HCC has a dismal five-year mortality estimate of >95%, ranking as the fourth leading cause of cancer-related mortality worldwide. Despite the recent progression in the treatment of HCC with multikinase inhibitors, immunotherapy, and antiangiogenic monoclonal antibodies, among other newly emerging therapeutics, the efficacy has varied among patients, making HCC a high priority for developing novel targeted therapeutic agents. CDK7 has been exploited as a therapeutic target in HCC. In the present study, we demonstrated that HCC cells were highly susceptible to THZ1, a selective covalent CDK7 inhibitor. We further discovered that transcription factor MYC-promoted cell proliferation renders cancer cells hypersensitive to apoptotic cell death with THZ1 treatment. Our findings indicate that targeting CDK7 with THZ1 may be a new plausible strategy for treating HCC, in which MYC plays crucial roles in cell proliferation and tumor growth.

Abstract

Hepatocellular carcinoma (HCC) is a lethal malignancy with high mortality. The inhibition of cyclin-dependent kinase 7 (CDK7) activity has shown therapeutic efficacy in HCC. However, the underlying molecular mechanisms remain elusive. Here, we show that three HCC lines, HepG2, Hep3B, and SK-Hep-1, were highly susceptible to the CDK7 inhibitor THZ1. In mouse models, THZ1 effectively reduced HepG2 tumor growth and tumor weight. THZ1 arrested cell cycle and triggered MYC-related apoptosis in HepG2. To evaluate how MYC protein levels affected THZ1-induced apoptotic cell death, we overexpressed MYC in HepG2 and found that exogenously overexpressed MYC promoted cell cycle progression and increased cells in the S phase. THZ1 drastically engendered the apoptosis of MYC-overexpressing HepG2 cells in the S and G2/M phases. Importantly, transcription-inhibition-induced apoptosis is associated with DNA damage, and exogenous MYC expression further enhanced the THZ1-induced DNA damage response in MYC-overexpressing HepG2 cells. Consistently, in the HepG2 xenografts, THZ1 treatment was associated with DNA-damage-induced cell death. Together, our data indicate that the converged effect of MYC-promoted cell cycle progression and CDK7 inhibition by THZ1 confers the hypersensitivity of HCC to DNA-damage-induced cell death. Our findings may suggest a new therapeutic strategy of THZ1 against HCC.

CDK9 Inhibitors in Cancer Research

Cyclin dependent kinase 9 (CDK9) played an essential role in regulating transcriptional elongation. Aberrations in CDK9 activity have been observed in various cancers, which made CDK9 was an attractive therapeutic...

Yes-activated protein promotes primary resistance of BRAF V600E mutant metastatic colorectal cancer cells to mitogen-activated protein kinase pathway inhibitors

Background

Most colorectal cancer (CRC) patients with the BRAF V600E mutation display resistance to chemotherapy and targeted medicinal treatments. Thus, exploring new drugs and drug resistance mechanisms for the BRAF V600E mutation has become an urgent clinical priority.

Methods

MTS experiment, cell cloning experiment, cell scratching experiment, Transwell experiment, chromatin immunoprecipitation (ChIP), quantitative polymerase chain reaction (qPCR) and flow cytometry are used. Detect the transcription and protein expression of YAP in colorectal cancer cell lines, establish a transient cell line with YAP gene overexpression and knockdown, and detect the effect of YAP gene expression on the biological functions of colorectal cancer cells RKO and HT-29. And further study the mechanism of YAP regulating the response of RAF and MEK targeted therapy.

Results

In this study, for the first time, we verified that the expression of transcription factor yes-associated protein (YAP) was upregulated in BRAF V600E mutant CRC cells. After knocking down YAP, we observed a reduction in the growth rate, proliferation, and invasion ability of colon cancer cells. We further verified that YAP knockdown increased sensitivity of BRAF V600E mutant CRC cells to mitogen-activated protein kinase (MAPK) pathway inhibitors. In addition, we clarified the mechanism underlying YAP regulation of RAF and MAPK/extracellular signal-regulated kinase (MEK)-targeted therapy response: YAP cooperates with RAF→MEK pathway inhibitors to regulate the cell cycle, increase cell G1/S phase arrest, and increase apoptosis.

Conclusions

These results suggest that YAP expression may be related to the primary resistance of MAPK inhibitors in metastatic CRC with the BRAF V600E mutation. Therefore, the combination of YAP and MAPK pathway inhibitors in BRAF V600E mutant metastatic CRC may present a promising treatment method.

NRAS mutant melanoma: Towards better therapies

Genetic alterations affecting RAS proteins are commonly found in human cancers. Roughly a fourth of melanoma patients carry activating NRAS mutations, rendering this malignancy particularly challenging to treat. Although the development of targeted as well as immunotherapies led to a substantial improvement in the overall survival of non-NRAS^mut melanoma patients (e.g. BRAF^mut), patients with NRAS^mut melanomas have an overall poorer prognosis due to the high aggressiveness of RAS^mut tumors, lack of efficient targeted therapies or rapidly emerging resistance to existing treatments. Understanding how NRAS-driven melanomas develop therapy resistance by maintaining cell cycle progression and survival is crucial to develop more effective and specific treatments for this group of melanoma patients. In this review, we provide an updated summary of currently available therapeutic options for NRAS^mut melanoma patients with a focus on combined inhibition of MAPK signaling and CDK4/6-driven cell cycle progression and mechanisms of the inevitably developing resistance to these treatments. We conclude with an outlook on the most promising novel therapeutic approaches for melanoma patients with constitutively active NRAS. STATEMENT OF SIGNIFICANCE: An estimated 75000 patients are affected by NRAS^mut melanoma each year and these patients still have a shorter progression-free survival than BRAF^mut melanomas. Both intrinsic and acquired resistance occur in NRAS-driven melanomas once treated with single or combined targeted therapies involving MAPK and CDK4/6 inhibitors and/or checkpoint inhibiting immunotherapy. Oncolytic viruses, mRNA-based vaccinations, as well as targeted triple-agent therapy are promising alternatives, which could soon contribute to improved progression-free survival of the NRAS^mut melanoma patient group.

Tectorigenin Inhibits Glioblastoma Proliferation by G0/G1 Cell Cycle Arrest

Background and objectives: Glioblastoma is one of the leading cancer-related causes of death of the brain region and has an average 5-year survival rate of less than 5%. The aim of this study was to investigate the effectiveness of tectorigenin, a naturally occurring flavonoid compound with anti-inflammatory, anti-oxidant, and anti-tumor properties, as a treatment for glioblastoma. A further goal was to use in vitro models to determine the underlying molecular mechanisms. Materials and Methods: Exposure to tectorigenin for 24 h dose-dependently reduced the viability of glioblastoma cells. Results: Significant cell cycle arrest at G0/G1 phase occurred in the presence of 200 and 300 µM tectorigenin. Treatment with tectorigenin clearly reduced the levels of phosphorylated retinoblastoma protein (p-RB) and decreased the expression of cyclin-dependent protein 4 (CDK4). Tectorigenin treatment also significantly enhanced the expression of p21, a CDK4 inhibitor. Conclusions: Collectively, our findings indicated that tectorigenin inhibited the proliferation of glioblastoma cells by cell cycle arrest at the G0/G1 phase.

MDM2 antagonists overcome intrinsic resistance to CDK4/6 inhibition by inducing p21

Intrinsic resistance of unknown mechanism impedes the clinical utility of inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) in malignancies other than breast cancer. Here, we used melanoma patient-derived xenografts (PDXs) to study the mechanisms for CDK4/6i resistance in preclinical settings. We observed that melanoma PDXs resistant to CDK4/6i frequently displayed activation of the phosphatidylinositol 3-kinase (PI3K)-AKT pathway, and inhibition of this pathway improved CDK4/6i response in a p21-dependent manner. We showed that a target of p21, CDK2, was necessary for proliferation in CDK4/6i-treated cells. Upon treatment with CDK4/6i, melanoma cells up-regulated cyclin D1, which sequestered p21 and another CDK inhibitor, p27, leaving a shortage of p21 and p27 available to bind and inhibit CDK2. Therefore, we tested whether induction of p21 in resistant melanoma cells would render them responsive to CDK4/6i. Because p21 is transcriptionally driven by p53, we coadministered CDK4/6i with a murine double minute (MDM2) antagonist to stabilize p53, allowing p21 accumulation. This resulted in improved antitumor activity in PDXs and in murine melanoma. Furthermore, coadministration of CDK4/6 and MDM2 antagonists with standard of care therapy caused tumor regression. Notably, the molecular features associated with response to CDK4/6 and MDM2 inhibitors in PDXs were recapitulated by an ex vivo organotypic slice culture assay, which could potentially be adopted in the clinic for patient stratification. Our findings provide a rationale for cotargeting CDK4/6 and MDM2 in melanoma.

Cell-state dynamics and therapeutic resistance in melanoma from the perspective of MITF and IFNγ pathways

Targeted therapy and immunotherapy have greatly improved the prognosis of patients with metastatic melanoma, but resistance to these therapeutic modalities limits the percentage of patients with long-lasting responses. Accumulating evidence indicates that a persisting subpopulation of melanoma cells contributes to resistance to targeted therapy or immunotherapy, even in patients who initially have a therapeutic response; however, the root mechanism of resistance remains elusive. To address this problem, we propose a new model, in which dynamic fluctuations of protein expression at the single-cell level and longitudinal reshaping of the cellular state at the cell-population level explain the whole process of therapeutic resistance development. Conceptually, we focused on two different pivotal signalling pathways (mediated by microphthalmia-associated transcription factor (MITF) and IFNγ) to construct the evolving trajectories of melanoma and described each of the cell states. Accordingly, the development of therapeutic resistance could be divided into three main phases: early survival of cell populations, reversal of senescence, and the establishment of new homeostatic states and development of irreversible resistance. On the basis of existing data, we propose future directions in both translational research and the design of therapeutic strategies that incorporate this emerging understanding of resistance.

Lanthanide-based peptide biosensor to monitor CDK4/cyclin D kinase activity

We describe a lanthanide biosensor that responds to CDK4 kinase activity in melanoma cell extracts through a significant and dose dependent increase in luminescence, thanks to sensitization of a DOTA[Tb³⁺] complex incorporated into a CDK4 substrate peptide by a unique tryptophan residue in an adjacent phosphoaminoacid binding moiety.

Targeting the PTTG1 oncogene impairs proliferation and invasiveness of melanoma cells sensitive or with acquired resistance to the BRAF inhibitor dabrafenib

The pituitary tumor transforming gene 1 (PTTG1) is implicated in tumor growth, metastasis and drug resistance. Here, we investigated the involvement of PTTG1 in melanoma cell proliferation, invasiveness and response to the BRAF inhibitor (BRAFi) dabrafenib. We also preliminary assessed the potential value of circulating PTTG1 protein to monitor melanoma patient response to BRAFi or to dabrafenib plus trametinib. Dabrafenib-resistant cell lines (A375R and SK-Mel28R) were more invasive than their drug-sensitive counterparts (A375 and SK-Mel28), but expressed comparable PTTG1 levels. Dabrafenib abrogated PTTG1 expression and impaired invasion of the extracellular matrix (ECM) in A375 and SK-Mel28 cells. In contrast, it affected neither PTTG1 expression in A375R and SK-Mel28R cells, nor ECM invasion in the latter cells, while further stimulated A375R cell invasiveness. Assessment of proliferation and ECM invasion in control and PTTG1-silenced A375 and SK-Mel28 cells, exposed or not to dabrafenib, demonstrated that the inhibitory effects of this drug were, at least in part, dependent on its ability to down-regulate PTTG1 expression. PTTG1-silencing also impaired proliferation and invasiveness of A375R and SK-Mel28R cells, and counteracted dabrafenib-induced stimulation of ECM invasion in A375R cells. Further experiments performed in A375R cells indicated that PTTG1-silencing impaired cell invasiveness through inhibition of MMP-9 and that PTTG1 expression and ECM invasion could be also reduced by the CDK4/6 inhibitor LEE011. PTTG1 targeting might, therefore, represent a useful strategy to impair proliferation and metastasis of melanomas resistant to BRAFi. Circulating PTTG1 also appeared to deserve further investigation as biomarker to monitor patient response to targeted therapy.

A novel multi-CDK inhibitor P1446A-05 restricts melanoma growth and produces synergistic effects in combination with MAPK pathway inhibitors

Nearly 100% of melanomas have a defect in the p16(INK4A):cyclin D-CDK4/6:RB pathway, leading to abnormal cell cycle control and unregulated cellular proliferation. Here, we report that P1446A-05, a novel multi-CDK inhibitor has significant inhibitory activity against cutaneous and uveal melanoma. Mechanistic studies revealed that P1446A-05 inhibits phosphorylation targets of CDK members, and induces cell cycle arrest and apoptosis irrespective of melanoma genotype or phenotype. Additionally, we show preclinical evidence that P1446A-05 can synergize with other small molecule inhibitors previously studied in melanoma. Collectively, these data demonstrate that targeting cell cycle and transcriptional CDKs with a small molecule multi-CDK inhibitor is a viable approach for developing novel anti-melanoma therapeutics.

Challenges in the delivery of therapies to melanoma brain metastases

Brain metastases are a major cause of morbidity and mortality in patients with advanced melanoma. Recent approval of several molecularly-targeted agents and biologics has brought hope to patients with this previously untreatable disease. However, patients with symptomatic melanoma brain metastases have often been excluded from pivotal clinical trials. This may be in part attributed to the fact that several of the approved small molecule molecularly-targeted agents are substrates for active efflux at the blood-brain barrier, limiting their effective delivery to brain metastases. We believe that successful treatment of melanoma brain metastases will depend on the ability of these agents to traverse the blood-brain barrier and reach micrometastases that are often not clinically detectable. Moreover, overcoming the emergence of a unique pattern of resistance, possibly through adequate delivery of combination targeted therapies in brain metastases will be important in achieving a durable response. These concepts, and the current challenges in the delivery of new treatments to melanoma brain metastases, are discussed in this review.

Characterization of the Methylthioadenosine Phosphorylase Polymorphism rs7023954 - Incidence and Effects on Enzymatic Function in Malignant Melanoma

Deficiency of methylthioadenosine phosphorylase (MTAP) supports melanoma development and progression through accumulation of its substrate 5’-methylthioadenosine (MTA), which leads amongst others to a constitutive inhibition of protein arginine methyltransferases (PRMTs) and activation of the transcription factor AP-1 via the receptor ADORA2B. Genetic association studies have also suggested that genetic polymorphism in MTAP may modulate the risk of melanoma. Here, we investigated the only globally common non-synonymous single nucleotide polymorphism (SNP) reported to date for MTAP. The SNP rs7023954 is located in exon 3 (c.166G>A), and leads to the conservative substitution of one branched-chain amino acid residue (valine) for another (isoleucine) at position 56 (p.Val56Ile). Whereas genotype frequencies in normal and primary melanoma tissues or cell lines were in Hardy-Weinberg equilibrium based on cDNA amplicon sequencing, a marked (P = 0.00019) deviation was observed in metastatic melanoma tissues and cell lines due to a deficit of heterozygotes. Enzyme assays conducted on the co-dominantly expressed alleles revealed no difference in the conversion rate of MTA to adenine and 5-methylthioribose-1-phosphate, indicating that this known enzymatic activity does not modulate the tumor suppressive function of MTAP.

Fluorescent peptide biosensor for monitoring CDK4/cyclin D kinase activity in melanoma cell extracts, mouse xenografts and skin biopsies

Melanoma constitutes the most aggressive form of skin cancer, which further metastasizes into a deadly form of cancer. The p16(INK4a)-Cyclin D-CDK4/6-pRb pathway is dysregulated in 90% of melanomas. CDK4/Cyclin D kinase hyperactivation, associated with mutation of CDK4, amplification of Cyclin D or loss of p16(INK4a) leads to increased risk of developing melanoma. This kinase therefore constitutes a key biomarker in melanoma and an emerging pharmacological target, however there are no tools enabling direct detection or quantification of its activity. Here we report on the design and application of a fluorescent peptide biosensor to quantify CDK4 activity in melanoma cell extracts, skin biopsies and melanoma xenografts. This biosensor provides sensitive means of comparing CDK4 activity between different melanoma cell lines and further responds to CDK4 downregulation by siRNA or small-molecule inhibitors. By affording means of monitoring CDK4 hyperactivity consequent to cancer-associated molecular alterations in upstream signaling pathways that converge upon this kinase, this biosensor offers an alternative to immunological identification of melanoma-specific biomarkers, thereby constituting an attractive tool for diagnostic purposes, providing complementary functional information to histological analysis, of particular utility for detection of melanoma onset in precancerous lesions. This is indeed the first fluorescent peptide biosensor which has been successfully implemented to monitor kinase activity in skin samples and melanoma tumour xenografts. Moreover by enabling to monitor response to CDK4 inhibitors, this biosensor constitutes an attractive companion assay to identify compounds of therapeutic relevance for melanoma.

Pharmacological cyclin dependent kinase inhibitors: Implications for colorectal cancer

Colorectal cancer accounts for a significant proportion of cancer deaths worldwide. The need to develop more chemotherapeutic agents to combat this disease is critical. Cyclin dependent kinases (CDKs), along with its binding partner cyclins, serve to control the growth of cells through the cell cycle. A new class of drugs, termed CDK inhibitors, has been studied in preclinical and now clinical trials. These inhibitors are believed to act as an anti-cancer drug by blocking CDKs to block the uncontrolled cellular proliferation that is hallmark of cancers like colorectal cancer. CDK article provides overview of the emerging drug class of CDK inhibitors and provides a list of ones that are currently in clinical trials.

CDK4 inhibitors an emerging strategy for the treatment of melanoma

Research into the cyclin-dependent kinases and their inhibitors is finally coming into the forefront of clinical research in cancer. Targeted therapies such as BRAF inhibitors have led the way in improving treatment outcomes in advanced melanoma. Based on detailed genomic knowledge of melanoma it is now time to extend targeted therapies beyond BRAF to fulfill the vision of precision medicine. The p16^INK4A-cyclin D-CDK4/6-retinoblastoma protein pathway (RB pathway) is dysregulated in more than 90% of melanomas and interacts biochemically and genetically with the RAS/RAF/MEK/ERK pathway. Recognizing and understanding these processes that drive melanomagenesis is essential to rationally develop new therapies. This paper reviews the mechanisms, background and progress of small molecule CDK4 inhibitors in the management of melanoma.

Oncogene-directed small molecule inhibitors for the treatment of cutaneous melanoma

Achievements in cancer genetics and molecular biology have revolutionized the treatment options available for advanced melanoma. Patients with certain molecularly defined melanomas have been the most fortunate beneficiaries of recently US FDA-approved therapies that target aberrant MAPK pathway signaling, yet response rates and duration of response remain suboptimal. Furthermore, many patients harbor melanomas for which no approved targeted therapies currently exist. Since the approval of vemurafenib, a selective BRAF V600E inhibitor, in 2011, there has been a surge of preclinical and clinical studies aimed at developing novel targeted therapies for a wide range of molecularly defined melanomas. In this review, we will examine the present status and future potential of molecularly targeted therapies directed at the most significant oncogenic signaling pathways in melanoma.