Development of novel CDK9 and CYP3A4 inhibitors for cancer therapy through field and computational approaches.

Cyclin-dependent kinase 9 (CDK9) and cytochrome P450 3A4 (CYP3A4) have emerged as promising targets in the development of anticancer drugs, presenting a consistent challenge in the quest for potent inhibitors. CDK9 inhibitors can selectively target fast-growing cancer cells by disrupting transcription elongation, which in turn hinders the production of proteins essential for cell cycle progression and survivaS. Understanding how CYP3A4 metabolizes specific chemotherapy drugs allows for personalized treatment plans, optimizing drug dosages according to a patient's metabolic profile. Since many cancer patients undergo combination therapies, and CYP3A4 is vital in drug metabolism, its inhibition or induction by one drug can alter the plasma levels of others, potentially leading to treatment failure or increased toxicity. Therefore, managing CYP3A4 activity is critical for effective cancer treatment. Employing a range of computational methodologies, this study systematically investigated the binding mechanisms of pyrimidine derivatives against CDK9 and CYP3A4. The field-based model demonstrated high R 2 values (0.99), with Q2 (0.66), demonstrating its ability to predict in silico inhibitory activity against the target of this study. The screening process followed in this work led to the discovery of powerful new inhibitor compounds. Of the 15 new compounds designed, three have a high affinity with the target (ranging from -8 to -9 kcal/mol kcal/mol) and were singled out through docking filtration for more detailed investigation. As well as, a reference compound with a substantial pIC50 value of 8.4, serving as the foundation for the development of the new compounds, was included for comparative analysis. To elucidate the essential features of CDK9 and CYP3A4 inhibitor design, a comparative analysis was conducted between 3D-QSAR-generated contours and molecular docking conformations of ligands. Molecular dynamics simulations were carried out for a duration of 100 ns on selected docked complexes, specifically those involving novel compounds with CDK9 and CYP3A4 enzymes. Additionally, the binding free energy for these complexes was assessed using the MM/PBSA method, which evaluates the free energy landscape of protein-ligand interactions. The results of MM/PBSA highlighted the strength of the new compounds in enhancing interactions with the target protein, which favors the results of molecular docking and MD simulation. These insights contribute to a deeper understanding of the mechanisms underlying CDK9 and CYP3A4 inhibition, offering potential avenues for the development of innovative and effective CDK9 inhibitors.

Discovery and preclinical profile of YK-2168, a differentiated selective CDK9 inhibitor in clinical development.

Emerging clinical evidence indicates that selective CDK9 inhibition may provide clinical benefits in the management of certain cancers. Many CDK9 selective inhibitors have entered clinical developments, and are being investigated. No clear winner has emerged because of unforeseen toxicity often observed in clinic with these agents. Therefore, a novel agent with differentiated profiles is still desirable. Herein, we report our design, syntheses of a novel azaindole series of selective CDK9 inhibitors. SAR studies led to a preclinical candidate YK-2168. YK2168 exhibited improved CDK9 selectivity over AZD4573 and BAY1251152; also showed differentiated intravenous PK profile and remarkable solid tumor efficacy in a mouse gastric cancer SNU16 CDX model in preclinical studies. YK-2168 is currently in clinical development in China (CTR20212900).

MOF-mediated acetylation of CDK9 promotes global transcription by modulating P-TEFb complex formation.

Cyclin-dependent kinase 9 (CDK9), a catalytic subunit of the positive transcription elongation factor b (P-TEFb) complex, is a global transcriptional elongation factor associated with cell proliferation. CDK9 activity is regulated by certain histone acetyltransferases, such as p300, GCN5 and P/CAF. However, the impact of males absent on the first (MOF) (also known as KAT8 or MYST1) on CDK9 activity has not been reported. Therefore, the present study aimed to elucidate the regulatory role of MOF on CDK9. We present evidence from systematic biochemical assays and molecular biology approaches arguing that MOF interacts with and acetylates CDK9 at the lysine 35 (i.e. K35) site, and that this acetyl-group can be removed by histone deacetylase HDAC1. Notably, MOF-mediated acetylation of CDK9 at K35 promotes the formation of the P-TEFb complex through stabilizing CDK9 protein and enhancing its association with cyclin T1, which further increases RNA polymerase II serine 2 residues levels and global transcription. Our study reveals for the first time that MOF promotes global transcription by acetylating CDK9, providing a new strategy for exploring the comprehensive mechanism of the MOF-CDK9 axis in cellular processes.

Heterocyclic Compounds as CDK9 Inhibitors: Structural Diversity, Mechanism of Action, and Therapeutic Potential in Cancer and Beyond.

Cyclin-dependent kinases (CDKs) are crucial proteins involved in key cellular processes, such as cell division and transcription. Their dysregulation plays a significant role in cancer development. Inhibiting cyclin-dependent kinase 9 (CDK9) impacts several survival pathways in cancer cells, presenting a promising therapeutic approach for various cancers. CDK9, in association with cyclin T1, forms the positive transcription elongation factor b (P-TEFb) complex, which phosphorylates the C-terminal domain (CTD) of RNA polymerase II (Pol II). This phosphorylation promotes the transition from transcription initiation to elongation. This review examines recent advancements in CDK9 modulators, with a particular emphasis on compounds currently in clinical trials.

Unraveling the CDK9/PP2A/ERK Network in Transcriptional Pause Release and Complement Activation in KRAS-mutant Cancers.

Selective inhibition of the transcription elongation factor (P-TEFb) complex represents a promising approach in cancer therapy, yet CDK9 inhibitors (CDK9i) are currently limited primarily to certain hematological malignancies. Herein, while initial responses to CDK9-targeted therapies are observed in vitro across various KRAS-mutant cancer types, their efficacy is far from satisfactory in nude mouse xenograft models. Mechanistically, CDK9 inhibition leads to compensatory activation of ERK-MYC signaling, accompanied by the recovery of proto-oncogenes, upregulation of immediate early genes (IEGs), stimulation of the complement C1r-C3-C3a cascade, and induction of tumor immunosuppression. The "paradoxical" regulation of PP2Ac activity involving the CDK9/Src interplay contributes to ERK phosphorylation and pause-release of RNA polymerase II (Pol II). Co-targeting of CDK9 and KRAS/MAPK signaling pathways eliminates ERK-MYC activation and prevents feedback activation mediated by receptor tyrosine kinases, leading to more effective control of KRAS-mutant cancers and overcoming KRASi resistance. Moreover, modulating the tumor microenvironment (TME) by complement system intervention enhances the response to CDK9i and potently suppresses tumor growth. Overall, the preclinical investigations establish a robust framework for conducting clinical trials employing KRASi/SOS1i/MEKi or immunomodifiers in combination with CDK9i to simultaneously target cancer cells and their crosstalk with the TME, thereby yielding improved responses in KRAS-mutant patients.

CDK9 inhibitors for the treatment of solid tumors.

Cyclin-dependent kinase 9 (CDK9) regulates mRNA transcription by promoting RNA Pol II elongation. CDK9 is now emerging as a potential therapeutic target for cancer, since its overexpression has been found to correlate with cancer development and worse clinical outcomes. While much work on CDK9 inhibition has focused on hematologic malignancies, the role of this cancer driver in solid tumors is starting to come into focus. Many solid cancers also overexpress CDK9 and depend on its activity to promote downstream oncogenic signaling pathways. In this review, we summarize the latest knowledge of CDK9 biology in solid tumors and the studies of small molecule CDK9 inhibitors. We discuss the results of the latest clinical trials of CDK9 inhibitors in solid tumors, with a focus on key issues to consider for improving the therapeutic impact of this drug class.

The CDK9-SPT5 Axis in Control of Transcription Elongation by RNAPII.

The RNA polymerase II (RNAPII) transcription cycle is regulated at every stage by a network of cyclin-dependent protein kinases (CDKs) and protein phosphatases. Progression of RNAPII from initiation to termination is marked by changing patterns of phosphorylation on the highly repetitive carboxy-terminal domain (CTD) of RPB1, its largest subunit, suggesting the existence of a CTD code. In parallel, the conserved transcription elongation factor SPT5, large subunit of the DRB sensitivity-inducing factor (DSIF), undergoes spatiotemporally regulated changes in phosphorylation state that may be directly linked to the transitions between transcription-cycle phases. Here we review insights gained from recent structural, biochemical, and genetic analyses of human SPT5, which suggest that two of its phosphorylated regions perform distinct functions at different points in transcription. Phosphorylation within a flexible, RNA-binding linker promotes release from the promoter-proximal pause-frequently a rate-limiting step in gene expression-whereas modifications in a repetitive carboxy-terminal region are thought to favor processive elongation, and are removed just prior to termination. Phosphorylations in both motifs depend on CDK9, catalytic subunit of positive transcription elongation factor b (P-TEFb); their different timing of accumulation on chromatin and function during the transcription cycle might reflect their removal by different phosphatases, different kinetics of phosphorylation by CDK9, or both. Perturbations of SPT5 regulation have profound impacts on viability and development in model organisms through largely unknown mechanisms, while enzymes that modify SPT5 have emerged as potential therapeutic targets in cancer; elucidating a putative SPT5 code is therefore a high priority.

Human promoter directionality is determined by transcriptional initiation and the opposing activities of INTS11 and CDK9.

RNA polymerase II (RNAPII) transcription initiates bidirectionally at many human protein-coding genes. Sense transcription usually dominates and leads to messenger RNA production, whereas antisense transcription rapidly terminates. The basis for this directionality is not fully understood. Here, we show that sense transcriptional initiation is more efficient than in the antisense direction, which establishes initial promoter directionality. After transcription begins, the opposing functions of the endonucleolytic subunit of Integrator, INTS11, and cyclin-dependent kinase 9 (CDK9) maintain directionality. Specifically, INTS11 terminates antisense transcription, whereas sense transcription is protected from INTS11-dependent attenuation by CDK9 activity. Strikingly, INTS11 attenuates transcription in both directions upon CDK9 inhibition, and the engineered recruitment of CDK9 desensitises transcription to INTS11. Therefore, the preferential initiation of sense transcription and the opposing activities of CDK9 and INTS11 explain mammalian promoter directionality.

Transcriptional regulation and therapeutic potential of cyclin-dependent kinase 9 (CDK9) in sarcoma.

Sarcomas include various subtypes comprising two significant groups - soft tissue and bone sarcomas. Although the survival rate for some sarcoma subtypes has improved over time, the current methods of treatment remain efficaciously limited, as recurrent, and metastatic diseases remain a major obstacle. There is a need for better options and therapeutic strategies in treating sarcoma. Cyclin dependent kinase 9 (CDK9) is a transcriptional kinase and has emerged as a promising target for treating various cancers. The aberrant expression and activation of CDK9 have been observed in several sarcoma subtypes, including rhabdomyosarcoma, synovial sarcoma, osteosarcoma, Ewing sarcoma, and chordoma. Enhanced CDK9 expression has also been correlated with poorer prognosis in sarcoma patients. As a master regulator of transcription, CDK9 promotes transcription elongation by phosphorylation and releasing RNA polymerase II (RNAPII) from its promoter proximal pause. Release of RNAPII from this pause induces transcription of critical genes in the tumor cell. Overexpression and activation of CDK9 have been observed to lead to the expression of oncogenes, including MYC and MCL-1, that aid sarcoma development and progression. Inhibition of CDK9 in sarcoma has been proven to reduce these oncogenes' expression and decrease proliferation and growth in different sarcoma cells. Currently, there are several CDK9 inhibitors in preclinical and clinical investigations. This review aims to highlight the recent discovery and results on the transcriptional role and therapeutic potential of CDK9 in sarcoma.

Discovery of novel CDK9 inhibitor with tridentate ligand: Design, synthesis and biological evaluation.

Cyclin-dependent kinase 9 (CDK9) plays a role in transcriptional regulation, which had become an attractive target for discovery of antitumor agent. In this work, beyond traditional CDK9 inhibitor with bidentate ligands in ATP binding domain, a series of novel CDK9 inhibitor with tridentate ligand were designed and synthesized. Surprisingly, this unique tridentate ligand structure endows better CDK9 inhibition selectivity compared to other CDK subtypes, and the lead candidate compound Z4-7a showed effective proliferation inhibition in HCT116 cells with acceptable pharmacokinetic properties. Research on the mechanism indicated that Z4-7a could induce apoptosis in the HCT116 cell line by inhibiting phosphorylation of RNA polymerase II at Ser2, which resulted in the inhibition of apoptosis-related genes and proteins expression. In brief, introduction of tridentate ligand might work as a promising strategy for the development of novel selective CDK9 inhibitor.

The CDK9 inhibitor enitociclib overcomes resistance to BTK inhibition and CAR-T therapy in mantle cell lymphoma.

Inhibitors of Bruton's tyrosine kinase (BTKi) and chimeric antigen receptor T-cell (CAR-T) therapy targeting CD19 are paradigm-shifting advances in treating patients with aggressive mantle cell lymphoma (MCL). However, clinical relapses following BTKi and CD19-directed CAR-T treatments are a fast-growing medical challenge. Development of novel therapies to overcome BTKi resistance (BTKi-R) and BTKi-CAR-T dual resistance (Dual-R) are urgently needed. Our single-cell RNA sequencing data revealed major transcriptomic reprogramming, with great enrichment of MYC-targets evolving as resistance to these therapies developed. Interestingly, cyclin-dependent kinase 9 (CDK9), a critical component of the positive transcription elongation factor-b complex, was among the top upregulated genes in Dual-R vs. BTKi-R samples. We therefore hypothesized that targeting CDK9 may turn off MYC-driven tumor survival and drug resistance. Enitociclib (formerly VIP152) is a selective CDK9 inhibitor whose potency against MCL has not been assessed. In this study, we found that enitociclib was highly potent in targeting lymphoma cells, with the half-maximal inhibitory concentration (IC50) ranging from 32 to 172 nM in MCL and diffuse large B-cell lymphoma cell lines. It inhibited CDK9 phosphorylation and downstream events including de novo synthesis of the short-lived proteins c-MYC, MCL-1, and cyclin D1, and induced apoptosis in a caspase-3-dependent manner. Enitociclib potently inhibited in vivo tumor growth of cell line-derived and patient-derived xenografts having therapeutic resistance. Our data demonstrate the potency of enitociclib in overcoming therapeutic resistance in MCL models and provide evidence in favor of its clinical investigation.

Retinoic acid enhances HIV-1 reverse transcription and transcription in macrophages via mTOR-modulated mechanisms.

The intestinal environment facilitates HIV-1 infection via mechanisms involving the gut-homing vitamin A-derived retinoic acid (RA), which transcriptionally reprograms CD4+ T cells for increased HIV-1 replication/outgrowth. Consistently, colon-infiltrating CD4+ T cells carry replication-competent viral reservoirs in people with HIV-1 (PWH) receiving antiretroviral therapy (ART). Intriguingly, integrative infection in colon macrophages, a pool replenished by monocytes, represents a rare event in ART-treated PWH, thus questioning the effect of RA on macrophages. Here, we demonstrate that RA enhances R5 but not X4 HIV-1 replication in monocyte-derived macrophages (MDMs). RNA sequencing, gene set variation analysis, and HIV interactor NCBI database interrogation reveal RA-mediated transcriptional reprogramming associated with metabolic/inflammatory processes and HIV-1 resistance/dependency factors. Functional validations uncover post-entry mechanisms of RA action including SAMHD1-modulated reverse transcription and CDK9/RNA polymerase II (RNAPII)-dependent transcription under the control of mammalian target of rapamycin (mTOR). These results support a model in which macrophages residing in the intestine of ART-untreated PWH contribute to viral replication/dissemination in an mTOR-sensitive manner.

Focus on current and emerging treatment options for glioma: A comprehensive review.

This comprehensive review delves into the current updates and challenges associated with the management of low-grade gliomas (LGG), the predominant primary tumors in the central nervous system. With a general incidence rate of 5.81 per 100000, gliomas pose a significant global concern, necessitating advancements in treatment techniques to reduce mortality and morbidity. This review places a particular focus on immunotherapies, discussing promising agents such as Zotiraciclib and Lerapolturev. Zotiraciclib, a CDK9 inhibitor, has demonstrated efficacy in glioblastoma treatment in preclinical and clinical studies, showing its potential as a therapeutic breakthrough. Lerapolturev, a viral immunotherapy, induces inflammation in glioblastoma and displays positive outcomes in both adult and pediatric patients. Exploration of immunotherapy extends to Pembrolizumab, Nivolumab, and Entrectinib, revealing the challenges and variabilities in patient responses. Despite promising preclinical data, the monoclonal antibody Depatuxizumab has proven ineffective in glioblastoma treatment, emphasizing the critical need to understand resistance mechanisms. The review also covers the success of radiation therapy in pediatric LGG, with evolving techniques, such as proton therapy, showing potential improvements in patient quality of life. Surgical treatment is discussed in the context of achieving a balance between preserving the patient's quality of life and attaining gross total resection, with the extent of surgical resection significantly influencing the survival outcomes. In addition to advancements in cancer vaccine development, this review highlights the evolving landscape of LGG treatment, emphasizing a shift toward personalized and targeted therapies. Ongoing research is essential for refining strategies and enhancing outcomes in the management of LGG.

CDK inhibition results in pharmacologic BRCAness increasing sensitivity to olaparib in BRCA1-WT and olaparib resistant in Triple Negative Breast Cancer.

One in three Triple Negative Breast Cancer (TNBC) is Homologous Recombination Deficient (HRD) and susceptible to respond to PARP inhibitor (PARPi), however, resistance resulting from functional HR restoration is frequent. Thus, pharmacologic approaches that induce HRD are of interest. We investigated the effectiveness of CDK-inhibition to induce HRD and increase PARPi sensitivity of TNBC cell lines and PDX models. Two CDK-inhibitors (CDKi), the broad range dinaciclib and the CDK12-specific SR-4835, strongly reduced the expression of key HR genes and impaired HR functionality, as illustrated by BRCA1 and RAD51 nuclear foci obliteration. Consequently, both CDKis showed synergism with olaparib, as well as with cisplatin and gemcitabine, in a range of TNBC cell lines and particularly in olaparib-resistant models. In vivo assays on PDX validated the efficacy of dinaciclib which increased the sensitivity to olaparib of 5/6 models, including two olaparib-resistant and one BRCA1-WT model. However, no olaparib response improvement was observed in vivo with SR-4835. These data support that the implementation of CDK-inhibitors could be effective to sensitize TNBC to olaparib as well as possibly to cisplatin or gemcitabine.

DNMT1-mediated epigenetic suppression of FBXO32 expression promoting cyclin dependent kinase 9 (CDK9) survival and esophageal cancer cell growth.

Esophageal cancer (EC) is a common and serious form of cancer, and while DNA methyltransferase-1 (DNMT1) promotes DNA methylation and carcinogenesis, the role of F-box protein 32 (FBXO32) in EC and its regulation by DNMT1-mediated methylation is still unclear. FBXO32 expression was examined in EC cells with high DNMT1 expression using GSE163735 dataset. RT-qPCR assessed FBXO32 expression in normal and EC cells, and impact of higher FBXO32 expression on cell proliferation, migration, and invasion was evaluated, along with EMT-related proteins. The xenograft model established by injecting EC cells transfected with FBXO32 was used to evaluate tumor growth, apoptosis, and tumor cells proliferation and metastasis. Chromatin immunoprecipitation (ChIP) assay was employed to study the interaction between DNMT1 and FBXO32. HitPredict, co-immunoprecipitation (Co-IP), and Glutathione-S-transferase (GST) pulldown assay analyzed the interaction between FBXO32 and cyclin dependent kinase 9 (CDK9). Finally, the ubiquitination assay identified CDK9 ubiquitination, and its half-life was measured using cycloheximide and confirmed through western blotting. DNMT1 negatively correlated with FBXO32 expression in esophageal cells. High FBXO32 expression was associated with better overall survival in patients. Knockdown of DNMT1 in EC cells increased FBXO32 expression and suppressed malignant phenotypes. FBXO32 repressed EC tumor growth and metastasis in mice. Enrichment of DNMT1 in FBXO32 promoter region led to increased DNA methylation and reduced transcription. Mechanistically, FBXO32 degraded CDK9 through promoting its ubiquitination.

TAT38 and TAT38 mimics potently inhibit adipogenesis by repressing C/EBPα, PPARγ, Pi-PPARγ, and SREBP1 expression.

Antiretroviral therapy-naive people living with HIV possess less fat than people without HIV. Previously, we found that HIV-1 transactivator of transcription (TAT) decreases fat in ob/ob mice. The TAT38 (a.a. 20-57) is important in the inhibition of adipogenesis and contains three functional domains: Cys-ZF domain (a.a. 20-35 TACTNCYCAKCCFQVC), core-domain (a.a. 36-46, FITKALGISYG), and protein transduction domain (PTD)(a.a. 47-57, RAKRRQRRR). Interestingly, the TAT38 region interacts with the Cyclin T1 of the P-TEFb complex, of which expression increases during adipogenesis. The X-ray crystallographic structure of the complex showed that the Cys-ZF and the core domain bind to the Cyclin T1 via hydrophobic interactions. To prepare TAT38 mimics with structural and functional similarities to TAT38, we replaced the core domain with a hydrophobic aliphatic amino acid (from carbon numbers 5 to 8). The TAT38 mimics with 6-hexanoic amino acid (TAT38 Ahx (C6)) and 7-heptanoic amino acid (TAT38 Ahp (C7)) inhibited adipogenesis of 3T3-L1 potently, reduced cellular triglyceride content, and decreased body weight of diet-induced obese (DIO) mice by 10.4-11 % in two weeks. The TAT38 and the TAT38 mimics potently repressed the adipogenic transcription factors genes, C/EBPα, PPARγ, and SREBP1. Also, they inhibit the phosphorylation of PPARγ. The TAT peptides may be promising candidates for development into a drug against obesity or diabetes.

Cartilage stem/progenitor cells-derived exosomes facilitate knee cartilage repair in a subacute osteoarthritis rat model.

Cartilage defects in the knee are often associated with the progression of degenerative osteoarthritis (OA), and cartilage repair is a useful strategy for managing this disease. However, cartilage repair is challenging because of the unique environment within the tissue. Recently, stem cell-based therapies have shed new light on this issue. In this study, we prepared exosomes (EXOs) from cartilage stem/progenitor cells (CSPCs) and found that treatment with EXOs increased the viability, migration, and proliferation of cultured primary chondrocytes. In a subacute OA rat model, the application of EXOs facilitated cartilage regeneration as evidenced by histological staining. Exosomal protein analysis together with bioinformatics suggested that cyclin-dependent kinase 9 (CDK9) is a key factor for chondrocyte growth and migration. Functional studies confirmed this prediction, that is, inhibiting CDK9 reduced the beneficial effects induced by EXOs in primary chondrocytes; while overexpression of CDK9 recapitulated the EXOs-induced phenotypes. RNA-Seq data showed that a set of genes involved in cell growth and migration were up-regulated by EXOs in chondrocytes. These changes could be partially reproduced by CDK9 overexpression. Overall, our data suggest that EXOs derived from primary CSPCs hold great therapeutic potential for treating cartilage defect-associated disorders such as degenerative OA, and that CDK9 is a key factor in this process.

Targeting CDK9 in Cancer: An Integrated Approach of Combining In Silico Screening with Experimental Validation for Novel Degraders.

The persistent threat of cancer remains a significant hurdle for global health, prompting the exploration of innovative approaches in the quest for successful therapeutic interventions. Cyclin-dependent kinase 9 (CDK9), a central player in transcription regulation and cell cycle progression, has emerged as a promising target to combat cancer. Its pivotal role in oncogenic pathways and the pressing need for novel cancer treatments has propelled CDK9 into the spotlight of drug discovery efforts. This article presents a comprehensive study that connects a multidisciplinary approach, combining computational methodologies, experimental validation, and the transformative Proteolysis-Targeting Chimera (PROTAC) technology. By uniting these diverse techniques, we aim to identify, characterize, and optimize a new class of degraders targeting CDK9. We explore these compounds for targeted protein degradation, offering a novel and potentially effective approach to cancer therapy. This cohesive strategy utilizes the combination of computational predictions and experimental insights, with the goal of advancing the development of effective anticancer therapeutics, targeting CDK9.

LncRNA lncMGR regulates skeletal muscle development and regeneration by recruiting CDK9 and sponging miRNAs.

Long non-coding RNAs (lncRNAs) play an essential role in vertebrate myogenesis and muscle diseases. However, the dynamic expression patterns, biological functions, and mechanisms of lncRNAs in skeletal muscle development and regeneration remain largely unknown. In this study, a novel lncRNA (named lncMGR) was differentially expressed during breast muscle development in fast- and slow-growing chickens. Functionally, lncMGR promoted myoblast differentiation, inhibited myoblast proliferation in vitro, and promoted myofiber hypertrophy and injury repair in vivo. Mechanistically, lncMGR increased the mRNA and protein expression of skeletal muscle myosin heavy chain 1 A (MYH1A) via both transcriptional and post-transcriptional regulation. Nuclear lncMGR recruited cyclin-dependent kinase 9 (CDK9) to the core transcriptional activation region of the MYH1A gene to activate MYH1A transcription. Cytoplasmic lncMGR served as a competitive endogenous RNA (ceRNA) to competitively absorb miR-2131-5p away from MYH1A and subsequently protected the MYH1A from miR-2131-5p-mediated degradation. Besides miR-2131-5p, cytoplasmic lncMGR could also sponge miR-143-3p to reconcile the antagonist between the miR-2131-5p/MYH1A-mediated inhibition effects and miR-143-3p-mediated promotion effects on myoblast proliferation, thereby inhibiting myoblast proliferation. Collectively, lncMGR could recruit CDK9 and sponge multiple miRNAs to regulate skeletal muscle development and regeneration, and could be a therapeutic target for muscle diseases.

Small molecule inhibitors of transcriptional cyclin-dependent kinases impose HIV-1 latency, presenting "block and lock" treatment strategies.

Current antiretroviral therapy for HIV-1 infection does not represent a cure for infection as viral rebound inevitably occurs following discontinuation of treatment. The "block and lock" therapeutic strategy is intended to enforce proviral latency and durably suppress viremic reemergence in the absence of other intervention. The transcription-associated cyclin-dependent protein kinases (tCDKs) are required for expression from the 5´ HIV-1 long-terminal repeat, but the therapeutic potential of inhibiting these kinases for enforcing HIV-1 latency has not been characterized. Here, we expanded previous observations to directly compare the effect of highly selective small molecule inhibitors of CDK7 (YKL-5-124), CDK9 (LDC000067), and CDK8/19 (Senexin A), and found each of these prevented HIV-1 provirus expression at concentrations that did not cause cell toxicity. Inhibition of CDK7 caused cell cycle arrest, whereas CDK9 and CDK8/19 inhibitors did not, and could be continuously administered to establish proviral latency. Upon discontinuation of drug administration, HIV immediately rebounded in cells that had been treated with the CDK9 inhibitor, while proviral latency persisted for several days in cells that had been treated with CDK8/19 inhibitors. These results identify the mediator kinases CDK8/CDK19 as potential "block and lock" targets for therapeutic suppression of HIV-1 provirus expression.