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

Immune evasion and resistance in breast cancer

Breast cancer (BC) is the most common malignancy in females with an increasing incidence in the last decade. The previously observed decline in BC mortality rates has also slowed down recently with an increase in the incidence of invasive BC. BC has various molecular subtypes. Among these subtypes, triple-negative breast cancer (TNBC) represents the most aggressive BC, with a poor prognosis. Because lack of the hormonal or human epidermal growth factor receptor 2 (HER2) receptors, TNBC is resistant to hormonal and HER2 targeted therapy effective for other BC subtypes. The good news is that TNBC has recently been considered an immunologically 'hot' tumor. Therefore, immunotherapy, particularly immune checkpoint inhibitor therapy, represents a promising therapeutic approach TNBC. However, a considerable percentage of patients with TNBC do not respond well to immunotherapy, indicating that TNBC seems to adopt several mechanisms to evade immune surveillance. Thus, it is crucial to investigate the mechanisms underlying TNBC immune evasion and resistance to immunotherapy. In this review, we examine and discuss the most recently discovered mechanisms for BC, with a particular focus on TNBC, to evade the immune surveillance via kidnapping the immune checkpoints, suppressing the immune responses in tumor microenvironment and inhibiting the tumor antigen presentation. Evaluation of these mechanisms in BC will hopefully guide future immunotherapeutic research and clinical trials.

Protein lactylation within the nucleus independently predicts the prognosis of non‑specific triple‑negative breast cancer

Protein lactylation represents a pervasive post-translational modification prevalent in histones and diverse proteins, fostering tumor initiation and progression. Nonetheless, the impact of protein lactylation on the prognosis of non-specific triple-negative breast cancer (TNBC) remains uncertain. In the present study, the pan-lysine lactylation (panKlac) levels in cytoplasmic and nuclear compartments were semi-quantitatively examined using a tissue microarray encompassing 77 non-specific TNBC tissues. The association of the prognosis of patients with the panKlac levels in the cytoplasmic and nuclear compartments or other tumor attributes was assessed using Kaplan-Meier and Cox regression analyses. Furthermore, the molecular pathways involved in the promotional effect of lactylation on cell proliferation were determined through a transcriptomic analysis. The results indicated that the panKlac levels were markedly higher in tumor tissues than in para-tumor mammary regions and showed no significant correlations with various clinicopathological parameters, such as tumor dimension, lymph node involvement or histological grading. Notably, high panKlac levels within the nucleus served as an independent predictor of recurrence-free survival, whereas high cytoplasmic panKlac levels were a protective factor for patient survival. The panKlac levels were also markedly elevated in the TNBC cell line, MDA-MB-231. Additionally, glycolysis inhibition significantly reduced the global panKlac levels and concurrently diminished cell proliferation. According to the comprehensive transcriptomic analysis results, pathways related to ribosomal subunit biosynthesis/assembly and aminoacyl-tRNA biosynthesis were involved in the tumor-promoting mechanisms of lactylation. Further results revealed the oncogenic propensity of tyrosyl-tRNA synthetase 1 (YARS1) and its association with lactate production. Overall, Klac levels within the nucleus are an independent prognostic indicator for patients with non-specific TNBC. It is imperative to delve deeper into the roles and mechanisms of nuclear protein lactylation and YARS1 in non-specific TNBC.

Clinical Progress of Targeted Therapy for Breast Cancer: A Comprehensive Review

The discovery of effective breast cancer therapy is both urgent and daunting, beset by a myriad of challenges that range from the disease's inherent heterogeneity to its complex molecular underpinnings. Drug resistance, the intricacies of the tumor microenvironment, and patient-specific variables further complicate this landscape. The stakes are even higher when dealing with subtypes like triple-negative breast cancer, which eludes targeted hormonal therapies due to its lack of estrogen, progesterone, and HER2 receptors. Strategies to overcome such challenges include combinations of drugs and identifying new drug targets. Developing new drugs based on such targets could be a better solution than relying on costly immunotherapy or combinational therapies. In this review, we have endeavored to comprehensively examine the proven therapeutic drug targets associated with breast cancer and elucidate their respective molecular mechanisms and current clinical status. This study aims to facilitate researchers in conducting a comparative analysis of different targets to select single and multi-targeted drug discovery approaches for breast cancer.

Mediator kinase inhibitors suppress triple-negative breast cancer growth and extend tumor suppression by mTOR and AKT inhibitors

Triple-negative breast cancers (TNBC) are treated primarily by chemotherapy and lack clinically validated therapeutic targets. In particular, inhibitors of the PI3K/AKT/mTOR pathway, abnormally activated in many breast cancers, failed to achieve clinical efficacy in TNBC due to the development of adaptive drug resistance, which is largely driven by the transcriptomic plasticity of TNBC. Expression of CDK8/19 Mediator kinases that control transcriptional reprogramming correlates with relapse-free survival and treatment failure in breast cancer patients, including TNBC. We now investigated how CDK8/19 inhibitors affect the growth of TNBC tumors and their response to mTOR and AKT inhibitors. In contrast to the effects of most anticancer drugs, all the tested human TNBC models (including patient-derived xenografts) responded to CDK8/19 inhibitors in vivo even when they did not respond in vitro. Furthermore, CDK8/19 inhibition extended the host survival of established lung metastases in a murine TNBC model, where the primary tumors were not significantly affected. CDK8/19 inhibitors synergized with an mTORC1 inhibitor everolimus and a pan-AKT inhibitor capivasertib in vitro and strongly potentiated these drugs in long-term in vivo studies. Transcriptomic analysis of tumors that responded or became adapted to everolimus revealed that drug adaptation in vivo was associated with major transcriptional changes in both tumor and stromal cells. Combining everolimus with a CDK8/19 inhibitor counteracted many of these changes and induced combination-specific effects on the expression of multiple genes that affect tumor growth. These results warrant the exploration of CDK8/19 Mediator kinase inhibitors as a new type of drugs for TNBC therapy.

Transcriptional Regulation of Protein Synthesis by Mediator Kinase Represents a Therapeutic Vulnerability in MYC-driven Medulloblastoma

MYC-driven medulloblastoma (MB) is a highly aggressive cancer type with poor prognosis and limited treatment options. Through CRISPR-Cas9 screening of MB cell lines, we identified the Mediator-associated kinase CDK8 as a critical regulator of MYC-driven MB. Loss of CDK8 substantially reduces MYC expression and induces pronounced transcriptional changes, consequently inhibiting MB growth and suppressing monosome assembly, resulting in decreased ribosome biogenesis and protein synthesis. Mechanistically, CDK8 regulates the occupancy of RNA polymerase II at specific chromatin loci, facilitating an epigenetic alteration that promotes the transcriptional regulation of ribosomal genes. Targeting CDK8 effectively diminishes the stem-like neoplastic cells characterized by hyperactive ribosome biogenesis. Furthermore, we demonstrated that the combined inhibition of CDK8 and mTOR synergizes to optimize therapeutic outcomes in vivo and in vivo. Overall, our findings establish a connection between CDK8-mediated transcriptional regulation and mRNA translation, suggesting a promising new therapeutic approach that targets the protein synthesis for MYC-driven MB. .

Hydrophobic tagging of small molecules: an overview of the literature and future outlook

INTRODUCTION

Hydrophobic tagging (HyT) technology presents a distinct therapeutic strategy diverging from conventional small molecule drugs, providing an innovative approach to drug design. This review aims to provide an overview of the HyT literature and future outlook to offer guidance for drug design.

AREAS COVERED

In this review, the authors introduce the composition, mechanisms and advantages of HyT technology, as well as summarize the detailed applications of HyT technology in anti-cancer, neurodegenerative diseases (NDs), autoimmune disorders, cardiovascular diseases (CVDs), and other fields. Furthermore, this review discusses key aspects of the future development of HyT molecules.

EXPERT OPINION

HyT emerges as a highly promising targeted protein degradation (TPD) strategy, following the successful development of proteolysis targeting chimeras (PROTAC) and molecular glue. Based on exploring new avenues, modification of the HyT molecule itself potentially enhances the technology. Improved synthetic pathways and emphasis on pharmacokinetic (PK) properties will facilitate the development of HyT. Furthermore, elucidating the biochemical basis by which the compound's hydrophobic moiety recruits the protein homeostasis network will enable the development of more precise assays that can guide the optimization of the linker and hydrophobic moiety.

Mediator kinase module proteins, genetic alterations and expression of super-enhancer regulated genes in colorectal cancer

BACKGROUND

Genetic alterations are well characterized as contributors to the pathogenesis of cancers. Epigenetic abnormalities can lead to perturbations of the expression of genes in cancer cells without structural defects. Deregulation of proteins of the transcription machinery may result in perturbations of target genes. Mediator, a multiprotein component of the transcription machinery facilitates the function of RNA polymerase II, which transcribes most human genes. A part of the mediator with kinase activity, called the Mediator kinase module shows genetic alterations in a sub-set of colorectal cancers.

METHODS

Data from publicly available genomic series of colorectal cancer patients were examined to determine alterations of Mediator kinase module component genes, including MED12, MED12L, MED13, MED13L, CDK8, CDK19, and CCNC. The prevalence of alterations in genomically defined colorectal cancer sub-sets was also interrogated. The effect of Mediator kinase module member gene expression on colorectal cancer relapse-free survival was investigated.

RESULTS

Mutations in genes of the Mediator kinase module were present in a small percentage of colorectal cancers, ranging between 2 to 10% for MED12 and MED13 and alternative units MED12L and MED13L and below 2% for kinases CDK8 and CDK19 and cyclin C. Amplifications of the CDK8 gene were observed in 3% to 5% of colorectal cancers. The highest prevalence of mutations was observed in MSI cancers and the equivalent CMS1 group, with other genomic groups showing much lower frequency. An association of higher expression of MED12 with inferior relapse-free survival was observed. In contrast, higher expression of cyclin C was associated with improved survival. Colorectal cancer cell lines with CDK8 amplifications displayed sensitivity to several small molecule inhibitors of the KRAS/PI3K pathway but not to BET inhibitors.

CONCLUSION

The Mediator kinase module is deregulated in a sub-set of colorectal cancers with differences observed in genomically defined groups. These variations may result in differences in sensitivity to targeted therapies and may have to be taken into consideration as such therapies are developed.

Transcriptional Regulation of Protein Synthesis by Mediator Kinase in MYC-driven Medulloblastoma

MYC-driven medulloblastoma (MB) is a highly aggressive cancer type with poor prognosis and limited treatment options. Through CRISPR-Cas9 screening across MB cell lines, we identified the Mediator-associated kinase CDK8 as the top dependence for MYC-driven MB. Loss of CDK8 markedly reduces MYC expression and impedes MB growth. Mechanistically, we demonstrate that CDK8 depletion suppresses ribosome biogenesis and mRNA translation. CDK8 regulates occupancy of phospho-Polymerase II at specific chromatin loci facilitating an epigenetic alteration that promotes transcriptional regulation of ribosome biogenesis. Additionally, CDK8-mediated phosphorylation of 4EBP1 plays a crucial role in initiating eIF4E-dependent translation. Targeting CDK8 effectively suppresses cancer stem and progenitor cells, characterized by increased ribosome biogenesis activity. We also report the synergistic inhibition of CDK8 and mTOR in vivo and in vitro . Overall, our findings establish a connection between transcription and translation regulation, suggesting a promising therapeutic approach targets multiple points in the protein synthesis network for MYC-driven MB.

Discovery of : A Selective, Durable, and Small-Molecule Degrader of the CDK8-Cyclin C Complex

The CDK8-cyclin C complex is an important anti-tumor target, but unlike CDK8, cyclin C remains undruggable. Modulators regulating cyclin C activity directly are still under development. Here, a series of hydrophobic tagging-based degraders of the CDK8-cyclin C complex were designed, synthesized, and evaluated to identify the first dual degrader, LL-K8-22, which induced selective and synchronous degradation of CDK8 and cyclin C. Proteomic and immunoblot studies exhibited that LL-K8-22 significantly degraded CDK8 without reducing CDK19 and did not degrade other cyclin proteins except cyclin C. Moreover, LL-K8-22 showed enhanced anti-proliferative effects over its parental molecule, BI-1347, with potency increased by 5-fold in MDA-MB-468 cells. LL-K8-22 exhibited more pronounced effects on CDK8-cyclin C downstream signaling than BI-1347, suppressing STAT1 phosphorylation more persistently. RNA-sequencing analysis revealed that LL-K8-22 inhibited E2F- and MYC-driven carcinogenic transcriptional programs. Overall, LL-K8-22 is the first-in-class degrader of cyclin C and would be useful for studying the unknown functions of cyclin C.

Computational Exploration of Anti-cancer Potential of Flavonoids against Cyclin-Dependent Kinase 8: An In Silico Molecular Docking and Dynamic Approach

Over the centuries, cancer has been considered one of the significant health threats. It holds the position in the list of deadliest diseases over the globe. In women, breast cancer is the most common among many cancers and is the second most common cancer all over the world, while lung cancer is the first. Cyclin-dependent kinase 8 (CDK8) has been identified as a critical oncogenic driver that is found in breast cancer and associated with tumor progression. Flavonoids were virtually screened against CDK8 using molecular docking, drug-likeness, ADMET prediction, and a molecular dynamics (MD) simulation approach to determine the potential flavonoid structure against CDK8. The results indicated that ZINC000005854718 showed the highest negative binding affinity of -10.7 kcal/mol with the targeted protein and passed all the drug-likeness parameters. Performed molecular dynamics simulation showed that docked complex systems have good conformational stability over 100 ns in different temperatures (298, 300, 305, 310, and 320 K). The comparison between calculated binding free energy via MM/PB(GB)SA methods and binding affinity calculated via molecular docking suggested tight binding of ZINC000005854718 with targeted protein. The results concluded that ZINC000005854718 has drug-like properties with tight and stable binding with the targeted protein.

NK cells and solid tumors: therapeutic potential and persisting obstacles

Natural killer (NK) cells, which are innate lymphocytes endowed with potent cytotoxic activity, have recently attracted attention as potential anticancer therapeutics. While NK cells mediate encouraging responses in patients with leukemia, the therapeutic effects of NK cell infusion in patients with solid tumors are limited. Preclinical and clinical data suggest that the efficacy of NK cell infusion against solid malignancies is hampered by several factors including inadequate tumor infiltration and persistence/activation in the tumor microenvironment (TME). A number of metabolic features of the TME including hypoxia as well as elevated levels of adenosine, reactive oxygen species, and prostaglandins negatively affect NK cell activity. Moreover, cancer-associated fibroblasts, tumor-associated macrophages, myeloid-derived suppressor cells, and regulatory T cells actively suppress NK cell-dependent anticancer immunity. Here, we review the metabolic and cellular barriers that inhibit NK cells in solid neoplasms as we discuss potential strategies to circumvent such obstacles towards superior therapeutic activity.

Targeting the Heterogeneous Genomic Landscape in Triple-Negative Breast Cancer through Inhibitors of the Transcriptional Machinery

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer defined by lack of the estrogen, progesterone and human epidermal growth factor receptor 2. Although TNBC tumors contain a wide variety of oncogenic mutations and copy number alterations, the direct targeting of these alterations has failed to substantially improve therapeutic efficacy. This efficacy is strongly limited by interpatient and intratumor heterogeneity, and thereby a lack in uniformity of targetable drivers. Most of these genetic abnormalities eventually drive specific transcriptional programs, which may be a general underlying vulnerability. Currently, there are multiple selective inhibitors, which target the transcriptional machinery through transcriptional cyclin-dependent kinases (CDKs) 7, 8, 9, 12 and 13 and bromodomain extra-terminal motif (BET) proteins, including BRD4. In this review, we discuss how inhibitors of the transcriptional machinery can effectively target genetic abnormalities in TNBC, and how these abnormalities can influence sensitivity to these inhibitors. These inhibitors target the genomic landscape in TNBC by specifically suppressing MYC-driven transcription, inducing further DNA damage, improving anti-cancer immunity, and preventing drug resistance against MAPK and PI3K-targeted therapies. Because the transcriptional machinery enables transcription and propagation of multiple cancer drivers, it may be a promising target for (combination) treatment, especially of heterogeneous malignancies, including TNBC.

Cyclin-dependent kinases in breast cancer: expression pattern and therapeutic implications

Presently, breast cancer (BC) is one of the most common malignancies diagnosed and the leading cause of tumor-related deaths among women worldwide. Cell cycle dysregulation is one of the hallmarks of cancer, resulting in uncontrolled cell proliferation. Cyclin-dependent kinases (CDKs) are central to the cell cycle control system, and deregulation of these kinases leads to the development of malignancies, including breast cancer. CDKs and cyclins have been reported as crucial components involved in tumor cell proliferation and metastasis. Given the aggressive nature, tumor heterogeneity, and chemoresistance, there is an urgent need to explore novel targets and therapeutics to manage breast cancer effectively. Inhibitors targeting CDKs modulate the cell cycle, thus throwing light upon their therapeutic aspect where the progression of tumor cells could be inhibited. This article gives a comprehensive account of CDKs in breast cancer progression and metastasis and recent developments in the modulation of CDKs in treating malignancies. We have also explored the expression pattern and prognostic significance of CDKs in breast cancer patients. The article will also shed light on the Implications of CDK inhibition and TGF-β signaling in breast cancer.