Breast Tumor Kinase (Brk/PTK6) Mediates Advanced Cancer Phenotypes via SH2-Domain Dependent Activation of RhoA and Aryl Hydrocarbon Receptor (AhR) Signaling

A PROTAC degrader suppresses oncogenic functions of PTK6 inducing apoptosis of breast cancer cells

Protein tyrosine kinase 6 (PTK6), a non-receptor tyrosine kinase, is an oncogenic driver in many tumor types. However, agents that therapeutically target PTK6 are lacking. Although several PTK6 kinase inhibitors have been developed, none have been clinically translated, which may be due to kinase-independent functions that compromise their efficacy. PTK6 kinase inhibitor treatment phenocopies some, but not all effects of PTK6 downregulation. PTK6 downregulation inhibits growth of breast cancer cells, but treatment with PTK6 kinase inhibitor does not. To chemically downregulate PTK6, we designed a PROTAC, MS105, which potently and specifically degrades PTK6. Treatment with MS105, but not PTK6 kinase inhibitor, inhibits growth and induces apoptosis of breast cancer cells, phenocopying the effects of PTK6 (short hairpin RNA) shRNA/CRISPR. In contrast, both MS105 and PTK6 kinase inhibitor effectively inhibit breast cancer cell migration, supporting the differing kinase dependencies of PTK6's oncogenic functions. Our studies support PTK6 degraders as a preferred approach to targeting PTK6 in cancer.

Trifolirhizin targets PTK6 to induce autophagy and exerts antitumor effects in nasopharyngeal carcinoma

Trifolirhizin, a natural flavonoid glycoside, has been proved to exert antitumor activities in various human malignant tumors. PTK6 was identified as a direct target of trifolirhizin based on public database SuperPred (https://prediction.charite.de/). Overexpressed PTK6 in a variety of tumors is closely associated with the malignant development of tumors. Herein, this present research was formulated to elaborate the effects of trifolirhizin on the biological behaviors of nasopharyngeal carcinoma (NPC) cells and to probe into the intrinsic mechanisms. The current study firstly elucidated the tumor-inhibiting functions of trifolirhizin in NPC malignant progression from the perspective of targeting inhibition of PTK6. In this work, CCK-8 for cell viability, EdU staining for cell proliferation, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining for cell apoptosis and immunofluorescence staining for LC3 expression were performed. Besides, levels of proliferation-related, apoptosis-related and autophagy-related proteins were detected by western blot analysis. Moreover, molecular docking of trifolirhizin with PTK6 was conducted to seek the compound-protein binding potential. It was demonstrated that trifolirhizin treatment inhibited the proliferation and promoted the apoptosis of NPC cells as well as strengthened autophagy in NPC cells. Furthermore, it was verified that trifolirhizin targeted PTK6 and negatively regulated PTK6 expression. The suppressive effects of trifolirhizin on the malignant behaviors of NPC cells and the enhancing effect of trifolirhizin on autophagy in NPC cells were partly abolished upon upregulation of PTK6. To conclude, findings suggested that trifolirhizin may downregulate PTK6 expression to induce autophagy and exert the antitumor activities in NPC.

A pyrazolopyridine as a novel AhR signaling activator with anti-breast cancer properties in vitro and in vivo

Breast cancer is one of the main causes of malignancy-related deaths globally and has a significant impact on women's quality of life. Despite significant therapeutic advances, there is a medical need for targeted therapies in breast cancer. Aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor mediates responses to environment stimuli, is emerging as a unique pleiotropic target. Herein, a combined molecular simulation and in vitro investigations identified 3-(3-fluorophenyl)-1H-pyrazolo[3,4-b]pyridine (3FPP) as a novel AhR ligand in T47D and MDA-MB-231 breast cancer cells. Its agonistic effects induced formation of the AhR-AhR nuclear translocator (Arnt) heterodimer and prompted its binding to the penta-nucleotide sequence, called xenobiotic-responsive element (XRE) motif. Moreover, 3FPP augmented the promoter-driven luciferase activities and expression of AhR-regulated genes encoding cytochrome P450 1A1 (CYP1A1) and microRNA (miR)-212/132 cluster. It reduced cell viability, migration, and invasion of both cell lines through AhR signaling. These anticancer properties were concomitant with reduced levels of B-cell lymphoma 2 (BCL-2), SRY-related HMG-box4 (SOX4), snail family zinc finger 2 (SNAI2), and cadherin 2 (CDH2). In vivo, 3FPP suppressed tumor growth and activated AhR signaling in an orthotopic mouse model. In conclusion, our results introduce the fused pyrazolopyridine 3FPP as a novel AhR agonist with AhR-specific anti-breast cancer potential in vitro and in vivo.

In Silico Screening of Multi-Domain Targeted Inhibitors for PTK6: A Strategy Integrating Drug Repurposing and Consensus Docking

Protein tyrosine kinase 6 (PTK6), also known as breast tumor kinase (BRK), serves as a non-receptor intracellular tyrosine kinase within the Src kinases family. Structurally resembling other Src kinases, PTK6 possesses an Src homology 3 (SH3) domain, an Src homology 2 (SH2) domain, and a tyrosine kinase domain (SH1). While considerable efforts have been dedicated to designing PTK6 inhibitors targeting the SH1 domain, which is responsible for kinase activity in various pathways, it has been observed that solely inhibiting the SH1 domain does not effectively suppress PTK6 activity. Subsequent investigations have revealed the involvement of SH2 and SH3 domains in intramolecular and substrate binding interactions, which are crucial for PTK6 function. Consequently, the identification of PTK6 inhibitors targeting not only the SH1 domain but also the SH2 and SH3 domains becomes imperative. Through an in silico structural-based virtual screening approach, incorporating drug repurposing and a consensus docking approach, we have successfully identified four potential ligands capable of concurrently inhibiting the tyrosine kinase domain and SH2/SH3 domains of PT6K simultaneously. This finding suggests potential pathways for therapeutic interventions in PTK6 inhibition.

Prognostic impact of PTK6 expression in triple negative breast cancer

BACKGROUND

The aim of this study was to investigate the expression of PTK6 in different groups of triple negative breast cancer and its impact on prognosis.

METHODS

Retrospective study of a total of 209 surgical specimens of breast cancer were identified by IHC or FISH methods as triple negative,and divided into a lymph node metastasis positive (LNM +)group (n = 102) and a lymph node metastasis negative(LNM-) group (n = 107) according to the lymph node status of the surgical specimen. PTK6 expression was detected by IHC technique in all surgical specimens. PTK6 expression and clinicopathological features was explored by Chi-square test. The prognosis of different groups of patients was analyzed by Kaplan-Meier survival analysis and COX analysis.

RESULTS

The incidence of PTK6 expression in the LNM + group (78.4%) was significantly higher than in the LNM- group (28%). Clinicopathological analysis showed that PTK6 expression in the LNM + group was negatively correlated with the 5-year survival of patients. Kaplan-Meier analysis showed that only PTK6 expression in the LNM + group was negatively correlated with OS and DFS. COX analysis also showed that PTK6 expression and N stage were independent prognostic factors for DFS in the LNM + group. No correlation was observed between HER2 and PTK6 expression in any of the groups.

CONCLUSIONS

This study suggests that PTK6 promotes tumor development and was associated with poor prognosis in the LNM + group of triple negative breast cancer. Inhibition of PTK6 may be a new approach for the treatment of triple negative breast cancer patients, especially those with metastasis.

Glucocorticoid Receptors Drive Breast Cancer Cell Migration and Metabolic Reprogramming via PDK4

Corticosteroids act on the glucocorticoid receptor (GR; NR3C1) to resolve inflammation and are routinely prescribed to breast cancer patients undergoing chemotherapy treatment to alleviate side effects. Triple-negative breast cancers (TNBCs) account for 15% to 20% of diagnoses and lack expression of estrogen and progesterone receptors as well as amplified HER2, but they often express high GR levels. GR is a mediator of TNBC progression to advanced metastatic disease; however, the mechanisms underpinning this transition to more aggressive behavior remain elusive. We previously showed that tissue/cellular stress (hypoxia, chemotherapies) as well as factors in the tumor microenvironment (transforming growth factor β [TGF-β], hepatocyte growth factor [HGF]) activate p38 mitogen-activated protein kinase (MAPK), which phosphorylates GR on Ser134. In the absence of ligand, pSer134-GR further upregulates genes important for responses to cellular stress, including key components of the p38 MAPK pathway. Herein, we show that pSer134-GR is required for TNBC metastatic colonization to the lungs of female mice. To understand the mechanisms of pSer134-GR action in the presence of GR agonists, we examined glucocorticoid-driven transcriptomes in CRISPR knock-in models of TNBC cells expressing wild-type or phospho-mutant (S134A) GR. We identified dexamethasone- and pSer134-GR-dependent regulation of specific gene sets controlling TNBC migration (NEDD9, CSF1, RUNX3) and metabolic adaptation (PDK4, PGK1, PFKFB4). TNBC cells harboring S134A-GR displayed metabolic reprogramming that was phenocopied by pyruvate dehydrogenase kinase 4 (PDK4) knockdown. PDK4 knockdown or chemical inhibition also blocked cancer cell migration. Our results reveal a convergence of GR agonists (ie, host stress) with cellular stress signaling whereby pSer134-GR critically regulates TNBC metabolism, an exploitable target for the treatment of this deadly disease.

Aryl Hydrocarbon Receptor as an Anticancer Target: An Overview of Ten Years Odyssey

Aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor belonging to the basic helix-loop-helix (bHLH)/per-Arnt-sim (PAS) superfamily, is traditionally known to mediate xenobiotic metabolism. It is activated by structurally diverse agonistic ligands and regulates complicated transcriptional processes through its canonical and non-canonical pathways in normal and malignant cells. Different classes of AhR ligands have been evaluated as anticancer agents in different cancer cells and exhibit efficiency, which has thrust AhR into the limelight as a promising molecular target. There is strong evidence demonstrating the anticancer potential of exogenous AhR agonists including synthetic, pharmaceutical, and natural compounds. In contrast, several reports have indicated inhibition of AhR activity by antagonistic ligands as a potential therapeutic strategy. Interestingly, similar AhR ligands exert variable anticancer or cancer-promoting potential in a cell- and tissue-specific mode of action. Recently, ligand-mediated modulation of AhR signaling pathways and the associated tumor microenvironment is emerging as a potential approach for developing cancer immunotherapeutic drugs. This article reviews advances of AhR in cancer research covering publication from 2012 to early 2023. It summarizes the therapeutic potential of various AhR ligands with an emphasis on exogenous ligands. It also sheds light on recent immunotherapeutic strategies involving AhR.

Targeted Therapy and Mechanisms of Drug Resistance in Breast Cancer

Breast cancer is the most common cause of cancer-related death in women worldwide. Multidrug resistance (MDR) has been a large hurdle in reducing BC death rates. The drug resistance mechanisms include increased drug efflux, enhanced DNA repair, senescence escape, epigenetic alterations, tumor heterogeneity, tumor microenvironment (TME), and the epithelial-to-mesenchymal transition (EMT), which make it challenging to overcome. This review aims to explain the mechanisms of resistance in BC further, identify viable drug targets, and elucidate how those targets relate to the progression of BC and drug resistance.

The Role of the Aryl Hydrocarbon Receptor (AhR) and Its Ligands in Breast Cancer

Breast cancer is a complex disease which is defined by numerous cellular and molecular markers that can be used to develop more targeted and successful therapies. The aryl hydrocarbon receptor (AhR) is overexpressed in many breast tumor sub-types, including estrogen receptor -positive (ER+) tumors; however, the prognostic value of the AhR for breast cancer patient survival is not consistent between studies. Moreover, the functional role of the AhR in various breast cancer cell lines is also variable and exhibits both tumor promoter- and tumor suppressor- like activity and the AhR is expressed in both ER-positive and ER-negative cells/tumors. There is strong evidence demonstrating inhibitory AhR-Rα crosstalk where various AhR ligands induce ER degradation. It has also been reported that different structural classes of AhR ligands, including halogenated aromatics, polynuclear aromatics, synthetic drugs and other pharmaceuticals, health promoting phytochemical-derived natural products and endogenous AhR-active compounds inhibit one or more of breast cancer cell proliferation, survival, migration/invasion, and metastasis. AhR-dependent mechanisms for the inhibition of breast cancer by AhR agonists are variable and include the downregulation of multiple genes/gene products such as CXCR4, MMPs, CXCL12, SOX4 and the modulation of microRNA levels. Some AhR ligands, such as aminoflavone, have been investigated in clinical trials for their anticancer activity against breast cancer. In contrast, several publications have reported that AhR agonists and antagonists enhance and inhibit mammary carcinogenesis, respectively, and differences between the anticancer activities of AhR agonists in breast cancer may be due in part to cell context and ligand structure. However, there are reports showing that the same AhR ligand in the same breast cancer cell line gives opposite results. These differences need to be resolved in order to further develop and take advantage of promising agents that inhibit mammary carcinogenesis by targeting the AhR.

Comprehensive Analysis Reveals PTK6 as a Prognostic Biomarker Involved in the Immunosuppressive Microenvironment in Breast Cancer

The significant mortality rate that is currently experienced by female breast cancer (BC) patients highlights the importance of locating potent and dependable biomarkers in BC patients. Over the past few years, a number of studies have demonstrated that PTK6 was dysregulated in a variety of cancers. However, its expression and the clinical importance it may have in patients with BC have not been explored. Based on datasets from the TCGA database and GTEx database, we studied the expressions and functions of PTK6 across 33 different kinds of cancer. In this study, we investigated the differential expression of PTK6 in tumor tissue compared to nontumor tissue as well as in various stages of cancer. ROC assays were used to conduct an investigation into the diagnostic potential of PTK6 in BC. After that, the Kaplan-Meier method, univariate analysis, and multivariate analysis were carried out in order to investigate the PTK6 gene's potential prognostic significance in patients with BC. ssGSEA was utilized in order to conduct an investigation of the immune infiltration. In this study, we discovered that the expressions of PTK6 were significantly raised in the majority of different types of malignancies, including BC. The diagnostic value of PTK6 expression was validated by ROC tests, demonstrating an AUC greater than 0.7. A positive PR, ER, and HER2 status was found to be related with high expression levels of PTK6. According to the results of a survival analysis, patients who had a high level of PTK6 expression had a shorter overall survival time than those who had a low level of PTK6 expression. Besides, we observed that PTK6 expressions were positively correlated with the abundance of NK CD56bright cells and Th17 cells and negatively correlated with that of Th1 cells, macrophages, B cells, T cells, aDC, DC, cytotoxic cells, Tem, TFH, NK CD56dim cells, Treg, and Tgd. In conclusion, PTK6 expression was found to be linked with the clinical phenotype of BC, and as a result, this finding may have consequences for the diagnosis, prognosis, and treatment of individuals with BC.

Sabizabulin, a Potent Orally Bioavailable Colchicine Binding Site Agent, Suppresses HER2+ Breast Cancer and Metastasis

HER2+ breast cancer accounts for 15% of all breast cancer cases. Current frontline therapy for HER2+ metastatic breast cancer relies on targeted antibodies, trastuzumab and pertuzumab, combined with microtubule inhibitors in the taxane class (paclitaxel or docetaxel). It is well known that the clinical efficacy of taxanes is limited by the development of chemoresistance and hematological and neurotoxicities. The colchicine-binding site inhibitors (CBSIs) are a class of promising alternative agents to taxane therapy. Sabizabulin (formerly known as VERU-111) is a potent CBSI that overcomes P-gp-mediated taxane resistance, is orally bioavailable, and inhibits tumor growth and distant metastasis in triple negative breast cancer (TNBC). Herein, we demonstrate the efficacy of sabizabulin in HER2⁺ breast cancer. In vitro, sabizabulin inhibits the proliferation of HER2+ breast cancer cell lines with low nanomolar IC₅₀ values, inhibits clonogenicity, and induces apoptosis in a concentration-dependent manner. In vivo, sabizabulin inhibits breast tumor growth in the BT474 (ER+/PR+/HER2+) xenograft model and a HER2+ (ER-/PR-) metastatic patient-derived xenograft (PDX) model, HCI-12. We demonstrate that sabizabulin is a promising alternative agent to target tubulin in HER2+ breast cancer with similar anti-metastatic efficacy to paclitaxel, but with the advantage of oral bioavailability and lower toxicity than taxanes.

Interference of PTK6/GAB1 signaling inhibits cell proliferation, invasion, and migration of cervical cancer cells

Protein tyrosine kinase 6 (PTK6) has shown important cancer-promoting effects in a variety of cancer types. Nonetheless, its vital role in cervical cancer has not been completely elucidated. The present study sought to address whether PTK6 is involved in the malignant progression of cervical cancer via its interaction with GRB2-associated binding 1 (GAB1). Western blotting was used to examine PTK6 and GAB1 expression levels. Cell Counting Kit-8, Transwell, wound healing, and terminal deoxynucleotidyl-transferase-mediated dUTP nick end labeling assays were performed to estimate the corresponding proliferative, migratory, invasive, and apoptotic abilities of the cells. Co-immunoprecipitation (Co-IP) assays confirmed binding of PTK6 to GAB1. The results revealed that the expression levels of PTK6 and GAB1 were markedly increased in cervical cancer cell lines compared with those noted in normal cervical epithelial cells. The cell proliferative, invasive, and migratory activities of cervical cancer cells were reduced in the absence of PTK6 expression, whereas the induction of apoptosis was aggravated under these conditions. The results of the Co-IP assay indicated that PTK6 expression was positively associated with GAB1. In addition, the suppressive effect of PTK6 silencing on the malignant phenotypes of cervical cancer cells was reversed following overexpression of GAB1. In summary, the present study indicated that knockdown of PTK6 expression protected against the malignant progression of cervical cancer, while overexpression of GAB1 counteracted the inhibitory effects of PTK6 knockdown on cervical cancer cells.

Adverse outcome pathway from activation of the AhR to breast cancer-related death

Adverse outcome pathways (AOPs) are formalized and structured linear concepts that connect one molecular initiating event (MIE) to an adverse outcome (AO) via different key events (KE) through key event relationships (KER). They are mainly used in eco-toxicology toxicology, and regulatory health issues. AOPs must respond to specific guidelines from the Organization for Economic Co-operation and Development (OECD) to weight the evidence between each KE. Breast cancer is the deadliest cancer in women with a poor prognosis in case of metastatic breast cancer. The role of the environments in the formation of metastasis has been suggested. We hypothesized that activation of the AhR (MIE), a xenobiotic receptor, could lead to breast cancer related death (AO), through different KEs, constituting a new AOP. An artificial intelligence tool (AOP-helpfinder), which screens the available literature, was used to collect all existing scientific abstracts to build a novel AOP, using a list of key words. Four hundred and seven abstracts were found containing at least a word from our MIE list and either one word from our AO or KE list. A manual curation retained 113 pertinent articles, which were also screened using PubTator. From these analyses, an AOP was created linking the activation of the AhR to breast cancer related death through decreased apoptosis, inflammation, endothelial cell migration, angiogenesis, and invasion. These KEs promote an increased tumor growth, angiogenesis and migration which leads to breast cancer metastasis and breast cancer related death. The evidence of the proposed AOP was weighted using the tailored Bradford Hill criteria and the OECD guidelines. The confidence in our AOP was considered strong. An in vitro validation must be carried out, but our review proposes a strong relationship between AhR activation and breast cancer-related death with an innovative use of an artificial intelligence literature search.

Epigenetic Deregulation of Protein Tyrosine Kinase 6 Promotes Carcinogenesis of Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) accounts for over 90% of oral cancers and causes considerable morbidity and mortality. Epigenetic deregulation is a common mechanism underlying carcinogenesis. DNA methylation deregulation is the epigenetic change observed during the transformation of normal cells to precancerous and eventually cancer cells. This study investigated the DNA methylation patterns of PTK6 during the development of OSCC. Bisulfite genomic DNA sequencing was performed to determine the PTK6 methylation level. OSCC animal models were established to examine changes in PTK6 expression in the different stages of OSCC development. The DNA methylation of PTK6 was decreased during the development of OSCC. The mRNA and protein expression of PTK6 was increased in OSCC cell lines compared with human normal oral keratinocytes. In mice, the methylation level of PTK6 decreased after treatment with 4-nitroquinoline 1-oxide and arecoline, and the mRNA and protein expression of PTK6 was increased. PTK6 hypomethylation can be a diagnostic marker of OSCC. Upregulation of PTK6 promoted the proliferation, migration, and invasion of OSCC cells. PTK6 promoted carcinogenesis and metastasis by increasing STAT3 phosphorylation and ZEB1 expression. The epigenetic deregulation of PTK6 can serve as a biomarker for the early detection of OSCC and as a treatment target.

An Overview of Potential Therapeutic Agents Targeting WNT/PCP Signaling

Since the discovery of the proto-oncogene Wnt1 (Int1) in 1982, WNT signaling has been identified as one of the most important pathways that regulates a wide range of fundamental developmental and physiological processes in multicellular organisms. The canonical WNT signaling pathway depends on the stabilization and translocation of β-catenin and plays important roles in development and homeostasis. The WNT/planar cell polarity (WNT/PCP) signaling, also known as one of the β-catenin-independent WNT pathways, conveys directional information to coordinate polarized cell behaviors. Similar to WNT/β-catenin signaling, disruption or aberrant activation of WNT/PCP signaling also underlies a variety of developmental defects and cancers. However, the pharmacological targeting of WNT/PCP signaling for therapeutic purposes remains largely unexplored. In this review, we briefly discuss WNT/PCP signaling in development and disease and summarize the known drugs/inhibitors targeting this pathway.