Combined VEGFR and MAPK pathway inhibition in angiosarcoma

WGCNA and integrative network analysis identify CHRNA5 and CTLA4 as potential therapeutic targets against angiosarcoma

Angiosarcomas are a type of soft-tissue sarcoma characterized by aggressive malignant tumors originating from endothelial cells of blood vessels or lymphatic vessels. Limited studies have been done to explore the molecular pathophysiology of the disease, with rather limited studies involving transcriptomic analyzes. This study was undertaken to identify the shared molecular signatures and gene modules associated with angiosarcomas of various origin. Transcriptomic data analysis of publicly available data was done followed by WGCNA to identify shared signature gene modules. The Maximal Clique Centrality algorithm was applied to gene modules, and unclustered network analysis was conducted on differentially expressed genes to identify true hub genes. The expression of candidate genes in various cancer types was analyzed using GEPIA. WGCNA analysis identified five significant modules, with the most enriched module being associated with angiogenesis and cell junction regulators. The intersection of true hub genes from MCC analysis of WGCNA modules and high-degree nodes from an unclustered network revealed eight consistently overexpressed genes in all angiosarcoma samples.Among the eight enriched genes, CHRNA5 and CTLA4, are exclusively overexpressed in angiosarcoma and not in other cancers of the same tissue origin, with significant drug-protein interactions suggesting their potential as therapeutic targets.

Ovarian angiosarcoma: A systematic review of literature and survival analysis

Ovarian angiosarcoma (OA) is rare, with only sporadic cases reported in English literature. We performed a systematic review of cases published in the PubMed, Science Direct, and Google Scholar databases with the aim of describing the reported clinicopathological features of OA. Fifty-three articles that reported 60 patients were reviewed. Of the 60 patients, 7 (11.6 %) were diagnosed with secondary (metastatic) ovarian angiosarcoma and 53 (88.3 %) were diagnosed with primary ovarian angiosarcoma. The mean age at presentation for ovarian angiosarcoma was 38.3±17.8 years. The average tumor size for ovarian angiosarcoma was 11.9±6.1 cm. Abdominal distention was reported in 45/60 (75 %). Microscopic examination revealed necrosis in 28/60 (46.7 %), pleomorphism in 32/59 (54.2 %), mitotic figures in 44/60 (73.3 %), spindle-shaped cells in 27/36 (75 %), epithelioid-shaped cells in 20/36 (55.5 %), and mixed epithelioid and spindle-shaped cells in 12/36 (33.3 %) patients. On immunohistochemistry CD 31 was positive in 41/41 (100 %), CD 34 in 38/39 (97.4 %), and Factor VIII related antigen in 18/21 (85.7 %) patients. Metastasis was present in 43/60 (71.6 %) patients. Chemotherapy and surgery was performed in 36/52 (69.2 %). The median follow-up time for ovarian angiosarcoma was 7 months (IQR1-IQR3:2-13.5 months). 24 (48 %) of the 50 patients with available survival data were alive and 26/50 (52 %) were dead of disease. Survival analyses (KM curves) revealed that the presence of necrosis (log-rank test; p = 0.05) and absence of spindle-shaped cells (log rank test; p = 0.04) on histopathology were associated with worse outcomes, while treatment with combined chemotherapy and surgical excision was associated with better survival (P < 0.001) therefore, prompt diagnosis and early treatment with combined chemotherapy and surgical excision can prolong survival in OA.

Genomic landscape and preclinical models of angiosarcoma

Angiosarcoma is a cancer that develops in blood or lymphatic vessels that presents a significant clinical challenge due to its rarity and aggressive features. Clinical outcomes have not improved in decades, highlighting a need for innovative therapeutic strategies to treat the disease. Genetically, angiosarcomas exhibit high heterogeneity and complexity with many recurrent mutations. However, recent studies have identified some common features within anatomic and molecular subgroups. To identify potential therapeutic vulnerabilities, it is essential to understand and integrate the mutational landscape of angiosarcoma with the models that exist to study the disease. In this review, we will summarize the insights gained from reported genomic alterations in molecular and anatomic subtypes of angiosarcoma, discuss several potential actionable targets, and highlight the preclinical disease models available in the field.

Elucidating the mechanism of plasticizers inducing breast cancer through network toxicology and molecular docking analysis

OBJECTIVE

The objective of this study was to elucidate the molecular mechanisms underlying the potential contribution of commonly utilized plasticizers, including Diethyl phthalate (DEP), Dimethyl phthalate (DMP), and Dioctyl phthalate (DOP), to the pathogenesis of breast cancer. This study aimed to highlight the complex interactions between these environmental chemicals and key molecular pathways implicated in tumorigenesis.

METHODS

We employed network toxicology and molecular docking techniques to analyze the interactions between plasticizers and key proteins implicated in breast cancer. Utilizing databases such as the TCGA, we performed an expression analysis of selected key genes in breast cancer tissue compared to normal controls. Enrichment analysis was conducted to identify the biological pathways associated with these genes.

RESULTS

Enrichment analysis highlighted the association of these plasticizer-targeted genes with pathways integral to adenocarcinoma development, suggesting a broad impact of plasticizers on hormone-dependent and other forms of cancers. Subsequent expression analysis using data from the TCGA breast cancer database indicated significant upregulation or downregulation of these genes in breast cancer tissues compared to normal controls, confirming their pivotal roles in tumor biology. Furthermore, the molecular docking analysis revealed that plasticizers, including DEP, DMP, and DOP, exhibit specific binding interactions with key proteins such as MAPK1, AKT1, SRC, ESR1, and ALB, which are crucial in the regulation of breast cancer pathogenesis.

CONCLUSION

The study provides evidence that exposure to plasticizers may influence breast cancer pathogenesis through interactions with critical proteins and signaling pathways. By employing network pharmacology, protein interactions, and molecular docking, our findings highlight the potential risks posed by plasticizers. These results underscore the need for further epidemiological and clinical research to fully understand the implications of plasticizer exposure on breast cancer risk, thus informing future preventive and therapeutic strategies.

miR-497 Target Gene Regulatory Network in Angiosarcoma

Angiosarcoma is a vascular sarcoma that is highly aggressive and metastatic. Because of its rarity, treatment options for patients are limited. Therefore, more research is needed to identify possible therapeutic vulnerabilities. We previously found that conditional deletion of Dicer1 drives angiosarcoma development in mice. Given the role of DICER1 in canonical miRNA biogenesis, this suggests that miRNA loss is important in angiosarcoma development. After testing miRNAs previously suggested to have a tumor-suppressive role in angiosarcoma, miRNA-497-5p (miR-497) suppressed cell viability most significantly. We also found that miR-497 overexpression led to significantly reduced cell migration and tumor formation. To understand the mechanism of miR-497 in tumor suppression, we identified clinically relevant target genes using a combination of RNA-sequencing data in an angiosarcoma cell line, expression data from patients with angiosarcoma, and target prediction algorithms. We validated miR-497 direct regulation of cyclin-D2, cyclin-dependent kinase 6, and vesicle amine transport protein 1 (VAT1). One of these genes, VAT1, is an understudied protein that has been suggested to promote cell migration and metastasis in other cancers. Indeed, we find that pharmacologic inhibition of VAT1 with the natural product neocarzilin A reduces angiosarcoma migration. Implications: This work supports the potent tumor-suppressive abilities of miR-497 in angiosarcoma, providing evidence for its potential as a therapeutic agent, and provides insight into the mechanisms of tumor suppression through analysis of the target gene regulatory network of miR-497.

Molecular and immune pathobiology of human angiosarcoma

Angiosarcoma is a rare endothelial-derived malignancy that is extremely diverse in anatomy, aetiology, molecular and immune characteristics. While novel therapeutic approaches incorporating targeted agents and immunotherapy have yielded significant improvements in patient outcomes across several cancers, their impact on angiosarcoma remains modest. Contributed by its heterogeneous nature, there is currently a lack of novel drug targets in this disease entity and no reliable biomarkers that predict response to conventional treatment. This review aims to examine the molecular and immune landscape of angiosarcoma in association with its aetiology, anatomical sites, prognosis and therapeutic options. We summarise current efforts to characterise angiosarcoma subtypes based on molecular and immune profiling. Finally, we highlight promising technologies such as single-cell spatial "omics" that may further our understanding of angiosarcoma and propose strategies that can be similarly applied for the study of other rare cancers.

Clinical course and vascular endothelial growth factor signaling system expression in maxillary angiosarcoma: A case report

Maxillary angiosarcoma, an aggressive tumor derived from vascular endothelial cells, is very rare. Recently, antivascular endothelial growth factor (VEGF) therapies have attracted considerable attention. We describe the clinical course of a patient with maxillary angiosarcoma and discuss the expression of VEGF signaling molecules assessed via immunohistological analysis. An 81-year-old man presented with an aggressive tumor in the left maxillary sinus. Biopsy revealed atypical nuclear cell proliferation, and the tumor was suspected to be a sarcoma. The maxillary malignancy was treated using a multidisciplinary approach with a combination of surgery, radiotherapy, and regional chemotherapy. Examination of the specimen obtained in the first surgery revealed maxillary angiosarcoma, found to be positive for CD31, while negative for CD34, D2-40, and factor Ⅷ. Although no pathological residual tumor was observed after the planned wide surgery, cervical lymph node and distant metastases occurred. The patient died 24 months after the first surgery. Staining revealed VEGF receptor (VEGFR) 1, VEGFR2, phosphorylated Ak strain transforming, mitogen-activated protein kinase, and signal transducer and activator of transcription 3 positivity. Although our findings do not indicate that anti-VEGF therapy is beneficial for treating maxillary angiosarcomas, we found that VEGFR signaling pathways were activated in maxillary angiosarcomas similar to angiosarcomas originating at other sites. Herein, we report a case of maxillary angiosarcoma, focused on VEGFR and signaling pathway activation. To our knowledge, this is the first report to describe VEGFR system immunostaining findings in maxillary angiosarcoma.

Primary Epithelioid Angiosarcoma of the Jejunal Mesentery Causing Abdominal Bleeding: Case Report and Literature Review

Gastrointestinal angiosarcoma is an extremely rare malignant tumor of the digestive tract, characterized by a very poor prognosis, with few patients surviving more than 1 year after diagnosis. This case report describes a 71-year-old female patient with a 3-year history of intermittent abdominal pain and significant exacerbation of abdominal pain and bloating 2 weeks prior to treatment. After surgical treatment, the pathological and immunohistochemical diagnosis was primary epithelioid angiosarcoma of the jejunal mesentery. The patient refused postoperative adjuvant chemotherapy and died 4 months after diagnosis due to widespread systemic metastasis. In addition, this article reviews 38 previously reported cases of primary gastrointestinal angiosarcoma, aiming to further understand angiosarcoma and thus guide clinical practitioners in providing more comprehensive treatment approaches.

Characterisation of new in vitro models and identification of potentially active drugs in angiosarcoma

Angiosarcoma is a rare soft tissue sarcoma originating from endothelial cells. Given that current treatments for advanced disease have shown limited efficacy, alternative therapies need to be identified. In rare diseases, patient-derived cell models are crucial for screening anti-tumour activity. In this study, cell line models were characterised in 2D and 3D cultures. The cell lines' growth, migration and invasion capabilities were explored, confirming them as useful tools for preclinical angiosarcoma studies. By screening a drug library, we identified potentially effective compounds: 8-amino adenosine impacted cell growth and inhibited migration and invasion at considerably low concentrations as a single agent. No synergistic effect was detected when combining with paclitaxel, gemcitabine or doxorubicin. These results suggest that this compound could be a potentially useful drug in the treatment of AGS.

Secondary Breast Angiosarcoma After a Primary Diagnosis of Breast Cancer: A Retrospective Analysis of the Surveillance, Epidemiology, and End Results (SEER) Database

OBJECTIVES

Angiosarcoma is a rare complication of breast-conserving therapy. This study evaluated the change in incidence between 1992 and 2016 of secondary breast angiosarcoma (SBA) in patients with a history of breast cancer and the impact of management strategies for the original breast carcinoma on angiosarcoma treatment.

METHODS

Breast cancer and angiosarcoma cases were abstracted from the Surveillance, Epidemiology, and End Result (SEER) database. SBAs were defined as angiosarcomas located in the breast occurring after a prior breast cancer diagnosis. Primary breast angiosarcomas (PBAs) were defined as an angiosarcoma diagnosis listed as "one primary only." Incidence rates were estimated using a proportion of the US total population. Survival was analyzed by the Kaplan-Meier method, and Cox proportional hazard models were used to assess the association of clinicopathologic characteristics on overall survival.

RESULTS

Between 1992 and 2016, 193 cases of SBA were reported in the SEER dataset in patients with a prior history of breast cancer. The incidence of breast angiosarcoma in patients with a prior diagnosis of breast cancer increased 3-fold from about 10 cases per 100,000 person-years to about 30 cases per 100,000 person-years over this same period ( P =0.0037). For treatment of SBA (n=193), almost all (95%) had surgery. Nine percent received radiation (compared with 35% of patients with PBA, P <0.001) and 23% received chemotherapy (vs. 45% for PBA, P =0.11).

CONCLUSIONS

We demonstrate an increasing incidence of SBA over the study period. These data can help inform shared decision-making for optimal management of locoregional breast cancer and raise awareness of secondary angiosarcoma.

Identification of genomic alterations with clinical impact in canine splenic hemangiosarcoma

Canine hemangiosarcoma (HSA) is an aggressive cancer of endothelial cells with short survival times. Understanding the genomic landscape of HSA may aid in developing therapeutic strategies for dogs and may also inform therapies for the rare and aggressive human cancer angiosarcoma. The objectives of this study were to build a framework for leveraging real-world genomic and clinical data that could provide the foundation for precision medicine in veterinary oncology, and to determine the relationships between genomic and clinical features in canine splenic HSA. One hundred and nine dogs with primary splenic HSA treated by splenectomy that had tumour sequencing via the FidoCure® Precision Medicine Platform targeted sequencing panel were enrolled. Patient signalment, weight, metastasis at diagnosis and overall survival time were retrospectively evaluated. The incidence of genomic alterations in individual genes and their relationship to patient variables including outcome were assessed. Somatic mutations in TP53 (n = 44), NRAS (n = 20) and PIK3CA (n = 19) were most common. Survival was associated with presence of metastases at diagnosis and germline variants in SETD2 and NOTCH1. Age at diagnosis was associated with somatic NRAS mutations and breed. TP53 and PIK3CA somatic mutations were found in larger dogs, while germline SETD2 variants were found in smaller dogs. We identified both somatic mutations and germline variants associated with clinical variables including age, breed and overall survival. These genetic changes may be useful prognostic factors and provide insight into the genomic landscape of hemangiosarcoma.

Target gene regulatory network of miR-497 in angiosarcoma

Angiosarcoma (AS) is a vascular sarcoma that is highly aggressive and metastatic. Due to its rarity, treatment options for patients are limited, therefore more research is needed to identify possible therapeutic vulnerabilities. We previously found that conditional deletion of Dicer1 drives AS development in mice. Given the role of DICER1 in canonical microRNA (miRNA) biogenesis, this suggests that miRNA loss is important in AS development. After testing miRNAs previously suggested to have a tumor-suppressive role in AS, microRNA-497-5p (miR-497) suppressed cell viability most significantly. We also found that miR-497 overexpression led to significantly reduced cell migration and tumor formation. To understand the mechanism of miR-497 in tumor suppression, we identified clinically relevant target genes using a combination of RNA-sequencing data in an AS cell line, expression data from AS patients, and target prediction algorithms. We validated miR-497 direct regulation of CCND2, CDK6, and VAT1. One of these genes, VAT1, is an understudied protein that has been suggested to promote cell migration and metastasis in other cancers. Indeed, we find that pharmacologic inhibition of VAT1 with the natural product Neocarzilin A reduces AS migration. This work provides insight into the mechanisms of miR-497 and its target genes in AS pathogenesis.

Primary ovarian angiosarcoma: Two case reports and review of literature

BACKGROUND

Angiosarcoma (AS) is a rare and highly aggressive soft tissue disease that most commonly arises in deep soft tissues. There are only a few reported cases of AS involving the ovary and even fewer reports of the underlying molecular abnormalities. Here, we briefly review two cases of primary ovarian AS (oAS) with specific molecular events and immune checkpoints. The clinical features and prognosis of the disease, diagnosis, differential diagnosis, and new treatment approaches are discussed based on a literature review.

CASE SUMMARY

Case 1: A 51-year-old female patient was admitted with right lower limb pain for 5 mo, and lower abdominal pain with hematuria for 1 mo. Partial removal of rectus abdominis muscle and fascia, partial hysterectomy, bilateral salpingo-oophorectomy, and inguinal and pelvic lymphadenectomy were performed. Pathology revealed primary oAS. Fluorescence in situ hybridization revealed c-MYC gene amplification. MESNA + ADM + IFO + DTIC (MAID) regimen was administered, but stable disease was achieved. The patient died 1 mo later. Case 2: A 41-year-old female patient presented with fatigue, nausea, decreased appetite, and diffuse abdominal pain. On physical examination, the abdomen was distended and a complex cystic mass was palpable in the right pelvic cavity. Pathology revealed primary oAS. MAID chemotherapy was administered and programmed death ligand 1 (PD-L1) staining was performed on the tumor samples. The patient benefited from anti-PD-1 immunotherapy and is alive without any evidence of disease 27 mo off therapy in follow-up.

CONCLUSION

Long-term survival benefit for primary oAS can be achieved by alternative therapeutic strategies using pathological indicators to inform treatment.

Benign and low-grade superficial endothelial cell neoplasms in the molecular era

Vascular tumors are the most common mesenchymal neoplasms of the skin and subcutis, and they encompass a heterogeneous group with diverse clinical, histological, and molecular features, as well as biological behavior. Over the past two decades, molecular studies have enabled the identification of pathogenic recurrent genetic alterations that can be used as additional data points to support the correct classification of these lesions. The purpose of this review is to summarize the available data related to superficially located benign and low-grade vascular neoplasms and to highlight recent molecular advances with the role of surrogate immunohistochemistry to target pathogenic proteins as diagnostic biomarkers.

Discovery and functional characterization of the oncogenicity and targetability of a novel NOTCH1-ROS1 gene fusion in pediatric angiosarcoma

Angiosarcomas are rare, malignant soft tissue tumors in children that arise in a wide range of anatomical locations and have limited targeted therapies available. Here, we report a rare case of a pediatric angiosarcoma (pAS) with Li-Fraumeni syndrome (LFS) expressing a novel NOTCH1-ROS1 gene fusion. Although both NOTCH1 and ROS1 are established proto-oncogenes, our study is the first to describe the mechanistic role of NOTCH1-ROS1 fusion arising via intrachromosomal rearrangement. NOTCH1-ROS1 displayed potent neoplastic transformation propensity in vitro, and harbors tumorigenic potential in vivo, where it induced oncogenic activation of the MAPK, PI3K/mTOR, and JAK-STAT signaling pathways in a murine allograft model. We found an unexpected contribution of the NOTCH1 extracellular region in mediating NOTCH1-ROS1 activation and oncogenic function, highlighting the contribution of both NOTCH1 and ROS1 fusion partners in driving tumorigenicity. Interestingly, neither membrane localization nor fusion protein dimerization were found to be essential for NOTCH1-ROS1 fusion oncogenicity. To target NOTCH1-ROS1-driven tumors, we tested both NOTCH1-directed inhibitors and ROS1-targeted tyrosine kinase inhibitors (TKI) in heterologous models (NIH3T3, Ba/F3). Although NOTCH1 inhibitors did not suppress NOTCH1-ROS1-driven oncogenic growth, we found that oral entrectinib treatment effectively suppressed the growth of NOTCH-ROS1-driven tumors. Taken together, we report the first known pAS case with a novel NOTCH1-ROS1 alteration along with a detailed report on the function and therapeutic targeting of NOTCH1-ROS1. Our study highlights the importance of genomic profiling of rare cancers such as pAS to reveal actionable drivers and improve patient outcomes.

Genetic context of oncogenic drivers dictates vascular sarcoma development in aP2‐Cre mice

Angiosarcomas are aggressive vascular sarcomas that arise from endothelial cells and have an extremely poor prognosis. Because of the rarity of angiosarcomas, knowledge of molecular drivers and optimized treatment strategies is lacking, highlighting the need for in vivo models to study the disease. Previously, we generated genetically engineered mouse models of angiosarcoma driven by aP2‐Cre‐mediated biallelic loss of Dicer1 or conditional activation of Kras^G12D with Cdkn2a loss that histologically and genetically resemble human tumors. In the present study, we found that DICER1 functions as a potent tumor suppressor and its deletion, in combination with either KRAS^G12D expression or Cdkn2a loss, is associated with angiosarcoma development. Independent of the genetic driver, the mTOR pathway was activated in all murine angiosarcoma models. Direct activation of the mTOR pathway by conditional deletion of Tsc1 with aP2‐Cre resulted in tumors that resemble intermediate grade human kaposiform hemangioendotheliomas, indicating that mTOR activation was not sufficient to drive the malignant angiosarcoma phenotype. Genetic dissection of the spectrum of vascular tumors identified genes specifically regulated in the aggressive murine angiosarcomas that are also enriched in human angiosarcoma. The genetic dissection driving the transition across the malignant spectrum of endothelial sarcomas provides an opportunity to identify key determinants of the malignant phenotype, novel therapies for angiosarcoma, and novel in vivo models to further explore angiosarcoma pathogenesis. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Plexiform neurofibroma: shedding light on the investigational agents in clinical trials

INTRODUCTION

Neurofibromatosis Type 1 (NF1) is an autosomal dominant genetic condition, which predisposes individuals to the development of plexiform neurofibromas (PN), benign nerve sheath tumors seen in 30-50% of patients with NF1. These tumors may cause significant pain and disfigurement or may compromise organ function. Given the morbidity associated with these tumors, therapeutic options for patients with NF1-related PN are necessary.

AREAS COVERED

We searched the www.clinicaltrials.gov database for 'plexiform neurofibroma.' This article summarizes completed and ongoing trials involving systemic therapies for PN.

EXPERT OPINION

Surgery is the mainstay treatment; however, complete resection is not possible in many cases. Numerous systemic therapies have been evaluated in patients with NF1, with MEK inhibitors (MEKi) showing the greatest efficacy for volumetric reduction and improvement in functional and patient-reported outcomes. The MEKi selumetinib is now FDA approved for the treatment of inoperable, symptomatic PN in pediatric NF1 patients. Questions remain regarding the use of this drug class in terms of when to initiate therapy, overall duration, reduced dosing schedules, and side effect management. Future studies are needed to fully understand the clinical application of MEKi and to evaluate other potential therapies through appropriate trial designs for this potentially devastating, manifestation in NF1.

A New Antitumor Direction: Tumor-Specific Endothelial Cells

Targeting tumor blood vessels is an important strategy for tumor therapies. At present, antiangiogenic drugs are known to have significant clinical effects, but severe drug resistance and side effects also occur. Therefore, new specific targets for tumor and new treatment methods must be developed. Tumor-specific endothelial cells (TECs) are the main targets of antiangiogenic therapy. This review summarizes the differences between TECs and normal endothelial cells, assesses the heterogeneity of TECs, compares tumorigenesis and development between TECs and normal endothelial cells, and explains the interaction between TECs and the tumor microenvironment. A full and in-depth understanding of TECs may provide new insights for specific antitumor angiogenesis therapies.

Hedyotis diffusa Willd. Suppresses Hepatocellular Carcinoma via Downregulating AKT/mTOR Pathways

Objective

Hedyotis diffusa Willd. (HDW) is a famous Chinese herbal medicine, traditionally used to treat cancer in China. Currently, the clinically used drugs for the treatment of hepatocellular carcinoma (HCC) still have poor efficacy and have many side effects. HDW has fewer side effects after taking it, so this study explores the inhibitory effect of HDW on HCC, which may become a promising drug for the treatment of HCC.

Methods

HCC cell lines such as SMMC-7721, SK-hep1, and Hep-G2 were treated with Hedyotis diffusa Willd. (HDW), after which migration was detected via transwell, while the proliferation of these cells was detected via MTT, CCK-8, and colony formation assays. Furthermore, protein levels were evaluated by western blotting, and Hep-G2 cells were implanted in nude mice to establish a xenograft model to evaluate the antitumor effect of the drug.

Results

HDW exhibited the ability to inhibit the proliferation and migration of HCC cells. And its anticancer mechanism in hepatocellular carcinoma may be via AKT/mTOR pathway. Moreover, the drug use of HDW in the mouse model system has achieved a good effect. Importantly, it did not cause significant weight loss or hepatorenal toxicity.

Conclusion

HDW can suppress the activation of the AKT/mTOR pathway in HCC cells, which may bring new light for the treatment of this kind of malignant tumor, but its exact mechanism still needs to be further explored.