Rac1 as a multifunctional therapeutic target to prevent and combat cancer metastasis

Rac1 promotes the reprogramming of glucose metabolism and the growth of colon cancer cells through upregulating SOX9

Metabolic reprogramming is the survival rule of tumor cells, and tumor cells can meet their high metabolic requirements by changing the energy metabolism mode. Metabolic reprogramming of tumor cells is an important biochemical basis of tumor malignant phenotypes. Ras-related C3 botulinum toxin substrate 1 (Rac1) is abnormally expressed in a variety of tumors and plays an important role in the proliferation, invasion, and migration of tumor cells. However, the role of Rac1 in tumor metabolic reprogramming is still unclear. Herein, we revealed that Rac1 was highly expressed in colon cancer tissues and cell lines. Rac1 promotes the proliferation, migration, and invasion of colon cancer cells by upregulating SOX9, which as a transcription factor can directly bind to the promoters of HK2 and G6PD genes and regulate their transcriptional activity. Rac1 upregulates the expression of SOX9 through the PI3K/AKT signaling pathway. Moreover, Rac1 can promote glycolysis and the activation of the pentose phosphate pathway in colon cancer cells by mediating the axis of SOX9/HK2/G6PD. These findings reveal novel regulatory axes involving Rac1/SOX9/HK2/G6PD in the development and progression of colon cancer, providing novel promising therapeutic targets.

BCAR1 plays critical roles in the formation and immunoevasion of invasive circulating tumor cells in lung adenocarcinoma

Background: We investigated the roles of breast cancer anti-estrogen resistance 1 (BCAR1/p130Cas) in the formation and immunoevasion of invasive circulating tumor cells (CTCs) in lung adenocarcinoma (LUAD). Methods: Biomarkers of CTCs including BCAR1 and CD274, were evaluated by the CanPatrol method. Proteomics analysis of LUAD cells and exosomes after BCAR1 overexpression (BCAR1-OE) was performed by mass spectrometry. Cell functions and relevant signaling pathways were investigated after BCAR1 knockdown (BCAR1-KO) or BCAR1-OE in LUAD cells. Lastly, in vitro and in vivo experiments were performed to confirm the roles of BCAR1 in the formation and immunoevasion of CTCs. Results: High expression of BCAR1 by CTCs correlated with CD274 expression and epithelial-to-mesenchymal transition (EMT). RAC1, together with BCAR1, was found to play an important role in the carcinogenesis of LUAD. RAC1 functioned with BCAR1 to induce EMT and to enhance cell proliferation, colony formation, cell invasion and migration, and anoikis resistance in LUAD cells. BCAR1 up-regulated CD274 expression probably by shuttling the short isoform of BRD4 (BRD4-S) into the nucleus. CTCs, as well as tumor formation, were prohibited in nude mice xenografted with BCAR1-KO cells. The co-expression of BCAR1/RAC1 and BCAR1/CD274 was confirmed in LUAD. BCAR1 expression in LUAD is an indicator of poor prognosis, and it associates with immunoevasion. Conclusion: BCAR1, as a new target for the treatment of LUAD, plays roles in the formation and immunoevasion of invasive CTCs. The mechanism includes triggering EMT via RAC1 signaling and up-regulating CD274 expression by shuttling BRD4-S into the nucleus.

Rac1, A Potential Target for Tumor Therapy

RAS-related C3 botulinum toxin substrate 1 (Rac.1) is one of the important members of Rho GTPases. It is well known that Rac1 is a cytoskeleton regulation protein that regulates cell adhesion, morphology, and movement. Rac1 is highly expressed in different types of tumors, which is related to poor prognosis. Studies have shown that Rac1 not only participates in the tumor cell cycle, apoptosis, proliferation, invasion, migration and angiogenesis, but also participates in the regulation of tumor stem cell, thus promoting the occurrence of tumors. Rac1 also plays a key role in anti-tumor therapy and participates in immune escape mediated by the tumor microenvironment. In addition, the good prospects of Rac1 inhibitors in cancer prevention and treatment are exciting. Therefore, Rac1 is considered as a potential target for the prevention and treatment of cancer. The necessity and importance of Rac1 are obvious, but it still needs further study.

Prospects for Radiopharmaceuticals as Effective and Safe Therapeutics in Oncology and Challenges of Tumor Resistance to Radiotherapy

The rapid advances in nuclear medicine have resulted in significant advantages for the field of oncology. The focus is on the application of radiopharmaceuticals as therapeuticals. In addition, the latest developments in cell biology (the understanding of the cell structure, function, metabolism, genetics, signaling, transformation) have given a strong scientific boost to radiation oncology. In this regard, the article discusses what is soon going to be a new jump in radiation oncology based on the already accumulated considerable knowledge at the cellular level about the mechanisms of cell transformation and tumor progression, cell response to radiation, cell resistance to apoptosis and radiation and cell radio-sensitivity. The mechanisms of resistance of tumor cells to radiation and the genetically determined individual sensitivity to radiation in patients (which creates the risk of radiation-induced acute and late side effects) are the 2 major challenges to overcome in modern nuclear medicine. The paper focuses on these problems and makes a detailed summary of the significance of the differences in the ionizing properties of radiopharmaceuticals and the principle of their application in radiation oncology that will shed additional light on how to make the anti-cancer radiotherapies more efficient and safe, giving some ideas for optimizations.

Inhibition of Rac1 reverses enzalutamide resistance in castration-resistant prostate cancer

Enzalutamide, an androgen receptor inhibitor, has been clinically approved for the treatment of metastatic castration-resistant prostate cancer (CRPC) in the United States. However, patients only benefit from enzalutamide for a short period of time as resistance may develop. Therefore, it is vital to develop a novel strategy to overcome enzalutamide resistance. Ras-related C3 botulinum toxin substrate 1 (Rac1), which is commonly upregulated in human cancer types, has been recognized as a key molecular component in tumorigenesis, invasion and metastasis. However, the role of Rac1 in enzalutamide-resistance in prostate cancer (PCa) remains unknown. In the present study, Rac1 was demonstrated to be upregulated in enzalutamide-resistant PCa cells, and Rac1 knockdown inhibited enzalutamide-resistant cell proliferation and colony formation. Western blotting results indicated that enzalutamide treatment downregulated the expression levels of JNK and activated transcription factor 2, as well as enhanced the Bax/Bcl-2 ratio and induced cleavage of poly-ADP ribose polymerase. Moreover, knockdown of Rac1 in MR49F cells significantly inhibited cell migration and invasion via the downregulation of Snail and the upregulation of E-cadherin. The results of a nude mouse xenograft tumor model using 22RV1 cells demonstrated that enzalutamide inhibited tumor growth after Rac1 knockdown dramatically, compared to vehicle and single treatment groups. Therefore, the present study provided novel evidence that Rac1 may serve a crucial role in enzalutamide resistance, and that targeting Rac1 may be a potential approach for the treatment of CRPC.

Radiotherapy targeting cancer stem cells "awakens" them to induce tumour relapse and metastasis in oral cancer

Radiotherapy is one of the most common treatments for oral cancer. However, in the clinic, recurrence and metastasis of oral cancer occur after radiotherapy, and the underlying mechanism remains unclear. Cancer stem cells (CSCs), considered the “seeds” of cancer, have been confirmed to be in a quiescent state in most established tumours, with their innate radioresistance helping them survive more easily when exposed to radiation than differentiated cancer cells. There is increasing evidence that CSCs play an important role in recurrence and metastasis post-radiotherapy in many cancers. However, little is known about how oral CSCs cause tumour recurrence and metastasis post-radiotherapy. In this review article, we will first summarise methods for the identification of oral CSCs and then focus on the characteristics of a CSC subpopulation induced by radiation, hereafter referred to as “awakened” CSCs, to highlight their response to radiotherapy and potential role in tumour recurrence and metastasis post-radiotherapy as well as potential therapeutics targeting CSCs. In addition, we explore potential therapeutic strategies targeting these “awakened” CSCs to solve the serious clinical challenges of recurrence and metastasis in oral cancer after radiotherapy.

Adaptive Responses to Monotherapy in Head and Neck Cancer: Interventions for Rationale-Based Therapeutic Combinations

Most Phase II and III clinical trials in head and neck cancer (HNC) combine two or more treatment modalities, which are based, in part, on knowledge of the molecular mechanisms of innate and acquired resistance to monotherapy. In this review, we describe the range of tumor-cell autonomously derived (intrinsic) and tumor-microenvironment-derived (extrinsic) acquired-resistance mechanisms to various FDA-approved monotherapies for HNC. Specifically, we describe how tumor cells and the tumor microenvironment (TME) respond to radiation, chemotherapy, targeted therapy (cetuximab), and immunotherapies [programmed cell death 1 (PD-1) inhibitors] and adapt to the selective pressure of these monotherapies. Due to the diversity of adaptive responses to monotherapy, monitoring the response to treatment in patients is critical to understand the path that leads to resistance and to guide the optimal therapeutic drug combinations in the clinical setting. We envisage that applying such a rationale-based therapeutic strategy will improve treatment efficacy in HNC patients.

DNA Damage Response in Quiescent Hematopoietic Stem Cells and Leukemia Stem Cells

In humans, hematopoietic stem cells (HSCs) adopt unique responsive pathways counteracting with the DNA-damaging assaults to weigh the balance between the maintenance of normal stem cell poor for whole-life blood regeneration and the transformation to leukemia stem cells (LSCs) for leukemia initiation. LSCs also take actions of combating with the attack launched by externally therapeutic drugs that can kill most leukemic cells, to avoid extermination and promote disease relapse. Therefore, the collection of knowledge about all these underlined mechanisms would present a preponderance for later studies. In this chapter, the universal DNA damage response (DDR) mechanisms were firstly introduced, and then DDR of HSCs were presented focusing on the DNA double-strand breaks in the quiescent state of HSCs, which poses a big advantage in promoting its transformation into preleukemic HSCs. Lastly, the DDR of LSCs were summarized based on the major outcomes triggered by different pathways in specific leukemia, upon which some aspects for future investigations were envisioned under our currently limited scope of knowledge.

Blocking hepatic metastases of colon cancer cells using an shRNA against Rac1 delivered by activatable cell-penetrating peptide

Hepatic metastasis is one of the critical progressions of colon cancer. Blocking this process is key to prolonging survival time in cancer patients. Studies on activatable cell-penetrating peptides (dtACPPs) have demonstrated their potential as gene carriers. It showed high tumor cell-targeting specificity and transfection efficiency and low cytotoxicity in the in vitro settings of drug delivery. However, using this system to silence target genes to inhibit metastasis in colorectal cancer cells has not been widely reported and requires further investigation. In this study, we observed that expression of Rac1, a key molecule for cytoskeletal reorganization, was higher in hepatic metastatic tumor tissue compared with prime colon cancer tissue and that patients with high Rac1-expressing colon cancer showed shorter survival time. Base on these findings, we created dtACPP-PEG-DGL (dtACPPD)/shRac1 nanoparticles and demonstrated that they downregulated Rac1 expression in colon cancer cells. Moreover, we observed inhibitory effects on migration, invasion and adhesion in HCT116 colorectal cancer cells in vitro, and our results showed that Rac1 regulated colon cancer cell matrix adhesion through the regulation of cytofilament dynamics. Moreover, mechanically, repression of Rac1 inhibiting cells migration and invasion by enhancing cell to cell adhesion and reducing cell to extracellular matrix adhesion. Furthermore, when atCDPPD/shRac1 nanoparticles were administered intravenously to a HCT116 xenograft model, significant tumor metastasis to the liver was inhibited. Our results suggest that atCDPP/shRac1 nanoparticles may enable the blockade of hepatic metastasis in colon cancer.

Silencing Ras-Related C3 Botulinum Toxin Substrate 1 Inhibits Growth and Migration of Hypopharyngeal Squamous Cell Carcinoma via the P38 Mitogen-Activated Protein Kinase Signaling Pathway

BACKGROUND Ras-related C3 botulinum toxin substrate 1 (Rac1) is implicated in a variety of cellular functions and is related to tumor growth and metastasis. This study aimed to explore the role of Rac1 in hypopharyngeal squamous cell carcinoma (HSCC). MATERIAL AND METHODS The Rac1 expression in HSCC tissues was determined by quantitative real-time polymerase chain reaction and Western blot analysis. The level of Rac1 in HSCC cells was downregulated by a Rac1-specific shRNA. Then, the growth and metastasis of HSCC cells were assessed in vitro by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay, flow cytometry, Hoechst staining, and Transwell assay. Moreover, cells transfected with Rac1 shRNA or negative control were injected subcutaneously into the right axilla of mice, and then the effects of Rac1 silencing on the growth of HSCC were also explored in vivo. Additionally, activation of the P38 mitogen-activated protein kinase (MAPK) signaling pathway was assessed by Western blot. RESULTS Rac1 was highly expressed in HSCC tissues. Silencing Rac1 inhibited the proliferation and cell cycle progress of HSCC cells, and induced their apoptosis. Rac1 silencing also suppressed the migration and invasion of HSCC cells. In vivo study showed that silencing Rac1 suppressed the growth of tumor bodies. Moreover, the P38 MAPK signaling pathway was implicated in the tumor-suppressing effect of Rac1 silencing in vitro and in vivo. CONCLUSIONS Silencing Rac1 suppressed the growth and migration of HSCC through the P38 MAPK signaling pathway. Due to its contribution in HSCC, Rac1 has the potential to become a promising antitumor therapeutic target for HSCC.

TIPE2 suppresses angiogenesis and non-small cell lung cancer (NSCLC) invasiveness via inhibiting Rac1 activation and VEGF expression

Non-small cell lung cancer (NSCLC) is one of the leading causes of all cancer-related deaths worldwide. Despite extensive efforts to improve the diagnosis and treatment of this neoplasm, limited progress has been made. Tumor necrosis factor (TNF)-alpha-induced protein 8-like 2 (TIPE2 or TNFAIP8L2) is a newly introduced negative immune regulator, which also controls tumorigenesis. However, the role of TIPE2 in angiogenesis is unknown. In the present study, we investigated the expression and roles of TIPE2 in NSCLC. TIPE2 upregulation in human NSCLC tissues was negatively associated with the primary tumor size, lymph node metastasis, and advanced clinical stage, which can be used to predict lymph node metastasis. Moreover, overexpression of TIPE2 not only inhibited the colony formation, migration, and invasion of NSCLC cells but also indirectly suppressed the proliferation, migration, and tube formation of vascular endothelial cells. Furthermore, TIPE2 suppressed tumor invasiveness and angiogenesis via inhibiting the activation of Rac1 and subsequently weakening its downstream effects, including F-actin polymerization and VEGF expression. Collectively, these results indicate that TIPE2 plays a key role in NSCLC metastasis, suggesting that forced TIPE2 expression might be a novel strategy for the treatment of NSCLC.

Relevance of small GTPase Rac1 pathway in drug and radio-resistance mechanisms: Opportunities in cancer therapeutics

Rac1 GTPase signaling pathway has a critical role in the regulation of a plethora of cellular functions governing cancer cell behavior. Recently, it has been shown a critical role of Rac1 in the emergence of resistance mechanisms to cancer therapy. This review describes the current knowledge regarding Rac1 pathway deregulation and its association with chemoresistance, radioresistance, resistance to targeted therapies and immune evasion. This supports the idea that interfering Rac1 signaling pathway could be an interesting approach to tackle cancer resistance.

Preferential targeting of cancer stem cells in the radiosensitizing effect of ABT-737 on HNSCC

Head and neck squamous cell carcinomas (HNSCC) are common human malignancies with poor clinical outcomes. The 5-year survival rates for patients with advanced stage HNSCC have not changed appreciably in the past few decades, underscoring a dire need for improved therapeutic options. HNSCC is frequently characterized by overexpression of anti-apoptotic Bcl-2 family members. Increased levels of these anti-apoptotic proteins have been associated with radio- and chemoresistance and poor clinical outcome. The aim of this study was to evaluate combined effects of radiation and ABT-737, a BH3-mimetic molecule, in HNSCC. Although ABT-737, as a single agent, was largely ineffective at promoting HNSCC cell death, we found that combining ABT-737 and radiation induced strong synergistic apoptosis in HNSCC cell lines and delayed tumoral growth in vivo. Moreover, we demonstrated for the first time that ABT-737, alone or in combination with radiation, can efficiently eliminate cancer stem cells (CSCs). Altogether, our results indicate that therapy targeting anti-apoptotic Bcl-2 family members could be a highly effective potential adjuvant to radiotherapy capable of targeting CSCs in HNSCC and therefore overcoming cancer recurrence and metastasis.

Disulfiram anti-cancer efficacy without copper overload is enhanced by extracellular H2O2 generation: antagonism by tetrathiomolybdate

Highlights

Background

Cu/Zn superoxide dismutases (SODs) like the extracellular SOD3 and cytoplasmic SOD1 regulate cell proliferation by generating hydrogen peroxide (H₂O₂). This pro-oxidant inactivates essential cysteine residues in protein tyrosine phosphatases (PTP) helping receptor tyrosine kinase activation by growth factor signaling, and further promoting downstream MEK/ERK linked cell proliferation. Disulfiram (DSF), currently in clinical cancer trials is activated by copper chelation, being potentially capable of diminishing the copper dependent activation of MEK1/2 and SOD1/SOD3 and promoting reactive oxygen species (ROS) toxicity. However, copper (Cu) overload may occur when co-administered with DSF, resulting in toxicity and mutagenicity against normal tissue, through generation of the hydroxyl radical (•OH) by the Fenton reaction.

Purpose

To investigate: a) whether sub-toxic DSF efficacy can be increased without Cu overload against human melanoma cells with unequal BRAF(V600E) mutant status and Her2-overexpressing SKBR3 breast cancer cells, by increasing H₂O₂from exogenous SOD; b) to compare the anti-tumor efficacy of DSF with that of another clinically used copper chelator, tetrathiomolybdate (TTM)

Results

a) without copper supplementation, exogenous SOD potentiated sub-toxic DSF toxicity antagonized by sub-toxic TTM or by the anti-oxidant N-acetylcysteine; b) exogenous glucose oxidase, another H₂O₂ generator resembled exogenous SOD in potentiating sub-toxic DSF.

Conclusions

potentiation of sub-lethal DSF toxicity by extracellular H₂O₂ against the human tumor cell lines investigated, only requires basal Cu and increased ROS production, being unrelated to non-specific or TTM copper chelator sequestration.

Significance

These findings emphasize the relevance of extracellular H₂O₂ as a novel mechanism to improve disulfiram anticancer effects minimizing copper toxicity.

RAC1 GTPase promotes the survival of breast cancer cells in response to hyper-fractionated radiation treatment

Radiation therapy is a staple approach for cancer treatment, whereas radioresistance of cancer cells remains a substantial clinical problem. In response to ionizing radiation (IR) induced DNA-damage, cancer cells can sustain/activate pro-survival signaling pathways, leading to apoptotic resistance and induction of cell cycle checkpoint/DNA repair. Previous studies show that Rac1 GTPase is overexpressed/hyperactivated in breast cancer cells and is associated with poor prognosis. Studies from our laboratory reveal that Rac1 activity is necessary for G2/M checkpoint activation and cell survival in response to IR exposure of breast and pancreatic cancer cells. In the present study, we investigated the effect of Rac1 on the survival of breast cancer cells treated with hyper-fractionated radiation (HFR), which is used clinically for cancer treatment. Results in this report indicate that Rac1 protein expression is increased in the breast cancer cells that survived HFR compared to parental cells. Furthermore, this increase of Rac1 is associated with enhanced activities of ERK1/2 and NF-κB signaling pathways and increased levels of anti-apoptotic protein Bcl-xL and Mcl-1, which are downstream targets of ERK1/2 and NF-κB signaling pathways. Using Rac1 specific inhibitor and dominant negative mutant N17Rac1, here we demonstrate that Rac1 inhibition decreases the phosphorylation of ERK1/2 and IκBα, as well as the levels of Bcl-xL and Mcl-1 protein in the HFR-selected breast cancer cells. Moreover, inhibition of Rac1 using either small molecule inhibitor or dominant negative N17Rac1 abrogates clonogenic survival of HFR-selected breast cancer cells and decreases the level of intact PARP, which is indicative of apoptosis induction. Collectively, results in this report suggest that Rac1 signaling is essential for the survival of breast cancer cells subjected to HFR and implicate Rac1 in radioresistance of breast cancer cells. These studies also provide the basis to explore Rac1 as a therapeutic target for radioresistant breast cancer cells.

Inhibition of the Rac1-WAVE2-Arp2/3 signaling pathway promotes radiosensitivity via downregulation of cofilin-1 in U251 human glioma cells

The Ras-related C3 botulinum toxin substrate 1 (Rac1)-WASP-family verprolin-homologous protein-2 (WAVE2)-actin-related protein 2/3 (Arp2/3) signaling pathway has been identified to be involved in cell migration and invasion in various types of cancer cell. Cofilin‑1 (CFL‑1), which is regulated by the Rac1‑WAVE2‑Arp2/3 signaling pathway, may promote radioresistance in glioma. Therefore, the present study aimed to investigate the potential role of the Rac1‑WAVE2‑Arp2/3 signaling pathway in radioresistance in U251 human glioma cells and elucidate its affect on CFL‑1 expression. Western blot analysis was performed to evaluate the protein expression of CFL‑1. In the present study, Rac1 was inhibited by NSC 23766, WAVE2 was inhibited by transfection with short hairpin (sh)RNA‑WAVE2 using Lipofectamine™ 2000 and Arp2/3 was inhibited by CK‑666. Cell viability was measured using the 3‑(4,5‑dimethylthiazol‑2‑yl)-2,5‑diphenyltetrazolium bromide assay, the cell migration ability was examined by a wound‑healing assay, and the cell invasion ability was assessed using a Transwell culture chamber system. The results showed that inhibition of the Rac1‑WAVE2‑Arp2/3 signaling pathway using NSC 23766, shRNA‑WAVE2 or CK‑666 reduced the cell viability, migration and invasion abilities in U251 human glioma cells, concordant with a reduced expression of CFL‑1. Furthermore, the expression of CFL‑1 was significantly increased in radioresistant U251 glioma cells when compared with normal U251 human glioma cells. These findings indicate that inhibition of the Rac1‑WAVE2‑Arp2/3 signaling pathway may promote radiosensitivity, which may partially result from the downregulation of CFL‑1 in U251 human glioma cells.

Radiation resistance: Cancer stem cells (CSCs) and their enigmatic pro-survival signaling

Despite the fact that radiation therapy is a highly effective therapeutic approach, a small intratumoral cell subpopulation known as "cancer stem cells" (CSCs) is radiation-resistant and possesses specific molecular properties protecting it against radiation-induced damage. The exact mechanisms of this radioresistance are still not fully elucidated, but they relate to these cells' enhanced DNA repair capacities and their low intracellular ROS concentrations, resulting from their up-regulation of ROS scavengers. The low ROS content is accompanied by disturbances in cell cycle regulation, so it can be assumed that either CSCs are quiescent or dormant themselves, or that this cell population consists of at least two cell subpopulations: the normally and the slowly proliferating cells (quiescent or dormant cells). Slowly dividing CSCs show concomitant dysregulation of the signaling molecules mediating both cell cycle progression and maintenance of cell stemness. Despite a massive accumulation of data concerning the mechanisms underlying DNA damage response in CSCs, it represents a challenge to researchers in the era of personalized medicine to elucidate the role of intracellular ROS and of signaling pathways associated with the radiation resistance of these cells; there is a clear need to understand the molecular mechanisms helping CSCs to survive radiation exposure.