Stromal CYR61 Confers Resistance to Mitoxantrone via Spleen Tyrosine Kinase Activation in Human Acute Myeloid Leukaemia

Drug resistance in human cancers - Mechanisms and implications

Cancers have complex etiology and pose a significant impact from the health care perspective apart from the socio-economic implications. The enormity of challenge posed by cancers can be understood from the fact that clinical trials for cancer therapy has yielded minimum potential promises compared to those obtained for other diseases. Surgery, chemotherapy and radiotherapy continue to be the mainstay therapeutic options for cancers. Among the challenges posed by these options, induced resistance to chemotherapeutic drugs is probably the most significant contributor for poor prognosis and ineffectiveness of the therapy. Drug resistance is a property exhibited by almost all cancer types including carcinomas, leukemias, myelomas, sarcomas and lymphomas. The mechanisms by which drug resistance is induced include the factors within the tumor microenvironment, mutations in the genes responsible for drug metabolism, changes in the surface drug receptors and increased drug efflux. We present here comprehensively the drug resistance in cancers along with their mechanisms. Also, apart from resistance to regularly used chemotherapeutic drugs, we present resistance induction to new generation therapeutic agents such as monoclonal antibodies. Finally, we have discussed the experimental approaches to understand the mechanisms underlying induction of drug resistance and potential ways to mitigate induced drug resistance.

Spleen tyrosine kinase (SYK): an emerging target for the assemblage of small molecule antitumor agents

INTRODUCTION

Spleen tyrosine kinase (SYK), a nonreceptor tyrosine kinase, has emerged as a vital component in the complex symphony of cancer cell survival and division. SYK activation (constitutive) is documented in various B-cell malignancies, and its inhibition induces programmed cell death. In some instances, it also acts as a tumor suppressor.

AREAS COVERED

Involvement of the SYK in the cancer growth, specifically in the progression of chronic lymphocytic leukemia (CLL), diffuse large B cell lymphomas (DLBCLs), acute myeloid leukemia (AML), and multiple myeloma (MM) is discussed. Therapeutic strategies to target SYK in cancer, including investigational SYK inhibitors, combinations of SYK inhibitors with other drugs targeting therapeutically relevant targets, and recent advancements in constructing new structural assemblages as SYK inhibitors, are also covered.

EXPERT OPINION

The SYK inhibitor field is currently marred by the poor translation rate of SYK inhibitors from preclinical to clinical studies. Also, dose-limited toxicities associated with the applications of SYK inhibitors have been evidenced. Thus, the development of new SYK inhibitory structural templates is in the need of the hour. To accomplish the aforementioned, interdisciplinary teams should incessantly invest efforts to expand the size of the armory of SYK inhibitors.

Targeting the redox vulnerability of acute myeloid leukaemia cells with a combination of auranofin and vitamin C

Acute myeloid leukaemia (AML) is a heterogeneous disease characterized by complex molecular and cytogenetic abnormalities. Pro-oxidant cellular redox status is a common hallmark of AML cells, providing a rationale for redox-based anticancer strategy. We previously discovered that auranofin (AUF), initially used for the treatment of rheumatoid arthritis and repositioned for its anticancer activity, can synergize with a pharmacological concentration of vitamin C (VC) against breast cancer cell line models. In this study, we observed that this drug combination synergistically and efficiently killed cells of leukaemic cell lines established from different myeloid subtypes. In addition to an induced elevation of reactive oxygen species and ATP depletion, a rapid dephosphorylation of 4E-BP1 and p70S6K, together with a strong inhibition of protein synthesis were early events in response to AUF/VC treatment, suggesting their implication in AUF/VC-induced cytotoxicity. Importantly, a study on 22 primary AML specimens from various AML subtypes showed that AUF/VC combinations at pharmacologically achievable concentrations were effective to eradicate primary leukaemic CD34+ cells from the majority of these samples, while being less toxic to normal cord blood CD34+ cells. Our findings indicate that targeting the redox vulnerability of AML with AUF/VC combinations could present a potential anti-AML therapeutic approach.

Hypoxia-initiated Cysteine-rich protein 61 secretion promotes chemoresistance of acute B lymphoblastic leukemia cells

The drug resistance is a major obstacle in acute B-lymphoblastic leukemia (B-ALL) treatment. Our previous study has indicated that increased levels of Cysteine-rich protein 61 (Cyr61) in the bone marrow can mitigate the chemosensitivity of B-ALL cells, though the specific source of Cyr61 in the bone marrow remains unknown. In this study, we aimed to investigate whether hypoxia can induce Cyr61 production in B-ALL cells, delineates the underlying mechanisms, and evaluates the effect of Cyr61 on the chemosensitivity of B-ALL cells under hypoxia conditions. The results indicate that hypoxia promotes Cyr61 production in B-ALL cells by activating the NF-κB pathway. Increased Cyr61 expression appears to reduce the chemosensitivity of B-ALL cell to vincristine (VCR) and daunorubicin (DNR) through autophagy under hypoxia. Notably, inhibition of Cyr61 restores the chemosensitivity of B-ALL cells to both chemotherapeutic agents. This study is the first time to report that hypoxia decreases the chemosensitivity of B-ALL cells by inducing Cyr61 production, suggesting that targeting Cyr61 or its associated pathways could potentially improve the clinical response of B-ALL patients.

Targeted inhibition of the PI3K/AKT/mTOR pathway by (+)-anthrabenzoxocinone induces cell cycle arrest, apoptosis, and autophagy in non-small cell lung cancer

Non-small cell lung cancer (NSCLC), characterized by low survival rates and a high recurrence rate, is a major cause of cancer-related mortality. Aberrant activation of the PI3K/AKT/mTOR signaling pathway is a common driver of NSCLC. Within this study, the inhibitory activity of (+)-anthrabenzoxocinone ((+)-ABX), an oxygenated anthrabenzoxocinone compound derived from Streptomyces, against NSCLC is demonstrated for the first time both in vitro and in vivo. Mechanistically, it is confirmed that the PI3K/AKT/mTOR signaling pathway is targeted and suppressed by (+)-ABX, resulting in the induction of S and G2/M phase arrest, apoptosis, and autophagy in NSCLC cells. Additionally, the augmentation of intracellular ROS levels by (+)-ABX is revealed, further contributing to the inhibition of the signaling pathway and exerting inhibitory effects on tumor growth. The findings presented in this study suggest that (+)-ABX possesses the potential to serve as a lead compound for the treatment of NSCLC.

Stromal bone marrow fibroblasts and mesenchymal stem cells support acute myeloid leukaemia cells and promote therapy resistance

The bone marrow (BM) is the primary site of adult haematopoiesis, where stromal elements (e.g. fibroblasts and mesenchymal stem cells [MSCs]) work in concert to support blood cell development. However, the establishment of an abnormal clone can lead to a blood malignancy, such as acute myeloid leukaemia (AML). Despite our increased understanding of the pathophysiology of the disease, patient survival remains suboptimal, mainly driven by the development of therapy resistance. In this review, we highlight the importance of bone marrow fibroblasts and MSCs in health and acute myeloid leukaemia and their impact on patient prognosis. We discuss how stromal elements reduce the killing effects of therapies via a combination of contact-dependent (e.g. integrins) and contact-independent (i.e. secreted factors) mechanisms, accompanied by the establishment of an immunosuppressive microenvironment. Importantly, we underline the challenges of therapeutically targeting the bone marrow stroma to improve acute myeloid leukaemia patient outcomes, due to the inherent heterogeneity of stromal cell populations. LINKED ARTICLES: This article is part of a themed issue on Cancer Microenvironment and Pharmacological Interventions. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.2/issuetoc.

An Updated Overview of the Role of CYP450 during Xenobiotic Metabolization in Regulating the Acute Myeloid Leukemia Microenvironment

Oxidative stress is associated with several acute and chronic disorders, including hematological malignancies such as acute myeloid leukemia, the most prevalent acute leukemia in adults. Xenobiotics are usually harmless compounds that may be detrimental, such as pharmaceuticals, environmental pollutants, cosmetics, and even food additives. The storage of xenobiotics can serve as a defense mechanism or a means of bioaccumulation, leading to adverse effects. During the absorption, metabolism, and cellular excretion of xenobiotics, three steps may be distinguished: (i) inflow by transporter enzymes, (ii) phases I and II, and (iii) phase III. Phase I enzymes, such as those in the cytochrome P450 superfamily, catalyze the conversion of xenobiotics into more polar compounds, contributing to an elevated acute myeloid leukemia risk. Furthermore, genetic polymorphism influences the variability and susceptibility of related myeloid neoplasms, infant leukemias associated with mixed-lineage leukemia (MLL) gene rearrangements, and a subset of de novo acute myeloid leukemia. Recent research has shown a sustained interest in determining the regulators of cytochrome P450, family 2, subfamily E, member 1 (CYP2E1) expression and activity as an emerging field that requires further investigation in acute myeloid leukemia evolution. Therefore, this review suggests that CYP2E1 and its mutations can be a therapeutic or diagnostic target in acute myeloid leukemia.

Repurposing Atovaquone as a Therapeutic against Acute Myeloid Leukemia (AML): Combination with Conventional Chemotherapy Is Feasible and Well Tolerated

Survival of pediatric AML remains poor despite maximized myelosuppressive therapy. The pneumocystis jiroveci pneumonia (PJP)-treating medication atovaquone (AQ) suppresses oxidative phosphorylation (OXPHOS) and reduces AML burden in patient-derived xenograft (PDX) mouse models, making it an ideal concomitant AML therapy. Poor palatability and limited product formulations have historically limited routine use of AQ in pediatric AML patients. Patients with de novo AML were enrolled at two hospitals. Daily AQ at established PJP dosing was combined with standard AML therapy, based on the Medical Research Council backbone. AQ compliance, adverse events (AEs), ease of administration score (scale: 1 (very difficult)-5 (very easy)) and blood/marrow pharmacokinetics (PK) were collected during Induction 1. Correlative studies assessed AQ-induced apoptosis and effects on OXPHOS. PDX models were treated with AQ. A total of 26 patients enrolled (ages 7.2 months-19.7 years, median 12 years); 24 were evaluable. A total of 14 (58%) and 19 (79%) evaluable patients achieved plasma concentrations above the known anti-leukemia concentration (>10 µM) by day 11 and at the end of Induction, respectively. Seven (29%) patients achieved adequate concentrations for PJP prophylaxis (>40 µM). Mean ease of administration score was 3.8. Correlative studies with AQ in patient samples demonstrated robust apoptosis, OXPHOS suppression, and prolonged survival in PDX models. Combining AQ with chemotherapy for AML appears feasible and safe in pediatric patients during Induction 1 and shows single-agent anti-leukemic effects in PDX models. AQ appears to be an ideal concomitant AML therapeutic but may require intra-patient dose adjustment to achieve concentrations sufficient for PJP prophylaxis.

DNA damage to bone marrow stromal cells by antileukemia drugs induces chemoresistance in acute myeloid leukemia via paracrine FGF10-FGFR2 signaling

Chemoresistance remains a major challenge in the current treatment of acute myeloid leukemia (AML). The bone marrow microenvironment (BMM) plays a complex role in protecting leukemia cells from chemotherapeutics, and the mechanisms involved are not fully understood. Antileukemia drugs kill AML cells directly but also damage the BMM. Here, we determined antileukemia drugs induce DNA damage in bone marrow stromal cells (BMSCs), resulting in resistance of AML cell lines to adriamycin and idarubicin killing. Damaged BMSCs induced an inflammatory microenvironment through NF-κB; suppressing NF-κB with small molecule inhibitor Bay11-7082 attenuated the prosurvival effects of BMSCs on AML cell lines. Furthermore, we used an ex vivo functional screen of 507 chemokines and cytokines to identify 44 proteins secreted from damaged BMSCs. Fibroblast growth factor-10 (FGF10) was most strongly associated with chemoresistance in AML cell lines. Additionally, expression of FGF10 and its receptors, FGFR1 and FGFR2, was increased in AML patients after chemotherapy. FGFR1 and FGFR2 were also widely expressed by AML cell lines. FGF10-induced FGFR2 activation in AML cell lines operates by increasing P38 MAPK, AKT, ERK1/2, and STAT3 phosphorylation. FGFR2 inhibition with small molecules or gene silencing of FGFR2 inhibited proliferation and reverses drug resistance of AML cells by inhibiting P38 MAPK, AKT, and ERK1/2 signaling pathways. Finally, release of FGF10 was mediated by β-catenin signaling in damaged BMSCs. Our data indicate FGF10-FGFR2 signaling acts as an effector of damaged BMSC-mediated chemoresistance in AML cells, and FGFR2 inhibition can reverse stromal protection and AML cell chemoresistance in the BMM.

Targeting the Tumor Microenvironment in Acute Myeloid Leukemia: The Future of Immunotherapy and Natural Products

The tumor microenvironment (TME) plays an essential role in the development, proliferation, and survival of leukemic blasts in acute myeloid leukemia (AML). Within the bone marrow and peripheral blood, various phenotypically and functionally altered cells in the TME provide critical signals to suppress the anti-tumor immune response, allowing tumor cells to evade elimination. Thus, unraveling the complex interplay between AML and its microenvironment may have important clinical implications and are essential to directing the development of novel targeted therapies. This review summarizes recent advancements in our understanding of the AML TME and its ramifications on current immunotherapeutic strategies. We further review the role of natural products in modulating the TME to enhance response to immunotherapy.

Defining the Transcriptional Control of Pediatric AML Highlights RARA as a Super-Enhancer Regulated Druggable Dependency

The first enhancer mapping of pediatric AML reveals that the most common SE-associated signature is one driven by RARA.

A RARA SE is common in pediatric AML and correlates to sensitivity to the retinoid tamibarotene both in vitro and in vivo.

Somatic mutations are rare in pediatric acute myeloid leukemia (pAML), indicating that alternate strategies are needed to identify targetable dependencies. We performed the first enhancer mapping of pAML in 22 patient samples. Generally, pAML samples were distinct from adult AML samples, and MLL (KMT2A)–rearranged samples were also distinct from non–KMT2A-rearranged samples. Focusing specifically on superenhancers (SEs), we identified SEs associated with many known leukemia regulators. The retinoic acid receptor alpha (RARA) gene was differentially regulated in our cohort, and a RARA-associated SE was detected in 64% of the study cohort across all cytogenetic and molecular subtypes tested. RARA SE+ pAML cell lines and samples exhibited high RARA messenger RNA levels. These samples were specifically sensitive to the synthetic RARA agonist tamibarotene in vitro, with slowed proliferation, apoptosis induction, differentiation, and upregulated retinoid target gene expression, compared with RARA SE− samples. Tamibarotene prolonged survival and suppressed the leukemia burden of an RARA SE+ pAML patient-derived xenograft mouse model compared with a RARA SE− patient-derived xenograft. Our work shows that examining chromatin regulation can identify new, druggable dependencies in pAML and provides a rationale for a pediatric tamibarotene trial in children with RARA-high AML.

Primary mesenchymal stromal cells in co-culture with leukaemic HL-60 cells are sensitised to cytarabine-induced genotoxicity, whilst leukaemic cells are protected

Tumour microenvironments are hallmarked in many cancer types. In haematological malignancies, bone marrow (BM) mesenchymal stromal cells (MSC) protect malignant cells from drug-induced cytotoxicity. However, less is known about malignant impact on supportive stroma. Notably, it is unknown whether these interactions alter long-term genotoxic damage in either direction. The nucleoside analogue cytarabine (ara-C), common in haematological therapies, remains the most effective agent for acute myeloid leukaemia, yet one third of patients develop resistance. This study aimed to evaluate the bidirectional effect of MSC and malignant cell co-culture on ara-C genotoxicity modulation. Primary MSC, isolated from patient BM aspirates for haematological investigations, and malignant haematopoietic cells (leukaemic HL-60) were co-cultured using trans-well inserts, prior to treatment with physiological dose ara-C. Co-culture genotoxic effects were assessed by micronucleus and alkaline comet assays. Patient BM cells from chemotherapy-treated patients had reduced ex vivo survival (P = 0.0049) and increased genotoxicity (P = 0.3172) than untreated patients. It was shown for the first time that HL-60 were protected by MSC from ara-C-induced genotoxicity, with reduced MN incidence in co-culture as compared to mono-culture (P = 0.0068). Comet tail intensity also significantly increased in ara-C-treated MSC with HL-60 influence (P = 0.0308). MSC sensitisation to ara-C genotoxicity was also demonstrated following co-culture with HL60 (P = 0.0116), which showed significantly greater sensitisation when MSC-HL-60 co-cultures were exposed to ara-C (P = 0.0409). This study shows for the first time that malignant HSC and MSC bidirectionally modulate genotoxicity, providing grounding for future research identifying mechanisms of altered genotoxicity in leukaemic microenvironments. MSC retain long-term genotoxic and functional damage following chemotherapy exposure. Understanding the interactions perpetuating such damage may inform modifications to reduce therapy-related complications, such as secondary malignancies and BM failure.

PAK1 Mediates Bone Marrow Stromal Cell-Induced Drug Resistance in Acute Myeloid Leukemia via ERK1/2 Signaling Pathway

Background

Chemoresistance is emerging as a major barrier to successful treatment in acute myeloid leukemia (AML), and bone marrow stromal cells (BMSCs) protect leukemia cells from chemotherapy eventually leading to recurrence. This study was designed to investigate the role of p21-activated kinase 1 (PAK1) in AML progression and chemosensitivity, highlighting the mechanism of stroma-mediated chemoresistance.

Methods

The GEPIA and TCGA datasets were used to analyze the relationship between PAK1 mRNA expression and various clinical parameters of AML patients. Cell proliferation and apoptosis were examined to evaluate the role of PAK1 on chemosensitivity in AML by silencing PAK1 with shRNA or small molecular inhibitor. Human BMSC (HS-5) was utilized to mimic the leukemia bone marrow microenvironment (BMM) in vitro, and co-culture model was established to investigate the role of PAK1 in BMSC-mediated drug resistance.

Results

p21-activated kinase 1 high expression was shown to be associated with shorter overall survival in AML patients. The silence of PAK1 could repress cell proliferation, promote apoptosis, and enhance the sensitivity of AML cells to chemotherapeutic agents. More importantly, BMSCs induced PAK1 up-regulation in AML cells, subsequently activating the ERK1/2 signaling pathway. The effect of BMSC-mediated apoptotic-resistance could be partly reversed by knock down of PAK1.

Conclusion

p21-activated kinase 1 is a potential prognostic predictor for AML patients. PAK1 may play a pivotal role in mediating BMM-induced drug resistance, representing a novel therapeutic target in AML.

Aberrantly low STAT3 and STAT5 responses are associated with poor outcome and an inflammatory gene expression signature in pediatric acute myeloid leukemia

The relapse rate for children with acute myeloid leukemia is nearly 40% despite aggressive chemotherapy and often stem cell transplant. We sought to understand how environment-induced signaling responses are associated with clinical response to treatment. We previously reported that patients whose AML cells showed low G-CSF-induced STAT3 activation had inferior event-free survival compared to patients with stronger STAT3 responses. Here, we expanded the paradigm to evaluate multiple signaling parameters induced by a more physiological stimulus. We measured STAT3, STAT5 and ERK1/2 responses to G-CSF and to stromal cell-conditioned medium for 113 patients enrolled on COG trials AAML03P1 and AAML0531. Low inducible STAT3 activity was independently associated with inferior event-free survival in multivariate analyses. For inducible STAT5 activity, those with the lowest and highest responses had inferior event-free survival, compared to patients with intermediate STAT5 responses. Using existing RNA-sequencing data, we compared gene expression profiles for patients with low inducible STAT3/5 activation with those for patients with higher inducible STAT3/5 signaling. Genes encoding hematopoietic factors and mitochondrial respiratory chain subunits were overexpressed in the low STAT3/5 response groups, implicating inflammatory and metabolic pathways as potential mechanisms of chemotherapy resistance. We validated the prognostic relevance of individual genes from the low STAT3/5 response signature in a large independent cohort of pediatric AML patients. These findings provide novel insights into interactions between AML cells and the microenvironment that are associated with treatment failure and could be targeted for therapeutic interventions.

CCN2 (Cellular Communication Network factor 2) in the bone marrow microenvironment, normal and malignant hematopoiesis

CCN2, formerly termed Connective Tissue Growth Factor, is a protein belonging to the Cellular Communication Network (CCN)-family of secreted extracellular matrix-associated proteins. As a matricellular protein it is mainly considered to be active as a modifier of signaling activity of several different signaling pathways and as an orchestrator of their cross-talk. Furthermore, CCN2 and its fragments have been implicated in the regulation of a multitude of biological processes, including cell proliferation, differentiation, adhesion, migration, cell survival, apoptosis and the production of extracellular matrix products, as well as in more complex processes such as embryonic development, angiogenesis, chondrogenesis, osteogenesis, fibrosis, mechanotransduction and inflammation. Its function is complex and context dependent, depending on cell type, state of differentiation and microenvironmental context. CCN2 plays a role in many diseases, especially those associated with fibrosis, but has also been implicated in many different forms of cancer. In the bone marrow (BM), CCN2 is highly expressed in mesenchymal stem/stromal cells (MSCs). CCN2 is important for MSC function, supporting its proliferation, migration and differentiation. In addition, stromal CCN2 supports the maintenance and longtime survival of hematopoietic stem cells, and in the presence of interleukin 7, stimulates the differentiation of pro-B lymphocytes into pre-B lymphocytes. Overexpression of CCN2 is seen in the majority of B-acute lymphoblastic leukemias, especially in certain cytogenetic subgroups associated with poor outcome. In acute myeloid leukemia, CCN2 expression is increased in MSCs, which has been associated with leukemic engraftment in vivo. In this review, the complex function of CCN2 in the BM microenvironment and in normal as well as malignant hematopoiesis is discussed. In addition, an overview is given of data on the remaining CCN family members regarding normal and malignant hematopoiesis, having many similarities and some differences in their function.

Cyr61 mediates oxaliplatin resistance in colorectal cancer cells by regulating Bcl-xL expression

Although the clinical application of oxaliplatin (L-OHP) has improved the survival of colorectal cancer (CRC) patients, approximately half of patients with CRC fail to achieve good clinical outcomes, indicating resistance to L-OHP therapy. Cysteine-rich protein 61 (Cyr61), a multifunctional extracellular matrix protein, is highly expressed in a variety of tumors; increased Cyr61 expression is known to be closely involved in the chemotherapeutic resistance of many tumors, but its role in the L-OHP resistance of CRC cells has not been studied. In this study, we aimed to investigate the role of Cyr61 in the L-OHP resistance of CRC cells and examine the underlying mechanism. Our findings showed that the mRNA and protein levels of Cyr61 in L-OHP-resistant cells were significantly increased compared with those in nonresistant cells. Knockdown of Cyr61 enhanced the chemosensitivity of L-OHP-resistant cells to L-OHP. Mechanistically, we found that overexpression of Cyr61 decreased L-OHP-induced apoptosis in drug-resistant CRC cells through the regulation of Bcl-xL. Collectively, our results revealed for the first time that Cyr61 plays a crucial role in the resistance of CRC cells to L-OHP and indicated that targeting Cyr61 may be a promising therapeutic strategy to overcome L-OHP resistance in CRC.

Atovaquone is active against AML by upregulating the integrated stress pathway and suppressing oxidative phosphorylation

Atovaquone, a US Food and Drug Administration-approved antiparasitic drug previously shown to reduce interleukin-6/STAT3 signaling in myeloma cells, is well tolerated, and plasma concentrations of 40 to 80 µM have been achieved with pediatric and adult dosing. We conducted preclinical testing of atovaquone with acute myeloid leukemia (AML) cell lines and pediatric patient samples. Atovaquone induced apoptosis with an EC50 <30 µM for most AML lines and primary pediatric AML specimens. In NSG mice xenografted with luciferase-expressing THP-1 cells and in those receiving a patient-derived xenograft, atovaquone-treated mice demonstrated decreased disease burden and prolonged survival. To gain a better understanding of the mechanism of atovaquone, we performed an integrated analysis of gene expression changes occurring in cancer cell lines after atovaquone exposure. Atovaquone promoted phosphorylation of eIF2α, a key component of the integrated stress response and master regulator of protein translation. Increased levels of phosphorylated eIF2α led to greater abundance of the transcription factor ATF4 and its target genes, including proapoptotic CHOP and CHAC1. Furthermore, atovaquone upregulated REDD1, an ATF4 target gene and negative regulator of the mechanistic target of rapamycin (mTOR), and caused REDD1-mediated inhibition of mTOR activity with similar efficacy as rapamycin. Additionally, atovaquone suppressed the oxygen consumption rate of AML cells, which has specific implications for chemotherapy-resistant AML blasts that rely on oxidative phosphorylation for survival. Our results provide insight into the complex biological effects of atovaquone, highlighting its potential as an anticancer therapy with novel and diverse mechanisms of action, and support further clinical evaluation of atovaquone for pediatric and adult AML.

Inhibition of CYR61-S100A4 Axis Limits Breast Cancer Invasion

Background and Objective: Matricellular proteins modulate the micro environment of tumors and are recognized to contribute to tumor cell invasion and dissemination. The cysteine-rich angiogenic inducer 61 (CYR61) is upregulated in mesenchymal transformed and invasive breast cancer cells. CYR61 correlates with poor prognosis of breast cancer patients. The signaling mechanism that causes invasive properties of cancer cells regarding to epithelial-mesenchymal transition (EMT) needs further research. In this study, we investigated the signaling mechanism, which is responsible for reduced cell invasion after suppression of CYR61 in mesenchymal transformed breast cancer cells and in triple negative breast cancer cells. Methods: We addressed this issue by generating a mesenchymal transformed breast cancer cell line using prolonged mammosphere cultivation. Western blotting and quantitative PCR were used to analyze gene expression alterations. Transient gene silencing was conducted using RNA interference. Proliferation was assessed using AlamarBlue assay. Invasiveness was analyzed using 2D and 3D invasion assays. Immune-histochemical analysis of patient tissue samples was performed to examine the prognostic value of CYR61 expression. Results: In this study, we investigated whether CYR61 could be used as therapeutic target and prognostic marker for invasive breast cancer. We discovered an interaction of CYR61 with metastasis-associated protein S100A4. Suppression of CYR61 by RNA interference reduced the expression of S100A4 dependent on ERK1/2 activity regulation. Non-invasive breast cancer cells became invasive due to extracellular CYR61 supplement. Immune-histochemical analysis of 239 patient tissue samples revealed a correlation of higher CYR61 and S100A4 expression with invasive breast cancer and metastasis. Conclusion: Our data suggest that suppression of CYR61 impedes the formation of an invasive cancer cell phenotype by reducing ERK1/2 phosphorylation thereby suppressing S100A4. These findings identify mechanisms by which CYR61 suppresses cell invasion and suggest it to be a potential therapeutic target and prognostic marker for invasive breast cancer and metastasis.

Cysteine-rich protein 61 regulates the chemosensitivity of chronic myeloid leukemia to imatinib mesylate through the nuclear factor kappa B/Bcl-2 pathway

Although the targeted tyrosine kinase inhibitor imatinib mesylate (IM) has achieved significant responses against CML in the clinical setting, a small proportion of patients fail to respond to IM treatment and their disease continues to progress, indicating resistance to IM therapy. As a secreted extracellular matrix protein, cysteine‐rich protein 61 (Cyr61) plays an important role in the resistance of solid tumors to chemotherapy, but its role in CML is unclear. In the present study, we observed that Cyr61 levels were upregulated in the plasma and bone marrow (BM) of patients with CML as well as in K562 cells. This upregulation of Cyr61 significantly decreased IM‐induced cellular apoptosis of K562 cells through nuclear factor kappa B/B‐cell lymphoma 2 pathways. Inhibition of Cyr61 restored the chemosensitivity of K562 cells to IM both in vitro and in vivo. Thus, our results showed for the first time that Cyr61 plays an important role in regulating the chemosensitivity of CML cells to IM, suggesting that selectively targeting Cyr61 directly or its relevant effector pathways may provide potential value in improving the clinical response of patients with CML to IM treatment.

Cyr61 decreases Cytarabine chemosensitivity in acute lymphoblastic leukemia cells via NF-κB pathway activation

Elevated Cyr61 levels have been reported in various malignancies. Elevation of Cyr61 protein levels contributes to the proliferation, metastasis, and chemotherapy resistance of malignant cells. Previously, it was discovered that Cyr61 is elevated in both the plasma and the bone marrow supernatants of patients with acute lymphoblastic leukemia (ALL), promoting ALL cell survival. However, the role of Cyr61 in the chemotherapeutic resistance of ALL cells remains unknown. The aim of the current study was to investigate the role of Cyr61 in regulating ALL cell chemosensitivity to Ara‑C. It was found that Cyr61 is overexpressed in bone marrow mononuclear cells from patients with ALL. Increased Cyr61 effectively decreased Ara‑C‑induced apoptosis of ALL cells, and its function was blocked by the use of the anti‑Cyr61 monoclonal antibody 093G9. Furthermore, Cyr61 increased the level of Bcl‑2 in Ara‑C‑treated ALL cells. Mechanistically, it was shown that Cyr61 affected ALL cell resistance to Ara‑C partially via the NF‑κB pathway. Taken together, the present study is the first, to the best of our knowledge, to reveal that Cyr61 is involved in ALL cell resistance through the NF‑κB pathway. The findings support a functional role for Cyr61 in promoting chemotherapy resistance, suggesting that targeting Cyr61 directly or its relevant effector pathways may improve the clinical responses of patients with ALL.

MiR-634 sensitizes glioma cells to temozolomide by targeting CYR61 through Raf-ERK signaling pathway

Glioma is the most common intracranial malignant tumors, accounting for about 40% of intracranial tumors. Primary or secondary drug resistance is one of the main reasons for the failure of treatment. The oncogenic or tumor-suppressive roles of miR-634 have been revealed in different types of cancer. However, the role of miR-634 in glioma remains unknown and whether miR-634 could sensitize glioma cells to temozolomide also is unclear. Here, we aim to investigate the biological function of miR-634 and the possible mechanisms in glioma. In this study, we found that miR-634 was downregulated in glioma tissues compared with normal brain tissues, and its expression was associated with tumor size and WHO grade. Importantly, glioma patients with low miR-634 expression showed a shorter survival time than patients which had high expression of miR-634. This study also showed that miR-634 was decreased in temozolomide-resistant glioma cells, and restoration of miR-634 could sensitize the resistant cells to temozolomide by targeting CYR61 through Raf-ERK signaling. Our study provides a potential target for overcome drug resistance in glioma.

Quercetin Suppresses CYR61-Mediated Multidrug Resistance in Human Gastric Adenocarcinoma AGS Cells

Cysteine-rich angiogenic inducer 61 (CYR61) is an extracellular matrix-associated protein involved in survival, tumorigenesis, and drug resistance. Therefore, we examined the effects of flavones against CYR61-overexpressing human gastric adenocarcinoma AGS (AGS-cyr61) cells, which show remarkable resistance to 5-fluorouracil (5-FU), adriamycin (ADR), tamoxifen (TAM), paclitaxel (PAC), and docetaxel (DOC). Among the tested flavones, quercetin had the lowest 50% inhibitory concentration (IC₅₀) and significantly reduced the viability of AGS-cyr61 cells compared with AGS cells. Quercetin: (1) reduced multidrug resistance-associated protein 1 and nuclear factor (NF)-kappa B p65 subunit levels; (2) reversed multidrug resistance (MDR); (3) inhibited colony formation and induced caspase-dependent apoptosis; and (4) suppressed migration and down-regulated epithelial-mesenchymal transition-related proteins in AGS-cyr61. Moreover, AGS-cyr61 cells treated with quercetin concentrations close to the IC₅₀ and simultaneously treated with 5-FU or ADR in the sub-lethal range showed strong synergism between quercetin and these two drugs. These findings indicate that CYR61 is a potential regulator of drug resistance and that quercetin may be a novel agent for improving the efficacy of anticancer drugs in AGS-cyr61 cells.

The Possible Importance of β3 Integrins for Leukemogenesis and Chemoresistance in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive bone marrow malignancy where the immature leukemia cells communicate with neighboring cells through constitutive cytokine release and through their cell surface adhesion molecules. The primary AML cells express various integrins. These heterodimeric molecules containing an α and a β chain are cell surface molecules that bind extracellular matrix molecules, cell surface molecules and soluble mediators. The β3 integrin (ITGB3) chain can form heterodimers only with the two α chains αIIb and αV. These integrins are among the most promiscuous and bind to a large number of ligands, including extracellular matrix molecules, cell surface molecules and soluble mediators. Recent studies suggest that the two β3 integrins are important for leukemogenesis and chemosensitivity in human AML. Firstly, αIIb and β3 are both important for adhesion of AML cells to vitronectin and fibronectin. Secondly, β3 is important for the development of murine AML and also for the homing and maintenance of the proliferation for xenografted primary human AML cells, and for maintaining a stem cell transcriptional program. These last effects seem to be mediated through Syk kinase. The β3 expression seems to be regulated by HomeboxA9 (HoxA9) and HoxA10, and the increased β3 expression then activates spleen tyrosine kinase (Syk) and thereby contributes to cytokine hypersensitivity and activation of β2 integrins. Finally, high integrin αV/β3 expression is associated with an adverse prognosis in AML and decreased sensitivity to the kinase inhibitor sorafenib; this integrin can also be essential for osteopontin-induced sorafenib resistance in AML. In the present article, we review the experimental and clinical evidence for a role of β3 integrins for leukemogenesis and chemosensitivity in AML.

Distinct signaling events promote resistance to mitoxantrone and etoposide in pediatric AML: a Children's Oncology Group report

Despite aggressive chemotherapy including mitoxantrone and etoposide, relapse occurs for almost half of children with acute myeloid leukemia (AML). Since both drugs inhibit topoisomerase II and cause DNA double strand breaks, resistance could be achieved by enhanced DNA damage repair (DDR), via homologous recombination (HR) and/or non-homologous end joining (NHEJ). An important source of extrinsic chemoresistance is the bone marrow stroma. We aimed to reveal intrinsic and stroma-induced signaling pathways that contribute to chemoresistance. Sixty diagnostic pediatric AML samples were cultured on or off stromal cells, with or without chemotherapy. We measured apoptosis, DNA damage signaling, and NHEJ/HR pathway activity by FACS analysis of intracellular cleaved PARP, γH2AX, pDNA-PKcs and pATM, respectively. Mitoxantrone strongly increased γH2AX and pDNA-PKcs. Neither chemotherapy drug induced pATM. DNA-PK inhibition alleviated mitoxantrone resistance for AML cells on and off stromal cells. Regarding stroma-induced signaling pathways, ERK1/2 was most consistently activated in primary AML cells by stromal cells. ERK1/2 inactivation partially restored chemosensitivity to AML cells on stromal cells. Additionally, low stroma-induced STAT3 activity and strong stroma-induced mitoxantrone resistance were associated with inferior clinical outcome. Taken together, the NHEJ DDR and ERK1/2 pathways are potential targets for reducing intrinsic and extrinsic chemotherapy resistance in pediatric AML.

TGF-β-induced stromal CYR61 promotes resistance to gemcitabine in pancreatic ductal adenocarcinoma through downregulation of the nucleoside transporters hENT1 and hCNT3

Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer in part due to inherent resistance to chemotherapy, including the first-line drug gemcitabine. Although low expression of the nucleoside transporters hENT1 and hCNT3 that mediate cellular uptake of gemcitabine has been linked to gemcitabine resistance, the mechanisms regulating their expression in the PDAC tumor microenvironment are largely unknown. Here, we report that the matricellular protein cysteine-rich angiogenic inducer 61 (CYR61) negatively regulates the nucleoside transporters hENT1 and hCNT3. CRISPR/Cas9-mediated knockout of CYR61 increased expression of hENT1 and hCNT3, increased cellular uptake of gemcitabine and sensitized PDAC cells to gemcitabine-induced apoptosis. In PDAC patient samples, expression of hENT1 and hCNT3 negatively correlates with expression of CYR61 . We demonstrate that stromal pancreatic stellate cells (PSCs) are a source of CYR61 within the PDAC tumor microenvironment. Transforming growth factor-β (TGF-β) induces the expression of CYR61 in PSCs through canonical TGF-β-ALK5-Smad2/3 signaling. Activation of TGF-β signaling or expression of CYR61 in PSCs promotes resistance to gemcitabine in PDAC cells in an in vitro co-culture assay. Our results identify CYR61 as a TGF-β-induced stromal-derived factor that regulates gemcitabine sensitivity in PDAC and suggest that targeting CYR61 may improve chemotherapy response in PDAC patients.

Interleukin-6 levels predict event-free survival in pediatric AML and suggest a mechanism of chemotherapy resistance

The tumor microenvironment can protect cancer cells from conventional anticancer therapies. Thus, targeting these protective mechanisms could eradicate therapy-resistant cancer cells and improve outcomes. Interleukin-6 (IL-6) provides extrinsic protection for several solid tumors and multiple myeloma. In pediatric acute myeloid leukemia (AML), IL-6-induced STAT3 signaling frequently becomes stronger at relapse, and increases in IL-6-induced STAT3 activity are associated with inferior survival after relapse. These findings suggested that the IL-6-induced STAT3 pathway may promote chemotherapy resistance and disease progression. Thus, we investigated the dysregulation of IL-6 levels in the bone marrow niche in pediatric patients with AML and the association between IL-6 levels and outcome. We measured levels of over 40 cytokines and growth factors in plasma from diagnostic bone marrow aspirates of 45 pediatric AML patients and 7 healthy sibling controls. Of the measured cytokines, only IL-6 levels were associated with event-free survival. Importantly, the effect of elevated IL-6 was most striking among children classified as having a low risk of relapse. In these patients, 5-year event-free survival was 82.5% ± 11% for patients with low IL-6 levels at diagnosis (n = 14) compared with 17.3% ± 11% for patients with elevated IL-6 (n = 13, log-rank P = .0003). In vitro, exogenous IL-6 reduced mitoxantrone-induced apoptosis in cell lines and primary pediatric AML samples. These results suggest that IL-6 levels at diagnosis could be used to help identify children at high risk of relapse, particularly those who are otherwise classified as low risk by current algorithms. Moreover, the IL-6 pathway could represent a target for overcoming environment-mediated chemotherapy resistance.

Cyr61 participates in the pathogenesis of acute lymphoblastic leukemia by enhancing cellular survival via the AKT/NF-κB signaling pathway

Cyr61 (CCN1) is the product of a growth factor–inducible immediate early gene and is involved in cell adhesion, survival, proliferation, and differentiation. Cyr61 is overexpressed in human tumors and is involved in the development of tumors. However, the role that Cyr61 plays in acute lymphoblastic leukemia (ALL) cells remains undetermined. The aim of this study was to identify the role of Cyr61 in regulating ALL cell survival. Here, we found that the level of Cyr61 was increased in the plasma and bone marrow (BM) from ALL patients compared with samples from normal control patients. Furthermore, we observed that Cyr61 could effectively stimulate Jurkat (T ALL cell lines), Nalm-6 (B ALL cell lines), and primary ALL cell survival. Mechanistically, we showed that Cyr61 stimulated ALL cell survival via the AKT/NF-κB signaling pathways and the consequent up-regulation of Bcl-2. Taken together, our study is the first to reveal that Cyr61 is elevated in ALL and promotes cell survival through the AKT/NF-κB pathway by up-regulating Bcl-2. Our findings suggest that Cyr61 plays an important role in the pathogenesis of ALL.

The role of the CCN family of proteins in blood cancers

Haematopoiesis is the term used to describe the production of blood cells. This is a tightly regulated hierarchical system in which mature circulating blood cells develop from a small population of haematopoietic stem (HSC) and progenitor cells within the microenvironment of the bone marrow. Molecular and genetic abnormalities arising in these stem cells lead to a block in the normal programme of proliferation and differentiation and result in the development of the blood cancers known as the leukaemias and lymphomas. Recently the regulatory role of the bone marrow microenvironment or niche has also become increasingly recognised. The interface between the bone and bone marrow (endosteum) and the region surrounding the blood vessels (perivascular) provide distinct niches harbouring quiescent HSC or proliferative HSC respectively. Current chemotherapeutic regimes can often successfully target the proliferative HSC but disease relapse occurs due to residual quiescent HSC. Understanding these developmental and regulatory processes and the associated cell communication mechanisms are thus crucial to the development of new treatment strategies. The CCN family of proteins have been recognised to play a key role in all aspects of haematopoiesis.