Beta1 integrin mediated adhesion increases Bim protein degradation and contributes to drug resistance in leukaemia cells

Exosomal integrins in tumor progression, treatment and clinical prediction (Review)

Integrins are a large family of cell adhesion molecules involved in tumor cell differentiation, migration, proliferation and neovascularization. Tumor cell‑derived exosomes carry a large number of integrins, which are closely associated with tumor progression. As crucial mediators of intercellular communication, exosomal integrins have gained attention in the field of cancer biology. The present review examined the regulatory mechanisms of exosomal integrins in tumor cell proliferation, migration and invasion, and emphasized their notable roles in tumor initiation and progression. The potential of exosomal integrins as drug delivery systems in cancer treatment was explored. Additionally, the potential of exosomal integrins in clinical tumor prediction was considered, while summarizing their applications in diagnosis, prognosis assessment and treatment response prediction. Thus, the present review aimed to provide guidance and insights for future basic research and the clinical translation of exosomal integrins. The study of exosomal integrins is poised to offer new perspectives and methods for precise cancer treatment and clinical prediction.

Targeting integrins in drug-resistant acute myeloid leukaemia

Acute myeloid leukaemia (AML) continues to have a poor prognosis, warranting new therapeutic strategies. The bone marrow (BM) microenvironment consists of niches that interact with not only normal haematopoietic stem cells (HSC) but also leukaemia cells like AML. There are many adhesion molecules in the BM microenvironment; therein, integrins have been of central interest. AML cells express integrins that bind to ligands in the microenvironment, enabling adhesion of leukaemia cells in the microenvironment, thereby initiating intracellular signalling pathways that are associated with cell migration, cell proliferation, survival, and drug resistance that has been described to mediate cell adhesion-mediated drug resistance (CAM-DR). Identifying and targeting integrins in AML to interrupt interactions with the microenvironment have been pursued as a strategy to overcome CAM-DR. Here, we focus on the BM microenvironment and review the role of integrins in CAM-DR of AML and discuss integrin-targeting strategies. 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.

Integrin Signaling Shaping BTK-Inhibitor Resistance

Integrins are adhesion molecules that function as anchors in retaining tumor cells in supportive tissues and facilitating metastasis. Beta1 integrins are known to contribute to cell adhesion-mediated drug resistance in cancer. Very late antigen-4 (VLA-4), a CD49d/CD29 heterodimer, is a beta1 integrin implicated in therapy resistance in both solid tumors and haematological malignancies such as chronic lymphocytic leukemia (CLL). A complex inside-out signaling mechanism activates VLA-4, which might include several therapeutic targets for CLL. Treatment regimens for this disease have recently shifted towards novel agents targeting BCR signaling. Bruton’s tyrosine kinase (BTK) is a component of B cell receptor signaling and BTK inhibitors such as ibrutinib are highly successful; however, their limitations include indefinite drug administration, the development of therapy resistance, and toxicities. VLA-4 might be activated independently of BTK, resulting in an ongoing interaction of CD49d-expressing leukemic cells with their surrounding tissue, which may reduce the success of therapy with BTK inhibitors and increases the need for alternative therapies. In this context, we discuss the inside-out signaling cascade culminating in VLA-4 activation, consider the advantages and disadvantages of BTK inhibitors in CLL and elucidate the mechanisms behind cell adhesion-mediated drug resistance.

Substrate Stiffness Modulates the Growth, Phenotype, and Chemoresistance of Ovarian Cancer Cells

Mechanical factors in the tumor microenvironment play an important role in response to a variety of cellular activities in cancer cells. Here, we utilized polyacrylamide hydrogels with varying physical parameters simulating tumor and metastatic target tissues to investigate the effect of substrate stiffness on the growth, phenotype, and chemotherapeutic response of ovarian cancer cells (OCCs). We found that increasing the substrate stiffness promoted the proliferation of SKOV-3 cells, an OCC cell line. This proliferation coincided with the nuclear translocation of the oncogene Yes-associated protein. Additionally, we found that substrate softening promoted elements of epithelial-mesenchymal transition (EMT), including mesenchymal cell shape changes, increase in vimentin expression, and decrease in E-cadherin and β-catenin expression. Growing evidence demonstrates that apart from contributing to cancer initiation and progression, EMT can promote chemotherapy resistance in ovarian cancer cells. Furthermore, we evaluated tumor response to standard chemotherapeutic drugs (cisplatin and paclitaxel) and found antiproliferation effects to be directly proportional to the stiffness of the substrate. Nanomechanical studies based on atomic force microscopy (AFM) have revealed that chemosensitivity and chemoresistance are related to cellular mechanical properties. The results of cellular elastic modulus measurements determined by AFM demonstrated that Young's modulus of SKOV-3 cells grown on soft substrates was less than that of cells grown on stiff substrates. Gene expression analysis of SKOV-3 cells showed that mRNA expression can be greatly affected by substrate stiffness. Finally, immunocytochemistry analyses revealed an increase in multidrug resistance proteins, namely, ATP binding cassette subfamily B member 1 and member 4 (ABCB1 and ABCB4), in the cells grown on the soft gel resulting in resistance to chemotherapeutic drugs. In conclusion, our study may help in identification of effective targets for cancer therapy and improve our understanding of the mechanisms of cancer progression and chemoresistance.

Polymeric siRNA delivery targeting integrin-β1 could reduce interactions of leukemic cells with bone marrow microenvironment

Uncontrolled proliferation of the myeloid cells due to BCR-ABL fusion has been successfully treated with tyrosine kinase inhibitors (TKIs), which improved the survival rate of Chronic Myeloid Leukemia (CML) patients. However, due to interactions of CML cells with bone marrow microenvironment, sub-populations of CML cells could become resistant to TKI treatment. Since integrins are major cell surface molecules involved in such interactions, the potential of silencing integrin-β1 on CML cell line K562 cells was explored using short interfering RNA (siRNA) delivered through lipid-modified polyethyleneimine (PEI) polymers. Reduction of integrin-β1 in K562 cells decreased cell adhesion towards human bone marrow stromal cells and to fibronectin, a major extracellular matrix protein for which integrin-β1 is a primary receptor. Interaction of K562 cells with fibronectin decreased the sensitivity of the cells to BCR-ABL siRNA treatment, but a combinational treatment with integrin-β1 and BCR-ABL siRNAs significantly reduced colony forming ability of the cells. Moreover, integrin-β1 silencing enhanced the detachment of K562 cells from hBMSC samples (2 out of 4 samples), which could make them more susceptible to TKIs. Therefore, the polymeric-siRNA delivery targeting integrin-β1 could be beneficial to reduce interactions with bone marrow microenvironment, aiding in the response of CML cells to therapeutic treatment.

Bone Marrow Mesenchymal Stromal Cells in Multiple Myeloma: Their Role as Active Contributors to Myeloma Progression

Multiple myeloma (MM) is a hematological malignancy of plasma cells that proliferate and accumulate within the bone marrow (BM). Work from many groups has made evident that the complex microenvironment of the BM plays a crucial role in myeloma progression and response to therapeutic agents. Within the cellular components of the BM, we will specifically focus on mesenchymal stromal cells (MSCs), which are known to interact with myeloma cells and the other components of the BM through cell to cell, soluble factors and, as more recently evidenced, through extracellular vesicles. Multiple structural and functional abnormalities have been found when characterizing MSCs derived from myeloma patients (MM-MSCs) and comparing them to those from healthy donors (HD-MSCs). Other studies have identified differences in genomic, mRNA, microRNA, histone modification, and DNA methylation profiles. We discuss these distinctive features shaping MM-MSCs and propose a model for the transition from HD-MSCs to MM-MSCs as a consequence of the interaction with myeloma cells. Finally, we review the contribution of MM-MSCs to several aspects of myeloma pathology, specifically to myeloma growth and survival, drug resistance, dissemination and homing, myeloma bone disease, and the induction of a pro-inflammatory and immunosuppressive microenvironment.

Cancer-Associated Fibroblasts as a Common Orchestrator of Therapy Resistance in Lung and Pancreatic Cancer

Cancer arises from mutations accruing within cancer cells, but the tumor microenvironment (TME) is believed to be a major, often neglected, factor involved in therapy resistance and disease progression. Cancer-associated fibroblasts (CAFs) are prominent and key components of the TME in most types of solid tumors. Extensive research over the past decade revealed their ability to modulate cancer metastasis, angiogenesis, tumor mechanics, immunosuppression, and drug access through synthesis and remodeling of the extracellular matrix and production of growth factors. Thus, they are considered to impede the response to current clinical cancer therapies. Therefore, targeting CAFs to counteract these protumorigenic effects, and overcome the resistance to current therapeutic options, is an appealing and emerging strategy. In this review, we discuss how CAFs affect prognosis and response to clinical therapy and provide an overview of novel therapies involving CAF-targeting agents in lung and pancreatic cancer.

Chronic Myeloid Leukemia: A Model Disease of the Past, Present and Future

Chronic myeloid leukemia (CML) has been a "model disease" with a long history. Beginning with the first discovery of leukemia and the description of the Philadelphia Chromosome and ending with the current goal of achieving treatment-free remission after targeted therapies, we describe here the journey of CML, focusing on molecular pathways relating to signaling, metabolism and the bone marrow microenvironment. We highlight current strategies for combination therapies aimed at eradicating the CML stem cell; hopefully the final destination of this long voyage.

Investigating the response of paediatric leukaemia-propagating cells to BCL-2 inhibitors

Relapse of paediatric acute lymphoblastic leukaemia (ALL) may occur due to persistence of resistant cells with leukaemia‐propagating ability (LPC). In leukaemia, the balance of B‐cell lymphoma‐2 (BCL‐2) family proteins is disrupted, promoting survival of malignant cells and possibly LPC. A direct comparison of BCL‐2 inhibitors, navitoclax and venetoclax, was undertaken on LPC subpopulations from B‐cell precursor (BCP) and T‐cell ALL (T‐ALL) cases in vitro and in vivo. Responses were compared to BCL‐2 levels detected by microarray analyses and Western blotting. In vitro, both drugs were effective against most BCP‐ALL LPC, except CD34⁻/CD19⁻ cells. In contrast, only navitoclax was effective in T‐ALL and CD34⁻/CD7⁻ LPC were resistant to both drugs. In vivo, navitoclax was more effective than venetoclax, significantly improving survival of mice engrafted with BCP‐ and T‐ALL samples. Venetoclax was not particularly effective against T‐ALL cases in vivo. The proportions of CD34⁺/CD19⁻, CD34⁻/CD19⁻ BCP‐ALL cells and CD34⁻/CD7⁻ T‐ALL cells increased significantly following in vivo treatment. Expression of pro‐apoptotic BCL‐2 genes was lower in these subpopulations, which may explain the lack of sensitivity. These data demonstrate that some LPC were resistant to BCL‐2 inhibitors and sustained remission will require their use in combination with other therapeutics.

Hsa_circ_CSPP1/MiR-361-5p/ITGB1 Regulates Proliferation and Migration of Cervical Cancer (CC) by Modulating the PI3K-Akt Signaling Pathway

This study aimed to investigate the regulatory mechanism of circular RNA CSPP1 (hsa_circ_CSPP1) in cervical cancer. Based on GEO database, differentially expressed circRNAs and mRNAs related to cervical cancer were screened out by R software. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and Gene Ontology (GO) term analysis were performed to analyze the functional and pathway enrichment of identified DEGs. In addition, Cytoscape software was used to build interaction network of DEGs. The mRNA expressions were examined by qRT-PCR. Western blot was conducted to view the expression of proteins. Cell proliferation and apoptosis were respectively evaluated using CCK-8 assay and flow cytometry, whereas cell migration abilities were detected by Transwell assay. The relationship among factors was validated by dual-luciferase reporter gene assay. The influence in cervical tumor growth was further verified through nude mouse model in vivo. Hsa_circ_CSPP1 and ITGB1 were high-expressed in cervical cancer, while miR-361-5p was low-expressed. Hsa_circ_CSPP1 knockdown or miR-361-5p overexpression could suppress cervical cancer cell proliferation and migration, whereas promoted cell apoptosis. In addition, further experiments demonstrated that both hsa_circ_CSPP1 and ITGB1 mRNA were targets of miR-361-5p. Repressing hsa_circ_CSPP1 restrained cell viability and mobility and induced apoptosis through sponging miR-361-5p. Meanwhile, miR-361-5p also inhibited cervical cancer tumorigenesis via downregulation of ITGB1. Knockdown of hsa_circ_CSPP1 impeded tumor growth through suppressing the expression of downstream gene ITGB1, PI3K, and Akt. Circular RNA hsa_circ_CSPP1 regulates cell migration and proliferation in cervical cancer through miR-361-5p/ITGB1 in PI3K-Akt signaling pathway.

Elucidating the expression and function of Numbl during cell adhesion-mediated drug resistance (CAM-DR) in multiple myeloma (MM)

Background

Cell adhesion-mediated drug resistance (CAM-DR) is a major clinical problem that prevents successful treatment of multiple myeloma (MM). In particular, the expression levels of integrin β1 and its sub-cellular distribution (internalization and trafficking) are strongly associated with CAM-DR development.

Methods

Development of an adhesion model of established MM cell lines and detection of Numbl and Integrinβ1 expression by Western Blot analysis. The interaction between Numbl and Integrinβ1 was assessed by a co-immunoprecipitation (CO-IP) method. Calcein AM assay was performed to investigate the levels of cell adhesion. Finally, the extent of CAM-DR in myeloma cells was measured using cell viability assay and flow cytometry analysis.

Results

Our preliminary date suggest that Numbl is differentially expressed in a cell adhesion model of MM cell lines. In addition to binding to the phosphotyrosine-binding (PTB) domain, the carboxyl terminal of Numbl can also interact with integrin β1 to regulate the cell cycle by activating the pro-survival PI3K/AKT signaling pathway. This study intends to verify and elucidate the interaction between Numbl and integrin β1 and its functional outcome on CAM-DR. We have designed and developed a CAM-DR model using MM cells coated with either fibronectin or bone marrow stromal cells. We assessed whether Numbl influences cell-cycle progression and whether it, in turn, contributes to activation of PI3K/AKT signal pathway through the adjustment of its carboxyl end. Finally, we showed that the interaction of Numbl with integrin β1 promotes the formation of CAM-DR in MM cells.

Conclusions

Our findings elucidated the specific molecular mechanisms of CAM-DR induction and confirmed that Numbl is crucial for the development of CAM-DR in MM cells.

Targeting the tumour stroma to improve cancer therapy

Cancers are not composed merely of cancer cells alone; instead, they are complex 'ecosystems' comprising many different cell types and noncellular factors. The tumour stroma is a critical component of the tumour microenvironment, where it has crucial roles in tumour initiation, progression, and metastasis. Most anticancer therapies target cancer cells specifically, but the tumour stroma can promote the resistance of cancer cells to such therapies, eventually resulting in fatal disease. Therefore, novel treatment strategies should combine anticancer and antistromal agents. Herein, we provide an overview of the advances in understanding the complex cancer cell-tumour stroma interactions and discuss how this knowledge can result in more effective therapeutic strategies, which might ultimately improve patient outcomes.

Current outlook on drug resistance in chronic myeloid leukemia (CML) and potential therapeutic options

Chronic myeloid leukemia cells are armed with several resistance mechanisms that can make current drugs ineffective. A better understanding of resistance mechanisms is yielding new approaches to management of the disease. Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm the hallmark of which, the breakpoint cluster region-Abelson (BCR-ABL) oncogene, has been the target of tyrosine kinase inhibitors (TKIs), which have significantly improved the survival of patients with CML. However, because of an increase in TKI resistance, it is becoming imperative to identify resistance mechanisms so that drug therapies can be better prescribed and new agents developed. In this review, we discuss the various BCR-ABL-dependent and -independent mechanisms of resistance observed in CML, and the range of therapeutic solutions available to overcome such resistance and to ultimately improve the survival of patients with CML.

DNA Ligase 1 is an essential mediator of sister chromatid telomere fusions in G2 cell cycle phase

Fusion of critically short or damaged telomeres is associated with the genomic rearrangements that support malignant transformation. We have demonstrated the fundamental contribution of DNA ligase 4-dependent classical non-homologous end-joining to long-range inter-chromosomal telomere fusions. In contrast, localized genomic recombinations initiated by sister chromatid fusion are predominantly mediated by alternative non-homologous end-joining activity that may employ either DNA ligase 3 or DNA ligase 1. In this study, we sought to discriminate the relative involvement of these ligases in sister chromatid telomere fusion through a precise genetic dissociation of functional activity. We have resolved an essential and non-redundant role for DNA ligase 1 in the fusion of sister chromatids bearing targeted double strand DNA breaks that is entirely uncoupled from its requisite engagement in DNA replication. Importantly, this fusogenic repair occurs in cells fully proficient for non-homologous end-joining and is not compensated by DNA ligases 3 or 4. The dual functions of DNA ligase 1 in replication and non-homologous end-joining uniquely position and capacitate this ligase for DNA repair at stalled replication forks, facilitating mitotic progression.

Chemoresistance of Cancer Cells: Requirements of Tumor Microenvironment-mimicking In Vitro Models in Anti-Cancer Drug Development

For decades, scientists have been using two-dimensional cell culture platforms for high-throughput drug screening of anticancer drugs. Growing evidence indicates that the results of anti-cancer drug screening vary with the cell culture microenvironment, and this variation has been proposed as a reason for the high failure rate of clinical trials. Since the culture condition-dependent drug sensitivity of anti-cancer drugs may negatively impact the identification of clinically effective drug candidates, more reliable in vitro cancer platforms are urgently needed. In this review article, we provide an overview of how cell culture conditions can alter drug efficacy and highlight the importance of developing more reliable cancer drug testing platforms for use in the drug discovery process. The environmental factors that can alter drug delivery and efficacy are reviewed. Based on these observations of chemoresistant tumor physiology, we summarize the recent advances in the fabrication of in vitro cancer models and the model-dependent cytotoxicity of anti-cancer drugs, with a particular focus on engineered environmental factors in these platforms. It is believed that more physiologically relevant cancer models can revolutionize the drug discovery process.

β1-Integrin Impacts Rad51 Stability and DNA Double-Strand Break Repair by Homologous Recombination

The molecular mechanisms underlying resistance to radiotherapy in breast cancer cells remain elusive. Previously, we reported that elevated β1-integrin is associated with enhanced breast cancer cell survival postirradiation, but how β1-integrin conferred radioresistance was unclear. Ionizing radiation (IR) induced cell killing correlates with the efficiency of DNA double-strand break (DSB) repair, and we found that nonmalignant breast epithelial (S1) cells with low β1-integrin expression have a higher frequency of S-phase-specific IR-induced chromosomal aberrations than the derivative malignant breast (T4-2) cells with high β1-integrin expression. In addition, there was an increased frequency of IR-induced homologous recombination (HR) repairosome focus formation in T4-2 cells compared with that of S1 cells. Cellular levels of Rad51 in T4-2 cells, a critical factor in HR-mediated DSB repair, were significantly higher. Blocking or depleting β1-integrin activity in T4-2 cells reduced Rad51 levels, while ectopic expression of β1-integrin in S1 cells correspondingly increased Rad51 levels, suggesting that Rad51 is regulated by β1-integrin. The low level of Rad51 protein in S1 cells was found to be due to rapid degradation by the ubiquitin proteasome pathway (UPP). Furthermore, the E3 ubiquitin ligase RING1 was highly upregulated in S1 cells compared to T4-2 cells. Ectopic β1-integrin expression in S1 cells reduced RING1 levels and increased Rad51 accumulation. In contrast, β1-integrin depletion in T4-2 cells significantly increased RING1 protein levels and potentiated Rad51 ubiquitination. These data suggest for the first time that elevated levels of the extracellular matrix receptor β1-integrin can increase tumor cell radioresistance by decreasing Rad51 degradation through a RING1-mediated proteasomal pathway.

The bone marrow microenvironment in health and disease at a glance

The bone marrow microenvironment (BMM) is the 'domicile' of hematopoietic stem cells, as well as of malignant processes that can develop there. Multiple and complex interactions with the BMM influence hematopoietic stem cell (HSC) physiology, but also the pathophysiology of hematological malignancies. Reciprocally, hematological malignancies alter the BMM, in order to render it more hospitable for malignant progression. In this Cell Science at a Glance article and accompanying poster, we highlight concepts of the normal and malignant hematopoietic stem cell niches. We present the intricacies of the BMM in malignancy and provide approaches for targeting the interactions between malignant cells and their BMM. This is done in an effort to augment existing treatment strategies in the future.

BM microenvironmental protection of CML cells from imatinib through Stat5/NF-κB signaling and reversal by Wogonin

Constitutive Stat5 activation enhanced cell survival and resistance to imatinib (IM) in chronic myelogenous leukemia (CML) cells. However, the mechanism of Stat5 activation in mediating resistance to IM in bone marrow (BM) microenvironment has not been evaluated precisely. In this study, we reported HS-5-derived conditioned medium (CM) significantly enhanced IM resistance in K562 and KU812. Interestingly, upregulation of the proportion of CD34+ subpopulation was found in CML cells. Subsequently, the BCR/ABL-independent activation of Stat5 increased P-glycoprotein (P-gp) activity in CM-mediated protection of CML stem cells (LSCs) from IM. Further research revealed Stat5 activation increased the DNA binding activity of NF-κB though binding of p-Stat5 and p-RelA in nucleus. Moreover, highly acetylated RelA was required for Stat5-mediated RelA nuclear binding. The study further confirmed that Wogonin potentiated the inhibitory effects of IM on leukemia development by suppressing Stat5 pathway both in CM model and the K562 xenograft model. In summary, results clearly demonstrated BCR/ABL-independent Stat5 survival pathway could contribute to resistance of CML LSCs to IM in BM microenvironment and suggested that natural durgs effectively inhibiting Stat5 may be an attractive approach to overcome resistance to BCR/ABL kinase inhibitors.

Integrating Models to Quantify Environment-Mediated Drug Resistance

Drug resistance is the single most important driver of cancer treatment failure for modern targeted therapies, and the dialog between tumor and stroma has been shown to modulate the response to molecularly targeted therapies through proliferative and survival signaling. In this work, we investigate interactions between a growing tumor and its surrounding stroma and their role in facilitating the emergence of drug resistance. We used mathematical modeling as a theoretical framework to bridge between experimental models and scales, with the aim of separating intrinsic and extrinsic components of resistance in BRAF-mutated melanoma; the model describes tumor-stroma dynamics both with and without treatment. Integration of experimental data into our model revealed significant variation in either the intensity of stromal promotion or intrinsic tissue carrying capacity across animal replicates. Cancer Res; 77(19); 5409-18. ©2017 AACR.

High-throughput profiling of signaling networks identifies mechanism-based combination therapy to eliminate microenvironmental resistance in acute myeloid leukemia

The bone marrow microenvironment is known to provide a survival advantage to residual acute myeloid leukemia cells, possibly contributing to disease recurrence. The mechanisms by which stroma in the microenvironment regulates leukemia survival remain largely unknown. Using reverse-phase protein array technology, we profiled 53 key protein molecules in 11 signaling pathways in 20 primary acute myeloid leukemia samples and two cell lines, aiming to understand stroma-mediated signaling modulation in response to the targeted agents temsirolimus (MTOR), ABT737 (BCL2/BCL-XL), and Nutlin-3a (MDM2), and to identify the effective combination therapy targeting acute myeloid leukemia in the context of the leukemia microenvironment. Stroma reprogrammed signaling networks and modified the sensitivity of acute myeloid leukemia samples to all three targeted inhibitors. Stroma activated AKT at Ser473 in the majority of samples treated with single-agent ABT737 or Nutlin-3a. This survival mechanism was partially abrogated by concomitant treatment with temsirolimus plus ABT737 or Nutlin-3a. Mapping the signaling networks revealed that combinations of two inhibitors increased the number of affected proteins in the targeted pathways and in multiple parallel signaling, translating into facilitated cell death. These results demonstrated that a mechanism-based selection of combined inhibitors can be used to guide clinical drug selection and tailor treatment regimens to eliminate microenvironment-mediated resistance in acute myeloid leukemia.

Growth of tyrosine kinase inhibitor-resistant Philadelphia-positive acute lymphoblastic leukemia: Role of bone marrow stromal cells

Human bone marrow stromal cells (hBMSCs) may contribute to the growth of tyrosine kinase inhibitor (TKI)-resistant chronic myelogenous leukemia (CML). However, there are certain differences in biology between CML and Philadelphia-positive acute lymphoblastic leukemia (Ph⁺ ALL). Little is known about the role and mechanism of hBMSCs on the growth of TKI-resistant Ph⁺ ALL. The current study co-cultured hBMSCs with the TKI-resistant SUP-B15. Next, the proliferation of SUP-B15 was detected using a Cell Counting Kit-8. Additionally, quantitative polymerase chain reaction and flow cytometry were used to detect the expression of the associated genes and proteins. The present study explores the role and mechanism of hBMSCs on the growth of TKI-resistant Ph⁺ ALL. The current study showed that hBMSCs promoted the proliferation of TKI-resistant Ph⁺ ALL. This was shown by the increase in cells in the S+G2-M phase of the cell cycle. It was also found that the expression of cyclins A, C, D1 and E was increased. Apoptosis was inhibited through upregulation of anti-apoptotic genes [B-cell lymphoma-2 (BCL-2) and BCL-extra large] and downregulation of apoptotic genes (BCL-XS, BCL-2-associated X protein, and caspases 3, 7 and 9). Expression of the breakpoint cluster region (BCR)-Abelson murine leukemia viral oncogene homolog 1 (ABL) gene, Wnt5a, and Wnt signaling pathway-associated genes (glycogen synthase kinase-3β, β-catenin, E-cadherin and phosphoinositide 3-kinase) and transcription factors (c-myc, ephrin type-B2, fibroblast growth factor 20 and matrix metalloproteinase 7) was also increased. Furthermore, the expression of drug resistance genes (low-density lipoprotein receptor, multidrug resistance-associated protein and multi-drug resistance gene) was increased and the expression of anti-oncogenes (death-associated protein kinase and interferon regulatory factor-1) was decreased. It was concluded that hBMSCs promote the growth of TKI-resistant Ph⁺ ALL by these aforementioned mechanisms. Therefore, targeting hBMSCs may be a promising approach for preventing the growth of TKI-resistant Ph⁺ ALL.

Targeting Intrinsic and Extrinsic Vulnerabilities for the Treatment of Multiple Myeloma

Multiple myeloma (MM) is a malignant plasma cell disorder, clinically characterized by osteolytic lesions, immunodeficiency, and renal disease. Over the past decade, MM therapy is significantly improved by the introduction of novel therapeutics such as immunomodulatory agents (thalidomide, lenalidomide, and pomalidomide), proteasome inhibitors (bortezomib, carfilzomib, and ixazomib), monoclonal antibodies (daratumumab and elotuzumab), histone deacetylase (HDAC) inhibitors (Panobinostat). The clinical success of these agents has clearly identified vulnerabilities intrinsic to the MM cell, as well as targets that emanate from the tumor microenvironment. Despite these significant improvements, MM remains incurable due to the development of drug resistance. This perspective will discuss more recent strategies which take advantage of multiple targets within the proteome recycling pathway, chromatin remodeling, and disruption of nuclear export. In addition, we will review the development of strategies designed to block opportunistic survival signaling that occurs between the MM cell and the tumor microenvironment including strategies for inhibiting myeloma-induced immune suppression. It has become clear that MM tumors continue to evolve on therapy leading to drug resistance. It will be important to understand the emerging drug resistant mechanisms and additional vulnerabilities that occur due to the development of clinical resistance. J. Cell. Biochem. 118: 15-25, 2017. © 2016 Wiley Periodicals, Inc.

The tumor microenvironment: An irreplaceable element of tumor budding and epithelial-mesenchymal transition-mediated cancer metastasis

Tumor budding occurs at the invasive front of cancer; the tumor cells involved have metastatic and stemness features, indicating a poor prognosis. Tumor budding is partly responsible for cancer metastasis, and its initiation is based on the epithelial-mesenchymal transition (EMT) process. The EMT process involves the conversion of epithelial cells into migratory and invasive cells, and is a profound event in tumorigenesis. The EMT, associated with the formation of cancer stem cells (CSCs) and resistance to therapy, results from a combination of gene mutation, epigenetic regulation, and microenvironmental control. Tumor budding can be taken to represent the EMT in vivo. The EMT process is under the influence of the tumor microenvironment as well as tumor cells themselves. Here, we demonstrate that the tumor microenvironment dominates EMT development and impacts cancer metastasis, as well as promotes CSC formation and mediates drug resistance. In this review, we mainly discuss components of the microenvironment, such as the extracellular matrix (ECM), inflammatory cytokines, metabolic products, and hypoxia, that are involved in and impact on the acquisition of tumor-cell motility and dissemination, the EMT, metastatic tumor-cell formation, tumor budding and CSCs, and cancer metastasis, including subsequent chemo-resistance. From our point of view, the tumor microenvironment now constitutes a promising target for cancer therapy.

Establishment and characterization of gemcitabine-resistant human cholangiocarcinoma cell lines with multidrug resistance and enhanced invasiveness

To establish and characterize the gemcitabine-resistant cholangiocarcinoma (CCA) cell lines, CCA KKU‑M139 and KKU‑M214 cell lines were exposed stepwisely to increasing gemcitabine (GEM). The resultant drug-resistant cell lines, KKU‑M139/GEM and KKU‑M214/GEM, retained the resistant phenotype in drug-free medium at least for 2 months. Sulforhodamine B assay demonstrated that KKU‑M139/GEM and KKU‑M214/GEM were 25.88- and 62.31-fold more resistant to gemcitabine than their parental cells. Both gemcitabine-resistant cell lines were cross-resistant to 5-fluorouracil (5-FU), doxorubicin and paclitaxel indicating their multidrug-resistant nature. Using reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR and western blot analyses, gemcitabine-resistant cells showed upregulation of RRM1 and downregulation of hENT1 and dCK. In relation to multidrug resistance, these cell lines showed upregulation of multidrug resistance protein 1 (MRP1) leading to an increase of drug efflux. Using cell adhesion and Boyden chamber transwell assays, these cell lines also showed higher cell adhesion, migration and invasion capabilities via the activations of protein kinase C (PKC), focal adhesion kinase (FAK), extracellular signal-regulated kinase-1/2 (ERK1/2) and nuclear factor-κB (NF-κB). Higher activity of matrix metalloproteinase-9 (MMP-9) and urokinase plasminogen activator (uPA) was also observed by a gelatin zymography assay and a casein-plasminogen zymography assay. Flow cytometry analysis indicated the G2/M arrest regulated by downregulation of cyclin B1 and cyclin-dependent kinase 1 (Cdk1) resulted in an extended population doubling time. Using Annexin V/propidium iodide staining, evasion of apoptosis via an intrinsic pathway was observed in both cell lines in association with upregulation of Bcl-2 and downregulation of Bax. Interestingly, Fas was additionally downregulated in KKU‑M214/GEM supporting the view of its higher GEM resistant characteristics. These findings indicate that long-term exposure of CCA cell lines to gemcitabine induce not only multidrug resistance but also enhance their invasiveness.

Natural course and biology of CML

Chronic myeloid leukaemia (CML) is a myeloproliferative disorder arising in the haemopoietic stem cell (HSC) compartment. This disease is characterised by a reciprocal t(9;22) chromosomal translocation, resulting in the formation of the Philadelphia (Ph) chromosome containing the BCR-ABL1 gene. As such, diagnosis and monitoring of disease involves detection of BCR-ABL1. It is the BCR-ABL1 protein, in particular its constitutively active tyrosine kinase activity, that forges the pathogenesis of CML. This aberrant kinase signalling activates downstream targets that reprogram the cell to cause uncontrolled proliferation and results in myeloid hyperplasia and 'indolent' symptoms of chronic phase (CP) CML. Without successful intervention, the disease will progress into blast crisis (BC), resembling an acute leukaemia. This advanced disease stage takes on an aggressive phenotype and is almost always fatal. The cell biology of CML is also centred on BCR-ABL1. The presence of BCR-ABL1 can explain virtually all the cellular features of the leukaemia (enhanced cell growth, inhibition of apoptosis, altered cell adhesion, growth factor independence, impaired genomic surveillance and differentiation). This article provides an overview of the clinical and cell biology of CML, and highlights key findings and unanswered questions essential for understanding this disease.

The ability of hyaluronan fragments to reverse the resistance of C6 rat glioma cell line to temozolomide and carmustine

Aim of the study

Hyaluronan (HA) is an extracellular matrix (ECM) polymer that may contribute to the emergence of anti-cancer drug resistance. Attempts to reverse drug resistance using small hyaluronan oligomers (oHA) are being made. The initial reports suggest that the oHA fraction may effectively reverse anti-cancer drug resistance in glioma models. However, the reversal effects of oHA of defined molecular length on glioma cells have not been investigated yet. In this study, we examined HA fragments containing 2 disaccharide units (oHA-2), 5 disaccharide units (oHA-5), and 68 kDa hyaluronan polymer (HA-68k) as agents possibly reversing the resistance of a C6 rat glioma cell line to temozolomide (TMZ) and carmustine (BCNU).

Material and methods

A 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) viability assay was used to assess the cytotoxicity of TMZ and BCNU in the presence or absence of the hyaluronan fragments. By comparing viability of the cells, the reversal effects of HA fragments on TMZ and BCNU resistance in C6 glioma cells were assessed.

Results

We found statistically significant decreases in the viability of cells in the presence of TMZ+oHA-5 as compared to TMZ alone (51.2 ±4.5 vs. 74.2 ±5.8, p = 0.0031), BCNU+o-HA5 as compared to BCNU alone (49.3 ±4.4 vs. 65.6 ±5.7, p = 0.0119), and BCNU+HA-68k as compared to BCNU alone (55.2 ±2.3 vs. 65.6 ±5.7, p = 0.0496).

Conclusions

Conclusions: Hyaluronan oligomers of 5 disaccharide units (oHA-5) significantly reversed the resistance of C6 cells to TMZ and BCNU. The results are only preliminary and a more thorough follow-up investigation is required to assess their actual role.

The impact of tumor stroma on drug response in breast cancer

In the last two decades the breast cancer mortality rate has steadily declined, in part, due to the availability of better treatment options. However, drug resistance still remains a major challenge. Resistance can be an inherent feature of breast cancer cells, but can also arise from the tumor microenvironment. This review aims to focus on the modulatory effect of the tumor microenvironment on the differing response of breast cancer subtypes to targeted drugs and chemotherapy.

Role of integrin alpha4 in drug resistance of leukemia

Chemotherapeutic drug resistance in acute lymphoblastic leukemia (ALL) is a significant problem, resulting in poor responsiveness to first-line treatment or relapse after transient remission. Classical anti-leukemic drugs are non-specific cell cycle poisons; some more modern drugs target oncogenic pathways in leukemia cells, although in ALL these do not play a very significant role. By contrast, the molecular interactions between microenvironment and leukemia cells are often neglected in the design of novel therapies against drug resistant leukemia. It was shown however, that chemotherapy resistance is promoted in part through cell–cell contact of leukemia cells with bone marrow (BM) stromal cells, also called cell adhesion-mediated drug resistance (CAM-DR). Incomplete response to chemotherapy results in persistence of resistant clones with or without detectable minimal residual disease (MRD). Approaches for how to address CAM-DR and MRD remain elusive. Specifically, studies using anti-functional antibodies and genetic models have identified integrin alpha4 as a critical molecule regulating BM homing and active retention of normal and leukemic cells. Pre-clinical evidence has been provided that interference with alpha4-mediated adhesion of ALL cells can sensitize them to chemotherapy and thus facilitate eradication of ALL cells in an MRD setting. To this end, Andreeff and colleagues recently provided evidence of stroma-induced and alpha4-mediated nuclear factor-κB signaling in leukemia cells, disruption of which depletes leukemia cells of strong survival signals. We here review the available evidence supporting the targeting of alpha4 as a novel strategy for treatment of drug resistant leukemia.

Miniaturized pre-clinical cancer models as research and diagnostic tools

Cancer is one of the most common causes of death worldwide. Consequently, important resources are directed towards bettering treatments and outcomes. Cancer is difficult to treat due to its heterogeneity, plasticity and frequent drug resistance. New treatment strategies should strive for personalized approaches. These should target neoplastic and/or activated microenvironmental heterogeneity and plasticity without triggering resistance and spare host cells. In this review, the putative use of increasingly physiologically relevant microfabricated cell-culturing systems intended for drug development is discussed. There are two main reasons for the use of miniaturized systems. First, scaling down model size allows for high control of microenvironmental cues enabling more predictive outcomes. Second, miniaturization reduces reagent consumption, thus facilitating combinatorial approaches with little effort and enables the application of scarce materials, such as patient-derived samples. This review aims to give an overview of the state-of-the-art of such systems while predicting their application in cancer drug development.

Integrin αV modulates the cellular pharmacology of copper and cisplatin by regulating expression of the influx transporter CTR1

The αV integrin is expressed in most cancer cells where it regulates a diverse array of cellular functions essential to the initiation, progression and metastasis of solid tumors. However, little is known about how αV integrin modulates cellular sensitivity to chemotherapeutic agents, particularly the platinum drugs. In this study, we found that down-regulation of αV sensitized human M21 cells to cisplatin (cDDP) through up-regulation of the copper influx transporter CTR1. Cells selected for low αV integrin expression (M21L) were more sensitive to cDDP, accompanied by increase in CTR1 mRNA and CTR1 protein levels, more intracellular cDDP accumulation and cDDP DNA adduct formation. Basal copper (Cu) content, Cu uptake, and Cu cytotoxicity were also increased. Transfection of a luciferase reporter construct containing the hCTR1 promoter sequence revealed an increase of the hCTR1 transcription activity in M21L cells. The basis for the increased hCTR1 transcription was related to an increase in the steady-state level of Sp1, a transcription factor known to drive hCTR1 expression. These results indicate that the αV integrin modulates sensitivity of human cells to the cytotoxic effect of cDDP by regulating expression of the Cu transporter CTR1, and introduce the concept that αV expression is linked to Cu homeostasis.

Mechanisms and insights into drug resistance in cancer

Cancer drug resistance continues to be a major impediment in medical oncology. Clinically, resistance can arise prior to or as a result of cancer therapy. In this review, we discuss different mechanisms adapted by cancerous cells to resist treatment, including alteration in drug transport and metabolism, mutation and amplification of drug targets, as well as genetic rewiring which can lead to impaired apoptosis. Tumor heterogeneity may also contribute to resistance, where small subpopulations of cells may acquire or stochastically already possess some of the features enabling them to emerge under selective drug pressure. Making the problem even more challenging, some of these resistance pathways lead to multidrug resistance, generating an even more difficult clinical problem to overcome. We provide examples of these mechanisms and some insights into how understanding these processes can influence the next generation of cancer therapies.

Microenvironmental protection of CML stem and progenitor cells from tyrosine kinase inhibitors through N-cadherin and Wnt-β-catenin signaling

Tyrosine kinase inhibitors (TKIs) are highly effective in treatment of chronic myeloid leukemia (CML) but do not eliminate leukemia stem cells (LSCs), which remain a potential source of relapse. TKI treatment effectively inhibits BCR-ABL kinase activity in CML LSCs, suggesting that additional kinase-independent mechanisms contribute to LSC preservation. We investigated whether signals from the bone marrow (BM) microenvironment protect CML LSCs from TKI treatment. Coculture with human BM mesenchymal stromal cells (MSCs) significantly inhibited apoptosis and preserved CML stem/progenitor cells following TKI exposure, maintaining colony-forming ability and engraftment potential in immunodeficient mice. We found that the N-cadherin receptor plays an important role in MSC-mediated protection of CML progenitors from TKI. N-cadherin-mediated adhesion to MSCs was associated with increased cytoplasmic N-cadherin-β-catenin complex formation as well as enhanced β-catenin nuclear translocation and transcriptional activity. Increased exogenous Wnt-mediated β-catenin signaling played an important role in MSC-mediated protection of CML progenitors from TKI treatment. Our results reveal a close interplay between N-cadherin and the Wnt-β-catenin pathway in protecting CML LSCs during TKI treatment. Importantly, these results reveal novel mechanisms of resistance of CML LSCs to TKI treatment and suggest new targets for treatment designed to eradicate residual LSCs in CML patients.

The β6-integrin-ERK/MAP kinase pathway contributes to chemo resistance in colon cancer

5-Fluorouracil (5-FU) is the most widely used chemo drug for the treatment of colon cancer. However, a sub-population of colon cancer patients do not respond to 5-FU and this treatment does not provide survival benefit due to chemo resistance. The mechanisms involved in 5-FU resistance are not fully understood and multiple factors have been involved in the sensitivity of cancer cells to 5-FU. We previously reported that β6-integrin plays an important role in invasion, metastasis and degradation of extracellular matrix of colon cancer. In this study, we investigated whether β6-integrin is associated with chemo resistance in colon cancer. We found that over-expression of β6-integrin protected SW480 and HT-29 colon cancer cells from 5-FU-induced growth inhibition and apoptosis, which were accompanied by changes in cytochrome C released from the mitochondria and activity of caspase-3 and caspase-9. Moreover, β6-integrin resulted in up-regulation of Bcl-2 and down-regulation of Bax. We also found that β6-integrin induced 5-FU resistance through the ERK/MAP kinase pathway and the β6-ERK2 direct binding. The results indicate β6-integrin might be a novel therapeutic target in colon cancer therapy.

Issues to be considered when studying cancer in vitro

Various cancer treatment approaches have shown promising results when tested preclinically. The results of clinical trials, however, are often disappointing. While searching for the reasons responsible for their failures, the relevance of experimental and preclinical models has to be taken into account. Possible factors that should be considered, including cell modifications during in vitro cultivation, lack of both the relevant interactions and the structural context in vitro have been summarized in the present review.

Overexpression of MDR1 and survivin, and decreased Bim expression mediate multidrug-resistance in multiple myeloma cells

Multidrug resistance represents a major obstacle for the chemotherapy of a wide variety of human tumors. To investigate the underlying mechanisms associated with resistance to anti-cancer drugs, we established anti-cancer drug-resistant multiple myeloma (MM) cell lines RPMI8226/ADM, RPMI8226/VCR, RPMI8226/DEX, and RPMI8226/L-PAM, the 50% inhibitory concentration values of which were 77-, 58-, 79-, and 30-fold higher than their parental cell lines, respectively. The resistant cell lines overexpressed MDR1 and survivin, or showed decreased Bim expression. These results indicated that regulating these factors with inhibitors might be a viable approach to increasing the susceptibility of quiescent MM cells to chemotherapy.

The impact of cell-cell contact, E-cadherin and EGF receptor on the cellular radiosensitivity of A431 cancer cells

Cell-cell contact is thought to be critically involved in mechanisms leading to radioresistance. Here, we assessed the influence of confluent compared to subconfluent cell culture conditions and the radiosensitizing ability of E-cadherin inhibition alone or in combination with C225-mediated EGFR inhibition in human squamous cell carcinoma cells. Our results show higher radioresistance under subconfluent growth conditions than under confluency. Delayed plating only resulted in higher radiation survival in confluently growing cells. While E-cadherin depletion significantly reduced basal clonogenic survival, increased the rate of apoptosis, and diminished cell adhesion, the cellular radiosensitivity remained unchanged under both subconfluent and confluent conditions. C225 decreased basal cell survival but failed to modify radiation survival. Additional treatment of E-cadherin knockdown cell cultures with C225 did not further reduce basal cell survival or lead to radiosensitization. Interestingly, E-cadherin silencing in 3D cell cultures did not alter radiosensitivity. Our data indicate that cell-cell contact and E-cadherin are not prominently involved in the regulation of radioresistance of human squamous cell carcinoma cells. In addition, no regulatory interaction between E-cadherin and EGFR in the radiation response was observed.

The mesenchymal tumor microenvironment: a drug-resistant niche

Drug and radiation resistance represent a challenge for most anticancer therapies. Diverse experimental approaches have provided evidence that the tumor-associated microenvironment constitutes both a protective shell that impedes drug or radiation access and a permissive or promotive microenvironment that encourages a nurturing cancer (i.e., cancer stem cell) niche where tumor cells overcome treatment- and cancer-induced stresses. Better understanding of the effects of the tumor microenvironment on cancer cells before, during and immediately after chemo- or radiotherapy is imperative to design new therapies aimed at targeting this tumor-protective niche. This review summarizes some of the known mesenchymal stromal effects that account for drug resistance, the main signal transduction pathways associated with this resistance and the therapeutic efforts directed to increase the success of current therapies. Special emphasis is given to environment-mediated drug resistance in general and to cell adhesion-mediated drug resistance in particular.

The tumor microenvironment is a dominant force in multidrug resistance

The emergence of clinical drug resistance is still one of the most challenging factors in cancer treatment effectiveness. Until more recently, the assumption has been that random genetic lesions are sufficient to explain the progression of malignancy and escape from chemotherapy. Here we propose an additional perspective, one in which the tumor cells despite the malignant genome could find a microenvironment either within the tumor or as a dormant cell to remain polar and blend into an organized context. Targeting this dynamic interplay could be considered a new avenue to prevent therapeutic resistance, and may even provide a promising effective cancer treatment.

Dependence of acute myeloid leukemia on adhesion within the bone marrow microenvironment

Acute myeloid leukemia (AML) cells home to the endosteal region of the bone marrow. They interact with bone marrow stromal components including extracellular matrix proteins, glycosaminoglycans, and stromal cells, by which they derive proliferative and growth inhibitory signals. Furthermore, adhesion to marrow stroma confers chemotherapy drug resistance and thereby promotes leukemia survival. A subpopulation of the leukemic blasts, known as leukemia stem cells, that are capable of propagating the leukemia, remain sheltered in the bone marrow microenvironment, exhibit resistance to chemotherapy, and serve as the origin of relapse after a variable period of remission. Detachment of these cells from the bone marrow in combination with chemotherapy may improve the outcome of therapy for AML.

Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR inhibitors: rationale and importance to inhibiting these pathways in human health

The Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR cascades are often activated by genetic alterations in upstream signaling molecules such as receptor tyrosine kinases (RTK). Integral components of these pathways, Ras, B-Raf, PI3K, and PTEN are also activated/inactivated by mutations. These pathways have profound effects on proliferative, apoptotic and differentiation pathways. Dysregulation of these pathways can contribute to chemotherapeutic drug resistance, proliferation of cancer initiating cells (CICs) and premature aging. This review will evaluate more recently described potential uses of MEK, PI3K, Akt and mTOR inhibitors in the proliferation of malignant cells, suppression of CICs, cellular senescence and prevention of aging. Ras/Raf/MEK/ERK and Ras/PI3K/PTEN/Akt/mTOR pathways play key roles in the regulation of normal and malignant cell growth. Inhibitors targeting these pathways have many potential uses from suppression of cancer, proliferative diseases as well as aging.

Roles of the Ras/Raf/MEK/ERK pathway in leukemia therapy

The Ras/Raf/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway is often implicated in sensitivity and resistance to leukemia therapy. Dysregulated signaling through the Ras/Raf/MEK/ERK pathway is often the result of genetic alterations in critical components in this pathway as well as mutations at upstream growth factor receptors. Unrestricted leukemia proliferation and decreased sensitivity to apoptotic-inducing agents and chemoresistance are typically associated with activation of pro-survival pathways. Mutations in this pathway and upstream signaling molecules can alter sensitivity to small molecule inhibitors targeting components of this cascade as well as to inhibitors targeting other key pathways (for example, phosphatidylinositol 3 kinase (PI3K)/phosphatase and tensin homologue deleted on chromosome 10 (PTEN)/Akt/mammalian target of rapamycin (mTOR)) activated in leukemia. Similarly, PI3K mutations can result in resistance to inhibitors targeting the Ras/Raf/MEK/ERK pathway, indicating important interaction points between the pathways (cross-talk). Furthermore, the Ras/Raf/MEK/ERK pathway can be activated by chemotherapeutic drugs commonly used in leukemia therapy. This review discusses the mechanisms by which abnormal expression of the Ras/Raf/MEK/ERK pathway can contribute to drug resistance as well as resistance to targeted leukemia therapy. Controlling the expression of this pathway could improve leukemia therapy and ameliorate human health.

Environmental-mediated drug resistance: a target for multiple myeloma therapy

Multiple myeloma is an incurable malignancy of mature clonal B cells. The refractory nature of this disease has long been attributed to the acquisition of drug resistance. Traditionally, mechanisms of drug resistance have been defined by genetic, acquired changes in the expression or function of specific genes products. However, over the past 10 years a large body of evidence has emerged demonstrating that in addition to mechanisms of drug resistance intrinsic to the cancer cell, there exist dynamic, de novo mechanisms coordinated by the tumor microenvironment resulting in a environmental-mediated drug resistance (EM-DR). Within this review we will provide an overview of some of these mechanisms of drug resistance and how they contribute to minimal residual disease and subsequent treatment failure. By understanding mechanisms of EM-DR, therapeutic targets can be identified and interventions designed to reduce minimal residual disease and improve clinical outcomes.

Targeting the translational apparatus to improve leukemia therapy: roles of the PI3K/PTEN/Akt/mTOR pathway

It has become apparent that regulation of protein translation is an important determinant in controlling cell growth and leukemic transformation. The phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homologue deleted on chromosome ten (PTEN)/Akt/mammalian target of rapamycin (mTOR) pathway is often implicated in sensitivity and resistance to therapy. Dysregulated signaling through the PI3K/PTEN/Akt/mTOR pathway is often the result of genetic alterations in critical components in this pathway as well as mutations at upstream growth factor receptors. Furthermore, this pathway is activated by autocrine transformation mechanisms. PTEN is a critical tumor suppressor gene and its dysregulation results in the activation of Akt. PTEN is often mutated, silenced and is often haploinsufficient. The mTOR complex1 (mTORC1) regulates the assembly of the eukaryotic initiation factor4F complex, which is critical for the translation of mRNAs that are important for cell growth, prevention of apoptosis and transformation. These mRNAs have long 5'-untranslated regions that are G+C rich, rendering them difficult to translate. Elevated mTORC1 activity promotes the translation of these mRNAs via the phosphorylation of 4E-BP1. mTORC1 is a target of rapamycin and novel active-site inhibitors that directly target the TOR kinase activity. Although rapamycin and novel rapalogs are usually cytostatic and not cytotoxic for leukemic cells, novel inhibitors that target the kinase activities of PI3K and mTOR may prove more effective for leukemia therapy.

The bone marrow microenvironment as a sanctuary for minimal residual disease in CML

Bcr-abl kinase inhibitors have provided proof of principal that targeted therapy holds great promise for the treatment of cancer. However, despite the success of these agents in treating chronic myelogenous leukemia (CML), the majority of patients continue to present with minimal residual disease contained within the bone marrow microenvironment. These clinical observations suggest that the bone marrow microenvironment may provide survival signals that contribute to the failure to eliminate minimal residual disease. The bone marrow microenvironment is comprised of multiple sub-domains which vary in cellular composition and gradients of soluble factors and matrix composition. Experimental evidence indicate that exposure of tumor cells to either bone marrow derived soluble factors or the extracellular matrix can confer a multi-drug resistance phenotype. Together, these data indicate that targeting such pathways may be a viable approach for increasing the efficacy of chemotherapy. Moreover, we propose that personalized medicine must go beyond understanding predictive models inherent to tumors but rather build predictive models that consider diversity in response due to interactions with the tumor microenvironment. Although review will focus on CML, understanding the contribution of the bone marrow microenvironment could contribute to rationale combination therapy in other types of leukemia, multiple myeloma and solid tumors which metastasize to the bone.

IGF-1 suppresses Bim expression in multiple myeloma via epigenetic and posttranslational mechanisms

Insulin-like growth factor-1 (IGF-1) is an important growth and survival factor in multiple myeloma (MM). Here, we demonstrate that IGF-1 induces significant down-regulation of the proapoptotic BH3-only protein Bim in MM cells. Reduced Bim levels by RNA interference (RNAi) protected cells from drug-induced cell death. The IGF-1-mediated down-regulation of Bim was the result of (1) reduced transcription by activation of the Akt pathway and inactivation of the transcription factor FoxO3a, (2) increased proteasome-mediated degradation of the Bim extra-long protein by activation of the mitogen-activated protein kinase pathway, and (3) epigenetic regulation of both the Bim and the FoxO3a promoter. Treatment of cells with the histone deacetylase inhibitor LBH589 resulted in a clear up-regulation in the expression of Bim. Furthermore, the methylation inhibitor 5-aza-2'deoxycytidine (decitabine) significantly increased the effects of LBH589. On IGF-1 treatment, the Bim promoter region was found to be unmethylated, whereas chromatin immunoprecipitation analysis of the IGF-1-treated cells showed both a reduced histone H3 tail Lys9 (H3K9) acetylation and an increased H3K9 dimethylation, which contributed actively to its silencing. These data identify a new mechanism in the IGF-1-dependent survival of MM cells and emphasize the need for IGF-1-targeted drug therapy.

Bim-targeted cancer therapy: a link between drug action and underlying molecular changes

In the past few years, the pro-apoptotic molecule Bim has attracted increasing attention as a plausible target for tumor therapy. A variety of normal and pathological systems regulated by Bim, dependent on cell type, apoptotic stimulation, and chemotherapeutic agents, have been documented. Bim promotes anoikis of many tumor cells, such as lung cancer, breast cancer, osteosarcoma, and melanoma. Various chemotherapeutic agents use Bim as a mediating executioner of cell death. Hence, Bim suppression supports metastasis and chemoresistance. Imatinib, gefitinib, bortezomib, and Bim protein itself are spotlighted as current and future Bim-targeting therapeutic agents. The potential benefits of Bim-targeted therapies are selectivity of treatment for tumor cells and reduction in tumor-associated phenomena such as chemoresistance and metastasis. Thus, Bim-targeting therapies may provide more effective and unique tumor management modalities in future. This review article discusses all these issues.

Neuropilin-1 antagonism in human carcinoma cells inhibits migration and enhances chemosensitivity

BACKGROUND

Neuropilin-1 (NRP1) is a non-tyrosine kinase receptor for vascular endothelial growth factor (VEGF) recently implicated in tumour functions.

METHODS

In this study we used a specific antagonist of VEGF binding to the NRP1 b1 domain, EG3287, to investigate the functional roles of NRP1 in human carcinoma cell lines, non-small-cell lung A549, kidney ACHN, and prostate DU145 cells expressing NRP1, and the underlying mechanisms involved.

RESULTS

EG3287 potently displaced the specific binding of VEGF to NRP1 in carcinoma cell lines and significantly inhibited the migration of A549 and ACHN cells. Neuropilin-1 downregulation by siRNA also decreased cell migration. EG3287 reduced the adhesion of A549 and ACHN cells to extracellular matrix (ECM), and enhanced the anti-adhesive effects of a beta1-integrin function-blocking antibody. EG3287 increased the cytotoxic effects of the chemotherapeutic agents 5-FU, paclitaxel, or cisplatin on A549 and DU145 cells, through inhibition of integrin-dependent cell interaction with the ECM.

CONCLUSIONS

These findings indicate that NRP1 is important for tumour cell migration and adhesion, and that NRP1 antagonism enhances chemosensitivity, at least in part, by interfering with integrin-dependent survival pathways. A major implication of this study is that therapeutic strategies targeting NRP1 in tumour cells may be particularly useful in combination with other drugs for combating tumour survival, growth, and metastatic spread independently of an antiangiogenic effect of blocking NRP1.

Cell adhesion molecules: role and clinical significance in cancer

There is a growing body of evidence suggesting that alterations in the adhesion properties of neoplastic cells endow them with an invasive and migratory phenotype. Indeed, changes in the expression or function of cell adhesion molecules have been implicated in all steps of tumor progression, including detachment of tumor cells from the primary site, intravasation into the blood stream, extravasation into distant target organs, and formation of the secondary lesions. This review presents recent data regarding the role of cell adhesion molecules in tumor development and progress with concern to their clinical exploitation as potential biomarkers in neoplastic diseases.