Upregulation of stem cell genes in multidrug resistant K562 leukemia cells

NK3.3-Derived Extracellular Vesicles Penetrate and Selectively Kill Treatment-Resistant Tumor Cells

Cancer treatments often become ineffective due to the development of tumor resistance, leading to metastasis and relapse. Treatments may also fail because of their inability to access cells deep within the tumor tissue. When this occurs, new therapeutic agents are needed. We previously reported that NK3.3EVs, extracellular vesicles (EVs) derived from the normal human natural killer (NK) cell line, NK3.3, have strong cytotoxic activity against leukemia and breast cancer cell lines, without harming normal cells. Here, we used a three-dimensional (3D) MCF7 breast cancer mammosphere model to reproduce a more physiological environment that NK3.3EVs would encounter in vivo. NK3.3EVs penetrated MCF7 mammospheres, inducing death by apoptosis. We generated an imatinib-resistant K562 chronic myeloid leukemia (CML) cell line to investigate whether NK3.3EVs were able to kill tumor cells resistant to front-line chemotherapy. NK3.3EVs were even more cytotoxic to imatinib-resistant cells than parental cells, inducing apoptosis via caspase-3/-7 activation. The small population of cancer stem cells (CSCs) within tumors also contributes to therapeutic resistance. NK3.3EVs reduced the CSC-like CD34+/CD38- subpopulation in imatinib-resistant and parental K562 cultures and decreased CSC-associated expression of tumor-promoting genes. Our results provide strong evidence that NK3.3EVs may be a potential new immunotherapeutic agent for difficult-to-treat cancers.

Addressing Drug Resistance in Cancer with Macromolecular Chemotherapeutic Agents

Drug resistance to chemotherapeutics is a recurrent issue plaguing many cancer treatment regimens. To circumvent resistance issues, we have designed a new class of macromolecules as self-contained chemotherapeutic agents. The macromolecular chemotherapeutic agents readily self-assemble into well-defined nanoparticles and show excellent activity in vitro against multiple cancer cell lines. These cationic polymers function by selectively binding and lysing cancer cell membranes. As a consequence of this mechanism, they exhibit significant potency against drug-resistant cancer cells and cancer stem cells, prevent cancer cell migration, and do not induce resistance onset following multiple treatment passages. Concurrent experiments with the small-molecule chemotherapeutic, doxorubicin, show aggressive resistance onset in cancer cells, a lack of efficacy against drug-resistant cancer cell lines, and a failure to prevent cancer cell migration. Additionally, the polymers showed anticancer efficacy in a hepatocellular carcinoma patient derived xenograft mouse model. Overall, these results demonstrate a new approach to designing anticancer therapeutics utilizing macromolecular compounds.

Transcriptional profiling of NCI/ADR-RES cells unveils a complex network of signaling pathways and molecular mechanisms of drug resistance

Background

Ovarian cancer has the highest mortality rate among all the gynecological cancers. This is mostly due to the resistance of ovarian cancer to current chemotherapy regimens. Therefore, it is of crucial importance to identify the molecular mechanisms associated with chemoresistance.

Methods

NCI/ADR-RES is a multidrug-resistant cell line that is a model for the study of drug resistance in ovarian cancer. We carried out a microarray-derived transcriptional profiling analysis of NCI/ADR-RES to identify differentially expressed genes relative to its parental OVCAR-8.

Results

Gene-expression profiling has allowed the identification of genes and pathways that may be important for the development of drug resistance in ovarian cancer. The NCI/ADR-RES cell line has differential expression of genes involved in drug extrusion, inactivation, and efficacy, as well as genes involved in the architectural and functional reorganization of the extracellular matrix. These genes are controlled through different signaling pathways, including MAPK–Akt, Wnt, and Notch.

Conclusion

Our findings highlight the importance of using orthogonal therapies that target completely independent pathways to overcome mechanisms of resistance to both classical chemotherapeutic agents and molecularly targeted drugs.

Gemcitabine-(5'-phosphoramidate)-[anti-IGF-1R]: molecular design, synthetic organic chemistry reactions, and antineoplastic cytotoxic potency in populations of pulmonary adenocarcinoma (A549)

One molecular-based approach that increases potency and reduces dose-limited sequela is the implementation of selective 'targeted' delivery strategies for conventional small molecular weight chemotherapeutic agents. Descriptions of the molecular design and organic chemistry reactions that are applicable for synthesis of covalent gemcitabine-monophosphate immunochemotherapeutics have to date not been reported. The covalent immunopharmaceutical, gemcitabine-(5'-phosphoramidate)-[anti-IGF-1R] was synthesized by reacting gemcitabine with a carbodiimide reagent to form a gemcitabine carbodiimide phosphate ester intermediate which was subsequently reacted with imidazole to create amine-reactive gemcitabine-(5'-phosphorylimidazolide) intermediate. Monoclonal anti-IGF-1R immunoglobulin was combined with gemcitabine-(5'-phosphorylimidazolide) resulting in the synthetic formation of gemcitabine-(5'-phosphoramidate)-[anti-IGF-1R]. The gemcitabine molar incorporation index for gemcitabine-(5'-phosphoramidate)-[anti-IGF-R1] was 2.67:1. Cytotoxicity Analysis - dramatic increases in antineoplastic cytotoxicity were observed at and between the gemcitabine-equivalent concentrations of 10-9  M and 10-7  M where lethal cancer cell death increased from 0.0% to a 93.1% maximum (100.% to 6.93% residual survival), respectively. Advantages of the organic chemistry reactions in the multistage synthesis scheme for gemcitabine-(5'-phosphoramidate)-[anti-IGF-1R] include their capacity to achieve high chemotherapeutic molar incorporation ratios; option of producing an amine-reactive chemotherapeutic intermediate that can be preserved for future synthesis applications; and non-dedicated organic chemistry reaction scheme that allows substitutions of either or both therapeutic moieties, and molecular delivery platforms.

Benzene Exposure Alters Expression of Enzymes Involved in Fatty Acid β-Oxidation in Male C3H/He Mice

Benzene is a well-known hematotoxic carcinogen that can cause leukemia and a variety of blood disorders. Our previous study indicated that benzene disturbs levels of metabolites in the fatty acid β-oxidation (FAO) pathway, which is crucial for the maintenance and function of hematopoietic and leukemic cells. The present research aims to investigate the effects of benzene on changes in the expression of key enzymes in the FAO pathway in male C3H/He mice. Results showed that benzene exposure caused reduced peripheral white blood cell (WBC), red blood cell (RBC), platelet (Pit) counts, and hemoglobin (Hgb) concentration. Investigation of the effects of benzene on the expression of FA transport- and β-oxidation-related enzymes showed that expression of proteins Cpt1a, Crat, Acaa2, Aldh1l2, Acadvl, Crot, Echs1, and Hadha was significantly increased. The ATP levels and mitochondrial membrane potential decreased in mice exposed to benzene. Meanwhile, reactive oxygen species (ROS), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) levels were significantly increased in the benzene group. Our results indicate that benzene induces increased expression of FA transport and β-oxidation enzymes, mitochondrial dysfunction, and oxidative stress, which may play a role in benzene-induced hematotoxicity.

HOXB4 knockdown reverses multidrug resistance of human myelogenous leukemia K562/ADM cells by downregulating P-gp, MRP1 and BCRP expression via PI3K/Akt signaling pathway

Multidrug resistance (MDR) plays a pivotal role in human chronic myelogenous leukemia (CML) chemotherapy failure. MDR is mainly associated with the overexpression of drug efflux transporters of the ATP-binding cassette (ABC) proteins. Phosphoinositide 3-kinase (PI3K)/Akt signaling cascade is involved in the MDR phenotype and is correlated with multidrug resistance 1 (MDR1)/P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP) expression in many human malignancies. Homeobox (HOX) B4, a member of the HOX gene family, has been reported to be correlated with occurrence, development, poor prognosis and drug resistance of human leukemia. In the present study, HOXB4 expression was analyzed in K562 cell line and its MDR subline K562/ADM. Compared with K562 cells, drug-resistant K562/ADM cells demonstrated evidently higher HOXB4 expression. In addition, we firstly investigated the reversal effect of HOXB4 deletion on K562/ADM cells and the underlying mechanism. The Cell Counting kit-8 (CCK-8) and flow cytometry assays showed that knockdown of HOXB4 enhanced chemosensitivity and decreased drug efflux in K562/ADM cells. Moreover, HOXB4 knockout led to downregulation of P-gp, MRP1 and BCRP expression and PI3K/Akt signaling activity, suggesting that repression of HOXB4 might be a key point to reverse MDR of K562/ADM cells.

Dexamethasone-(C21-phosphoramide)-[anti-EGFR]: molecular design, synthetic organic chemistry reactions, and antineoplastic cytotoxic potency against pulmonary adenocarcinoma (A549)

PURPOSE

Corticosteroids are effective in the management of a variety of disease states, such as several forms of neoplasia (leukemia and lymphoma), autoimmune conditions, and severe inflammatory responses. Molecular strategies that selectively "target" delivery of corticosteroids minimize or prevents large amounts of the pharmaceutical moiety from passively diffusing into normal healthy cell populations residing within tissues and organ systems.

MATERIALS AND METHODS

The covalent immunopharmaceutical, dexamethasone-(C21-phosphoramide)-[anti-EGFR] was synthesized by reacting dexamethasone-21-monophosphate with a carbodiimide reagent to form a dexamethasone phosphate carbodiimide ester that was subsequently reacted with imidazole to create an amine-reactive dexamethasone-(C21-phosphorylimidazolide) intermediate. Monoclonal anti-EGFR immunoglobulin was combined with the amine-reactive dexamethasone-(C21-phosphorylimidazolide) intermediate, resulting in the synthesis of the covalent immunopharmaceutical, dexamethasone-(C21-phosphoramide)-[anti-EGFR]. Following spectrophotometric analysis and validation of retained epidermal growth factor receptor type 1 (EGFR)-binding avidity by cell-ELISA, the selective anti-neoplasic cytotoxic potency of dexamethasone-(C21-phosphoramide)-[anti-EGFR] was established by MTT-based vitality stain methodology using adherent monolayer populations of human pulmonary adenocarcinoma (A549) known to overexpress the tropic membrane receptors EGFR and insulin-like growth factor receptor type 1.

RESULTS

The dexamethasone:IgG molar-incorporation-index for dexamethasone-(C21-phosphoramide)-[anti-EGFR] was 6.95:1 following exhaustive serial microfiltration. Cytotoxicity analysis: covalent bonding of dexamethasone to monoclonal anti-EGFR immunoglobulin did not significantly modify the ex vivo antineoplastic cytotoxicity of dexamethasone against pulmonary adenocarcinoma at and between the standardized dexamethasone equivalent concentrations of 10(-9) M and 10(-5) M. Rapid increases in antineoplastic cytotoxicity were observed at and between the dexamethasone equivalent concentrations of 10(-9) M and 10(-7) M where cancer cell death increased from 7.7% to a maximum of 64.9% (92.3%-35.1% residual survival), respectively, which closely paralleled values for "free" noncovalently bound dexamethasone.

DISCUSSION

Organic chemistry reaction regimens were optimized to develop a multiphase synthesis regimen for dexamethasone-(C21-phosphoramide)-[anti-EGFR]. Attributes of dexamethasone-(C21-phosphoramide)-[anti-EGFR] include a high dexamethasone molar incorporation-index, lack of extraneous chemical group introduction, retained EGFR-binding avidity ("targeted" delivery properties), and potential to enhance long-term pharmaceutical moiety effectiveness.

Elevated expression of ABCB5 in ocular surface squamous neoplasia

ATP-binding cassette subfamily B member 5 (ABCB5) is a new member of the ATP-binding cassette superfamily and has been reported as a novel marker for limbal stem cell (LSC), which is essential for corneal homeostasis. ABCB5 expression has also been discovered in the subpopulation of several cancer cells containing the cancer stem cell (CSC). However, the pathogenetic relationship between LSC and CSC and ABCB5 in the ocular surface squamous neoplasm (OSSN) is still entirely unknown. To improve understanding of the role of ABCB5 in OSSN, we performed immunohistochemistry for ABCB5 in nine OSSN case series. While expression of ABCB5 is restricted to the basal epithelial cell layer in the normal limbus, elevated expressions of ABCB5 were clearly observed in all OSSN, and there was some breadth in the range of intensity of ABCB5 expression. Interestingly, the elevated expression patterns of ABCB5 in OSSN could be classified in three categories: perivascular, marginal and diffuse patterns. Our findings demonstrated for the first time that the expression of ABCB5 was upregulated in OSSN and that elevated expression of ABCB5 may be involved in the pathogenesis of OSSN.

Fludarabine- (C2-methylhydroxyphosphoramide)- [anti-IGF-1R]: Synthesis and Selectively "Targeted"Anti-Neoplastic Cytotoxicity against Pulmonary Adenocarcinoma (A549)

INTRODUCTION

Many if not most conventional small molecular weight chemotherapeutics are highly potent against many forms of neoplastic disease. Unfortunately, majority of an administered dose unintentionally diffuses passively into normal tissues and healthy organ systems following intravenous administration. One strategy for both increasing potency and reducing dose-limited sequela is the selective "targeted" delivery of conventional chemotherapeutic agents.

MATERIALS AND METHODS

The fludarabine-(C₂- methylhydroxyphosphoramide)-[anti-IGF-1R] was synthesized by initially reacting fludarabine with a carbodiimide to form a fludarabine carbodiimide phosphate ester intermediate that was subsequently reacted with imidazole to create an amine-reactive fludarabine- (C₂-phosphorylimidazolide) intermediate. Monoclonal anti-IGF-1R immunoglobulin was combined with the amine-reactive fludarabine- (C₂-phosphorylimidazolide) intermediate resulting in the synthesis of covalent fludarabine-(C₂-methylhydroxyphosphoramide)- [anti-IGF-1R] immunochemotherapeutic. Residual fludarabine and un-reacted reagents were removed by serial microfiltration (MWCO 10,000) and monitored by analytical-scale HP-TLC. Retained IGF-1R binding-avidity of fludarabine-(C₂- methylhydroxyphosphoramide)-[anti-IGF-1R] was established by cell-ELISA using pulmonary adenocarcinoma cell (A549) which over-expresses IGF-1R and EGFR. Anti-neoplastic cytotoxic potency of fludarabine-(C₂-methylhydroxyphosphoramide)-[anti- IGF-1R] was determined against pulmonary adenocarcinoma (A549) using an MTT-based vitality stain methodology.

RESULTS

The fludarabine molar-incorporation-index for fludarabine- (C₂-methylhydroxyphosphoramide)-[anti-IGF-R1] was 3.67:1 while non-covalently bound fludarabine was not detected by analytical scale HP-TLC following serial micro-filtration. Size-separation fludarabine-(C₂-methylhydroxyphosphoramide)-[anti- IGF-1R] by SDS-PAGE with chemo luminescent autoradiography detected only a single 150-kDa band. Cell-ELISA of fludarabine- (C₂-methylhydroxyphosphoramide)-[anti-IGF-1R] measuring total immunoglobulin bound to exterior surface membranes of pulmonary adenocarcinoma (A549) increased with elevations in immunoglobulin-equivalent concentrations of the covalent fludarabine immunochemotherapeutic. Between the fludarabine-equivalent concentrations of 10^-10 M and 10^-5 M both fludarabine-(C₂- methylhydroxyphosphoramide)-[anti-IGF-1R] and fludarabine had ex-vivo anti-neoplastic cytotoxic potency levels that increased rapidly between the fludarabine-equivalent concentrations of 10^-6 M and 10^-5 M where cancer cell death percentages increased from 24.4% to a maximum of 94.7% respectively.

CONCLUSION

The molecular design and organic chemistry reaction schemes were developed for synthesizing fludarabine-(C₂- methylhydroxyphosphoramide)-[anti-IGF-1R] which possessed both properties of selective "targeted" delivery and anti-neoplastic cytotoxic potency equivalent to fludarabine chemotherapeutic.

Role of drug transport and metabolism in the chemoresistance of acute myeloid leukemia

Acute myeloid leukemia is a clonal but heterogeneous disease differing in molecular pathogenesis, clinical features and response to chemotherapy. This latter frequently consists of a combination of cytarabine and anthracyclines, although etoposide, demethylating agents, and other drugs are also used. Unfortunately, chemoresistance is a common and serious problem. Multiple mechanisms account for impaired effectiveness of drugs and reduced levels of active agents in target cells. The latter can be due to lower drug uptake, increased export or decreased intracellular proportion of active/inactive agent due to changes in the expression/function of enzymes responsible for the activation of pro-drugs and the inactivation of active agents. Characterization of the "resistome", or profile of expressed genes accounting for multi-drug resistance (MDR) phenotype, would permit to predict the lack of response to chemotherapy and would help in the selection of the best pharmacological regime for each patient and moment, and to develop strategies of chemosensitization.

Changes in gene expression profile in two multidrug resistant cell lines derived from a same drug sensitive cell line

Resistance to chemotherapy is one of the most relevant aspects of treatment failure in cancer. Cell lines are used as models to study resistance. We analyzed the transcriptional profile of two multidrug resistant (MDR) cell lines (Lucena 1 and FEPS) derived from the same drug-sensitive cell K562. Microarray data identified 130 differentially expressed genes (DEG) between K562 vs. Lucena 1, 1932 between K562 vs. FEPS, and 1211 between Lucena 1 versus FEPS. The NOTCH pathway was affected in FEPS with overexpression of NOTCH2 and HEY1. The highly overexpressed gene in MDR cell lines was ABCB1, and both presented the ABCB1 promoter unmethylated.

The clinical relevance and prognostic significance of adenosine triphosphate ATP-binding cassette (ABCB5) and multidrug resistance (MDR1) genes expression in acute leukemia: an Egyptian study

AIM

Multidrug resistance (MDR1) represents a major obstacle in the chemotherapeutic treatment of acute leukemia (AL). Adenosine triphosphate ATP-binding cassette (ABCB5) and MDR1 genes are integral membrane proteins belonging to ATP-binding cassette transporters superfamily.

PURPOSE

The present work aimed to investigate the impact of ABCB5 and MDR1 genes expression on the response to chemotherapy in a cohort of Egyptian AL patients. The study included 90 patients: 53 AML cases and 37 ALL cases in addition to 20 healthy volunteers as controls.

METHODS

Quantitative assessment of MDR1 and ABCB5 genes expression was performed by quantitative real-time polymerase chain reaction. Additional prognostic molecular markers were determined as internal tandem duplications of the FLT3 gene (FLT3-ITD) and nucleophosmin gene mutation (NPM1) for AML cases, and mbcr-abl fusion transcript for B-ALL cases.

RESULTS

In AML patients, ABCB5 and MDR1 expression levels did not differ significantly between de novo and relapsed cases and did not correlate with the overall survival or disease-free survival. AML patients were stratified according to the studied genetic markers, and complete remission rate was found to be more prominent in patients having low expression of MDR1 and ABCB5 genes together with mutated NPM1 gene. In ALL patients, ABCB5 gene expression level was significantly higher in relapsed cases and MDR1 gene expression was significantly higher in patients with resistant disease.

CONCLUSION

In conclusion, the results obtained by the current study provide additional evidence of the role played by these genes as predictive factors for resistance of leukemic cells to chemotherapy and hence treatment outcome.

Genomic analysis of drug resistant gastric cancer cell lines by combining mRNA and microRNA expression profiling

Understanding the mechanism underlying multidrug resistance and identifying effective targets that can overcome it is of critical importance. In this study, mRNA and miRNA expression profiling of the drug resistant sublines, SGC7901/VCR and SGC7901/ADR, and their parental gastric cancer cell line SGC7901 were performed. A significant number of genes and a limited subset of miRNAs were commonly dysregulated, which were further validated using qRT-PCR. GO and KEGG pathway analyses of the commonly dysregulated genes indicated that the MAPK signalling pathway may be involved in multidrug resistance, which was further validated using immunoblotting and MTT assay. Finally a primary multidrug resistance network in gastric cancer, consisting of the commonly dysregulated genes and miRNAs, was established and functional miRNA-mRNA pairs were identified. The commonly dysregulated genes and miRNAs identified in this study may represent good therapeutic targets and further study of these targets may increase our understanding of the mechanisms underlying multidrug resistance.

Prognostic significance of HOXB4 in de novo acute myeloid leukemia

As research into hematopoiesis advances, new factors associated with hematopoietic stem cell (HSC) activity have been discovered, and the contribution of HSC factors to hematopoiesis is now actively being investigated. Since the involvement of stem cells is considered to be important in hematological malignancies as well as normal hematopoiesis, we examined the expression of newly defined HSC factors including HOXB4, TCFEC, HMGB-1, FOS, and SPI-1 in the bone marrow (BM) from de novo acute myeloid leukemia (AML) patients. Expression levels of mRNA extracted from frozen specimens of AML patients and normal controls were measured by real-time polymerase chain reaction (PCR). Among the HSC factors, HOXB4 exhibited significantly higher expression in the BM of AML as compared with normal controls. Immunostaining for HOXB4 revealed that the HOXB4-positive cell ratios correlated well with the expression levels of mRNA for HOXB4 in AML BM. Based on the HOXB4-positive cell ratio, AML patients were divided into two groups (cases with higher ratios and lower ratios). The group with higher HOXB4-positive cell ratios had better prognoses as compared with the group with lower ratios. Multivariate analysis confirmed the HOXB4-positivity as an independent predictor of overall survival of AML patients. Lastly, mRNA expression levels for HOXB4 were inversely correlated with the expression levels of at least two genes, including ABCB1, which is known to be a multidrug-resistance gene. Our study distinguishes a subgroup of AML with higher HOXB4 expression and better prognosis, and this might be reflected by relative drug sensitivity in leukemic cells.

IGF signaling contributes to malignant transformation of hematopoietic progenitors by the MLL-AF9 oncoprotein

Malignant transformation of normal hematopoietic progenitors is a multistep process that likely requires interaction between collaborating oncogenic signals at critical junctures. For instance, the MLL-AF9 fusion oncogene is thought to contribute to myeloid leukemogenesis by driving a hematopoietic stem cell-like "self-renewal" gene expression signature in committed myeloid progenitors. In addition, insulin-like growth factor (IGF) signaling has been implicated in self-renewal/pluripotency in hematopoietic and embryonic stem cell contexts and supports cell growth/survival by activation of downstream pathways, including phosphatidylinositol 3-kinase/Akt and Ras/Raf/extracellular signal-regulated kinase. We hypothesized that IGF signaling could be an important contributor in the process of cellular transformation and/or clonal propagation. Utilizing an MLL-AF9 mouse bone marrow transplantation model of acute myelogenous leukemia, we discovered that committed myeloid progenitor cells with genetically reduced levels of IGF1R were less susceptible to leukemogenic transformation due, at least in part, to a cell-autonomous defect in clonogenic activity. Rather unexpectedly, genetic deletion of IGF1R by inducible Cre recombinase had no effect on growth/survival of established leukemia cells. These findings suggest that IGF1R signaling contributes to transformation of normal myeloid progenitor cells, but is not required for propagation of the leukemic clone once it has become established. We also show that treatment of mouse MLL-AF9 acute myelogenous leukemia cells with BMS-536924, an IGF1R/insulin receptor-selective tyrosine kinase inhibitor, blocked cell growth, suggesting its efficacy in this model may be due to inhibition of insulin receptor and/or related tyrosine kinases, and raising the possibility that similar IGF1R inhibitors in clinical development may be acting through alternate/related pathways.

HG-829 is a potent noncompetitive inhibitor of the ATP-binding cassette multidrug resistance transporter ABCB1

Transmembrane drug export mediated by the ATP-binding cassette (ABC) transporter P-glycoprotein contributes to clinical resistance to antineoplastics. In this study, we identified the substituted quinoline HG-829 as a novel, noncompetitive, and potent P-glycoprotein inhibitor that overcomes in vitro and in vivo drug resistance. We found that nontoxic concentrations of HG-829 restored sensitivity to P-glycoprotein oncolytic substrates. In ABCB1-overexpressing cell lines, HG-829 significantly enhanced cytotoxicity to daunorubicin, paclitaxel, vinblastine, vincristine, and etoposide. Coadministration of HG-829 fully restored in vivo antitumor activity of daunorubicin in mice without added toxicity. Functional assays showed that HG-829 is not a Pgp substrate or competitive inhibitor of Pgp-mediated drug efflux but rather acts as a noncompetitive modulator of P-glycoprotein transport function. Taken together, our findings indicate that HG-829 is a potent, long-acting, and noncompetitive modulator of P-glycoprotein export function that may offer therapeutic promise for multidrug-resistant malignancies.

Molecular evolutionary analysis of ABCB5: the ancestral gene is a full transporter with potentially deleterious single nucleotide polymorphisms

BACKGROUND

ABCB5 is a member of the ABC protein superfamily, which includes the transporters ABCB1, ABCC1 and ABCG2 responsible for causing drug resistance in cancer patients and also several other transporters that have been linked to human disease. The ABCB5 full transporter (ABCB5.ts) is expressed in human testis and its functional significance is presently unknown. Another variant of this transporter, ABCB5 beta possess a "half-transporter-like" structure and is expressed in melanoma stem cells, normal melanocytes, and other types of pigment cells. ABCB5 beta has important clinical implications, as it may be involved with multidrug resistance in melanoma stem cells, allowing these stem cells to survive chemotherapeutic regimes.

METHODOLOGY/PRINCIPAL FINDINGS

We constructed and examined in detail topological structures of the human ABCB5 protein and determined in-silico the cSNPs (coding single nucleotide polymorphisms) that may affect its function. Evolutionary analysis of ABCB5 indicated that ABCB5, ABCB1, ABCB4, and ABCB11 share a common ancestor, which began duplicating early in the evolutionary history of chordates. This suggests that ABCB5 has evolved as a full transporter throughout its evolutionary history.

CONCLUSIONS/SIGNIFICANCE

From our in-silco analysis of cSNPs we found that a large number of non-synonymous cSNPs map to important functional regions of the protein suggesting that these SNPs if present in human populations may play a role in diseases associated with ABCB5. From phylogenetic analyses, we have shown that ABCB5 evolved as a full transporter throughout its evolutionary history with an absence of any major shifts in selection between the various lineages suggesting that the function of ABCB5 has been maintained during mammalian evolution. This finding would suggest that ABCB5 beta may have evolved to play a specific role in human pigment cells and/or melanoma cells where it is predominantly expressed.

The therapeutic promise of the cancer stem cell concept

Cancer stem cells (CSCs) are a subpopulation of tumor cells that selectively possess tumor initiation and self-renewal capacity and the ability to give rise to bulk populations of nontumorigenic cancer cell progeny through differentiation. As we discuss here, they have been prospectively identified in several human malignancies, and their relative abundance in clinical cancer specimens has been correlated with malignant disease progression in human patients. Furthermore, recent findings suggest that clinical cancer progression driven by CSCs may contribute to the failure of existing therapies to consistently eradicate malignant tumors. Therefore, CSC-directed therapeutic approaches might represent translationally relevant strategies to improve clinical cancer therapy, in particular for those malignancies that are currently refractory to conventional anticancer agents directed predominantly at tumor bulk populations.

Identification and targeting of cancer stem cells

Cancer stem cells (CSC) represent malignant cell subsets in hierarchically organized tumors, which are selectively capable of tumor initiation and self-renewal and give rise to bulk populations of non-tumorigenic cancer cell progeny through differentiation. Robust evidence for the existence of prospectively identifiable CSC among cancer bulk populations has been generated using marker-specific genetic lineage tracking of molecularly defined cancer subpopulations in competitive tumor development models. Moreover, novel mechanisms and relationships have been discovered that link CSC to cancer therapeutic resistance and clinical tumor progression. Importantly, proof-of-principle for the potential therapeutic utility of the CSC concept has recently been provided by demonstrating that selective killing of CSC through a prospective molecular marker can inhibit tumor growth. Herein, we review these novel and translationally relevant research developments and discuss potential strategies for CSC-targeted therapy in the context of resistance mechanisms and molecular pathways preferentially operative in CSC.