Design and construction of a new human naïve single-chain fragment variable antibody library, IORISS1.

Human monoclonal antibodies are a powerful tool with increasingly successful exploitations and the single chain fragment variable format can be considered the building block for the implementation of more complex and effective antibody-based constructs. Phage display is one of the best and most efficient methods to isolate human antibodies selected from an efficient and variable phage display library. We report a method for the construction of a human naïve single-chain variable fragment library, termed IORISS1. Many different sets of oligonucleotide primers as well as optimized electroporation and ligation reactions were used to generate this library of 1.2×10(9) individual clones. The key difference is the diversity of variable gene templates, which was derived from only 15 non-immunized human donors. The method described here, was used to make a new human naïve single-chain fragment variable phage display library that represents a valuable source of diverse antibodies that can be used as research reagents or as a starting point for the development of therapeutics. Using biopanning, we determined the ability of IORISS1 to yield antibodies. The results we obtained suggest that, by using an optimized protocol, an efficient phage antibody library can be generated.

Process development of a human recombinant diabody expressed in E. coli: engagement of CD99-induced apoptosis for target therapy in Ewing's sarcoma.

Ewing's sarcoma (EWS) is the second most common primary bone tumor in pediatric patients characterized by over expression of CD99. Current management consists in extensive chemotherapy in addition to surgical resection and/or radiation. Recent improvements in treatment are still overshadowed by severe side effects such as toxicity and risk of secondary malignancies; therefore, more effective strategies are urgently needed. The goal of this work was to develop a rapid, inexpensive, and "up-scalable" process of a novel human bivalent single-chain fragment variable diabody (C7 dAbd) directed against CD99, as a new therapeutic approach for EWS. We first investigated different Escherichia coli constructs of C7 dAbd in small-scale studies. Starting from 60 % soluble fraction, we obtained a yield of 25 mg C7 dAbd per liter of bacterial culture with the construct containing pelB signal sequence. In contrast, a low recovery of C7 dAbd was achieved starting from periplasmic inclusion bodies. In order to maximize the yield of C7 dAbd, large-scale fermentation was optimized. We obtained from 75 % soluble fraction 35 mg C7 dAbd per L of cell culture grown in a synthetic media containing 3 g/L of vegetable peptone and 1 g/L of yeast extract. Furthermore, we demonstrated the better efficacy of the cell lysis by homogenization versus periplasmic extraction, in reducing endotoxin level of the C7 dAbd. For gram-scale purification, a direct aligned two-step chromatography cascade based on binding selectivity was developed. Finally, we recovered C7 dAbd with low residual process-related impurities, excellent reactivity, and apoptotic ability against EWS cells.

The human antibody fragment DIATHIS1 specific for CEACAM1 enhances natural killer cell cytotoxicity against melanoma cell lines in vitro.

Several lines of evidence show that de novo expression of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is strongly associated with reduced disease-free survival of patients affected by metastatic melanoma. Previously published investigations report that homophilic interactions between CEACAM1 expressed on natural killer (NK) cells and tumors inhibit the NK cell-mediated killing independently of major histocompatibility complex class I recognition. This biological property can be physiologically relevant in metastatic melanoma because of the increased CEACAM1 expression observed on NK cells from some patients. Moreover, this inhibitory mechanism in many cases might hinder the efficacy of immunotherapeutic treatments of CEACAM1 malignancies because of tumor evasion by activated effector cells. In the present study, we designed an in vitro experimental model showing that the human single-chain variable fragment (scFv) DIATHIS1 specific for CEACAM1 is able to enhance the lytic machinery of NK cells against CEACAM1 melanoma cells. The coincubation of the scFv DIATHIS1 with CEACAM1 melanoma cells and NK-92 cell line significantly increases the cell-mediated cytotoxicity. Moreover, pretreatment of melanoma cells with scFv DIATHIS1 promotes the activation and the degranulation capacity of in vitro-expanded NK cells from healthy donors. It is interesting to note that the melanoma cell line MelC and the primary melanoma cells STA that respond better to DIATHIS1 treatment, express higher relative levels of CEACAM1-3L and CEACAM1-3S splice variants isoforms compared with Mel501 cells that are less responsive to DIATHIS1-induced NK cell-mediated cytotoxicity. Taken together, our results suggest that the fully human antibody fragment DIATHIS1 originated by biopanning approach from a phage antibody library may represent a relevant biotechnological platform to design and develop completely human antimelanoma therapeutics of biological origin.

CD99 triggering in Ewing sarcoma delivers a lethal signal through p53 pathway reactivation and cooperates with doxorubicin.

PURPOSE: The paucity of new drugs for the treatment of Ewing sarcoma (EWS) limits the cure of these patients. CD99 has a strong membranous expression in EWS cells and, being also necessary for tumor survival, is a suitable target to aim at. In this article, we described a novel human monospecific bivalent single-chain fragment variable diabody (dAbd C7) directed against CD99 of potential clinical application. EXPERIMENTAL DESIGN: In vitro and in vivo evaluation of cell death and of the molecular mechanisms triggered by anti-CD99 agents were performed alone or in combination with doxorubicin to demonstrate efficacy and selectivity of the new dAbd C7. RESULTS: The dAbd C7 induced rapid and massive EWS cell death through Mdm2 degradation and p53 reactivation. Mdm2 overexpression as well as silencing of p53 in p53wt EWS cells decreased CD99-induced EWS cell death, whereas treatment with nutlin-3 enhanced it. Furthermore, cell death was associated with induction of p21, bax, and mitochondrial depolarization together with substantial inhibition of tumor cell proliferation. Combined treatment of anti-CD99 dAbd C7 with doxorubicin was additive both in vitro and in vivo against EWS xenografts. Normal mesenchymal stem cells showed no p53 activation and were resistant to cell death, unless transformed by EWS-FLI, the oncogenic driver of EWS. CONCLUSIONS: These results indicate that dAbd C7 is a suitable candidate tool to target CD99 in patients with EWS able to spare normal stem cells from death as it needs an aberrant genetic context for the efficient delivery of CD99-triggered cell death.

Blocking monocyte transmigration in in vitro system by a human antibody scFv anti-CD99. Efficient large scale purification from periplasmic inclusion bodies in E. coli expression system.

Migration of leukocytes into site of inflammation involves several steps mediated by various families of adhesion molecules. CD99 play a significant role in transendothelial migration (TEM) of leukocytes. Inhibition of TEM by specific monoclonal antibody (mAb) can provide a potent therapeutic approach to treating inflammatory conditions. However, the therapeutic utilization of whole IgG can lead to an inappropriate activation of Fc receptor-expressing cells, inducing serious adverse side effects due to cytokine release. In this regard, specific recombinant antibody in single chain variable fragments (scFvs) originated by phage library may offer a solution by affecting TEM function in a safe clinical context. However, this consideration requires large scale production of functional scFv antibodies and the absence of toxic reagents utilized for solubilization and refolding step of inclusion bodies that may discourage industrial application of these antibody fragments. In order to apply the scFv anti-CD99 named C7A in a clinical setting, we herein describe an efficient and large scale production of the antibody fragments expressed in E. coli as periplasmic insoluble protein avoiding gel filtration chromatography approach, and laborious refolding step pre- and post-purification. Using differential salt elution which is a simple, reproducible and effective procedure we are able to separate scFv in monomer format from aggregates. The purified scFv antibody C7A exhibits inhibitory activity comparable to an antagonistic conventional mAb, thus providing an excellent agent for blocking CD99 signaling. This protocol can be useful for the successful purification of other monomeric scFvs which are expressed as periplasmic inclusion bodies in bacterial systems.

Isolation of a new human scFv antibody recognizing a cell surface binding site to CEACAM1. Large yield production, purification and characterization in E. coli expression system.

The CEACAM1 cell adhesion molecule has recently received considerable interest as a tumour target antigen since its re-expression often occurs in the advanced stages of multiple malignancies including malignant melanoma, non-small cell lung cancer and other types of solid tumors. In this study, we describe the expression-purification and characterization of the new single chain variable fragment (scFv) antibody named DIATHIS1, that recognizes the N-terminal IgV-like domain present in CEACAM1. Three validation batches show that the production process is robust and reproducible. The scFv DIATHIS1 is formulated as a naturally occurring mixture of monomer and dimer. The antibody is biophysically stable at low temperature (-80°C), different concentrations and remains biologically active for at least 24months. The thermal stability of scFv DIATHIS1 at 37°C shows important features for its activity in vivo. The dimer behaves as a reservoir converting slowly into monomer. The monomer and dimer forms of scFv DIATHIS1 were isolated and characterized, showing high reactivity for CEACAM1. This new composition of antibody could have advantageous pharmacokinetics parameters over conventional scFv for in vivo applications.

Raltegravir does not revert efflux activity of MDR1-P-glycoprotein in human MDR cells.

BACKGROUND: Raltegravir (Isentress®)(RALT) has demonstrated excellent efficacy in both treatment-experienced and naïve patients with HIV-1 infection, and is the first strand transfer integrase inhibitor to be approved for use in HIV infected adults worldwide. Since the in vivo efficacy of this class of antiviral drugs depends on their access to intracellular sites where HIV-1 replicates, we analyzed the biological effects induced by RALT on human MDR cell systems expressing multidrug transporter MDR1-P-glycoprotein (MDR1-Pgp). METHODS: Our study about RALT was performed by using a set of consolidated methodologies suitable for evaluating the MDR1-Pgp substrate nature of chemical and biological agents, namely: i) assay of drug efflux function; ii) analysis of MDR reversing capability by using cell proliferation assays; iii) monoclonal antibody UIC2 (mAb) shift test, as a sensitive assay to analyze conformational transition associated with MDR1-Pgp function; and iv) induction of MDR1-Pgp expression in MDR cell variant subjected to RALT exposure. RESULTS: Functional assays demonstrated that the presence of RALT does not remarkably interfere with the efflux mechanism of CEM-VBL100 and HL60 MDR cells. Accordingly, cell proliferation assays clearly indicated that RALT does not revert MDR phenotype in human MDR1-Pgp expressing cells. Furthermore, exposure of CEM-VBL10 cells to RALT does not induce MDR1-Pgp functional conformation intercepted by monoclonal antibody (mAb) UIC2 binding; nor does exposure to RALT increase the expression of this drug transporter in MDR1-Pgp expressing cells. CONCLUSIONS: No evidence of RALT interaction with human MDR1-Pgp was observed in the in vitro MDR cell systems used in the present investigation, this incorporating all sets of studies recommended by the FDA guidelines. Taken in aggregate, these data suggest that RALT may express its curative potential in all sites were HIV-1 penetrates, including the MDR1-Pgp protected blood/tissue barrier. Moreover RALT, evading MDR1-Pgp drug efflux function, would not interfere with pharmacokinetic profiles of co-administered MDR1-Pgp substrate antiretroviral drugs.

The biology of MDR1-P-glycoprotein (MDR1-Pgp) in designing functional antibody drug conjugates (ADCs): the experience of gemtuzumab ozogamicin.

BACKGROUND: The treatment of cancer remains a formidable challenge owing to the difficulties in differentiating tumor cells from healthy cells to ameliorate the disease without causing intolerable toxicity to patients. In addition, the emergence of MDR1-Pgp mediated multi-drug resistance (MDR) it is a biological phenomenon that inhibits the curative potential of chemotherapeutic treatments. One way to improve the selectivity of therapeutic molecules in tumors would be to target them on the tumor site, thereby sparing normal tissues. AIMS: In this overview, we will discuss the biological factors influencing the safety and efficacy of the humanized mAb hP67.6 linked to the potent cytotoxic drug calicheamicingamma1 (gemtuzumab ozogamicin) that target CD33 cell surface antigen expressed on AML cells. In addition, we highlight key aspects of MDR1-Pgp biology as a platform to understand its functional role in gemtuzumab ozogamicin immunotherapy which is tightly linked to an accurate assessment of the MDR status of AML cells. DISCUSSION: Several factors may affect the efficacy and safety of immunoconjugates. These include the common issues of chemical and antibody therapeutics such as specificity, heterogeneous target antigen expression and the complex pharmacokinetics profile of conveyed antibody. Further, the delivered drug may not be sufficient for providing therapeutic benefit, since the curative cytotoxic compound may be affected by intrinsic or acquired resistance of target cells. These and other potential problems, as well as the possible ways to overcome them will be discussed in this review by examining the biological factors involved in safety and efficacy of the first in class antibody drug conjugate (ADC) gentuzumab ozogamicin. Despite this set-back, the extensive recorded data and the lessons learned from gentuzumab ozogamicin recently withdrawn from the market for safety concerns helped to pave the way for next generations of clinically promising new ADCs which are currently investigated in clinical trials and two of them, Brentuximab vedotin, and Trastuzumab emtansine (T-DM1) have been recently approved for commercial distribution in US by Food and Drug Administration (FDA).

Targeting MDR1-P-glycoprotein (MDR1-Pgp) in immunochemotherapy of acute myeloid leukemia (AML).

BACKGROUND: Monoclonal antibodies represent the fastest growing sector of pharmaceutical biotechnology and a number of antibody-based biopharmaceuticals have been approved for cancer treatment. However, in many cases the antibodies used for the treatment of tumors offer only a modest survival benefit to cancer patients. AIMS: In the present review-article we intend to analyze: i) the curative regimen gemtuzumab ozogamicin (GO) -mediate characterized by the absence of cytotoxic drugs MDR1-Pgp substrates to overcome the mechanism of action of this multidrug transporter, ii) the safety and efficacy of MDR reversing strategy in AML outcome and, iii) chemical and biological MDR modulators playing a dual relevant medical role as a therapeutic and MDR reversing agents but not yet entered in the clinical setting of AML. Since the similar multidrug transporter protein MDR1-Pgp and its down modulation factors may affect safety and efficacy of already generated antibody drug conjugates (ADCs) a comprehensive overview of the most clinically representative immunoconjugates is reported. DISCUSSION: ADCs represent one of the most promising strategies to enhance the antitumor activity of antibodies. ADCs comprise an antibody (or an antibody fragment) conjugated to a cytotoxic drug via a chemical linker. The therapeutic concept of ADCs is to use an antibody as a vehicle to selectively delivering a cytotoxic drug specifically to a tumor cell, in most cases by means of binding to target cell surface antigen. As a consequence, ADCs have significant potential for enhancing the antitumor activity of "naked" antibodies and reducing the systemic toxicity of the conjugated drugs.

Clinical development of monoclonal antibody-based drugs in HIV and HCV diseases.

Today there are many licensed antiviral drugs, but the emergence of drug resistant strains sometimes invalidates the effects of the current therapies used in the treatment of infectious diseases. Compared to conventional antiviral drugs, monoclonal antibodies (mAbs) used as pharmacological molecules have particular physical characteristics and modes of action, and, therefore, they should be considered as a distinct therapeutic class. Despite being historically validated, antibodies may represent a novel tool for combatting infectious diseases. The current high cost of mAbs' production, storage and administration (by injection only) and the consequent obstacles to development are outweighed by mAbs' clinical advantages. These are related to a low toxicity combined with high specificity and versatility, which allows a specific antibody to mediate various biological effects, ranging from the virus neutralization mechanisms to the modulation of immune responses.This review briefly summarizes the recent technological advances in the field of immunoglobulin research, and the current status of mAb-based drugs in clinical trials for HIV and HCV diseases. For each clinical trial the available data are reported and the emerging conceptual problems of the employed mAbs are highlighted.This overview helps to give a clear picture of the efficacy and challenges of the mAbs in the field of these two infectious diseases which have such a global impact.

Generation of human single-chain antibody to the CD99 cell surface determinant specifically recognizing Ewing's sarcoma tumor cells.

The survival of pediatric patients with cancer entities including osteosarcoma and Ewing's sarcoma (ES), remains extremely low hence novel treatment approaches are urgently needed. Therefore, based on the concept of targeted therapy, numerous potential targets for the treatment of these cancers have been evaluated pre-clinically or in some cases even clinically during the last decade. In ES the CD99 protein is an attractive target antigen. In this respect, a new entry site for therapeutic intervention may derive from specific human antibodies against CD99. Human scFvC7 was isolated from a semi-synthetic ETH-2 antibody phage library panned on the extracellular portion of recombinant human CD99 protein. The scFvC7 was genetically sequenced, tested for CD99 recognition on an array of recombinant CD99 fragments and measured for binding affinity by ELISA. Finally, it was tested for staining CD99 antigen on a large panel of tumor and normal cells and tissues by cytofluorimetric and immunohistochemical assays. The new antibody scFvC7 recognizes the CD99 extracellular domain included between residues 50 and 74 with a binding affinity of 2.4 x 10(-8) M. In contrast with all other antibodies to CD99 so far isolated, scFvC7 shows a unique specificity in cancer cell recognition: It stained prevalently ES cells while no or weak reactivity was observed on the majority of the other tumor and normal cells and tissues. Thanks to its properties the new anti-CD99 antibody here described represents the first step towards the construction of new selective ES therapeutics.

The expression and modulation of CEACAM1 and tumor cell transformation.

BACKGROUND: In this review, we focus our discussion on one class of carcinoembryonic antigen- related cell adhesion molecules, Carcinoembryonic antigen-related cell adhesion molecules 1 (CEACAM1). This has been observed in several malignant transformations to be subjected to complex mechanisms of modulation and dysregulation. AIMS: Restoration of CEACAM1 expression in tumor cell lines often abolishes their oncogenicity in vivo, and therefore, this adhesion molecule has been regarded as a tumor suppressor. In contrast, de novo expression of CEACAM1 is found with the progression of malignancy and metastatic spread in a large array of cancer tissues which include melanoma, Non Small Cell Lung Carcinoma (NSCLC) as well as bladder, prostate, thyroid, breast, colon and gastric carcinomas. DISCUSSION: We report and discuss the most significant findings confirming at immunohistochemical and clinical level the correlation between poor prognosis and expression of CEACAM1 on the cell surface of tumors.

P-glycoprotein binds to ezrin at amino acid residues 149-242 in the FERM domain and plays a key role in the multidrug resistance of human osteosarcoma.

Overexpression of the mdr1 gene encoding P-glycoprotein (Pgp) exerts a major role in reducing the effectiveness of cytotoxic therapy in osteosarcoma. The interaction between actin and Pgp has been shown to be instrumental in the establishment of multidrug resistance (MDR) in human tumor cells. The cytoskeleton linker ezrin exerts a pivotal role in maintaining the functional connection between actin and Pgp. We investigated the role of ezrin in a human multidrug-resistant osteosarcoma cell line overexpressing Pgp and compared it to its counterpart that overexpresses an ezrin deletion mutant. The results showed that Pgp binds at amino acid residues 149-242 of the N-terminal domain of ezrin. The interaction between ezrin and Pgp occurs in the plasma membrane of MDR cells, where they also co-localize with the ganglioside G(M1) located in lipid rafts. The overexpression of the ezrin deletion mutant entirely restored drug susceptibility of osteosarcoma cells, consistent with Pgp dislocation to cytoplasmic compartments and abrogation of G(M1) /Pgp co-localization at the plasma membrane. Our study provides evidence that ezrin exerts a key role in MDR of human osteosarcoma cells through a Pgp-ezrin-actin connection that is instrumental for the permanence of Pgp into plasma membrane lipid rafts. We also show for the first time that Pgp-binding site is localized to amino acid residues 149-242 of the ezrin Band 4.1, Ezrin/Radixin/Moesin (FERM) domain, thus proposing a specific target for future molecular therapy aimed at counteracting MDR in osteosarcoma patients.

The cancer stem cell selective inhibitor salinomycin is a p-glycoprotein inhibitor.

Salinomycin, a polyether antibiotic acting as a highly selective potassium ionophore and widely used as an anticoccidial drug, was recently shown to act as a specific inhibitor of cancer stem cells. In the present study we report that salinomycin acts as a potent inhibitor of multidrug resistance gp170, as evidenced through drug efflux assays in MDR cancer cell lines overexpressing P-gp (CEM-VBL 10 and CEM-VBL 100; A2780/ADR). Conformational P-gp assay provided evidence that the inhibitory effect of salinomycin on P-gp function could be mediated by the induction of a conformational change of the ATP transporter. Treatment of the MDR cell lines with salinomycin restored a normal drug sensitivity of these cells. The observation that salinomycin is a MDR-1 inhibitor may have important implications for the understanding of the mechanisms through which this drug impairs the viability of cancer stem cells. Interestingly, nigericin and abamectin, two additional drugs identified as cancer stem cells inhibitors, also act as potent gp170 inhibitors.

Multidrug transporter proteins and cellular factors involved in free and mAb linked calicheamicin-gamma1 (gentuzumab ozogamicin, GO) resistance and in the selection of GO resistant variants of the HL60 AML cell line.

In this study we elucidated the role of ATP-binding cassette (ABC) multi-drug transporter proteins and cellular factors such as Bcl-2 expression and CD33 down-modulation contributing to free and hP67.6 mAb linked calicheamicin-gamma1 (CalC-gamma1) resistance. We analyzed in a well designed HL60 cell system the relationship between the expression of ABC proteins, Bcl-2 and CD33 modulation with the activity of free and mAb-linked CalC-gamma1. The results herein reported and discussed, strongly suggest that both MDR1-Pgp and MRP1 efflux systems are engaged by CalC-gamma1, but only MDR1-Pgp over-expression efficiently abrogates drug cytotoxicity in MDR cells. Paradoxically, Bcl-2 expression, as observed for other anticancer compounds belonging to the enediyne family of drugs, confers CalC-gamma1 susceptibility rather than resistance in HL60 cells. Further, the isolation of a resistant HL60 subline (HL60AL) that was developed by exposing the parental sensitive cells to sub-effective doses of gemtuzumab ozogamicin (GO) over an extended period of time shows a reduced level of CD33 expression that represents an important escape mechanism of HL60 MDR cells to the cytotoxic effect of GO.

Human monoclonal antibodies in single chain fragment variable format with potent neutralization activity against influenza virus H5N1.

Effective diagnostic and therapeutic strategies are needed to control and combat the highly pathogenic avian influenza virus (AIV) subtype H5N1. To this end, we developed human monoclonal antibodies (mAbs) in single chain fragment variable (scFv) format towards the H5N1 avian influenza virus to gain new insights for the development of immunotherapy against human cases of H5N1. Using a biopanning based approach a large array of scFvs against H5N1 virus were isolated from the human semi-synthetic ETH-2 phage antibody library. H5N1 ELISA-positive scFvs with unique variable heavy (VH) and light (VL) chain gene sequences showed different biochemical properties and neutralization activity across H5N1 viral strains. In particular, the scFv clones AV.D1 and AV.C4 exerted a significant inhibition of the H5N1 A/Vietnam/1194/2004 virus infection in a pseudotype-based neutralization assay. Interestingly, these two scFvs displayed a cross-clade neutralizing activity versus A/whooping swan/Mongolia/244/2005 and A/Indonesia/5/2005 strains. These studies provide proof of the concept that human mAbs in scFv format with well-defined H5N1 recognition patterns and in vitro neutralizing activity can be easily and rapidly isolated by biopanning selection of an entirely artificial antibody repertoire using inactivated H5N1 virus as a bait.

The glutathione S-transferase inhibitor 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol overcomes the MDR1-P-glycoprotein and MRP1-mediated multidrug resistance in acute myeloid leukemia cells.

PURPOSE: There has been an ever growing interest in the search for new anti-tumor compounds that do not interact with MDR1-Pgp and MRP1 drug transporters and so circumvent the effect of these proteins conferring multidrug resistance (MDR) and poor prognosis in AML patients. We have investigated the cytotoxic activity of the strong glutathione S-transferase (GST) inhibitor 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX) on AML (HL60) cell lines. METHODS: Functional drug efflux studies and cell proliferation assays were performed on both sensitive and MDR AML (HL60) cells after incubation with NBDHEX. Moreover, the mode of cell death (apoptosis vs. necrosis) as well as the correlation between NBDHEX susceptibility and GST activity or Bcl-2 expression was investigated. RESULTS: NBDHEX is not a substrate of either MDR1-Pgp or MRP1 efflux pumps; in fact, it is not only cytotoxic toward the parental HL60 cell line, but also overcomes the MDR phenotype of its HL60/DNR and HL60/ADR variants. CONCLUSIONS: The data herein reported show that NBDHEX mediates efficient killing of both MDR1-Pgp and MRP1 over-expressing AML cells. Therefore, this drug can potentially be used as an effective agent for treating MDR in AML patients.

Inhibition of MDR1 activity in vitro by a novel class of diltiazem analogues: toward new candidates.

The reversal of multidrug resistance by 22 molecules [8-aryl-8-hydroxy-5-R'-8H-[1,4]thiazino[3,4-c][1,2,4]oxadiazol-3-ones (1a-i) and 8-aryl-8-alkoxy-5-methyl-8H-[1,4]thiazino[3,4-c][1,2,4]oxadiazol-3-ones (2a-m)] related to myocardial-calcium-channel-modulator diltiazem was studied in multidrug resistant A2780/DX3 and their sensitive counterpart A2780 cells. MTT, cytofluorimetry assays, and fluorescence microscopy analyses were used to define activity and accumulation of doxorubicin with or without the diltiazem-like modulators. Of the 22 molecules, 1a, 2f, 2g, and 2m were able to overcome the established criteria for the selection in A2780/DX3 cells (IC(50) reduction > or = 25%), but only 2f, 2g, and 2m caused a significant increase of intracellular accumulation of doxorubicin. In conclusion, experiments lead to the identification of three diltiazem-like molecules able to increase the intracellular accumulation of doxorubicin by inhibiting the MDR1 function, thus potentiating its antiproliferative activity in multidrug resistant A2780/DX3 cells.

Generation and characterization of a human single-chain fragment variable (scFv) antibody against cytosine deaminase from yeast.

BACKGROUND: The ability of cytosine deaminase (CD) to convert the antifungal agent 5-fluorocytosine (5-FC) into one of the most potent and largely used anticancer compound such as 5-fluorouracil (5-FU) raised considerable interest in this enzyme to model gene or antibody - directed enzyme-prodrug therapy (GDEPT/ADEPT) aiming to improve the therapeutic ratio (benefit versus toxic side-effects) of cancer chemotherapy. The selection and characterization of a human monoclonal antibody in single chain fragment (scFv) format represents a powerful reagent to allow in in vitro and in vivo detection of CD expression in GDEPT/ADEPT studies. RESULTS: An enzymatic active recombinant CD from yeast (yCD) was expressed in E. coli system and used as antigen for biopanning approach of the large semi-synthetic ETH-2 antibody phage library. Several scFvs were isolated and specificity towards yCD was confirmed by Western blot and ELISA. Further, biochemical and functional investigations demonstrated that the binding of specific scFv with yCD did not interfere with the activity of the enzyme in converting 5-FC into 5-FU. CONCLUSION: The construction of libraries of recombinant antibody fragments that are displayed on the surface of filamentous phage, and the selection of phage antibodies against target antigens, have become an important biotechnological tool in generating new monoclonal antibodies for research and clinical applications. The scFvH5 generated by this method is the first human antibody which is able to detect yCD in routinary laboratory techniques without interfering with its enzymatic function.

Genetic construction, expression, and characterization of a single chain anti-CEA antibody fused to cytosine deaminase from yeast.

We report the genetic construction and expression of a fusion protein between a single chain fragment variable (scFv) human antibody (E8) specific for CEA cell surface antigen and yeast cytosine deaminase (yCD). Sequences encoding for the scFvE8 human monoclonal antibody recognizing an epitope shared by CEACAM1, CEACAM3 and CEACAM5 isoforms were assembled with a monomer of yCD. The construct was placed under the transcriptional regulation of the lac promoter, and in frame with 6xHis tag for protein purification. After transformation and induction of E. coli, the protein was recovered from cell lysates and processed for purification. The scFvE8:yCD fusion protein possessed the binding specificity for melanoma (Mel P5) and colon carcinoma (LoVo) cell lines similar to its cognate human scFv antibody. The scFv8:yCD system showed the ability to render tumor cells susceptible to the far less toxic substrate 5-fluorocytosine (5-FC) by its enzymatic conversion into 5-fluorouracil (5-FU). In vitro pre-treatment of Mel P5 and LoVo cell lines with scFvE8:yCD followed by cell washing and incubation with 5-FC, resulted in significant cell killing supporting the utility of this fusion protein as an agent for tumor-selective prodrug activation. This study shows the feasibility of constructing fusion proteins in a prokaryotic cell based system consisting of a human scFv antibody and yCD to convert the antifungal agent 5-FC to 5-FU, one of the widely used anticancer agent.