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ABSTRACT: The most successful clinical studies of immunotherapy in patients with non-Hodgkin's lymphoma (NHL) use the antibody rituximab (RTX) targeting CD20(+) B-cell tumors. Rituximab radiolabeled with β(-) emitters could potentiate the therapeutic efficacy of the antibody by virtue of the particle radiation. Here, we report on a direct radiolabeling approach of rituximab with the (99m)Tc- and (188)Re-tricarbonyl core (IsoLink technology).
The native format of the antibody (RTX(wt)) as well as a reduced form (RTX(red)) was labeled with (99m)Tc/(188)Re(CO)(3). The partial reduction of the disulfide bonds to produce free sulfhydryl groups (-SH) was achieved with 2-mercaptoethanol. Radiolabeling efficiency, in vitro human plasma stability as well as transchelation toward cysteine and histidine was investigated. The immunoreactivity and binding affinity were determined on Ramos and/or Raji cells expressing CD20. Biodistribution was performed in mice bearing subcutaneous Ramos lymphoma xenografts.
The radiolabeling efficiency and kinetics of RTX(red) were superior to that of RTX(wt) ((99m)Tc: 98% after 3 h for RTX(red) vs. 70% after 24 h for RTX(wt)). (99m)Tc(CO)(3)-RTX(red) was used without purification for in vitro and in vivo studies whereas (188)Re(CO)(3)-RTX(red) was purified to eliminate free (188)Re-precursor. Both radioimmunoconjugates were stable in human plasma for 24 h at 37 °C. In contrast, displacement experiments with excess cysteine/histidine showed significant transchelation in the case of (99m)Tc(CO)(3)-RTX(red) but not with pre-purified (188)Re(CO)(3)-RTX(red). Both conjugates revealed high binding affinity to the CD20 antigen (K(d) = 5-6 nM). Tumor uptake of (188)Re(CO)(3)-RTX(red) was 2.5 %ID/g and 0.8 %ID/g for (99m)Tc(CO)(3)-RTX(red) 48 h after injection. The values for other organs and tissues were similar for both compounds, for example the tumor-to-blood and tumor-to-liver ratios were 0.4 and 0.3 for (99m)Tc(CO)(3)-RTX(red) and for (188)Re(CO)(3)-RTX(red) 0.5 and 0.5 (24 h pi).
Rituximab could be directly and stably labeled with the matched pair (99m)Tc/(188)Re using the IsoLink technology under retention of the biological activity. Labeling kinetics and yields need further improvement for potential routine application in radioimmunodiagnosis and therapy.
Nuclear Medicine and Biology 01/2011; 38(1):19-28. · 3.02 Impact Factor
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Christian Zahnd,
Martin Kawe,
Michael T Stumpp,
Christine de Pasquale,
Rastislav Tamaskovic,
Gabriela Nagy-Davidescu,
Birgit Dreier,
Roger Schibli,
H Kaspar Binz, Robert Waibel,
Andreas Plückthun
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ABSTRACT: Slow-clearing, tumor-targeting proteins such as monoclonal antibodies typically exhibit high tumor accumulation but low tissue contrast, whereas intermediate-sized proteins such as scFvs show faster clearance but only moderate tumor accumulation. For both, tumor targeting does not seem to improve further above an optimal affinity. We show here that with very small high-affinity proteins such as designed ankyrin repeat proteins (DARPins), these limits can be overcome. We have systematically investigated the influence of molecular mass and affinity on tumor accumulation with DARPins with specificity for HER2 in SK-OV-3.ip nude mouse xenografts. DARPins with a mass of 14.5 kDa and affinities between 270 nmol/L and 90 pmol/L showed a strong correlation of tumor accumulation with affinity to HER2, with the highest affinity DARPin reaching 8% ID/g after 24 hours and 6.5% ID/g after 48 hours (tumor-to-blood ratio >60). Tumor autoradiographs showed good penetration throughout the tumor mass. Genetic fusion of two DARPins (30 kDa) resulted in significantly lower tumor accumulation, similar to values observed for scFvs, whereas valency had no influence on accumulation. PEGylation of the DARPins increased the circulation half-life, leading to higher tumor accumulation (13.4% ID/g after 24 hours) but lower tumor-to-blood ratios. Affinity was less important for tumor uptake of the PEGylated constructs. We conclude that two regimes exist for delivering high levels of drug to a tumor: small proteins with very high affinity, such as unmodified DARPins, and large proteins with extended half-life, such as PEGylated DARPins, in which the importance of affinity is less pronounced.
Cancer Research 02/2010; 70(4):1595-605. · 7.86 Impact Factor
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ABSTRACT: A key limitation in developing radiotherapeutic proteins is the expense of manufacturing the drug in small batches using traditional reaction vessels. Removing limitations on the quantity of protein labeled at any one time significantly decreases the cost of production, and nowhere is the need for cost-effective radiotherapeutics more acute than in the treatment of cancer.
We describe a novel method that can rapidly radiolabel, theoretically, unlimited amounts of protein, without causing significant damage to binding potency or structural integrity. Our process controls the reaction rate for the isotope and reactants as they simultaneously flow through a reaction tube.
We have demonstrated proof of principle by labeling nearly a gram of antibody with 481 GBq (13 Ci) of (131)I during a single 30-min reaction run.
Simple to construct, our system is already used to manufacture a radiolabeled antibody, both in the United States and in India, as part of clinical trials to treat glioblastoma multiforme. Modified, this system may be also applicable for nonradioactive labeling.
Journal of Nuclear Medicine 07/2009; 50(7):1178-86. · 6.38 Impact Factor
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Robert Waibel,
Hansjörg Treichler,
Niklaus G Schaefer,
Dave R van Staveren,
Stefan Mundwiler,
Susanne Kunze,
Martin Küenzi,
Roger Alberto,
Jakob Nüesch,
Alexander Knuth,
Holger Moch,
Roger Schibli,
Pius August Schubiger
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ABSTRACT: Rapidly growing cells show an increased demand for nutrients and vitamins. The objective of our work is to exploit the supply route of vitamin B12 to deliver new derivatives of this vital vitamin to hyperproliferative cells. To date, radiolabeled ((57)Co and (111)In) vitamin B12 derivatives showed labeling of tumor tissue but also undesired high accumulation of radioactivity in normal tissue. By abolishing the interaction of a tailored vitamin B12 derivative to its transport protein transcobalamin II and therefore interrupting transcobalamin II receptor and megalin mediated uptake in normal tissue, preferential accumulation of a radiolabeled vitamin in cancer tissue could be accomplished. We identified transcobalamin I on tumors as a possible new receptor for this preferential accumulation of vitamin-mediated targeting. The low systemic distribution of radioactivity and the high tumor to blood ratio opens the possibility of a more successful clinical application of vitamin B12 for imaging or therapy.
Cancer Research 05/2008; 68(8):2904-11. · 7.86 Impact Factor
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ABSTRACT: In a phase I/II clinical study, we investigated tumor targeting in patients with head and neck squamous cell carcinomas (SCC), using an antibody directed against the extra-domain-B of fibronectin (EDB), a marker of angiogenesis and tissue remodeling.
Five patients with SCC were injected with the 123-iodine-radiolabeled L19(scFv)2 antibody and underwent scintigraphic detection with single photon emission tomography with computerized tomography (SPECT/CT). In addition, 18F-fluorodeoxyglucose (18FDG) positron emission tomography with computerized tomography (PET/CT) was performed.
Successful targeting of the primary tumor could be achieved in 4 of 5 patients and was comparable to PET imaging. No side effects were observed.
Tumor targeting with the L19(scFv)2 antibody is also feasible for head and neck SCC.
These results may serve as a base for future therapeutical applications in human beings, with modified versions of the L19(scFv)2 antibody, designed to selectively deliver bioactive molecules into malignant tumors.
Otolaryngology Head and Neck Surgery 05/2007; 136(4):543-8. · 1.72 Impact Factor
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ABSTRACT: A major goal in antibody design for cancer therapy is to tailor the pharmacokinetic properties of the molecule according to specific treatment requirements. Key parameters determining the pharmacokinetics of therapeutic antibodies are target specificity, affinity, stability, and size. Using the p185HER-2 (HER-2)-specific scFv 4D5 as model system, we analyzed how changes in molecular weight and valency independently affect antigen binding and tumor localization. By employing multimerization and PEGylation, four different antibody formats were generated and compared with the scFv 4D5. First, dimeric and tetrameric miniantibodies were constructed by fusion of self-associating, disulfide-linked peptides to the scFv 4D5. Second, we attached a 20-kDa PEG moiety to the monovalent scFv and to the divalent miniantibody at the respective C terminus. In all formats, serum stability and full binding reactivity of the scFv 4D5 were retained. Functional affinity, however, did change. An avidity increase was achieved by multimerization, whereas PEGylation resulted in a 5-fold decreased affinity. Nevertheless, the PEGylated monomer showed an 8.5-fold, and the PEGylated dimer even a 14.5-fold higher tumor accumulation than the corresponding scFv, 48 h post-injection, because of a significantly longer serum half-life. In comparison, the non-PEGylated bivalent and tetravalent miniantibodies showed only a moderate increase in tumor localization compared with the scFv, which correlated with the degree of multimerization. However, these non-PEGylated formats resulted in higher tumor-to-blood ratios. Both multimerization and PEGylation represent thus useful strategies to tailor the pharmacokinetic properties of therapeutic antibodies and their combined use can additively improve tumor targeting.
Journal of Biological Chemistry 12/2006; 281(46):35186-201. · 4.77 Impact Factor
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ABSTRACT: A major goal in antibody design for cancer therapy is to tailor the pharmacokinetic properties of the molecule according to
specific treatment requirements. Key parameters determining the pharmacokinetics of therapeutic antibodies are target specificity,
affinity, stability, and size. Using the p185HER-2 (HER-2)-specific scFv 4D5 as model system, we analyzed how changes in molecular weight and valency independently affect antigen
binding and tumor localization. By employing multimerization and PEGylation, four different antibody formats were generated
and compared with the scFv 4D5. First, dimeric and tetrameric miniantibodies were constructed by fusion of self-associating,
disulfide-linked peptides to the scFv 4D5. Second, we attached a 20-kDa PEG moiety to the monovalent scFv and to the divalent
miniantibody at the respective C terminus. In all formats, serum stability and full binding reactivity of the scFv 4D5 were
retained. Functional affinity, however, did change. An avidity increase was achieved by multimerization, whereas PEGylation
resulted in a 5-fold decreased affinity. Nevertheless, the PEGylated monomer showed an 8.5-fold, and the PEGylated dimer even
a 14.5-fold higher tumor accumulation than the corresponding scFv, 48 h post-injection, because of a significantly longer
serum half-life. In comparison, the non-PEGylated bivalent and tetravalent miniantibodies showed only a moderate increase
in tumor localization compared with the scFv, which correlated with the degree of multimerization. However, these non-PEGylated
formats resulted in higher tumor-to-blood ratios. Both multimerization and PEGylation represent thus useful strategies to
tailor the pharmacokinetic properties of therapeutic antibodies and their combined use can additively improve tumor targeting.
Journal of Biological Chemistry 11/2006; 281(46):35186-35201. · 4.77 Impact Factor
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ABSTRACT: [(Methyl-pyridin-2-ylmethyl-amino)-methyl]-phosphonic acid is a new bifunctional chelator for the fac-[(99m)Tc(CO(3))](+) core which can be linked to biomolecules via formation of phosphonic acid esters. Its synthesis and the coupling to model alcohols and to a bioactive molecule (cobinamide) are described. The rhenium complexes [Re(CO)(3)L] of the esters have been prepared and characterized, one of them by X-ray crystallography. The model esters could be labeled with [(99m)Tc(OH(2))(3)(CO)(3)](+) under mild conditions and relatively low ligand concentration with >97% yield and only one isomer formed. The (99m)Tc-labeled cobinamide analog was a mixture of four isomers. It bound strongly to transcobalamin I (TC I, haptocorrin) but only slightly to transcobalamin II (TC II) and intrinsic factor (IF), reflecting the binding abilities of cobinamide. Biodistribution studies in mice with B(16) melanoma exhibited fast clearance with no specific tissue binding.
Nuclear Medicine and Biology 07/2005; 32(5):473-84. · 3.02 Impact Factor
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ABSTRACT: S-Alkylated cysteines are used as efficient tridentate N,O,S-donor-atom ligands for the fac-[M(CO)3]+ moiety (M=99mTc or Re). Reaction of (Et4N)2[ReBr3(CO)3] (3) with the model S-benzyl-L-cysteine (2) leads to the formation of [Re(2′)(CO)3] (4) as the exclusive product (2′=C-terminal anion of 2). The tridentate nature of the alkylated cysteine in 4 was established by X-ray crystallography. Compound 2 reacts with [99mTc(OH2)3(CO)3]+ under mild conditions (10−4M, 50°, 30 min) to afford [99mTc(2′)(CO)3] (5) and represents, therefore, an efficient chelator for the labelling of biomolecules. L-Cysteine, S-alkylated with a 3-aminopropyl group (→7), was conjugated via a peptide coupling sequence with Coα-[α-(5,6-dimethyl-1H-benzimidazolyl)]-Coβ-cyanocobamic b-acid (6), the b-acid of cyanocob(III)alamin (vitamin B12) (Scheme 3). More convenient was a one-pot procedure with a derivative of vitamin B12 comprising a free amine group at the b-position. This amine 15 was treated with NHS (N-hydroxysuccinimide)-activated 1-iodoacetic acid 14 to introduce an I-substituent in vitamin B12. Subsequent addition of unprotected L-cysteine resulted in nucleophilic displacement of the I-atom by the S-substituent, affording the vitamin B12 alkylated cysteine fragment 17 (Scheme 4). The procedure was quantitative and did not require purification of intermediates. Both cobalamin–cysteine conjugates could be efficiently labelled with [99mTc(OH2)3(CO)3]+ (1) under conditions identical to those of the model complex 5. Biodistribution studies of the cobalamin conjugates in mice bearing B10-F16 melanoma tumors showed a tumor uptake of 8.1±0.6% and 4.4±0.5% injected dose per gram of tumor tissue after 4 h and 24 h, respectively (Table 1).
Helvetica Chimica Acta 03/2005; 88(3):447 - 460. · 1.48 Impact Factor
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ABSTRACT: The research and development of smart radiodrugs is the goal of the Center of Radiopharmaceutical Science of ETH, PSI, and USZ. Positron Emission Tomography (PET) allows the non-invasive visualization of biochemical processes within the body. Radiolabeled PET-tracers allow the study of neurophysiological diseases like Alzheimer, Parkinson's disease or the imaging of metastatic tumors. PET-techniques are nowadays an important part of routine nuclear medicine diagnosis. Tumor-cell targeting biomolecules (e.g. antibodies or peptides) coupled to therapeutic radionuclides can sterilize the malignant cells while sparing healthy tissue. This so-called targeted radionuclide therapy has made tremendous progress in the recent years and the first approved radiotherapeutics are available for clinical use.
CHIMIA International Journal for Chemistry 09/2004; 58(10):731-735. · 1.21 Impact Factor
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ABSTRACT: Purpose: Epithelial cell adhesion molecule (Ep-CAM) is a tumor-associated antigen overexpressed in many solid tumors but shows limited expression in normal epithelial tissues. To exploit this favorable expression pattern for targeted cancer therapy, an Ep-CAM-specific recombinant immunotoxin was developed and its antitumor activity investigated.
02/2004;
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Methods in molecular biology (Clifton, N.J.) 02/2004; 248:481-94.
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ABSTRACT: The ribonuclease barnase (12 kDa) and its inhibitor barstar (10 kDa) form a very tight complex in which all N and C termini are accessible for fusion. Here we exploit this system to create modular targeting molecules based on antibody scFv fragment fusions to barnase, to two barnase molecules in series and to barstar. We describe the construction, production and purification of defined dimeric and trimeric complexes. Immobilized barnase fusions are used to capture barstar fusions from crude extracts to yield homogeneous, heterodimeric fusion proteins. These proteins are stable, soluble and resistant to proteolysis. Using fusions with anti-p185(HER2-ECD) 4D5 scFv, we show that the anticipated gain in avidity from monomer to dimer to trimer is obtained and that favorable tumor targeting properties are achieved. Many permutations of engineered multispecific fusion proteins become accessible with this technology of quasi-covalent heterodimers.
Nature Biotechnology 01/2004; 21(12):1486-92. · 23.27 Impact Factor
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ABSTRACT: The ribonuclease barnase (12 kDa) and its inhibitor barstar (10 kDa) form a very tight complex in which all N and C termini are accessible for fusion. Here we exploit this system to create modular targeting molecules based on antibody scFv fragment fusions to barnase, to two barnase molecules in series and to barstar. We describe the construction, production and purification of defined dimeric and trimeric complexes. Immobilized barnase fusions are used to capture barstar fusions from crude extracts to yield homogeneous, heterodimeric fusion proteins. These proteins are stable, soluble and resistant to proteolysis. Using fusions with anti-p185HER2-ECD 4D5 scFv, we show that the anticipated gain in avidity from monomer to dimer to trimer is obtained and that favorable tumor targeting properties are achieved. Many permutations of engineered multispecific fusion proteins become accessible with this technology of quasi-covalent heterodimers.
Nature Biotechnology 11/2003; 21(12):1486-1492. · 23.27 Impact Factor
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ABSTRACT: Epithelial cell adhesion molecule (Ep-CAM) is a tumor-associated antigen overexpressed in many solid tumors but shows limited expression in normal epithelial tissues. To exploit this favorable expression pattern for targeted cancer therapy, an Ep-CAM-specific recombinant immunotoxin was developed and its antitumor activity investigated.
The immunotoxin 4D5MOCB-ETA was developed by genetically fusing a truncated form of Pseudomonas aeruginosa exotoxin A (ETA) (ETA(252-608)KDEL) to the highly stable humanized single-chain antibody fragment (scFv) 4D5MOCB. Cytotoxicity of 4D5MOCB-ETA was measured in cell growth and leucine incorporation assays in vitro. Tumor localization and antitumor activity were assessed in athymic mice bearing established human tumor xenografts.
Fusion of the toxin moiety to the scFv did neither affect its thermal stability nor its antigen-binding affinity. In vitro, 4D5MOCB-ETA potently and specifically inhibited protein synthesis and reduced the viability of Ep-CAM-positive carcinoma cells of diverse histological origins with IC(50)s ranging from 0.005 to 0.2 pM. Upon systemic administration in mice, 4D5MOCB-ETA showed similar organ distribution as the scFv 4D5MOCB and preferentially localized to Ep-CAM-positive tumor xenografts with a tumor:blood ratio of 5.4. The potent antitumor activity of 4D5MOCB-ETA was demonstrated by its ability to strongly inhibit the growth and induce regression of relatively large tumor xenografts derived from lung, colon, or squamous cell carcinomas.
We describe for the first time the development of a fully recombinant Ep-CAM-specific immunotoxin and demonstrate its potent activity against solid tumors of various histological origins. 4D5MOCB-ETA is currently being evaluated in a Phase I study in patients with refractory squamous cell carcinoma of the head and neck.
Clinical Cancer Research 08/2003; 9(7):2837-48. · 7.74 Impact Factor
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ABSTRACT: A general synthetic approach for potent tridentate, bifunctional chelating agent (BFCA) for the [M(CO)(3)](+) fragment (M = (99g)Tc, (99m)Tc, and Re) has been elaborated. The strategy allows the facile preparation of BFCA with a pendent amino or carboxylic acid functionality for coupling to peptides and proteins via formation of an amide bond. [(5-amino-pentyl)-pyridin-2-yl-methyl-amino]-acetic acid (APPA) and [pyridin-2-yl-methyl-amino]-diacetic acid (PADA) were synthesized according to this protocol. The BFCA were labeled with the [M(CO)(3)](+) fragment, which resulted in formation of uniform products with a ligand to metal ratio of 1:1. The complexes have been fully characterized by means of mass spectrometry, IR, and NMR ((1)H, (13)C, (99)Tc) spectroscopy. Coordination of the tricarbonyl core with APPA and PADA was exclusively tridentate (via the acid function, the ternary amine, and the pyridine nitrogen). On the n.c.a. level the complexes were almost quantitatively formed (yield >90%) at ligand concentrations of 10+/-2 microM (PADA) or 50+/-4 microM (APPA) after 30 min at 70 degrees C. Chromatographic behavior of the (99m)Tc complexes is similar to that of the corresponding (99)Tc/Re complexes suggesting the identical chemical structure. Pharmacokinetic experiments with the (99m)Tc-APPA complex were performed in BALB/c mice and compared with previously published results of the (99m)Tc-PADA complex. The (99m)Tc-APPA complex revealed good clearance from the blood pool (0.29 +/- 0.03% ID after 24h p.i.) and a low uptake in the liver (2.41 +/- 0.14% ID/g), in the kidneys (2.81 +/- 0.12% ID/g) and other tissue and organs.
Nuclear Medicine and Biology 07/2003; 30(5):465-70. · 3.02 Impact Factor
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ABSTRACT: To develop new recombinant monoclonal antibody fragments for therapy and imaging, it is indispensable to have a simple and easy procedure to handle the eukaryotic expression system for production of proteins in high amounts. Gene amplification techniques such as the dehydrofolate reductase (DHFR) system in Chinese hamster ovary cells or the glutamine synthase system in myeloma cells have a couple of disadvantages. The selection procedure is complex, time-consuming, and not fruitful in all cases. The toxic drug methotrexate (for the DHFR system) can increase the production rate but decreases the specific growth rate of the cells. The production rate is not always stable over a long-term cultivation period. To overcome these problems, we are using stably transfected human embryonic kidney (HEK-293) cells in combination with an efficient screening method. Sodium butyrate can increase the expression of recombinant antibody fragments in the transfectomas up to 500 micrograms/4.2 x 10(7) cells/24 h corresponding to 175 micrograms/mL culture medium. This strategy allows a rapid development of new recombinant monoclonal antibody fragments and allows one to proceed rapidly to in vivo testing.
BioTechniques 06/2003; 34(5):968-72. · 2.67 Impact Factor
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ABSTRACT: The epithelial glycoprotein-2 is abundantly expressed on many solid tumors and is a suitable target for antibody-based therapy. In the present study, an antiepithelial glycoprotein-2 single-chain Fv (scFv) was derived from the hybridoma MOC31 by phage display. Despite its high affinity (K D # 3.9 # 10 M), however, this antibody fragment failed to significantly enrich at lung tumor xenografts in mice, mostly because of its insufficient thermal stability. To overcome this limitation, the antigenbinding residues of the MOC31 scFv fragment were grafted onto the framework of the highly stable and well-folding anti-c-erbB2 scFv 4D5. Further modification of the resulting 4D5 MOC-A, which was performed by transferring eight additional residues of the heavy chain variable domain core of the parent MOC31 antibody, produced 4D5 MOC-B, resulting in increased serum stability at 37C and also significantly improved expression behavior while retaining the antigen specificity and affinity of the parent MOC31 scFv. In mice, the scFv 4D5 MOC-B, which was radiolabeled with technetium using a new histidine-tag specific labeling method (Waibel et al., Nature Biotechnol., 17: 897--901, 1999), showed favorable blood clearance and efficient enriches at lung tumor xenografts, with a tumor:blood ratio of 5.25 and a total dose of 1.47% injected dose per gram after 24 h. Biophysical properties such as high thermal stability are thus decisive for whether these molecules are useful in vivo, and our approach may provide a general strategy to solve this problem. This is also the first report of using a humanized anti-EGP-2 scFv in vivo for targeting solid tumors, which is a promising targeting moiety for the diagnostics and therapy of EGP-2-positive tumors in patients.
10/2002;
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ABSTRACT: this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact
10/2002;
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ABSTRACT: Multimerization of antibody fragments increases the valency and the molecular weight, both identified as key features in the
design of the optimal targeting molecule. Here, we report the construction of mono-, di-, and tetrameric variants of the anti-tumor
p185HER-2 single chain Fv fragment 4D5 by fusion of self-associating peptides to the carboxyl terminus. Dimeric miniantibodies with
a synthetic helix-turn-helix domain and tetrameric ones with the multimerization domain of the human p53 protein were produced
in functional form in the periplasm of Escherichia coli. We have directly compared these molecules and the single-chain Fv fragment in the targeting of SK-OV-3 xenografts. Tetramerization
of the 4D5 antibody fragment resulted in increased serum persistence, significantly reduced off-rate, due to the avidity effect,
both in surface plasmon resonance measurements on purified p185HER-2 and on SK-OV-3 cells. The99mtechnetium-tricarbonyl-labeled tetrameric 4D5-p53 miniantibody localized with the highest dose at the tumor and remained stably
bound for at least 72 h. The highest total dose was 4.3% injected dose/g after 24 h, whereas the highest tumor-to-blood ratio
was found to be 13.5:1 after 48 h, with a total dose of 3.2% injected dose/g. The tetramer shows no higher avidity than the
dimer, presumably since the simultaneous binding to more than two antigen molecules on the surface of cells is not possible,
and the improvement in performance over the dimer must at least be due in part to the molecular weight. These results demonstrate
that multimerization by self-associating peptides can be used for the development of more effective targeting molecules for
medical diagnostics and therapy.
Journal of Biological Chemistry 04/2001; 276(17):14385-14392. · 4.77 Impact Factor
