Most human carcinoma cell lines lack the high-affinity receptors for adenovirus serotype 5 (Ad5) at their surface and are nonpermissive to Ad5. We therefore tested the efficiency of retargeting Ad5 to alternative cellular receptors via immunoglobulin (Ig)-binding domains inserted at the extremity of short-shafted, knobless fibers. The two recombinant Ad5's constructed, Ad5/R7-Z wt -Z wt and Ad5/R7-C2-C2, carried tandem Ig-binding domains from Staphylococcal protein A (abbreviated Z wt ) and from Streptococcal protein G (C2), respectively. Both viruses bound their specific Ig isotypes with the expected affinity. They transduced human carcinoma cells independently of the CAR pathway, via cell surface receptors targeted by specific monoclonal antibodies, that is, EGF-R on A549, HT29 and SW1116, HER-2/ neu on SK-OV-3 and SK-BR-3, CA242 (epitope recognized by the monoclonal antibody C242) antigen on HT29 and SW1116, and PSMA (prostate-specific membrane antigen) expressed on HEK-293 cells, respectively. However, Colo201 and Colo205 cells were neither transduced by targeting CA242 or EGF-R nor were LNCaP cells transduced by targeting PSMA. Our results suggested that one given surface receptor could mediate transduction of certain cells but not others, indicating that factors and steps other than cell surface expression and virus-receptor interaction are additional determinants of Ad5-mediated transduction of tumor cells. Using penton base RGD mutants, we found that one of these limiting steps was virus endocytosis. Gene Therapy (2005) 12, 211-224.

Affinity chromatography provides an excellent platform for protein purification, which is a key step in the large scale downstream processing of therapeutic monoclonal antibodies (Mabs). Protein A chromatography constitutes the gold standard for Mab purification. However, the required acidic conditions (2.8-3.5) for elution from the affinity matrix limit their applicability, particularly for next generation antibodies and antibody fusion proteins, since denaturation and irreversible aggregation can occur due to the acidic buffer conditions. Here we describe a generic procedure for the generation of antigen-specific chromatography ligands with tailor-made elution conditions. To this end, we generated a scFv-library based on mRNA from a chicken immunized with human Fc. The antibody repertoire was displayed on yeast Saccharomyces cerevisiae screened via FACS toward pH-and magnesium-responsive scFvs which specifically recognize human IgG antibodies. Isolated scFvs were reformatted, produced in Escherichia coli and immobilized on NHS-agarose columns. Several scFvs were identified that mediated antibody binding at neutral pH and antibody recovery at pH values of 4.5 and higher or even at neutral pH upon MgCl 2 exposure. The iterative screening methodology established here is generally amenable to the straightforward isolation of stimulus-responsive antibodies that may become valuable tools for a variety of applications.

Herein, we present the design, synthesis, and biological evaluation of novel integrin-targeting molecular hybrids combining RGD peptides and a potent cytotoxin presented on dextran polysaccharides. Based on an aglycosylated Fc as a centerpiece, endosomal-cleavable cytotoxic agent monomethyl auristatin E (MMAE) and dextran as multimerization site were covalently connected by two bioorthogonal enzyme-mediated reactions site-specifically. Decoration of dextran with cyclic RGD peptides, introduced by copper “click” reaction, resulted in the final constructs with the potential to kill integrin-overexpressing tumor cells. We found that these modifications had little impact on the stability of the Fc scaffold and the RGD-bearing construct showed good binding properties of αvβ3-expressing U87MG cells. Furthermore, the construct showed a remarkable antiproliferative activity. These results demonstrate the general capability of our design to provoke receptor-mediated endocytosis upon binding to the cellular surface, followed by endosomal cleavage of the linkage between Fc-dextran and MMAE and its subsequent release. Our approach opens new avenues to transcribe small molecule binders into tailor-made multimeric molecular hybrids with antitumor potential.

Sactipeptides are ribosomally synthesized peptides containing a unique sulfur to α‐carbon crosslink. Catalyzed by sactisynthases, this thioether pattern endows sactipeptides with enhanced structural, thermal, and proteolytic stability, which makes them attractive scaffolds for the development of novel biotherapeutics. Herein, we report the in‐depth study on the substrate tolerance of the sactisynthase AlbA to catalyze the formation of thioether bridges in sactipeptides. We identified a possible modification site within the sactipeptide subtilosin A allowing for peptide engineering without compromising formation of thioether bridges. A panel of natural and hybrid sactipeptides was produced to study the AlbA‐mediated formation of thioether bridges, which were identified mass‐spectrometrically. In a proof‐of‐principle study, we re‐engineered subtilosin A to a thioether‐bridged, specific streptavidin targeting peptide, opening the door for the functional engineering of sactipeptides.

Sactipeptide sind ribosomal synthetisierte Peptide, die eine einzigartige Verknüpfung von Schwefel und α-Kohlenstoffen enthalten. Die Bildung von Thioetherbrücken wird in diesen Molekülen durch Sactisynthasen katalysiert. Diese spezielle Art der Verknüpfung verleiht Sactipeptiden eine erhöhte strukturelle, thermische und proteolytische Stabilität, was sie zu attraktiven Gerüsten für die Entwicklung neuer Biotherapeutika macht. In diesem Artikel berichten wir über eine Studie zur Substrattoleranz der Sactisynthase AlbA, die die Bildung von Thioetherbrücken im Sactipeptid Subtilosin A katalysiert. Wir haben eine Modifikationsstelle innerhalb dieses Sactipeptids identifiziert, die ein Peptid-Engineering ohne Beeinträchtigung der Bildung von Thioetherbrücken ermöglicht. Eine Reihe von natürlichen und hybriden Sactipeptidkonstrukten wurde hergestellt, um die AlbA vermittelte Bildung von Thioetherbrücken zu untersuchen und diese massenspektrometrisch zu identifizieren. In einer Proofof-Principle-Studie haben wir Subtilosin A mit einer neue Funktion ausgestattet, ein Thioether-verbrücktes Streptavidin-bindendes Peptid generiert und damit die Tür für das funktionelle Engineering von Sactipeptiden weiter geöffnet.