Phase I clinical study of the recombinant antibody toxin scFv(FRP5)-ETA specific for the ErbB2/HER2 receptor in patients with advanced solid malignomas

INTRODUCTION: ScFv(FRP5)-ETA is a recombinant antibody toxin with binding specificity for ErbB2 (HER2). It consists of an N-terminal single-chain antibody fragment (scFv), genetically linked to truncated Pseudomonas exotoxin A (ETA). Potent antitumoral activity of scFv(FRP5)-ETA against ErbB2-overexpressing tumor cells was previously demonstrated in vitro and in animal models. Here we report the first systemic application of scFv(FRP5)-ETA in human cancer patients. METHODS: We have performed a phase I dose-finding study, with the objective to assess the maximum tolerated dose and the dose-limiting toxicity of intravenously injected scFv(FRP5)-ETA. Eighteen patients suffering from ErbB2-expressing metastatic breast cancers, prostate cancers, head and neck cancer, non small cell lung cancer, or transitional cell carcinoma were treated. Dose levels of 2, 4, 10, 12.5, and 20 μg/kg scFv(FRP5)-ETA were administered as five daily infusions each for two consecutive weeks. RESULTS: No hematologic, renal, and/or cardiovascular toxicities were noted in any of the patients treated. However, transient elevation of liver enzymes was observed, and considered dose limiting, in one of six patients at the maximum tolerated dose of 12.5 μg/kg, and in two of three patients at 20 μg/kg. Fifteen minutes after injection, peak concentrations of more than 100 ng/ml scFv(FRP5)-ETA were obtained at a dose of 10 μg/kg, indicating that predicted therapeutic levels of the recombinant protein can be applied without inducing toxic side effects. Induction of antibodies against scFv(FRP5)-ETA was observed 8 days after initiation of therapy in 13 patients investigated, but only in five of these patients could neutralizing activity be detected. Two patients showed stable disease and in three patients clinical signs of activity in terms of signs and symptoms were observed (all treated at doses ≥ 10 μg/kg). Disease progression occurred in 11 of the patients. CONCLUSION: Our results demonstrate that systemic therapy with scFv(FRP5)-ETA can be safely administered up to a maximum tolerated dose of 12.5 μg/kg in patients with ErbB2-expressing tumors, justifying further clinical development

Molecular Design, Functional Characterization and Structural Basis of a Protein Inhibitor Against the HIV-1 Pathogenicity Factor Nef

Increased spread of HIV-1 and rapid emergence of drug resistance warrants development of novel antiviral strategies. Nef, a critical viral pathogenicity factor that interacts with host cell factors but lacks enzymatic activity, is not targeted by current antiviral measures. Here we inhibit Nef function by simultaneously blocking several highly conserved protein interaction surfaces. This strategy, referred to as “wrapping Nef”, is based on structure-function analyses that led to the identification of four target sites: (i) SH3 domain interaction, (ii) interference with protein transport processes, (iii) CD4 binding and (iv) targeting to lipid membranes. Screening combinations of Nef-interacting domains, we developed a series of small Nef interacting proteins (NIs) composed of an SH3 domain optimized for binding to Nef, fused to a sequence motif of the CD4 cytoplasmic tail and combined with a prenylation signal for membrane association. NIs bind to Nef in the low nM affinity range, associate with Nef in human cells and specifically interfere with key biological activities of Nef. Structure determination of the Nef-inhibitor complex reveals the molecular basis for binding specificity. These results establish Nef-NI interfaces as promising leads for the development of potent Nef inhibitors

Synthesis and applications of chemical probes for human O6-alkylguanine-DNA alkyltransferase

The design and synthesis of chem. probes to study and to elucidate complex biol. problems is becoming an increasingly important field in chem. We are interested in the repair of O6-alkylated guanines in DNA, a DNA lesion that results from alkylation by S-adenosylmethionine or exogenous toxins and which has been shown to be highly mutagenic and carcinogenic. The DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT; EC 2.1.1.63) reverses this alkylation by transferring the alkyl group to a reactive cysteine residue in the protein, leading to repaired DNA and an irreversibly alkylated protein. The expression level of human AGT (hAGT) in tumor cells is also crucial for their sensitivity to chemotherapeutic agents that alkylate DNA, such as 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and temozolomide. Consequently, hAGT has become a target in cancer chemotherapy, as its inhibition would increase the efficiency of currently used DNA-alkylating drugs. A simple and reliable assay to measure the activity of hAGT in cell exts. would be of great importance for research on the role of hAGT in the chemotherapy of tumors, as currently used assays rely on radioactively labeled substrates and a subsequent HPLC sepn. We describe here the synthesis of oligonucleotides contg. O6-alkylated guanine derivs. of the type 1 and 2 that serve as affinity labels for hAGT and their use in a highly specific assay for this alkyltransferase. In addn., we introduce a novel system for the directed mol. evolution of hAGT, which relies on the display of active hAGT on phage l and on oligonucleotides contg. O6-alkylated guanine derivs. of the type 1 and 2. [on SciFinder (R)

Methods using o<6>-alkylguanine-dna alkyltransferases

A method using O-alkylguanine-DNA alkyltransferases (AGT) is disclosed for transferring a label from a substrate to a fusion protein comprising the AGT. This allows the detection and/or manipulating of the fusion protein, both in vitro and in vivo, by attaching molecules to the fusion proteins that introduce a new physical or chemical property to the fusion protein. Examples of such molecules are, among others, spectroscopic probes or reporter molecules, affinity tags, molecules generating reactive radicals, cross-linkers, ligands mediating protein-protein interactions or molecules suitable for the immobilisation of the fusion protein

A general method for the covalent labeling of fusion proteins with small molecules in vivo

Characterizing the movement, interactions, and chem. microenvironment of a protein inside the living cell is crucial to a detailed understanding of its function. Most strategies aimed at realizing this objective are based on genetically fusing the protein of interest to a reporter protein that monitors changes in the environment of the coupled protein. Examples include fusions with fluorescent proteins, the yeast two-hybrid system, and split ubiquitin. However, these techniques have various limitations, and considerable effort is being devoted to specific labeling of proteins in vivo with small synthetic mols. capable of probing and modulating their function. These approaches are currently based on the noncovalent binding of a small mol. to a protein, the formation of stable complexes between biarsenical compds. and peptides contg. cysteines, or the use of biotin acceptor domains. Here we describe a general method for the covalent labeling of fusion proteins in vivo that complements existing methods for noncovalent labeling of proteins and that may open up new ways of studying proteins in living cells