Structural basis for pure antagonism of integrin αVβ3 by a high affinity form of fibronectin

Integrins are important therapeutic targets. However, current RGD-based anti-integrin drugs are also partial agonists, inducing conformational changes that trigger potentially fatal immune reactions and paradoxical cell adhesion. Here we describe the first crystal structure of αVβ3 bound to a physiologic ligand: the 10th type III RGD-domain of wild-type fibronectin (wtFN10), or to a high affinity mutant (hFN10) that acts as a pure antagonist. Comparison of these structures revealed a central π - π interaction between Trp1496 in the RGD-containing loop of hFN10 and Tyr122 of the β3-subunit that blocked conformational changes triggered by wtFN10, and trapped hFN10-bound αVβ3 in an inactive conformation. Removing the Trp1496 or Tyr122 side-chains, or reorienting Trp1496 away from Tyr122, converted hFN10 into a partial agonist. The findings offer new insights on the mechanism of integrin activation and a basis for design of RGD-based pure antagonists

The α-Subunit Regulates Stability of the Metal Ion at the Ligand-associated Metal Ion-binding Site in β3 Integrins*

The aspartate in the prototypical integrin-binding motif Arg-Gly-Asp binds the integrin βA domain of the β-subunit through a divalent cation at the metal ion-dependent adhesion site (MIDAS). An auxiliary metal ion at a ligand-associated metal ion-binding site (LIMBS) stabilizes the metal ion at MIDAS. LIMBS contacts distinct residues in the α-subunits of the two β3 integrins αIIbβ3 and αVβ3, but a potential role of this interaction on stability of the metal ion at LIMBS in β3 integrins has not been explored. Equilibrium molecular dynamics simulations of fully hydrated β3 integrin ectodomains revealed strikingly different conformations of LIMBS in unliganded αIIbβ3 versus αVβ3, the result of stronger interactions of LIMBS with αV, which reduce stability of the LIMBS metal ion in αVβ3. Replacing the αIIb-LIMBS interface residue Phe(191) in αIIb (equivalent to Trp(179) in αV) with Trp strengthened this interface and destabilized the metal ion at LIMBS in αIIbβ3; a Trp(179) to Phe mutation in αV produced the opposite but weaker effect. Consistently, an F191/W substitution in cellular αIIbβ3 and a W179/F substitution in αVβ3 reduced and increased, respectively, the apparent affinity of Mn(2+) to the integrin. These findings offer an explanation for the variable occupancy of the metal ion at LIMBS in αVβ3 structures in the absence of ligand and provide new insights into the mechanisms of integrin regulation

Cordectomy by CO2 laser or radiotherapy for small T1a glottic carcinomas:Costs, local control, survival, quality of life, and voice quality

Background, The clinical results of radiotherapy and endoscopic cordectomy for T1a glottic carcinoma are reported to be similar, but costs of both treatments may differ. Therefore, we retrospectively evaluated the costs, voice quality, quality of life, and clinical results of both treatments. Methods. Costs and effects from the first visit up to 2 years of follow-up were calculated, based on chart data of 35 and 54 patients who were treated with curative intent for T1 a glottic carcinoma from 1995 to 1999 with radiotherapy and endoscopic cordectomy, respectively. Voice quality and quality of life were evaluated by means of patient questionnaires. Results. Total costs (in Euros) of radiotherapy and CO2-laser cordectomy were EURO8322 and EURO4434, respectively, including the costs of treating possible recurrences. The effects of both treatments were equal, including voice quality and quality of life. Conclusions. We conclude that endoscopic cordectomy is an efficient alternative for radiotherapy for these patients. (c) 2006 Wiley Periodicals, Inc

Structural Basis of the Differential Binding of Engineered Knottins to Integrins αVβ3 and α5β1

Targeting both integrins αVβ3 and α5β1 simultaneously appears to be more effective in cancer therapy than targeting each one alone. The structural requirements for bispecific binding of ligand to integrins have not been fully elucidated. RGD-containing knottin 2.5F binds selectively to αVβ3 and α5β1, whereas knottin 2.5D is αVβ3 specific. To elucidate the structural basis of this selectivity, we determined the structures of 2.5F and 2.5D as apo proteins and in complex with αVβ3, and compared their interactions with integrins using molecular dynamics simulations. These studies show that 2.5D engages αVβ3 by an induced fit, but conformational selection of a flexible RGD loop accounts for high-affinity selective binding of 2.5F to both integrins. The contrasting binding of the highly flexible low-affinity linear RGD peptides to multiple integrins suggests that a "Goldilocks zone" of conformational flexibility of the RGD loop in 2.5F underlies its selective binding promiscuity to integrins

The α-Subunit Regulates Stability of the Metal Ion at the Ligand-associated Metal Ion-binding Site in β3 Integrins

The aspartate in the prototypical integrin-binding motif Arg-Gly-Asp binds the integrin βA domain of the β-subunit through a divalent cation at the metal ion-dependent adhesion site (MIDAS). An auxiliary metal ion at a ligand-associated metal ion-binding site (LIMBS) stabilizes the metal ion at MIDAS. LIMBS contacts distinct residues in the α-subunits of the two β(3) integrins α(IIb)β(3) and α(V)β(3), but a potential role of this interaction on stability of the metal ion at LIMBS in β(3) integrins has not been explored. Equilibrium molecular dynamics simulations of fully hydrated β(3) integrin ectodomains revealed strikingly different conformations of LIMBS in unliganded α(IIb)β(3) versus α(V)β(3), the result of stronger interactions of LIMBS with α(V), which reduce stability of the LIMBS metal ion in α(V)β(3). Replacing the α(IIb)-LIMBS interface residue Phe(191) in α(IIb) (equivalent to Trp(179) in α(V)) with Trp strengthened this interface and destabilized the metal ion at LIMBS in α(IIb)β(3); a Trp(179) to Phe mutation in α(V) produced the opposite but weaker effect. Consistently, an F191/W substitution in cellular α(IIb)β(3) and a W179/F substitution in α(V)β(3) reduced and increased, respectively, the apparent affinity of Mn(2+) to the integrin. These findings offer an explanation for the variable occupancy of the metal ion at LIMBS in α(V)β(3) structures in the absence of ligand and provide new insights into the mechanisms of integrin regulation

Atomic Basis for the Species-specific Inhibition of αV Integrins by Monoclonal Antibody 17E6 Is Revealed by the Crystal Structure of αVβ3 Ectodomain-17E6 Fab Complex*

The function-blocking, non-RGD-containing, and primate-specific mouse monoclonal antibody 17E6 binds the αV subfamily of integrins. 17E6 is currently in phase II clinical trials for treating cancer. To elucidate the structural basis of recognition and the molecular mechanism of inhibition, we crystallized αVβ3 ectodomain in complex with the Fab fragment of 17E6. Protein crystals grew in presence of the activating cation Mn(2+). The integrin in the complex and in solution assumed the genuflected conformation. 17E6 Fab bound exclusively to the Propeller domain of the αV subunit. At the core of αV-Fab interface were interactions involving Propeller residues Lys-203 and Gln-145, with the latter accounting for primate specificity. The Propeller residue Asp-150, which normally coordinates Arg of the ligand Arg-Gly-Asp motif, formed contacts with Arg-54 of the Fab that were expected to reduce soluble FN10 binding to cellular αVβ3 complexed with 17E6. This was confirmed in direct binding studies, suggesting that 17E6 is an allosteric inhibitor of αV integrins

Compliance and efficiency before and after implementation of a clinical practice guideline for laryngeal carcinomas.

Contains fulltext : 49983.pdf (publisher's version ) (Closed access)We evaluated whether the implementation of a nationwide clinical practice guideline for diagnosis, treatment and follow-up of laryngeal carcinomas led to changes in hospital costs, balanced against clinical changes observed following the guideline's implementation. Charts of 822 patients with larynx carcinoma (459 treated before the introduction of the guideline and 363 thereafter) in five hospitals were retrospectively investigated. In all phases, no differences in total hospital costs were observed after the guideline's implementation. Total mean costs were Euro 3,207 (95%CI 3,091-3,395) for diagnosis, Euro 3,169 (2,153-4,182), Euro 5,026 (3,996-6,057), Euro 6,458 (5,579-7,337), Euro 8,037 (7,469-8,606), Euro 12,765 (10,763-14,769), Euro 19,227 (16,848-21,605) for treatment of dysplasia, carcinoma in situ, T1, T2, T3 and T4 carcinoma, respectively, and Euro 1,856 (1,491-2,220) for 1 year disease-free follow-up. In an earlier study, we observed several positive changes after the guideline's implementation. Balanced against the equal costs before and after the guideline's implementation, we conclude that the efficiency of the care process improved