Italian survey on cetuximab-based therapy of elderly patients with metastatic colorectal cancer.

Purpose: There is no consensus on the use of cetuximab in elderly patients with metastatic colorectal cancer. To this end, a survey was carried in 17 Italian oncology centers.

Methods: The centers answered a 29-item questionnaire structured as follows: (i) demographic characteristics; (ii) medical history; (iii) assessment of RAS/BRAF mutations and DPD/UGT polymorphism before treatment; (iv) treatment schemes and side effects; (v) geriatric assessment and customization of treatment.

Quality of life, compliance, safety and effectiveness in fit older metastatic colorectal patients with cancer treated in first-line with chemotherapy plus cetuximab: A restrospective analysis from the ObservEr study.

Objectives: The influence of age (<70 years and ≥70 years) was retrospectively studied on the quality of life (QoL), incidence of side effects (including skin reactions) and efficacy of chemotherapy plus cetuximab in patients with KRAS wild type (WT) metastatic colorectal cancer (mCRC).

Methods: 225 patients of the Observed study (PS 0-1) were retrieved based on age (< 70 and ≥70 years) and evaluated through EORTC QLQ-C30 and DLQI questionnaires.

Results: The two patient groups (141 < 70 and 84 ≥ 70 years, respectively) were balanced with no differences in any of the clinical and pathological characteristics considered.

Observational study on quality of life, safety, and effectiveness of first-line cetuximab plus chemotherapy in KRAS wild-type metastatic colorectal cancer patients: the ObservEr Study.

Cetuximab improves efficacy when added to chemotherapy for metastatic colorectal cancer (mCRC). Effective management of skin reactions from cetuximab improves quality of life (QoL), and treatment compliance in clinical trials. No data are available from real-world settings.

Experimental and simulative dissociation of dimeric Cu,Zn superoxide dismutase doubly mutated at the intersubunit surface.

The equilibrium properties of dimeric Photobacterium leiognathi Cu,Zn superoxide dismutase mutant bearing two negative charges in the amino acid clusters at the association interface has been studied, experimentally and computationally, and compared to those of the native enzyme. Pressure-dependent dissociation is observed for the mutant, as observed by the fluorescence shift of the unique tryptophan residue located at the intersubunit surface. The spectral shift occurs slowly, reaching a plateau after 15-20 min, and is fully reversible.

Superefficient enzymes.

Diffusion-controlled enzymes are characterized by second-order rate constants in the range 10(8)-10(10) M(-1)s(-1). These values are at the upper end of the observed rates of many enzyme-substrate reactions and have been predicted by theoretical studies on bimolecular reaction in solution. Such enzymes are considered to be perfect, since their rate-limiting step is not due to any chemical event but to the diffusional association rate between the enzyme and the substrate.

Dynamic features of the subunit interface of Cu,Zn superoxide dismutase as probed by tryptophan phosphorescence.

As part of the more general inquiry on the molecular basis of specific recognition between macromolecules, the subunit-subunit interface structure of dimeric superoxide dismutase from Photobacterium leiognathi has been probed selectively by the phosphorescence emission of Trp-73, located at the subunit contact region. Copper at the catalytic site was found to quench completely the delayed emission and therefore all studies were conducted with the copper-free or Cd(2+)-substituted protein. The spectrum at 140 K is diagnostic for an indole ring located in a hydrophobic environment whereas a degree of spectral broadening indicates that the local structure is not unique.

Dynamics-function correlation in Cu, Zn superoxide dismutase: a spectroscopic and molecular dynamics simulation study.

A single mutation (Val29-->Gly) at the subunit interface of a Cu, Zn superoxide dismutase dimer leads to a twofold increase in the second order catalytic rate, when compared to the native enzyme, without causing any modification of the structure or the electric field distribution. To check the role of dynamic processes in this catalytic enhancement, the flexibility of the dimeric protein at the subunit interface region has been probed by the phosphorescence and fluorescence properties of the unique tryptophan residue. Multiple spectroscopic data indicate that Trp83 experiences a very similar, and relatively hydrophobic, environment in both wild-type and mutant protein, whereas its mobility is distinctly more restrained in the latter.

Single mutations at the subunit interface modulate copper reactivity in Photobacterium leiognathi Cu,Zn superoxide dismutase.

The functional properties and X-ray structures of five mutant forms of Photobacterium leiognathi Cu,Zn superoxide dismutase carrying single mutations at residues located at the dimer association interface have been investigated. When compared to the wild-type enzyme, the three-dimensional structures of the mutants show structural perturbations limited to the proximity of the mutation sites and substantial identity of active site geometry. Nonetheless, the catalytic rates of all mutants, measured at neutral pH and low ionic strength by pulse radiolysis, are higher than that of the wild-type protein.

Single mutation at the intersubunit interface confers extra efficiency to Cu,Zn superoxide dismutase.

The Val28-->Gly single mutant at the subunit interface of Cu,Zn superoxide dismutase from Photobacterium leiognathi displays a k(cat)/K(M) value of 1.7x10(10) M(-1) s(-1), twice that of the native enzyme. Analysis of the three-dimensional structure indicates that the active site Cu,Zn center is not perturbed, slight structural deviations being only localized in proximity of the mutation site.

Functional and crystallographic characterization of Salmonella typhimurium Cu,Zn superoxide dismutase coded by the sodCI virulence gene.

The functional and three-dimensional structural features of Cu,Zn superoxide dismutase coded by the Salmonella typhimurium sodCI gene, have been characterized. Measurements of the catalytic rate indicate that this enzyme is the most efficient superoxide dismutase analyzed so far, a feature that may be related to the exclusive association of the sodCI gene with the most pathogenic Salmonella serotypes. The enzyme active-site copper ion is highly accessible to external probes, as indicated by quenching of the water proton relaxation rate upon addition of iodide.

Single mutation induces a metal-dependent subunit association in dimeric Cu,Zn superoxide dismutase.

Tryptophan 83, a residue strongly involved in the intersubunit interaction of the Cu,Zn superoxide dismutases from Photobacterium leiognathi, has been selectively mutated to phenylalanine or tyrosine. The recombinant mutant enzymes expressed in Escherichia coli were purified in two well distinct and stable forms, one dimeric and fully active and the other monomeric and devoid of metals. In agreement, in vitro experiments indicate that the removal and addition of zinc in the mutant enzymes induces monomerization and dimerization, respectively, while does not perturb the dimeric association of the native protein.

Role of the tertiary and quaternary structures in the stability of dimeric copper, zinc superoxide dismutases.

The equilibrium unfolding process of human Cu,Zn superoxide dismutase has been quantitatively monitored through circular dichroism and fluorescence spectroscopy as a function of increasing guanidinium hydrochloride concentration. The process occurs through the formation of a monomeric intermediate species following a three-state transition equilibrium. Comparison with the stability of the prokaryotic Cu,Zn SOD from P.

Evidence of stable monomeric species in the unfolding of Cu,Zn superoxide dismutase from Photobacterium leiognathi.

The equilibrium unfolding process of Photobacterium leiognathi Cu,Zn superoxide dismutase has been quantitatively monitored through circular dichroism (CD) and fluorescence spectroscopy, upon increasing the guanidinium hydrochloride concentration. The study has been undertaken for both the holo- and the copper-free derivative to work out the role of copper in protein stability. In both cases the unfolding was reversible.

Incoherent neutron scattering of copper azurin: a comparison with molecular dynamics simulation results.

The low-frequency dynamics of copper azurin has been studied at different temperatures for a dry and deuterium hydrated sample by incoherent neutron scattering and the experimental results have been compared with molecular dynamics (MD) simulations carried out in the same temperature range. Experimental Debye-Waller factors are consistent with a dynamical transition at approximately 200 K which appears partially suppressed in the dry sample. Inelastic and quasielastic scattering indicate that hydration water modulates both vibrational and diffusive motions.

Characterization of the spectroscopic properties of the Cu,Co cluster in a prokaryotic superoxide dismutase.

A Cu,Co derivative of the Cu,ZnSOD from Photobacterium leiognathi, in which cobalt has been selectively substituted for zinc, has been prepared and spectroscopically investigated. The derivative shows three bands in the visible region at 530, 566, and 600 nm when copper is in the oxidized state. Reduction or depletion of the copper ion produce a shift of the band absorbing at 600 to 590 nm because of the detachment from copper of the imidazolate bridging the two metals when copper is in the oxidized state.

Evolutionary constraints for dimer formation in prokaryotic Cu,Zn superoxide dismutase.

Prokaryotic Cu,Zn superoxide dismutases are characterized by a distinct quaternary structure, as compared to that of the homologous eukaryotic enzymes. Here we report a newly determined crystal structure of the dimeric Cu,Zn superoxide dismutase from Photobacterium leiognathi (crystallized in space group R32, refined at 2.5 A resolution, R-factor 0.

On the coordination and oxidation states of the active-site copper ion in prokaryotic Cu,Zn superoxide dismutases.

The active-site copper ion of the prokaryotic Cu,Zn superoxide dismutase from P. leiognathi is found to undergo reversible reduction upon irradiation of the protein solution with a high-intensity X-ray beam from a third-generation synchrotron source. The same phenomenon is observed for the enzyme crystals, whose diffraction pattern has been obtained from synchrotron sources.

Cu,Zn superoxide dismutase from Photobacterium leiognathi is an hyperefficient enzyme.

The catalytic rate constant of recombinant Photobacterium leiognathi Cu,Zn superoxide dismutase has been determined as a function of pH by pulse radiolysis. At pH 7 and low ionic strength (I = 0.02 M) the catalytic rate constant is 8.

Fourier transform infrared analysis of the interaction of azide with the active site of oxidized and reduced bovine Cu,Zn superoxide dismutase.

Binding of azide to the native and arginine-modified bovine Cu,Zn superoxide dismutase in the oxidized and reduced form and to the copper-free derivative has been investigated by Fourier transform infrared spectroscopy. The antisymmetric stretching band of the azide is shifted to higher energy upon coordination to the copper atom of the oxidized form of the native enzyme. Similar spectral changes occur upon interaction of the anion with the Cu-diethylenetriamine model compound.

Evidence of his61 imidazolate bridge rupture in reduced crystalline Cu,Zn superoxide dismutase.

X-ray absorption spectroscopy has been carried out on the copper K edge in oxidized and reduced bovine Cu,Zn SOD in solution and in crystalline state. The results indicate that the copper coordination geometry is unaffected by the solution or by the crystalline state of the protein, in both oxidation states. Moreover the two oxidation states of the active copper ion are reflected under, all the experimental conditions, by distinct coordination spheres around the catalytic metal, which is four-coordinated and three-coordinated in the Cu(II) and in the Cu(I) enzyme, respectively.

Characterization of Cu,Zn superoxide dismutase from the bathophile fish, Lampanyctus crocodilus.

Cu,Zn SOD from the bathophile teleost Lampanyctus crocodilus (LSOD) shows a high degree of homology with the sequence of the enzymes from other teleostean fish species. The catalytic properties of LSOD are very similar to those of the bovine enzyme, albeit with higher sensitivity to thermal denaturation. The apparent molecular mass of LSOD (37.

Spectroscopic characterization of recombinant Cu,Zn superoxide dismutase from Photobacterium leiognathi expressed in Escherichia coli: evidence for a novel catalytic copper binding site.

Cu,Zn superoxide dismutase from Photobacterium leiognathi has been cloned and expressed in Escherichia coli. The circular dichroism spectrum in the UV region of the recombinant protein indicates an higher content of random coil structure with respect to the eukaryotic enzymes. Investigation of the active site by optical, CD, and EPR spectroscopy indicates a different coordination geometry around the catalytic copper site with respect to the eukaryotic enzymes.

Low-temperature optical spectroscopy of cobalt in Cu,Co superoxide dismutase: a structural dynamics study of the solvent-unaccessible metal site.

The temperature dependence (300 to 10 K) of the electronic absorption spectra of the cobalt chromophore in bovine superoxide dismutase (SOD) having the native Zn(II) ion selectivity replaced by Co(II) has been investigated in four different derivatives: Cu(II),Co(II) SOD, N3(-)-Cu(II), Co(II) SOD, Cu(I),Co(II) SOD, and E,Co(II) SOD in which the copper ion has been selectively removed. In the Cu(II),Co(II) SOD, the cobalt spectrum is characterized at room temperature by three bands centered at 18,472, 17,670, and 16,793 cm-1; the low-frequency band is split, at low temperatures, into two components, indicating a lower symmetry contribution to a predominantly tetrahedral crystal field. Addition of N3- to the Cu(II),Co(II) SOD introduces slight changes in all the Co(II) visible bands, indicating the occurrence of minor perturbations of the structural cobalt site upon anion binding to the catalytic copper site.

Low-temperature optical spectroscopy of native and azide-reacted bovine Cu,Zn superoxide dismutase. A structural dynamics study.

The optical absorption spectra of native and N(3-)-reacted Cu,Zn superoxide dismutase (SOD) has been studied in the temperature range 300-10 K. The broad d-d bands observed in the room temperature spectrum, centered at 14,700 cm-1 (native enzyme) and at 15,550 cm-1 (N(3-)-reacted enzyme), are clearly split at low temperature into two bands each, centered at 12,835 and 14,844 cm-1 and at 14,418 and 16,300 cm-1, respectively. The thermal behavior of the 23,720 cm-1 band present in the spectrum of the native enzyme indicates that this band belongs to the His61-->Cu(II) ligand to metal charge transfer transition.