Electron spin resonance and magnetic relaxation studies of gadolinium(III) complexes with human transferrin

Protein-Based Nanomedicine for Therapeutic Benefits of Cancer

Proteins, a type of natural biopolymer that possess many prominent merits, have been widely utilized to engineer nanomedicine for fighting against cancer. Motivated by their ever-increasing attention in the scientific community, this review aims to provide a comprehensive showcase on the current landscape of protein-based nanomedicine for cancer therapy. On the basis of role differences of proteins in nanomedicine, protein-based nanomedicine engineered with protein therapeutics, protein carriers, enzymes, and composite proteins is introduced. The cancer therapeutic benefits of the protein-based nanomedicine are also discussed, including small-molecular therapeutics-mediated therapy, macromolecular therapeutics-mediated therapy, radiation-mediated therapy, reactive oxygen species-mediated therapy, and thermal effect-mediated therapy. Lastly, future developments and potential challenges of protein-based nanomedicine are elucidated toward clinical translation. It is believed that protein-based nanomedicine will play a vital role in the battle against cancer. We hope that this review will inspire extensive research interests from diverse disciplines to further push the developments of protein-based nanomedicine in the biomedical frontier, contributing to ever-greater medical advances.

Multi-Targeted Anticancer Activity of Imidazolate Phosphane Gold(I) Compounds by Inhibition of DHFR and TrxR in Breast Cancer Cells

A class of phosphane gold(I) compounds, made of azoles and phosphane ligands, was evaluated for a screening on the regards of Breast Cancer cell panels (BC). The compounds possess N-Au-P or Cl-Au-P bonds around the central metal, and they differ for the presence of aprotic or protic polar groups in the azoles and/or the phosphane moieties to tune their hydrophilicity. Among the six candidates, only the compounds having the P-Au-N environment and not displaying neither the hydroxyl nor carboxyl groups in the ligands were found active. The compounds were screened by MTT tests in SKBR3, A17, and MDA-MB231 cancer cells, and two compounds (namely the 4,5-dicyano-imidazolate-1yl-gold(I)-(triphenylphosphane, 5, and 4,5-dichloro-imidazolate-1yl-gold(I)-triphenylphosphane, 6) were found very cytotoxic, with the most active with an IC₅₀ value of 3.46 μM in MDA-MB231 cells. By performing enzymatic assays in the treated cells lysates, the residual enzymatic activity of dihydrofolate reductase (DHFR) has been measured after cell treatment for 4 or 12 h in comparison with control cells. Upon 12 h of treatment, the activity of DHFR was significantly reduced in both SKBR3 and A17 cells by compounds 5 and 6, but not in human MDA-MB231 cells; interestingly, it was found remarkably high after 4 h of treatment, revealing a time dependence for the DHFR enzymatic assays. The DHFR inhibition data have been compared to those for the thioredoxin reductase (TrxR), the most recognized molecular target for gold compounds. For this latter, similar residual activities (i.e., 37 and 49% for the match of SKBR3 cells and compound 5 or 6, respectively) were found. Binding studies on the regards of ct-DNA (calf-thymus-DNA) and of plasma transporters proteins, such as BSA (bovine serum albumin) and ATF (apo transferrin), were performed. As expected for gold compounds, the data support strong binding to proteins (K_sv values range: 1.51 ÷ 2.46 × 10⁴ M⁻¹) and a weaker interaction with ct-DNA's minor groove (K_sv values range: 1.55 ÷ 6.12 × 10³ M⁻¹).

Direct vibrational structure of protein metal-binding sites from near-infrared Yb3+ vibronic side band spectroscopy

Near-infrared Yb3+ vibronic side band (VSB) spectroscopy is used to obtain structural information of metal binding sites in metalloproteins. This technique provides a selective "IR-like" vibrational spectrum of those ligands chelated to the Yb3+ ion. VSB spectra of various model complexes of Yb3+ representing different ligand types were studied to provide references for the VSB spectra of Yb(3+)-reconstituted metalloproteins. Ca2+ in the calcium-binding protein parvalbumin and Fe3+ in the iron-transporting protein transferrin were replaced with Yb3+. The fluorescence of Yb3+ reconstituted into these two proteins exhibits weak VSBs whose energy shifts, with respect to the main 2F5/2-->2F7/2 Yb3+ electronic transition, represent the vibrational frequencies of the Yb3+ ligands. The chemical nature of the ligands of the Yb3+ in these proteins, as deduced by the observed VSB frequencies, is entirely in agreement with their known crystal structures. For transferrin, replacement of the 12CO3(2-) metal counterion with 13CO3(2-) yielded the expected isotopic shift for the VSBs corresponding to the carbonate vibrational modes. This technique demonstrates enormous potential in elucidating the localized structure of metal binding sites in proteins.

Polymetallic macromolecules are potential contrast agents of improved efficiency

The commercial synthetic homopolypeptide polyaspartate (average MW = 30,000, approximately 220 monomers) in solution quantitatively binds up to 40 mol Gd3+ ions per mole of polyaspartate. The water proton relaxivity of the solutions is far higher than that of clinically used or commonly investigated gadolinium(III) complexes. It is shown that polymetallic macromolecular complexes combine the high relaxing efficiency of monometallic macromolecular complexes with the favorable metal/ligand mass ratio of small monometallic complexes.

Egg-white and blood-serum proteins functioning by noncovalent interactions: studies by chemical modification and comparative biochemistry

Some of the more interesting and important proteins are those that function by forming associations or complexes with other substances. The structure-function relationships of three of these with very different substances are transferrins, which chelate metal ions; avian ovomucoids, which form complexes with proteolytic enzymes; and antifreeze glycoproteins, which interact at the ice-solution interface. Interrelating studies on the comparative biochemistry with studies using chemical modification have helped identify the side-chain groups of the proteins involved in function as well as to be useful for studies on general protein chemistry. The most strongly associated interaction is the chelation of iron by transferrin, with an association constant of approximately 10(21); tyrosines, histidines, and sometimes aspartate are involved. For ovomucoids, individual substratelike residues such as lysine are involved in a Michaelis-like complex, and association constants are as high as 10(10). By contrast, the antifreeze glycoproteins appear to function by a polymeric interaction at the surface of ice, with a much weaker association.

Energy transfer as a probe of protein dynamics in the proteins transferrin and calmodulin

We have initiated an investigation into the usefulness of fluorescence energy transfer in probing protein dynamics. Our analysis involves measuring the energy transfer efficiency while perturbing the protein conformational equilibrium with heat. As the temperature increases, the amplitudes of vibrations increase, and fluorescence energy transfer should also increase if the donor and acceptor are in a flexible region of the protein. A theoretical analysis developed by Somogyi and co-workers for the temperature dependence of dipole-dipole energy transfer (Somogyi, B., J. Matko, S. Papp, J. Hevessey, G. R. Welch, and S. Damjanovich. 1984. Biochemistry. 23:3403-3411) was tested by the authors in one protein system. Energy transfer from tryptophan to a pyridoxamine derivatized side group in RNase increased 40% over 25 degrees C. Here we report further testing of this model in two additional protein systems: calmodulin, a calcium activated regulatory protein, and transferrin, a blood serum iron shuttle. Our studies show a slight differential sensitivity of the transfer efficiency to heat for the two systems. Normalized energy transfer over 6.5 A in calmodulin from a tyrosine donor to a Tb(III) acceptor increases 40% from 295 to 320 K. Normalized energy transfer over 42 A in transferrin from a Tb(III) donor to an Fe(III) acceptor increases 35% over the same temperature range. Whereas these results demonstrate that thermally induced fluctuations do increase energy transfer as predicted by Somogyi, they also appear rather insensitive to the nature of the protein host environment. In contrast to the Förster processes examined above, energy transfer over very short distances has shown an anomalously high temperature dependence.

Mössbauer studies of electrophoretically purified monoferric and diferric human transferrin

Electrophoretically purified 57Fe-enriched monoferric and diferric human transferrins and selectively labeled complexes ([C-56Fe,N-57Fe]transferrin and [C-57Fe,N-56Fe]transferrin) were studied by Mössbauer spectroscopy. The data were recorded at 4.2 K over a wide range of applied magnetic fields (0.05-6 T) and were analyzed by a spin-Hamiltonian formalism. Characteristic hyperfine parameters were found and the obtained zero-field splitting parameters (D = 0.25 +/- 0.05 cm-1 and E/D = 0.30 +/- 0.02) agree with previous electron paramagnetic resonance (EPR) findings. The weak-field spectra of the [N-57Fe]transferrin are slightly broader than those of the [C-57Fe]transferrin, indicating that the N-terminal iron site may be more heterogeneous. However, the absorption line positions and the relative intensities of the subspectra originating from the three Kramers doublets of each Fe3+ site are identical. Thus the electronic structures of the two iron sites can be described by the same set of spin-Hamiltonian parameters, indicating that the ligand environments for the two sites are the same, as suggested by the recent X-ray crystallographic studies. This suggestion is further supported by the observation that the strong-field spectra of the two monoferric transferrins are indistinguishable. The selectively labeled mixed-isotope transferrins exhibit spectra that are identical to those of the corresponding monoferric 57Fe-enriched transferrins, implying that the occupation of one iron site has little or no effect on the immediate environment of the other site, a finding that is not surprising since the two sites are separated by approximately 4.2 nm.

An extended-X-ray-absorption-fine-structure study of freeze-dried and solution ovotransferrin. Evidence for water co-ordination at the metal-binding sites

Our previous extended-X-ray-absorption-fine-structure (e.x.a.f.s.) study has shown that the probable iron environment in chicken ovotransferrin involves two low-Z ligands (consistent with phenolate linkages) at 0.185(1) nm and four low-Z ligands at 0.204(1) nm [Garratt, Evans, Hasnain & Lindley (1986) Biochem. J. 233, 479-484]. Herein we provide additional information from the e.x.a.f.s. and near-edge structure suggestive of a decrease in the co-ordination number of ovotransferrin-bound iron upon freeze-drying. These effects are reversible, and exposure of the freeze-dried material to a humid atmosphere results in reversion to the solution spectra. Progressive rehydration was monitored by using e.p.r. spectroscopy and was confirmed by recording the high-resolution X-ray-absorption near-edge structure (x.a.n.e.s.). The results suggest the presence of a labile water molecule at the iron-binding sites of ovotransferrin in solution.