Safety, sterility and stability of direct-from-vial multiple dosing intravitreal injection of bevacizumab.

BACKGROUND: This study aims to determine the stability, sterility and safety of bevacizumab multiple dosing from a single vial without prior aliquoting. METHODS: In-vitro and human study. Six bevacizumab vials, used in multiple patients on a single day by direct withdrawal from the vial, and stored in 4°C up to a variable period, were tested for stability (high-performance liquid chromatography; [HPLC]), sterility (culture), conformational stability by circular dichroism and fluorescence spectroscopy and the rubber cork structural integrity (electron microscopy [EM]). RESULTS: HPLC of all six samples of used bevacizumab and the control bevacizumab sample were similar; culture was negative; and the EM of rubber corks did not show an open communication. Spectroscopic studies indicated drug conformational stability. Further, there was no infection or inflammation in 221 consecutive patients (973 injections) when bevacizumab was stored at 4°C and used for one week. CONCLUSION: Bevacizumab does not lose stability when stored at 4°C. It may be used for a week by direct withdrawal from the vial without fear of infection or inflammation if all standard precautions related to intravitreal injection are adhered to.

Q2N and S65D substitutions of ubiquitin unravel functional significance of the invariant residues Gln2 and Ser65.

Ubiquitin is a small, globular protein, structure of which has been perfected and conserved through evolution to manage diverse functions in the macromolecular metabolism of eukaryotic cells. Several non-homologous proteins interact with ubiquitin through entirely different motifs. Though the roles of lysines in the multifaceted functions of ubiquitin are well documented, very little is known about the contribution of other residues. In the present study, the importance of two invariant residues, Gln2 and Ser65, have been examined by substituting them with Asn and Asp, respectively, generating single residue variants of ubiquitin UbQ2N and UbS65D. Gln2 and Ser65 form part of parallel G1 ß-bulge adjacent to Lys63, a residue involved in DNA repair, cell-cycle regulated protein synthesis and imparting resistance to protein synthesis inhibitors. The secondary structure of variants is similar to that of UbF45W, a structural homologue of wild-type ubiquitin (UbWt). However, there are certain functional differences observed in terms of resistance to cycloheximide, while there are no major differences pertaining to growth under normal conditions, adherence to N-end rule and survival under heat stress. Further, expression of UbQ2N impedes protein degradation by ubiquitin fusion degradation (UFD) pathway. Such differential responses with respect to functions of ubiquitin produced by mutations may be due to interference in the interactions of ubiquitin with selected partner proteins, hint at biomedical implications.

Glutamate64 to glycine substitution in G1 beta-bulge of ubiquitin impairs function and stabilizes structure of the protein.

Ubiquitin is a globular protein with a highly conserved sequence. Sequence conservation and compact structure make it an ideal protein for structure-function studies. One of the atypical secondary structural features found in ubiquitin is a parallel G1 beta-bulge. Glutamate at 64 is the first residue of this beta-bulge and the third residue in a type II turn. However, glycine is seen in these positions in several proteins. To understand the effects of substitution of glutamate64 by glycine on the structure, stability and function of ubiquitin, mutant UbE64G has been constructed and characterized in Saccharomyces cerevisiae. The secondary and tertiary structures of UbE64G mutant protein are only marginally different from wild-type protein (UbWt) and fluorescent form of ubiquitin (UbF45W). The earlier studies have shown that the structure and stability of UbWt and UbF45W were similar. However, UbE64G has less surface hydrophobicity than UbWt. UbE64G is found to be more stable compared with UbF45W towards guanidinium chloride induced denaturation. In vivo, complementation shows substrate proteins with Pro as the N-terminal residue, which undergo ubiquitination, have extended half-lives with UbE64G. This altered preference for Pro as opposed to Met might be related to natural preference of glutamate at 64th position in ubiquitin.