1. A humanised mouse model of cytokine release: comparison of CD3-specific antibody fragments
S Shaw, S L Malcolm, E L Smith, T Bourne J Immunol Methods . 2012 Oct 31;384(1-2):33-42. doi: 10.1016/j.jim.2012.07.001.
CD3-specific antibodies have shown clinical efficacy in both transplantation and autoimmunity. However, targeting CD3 in this way can lead to T-cell activation and a serious cytokine release syndrome mediated by Fcγ receptor binding. An in vivo mouse model has been developed using severe combined immunodeficient (SCID) mice to detect human T-cell depletion and cytokine release into the circulation after administration of OKT3. This system has been used to evaluate OKT3 antibody fragments lacking the entire Fc region alongside whole antibody constructs. These data clearly show that cytokine release is detected with all OKT3 antibody constructs and fragments tested and these can be ranked from highest to lowest as follows: mIgG2a>hIgG1 (Ala-Ala)>hIgG1 diFab' maleimide (DFM)>hIgG1 F(ab')₂>mIgG2a F(ab')₂>hIgG1 Fab'. Furthermore, the monovalent hIgG1 Fab' fragment gives the least cytokine release but it does not deplete human T-cells in this assay format. This suggests that T-cell activation may be playing a role in the mechanism of action of anti-CD3 antibodies and consequently the unwanted cytokine release is potentially unavoidable for this class of molecules. This model system provides a useful tool to aid in understanding and reducing the potential risks of cytokine release following antibody therapy.
2. Total synthesis and evaluation of [Psi[CH2NH]Tpg4]vancomycin aglycon: reengineering vancomycin for dual D-Ala-D-Ala and D-Ala-D-Lac binding
Brendan M Crowley, Dale L Boger J Am Chem Soc . 2006 Mar 8;128(9):2885-92. doi: 10.1021/ja0572912.
An effective synthesis of [Psi[CH(2)NH]Tpg(4)]vancomycin aglycon (5) is detailed in which the residue 4 amide carbonyl of vancomycin aglycon has been replaced with a methylene. This removal of a single atom was conducted to enhance binding to D-Ala-D-Lac, countering resistance endowed to bacteria that remodel their D-Ala-D-Ala peptidoglycan cell wall precursor by a similar single atom change (ester O for amide NH). Key elements of the approach include a synthesis of the modified vancomycin ABCD ring system featuring a reductive amination coupling of residues 4 and 5 for installation of the deep-seated amide modification, the first of two diaryl ether closures for formation of the modified CD ring system (76%, 2.5-3:1 kinetic atropodiastereoselectivity), a Suzuki coupling for installation of the hindered AB biaryl bond (90%) on which the atropisomer stereochemistry could be thermally adjusted, and a macrolactamization closure of the AB ring system (70%). Subsequent DE ring system introduction enlisted a room-temperature aromatic nucleophilic substitution reaction for formation of the remaining diaryl ether (86%, 6-7:1 kinetic atropodiastereoselectivity), completing the carbon skeleton of 5. Consistent with expectations and relative to the vancomycin aglycon, 5 exhibited a 40-fold increase in affinity for D-Ala-D-Lac (K(a) = 5.2 x 10(3) M(-1)) and a 35-fold reduction in affinity for D-Ala-D-Ala (K(a) = 4.8 x 10(3) M(-1)), providing a glycopeptide analogue with balanced, dual binding characteristics. Beautifully, 5 exhibited antimicrobial activity (MIC = 31 microg/mL) against a VanA-resistant organism that remodels its D-Ala-D-Ala cell wall precursor to d-Ala-d-Lac upon glycopeptide antibiotic challenge, displaying a potency that reflects these binding characteristics.
3. Does Thermal Breathing Affect Collision Cross Sections of Gas-Phase Peptide Ions? An Ab Initio Molecular Dynamics Study
Xiaosong Li, František Tureček, Robert Pepin, Matthew F Bush, Alessio Petrone, Kenneth J Laszlo J Phys Chem Lett . 2016 Jul 21;7(14):2765-71. doi: 10.1021/acs.jpclett.6b01187.
Ab initio molecular dynamics (AIMD) with density functional theory (DFT) was applied to explore conformational motions and collision cross sections (Ω) of folded (2) and extended (7) conformers of doubly charged peptide ions, (Ala-Ala-Leu-Arg + 2H)(2+), in the gas phase at 300 and 473 K. The experimental Ω of (Ala-Ala-Leu-Arg +2H)(2+) was measured as 149 ± 1.2 Å(2) at 298 K. Thermally distributed mean values of Ω for 2 and 7 at 300 and 473 K were only 0.8-1.1% larger than for the equilibrium 0 K structures. Long (>10 ps) trajectory calculations indicated entropy-driven conformational change of 2 to 7 that occurred at random within a ~ 4 ps time window. The experimental Ω was found to fit the calculated population averaged values for 2 and 7, indicating a rapid conformer interconversion. Overall, thermal breathing had only a minor effect on the peptide ion collision cross sections.
