MHC-associated peptide proteomics enabling highly sensitive detection of immunogenic sequences for the development of therapeutic antibodies with low immunogenicity.

Immunogenicity is a key factor capable of influencing the efficacy and safety of therapeutic antibodies. A recently developed method called MHC-associated peptide proteomics (MAPPs) uses liquid chromatography/mass spectrometry to identify the peptide sequences derived from a therapeutic protein that are presented by major histocompatibility complex class II (MHC II) on antigen-presenting cells, and therefore may induce immunogenicity. In this study, we developed a MAPPs technique (called Ab-MAPPs) that has high throughput and can efficiently identify the MHC II-presented peptides derived from therapeutic antibodies using magnetic nanoparticle beads coated with a hydrophilic polymer in the immunoprecipitation process. The magnetic beads could identify more peptides and sequence regions originating from infliximab and adalimumab in a shorter measurement time than Sepharose beads, which are commonly used for MAPPs. Several sequence regions identified by Ab-MAPPs from infliximab corresponded to immunogenic sequences reported by other methods, which suggests the method's high potential for identifying significant sequences involved in immunogenicity. Furthermore, our study suggests that the Ab-MAPPs method can recognize the difference of a single amino acid residue between similar antibody sequences with different levels of T-cell proliferation activity and can identify potentially immunogenic peptides with high binding affinity to MHC II. In conclusion, Ab-MAPPs is useful for identifying the immunogenic sequences of therapeutic antibodies and will contribute to the design of therapeutic antibodies with low immunogenicity during the drug discovery stage.

Quantitative prediction of mechanism-based inhibition caused by mibefradil in rats.

It was previously demonstrated that mibefradil, which shows mechanism-based inhibition in humans, also caused drug-drug interactions (DDIs) with midazolam (MDZ) in rats. In this study, we aimed to quantitatively predict the DDIs observed in rats using a physiologically based pharmacokinetic (PBPK) model from in vitro inactivation parameters. For more precise predictions, contribution ratios of cytochrome P450 (P450) isozymes involved in MDZ metabolism and inactivation parameters of mibefradil against each isozyme were incorporated in the predictive model. The evaluation of metabolic rate using recombinant P450s suggested that CYP3A2 and CYP2C11 contributed to 89 and 11% of MDZ metabolism, respectively. Inactivation studies of mibefradil against the two isozymes showed that the maximal inactivation rate constants (k(inact)) were considerable in both isozymes (0.231-0.565 min(-1)), whereas the inhibitor concentration producing half the k(inact) (K(I, app)) of CYP3A2 (0.263-0.410 µM) was a good deal lower than that for CYP2C11 (6.82-11.4 µM). As a result of predicting the DDIs using the PBPK model, predicted increases in areas under the concentration-time curve of MDZ with coadministration of mibefradil (284 and 510% at 6 and 12 mg/kg mibefradil, respectively) closely corresponded to the observed values (226 and 545%, respectively). From those results, it was thought that the construction of a predictive model for DDIs using the PBPK model in detail would enable us to quantitatively predict in vivo DDIs from in vitro data. This approach to predict DDIs on the basis of the contributing isozymes would be important for predicting clinical DDIs of drugs metabolized by multiple enzymes.

Nonlinear intestinal pharmacokinetics of mitemcinal, the first acid-resistant non-peptide motilin receptor agonist, in rats.

The objective was to investigate the mechanism of nonlinear pharmacokinetics of mitemcinal, the first acid-resistant non-peptide motilin agonist, in rats. Super-proportional increases of the cumulative rates of radioactivity excreted into bile and urine following oral administration of [3H]-mitemcinal suggested nonlinear absorption of mitemcinal in rats. To evaluate the fraction dose absorbed (Fa) and intestinal availability (Fg), [3H]-mitemcinal was orally administrated to rats, and tritium radioactivity and unchanged mitemcinal concentration were determined in the portal blood. Fa values for 0.2 mg/kg1, 0.5 mg/kg, and 5.0 mg/kg dose groups were 0.314, 0.353, and 0.569, respectively. Corresponding Fg values were 0.243, 0.296, and 0.513, respectively. In Caco-2 experiments, the permeation of [3H]-mitemcinal in the secretory direction was larger than in the absorptive direction and was inhibited by P-glycoprotein (P-gp) substrate digoxin. The results indicate that the saturation of P-gp-mediated membrane permeation and intestinal metabolism causes the nonlinear pharmacokinetics of mitemcinal in rats.