A Fully Automated Method for the Determination of Serum Belatacept and Its Application in a Pharmacokinetic Investigation in Renal Transplant Recipients.

BACKGROUND: Belatacept (Nulojix; Bristol-Myers Squibb, New York, NY) is a biological immunosuppressive drug used for the prophylaxis of acute rejection after renal transplantation. Few studies have described belatacept pharmacokinetics, and the effect of therapeutic drug monitoring has not been investigated. We have developed a drug-capture assay (using drug target) to measure belatacept in serum and applied this assay in a pharmacokinetic study in renal transplant recipients. METHODS: CD80 was used to trap belatacept onto streptavidin-coated wells. Captured drug was quantified using Eu-labeled protein A and time-resolved fluorescence. The assay was applied in a pilot pharmacokinetic study in renal transplanted patients receiving belatacept infusions. Belatacept serum concentrations were determined at several time points between belatacept infusions. A simple population pharmacokinetic model was developed to visualize measured and predicted belatacept serum concentrations. RESULTS: The assay range was 0.9-30 mg/L with accuracy within 91%-99% and coefficients of variation ranging from 1.2% to 3.6%. Predilution extended the measurement range to 130 mg/L with an accuracy of 90% and coefficients of variation of 3.8%. Samples were stable during storage at 4°C for 15 days and during 2 freeze-thaw cycles. Belatacept concentrations were determined in a total of 203 serum samples collected during 26 infusion intervals from 5 renal transplant recipients. The population pharmacokinetic model visualized both measured and predicted concentrations. CONCLUSIONS: We have developed an automated, accurate, and precise assay for the determination of belatacept serum concentrations. The assay was successfully applied in a pharmacokinetic study in renal transplant recipients receiving belatacept infusions.

Application of nSMOL coupled with LC-MS bioanalysis for monitoring the Fc-fusion biopharmaceuticals Etanercept and Abatacept in human serum.

The principle of nano-surface and molecular-orientation limited (nSMOL) proteolysis has a unique characteristic Fab-selective proteolysis for antibody bioanalysis that is independent of a variety of monoclonal antibodies by the binding antibody Fc via Protein A/G in a pore with 100 nm diameter and modified trypsin immobilization on the surface of nanoparticles with 200 nm diameter. Since minimizing peptide complexity and protease contamination while maintaining antibody sequence specificity enables a rapid and broad development of optimized methods for liquid chromatography-mass spectrometry (LC-MS) bioanalysis, the application of regulatory LC-MS for monitoring antibody biopharmaceuticals is expected. nSMOL is theoretically anticipated to be applicable for representative Fc-fusion biopharmaceuticals, because Protein A/G-binding site Fc exists on the C-terminus, and its functional domain is available to orient and interact with the reaction solution. In this report, we describe the validated LC-MS bioanalysis for monitoring Ethanercept and Abatacept using nSMOL technology. The quantitation range of Ethanercept in human serum was from 0.195 to 100 µg/mL using the signature peptide VFCTK (aa.43-47), and that of Abatacept was from 0.391 to 100 µg/mL using the signature peptide MHVAQPAVVLASSR (aa.1-14). Both proteins fulfilled the guideline criteria for low-molecular-weight drug compounds. The results indicate that the clinical and therapeutic monitoring for antibody and Fc-fusion biopharmaceuticals are adequately applicable using nSMOL proteolysis coupled with LC-MS bioanalysis.

Immunosuppressive effect of ASP2408, a novel CD86-selective variant of CTLA4-Ig, in rats and cynomolgus monkeys.

The CTLA4-Ig fusion proteins abatacept and belatacept inhibit CD28-mediated T cell activation by binding CD80 (B7-1) and CD86 (B7-2) costimulatory ligands and are clinically proven immunosuppressants used for rheumatoid arthritis and renal transplantation, respectively. Abatacept and belatacept preferentially bind CD80, yet CD86 has been implicated as the dominant ligand for CD28-mediated costimulation of T cells. We investigated the immunosuppressive effects of ASP2408, a novel CTLA4-Ig with CD86 selectivity and high potency created by directed evolution methods. Here we evaluated the effect of ASP2408 in vitro using cynomolgus monkey and rat T cell proliferation assays and in vivo using cynomolgus monkey tetanus toxoid (TTx) immunization and a rat rheumatoid arthritis model. ASP2408 was 290-fold and 21-fold more potent in suppressing in vitro monkey T cell proliferation than abatacept and belatacept, respectively. ASP2408 inhibited anti-TTx immunological reactions in cynomolgus monkey at a 10-fold lower dose level than belatacept, through complete CD86 and partial CD80 receptor occupancies, and also suppressed inflammation in the rat collagen-induced arthritis model. Overall, improved immunosuppressive potency of ASP2408 relative to abatacept and belatacept correlated well with improved CD86 binding affinity. These results may support the advantage of preferential enhancement of CD86 binding affinity to inhibit T cell-mediated immune response and improved dosing convenience in humans relative to abatacept or belatacept.

Glycan structure and serum half-life of recombinant CTLA4Ig, an immunosuppressive agent, expressed in suspension-cultured rice cells with coexpression of human ß1,4-galactosyltransferase and human CTLA4Ig.

Human cytotoxic T-lymphocyte antigen 4-immunoglobulin (hCTLA4Ig) is an immunosuppressive therapeutic, and recently produced rice cell-derived hCTLA4Ig (hCTLA4Ig(P)) reportedly exhibits in vitro immunosuppressive activities equivalent to those of Chinese hamster ovary cell-derived hCTLA4Ig (hCTLA4Ig(M)). However, limitations of hCTLA4Ig(P) include shortened in vivo half-life as well as the presence of nonhuman N-glycans containing (ß1-2)-xylose and α1,3-fucose, which cause immunogenic reactions in humans. In the present study, human ß1,4-galactose-extended hCTLA4Ig(P) (hCTLA4Ig(P)-Gal) was expressed through the coexpression of human ß1,4-galactosyltransferase (hGalT) and hCTLA4Ig in an attempt to overcome these unfavorable effects. The results indicated that both encoding hGalT and hCTLA4Ig were successfully coexpressed, and the analysis of N-glycan and its relative abundance in purified hCTLA4Ig(P)-Gal indicated that not only were the two glycans containing (ß1-4)-galactose newly extended, but also glycans containing both ß1,2-xylose and α1,3-fucose were markedly reduced and high-mannose-type glycans were increased compared to those of hCTLA4Ig(P), respectively. Unlike hCTLA4Ig(P), hCTLA4Ig(P)-Gal was effective as an acceptor via (ß1-4)-galactose for in vitro sialylation. Additionally, the serum half-life of intravenously injected hCTLA4Ig(P)-Gal in Sprague-Dawley rats was 1.9 times longer than that of hCTLA4Ig(P), and the clearance pattern of hCTLA4Ig(P)-Gal was close to that for hCTLA4Ig(M). These results indicate that the coexpression with hGalT and hCTLA4Ig(P) is useful for both reducing glycan immunogens and increasing in vivo stability. This is the first report of hCTLA4Ig as an effective therapeutics candidate in glycoengineered rice cells.

Therapeutic Drug Monitoring of Belatacept in Kidney Transplantation.

Belatacept is a novel immunosuppressive drug that inhibits the co-stimulatory signal required for T-cell activation and has been approved for the prevention of acute rejection after kidney transplantation. In this article, the need for and possibility of therapeutic drug monitoring (TDM) of belatacept is reviewed. Clinical studies have defined the upper limit of the therapeutic window, but the lower limit is unknown. The pharmacokinetics and pharmacodynamics of belatacept display only limited interpatient variability but no data are available on the intrapatient variability of these parameters. Several assays to measure serum belatacept concentrations and its in vitro immunologic effects have been developed, but these are not commercially available and require validation. Importantly, pharmacodynamic assays have not been correlated with clinical outcomes (both efficacy and safety) and have only used surrogate laboratory readouts. TDM is likely to become feasible in the near future if these assays are developed further. However, because its pharmacokinetics and pharmacodynamics seem to vary little between individual patients, it may not be necessary to perform TDM for this drug. There could be a role for such an approach if one seeks to lower the belatacept doses further in an attempt to minimize adverse events. A future, prospective concentration-ranging study that defines the lower end of the belatacept therapeutic window should, however, be conducted first to provide the rationale for performing TDM of this novel immunosuppressant.