Insulin glargine and its two active metabolites: A sensitive (16pM) and robust simultaneous hybrid assay coupling immunoaffinity purification with LC-MS/MS to support biosimilar clinical studies.

MK-1293 is a newly approved follow-on/biosimilar insulin glargine for the treatment of Type 1 and Type 2 diabetics. To support pivotal clinical studies during biosimilar evaluation, a sensitive, specific and robust liquid chromatography and tandem mass spectrometry (LC-MS/MS) assay for the simultaneous quantification of glargine and its two active metabolites, M1 and M2 were developed. Strategies to overcome analytical challenges, so as to optimize assay sensitivity and improve ruggedness, were evolved, resulting in a fully validated LC-MS/MS method with a lower limit of quantification (LLOQ) at 0.1ng/mL (∼16pM, equivalent to ∼2.8µU/mL) for glargine, M1 and M2, respectively, using 0.5mL of human plasma. The assay employed hybrid methodology that combined immunoaffinity purification and reversed-phase chromatography followed by electrospray-MS/MS detection operated under positive ionization mode. Stable-isotope labeled 6[D10]Leu-glargine and 4[D10]Leu-M1 were used as internal standards. With a calibration range from 0.1 to 10ng/mL, the intra-run precision (n=5) and accuracy were <6.21%, and 96.9-102.1%, while the inter-run (n=5/run for 7days) precision and accuracy were <9.55% and 96.5-105.1%, respectively, for all 3 analytes. Matrix effect, recovery, analyte stability, and interferences from control matrix, potential concomitant medications and anti-drug antibody were assessed. The assay was fully automated and has been successfully used in support of biosimilar clinical studies. Greater than 94.3% of incurred sample reanalysis (ISR) results met acceptance criteria, demonstrating the robustness of the assay. The strategic considerations during method development and validation are discussed, and can be applied to quantification of other peptides, especially insulin analogs, in the future.

Identification of proteins binding to E-Box/Ku86 sites and function of the tumor suppressor SAFB1 in transcriptional regulation of the human xanthine oxidoreductase gene.

The xanthine oxidoreductase gene (XOR) encodes an important source of reactive oxygen species and uric acid, and its expression is associated with various human diseases including several forms of cancer. We previously reported that basal human XOR (hXOR) expression is restricted or repressed by E-box and TATA-like elements and a cluster of transcriptional proteins, including AREB6-like proteins and DNA-dependent protein kinase (DNA-PK). We now demonstrate that the cluster contains the tumor suppressors SAFB1, BRG1, and SAF-A. We further demonstrate that SAFB1 silencing increases hXOR expression and that SAFB1 directly binds to the E-box. Multiple studies in vitro and in vivo including pulldown, immunoprecipitation and chromatin immunoprecipitation analyses indicate that SAFB1, Ku86, and BRG1 associate with each other. The results suggest that the SAFB1 complex binds to the hXOR promoter in a chromatin environment and plays a critical role in restricting hXOR expression via its direct interaction with the E-box, DNA-PK, and tumor suppressors. Moreover, we demonstrate that the cytokine, oncostatin M (OSM), induces the phosphorylation of SAFB1 and that the OSM-induced hXOR mRNA expression is significantly inhibited by silencing the DNA-PK catalytic subunit or SAFB1 expression. The present studies for the first time demonstrate that hXOR is a tumor suppressor-targeted gene and that the phosphorylation of SAFB1 is regulated by OSM, providing a molecular basis for understanding the role of SAFB1-regulated hXOR transcription in cytokine stimulation and tumorigenesis.

Characterization of proteins binding to E-box/Ku86 sites and function of Ku86 in transcriptional regulation of the human xanthine oxidoreductase gene.

We reported previously that E-box and TATA-like elements repress human xanthine oxidoreductase gene (hXOR) expression. In the present investigation, we determined the means by which the E-box site functions in this basal repression. DNA affinity purification demonstrated that at least five proteins are involved in the nuclear protein complex binding to the E-box and adjacent Ku86-binding sites. Amino acid sequence analysis demonstrated that three proteins, DNA-PK catalytic subunit, Ku86, and Ku70 are components of DNA-dependent protein kinase (DNA-PK). By electrophoretic mobility shift assays, gel-shift, and site-directed mutagenesis, we confirmed Ku86 binding to the Ku86 site. Studies indicated that the other two proteins of the complex are AREB6-like proteins binding to the E-box. Pull-down and immunoprecipitation analyses demonstrated the binding of Ku86 to AREB6-like proteins. The functional loss of Ku86 increases hXOR promoter activity and transcript expression. Based on the findings, we propose that DNA-PK/AREB6-like proteins play a central role in repression of basal hXOR activity. AREB6-like proteins specifically bind to the E-box, whereas Ku86 binds an adjacent site and recruits DNA-PK catalytic subunit and Ku70 proteins. A working model is presented to account for the role of DNA-PK and AREB6-like proteins in regulating hXOR activity.