Application of Pharmacokinetic/Pharmacodynamic Modeling to Bridge Mouse Antitumor Efficacy and Monkey Toxicology Data for Determining the Therapeutic Index of an Interleukin-10 Fc Fusion Protein.

Pharmacokinetic/pharmacodynamic (PK/PD) modeling was performed to quantitatively integrate preclinical pharmacology and toxicology data for determining the therapeutic index (TI) of an interleukin-10 (IL-10) fragment crystallizable (Fc) fusion protein. Mouse Fc fused with mouse IL-10 (mFc-mIL-10) was studied in mice for antitumor efficacy, and the elevation of interleukin-18 (IL-18) was examined as a PD biomarker. The in vivo mFc-mIL-10 EC50 for the IL-18 induction was estimated to be 2.4 nM, similar to the in vitro receptor binding affinity (Kd) of 3.2 nM. The IL-18 induction was further evaluated in cynomolgus monkeys, where the in vivo induction EC50 by a human IL-10 human Fc-fusion protein (hFc-hIL-10) was 0.08 nM vs. 0.3 nM measured as the in vitro Kd. The extent of the IL-18 induction correlated with mouse antitumor efficacy and was used to connect mouse efficacy to that in monkeys. The PD-based efficacious dose projected in monkeys was comparable to the results obtained using a PK-based method in which mouse efficacious exposure was targeted and corrected for affinity differences between the species. Furthermore, PK/PD relationships were developed for anemia and thrombocytopenia in monkeys treated with hFc-hIL-10, with thrombocytopenia predicted to be dose-limiting toxicity. Using quantitative pharmacology and toxicology information obtained through modeling work in the same species, the TI of hFc-hIL-10 in monkeys was determined to be 2.4 (vs. PD-based efficacy) and 1.2-3 (vs. PK-based efficacy), indicating a narrow safety margin. The model-based approaches were proven valuable to the developability assessment of the IL-10 Fc-fusion protein.

Target-Mediated Drug Disposition Affects the Pharmacokinetics of Interleukin-10 Fragment Crystallizable Fusion Proteins at Pharmacologically Active Doses.

Fragment crystallizable (Fc) fusion is commonly used for extending the half-life of biotherapeutics such as cytokines. In this work, we studied the pharmacokinetics of Fc-fused interleukin-10 (IL-10) proteins that exhibited potent antitumor activity in mouse syngeneic tumor models. At pharmacologically active doses of ≥0.1 mg/kg, both mouse Fc-mouse IL-10 and human Fc-human IL-10, constructed as the C terminus of the Fc domain fused with IL-10 via a glycine-serine polypeptide linker, exhibited nonlinear pharmacokinetics after intravenous administration to mice at the doses of 0.05, 0.5, and 5 mg/kg. With a nominal dose ratio of 1:10:100; the ratio of the area under the curve for mouse Fc-mouse IL-10 and human Fc-human IL-10 was 1:181:1830 and 1:75:633, respectively. In contrast, recombinant mouse or human IL-10 proteins exhibited linear pharmacokinetics in mice. Compartmental analysis, using the Michaelis-Menten equation with the in vitro IL-10 receptor alpha binding affinity inputted as the Km, unified the pharmacokinetic data across the dose range. Additionally, nontarget-mediated clearance estimated for fusion proteins was ∼200-fold slower than that for cytokines, causing the manifestation of target-mediated drug disposition (TMDD) in the fusion protein pharmacokinetics. The experimental data generated with a mouse IL-10 receptor alpha-blocking antibody and a human Fc-human IL-10 mutant with a reduced receptor binding affinity showed significant improvements in pharmacokinetics, supporting TMDD as the cause of nonlinearity. Target expression and its effect on pharmacokinetics must be determined when considering using Fc as a half-life extension strategy, and pharmacokinetic evaluations need to be performed at a range of doses covering pharmacological activity. SIGNIFICANCE STATEMENT: Target-mediated drug disposition can manifest to affect the pharmacokinetics of a fragment crystallizable (Fc)-fused cytokine when the nontarget-mediated clearance of the cytokine is decreased due to neonatal Fc receptor-mediated recycling and molecular weight increases that reduce the renal clearance. The phenomenon was demonstrated with interleukin-10 Fc-fusion proteins in mice at pharmacologically active doses. Future drug designs using Fc as a half-life extension approach for cytokines need to consider target expression and its effect on pharmacokinetics at relevant doses.

Impact of Drug Conjugation on Thermal and Metabolic Stabilities of Aglycosylated and N-Glycosylated Antibodies.

N-linked glycosylation is one of the most common and complex posttranslational modifications that govern the biological functions and physicochemical properties of therapeutic antibodies. We evaluated thermal and metabolic stabilities of antibody-drug conjugates (ADCs) with payloads attached to the C'E loop in the immunoglobulin G (IgG) Fc CH2 domain, comparing the glycosylated and aglycosylated Fc ADC variants. Our study revealed that introduction of small-molecule drugs into an aglycosylated antibody can compensate for thermal destabilization originating from structural distortions caused by elimination of N-linked glycans. Depending on the conjugation site, glycans had both positive and negative effects on plasma stability of ADCs. The findings highlight the importance of consideration for selection of conjugation site to achieve desirable physicochemical properties and plasma stability.

Characterization of Mauritian Cynomolgus Macaque FcγR Alleles Using Long-Read Sequencing.

The FcγRs are immune cell surface proteins that bind IgG and facilitate cytokine production, phagocytosis, and Ab-dependent, cell-mediated cytotoxicity. FcγRs play a critical role in immunity; variation in these genes is implicated in autoimmunity and other diseases. Cynomolgus macaques are an excellent animal model for many human diseases, and Mauritian cynomolgus macaques (MCMs) are particularly useful because of their restricted genetic diversity. Previous studies of MCM immune gene diversity have focused on the MHC and killer cell Ig-like receptor. In this study, we characterize FcγR diversity in 48 MCMs using PacBio long-read sequencing to identify novel alleles of each of the four expressed MCM FcγR genes. We also developed a high-throughput FcγR genotyping assay, which we used to determine allele frequencies and identify FcγR haplotypes in more than 500 additional MCMs. We found three alleles for FcγR1A, seven each for FcγR2A and FcγR2B, and four for FcγR3A; these segregate into eight haplotypes. We also assessed whether different FcγR alleles confer different Ab-binding affinities by surface plasmon resonance and found minimal difference in binding affinities across alleles for a panel of wild type and Fc-engineered human IgG. This work suggests that although MCMs may not fully represent the diversity of FcγR responses in humans, they may offer highly reproducible results for mAb therapy and toxicity studies.

IL-2/CD25: A Long-Acting Fusion Protein That Promotes Immune Tolerance by Selectively Targeting the IL-2 Receptor on Regulatory T Cells.

Low-dose IL-2 represents an immunotherapy to selectively expand regulatory T cells (Tregs) to promote tolerance in patients with autoimmunity. In this article, we show that a fusion protein (FP) of mouse IL-2 and mouse IL-2Rα (CD25), joined by a noncleavable linker, has greater in vivo efficacy than rIL-2 at Treg expansion and control of autoimmunity. Biochemical and functional studies support a model in which IL-2 interacts with CD25 in the context of this FP in trans to form inactive head-to-tail dimers that slowly dissociate into an active monomer. In vitro, IL-2/CD25 has low sp. act. However, in vivo IL-2/CD25 is long lived to persistently and selectively stimulate Tregs. In female NOD mice, IL-2/CD25 administration increased Tregs within the pancreas and reduced the instance of spontaneous diabetes. Thus, IL-2/CD25 represents a distinct class of IL-2 FPs with the potential for clinical development for use in autoimmunity or other disorders of an overactive immune response.

Dissecting Therapeutic Resistance to ERK Inhibition.

The MAPK pathway is frequently activated in many human cancers, particularly melanomas. A single-nucleotide mutation in BRAF resulting in the substitution of glutamic acid for valine (V(600E)) causes constitutive activation of the downstream MAPK pathway. Selective BRAF and MEK inhibitor therapies have demonstrated remarkable antitumor responses in BRAF(V600) (E)-mutant melanoma patients. However, initial tumor shrinkage is transient and the vast majority of patients develop resistance. We previously reported that SCH772984, an ERK 1/2 inhibitor, effectively suppressed MAPK pathway signaling and cell proliferation in BRAF, MEK, and concurrent BRAF/MEK inhibitor-resistant tumor models. ERK inhibitors are currently being evaluated in clinical trials and, in anticipation of the likelihood of clinical resistance, we sought to prospectively model acquired resistance to SCH772984. Our data show that long-term exposure of cells to SCH772984 leads to acquired resistance, attributable to a mutation of glycine to aspartic acid (G(186D)) in the DFG motif of ERK1. Structural and biophysical studies demonstrated specific defects in SCH772984 binding to mutant ERK. Taken together, these studies describe the interaction of SCH772984 with ERK and identify a novel mechanism of ERK inhibitor resistance through mutation of a single residue within the DFG motif. Mol Cancer Ther; 15(4); 548-59. ©2016 AACR.