Xiao-Yan Zhao

Targeting tomoregulin for radioimmunotherapy of prostate cancer.

Radiotherapy is an effective approach for the treatment of local prostate cancer. However, once prostate cancer metastasizes, radiotherapy cannot be used due to the distribution of multiple metastases to lymph nodes and bones. In contrast, radioimmunotherapy should still be efficacious in metastatic prostate cancer as radioisotopes are brought to tumor cells by targeting antibodies. Here we identify and validate a prostate-expressed molecule, tomoregulin, as a target for radioimmunotherapy of prostate cancer. Tomoregulin is a transmembrane protein selectively expressed in the brain, prostate, and prostate cancer, but not expressed in other normal tissues. Immunohistochemical studies of tomoregulin protein in clinical samples show its location in the luminal epithelium of normal prostate, benign prostatic hyperplasia, and prostatic intraepithelial neoplasia. More importantly, the tomoregulin protein is expressed in primary prostate tumors and in their lymph node and bone metastases. The nature of tomoregulin as a transmembrane protein and its tissue-specific expression make tomoregulin an attractive target for radioimmunotherapy, in which tomoregulin-specific antibodies will deliver a radioisotope to prostate tumor cells and metastases. Indeed, biodistribution studies using a prostate tumor xenograft model showed that the (111)In-labeled anti-tomoregulin antibody 2H8 specifically recognizes tomoregulin protein in vivo, leading to a strong tumor-specific accumulation of the antibody. In efficacy studies, a single i.p. dose of 150 microCi (163 microg) (90)Y-labeled 2H8 substantially inhibits the growth rate of established LNCaP human prostate tumor xenograft in nude mice but produces no overt toxicity despite cross-reactivity of 2H8 with mouse tomoregulin. Our data clearly validate tomoregulin as a target for radioimmunotherapy of prostate cancer.

Obligate Multivalent Recognition of Cell Surface Tomoregulin following Selection from a Multivalent Phage Antibody Library

A therapeutic antibody candidate (AT-19) isolated using multivalent phage display binds native tomoregulin (TR) as a mul-timer not as a monomer. This report raises the importance of screening and selecting phage antibodies on native antigen and reemphasizes the possibility that potentially valuable antibodies are discarded when a monomeric phage display system is used for screening. A detailed live cell panning selection and screening method to isolate multivalently active antibodies is described. AT-19 is a fully human antibody recognizing the cell surface protein TR, a proposed prostate cancer target for therapeutic antibody internalization. AT-19 was isolated from a multivalent single-chain variable fragment (scFv) antibody library rescued with hyperphage. The required multivalency for isolation of AT-19 is supported by fluorescence activated cell sorting data demonstrating binding of the multivalent AT-19 phage particles at high phage concentrations and failure of monovalent particles to bind. Pure monomeric scFv AT-19 does not bind native receptor on cells, whereas dimeric scFv or immunoglobulin G binds with nanomolar affinity. The isolation of AT-19 antibody with obligate bivalent binding activity to native TR is attributed to the use of a multivalent display of scFv on phage and the method for selecting and screening by alternate use of 2 recombinant cell lines.

Mechanistic Modeling of the Pharmacodynamic and Pharmacokinetic Relationship of Tissue Factor Pathway Inhibitor-Neutralizing Antibody (BAY 1093884) in Cynomolgus Monkeys

BAY 1093884 is a fully human monoclonal antibody against the tissue factor pathway inhibitor (TFPI) in development as prophylaxis in patients with hemophilia with or without inhibitors. In vitro, BAY 1093884 binds to human, mouse, and monkey TFPI. The objective of this study was to find a pharmacodynamic (PD) biomarker after administration of BAY 1093884 to normal monkeys. In monkey plasma, BAY 1093884 exhibited an IC50 (concentration that inhibits 50%) of 4.65 and 6.19xa0nM for free TFPI and diluted prothrombin time (dPT), respectively. The BAY 1093884 pharmacokinetic (PK) profile and its PD effects on dPT and free TFPI levels were assessed after intravenous and subcutaneous administration of BAY 1093884 (5 and 20xa0mg/kg) to female cynomolgus monkeys. Free TFPI concentrations in plasma decreased rapidly and increased to baseline in a dose-dependent manner. dPT clotting time was shortened and correlated with free TFPI levels and drug concentration in plasma, demonstrating the relationship between PD activities (dPT clotting time and free TFPI levels) and drug concentration. BAY 1093884 exhibited nonlinear PK, and a target-mediated drug disposition model was used to characterize the BAY 1093884 versus TFPI concentration–response relationship. We concluded that a mechanism-based PK/PD binding model could be useful for predicting human response to BAY 1093884. For the first-in-human study, measurement of free TFPI will be included as part of the dose-escalation design.