Mary Haak-Frendscho

Biacore surface matrix effects on the binding kinetics and affinity of an antigen/antibody complex

To characterize a proprietary therapeutic monoclonal antibody (mAb) candidate, a rigorous biophysical study consisting of 53 Biacore and kinetic exclusion assay (KinExA) experiments was undertaken on the therapeutic mAb complexing with its target antigen. Unexpectedly, the observed binding kinetics depended on the chip used, suggesting that the negatively charged carboxyl groups on CM5, CM4, and C1 chips were adversely affecting the Biacore kinetic results. To study this hypothesis, Biacore solution-phase and KinExA equilibrium titrations, as well as KinExA kinetic measurements, were performed to establish accurate values for the affinity and kinetic rate constants of the binding reaction between antigen and mAb. The results revealed that as the negative charge on the biosensor surface decreased, the binding kinetics and K(D) approached the accurate binding parameters more closely when measured in solution. Two potential causes for the artifactual Biacore surface-based measurements are (i) steric hindrance of antigen binding arising from an interaction of the negatively charged carboxymethyldextran matrix with the mAb, which is a highly basic protein with a pI of 9.4, and (ii) an electrostatic repulsion between the negatively charged antigen and the carboxymethyldextran matrix. Importantly, simple diagnostic tests can be performed early in the measurement process to identify these types of matrix-mediated artifacts.

Preclinical Efficacy and Safety Assessment of an Antibody-Drug Conjugate Targeting the c-RET Proto-Oncogene for Breast Carcinoma

Purpose: The RET proto-oncogene has been implicated in breast cancer, and the studies herein describe the preclinical and safety assessment of an anti-RET antibody–drug conjugate (ADC) being developed for the treatment of breast cancer. Experimental Design: RET protein expression was analyzed in breast tumor samples using tissue microarrays. The fully human anti-RET antibody (Y078) was conjugated to the DM1 and DM4 derivatives of the potent cytotoxic agent maytansine using thioether and disulfide linkers, respectively. The resulting compounds, designated Y078-DM1 and Y078-DM4, were evaluated for antitumor activity using human breast cancer cell lines and established tumor xenograft models. A single-dose, 28-day, safety study of Y078-DM1 was performed in cynomolgus monkeys. Results: By immunohistochemistry, RET expression was detected in 57% of tumors (1,596 of 2,800 tumor sections) and was most common in HER2-positive and basal breast cancer subtypes. Potent in vitro cytotoxicity was achieved in human breast cancer cell lines that have expression levels comparable with those observed in breast cancer tissue samples. Dose-response studies in xenograft models demonstrated antitumor activity with both weekly and every-3-weeks dosing regimens. In cynomolgus monkeys, a single injection of Y078-DM1 demonstrated dose-dependent, reversible drug-mediated alterations in blood chemistry with evidence of on-target neuropathy. Conclusions: RET is broadly expressed in breast cancer specimens and thus represents a potential therapeutic target; Y078-DM1 and Y078-DM4 demonstrated antitumor activity in preclinical models. Optimization of the dosing schedule or an alternate cytotoxic agent with a different mechanism of action may reduce the potential risk of neuropathy. Clin Cancer Res; 21(24); 5552–62. ©2015 AACR.