Armed Antibodies Targeting the Mucin Repeats of the Ovarian Cancer Antigen, MUC16, Are Highly Efficacious in Animal Tumor Models

Abstract

MUC16 is a well-validated cell surface marker for serous adenocarcinomas of the ovary and other gynecologic malignancies that is distinguished by highly repetitive sequences (''mucin repeats'') in the extracellular domain (ECD). We produced and compared two monoclonal antibodies: one (11D10) recognizing a unique, nonrepeating epitope in the ECD and another (3A5) that recognizes the repeats and binds multiple sites on each MUC16 protein. 3A5 conjugated to cytotoxic drugs exhibited superior toxicity against tumor cells in vitro and in tumor xenograft models compared with antibody-drug conjugates of 11D10. Importantly, drug conjugates of 3A5 were well tolerated in primates at levels in excess of therapeutic doses. Additionally, the presence of circulating CA125 in a rat model did not exacerbate the toxicity of 3A5 drug conjugates. We conclude that targeting the repeat MUC16 domains, thereby increasing cell-associated levels of drug-conjugated antibody, provides superior efficacy in vitro and in vivo without compromising safety. [Cancer Res 2007;67(10):4924-32]

An Antimesothelin-Monomethyl Auristatin E Conjugate with Potent Antitumor Activity in Ovarian, Pancreatic, and Mesothelioma Models

“…Nonetheless, in all lines, aMSLN accumulation in lysosomes was far slower than most other ADC targets (25,36,42), likely explaining the higher activity with cleavable vcMMAE than mc-or vc-MMAF, and also the lower (by an order of magnitude) in vitro potency on OVCAR3 cells (20 nmol/L) compared with other vcMMAE conjugates to similarly expressed endogenous targets in other adherent cell lines. Our efficacy data in OVCAR3 cells and xenografts are similar to those of aMuc16-auristatin conjugates, which also internalize slowly (27,43). Unexpectedly, endogenous (but not exogenous) mesothelin was upregulated up to 10-fold in vivo by an unknown mechanism in all the lines tested (including others not shown).…”

“…Scatchard analysis was as described (27) except 125 Ih7D9.v3 was incubated for 2 hours at room temperature.…”

“…In vitro efficacy was assayed with CellTiterGlo II (Promega) as described (27), except with 2,000 gD-MSLN-HT1080 cells per well.…”

“…Cells or tumor fragments were implanted subcutaneously into female mice as summarized in Supplementary Table S2, except OVCAR3 were in the mammary fat pad (27). Mice were randomized into groups of 8 to 11 with tumors averaging approximately 150 mm 3 .…”

Effect of Immune Complex Formation on the Distribution of a Novel Antibody to the Ovarian Tumor Antigen CA125

“…3A5 was previously found to bind more sites per cell than an antibody that binds to a single epitope (Chen et al, 2007). This property is hypothesized to enhance the therapeutic effectiveness of 3A5 and explains why 3A5 is currently a component of an antibody-drug conjugate strategy (Trail et al, 2003;Polakis, 2005;Wu and Senter, 2005;Chen et al, 2007;Junutula et al, 2008).…”