Genetic signature of prostate cancer mouse models resistant to optimized hK2 targeted α-particle therapy
Mesude Bicak, Katharina Lückerath, Teja Kalidindi, Michael E. Phelps, Sven‐Erik Strand, Michael J. Morris, Caius G. Radu, Robert Damoiseaux, Mari Peltola, Norbert Peekhaus, Austin Ho, Darren R. Veach, Ann-Christin Malmborg Hager, Steven M. Larson, Hans Lilja, Michael R. McDevitt, Robert J. Klein, David Ulmert
Abstract
Hu11B6 is a monoclonal antibody that internalizes in cells expressing androgen receptor (AR)-regulated prostate-specific enzyme human kallikrein-related peptidase 2 (hK2; KLK2 ). In multiple rodent models, Actinium-225–labeled hu11B6-IgG 1 ([ 225 Ac]hu11B6-IgG 1 ) has shown promising treatment efficacy. In the present study, we investigated options to enhance and optimize [ 225 Ac]hu11B6 treatment. First, we evaluated the possibility of exploiting IgG 3 , the IgG subclass with superior activation of complement and ability to mediate FC-γ-receptor binding, for immunotherapeutically enhanced hK2 targeted α-radioimmunotherapy. Second, we compared the therapeutic efficacy of a single high activity vs. fractionated activity. Finally, we used RNA sequencing to analyze the genomic signatures of prostate cancer that progressed after targeted α-therapy. [ 225 Ac]hu11B6-IgG 3 was a functionally enhanced alternative to [ 225 Ac]hu11B6-IgG 1 but offered no improvement of therapeutic efficacy. Progression-free survival was slightly increased with a single high activity compared to fractionated activity. Tumor-free animals succumbing after treatment revealed no evidence of treatment-associated toxicity. In addition to up-regulation of canonical aggressive prostate cancer genes, such as MMP7 , ETV1 , NTS , and SCHLAP1 , we also noted a significant decrease in both KLK3 (prostate-specific antigen ) and FOLH1 (prostate-specific membrane antigen) but not in AR and KLK2 , demonstrating efficacy of sequential [ 225 Ac]hu11B6 in a mouse model.