Targeting, Imaging, and Therapy Using a Humanized Antiprostate Stem Cell Antigen (PSCA) Antibody

Abstract

The murine 1G8 (micro1G8) monoclonal antibody directed against prostate stem cell antigen (PSCA) prevents prostate tumor establishment, growth, and metastasis in murine models. To further delineate in vivo targeting properties, micro1G8 was radiolabeled with In-111 and evaluated in nude mice bearing PC3-PSCA xenografts. Tumor activity ranged from 11.8% to 17.1% injected dose per gram (ID/g) at 24 to 96 hours postinjection. To extend the clinical applicability of micro1G8, a chimeric 1G8 antibody was produced that exhibited specific binding to PSCA and significant antitumor effect over micro1G8 in established LAPC-9 prostate cancer xenografts (P=0.0014). However, low expression yields and instability prompted us to humanize 1G8 by grafting the complementary determining regions onto the stable, human Fv framework of anti-p185 4D5v8 (trastuzumab). Two humanized 1G8 (hu1G8) versions (A and B) that differed in the number of murine residues present in the C-terminal half of CDR-H2, were produced. Biacore binding studies demonstrated affinities of 1.47 nM for micro1G8 and 3.74 nM for hu2B3-B, representing a 2.5-fold reduction. Tumor targeting of version B radioiodinated with I was evaluated by serial microPET imaging. Specific tumor targeting of I-hu1G8-B to PC3-PSCA [12.7 (+/-1.6)% ID/g at 94 h] and LAPC-9 [6.6 (+/-0.9)% ID/g at 168 h) xenografts was observed. Inhibition of tumor growth by hu1G8-B was demonstrated in mice bearing low-expressing SW-780-PSCA bladder carcinoma xenografts. In this model, the micro1G8 was ineffective, whereas the hu1G8-B exhibited approximately 50% inhibitory effect. These data support further development of hu1G8 anti-PSCA antibody for targeted imaging and therapy for tumors of urogenital origin.

Prostate Cancer Immunotherapy: Beyond Immunity to Curability

“…Hundreds of prostate lineage-unique proteins (PLUP) exist among the 37,000þ normal human prostate lineage-unique open reading frames in EST and SAGE libraries (13 177 Lu-J591 combined with hormonal therapy are now being evaluated for OS benefit in patients with mCRPC. In addition to anti-PSMA, PSCA antibodies and minibodies both show impressive affinity, localization, and antitumor effects in chemotherapy and hormone-refractory xenograft models of human prostate cancer (15).…”

PSCA and MUC1 in non-small-cell lung cancer as targets of chimeric antigen receptor T cells

“…To redirect T lymphocytes to PSCA and MUC1, we used a second-generation PSCA-specific CAR and MUC1-specific CAR, which respectively consisted of the single-chain variable fragments (scFvs) derived from the humanized 1G8 anti-PSCA antibody 33 and anti-MUC1 HMFG2 monoclonal antibody, 34 and signaling domains from the co-stimulatory molecule CD28 and the CD3z (Fig. 3A).…”

“…To generate CAR-PSCA and CAR-MUC1 lentiviral vectors, scFvs derived from the humanized 1G8 anti-PSCA antibody 33 and anti-MUC1 HMFG2 monoclonal antibody 34 were codon optimized and synthesized by Genscript (Piscataway, NJ, USA). These scFvs were cloned into a CAR-encoding vector backbone comprising the CD8a leader sequence, human IgD hinge, portions of the CD28 transmembrane domains and the CD28 and CD3zendodomains within the second-generation lentiviral vector pWPXLd.…”

Improved Modeling of In Vivo Kinetics of Slowly Diffusing Radiotracers for Tumor Imaging

“…PSCA is additionally overexpressed in bladder and pancreatic cancers. Although previous work has shown that 124 I-labeled anti-PSCA minibodies exhibit high-contrast images of PSCA-expressing targets at relatively early time points (6–44 h), no work has yet been done to quantify the kinetics of these systems (28,29). …”