Evaluation of anti-podoplanin rat monoclonal antibody NZ-1 for targeting malignant gliomas

Introduction: Podoplanin/aggrus is a mucin-like sialoglycoprotein that is highly expressed in malignant gliomas. Podoplanin has been reported to be a novel marker to enrich tumor-initiating cells, which are thought to resist conventional therapies and to be responsible for cancer relapse. The purpose of this study was to determine whether an anti-podoplanin antibody is suitable to target radionuclides to malignant gliomas. Methods: The binding affinity of an anti-podoplanin antibody, NZ-1 (rat IgG_2a), was determined by surface plasmon resonance and Scatchard analysis. NZ-1 was radioiodinated with ¹²⁵I using Iodogen [¹²⁵I-NZ-1(Iodogen)] or N-succinimidyl 4-guanidinomethyl 3-[¹³¹I]iodobenzoate ([¹³¹I]SGMIB-NZ-1), and paired-label internalization assays of NZ-1 were performed. The tissue distribution of ¹²⁵I-NZ-1(Iodogen) and that of [¹³¹I]SGMIB-NZ-1 were then compared in athymic mice bearing glioblastoma xenografts. Results: The dissociation constant (K_D) of NZ-1 was determined to be 1.2×10^-10 M by surface plasmon resonance and 9.8×10^-10 M for D397MG glioblastoma cells by Scatchard analysis. Paired-label internalization assays in LN319 glioblastoma cells indicated that [¹³¹I]SGMIB-NZ-1 resulted in higher intracellular retention of radioactivity (26.3±0.8% of initially bound radioactivity at 8 h) compared to that from the ¹²⁵I-NZ-1(Iodogen) (10.0±0.1% of initially bound radioactivity at 8 h). Likewise, tumor uptake of [¹³¹I]SGMIB-NZ-1 (39.9±8.8 %ID/g at 24 h) in athymic mice bearing D2159MG xenografts in vivo was significantly higher than that of ¹²⁵I-NZ-1(Iodogen) (29.7±6.1 %ID/g at 24 h). Conclusions: The overall results suggest that an anti-podoplanin antibody NZ-1 warrants further evaluation for antibody-based therapy against glioblastoma.