Molecular Targeting and Treatment of Composite EGFR and EGFRvIII-Positive Gliomas Using Boronated Monoclonal Antibodies

Abstract

Purpose: The purpose of the present study was to evaluate the anti–epidermal growth factor receptor (EGFR) monoclonal antibody (mAb), cetuximab, (IMC-C225) and the anti-EGFRvIII mAb, L8A4, used in combination as delivery agents for boron neutron capture therapy (BNCT) of a rat glioma composed of a mixture of cells expressing either wild-type (F98_EGFR) or mutant receptors(F98_npEGFRvIII). Experimental Design: A heavily boronated polyamidoamine dendrimer (BD) was linked by heterobifunctional reagents to produce the boronated mAbs, BD-C225 and BD-L8A4. For in vivo biodistribution and therapy studies, a mixture of tumor cells were implanted intracerebrally into Fischer rats. Biodistribution studies were carried out by administering ¹²⁵I-labeled bioconjugates via convection-enhanced delivery (CED), and for therapy studies, nonradiolabeled bioconjugates were used for BNCT. This was carried out 14 days after tumor implantation and 24 h after CED at the Massachusetts Institute of Technology nuclear reactor. Results: Following CED of a mixture of ¹²⁵I-BD-C225 and ¹²⁵I-BD-L8A4 to rats bearing composite tumors, 61.4% of the injected dose per gram (ID/g) was localized in the tumor compared with 30.8% ID/g for ¹²⁵I-BD-L8A4 and 34.7% ID/g for ¹²⁵I-BD-C225 alone. The corresponding calculated tumor boron values were 24.4 μg/g for rats that received both mAbs, and 12.3 and 13.8 μg/g, respectively, for BD-L8A4 or BD-C225 alone. The mean survival time of animals bearing composite tumors, which received both mAbs, was 55 days (P < 0.0001) compared with 36 days for BD-L8A4 and 38 days for BD-C225 alone, which were not significantly different from irradiated controls. Conclusions: Both EGFRvIII and wild-type EGFR tumor cell populations must be targeted using a combination of BD-cetuximab and BD-L8A4. Although in vitro C225 recognized both receptors, in vivo it was incapable of delivering the requisite amount of ¹⁰B for BNCT of EGFRvIII-expressing gliomas.