Molecular Targeting and Treatment of EGFRvIII-Positive Gliomas Using Boronated Monoclonal Antibody L8A4

Purpose: The purpose of the present study was to evaluate a boronated EGFRvIII-specific monoclonal antibody, L8A4, for boron neutron capture therapy (BNCT) of the receptor-positive rat glioma, F98 npEGFRvIII . Experimental Design: A heavily boronated polyamido amine (PAMAM) dendrimer (BD) was chemically linked to L8A4 by two heterobifunctional reagents, N -succinimidyl 3-(2-pyridyldithio)propionate and N -( k -maleimidoundecanoic acid)hydrazide. For in vivo studies, F98 wild-type receptor-negative or EGFRvIII human gene-transfected receptor-positive F98 npEGFRvIII glioma cells were implanted i.c. into the brains of Fischer rats. Biodistribution studies were initiated 14 days later. Animals received [ 125 I]BD-L8A4 by either convection enhanced delivery (CED) or direct i.t. injection and were euthanized 6, 12, 24, or 48 hours later. Results: At 6 hours, equivalent amounts of the bioconjugate were detected in receptor-positive and receptor-negative tumors, but by 24 hours the amounts retained by receptor-positive gliomas were 60.1% following CED and 43.7% following i.t. injection compared with 14.6% ID/g by receptor-negative tumors. Boron concentrations in normal brain, blood, liver, kidneys, and spleen all were at nondetectable levels (6 months) and those that received BD-L8A4 alone had a mean ± SE survival time of 70.4 ± 11.1 days with 10% long-term survivors compared with 40.1 ± 2.2 days for i.v. BPA and 30.3 ± 1.6 and 26.3 ± 1.1 days for irradiated and untreated controls, respectively. Conclusions: These data convincingly show the therapeutic efficacy of molecular targeting of EGFRvIII using either boronated monoclonal antibody L8A4 alone or in combination with BPA and should provide a platform for the future development of combinations of high and low molecular weight delivery agents for BNCT of brain tumors.