In the present report we have summarized studies carried out over the past five years on molecular targeting of the
epidermal growth factor receptor (EGFR) and its mutant
isoform, EFGRvIII, for BNCT of genetically engineered F98 rat
gliomas, expressing either wildtype (F98(EGFR)) or mutant receptors (F98(npEGFRvIII)).
EGF or the
monoclonal antibodies (mAbs),
cetuximab (IMC-C225) and L8A4, which recognize wildtype EGFR and
EGFRvIII, respectively, were heavily boronated using
polyamidoamine (PAMAM)
dendrimers (BD) linked to the targeting vehicles by means of heterobifunctional
reagents. Boronated
EGF or mAbs, alone or in combination with i.v. boronophenylalanine (BPA), were administered intracerebrally (i.c.) by either intratumoral (i.t.) injection or convection enhanced delivery (CED) to rats bearing F98
gliomas following which BNCT was initiated. The best survival data were obtained in rats bearing F98(npEGFRvIII)
gliomas that had received CED of BD-L8A4 either alone or in combination with i.v. boronophenylalanine (BPA). Studies carried out in rats bearing composite
tumors (F98(EGFR)/F98(npEGFRvIII)) demonstrated that it was essential to target both
tumor cell populations in order to obtain an optimal
therapeutic effect. Based on these observations, we have concluded that EGFR targeting vehicles are useful, but not stand-alone
boron delivery agents due to the heterogeneity of receptor expression in
brain tumors. They could, however, be quite useful in combination with the two drugs that currently are being used clinically, BPA and
sodium borocaptate (BSH) for BNCT of either
brain tumors or head and
neck cancers.