Regional treatment of epidermal growth factor receptor vIII-expressing neoplastic meningitis with a single-chain immunotoxin, MR-1.
The incidence of neoplastic meningitis is on the rise. Neoplastic meningitis can result from a direct seeding of the neuraxis by primary brain tumors or by hematogeneous spread of systemic solid tumors. A frequent genetic alteration in primary brain tumors such as gliomas is an in-frame deletion in the epidermal growth factor receptor (EGFR) gene EGFRvIII, which brings together what were normally distant polypeptide sequences in the intact receptor. A novel glycine is formed at the fusion junction, resulting in a unique and tumor-specific target. By using phage display, we have isolated a single-chain antibody specific for the EGFRvIII mutation and expressed it with a modified form of the Pseudomonas exotoxin to form the immunotoxin MR1scFvPE38KDEL (MR-1). The multiple dose toxicity and therapeutic efficacy of MR-1 immunotoxin were tested in an athymic rat model of neoplastic meningitis. The maximally tolerated doses in non-tumor-bearing rats were three doses of 3 microg each. For therapeutic studies, the target was a neoplastic meningitis induced by intrathecal inoculation of the EGFRvIII-expressing human glioma U87MG.deltaEGFR. A dose escalation study compared the survival of three equal doses of 1, 2, and 3 microg of MR-1 immunotoxin with saline or 3 microg of the control immunotoxin specific for the interleukin 2 receptor, anti-Tac. All animals treated with three doses of saline or 3 microg of anti-Tac died, with median survival of 7 and 10 days, respectively. There were 75% (six of eight) long-term survivors in the group treated with three doses of 1 microg and 57% (four of seven) long-term survivors in the groups treated with three doses of either 2 or 3 microg of MR-1 immunotoxin. None of the MR-1 immunotoxin-treated groups reached median survival by the termination of the study at 53 days. Therefore, median survival was estimated to be >53 days, resulting in an estimated increase in median survival of >657% compared with saline and 430% versus anti-Tac. Compartmental therapy with three doses of 2 microg of MR-1 immunotoxin is effective in the treatment of EGFRvIII-expressing neoplastic meningitis. This dose was found to have no clinical or histopathological effects on non-tumor-bearing animals. MR-1 immunotoxin is, therefore, considered specific and safe within its therapeutic window. Phase I clinical trials for tumors invading the intrathecal space that express the EGFRvIII target should be initiated.
Archer
G E
GE
Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Sampson
J H
JH
Lorimer
I A
IA
McLendon
R E
RE
Kuan
C T
CT
Friedman
A H
AH
Friedman
H S
HS
Pastan
I H
IH
Bigner
D D
DD
D036002:ADP Ribose Transferases; D000818:Animals; D000918:Antibody Specificity; D001427:Bacterial Toxins; D066246:ErbB Receptors / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D005098:Exotoxins / Q000494:pharmacology* / Q000633:toxicity; D005260:Female; D006801:Humans; D007135:Immunoglobulin Variable Region / Q000494:pharmacology* / Q000633:toxicity; D000922:Immunotoxins / Q000494:pharmacology* / Q000633:toxicity; D007278:Injections, Spinal; D008577:Meningeal Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D009154:Mutation; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D011923:Rats, Nude; D014407:Tumor Cells, Cultured; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D001427:Bacterial Toxins; D066246:ErbB Receptors; D005098:Exotoxins; D007135:Immunoglobulin Variable Region; D000922:Immunotoxins; D011500:Protein Synthesis Inhibitors; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A