Interstitial infusion of glioma-targeted recombinant immunotoxin 8H9scFv-PE38

Abstract

Monoclonal antibodies have the potential to target therapy for high-grade gliomas. Monoclonal antibody 8H9 is specific for membrane protein B7H3 and is reactive with most human high-grade gliomas. We tested the 8H9scFv-PE38 recombinant Pseudomonas immunotoxin in a preclinical model of high-grade glioma. The half maximal inhibitory concentration (IC(50)) of 8H9scFv-PE38 in vitro was determined using glioblastoma cell lines U87 and U251. Maximum tolerated infusion dose of 8H9scFv-PE38 following interstitial infusion to the striatum and pons was defined using athymic rats. Maximum tolerated infusion dose of 8H9scFv-PE38 or PBS control were interstitially delivered to athymic rats xenografted with U87 in the striatum or brain stem. Radiographic response and survivals were measured and compared between treatment groups. The in vitro IC(50) of 8H9scFv-PE38 for U87 was 1,265 ng/mL and, for U251, 91 ng/mL. The maximum tolerated infusion doses of interstitially infused 8H9scFv-PE38 to the striatum and brain stem were 0.75 and 1.8 mug, respectively. For rats harboring intracranial U87 xenografts, infusion of 8H9scFv-PE38 increased mean survival (striatum, 43.4 versus 24.6 days; brain stem, 80.6 versus 45.5 days; n = 28 total) and produced three long-term survivors past 120 days. None of the 14 placebo-treated animals survived >54 days. Tumors also showed volumetric response to infusion of 8H9scFv-PE38 by magnetic resonance imaging. Interstitial infusion of 8H9scFv-PE38 shows potential for the treatment of hemispherical and brain stem glioma. Mol Cancer Ther; 9(4); 1039-46. (c)2010 AACR.

Figure 1

The in vitro growth inhibition of U87 (A) and U251 (B) by 8H9scFv-PE38 is demonstrated as a function of OD (with standard error). From this data, IC₅₀ calculations were 1265 ng/ml for U87 and 91 ng/ml for U251.

Figure 2

Low magnification H&E brain stem sections following interstitial infusion of 1.2 (A), 1.8 (B), and 2.4 (C) μg of 8H9scFv-PE38. With increasing dose, necrotic change becomes more evident (circled).

Figure 3

Kaplan-Meier survival plot for all animals with U87 xenografts, striatal and brain stem tumors pooled together, in this series (n=28 total). Red = 8H9scFv-PE38 and black = PBS control.

Figure 4

Apparent radiographic response of a striatal U87 xenograft following CED of 8H9scFv-PE38. Establishment of tumor is confirmed 1 week following inoculation on sagittal T2-weighted MRI (A, arrow). One and two weeks following treatment, axial MRI shows post-treatment edema and necrosis with small evidence of residual tumor (B, C). However, at 5 weeks following tumor inoculation, tumor recurrence is evident (D).

Figure 5

U87 xenograft volume-fold change (with standard error) as determined by MRI performed two weeks following treatment with 8H9-PE38 versus placebo in the striatum (A) and brain stem (B).