Three alternate day injections (qod) of IL-13 toxin (250 microg/kg/day) into other subcutaneous U87 glioblastoma tumors also produced durable complete responses (CR) in all 5 mice.
We have previously demonstrated that human brain tumor cells, in particular glioblastoma multiforme (GBM), express abundant receptors for interleukin-13 on the cell surface.
Most (17/18) GBMs stained specifically for IL13 binding sites while sections from 3/11 low-grade gliomas, 5/5 high-grade gliomas (grade III), 3/5 oligodendrogliomas (all three were anaplastic), and 1/2 gliosarcomas also showed specific binding for IL13.
The GBM-associated IL-13 receptor was both quantitatively and qualitatively different from and, thus, more restrictive than the shared signaling receptor of normal tissue: it was IL-4 independent.