Immunotoxin pharmacokinetics: a comparison of the anti-glioblastoma bi-specific fusion protein (DTAT13) to DTAT and DTIL13

Abstract

DTAT13, a novel recombinant bispecific immunotoxin (IT) consisting of truncated diphtheria toxin, an amino-terminal (AT) fragment of the urokinase-type plasminogen activator (uPa), and a fragment of human IL-13 was assembled in order to target receptors on glioblastoma multiforme (GBM) and its associated neovasculature. Previous in vitro studies confirmed the efficacy of DTAT13 against various GBM cell lines expressing both IL-13 receptor or uPA receptor, and previous in vivo testing demonstrated the efficacy of DTAT13 in significantly inhibiting a range of xenograft tumors and showed that DTAT13 was 160- and 8-fold less toxic to the parental fusion IT, DTAT and DTIL13, respectively. To further understand the properties of DTAT13, pharmacokinetic/biodistribution experiments were performed. Binding analysis revealed that the IL-13 domain functioned independently of the uPA domain and that the K (d) for each binding domain was essentially the same as that of DTIL13 and DTAT. Flow cytometry studies indicated that DTAT13 bound better than DTAT or DTIL13. Analysis of the rate of protein synthesis inhibition in U87 MG cells by DTAT13 compared to DTAT revealed a faster rate of inhibition with DTAT13 compared to DTAT. The rate of protein synthesis inhibition of DTAT13 was identical to that of DTIL13 in U373 MG cells. Intracranial biodistribution studies revealed that DTAT13 was able to cross to the contralateral hemisphere unlike DTIL13 but similar to DTAT. These studies show that DTAT13 has properties encompassing those of both DTIL13 and DTAT and warrants further consideration for clinical development.

Genetically designing a more potent antipancreatic cancer agent by simultaneously co-targeting human IL13 and EGF receptors in a mouse xenograft model

“…In some reports, inclusion of a second ligand enhances activity,47 48 but not in others 49. Currently, no method exists which predicts whether a given bispecific will be successful.…”

A novel bispecific immunotoxin delivered by human bone marrow-derived mesenchymal stem cells to target blood vessels and vasculogenic mimicry of malignant gliomas

“…The clinical application of immunotoxins has several limitations, including 1) difficulties in penetrating and specifically locating tumors and reaching the desired concentration, and 2) nonspecific associated neural toxicity, which reduces resistance and narrows the therapeutic time window 14,15. Therefore, new approaches of immunotoxin delivery to overcome these obstacles are critical.…”

Dual targeting strategies with bispecific antibodies

“…This bispecific antibody inhibited For example, dual targeted toxins were generated fusing IL-13 and EGF with Diphtheria toxin. [118][119][120][121][122] In other studies, IL-13 was combined with uPA, [123][124][125] IL-4 with EGF, 126,127 or EGF with uPA, 128 fused either to Diphtheria toxin or Pseudomonas exotoxin A ( Table 2). Superior activities were seen with this BLTs, e.g., after intratumor injections into subcutaneous xenograft tumors.…”