In vitro efficacy of transferrin-toxin conjugates against glioblastoma multiforme

Abstract

The cytotoxic activity of immunotoxins constructed with human diferric transferrin (Tfn) as the carrier ligand and an abrin variant Pseudomonas exotoxin A (PE) and the diphtheria toxin mutant cross-reacting material (CRM) 107 as the toxin moieties were studied in vitro. Three malignant human cell lines, the glioblastomas multiforme SNB19 and SF295 and the LOX melanoma, and a nonhuman control murine melanoma cell line B16 were assessed. The presence of transferrin receptors on the cell lines was confirmed by direct 125I-Tfn binding assays. The 50% protein synthesis inhibitory concentration (IC50) values for all cell lines demonstrated that Tfn-abrin variant and Tfn-PE had comparable potency and were both more effective than Tfn-CRM 107. Monensin, a carboxylic ionophore, potentiated the effect of Tfn-abrin variant against glioma cells approximately 35-fold with IC50 values of 4.0 x 10(-13) M and 4.7 x 10(-12) M for SNB19 and SF295, respectively. Cytotoxic activity of Tfn-abrin variant (with or without monensin) and Tfn-PE was correlated with the degree of Tfn receptor expression measured on the cell lines. The exquisite in vitro cytotoxicity of Tfn-abrin variant and Tfn-PE immunotoxins against glioma and melanoma cells warrants further in vivo evaluation and future consideration of these agents for potential clinical application against glioblastoma multiforme and leptomeningeal neoplasia.

Brain tumor iron uptake measured with positron emission tomography and 52Fe-citrate

“…diphtheria toxins, can enter cells via TfR resulting in tumor cell death in vitro [23][24][25]. The mode of toxin action is attributed to inactivation of protein synthesis [26].…”

Combining Cytotoxic and Immune-Mediated Gene Therapy to Treat Brain Tumors

“…Receptors for the urokinase-type plasminogen activator (uPA) [179], transferrin [180][181][182], pleiotropic immunoregulatory cytokines [183][184][185][186][187][188] and growth factors [189,190] are overexpressed by human brain tumors but are virtually absent in the normal brain. Such specificity makes these receptors very attractive targets for targeted therapeutic approaches in glioma, minimizing any putative adverse side effects to normal brain tissue.…”

“…The cytotoxic activity of targeted toxins constructed with human transferrin fused to Pseudomonas toxin or with Diphteria toxin was detected in human brain tumor cell lines [180,182]. In ex vivo experiments, pediatric brain tumor tissues were shown to be sensitive to transferrin-diphteria toxin [182], being that the toxin efficacy correlated with tumor grade.…”

Delivery of drugs, proteins and genes into cells using transferrin as a ligand for receptor-mediated endocytosis

“…In particular, monensin has been shown to strongly enhance the cytotoxicity of immunotoxins such as TfR-targeted ricin A or methotrexate as described by Raso and colleagues [25,30,32,34,38,42] and other groups [35,39,41,65]. The mechanism of action of monensin in this process is not clear.…”