Sensitivity of human glioma cells to cytotoxic heteroconjugates

Abstract

Several anti-human glioma cytotoxic conjugates were studied in vitro. Monoclonal antibodies (MAbs) to the GE2 glioma-associated antigen (anti-GE 2) and MAbs to HLA-DR antigens (D1/12) or human diferric transferrin (Tfn) were linked to the potent cytotoxin ricin (anti-GE 2-ricin) or to its A subunit (anti-GE 2-RTA, D1/12-RTA, Tfn-RTA). Anti-GE 2-RTA had low cytotoxic activity in both the absence and the presence of lysosomotropic substances inhibiting intracellular degradation. Anti-GE 2-ricin was about 1,000 times more toxic than RTA alone, but showed only 14-fold target specificity. D1/12-RTA was about 20 times more toxic than RTA and its cytotoxic effect increased about 6- to 7-fold when cell-surface HLA-DR antigen expression was enhanced by IFN-gamma treatment. Human diferric Tfn linked to RTA demonstrated the highest cytotoxic activity, being about 5,000 times more toxic than RTA alone for glioma cells and about 6,000 times more toxic for Jurkat cells in the presence of the carboxylic ionofore monensin. Ricin toxin was only about 5 times more toxic for Jurkat and glioma cells than Tfn-RTA-monensin. Tfn-RTA was over 100,000 times more potent than the chemotherapeutic agent BCNU in reducing glioma cell survival in vitro. Addition of 80% human pooled cerebrospinal fluid (CSF) reduced Tfn-RTA toxicity about 10-fold. Kinetics of Tfn-RTA cytotoxicity at non-saturating concentrations indicated that over 80% of target cells could be killed within 8-10 hr in the absence and within 10-12 hr in the presence of human pooled CSF.

In vitro efficacy of transferrin-toxin conjugates against glioblastoma multiforme

“…The mouse Glioblastoma multiforme, a rapidly dividing primary, malignant brain tumor, has been shown by many investigators to express high numbers of TR's in vitro and in vivo. 9 been identified on glioblastoma multiforme tissue samples by immunohistochemistry, a radioreceptor assay, and solid-phase indirect radioimmunoassay) z5~ In addition to other techniques that have detected TR's on glioma cells in vitro, 95~'-~6 the direct binding of radiolabeled Tfn to the SNB19 and SF295 glioma cell lines in this study indicates TR expression on the cell surface. The differential expression of TR on glioblastoma compared to normal brain tissue suggests that TR's may be a suitable target for Tfn-toxin therapy.…”

“…Our Tfn-PE conjugate demonstrated comparable cytotoxicity in our glioma cell lines when compared to other reported immunotoxins in different glioma cells. 9"32"51 In the presence of monensin, SNB19 and SF295 cells were more susceptible to Tfn-abrin variant than were other glioma lines tested by Zovickian, et al, 66 Recht, el al., 5~ Johnson,etal., or Colombatti,et al,9 where Tfn and anti-TR monoclonal antibodies were used as the cartier ligands and ricin, ricin A chain, and CRM 107 were the toxin moieties. Although the mechanism by which monensin potentiates plant-derived abrin and ricin immunotoxins is unclear, disruption of vesicle movement in cells and alteration of endosomal pH have been implicated.…”

“…32-5L66 As previously done by Johnson, et al, 32 and Colombatti, etal., 9 we have constructed our conjugates with a Tfn carrier to presumably increase transvascular and intratumoral diffusion by decreasing molecular weight and size. A reduction in size may facilitate penetration of toxin conjugates into malignant brain-tumor tissue, after either intrathecal, intratumoral, or intra-arterial delivery, resulting in improved clinical efficacy.…”

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.…”

Prognostic importance of transferrin receptor expression and correlation with K1-67 labelling indices in intracranial meningiomas

“…19 Normal, healthy brain tissue expresses no significant level of TfR as compared with neoplastic tissue. 20 The presence of TfR has been demonstrated on human melanoma cell lines and glioblastoma multiforme (GBM) cell derived lines, in vivo. Proliferating cells and growing tumour cells express larger amounts of TfR than normal resting cells.…”