Transferrin receptor ligand-targeted toxin conjugate (Tf-CRM107) for therapy of malignant gliomas

The authors review the preclinical and clinical results of the ligand-targeted toxin conjugate Transferrin-CRM107 (Tf-CRM107), for the treatment of malignant gliomas. Tf-CRM107 is a conjugate protein of diphtheria toxin with a point mutation (CRM107) linked by a thioester bond to human transferrin (Tf). This conjugate exhibits potent cytotoxicity in vitro against mammalian cells expressing the transferrin receptor with activity at picomolar concentrations. Phase I clinical trial results demonstrated that Tf-CRM107, delivered via a high- flow convection method utilizing stereotactically placed catheters, produced tumor response in patients with malignant brain tumors refractory to conventional therapy without severe neurologic or systemic toxicity. The results of a Phase II study are also summarized. Tf-CRM107 treatment results in complete and partial tumor response without severe toxicity in 35% of the evaluable patients. These datawarrant a Phase III study as well as continued research in the field of targeted toxin therapy. Future directions of research include optimizing Tf-CRM107 delivery to targeted brain regions, and improving the treatment efficacy by combining with other toxin conjugates targeted to different receptors.