Engineering and production of saporin chimeric toxins against human glioblastoma

PDZ domains are found in proteins involved in cellular processes, from the signal transduction to the transport and particularly in synapse formation in mammals. They recognize and bind short peptide sequences located at the C-terminus of a protein. Recognition of the C-termini represents a ‘non-invasive’ interaction, and that can be used as a target by various PDZ domains. In the research of new engineered toxins to target cancer cells, we have studied PDZ protein domain as possible tools for cellular targeting of the ribosome inactivating protein saporin. We have focussed our attention to the PDZ domain from hCASK (human calcium/calmodulin-dependent serine protein kinase) that has been demonstrated to bind extracellular CD98, recognized as a marker for several human tumors. and particularly considered a negative prognostic factor for human glioblastoma. hCASK-SAP chimeras (with one or two PDZ domains) are able to induce cell cytotoxicity in a dose-dependent and/or time dependent manner on human glioblastoma cells (GL15 and U87). Moreover the hCASK-SAP constructs proved to be toxic, with increasing activity as a function of the number of PDZ domains, and induce cell death by apoptotic mechanisms.