One of the main problems of conventional anticancer therapy is multidrug resistance (MDR), whereby cells acquire resistance to structurally and functionally unrelated drugs following chemotherapeutic treatment. One of the main causes of MDR is overexpression of the P-glycoprotein transporter. In addition to extruding the chemotherapeutic drugs, it also inhibits apoptosis through the inhibition of caspases. To overcome MDR, we constructed a novel chimeric protein, interleukin (IL)-2 granzyme A (IGA), using IL-2 as a targeting moiety and granzyme A as a killing moiety, fused at the cDNA level. IL-2 binds to the high-affinity IL-2 receptor that is expressed in an array of abnormal cells, including malignant cells. Granzyme A is known to cause caspase 3-independent cell death. We show here that the IGA chimeric protein enters the target sensitive and MDR cancer cells overexpressing IL-2 receptor and induces caspase 3-independent cell death. Specifically, after its entry, IGA causes a decrease in the mitochondrial potential, triggers translocation of nm23-H1, a granzyme A-dependent DNase, from the cytoplasm to the nucleus, where it causes single-strand DNA nicks, thus causing cell death. Moreover, IGA is able to overcome MDR and kill cells resistant to chemotherapeutic drugs. We believe that overcoming MDR with targeted molecules such as IGA chimeric protein that causes caspase-independent apoptotic cell death could be applied to many other resistant types of tumors using the appropriate targeting moiety. Thus, this novel class of targeted molecules could open up new vistas in the fight against human cancer.
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