The invention generally relates to compositions and methods for treating cancer. In certain embodiments, the invention provides methods that involve treating a cancer in a patient in which cancerous cells overexpress epidermal growth factor receptor as compared to non-cancerous cells. The methods involve administering a first composition including anthrax protective antigen modified to bind an epidermal growth factor receptor of a cell, and administering a second composition including anthrax lethal factor N-terminus fused to a catalytic domain of Diphtheria Toxin A. Binding of anthrax lethal factor N-terminus to anthrax protective antigen results in internalization of Diphtheria Toxin A into the cancerous cell, which triggers apoptosis by inactivation of critical elongation factors.
