Methods of treating a cancer in a patient are provided. The methods can include obtaining a tumor sample from a patient, detecting whether CCNG1 gene expression is present in the tumor sample, diagnosing the patient with a CCNG1 inhibitor-responsive cancer when the presence of CCNG1 gene expression in the tumor sample is detected, and/or administering an effective amount of a CCNG1 inhibitor to the diagnosed patient. CCNG1 inhibitors can include a viral vector having a binding peptide that is configured to bind one or more signature (SIG) elements of an invading tumor and at least one cytocidal gene. CCNG1 inhibitors including cell penetrating peptides are also provided.