In order to verify that the improved therapeutic efficacy and reduced toxicity of the PPA1-DOX conjugate is attributed to the tumor-targeted delivery offered by the PPA1 polypeptide, but not to the random changes in the surface modification of DOX, a random polypeptide (RAN) was conjugated to DOX as a control and the biodistribution of the fluorescence labelled compound was evaluated in the CT26-bearing mice after intravenous injection. The gene discussed is PPA1; the disease is neoplasm.