Protein tyrosine kinase 7 (PTK7) aptamer covalently coupled with Dox for treatment of lymphocytic leukemia via an acid-sensitive linker 137, etc. These conjugates have shown good specificity of tumor targeting ability, fast drug release efficiency, significantly reduced off-target effects, and significantly improved therapeutic effects in both in vivo and in vitro studies. This evidence concerns the gene PTK7 and lymphoid leukemia.