To determine whether the lung cancer-targeting peptide SP5-2 could be used to improve the chemotherapeutic efficacy of cancer treatment, we coupled the peptide to liposomes containing anticancer drugs. SCID mice bearing size-matched, CL1-5-derived xenografts were treated with (1) SP5-2-conjugated liposomal doxorubicin (SP5-2-LD), (2) mutant peptide-conjugated liposomal doxorubicin (MP5-2-LD), (3) non-targeted liposomal doxorubicin (LD), (4) free doxorubicin (FD), or (5) equivalent volumes of phosphate-buffered saline (PBS). All the formulations were injected intravenously (i.v.) at a total doxorubicin dosage of 8 mg/kg (1 mg/kg twice a week for a total of eight injections).