Selective delivery of doxorubicin to patients with breast carcinoma metastases by stealth liposomes

BACKGROUND Stealth liposomes hold promise as a mode of delivering cytotoxic agents selectively to tumors in cancer patients. The objective of this study was to determine whether stealth liposomal doxorubicin accumulates selectively in bone metastases based on clinical material obtained from two patients with breast carcinoma. METHODS Tumor tissue was obtained from two women (ages 33 years and 41 years, respectively) with metastatic breast carcinoma who responded to treatment with stealth liposomal doxorubicin and later underwent a surgical fixation procedure to treat a pathologic fracture of the femur. Drug levels in the tumor and adjacent muscle were examined by high performance liquid chromatography analysis in both patients and by fluorescence microscopy in one of the patients. RESULTS Bone tumor fragments obtained during surgery performed 6 days after the administration of the 12th course of stealth liposomal doxorubicin in 1 patient and 12 days after the administration of the 16th course of stealth liposomal doxorubicin in the second patient had a 10‐fold greater concentration of liposomal doxorubicin than tumor free muscle. Doxorubicin fluorescence and specific nuclear staining showed good colocalization, thus confirming the presence of the liposome‐delivered drug in the nuclei of tumor cells. CONCLUSIONS Using skeletal muscle as a comparator, stealth liposomal doxorubicin accumulates selectively in metastatic breast carcinoma cells within bone. Cancer 1999;86:72–8. © 1999 American Cancer Society. Drug levels in bone tumor fragments obtained from two breast carcinoma patients several days after the injection of stealth liposomal doxorubicin were tenfold higher than in adjacent muscle, indicating selective drug accumulation in bone metastases.