Delivery of liposomal doxorubicin (Doxil) in a breast cancer tumor model: investigation of potential enhancement by pulsed-high intensity focused ultrasound exposure.

RATIONALE AND OBJECTIVES: To investigate the potential of using pulsed high-intensity focused ultrasound (HIFU) exposures to enhance the delivery, and hence therapeutic effect of liposomal doxorubicin (Doxil) in a murine breast cancer tumor model. MATERIALS AND METHODS: Tumors were grown in the bilateral flanks of mice using a mammary adenocarcinoma cell line. Experiments consisted of exposing one of two tumors to pulsed-HIFU, followed by tail vein injections of Doxil. Tumor growth rates were monitored, and assays carried out for doxorubicin concentration in these tumors as well as in a second (squamous cell carcinoma) tumor model and in muscle. Laser scanning confocal microscopy was used with fluorescent probes to observe both the uptake of polystyrene nanoparticles and dilation of exposed blood vessels. Additional experiments involving histologic analysis and real-time temperature measurements were performed to determine the safety of the exposures. RESULTS: Pulsed-HIFU exposures were shown to be safe, producing no apparent deleterious effects in the tumors. The exposures, however, were not found to enhance the delivery of Doxil, and consequently did not allow for lower doses for obtaining tumor regression. Imaging with a fluorescent dextran showed blood vessels to be dilated as a result of the exposures. Experiments with polystyrene nanoparticles of similar size to the liposomes showed a greater abundance to be present in the treated tumors. CONCLUSION: Although past studies have shown the advantages of pulsed-HIFU exposures for enhancing delivery, this was not observed with the liposomes, apparently because of their inherent ability to preferentially accumulate into tumors on their own. Potential mechanisms for enhanced uptake of non-liposomal nanoparticles are discussed.

Synthesis, in vitro, and in vivo characterization of an integrin alpha(v)beta(3)-targeted molecular probe for optical imaging of tumor.

Integrin alpha(v)beta(3) is a widely-recognized target for the development of targeted molecular probes for imaging pathological conditions. alpha(v)beta(3) is a cell-surface receptor protein that is upregulated in various pathological conditions including osteoporosis, rheumatoid arthritis, macular degeneration, and cancer. The synthesis of an alpha(v)beta(3)-targeted optical probe 7 from compound 1, and its in vitro and in vivo characterization is described. A series of aliphatic carbamate derivatives of the potent non-peptide integrin antagonist 1 was synthesized and the binding affinity to alpha(v)beta(3) was determined in both enzyme linked immunosorbent assay (ELISA) and cell adhesion inhibition assays. The hydrophobic carbamate-linked appendages improved the binding affinity of the parent compound for alpha(v)beta(3) by 2-20 times. A Boc-protected neopentyl derivative in the series is shown to have the best binding affinity to alpha(v)beta(3) (IC(50)=0.72 nM) when compared to compound 1 as well as to c-RGDfV. Optical probe 7 utilizes the neopentyl linker and demonstrates increased binding affinity and significant tumor cell uptake in vitro as well as specific tumor accumulation and retention in vivo. These results illustrate the potential of employing integrin-targeted molecular probes based on 1 to image a multitude of diseases associated with alpha(v)beta(3) overexpression.