Figure 3.

Fate of thermally responsive nanostructures in vivo. a) Fluorescence images of organs from mice, where one tumor was heated at 45 °C for 30 min immediately after injection of various VT750-labeled nanoparticle formulations. The NIR-fluorescent molecular probes VT750 (750 nm excitation, 780 nm emission) were either attached to the nanoparticle surface (TSM-VT750, NSL-VT750, and TSL-VT750) or encapsulated in the internal space of nanoparticles (VT750@NSL and VT750@TSL). Mice bearing bilateral MDA-MB-435 tumors were intravenously injected with various VT750-labeled nanoparticle formulations and one tumor was immediately heated at 45 °C for 30 min in a temperature-controlled water bath. At 2 h post-injection, the tissues were collected from the mice and imaged with a NIR fluorescence imaging system. b) Biodistribution of DOX for various therapeutic nanoparticle formulations after GNR-mediated photothermal heating. Mice bearing bilateral MDA-MB-435 tumors were injected with GNRs (10 mg Au kg⁻¹). At 72 h post-injection, the indicated free DOX or therapeutic nanoparticle formulation was administered and one tumor was immediately irradiated (810 nm, ~0.75 W cm⁻²) for 30 min while maintaining an average tumor surface temperature of ~45 °C under IR thermographic surveillance. 24 h post-injection of the therapeutic nanoparticles, the tissues were collected from the mice and the native fluorescence intensity from DOX was quantified as a percentage of injected dose per tissue mass. Values represent the mean and the error bars indicate standard deviation. The differences in DOX concentration released from TSL in the heated tumor, relative to the other formulations (TSM and NSL), are significant (*P <0.05). c) Histological analysis of DOX distribution in MDA-MB-435 tumors treated with free DOX or the indicated therapeutic nanoparticle formulations and then subjected to GNR-mediated photothermal heating. The tissues were collected for hisotological analysis 6 h post-injection of the therapeutic nanoparticles (red: DOX, blue: DAPI nuclear stain, green: Alexa Fluor 488 labeled on the therapeutic nanoparticles). Abbreviations: NP, nanoparticle; T+, tumor heated to 45 °C; T−, tumor maintained at ambient temperature; Li, liver; Sp, spleen; K, kidney; Lu, lung; Bl, blood; Br, brain; H, heart. The scale bar indicates 200 μm.