Specific markers, micro-environmental anomalies and tropism: opportunities for gold nanorods targeting of tumors in laser-induced hyperthermia

Gold nanorods (GNRs) are optimal contrast agents for near-infrared (NIR) laser-induced photothermal ablation of cancer. Selective targeting of cancer cells can be pursued by attaching specific molecules on the particles surface or by the use of cellular vectors loaded with GNRs. We performed and tested various targeting approaches by means of GNRs functionalization with (i) antibodies against Cancer-Antigen-125 (CA-125), (ii) inhibitors of the carbonic anhydrase 9 (CA9) and (iii) by the use of macrophages as cellular vectors. GNRs with a NIR absorption band at 810 nm were synthesized and PEGylated. For GNRs functionalization the targets of choice were CA-125, the most widely used biomarker for ovarian cancer, and CA9, overexpressed by hypoxic cells which are often located within the tumor mass. In the case of cellular vectors, to be used as Trojan horses naturally able to reach tumor areas, the surface of PEG-GNRs was modified to achieve unspecific interactions with macrophage membranes. In all cases the cellular uptake was evaluated by silver staining and cell viability was assessed by MTT test. Then tests of laser-induced GNRs-mediated hyperthermia were performed in various cell cultures illuminating with an 810 nm diode laser (CW, 0,5-4 W/cm2 power density, 1-10 min exposure time) and cell death was evaluated. Each targeting strategy we tested may be used alone or in combination, to maximize the tumor loading and therefore the efficiency of the laser treatment. Moreover, a multiple approach could help when the tumor variability interferes with the targeting directed to a single marker.