Figure 2. Growth inhibition of established lung tumor xenografts by synthetic let-7 oligonucleotides.

(A) Three × 10⁶ H460 lung cancer cells in 50% matrigel were subcutaneously injected into immunodeficient NOD/SCID mice. On days 11, 14, 17 and 20, synthetic let-7b or miR-NC double-stranded and ready-to-use miRNAs conjugated with the siPORTamine transfection reagent were intratumorally delivered into groups of six animals. As additional negative controls, tumor-bearing mice received intratumoral injections of PBS (n=5) or the lipid formulation lacking any oligonucleotide (siPORT; n=6). Caliper measurements were taken to determine the length and width of each tumor and to calculate total tumor volumes. Standard deviations are shown in the graph. Arrows indicate days of treatment. (B) Images of mice carrying H460 tumors after sacrifice on day 21. Subcutaneous lung tumors are indicated by arrows. (C) Tumor histologies and immunohistochemistry staining specific for Ki-67 and active caspase 3 are shown. v, area containing viable H460 tumor cells; d, area containing dead cells, cell debris or cells undergoing cell death. No difference in caspase activity was detected between experiment and controls.