Effect of miR-21-knockdown on MCF-7 cells growth in nude mice: in vivo functional studies. MCF-7 cells (107 cells/tumor), treated with PNA-antimiR-21 or PNA-control (100 nM for 48 h) without transfection reagents, were injected subcutaneously into the left axilla of nude mice. (a) Growth curves for MCF/PNA-antimiR-21 (n = 5) vs. MCF/PNA-control (n = 8) cells in an in vivo proliferation assay. All P-values > 0.05. (b) Tumors were weighed after animals were killed at 17 days post-tumor-cell injection. Decreasing trend for both number and size of tumors from MCF/PNA-antimiR-21 compared with MCF/PNA-control group, although differences were not significant (P = 0.065, Mann-Whitney test). (c) Mice and tumors extracted from MCF/PNA-antimiR-21 and MCF/PNA-control groups. (d) Representative photomicrographs of CISH for miR-21 on xenograft tumor sections obtained from mice bearing MCF/PNA-antimiR-21 or MCF/PNA-control groups (× 400). (e) qRT-PCR analysis of miR-21 expression in MCF-7 cells 48 h post PNA-treatment and in xenograft tumors after mice sacrifice. Data in (a), (b) and (e) indicate the mean + SD. * P < 0.05, ** P < 0.01. PNA, peptide nucleic acid.