**3.18 miR-221 and miR-222**

miR-221 and miR-222 are miRNA in cluster distribution with high homogeneity. Studies have shown that tumor suppressor gene p27 (Fornari *et al,* 2008), p57(Fornari *et al,* 2008), pro-apoptotic factor Bim and Bmf (Gramantieri *et al,* 2009) are all target genes of mir-222/mir-221. studies in recent years have shown that miR-221and miR-222 participate in the development of bladder cancer, HCC, prostate cancer and melanoma. Artificially synthesized small RNA precisely compensatory with miRNA can be used as an miRNA inhibitor to silence endogenous miRNA. Mercatelli *et al* (Mercatelli *et al,* 2008) used anti miR-221 and anti miR-222 inhibitors and a negative control inhibitor to intervene transplanted prostate cancer in nude mice for 33 days, and found that the means tumor size of the intervention group and the control group was 197.2mm3 and 276.82mm3 respectively, indicating that regulation of miR221/222 via RNAi could be used as the target of tumor treatment.
