Systemic administration of miRNA mimics by liposomal delivery system in animal model of colorectal carcinoma.

MiRNAs are important regulators of gene expression and changes in their levels are linked with various pathological states, including solid tumors. MiR-215 has been identified as a tumor suppressor in colorectal cancer (CRC). Following our previous in vitro and in vivo experiments, the aim of this project was to study the possibility of increasing the levels of miR-215 in tumor cells by systemic administration of miRNA mimics in liposomal delivery system in vivo. By subcutaneous xenotransplantation of human cancer cells to NSG mice, CRC model was established. The treatment (miR-215 mimics in liposomes [20 and 40 microg/mouse], control oligonucleotide in liposomes, or saline) was administered repeatedly by i.v. injection via tail-vein. Animals were sacrificed, tumor were dissected and measured by a caliper. Expression of miR-215 in tumors, lungs and liver was quantified by RT-PCR. There was no significant differences in tumor volume and miR-215 expression between all three treatment groups. Therefore, the decrease in tumor volume was not achieved. By comparing the levels of miR-215 in lungs, liver and tumors after the treatment, we suggest that the liposomes are accumulated in the lungs and do not concentrate sufficiently in the tumor site to exert significant tumor-suppressive effect.