Previous work by us and others reported decreased expression of miR-199a-3p in hepatocellular carcinoma (HCC) tissues compared to adjacent benign tissue. We report here a significant reduction of miR-199a-3p expression in 7 HCC cell lines. To determine if miR-199a-3p has a tumor suppressive role, pre-miR-199a-3p oligonucleotides were transfected into the HCC cell lines. Pre-miR-199a-3p oligonucleotide reduced cell proliferation by approximately 60% compared to control oligonucleotide in only two cell lines (SNU449 and SNU423); the proliferation of the other 5 treated cell lines was similar to control oligonucleotide. A pre-miR-199a-3p oligonucleotide formulated with chemical modifications to enhance stability while preserving processing, reduced cell proliferation in SNU449 and SNU423 to the same extent as the commercially available pre-miR-199a-3p oligonucleotide. Furthermore, only the duplex miR-199a-3p oligonucleotide, and not the guide strand alone, was effective at reducing cell viability. Since a CD44 variant was essential for c-Met signaling [V. Orian-Rousseau, L Chen, J.P. Sleeman, P. Herrlich, H. Ponta, CD44 is required for two consecutive steps in HGF/c-Met signaling, Genes Dev. 16 (2002) 3074-3086] and c-Met is a known miR-199a-3p target, we hypothesized that miR-199a-3p may also target CD44. Immunoblotting confirmed that only the two HCC lines that were sensitive to the effects of pre-miR-199a-3p were CD44+. Direct targeting of CD44 by miR-199a-3p was confirmed using luciferase reporter assays and immunoblotting. Transfection of miR-199a-3p into SNU449 cells reduced in vitro invasion and sensitized the cells to doxorubicin; both effects were enhanced when hyaluronic acid (HA) was added to the cell cultures. An inverse correlation between the expression of miR-199a-3p and CD44 protein was noted in primary HCC specimens. The ability of miR-199a-3p to selectively kill CD44+ HCC may be a useful targeted therapy for CD44+ HCC. (C) 2010 Elsevier Inc. All rights reserved.