Enhanced antitumor effects of novel intracellular delivery of an active form of menaquinone-4, menahydroquinone-4, into hepatocellular carcinoma.

Reduced cellular uptake of menaquinone-4 (MK-4), a vitamin K2 homolog, in human hepatocellular carcinoma (HCC) limits its usefulness as a safe long-term antitumor agent for recurrent HCC and produces des-g gamma-carboxy prothrombin (DCP). We hypothesized that effective delivery of menahydroquinone-4 (MKH), the active form of MK-4 for g-glutamyl carboxylation, into HCC cells is critical for regulating HCC growth, and may enable it to be applied as a safe antitumor agent. In this study, we verified this hypothesis using menahydroquinone-4 1,4-bis-N, N-dimethylglycinate hydrochloride (MKH-DMG), a prodrug of MKH, and demonstrated its effectiveness. Intracellular delivery of MKH and subsequent growth inhibition of PLC/PRF/5 and Hep3B (DCPpositive) and SK-Hep-1 (DCP-negative) cells after MKH-DMG administration were determined and compared with MK-4. The activity of MKH-DMG against tumor progression in the liver alongside DCP formation was determined in a spleen-liver metastasis mouse model. MKH-DMG exhibited greater intracellular delivery of MKH in vitro (AUC(0-72) hour of MKH) and increased growth-inhibitory activity against both DCP-positive and DCP-negative HCC cell lines. The phenomena of MKH delivery into cells in parallel with simultaneous growth inhibition suggested that MKH is the active form for growth inhibition of HCCcells. Cell-cycle arrest was determined to be involved in the growth inhibition mechanisms of MKH-DMG. Furthermore, MKH-DMG showed significant inhibition of tumor progression in the liver, and a substantial decrease in plasma DCP levels in the spleen-liver metastasis mouse model. Our results suggest that MKH-DMG is a promising new candidate antitumor agent for safe long-termtreatment of HCC. (C) 2014 AACR.