In vivo efficacy of OSU-HDAC42, a novel phenylbutyrate-based histone deacetylase inhibitor, in human hepatocellular carcinoma animal models Free

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Purpose: To carry out in vitro and in vivo mechanistic validation of the antitumor effect of OSU-HDAC42 vis-à-vis suberoylanilide hydroxamic acid (SAHA) in human hepatocellular carcinoma (HCC) cells. We hypothesize that HDAC inhibitors mediate antitumor effects in HCC by targeting multiple signaling pathways pertinent to cell cycle arrest and apoptosis induction.

Experimental Design: The in vitro effects of OSU-HDAC42 and SAHA were evaluated in Hep3B, Huh7, and PLC5 HCC cell lines versus normal hepatic cells. Cell viability, apoptosis, and signaling targets were determined by MTT assay, flow cytometry, and immunoblotting, respectively. The in vivo effects of these two drugs were assessed in both subcutaneous ectopic and intrahepatic orthotopic PLC5 xenograft tumor models with PLC5 in immunocompromised mice. Drugs were given orally at 25 mg/kg/day for 3 - 4 weeks. In vivo end points included tumor volumes and intratumoral changes in the expression of target proteins.

Results: OSU-HDAC42 was more potent than SAHA in suppressing cell viability and in inducing apoptosis in all three cancer cell lines, with the IC50 of approximately 0.5 µM and 3 - 5 µM, respectively. This differential antiproliferative effect could be attributable to differences in the respective effects on cell cycle arrest and apoptosis induction through a series of signaling targets, including p21, Bcl-xL, and the inhibitor of apoptosis protein family members cIAP-1, and cIAP-2. It is noteworthy that normal hepatic cells were an-order-of-magnitude less sensitive to the antiproliferative effect of OSU-HDAC42 as compared to the three cancer cell lines. Oral OSU-HDAC42 at 25 mg/kg/day for 21 and 28 days suppressed 85% and 91% PLC5 tumor growth in ectopic and orthotopic models, respectively, vis-à-vis 56% and 66%, respectively for the same dose regimen of SAHA. Western blotting indicates that intratumoral levels of Bcl-xL and cIAP-1 were reduced to a much greater extent in OSU-HDAC42-treated mice than those in SAHA-treated animals. Moreover, in the orthotopic xenografts model, two in the control group (N = 7) and one in the SAHA treatment group (N = 6), but none of the OSU-HDAC42 treatment group (N = 6) had intra-abdominal tumor bleeding.Conclusions: OSU-HDAC42 is a potent orally bioavailable HDAC inhibitor, as well as targets regulating multiple aspects of HCC growth and survival. This agent might have translational potential in HCC treatment, and warrants further investigation in this regard.