Regulator of Cullins-1 (ROC1) or RING box protein-1 (RBX1) is an essential RING component of Cullin-RING ligase (CRL). Our previous studies showed that ROC1 is required for the growth of several cancer cell lines while ROC1 siRNA silencing inactivates CRL, leading to cell cycle arrest, cell senescence and/or apoptosis. However, it is completely unknown whether ROC1 knockdown triggers autophagic response by inactivating CRL. Moreover, the role of ROC1 in liver cancer remains elusive. In this study, we reported that ROC1 knockdown significantly inhibited the growth of liver cancer cells by sequentially and independently inducing autophagy and p21-dependent cell senescence. Mechanism analysis revealed that ROC1 silencing triggered autophagy by inhibition of mammalian target of rapamycin (mTOR) activity due to accumulation of mTOR-inhibitory protein Deptor, a substrate of CRL. Consistently, Deptor knockdown significantly blocked autophagy response upon ROC1 silencing. Biologically, autophagy response upon ROC1 silencing was a survival signal, and blockage of autophagy pathway sensitized cancer cells to apoptosis. Finally, we demonstrated that ROC1 was overexpressed in hepatocellular carcinomas, which is associated with poor prognosis of liver cancer patients. These findings suggest that ROC1 is an appealing drug target for liver cancer and provide a proof-of-concept evidence for a novel drug combination of ROC1 inhibitor and an autophagy inhibitor for effective treatment of liver cancer by enhancing apoptosis.
Taranabant is a cannabinoid-1 receptor inverse agonist for the treatment of obesity. This study evaluated the safety, pharmacokinetics, and pharmacodynamics of taranabant (5, 7.5, 10, or 25 mg once daily for 14 days) in 60 healthy male subjects. Taranabant was rapidly absorbed, with a median t(max) of 1.0 to 2.0 hours and a t(1/2) of approximately 74 to 104 hours. Moderate accumulation was observed in C(max) (1.18- to 1.40-fold) and AUC(0-24 h) (1.5- to 1.8-fold) over 14 days for the 5-, 7.5-, and 10-mg doses, with an accumulation half-life ranging from 15 to 21 hours. Steady state was reached after 13 days. After multiple-dose administration, plasma AUC(0-24 h) and C(max) of taranabant increased dose proportionally (5-10 mg) and increased somewhat less than dose proportionally for 25 mg. Taranabant was generally well tolerated up to doses of 10 mg and exhibited multiple-dose pharmacokinetics consistent with once-daily dosing.
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