Tegobuvir

Tegobuvir (TGV) is a non-nucleoside of HCV RNA replication EC50s of ＜ 16 nM against genotype 1 and ＞100 nM for other genotypes. [1, 2]

Tegobuvir inhibited HCV replication by targeting the NS5B polymerase. The NS5B polymerase is an RNA polymerase which is responsible for HCV replication and is RNA-dependent RNA polymerase.[3, 4] The HCV NS5B contains canonical thumb, finger, and palm subdomains.[3]

Tegobuvir has potent activity against genotypes 1a and 1b HCV in HCV replicons in vitro, and in HCV genotype 1-infected patients and GT 1a EC50 is 17-fold higher than that observed in GT 1b.[5] However, It exhibited reduced activity against GT2a replicons and GT2a infectious virus. Furthermore, the C445F mutation selected by tegobuvir caused a 7.1 fold increase in EC50.[2] Thus, it indicated that the mechanism of tegobuvir is related to HCV NS5B. The data from different mutation of NS5B including C316Y, C445F, and Y452H indicated that the inhibitory effect is due to the interaction with the hairpin in the thumb subdomain.[2] But, The mechanism of TGV still has not been clearly defined. TGV does not have any inhibition effect on NS5B enzymatic activity with recombinant NS5B proteins.[5] A decrease in antiviral potency of TGV was observed when a CYP1A inhibitor was combined used in antiviral assays. It demonstrated that TGV binds to the NS5B polymerase after undergoing a multistep metabolic activation pathway.[5] The activity of TGV also is related to the specific glutathione adducts.[5] Besides the sub-type differences, TGV also is less potent against the GT 1b replicon in the HeLa cell line with EC50＞10?M.

When individual patients treated only with tegobuvir with 8 days, it demonstrated median reductions of 1.5 log10 IU/mL in HCV RNA. But, rates of RVR (HCV RNA< 25 IU/mL at week 4) was enhanced when treated with Peg-IFN and RBV at the same time.[5]

References:
[1].  Zeuzem S, Andreone P, Pol S, Lawitz E, Diago M, Roberts S, Focaccia R, Younossi Z, Foster GR, Horban A et al: Telaprevir for retreatment of HCV infection. N Engl J Med 2011, 364(25):2417-2428.
[2].  Wong KA, Xu S, Martin R, Miller MD, Mo H: Tegobuvir (GS-9190) potency against HCV chimeric replicons derived from consensus NS5B sequences from genotypes 2b, 3a, 4a, 5a, and 6a. Virology 2012, 429(1):57-62.
[3].  Shih IH, Vliegen I, Peng B, Yang H, Hebner C, Paeshuyse J, Purstinger G, Fenaux M, Tian Y, Mabery E et al: Mechanistic characterization of GS-9190 (Tegobuvir), a novel nonnucleoside inhibitor of hepatitis C virus NS5B polymerase. Antimicrob Agents Chemother 2011, 55(9):4196-4203.
[4].  Behrens SE, Tomei L, De Francesco R: Identification and properties of the RNA-dependent RNA polymerase of hepatitis C virus. EMBO J 1996, 15(1):12-22.
[5].  Hebner CM, Han B, Brendza KM, Nash M, Sulfab M, Tian Y, Hung M, Fung W, Vivian RW, Trenkle J et al: The HCV non-nucleoside inhibitor Tegobuvir utilizes a novel mechanism of action to inhibit NS5B polymerase function. PLoS One 2012, 7(6):e39163.

In vitro combinations containing Tegobuvir are highly efficient in curing cells from HCV replicon and in delaying/preventing the development of drug resistance.[Pubmed:26036224]

Antiviral Res. 2015 Aug;120:112-21.

Tegobuvir (GS-9190) is a non-nucleoside inhibitor of HCV RNA replication with proven antiviral activity in HCV-infected patients. The in vitro antiviral activity of Tegobuvir, when combined with one or two other direct acting antivirals (DAA) was assessed. When Tegobuvir was combined with either interferon alpha-2b, ribavirin, the protease inhibitor (PI) VX-950, the nucleoside polymerase inhibitor (NI) 2'-C-methylcytidine or various non-nucleoside polymerase inhibitors, an overall additive antiviral activity was observed. Adding Tegobuvir (at concentrations of 6, 30 or 150nM) to replicon-containing cells in the presence of suboptimal concentrations of the PI or of the various polymerase inhibitors either markedly delayed or completely prevented resistance development against these latter compounds. Tegobuvir (15nM), when combined with the PI, was able to cure replicon-containing cells from their replicon after a single passage, whereas either compound alone (at 2-fold higher concentration) was not. The triple combination of Tegobuvir (10nM), the PI and the NI resulted in clearance of replicon RNA after only two passages. In contrast, the inhibitors when used alone at 3-fold higher concentrations were not able to cure the cells from the replicon, after as long as 6 passages. Combinations containing low concentrations of Tegobuvir are thus highly effective in curing cells from HCV replicon and in delaying or preventing the development of resistance against other DAA.

The HCV non-nucleoside inhibitor Tegobuvir utilizes a novel mechanism of action to inhibit NS5B polymerase function.[Pubmed:22720059]

PLoS One. 2012;7(6):e39163.

Tegobuvir (TGV) is a novel non-nucleoside inhibitor (NNI) of HCV RNA replication with demonstrated antiviral activity in patients with genotype 1 chronic HCV infection. The mechanism of action of TGV has not been clearly defined despite the identification of resistance mutations mapping to the NS5B polymerase region. TGV does not inhibit NS5B enzymatic activity in biochemical assays in vitro, suggesting a more complex antiviral mechanism with cellular components. Here, we demonstrate that TGV exerts anti-HCV activity utilizing a unique chemical activation and subsequent direct interaction with the NS5B protein. Treatment of HCV subgenomic replicon cells with TGV results in a modified form of NS5B with a distinctly altered mobility on a SDS-PAGE gel. Further analysis reveals that the aberrantly migrating NS5B species contains the inhibitor molecule. Formation of this complex does not require the presence of any other HCV proteins. The intensity of the aberrantly migrating NS5B species is strongly dependent on cellular glutathione levels as well as CYP 1A activity. Furthermore analysis of NS5B protein purified from a heterologous expression system treated with TGV by mass spectrometry suggests that TGV undergoes a CYP- mediated intracellular activation step and the resulting metabolite, after forming a glutathione conjugate, directly and specifically interacts with NS5B. Taken together, these data demonstrate that upon metabolic activation TGV is a specific, covalent inhibitor of the HCV NS5B polymerase and is mechanistically distinct from other classes of the non-nucleoside inhibitors (NNI) of the viral polymerase.

All-oral combination of ledipasvir, vedroprevir, tegobuvir, and ribavirin in treatment-naive patients with genotype 1 HCV infection.[Pubmed:24501005]

Hepatology. 2014 Jul;60(1):56-64.

UNLABELLED: This phase II trial assessed the efficacy and safety of a combination regimen of the nonstructural protein (NS)5A inhibitor ledipasvir (LDV), NS3 protease inhibitor vedroprevir (VDV), non-nucleoside NS5B inhibitor Tegobuvir (TGV), and ribavirin (RBV) in treatment-naive patients with chronic hepatitis C virus (HCV) genotype 1 without cirrhosis. Patients were randomized 1:2 to LDV 30 mg once daily (QD; Arm 1; n = 46) or LDV 90 mg QD (Arm 2; n = 94); patients in both arms also received VDV 200 mg QD, TGV 30 mg twice-daily, and RBV 1,000-1,200 mg/day. Patients in Arm 2 with vRVR, defined as HCV RNA below the lower limit of quantification (LLOQ) from treatment weeks 2 to 10, were randomized 1:1 to stop treatment at 12 weeks or continue for 24 weeks. Sustained virologic response 12 weeks after treatment (SVR12) was higher in patients receiving 90 mg of LDV for 24 weeks (63%), compared with LDV 90 mg for 12 weeks (54%) and LDV 30 mg for 24 weeks (48%). In patients with very rapid virologic response (vRVR) in Arm 2, SVR12 was achieved by 68% and 81% of patients treated for 12 and 24 weeks, respectively. Virologic breakthrough was more common in patients with HCV genotype 1a and was associated with resistance-associated variants for all three direct-acting antiviral agents (DAAs); however, in all but 1 patient who relapsed, resistance-associated variants directed against only one or two of the DAAs were detected. The most common adverse events were fatigue, headache, nausea, rash, and diarrhea. CONCLUSION: In patients with HCV genotype 1, an interferon-free regimen containing LDV/VDV/TGV/RBV was well tolerated and led to SVR12 in up to 63% of patients. LDV 90 mg is currently being investigated in combination with the nucleotide polymerase inhibitor, sofosbuvir.

Tegobuvir (GS-9190) potency against HCV chimeric replicons derived from consensus NS5B sequences from genotypes 2b, 3a, 4a, 5a, and 6a.[Pubmed:22543048]

Virology. 2012 Jul 20;429(1):57-62.

With the exception of nucleoside analogs, few direct acting antivirals in clinical development are active across the six major hepatitis C virus genotypes. We report novel consensus sequence chimeras for genotypes 2b, 3a, 4a, 5a, and 6a NS5B and show variable susceptibilities over a panel of NS5B inhibitors. Tegobuvir (GS-9190) had EC(50)s of <16 nM against genotype 1 and >100 nM for other genotypes tested here. An NS5B F445C mutation engineered into the GT3a, 4a, and 6a chimeric replicons lowered the Tegobuvir EC(50) to levels comparable to those for genotype 1a, but did not considerably alter the EC(50) of site 2 or nucleoside analog inhibitors. These data support the use of HCV chimeras in profiling direct acting antivirals across genotypes and specifically determines the impact of the C445F NS5B polymorphism on Tegobuvir potency against genotypes 3a, 4a, and 6a.