- Email: [email protected]
967 PRECLINICAL CHARACTERIZATION OF SCH 900518, A NOVEL MECHANISM-BASED INHIBITOR OF HCV NS3 PROTEASE
05h: VIRAL HEPATITIS − h) HEPATITIS C − CLINICAL (NEW COMPOUNDS, RESISTANCE) 966 IDX184, A LIVER-TARGETED NUCLEOTIDE HCV POLYMERASE INHIBITOR: RESULTS OF A FIRST-IN-MAN SAFETY AND PHARMACOKINETIC STUDY X.-J. Zhou, K. Pietropaolo, J. Sullivan-Bolyai, B. Kuca, W. Liu, L. Xu, B. Belanger, S. Khan, D. Mayers. Idenix Pharmaceuticals, Inc., Cambridge, MA, USA E-mail: [email protected] Background and Aims: IDX184 is a liver-targeted nucleotide prodrug designed to enhance formation of its active triphosphate in the liver, while minimizing systemic exposure to the parent drug and its nucleoside metabolite (NM). Multilog viral load reductions were observed in HCVinfected chimpanzees receiving 10 mg/kg IDX184 for 3 days. This firstin-man study investigated single ascending dose safety and the pharmacokinetics of IDX184. Methods: Single ascending oral doses of 5, 10, 25, 50, 75 and 100 mg IDX184 were administered sequentially to cohorts of 8 healthy subjects randomized 6:2, active: placebo. Plasma levels of IDX184 and NM were quantitated using a validated LC-MS/MS methodology. Results: IDX184 was rapidly absorbed (median Tmax: 0.25−0.5 h) and eliminated (mean t1/ 2 : 0.6−1 h). Plasma concentrations of NM increased gradually (median Tmax: 4−6 h). Plasma exposure of IDX184 and NM was low and dose-related: the respective mean Cmax values ranged from 1.1 to 17 and 1.7 to 19 ng/mL, and mean total AUC values ranged from 1.2 to 22.7 and 17.3 to 334 ng*h/mL. Mean NM plasma concentrations 24 h after dosing were 0.6−3 ng/mL for 25–100 mg doses. Mean t1/ 2 for NM ranged from 18 to 43 h for doses 25 mg.IDX184 was well tolerated with no discontinuations, SAEs, dose-limiting toxicities, or dose-dependence of AEs. Overall, the incidence of AEs and laboratory abnormalities was low and similar among subjects receiving IDX184 or placebo. Dizziness was the most common AE which occurred more frequently in placebo subjects. All AEs were mild to moderate and resolved at the end of study. Conclusions: IDX184 appeared to be safe and well tolerated in this study. Consistent with a liver-targeting approach, systemic exposure of parent drug and metabolite was low. Importantly, systemic levels of NM obtained with 25 to 100 mg doses of IDX184 in this study are comparable to those associated with potent antiviral effects in HCV-infected chimpanzees. The favorable safety and pharmacokinetic profiles warrant further clinical development of IDX184 in HCV-infected patients. 967 PRECLINICAL CHARACTERIZATION OF SCH 900518, A NOVEL MECHANISM-BASED INHIBITOR OF HCV NS3 PROTEASE X. Tong1 , A. Arasappan2 , F. Bennett2 , R. Chase1 , B. Feld1 , Z. Guo3 , A. Hart1 , V. Madison3 , B. Malcolm1 , J. Pichardo1 , A. Prongay3 , R. Ralston1 , A. Skelton1 , E. Xia1 , F.G. Njoroge2 . 1 Virology, 2 Medicinal Chemistry, 3 Structural Chemistry, Schering-Plough Research Institute, Kenilworth, IL, USA E-mail: [email protected] Background and Aims: Small molecule HCV NS3 protease inhibitors have shown antiviral activity as monotherapy and in combination with pegylated interferon-alpha and ribavirin in clinical trials; however, clinical efficacy can be limited by inadequate drug exposure and development of viral resistance. Improvement in inhibitor potency and pharmacokinetic properties offers opportunities to overcome such limitations and to further increase SVR. Methods: Inhibition of HCV NS3 protease was measured using a singlechain NS3 (3-181)/4A protease. The antiviral effect and resistance study of protease inhibitors were evaluated using genotype 1b HCV replicon cells. Results: Combination of medicinal chemistry and structure-based design has led to the discovery of SCH 900518, a novel ketoamide protease inhibitor which forms a reversible covalent bond with the active site serine with an inhibition constant (Ki*) of 7 nM. SCH 900518 showed a 10-fold improvement in replicon potency (EC90 = 40 nM) compared to boceprevir
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and telaprevir. In biochemical assays, SCH 900518 was active against proteases of genotypes 1a, 1b, 2 and 3. A 2-week treatment with 5×EC90 of the inhibitor reduced replicon RNA by 3-log. High exposures of SCH 900518 had minimal effects on a variety of human normal and tumor cell lines. Selection of replicon cells with SCH 900518 resulted in outgrowth of several major resistant mutants (T54A/S, A156S/T/V). Preclinical crossresistance studies demonstrated that the majority of mutations against boceprevir and telaprevir showed similar fold loss of activity against all three inhibitors; however, SCH 900518 retained more activity against these mutants due to its higher intrinsic potency. Combination treatment with interferon-alpha enhanced inhibition of replicon RNA and suppressed emergence of resistant replicon colonies, supporting the use of SCH 900518/peginterferon combination therapy in the clinic. Conclusions: The preclinical characterization of SCH 900518 supports its progression towards clinical evaluation of safety, pharmacokinetic and pharmacodynamic parameters. 968 GENOTYPIC CHARACTERISATION OF HCV NS5B FOLLOWING 8-DAY MONOTHERAPY WITH THE POLYMERASE INHIBITOR PF-00868554 IN HCV-INFECTED SUBJECTS P. Troke1 , M. Lewis2 , P. Simpson2 , E. van der Ryst3 , J. Hammond4 , C. Craig1 , M. Perros1 , M. Westby1 . 1 Antivirals, 2 Experimental Biological Sciences, 3 Clinical Development, Pfizer Global Research and Development, Sandwich, UK; 4 Clinical Development, Pfizer Global Research and Development, New London, CT, USA E-mail: philip.troke@pfizer.com Background: PF-00868554 is a novel, potent, non-nucleoside inhibitor of the HCV NS5B polymerase. PF-00868554 inhibits genotype 1 replicons in vitro (59 nM mean EC50). Changes at amino acid 423 were the predominant mutation encoded by resistant variants generated during in vitro passage experiments. Mean maximum reductions (log10) in HCV RNA of 0.97, 1.84, 1.74, and 2.13 were achieved in HCV-infected subjects following 8 days of monotherapy with PF-008686554 at doses of 100, 300 or 450 mg BID and 300 mg TID, respectively. Changes of NS5B genotype following short-term monotherapy are described. Methods: Study A8121002 was a double-blind, placebo-controlled monotherapy study in subjects infected with genotype 1 HCV. Four cohorts of 8 subjects were randomized (6:2) to receive oral doses of PF-00868554, or placebo, for 8 days. Plasma samples for virologic analysis were collected at Screening, Day 8 and Follow-Up (Day 28). The HCV NS5B region was sequenced and the derived translations aligned to reference sequences according to genotype (genotype 1a: H77, NC_004102; genotype 1b: Con1, AJ238799). Sequences obtained at Day 8 and Day 28 were compared with the Screening sample for each subject. Results: Fifteen genotype 1a and sixteen genotype 1b subjects were enrolled in the study. All 31 subjects encoded wild-type M423 at screening. At Day 8, mutations at position 423 were identified in 11 of the 24 subjects dosed with PF-00868554, and 0 of 7 placebo subjects. Six subjects treated with PF-00868554 showed on-treatment viral load rebound of >0.5 log from NADIR to Day 8; virus from all 6 encoded M423 mutations at Day 8. At Follow-Up, 6 of the 11 subjects with 423 mutations at Day 8 had reverted back to methionine. One subject receiving 450 mg BID did not respond to PF-00868554. An uncommon variant, R422K, was identified in this subject at all timepoints. This mutation was also detected at Day 8 in another subject (300 mg TID), although this subject showed a continuous decline in viral load throughout dosing. Conclusions: Consistent with previous findings in vitro, the predominant mechanism of resistance to PF-00868554 during 8 days monotherapy was through mutation at residue 423 (11/24).
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and telaprevir. In biochemical assays, SCH 900518 was active against proteases of genotypes 1a, 1b, 2 and 3. A 2-week treatment with 5×EC90 of the inhibitor reduced replicon RNA by 3-log. High exposures of SCH 900518 had minimal effects on a variety of human normal and tumor cell lines. Selection of replicon cells with SCH 900518 resulted in outgrowth of several major resistant mutants (T54A/S, A156S/T/V). Preclinical crossresistance studies demonstrated that the majority of mutations against boceprevir and telaprevir showed similar fold loss of activity against all three inhibitors; however, SCH 900518 retained more activity against these mutants due to its higher intrinsic potency. Combination treatment with interferon-alpha enhanced inhibition of replicon RNA and suppressed emergence of resistant replicon colonies, supporting the use of SCH 900518/peginterferon combination therapy in the clinic. Conclusions: The preclinical characterization of SCH 900518 supports its progression towards clinical evaluation of safety, pharmacokinetic and pharmacodynamic parameters. 968 GENOTYPIC CHARACTERISATION OF HCV NS5B FOLLOWING 8-DAY MONOTHERAPY WITH THE POLYMERASE INHIBITOR PF-00868554 IN HCV-INFECTED SUBJECTS P. Troke1 , M. Lewis2 , P. Simpson2 , E. van der Ryst3 , J. Hammond4 , C. Craig1 , M. Perros1 , M. Westby1 . 1 Antivirals, 2 Experimental Biological Sciences, 3 Clinical Development, Pfizer Global Research and Development, Sandwich, UK; 4 Clinical Development, Pfizer Global Research and Development, New London, CT, USA E-mail: philip.troke@pfizer.com Background: PF-00868554 is a novel, potent, non-nucleoside inhibitor of the HCV NS5B polymerase. PF-00868554 inhibits genotype 1 replicons in vitro (59 nM mean EC50). Changes at amino acid 423 were the predominant mutation encoded by resistant variants generated during in vitro passage experiments. Mean maximum reductions (log10) in HCV RNA of 0.97, 1.84, 1.74, and 2.13 were achieved in HCV-infected subjects following 8 days of monotherapy with PF-008686554 at doses of 100, 300 or 450 mg BID and 300 mg TID, respectively. Changes of NS5B genotype following short-term monotherapy are described. Methods: Study A8121002 was a double-blind, placebo-controlled monotherapy study in subjects infected with genotype 1 HCV. Four cohorts of 8 subjects were randomized (6:2) to receive oral doses of PF-00868554, or placebo, for 8 days. Plasma samples for virologic analysis were collected at Screening, Day 8 and Follow-Up (Day 28). The HCV NS5B region was sequenced and the derived translations aligned to reference sequences according to genotype (genotype 1a: H77, NC_004102; genotype 1b: Con1, AJ238799). Sequences obtained at Day 8 and Day 28 were compared with the Screening sample for each subject. Results: Fifteen genotype 1a and sixteen genotype 1b subjects were enrolled in the study. All 31 subjects encoded wild-type M423 at screening. At Day 8, mutations at position 423 were identified in 11 of the 24 subjects dosed with PF-00868554, and 0 of 7 placebo subjects. Six subjects treated with PF-00868554 showed on-treatment viral load rebound of >0.5 log from NADIR to Day 8; virus from all 6 encoded M423 mutations at Day 8. At Follow-Up, 6 of the 11 subjects with 423 mutations at Day 8 had reverted back to methionine. One subject receiving 450 mg BID did not respond to PF-00868554. An uncommon variant, R422K, was identified in this subject at all timepoints. This mutation was also detected at Day 8 in another subject (300 mg TID), although this subject showed a continuous decline in viral load throughout dosing. Conclusions: Consistent with previous findings in vitro, the predominant mechanism of resistance to PF-00868554 during 8 days monotherapy was through mutation at residue 423 (11/24).