Tsu-An Hsu

Isatin-β-thiosemicarbazones as potent herpes simplex virus inhibitors

A series of isatin-β-thiosemicarbazones have been designed and evaluated for antiviral activity against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in a plaque reduction assay. Their cytotoxicity was examined using human rhabdomyosarcoma cells (RD cells). Several derivatives of isatin-β-thiosemicarbazone exhibited significant and selective antiviral activity with low cytotoxicity. It was found that the thiourea group at thiosemicarbazone and the NH functionality at isatin were essential for their antiherpetic activity. The synthesis and structure-activity relationship studies are presented.

Design, synthesis, and anti-HCV activity of thiourea compounds

A series of thiourea derivatives were synthesized and their antiviral activity was evaluated in a cell-based HCV subgenomic replicon assay. SAR studies revealed that the chain length and the position of the alkyl linker largely influenced the in vitro anti-HCV activity of this class of potent antiviral agents. Among this series of compounds synthesized, the thiourea derivative with a six-carbon alkyl linker at the meta-position of the central phenyl ring (10) was identified as the most potent anti-HCV inhibitor (EC(50) = 0.047 microM) with a selectivity index of 596.

Design and efficient synthesis of novel arylthiourea derivatives as potent hepatitis C virus inhibitors

A novel class of arylthiourea HCV inhibitors bearing various functionalities, such as cyclic urea, cyclic thiourea, urea, and thiourea, on the alkyl linker were designed and synthesized. Herein we report the synthesis and structure-activity relationships (SARs) of this novel class of arylthiourea derivatives that showed potent inhibitory activities against HCV in the cell-based subgenomic HCV replicon assay. Among compounds tested, the new carbazole derivative 64, which has an eight-carbon linkage between the phenyl and carbazole rings and a tolyl group at the N-9 position of carbazole, was found to possess strong anti-HCV activity (EC50=0.031 microM), lower cytotoxicity (CC50 >50 microM), and higher selectivity index (SI >1612) compared to its derivatives.

Resistance Analysis and Characterization of a Thiazole Analogue, BP008, as a potent Hepatitis C Virus NS5A Inhibitor.

ABSTRACT Hepatitis C virus (HCV) is a global health problem, affecting approximately 3% of the worlds population. The standard treatment for HCV infection is often poorly tolerated and ineffective. Therefore, the development of novel or more effective treatment strategies to treat chronic HCV infection is urgently needed. In this report, BP008, a potent small-molecule inhibitor of HCV replication, was developed from a class of compounds with thiazol core structures by means of utilizing a cell-based HCV replicon system. The compound reduced the reporter expression of the HCV1b replicon with a 50% effective concentration (EC50) and selective index value of 4.1 ± 0.7 nM and >12,195, respectively. Sequencing analyses of several individual clones derived from BP008-resistant RNAs purified from cells harboring HCV1b replicon revealed that amino acid substitutions mainly within the N-terminal region (domain I) of NS5A were associated with decreased inhibitor susceptibility. Q24L, P58S, and Y93H are the key substitutions for resistance selection; F149L and V153M play the compensatory role in the replication and drug resistance processes. Moreover, BP008 displayed synergistic effects with alpha interferon (IFN-α), NS3 protease inhibitor, and NS5B polymerase inhibitor, as well as good oral bioavailability in SD rats and favorable exposure in rat liver. In summary, our results pointed to an effective small-molecule inhibitor, BP008, that potentially targets HCV NS5A. BP008 can be considered a part of a more effective therapeutic strategy for HCV in the future.

Resistance Studies of a Dithiazol Analogue, DBPR110, as a Potential Hepatitis C Virus NS5A Inhibitor in Replicon Systems

ABSTRACT Hepatitis C virus (HCV), a member of the Flaviviridae family, affects approximately 3% of the worlds population and is becoming the leading cause of liver disease in the world. Therefore, the development of novel or more effective treatment strategies to treat chronic HCV infection is urgently needed. In our previous study, we identified a potential HCV NS5A inhibitor, BP008. After further systemic optimization, we discovered a more potent HCV inhibitor, DBPR110. DBPR110 reduced the reporter expression of the HCV1b replicon with a 50% effective concentration (EC50) and a selective index value of 3.9 ± 0.9 pM and >12,800,000, respectively. DBPR110 reduced HCV2a replicon activity with an EC50 and a selective index value of 228.8 ± 98.4 pM and >173,130, respectively. Sequencing analyses of several individual clones derived from the DBPR110-resistant RNAs purified from cells harboring genotype 1b and 2a HCV replicons revealed that amino acid substitutions mainly within the N-terminal region (domain I) of NS5A were associated with decreased inhibitor susceptibility. P58L/T and Y93H/N in genotype 1b and T24A, P58L, and Y93H in the genotype 2a replicon were the key substitutions for resistance selection. In the 1b replicon, V153M, M202L, and M265V play a compensatory role in replication and drug resistance. Moreover, DBPR110 displayed synergistic effects with alpha interferon (IFN-α), an NS3 protease inhibitor, and an NS5B polymerase inhibitor. In summary, our results present an effective small-molecule inhibitor, DBPR110, that potentially targets HCV NS5A. DBPR110 could be part of a more effective therapeutic strategy for HCV in the future.

Design and synthesis of indole, 2,3-dihydro-indole, and 3,4-dihydro-2H-quinoline-1-carbothioic acid amide derivatives as novel HCV inhibitors

An efficient synthetic methodology to provide indole, 2,3-dihydro-indole, and 3,4-dihydro-2H-quinoline-1-carbothioic acid amide derivatives is described. These conformationally restricted heterobicyclic scaffolds were evaluated as a novel class of HCV inhibitors. Introduction of an acyl group at the NH(2) of the thiourea moiety has been found to enhance inhibitory activity. The chain length and the position of the alkyl group on the indoline aromatic ring markedly influenced anti-HCV activity. The indoline scaffold was more potent than the corresponding indole and tetrahydroquinoline scaffolds and analogue 31 displayed excellent activity (EC(50)=510nM) against HCV without significant cytotoxicity (CC(50) >50microM).

A Potent, Selective, and Orally Bioavailable HCV NS5A Inhibitor for Treatment of Hepatitis C Virus: (S)-1-((R)-2-(Cyclopropanecarboxamido)-2-phenylacetyl)-N-(4-phenylthiazol-2-yl)pyrrolidine-2-carboxamide

Starting from the initial lead 4-phenylthiazole 18, a modest HCV inhibitor (EC50 = 9440 nM), a series of structurally related thiazole derivatives has been identified as a novel chemical class of potent and selective HCV NS5A inhibitors. The introduction of a carboxamide group between the thiazole and pyrrolidine ring (42) of compound 18 resulted in a dramatic increase in activity (EC50 = 0.92 nM). However, 42 showed only moderate pharmacokinetic properties and limited oral bioavalability of 18.7% in rats. Further optimization of the substituents at the 4-position of the thiazole ring and pyrrolidine nitrogen of the lead compound 42 led to the identification of compound 57, a highly potent and selective NS5A inhibitor of HCV (EC50 = 4.6 nM), with greater therapeutic index (CC50/EC50 > 10000). Pharmacokinetic studies revealed that compound 57 had a superior oral exposure and desired bioavailability of 45% after oral administration in rats.

Targeting Tumor Associated Phosphatidylserine with New Zinc Dipicolylamine-Based Drug Conjugates

A series of zinc(II) dipicolylamine (ZnDPA)-based drug conjugates have been synthesized to probe the potential of phosphatidylserine (PS) as a new antigen for small molecule drug conjugate (SMDC) development. Using in vitro cytotoxicity and plasma stability studies, PS-binding assay, in vivo pharmacokinetic studies, and maximum tolerated dose profiles, we provided a roadmap and the key parameters required for the development of the ZnDPA based drug conjugate. In particular, conjugate 24 induced tumor regression in the COLO 205 xenograft model and exhibited a more potent antitumor effect with a 70% reduction of cytotoxic payload compared to that of the marketed irinotecan when dosed at the same regimen. In addition to the validation of PS as an effective pharmacodelivery target for SMDC, our work also provided the foundation that, if applicable, a variety of therapeutic agents could be conjugated in the same manner to treat other PS-associated diseases.