Evaluation of the in vitro anti-HBV activity of clevudine in combination with other nucleoside/nucleotide inhibitors.
BACKGROUND
To reduce the incidence of drug resistance and to maintain viral suppression, patients chronically infected with HBV might require combination therapy using two or more drugs with different resistance profiles. We investigated the activity of clevudine (CLV) in combination with other nucleoside/nucleotide analogues to determine if these combinations were compatible in vitro.


METHODS
Using the HepAD38 cell line, which expresses wild-type HBV, and a real-time PCR assay, we tested the anti-HBV activity of CLV in combination with entecavir, lamivudine, adefovir, tenofovir and telbivudine (TBV). We evaluated the uptake and phosphorylation of CLV in the presence of TBV, using HepAD38 cells and primary hepatocytes to determine the effect of TBV on the phosphorylation of CLV and vice versa. Phosphorylation of TBV and CLV to their corresponding monophosphate by deoxycytidine kinase, thymidine kinase-1 and thymidine kinase-2, and the phosphorylation of TBV monophosphate and CLV monophosphate by thymidylate kinase was evaluated and compared.


RESULTS
When CLV was combined with entecavir, lamivudine, adefovir or tenofovir, a synergistic antiviral effect was observed; however, the combination of CLV and TBV gave an antagonistic antiviral response. The results of in vitro metabolism and enzyme studies suggest that the antagonism observed with the CLV/TBV combination involves competition for uptake and phosphorylation.


CONCLUSIONS
The results of our studies demonstrate that combination treatments can provide enhanced antiviral activity and, when used in conjunction with appropriate metabolic investigations, provide a rational basis for the design and development of combination regimens for treating chronic HBV infection.
Pharmasset, Inc., Princeton, NJ, USA.
Congrong
C
Niu
Haiying
H
Bao
Tatiana
T
Tolstykh
Holly M
HM
Micolochick Steuer
Eisuke
E
Murakami
Brent
B
Korba
Phillip A
PA
Furman
D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D019380:Anti-HIV Agents / Q000494:pharmacology*; D000998:Antiviral Agents / Q000494:pharmacology*; D001086:Arabinofuranosyluracil / Q000031:analogs & derivatives / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D004336:Drug Antagonism; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D006147:Guanine / Q000031:analogs & derivatives / Q000494:pharmacology; D006515:Hepatitis B virus / Q000187:drug effects*; D022781:Hepatocytes / Q000187:drug effects / Q000821:virology; D006801:Humans; D019259:Lamivudine / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D009705:Nucleosides / Q000494:pharmacology*; D009711:Nucleotides / Q000494:pharmacology*; D063065:Organophosphonates / Q000494:pharmacology; D011744:Pyrimidinones / Q000494:pharmacology; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology*; D000077712:Telbivudine; D000068698:Tenofovir; D013936:Thymidine / Q000031:analogs & derivatives
D019380:Anti-HIV Agents; D000998:Antiviral Agents; D009705:Nucleosides; D009711:Nucleotides; D063065:Organophosphonates; D011744:Pyrimidinones; D018894:Reverse Transcriptase Inhibitors; D000077712:Telbivudine; D019259:Lamivudine; D001086:Arabinofuranosyluracil; C413685:entecavir; D006147:Guanine; C053001:adefovir; D000068698:Tenofovir; C034935:clevudine; D000225:Adenine; D013936:Thymidine