Adefovir dipivoxil for the treatment of HBeAg-positive chronic hepatitis B: a review of the major clinical studies

Investigation of the Structure and Dynamics of Antiviral Drug Adefovir Dipivoxil by Site-Specific Spin-Lattice Relaxation Time Measurements and Chemical Shift Anisotropy Tensor Measurements

Adefovir is regarded as a potential antiviral agent. However, it cannot be considered as a valuable drug candidate due to its high polarity that limits its permeability across the human intestinal mucosa. When the ribose phosphate group of adefovir is replaced by the isopolar phosphonomethyl ether functionality, it neutralizes the negative charge of the drug. This makes the drug lipid-soluble and potent to diffuse across the cell membrane. The prodrug adefovir dipivoxil is regarded as a potent antiviral drug against hepatitis B virus (HBV), human immunodeficiency virus (HIV), Rauscher murine leukemia virus (R-MuLV), murine cytomegalovirus (MCMV), herpes simplex virus (HSV), simian immunodeficiency virus (SIV), and feline immunodeficiency virus (FIV). The correlation between the structure and the dynamics of adefovir dipivoxil is determined by measuring the principal components of chemical shift anisotropy (CSA) tensor, site-specific spin-lattice relaxation time, and molecular correlation time at crystallographically different carbon nuclei sites. The CSA parameters, spin-lattice relaxation time, and molecular correlation time of phosphorous nucleus of the organophosphate group of adefovir dipivoxil molecule are also determined. The spin-lattice relaxation time of carbon nuclei varies from 1 to 107 s. The range of molecular correlation time also varies from 10-4 to 10-8 s. These remarkable diversities of motional dynamics of the molecules imply that there exist various motional degrees of freedom within this valuable drug and these motional degrees of freedom are independent of each other, which may be the reason for the biological activities exhibited by the drug. The correlation between structure and dynamics of such an important antiviral drug adefovir dipivoxil can be visualized by these types of extensive spectroscopic measurements, which will enlighten the path of inventing advanced medicine in the pharmaceutical industry, and it will also illuminate the understanding of the structure-activity relationships of antiviral drug.

Host-Directed Antiviral Therapy

Antiviral drugs have traditionally been developed by directly targeting essential viral components. However, this strategy often fails due to the rapid generation of drug-resistant viruses. Recent genome-wide approaches, such as those employing small interfering RNA (siRNA) or clustered regularly interspaced short palindromic repeats (CRISPR) or those using small molecule chemical inhibitors targeting the cellular "kinome," have been used successfully to identify cellular factors that can support virus replication. Since some of these cellular factors are critical for virus replication, but are dispensable for the host, they can serve as novel targets for antiviral drug development. In addition, potentiation of immune responses, regulation of cytokine storms, and modulation of epigenetic changes upon virus infections are also feasible approaches to control infections. Because it is less likely that viruses will mutate to replace missing cellular functions, the chance of generating drug-resistant mutants with host-targeted inhibitor approaches is minimized. However, drug resistance against some host-directed agents can, in fact, occur under certain circumstances, such as long-term selection pressure of a host-directed antiviral agent that can allow the virus the opportunity to adapt to use an alternate host factor or to alter its affinity toward the target that confers resistance. This review describes novel approaches for antiviral drug development with a focus on host-directed therapies and the potential mechanisms that may account for the acquisition of antiviral drug resistance against host-directed agents.

Pharmacokinetics, safety and tolerance of single- and multiple-dose adefovir dipivoxil in healthy Chinese subjects

AIMS

To assess the pharmacokinetics, safety and tolerance of single- and multiple-dose adefovir dipivoxil (ADV) in healthy Chinese subjects.

METHODS

Forty-two healthy subjects were randomized into 5, 10, 20, 40 and 60-mg dose groups for safety assessment. Nine and 10 healthy males were enrolled for a single-dose pharmacokinetic profile and assessment of the effect of food on the pharmacokinetics of adefovir (PMEA), respectively. Another 10 healthy subjects were enrolled for a multiple-dose safety assessment and pharmacokinetic profile. Safety and tolerance were evaluated by monitoring adverse events and laboratory parameters, and pharmacokinetics were assessed by determining PMEA concentrations with a validated LC-MS/MS method.

RESULTS

No serious adverse events occurred. The pharmacokinetic parameters of PMEA following ADV 10, 20 and 40 mg were: geometric mean [95% confidence interval (CI)] for AUC(0-24 h) 227 (205, 253), 423 (361, 506) and 686 (585, 828) microg l(-1) h, C(max) 23.0 (20.7, 27.3), 47.4 (42.8, 53.2) and 83.6 (72.6, 97.4) microg l(-1), arithmetic mean (95% CI) for t(1/2) 6.8 (6.3, 7.3), 7.4 (6.7, 8.1) and 7.7 (6.5, 8.9) h, median value (range) for t(max) 1.00 (1.00-2.00), 0.75 (0.75-2.50) and 1.00 (0.75-2.00) h, respectively. The steady-state pharmacokinetics parameters were similar to those following a single dose. The AUC of PMEA was unaffected by food.

CONCLUSION

ADV is safe and well tolerated in healthy Chinese subjects. The mean C(max) of PMEA is proportional to dose, but the linearity of AUC needs further study. There is no accumulation following multiple doses of ADV and the extent of absorption of PMEA is unaffected by food.