Study for mechanism of drug-resistance of hepatitis B virus against anti-viral therapy for patients with chronic hepatitis B virus infection

乙型肝炎病毒（HBV）是慢性肝病（如慢性肝炎、肝硬化和肝细胞癌）的主要病因之一。乙型肝炎病毒感染通常是慢性持续的，在一生中并不是自限性的。因此，通过抗病毒治疗控制和抑制病毒复制和肝损害具有重要意义。近年来，拉米夫定作为一种抑制病毒复制的核苷酸类似物被广泛应用于慢性乙型肝炎患者。拉米夫定对HBV具有很强的抗病毒活性，但每年有三分之一的患者在治疗过程中出现病毒突破。因此，研究病毒在抗病毒治疗过程中产生耐药的机制具有重要意义。我们调查了在拉米夫定治疗期间出现病毒突破的患者的背景及其病毒DNA序列。与治疗反应良好相关的因素是较高的ALT水平和阴性hbeag状态。与耐药相关的因素仅为HBV基因型。因此，我们将研究逆转录酶突变与HBV基因型之间的关系。在逆转录酶区，不同HBV基因型的核苷酸序列存在一定的异质性。热点突变与各基因型的异质性之间存在重要的关系。利用载体系统在Huh7细胞中构建的与各基因型HBV全基因组序列重组的复制模型，进一步研究其耐药机制。此外，其他核苷酸类似物，如阿德福韦或恩替卡韦，也应以同样的方法进行研究。

Hepatitis B virus (HBV) is one of the major cause of chronic liver diseases, such as chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. HBV infection usually continues chronically, in life-time and is not self-limited. Thus, it is important to control and suppress the viral replication and liver damage by anti-viral therapy. Recently, lamivudine, which is one of the nucleotide analogue suppressing viral replication, is widely used for patients with chronic hepatitis B. This drug has very strong anti-viral activity against HBV, however one thirds of patients treated with this drug show viral breakthrough during therapy year by year. So, it is very important to investigate the mechanism of developing drug-resistance during anti-viral therapy.We investigated the background of the patients and their viral DNA sequences in patients who developed viral breakthrough during lamivudine therapy. The factors which are related with favorable response to the therapy were higher ALT levels and negative-HBeAg status. In contrast, the factors which associated with drug-resistance were only HBV genotype. So, we are going to study the relation between the reversetranscriptase mutations and HBV genotypes. In the reversetranscriptase region, there are some heterogeneities of nucleotide sequences among different HBV genotypes. The relation is important between hot spot mutations and heterogeneities of each genotype. Using the replication model which is constructed by vector system in Huh7 cells recombined with full-genomic sequences of HBV of each genotype, the mechanism of drug-resistance will be further investigated. In addition, the other nucleotide analogues, like adefovir or entecavir, should be also investigated in the same method.