thymalfasin and Hepatoblastoma

Cytokine-mediated apoptotic destruction of viral-infected cells, downregulation of virus production and inhibition of anchorage dependent (clonal) cell growth were evaluated using virus-transfected human hepatoblastoma (HepG2) cells. The cytokines evaluated were interferon alpha (IFN-alpha), tumour necrosis factor alpha (TNF-alpha) and thymosin alpha 1 (T alpha 1), all of which have previously been implicated in control of various viral infections. The viruses evaluated were Hepatitis B (HBV) and the transforming virus, SV-40. TNF-alpha-induced apoptosis in the HBV-transfected cell line and the control HepG2 cells but not the HepG2 cells transfected with SV-40 virus. IFN-alpha and T alpha 1 had no effect on apoptosis. TNF-alpha also prevented the clonal growth of the HBV-HepG2 and control HepG2 but enhanced the growth of the SV-40-transfected HepG2 cells. IFN-alpha inhibited the clonal growth of all three cell lines in contrast to T alpha 1 which inhibited the clonal growth of only the HBV-transfected cells. Although TNF-alpha, IFN-alpha, and T alpha 1 when given alone did not significantly inhibit HBV-DNA production in the culture supernatant from HBV-HepG2 cells, the combination of T alpha 1 and IFN-alpha resulted in a statistically significant inhibition of virus production. These studies demonstrate that HepG2 cells transfected with HBV and SV-40 are useful for defining the mechanisms of cytokine activity. The HBV-transfected cells are especially useful in defining possible in vivo differences in responses to cytokines with respect to HBV production, apoptosis and clonal cell growth. Multiple mechanisms through which different cytokines can influence HBV infection and hepatoblastoma growth were identified and the importance of defining effective combinations to improve therapy in vivo demonstrated.

Topics: Apoptosis; Cell Division; Hepatitis B virus; Hepatoblastoma; Humans; Interferon-alpha; Simian virus 40; Thymalfasin; Thymosin; Transfection; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha

Thymosin-alpha 1 is a biological response modifier that has been used clinically, alone and in combination with interferon-alpha for the treatment of chronic hepatitis B viral infection. Both immunomodulatory and immediate intracellular mechanisms have been postulated to explain the effect of these two agents on HBV-infected hepatocytes.. In this study, hepatitis B transfected HepG2 hepatoblastoma cells (HepG2-Nu2), derived from 2.2.15 cells, were used as an in vitro model to determine the efficacy of thymosin-alpha 1 and interferon-alpha, individually and combined, as proliferation inhibitors of HBV-infected cells. For comparison, parental HepG2 cells and an SV40-transfected HepG2 cell line (HepG2P9T2) were also evaluated.. In a clonogenic soft agar assay, thymosin-alpha 1 inhibited the anchorage-independent growth of the HepG2-Nu2 cells by 40% compared with untreated controls, but did not inhibit parental HepG2 or HepG2P9T2 clonal growth. The response was dose dependent over concentrations spanning three log units. In comparison, 10000 units/ml of interferon-alpha inhibited parental HepG2, HepG2-N4Z and HepG2P9T2 by 33%, 41% and 87%, respectively. The combination of thymosin-alpha 1 and interferon-alpha consistently inhibited HepG2-Nu2 clonal growth more effectively than either treatment alone, reaching maximum inhibition levels of 51%.. Thymosin-alpha 1 specifically inhibits the tumorigenic growth of HBV-transfected HepG2 cells in contrast to the general inhibition displayed by interferon-alpha. This panel of cell lines may be an important resource for dissecting the mechanism by which thymosin, alone or in combination with other drugs, influences HBV-infected hepatocytes and/or HBV-associated carcinoma.

Topics: Adjuvants, Immunologic; Antiviral Agents; Cell Division; Cell Transformation, Viral; DNA, Viral; Dose-Response Relationship, Drug; Drug Therapy, Combination; Enzyme-Linked Immunosorbent Assay; Hepatitis B virus; Hepatoblastoma; Humans; Interferon-alpha; Liver Neoplasms; Thymalfasin; Thymosin; Transfection; Tumor Cells, Cultured; Virus Replication