Conjugates between monoclonal antibodies to HBsAg and cytosine arabinoside

Chemotherapeutic agents such as cytosine arabinoside (ARA-C) and adenine arabinoside (ARA-A) have been shown to eliminate or suppress replication of some DNA viruses. These effects were however associated with systemic side-effects to the treated hosts. We are currently exploring a strategy to construct conjugates between these antiviral agents and monoclonal antibodies directed against viral surface proteins. Such conjugates should enable specific delivery of the antiviral agents to their preferred site of action. In the present study, monoclonal antibodies to hepatitis B virus surface antigen (HBsAg) of the IgG2a and IgM isotypes were conjugated to ARA-C via a dextran bridge. The use of dextran enables the binding of a high number of drug molecules to the antibody with minimal loss of activity. Briefly, partially oxidized dextran was coupled to ARA-C and then to monoclonal anti-HBs. Following the conjugation process, the IgG2a anti-HBs-(dex)-ARA-C conjugate retained its capacity to bind to HBsAg fixed to a solid matrix as compared to non-conjugated homologous antibodies. Conjugates between ARA-C and IgM anti-HBs lost a significant degree of their binding activity to purified HBsAg. However, conjugates containing anti-HBs of both isotypes bound specifically to PLC/PRF/5 human hepatoma cells that express HBsAg on their cell surface. Conjugates containing non relevant monoclonal antibodies did not bind to target cells. Pharmacologic activity of the various compounds was assessed by an [3H]thymidine incorporation assay in hepatoma cells in culture. IgM and IgG2a containing conjugates caused suppression of [3H]thymidine incorporation into PLC/PRF/5 cells. This effect was more pronounced for conjugates containing monoclonal IgM anti-HBs.(ABSTRACT TRUNCATED AT 250 WORDS)