We have previously shown that certain tyrphostin derivatives, known as protein tyrosine blockers, inhibited Moloney murine leukemia virus (Mo-MuLV) replication in acutely and chronically infected NIH/3T3 cells, without affecting cell viability or growth. In our present work, we examined the stages in the viral life cycle that are affected by tyrphostin AG-555. We found that this drug inhibited the integration of the viral DNA into the host genome in acutely infected cells. This compound also reduced the level of viral RNA and specifically inhibited viral protein synthesis in NIH/3T3/Mo-MuLV chronically infected cells while no effect on the cellular beta-actin was observed. Since tyrphostin AG-555 inhibited both the early stages (integration process) and the late stages (viral protein synthesis) in the virus life cycle, it offers a potential advantage over other compounds which affect only one stage in the viral life cycle. Therefore, tyrphostin AG-555 may be considered as a potent antiretroviral drug.

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