Indirubin-3′-monoxime, a derivative of a Chinese antileukemia medicine, inhibits P-TEFb function and HIV-1 replication

Abstract

To evaluate the effects of the cyclin dependent kinase (CDK) inhibitor Indirubin-3'-monoxime (IM) on Tat-mediated transactivation function, a step of the HIV-1 cycle that is not currently targeted in antiviral therapy. The effects of IM on CDK implicated in HIV-1 Tat transactivation function were evaluated by kinase assays, transfection experiments, RNase protection assay and RT-PCR analysis of viral transcripts. The antiviral effect of IM was investigated in cells from HIV-1 infected individuals as well as in cell lines, primary lymphocytes and monocyte-derived macrophages. The antiviral activity of IM was also tested against drug-resistant HIV-1. IM inhibits the kinase activity of CDK9 [50% inhibitory concentration (IC50) of 0.05 microM], the catalytic subunit of Positive transcription elongation factor b (P-TEFb). Inhibition of CDK9 activity by IM results in abrogation of Tat-induced expression of HIV-1 RNA in cell lines. In addition, IM inhibits the replication of HIV-1 in both peripheral blood mononuclear cells (IC50 of 1 microM) and macrophages (IC50 of 0.5 microM). IM is effective against primary and drug-resistant strains of HIV-1. Importantly, the antiviral effects of the drug were seen at concentrations that did not affect cell proliferation. Non-toxic concentrations of IM inhibit HIV-1 by blocking viral gene expression mediated by the cellular factor P-TEFb. The drug is effective against wild-type and drug-resistant strains of HIV-1. IM may help control replication of HIV-1 in patients by disrupting a step of the HIV-1 cycle that is not being targeted in current antiretroviral treatments.