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Background: During HAART the number of HIV-infected cells in vivo rapidly declines due to the short life span of activated/infected T-lymphocytes, killing by cytotoxic T-cells, and the intrinsic cytotoxicity of HIV.  Nonetheless, even after several years of successful HAART substantial numbers of infected cells still remain.  These are mostly memory T-lymphocytes, carrying an integrated viral genome and presumably expressing very low levels of viral proteins (latent reservoir).  Our goal was to explore a new class of anti-HIV compounds that selectively kill HIV- infected cells.  Such drugs could reduce the size of the latent reservoir when used in combination with HAART.  Since HIV infection affects normal cellular physiology, infected cells could be more vulnerable than uninfected cells to inhibitors of specific cellular enzymes.  In support of this premise, several classes of compounds including cyclin dependent kinase (CDK) inhibitors have been reported to selectively kill HIV-infected cells.

Methods: More than 30 CDK inhibitors and structurally related molecules were simultaneously tested against chronically infected and uninfected CEM T-cells.  Cell killing was measured by XTT assay and a selectivity ratio between infected and uninfected cells was calculated.  The most selective inhibitors were then tested for anti-HIV activity in acutely infected primary T-lymphocytes and macrophages by measuring p24 production 4 days after infection with drug treatment.

Results:  Several CDK inhibitors including, two purine analogs, one pyrazine derivative, and one paullone derivative, were 10- to 80- fold more toxic to infected cells than to uninfected cells.  Six compounds showed moderate selectivity (4- to 10-fold), 8 compounds showed poor selectivity (0.5- to 4- fold) and several compounds were not toxic in both cells up to 200 mM.  Some compounds that were not effective alone showed selectivity when used in combination, suggesting that simultaneous inhibition of several different CDK may be required for selective killing of HIV-infected cells.  The selective compounds also showed anti-HIV activity in primary T-cells and macrophages.

Conclusions:  Screening of cyclin dependent kinase inhibitors for selective killing of HIV infected T-cell lines has led to the discovery of compounds that also show antiviral effects in primary T-lymphocytes and macrophages.

Keywords: CDK inhibitor; latent reservoir; cell cycle