Targeting KSHV processivity to prevent oral KS in AIDS

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DESCRIPTION (provided by applicant): Oral Kaposi's sarcoma is the classic malignancy associated with AIDS and is caused by the opportunistic virus, Kaposi's sarcoma herpesvirus. The recently discovered processivity factor (PF-8) of KSHV is an exciting new therapeutic target for eliminating oral KS. PF-8 binds and tethers KSHV DNA polymerase (Pol-8) on the DNA. In so doing, PF-8 enables Pol-8 to be processive, i.e., to incorporate thousands of nucleotides continuously without dissociating from the template. By contrast, Pol-8 alone incorporates only three nucleotides. The inability of a KSHV PF-8 deletion mutant virus to replicate confirms that PF-8 is essential for viral propagation. Important features of PF-8 that define precise targets for therapeutic intervention include two domains that are required to form PF-8 homo-dimers and a discrete Pol-8 binding domain. In addition to stabilizing Pol-8 on the DNA, PF-8 has been shown to be necessary for transporting Pol-8 into the nucleus via a nuclear localization signal. Significantly, the attractiveness of targeting PF-8 is its specificity for Pol-8 and no other viral or cellular proteins. The goal of this study is to focus on discovering PF-8 therapeutic compounds by using several complementary approaches. The first approach will be to validate compounds we have already identified from a small primary screen of the NCI combinatorial library that inhibited PF-8/Pol-8 processive DNA synthesis using our newly invented Rapid Plate Assay. We will identify additional compounds by high throughput screening of the NCI library. The second approach will be to employ a refined assay to screen for inhibitors that prevent formation of PF-8 homo-dimers, which are essential for processivity function. Our third approach will be to employ peptides to target PF-8 protein-interaction domains. These peptides, one of which has already been shown to block processivity by probably inhibiting PF-8 homo-dimerization, will be used to design therapeutic peptidomimetics. All of the inhibitors will be examined in cell-based assays for their abilities to block KSHV lytic infection as well as to eliminate latent KS-like spindle cells. Since KSHV lytic infection is apparently crucial in sustaining KS tumors, therapeutics that specifically block PF-8-dependent processive DNA synthesis are predicted to eliminate oral KS tumors directly with minimal secondary effects.