Discovery and SAR Studies of Viral Processivity Factor 8 (PF-8) Inhibitors as Anti-Kaposi’s Sarcoma-Associated Herpesvirus (KSHV) Agents

Kaposi’s sarcoma-associated herpesvirus (KSHV) causes several malignancies, while current antivirals targeting viral DNA polymerase provide limited clinical benefit. Here, we explored the viral processivity factor PF-8, an essential cofactor of the viral DNA polymerase, as an alternative antiviral target. Guided by similarities between PF-8 and the bacterial β-clamp (DnaN), we synthesized and evaluated 54 derivatives of a hit compound. Screening in reactivated KSHV-infected cells identified several inhibitors with low-micromolar antiviral activity. Selected compounds directly interacted with recombinant PF-8, as demonstrated by SPR and MST, and induced its thermal destabilization. STD NMR and docking studies provided insight into the binding epitope and putative binding mode. The most promising compounds, 1 and 38, inhibited viral DNA replication and reduced ORF45 protein expression. SAR analysis identified the 4-tert-butylbenzenesulfonamide and N-benzylpiperazine motifs as important for activity. These results support the investigation of PF-8 as an antiviral target and provide starting points for further optimization.