Discovery of acylphloroglucinol-based meroterpenoid enantiomers as KSHV inhibitors from Hypericum japonicum

Kaposi's sarcoma associated herpesvirus (KSHV) has gained considerable attention as a type of carcinogenic pathogen. Recent research suggests that KSHV has participated in the pathogenesis of Kaposi's sarcoma-related malignant neoplastic diseases. Viral lytic infection might be pivotal for the etiopathogenesis of KSHV-induced diseases; however, most clinical KSHV lytic replication inhibitors like ganciclovir, nelfinavir, or cidofovir do not restrain virus replication effectively enough to achieve clinical efficacy. In our continued pharmaceutical studies on Chinese herbal medicines, new acylphloroglucinol-based meroterpenoid enantiomers have been discovered from Hypericum japonicum. Most of these metabolites have potential inhibitory activities that target KSHV lytic replication. Amongst these analogues, compounds 1a and 1b possess an unreported ring system cyclopenta[b]chromene. Compounds 1a with 4a exhibit stronger inhibitory activities towards the lytic replication of KSHV in Vero cells. In addition, 1a and 4a have IC(50) values of 8.30 and 4.90 μM and selectivity indexes of 23.49 and 25.70, respectively. Qualitative and quantitative SAR and molecular docking studies for acylphloroglucinol-based meroterpenoids with regard to anti-KSHV activity were conducted. An explanation for the variation in the activity and selectivity indexes was proposed in accordance with the predicted binding pose found with molecular docking to a putative target, thymidylate synthase (kTS). Compounds 1a and 4a have potential for further development and optimization of their anti-KSHV activities which could lead to new candidate drugs.