Primary effusion lymphoma (PEL) caused by Kaposi sarcoma-associated herpesvirus (KSHV) is an aggressive
malignancy with poor prognosis even under
chemotherapy. Currently, there is no specific treatment for PEL therefore requiring new
therapies. Both
histone deacetylases (HDACs) and bromodomain-containing
protein 4 (BRD4) have been found as therapeutic targets for PEL through inducing viral lytic reactivation. However, the strategy of dual targeting with one agent and potential synergistic effects have never been explored. In the current study, we first demonstrated the synergistic effect of concurrently targeting HDACs and BRD4 on KSHV reactivation by using SAHA or
entinostat (HDACs inhibitors) and (+)-JQ1 (BRD4 inhibitor), which indicated dual blockage of HDACs/BRD4 is a viable therapeutic approach. We were then able to rationally design and synthesize a series of new small-molecule inhibitors targeting HDACs and BRD4 with a balanced activity profile by generating a hybrid of the key binding motifs between (+)-JQ1 and
entinostat or SAHA. Upon two iterative screenings of optimized compounds, a pair of epimers, 009P1 and 009P2, were identified to better inhibit the growth of KSHV positive
lymphomas compared to (+)-JQ1 or SAHA alone at low nanomolar concentrations, but not KSHV negative control cells or normal cells. Mechanistic studies of 009P1 and 009P2 demonstrated significantly enhanced viral reactivation, cell cycle arrest and apoptosis in KSHV+
lymphomas through dually targeting HDACs and BRD4 signaling activities. Importantly, in vivo preclinical studies showed that 009P1 and 009P2 dramatically suppressed KSHV+
lymphoma progression with oral bioavailability and minimal visible toxicity. These data together provide a novel strategy for the development of agents for inducing lytic activation-based
therapies against these viruses-associated
malignancies.