Targeting the host transcription factor HSF1 prevents human cytomegalovirus replication in vitro and in vivo.

FDA-approved antivirals against HCMV have several limitations, including only targeting the later stages of the viral replication cycle, adverse side effects, and the emergence of drug-resistant strains. Antivirals targeting host factors specifically activated within infected cells and necessary for viral replication could address the current drawbacks of anti-HCMV standard-of-care drugs. In this study, we found HCMV infection stimulated the activation of the stress response transcription factor heat shock transcription factor 1 (HSF1). HCMV entry into fibroblasts rapidly increased HSF1 activity and subsequent relocalization from the cytoplasm to the nucleus, which was maintained throughout viral replication and in contrast to the transient burst of activity induced by canonical heat shock. Prophylactic pharmacological inhibition or genetic depletion of HSF1 prior to HCMV infection attenuated the expression of all classes of viral genes, including immediate early (IE) genes, and virus production, suggesting HSF1 promotes the earliest stages of the viral replication cycle. Therapeutic treatment with SISU-102, an HSF1 inhibitor tool compound, after IE expression also reduced the levels of L proteins and progeny production, suggesting HSF1 regulates multiple steps along the HCMV replication cycle. Leveraging a newly developed human skin xenograft transplant murine model, we found prophylactic treatment with SISU-102 significantly attenuated viral replication in transplanted human skin xenografts as well as viral dissemination to distal sites. These data demonstrate HCMV infection rapidly activates and relocalizes HSF1 to the nucleus to promote viral replication, which can be exploited as a host-directed antiviral strategy. One Sentence Summary: Inhibiting of HSF1 as a host-directed antiviral therapy attenuates HCMV replication in vitro and in vivo.