Identification of an isoquinoline-derived quinazoline hybrid as a transcriptional inhibitor of fatty acid synthase to suppress hepatitis C virus production.

Host-directed antiviral strategies provide an alternative approach to overcome the rapid emergence of drug-resistant viruses. Fatty acid synthase (FASN), a key enzyme in de novo lipogenesis, is exploited by multiple viruses to support their life cycles. To date, FASN-targeted therapies have focused on enzyme activity inhibition. However, since catalytic inhibition of FASN carries the risk of disrupting lipid homeostasis in normal tissues, FASN expression suppression was considered a potentially effective alternative. To identify inhibitors of FASN expression, we established a CRISPR-engineered HuH-7 reporter cell line in which a HiBiT tag was knocked into the endogenous FASN locus, enabling quantitative monitoring of native FASN protein levels. The high-throughput screening of 19,912 small molecules resulted in the identification of a potent suppressor of FASN production: an isoquinoline-derived quinazoline hybrid designated IQZ-1. Promoter analyses revealed that IQZ-1 inhibits FASN transcription at least via the proximal sterol regulatory elements of the FASN promoter. Using hepatitis C virus (HCV) as a lipid-dependent model virus, we demonstrated that IQZ-1 significantly reduced intracellular viral RNA levels and markedly suppressed infectious particle production. Subgenomic replicon analyses indicated partial inhibition of viral genome replication, while immunofluorescence studies revealed reduced abundance of lipid droplets, essential platforms for HCV virion formation, in infected cells. These findings suggest that transcriptional suppression of FASN impairs both membrane-associated replication complex formation and virion assembly. Collectively, our results establish proof of concept that targeting FASN synthesis, rather than enzymatic activity, effectively disrupts lipid-dependent viral propagation and represents a promising host-directed antiviral strategy.