Conventional drug discovery and development takes an average of 12 years and costs hundreds of millions of dollars for each new drug that reaches patients. Repositioning of approved drugs and clinical-stage compounds with existing preclinical and clinical data can greatly expedite the process, particularly for rare, low-prevalence diseases and for rapidly-spreading infectious diseases, such as Zika virus. We are applying new technologies and approaches for screening, such as phenotypic cell-based disease models using human-derived induced pluripotent stem (iPS) cells and high-content screening platforms. Our approach is to collaborate with leading investigators from across the research ecosystem, including at NIH, academic institutions, and biopharmaceutical companies. Our objectives include (1) development of disease relevant assays using human neural progenitor cells and astrocytes; (2) drug repurposing screening to identify active compounds that protect neuronal cells from Zika virus-caused cell death and inhibit virus replication; (3) confirmation of compound activity in in vitro assays and animal models; and (4) advancement of the newly identified compounds to clinical trials for the treatment of Zika virus infection. Despite rapid progress in the preclinical development of vaccines against Zika virus (ZIKV), testing the safety and efficacy of vaccines in humans can take a substantial amount of time. Effective countermeasures, including small-molecule therapeutics, are also urgently needed. In response to the current global health emergency posed by the ZIKV outbreak and its link to microcephaly and other neurological conditions, we developed two ultra-high-throughput assays using human neural cells. We performed a drug repurposing screen of a library of approximately 6000 compounds, including approved drugs, clinical trial drug candidates and other pharmacologically active compounds. We previously found that ZIKV infection in human neuronal progenitor cells (hNPCs) induces the activation of caspase-3, leading to cell death. For the current work, we designed a primary compound-screening assay that measures Zika virus-induced caspase-3 activity in iPS cell-derived hNPCs and astrocytes. To confirm primary screening hits, we designed a secondary assay, measuring ATP content, to determine cell viability after ZIKV infection and compound toxicity. Additionally, we measured the ZIKV protein NS1, viral RNA, and virus titer to confirm the activity of identified compounds. So far, we have identified two categories of compounds for further evaluation: those that protect against ZIKV-induced cell death (neuroprotective) and those that suppress ZIKV replication (antiviral). The most potent neuroprotective compound identified was emricasan, a pan-caspase inhibitor. Two promising antiviral compounds were identified, including niclosamide, an FDA-approved drug for treating worm infections in humans and livestock, and PHA-690509, an investigational compound that functions as a cyclin-dependent kinase inhibitor. We explored combination and sequential treatment with these two categories of compounds in vitro, with future animal studies planned to evaluate in vivo efficacy and safety. Our overall findings and the tools we have developed should significantly advance current ZIKV research and have an immediate effect on the development of anti-ZIKV therapeutics. Moreover, our findings could have implications for combating infections by other related viruses, such as dengue, chikungunya, and West Nile. In addition, we have deposited all drug screening data from eleven screening assays into the PubChem database for open access. This will allow other researchers to access the drug repurposing screening data quickly, which may lead to identification of additional therapeutics for treatment of Zika virus infection.

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