Leah S. Torrie

The recent emergence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the underlying cause of Coronavirus Disease 2019 (COVID-19), has led to a worldwide pandemic causing substantial morbidity, mortality, and economic devastation. In response, many laboratories have redirected attention to SARS-CoV-2, meaning there is an urgent need for tools that can be used in laboratories unaccustomed to working with coronaviruses. Here we report a range of tools for SARS-CoV-2 research. First, we describe a facile single plasmid SARS-CoV-2 reverse genetics system that is simple to genetically manipulate and can be used to rescue infectious virus through transient transfection (without in vitro transcription or additional expression plasmids). The rescue system is accompanied by our panel of SARS-CoV-2 antibodies (against nearly every viral protein), SARS-CoV-2 clinical isolates, and SARS-CoV-2 permissive cell lines, which are all openly available to the scientific community. Using these tools, we demonstrate here that the controversial ORF10 protein is expressed in infected cells. Furthermore, we show that the promising repurposed antiviral activity of apilimod is dependent on TMPRSS2 expression. Altogether, our SARS-CoV-2 toolkit, which can be directly accessed via our website at https://mrcppu-covid.bio/, constitutes a resource with considerable potential to advance COVID-19 vaccine design, drug testing, and discovery science.

Many insects are highly resistant to plant toxins, such as the cardiac glycoside ouabain. How can the epithelia that must handle such toxins, also be refractory to them? In Drosophila, the Malpighian (renal) tubule contains large amounts of Na(+),K(+) ATPase that is known biochemically to be exquisitely sensitive to ouabain, yet the intact tissue is almost unaffected by even extraordinary concentrations. The explanation is that the tubules are protected by an active ouabain transport system, colocated with the Na(+),K(+) ATPase, thus preventing ouabain from reaching inhibitory concentrations within the basolateral infoldings of principal cells. These data show that the Na(+),K(+) ATPase, previously thought to be unimportant, may be as vital in insect tissues as in vertebrates, but can be cryptic to conventional pharmacology.

Malaria and cryptosporidiosis, caused by apicomplexan parasites, remain major drivers of global child mortality. New drugs for the treatment of malaria and cryptosporidiosis, in particular, are of high priority; however, there are few chemically validated targets. The natural product cladosporin is active against blood- and liver-stage Plasmodium falciparum and Cryptosporidium parvum in cell-culture studies. Target deconvolution in P. falciparum has shown that cladosporin inhibits lysyl-tRNA synthetase ( Pf KRS1). Here, we report the identification of a series of selective inhibitors of apicomplexan KRSs. Following a biochemical screen, a small-molecule hit was identified and then optimized by using a structure-based approach, supported by structures of both Pf KRS1 and C. parvum KRS ( Cp KRS). In vivo proof of concept was established in an SCID mouse model of malaria, after oral administration (ED 90 = 1.5 mg/kg, once a day for 4 d). Furthermore, we successfully identified an opportunity for pathogen hopping based on the structural homology between Pf KRS1 and Cp KRS. This series of compounds inhibit Cp KRS and C. parvum and Cryptosporidium hominis in culture, and our lead compound shows oral efficacy in two cryptosporidiosis mouse models. X-ray crystallography and molecular dynamics simulations have provided a model to rationalize the selectivity of our compounds for Pf KRS1 and Cp KRS vs. (human) Hs KRS. Our work validates apicomplexan KRSs as promising targets for the development of drugs for malaria and cryptosporidiosis.