A potent antimalarial benzoxaborole targets a Plasmodium falciparum cleavage and polyadenylation specificity factor homologue

Abstract

Benzoxaboroles are effective against bacterial, fungal and protozoan pathogens. We report potent activity of the benzoxaborole AN3661 against Plasmodium falciparum laboratory-adapted strains (mean IC50 32 nM), Ugandan field isolates (mean ex vivo IC50 64 nM), and murine P. berghei and P. falciparum infections (day 4 ED90 0.34 and 0.57 mg kg−1, respectively). Multiple P. falciparum lines selected in vitro for resistance to AN3661 harboured point mutations in pfcpsf3, which encodes a homologue of mammalian cleavage and polyadenylation specificity factor subunit 3 (CPSF-73 or CPSF3). CRISPR-Cas9-mediated introduction of pfcpsf3 mutations into parental lines recapitulated AN3661 resistance. PfCPSF3 homology models placed these mutations in the active site, where AN3661 is predicted to bind. Transcripts for three trophozoite-expressed genes were lost in AN3661-treated trophozoites, which was not observed in parasites selected or engineered for AN3661 resistance. Our results identify the pre-mRNA processing factor PfCPSF3 as a promising antimalarial drug target.

Identification of a potent benzoxaborole drug candidate for treating cryptosporidiosis

“…Furthermore, related HAT and AAT lead compounds, also 6-amides like AN7973, target Cleavage and Polyadenylation Specific Factor 3 (CPSF3), an endonuclease that functions in mRNA processing 46 . It is known that other oxaboroles inhibit CPSF3 in Plasmodium falciparum 28 , and Cryptosporidium CPSF3 is greater than 40% identical to that of P. falciparum at the amino acid level. It therefore seems possible that AN7973 inhibits Cryptosporidium CPSF3 as well.…”

“…They typically engage with proteins through interaction of an electrophilic boron atom with nucleophilic partner residues (e.g., serine, threonine or tyrosine) or with metal cations (e.g., Zn 2+ , Mg 2+ ) present in the active site of enzymes, acting as a phosphate mimetic. Potent benzoxaborole inhibitors of bacterial 21,22 , fungal 23 , and protozoan 24 pathogens have been identified that work by inhibiting various essential microbial enzymes 22,23,[25][26][27][28] . Tavaborole, a leucyl-tRNA synthetase inhibitor, is approved for treatment of onychomycosis, and crisaborole, which targets human phosphodiesterase 4, was recently approved for treatment of atopic dermatitis 20,29 .…”

“…Plasmodium parasites, which cause malaria, are members of the phylum Apicomplexa, and are therefore genetically related to Cryptosporidium parasites. Given this and the recent identification of benzoxaboroles with potent antimalarial activity 28,30,31 , we screened a library of benzoxaborole compounds for anticryptosporidial activity. Here, we report identification of a novel drug candidate, AN7973, for treatment of cryptosporidiosis.…”

Targeting Toxoplasma gondii CPSF 3 as a new approach to control toxoplasmosis

“…In another study, it is shown that AN3661 is also active against the human malaria parasite P. falciparum (Sonoiki et al , ). Interestingly, T. gondii and P. falciparum parasite lines selected for resistance to AN3661 both harboured mutations in residues located in the active site of CPSF3.…”

Quantitation of vector uptake reveals non-Poissonian transfection dynamics in Plasmodium falciparum

“…In principle, this should provide an advantage for genome editing, as the introduction of a double strand break in the parasite DNA coupled with homology templates that provide the desired modification should result in consistent homology-directed repair without competing error-prone events. As a result, the application of CRISPR/Cas9 in P. falciparum has relied on donor templates and has been used to knockout genes [8,9], and validate key drug resistance mechanisms [10][11][12]. However the absence of NHEJ, coupled with the low transfection efficiency noted above, has made systematic largescale gRNA-based gene disruption screens that have been revolutionary in other organisms elusive so far [6,13].…”