Compounds from the Medicines for Malaria Venture Box Inhibit In Vitro Growth of Babesia divergens, a Blood-Borne Parasite of Veterinary and Zoonotic Importance

Abstract

Babesiosis is an infectious disease with an empty drug pipeline. A search inside chemical libraries for novel potent antibabesial candidates may help fill such an empty drug pipeline. A total of 400 compounds (200 drug-like and 200 probe-like) from the Malaria Box were evaluated in the current study against the in vitro growth of Babesia divergens (B. divergens), a parasite of veterinary and zoonotic importance. Novel and more effective anti-B. divergens drugs than the traditionally used ones were identified. Seven compounds (four drug-like and three probe-like) revealed a highly inhibitory effect against the in vitro growth of B. divergens, with IC₅₀s ≤ 10 nanomolar. Among these hits, MMV006913 exhibited an IC₅₀ value of 1 nM IC₅₀ and the highest selectivity index of 32,000. The atom pair fingerprint (APfp) analysis revealed that MMV006913 and MMV019124 showed maximum structural similarity (MSS) with atovaquone and diminazene aceturate (DA), and with DA and imidocarb dipropionate (ID), respectively. MMV665807 and MMV665850 showed MMS with each other and with ID. Of note, a high concentration (0.75 IC₅₀) of MMV006913 caused additive inhibition of B. divergens growth when combined with DA at 0.75 or 0.50 IC₅₀. The Medicines for Malaria Venture box is a treasure trove of anti-B. divergens candidates according to the obtained results.

Keywords: Babesia divergens; MMV006913; in vitro; large-scale screening; malaria box.

Figure 1

Drug-like and probe-like compounds with potential (IC₅₀ < 1 µM) against B. divergens identified from in vitro screening of the Malaria Box. (A). Drug-like compounds. (B). Probe-like compounds. The data are the means of two independent experiments.

Figure 2

Inhibition of B. divergens in vitro growth by MMV drug-like compounds. (a). Relationship between MMV666116, MMV666081, MMV665906, MMV665891, and MMV009060 concentrations (nM) and RFUs for the parasite. (b). Relationship between MMV666067, MMV666093, MMV142383, MMV665799, and MMV665800 concentrations (nM) and RFUs for the parasite. (c). Relationship between MMV019758, MMV666102, MMV665879, MMV665807, and MMV665850 concentrations (nM) and RFUs for the parasite. (d). Relationship between MMV006706, MMV019124, MMV006913, and MMV084940 concentrations (nM) and RFUs for the parasite. Each value is presented as the mean of three independent experiments after subtraction of the background fluorescence for nonparasitized RBCs. The lowest drug concentrations for which inhibition of B. divergens growth was statistically significant (p < 0.05) are indicated by a rectangle.

Figure 3

Inhibition of B. divergens in vitro growth by MMV probe-like compounds. (a). Relationship between MMV006787, MMV085471, MMV000443, MMV665934, and MMV665797 concentrations (nM) and RFUs for the parasite. (b). Relationship between MMV665969, MMV666109, MMV019241, MMV007224, and MMV000445 concentrations (nM) and RFUs for the parasite. (c). Relationship between MMV019995, MMV665943, MMV007273, MMV000699, and MMV000720 concentrations (nM) and RFUs for the parasite. (d). Relationship between MMV020912, MMV666054, MMV007208, and MMV000619 concentrations (nM) and RFUs for the parasite. Each value is presented as the mean of three independent experiments after subtraction of the background fluorescence for nonparasitized RBCs. The lowest drug concentrations for which inhibition of B. divergens growth was statistically significant (p < 0.05) are indicated by a rectangle.

Figure 4

Chemical structures of drug-like and probe-like compounds exhibited a high potential (IC₅₀ ≤ 10 nM) against B. divergens identified from in vitro screening of the Malaria Box. MMV structures were provided by the MMV as part of the supporting information for the Malaria Box. ^dr drug-like compounds. ^pr probe-like compound.

Figure 5

Hierarchical clustering analysis. The hierarchical clustering analysis was performed using ChemmineR software and highlights the structural similarities between the MMV compounds with potent anti-B. divergens activity and the commonly used antibabesial drugs (diminazene aceturate, imidocarb dipropionate, and atovaquone). Dissimilarity is reported using a scale unit of 0.05.