Novel 3-Trifluoromethyl-1,2,4-oxadiazole Analogues of Astemizole with Multi-stage Antiplasmodium Activity and In Vivo Efficacy in a Plasmodium berghei Mouse Malaria Infection Model

Abstract

Iterative medicinal chemistry optimization of an ester-containing astemizole (AST) analogue 1 with an associated metabolic instability liability led to the identification of a highly potent 3-trifluoromethyl-1,2,4-oxadiazole analogue 23 (Pf NF54 IC 50 = 0.012 μM; Pf K1 IC 50 = 0.040 μM) displaying high microsomal metabolic stability (HLM CL int < 11.6 μL•min −1 • mg −1 ) and > 1000-fold higher selectivity over hERG compared to AST. In addition to asexual blood stage activity, the compound also shows activity against liver and gametocyte life cycle stages and demonstrates in vivo efficacy in Plasmodium berghei-infected mice at 4 × 50 mg•kg −1 oral dose. Preliminary interrogation of the mode of action using live-cell microscopy and cellular heme speciation revealed that 23 could be affecting multiple processes in the parasitic digestive vacuole, with the possibility of a novel target at play in the organelles associated with it.

In Vitro Antimalarial Activity of Trichothecenes against Liver and Blood Stages of Plasmodium Species

“…Malaria is a serious infectious disease that affects almost half of the world’s population, with over 200 million cases reported annually. − According to the WHO, there were approximately 249 million reported cases of malaria in 85 countries in 2022. After decades of year-over-year declines, there was an increase of 11 million cases between 2019 and 2020, which has been attributed to suspended control efforts due to the COVID-19 pandemic and international conflicts .…”

hERG, Plasmodium Life Cycle, and Cross Resistance Profiling of New Azabenzimidazole Analogues of Astemizole

“…Compound 1 displayed high in vitro antiplasmodium activity (Pf NF54/K1 = 0.012/ 0.040 μM) and demonstrated in vivo efficacy in a Plasmodium berghei mouse malaria infection model (P. berghei, 99% activity when administered orally at 50 mg•kg −1 once daily for 4 days, with mouse survival of 14-days), and a relatively good pharmacokinetic (PK) profile. 13 Despite its >1000-fold increase in selectivity over hERG K + channels compared to AST, it still possesses a potential cardiotoxicity liability signaled by the high hERG inhibition activity (IC 50 = 0.63 μM) and a low selectivity index (SI = 53). Henceforth, we sought to use compound 1 as a template to design new analogues with potentially further reduced hERG channel inhibition activity while retaining in vitro antiplasmo-dium potency, antimalarial efficacy, and good absorption distribution metabolism and excretion (ADME) properties.…”

“…This modification was envisaged not to drastically abrogate antiplasmodium activity and physicochemical and metabolism profiles based on previous observations. 13 Having previously utilized most hERG-affinity reducing strategies, 14,15 we turned to reducing the basicity of the piperidine 3°nitrogen via β-fluorination (SAR 1, Figure 1) and subtle modifications around the benzimidazole phenyl ring through insertion of a nitrogen atom to generate azabenzimidazoles and concomitantly substituting the benzimidazole ring with previously explored tolerated groups (CH 3 -and Cl-, SAR 2, Figure 1). 13 The synthesis of target compounds involved N,N′dicyclohexylcarbodiimide (DCC)-mediated cyclization of commercially available 1,2-aromatic diamines with appropriately substituted N-Boc-protected piperidine isothiocyanates 4a−4c (Scheme 1B,C) 13 in MeCN to produce 2-amino benzimidazoles 5a−5f in high yields (78−93%).…”

“…Liver-stage inhibitory activity (11, PbHepG2 IC 50 = 2.30 μM) was retained, albeit ∼4-fold lower compared to 1 (PbHepG2 IC 50 = 0.49 μM) and AST (PbHepG2 IC 50 = 0.59 μM). 13 Metabolic stability of compounds 9−12 showing Pf NF54 IC 50 < 0.10 μM was evaluated using mouse, human and rat liver microsomes (Table 3, data for rat not shown). All tested derivatives were metabolically stable in all microsome species (Table 3).…”

“…Notably, when the oral 10 mg/kg data for both compounds is extrapolated to 50 mg/kg, assuming linearity in exposure, the resulting free concentrations are lower than a previously reported AST analogue, which explains the much better in vivo efficacy of that compound (99.5% reduction in parasitaemia at the same dose, 4 × 50 mg/kg, as in this work) in the P. berghei model. 13 AST and its analogues are known inhibitors of the heme detoxification pathway. The disruption of the machinery in the parasitic hemozoin formation pathway potentially contributes to the antiplasmodium mechanism of action (MoA) of AST and its derivatives.…”