Profiling of Flavonol Derivatives for the Development of Antitrypanosomatidic Drugs

Abstract

Flavonoids represent a potential source of new antitrypanosomatidic leads. Starting from a library of natural products, we combined target-based screening on pteridine reductase 1 with phenotypic screening on Trypanosoma brucei for hit identification. Flavonols were identified as hits, and a library of 16 derivatives was synthesized. Twelve compounds showed EC50 values against T. brucei below 10 μM. Four X-ray crystal structures and docking studies explained the observed structure-activity relationships. Compound 2 (3,6-dihydroxy-2-(3-hydroxyphenyl)-4H-chromen-4-one) was selected for pharmacokinetic studies. Encapsulation of compound 2 in PLGA nanoparticles or cyclodextrins resulted in lower in vitro toxicity when compared to the free compound. Combination studies with methotrexate revealed that compound 13 (3-hydroxy-6-methoxy-2-(4-methoxyphenyl)-4H-chromen-4-one) has the highest synergistic effect at concentration of 1.3 μM, 11.7-fold dose reduction index and no toxicity toward host cells. Our results provide the basis for further chemical modifications aimed at identifying novel antitrypanosomatidic agents showing higher potency toward PTR1 and increased metabolic stability.

High-resolution crystal structure of Trypanosoma brucei pteridine reductase 1 in complex with an innovative tricyclic-based inhibitor

“…Recombinant TbPTR1 was expressed and purified using established methods (Borsari et al, 2016). Spectrophotometric assays were performed at 25 C in 20 mM sodium acetate buffer pH 5.…”

“…The TbPTR1 inhibitors developed to date were conceived as substrate-competitive inhibitors and are based on a wide variety of scaffolds, including 2,4-diaminopteridine (Dawson et al, 2006;Tulloch et al, 2010), quinazoline (Dawson et al, 2010), 2,4-diaminopyrrolopyrimidine (Tulloch et al, 2010), chromone (Borsari et al, 2016;Di Pisa et al, 2017), 2-aminothiadiazole (Linciano et al, 2017), 2-aminobenzimidazole (Mpamhanga et al, 2009), triazine (Tulloch et al, 2010), 1,6-dihydrotriazine (Landi et al, 2019) and 2-aminobenzothiazole (Linciano et al, 2019). More than 60 crystal structures of TbPTR1-inhibitor complexes have now been deposited in the Protein Data Bank (PDB), clarifying the key binding interactions that occur inside the catalytic cavity (Pozzi et al, 2018).…”

Active Natural Product Scaffolds against Trypanosomatid Parasites: A Review

“…52 Flavon-3-ol natural products have been shown to inhibit T. brucei pteridine reductase 1 (TbPTR1), with compounds 1 and 2 showing low micromolar IC50 values of 12.8 and 13.9 M respectively. 46 PTR1 has been genetically validated as essential in T. brucei and plays a key role for in vivo virulence. 53 With their synthetic accessibility, which is discussed later in this review, flavonoids are placed as having a potentially strong core structure for the development of future lead compounds, and have a strong resource of SAR studies, and examples demonstrating in vivo activity and on-target effects against a potential new drug target in T. brucei.…”

“…89 with an EC50 of 0.46 M and a similar SI of 2.4. 94 A related natural product deoxyelephantopin (46), was identified through a bioassay-guided isolation from the tropical plant species…”

“…Molducin, however showed significant toxicity and caused death of the mice at day 7. Further selected sesquiterpene natural products and synthetic derivatives(44)(45)(46)(47)(48)(49) with reported activity against trypanosomatids Nobilin (44), a natural product isolated from Anthemis nobilis, displays a 5-10 fused core structure related to the 5-7-5 core observed for other trypanocidal sesquiterpenes. It exhibited potent trypanocidal activity with an EC50 value of 3.2 M against the T. b. rhodesiense bloodstream form with a modest SI of 2.1 when compared to L6 cells.…”