Flavonoid Derivatives as New Potent Inhibitors of Cysteine Proteases: An Important Step toward the Design of New Compounds for the Treatment of Leishmaniasis

Abstract

Leishmaniasis is a neglected tropical disease, affecting more than 350 million people globally. However, there is currently no vaccine available against human leishmaniasis, and current treatment is hampered by high cost, side-effects, and painful administration routes. It has become a United Nations goal to end leishmaniasis epidemics by 2030, and multitarget drug strategy emerges as a promising alternative. Among the multitarget compounds, flavonoids are a renowned class of natural products, and a structurally diverse library can be prepared through organic synthesis, which can be tested for biological effectiveness. In this study, we synthesised 17 flavonoid analogues using a scalable, easy-to-reproduce, and inexpensive method. All synthesised compounds presented an impressive inhibition capacity against rCPB2.8, rCPB3, and rH84Y enzymes, which are highly expressed in the amastigote stage, the target form of the parasite. Compounds 3c, f12a, and f12b were found to be effective against all isoforms. Furthermore, their intermolecular interactions were also investigated through a molecular modelling study. These compounds were highly potent against the parasite and demonstrated low cytotoxic action against mammalian cells. These results are pioneering, representing an advance in the investigation of the mechanisms behind the antileishmanial action of flavonoid derivatives. Moreover, compounds have been shown to be promising leads for the design of other cysteine protease inhibitors for the treatment of leishmaniasis diseases.

Investigation of the Potential Targets behind the Promising and Highly Selective Antileishmanial Action of Synthetic Flavonoid Derivatives

“…Interestingly, 3c was also the chalcone derivative that demonstrated the greatest action in inhibiting cysteine protease in our previous study. 15 Although it had not shown a dose− response relationship, compound 1c also stood out by inducing high NO production even at the lowest concentration tested of 6.25 μg/mL (18.75 ± 2.66 μg/mL). Among the synthetic flavonols, f12a had the most relevant influence on increasing NO production at 50 μg/mL which is the highest treatment concentration (13.77 ± 1.10 μg/mL).…”

“…Interestingly, this pharmacological behavior was also observed when testing these synthetic chalcones against the promastigote form. 15 The influence of halogen atoms on antileishmanial activity has not been analyzed only for this set of compounds. These substituents are reported for their high and selective antimicrobial actions and are considered a pharmacophore for several classes of molecules.…”

“…Previous in silico ADME studies of these compounds demonstrated that all flavonoid derivatives had logS values greater than −4 and logP ≤ 5 (Table 1), following the aspects postulated by the rule of 5. 15,46 The logP values of the tested compounds are very similar; however, the water solubility of a molecule can also be determined by its physical form. Amorphous and crystalline forms stand out in medicinal chemistry.…”

“…Although these compounds are used in clinical therapy, their ADME parameters impair a possible oral administration due to its poor bioviability. 15 This route of administration is desirable for the treatment of most diseases. Advantages include ease of administration, cost-effective manufacturing, easy storage conditions, high patient compliance, and a more accurate self-administered dose.…”

“…Through enzymatic inhibition assays, we had assumed that cysteine protease inhibition may be the main mechanism of action behind the antileishmanial activity of these compounds (Table S1, Supporting Information). 15 However, since flavonoids are considered as multitarget drugs, the concept of "one drug, one target" cannot be adopted. 16,17 These compounds have attracted considerable attention as a possible solution for complex diseases such as leishmaniases, as they can act in multiple molecular pathways.…”