Falcipain Inhibitors Based on the Natural Product Gallinamide A Are Potent in Vitro and in Vivo Antimalarials

Abstract

A library of analogues of the cyanobacterium-derived depsipeptide natural product gallinamide A were designed and prepared using a highly efficient and convergent synthetic route. Analogues were shown to exhibit potent inhibitory activity against the Plasmodium falciparum cysteine proteases falcipain 2 and falcipain 3 and against cultured chloroquine-sensitive (3D7) and chloroquine-resistant (W2) strains of P. falciparum. Three lead compounds were selected for evaluation of in vivo efficacy against Plasmodium berghei infection in mice on the basis of their improved blood, plasma, and microsomal stability profiles compared with the parent natural product. One of the lead analogues cured P. berghei-infected mice in the Peters 4 day-suppressive test when administered 25 mg kg −1 intraperitoneally daily for 4 days. The compound was also capable of clearing parasites in established infections at 50 mg kg −1 intraperitoneally daily for 4 days and exhibited moderate activity when administered as four oral doses of 100 mg kg −1 . ■ INTRODUCTIONMalaria is a mosquito-transmitted disease caused by parasites of the genus Plasmodium. 1 Almost half the global population lives in malaria endemic areas and is at high risk of infection. The most virulent human parasite is Plasmodium falciparum, which leads to a severe infection that is often deadly, especially for children. Each year there are over 200 million new cases of malaria, and in 2017, the disease was responsible for an estimated 435 000 deaths. 2 A major global health concern is that the currently employed drug regimens for malaria are rapidly losing their effectiveness due to the emergence of drugresistant parasites. Particularly concerning is the rapid emergence of resistance against the artemisinin (ART)-based combination therapies that serve as the cornerstone of antimalarial therapy. 2,3 The widespread resistance of Plasmodium against currently available drugs and the lack of an efficacious vaccine underscores the need for the development of novel antimalarials that operate through unique mechanisms of action. Many therapeutics in clinical use are either natural products or natural product derivatives. 4 The use of natural products as privileged biologically active scaffolds from which to develop new anti-infectives has proven to be a highly successful strategy, 5 e.g., in the development and clinical 49 approval of lipopeptide and glycopeptide antibiotic analogues 6 50 and antimalarial artemisinins. 7 51 We have recently explored analogues of gallinamide A (1), a 52 linear depsipeptide natural product isolated independently in 53 2009 from Schizothrix 8 and Symploca 9 species of cyanobacteria 54 f1 as antimalarial leads (Figure 1). 10 The natural product and 55 structural analogues have been shown to possess potent 56 inhibitory activity against P. falciparum growth in vitro. The 57 mechanism of action of these natural product analogues is due 58 to the inhibition of cysteine proteases, namely, falcipain 2 59 (FP2) and falcipain 3 (FP3), 11 which are critical for...

Quinoline-triazole hybrids inhibit falcipain-2 and arrest the development ofPlasmodium falciparumat the trophozoite stage

“…9,10 "Gallinamide A" analogues have been found to exhibit effective inhibiting ability for FP2, FP3 and for the development of P. falciparum in vitro. 11 Along with this, E64 (Fig. 1b) an epoxide and an important irreversible inhibitor against general cysteine proteases and displayed a signicant outcome on growth, adherence and viability of parasite trophozoites.…”

In silico Guided Drug Repurposing: Discovery of New Competitive and Non-competitive Inhibitors of Falcipain-2

“…A second library, called DUDE-B, was obtained to validate the ensemble that showed the best performance in the DUDE-A screen. For that purpose, we compiled from literature 33 recently reported active compounds against FP-2 (IC50 ≤ 5 μM; Nizi et al, 2018; Stoye et al, 2019). The DUDE-B library was generated by merging these 33 active compounds with 4,337 decoys from the DUD-E website.…”

Potentin vitroanti-SARS-CoV-2 activity by gallinamide A and analogues via inhibition of cathepsin L

“…Series 1 consist of depsipeptide compounds 2-10 , with various aliphatic residues incorporated at the pseudo- N -terminus, the α,β-unsaturated moiety and on the pyrrolinone ring ( Figure 2 ) ( 37 ). Series 2 is comprised of indolylpyrrolinone analogues 11-23 that have varied functionality at the pseudo- N -terminus and the three amino acid residues within the linear chain ( 39 ). Finally, series 3 analogues ( 24-33 ) possess a number of biaryl-moieties appended to the pyrrolinone unit, and dimethylvaline or methylpiperidine functionalities at the pseudo- N -terminus.…”

“…The copyright holder for this this version posted December 25, 2020. ; https://doi.org /10.1101/2020.12.23.424111 doi: bioRxiv preprint analogues have already been safely examined in vivo for other infectious indications (39).…”

“…The natural product has several unusual structural features including a pyrrolinone derived from L-alanine and an ,-unsaturated imide moiety ( Figure 1B). Notably, gallinamide A has been demonstrated to be a potent covalent inhibitor of several parasite-derived cysteine proteases (35)(36)(37), as well as human CatL (38), with several synthetic analogues of the natural product also shown to have potent in vivo antimalarial activity in a murine model (39). Given the importance of CatL for cellular entry of SARS-CoV-2, we sought to investigate whether the CatL inhibitory activity of gallinamide A could be leveraged for SARS-CoV-2 antiviral activity.…”