Novel Harmicines with Improved Potency against Plasmodium

Discovery of harmiprims, harmine-primaquine hybrids, as potent and selective anticancer and antimalarial compounds

Although cancer and malaria are not etiologically nor pathophysiologically connected, due to their similarities successful repurposing of antimalarial drugs for cancer and vice-versa is known and used in clinical settings and drug research and discovery. With the growing resistance of cancer cells and Plasmodium to the known drugs, there is an urgent need to discover new chemotypes and enrich anticancer and antimalarial drug portfolios. In this paper, we present the design and synthesis of harmiprims, hybrids composed of harmine, an alkaloid of the β-carboline type bearing anticancer and antiplasmodial activities, and primaquine, 8-aminoquinoline antimalarial drug with low antiproliferative activity, covalently bound via triazole or urea. Evaluation of their antiproliferative activities in vitro revealed that N-9 substituted triazole-type harmiprime was the most selective compound against MCF-7, whereas C1-substituted ureido-type hybrid was the most active compound against all cell lines tested. On the other hand, dimeric harmiprime was not toxic at all. Although spectrophotometric studies and thermal denaturation experiments indicated binding of harmiprims to the ds-DNA groove, cell localization showed that harmiprims do not enter cell nucleus nor mitochondria, thus no inhibition of DNA-related processes can be expected. Cell cycle analysis revealed that C1-substituted ureido-type hybrid induced a G1 arrest and reduced the number of cells in the S phase after 24 h, persisting at 48 h, albeit with a less significant increase in G1, possibly due to adaptive cellular responses. In contrast, N-9 substituted triazole-type harmiprime exhibited less pronounced effects on the cell cycle, particularly after 48 h, which is consistent with its moderate activity against the MCF-7 cell line. On the other hand, screening of their antiplasmodial activities against the erythrocytic, hepatic, and gametocytic stages of the Plasmodium life cycle showed that dimeric harmiprime exerts powerful triple-stage antiplasmodial activity, while computational analysis showed its binding within the ATP binding site of PfHsp90.

Synthesis, antiproliferative and antiplasmodial evaluation of new chloroquine and mefloquine-based harmiquins

Here we present the synthesis and evaluation of the biological activity of new hybrid compounds, ureido-type (UT) harmiquins, based on chloroquine (CQ) or mefloquine (MQ) scaffolds and β-carboline alkaloid harmine against cancer cell lines and Plasmodium falciparum. The hybrids were prepared from the corresponding amines by 1,1'-carbonyldiimidazole (CDI)-mediated synthesis. In vitro evaluation of the biological activity of the title compounds revealed two hit compounds. Testing of the antiproliferative activity of the new UT harmiquins, and previously prepared triazole-(TT) and amide-type (AT) CQ-based harmiquins, against a panel of human cell lines, revealed TT harmiquine 16 as the most promising compound, as it showed pronounced and selective activity against the tumor cell line HepG2 (IC 50 = 5.48 ± 3.35 μmol L-1). Screening of the antiplasmodial activities of UT harmiquins against erythrocytic stages of the Plasmodium life cycle identified CQ-based UT harmiquine 12 as a novel antiplasmodial hit because it displayed low IC 50 values in the submicromolar range against CQ-sensitive and resistant strains (IC 50 0.06 ± 0.01, and 0.19 ± 0.02 μmol L-1, respectively), and exhibited high selectivity against Plasmodium, compared to mammalian cells (SI = 92).

Design, synthesis and antiplasmodial evaluation of new amide-, carbamate-, and ureido-type harmicines

Malaria, one of the oldest parasitic diseases, remains a global health threat, and the increasing resistance of the malaria parasite to current antimalarials is forcing the discovery of new, effective drugs. Harmicines, hybrid compounds in which harmine/β-carboline alkaloids and cinnamic acid derivatives are linked via an amide bond or a triazole ring, represent new antiplasmodial agents. In this work, we used a multiple linear regression technique to build a linear quantitative structure-activity relationship (QSAR) model, based on a group of 40 previously prepared amide-type (AT) harmicines and their antiplasmodial activities against erythrocytic stage of chloroquine-sensitive strain of P. falciparum (Pf3D7). After analysing the QSAR model, new harmicines were designed and synthesized: six amide-type, eleven carbamate-type and two ureido-type harmicines at the N-9 position of the β-carboline core. Subsequently, we evaluated the antiplasmodial activity of the new harmicines against the erythrocytic and hepatic stages of the Plasmodium life cycle in vitro and their antiproliferative activity against HepG2 cells. UT harmicine (E)-1-(2-(7-methoxy-1-methyl-9H-pyrido[3,4-b]indol-9-yl)ethyl)-3-(3-(3-(trifluoromethyl)phenyl)allyl)urea at the N-9 position of the β-carboline ring exhibited pronounced antiplasmodial activity against both the erythrocytic and the hepatic stages of the Plasmodium life cycle, accompanied by good selectivity towards Plasmodium.

In vitro and in vivo Efficacies of Novel Harmine Derivatives in the Treatment of Cystic Echinococcosis

Introduction

Cystic echinococcosis (CE) is a chronic zoonotic parasitic disease caused by the larvae of the Echinococcus granulosus sensu lato (s.l.) cluster. The current existing drugs have limited therapeutic efficacy against cystic echinococcosis, and thus, there is an urgent need to develop new drugs.

Methods

In this study, 7 harmine (HM) derivatives were screened and the effects of HM derivatives on E. granulosus sensu stricto (s.s.) were evaluated by in vitro and mouse experiments. The safety of the HM derivatives was assessed by cytotoxicity assays, acute toxicity study in animals and subacute toxicity study.

Results

These results show that the HM derivatives H-2-168 and DH-004 exhibited more significant antiparasitic effects at an initial concentration of 40 μM. The results of further studies showed that H-2-168 and DH-004 had dose-dependent effects against protoscoleces and had satisfactory therapeutic outcomes in vivo. Electron microscopy observations demonstrated that H-2-168 and DH-004 caused severe disruption of the parasite ultrastructure. Notably, the results of the acute toxicity and subchronic toxicity studies showed that H-2-168 and DH-004 had significantly improved safety. In addition, we found that H-2-168 and DH-004 induced DNA damage in E. granulosus s.s., which may be the mechanism by which these drugs produce their therapeutic effects.

Discussion

Overall, the data from this work demonstrate that H-2-168 and DH-004 are highly effective candidate compounds with low toxicity for the treatment of CE and will provide a new therapeutic strategy for CE pharmacological treatment.

Synthesis and Biological Evaluation of New Quinoline and Anthranilic Acid Derivatives as Potential Quorum Sensing Inhibitors

Inhibiting quorum sensing (QS), a central communication system, is a promising strategy to combat bacterial pathogens without antibiotics. Here, we designed novel hybrid compounds targeting the PQS (Pseudomonas quinolone signal)-dependent quorum sensing (QS) of Pseudomonas aeruginosa that is one of the multidrug-resistant and highly virulent pathogens with urgent need of new antibacterial strategies. We synthesized 12 compounds using standard procedures to combine halogen-substituted anthranilic acids with 4-(2-aminoethyl/4-aminobuthyl)amino-7-chloroquinoline, linked via 1,3,4-oxadiazole. Their antibiofilm activities were first pre-screened using Gram-negative Chromobacterium violaceum-based reporter, which identified compounds 15-19 and 23 with the highest anti-QS and minimal bactericidal effects in a single experiment. These five compounds were then evaluated against P. aeruginosa PAO1 to assess their ability to prevent biofilm formation, eradicate pre-formed biofilms, and inhibit virulence using pyocyanin as a representative marker. Compound 15 displayed the most potent antibiofilm effect, reducing biofilm formation by nearly 50% and pre-formed biofilm masses by 25%. On the other hand, compound 23 exhibited the most significant antivirulence effect, reducing pyocyanin synthesis by over 70%. Thus, our study highlights the potential of 1,3,4-oxadiazoles 15 and 23 as promising scaffolds to combat P. aeruginosa. Additionally, interactive QS systems should be considered to achieve maximal anti-QS activity against this clinically relevant species.

Current development of β-carboline derived potential antimalarial scaffolds

β-Carboline alkaloids are an eminent class of nitrogen-based natural alkaloids and therapeutic molecules which exert various pharmacological activities through diverse mechanisms. A lot of attention has recently been directed towards this moiety in order to develop effective antimalarial drugs. "Malaria", an acute febrile illness caused by diverse Plasmodium parasites, is a continuing and escalating problem that devastates economically less developed countries by significantly increased morbidity and mortality rates. The mounting parasite resistance towards the antimalarial drugs and augmenting the 'habitat of the insect vector' are creating a catastrophe, indicating an urgent need for new efficacious therapeutics to combat this tropical disease. This article comprehensively encapsulates the clinical and preclinical antimalarial scaffolds comprising β-carboline moiety in their structure. Herein, various classes of natural and semi-synthetic analogues of β-carbolines reported in the last decade (2011-2021) have been extensively studied and illustrated. This review will help the readers to develop an insight into the β-carboline based antimalarials and molecular mechanisms lying behind their mode of action, which is anticipated to be beneficial for the future development of new β-carboline based therapeutics.

Application of cinnamic acid in the structural modification of natural products: A review

Natural products can generally exhibit a variety of biological activities, but most show mediocre performance in preliminary activity evaluation. Natural products often require structural modification to obtain promising lead compounds. Cinnamic acid (CA) is readily available and has diverse biological activities and low cytotoxicity. Introducing CA into natural products may improve their performance, enhance biological activity, and reduce toxic side effect. Herein, we aimed to discuss related applications of CA in the structural modification of natural products and provide a theoretical basis for future derivatization and drug development of natural products. Published articles, web databases (PubMed, Science Direct, SCI Finder, and CNKI), and clinical trial websites (https://clinicaltrials.gov/) related to natural products and CA derivatives were included in the discussion. Based on the inclusion criteria, 128 studies were selected and discussed herein. Screening natural products of CA derivatives allowed for classification by their biological activities. The full text is organized according to the biological activities of the derivatives, with the following categories: anti-tumor, neuroprotective, anti-diabetic, anti-microbial, anti-parasitic, anti-oxidative, anti-inflammatory, and other activities. The biological activity of each CA derivative is discussed in detail. Notably, most derivatives exhibited enhanced biological activity and reduced cytotoxicity compared with the lead compound. CA has various advantages and can be widely used in the synthesis of natural product derivatives to enhance the properties of drug candidates or lead compounds.

Structural Basis of Parasitic HSP90 ATPase Inhibition by Small Molecules

Protozoan parasites are responsible for several harmful and widespread human diseases that cause high morbidity and mortality. Currently available treatments have serious limitations due to poor efficiency, strong adverse effects, and high cost. Hence, the identification of new targets and the development of specific drug therapies against parasitic diseases are urgent needs. Heat shock protein 90 (HSP90) is an ATP-dependent molecular chaperone that plays a key role in parasite survival during the various differentiation stages, spread over the vector insect and the human host, which they undergo during their life cycle. The N-terminal domain (NTD) of HSP90, containing the main determinants for ATPase activity, represents the most druggable domain for inhibitor targeting. The molecules investigated on parasite HSP90 are mainly developed from known inhibitors of the human counterpart, and they have strong limitations due to selectivity issues, accounting for the high conservation of the ATP-binding site between the parasite and human proteins. The current review highlights the recent structural progress made to support the rational design of new molecules able to effectively block the chaperone activity of parasite HSP90.

Harmicens, Novel Harmine and Ferrocene Hybrids: Design, Synthesis and Biological Activity

Cancer and malaria are both global health threats. Due to the increase in the resistance to the known drugs, research on new active substances is a priority. Here, we present the design, synthesis, and evaluation of the biological activity of harmicens, hybrids composed of covalently bound harmine/β-carboline and ferrocene scaffolds. Structural diversity was achieved by varying the type and length of the linker between the β-carboline ring and ferrocene, as well as its position on the β-carboline ring. Triazole-type harmicens were prepared using Cu(I)-catalyzed azide-alkyne cycloaddition, while the synthesis of amide-type harmicens was carried out by applying a standard coupling reaction. The results of in vitro biological assays showed that the harmicens exerted moderate antiplasmodial activity against the erythrocytic stage of P. falciparum (IC50 in submicromolar and low micromolar range) and significant and selective antiproliferative activity against the MCF-7 and HCT116 cell lines (IC50 in the single-digit micromolar range, SI > 5.9). Cell localization experiments showed different localizations of nonselective harmicene 36 and HCT116-selective compound 28, which clearly entered the nucleus. A cell cycle analysis revealed that selective harmicene 28 had already induced G1 cell cycle arrest after 24 h, followed by G2/M arrest with a concomitant drastic reduction in the percentage of cells in the S phase, whereas the effect of nonselective compound 36 on the cell cycle was much less pronounced, which agreed with their different localizations within the cell.

Anthranilamides with quinoline and β-carboline scaffolds: design, synthesis, and biological activity

In the present study, we report the design and synthesis of novel amide-type hybrid molecules based on anthranilic acid and quinoline or β-carboline heterocyclic scaffolds. Three types of biological screenings were performed: (i) in vitro antiproliferative screening against a panel of solid tumor and leukemia cell lines, (ii) antiviral screening against several RNA viruses, and (iii) anti-quorum sensing screening using gram-negative Chromobacterium violaceum as the reporter strain. Antiproliferative screening revealed a high activity of several compounds. Anthranilamides 12 and 13 with chloroquine core and halogenated anthranilic acid were the most active agents toward diverse cancer cell lines such as glioblastoma, pancreatic adenocarcinoma, colorectal carcinoma, lung carcinoma, acute lymphoblastic, acute myeloid, chronic myeloid leukemia, and non-Hodgkin lymphoma, but also against noncancerous cell lines. Boc-protected analogs 2 and 3 showed moderate activities against the tested cancer cells without toxic effects against noncancerous cells. A nonhalogenated quinoline derivative 10 with N-benzylanthranilic acid residue was equally active as 12 and 13 and selective toward tumor cells. Chloroquine and quinoline anthranilamides 10-13 exerted pronounced antiviral effect against human coronaviruses 229E and OC43, whereas 12 and 13 against coronavirus OC43 (EC₅₀ values in low micromolar range; selectivity indices from 4.6 to > 10.4). Anthranilamides 14 and 16 with PQ core inhibited HIV-1 with EC₅₀ values of 9.3 and 14.1 µM, respectively. Compound 13 displayed significant anti-quorum/biofilm effect against the quorum sensing reporter strain (IC₅₀ of 3.7 μM) with no apparent bactericidal effect.

Synthesis and Biological Evaluation of Harmirins, Novel Harmine-Coumarin Hybrids as Potential Anticancer Agents

As cancer remains one of the major health burdens worldwide, novel agents, due to the development of resistance, are needed. In this work, we designed and synthesized harmirins, which are hybrid compounds comprising harmine and coumarin scaffolds, evaluated their antiproliferative activity, and conducted cell localization and cell cycle analysis experiments. Harmirins were prepared from the corresponding alkynes and azides under mild reaction conditions using Cu(I) catalyzed azide–alkyne cycloaddition, leading to the formation of the 1H-1,2,3-triazole ring. Antiproliferative activity of harmirins was evaluated in vitro against four human cancer cell lines (MCF-7, HCT116, SW620, and HepG2) and one human non-cancer cell line (HEK293T). The most pronounced activities were exerted against MCF-7 and HCT116 cell lines (IC₅₀ in the single-digit micromolar range), while the most selective harmirins were 5b and 12b, substituted at C-3 and O-7 of the β-carboline core and bearing methyl substituent at position 6 of the coumarin ring (SIs > 7.2). Further experiments demonstrated that harmirin 12b is localized exclusively in the cytoplasm. In addition, it induced a strong G1 arrest and reduced the percentage of cells in the S phase, suggesting that it might exert its antiproliferative activity through inhibition of DNA synthesis, rather than DNA damage. In conclusion, harmirin 12b is a novel harmine and coumarin hybrid with significant antiproliferative activity and warrants further evaluation as a potential anticancer agent.

Inhibitors of the Plasmodium falciparum Hsp90 towards Selective Antimalarial Drug Design: The Past, Present and Future

Malaria is still one of the major killer parasitic diseases in tropical settings, posing a public health threat. The development of antimalarial drug resistance is reversing the gains made in attempts to control the disease. The parasite leads a complex life cycle that has adapted to outwit almost all known antimalarial drugs to date, including the first line of treatment, artesunate. There is a high unmet need to develop new strategies and identify novel therapeutics to reverse antimalarial drug resistance development. Among the strategies, here we focus and discuss the merits of the development of antimalarials targeting the Heat shock protein 90 (Hsp90) due to the central role it plays in protein quality control.

Further investigation of harmicines as novel antiplasmodial agents: Synthesis, structure-activity relationship and insight into the mechanism of action

The rise of the resistance of the malaria parasite to the currently approved therapy urges the discovery and development of new efficient agents. Previously we have demonstrated that harmicines, hybrid compounds composed from β-carboline alkaloid harmine and cinnamic acid derivatives, linked via either triazole or amide bond, exert significant antiplasmodial activity. In this paper, we report synthesis, antiplasmodial activity and cytotoxicity of expanded series of novel triazole- and amide-type harmicines. Structure-activity relationship analysis revealed that amide-type harmicines 27, prepared at N-9 of the β-carboline core, exhibit superior potency against both erythrocytic stage of P. falciparum and hepatic stages of P. berghei. Notably, harmicine 27a, m-(trifluoromethyl)cinnamic acid derivative, exhibited the most favourable selectivity index (SI = 1105). Molecular dynamics simulations revealed the ATP binding site of P. falciparum heat shock protein 90 as a druggable binding location, confirmed the usefulness of the harmine's N-9 substitution and identified favourable N-H … π interactions involving Lys45 and the aromatic phenyl unit in the attached cinnamic acid fragment as crucial for the enhanced biological activity. Thus, those compounds were identified as promising and valuable leads for further derivatization in the search of novel, more efficient antiplasmodial agents.

Potentiometric Surfactant Sensor Based on 1,3-Dihexadecyl-1H-benzo[d]imidazol-3-ium for Anionic Surfactants in Detergents and Household Care Products

A 1,3-dihexadecyl-1H-benzo[d]imidazol-3-ium-tetraphenylborate (DHBI-TPB) ion-pair implemented in DHBI-TPB surfactant sensor was used for the potentiometric quantification of anionic surfactants in detergents and commercial household care products. The DHBI-TPB ion-pair was characterized by FTIR spectroscopy and computational analysis which revealed a crucial contribution of the C-H∙∙∙π contacts for the optimal complex formation. The DHBI-TPB sensor potentiometric response showed excellent analytical properties and Nernstian slope for SDS (60.1 mV/decade) with LOD 3.2 × 10^-7 M; and DBS (58.4 mV/decade) with LOD 6.1 × 10^-7 M was obtained. The sensor possesses exceptional resistance to different organic and inorganic interferences in broad pH (2-10) range. DMIC used as a titrant demonstrated superior analytical performances for potentiometric titrations of SDS, compared to other tested cationic surfactants (DMIC > CTAB > CPC > Hyamine 1622). The combination of DHBI-TPB sensor and DMIC was successfully employed to perform titrations of the highly soluble alkane sulfonate homologues. Nonionic surfactants (increased concentration and number of EO groups) had a negative impact on anionic surfactant titration curves and a signal change. The DHBI-TPB sensor was effectively employed for the determination of technical grade anionic surfactants presenting the recoveries from 99.5 to 101.3%. The sensor was applied on twelve powered samples as well as liquid-gel and handwashing home care detergents containing anionic surfactants. The obtained results showed good agreement compared to the outcomes measured by ISE surfactant sensor and a two-phase titration method. The developed DHBI-TPB surfactant sensor could be used for quality control in industry and has great potential in environmental monitoring.