Prospects of an alternative treatment against Trypanosoma cruzi based on abietic acid derivatives show promising results in Balb/c mouse model

Bi- and tricyclic diterpenoids: landmarks from a decade (2013-2023) in search of leads against infectious diseases

Covering: 2013 to 2023In an era where antimicrobial resistance severely threatens our ability to treat infections, the discovery of new drugs that belong to different chemical classes and/or bear original modes of action is urgently needed. In this case, diterpenoids comprise a productive field with a proven track record in providing new anti-infectives to tackle bacterial infections and malaria. This review highlights the potential of both naturally occurring and semi-synthetic bi- and tricyclic diterpenoids to become leads in search of new drugs to treat infections caused by bacteria, fungi, viruses and protozoan parasites. The literature from the last decade (2013-2023) is covered, focusing on naturally occurring and semi-synthetic bicyclic (labdanes and labdane-type) and tricyclic (all classes) diterpenoids, detailing their relevant biological activities in the context of infection, which are explained through structure-activity relationships.

Antiedematogenic and Analgesic Activities of Abietic Acid in Mice

Exacerbated inflammatory responses to harmful stimuli can lead to significant pain, edema, and other complications that require pharmacological intervention. Abietic acid (AA) is a diterpene found as a significant constituent in pine species, and evidence has identified its biological potential. The present study aimed to evaluate abietic acid's antiedematogenic and anti-inflammatory activity in mice. Swiss mice (Mus musculus) weighing 20-30 g were treated with AA at 50, 100, and 200 mg/kg. The central nervous system (CNS) effects were evaluated using open-field and rotarod assays. The antinociceptive and anti-inflammatory screening was assessed by the acetic acid and formalin tests. The antiedematogenic activity was investigated by measuring paw edema induced by carrageenan, dextran, histamine, arachidonic acid, and prostaglandin, in addition to using a granuloma model. The oral administration of abietic acid (200 mg/Kg) showed no evidence of CNS effects. The compound also exhibited significant antiedematogenic and anti-inflammatory activities in the carrageenan and dextran models, mostly related to the inhibition of myeloperoxidase (MOP) activity and histamine action and, to a lesser extent, the inhibition of eicosanoid-dependent pathways. In the granuloma model, abietic acid's effect was less expressive than in the acute models investigated in this study. In conclusion, abietic acid has analgesic and antiedematogenic activities related to anti-inflammatory mechanisms.

Enhancing the Antifungal Efficacy of Fluconazole with a Diterpene: Abietic Acid as a Promising Adjuvant to Combat Antifungal Resistance in Candida spp

The increasing antifungal resistance rates against conventional drugs reveal the urgent need to search for new therapeutic alternatives. In this context, natural bioactive compounds have a critical role in antifungal drug development. Since evidence demonstrates that abietic acid, a diterpene found in Pinus species, has significant antimicrobial properties, this study aimed to evaluate the antifungal activity of abietic acid against Candida spp and its ability to potentiate the activity of fluconazole. Abietic acid was tested both individually and in combination with fluconazole against Candida albicans (CA INCQS 40006), Candida krusei (CK INCQS 40095), and Candida tropicalis (CT INCQS 40042). The microdilution method was used to determine the IC50 and the cell viability curve. Minimum Fungicidal Concentration (MFC) was determined by subculture in a solid medium. The plasma membrane permeability was measured using a fluorescent SYTOX Green probe. While the IC50 of the drugs alone ranged between 1065 and 3255 μg/mL, the IC50 resulting from the combination of abietic acid and fluconazole ranged between 7563 and 160.1 μg/mL. Whether used in combination with fluconazole or isolated, abietic acid exhibited Minimum Fungicidal Concentration (MFC) values exceeding 1024 μg/mL against Candida albicans, Candida krusei and Candida tropicalis. However, it was observed that the antifungal effect of fluconazole was enhanced when used in combination with abietic acid against Candida albicans and Candida tropicalis. These findings suggest that while abietic acid alone has limited inherent antifungal activity, it can enhance the effectiveness of fluconazole, thereby reducing antifungal resistance.

In Vivo Biological Evaluation of a Synthetic Royleanone Derivative as a Promising Fast-Acting Trypanocidal Agent by Inducing Mitochondrial-Dependent Necrosis

The life-long and life-threatening Chagas disease is one of the most neglected tropical diseases caused by the protozoan parasite Trypanosoma cruzi. It is a major public health problem in Latin America, as six to seven million people are infected, being the principal cause of mortality in many endemic regions. Moreover, Chagas disease has become widespread due to migrant populations. Additionally, there are no vaccines nor effective treatments to fight the disease because of its long-term nature and complex pathology. Therefore, these facts emphasize how crucial the international effort for the development of new treatments against Chagas disease is. Here, we present the in vitro and in vivo trypanocidal activity of some oxygenated abietane diterpenoids and related compounds. The 1,4-benzoquinone 15, not yet reported, was identified as a fast-acting trypanocidal drug with efficacy against different strains in vitro and higher activity and lower toxicity than benznidazole in both phases of murine Chagas disease. The mode of action was also evaluated, suggesting that quinone 15 kills T. cruzi by inducing mitochondrion-dependent necrosis through a bioenergetics collapse caused by a mitochondrial membrane depolarization and iron-containing superoxide dismutase inhibition. Therefore, the abietane 1,4-benzoquinone 15 can be considered as a new candidate molecule for the development of an appropriate and commercially accessible anti-Chagas drug.

In vitro anti-trypanosomal potential of kaurane and pimarane semi-synthetic derivatives

As part of the search for anti-trypanosomal agents, this work presents the production of sixteen derivatives. All of them were obtained from two natural diterpenes, one with kaurane skeleton (ent-kaurenoic acid) and other with a pimarane skeleton (ent-pimaradienoic acid). Then, the eighteen compounds were assayed against epimastigote form of Trypanosoma cruzi, with the derivatives showing increase of activity in relation to their precursors. Moreover, the most active derivative presented an IC₅₀ <12.5 µM (estimated 0.8 µM), lower than Benznidazole (IC₅₀ = 9.8 µM), used as control. The esterification of acid diterpenes showed to be an interesting way in the search for anti-trypanosomal agents.

Diterpenoids from the Root Bark of Pinus massoniana and Evaluation of Their Phosphodiesterase Type 4D Inhibitory Activity

Thirty-two diterpenoids were obtained from the root bark of Pinus massoniana, and, among them, five compounds (pinmassins A-E) were identified as undescribed analogues. Spectroscopic methods, X-ray single-crystal diffraction analysis, and ECD calculations were applied to establish the structure of the new isolates. Pinmassin D (4) and abieta-8,11,13,15-tetraen-18-oic acid (23) showed moderate phosphodiesterase type 4D (PDE4D) inhibitory effects with IC₅₀ values of 2.8 ± 0.18 and 3.3 ± 0.50 μM, respectively, and their binding modes were investigated by a molecular docking study.

Identification of a diverse synthetic abietane diterpenoid library and insight into the structure-activity relationships for antibacterial activity

A diverse natural product-like (NPL) synthetic abietane diterpenoid library containing 86 compounds were obtained and the SARs were studied based on their antibacterial potential. Further in vitro cytotoxic and in silico drug-like properties evaluation showed that the potent antibacterial compound 84 had good drug-like properties and displayed low cytotoxicity toward noncancerous mammalian cells, indicating the study of AA and DHAA might be a good starting point for the search of novel antimicrobial molecules. Future work should be focused on the optimization of their potency and selectivity.

Click chemistry-based synthesis and anticancer activity evaluation of novel C-14 1,2,3-triazole dehydroabietic acid hybrids

A concise and efficient synthetic approach has been established to readily access a series of novel C-14 1,2,3-triazole-tethered dehydroabietic acid derivatives in moderate to high yields. In vitro antiproliferative activity evaluation indicated that most of the hybrids exhibited potent inhibitory activities in a variety of cancer cell lines with low micromolar to submicromolar IC₅₀ values. Further studies demonstrated that some of these analogues such as 20, 21, and 24 were also effective against adriamycin-resistant MCF-7 clone at low concentrations in a dose-dependent manner. Notably, the most potent compound 24, which possesses a 3-(tert-butoxycarbonylamino)phenyl-substituted triazole moiety, not only exhibited obviously improved IC₅₀ values ranging from 0.7 to 1.2 μM against a panel of tested cancer cells, but also showed very weak cytotoxicity on normal cells. Preliminary mechanism studies indicated that compound 24 could induce apoptosis in MDA-MB-231 cells and was worth developing into a novel natural product-like anticancer lead by proper structure modification.

Simple dialkyl pyrazole-3,5-dicarboxylates show in vitro and in vivo activity against disease-causing trypanosomatids

The synthesis and antiprotozoal activity of some simple dialkyl pyrazole-3,5-dicarboxylates (compounds 2-6) and their sodium salts (pyrazolates) (compounds 7-9) against Trypanosoma cruzi, Leishmania infantum and Leishmania braziliensis are reported. In most cases the studied compounds showed, especially against the clinically significant amastigote forms, in vitro activities higher than those of the reference drugs (benznidazole for T. cruzi and glucantime for Leishmania spp.); furthermore, the low non-specific cytotoxicities against Vero cells and macrophages shown by these compounds led to good selectivity indexes, which are 8-72 times higher for T. cruzi amastigotes and 15-113 times higher for Leishmania spp. amastigotes than those of the respective reference drugs. The high efficiency of diethyl ester 3 and its sodium salt 8 against the mentioned protozoa was confirmed by further in vitro assays on infection rates and by an additional in vivo study in a murine model of acute and chronic Chagas disease. The inhibitory capacity of compounds 3 and 8 on the essential iron superoxide dismutase of the aforementioned parasites may be related to the observed anti-trypanosomatid activity. The low acute toxicity of compounds 3 and 8 in mice is also reported in this article.

Antiprotozoal Activity of Triazole Derivatives of Dehydroabietic Acid and Oleanolic Acid

Tropical parasitic diseases such as Chagas disease and leishmaniasis are considered a major public health problem affecting hundreds of millions of people worldwide. As the drugs currently used to treat these diseases have several disadvantages and side effects, there is an urgent need for new drugs with better selectivity and less toxicity. Structural modifications of naturally occurring and synthetic compounds using click chemistry have enabled access to derivatives with promising antiparasitic activity. The antiprotozoal activity of the terpenes dehydroabietic acid, dehydroabietinol, oleanolic acid, and 34 synthetic derivatives were evaluated against epimastigote forms of Trypanosoma cruzi and promastigotes of Leishmaniabraziliensis and Leishmania infantum. The cytotoxicity of the compounds was assessed on NCTC-Clone 929 cells. The activity of the compounds was moderate and the antiparasitic effect was associated with the linker length between the diterpene and the triazole in dehydroabietinol derivatives. For the oleanolic acid derivatives, a free carboxylic acid function led to better antiparasitic activity.

Diterpenes as lead molecules against neglected tropical diseases

Nowadays, neglected tropical diseases (NTDs) are reported to be present everywhere. Poor and developing areas in the world have received great attention to NTDs. Drug resistance, safety profile, and various challenges stimulate the search for alternative medications. Plant-based drugs are viewed with great interest, as they are believed to be devoid of side effects. Diterpenes, a family of essential oils, have showed attractive biological effects. A systematic review of the literature was carried out to summarize available evidences of diterpenes against NTDs. For this, databases were searched using specific search terms. Among the 2338 collected reports, a total of 181 articles were included in this review. Of them, 148 dealt with investigations using single organisms, and 33 used multiple organisms. No mechanisms of action were reported in the case of 164 reports. A total of 93.92% were related to nonclinical studies, and 4.42% and 1.66% dealt with preclinical and clinical studies, respectively. The review displays that many diterpenes are effective upon Chagas disease, chikungunya, echinococcosis, dengue, leishmaniasis, leprosy, lymphatic filariasis, malaria, schistosomiasis, and tuberculosis. Indeed, diterpenes are amazing drug candidates against NTDs. Copyright © 2016 John Wiley & Sons, Ltd.

Antibacterial profiling of abietane-type diterpenoids

Abietic and dehydroabietic acid are interesting diterpenes with a highly diverse repertoire of associated bioactivities. They have, among others, shown antibacterial and antifungal activity, potentially valuable in the struggle against the increasing antimicrobial resistance and imminent antibiotic shortage. In this paper, we describe the synthesis of a set of 9 abietic and dehydroabietic acid derivatives containing amino acid side chains and their in vitro antimicrobial profiling against a panel of human pathogenic microbial strains. Furthermore, their in vitro cytotoxicity against mammalian cells was evaluated. The experimental results showed that the most promising compound was 10 [methyl N-(abiet-8,11,13-trien-18-yl)-d-serinate], with an MIC₉₀ of 60μg/mL against Staphylococcus aureus ATCC 25923, and 8μg/mL against methicillin-resistant S. aureus, Staphylococcus epidermidis and Streptococcus mitis. The IC₅₀ value for compound 10 against Balb/c 3T3 cells was 45μg/mL.

Current drug therapy and pharmaceutical challenges for Chagas disease

One of the most significant health problems in the American continent in terms of human health, and socioeconomic impact is Chagas disease, caused by the protozoan parasite Trypanosoma cruzi. Infection was originally transmitted by reduviid insects, congenitally from mother to fetus, and by oral ingestion in sylvatic/rural environments, but blood transfusions, organ transplants, laboratory accidents, and sharing of contaminated syringes also contribute to modern day transmission. Likewise, Chagas disease used to be endemic from Northern Mexico to Argentina, but migrations have earned it global. The parasite has a complex life cycle, infecting different species, and invading a variety of cells - including muscle and nerve cells of the heart and gastrointestinal tract - in the mammalian host. Human infection outcome is a potentially fatal cardiomyopathy, and gastrointestinal tract lesions. In absence of a vaccine, vector control and treatment of patients are the only tools to control the disease. Unfortunately, the only drugs now available for Chagas' disease, Nifurtimox and Benznidazole, are relatively toxic for adult patients, and require prolonged administration. Benznidazole is the first choice for Chagas disease treatment due to its lower side effects than Nifurtimox. However, different strategies are being sought to overcome Benznidazole's toxicity including shorter or intermittent administration schedules-either alone or in combination with other drugs. In addition, a long list of compounds has shown trypanocidal activity, ranging from natural products to specially designed molecules, re-purposing drugs commercialized to treat other maladies, and homeopathy. In the present review, we will briefly summarize the upturns of current treatment of Chagas disease, discuss the increment on research and scientific publications about this topic, and give an overview of the state-of-the-art research aiming to produce an alternative medication to treat T. cruzi infection.

Abietane-Type Diterpenoid Amides with Highly Potent and Selective Activity against Leishmania donovani and Trypanosoma cruzi

Dehydroabietylamine (1) was used as a starting material to synthesize a small library of dehydroabietyl amides by simple and facile methods, and their activities against two disease-causing trypanosomatids, namely, Leishmania donovani and Trypanosoma cruzi, were assayed. The most potent compound, 10, an amide of dehydroabietylamine and acrylic acid, was found to be highly potent against these parasites, displaying an IC50 value of 0.37 μM against L. donovani axenic amastigotes and an outstanding selectivity index of 63. Moreover, compound 10 fully inhibited the growth of intracellular amastigotes in Leishmania donovani-infected human macrophages with a low IC50 value of 0.06 μM. This compound was also highly effective against T. cruzi amastigotes residing in L6 cells with an IC50 value of 0.6 μM and high selectivity index of 58, being 3.5 times more potent than the reference compound benznidazole. The potent activity of this compound and its relatively low cytotoxicity make it attractive for further development in pursuit of better drugs for patients suffering from leishmaniasis and Chagas disease.

Antiprotozoal activity of dehydroabietic acid derivatives against Leishmania donovani and Trypanosoma cruzi

Dehydroabietic acid derivatives have potent antiprotozoal activity and selectivity against L. donovani and T. cruzi.