Synthesis of primaquine glyco-conjugates as potential tissue schizontocidal antimalarial agents

Exploring the unexplored chemical space: Rational identification of new Tafenoquine analogs with antimalarial properties

Patents tend to define a huge chemical space described by the combinatorial nature of Markush structures. However, the optimization of new principal active ingredient is frequently driven by a simple Free Wilson approach. This procedure leads to a highly focused study on the chemical space near a hit compound leaving many unexplored regions that may present highly biological active reservoirs. This study aims to demonstrate that this unveiled chemical space can hide compounds with interesting potential biological activity that would be worth pursuing. This underlines the value and necessity of broadening an approach beyond conventional strategies. Hence, we advocate for an alternative methodology that may be more efficient in the early drug discovery stages. We have selected the case of Tafenoquine, a single-dose treatment for the radical cure of P. vivax malaria approved by the FDA in 2018, as an example to illustrate the process. Through the deep exploration of the Tafenoquine chemical space, seven compounds with potential antimalarial activity have been rationally identified and synthesized. This small set is representative of the chemical diversity unexplored by the 58 analogs reported to date. After biological assessment, results evidence that our approach for rational design has proven to be a very efficient exploratory methodology suitable for the early drug discovery stages.

A nanochitosan-D-galactose formulation increases the accumulation of primaquine in the liver

Primaquine is the mainstream antimalarial drug to prevent Plasmodium vivax relapses. However, this drug can induce hemolysis in patients with glucose-6-phosphate dehydrogenase deficiency. Nanostructure formulations of primaquine loaded with D-galactose were used as a strategy to target the drug to the liver and decrease the hemolytic risks. Nanoemulsion (NE-Pq) and nanochitosan (NQ-Pq) formulations of primaquine diphosphate containing D-galactose were prepared and characterized by their physicochemistry properties. Pharmacokinetic and biodistribution studies were conducted using Swiss Webster mice. A single dose of 10 mg/kg of each nanoformulation or free primaquine solution was administered by gavage to the animals, which were killed at 0.5, 1, 2, 4, 8, and 24 hours. Blood samples and tissues were collected, processed, and analyzed by high-performance liquid chromatography. The nanoformulation showed sizes around 200 nm (NE-Pq) and 400 nm (NQ-Pq) and physicochemical stability for over 30 days. Free primaquine solution achieved higher primaquine Cmax in the liver than NE-Pq or NQ-Pq at 0.5 hours. However, the half-life and mean residence time (MRT) of primaquine in the liver were three times higher with the NQ-Pq formulation than with free primaquine, and the volume distribution was four times higher. Conversely, primaquine's half-life, MRT, and volume distribution in the plasma were lower for NQ-Pq than for free primaquine. NE-Pq, on the other hand, accumulated more in the lungs but not in the liver. Galactose-coated primaquine nanochitosan formulation showed increased drug targeting to the liver compared to free primaquine and may represent a promising strategy for a more efficient and safer radical cure for vivax malaria.

Suppressive, Curative, and Prophylactic Effects of Maesa lanceolata Forssk. against Rodent Malaria Parasite Plasmodium berghei

The artemisinin partial resistance is believed to be spread to artemisinin-based combination therapy partner drugs. As a result, new antiplasmodial compounds are required to treat resistant malaria infections. In the invention of antimalarial substances, claimed medical plants are precious resources. So, the current study was designed to assess the antiplasmodial effects of Maesa lanceolata in mice. In this study, preliminary phytoconstituent and in vivo acute oral toxicity tests were done. Early infection, established infection, and residual infection tests were employed to determine the antimalarial effects of the test drugs. Three doses (200, 400, and 600 mg/kg) of the extracts were provided orally to the test mice. Analysis of variance (one-way) followed by post hoc Tukey's test was used to analyze the difference between and within groups. Terpenoids, tannins, saponins, flavonoids, and alkaloids were detected in the phytochemical constituent analysis. Both 80% methanolic crude extract and solvent fractions had no toxic result at the 2000 mg/kg dose. All test drug doses suppressed parasite levels in a significant manner at all tests. The activity of chloroform fraction (maximum percentage suppression, 81.28%) overwhelms the crude extract activity. The curative effects of 80% methanolic crude extract, with a maximum of 80.22% parasitemia suppression, were greater than its suppressive and prophylactic effects. The 400 mg/kg dose of chloroform fraction resulted in a maximum survival period (18 days) than other doses of tested materials. The results of this investigation provide support for the activity of M. lanceolata leaf extract against malaria.

Deconstructing Markush: Improving the R&D Efficiency Using Library Selection in Early Drug Discovery

Most of the product patents claim a large number of compounds based on a Markush structure. However, the identification and optimization of new principal active ingredients is frequently driven by a simple Free Wilson approach, leading to a highly focused study only involving the chemical space nearby a hit compound. This fact raises the question: do the tested compounds described in patents really reflect the full molecular diversity described in the Markush structure? In this study, we contrast the performance of rational selection to conventional approaches in seven real-case patents, assessing their ability to describe the patent's chemical space. Results demonstrate that the integration of computer-aided library selection methods in the early stages of the drug discovery process would boost the identification of new potential hits across the chemical space.

Site-selective C5-H and N-H alkylation of unprotected 8-aminoquinolines

8-Aminoquinolines are the building blocks of many pharmaceutical compounds, which has motivated the scientific community to develop new ways to derivatize these compounds. In this work, we performed a site-selective C5-H and N-H alkylation of 8-aminoquinolines using para-quinone methides under extremely mild conditions. C5-H alkylation was performed using protecting group-free 8-aminoquinolines and in metal-free conditions. N-H alkylations were also carried out under mild conditions. All corresponding alkylation products were obtained in high to excellent yields.

Chemoprophylaxis under sporozoites-lumefantrine (CPS-LMF) immunization induce protective immune responses against Plasmodium yoelii sporozoites infection in mice

Malaria represents one of the major life-threatening diseases that poses a huge socio-economic impact, worldwide. Chemoprophylaxis vaccination using a relatively low number of wild-type infectious sporozoites represents an attractive and effective vaccine strategy against malaria. However, the role of immune responses to pre-erythrocytic versus blood-stage parasites in protection against different antimalarial drugs remains unclear. Here, in the present study, we explored the immune responses against the repetitive inoculation of live Plasmodium yoelii (P. yoelii) sporozoites in an experimental Swiss mouse model under antimalarial drug lumefantrine chemoprophylaxis (CPS-LMF). We monitored the liver stage parasitic load, pro/anti-inflammatory cytokines expression, and erythrocytic stage patency, following repetitive cycles of sporozoites inoculations. It was found that repetitive sporozoites inoculation under CPS-LMF results in delayed blood-stage infection during the fourth sporozoites challenge, while sterile protection was produced in mice following the fifth cycle of sporozoites challenge. Intriguingly, we observed a significant up-regulation of pro-inflammatory cytokines (IFN-γ, TNF-α and IL-12) and iNOS response and down-regulation of anti-inflammatory cytokines (IL-4, IL-10 and TGF-β) in the liver HMNC (hepatic mononuclear cells) and spleen cells after 4th and 5th cycle of sporozoites challenge in the CPS-LMF mice. Meanwhile, we also noticed that the liver stage parasites load under CPS-LMF immunization has gradually reduced after 2nd, 3rd, 4th and 5th sporozoites challenge. Overall, our study suggests that chemoprophylaxis vaccination under LMF drug cover develops strong immune responses and confer superior long-lasting protection against P. yoelii sporozoites. Furthermore, this vaccination strategy can be used to study the protective and stage-specific immunity against new protective antigens.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03022-0.

Current status and strategic possibilities on potential use of combinational drug therapy against COVID-19 caused by SARS-CoV-2

The spread of new coronavirus infection starting December 2019 as novel SARS-CoV-2, identified as the causing agent of COVID-19, has affected all over the world and been declared as pandemic. Approximately, more than 8,807,398 confirmed cases of COVID-19 infection and 464,483 deaths have been reported globally till the end of 21 June 2020. Until now, there is no specific drug therapy or vaccine available for the treatment of COVID-19. However, some potential antimalarial drugs like hydroxychloroquine and azithromycin, antifilarial drug ivermectin and antiviral drugs have been tested by many research groups worldwide for their possible effect against the COVID-19. Hydroxychloroquine and ivermectin have been identified to act by creating the acidic condition in cells and inhibiting the importin (IMPα/β1) mediated viral import. There is a possibility that some other antimalarial drugs/antibiotics in combination with immunomodulators may help in combatting this pandemic disease. Therefore, this review focuses on the current use of various drugs as single agents (hydroxychloroquine, ivermectin, azithromycin, favipiravir, remdesivir, umifenovir, teicoplanin, nitazoxanide, doxycycline, and dexamethasone) or in combinations with immunomodulators additionally. Furthermore, possible mode of action, efficacy and current stage of clinical trials of various drug combinations against COVID-19 disease has also been discussed in detail.Communicated by Ramaswamy H. Sarma.

Plants-Derived Biomolecules as Potent Antiviral Phytomedicines: New Insights on Ethnobotanical Evidences against Coronaviruses

SARS-CoV-2 infection (COVID-19) is in focus over all known human diseases, because it is destroying the world economy and social life, with increased mortality rate each day. To date, there is no specific medicine or vaccine available against this pandemic disease. However, the presence of medicinal plants and their bioactive molecules with antiviral properties might also be a successful strategy in order to develop therapeutic agents against SARS-CoV-2 infection. Thus, this review will summarize the available literature and other information/data sources related to antiviral medicinal plants, with possible ethnobotanical evidence in correlation with coronaviruses. The identification of novel antiviral compounds is of critical significance, and medicinal plant based natural compounds are a good source for such discoveries. In depth search and analysis revealed several medicinal plants with excellent efficacy against SARS-CoV-1 and MERS-CoV, which are well-known to act on ACE-2 receptor, 3CLpro and other viral protein targets. In this review, we have consolidated the data of several medicinal plants and their natural bioactive metabolites, which have promising antiviral activities against coronaviruses with detailed modes of action/mechanism. It is concluded that this review will be useful for researchers worldwide and highly recommended for the development of naturally safe and effective therapeutic drugs/agents against SARS-CoV-2 infection, which might be used in therapeutic protocols alone or in combination with chemically synthetized drugs.

Profiling and Role of Bioactive Molecules from Puntius sophore (Freshwater/Brackish Fish) Skin Mucus with Its Potent Antibacterial, Antiadhesion, and Antibiofilm Activities

Epidermal fish mucus comprises of diverse bioactive metabolites which plays an immense role in defense mechanisms and other important cellular activities. Primarily, this study aims to screen the unexplored mucus extract of Puntius sophore(P. sophore) for its antagonistic potential against common pathogens, which are commonly implicated in foodborne and healthcare associated infections, with effects on their adhesion and biofilm formation. Profiling of the skin mucus was carried out by High Resolution-Liquid Chromatography Mass Spectrometry (HR-LCMS), followed by antibacterial activity and assessment of antibiofilm potency and efficacy on the development, formation, and texture of biofilms. Furthermore, bacterial cell damage, viability within the biofilm, checkerboard test, and cytotoxicity were also evaluated. As a result, P. sophore mucus extract was found to be effective against all tested strains. It also impedes the architecture of biofilm matrix by affecting the viability and integrity of bacterial cells within biofilms and reducing the total exopolysaccharide content. A synergy was observed between P. sophore mucus extract and gentamicin for Escherichia coli(E. coli), Pseudomonas aeruginosa(P. aeruginosa), and Bacillus subtilis(B. subtilis), whereas, an additive effect for Staphylococcus aureus(S. aureus). Thus, our findings represent the potent bioactivities of P. sophore mucus extract for the first time, which could be explored further as an alternative to antibiotics or chemically synthesized antibiofilm agents.

Cordycepin for Health and Wellbeing: A Potent Bioactive Metabolite of an Entomopathogenic Cordyceps Medicinal Fungus and Its Nutraceutical and Therapeutic Potential

Cordyceps is a rare naturally occurring entomopathogenic fungus usually found at high altitudes on the Himalayan plateau and a well-known medicinal mushroom in traditional Chinese medicine. Cordyceps contains various bioactive components, out of which, cordycepin is considered most vital, due to its utmost therapeutic as well as nutraceutical potential. Moreover, the structure similarity of cordycepin with adenosine makes it an important bioactive component, with difference of only hydroxyl group, lacking in the 3′ position of its ribose moiety. Cordycepin is known for various nutraceutical and therapeutic potential, such as anti-diabetic, anti-hyperlipidemia, anti-fungal, anti-inflammatory, immunomodulatory, antioxidant, anti-aging, anticancer, antiviral, hepato-protective, hypo-sexuality, cardiovascular diseases, antimalarial, anti-osteoporotic, anti-arthritic, cosmeceutical etc. which makes it a most valuable medicinal mushroom for helping in maintaining good health. In this review, effort has been made to bring altogether the possible wide range of cordycepin’s nutraceutical potential along with its pharmacological actions and possible mechanism. Additionally, it also summarizes the details of cordycepin based nutraceuticals predominantly available in the market with expected global value. Moreover, this review will attract the attention of food scientists, nutritionists, pharmaceutical and food industries to improve the use of bioactive molecule cordycepin for nutraceutical purposes with commercialization to aid and promote healthy lifestyle, wellness and wellbeing.

Neurological disorder and psychosocial aspects of cerebral malaria: what is new on its pathogenesis and complications? A minireview

Recently, malaria is remain considered as the most prevalent infectious disease, affecting the human health globally. High morbidity and mortality worldwide is often allied with cerebral malaria (CM) based disorders of the central nervous system, especially across many tropical and sub-tropical regions. These disorders are characterised by the infection of Plasmodium species, which leads to acute or chronic neurological disorders, even after having active/effective antimalarial drugs. Furthermore, even during the treatment, individual remain sensitive for neurological impairments in the form of decrease blood flow and vascular obstruction in brain including many more other changes. This review briefly explains and update on the epidemiology, burden of disease, pathogenesis and role of CM in neurological disorders with behaviour and function in mouse and human models. Moreover, the social stigma, which plays an important role in neurological disorders and a factor for assessing CM, is also discussed in this review.

Primaquine derivatives: Modifications of the terminal amino group

Numerous modifications of the well-known antimalarial drug primaquine, both at the quinoline ring and at the primary amino group, have been reported, mostly to obtain antimalarial agents with improved bioavailability, reduced toxicity and/or prolonged activity. Modifications of the terminal amino group were made with the main idea to prevent the metabolic pathway leading to inactive and toxic carboxyprimaquine (follow-on strategy), but also to get compounds with different activity (repurposing strategy). The modifications undertaken until 2009 were included in a review published in the same year. The present review covers various classes of primaquine N-derivatives with diverse biological profiles, prepared in the last decade by our research group as well as the others. We have summarized the synthetic procedures applied for their preparation and discussed the main biological results. Several hits for the development of novel antiplasmodial, anticancer, antimycobacterial and antibiofilm agents were identified.

SAHAquines, Novel Hybrids Based on SAHA and Primaquine Motifs, as Potential Cytostatic and Antiplasmodial Agents

We report the synthesis of SAHAquines and related primaquine (PQ) derivatives. SAHAquines are novel hybrid compounds that combine moieties of suberoylanilide hydroxamic acid (SAHA), an anticancer agent with weak antiplasmodial activity, and PQ, an antimalarial drug with low antiproliferative activity. The preparation of SAHAquines is simple, cheap, and high yielding. It includes the following steps: coupling reaction between primaquine and a dicarboxylic acid monoester, hydrolysis, a new coupling reaction with O-protected hydroxylamine, and deprotection. SAHAquines 5 a-d showed significant reduction in cell viability. Among the three human cancer cell lines (U2OS, HepG2, and MCF-7), the most responsive were the MCF-7 cells. The antibodies against acetylated histone H3K9/H3K14 in MCF-7 cells revealed a significant enhancement following treatment with N-hydroxy-N'-{4-[(6-methoxyquinolin-8-yl)amino]pentyl}pentanediamide (5 b). Ethyl (2E)-3-({4-[(6-methoxyquinolin-8-yl)amino]pentyl}carbamoyl)prop-2-enoate (2 b) and SAHAquines were the most active compounds against both the hepatic and erythrocytic stages of Plasmodium parasites, some of them at sub-micromolar concentrations. The results of our research suggest that SAHAquines are promising leads for new anticancer and antimalarial agents.