Combination of chiroptical, absorption and fluorescence spectroscopic methods reveals multiple, hydrophobicity-driven human serum albumin binding of the antimalarial atovaquone and related hydroxynaphthoquinone compounds

Lapachol, a natural food component, interacts with human serum albumin: Insights of its impact on the pharmacokinetics of clinically used drugs

Lapachol (LAP), a natural 1,4-naphthoquinone used in popular medicine of South American, is an antioxidant and antimicrobial compound used as a food additive; however, its interactive profile with the main protein carrier of compounds in the human bloodstream (human serum albumin, HSA) was not still characterized. Additionally, the impact of LAP in binding clinically drugs to albumin is still unknown. Thus, the present work describes the interaction HSA:LAP using different biophysical techniques, i.e., 1H saturation-transfer difference nuclear magnetic resonance (1H STD-NMR), isothermal titration calorimetry (ITC), steady-state and time-resolved fluorescence measurements combined with molecular docking calculations. LAP interacts with subdomain region IIA (site I), mainly driven by enthalpy effects, while subdomain region IB (site III) was identified as the second binding site, mainly driven by entropy effects. The binding is spontaneous, strong (binding constant average, Kaverage ≈ 4.45 × 105 M-1), and there is a positive cooperativity in the presence of ibuprofen, with the LAP structure fully buried into the protein cavities. Overall, LAP might impact the residence time (pharmacokinetic profile) of drugs that bind to subdomains regions IIA and IB of albumin, e.g., warfarin, phenylbutazone, diflunisal, naproxen, camptothecin, doxorubicin, daunorubicin, suramin, and tyrosine kinase inhibitors.

A randomized, open-label two-period crossover pilot study to evaluate the relative bioavailability in the fed state of atovaquone-proguanil (Atoguanil™) versus atovaquone-proguanil hydrochloride (Malarone®) in healthy adult participants

Atoguanil™ is a novel complex of atovaquone (ATV) and proguanil (PG) with enhanced ATV bioavailability compared to Malarone®. This pilot study assessed whether the relative bioavailability (Frel) of ATV, PG, and the primary PG metabolite cycloguanil (CG) following a single oral dose in the fed state of Atoguanil was similar to Malarone despite a 50% lower ATV dose. This open-label, single-dose, randomized 2-period, 2-treatment, balanced crossover study was conducted between 17th November 2021 and 18th March 2022. Eligible participants (aged 18-55 years) were randomized (1:1) in period 1 to Atoguanil (ATV/PG 500/348 mg) or Malarone (ATV/PG hydrochloride 1000/400 mg) administered following a high-fat, high caloric meal. After a 24-day washout period, participants crossed treatment arms. For the doses tested, Frel was assumed similar if 90%CIs were between 80 and 125% for the geometric mean ratio of the least square mean differences for each exposure parameter. In 15 evaluable participants, Frel was similar for ATV Cmax (93.6% [90%CI 83.6, 104.9]) but not AUC0-inf (77.8% [67.4, 89.8]), for PG AUC0-inf (95.6% [92.1, 99.2]) but not Cmax (82.4% [75.8, 89.5]), and for both CG Cmax (100.8% [95.0, 107.0]) and AUC0-inf (102.9% [98.4, 107.7]). Nine adverse events occurred; all were of mild severity and not considered treatment related. At the doses tested, ATV Frel was lower following Atoguanil versus Malarone based on AUC0-inf, though when adjusted for dose Frel increased by 156%. Both drugs were well tolerated with no safety concerns. ClinicalTrials.gov: NCT04866602 (April 26th, 2021).

Identification of FDA Approved Drugs with Antiviral Activity against SARS-CoV-2: A Tale from structure-based drug repurposing to host-cell mechanistic investigation

The continuing heavy toll of the COVID-19 pandemic necessitates development of therapeutic options. We adopted structure-based drug repurposing to screen FDA-approved drugs for inhibitory effects against main protease enzyme (Mpro) substrate-binding pocket of SARS-CoV-2 for non-covalent and covalent binding. Top candidates were screened against infectious SARS-CoV-2 in a cell-based viral replication assay. Promising candidates included atovaquone, mebendazole, ouabain, dronedarone, and entacapone, although atovaquone and mebendazole were the only two candidates with IC50s that fall within their therapeutic plasma concentration. Additionally, we performed Mpro assays on the top hits, which demonstrated inhibition of Mpro by dronedarone (IC50 18 µM), mebendazole (IC50 19 µM) and entacapone (IC50 9 µM). Atovaquone showed only modest Mpro inhibition, and thus we explored other potential mechanisms. Although atovaquone is Dihydroorotate dehydrogenase (DHODH) inhibitor, we did not observe inhibition of DHODH at the respective SARS-CoV-2 IC50. Metabolomic profiling of atovaquone treated cells showed dysregulation of purine metabolism pathway metabolite, showing that ecto-5′-nucleotidase (NT5E) is downregulated by atovaquone at concentrations equivalent to its antiviral IC50. Atovaquone and mebendazole are promising candidates targeting SARS-CoV-2, however atovaquone did not significantly inhibit Mpro at therapeutically meaningful concentrations but may inhibit SARS-CoV-2 viral replication by targeting host purine metabolism.

The anti-malarial drug atovaquone potentiates platinum-mediated cancer cell death by increasing oxidative stress

Platinum chemotherapies are highly effective cytotoxic agents but often induce resistance when used as monotherapies. Combinatorial strategies limit this risk and provide effective treatment options for many cancers. Here, we repurpose atovaquone (ATQ), a well-tolerated & FDA-approved anti-malarial agent by demonstrating that it potentiates cancer cell death of a subset of platinums. We show that ATQ in combination with carboplatin or cisplatin induces striking and repeatable concentration- and time-dependent cell death sensitization in vitro across a variety of cancer cell lines. ATQ induces mitochondrial reactive oxygen species (mROS), depleting intracellular glutathione (GSH) pools in a concentration-dependent manner. The superoxide dismutase mimetic MnTBAP rescues ATQ-induced mROS production and pre-loading cells with the GSH prodrug N-acetyl cysteine (NAC) abrogates the sensitization. Together, these findings implicate ATQ-induced oxidative stress as key mediator of the sensitizing effect. At physiologically achievable concentrations, ATQ and carboplatin furthermore synergistically delay the growth of three-dimensional avascular spheroids. Clinically, ATQ is a safe and specific inhibitor of the electron transport chain (ETC) and is concurrently being repurposed as a candidate tumor hypoxia modifier. Together, these findings suggest that ATQ is deserving of further study as a candidate platinum sensitizing agent.

Palladium(ii)-catalyzed hydroxy-involved enolate-type efficient C–C functionalization of hydroxynaphthoquinones at room temperature

A simple, mild, efficient and scalable strategy has been developed for synthesizing hydroxynaphthoquinones via a Pd-catalyzed hydroxy-involved enolate-type reaction.

The antimalarial drug atovaquone binds to saposin B with comparable affinity to coenzyme Q10

Saposin B, a known binder/transporter of coenzyme Q10, is shown to strongly bind atovaquone, a front-line antimalarial drug and competitive inhibitor of CoQ10.

Antimalarial pharmacology and therapeutics of atovaquone

Atovaquone is used as a fixed-dose combination with proguanil (Malarone) for treating children and adults with uncomplicated malaria or as chemoprophylaxis for preventing malaria in travellers. Indeed, in the USA, between 2009 and 2011, Malarone prescriptions accounted for 70% of all antimalarial pre-travel prescriptions. In 2013 the patent for Malarone will expire, potentially resulting in a wave of low-cost generics. Furthermore, the malaria scientific community has a number of antimalarial quinolones with a related pharmacophore to atovaquone at various stages of pre-clinical development. With this in mind, it is timely here to review the current knowledge of atovaquone, with the purpose of aiding the decision making of clinicians and drug developers involved in the future use of atovaquone generics or atovaquone derivatives.

Evaluation of drug-human serum albumin binding interactions with support vector machine aided online automated docking

MOTIVATION

Human serum albumin (HSA), the most abundant plasma protein is well known for its extraordinary binding capacity for both endogenous and exogenous substances, including a wide range of drugs. Interaction with the two principal binding sites of HSA in subdomain IIA (site 1) and in subdomain IIIA (site 2) controls the free, active concentration of a drug, provides a reservoir for a long duration of action and ultimately affects the ADME (absorption, distribution, metabolism, and excretion) profile. Due to the continuous demand to investigate HSA binding properties of novel drugs, drug candidates and drug-like compounds, a support vector machine (SVM) model was developed that efficiently predicts albumin binding. Our SVM model was integrated to a free, web-based prediction platform (http://albumin.althotas.com). Automated molecular docking calculations for prediction of complex geometry are also integrated into the web service. The platform enables the users (i) to predict if albumin binds the query ligand, (ii) to determine the probable ligand binding site (site 1 or site 2), (iii) to select the albumin X-ray structure which is complexed with the most similar ligand and (iv) to calculate complex geometry using molecular docking calculations. Our SVM model and the potential offered by the combined use of in silico calculation methods and experimental binding data is illustrated.