Rational Design of Novel Inhibitors of α-Glucosidase: An Application of Quantitative Structure Activity Relationship and Structure-Based Virtual Screening

Targeting α-amylase enzyme through multi-fold structure-based virtual screening and molecular dynamic simulation

α-Amylase play important role in hydrolyses of α-bonds of large α-linked polysaccharides; thus, it is a potential drug target in diabetes mellites (DM) and its inhibition is one of the therapeutic strategies in DM. With the aim to discover novel and safer therapeutic molecules to combat diabetes, a huge dataset of ∼0.69 billion compounds from ZINC20 database were screened against α-amylase using multi-fold structure-based virtual screening protocol. Based on receptor-based pharmacophore model, docking results, pharmacokinetic profile, molecular interactions with α-amylase, several compounds were retrieved as lead candidates to be further scrutinized in the in vitro assay and in vivo animal testing. Among the selected hits, CP26 exhibited the highest binding free energy in MMGB-SA analysis, followed by CP7 and CP9, which is higher than the binding free energy of acarbose. While CP20 and CP21 showed comparative binding free energy to acarbose. All the selected ligands showed acceptable binding energy range, therefore, several molecules with enhanced efficacy can be designed by derivatizing these molecules. The in-silico results indicates that the selected molecules could serve as potential selective α-amylase inhibitors and can be used for the treatment of diabetes.Communicated by Ramaswamy H. Sarma.

Synthesis of obovatol and related neolignan analogues as α-glucosidase and α-amylase inhibitors

Diabetes mellitus is a metabolic disease characterized by hyperglycemia, which can be counteracted by the inhibition of α-glucosidase (α-Glu) and α-amylase (α-Amy), enzymes responsible for the hydrolysis of carbohydrates. In recent decades, many natural compounds and their bioinspired analogues have been studied as α-Glu and α-Amy inhibitors. However, no studies have been devoted to the evaluation of α-Glu and α-Amy inhibition by the neolignan obovatol (1). In this work, we report the synthesis of 1 and a library of new analogues. The synthesis of these compounds was achieved by implementing methodologies based on: phenol allylation, Claisen/Cope rearrangements, methylation, Ullmann coupling, demethylation, phenol oxidation and Michael-type addition. Obovatol (1) and ten analogues were evaluated for their in vitro inhibitory activity towards α-Glu and α-Amy. Our investigation highlighted that the naturally occurring 1 and four neolignan analogues (11, 22, 26 and 27) were more effective inhibitors than the hypoglycemic drug acarbose (α-Amy: 34.6 µM; α-Glu: 248.3 µM) with IC5O value of 6.2-23.6 µM toward α-Amy and 39.8-124.6 µM toward α-Glu. Docking investigations validated the inhibition outcomes, highlighting optimal compatibility between synthesized neolignans and both the enzymes. Concurrently circular dichroism spectroscopy detected the conformational changes in α-Glu induced by its interaction with the studied neolignans. Detailed studies through fluorescence measurements and kinetics of α-Glu and α-Amy inhibition also indicated that 1, 11, 22, 26 and 27 have the greatest affinity for α-Glu and 1, 11 and 27 for α-Amy. Surface plasmon resonance imaging (SPRI) measurements confirmed that among the compounds studied, the neolignan 27 has the greater affinity for both enzymes, thus corroborating the results obtained by kinetics and fluorescence quenching. Finally, in vitro cytotoxicity of the investigated compounds was tested on human colon cancer cell line (HCT-116). All these results demonstrate that these obovatol-based neolignan analogues constitute promising candidates in the pursuit of developing novel hypoglycemic drugs.

Synthesis of novel hydrazide Schiff bases with anti-diabetic and anti-hyperlipidemic effects: in-vitro, in-vivo and in-silico approaches

The increasing global incidence of non-insulin-dependent diabetes mellitus (NIDDM) necessitates innovative therapeutic solutions. This study focuses on the design, synthesis and biological evaluation of Schiff base derivatives from 2-bromo-2-(2-chlorophenyl) acetic acid, particularly hydrazone compounds 4a and 4b. Both in-vitro and in-vivo assays demonstrate these derivatives' strong antidiabetic and anti-hyperlipidemic properties. In a 15-d experiment, we administered 4a and 4b at doses of 2.5 and 5 mg/kg body weight, which effectively improved symptoms of alloxan-induced diabetes in mice. These symptoms included weight loss, increased water consumption and high blood glucose levels. The compounds also normalized abnormal levels of total cholesterol (TC), triacylglycerol (TG) and low-density lipoprotein cholesterol (LDL-C), while raising the levels of high-density lipoprotein cholesterol (HDLC). Computational analysis showed that these compounds effectively inhibited the α-glucosidase enzyme by interacting with key catalytic residues, specifically Asp214 and Asp349. These computational results were confirmed through in-vitro tests, where 4a and 4b showed strong α-glucosidase inhibitory activity, with IC50 values of 0.70 ± 0.11 and 10.29 ± 0.30 µM, respectively. These compounds were more effective than the standard drug, acarbose, which had an IC50 value of 873.34 ± 1.67 µM. Mechanistic studies further indicated competitive inhibition, reinforcing the therapeutic potential of 4a and 4b for NIDDM treatment.Communicated by Ramaswamy H. Sarma.

Biochemical and computational inhibition of α-glucosidase by novel metronidazole-linked 1H-1,2,3-triazole and carboxylate moieties: kinetics and dynamic investigations

In the current study, metronidazole derivatives containing 1H-1,2,3-triazole and carboxylate moieties were evaluated in vitro and by computational methods for their anti-diabetic potential to insight into their medicinal use for the management of type II diabetes mellitus. Interestingly all 14 compounds displayed high to significant inhibitory capability against the key carbohydrate's digestive enzyme α-glucosidase with IC50 values in range of 9.73-56.39 μM, as compared to marketed drug acarbose (IC50 = 873.34 ± 1.67 μM). Compounds 5i and 7c exhibited the highest inhibition, therefore, these two compounds were further evaluated for their mechanistic studies to explore its type of inhibition. Compounds 5i and 7c both displayed a concentration-dependent (competitive type of inhibition) with Ki values 7.14 ± 0.01, 6.15 ± 0.02 μM, respectively, which conclude their favourable interactions with the active site residues of the α-glucosidase. Interestingly all compounds are non-cytotoxic against BJ cell line. To further validate our findings, in-silico approaches like molecular docking, and molecular dynamic simulations were applied to investigate the mode of bindings of compounds with the enzyme and identifies their inhibition mechanism, which strongly complements our experimental findings.Communicated by Ramaswamy H. Sarma.

In silico exploration of the potential inhibitory activities of in-house and ZINC database lead compounds against alpha-glucosidase using structure-based virtual screening and molecular dynamics simulation approach

Inhibitors of α-glucosidase have been used to treat type-2 diabetes (T2DM) by preventing the breakdown of carbohydrates into glucose and prevent enhancing glucose conversion. Structure-based virtual screening (SBVS) was used to generate novel chemical scaffold-ligand α-glucosidase inhibitors. The databases were screened against the receptor α-glucosidase using SBVS and molecular dynamics simulation (MDS) techniques in this study. Based on molecular docking studies, three and two compounds of α-glucosidase inhibitors were chosen from a commercial database (ZINC) and an In-house database for this study respectively. The mode of binding interactions of the selected compounds later predicted their α-glucosidase inhibitory potential. Finally, one out of three lead compound from ZINC and one out of two lead compound from In-house database were shortlisted based on interactions. Furthermore, MDS and post-MDS strategies were used to refine and validate the shortlisted leads along with the reference acarbose/α-glucosidase. The Hits' ability to inhibit α-glucosidase was predicted by SBVS, indicating that these compounds have good inhibitory activities. The lead inhibitor's structure may serve as templates for the design of novel inhibitors, and in vitro testing to confirm their anti-diabetic potential is necessary. These insights can help rationally design new effective anti-diabetic drugs.Communicated by Ramaswamy H. Sarma.

In-vivo anti-diabetic and anti-hyperlipidemic effects of natural metabolites from resin of Commiphora mukul and their in-silico to in-vitro target fishing

Diabetes mellitus is a rapidly spreading global metabolic disorder that has serious social, health, and economic consequences. Herein, we have evaluated in vivo antidiabetic and antihyperlipidemic effects of myrrhanone-B and myrrhanol-B (isolated from Commiphora mukul Hook). We observed that treatment with myrrhanone-B and myrrhanol-B at a dose of 5 and 10 mg/kg body weight for 21 days significantly improved body weight loss, water consumption, and the concentration of blood glucose level (BGL) in alloxan (120 mg/kg) induced diabetic mice, which indicates that the compounds possess strong anti-diabetic activities. In the biochemical analysis, these compounds improved an abnormal level of total cholesterol (TC), triacylglycerol (TG), and low-density lipoprotein cholesterol (LDL-C) to a normal level and increased the high-density lipoprotein cholesterol level (HDLC). Later, drug target of compounds was predicted through in-silico docking which shows that these compounds nicely fit in the active site of α-glucosidase enzyme and mediates excellent interactions with the catalytic residues, Asp214 and Asp349. The in-silico results were confirmed by in-vitro testing of myrrhanone-B and myrrhanol-B against α-glucosidase where both the compounds exhibited excellent inhibitory potency with IC50 values of 19.50 ± 0.71, and 16.11 ± 0.69 µM, respectively. Furthermore, mechanistic study was conducted to observe their binding mechanism, which reflect that myrrhanol-B has mixed type of inhibition (ki = 12.33 ± 0.030 µM), while myrrhanone-B demonstrates competitive type of inhibition (ki =14.53 ± 0.040 µM).

Synthesis, biological evaluation, and molecular docking study of chromen-linked hydrazine carbothioamides as potent α-glucosidase inhibitors

Inhibiting α-glucosidase is a reliable method for reducing blood sugar levels in diabetic individuals. Several novel chromen-linked hydrazine carbothioamide (3a-r) were designed and synthesized by condensation of chromone-3-carbaldehyde with a variety of substituted thiosemicarbazides. The structures of these new analogues were elucidated through various advanced spectroscopic techniques (1 H NMR, 13 C NMR, and ESI-MS). The resulted compounds were screened for α-glucosidase inhibitory potential and all the compounds (3a-r) exhibited potent inhibition of α-glucosidase with IC50 values ranging 0.29-53.70 µM. Among them compounds 3c, 3f, 3h, and 3r displayed the highest α-glucosidase inhibitor capability with IC50 values of 1.50, 1.28, 1.08, and 0.29 µM, respectively. Structure-activity relationship showed that different substituted groups are responsible for the variation in the α-glucosidase inhibition. The kinetics studies of the most active inhibitor (3r) were performed, to investigate the mode of inhibition and dissociation constants (Ki), that indicated a competitive inhibitor with Ki value of 1.47 ± 0.31 µM. Furthermore, molecular docking studies was performed to reveal the possible interactions, such as H-bonding, or π-π stacking, with the key residues of α-glucosidase. Docking analysis revealed the importance of hydrazine carbothioamide moiety of compounds in the attachment of ligands with the crucial residues of α-glucosidase. The estimated pharmacokinetic, physicochemical, and drug likeness properties of compounds 3a-r reflects that these molecules have acceptable range of these properties.

Biological significance of carbohydrate active enzymes and searching their inhibitors for therapeutic applications

Glycans are the most abundant and diverse group of biomolecules with a crucial role in all the biological processes. Their structural and functional diversity is not genetically encoded, but depends on Carbohydrate Active Enzymes (CAZymes) which carry out all catalytic activities in terms of synthesis, modification, and degradation. CAZymes comprise large families of enzymes with specific functions and are widely used for various commercial applications ranging from biofuel production to textile and food industries with impact on biorefineries. To understand the structure and functional mechanism of these CAZymes for their modification for industrial use, together with knowledge of therapeutic aspects of their dysfunction associated with various diseases, CAZyme inhibitors can be used as a valuable tool. In search for new inhibitors, the screening of various secondary metabolites using high-throughput techniques and rational design techniques have been explored. The inhibitors can thus help tune CAZymes and are emerging as a potential research interest.

Structure-based small inhibitors search combined with molecular dynamics driven energies for human programmed cell death-1 (PD-1) protein

Human immune system is specialized in distinguishing normal cells from foreign particles mainly through proteins expressed on immune cells called 'checkpoints'. Immune checkpoints work as a switch to activate and deactivate immune responses. T cells express one of the immune checkpoint, human programmed cell death-1 (PD-1), which normally operates as an off-switch function to protect the normal cell from T-cell attack. Binding of PD-1 to its ligand, the programmed cell death ligand (PD-L1/2) expressed on myeloid/cancer cells, induce downstream inhibitory signals, leading to tumor immune evasion. Targeting PD-1 or PD-L1 can boost the immune response against cancer cells. To design novel small molecule inhibitors for the PD-1, in silico structure-based screening on pharmacophoric points and molecular docking were performed. Based on the docking score and significant binding interaction with the crucial residues of PD-1 (Thr59, Glu61, Ser62, Glu84, Arg86 and Ala132), compounds were selected from the ZINC20 database, and their dynamic behavior and conformational stability were examined through molecular dynamic simulations. Besides, the Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) method was used to calculate the binding strength of each selected inhibitor complexed with PD-1. The binding energy calculations revealed that these selected inhibitors show a considerable affinity for PD-1. The selected novel inhibitors exhibit excellent drug-like and pharmacokinetic properties (absorption, distribution, metabolism, excretion and toxicity). In conclusion, the identified novel compounds (ZINC1443480030, ZINC1002854123, ZINC988238128, ZINC1481242350, ZINC1001739421, ZINC1220816434 and ZINC1167786692) from the current study can be validated in-vitro as potential PD-1 inhibitors and for discovery of novel drugs against PD-1 in the future.Communicated by Ramaswamy H. Sarma.

Bio-Oriented Synthesis of Novel Polyhydroquinoline Derivatives as α-Glucosidase Inhibitor for Management of Diabetes

Polyhydroquinoline derivatives (1-15) were synthesized through an unsymmetrical Hantzsch reaction in excellent yields by treating 3,5-dibromo-4-hydroxybenzaldehyde, dimedone, ammonium acetate, and ethyl acetoacetate in ethanol solvent. The structures of the synthesized compounds (1-15) were deduced through different spectroscopic techniques such as 1H NMR, 13C NMR, and HR-ESI-MS. The synthesized products were tested for their α-glucosidase inhibitory activity where compounds 11 (IC50 = 0.56 ± 0.01 μM), 10 (IC50 = 0.94 ± 0.01 μM), 4 (IC50 = 1.47 ± 0.01 μM), 2 (IC50 = 2.20 ± 0.03 μM), 6 (IC50 = 2.20 ± 0.03 μM), 12 (IC50 = 2.22 ± 0.07 μM), 7 (IC50 = 2.76 ± 0.04 μM), 9 (IC50 = 2.78 ± 0.03 μM), and 3 (IC50 = 2.88 ± 0.05 μM) exhibited high potential for the inhibition of α-glucosidase, while the rest of the compounds (8, 5, 14, 15, and 13) showed significant α-glucosidase inhibitory potential with IC50 values of 3.13 ± 0.10, 3.34 ± 0.06, 4.27 ± 0.13, 6.34 ± 0.15, and 21.37 ± 0.61 μM, respectively. Among the synthesized series, two compounds, i.e., 11 and 10, showed potent α-glucosidase inhibitory potential higher than the standard. All the compounds were compared with standard drug "acarbose" (IC50 = 873.34 ± 1.67 μM). An in silico method was used to predict their mode of binding within the active site of enzyme to understand their mechanism of inhibition. Our in silico observation complements with the experimental results.

Synthesis of new phenoxymethylcoumarin clubbed 4-arylthiazolylhydrazines as α-glucosidase inhibitors and their kinetics and molecular docking studies

The current studies mainly demonstrate the coumarin based azomethine-clubbed thiazoles synthesis and their in-vitro evaluation for the first time against α-glucosidase. Due to the catalytic role of α-glucosidase, it has become a precise target for the treatment of type diabetes mellitus (T2DM). The high rate of prevalence of diabetes and its associated health related problems led us to scrutinize the anti-diabetic capability of the synthesized thiazole derivatives (6a-6k). The anticipated structures of prepared compounds were confirmed through FT-IR and NMR spectroscopic methods. All the compounds showed several times potent activity than the standard drug, acarbose (IC₅₀ = 873.34 ± 1.67 µM) against α-glucosidase with IC₅₀ values in range of 0.87 ± 0.02-322.61 ± 1.14 µM. The compound 6k displayed the highest anti-diabetic activity (IC₅₀ = 1.88 ± 0.03 µM). Kinetic study revealed that these are competitive inhibitors for α-glucosidase. The mode of binding of the synthesized molecules were further evaluated by molecular docking, which reflects the importance of azomethine group in protein-ligand interaction. The docking scores are complementary with the IC₅₀ values of compounds while the interaction pattern of the compounds clearly demonstrates their structure-activity relationship. Current study reported medicinal importance of thiazole derivative as future drug candidates for the management of Type 2 Diabetes Mellitus (T2DM).

Novel 5-(Arylideneamino)-1H-Benzo[d]imidazole-2-thiols as Potent Anti-Diabetic Agents: Synthesis, In Vitro α-Glucosidase Inhibition, and Molecular Docking Studies

A novel series of multifunctional benzimidazoles has been reported as potent inhibitors of α-glucosidase. The procedure relies on the synthesis of 5-amino-1H-benzo[d]imidazole-2-thiol 5 via the multistep reaction through 2-nitroaniline 1, benzene-1,2-diamine 2, 1H-benzo[d]imidazole-2-thiol 3, and 5-nitro-1H-benzo[d]imidazole-2-thiol 4. Further treatment of 5 with aromatic aldehydes 6a-m provided access to the target 5-(arylideneamino)-1H-benzo[d]imidazole-2-thiols 7a-m. The results of the bioactivity assessment revealed all the compounds as excellent inhibitors of the enzyme (IC₅₀ range: 0.64 ± 0.05 μM to 343.10 ± 1.62 μM) than acarbose (873.34 ± 1.21). Among them, 7i was the most active inhibitor (IC₅₀: 0.64 ± 0.05 μM) followed by 7d (IC₅₀: 5.34 ± 0.16 μM), 7f (IC₅₀: 6.46 ± 0.30 μM), 7g (IC₅₀: 8.62 ± 0.19 μM), 7c (IC₅₀: 9.84 ± 0.08 μM), 7m (IC₅₀: 11.09 ± 0.79 μM), 7a (IC₅₀: 11.84 ± 0.26 μM), 7e (IC₅₀: 16.38 ± 0.53 μM), 7j (IC₅₀: 18.65 ± 0.74 μM), 7h (IC₅₀: 20.73 ± 0.59 μM), 7b (IC₅₀: 27.26 ± 0.30 μM), 7k (70.28 ± 1.52 μM) and finally 7l (IC₅₀: 343.10 ± 1.62 μM). Molecular docking revealed important interactions with the enzyme, thereby supporting the experimental findings.

Design, synthesis, in vitro α-glucosidase inhibition, docking, and molecular dynamics of new phthalimide-benzenesulfonamide hybrids for targeting type 2 diabetes

In the present work, a new series of 14 novel phthalimide-benzenesulfonamide derivatives 4a-n were synthesized, and their inhibitory activity against yeast α-glucosidase was screened. The obtained results indicated that most of the newly synthesized compounds showed prominent inhibitory activity against α-glucosidase. Among them, 4-phenylpiperazin derivative 4m exhibited the strongest inhibition with the IC50 value of 52.2 ± 0.1 µM. Enzyme kinetic study of compound 4m proved that its inhibition mode was competitive and Ki value of this compound was calculated to be 52.7 µM. In silico induced fit docking and molecular dynamics studies were performed to further investigate the interaction, orientation, and conformation of the target compounds over the active site of α-glucosidase. Obtained date of these studies demonstrated that our new compounds interacted as well with the α-glucosidase active site with the acceptable binding energies. Furthermore, in silico druglikeness/ADME/Toxicity studies of compound 4m were performed and predicted that this compound is druglikeness and has good ADME and toxicity profiles.

Bio-Oriented Synthesis of Novel (S)-Flurbiprofen Clubbed Hydrazone Schiff’s Bases for Diabetic Management: In Vitro and In Silico Studies

A new series of (S)-flurbiprofen derivatives 4a–4p and 5a–5n were synthesized with different aromatic or aliphatic aldehydes and ketones to produce Schiff’s bases and their structures were confirmed through HR-ESI-MS, ¹H, and ¹³C-NMR spectroscopy. The α-glucosidase inhibitory activities of the newly synthesized compounds were scrutinized, in which six compounds 5k, 4h, 5h, 4d, 4b, and 5i showed potent inhibition in the range of 0.93 to 10.26 µM, respectively, whereas fifteen compounds 4c, 4g, 4i, 4j, 4l, 4m, 4o, 4p, 5c, 5d, 5j, 5l, 5m, 5n and 1 exhibited significant inhibitory activity with IC₅₀ in range of = 11.42 to 48.39 µM. In addition, compounds 5g, 5f, 4k, 4n, and 4f displayed moderate-to-low activities. The modes of binding of all the active compounds were determined through the molecular docking approach, which revealed that two residues, specifically Glu277 and His351 are important in the stabilization of the active compounds in the active site of α-glucosidase. Furthermore, these compounds block the active site with high binding energies (−7.51 to −3.36 kcal/mol) thereby inhibiting the function of the enzyme.

Parthenolide reverses the epithelial to mesenchymal transition process in breast cancer by targeting TGFbeta1: In vitro and in silico studies

AIMS

Breast cancer metastasis is the leading cause of mortality among breast cancer patients. Epithelial to mesenchymal transition (EMT) is a biological process that plays a fundamental role in facilitating breast cancer metastasis. The present study assessed the efficacy of parthenolide (PTL Tanacetum parthenium) on EMT and its underlying mechanisms in both lowly metastatic, estrogen-receptor positive, MCF-7 cells and highly metastatic, triple-negative MDA-MB-231 cells.

MAIN METHODS

MCF-7 and MDA-MB-231 cells were treated with PTL (2 μM and 5 μM). Cell viability was determined by MTT (3-(4,5-dimethy lthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. Apoptosis was analyzed by the FITC (fluorescein isothiocyanate) annexin V apoptosis detection kit. The monolayer wound scratch assay was employed to evaluate cancer cell migration. Proteins were separated and identified by Western blotting. Gene expression was analyzed by quantitative real-time PCR.

KEY FINDINGS

PTL treatment significantly reduced cell viability and migration while inducing apoptosis in both cell lines. Also, PTL treatment reverses the EMT process by decreasing the mesenchymal marker vimentin and increasing the epithelial marker E-cadherin compared to the control treatment. Importantly, PTL downregulates TWIST1 (a transcription factor and regulator of EMT) gene expression, concomitant with the reduction of transforming growth factor beta1 (TGFβ1) protein and gene expression in both cell lines. Additionally, molecular docking studies suggest that PTL may induce anticancer properties by targeting TGFβ1 in both breast cancer cell lines.

SIGNIFICANCE

Our findings provide insights into the therapeutic potential of PTL to mitigate EMT and breast cancer metastasis. These promising results demand in vivo studies.

Identification of Novel Potential Anti-Diabetic Candidates targeting Human Pancreatic ɑ-Amylase and Human ɑ-Glycosidase: An Exhaustive Structure-based Screening

Diabetes is a major health issue that half a billion people affected worldwide. It is a serious, long-term medical condition majorly impacting the lives and well-being of individuals, families, and societies at large. It is amongst the top 10 diseases responsible for the death amongst adults with an expected rise to 10.2% (578 million) by 2030 and 10.9% (700 million) by 2045. The carbohydrates absorbed into the body are hydrolyzed by pancreatic α-amylase and other enzymes, human α-glucosidase. The α-amylase and α-glucosidase are validated therapeutic targets in the treatment of Type II diabetes (T2DM) as they play a vital role in modulating the blood glucose post meal. Herein, we report novel and diverse molecules as potential candidates, with predicted affinity for α-amylase and α-glucosidase. These molecules have been identified via hierarchical multistep docking of small molecules database with the estimated binding free energies. A Glide XP Score cutoff −8.00 kcal/mol was implemented to filter out non potential molecules. Four molecules viz. amb22034702, amb18105639, amb17153304, and amb9760832 have been identified after an exhaustive computational study involving, evaluation of binding interactions and assessment of the pharmacokinetics and toxicity profiles. The in-depth analysis of protein– ligand interactions was performed using a 100ns molecular dynamics (MD) simulation to establish the dynamic stability. Furthermore MM-GBSA based binding free energies were computed for 1000 trajectory snapshots to ascertain the strong binding affinity of these molecules for α-amylase and αglucosidase. The identified molecules can be considered as promising candidates for further drug development through necessary experimental assessments.