Imatinib: a selective tyrosine kinase inhibitor

Overcoming Secondary Mutations of Type II Kinase Inhibitors

Type II kinase inhibitors bind in the "DFG-out" kinase conformation and are generally considered to be more potent and selective than type I inhibitors, which target a DFG-in conformation. Nine type II inhibitors are currently clinically approved, with more undergoing clinical development. Resistance-conferring secondary mutations emerged with the first series of type II inhibitors, most commonly at residues within the kinase activation loop and at the "gatekeeper" position. Recently, new inhibitors have been developed to overcome such mutations; however, mutations activating other pathways (and/or other targets) have subsequently emerged on occasion. Here, we systematically summarize the secondary mutations that confer resistance to type II inhibitors, the structural basis for resistance, newer inhibitors designed to overcome resistance, as well as the challenges and opportunities for the development of new inhibitors to overcome secondary kinase domain mutations.

EMMAs: Implementation and Assessment of a Suite of Cross-Disciplinary, Case-Based High School Activities to Explore Three-Dimensional Molecular Structure, Noncovalent Interactions, and Molecular Dynamics

Students frequently develop misconceptions about noncovalent interactions that make it challenging for them to appropriately interpret aspects of molecular structure and interactions critical to myriad applications. We hypothesized that computational molecular modeling and visualization could provide a valuable approach to help address these core misconceptions when students are first exposed to these concepts in secondary school chemistry courses. Here, we present a series of activities exploring biomolecular drug-target interactions using molecular visualization software and an introduction to molecular dynamics methods that were implemented in secondary school classrooms. A pre- and postsurvey approach that incorporated Likert response type, written free response, and drawing-based items demonstrated that students gained an enhanced conceptualization of intermolecular interactions, particularly related to aspects of shape complementarity, after completing the activities. Students also expressed increased comfort with and facility in utilizing different three-dimensional representations of molecules in their postsurvey responses. The activities led to an increased appreciation of interdisciplinary connections of chemistry with mathematics and physics. Overall, the modular activities presented provide a relatively time-efficient and accessible manner to help promote an understanding of a traditionally challenging topic for beginning chemistry students while introducing them to contemporary research tools.

Targeting Protein Kinases to Protect Beta-Cell Function and Survival in Diabetes

The prevalence of diabetes is increasing worldwide. Massive death of pancreatic beta-cells causes type 1 diabetes. Progressive loss of beta-cell function and mass characterizes type 2 diabetes. To date, none of the available antidiabetic drugs promotes the maintenance of a functional mass of endogenous beta-cells, revealing an unmet medical need. Dysfunction and apoptotic death of beta-cells occur, in particular, through the activation of intracellular protein kinases. In recent years, protein kinases have become highly studied targets of the pharmaceutical industry for drug development. A number of drugs that inhibit protein kinases have been approved for the treatment of cancers. The question of whether safe drugs that inhibit protein kinase activity can be developed and used to protect the function and survival of beta-cells in diabetes is still unresolved. This review presents arguments suggesting that several protein kinases in beta-cells may represent targets of interest for the development of drugs to treat diabetes.

Docking, Synthesis and Evaluation of 4-hydroxy-1-phenyl-2(1H)-quinolone Derivatives as Anticancer Agents

BACKGROUND

The estimated number of cancer cases in India for the year 2022 was found to be 14,61,427. The development of chemotherapeutic agents has reduced the mortality rate, however, they have high toxicity which is a disadvantage. Many researchers have found out that quinolin-2- one possesses anticancer activity, with this background we thought of synthesizing the quinolin-2-one derivatives.

OBJECTIVE

This study aimed to carry out docking, synthesis, characterization, and evaluation of 2-(2- (4-Hydroxy-2-oxoquinolin-1(2H)-yl)phenyl/ substituted phenyl)-3-(phenylamino) thiazolidon-4-one derivatives (IVa-g) as an anticancer agent.

METHOD

Diphenylamine and malonic acid treated with phosphoryl chloride gave compound I, which on formylation afforded compound II, which on reaction with various substituted aromatic phenylhydrazine derivatives gave compounds IIIa-g, which on further reaction with thioglycolic acid and anhydrous zinc chloride yielded the compounds IVa-g.

RESULT

Among all the synthesized novel derivatives, compounds IV a-d showed 50% lysis in the IC50 range of 25-50μg for the A549 cell line, and compounds IVa, and IVb showed 50% lysis in the IC50 range of 25-50μg for the MDA-MB cell line. The compound, 3-((4-fluorophenyl)amino)-2-(2-(4- hydroxy-2-oxoquinolin-1(2H)-yl)phenyl)thiazolidin-4-one (IVg) was found to be the most active against both the cell line, A549 and MDA-MB with IC50 value of 0.0298μmol and 0.0338μmol respectively. The docking results revealed that the synthesized compounds exhibited well-conserved hydrogen bonding with one or more amino acid residues in the active pocket of EGFR tyrosine kinase domain with 4-anilinoquinazoline inhibitor erlotinib (PDB ID:1M17). Compound IVg showed the highest MolDock score of -137.813 compared to the standard drug Imatinib having a MolDock score of -119.354.

CONCLUSION

Compound IVg showed the highest MolDock score and was also found to be most potent against both the cell line, A549, and MDA-MB.

Design and Synthesis of Ketenimine Sulfonamide Conjugates through Multicomponent Reactions; A Combined Cytotoxic Analysis and Computational Exploration

Multicomponent reactions involving zwitterion generated from dimethyl acetylenedicarboxylate, aryl sulfonamide, and isocyanide to generate sulfonamide-conjugated ketenimines is reported. The synthetic strategy adopted is highly atom economical and stereoselective. Ketenimine sulfonamide analogues are key intermediates for further synthetic conversions to generate a combinatorial library of compounds. Furthermore, sulfonamide compounds are known to possess a broad spectrum of biological applications. All the novel molecules synthesized exhibit the potential to target the nonhomologous DNA end-joining (NHEJ) pathway with cytotoxic ability. Computational studies compliment the in vitro biological assays of the 8 small-molecule inhibitors. DNA double-strand breaks (DSBs) are considered as the most lethal among different DNA damages. NHEJ repairs about 70% of the DSBs generated in cells within mammals. The DNA-dependent protein kinase catalytic subunit is one of the PI3 kinases associated with NHEJ. Compounds DK01-DK08 were investigated for their ability to induce cancer cell death by treating with two leukemic cell lines where NHEJ is high. Results showed that bromoaryl (DK04)- and nitroaryl (DK05)-conjugated molecules showed excellent biological activity, having IC50 values of ∼2 μM in Nalm6 cell lines.

KIT and PDGFRA Mutations and Survival of Gastrointestinal Stromal Tumor Patients Treated with Adjuvant Imatinib in a Randomized Trial

PURPOSE

Limited data are available about the influence of KIT and PDGFRA mutations on overall survival (OS) of patients with gastrointestinal stromal tumor (GIST) treated with adjuvant imatinib.

PATIENTS AND METHODS

The Scandinavian Sarcoma Group XVIII/AIO multicenter trial accrued 400 patients with a high risk for GIST recurrence after macroscopically complete surgery between February 4, 2004, and September 29, 2008. The patients received adjuvant imatinib 400 mg/day for either 1 year or 3 years based on random allocation. We analyzed using conventional sequencing KIT and PDGFRA mutations centrally from 341 (85%) patients who had localized, centrally confirmed GIST, and correlated the results with recurrence-free survival (RFS) and OS in exploratory analyses.

RESULTS

During a median follow-up time of 10 years, 164 RFS events and 76 deaths occurred. Most patients were re-treated with imatinib when GIST recurred. Patients with KIT exon 11 deletion or indel mutation treated with 3 years of adjuvant imatinib survived longer than patients treated for 1 year [10-year OS 86% versus 64%, respectively; HR, 0.34; 95% confidence interval (CI), 0.15-0.72; P = 0.007], and also had longer RFS (10-year RFS 47% versus 29%; HR, 0.48; 95% CI, 0.31-0.74; P < 0.001). Patients with KIT exon 9 mutation had unfavorable OS regardless of the duration of adjuvant imatinib.

CONCLUSIONS

Compared with 1 year of imatinib, 3 years of adjuvant imatinib led to 66% reduction in the estimated risk of death and a high 10-year OS rate in the subset of patients with a KIT exon 11 deletion/indel mutation.

Evaluation of separation performance for eggshell-based reversed-phase HPLC columns by controlling particle size and application in quantitative therapeutic drug monitoring

Eggshell-based reversed-phase packing materials were applied to an analytical column for high-performance liquid chromatography. Commercially available eggshell powder was classified by a cyclone system to obtain three types of particles with different diameters (arithmetic mean ± standard deviation: 4.3 ± 3.8, 5.6 ± 3.3, and 9.5 ± 5.5 μm). Sedimentation separation removed tiny particles from each sample, resulting in particles with arithmetic means of 6.6 ± 5.5, 7.3 ± 4.5, and 10.2 ± 5.0 μm, respectively. The unclassified particles and three particle types treated with sedimentation separation were subsequently packed into analytical columns (150 mm × 4.6 mm I.D.), and their separation efficiencies were evaluated by comparing their height equivalent to a theoretical plate (HETP). The column without sedimentation separation exhibited the highest HETP, whereas the columns with sedimentation separation showed better separation efficiency and lower back pressure. The column with the best separation efficiency was applied for the separation of 10 alkylbenzenes and 5 steroids, and all peaks were observed with complete separation (peak resolution: R_S > 1.5). Finally, the column was used for quantitative analysis of voriconazole, an azole antifungal agent, and imatinib, a first-generation molecularly targeted drug for cancer treatment, in spiked whole blood. Excellent accuracy (99.1-102.8%) and precision (0.6-1.9%) were observed for the spiked drugs and long-term stability (>3000 column volumes of mobile phase flow) indicated good applicability of the developed eggshell-based column as an analytical column for routine analyses of therapeutic drugs in blood.

Analysis of histology-agnostic targets among soft tissue and bone sarcomas in the AACR GENIE database

Background

The development of novel therapies for patients with sarcoma is challenging due to the rarity and diversity of these mesenchymal neoplasms. Hence, histology-agnostic approvals can be of particular interest for the treatment of patients with soft tissue and bone sarcoma.

Methods

We queried the American Association for Cancer Research (AACR) Project Genomics Evidence Neoplasia Information Exchange (GENIE) database Cohort v12.0-Public to investigate the prevalence of currently Food and Drug Administration (FDA)-approved and other potentially actionable histology-agnostic alterations in patients with soft tissue and bone sarcoma. Targets were identified by a literature review by the authors. Results are presented for each cohort identified in the GENIE database, namely: (1) soft tissue sarcoma (STS), (2) gastrointestinal stromal tumor (GIST), (3) bone sarcoma, (4) uterine sarcoma, and (5) breast sarcoma.

Results

We identified 7,512 samples of 6,955 patients with sarcoma in the AAACR GENIE database v12.0-Public. Molecular alterations that could lead to the clinical use of a currently approved histology-agnostic therapy were identified in 2.1% of sarcomas (2.6% STS, 1.3% GIST, 1.4% bone, 2.7% uterine, and 0% breast). In addition, 2.9% of patients could be eligible for future histology-agnostic approvals. These specific mutations, fusions, and amplifications occurred in multiple histotypes in all cohorts.

Discussion

Exploring a public large-scale genomic database, we identified that 5% of patients with sarcoma could be eligible for current histology-agnostic FDA-approved drugs or future potential histology-agnostic indications. These actionable alterations were present in a wide variety of histologies in soft tissue and bone sarcomas, highlighting that next-generation sequencing can be considered for patients with advanced sarcoma to guide treatment strategies.

Recent Advances in RNA m6A Modification in Solid Tumors and Tumor Immunity

An analogous field to epigenetics is referred to as epitranscriptomics, which focuses on the study of post-transcriptional chemical modifications in RNA. RNA molecules, including mRNA, tRNA, rRNA, and other non-coding RNA molecules, can be edited with numerous modifications. The most prevalent modification in eukaryotic mRNA is N6-methyladenosine (m6A), which is a reversible modification found in over 7000 human genes. Recent technological advances have accelerated the characterization of these modifications, and they have been shown to play important roles in many biological processes, including pathogenic processes such as cancer. In this chapter, we discuss the role of m6A mRNA modification in cancer with a focus on solid tumor biology and immunity. m6A RNA methylation and its regulatory proteins can play context-dependent roles in solid tumor development and progression by modulating RNA metabolism to drive oncogenic or tumor-suppressive cellular pathways. m6A RNA methylation also plays dynamic roles within both immune cells and tumor cells to mediate the anti-tumor immune response. Finally, an emerging area of research within epitranscriptomics studies the role of m6A RNA methylation in promoting sensitivity or resistance to cancer therapies, including chemotherapy, targeted therapy, and immunotherapy. Overall, our understanding of m6A RNA methylation in solid tumors has advanced significantly, and continued research is needed both to fill gaps in knowledge and to identify potential areas of focus for therapeutic development.

Electronic and structural study of T315I mutated form in DFG-out conformation of BCR-ABL inhibitors

In this work, the four main drugs for the treatment of chronic myeloid leukemia were analyzed, being imatinib, dasatinib, nilotinib and ponatinib followed by four derivative molecules of nilotinib and ponatinib. For these derivative molecules, the fluorine atoms were replaced by hydrogen and chlorine atoms in order to shade light to the structural effects on this set of inhibitors. Electronic studies were performed at density functional theory level with the B3LYP functional and 6-311+G(d,p) basis set. The frontier molecular orbitals, gap HOMO-LUMO, and NBO were analyzed and compared to docking studies for mutant T315I tyrosine kinase protein structure code 3IK3, in the DFG-out conformation. Structural similarities were pointed out, such as the presence of groups common to all inhibitors and modifications raised up on new generations of imatinib-based inhibitors. One of them is the trifluoromethyl group present in nilotinib and later included in ponatinib, in addition to the 1-methylpiperazin-1-ium group that is present in imatinib and ponatinib. The frontier molecular orbitals of imatinib and ponatinib are contributing to the same amino acid residues, and the ineffectiveness of imatinib against the T315I mutation was discussed.Communicated by Ramaswamy H. Sarma.

Docking-Based Virtual Screening Enables Prioritizing Protein Kinase Inhibitors With In Vitro Phenotypic Activity Against Schistosoma mansoni

Schistosomiasis is a parasitic neglected disease with praziquantel (PZQ) utilized as the main drug for treatment, despite its low effectiveness against early stages of the worm. To aid in the search for new drugs to tackle schistosomiasis, computer-aided drug design has been proved a helpful tool to enhance the search and initial identification of schistosomicidal compounds, allowing fast and cost-efficient progress in drug discovery. The combination of high-throughput in silico data followed by in vitro phenotypic screening assays allows the assessment of a vast library of compounds with the potential to inhibit a single or even several biological targets in a more time- and cost-saving manner. Here, we describe the molecular docking for in silico screening of predicted homology models of five protein kinases (JNK, p38, ERK1, ERK2, and FES) of Schistosoma mansoni against approximately 85,000 molecules from the Managed Chemical Compounds Collection (MCCC) of the University of Nottingham (UK). We selected 169 molecules predicted to bind to SmERK1, SmERK2, SmFES, SmJNK, and/or Smp38 for in vitro screening assays using schistosomula and adult worms. In total, 89 (52.6%) molecules were considered active in at least one of the assays. This approach shows a much higher efficiency when compared to using only traditional high-throughput in vitro screening assays, where initial positive hits are retrieved from testing thousands of molecules. Additionally, when we focused on compound promiscuity over selectivity, we were able to efficiently detect active compounds that are predicted to target all kinases at the same time. This approach reinforces the concept of polypharmacology aiming for “one drug-multiple targets”. Moreover, at least 17 active compounds presented satisfactory drug-like properties score when compared to PZQ, which allows for optimization before further in vivo screening assays. In conclusion, our data support the use of computer-aided drug design methodologies in conjunction with high-throughput screening approach.

Resistance to Tyrosine Kinase Inhibitors in Chronic Myeloid Leukemia-From Molecular Mechanisms to Clinical Relevance

Simple Summary

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasia associated with a molecular alteration, the fusion gene BCR-ABL1, that encodes the tyrosine kinase oncoprotein BCR-ABL1. This led to the development of tyrosine kinase inhibitors (TKI), with Imatinib being the first TKI approved. Although the vast majority of CML patients respond to Imatinib, resistance to this targeted therapy contributes to therapeutic failure and relapse. Here we review the molecular mechanisms and other factors (e.g., patient adherence) involved in TKI resistance, the methodologies to access these mechanisms, and the possible therapeutic approaches to circumvent TKI resistance in CML.

Abstract

Resistance to targeted therapies is a complex and multifactorial process that culminates in the selection of a cancer clone with the ability to evade treatment. Chronic myeloid leukemia (CML) was the first malignancy recognized to be associated with a genetic alteration, the t(9;22)(q34;q11). This translocation originates the BCR-ABL1 fusion gene, encoding the cytoplasmic chimeric BCR-ABL1 protein that displays an abnormally high tyrosine kinase activity. Although the vast majority of patients with CML respond to Imatinib, a tyrosine kinase inhibitor (TKI), resistance might occur either de novo or during treatment. In CML, the TKI resistance mechanisms are usually subdivided into BCR-ABL1-dependent and independent mechanisms. Furthermore, patients’ compliance/adherence to therapy is critical to CML management. Techniques with enhanced sensitivity like NGS and dPCR, the use of artificial intelligence (AI) techniques, and the development of mathematical modeling and computational prediction methods could reveal the underlying mechanisms of drug resistance and facilitate the design of more effective treatment strategies for improving drug efficacy in CML patients. Here we review the molecular mechanisms and other factors involved in resistance to TKIs in CML and the new methodologies to access these mechanisms, and the therapeutic approaches to circumvent TKI resistance.

Graphene quantum dots decorated with imatinib for leukemia treatment

The use of graphene quantum dots as biomedical device and drug delivery system has been increasing. This nanoplatform of pure carbon has showed unique properties and showed to be safe for human use. The imatinib is a molecule designed to specifically inhibit the tyrosine kinase, used for leukemia treatment. In this study, we successfully decorated the graphene quantum dots (GQDs@imatinb) by a carbodiimide crosslinking reaction. The GQDs@imatinb were characterized by FTIR and AFM. The nanoparticles' in vitro behaviors were evaluated by cellular trafficking (internalization) assay and cell viability and apoptosis assays in various cancer cell lines, including suspension (leukemia) cells and adherent cancer cells. The results showed that the incorporation of the imatinib on the surface of the graphene quantum dots did not change the nanoparticles' morphology and properties. The GQDs@imatinb could be efficiently internalized and kill cancer cells via the induction of apoptosis. The data indicated that the prepared GQDs@imatinb might be a great drug nano-platform for cancer, particularly leukemia treatments.

Site-Selective Deoxygenative Amination of Azine N-Oxides with Carbodiimides under Catalyst-, Activator-, Base-, and Solvent-Free Conditions

An operationally simple method for synthesizing 2-amino azines via [3+2] dipolar cycloaddition of azine N-oxide with carbodiimide has been demonstrated. The reaction can proceed smoothly under simple heating conditions without any transition metal catalyst, activator, base, and solvent. This transformation demonstrates a broad substrate scope and produces CO₂ as the only co-product. The applicability of this method is highlighted by the late-stage modification of bioactive molecules, including quinine, (±)-α-tocopherol, and tryptamine modified quinoline.

Protein Kinases: Potential Drug Targets Against Schistosoma japonicum

Schistosoma japonicum (S. japonicum) infection can induce serious organ damage and cause schistosomiasis japonica which is mainly prevalent in Asia and currently one of the most seriously neglected tropical diseases. Treatment of schistosomiasis largely depends on the drug praziquantel (PZQ). However, PZQ exhibits low killing efficacy on juvenile worms and the potential emergence of its drug resistance is a continual concern. Protein kinases (PKs) are enzymes that catalyze the phosphorylation of proteins and can participate in many signaling pathways in vivo. Recent studies confirmed the essential roles of PKs in the growth and development of S. japonicum, as well as in schistosome-host interactions, and researches have screened drug targets about PKs from S. japonicum (SjPKs), which provide new opportunities of developing new treatments on schistosomiasis. The aim of this review is to present the current progress on SjPKs from classification, different functions and their potential to become drug targets compared with other schistosomes. The efficiency of related protein kinase inhibitors on schistosomes is highlighted. Finally, the current challenges and problems in the study of SjPKs are proposed, which can provide future guidance for developing anti-schistosomiasis drugs and vaccines.

Microwave-Assisted Regioselective Suzuki Coupling of 2,4-Dichloropyrimidines with Aryl and Heteroaryl Boronic Acids

Suzuki coupling reaction has been often used for the preparation of a diverse set of substituted pyrimidines. In this study, the Suzuki coupling of 2,4-dichloropyrimidines with aryl and heteroaryl boronic acids was investigated. A thorough screening of reaction conditions and the use of microwave irradiation led to a very efficient and straightforward synthetic procedure providing C4-substituted pyrimidines in good to excellent yields. Short reaction time (15 min) and extremely low catalyst loading (0.5 mol%) are the main advantages of our tetrakis(triphenylphosphine)palladium(0) catalyzed microwave-assisted procedure, which could be used for quick and low-cost regioselective preparation of substituted pyrimidine rings.

High-resolution AP-SMALDI MSI as a tool for drug imaging in Schistosoma mansoni

Schistosoma mansoni is a parasitic flatworm causing schistosomiasis, an infectious disease affecting several hundred million people worldwide. Schistosomes live dioeciously, and upon pairing with the male, the female starts massive egg production, which causes pathology. Praziquantel (PZQ) is the only drug used, but it has an inherent risk of resistance development. Therefore, alternatives are needed. In the context of drug repurposing, the cancer drug imatinib was tested, showing high efficacy against S. mansoni in vitro. Besides the gonads, imatinib mainly affected the integrity of the intestine in males and females. In this study, we investigated the potential uptake and distribution of imatinib in adult schistosomes including its distribution kinetics. To this end, we applied for the first time atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging (AP-SMALDI MSI) for drug imaging in paired S. mansoni. Our results indicate that imatinib was present in the esophagus and intestine of the male as early as 20 min after in vitro exposure, suggesting an oral uptake route. After one hour, the drug was also found inside the paired female. The detection of the main metabolite, N-desmethyl imatinib, indicated metabolization of the drug. Additionally, a marker signal for the female ovary was successfully applied to facilitate further conclusions regarding organ tropism of imatinib. Our results demonstrate that AP-SMALDI MSI is a useful method to study the uptake, tissue distribution, and metabolization of imatinib in S. mansoni. The results suggest using AP-SMALDI MSI also for investigating other antiparasitic compounds and their metabolites in schistosomes and other parasites.

Combining targeted therapy with immunotherapy (interferon-α): Rational, efficacy in gastrointestinal stromal tumor model and implications in other malignancies

Imatinib revolutionized gastrointestinal stromal tumor (GIST) treatment but median-progression-free-survival of unresectable/metastatic disease is < 2 y. B-RAF(V600)-mutated-melanoma responds to vemurafenib dramatically but median-progression-free-survival is < 9 mo. Combining imatinib with immunotherapy (peginterferon α-2b) in GIST showed significant induction of antitumor immunity and highly promising clinical outcomes. This strategy warrants further testing in other malignancies.

Alkaloids as Anticancer Agents: A Review of Chinese Patents in Recent 5 Years

BACKGROUND

In recent years, many novel alkaloids with anticancer activity have been found in China, and some of them are promising for developing as anticancer agents.

OBJECTIVE

This review aims to provide a comprehensive overview of the information about alkaloid anticancer agents disclosed in Chinese patents, and discusses their potential to be developed as anticancer drugs used clinically.

METHODS

Anticancer alkaloids disclosed in Chinese patents in recent 5 years were presented according to their mode of actions. Their study results published on PubMed, and SciDirect databases were presented.

RESULTS

More than one hundred anticancer alkaloids were disclosed in Chinese patents and their mode of action referred to arresting cell cycle, inhibiting protein kinases, affecting DNA synthesis and p53 expression, etc. Conclusion: Many newly found alkaloids displayed potent anticancer activity both in vitro and in vivo, and some of the anticancer alkaloids acted as protein kinase inhibitors or CDK inhibitors possess the potential for developing as novel anticancer agents.

Naturally Inspired Pyrimidines Analogues for Alzheimer's Disease

Alzheimer's disease (AD) is a multifarious and developing neurodegenerative disorder. The treatment of AD is still a challenge and availability of drug therapy on the basis of symptoms is not up to the mark. In the context of existence, which is getting worse for the human brain, it is necessary to take care of all critical measures. The disease is caused due to multidirectional pathology of the body, which demands the multi-target-directed ligand (MTDL) approach. This gives hope for new drugs for AD, summarized here in with the pyrimidine based natural product inspired molecule as a lead. The review is sufficient in providing a list of chemical ingredients of the plant to cure AD and screen them against various potential targets of AD. The synthesis of a highly functionalized scaffold in one step in a single pot without isolating the intermediate is a challenging task. In few examples, we have highlighted the importance of this kind of reaction, generally known as multi-component reaction. Multi-component is a widely accepted technique by the drug discovery people due to its high atom economy. It reduces multi-step process to a one-step process, therefore the compounds library can be made in minimum time and cost. This review has highlighted the importance of multicomponent reactions by giving the example of active scaffolds of pyrimidine/fused pyrimidines. This would bring importance to the fast as well as smart synthesis of bio-relevant molecules.

Computational and Biological Investigations on Abl1 Tyrosine Kinase: A Review

Abl1 tyrosine kinase is a validated target for the treatment of chronic myeloid leukemia. It is a form of cancer that is difficult to treat and much research is being done to identify new molecular entities and to tackle drug resistance issues. In recent years, drug resistance of Abl1 tyrosine kinase has become a major healthcare concern. Second and third-generation TKI reported better responses against the resistant forms; still they had no impact on long-term survival prolongation. New compounds derived from natural products and organic small molecule inhibitors can lay the foundation for better clinical therapies in the future. Computational methods, experimental and biological studies can help us understand the mechanism of drug resistance and identify novel molecule inhibitors. ADMET parameters analysis of reported drugs and novel small molecule inhibitors can also provide valuable insights. In this review, available therapies, point mutations, structure-activity relationship and ADMET parameters of reported series of Abl1 tyrosine kinase inhibitors and drugs are summarised. We summarise in detail recent computational and molecular biology studies that focus on designing drug molecules, investigation of natural product compounds and organic new chemical entities. Current ongoing research suggests that selective targeting of Abl1 tyrosine kinase at the molecular level to combat drug resistance in chronic myeloid leukemia is promising.

Targeting Kinases in Fasciola hepatica: Anthelminthic Effects and Tissue Distribution of Selected Kinase Inhibitors

Protein kinases have been discussed as promising druggable targets in various parasitic helminths. New drugs are also needed for control of fascioliasis, a food-borne trematode infection and worldwide spread zoonosis, caused by the liver fluke Fasciola hepatica and related species. In this study, we intended to move protein kinases more into the spotlight of Fasciola drug research and characterized the fasciolicidal activity of two small-molecule inhibitors from human cancer research: the Abelson tyrosine kinase (ABL-TK) inhibitor imatinib and the polo-like 1 (PLK1) inhibitor BI2536. BI2536 reduced viability of 4-week-old immature flukes in vitro, while adult worms showed a blockade of egg production. Together with a significantly higher transcriptional expression of PLK1 in adult compared to immature worms, this argues for a role of PLK1 in fluke reproduction. Both fluke stages expressed ABL1-TK transcripts at similar high levels and were affected by imatinib. To study the uptake kinetic and tissue distribution of imatinib in F. hepatica, we applied matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) for the first time in this parasite. Drug imaging revealed the accumulation of imatinib in different fluke tissues from 20 min to 12 h of exposure. Furthermore, we show that imatinib is metabolized to N-desmethyl imatinib by F. hepatica, a bioactive metabolite also found in humans. Besides the vitellarium, gastrodermal tissue showed strong signal intensities. In situ hybridization demonstrated the gastrodermal presence of abl1 transcripts. Finally, we assessed transcriptional changes of physiologically important genes in imatinib-treated flukes. Moderately increased transcript levels of a gene encoding a multidrug resistance protein were detected, which may reflect an attempt to defend against imatinib. Increased expression levels of the cell cycle dependently expressed histone h2b and of two genes encoding superoxide dismutases (SODs) were also observed. In summary, our pilot study demonstrated cross-stage activity of imatinib but not BI2536 against immature and adult F. hepatica in vitro; a fast incorporation of imatinib within minutes, probably via the oral route; and imatinib-induced expression changes of physiologically relevant genes. We conclude that kinases are worth analyzing in more detail to evaluate the potential as therapeutic targets in F. hepatica.

Prion protein signaling induces M2 macrophage polarization and protects from lethal influenza infection in mice

The cellular prion protein, PrPC, is a glycosylphosphatidylinositol anchored-membrane glycoprotein expressed most abundantly in neuronal and to a lesser extent in non-neuronal cells. Its conformational conversion into the amyloidogenic isoform in neurons is a key pathogenic event in prion diseases, including Creutzfeldt-Jakob disease in humans and scrapie and bovine spongiform encephalopathy in animals. However, the normal functions of PrPC remain largely unknown, particularly in non-neuronal cells. Here we show that stimulation of PrPC with anti-PrP monoclonal antibodies (mAbs) protected mice from lethal infection with influenza A viruses (IAVs), with abundant accumulation of anti-inflammatory M2 macrophages with activated Src family kinases (SFKs) in infected lungs. A SFK inhibitor dasatinib inhibited M2 macrophage accumulation in IAV-infected lungs after treatment with anti-PrP mAbs and abolished the anti-PrP mAb-induced protective activity against lethal influenza infection in mice. We also show that stimulation of PrPC with anti-PrP mAbs induced M2 polarization in peritoneal macrophages through SFK activation in vitro and in vivo. These results indicate that PrPC could activate SFK in macrophages and induce macrophage polarization to an anti-inflammatory M2 phenotype after stimulation with anti-PrP mAbs, thereby eliciting protective activity against lethal infection with IAVs in mice after treatment with anti-PrP mAbs. These results also highlight PrPC as a novel therapeutic target for IAV infection.

Challenges and Opportunities in Cancer Drug Resistance

There has been huge progress in the discovery of targeted cancer therapies in recent years. However, even for the most successful and impactful cancer drugs which have been approved, both innate and acquired mechanisms of resistance are commonplace. These emerging mechanisms of resistance have been studied intensively, which has enabled drug discovery scientists to learn how it may be possible to overcome such resistance in subsequent generations of treatments. In some cases, novel drug candidates have been able to supersede previously approved agents; in other cases they have been used sequentially or in combinations with existing treatments. This review summarizes the current field in terms of the challenges and opportunities that cancer resistance presents to drug discovery scientists, with a focus on small molecule therapeutics. As part of this review, common themes and approaches have been identified which have been utilized to successfully target emerging mechanisms of resistance. This includes the increase in target potency and selectivity, alternative chemical scaffolds, change of mechanism of action (covalents, PROTACs), increases in blood-brain barrier permeability (BBBP), and the targeting of allosteric pockets. Finally, wider approaches are covered such as monoclonal antibodies (mAbs), bispecific antibodies, antibody drug conjugates (ADCs), and combination therapies.

Phosphine Oxides from a Medicinal Chemist's Perspective: Physicochemical and in Vitro Parameters Relevant for Drug Discovery

Phosphine oxides and related phosphorus-containing functional groups such as phosphonates and phosphinates are established structural motifs that are still underrepresented in today's drug discovery projects, and only few examples can be found among approved drugs. In this account, the physicochemical and in vitro properties of phosphine oxides and related phosphorus-containing functional groups are reported and compared to more commonly used structural motifs in drug discovery. Furthermore, the impact on the physicochemical properties of a real drug scaffold is exemplified by a series of phosphorus-containing analogs of imatinib. We demonstrate that phosphine oxides are highly polar functional groups leading to high solubility and metabolic stability but occasionally at the cost of reduced permeability. We conclude that phosphine oxides and related phosphorus-containing functional groups are valuable polar structural elements and that they deserve to be considered as a routine part of every medicinal chemist's toolbox.

S100A4 expression is associated with poor prognosis in patients with resectable gastrointestinal stromal tumor

S100A4 is particularly associated with the progression and metastasis of numerous human malignancies. This study was designed to examine the clinicopathologic significance of S100A4 in gastrointestinal stromal tumor (GISTs). The level of OPNS100A4 expression in a large cohort of resectable GISTs was evaluated with immunohistochemistry. Its correlation with the clinicopathologic parameters of patients with resectable GISTs was analyzed. A survival analysis was performed to evaluate the prognostic significance of S100A4 expression using Kaplan-Meier method. Results: In 108 patients with resectable GISTs, the most high-risk GISTs had a strong level of S100A4 expression. Strong S100A4 expression was significantly associated with tumor size, mitosis, and recurrence, but not gender and age. Patients with weak S100A4 expression had a relatively longer disease-free survival compared to patients with strong S100A4 expression.Therefore, S100A4 expression is a putative marker for tumor progression and an adverse prognosis in GISTs.

A perspective on the discovery of selected compounds with anthelmintic activity against the barber's pole worm-Where to from here?

Parasitic roundworms (nematodes) cause substantial morbidity and mortality in animals worldwide. Anthelmintic treatment is central to controlling these worms, but widespread resistance to most of the commercially available anthelmintics for veterinary and agricultural use is compromising control, such that there is an urgency to discover new and effective drugs. The purpose of this article is to review information on parasitic nematodes, the treatment and control of parasitic nematode infections and aspects of discovering new anthelmintics in the context of anthelmintic resistance problems, and then to discuss some progress that our group has made in identifying selected compounds with activity against nematodes. The focus of our recent work has been on discovering new chemical entities and known drugs with anthelmintic activities against Haemonchus contortus as well as other socioeconomically important parasitic nematodes for subsequent development. Using whole worm-based phenotypic assays, we have been screening compound collections obtained via product-development-partnerships and/or collaborators, and active compounds have been assessed for their potential as anthelmintic candidates. Following the screening of 15,333 chemicals from five distinct compound collections against H. contortus, we have discovered one new chemical entity (designated SN00797439), two human kinase inhibitors (SNS-032 and AG-1295), 14 tetrahydroquinoxaline analogues, one insecticide (tolfenpyrad) and two tolfenpyrad (pyrazole-5-carboxamide) derivatives (a-15 and a-17) with anthelmintic activity in vitro. Some of these 20 'hit' compounds have selectivity against H. contortus in vitro when compared to particular human cell lines. In our opinion, some of these compounds could represent starting points for 'lead' development. Accordingly, the next research steps to be pursued include: (i) chemical optimisation of representative chemicals via structure-activity relationship (SAR) evaluations; (ii) assessment of the breadth of spectrum of anthelmintic activity on a range of other parasitic nematodes, such as strongyloids, ascaridoids, enoplids and filarioids; (iii) detailed investigations of the absorption, distribution, metabolism, excretion and toxicity (ADMET) of optimised chemicals with broad nematocidal or nematostatic activity; and (iv) establishment of the modes of action of lead candidates.

Deoxygenative Amination of Azine-N-oxides with Acyl Azides via [3 + 2] Cycloaddition

A transition-metal-free deoxygenative C-H amination reaction of azine-N-oxides with acyl azides is described. The initial formation of an isocyanate from the starting acyl azide via a Curtius rearrangement can trigger a [3 + 2] dipolar cycloaddition of polar N-oxide fragments to generate the aminated azine derivative. The applicability of this method is highlighted by the late-stage and sequential amination reactions of complex bioactive compounds, including quinidine and fasudil. Moreover, the direct transformation of aminated azines into various bioactive N-heterocycles illustrates the significance of this newly developed protocol.

Synthesis, Structural Characterization, and Biological Activity of New Pyrazolo[4,3-e][1,2,4]triazine Acyclonucleosides

A series of new pyrazolo[4,3-e][1,2,4]triazine acyclonucleosides 2–5 and 8 were prepared and evaluated for their anticancer activity against human cancer cell lines (MCF-7, K-562) and CDK2/E, as well as Abl protein kinases inhibitors. Lipophilicity of the compounds was determined using C-18 and immobilized artificial membrane (IAM) chromatography. In order to confirm the molecular structures and synthesis pathway of new acyclonucleosides, X-ray analysis was performed for model compound 3. Theoretical calculations at the DFT/B3LYP/6-311++G(d,p) level were used for the characterization of electronic structures of 1–8. The potential antiviral activity of acyclonucleosides 2–8 was tested in silico using molecular docking method.

Identification of novel selective Mtb-DHFR inhibitors as antitubercular agents through structure-based computational techniques

Inhibition of dihydrofolate reductase from Mycobacterium tuberculosis-dihydrofolate reductase (Mtb-DHFR) has emerged as a promising approach for the treatment of tuberculosis. To identify novel Mtb-DHFR inhibitors, structure-based virtual screening (SBVS) of the Molecular Diversity Preservation International (MolMall) database was performed using Glide against the Mtb-DHFR and h-DHFR enzymes. On the basis of SBVS, receptor fit, drug-like filters, and ADMET (absorption, distribution, metabolism, excretion, and toxicity) analysis, 16 hits were selected and tested for their antitubercular activity against the H₃₇ R_V strain of M. tuberculosis. Five compounds showed promising activity with compounds 11436 and 15275 as the most potent hits with IC₅₀ values of 0.65 and 12.51 μM, respectively, against the H₃₇ R_V strain of M. tuberculosis. The two compounds were further tested in the Mtb-DHFR and h-DHFR enzymatic assay for selectivity and were found to be three- to eight-fold selective towards Mtb-DHFR over h-DHFR with minimum inhibitory concentration values of 5.50, 73.89 µM and 42.00, 263.00 µM, respectively. In silico simulation studies also supported the stability of the protein-ligand complex formation. The present study demonstrates the successful utilization of in silico SBVS tools for the identification of novel and potential Mtb-DHFR inhibitors and compound 11436 ((2,4-dihydroxyphenyl)(3,4,5-trihydroxyphenyl)methanone) as a potential lead for the development of novel Mtb-DHFR inhibitors.

A Chemical Approach to Overcome Tyrosine Kinase Inhibitors Resistance: Learning from Chronic Myeloid Leukemia

BACKGROUND

The possibilities of treatment for oncological diseases are growing enormously in the last decades. Unfortunately, these developments have led to the onset of resistances with regards to the new treatments. This is particularly true if we face with the therapeutic field of Tyrosine Kinase Inhibitors (TKIs). This review gives an overview of possible TKI resistances that can occur during the treatment of an oncologic diesease and available strategies that can be adopted, taking cues from a successful example such as CML.

METHODS

We performed a literature search for peer-reviewed articles using different databases, such as PubMed and Scopus, and exploiting different keywords and different logical operators.

RESULTS

68 papers were included in the review. Twenty-four papers give an overview of the causes of TKIs resistances in the wide oncologic field. The remaining papers deal CML, deeply analysing the TKIs Resistances present in this pathology and the strategies adopted to overcome them.

CONCLUSION

The aim of this review is to furnish an overview and a methodological guideline for the approach and the overcoming of TKIs Resistances.

Evaluation of oxidative stress responses in human circulating blood cells after imatinib mesylate treatment - Implications to its mechanism of action

Imatinib mesylate (IM) is the first developed protein kinase inhibitor and recently it has topped consumption rates among targeted and total anticancer drugs. Although there are indications that IM possesses cyto/genotoxic activities against normal non-target cells as well, there is a lack of information regarding the underlying mechanism involved in those actions. Therefore, we aimed to evaluate the response of human circulating blood cells towards oxidative stress after IM treatment (0.0001–10 µg/mL) in vitro. Based on the results, IM had an influence on all of the oxidative stress parameters tested. Lower concentrations of IM induced an increase of glutathione level, following its decrease at higher IM concentrations indicating impairment in oxidative stress defences. Concomitant to a glutathione decrease, an increase of malondialdehyde and protein carbonyls level was observed indicating oxidative damage of lipids and proteins. The observed effects overlapped with the observed formation of oxidative base damage detected by formamidopyrimidine-DNA glycosylase modified-comet assay indicating that IM managed to induce oxidative DNA damage. Our results provide novelty in their mechanistic approach to IM-induced toxicity in non-target cells and suggest that IM can affect blood cells and induce oxidative stress.

Synthesis, Biological Activities and Docking Studies of Novel 4-(Arylaminomethyl)benzamide Derivatives as Potential Tyrosine Kinase Inhibitors

A number of new compounds containing the 4-(aminomethyl)benzamide fragment as a linker were designed and synthesized, and their biological activities were evaluated as potential anticancer agents. The cytotoxicity activity of the designed compounds was studied in two hematological and five solid cell lines in comparison with the reference drugs. Targeted structures against eight receptor tyrosine kinases including EGFR, HER-2, HER-4, IGF1R, InsR, KDR, PDGFRa, and PDGFRb were investigated. The majority of the compounds showed a potent inhibitory activity against the tested kinases. The analogues 11 and 13 with the (trifluoromethyl)benzene ring in the amide or amine moiety of the molecule were proven to be highly potent against EGFR, with 91% and 92% inhibition at 10 nM, respectively. The docking of synthesized target compounds for nine protein kinases contained in the Protein Data Bank (PDB) database was carried out. The molecular modeling results for analogue 10 showed that the use of the 4-(aminomethyl)benzamide as a flexible linker leads to a favorable overall geometry of the molecule, which allows one to bypass the bulk isoleucine residue and provides the necessary binding to the active center of the T315I-mutant Abl (PDB: 3QRJ).

Possible Role and Therapeutic Target of PDGF-D Signalling in Colorectal Cancer

Platelet-derived growth factor D (PDGF-D) has been shown to mediate cellular processes of importance in cancer progression. This study aimed to investigate the expression and putative involvement of PDGF-D signaling in colorectal carcinogenesis. PDGF-D was expressed in vascular endothelial cells in tumor and normal tissues. PDGF-D stimulation of cells altered genes of importance in carcinogenic processes. In addition, PDGF-D increased the proliferation rate while imatinib inhibited these effects. PDGF-D and its PDGF receptor beta (PDGFR-β) are expressed in colorectal cancer and blockage of PDGF-D/PDGFR-β signaling using tyrosine kinase inhibitors, such as imatinib, might be important in inhibiting tumor-promoting actions.

The ABL kinase inhibitor imatinib causes phenotypic changes and lethality in adult Schistosoma japonicum

Schistosomiasis caused by different species of schistosome parasites is one of the most debilitating helminthic diseases of humans worldwide. For decades, chemotherapy is the main method of controlling schistosomiasis. However, the fear of drug resistance has motivated the search for alternatives. It has been demonstrated that the ABL kinase inhibitor imatinib affected the development and survival of Schistosoma mansoni in vitro; however, there is still lack of information on whether imatinib also affects other schistosome species such as Schistosoma japonicum. In the present study, the anti-schistosomal potency of imatinib on adult S. japonicum was investigated in vitro, and the results showed that imatinib had a significant impact on various physiological processes of S. japonicum adult worms. Besides its negative effects on worm motility, pairing stability, and gonad development, imatinib caused pathological changes in the gastrodermis as well as the death of the parasite. Our findings suggest that imatinib is an intriguing candidate for further development as an option to fight S. japonicum.

Antiproliferative effects of imatinib mesylate on ZR‑75‑1 and MDA‑MB‑231 cell lines via PDGFR‑β, PDGF‑BB, c‑Kit and SCF expression

Imatinib mesylate is an anti‑neoplastic targeted chemotherapeutic agent, which can inhibit tyrosine kinase receptors, including BCR‑ABL, platelet‑derived growth factor receptors (PDGFRs) and c‑Kit. Cellular processes, including differentiation, proliferation and survival are regulated by these receptors. The present study aimed to evaluate the antiproliferative effects of imatinib mesylate, and its effects on apoptotic induction and cell cycle arrest in breast cancer cell lines. In addition, the study aimed to determine whether the effects of this drug were associated with the mRNA and protein expression levels of PDGFR‑β, c‑Kit, and their corresponding ligands PDGF‑BB and stem cell factor (SCF), which may potentially modulate cell survival and proliferation. To assess the antiproliferative effects of imatinib mesylate, an MTS assay was conducted following treatment of cells with 2‑10 µM imatinib mesylate for 96, 120 and 144 h; accordingly the half maximal inhibitory concentration of imatinib mesylate was calculated for each cell line. In addition, the proapoptotic effects and cytostatic activity of imatinib mesylate were investigated. To evaluate the expression of imatinib‑targeted genes, PDGFR‑β, c‑Kit, PDGF‑BB and SCF, under imatinib mesylate treatment, mRNA expression was detected using semi‑quantitative polymerase chain reaction and protein expression was detected by western blot analysis in ZR‑75‑1 and MDA‑MB‑231 breast carcinoma cell lines. Treatment with imatinib mesylate suppressed cell proliferation, which was accompanied by apoptotic induction and cell cycle arrest in the investigated cell lines. In addition, PDGFR‑β, PDGF‑BB, c‑Kit and SCF were expressed in both breast carcinoma cell lines; PDGFR‑β and c‑Kit, as imatinib targets, were downregulated in response to imatinib mesylate treatment. The present results revealed that at least two potential targets of imatinib mesylate were expressed in the two breast carcinoma cell lines studied. In conclusion, the antiproliferative, cytostatic and proapoptotic effects of imatinib mesylate may be the result of a reduction in the expression of c‑Kit and PDGFR tyrosine kinase receptors, thus resulting in suppression of the corresponding ligand PDGF‑BB. Therefore, imatinib mesylate may be considered a promising target therapy for the future treatment of breast cancer.

Small-Molecule Screens: A Gateway to Cancer Therapeutic Agents with Case Studies of Food and Drug Administration-Approved Drugs

High-throughput screening (HTS) of small-molecule libraries accelerates the discovery of chemical leads to serve as starting points for probe or therapeutic development. With this approach, thousands of unique small molecules, representing a diverse chemical space, can be rapidly evaluated by biologically and physiologically relevant assays. The origins of numerous United States Food and Drug Administration-approved cancer drugs are linked to HTS, which emphasizes the value in this methodology. The National Institutes of Health Molecular Libraries Program made HTS accessible to the public sector, enabling the development of chemical probes and drug-repurposing initiatives. In this work, the impact of HTS in the field of oncology is considered among both private and public sectors. Examples are given for the discovery and development of approved cancer drugs. The importance of target validation is discussed, and common assay approaches for screening are reviewed. A rigorous examination of the PubChem database demonstrates that public screening centers are contributing to early-stage drug discovery in oncology by focusing on new targets and developing chemical probes. Several case studies highlight the value of different screening strategies and the potential for drug repurposing.

Challenges and Recent Advances in Medulloblastoma Therapy

Medulloblastoma (MB) is the most common childhood brain tumor, which occurs in the posterior fossa. MB tumors are highly heterogeneous and have diverse genetic make-ups, with differential microRNA (miRNA) expression profiles and variable prognoses. MB can be classified into four subgroups, each with different origins, pathogenesis, and potential therapeutic targets. miRNA and small-molecule targeted therapies have emerged as a potential new therapeutic paradigm in MB treatment. However, the development of chemoresistance due to surviving cancer stem cells and dysregulation of miRNAs remains a challenge. Combination therapies using multiple drugs and miRNAs could be effective approaches. In this review we discuss various MB subtypes, barriers, and novel therapeutic options which may be less toxic than current standard treatments.

SCF-KIT signaling induces endothelin-3 synthesis and secretion: Thereby activates and regulates endothelin-B-receptor for generating temporally- and spatially-precise nitric oxide to modulate SCF- and or KIT-expressing cell functions

We demonstrate that SCF-KIT signaling induces synthesis and secretion of endothelin-3 (ET3) in human umbilical vein endothelial cells and melanoma cells in vitro, gastrointestinal stromal tumors, human sun-exposed skin, and myenteric plexus of human colon post-fasting in vivo. This is the first report of a physiological mechanism of ET3 induction. Integrating our finding with supporting data from literature leads us to discover a previously unreported pathway of nitric oxide (NO) generation derived from physiological endothelial NO synthase (eNOS) or neuronal NOS (nNOS) activation (referred to as the KIT-ET3-NO pathway). It involves: (1) SCF-expressing cells communicate with neighboring KIT-expressing cells directly or indirectly (cleaved soluble SCF). (2) SCF-KIT signaling induces timely local ET3 synthesis and secretion. (3) ET3 binds to ETBR on both sides of intercellular space. (4) ET3-binding-initiated-ETBR activation increases cytosolic Ca²⁺, activates cell-specific eNOS or nNOS. (5) Temporally- and spatially-precise NO generation. NO diffuses into neighboring cells, thus acts in both SCF- and KIT-expressing cells. (6) NO modulates diverse cell-specific functions by NO/cGMP pathway, controlling transcriptional factors, or other mechanisms. We demonstrate the critical physiological role of the KIT-ET3-NO pathway in fulfilling high demand (exceeding basal level) of endothelium-dependent NO generation for coping with atherosclerosis, pregnancy, and aging. The KIT-ET3-NO pathway most likely also play critical roles in other cell functions that involve dual requirement of SCF-KIT signaling and NO. New strategies (e.g. enhancing the KIT-ET3-NO pathway) to harness the benefit of endogenous eNOS and nNOS activation and precise NO generation for correcting pathophysiology and restoring functions warrant investigation.