Molecular Principle of Topotecan Resistance by Topoisomerase I Mutations through Molecular Modeling Approaches

In vitro evolution and whole genome analysis to study chemotherapy drug resistance in haploid human cells

In vitro evolution and whole genome analysis has proven to be a powerful method for studying the mechanism of action of small molecules in many haploid microbes but has generally not been applied to human cell lines in part because their diploid state complicates the identification of variants that confer drug resistance. To determine if haploid human cells could be used in MOA studies, we evolved resistance to five different anticancer drugs (doxorubicin, gemcitabine, etoposide, topotecan, and paclitaxel) using a near-haploid cell line (HAP1) and then analyzed the genomes of the drug resistant clones, developing a bioinformatic pipeline that involved filtering for high frequency alleles predicted to change protein sequence, or alleles which appeared in the same gene for multiple independent selections with the same compound. Applying the filter to sequences from 28 drug resistant clones identified a set of 21 genes which was strongly enriched for known resistance genes or known drug targets (TOP1, TOP2A, DCK, WDR33, SLCO3A1). In addition, some lines carried structural variants that encompassed additional known resistance genes (ABCB1, WWOX and RRM1). Gene expression knockdown and knockout experiments of 10 validation targets showed a high degree of specificity and accuracy in our calls and demonstrates that the same drug resistance mechanisms found in diverse clinical samples can be evolved, discovered and studied in an isogenic background.

Dissecting the role of ALK double mutations in drug resistance to lorlatinib with in-depth theoretical modeling and analysis

Anaplastic lymphoma kinase (ALK) is implicated in the genesis of multiple malignant tumors. Lorlatinib stands out as the most advanced and effective inhibitor currently used in the clinic for the treatment of ALK-positive non-small cell lung cancer. However, resistance to lorlatinib has inevitably manifested over time, with double/triple mutations of G1202, L1196, L1198, C1156 and I1171 frequently observed in clinical practice, and tumors regrow within a short time after treatment with lorlatinib. Therefore, elucidating the mechanism of resistance to lorlatinib is paramount in paving the way for innovative therapeutic strategies and the development of next-generation drugs. In this study, we leveraged multiple computational methodologies to delve into the resistance mechanisms of three specific double mutations of ALKG1202R/L1196M, ALKG1202R/L1198F and ALKI1171N/L1198F to lorlatinib. We analyzed these mechanisms through qualitative (PCA, DCCM) and quantitative (MM/GBSA, US) kinetic analyses. The qualitative analysis shows that these mutations exert minimal perturbations on the conformational dynamics of the structural domains of ALK. The energetic and structural assessments show that the van der Waals interactions, formed by the conserved residue Leu1256 within the ATP-binding site and the residues Glu1197 and Met1199 in the hinge domain with lorlatinib, play integral roles in the occurrence of drug resistance. Furthermore, the US simulation results elucidate that the pathways through which lorlatinib dissociates vary across mutant systems, and the distinct environments during the dissociation process culminate in diverse resistance mechanisms. Collectively, these insights provide important clues for the design of novel inhibitors to combat resistance.

Synergy between human DNA ligase I and topoisomerase 1 unveils new therapeutic strategy for the management of colorectal cancer

DNA topoisomerase 1 (Topo 1) is a pivotal player in various DNA processes, including replication, repair, and transcription. It serves as a target for anticancer drugs like camptothecin and its derivatives (Topotecan and SN-38/Irinotecan). However, the emergence of drug resistance and the associated adverse effects, such as alopecia, anemia, dyspnea, fever, chills, and painful or difficult urination, pose significant challenges in Topo 1-targeted therapy, necessitating urgent attention. Human DNA Ligase 1 (hLig I), recognized primarily for its role in DNA replication and repair of DNA breaks, intriguingly exhibits a DNA relaxation activity akin to Topo 1. This raised the hypothesis that hLig I might compensate for Topo 1 inhibition, contributing to resistance against Topo 1 inhibitors. To explore this hypothesis, we assessed the efficacy of hLig I inhibition alone and in combination with Topo 1 in cancer cells. As anticipated, the overexpression of hLig I was observed after Topo 1 inhibition in colorectal cancer cells, affirming our hypothesis. Previously identified as an inhibitor of hLig I's DNA relaxation activity, compound 27 (C 27), when combined with Topotecan, demonstrated a synergistic antiproliferative effect on colorectal cancer cells. Notably, cells with downregulated hLig I (via siRNA, inhibitors, or genetic manipulation) exhibited significantly heightened sensitivity to Topotecan. This observation strongly supports the concept that hLig I contribute to resistance against clinically relevant Topo 1 inhibitors in colorectal cancers. In conclusion, our findings offer evidence for the synergistic impact of combining hLig I inhibitors with Topotecan in the treatment of colorectal cancers, providing a promising strategy to overcome resistance to Topo 1 inhibitors.Communicated by Ramaswamy H. Sarma.

Applying molecular docking to pesticides

Pesticide creation is related to the development of sustainable agricultural and ecological safety, and molecular docking technology can effectively help in pesticide innovation. This paper introduces the basic theory behind molecular docking, pesticide databases, and docking software. It also summarizes the application of molecular docking in the pesticide field, including the virtual screening of lead compounds, detection of pesticides and their metabolites in the environment, reverse screening of pesticide targets, and the study of resistance mechanisms. Finally, problems with the use of molecular docking technology in pesticide creation are discussed, and prospects for the future use of molecular docking technology in new pesticide development are discussed. © 2023 Society of Chemical Industry.

Towards establishment of a plant-based model to assess the novel anti-cancerous lead molecule(s): An in silico, in vivo and in vitro assessment of some potential anti-cancerous drugs on Lathyrus sativus L

The drug development process is one of the important aspects of medical biology. The classical lead identification strategy in the way of drug development based on animal cell is time-consuming, expensive and involving ethical issues. The following study aims to develop a novel plant-based screening of drugs. Study shows the efficacy of certain anti-cancerous drugs (Pemetrexed, 5-Fluorouracil, Methotrexate, Topotecan and Etoposide) on a plant-based (Lathyrus sativus L.) system. Two important characteristics of cancer cells were observed in the colchicine-treated polyploid cell and the callus, where the chromosome numbers were unusual and the division of cells were uncontrolled respectively. With increasing concentration, the drugs significantly reduced the mitotic index, ploidy level and callus growth. Increasing Pemetrexed concentration decreased the plant DHFR activity. A decrease in total RNA content was observed in 5-FU and Methotrexate with increasing concentrations of the drugs. Etoposide and Topotecan inhibited plant topoisomerase II and topoisomerase I activities, which was justified through plasmid nicking and comet assay, respectively. Molecular and biochemical study revealed similar results to the animal system. The in silico study had been done, and the structural similarity of drug binding domains of L. sativus and human beings had also been established. The binding site of the selected drugs to the domains of plant target proteins was also determined. Experimental results are significant in terms of the efficacy of known anti-cancerous drugs on the plant-based system. The proposed assay system is a cost-effective, convenient and less time-consuming process for primary screening of anti-cancerous lead molecules.

Mechanism of action of non-camptothecin inhibitor Genz-644282 in topoisomerase I inhibition

Topoisomerase I (TOP1) controls the topological state of DNA during DNA replication, and its dysfunction due to treatment with an inhibitor, such as camptothecin (CPT), causes replication arrest and cell death. Although CPT has excellent cytotoxicity, it has the disadvantage of instability under physiological conditions. Therefore, new types of TOP1 inhibitor have attracted particular attention. Here, we characterised the effect of a non-camptothecin inhibitor, Genz-644282 (Genz). First, we found that treatment with Genz showed cytotoxicity by introducing double-strand breaks (DSBs), which was suppressed by co-treatment with aphidicolin. Genz-induced DSB formation required the functions of TOP1. Next, we explored the advantages of Genz over CPT and found it was effective against CPT-resistant TOP1 carrying either N722S or N722A mutation. The effect of Genz was also confirmed at the cellular level using a CPT-resistant cell line carrying N722S mutation in the TOP1 gene. Moreover, we found arginine residue 364 plays a crucial role for the binding of Genz. Because tyrosine residue 723 is the active centre for DNA cleavage and re-ligation by TOP1, asparagine residue 722 plays crucial roles in the accessibility of the drug. Here, we discuss the mechanism of action of Genz on TOP1 inhibition.

Probing Allosteric Regulation Mechanism of W7.35 on Agonist-Induced Activity for μOR by Mutation Simulation

The residue located at 15 positions before the most conserved residue in TM7 (7.35 of Ballesteros-Weinstein number) plays important roles in ligand binding and the receptor activity for class A GPCRs. Nevertheless, its regulation mechanism has not been clearly clarified in experiments, and some controversies also exist for its impact on μ-opioid receptors (μOR) bound by agonists. Thus, we chose the μ-opioid receptor (μOR) of class A GPCRs as a representative and utilized a microsecond accelerated molecular dynamics simulation (aMD) coupled with a protein structure network (PSN) to explore the effect of W318^7.35 on its functional activity induced by the agonist endomorphin2 mainly by a comparison of the wild system and its W7.35A mutant. When endomorphin2 binds to the wild-type μOR, TM6 in μOR moves outward to form an open intracellular conformation that is beneficial to accommodating the β-arrestin transducer, rather than the G-protein transducer due to the clash with the α5 helix of G-protein, thus acting as a β-arrestin biased agonist. However, the W318A mutation induces the intracellular part of μOR to form a closed state, which disfavors coupling with either G-protein or β-arrestin. The allosteric pathway analysis further reveals that the binding of endomorphin2 to the wild-type μOR transmits more activation signals to the β-arrestin binding site while the W318A mutation induces more structural signals to transmit to common binding residues of the G protein and β-arrestin. More interestingly, the residue at the 7.35 position regulates the shortest allosteric pathway in indirect ways by influencing the interactions between other ligand-binding residues and endomorphin2. W293^6.48 and F289^6.44 are important for regulating the different activities of μOR induced either by the agonist or by the mutation. Y336^7.53, F343^8.50, and D340^8.47 play crucial roles in activating the β-arrestin biased signal induced by the agonist endomorphin2, while L158^3.43 and V286^6.41 devote important contributions to the change in the activity of endomorphin2 from the β-arrestin biased agonist to the antagonist upon the W318A mutation.

Molecular modeling approaches to address drug-metabolizing enzymes (DMEs) mediated chemoresistance: a review

Resistance against clinically approved anticancer drugs is the main roadblock in cancer treatment. Drug metabolizing enzymes (DMEs) that are capable of metabolizing a variety of xenobiotic get overexpressed in malignant cells, therefore, catalyzing drug inactivation. As evident from the literature reports, the levels of DMEs increase in cancer cells that ultimately lead to drug inactivation followed by drug resistance. To puzzle out this issue, several strategies inclusive of analog designing, prodrug designing, and inhibitor designing have been forged. On that front, the implementation of computational tools can be considered a fascinating approach to address the problem of chemoresistance. Various research groups have adopted different molecular modeling tools for the investigation of DMEs mediated toxicity problems. However, the utilization of these in-silico tools in maneuvering the DME mediated chemoresistance is least considered and yet to be explored. These tools can be employed in the designing of such chemotherapeutic agents that are devoid of the resistance problem. The current review canvasses various molecular modeling approaches that can be implemented to address this issue. Special focus was laid on the development of specific inhibitors of DMEs. Additionally, the strategies to bypass the DMEs mediated drug metabolism were also contemplated in this report that includes analogs and pro-drugs designing. Different strategies discussed in the review will be beneficial in designing novel chemotherapeutic agents that depreciate the resistance problem.

Discovery of novel natural compound inhibitors targeting estrogen receptor α by an integrated virtual screening strategy

Estrogen receptor (ER) is a nuclear hormone receptor and plays an important role in mediating the cellular effects of estrogen. ER can be classified into two receptors: estrogen receptor alpha (ERα) and beta (ERβ), and the former is expressed in 50~80% of breast tumors and has been extensively investigated in breast cancer for decades. Excessive exposure to estrogen can obviously stimulate the growth of breast cancers primarily mediated by ERα, and thus anti-estrogen therapies by small molecules are of concern to clinicians and pharmaceutical industry in the treatment of ERα-positive breast cancers. Although a series of estrogen receptor modulators have been developed, these drugs can lead to resistance and side effects. Therefore, the development of small molecule inhibitors with high target specificity has been intensified. In this pursuit, an integrated computer-aided virtual screening technique, including molecular docking and pharmacophore model screening, was used to screen traditional Chinese medicine (TCM) databases. The compounds with high docking scores and fit values were subjected to ADME (adsorption, distribution, metabolism, excretion) and toxicity prediction, and ten hits were identified as potential inhibitors targeting ERα. Molecular docking was used to investigate the binding modes between ERα and three most potent hits, and molecular dynamic simulations were chosen to explore the stability of these complexes. The rank of the predicted binding free energies evaluated by MM/GBSA is consistent with the docking score. These novel scaffolds discovered in the present study can be used as critical starting point in the drug discovery process for treating ERα-positive breast cancer. Graphical abstract .

Machine Learning Models Combined with Virtual Screening and Molecular Docking to Predict Human Topoisomerase I Inhibitors

In this work, random forest (RF), support vector machine, k-nearest neighbor and C4.5 decision tree, were used to establish classification models for predicting whether an unknown molecule is an inhibitor of human topoisomerase I (Top1) protein. All these models have achieved satisfactory results, with total prediction accuracies from 89.70% to 97.12%. Through comparative analysis, it can be found that the RF model has the best forecasting effect. The parameters were further optimized to generate the best-performing RF model. At the same time, features selection was implemented to choose properties most relevant to the inhibition of Top1 from 189 molecular descriptors through a special RF procedure. Subsequently, a ligand-based virtual screening was performed from the Maybridge database by the optimal RF model and 596 hits were picked out. Then, 67 molecules with relative probability scores over 0.7 were selected based on the screening results. Next, the 67 molecules above were docked to Top1 using AutoDock Vina. Finally, six top-ranked molecules with binding energies less than −10.0 kcal/mol were screened out and a common backbone, which is entirely different from that of existing Top1 inhibitors reported in the literature, was found.

Molecular dynamics investigation on the Asciminib resistance mechanism of I502L and V468F mutations in BCR-ABL

Asciminib, a highly selective non-ATP competitive inhibitor of BCR-ABL, has demonstrated to be a promising drug for patients with chronic myeloid leukemia. It is a pity that two resistant mutations (I502L and V468F) have been found during the clinical trial, which is a challenge for the curative effect of Asciminib. In this study, molecular dynamics simulations and molecular mechanics generalized Born surface area (MM-GB/SA) calculations were performed to investigate the molecular mechanism of Asciminib resistance induced by the two mutants. The obtained results indicate that the mutations have adversely influence on the binding of Asciminib to BCR-ABL, as the nonpolar contributions decline in the two mutants. In addition, I502L mutation causes α-helix I' (αI') to shift away from the helical bundle composed of αE, αF, and αH, making the distance between αI' and Asciminib increased. For V468F mutant, the side chain of Phe468 occupies the bottom of the myristoyl pocket (MP), which drives Asciminib to shift toward the outside of MP. Our results provide the molecular insights of Asciminib resistance mechanism in BCR-ABL mutants, which may help the design of novel inhibitors.

Molecular mechanism of point mutation-induced Monopolar spindle 1 (Mps1/TTK) inhibitor resistance revealed by a comprehensive molecular modeling study

Background

Monopolar spindle 1 (Mps1/TTK) is an apical dual-specificity protein kinase in the spindle assembly checkpoint (SAC) that guarantees accurate segregation of chromosomes during mitosis. High levels of Mps1 are found in various types of human malignancies, such as glioblastoma, osteosarcoma, hepatocellular carcinoma, and breast cancer. Several potent inhibitors of Mps1 exist, and exhibit promising activity in many cell cultures and xenograft models. However, resistance due to point mutations in the kinase domain of Mps1 limits the therapeutic effects of these inhibitors. Understanding the detailed resistance mechanism induced by Mps1 point mutations is therefore vital for the development of novel inhibitors against malignancies.

Methods

In this study, conventional molecular dynamics (MD) simulation and Gaussian accelerated MD (GaMD) simulation were performed to elucidate the resistance mechanisms of Cpd-5, a potent Mps1 inhibitor, induced by the four representative mutations I531M, I598F, C604Y, S611R.

Results

Our results from conventional MD simulation combined with structural analysis and free energy calculation indicated that the four mutations weaken the binding affinity of Cpd-5 and the major variations in structural were the conformational changes of the P-loop, A-loop and αC-helix. Energetic differences of per-residue between the WT system and the mutant systems indicated the mutations may allosterically regulate the conformational ensemble and the major variations were residues of Ile-663 and Gln-683, which located in the key loops of catalytic loop and A-loop, respectively. The large conformational and energetic differences were further supported by the GaMD simulations. Overall, these obtained molecular mechanisms will aid rational design of novel Mps1 inhibitors to combat inhibitor resistance.

Exploring the binding mechanisms of PDE5 with chromeno[2,3-c]pyrrol-9(2H)-one by theoretical approaches

Cyclic nucleotide phosphodiesterase type 5 (PDE5), exclusively specific for the cyclic guanosine monophosphate (cGMP), is an important drug target for the treatment of erectile dysfunction and pulmonary arterial hypertension (PAH). Although many PDE5 inhibitors have been approved, such as sildenafil, vardenafil, tadalafil and so on, extensive studies have reported some side effects, such as vision disturbance and hearing loss as a result of the amino acid sequence and the secondary structural similarity of other PDEs to the catalytic domain of PDE5. In this study, multiple docking strategies, molecular dynamics (MD) simulations, free energy calculations and decomposition were employed to explore the structural determinants of PDE5 with a series of chromeno[2,3-c]pyrrol-9(2H)-one derivatives. First, reliable docking results were obtained using quantum mechanics/molecular mechanics (QM/MM) docking. Then, MD simulations and MM/GBSA free energy calculations were used to explore the dynamic binding process and characterize the binding modes of the inhibitors with different activities. The predicted binding free energies are in good agreement with the experimental data, and the MM/GBSA free energy decomposition analysis sheds light on the importance of hydrogen bonds with Gln817, π-π stacks against Phe820 and hydrophobic residues for the PDE5 binding of the studied inhibitors. The structural and energetic insights obtained here are useful for understanding the molecular mechanism of ligand binding and designing novel potent and selective PDE5 inhibitors with new scaffolds.

Binding mechanism of kinase inhibitors to EGFR and T790M, L858R and L858R/T790M mutants through structural and energetic analysis

Experimental studies have demonstrated that L858R mutation in the EGF receptor (EGFR) confers tumor sensitivity whereas T790M and L858R/T790M mutations cause resistance to tyrosine kinase inhibitors in patients with non-small cell lung cancer. Theoretical studies have been carried out to try to clarify the structural and energetic details linked to acquired resistance to Gefitinib, Erlotinib or Lapatinib, however, some of these studies are contradictory with each other and with experimental reports and did not mention whether the study was performed by considering the inactive or active EGFR states. In this study, we combined structural data and molecular dynamic simulations coupled to a molecular mechanics generalized Born surface area approach to provide insight into the binding mechanism between three FDA-approved drugs (Erlotinib, Gefitinib and Lapatinib) that target the wild-type and T790M, L858R and L858R/T790M mutants of EGFR. Structural analysis showed that the drugs impact differently the conformational space of active and inactive EGFR. Energetic analysis pointed out that some ligands have better affinity for the inactive EGFR than the active EGFR state. Comparative analysis of the molecular recognition of Gefitinib, Erlotinib and Lapatinib provided insight into the drug sensitivity or resistance observed for the three FDA-approved drugs evaluated.

Insight into tetrodotoxin blockade and resistance mechanisms of Nav 1.2 sodium channel by theoretical approaches

Na_v 1.2, a member of voltage-gated sodium channels (Na_v s) that are responsible for the generation and propagation of action potentials along the cell membrane, and play a vital role in the process of information transmission within the nervous system and muscle contraction, is preferentially expressed in the central nervous system. As a potent and selective blocker of Na_v s, tetrodotoxin (TTX) has been extensively studied in biological and chemical sciences, whereas the detailed mechanism by which it blocks nine Na_v 1 channel subtypes remain elusive. Despite the high structural similarity, the TTX metabolite 4,9-anhydro-TTX is 161 times less effective toward the mammalian Na_v 1.2, which puzzled us to ask a question why such a subtle structural variation results in the largely binding affinity difference. In the current work, an integrated computational strategy, including homology modeling, induced fit docking, explicit-solvent MD simulations, and free energy calculations, was employed to investigate the binding mechanism and conformational determinants of TTX analogs. Based on the computational results, the H-bond interactions between C4-OH and C9-OH of TTX and the outer ring carboxylates of the selectivity-filter residues, and the cation-π interaction between the primary amine of guanidinium of TTX and Phe385 determine the difference of their binding affinities. Moreover, the computationally simulations were carried out for the D384N and E945K mutants of hNa_v 1.2-TTX, and the rank of the predicted binding free energies is in accordance with the experimental data. These observations provide a valuable model to design potent and selective neurotoxins of Na_v 1.2 and shed light on the blocking mechanism of TTX to sodium channels.

Importance of protein flexibility on molecular recognition: modeling binding mechanisms of aminopyrazine inhibitors to Nek2

NIMA-related kinase 2 (Nek2) plays a significant role in cell cycle regulation, and overexpression of Nek2 has been observed in several types of carcinoma, suggesting it is a potential target for cancer therapy. In this study, we attempted to gain more insight into the binding mechanisms of a series of aminopyrazine inhibitors of Nek2 through multiple molecular modeling techniques, including molecular docking, molecular dynamics (MD) simulations and free energy calculations. The simulation results showed that the induced fit docking and ensemble docking based on multiple protein structures yield better predictions than conventional rigid receptor docking, highlighting the importance of incorporating receptor flexibility into the accurate predictions of the binding poses and binding affinities of Nek2 inhibitors. Additionally, we observed that the Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) calculations did not show better performance than the docking scoring to rank the binding affinities of the studied inhibitors, suggesting that MM/GBSA is system-dependent and may not be the best choice for the Nek2 systems. Moreover, the detailed information on protein-ligand binding was characterized by the MM/GBSA free energy decomposition, and a number of derivatives with improved docking scores were designed. It is expected that our study can provide valuable information for the future rational design of novel and potent inhibitors of Nek2.

How Does the L884P Mutation Confer Resistance to Type-II Inhibitors of JAK2 Kinase: A Comprehensive Molecular Modeling Study

Janus kinase 2 (JAK2) has been regarded as an essential target for the treatment of myeloproliferative neoplasms (MPNs). BBT594 and CHZ868, Type-II inhibitors of JAK2, illustrate satisfactory efficacy in preclinical MPNs and acute lymphoblastic leukemia (ALL) models. However, the L884P mutation of JAK2 abrogates the suppressive effects of BBT594 and CHZ868. In this study, conventional molecular dynamics (MD) simulations, umbrella sampling (US) simulations and MM/GBSA free energy calculations were employed to explore how the L884P mutation affects the binding of BBT594 and CHZ868 to JAK2 and uncover the resistance mechanism induced by the L884P mutation. The results provided by the US and MD simulations illustrate that the L884P mutation enhances the flexibility of the allosteric pocket and alters their conformations, which amplify the conformational entropy change (−TΔS) and weaken the interactions between the inhibitors and target. Additionally, the structural analyses of BBT594 and CHZ868 in complex with the WT JAK2 illustrate that the drug tail with strong electronegativity and small size located in the allosteric pocket of JAK2 may enhance anti-resistance capability. In summary, our results highlight that both of the changes of the conformational entropies and enthalpies contribute to the L884P-induced resistance in the binding of two Type-II inhibitors into JAK2 kinase.

Substitutions in Spodoptera exigua topoisomerase I modulate its relaxation activity and camptothecin sensitivity

BACKGROUND

Topoisomerase I (Top I) is referred as the cellular target of the camptothecins (CPTs) which are now being explored as potential pesticides for insect control. Three amino acid substitutions, including L530P, A653T and S729T, in Top Is of insects were found in our previous studies. In order to investigate the effect of these three substitutions, a comparative analysis was conducted between the wild-type and mutant Top Is in Spodoptera exigua Hübner.

RESULTS

The optimal salt concentration of A653T and S729T was 150 mm, which is consistent with that of the wild-type Top I, while the mutant L530P showed maximum relaxation activity at a lower KCl concentration (100 mm). The mutated L530P and A653T Top Is showed a higher relaxation efficiency owing to an increased relaxation velocity toward the negatively supercoiled plasmid pBR322 DNA, which rendered L530P and A653T resistant to CPTs, whereas mutant S729T exhibited sensitivity to CPTs as a result of a decreased relaxation activity toward plasmid pBR322 DNA.

CONCLUSIONS

These results suggested that the polymorphism in Top I of insects was related to the biological activity of CPTs, which provided the basic information for reasonable usage of CPTs to control insect pests. © 2016 Society of Chemical Industry.

Theoretical studies on the selective mechanisms of GSK3β and CDK2 by molecular dynamics simulations and free energy calculations

Glycogen synthase kinase 3 (GSK3) is a serine/threonine protein kinase which is widely involved in cell signaling and controls a broad number of cellular functions. GSK3 contains α and β isoforms, and GSK3β has received more attention and becomes an attractive drug target for the treatment of several diseases. The binding pocket of cyclin-dependent kinase 2 (CDK2) shares high sequence identity to that of GSK3β, and therefore, the design of highly selective inhibitors toward GSK3β remains a big challenge. In this study, a computational strategy, which combines molecular docking, molecular dynamics simulations, free energy calculations, and umbrella sampling simulations, was employed to explore the binding mechanisms of two selective inhibitors to GSK3β and CDK2. The simulation results highlighted the key residues critical for GSK3β selectivity. It was observed that although GSK3β and CDK2 share the conserved ATP-binding pockets, some different residues have significant contributions to protein selectivity. This study provides valuable information for understanding the GSK3β-selective binding mechanisms and the rational design of selective GSK3β inhibitors.

Pharmacogenomics of second-line drugs used for treatment of unresponsive or relapsed osteosarcoma patients

Second-line treatment of high-grade osteosarcoma (HGOS) patients is based on different approaches and chemotherapy protocols, which are not yet standardized. Although several drugs have been used in HGOS second-line protocols, none of them has provided fully satisfactory results and the role of rescue chemotherapy is not well defined yet. This article focuses on the drugs that have most frequently been used for second-line treatment of HGOS, highlighting the present knowledge on their mechanisms of action and resistance and on gene polymorphisms with possible impact on treatment sensitivity or toxicity. In the near future, validation of the so far identified candidate genetic biomarkers may constitute the basis for tailoring treatment by taking the patients' genetic background into account.

Topoisomerases: Resistance versus Sensitivity, How Far We Can Go?

DNA topoisomerases are ubiquitously present remarkable molecular machines that help in altering topology of DNA in living cells. The crucial role played by these nucleases during DNA replication, transcription, and recombination vis-à-vis less sequence similarity among different species makes topoisomerases unique and attractive targets for different anticancer and antibacterial drugs. However, druggability of topoisomerases by the existing class of molecules is increasingly becoming questationable due to resistance development predominated by mutations in the corresponding genes. The current scenario facing a decline in the development of new molecules further comprises an important factor that may challenge topoisomerase-targeting therapy. Thus, it is imperative to wisely use the existing inhibitors lest with this rapid rate of losing grip over the target we may not go too far. Furthermore, it is important not only to design new molecules but also to develop new approaches that may avoid obstacles in therapies due to multiple resistance mechanisms. This review provides a succinct account of different classes of topoisomerase inhibitors, focuses on resistance acquired by mutations in topoisomerases, and discusses the various approaches to increase the efficacy of topoisomerase inhibitors. In a later section, we also suggest the possibility of using bisbenzimidazoles along with efflux pump inhibitors for synergistic bactericidal effects.

Computational Study of Anticancer Drug Resistance Caused by 10 Topisomerase I Mutations, Including 7 Camptothecin Analogs and Lucanthone

Although Camptothecin and its analogs as Topoisomerase I poisons can effectively treat cancers, serious drug resistance has been identified for this class of drugs. Recent computational studies have indicated that the mutations near the active binding site of the drug can significantly weaken the drug binding and cause drug resistance. However, only Topotecan and three mutations have been previously analyzed. Here we present a comprehensive binding study of 10 Topoisomerase I mutants (N722S, N722A, D533G, D533N, G503S, G717V, T729A, F361S, G363C, and R364H) and 8 poisons including 7 Camptothecin analogs as well as a new generation Topoisomerase I drug, Lucanthone. Utilizing Glide docking followed by MMGBSA calculations, we determined the binding energy for each complex. We examine the relative binding energy changes with reference to the wild type, which are linked to the degree of drug resistance. On this set of mutant complexes, Topotecan and Camptothecin showed much smaller binding energies than a set of new Camptothecin derivatives (Lurtotecan, SN38, Gimatecan, Exatecan, and Belotecan) currently under clinical trials. We observed that Lucanthone exhibited comparable results to Topotecan and Camptothecin, indicating that it may serve as a promising candidate for future studies as a Topoisomerase I poison. Our docked results on Topotecan were also validated by a set of molecular dynamics simulations. In addition to a good agreement on the MMGBSA binding energy change, our simulation data also shows there is larger conformation fluctuation upon the mutations. These results may be utilized to further advancements of Topoisomerase I drugs that are resistant to mutations.

Molecular principle of the cyclin-dependent kinase selectivity of 4-(thiazol-5-yl)-2-(phenylamino) pyrimidine-5-carbonitrile derivatives revealed by molecular modeling studies

Due to the high sequence identity of the binding pockets of cyclin-dependent kinases (CDKs), designing highly selective inhibitors towards a specific CDK member remains a big challenge.

Revealing the favorable dissociation pathway of type II kinase inhibitors via enhanced sampling simulations and two-end-state calculations

How does a type II inhibitor bind to/unbind from a kinase target is still a confusing question because the small molecule occupies both the ATP pocket and the allosteric pocket of the kinase binding site. Here, by using enhanced sampling simulations (umbrella sampling, US) and two-end-state free energy calculations (MM/GSBA), we systemically studied the dissociation processes of two distinct small molecules escaping from the binding pocket of p38 MAP kinase through the allosteric channel and the ATP channel. The results show that the unbinding pathways along the allosteric channel have much lower PMF depths than those along the ATP channel, suggesting that the allosteric channel is more favorable for the dissociations of the two inhibitors and thereby supporting the general understanding that the largest channel of a target is usually the entry/exit pathway for the binding/dissociation of small molecules. Interestingly, the MM/GBSA approach yielded similar PMF profiles compared with those based on US, a much time consuming approach, indicating that for a general study, such as detecting the important transition state of a ligand binding/unbinding process, MM/GBSA may be a feasible choice.

Exploring resistance mechanisms of HCV NS3/4A protease mutations to MK5172: insight from molecular dynamics simulations and free energy calculations

Mutations at a number of key positions (Ala156, Asp168 and Arg155) of the HCV NS3/4A protease can induce medium to high resistance to MK5172.

Camptothecin sensitizes human hepatoma Hep3B cells to TRAIL-mediated apoptosis via ROS-dependent death receptor 5 upregulation with the involvement of MAPKs

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in various types of malignant cancer cells, but several cancers have acquired potent resistance to TRAIL-induced cell death by unknown mechanisms. Camptothecin (CPT) is a quinolone alkaloid that induces cytotoxicity in a variety of cancer cell lines. However, it is not known whether CPT triggers TRAIL-induced cell death. In this study, we found that combined treatment with subtoxic doses of CPT and TRAIL (CPT-TRAIL) potentially enhanced apoptosis in a caspase-dependent manner. CPT-TRAIL effectively induced the expression of death receptor (DR) 5, which is a specific receptor of TRAIL, and treatment with a chimeric blocking antibody for DR5 reduced CPT-TRAIL-induced cell death, indicating that CPT functionally triggers DR5-mediated cell death in response to TRAIL. CPT-induced generation of reactive oxygen species (ROS) also preceded the upregulation of DR5 in response to TRAIL. The involvement of ROS in DR5 upregulation confirmed that pretreatment with antioxidants, including N-acetyl-L-cysteine and glutathione, significantly inhibits CPT-TRAIL-induced cell death by suppressing DR5 expression. The specific inhibitors of ERK and p38 also decreased CPT-TRAIL-induced cell death by blocking DR5 expression. In conclusion, our results suggest that CPT sensitizes cancer cells to TRAIL-mediated apoptosis via ROS and ERK/p38-dependent DR5 upregulation.

P-loop conformation governed crizotinib resistance in G2032R-mutated ROS1 tyrosine kinase: clues from free energy landscape

Tyrosine kinases are regarded as excellent targets for chemical drug therapy of carcinomas. However, under strong purifying selection, drug resistance usually occurs in the cancer cells within a short term. Many cases of drug resistance have been found to be associated with secondary mutations in drug target, which lead to the attenuated drug-target interactions. For example, recently, an acquired secondary mutation, G2032R, has been detected in the drug target, ROS1 tyrosine kinase, from a crizotinib-resistant patient, who responded poorly to crizotinib within a very short therapeutic term. It was supposed that the mutation was located at the solvent front and might hinder the drug binding. However, a different fact could be uncovered by the simulations reported in this study. Here, free energy surfaces were characterized by the drug-target distance and the phosphate-binding loop (P-loop) conformational change of the crizotinib-ROS1 complex through advanced molecular dynamics techniques, and it was revealed that the more rigid P-loop region in the G2032R-mutated ROS1 was primarily responsible for the crizotinib resistance, which on one hand, impaired the binding of crizotinib directly, and on the other hand, shortened the residence time induced by the flattened free energy surface. Therefore, both of the binding affinity and the drug residence time should be emphasized in rational drug design to overcome the kinase resistance.

Cancers can eventually confer drug resistance to the continued medication. In most cases, mutations occurred in a drug target can attenuate the binding affinity of the drugs. Here, we studied the drug resistance mechanisms of the mutations G2032R in the ROS1 tyrosine kinase in fusion-type NSCLC. It is well known that the phosphate-binding loop (P-loop) plays a vital role in the binding of competitive inhibitors in tyrosine kinases, and numerous mutations have been found occurred around the P-loop, which may affect the binding/unbinding process of a drug. Free energy surfaces were constructed to characterize the impact of the mutation to the binding/unbinding process of a well-known NSCLC drug, crizotinib. Two advanced free energy calculation methods, namely funnel based well-tempered metadynamics and umbrella sampling based absolute binding free energy calculation achieved consistent results with the experimental data, suggesting that the rigid P-loop of the mutated target was mainly responsible for the crizotinib resistance to ROS1 tyrosine kinase.

MD and QM/MM studies on long-chain L-α-hydroxy acid oxidase: substrate binding features and oxidation mechanism

Long-chain L-α-hydroxy acid oxidase (LCHAO) is a flavin mononucleotide (FMN)-dependent oxidase that dehydrogenates l-α-hydroxy acids to keto acids. There were two different mechanisms, named as hydride transfer (HT) mechanism and carbanion (CA) mechanism, respectively, proposed about the catalytic process for the FMN-dependent L-α-hydroxy acid oxidases on the basis of biochemical data. However, crystallographic and kinetic studies could not provide enough evidence to prove one of the mechanisms or eliminate the alternative. In the present studies, theoretical computations were carried out to study the molecular mechanism for LCHAO-catalyzed dehydrogenation of L-lactate. Our molecular dynamics (MD) simulations indicated that L-lactate prefers to bind with LCHAO in a hydride transfer mode rather than a carbanion mode. Quantum mechanics/molecular mechanics (QM/MM) calculations were further carried out to obtain the optimized structures of reactants, transition states, and products at the level of ONIOM-EE (B3LYP/6-311++G(d,p)//B3LYP/6-31G(d,p):AMBER). Quantum chemical studies indicated that LCHAO-catalyzed dehydrogenation of L-lactate would be a stepwise catalytic reaction in a hydride transfer mechanism but not a carbanion mechanism. MD simulations, binding free energy calculations, and QM/MM computations were also implemented on the complex between L-lactate and Y129F mutant LCHAO. By comparing the Y129F mutant system with the wild-type system, it was further confirmed that the key residue Tyr129 in the active site of LCHAO would not affect L-lactate's binding to LCHAO but play an important role on the catalytic reaction process through an H-bond interaction.