Urea derivatives of STI571 as inhibitors of Bcr-Abl and PDGFR kinases

In vivo deposition of poorly soluble drugs

Administered drug molecules, whether dissolved or solubilized, have the potential to precipitate and accumulate as solid forms in tissues and cells within the body. This phase transition can significantly impact the pharmacokinetics of treatment. It is thus crucial to gain an understanding of how drug solubility/permeability, drug formulations and routes of administration affect in vivo behaviors of drug deposition. This review examines literature reports on the drug deposition in tissues and cells of poorly water-soluble drugs, as well as underlying physical mechanisms that lead to precipitation. Our work particularly highlights drug deposition in macrophages and the subcellular fate of precipitated drugs. We also propose a tissue permeability-based classification framework to evaluate precipitation potentials of poorly soluble drugs in major organs and tissues. The impact on pharmacokinetics is further discussed and needs to be considered in developing drug delivery systems. Finally, bioimaging techniques that are used to examine aggregated states and the intracellular trafficking of absorbed drugs are summarized.

Transporter-Mediated Cellular Distribution of Tyrosine Kinase Inhibitors as a Potential Resistance Mechanism in Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) is a hematologic neoplasm characterized by the expression of the BCR::ABL1 oncoprotein, a constitutively active tyrosine kinase, resulting in uncontrolled growth and proliferation of cells in the myeloid lineage. Targeted therapy using tyrosine kinase inhibitors (TKIs) such as imatinib, nilotinib, dasatinib, bosutinib, ponatinib and asciminib has drastically improved the life expectancy of CML patients. However, treatment resistance occurs in 10-20% of CML patients, which is a multifactorial problem that is only partially clarified by the presence of TKI inactivating BCR::ABL1 mutations. It may also be a consequence of a reduction in cytosolic TKI concentrations in the target cells due to transporter-mediated cellular distribution. This review focuses on drug-transporting proteins in stem cells and progenitor cells involved in the distribution of TKIs approved for the treatment of CML. Special attention will be given to ATP-binding cassette transporters expressed in lysosomes, which may facilitate the extracytosolic sequestration of these compounds.

Synthesis and biological evaluation of novel aromatic amide derivatives as potential BCR-ABL inhibitors

BCR-ABL1 kinase is a key driver of the pathophysiology of chronic myeloid leukemia (CML). Current treatments need to broaden the chemical diversity of BCR-ABL1 kinase inhibitors to overcome drug resistance. We designed and synthesized a series of aromatic amide derivatives based on several generations of BCR-ABL1 kinase inhibitors. Biological studies showed that compared with Imatinib, these compounds showed significant proliferation inhibitory activities of HL-60 and K562 in cell activity assay. Compounds 4g and 4j exhibited significant anti-tumor activity against the K562 cells with IC₅₀ values of 6.03 ± 0.49 μM and 5.66 ± 2.06 μM respectively. Compounds 4g and 4j, as potential BCR-ABL1 inhibitors, inhibit the phosphorylation of ABL1 and CRKL in a dose-dependent manner. Therefore, compounds 4g and 4j can be used as a starting point for further optimization.

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.

3D-QSAR Assisted Design of Novel 7-Deazapurine Derivatives as TNNI3K Kinase Inhibitors Using Molecular Docking and Molecular Dynamics Simulation

Background:

Cardiac troponin I-interacting kinase (TNNI3K) is a cardiac-specific kinase that belongs to MAPKKK family. It is a dual-function kinase with tyrosine and serine/threonine kinase activity. Over-expression of TNNI3K results in various cardiovascular diseases such as cardiomyopathy, ischemia/reperfusion injury, heart failure, etc. Since, it is a cardiac-specific kinase and expressed only in heart tissue, it is an ideal molecular target to treat cardiac diseases. The main objective of the work is to study and understand the structure-activity relationship of the reported deazapurine derivatives and to use the 3D-QSAR and docking results to design potent and novel TNNI3K inhibitors of this series.

Methods:

In the present study, we have used molecular docking 3D QSAR, and molecular dynamics simulation to understand the structure-activity correlation of reported TNNI3K inhibitors and to design novel compounds of deazapurine derivatives with increased activity.

Results:

Both CoMFA (q2=0.669, NOC=5, r2=0.944) and CoMSIA (q2=0.783, NOC=5, r2=0.965) have resulted in satisfactory models. The models were validated using external test set, Leave-out- Five, bootstrapping, progressive scrambling, and rm2 metrics calculations. The validation procedures showed the developed models were robust and reliable. The docking results and the contour maps analysis helped in the better understanding of the structure-activity relationship.

Conclusion:

This is the first report on 3D-QSAR modeling studies of TNNI3K inhibitors. Both docking and MD results were consistent and showed good correlation with the previous experimental data. Based on the information obtained from contour maps, 31 novel TNNI3K inhibitors were designed. These designed compounds showed higher activity than the existing dataset compounds.

A Structural View on Medicinal Chemistry Strategies against Drug Resistance

The natural phenomenon of drug resistance is a widespread issue that hampers the performance of drugs in many major clinical indications. Antibacterial and antifungal drugs are affected, as well as compounds for the treatment of cancer, viral infections, or parasitic diseases. Despite the very diverse set of biological targets and organisms involved in the development of drug resistance, the underlying molecular mechanisms have been identified to understand the emergence of resistance and to overcome this detrimental process. Detailed structural information on the root causes for drug resistance is nowadays frequently available, so next-generation drugs can be designed that are anticipated to suffer less from resistance. This knowledge-based approach is essential for fighting the inevitable occurrence of drug resistance.

Synthesis, anticancer activity, toxicity evaluation and molecular docking studies of novel phenylaminopyrimidine-(thio)urea hybrids as potential kinase inhibitors

Thirty-two novel urea/thiourea compounds as potential kinase inhibitor were designed, synthesized and evaluated for their cytotoxic activity on breast (MCF7), colon (HCT116) and liver (Huh7) cancer cell lines. Compounds 10, 19 and 30 possessing anticancer activity with IC₅₀ values of 0.9, 0.8 and 1.6μM respectively on Huh7 cells were selected for further studies. These hit compounds were tested against liver carcinoma panel. Real time cell electronic sensing assay was used to evaluate the effects of the compounds 10, 19 and 30 on the growth pattern of liver cancer cells. Apoptotic cell death and cell cycle analysis upon treatment of liver carcinoma cells with hit compounds were determined. A significant apoptotic cell death was detected upon treatment of Huh7 and Mahlavu cells with compound 30 after 48 h of treatment. Additionally, compound 10 caused cell cycle arrest at G0/G1 phase. Mutagenicity of hit compounds was evaluated. Assertively, these compounds were not found to be mutagenic on Salmonella typhimurium strains TA98 and TA100. To understand the binding modes of the synthesized compounds, molecular docking studies were performed using the crystal data of VEGFR and Src-kinase enzymes in correlation with anticancer activities.

PI3K isoform inhibition associated with anti Bcr-Abl drugs shows in vitro increased anti-leukemic activity in Philadelphia chromosome-positive B-acute lymphoblastic leukemia cell lines

B-acute lymphoblastic leukemia (B-ALL) is a malignant disorder characterized by the abnormal proliferation of B-cell progenitors. Philadelphia chromosome-positive (Ph+) B-ALL is a subtype that expresses the Bcr-Abl fusion protein which represents a negative prognostic factor. Constitutive activation of the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) network is a common feature of B-ALL, influencing cell growth and survival. In the present study, we aimed to investigate the efficacy of PI3K isoform inhibition in B-ALL cell lines harboring the Bcr-Abl fusion protein.We studied the effects of anti Bcr-Abl drugs Imatinib, Nilotinib and GZD824 associated with PI3K isoform inhibitors. We used a panel of six compounds which specifically target PI3K isoforms including the pan-PI3K inhibitor ZSTK474, p110α BYL719 inhibitor and the dual p110γ/p110δ inhibitor IPI145. The effects of single drugs and of several drug combinations were analyzed to assess cytotoxicity by MTS assays, apoptosis and autophagy by flow cytometry and Western blot, as well as the phosphorylation status of the pathway.ZSTK474, BYL719 and IPI145 administered in combination with imatinib, nilotinib and GZD824 for 48 h, decreased cell viability, induced apoptosis and autophagy in a marked synergistic manner.These findings suggest that selected PI3K isoform inhibitors used in combination with anti Bcr-Abl drugs may be an attractive novel therapeutic intervention in Ph+ B-ALL.

Nilotinib

With imatinib still being linked to the breakthrough in CML therapy and probably being the most prescribed drug, second-generation TKIs are increasingly gaining importance. Showing higher response rates while not leading to more adverse events, nilotinib has become an attractive option in the first-line treatment of chronic-phase chronic myeloid leukemia. By reaching deep and long-lasting molecular remissions, discontinuation of TKIs is becoming one of the central topics of future CML therapy. Stopping nilotinib seems safe and provides a stable remission in about half of the eligible patients, though long-term data are still missing.

Recent developments in chemical reactivity of N,N-dimethylenamino ketones as synthons for various heterocycles

This review demonstrates the high number of synthetic applications of enaminones in the preparation of acyclic, carbocyclic, heterocyclic and fused heterocyclic compounds.

Opening the door to the development of novel Abl kinase inhibitors

The discovery of the importance of kinase activity and its relationship to the emergence and proliferation of cancer cells, due to changes in normal physiology, opened a remarkable pathway for the treatment of chronic myelogenous leukemia through intense search of drug candidates. Six Abl kinase inhibitors have received the US FDA approval as chronic myelogenous leukemia treatment, and continuous efforts in obtaining new, more effective and selective molecules are being carried out. Herein we discuss the mechanisms of Abl inhibition, structural features and ligand/protein interactions that are important for the design of new Abl kinase inhibitors. This review provides a broad overview of binding mode predictions, through molecular docking, which can be an approach to discover novel Abl kinase inhibitors.

ABCB1 Overexpression Is a Key Initiator of Resistance to Tyrosine Kinase Inhibitors in CML Cell Lines

The tyrosine kinase inhibitor (TKI) imatinib has resulted in excellent responses in the majority of Chronic Myeloid Leukaemia (CML) patients; however, resistance is observed in 20–30% of patients. More recently, resistance to the second generation TKIs, nilotinib and dasatinib, has also been observed albeit at a lower incidence. ABCB1 has previously been implicated in TKI export and its overexpression linked to TKI resistance. In this study the dynamics of nilotinib resistance was studied in CML cell lines with particular focus on ABCB1 expression levels during development of resistance. Results revealed ABCB1 overexpression is likely an important initiator of nilotinib resistance in vitro. ABCB1 overexpression was also observed in cell lines as an intermediate step during development of resistance to imatinib and dasatinib in vitro. We conclude that ABCB1 overexpression may provide an initial platform to facilitate development of additional mechanisms for resistance to TKIs. This provides a rationale for investigating this phenomenon in patients undergoing TKI therapy.

Lead Discovery of Type II BRAF V600E Inhibitors Targeting the Structurally Validated DFG-Out Conformation Based upon Selected Fragments

The success of the first approved kinase inhibitor imatinib has spurred great interest in the development of type II inhibitors targeting the inactive DFG-out conformation, wherein the Phe of the DFG motif at the start of the activation loop points into the ATP binding site. Nevertheless, kinase inhibitors launched so far are heavily biased toward type I inhibitors targeting the active DFG-in conformation, wherein the Phe of the DFG motif flips by approximately 180° relative to the inactive conformation, resulting in Phe and Asp swapping their positions. Data recently obtained with structurally validated type II inhibitors supported the conclusion that type II inhibitors are more selective than type I inhibitors. In our type II BRAF V600E inhibitor lead discovery effort, we identified phenylaminopyrimidine (PAP) and unsymmetrically disubstituted urea as two fragments that are frequently presented in FDA-approved protein kinase inhibitors. We therefore defined PAP and unsymmetrically disubstituted urea as privileged fragments for kinase drug discovery. A pharmacophore for type II inhibitors, 4-phenylaminopyrimidine urea (4-PAPU), was assembled based upon these privileged fragments. Lead compound SI-046 with BRAF V600E inhibitory activity comparable to the template compound sorafenib was in turn obtained through preliminary structure-activity relationship (SAR) study. Molecular docking suggested that SI-046 is a bona fide type II kinase inhibitor binding to the structurally validated "classical DFG-out" conformation of BRAF V600E. Our privileged fragments-based approach was shown to efficiently deliver a bona fide type II kinase inhibitor lead. In essence, the theme of this article is to showcase the strategy and rationale of our approach.

An optimized approach in the synthesis of imatinib intermediates and analogues

We revisited the classical synthetic procedure for imatinib synthesis providing an improved and optimized approach in the preparation of a series of new imatinib analogues.

Current aspects in resistance against tyrosine kinase inhibitors in chronic myelogenous leukemia

Resistance against tyrosine kinase inhibitors (TKIs) represents a relevant clinical problem in treatment of chronic myelogenous leukemia (CML). On the basis of their activity against the spectrum of BCR-ABL mutations that have shown to be the most prominent mechanism of resistance to imatinib, new TKIs have been classified as second generation (such as nilotinib, dasatinib and bosutinib) or third generation (also cover- ing T315I such as ponatinib) TKIs. However, mutations in BCR-ABL only account for about half of the cases of treatment failure under TKI and other mechanisms either rendering the leukemic cells still dependent of BCR-ABL activity or supporting oncogenic properties of the leukemic cells independent of BCR-ABL signaling have been identified. A detailed understanding of the different underlying resistance mechanisms will be the prerequisite to eventually overcome clinical resistance and for the successful use of tailored combinations of targeted inhibitors in the future.

Nilotinib

Targeted therapy of Philadelphia chromosome-positive chronic myeloid leukemia (CML) using the tyrosine kinase inhibitor imatinib mesylate has been one of the most striking achievements in modern cancer medicine. However, while imatinib can establish long-term remission in many cases, resistance to or intolerance of imatinib is eventually experienced by a substantial number of patients. Subsequent advances have led to the development of novel tyrosine kinase inhibitors (TKIs). One such inhibitor, nilotinib, was rationally designed to increase its affinity and specificity for the oncogenic tyrosine kinase Bcr-Abl compared with imatinib and has been shown to be effective after imatinib failure. Recently, nilotinib has been shown to be more effective when used as first-line therapy of chronic phase CML.

Inhibition of PI3K/mTOR overcomes nilotinib resistance in BCR-ABL1 positive leukemia cells through translational down-regulation of MDM2

Chronic myeloid leukemia (CML) is a cytogenetic disorder resulting from formation of the Philadelphia chromosome (Ph), that is, the t(9;22) chromosomal translocation and the formation of the BCR-ABL1 fusion protein. Tyrosine kinase inhibitors (TKI), such as imatinib and nilotinib, have emerged as leading compounds with which to treat CML. t(9;22) is not restricted to CML, 20-30% of acute lymphoblastic leukemia (ALL) cases also carry the Ph. However, TKIs are not as effective in the treatment of Ph+ ALL as in CML. In this study, the Ph+ cell lines JURL-MK2 and SUP-B15 were used to investigate TKI resistance mechanisms and the sensitization of Ph+ tumor cells to TKI treatment. The annexin V/PI (propidium iodide) assay revealed that nilotinib induced apoptosis in JURL-MK2 cells, but not in SUP-B15 cells. Since there was no mutation in the tyrosine kinase domain of BCR-ABL1 in cell line SUP-B15, the cells were not generally unresponsive to TKI, as evidenced by dephosphorylation of the BCR-ABL1 downstream targets, Crk-like protein (CrkL) and Grb-associated binder-2 (GAB2). Resistance to apoptosis after nilotinib treatment was accompanied by the constitutive and nilotinib unresponsive activation of the phosphoinositide 3-kinase (PI3K) pathway. Treatment of SUP-B15 cells with the dual PI3K/mammalian target of rapamycin (mTOR) inhibitor BEZ235 alone induced apoptosis in a low percentage of cells, while combining nilotinib and BEZ235 led to a synergistic effect. The main role of PI3K/mTOR inhibitor BEZ235 and the reason for apoptosis in the nilotinib-resistant cells was the block of the translational machinery, leading to the rapid downregulation of the anti-apoptotic protein MDM2 (human homolog of the murine double minute-2). These findings highlight MDM2 as a potential therapeutic target to increase TKI-mediated apoptosis and imply that the combination of PI3K/mTOR inhibitor and TKI might form a novel strategy to combat TKI-resistant BCR-ABL1 positive leukemia.

Identification of type II inhibitors targeting BRAF using privileged pharmacophores

V-RAF murine sarcoma viral oncogene homologue B1 (BRAF) is the most frequently mutated protein kinase in human cancers. The most common mutant BRAF V600E constitutively activates the RAS/RAF/MEK/ERK signaling pathway. BRAF has been validated as an important therapeutic target in human cancers. Phenylaminopyrimidine and unsymmetrical diaryl urea are two privileged pharmacophores in kinase inhibitor drug discovery. Herein, we describe the design of a novel hybrid pharmacophore, 4-phenylaminopyrimidine urea, using the above two pharmacophores. A new series of compounds were in turn synthesized and evaluated to successfully identify selective inhibitors of BRAF and oncogenic BRAF V600E. Once daily oral dosing of lead compound 3 demonstrated sustained antitumor efficacy in A549 human non-small-cell lung cancer xenograft model. Molecular docking suggested that compound 3 might be a type II kinase inhibitor binding to the DFG-out conformation of BRAF.

The background, discovery and clinical development of BCR-ABL inhibitors

The story of the inhibition of BCR-ABL as a treatment for chronic myelogenous leukaemia serves to illustrate key aspects of the kinase drug discovery and development process. Firstly, elucidation of the disease mechanism enabled identification of the molecular target(s) which catalysed pharmaceutical research and resulted in Gleevec(®) (Novartis) as the first FDA approved BCR-ABL inhibitor. However, clinical success was soon tempered by the emergence of drug resistance through various mechanisms. Using rational drug design, several hypotheses were devised to overcome resistance issues leading to the development of second generation inhibitors, providing clinicians and patients with greater therapeutic choice.

Nilotinib-associated vascular events

Anecdotal evidence suggests that nilotinib therapy may be associated with severe peripheral artery occlusive disease (PAOD). The authors describe the experience at M.D. Anderson Cancer Center regarding vascular events associated with nilotinib therapy in patients with chronic myeloid leukemia. Overall, 5 cases of PAOD were identified among 233 patients, for an incidence of 2%. Nilotinib is a highly selective inhibitor of the inactive conformation of ABL1 kinase. An improved topologic fit to the ABL1 protein-binding surface contributes to its increased potency over imatinib. This higher selectivity in vitro translated to an improved tolerability in vivo. In fact, nilotinib therapy in the frontline phase III ENESTnd (Evaluating Nilotinib Efficacy and Safety in Clinical Trials-Newly Diagnosed Patients) study was associated with an improved toxicity profile compared with that of imatinib. Intriguingly, several cases of severe peripheral artery occlusive disease (PAOD) have been reported among patients treated with nilotinib in small series. We have identified 5 patients with chronic myeloid leukemia (CML) in whom vascular events developed that were likely related to nilotinib therapy among 233 (2%) patients treated at our institution: 1 patient had recurrent Raynaud syndrome, a second patient had recurrent cerebrovascular accidents, and 3 other patients had PAOD (2 of them with other vascular events, including coronary artery disease and pulmonary emboli, respectively). Risk factors for vascular disease were present in only 1 patient with a history of diabetes mellitus. Although the incidence of vascular events is low, this potential complication should be taken into account when selecting nilotinib for the treatment of CML.

Nilotinib for the treatment of chronic myeloid leukemia

The introduction of targeted therapy has revolutionized the treatment of chronic myeloid leukemia (CML). The pivotal role of the Philadelphia chromosome, resulting from the breakpoint cluster region-Abelson (BCR-ABL) translocation, led to the development of imatinib mesylate, a tyrosine kinase inhibitor with significant activity against the BCR-ABL oncoprotein. Unprecedented clinical activity in CML led to rapid approval and established first-line therapy with imatinib mesylate as the standard of care in most patients. However, the occurrence of imatinib resistance or intolerance has sparked the development of newer drugs with increased activity or specificity. Nilotinib is a second-generation tyrosine kinase inhibitor that has been rationally designed on the basis of imatinib. An overview is given on clinical results in imatinib-resistant or -intolerant patients that led to its current approval as second-line therapy for the chronic and accelerated phases of CML. Future studies will address the role of nilotinib as first-line therapy, in combination strategies and in the context of specific BCR-ABL mutations.

The expanding role of nilotinib in chronic myeloid leukemia

IMPORTANCE OF THE FIELD

Several therapeutic options, including tyrosine kinase inhibitors, exist for the treatment of patients with Philadelphia chromosome (Ph)-positive chronic myeloid leukemia (CML). Despite impressive results, there is room for improvement for those patients who are either resistant or intolerant to imatinib.

AREAS COVERED IN THIS REVIEW

An overview is given on the clinical results with nilotinib, a rationally designed second-generation tyrosine kinase inhibitor, as first- and second-line therapy in patients with Ph-positive CML. Important factors in predicting resistance to nilotinib and guiding therapeutic decisions are addressed.

WHAT THE READER WILL GAIN

Knowledge on the clinical efficacy and safety of nilotinib after imatinib failure and as first-line treatment. Point mutations in the kinase domain (KD) of BCR-ABL1 are important determinants of clinical sensitivity to currently available tyrosine kinase inhibitors, including nilotinib. Information on specific BCR-ABL1 KD mutations and safety profiles assist in therapeutic decision making.

TAKE HOME MESSAGE

Nilotinib is a highly effective and well-tolerated therapeutic option in patients with Ph-positive CML after imatinib failure. Early evidence demonstrating increased efficacy has allowed expanding nilotinib to previously untreated patients in chronic phase. Insights into mechanisms of resistance to tyrosine kinase inhibitors and predictive factors for response will allow for a more individualized use of these agents.

Structural resemblances and comparisons of the relative pharmacological properties of imatinib and nilotinib

Although orphan drug applications required by the EMEA must include assessments of similarity to pre-existing products, these can be difficult to quantify. Here we illustrate a paradigm in comparing nilotinib to the prototype kinase inhibitor imatinib, and equate the degree of structural similarity to differences in properties. Nilotinib was discovered following re-engineering of imatinib, employing structural biology and medicinal chemistry strategies to optimise cellular potency and selectivity towards BCR-ABL1. Through evolving only to conserve these properties, this resulted in significant structural differences between nilotinib and imatinib, quantified by a Daylight-fingerprint-Tanimoto similarity coefficient of 0.6, with the meaning of this absolute measure being supported by an analysis of similarity distributions of similar drug-like molecules. This dissimilarity is reflected in the drugs having substantially different preclinical pharmacology and a lack of cross-intolerance in CML patients, which translates into nilotinib being an efficacious treatment for CML, with a favourable side-effect profile.

Nilotinib

Therapy with imatinib mesylate is a standard of care for most patients with Philadelphia chromosome-positive chronic myeloid leukemia (CML). However, resistance or intolerance to imatinib develops in a considerable number of patients leading to relapse or discontinuation of treatment. Nilotinib is a rationally designed second-generation tyrosine kinase inhibitor (TKI) with improved affinity and specificity against the BCR-ABL kinase, when compared with imatinib. Considerable efficacy after imatinib failure has been demonstrated in clinical trials leading to nilotinib's current approval as second-line therapy for CML in chronic and accelerated phase (AP). The role of nilotinib as first-line treatment for CML, in combinatorial strategies and in the context of specific BCR-ABL mutations, requires future studies.

Extended kinase profile and properties of the protein kinase inhibitor nilotinib

As a drug used to treat imatinib-resistant and -intolerant, chronic and advanced phase chronic myelogenous leukaemia, nilotinib is well characterised as a potent inhibitor of the Abl tyrosine kinase activity of wild-type and imatinib-resistant mutant forms of BCR-Abl. Here we review the profile of nilotinib as a protein kinase inhibitor. Although an ATP-competitive inhibitor of Abl, nilotinib binds to a catalytically inactive conformation (DFG-out) of the activation loop. As a consequence of this, nilotinib exhibits time-dependent inhibition of Abl kinase in enzymatic assays, which can be extrapolated to other targets to explain differences between biochemical activity and cellular assays. Although these differences confound assessment of kinase selectivity, as assessed using a combination of protein binding and transphosphorylation assays, together with cellular autophosporylation and proliferation assays, well established kinase targets of nilotinib in rank order of inhibitory potency are DDR-1>DDR-2>BCR-Abl (Abl)>PDGFRalpha/beta>KIT>CSF-1R. In addition nilotinib has now been found to bind to both MAPK11 (p38beta) and MAPK12 (p38alpha), as well as with very high affinity to ZAK kinase. Although neither enzymatic nor cellular data are yet available to substantiate the drug as an inhibitor of ZAK phosphorylation, modeling predicts that it binds in an ATP-competitive fashion.

Design and synthesis of novel 2-phenylaminopyrimidine (PAP) derivatives and their antiproliferative effects in human chronic myeloid leukemia cells

A series of novel 2-phenylaminopyrimidine (PAP) derivatives structurally related to STI-571 were designed and synthesized. The abilities of these compounds to inhibit proliferation were tested in human chronic myeloid leukemia K562 cells. (E)-3-(2-bromophenyl)-N-[4-methyl-3-(4-pyridin-3-yl-pyrimidin-2-ylamino)phenyl]acrylamide(12d) was the most effective cell growth inhibitor and was 3-fold more potent than STI-571.

Nilotinib: a second-generation tyrosine kinase inhibitor for chronic myeloid leukemia

Imatinib mesylate is currently the standard of care for chronic myeloid leukemia (CML) patients in early chronic phase. However, the emergence of resistance and intolerance has dampened the enthusiasm for this drug. To overcome this phenomenon, different strategies have been developed, including novel targeted agents. Nilotinib, formerly known as AMN107, is a second-generation tyrosine kinase inhibitor 30-fold more potent than imatinib, with high affinity and selectivity on BCR/ABL, and also active against a wide range of mutant clones, except T315I mutation. Phase II trials of nilotinib showed high activity in imatinib-resistant or intolerant CML patients, whereas front-line treatment of the disease in chronic phase demonstrated rapid and stable cytogenetic responses and increasing molecular responses. We here review the development of nilotinib and the efficacy data in phase II and front-line trials. The aim of this review is to evaluate the pharmacology, pharmacokinetic and pharmacodynamic properties of the drug and the recent results of clinical trials performed in patients with CML and Ph+ acute lymphoblastic leukemia (ALL).

Ab initio investigation of the fragmentation of 5,5-diamino-substituted 1,4,2-oxathiazoles

The mechanism for the fragmentation of 5,5-diamino-1,4,2-oxathiazole derivatives has been studied at the CCSD(T)/6-311+G(3df,2p)//MP2/6-31+G(2df,p) level of theory. The calculations suggest that the fragmentation occurs via a stepwise process involving the formation of polar intermediates that lie in shallow potential wells. We find a large thermodynamic driving force for fragmentation, which together with a weakening of the C-S bond through electron donation by the amino substituents provides the impetus for a low-barrier fragmentation.

Refining targeted therapies in chronic myeloid leukemia: development and application of nilotinib, a step beyond imatinib

The BCR-ABL kinase inhibitor imatinib mesylate is currently the standard therapy for patients with chronic myeloid leukemia (CML). Despite the remarkable results achieved with imatinib for the treatment of CML, the emergence of resistance to this drug has become a significant problem. Mutations within the ABL kinase domain have been identified as the main mechanism of resistance to imatinib. Other mechanisms include genomic amplification of BCR-ABL and modulation of drug efflux or influx transporters. Several strategies have been developed to overcome the problem of imatinib resistance, including dose escalation of imatinib, combination treatments, or novel targeted agents. Nilotinib is a tyrosine kinase inhibitor 30-fold more potent than imatinib, active against a wide range of mutant clones, except T315I. Phase I-II trials of nilotinib showed high activity in imatinib-resistant CML and Ph+ acute lymphoblastic leukemia. We here review the development of nilotinib and the activity of this agent in CML patients and in other forms of sensitive neoplasms.

Potent platelet-derived growth factor-beta receptor (PDGF-betaR) inhibitors: Synthesis and structure-activity relationships of 7-[3-(cyclohexylmethyl)ureido]-3-{1-methyl-1H-pyrrolo[2,3-b]pyridin-3-yl}quinoxalin-2(1H)-one derivatives

We found previously that 7-[3-(cyclohexylmethyl)ureido]-3-{1-methyl-1H-pyrrolo[2,3-b]pyridin-3-yl}quinoxalin-2(1H)-one (7d-6) has considerable potency as a PDGF inhibitor. This compound showed potent inhibitory activity in a PDGF-induced CPA (Cell Proliferation Assay) and APA (Auto-Phosphorylation Assay) (IC50 = 0.05 micromol/l in CPA, 0.03 micromol/l in APA). Therefore, we tried to develop a novel and effective PDGF-betaR inhibitor by optimizing a series of its derivatives. We found that trifluoroacetic acid (TFA)-catalyzed coupling of pyrrolo[2,3-b]pyridines with quinoxalin-2-ones proceeded efficiently under mild oxidation condition with manganese(IV) oxide (MnO2) in situ, so this method was applied to prepare a series of derivatives. Results of in vitro screening of newly synthesized derivatives identified compound 7d-9 as having potent (IC50 = 0.014 micromol/l in CPA, 0.007 micromol/l in APA) and selective [IC50 values against vascular endothelial growth factor receptor 2 (VEGFR2, kinase domain region, KDR), epidermal growth factor receptor (EGFR), c-Met (hepatocyte growth factor receptor) and insulin growth factor I receptor (IGF-IR)/IC50 against PDGFR were each >1000] inhibitory activity. Moreover, in this series of derivatives, 7b-2 showed potent inhibitory activity toward both PDGF- and VEGF-induced signaling (PDGFR: IC50 = 0.004 micromol/l in CPA, 0.0008 micromol/l in APA, KDR: IC50 = 0.008 micromol/l in APA). Herein we report a new and convenient synthetic method for this series of derivatives and its SAR study.

Structural investigation of PAP derivatives by CoMFA and CoMSIA reveals novel insight towards inhibition of Bcr-Abl oncoprotein

Molecular modeling by 3D-QSAR comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were employed on a series of phenylaminopyrimidine-based (PAP) Bcr-Abl inhibitors. The chemical structures of 63 PAP analogues were aligned using a template extracted from the crystal structure of STI571 bound to Abl kinase. Subsequently, the structures built were divided into training and test sets that include 53 and 10 compounds, respectively. Statistical results showed that the 3D-QSAR models generated from CoMSIA were superior to CoMFA (CoMSIA; q2=0.66, r2=0.94, N=3, F=139.09, r2pred=0.64 while CoMFA; q2=0.53, r2=0.73, N=3, F=43.53, r2pred=0.61). Based on the contour interpretation, the attachment of hydrophobic and bulky groups to the phenyl and pyrrolidine (D- and E-ring of NS-187, respectively) along with highly electronegative groups around the D-ring are important structural features for the design of second-generation Bcr-Abl inhibitors. The generated models are predictive based on reproducible values of the predicted compared with experimental activities in the test set. Further, the complementary analysis of contour maps to the Bcr-Abl binding site suggested the anchor points for binding affinity.

Meeting report: targeting the kinome--20 years of tyrosine kinase inhibitor research in Basel

With basic and pharmaceutical researchers, chemists, pharmacologists, and clinicians, the Targeting the Kinome meeting brought together a tremendous group of scientists to discuss the past, present, and future of protein kinase research, with a special emphasis on cancer therapy development. The topics ranged from the kinases themselves as drug targets through the interactions that the actions of these enzymes promote, to the physiological and pathological processes they regulate. Attendees gained insight into drug development, as well as increased understanding of how normal cellular processes are subverted during oncogenesis, which may lead to new targets for intervention.

Structural biology contributions to the discovery of drugs to treat chronic myelogenous leukaemia

Chronic myelogenous leukaemia (CML) results from the Bcr-Abl oncoprotein, which has a constitutively activated Abl tyrosine kinase domain. Although most chronic phase CML patients treated with imatinib as first-line therapy maintain excellent durable responses, patients who have progressed to advanced-stage CML frequently fail to respond or lose their response to therapy owing to the emergence of drug-resistant mutants of the protein. More than 40 such point mutations have been observed in imatinib-resistant patients. The crystal structures of wild-type and mutant Abl kinase in complex with imatinib and other small-molecule Abl inhibitors were determined, with the aim of understanding the molecular basis of resistance and to aid in the design and optimization of inhibitors active against the resistance mutants. These results are presented in a way which illustrates the approaches used to generate multiple structures, the type of information that can be gained and the way that this information is used to support drug discovery.

Beneficial effects of combining nilotinib and imatinib in preclinical models of BCR-ABL+ leukemias

Drug resistance resulting from emergence of imatinib-resistant BCR-ABL point mutations is a significant problem in advanced-stage chronic myelogenous leukemia (CML). The BCR-ABL inhibitor, nilotinib (AMN107), is significantly more potent against BCR-ABL than imatinib, and is active against many imatinib-resistant BCR-ABL mutants. Phase 1/2 clinical trials show that nilotinib can induce remissions in patients who have previously failed imatinib, indicating that sequential therapy with these 2 agents has clinical value. However, simultaneous, rather than sequential, administration of 2 BCR-ABL kinase inhibitors is attractive for many reasons, including the theoretical possibility that this could reduce emergence of drug-resistant clones. Here, we show that exposure of a variety of BCR-ABL+ cell lines to imatinib and nilotinib results in additive or synergistic cytotoxicity, including testing of a large panel of cells expressing BCR-ABL point mutations causing resistance to imatinib in patients. Further, using a highly quantifiable bioluminescent in vivo model, drug combinations were at least additive in antileukemic activity, compared with each drug alone. These results suggest that despite binding to the same site in the same target kinase, the combination of imatinib and nilotinib is highly efficacious in these models, indicating that clinical testing of combinations of BCR-ABL kinase inhibitors is warranted.

AMN107 (nilotinib): a novel and selective inhibitor of BCR-ABL

Chronic myelogenous leukaemia (CML) and Philadelphia chromosome positive (Ph+) acute lymphoblastic leukaemia (ALL) are caused by the BCR-ABL oncogene. Imatinib inhibits the tyrosine kinase activity of the BCR-ABL protein and is an effective, frontline therapy for chronic-phase CML. However, accelerated or blast-crisis phase CML patients and Ph+ ALL patients often relapse due to drug resistance resulting from the emergence of imatinib-resistant point mutations within the BCR-ABL tyrosine kinase domain. This has stimulated the development of new kinase inhibitors that are able to over-ride resistance to imatinib. The novel, selective BCR-ABL inhibitor, AMN107, was designed to fit into the ATP-binding site of the BCR-ABL protein with higher affinity than imatinib. In addition to being more potent than imatinib (IC50< 30 nM) against wild-type BCR-ABL, AMN107 is also significantly active against 32/33 imatinib-resistant BCR-ABL mutants. In preclinical studies, AMN107 demonstrated activity in vitro and in vivo against wild-type and imatinib-resistant BCR-ABL-expressing cells. In phase I/II clinical trials, AMN107 has produced haematological and cytogenetic responses in CML patients, who either did not initially respond to imatinib or developed imatinib resistance. Dasatinib (BMS-354825), which inhibits Abl and Src family kinases, is another promising new clinical candidate for CML that has shown good efficacy in CML patients. In this review, the early characterisation and development of AMN107 is discussed, as is the current status of AMN107 in clinical trials for imatinib-resistant CML and Ph+ ALL. Future trends investigating prediction of mechanisms of resistance to AMN107, and how and where AMN107 is expected to fit into the overall picture for treatment of early-phase CML and imatinib-refractory and late-stage disease are discussed.

Characterization of AMN107, a selective inhibitor of native and mutant Bcr-Abl

The Bcr-Abl tyrosine kinase oncogene causes chronic myelogenous leukemia (CML) and Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL). We describe a novel selective inhibitor of Bcr-Abl, AMN107 (IC50 <30 nM), which is significantly more potent than imatinib, and active against a number of imatinib-resistant Bcr-Abl mutants. Crystallographic analysis of Abl-AMN107 complexes provides a structural explanation for the differential activity of AMN107 and imatinib against imatinib-resistant Bcr-Abl. Consistent with its in vitro and pharmacokinetic profile, AMN107 prolonged survival of mice injected with Bcr-Abl-transformed hematopoietic cell lines or primary marrow cells, and prolonged survival in imatinib-resistant CML mouse models. AMN107 is a promising new inhibitor for the therapy of CML and Ph+ ALL.