A biophysical framework for double-drugging kinases.

Selective orthosteric inhibition of kinases has been challenging due to the conserved active site architecture of kinases and emergence of resistance mutants. Simultaneous inhibition of distant orthosteric and allosteric sites, which we refer to as "double-drugging", has recently been shown to be effective in overcoming drug resistance. However, detailed biophysical characterization of the cooperative nature between orthosteric and allosteric modulators has not been undertaken. Here, we provide a quantitative framework for double-drugging of kinases employing isothermal titration calorimetry, Förster resonance energy transfer, coupled-enzyme assays, and X-ray crystallography. We discern positive and negative cooperativity for Aurora A kinase (AurA) and Abelson kinase (Abl) with different combinations of orthosteric and allosteric modulators. We find that a conformational equilibrium shift is the main principle governing cooperativity. Notably, for both kinases, we find a synergistic decrease of the required orthosteric and allosteric drug dosages when used in combination to inhibit kinase activities to clinically relevant inhibition levels. X-ray crystal structures of the double-drugged kinase complexes reveal the molecular principles underlying the cooperative nature of double-drugging AurA and Abl with orthosteric and allosteric inhibitors. Finally, we observe a fully closed conformation of Abl when bound to a pair of positively cooperative orthosteric and allosteric modulators, shedding light on the puzzling abnormality of previously solved closed Abl structures. Collectively, our data provide mechanistic and structural insights into rational design and evaluation of double-drugging strategies.

Imatinib can act as an Allosteric Activator of Abl Kinase.

Imatinib is an ATP-competitive inhibitor of Bcr-Abl kinase and the first drug approved for chronic myelogenous leukemia (CML) treatment. Here we show that imatinib binds to a secondary, allosteric site located in the myristoyl pocket of Abl to function as an activator of the kinase activity. Abl transitions between an assembled, inhibited state and an extended, activated state. The equilibrium is regulated by the conformation of the αΙ helix, which is located nearby the allosteric pocket. Imatinib binding to the allosteric pocket elicits an αΙ helix conformation that is not compatible with the assembled state, thereby promoting the extended state and stimulating the kinase activity. Although in wild-type Abl the catalytic pocket has a much higher affinity for imatinib than the allosteric pocket does, the two binding affinities are comparable in Abl variants carrying imatinib-resistant mutations in the catalytic site. A previously isolated imatinib-resistant mutation in patients appears to be mediating its function by increasing the affinity of imatinib for the allosteric pocket, providing a hitherto unknown mechanism of drug resistance. Our results highlight the benefit of combining imatinib with allosteric inhibitors to maximize their inhibitory effect on Bcr-Abl.

Investigation on the interaction behavior of afatinib, dasatinib, and imatinib docked to the BCR-ABL protein.

Chronic myeloid leukemia (CML) is a pathological condition associated with the uncontrolled proliferation of white blood cells and respective loss of function. Imatinib was the first drug that could effectively treat this condition, but its use is hindered by the development of mutations of the BCR-ABL protein, which are the cause of resistance. Therefore, dasatinib and afatinib present similarities that can be explored to discover new molecules capable of overcoming the effects of imatinib. Afatinib exhibited electronic and docking behavior, indicating that a replacement with some minor modifications could design a new potential inhibitor. The amide group in each candidate is clearly of pharmacophoric importance, and it needs to concentrate a negative region. Sulfur group presents a good pharmacophoric profile, which was shown by dasatinib results, adding to the influence of the Met318 residue in the target protein active site configuration. This behavior suggests that the sulfur atom and other fragments that have an affinity for the methionine sidechain may provide a significant positive effect when present in TKI molecules such as afatinib or dasatinib.

Genomics-guided targeting of stress granule proteins G3BP1/2 to inhibit SARS-CoV-2 propagation.

SARS-CoV-2 nucleocapsid (N) protein undergoes RNA-induced phase separation (LLPS) and sequesters the host key stress granule (SG) proteins, Ras-GTPase-activating protein SH3-domain-binding protein 1 and 2 (G3BP1 and G3BP2) to inhibit SG formation. This will allow viral packaging and propagation in host cells. Based on a genomic-guided meta-analysis, here we identify upstream regulatory elements modulating the expression of G3BP1 and G3BP2 (collectively called G3BP1/2). Using this strategy, we have identified FOXA1, YY1, SYK, E2F-1, and TGFBR2 as activators and SIN3A, SRF, and AKT-1 as repressors of G3BP1/2 genes. Panels of the activators and repressors were then used to identify drugs that change their gene expression signatures. Two drugs, imatinib, and decitabine have been identified as putative modulators of G3BP1/2 genes and their regulators, suggesting their role as COVID-19 mitigation agents. Molecular docking analysis suggests that both drugs bind to G3BP1/2 with a much higher affinity than the SARS-CoV-2 N protein. This study reports imatinib and decitabine as candidate drugs against N protein and G3BP1/2 protein.

Antiviral drug design based on the opening mechanism of spike glycoprotein in SARS-CoV-2.

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters the host cell after the receptor binding domain (RBD) of the virus spike (S) glycoprotein binds to the human angiotensin-converting enzyme 2 (hACE2). This binding requires the RBD to undergo a conformational change from a closed to an open state. In the present study, a key pair of salt bridges formed by the side chains of K537 and E619, residues at the interfaces of SD1 and SD2, respectively, was identified to promote the opening of the RBD. Mutations of K537Q and E619D reduced their side chain lengths and eliminated this pair of salt bridges; as a result, the opening of the RBD was not observed in the MD simulations. Thus, blocking the formation of this pair of salt bridges is a promising approach for treating novel coronavirus disease 2019 (COVID-19). FDA approved drug molecules were screened by their capabilities of blocking the formation of the key pair of salt bridges, achieved by their positional stabilities in the cavity containing the side chains of K537 and E619 formed in the interface between SD1 and SD2. Simeprevir, imatinib, and naldemedine were identified to possess the desired capability with the most favorable interaction energies.

Novel α-Aminophosphonates of imatinib Intermediate: Synthesis, anticancer Activity, human Abl tyrosine kinase Inhibition, ADME and toxicity prediction.

An efficient method for the synthesis of a new class of α-aminophosphonates of imatinib derivative has been developed in one-pot Kabachnik-Fields reaction of N-(5-amino-2-methyl phenyl)-4-(3-pyridyl)-2-pyrimidine amine with various aldehydes and diethyl phosphite under microwave irradiation and neat conditions using NiO nanoparticles as an reusable and heterogeneous catalyst, with 96% yield at 450 W within 15 min. All the compounds were evaluated for their in vitro cytotoxicity with various cancer cell lines by MTT assay method. Compounds with halo (4f, -4Br, IC50 = 1.068 ± 0.88 µM to 2.033 ± 0.97 µM), nitro substitution (4 h, -3NO2, IC50 = 1.380 ± 0.94 µM to 2.213 ± 0.64 µM), (4 g, -4NO2, IC50 = 1.402 ± 0.79 µM to 2.335 ± 0.73 µM) and (4i, 4-Cl, 3-NO2, IC50 = 1.437 ± 0.92 µM to 2.558 ± 0.76 µM) were showed better anticancer activity when compared with standard drugs Doxorubicin and Imatinib using MTT assay method. Further in silico target hunting reveals the anticancer activity of the designed compounds by inhibiting human ABL tyrosine kinase and all the designed compounds have shown significant drug-like characteristics.

Co-delivery of rituximab targeted curcumin and imatinib nanostructured lipid carriers in non-Hodgkin lymphoma cells.

The aim of the present study was production of nanostructured lipid carriers (NLCs) of curcumin and imatinib for co-administration in non-Hodgkin lymphoma cells. NLCs were prepared and conjugated to rituximab to target CD20 receptors of lymphoma cell lines. Oleic acid or Labrafac and glyceryl monostearate or lecithin were used for production of NLCs. The antibody coupling efficiency to NLCs and their physical characteristics were studied. The cytotoxicity of NLCs on Jurkat T cells (CD20 receptor negative) and Ramos B cells (CD20 receptor positive) was studied by MTT assay. The cellular uptake was determined by fluorescent microscopy. The results indicated both curcumin and imatinib targeted NLCs had a significant cytotoxic effect much higher than the free drugs and non-targeted NLCs on Ramos cells. In both cell lines, the cytotoxicity of the co-administrated drugs was significantly higher than each drug alone. In Ramos cells the co-administration of curcumin (15 µg/ml)/imatinib (5 µg/ml) decreased the free curcumin IC50 from 8.3 ± 0.9 to 1.9 ± 0.2 µg/ml, and curcumin targeted NLCs from 6.7 ± 0.1 to 1.3 ± 0.2 µg/ml. In this case the IC50 of imatinib was reduced from 11.1 ± 0.7 to 2.3 ± 0.1 µg/ml and imatinib targeted NLCs from 4.3 ± 0.1 to 1.4 ± 0.0 µg/ml. The co-administration of ritoximab conjugated NLCs of curcumin and imatinib may enhance cytotoxicity of imatinib in treatment of non-Hodgkin lymphoma.

Recent advances in Bcr-Abl tyrosine kinase inhibitors for overriding T315I mutation.

BCR-ABL is a gene produced by the fusion of the bcr gene and the c-abl proto-oncogene and is considered to be the main cause of chronic myelogenous leukemia (CML) production. Therefore, the development of selective Bcr-Abl kinase inhibitors is an attractive strategy for the treatment of CML. However, in the treatment of CML with a Bcr-Abl kinase inhibitor, the T315I gatekeeper mutant disrupts the important contact interaction between the inhibitor and the enzyme, resistant to the first- and second-generation drugs currently approved, such as imatinib, bosutinib, nilotinib, and dasatinib. In order to overcome this special resistance, several different strategies have been explored, and many molecules have been studied to effectively inhibit Bcr-Abl T315I. Some of these molecules are still under development, and some are being studied preclinically, and still others are in clinical research. Herein, this review reports some of the major examples of third-generation Bcr-Abl inhibitors against the T315I mutation.

Intermolecular Interactions in Crystal Structures of Imatinib-Containing Compounds.

Imatinib, one of the most used therapeutic agents to treat leukemia, is an inhibitor that specifically blocks the activity of tyrosine kinases. The molecule of imatinib is flexible and contains several functional groups able to take part in H-bonding and hydrophobic interactions. Analysis of molecular conformations for this drug was carried out using density functional theory calculations of rotation potentials along single bonds and by analyzing crystal structures of imatinib-containing compounds taken from the Cambridge Structural Database and the Protein Data Bank. Rotation along the N-C bond in the region of the amide group was found to be the reason for two relatively stable molecular conformations, an extended and a folded one. The role of various types of intermolecular interactions in stabilization of the particular molecular conformation was studied in terms of (i) the likelihood of H-bond formation, and (ii) their contribution to the Voronoi molecular surface. It is shown that experimentally observed hydrogen bonds are in accord with the likelihood of their formation. The number of H-bonds in ligand-receptor complexes surpasses that in imatinib salts due to the large number of donors and acceptors of H-bonding within the binding pocket of tyrosine kinases. Contribution of hydrophilic intermolecular interactions to the Voronoi molecular surface is similar for both conformations, while π...π stacking is more typical for the folded conformation of imatinib.

Diversity of Long-Lived Intermediates along the Binding Pathway of Imatinib to Abl Kinase Revealed by MD Simulations.

Imatinib, a drug used for the treatment of chronic myeloid leukemia and other cancers, works by blocking the catalytic site of pathological constitutively active Abl kinase. While the binding pose is known from X-ray crystallography, the different steps leading to the formation of the complex are not well understood. The results from extensive molecular dynamics simulations show that imatinib can primarily exit the known crystallographic binding pose through the cleft of the binding site or by sliding under the αC helix. Once displaced from the crystallographic binding pose, imatinib becomes trapped in intermediate states. These intermediates are characterized by a high diversity of ligand orientations and conformations, and relaxation timescales within this region may exceed 3-4 ms. Analysis indicates that the metastable intermediate states should be spectroscopically indistinguishable from the crystallographic binding pose, in agreement with tryptophan stopped-flow fluorescence experiments.

Conformational states dynamically populated by a kinase determine its function.

Protein kinases intrinsically sample a number of conformational states with distinct catalytic and binding activities. We used nuclear magnetic resonance spectroscopy to describe in atomic-level detail how Abl kinase interconverts between an active and two discrete inactive structures. Extensive differences in key structural elements between the conformational states give rise to multiple intrinsic regulatory mechanisms. The findings explain how oncogenic mutants can counteract inhibitory mechanisms to constitutively activate the kinase. Energetic dissection revealed the contributions of the activation loop, the Asp-Phe-Gly (DFG) motif, the regulatory spine, and the gatekeeper residue to kinase regulation. Characterization of the transient conformation to which the drug imatinib binds enabled the elucidation of drug-resistance mechanisms. Structural insight into inactive states highlights how they can be leveraged for the design of selective inhibitors.

Nanohydroxyapatite-Mediated Imatinib Delivery for Specific Anticancer Applications.

In the present study, a nanoapatite-mediated delivery system for imatinib has been proposed. Nanohydroxyapatite (nHAp) was obtained by co-precipitation method, and its physicochemical properties in combination with imatinib (IM) were studied by means of XRPD (X-ray Powder Diffraction), SEM-EDS (Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy), FT-IR (Fourier-Transform Infrared Spectroscopy), absorption spectroscopy as well as DLS (Dynamic Light Scattering) techniques. The obtained hydroxyapatite was defined as nanosized rod-shaped particles with high crystallinity. The amorphous imatinib was obtained by conversion of its crystalline form. The beneficial effects of amorphous pharmaceutical agents have been manifested in the higher dissolution rate in body fluids improving their bioavailability. Imatinib-to-hydroxyapatite interactions on the surface were confirmed by SEM images as well as absorption and FT-IR spectroscopy. The cytotoxicity of the system was tested on NI-1, L929, and D17 cell lines. The effectiveness of imatinib was not affected by nHAp modification. The calculated IC50 values for drug-modified nHAp were similar to those for the drug itself. However, higher cytotoxicity was observed at higher concentrations of imatinib, in comparison with the drug alone.

An ultra-long circulating nanoparticle for reviving a highly selective BCR-ABL inhibitor in long-term effective and safe treatment of chronic myeloid leukemia.

Nanotechnology has demonstrated great promise for the development of more effective and safer cancer therapies. We recently developed a highly selective inhibitor of BCR-ABL fusion tyrosine kinase for chronic myeloid leukemia (CML). However, the poor drug-like properties were hurdles to its further clinical development. Herein, we re-investigate it by conjugating an amphiphilic polymer and self-assembling into a nanoparticle (NP) with a high loading (~10.3%). The formulation greatly improved its solubility and drastically extended its circulation half-life from ~5.3 to ~117 h (>20-fold). In the 150 days long-term engraftment model experiment, long intravenous dosing intervals of the NPs (every 4 or 8 days) exhibited much better survival and negligible toxicities as compared to daily oral administration of the inhibitor. Moreover, the NPs showed excellent inhibition of tumor growth in the subcutaneous xenograft model. All results suggest that the ultra-long circulating pro-drug NP may provide an effective and safe therapeutic strategy for BCR-ABL-positive CML.

Encapsulation of Imatinib in Targeted KIT-5 Nanoparticles for Reducing its Cardiotoxicity and Hepatotoxicity.

BACKGROUND: Using imatinib, a tyrosine kinase inhibitor drug used in lymphoblastic leukemia, has always had limitations due to its cardiotoxicity and hepatotoxicity side effects. The objective of this study is to develop a target-oriented drug carrier to minimize these adverse effects by the controlled release of the drug. METHODS: KIT-5 nanoparticles were functionalized with 3-aminopropyltriethoxysilane and conjugated to rituximab as the targeting agent for the CD20 positive receptors of the B-cells. Then they were loaded with imatinib and their physical properties were characterized. The cell cytotoxicity of the nanoparticles was studied by MTT assay in Ramos (CD20 positive) and Jurkat cell lines (CD20 negative) and their cellular uptake was shown by fluorescence microscope. Wistar rats received an intraperitoneal injection of 50 mg/kg of the free drug or targeted nanoparticles for 21 days. Then the level of aspartate Aminotransferase (AST), alanine Aminotransferase (ALT), Alkaline Phosphatase (ALP) and Lactate Dehydrogenase (LDH) were measured in serum of animals. The cardiotoxicity and hepatotoxicity of the drug were also studied by hematoxylin and eosin staining of the tissues. RESULTS: The targeted nanoparticles of imatinib showed to be more cytotoxic to Ramos cells rather than Jurkat cells. The results of the biochemical analysis displayed a significant reduction in AST, ALT, ALP, and LDH levels in animals treated with targeted nanoparticles, compared to the free drug group. By comparison with the free imatinib, histopathological results represented less cardiotoxicity and hepatotoxicity in the animals, which received the drug through the current designed delivery system. CONCLUSION: The obtained results confirmed that the rituximab targeted KIT-5 nanoparticles are promising in the controlled release of imatinib and could decrease its cardiotoxicity and hepatotoxicity side effects.

Quantification of imatinib and related compounds using capillary electrophoresis-tandem mass spectrometry with field-amplified sample stacking.

A quantification method for imatinib (IM), its major metabolite N-desmethyl imatinib (NDI), and a degradation by-product was developed using CE-MS combined with an online concentration technique. The use of multiple reaction monitoring (MRM)-MS/MS further improved the sensitivity of this technology. Liquid-liquid extraction (LLE) using tertiary butyl methyl ether yielded high recovery and reproducibility for the pretreatment of serum samples. The recovery rate exceeded 83% for all three analytes, and was 90% for IM. To improve quantification results, a conductivity-induced online analyte concentration technique, field-amplified sample stacking (FASS), was used. The S/N ratios were improved at least 10-fold when compared with conventional capillary zone electrophoresis. The detection limits were 0.2 ng/mL for IM, 0.4 ng/mL for NDI, and 4 ng/mL for the degradation by-product. These results are superior to those previously obtained by other reported methods. The new method was validated in terms of its selectivity, intra- and interday repeatability and accuracy, and sample storage stability, following the guidelines issued by the European Medicines Agency. Considering the convenient pretreatment procedure (LLE), superior sensitivity, and fast analysis speed (<15 min), this method can be useful in the determination of imatinib levels in blood.

Targeting MDR-1 gene expression, BAX/BCL2, caspase-3, and Ki-67 by nanoencapsulated imatinib and hesperidin to enhance anticancer activity and ameliorate cardiotoxicity.

There is a great demand to introduce new approaches into cancer treatment field due to incidence of increased breast cancer all over the world. The current study was designed to evaluate the role of imatinib mesylate (IM) and/or hesperidin (HES) nanoparticles alone or in combination in enhancing the anticancer activity and to investigate the ability of nanoencapsulation to reduce cardiotoxicity of IM in solid Ehrlich carcinoma (SEC)-bearing mice. IM and HES were loaded into PLGA (poly(lactic-co-glycolic acid) polymer. SEC was induced in female albino mice as a model for experimentally induced breast cancer. Mice were randomly divided into eight groups (n = 10). On day 28 from tumor inoculation, mice were sacrificed and blood samples were collected in heparinized tubes for hematological studies, biochemical determination of lactate dehydrogenase (LDH), and glutamic oxaloacetic transaminase (SGOT) levels. In addition, tumor and cardiac tissues were utilized for histopathological examination as well as determination of MDR-1 gene expression. Immunohistochemical staining of BAX and BCL-2 was done. Nano IM- and/or Nano HES-treated groups showed a significant reduction in tumor volume, weight, hematological, cardiac markers, and tumor MDR-1 gene downregulation compared to free conventional treated groups. In conclusion, the use of HES as an adjuvant therapy with IM could improve its cytotoxic effects and limit its cardiac toxicity. Furthermore, nanoencapsulation of IM and/or HES with PLGA polymer showed a remarkable anticancer activity.

Study of the binding affinity between imatinib and α-1 glycoprotein using nuclear spin relaxation and isothermal titration calorimetry.

Imatinib is a selective tyrosine kinase inhibitor, successfully used for the treatment of chronic myelogenous leukaemia and gastrointestinal stromal tumors. Binding of drugs to proteins influence their pharmacokinetic and pharmacodynamics action. In the blood, the drug is distributed in the body in the free form or bound to plasma protein. Albumin and α-1 glycoprotein (AGP) are plasma proteins with the highest affinity for drug substances. Drugs which are weak acids mainly bind to plasma albumin, while drugs that are bases have affinity for α-1 glycoprotein. The main goal of this study is to quantitatively evaluate the interaction between imatinib mesylate (IMT) and α-1 glycoprotein to characterize the nature and forces underlying the formation of a molecular complex. Relaxation experiments provide quantitative information about the relationship between the binding affinity and structure of IMT. Thus, association constant was determined as Ka = 873.36 M-1. The ITC data revealed that the binding was an entropy driven process and the association constant Ka = 3.22 × 103 M-1, with a 1:1 stoichiometry. The results obtained by NMR and ITC were complemented with a molecular docking study.

S2P peptide-conjugated PLGA-Maleimide-PEG nanoparticles containing Imatinib for targeting drug delivery to atherosclerotic plaques.

BACKGROUND: Imatinib is a platelet-derived growth factor receptor (PDGFR) inhibitor with very low water solubility. Previous studies in atherosclerosis have shown that PDGFR activity has an egregious effect on vascular disease and progression of atherosclerosis. Specific ligands of atherosclerotic plaques can be used for targeting of nanoparticles. Studies in atherosclerosis proved that stabilin-2 is a glycoprotein which exists abundantly in atherosclerotic plaques and it is produced from both macrophages and endothelial cells. OBJECTIVES: The objective of this study is the targeting drug delivery to atherosclerotic plaques by using imatinib-loaded nanoparticles modified by S2P peptide. METHODS: The imatinib-loaded nanoparticles were fabricated through a modified emulsion/solvent evaporation technique. After fabricating PLGA nanoparticles, maleimide PEG was used as linker between PLGA nanoparticles and S2P peptide. Because of presence cysteine in both side of S2P peptide, maleimide formed a thiolether linkage by thiol group of cysteine. Then the physicochemical analysis like H-NMR, FT-IR, DSC, SEM, particle size, zeta potential, and drug release were studied. RESULTS: Stabilin-2 peptide with sequence of CRTLTVRKC is a specific ligand to stabilin-2, so it was synthesized for using as the targeting agent for atherosclerosis. S2P peptide conjugation to the surface of nanoparticles was proved by H-NMR and FT-IR, and the percentage of S2P peptide in nanoparticles was 1.3%. The final nanoparticles were spherical and their size were 183 nm. The loading capacity of the imatinib-loaded nanoparticles was 5.05%. The sustained release profile was observed for peptide targeted nanoparticles. CONCLUSION: The chosen method was simple, reproducible, and specific in peptide conjugation of nanoparticles for targeting delivery to atherosclerotic regions. Graphical abstract .

Synthesis of imatinib, a tyrosine kinase inhibitor, labeled with carbon-14.

Imatinib (Gleevec) is a multiple tyrosine kinase inhibitor that decreases the activity of the fusion oncogene called BCR-ABL (breakpoint cluster region protein-Abelson murine leukemia viral oncogene homolog) and is clinically used for the treatment of chronic myelogenous leukemia and acute lymphocytic leukemia. Small molecule drugs, such as imatinib, can bind to several cellular proteins including the target proteins in the cells, inducing undesirable effects along with the effects against the disease. In this study, we report the synthetic optimization for 14 C-labeling and radiosynthesis of [14 C]imatinib to analyze binding with cellular proteins using accelerator mass spectroscopy. 14 C-labeling of imatinib was performed by the synthesis of 14 C-labeld 2-aminopyrimidine intermediate using [14 C]guanidine·HCl, which includes an in situ reduction of an inseparable byproduct for easy purification by HPLC, followed by a cross-coupling reaction with aryl bromide precursor. The radiosynthesis of [14 C]imatinib (specific activity, 631 MBq/mmol; radiochemical purity, 99.6%) was achieved in six steps with a total chemical yield of 29.2%.

Overcoming imatinib resistance in chronic myelogenous leukemia cells using non-cytotoxic cell death modulators.

Recent studies examined the possibility to overcome imatinib resistance in chronic myeloid leukemia (CML) patients by combination therapy with peroxisome proliferator-activated receptor gamma (PPARγ) ligands. Pioglitazone, a full PPARγ agonist, improved the survival of patients by the gradual elimination of the residual CML stem cell pool. To evaluate the importance of the pharmacological profile of PPARγ agonists on the ability to circumvent resistance, the partial PPARγ agonist 4'-((2-propyl-1H-benzo[d]imidazol-1-yl)methyl)-[1,1'-biphenyl]-2-carboxylic acid, derived from telmisartan, and other related derivatives were investigated. The 4-substituted benzimidazole derivatives bearing a [1,1'-biphenyl]-2-carboxamide moiety sensitized K562-resistant cells to imatinib treatment. Especially the derivatives 18a-f, which did not activate PPARγ to more than 40% at 10 µM, retrieved the cytotoxicity of imatinib in these cells. The cell death modulating properties were higher than that of pioglitazone. It is of interest to note that all novel compounds were not cytotoxic neither on non-resistant nor on resistant cells. They exerted antitumor potency only in combination with imatinib.